CN114591750A

CN114591750A - Liquid crystal aligning agent, liquid crystal alignment film and liquid crystal display element

Info

Publication number: CN114591750A
Application number: CN202210206178.6A
Authority: CN
Inventors: 王柏扬; 王耀群; 蔡明睿
Original assignee: Daxin Materials Corp
Current assignee: Daxin Materials Corp
Priority date: 2015-09-14
Filing date: 2016-08-17
Publication date: 2022-06-07
Also published as: CN106520142A; TW201710320A; TWI549992B

Abstract

A liquid crystal aligning agent comprises a polymer and a solvent. The polymer is obtained by reacting a diamine component with a tetracarboxylic dianhydride component, wherein the diamine component comprises a compound represented by formula 1, and the tetracarboxylic dianhydride component comprises a compound represented by formula 2:

in formula 1, X is a single bond, -O-, -COO-or-OCO-, A and B are each independently phenylene, cyclohexylene or piperazinyl, R¹is-H or-CH₃And R²is-H or C₁‑C₅An alkyl group.

Description

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

The present invention is a divisional application based on the patent application having the application date of 2016, 8, 17, and the application number of 201610677514.X, entitled "liquid crystal aligning agent, liquid crystal alignment film, and liquid crystal display element".

Technical Field

The present invention relates to a liquid crystal aligning agent, a liquid crystal alignment film and a liquid crystal display device, and more particularly, to a liquid crystal aligning agent suitable for a polymer stable alignment type liquid crystal display device, a liquid crystal alignment film made of the liquid crystal aligning agent, and a liquid crystal display device having the liquid crystal alignment film.

Background

Liquid crystal displays have advantages of small size, light weight, low power consumption and good display quality, and have become the mainstream of flat panel displays in recent years. As the display specification of the lcd continuously develops toward a large size, the market demand for the lcd has increased in characteristics such as High Contrast Ratio (High Contrast Ratio), fast response and wide viewing angle. In order to overcome the viewing angle problem of large-sized liquid crystal display panels, the wide viewing angle technology of liquid crystal display panels is continuously improved and broken through. At present, the common wide-viewing angle technologies include a Multi-domain Vertical Alignment (MVA) technology and a Polymer Stabilized Alignment (PSA) technology.

The polymer stable alignment technique is to irradiate ultraviolet light or heat while applying a specific voltage to a liquid crystal layer including a liquid crystal material and a monomer to polymerize the monomer and form a polymer layer on an alignment film to assist the liquid crystal material in alignment. However, in the One Drop Fill (ODF) method commonly used today for filling a liquid crystal layer, the monomer is usually not uniformly dispersed on the alignment film, so that the alignment is not uniform, so-called Drop marks, which causes the problem of dot-shaped color unevenness (Drop mura) of the liquid crystal display. Accordingly, it is an object of active research by those skilled in the art to provide an alignment film having good wettability to monomers and still having good vertical alignment ability.

Disclosure of Invention

The invention provides a liquid crystal alignment agent which can be used for manufacturing a liquid crystal alignment film which has high hydrophilicity, high surface energy and excellent vertical alignment capability and is suitable for a polymer stable alignment type liquid crystal display element.

The liquid crystal alignment agent comprises a polymer and a solvent. The polymer is obtained by reacting a diamine component with a tetracarboxylic dianhydride component, wherein the diamine component comprises a compound represented by formula 1, and the tetracarboxylic dianhydride component comprises a compound represented by formula 2:

in formula 1, X is a single bond, -O-, -COO-or-OCO-, A and B are each independently phenylene, cyclohexylene or piperazinyl, R¹is-H or-CH₃And R²is-H or C₁-C₅An alkyl group.

In one embodiment of the present invention, R in the above formula 1¹is-H, and at least one of A and B is piperazinyl.

In one embodiment of the present invention, the diamine component includes at least one of compounds represented by formula 3, formula 4, and formula 5:

in one embodiment of the present invention, the diamine component includes at least one of compounds represented by formula 6, formula 7, formula 8, and formula 9:

in one embodiment of the present invention, the diamine component further includes at least one selected from the group consisting of p-phenylenediamine, 4 ' -diaminodiphenylmethane, 5(6) -amino-1- (4-aminophenyl) -1, 3, 3-trimethylindane, 4 ' -diaminodiphenyl ether, 4 ' -diamino-2, 2 ' -dimethyl-1, 1 ' -biphenyl, 4 ' -bis (4-aminophenoxy) biphenyl, and 2, 2 ' -bis [4- (4-aminophenoxyphenyl) ] propane.

In one embodiment of the present invention, the content of the compound represented by formula 1 is 1 mol% or more based on the total number of moles of the diamine component.

In one embodiment of the present invention, the tetracarboxylic dianhydride component further includes at least one selected from the group consisting of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride, tetrahydronaphthalene dianhydride, 3 ', 4,4 ' -biphenyltetracarboxylic dianhydride, 4,4 ' -oxydiphthalic anhydride, and 3,3 ', 4,4 ' -benzophenonetetracarboxylic dianhydride.

In one embodiment of the present invention, the content of the compound represented by formula 2 is 20 mol% or more based on the total number of moles of the tetracarboxylic dianhydride component.

In an embodiment of the invention, the polymer includes polyamic acid, polyimide, a copolymer of polyamic acid and polyimide, or a mixture of polyamic acid and polyimide.

The liquid crystal alignment film is prepared from the liquid crystal alignment agent.

The liquid crystal display element comprises the liquid crystal alignment film and a liquid crystal layer arranged on one side of the liquid crystal alignment film, wherein the liquid crystal layer comprises liquid crystal molecules and polymerizable monomers.

In view of the above, the present invention provides a liquid crystal aligning agent comprising a polymer obtained by reacting a diamine component containing a compound represented by the above formula 1 and a tetracarboxylic dianhydride component containing a compound represented by the above formula 2. Therefore, the liquid crystal alignment agent has good coating performance, and the formed liquid crystal alignment film has high hydrophilicity and high surface energy, so that the liquid crystal alignment film can have good wettability with liquid crystal molecules and polymerizable monomers, and the liquid crystal molecules and the polymerizable monomers can be uniformly dispersed on the liquid crystal alignment film. In addition, on the premise of matching with PSA technology, the liquid crystal display element made of the liquid crystal alignment film not only can avoid the problem of point-like color phase unevenness caused by uneven diffusion of polymerizable monomers, but also has the advantages of high response speed, good electrical performance and the like, thereby having good display quality.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.

The invention comprises the following steps:

1. a liquid crystal alignment agent comprising:

a polymer obtained by reacting a diamine component with a tetracarboxylic dianhydride component; and

a solvent, a water-soluble organic solvent,

wherein the diamine component comprises a compound represented by formula 1, and the tetracarboxylic dianhydride component comprises a compound represented by formula 2:

in formula 1, X is a single bond, -O-, -COO-or-OCO-;

a and B are each independently phenylene or cyclohexylene;

R¹is-H or-CH₃(ii) a And

R²is-H or C₁-C₅An alkyl group, a carboxyl group,

2. the liquid crystal aligning agent according to item 1, wherein the diamine component includes at least one of compounds represented by formulae 4 and 5:

3. the liquid crystal aligning agent according to item 1, wherein the diamine component includes at least one of compounds represented by formula 7, formula 8, and formula 9:

4. the liquid crystal aligning agent according to item 1, wherein the diamine component further comprises at least one selected from the group consisting of p-phenylenediamine, 4 ' -diaminodiphenylmethane, 5(6) -amino-1- (4-aminophenyl) -1, 3, 3-trimethylindane, 4 ' -diaminodiphenyl ether, 4 ' -diamino-2, 2 ' -dimethyl-1, 1 ' -biphenyl, 4 ' -bis (4-aminophenoxy) biphenyl, and 2, 2 ' -bis [4- (4-aminophenoxyphenyl) ] propane.

5. The liquid crystal alignment agent according to item 3, wherein a content of the compound represented by formula 1 is 1 mol% or more based on a total mole number of the diamine component.

6. The liquid crystal aligning agent according to item 1, wherein the tetracarboxylic dianhydride component further comprises at least one selected from the group consisting of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride, tetrahydronaphthalene dianhydride, 3 ', 4,4 ' -biphenyltetracarboxylic dianhydride, 4,4 ' -oxydiphthalic anhydride, and 3,3 ', 4,4 ' -benzophenonetetracarboxylic dianhydride.

7. The liquid crystal aligning agent according to item 1 or 5, wherein the content of the compound represented by formula 2 is 20 mol% or more based on the total molar number of the tetracarboxylic dianhydride component.

8. The liquid crystal aligning agent according to item 1, wherein the polymer comprises polyamic acid, polyimide, a copolymer of polyamic acid and polyimide, or a mixture of polyamic acid and polyimide.

9. A liquid crystal alignment film made of the liquid crystal aligning agent according to any one of items 1 to 8.

10. A liquid crystal display element comprising:

a liquid crystal alignment film according to the liquid crystal alignment film of item 9; and

and a liquid crystal layer disposed on one side of the liquid crystal alignment film, wherein the liquid crystal layer includes liquid crystal molecules and polymerizable monomers.

Drawings

FIG. 1 is a scanning electron microscope image of an acrylic polymer film when the surface distribution configuration is judged to be optimal.

FIG. 2 is a scanning electron microscope image of an acrylic polymer film when the surface distribution pattern is judged to be defective.

Detailed Description

It should be noted at the outset that the range denoted by "a numerical value to another numerical value" is a general expression avoiding the recitation of all numerical values in the range in the specification. Thus, recitation of a range of values herein is intended to mean both the inclusion of any value in the range and the exclusion of any other range of values encompassed within the range, as if the range and range were explicitly recited in the specification.

Further, herein, a group may represent a substituted or unsubstituted group if it is not particularly specified whether the group is substituted or not. For example, "alkyl" may represent a substituted or unsubstituted alkyl group. In addition, when a group is described as "CX", it means that the main chain of the group has X carbon atoms.

Further, herein, the structure of the compound is sometimes represented by a bond line type (skeletton formula). This notation may omit carbon atoms, hydrogen atoms, and carbon-hydrogen bonds. Of course, the functional groups in the formula are clearly shown in the drawings.

One embodiment of the present invention provides a liquid crystal alignment agent including a polymer obtained by reacting a diamine component with a tetracarboxylic dianhydride component, and a solvent, wherein the diamine component includes a compound represented by formula 1, and the tetracarboxylic dianhydride component includes a compound represented by formula 2:

In the present embodiment, when X is-COO-or-OCO-, two amino groups (-NH) in formula 1₂) Preferably at positions 3 and 5 relative to X.

In the present embodiment, R¹May be-H, and at least one of A and B may be piperazinyl.

In the present embodiment, R¹Can be-CH₃And A and B may each independently be phenylene or cyclohexylene.

In this embodiment, if R²The alkyl group with a carbon number greater than 5 makes the formed liquid crystal alignment film relatively hydrophobic, so that when the liquid crystal alignment film is applied to a polymer stable alignment type liquid crystal display device, liquid crystal molecules and polymerizable monomers cannot be uniformly dispersed on the liquid crystal alignment film, thereby causing a problem of uneven dot-shaped color.

In the present embodiment, the diamine component may include at least one of the compounds represented by formula 3, formula 4, and formula 5:

wherein X, R in formula 3, formula 4 and formula 5¹And R²The definitions of (A) are as described above.

Specifically, in the present embodiment, the diamine component may include at least one of the compounds represented by formula 6, formula 7, formula 8, and formula 9:

in the present embodiment, the diamine component may further include another diamine compound, for example, at least one selected from the group consisting of p-phenylenediamine, 4 ' -diaminodiphenylmethane, 5(6) -amino-1- (4-aminophenyl) -1, 3, 3-trimethylindane, 4 ' -diaminodiphenyl ether, 4 ' -diamino-2, 2 ' -dimethyl-1, 1 ' -biphenyl, 4 ' -bis (4-aminophenoxy) biphenyl, and 2, 2 ' -bis [4- (4-aminophenoxyphenyl) ] propane. In detail, in the present embodiment, the diamine compound represented by formula 1 is a diamine compound having a side chain for vertically aligning liquid crystal molecules, and the other diamine compound is a main chain diamine compound.

In the present embodiment, the content of the compound represented by formula 1 is 1 mol% or more, preferably 5 to 50 mol%, more preferably 10 to 40 mol%, based on the total number of moles of the diamine component; the diamine compound is contained in an amount of 5 to 99 mol%, preferably 50 to 95 mol%, more preferably 60 to 90 mol%.

In the present embodiment, the tetracarboxylic dianhydride component may include only the compound represented by formula 2. However, in the present invention, the tetracarboxylic dianhydride component may optionally further include at least one selected from the group consisting of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (1, 2,3, 4-cyclobutanetetracarboxylic dianhydride, CBDA), tetrahydronaphthalene dianhydride, 3 ', 4,4 ' -biphenyltetracarboxylic dianhydride, 4,4 ' -oxydiphthalic anhydride and 3,3 ', 4,4 ' -benzophenone tetracarboxylic dianhydride, within a range that does not impair the effects of the present invention. Specifically, in the present embodiment, the content of the compound represented by formula 2 is 20 mol% or more, preferably 50 mol% or more, and more preferably 80 mol% or more, based on the total number of moles of the tetracarboxylic dianhydride component.

In the present embodiment, the polymer may include polyamic acid, polyimide, a copolymer of polyamic acid and polyimide, or a mixture of polyamic acid and polyimide depending on the degree of polymerization and dehydration ring closure during the reaction of the diamine component and the tetracarboxylic dianhydride component. That is, the reaction of the diamine component and the tetracarboxylic dianhydride component may include a subsequent dehydration ring-closure reaction (i.e., imidization reaction) in addition to the polymerization reaction of the diamine component and the tetracarboxylic dianhydride component. Further, in the present embodiment, the imidization ratio of the polymer is 40% or more, preferably 60% or more, and more preferably 80% or more. By having the polymer having the imidization ratio within the range, a liquid crystal aligning agent which is good in coatability, and can form a liquid crystal alignment film having high hydrophilicity, high surface energy, good electrical properties, and excellent vertical alignment ability can be obtained.

Further, since the reaction of the diamine component with the tetracarboxylic dianhydride component to produce the polyamic acid, or the reaction of the polyamic acid with the imidization reaction to produce the polyimide, etc., is well known to those skilled in the art, those skilled in the art can produce the polymer of the present invention based on the knowledge thereof. The synthesis of the copolymer of polyamic acid and polyimide is only described in detail below, and the details are not repeated.

In this embodiment, the synthesis of the copolymer of polyamic acid and polyimide is completed in an organic solvent, and the organic solvent used is preferably an organic solvent with better solubility and an organic solvent with lower solubility.

Examples of the organic solvent having a preferable solubility for the copolymer of polyamic acid and polyimide include N-methyl-2-pyrrolidone, N-isopropyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone, N-dimethylformamide, N-dimethylacetamide, N-methylcaprolactam, dimethylsulfoxide, tetramethylurea, hexamethylphosphoramide, and γ -butyrolactone, and two or more of these solvents can be used in combination.

The organic solvent having poor solubility for the copolymer of polyamic acid and polyimide may be used in combination with the organic solvent, provided that the copolymer of polyamic acid and polyimide is uniformly dispersed in the organic solvent without being separated. In detail, the organic solvents having poor solubility include: methanol, ethanol, isopropanol, n-butanol, cyclohexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol 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, and the like.

In detail, the synthesis of the copolymer of polyamic acid and polyimide requires imidization, which can be performed by (1) direct heating for dehydration and ring closure, and (2) adding a dehydrating agent and a catalyst.

Method (1): the reaction temperature for the ring closure by heating dehydration may be 50 ℃ to 300 ℃, preferably 100 ℃ to 250 ℃. When the reaction temperature is less than 50 ℃, the dehydration ring-closure reaction does not proceed.

Method (2): the reaction temperature for dehydration ring-closing by adding a dehydrating agent and a catalyst may be 20 to 150 ℃ and preferably 0 to 120 ℃. As the dehydrating agent, an acid anhydride such as acetic anhydride, propionic anhydride, trifluoroacetic anhydride or the like can be used. The amount of the dehydrating agent to be used is determined depending on the desired imidization ratio, and is preferably from 0.01 to 20 mol per 1 mol of recurring units of the copolymer of polyamic acid and polyimide. As the catalyst, tertiary amines such as triethylamine, pyridine, lutidine and the like can be used, and the amount of the catalyst to be used is preferably 0.01 to 10 moles per 1 mole of the dehydrating agent.

It is to be noted that, in the present embodiment, the liquid crystal aligning agent can have good coatability and can form a liquid crystal alignment film having high hydrophilicity, high surface energy, good electrical properties, and excellent vertical alignment ability by reacting the polymer with the diamine component containing the compound represented by formula 1 and the tetracarboxylic dianhydride component containing the compound represented by formula 2.

In the present embodiment, the solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N-isopropyl-2-pyrrolidone (NIP), γ -Butyrolactone (GBL), 1, 3-Dimethyl-3, 4, 5, 6-tetrahydro-2(1H) -pyrimidinone (1, 3-Dimethyl-3, 4, 5, 6-tetrahydro-2(1H) -pyrimidinone, DMPU), 1, 3-Dimethyl-2-imidazolidinone (1, 3-Dimethyl-2-imidazolidone, DMEU), 1, 2-propanediol Carbonate (1, 2-Propylene Carbonate, PC), Dimethyl succinate (DBME), Dimethyl Carbonate (DMC), N-Diethylpropionamide (DEPA), Ethylene Carbonate (EC), N-Diethylformamide (N, N-Diethylformamide, DEF), N-Methylformamide (NMF), N-Dimethylformamide (DMF). In addition, in this embodiment, the solvent may further include at least one of butyl cellosolve (2-Butoxyethanol, BC), 2- (2-Butoxyethoxy) ethanol (2- (2-Butoxyethoxy) ethanol, DB), 2- (2-Methoxyethoxy) ethanol (2- (2-Methoxyethoxy) ethanol, DM), Dipropylene glycol monomethyl ether (DPM), hydroxymethyl dioxolanone (GC), 4-methyl-4-Hydroxy-2-pentanone (4-Hydroxy-4-methyl-2-pentanone, DAA), and Dipropylene glycol dimethyl ether (di) (propylene glycol) dimethyl ether, DMM), and may be used as a leveling agent in coating.

In addition, in consideration of viscosity and volatility, the content of the polymer is, for example, 2 wt% to 10 wt% based on the total weight of the liquid crystal aligning agent of the present embodiment. In detail, when the content of the polymer is less than 2 wt%, the film thickness of the liquid crystal alignment film formed later is too thin, thereby reducing the liquid crystal alignment; when the content of the polymer is more than 10% by weight, the coating quality is affected.

In addition, in the present embodiment, the liquid crystal aligning agent may further optionally contain other components, for example, an organic silicon (oxy) alkane compound or an epoxy compound. The organosilicon (oxy) alkane compound is not particularly limited, and may be aminopropyltrimethoxysilane, aminopropyltriethoxysilane, vinylmethylsilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, N-ethoxycarbonyl-3-aminopropyltrimethoxysilane, N-ethoxycarbonyl-3-glycidoxypropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (3-epoxycyclohexyl) ethyltrimethoxysilane, 3-ureidopropyltrimethoxysilane, N-ethyltrimethoxysilane, N-ethylcarbonyltrimethoxysilane, N-ethylcarbonylpropyltrimethoxysilane, N-ethyltrimethoxysilane, N-ethylcarbonylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N-ethyltrimethoxysilane, 3-ethyltrimethoxysilane, N-propyltrimethoxysilane, N-ethyltrimethoxysilane, N-propyltrimethoxysilane, N-ethyltrimethoxysilane, N-isopropyltrimethoxysilane, N-propyltrimethoxysilane, N-t-N-t-or a mixture, N-t-or a mixture thereof, N-or a mixture thereof, N-or a mixture thereof, N-ethoxycarbonyl-3-aminopropyltriethoxysilane, N-triethoxysilylpropyl triethylenetriamine, N-trimethoxysilylpropyl triethylenetriamine, N-bis (oxyethyl) -3-aminopropyltrimethoxysilane or N-bis (oxyethyl) -3-aminopropyltriethoxysilane, etc.

In the case that the liquid crystal alignment agent contains the organic silicon (oxoalkane compound, if the content of the organic silicon (oxoalkane compound in the liquid crystal alignment agent is too large, the formed liquid crystal alignment film is easy to generate poor alignment; if the content of the organic silane compound in the liquid crystal alignment agent is too low, the formed liquid crystal alignment film is prone to have poor film brushing property and excessive powder shaving. In view of improving the adherence of the liquid crystal alignment film to the substrate surface without affecting the properties required of the original liquid crystal alignment film, the concentration of the organic silane compound of the liquid crystal alignment agent is preferably 0.01 to 5% by weight, particularly preferably 0.1 to 3% by weight, based on the weight of all polymers in the liquid crystal alignment agent.

The epoxy compound is not particularly limited, and may be ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1, 6-hexanediol diglycidyl ether, glycerol diglycidyl ether, 2-dibromoneopentyl glycol diglycidyl ether, 1, 3, 5, 6-tetraglycidyl-2, 4-hexanediol, N, N, N ', N ' -tetraglycidyl-m-xylylene, 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N, N ', N ' -tetraglycidyl-4, 4 ' -diaminodiphenylmethane, 3- (N-allyl-N-glycidyl) aminopropyltrimethoxysilane, 3- (N, N-diglycidyl) aminopropyltrimethoxysilane.

When the liquid crystal alignment agent contains an epoxy compound, if the content of the epoxy compound in the liquid crystal alignment agent is too high, the formed liquid crystal alignment film is easy to generate poor alignment; if the content of the epoxy compound in the liquid crystal alignment agent is too small, the resulting liquid crystal alignment film is likely to have poor film-brushing properties and excessive dust, and the concentration of the epoxy compound in the liquid crystal alignment agent is preferably 0.01 to 3 wt%, particularly preferably 0.1 to 2 wt%, based on the total weight of the liquid crystal alignment agent, in view of improving the adhesion of the liquid crystal alignment film to the substrate surface without affecting the properties required for the original liquid crystal alignment film.

Another embodiment of the present invention provides a liquid crystal alignment film made of the liquid crystal alignment agent of any of the previous embodiments. In detail, the method for manufacturing the liquid crystal alignment film includes, for example, the steps of: and coating the liquid crystal alignment agent on a substrate, and performing heating treatment.

Generally, the film thickness of the liquid crystal alignment film formed by the above method is preferably 0.005 μm to 0.5. mu.m. The thickness of the liquid crystal alignment film is generally adjusted according to the viscosity of the liquid crystal alignment agent and the coating method of the liquid crystal alignment agent. The thickness of the liquid crystal alignment film can be measured by a common film thickness measuring device such as a level difference meter or an ellipsometer (ellipsometer).

In this embodiment, any conventionally known substrate can be used as the substrate, and it is preferable that the substrate can withstand the process conditions described later. Examples thereof include: plastic substrates, glass epoxy substrates, glass substrates, ceramic substrates, metal substrates, and the like. Examples of the material of the plastic substrate include: thermosetting resins (e.g., epoxy resins, phenol resins, polyimide resins, polyester resins, etc.), thermoplastic resins (e.g., phenoxy resins, polyethersulfone, polysulfone, polyphenylenesulfone (etc.) and the like). Examples of the material of the ceramic substrate include: alumina, aluminum nitride, zirconia, silicon nitride, silicon carbide, and the like. Examples of the material of the glass substrate include: sodium glass, potassium glass, borosilicate glass, quartz glass, aluminosilicate glass, lead glass, and the like. Examples of the material of the metal substrate include: aluminum, zinc, copper, and the like. The substrate may have a structure in which two or more layers are laminated (laminated) such as the plastic substrate, the glass substrate, the ceramic substrate, and the metal substrate. Of course, the substrate may also be a substrate with a patterned transparent conductive film.

In the present embodiment, examples of the coating method include: an application by roller (APR coating), a spin coating (spin coating), an inkjet coating (IJP coating), or a print coating.

In the present embodiment, the heating treatment is mainly intended to remove the solvent in the liquid crystal alignment agent and promote the dehydration ring-closure reaction of the non-cyclized polyamic acid. Specifically, the heat treatment is performed in an oven or an infrared oven, or on a hot plate, for example, and includes a pre-baking step and a fixing step. In this embodiment, the temperature of the pre-baking step is, for example, 50 ℃ to 150 ℃, preferably 70 ℃ to 100 ℃, and more preferably 85 ℃; the duration of the pre-baking step is, for example, 30 seconds to 300 seconds, preferably 105 seconds to 165 seconds, and more preferably 135 seconds; the temperature of the fixing and baking step is, for example, 100 ℃ to 300 ℃, preferably 180 ℃ to 250 ℃, more preferably 230 ℃; the time of the baking step is, for example, 10 minutes to 60 minutes, preferably 20 minutes to 40 minutes, and more preferably 30 minutes.

A further embodiment of the present invention provides a liquid crystal display element characterized by comprising the liquid crystal alignment film of any one of the preceding embodiments, and a liquid crystal layer disposed on one side of the liquid crystal alignment film, wherein the liquid crystal layer comprises liquid crystal molecules and polymerizable monomers. Specifically, the liquid crystal display device of the present embodiment is a polymer stable alignment type liquid crystal display device. The liquid crystal molecules and the polymerizable monomers may be any liquid crystal molecules and polymerizable monomers, respectively, which are known to those skilled in the art to be suitable for a polymer stable alignment type liquid crystal display device. Of course, the liquid crystal display device of the present embodiment also has other known components of the liquid crystal display device, such as a substrate, an electrode layer, a color filter, a polarizer, a sealant layer, and the like. The manufacturing method and the constituent elements of the liquid crystal display device can be arbitrarily selected from conventional techniques except for using the liquid crystal alignment film, and thus are not described in detail herein.

It is worth mentioning that, as mentioned above, since the liquid crystal alignment film in the foregoing embodiment has high hydrophilicity and high surface energy, the liquid crystal alignment film has good wettability with the liquid crystal molecules and the polymerizable monomers, thereby enabling the liquid crystal molecules and the polymerizable monomers to be uniformly dispersed on the liquid crystal alignment film. In this way, by using the liquid crystal alignment film, the liquid crystal display device of the present embodiment can avoid the problem of dot-like color unevenness caused by alignment unevenness, and has advantages of high response speed, good electrical properties, and the like, thereby having good display quality.

[ experiment ]

The present invention will be described more specifically below with reference to synthesis examples, and comparative examples. Although the following experiments are described, the materials used, the amounts and ratios thereof, the details of the treatment, the flow of the treatment, and the like may be appropriately changed without departing from the scope of the present invention. Therefore, the present invention should not be construed restrictively based on the experiments described below.

< method for synthesizing diamine Compound >

Synthesis example 1

The synthesis method of the compound represented by the above formula 6 is as follows.

1-fluoro-2, 4-dinitrobenzene (1-fluoro-2, 4-dinitrobenzene, DNFB) (102.36g) was mixed with Tetrahydrofuran (THF) (500ml) in a 1000ml round bottom flask, which now appeared to be a yellow clear liquid. 1-phenylpiperazine (1-phenylpiperazine, PP) (81.12g) was then added slowly over a period of time with constant stirring with the magnet, whereupon the yellow clear liquid turned gradually to an orange-red liquid with the precipitation of an orange-yellow solid. After the addition was complete, the temperature was raised to 80 ℃ by means of an oil bath and refluxing was carried out for 6 hours with continuous stirring at an internal temperature of 65 ℃. After warming up, the orange-yellow liquid was slowly dropped into isopropyl alcohol (IPA) (1500ml) to precipitate and wash off excess starter and impurities. After collecting a yellow solid by filtration, the solid was washed with a mixture of water (1500ml) and IPA (500ml), stirred for 6 hours by washing, and then collected by filtration and vacuum-dried for 8 hours to obtain 1- (2, 4-dinitrophenyl) -4-phenylpiperazine (1- (2, 4-dinitrophenyl) -4-phenylpiperazine) (131.83g, yield: 80.3%) as a yellow solid, which was represented by the following structure.

Subsequently, 1- (2, 4-dinitrophenyl) -4-phenylpiperazine (200g) and THF (660g) were charged into a reaction vessel, and the mixture was heated to 80 ℃ to dissolve the compound. Stopping heating and naturally returning the temperature after the solution is clear. On alternate days, after filtration, high vacuum was applied to obtain 1- (2, 4-dinitrophenyl) -4-phenylpiperazine as dark yellow massive crystals (yield: 68%).

Thereafter, 1- (2, 4-dinitrophenyl) -4-phenylpiperazine (49.25g) and THF (250ml) were mixed in a 1000ml round-bottomed flask and 10% palladium on carbon catalyst (Pd/C) (9.85g) was added. Next, 80% aqueous hydrazine (49.29g) was slowly injected under nitrogen atmosphere with continuous stirring using a mechanical stirrer by using a micro pump. At this point, the mixture started to bubble and exothermically, whereas the temperature rose from room temperature 26 ℃ to 60 ℃ over 20 minutes with the addition of about 15g of aqueous hydrazine. Then, the temperature was maintained at 60 ℃ until the injection of aqueous hydrazine was completed. At this point, the solution gradually turned from a yellow liquid to a yellow clear liquid. After that, stirring was carried out at room temperature under a nitrogen atmosphere for 12 hours to obtain a transparent, clear, colorless liquid. Next, Pd/C was filtered with celite to give a pale yellow liquid. After concentrating the liquid to about 100ml, the concentrated liquid was slowly dropped into n-hexane (738.72ml) using an addition funnel and stirred for 6 hours. Then, after filtration, high vacuum was applied for 12 hours to obtain a compound represented by formula 6 as a goose-white powder (37.19g, yield: 92.4%).¹H NMR(400MHz，d-DMSO)：δ(ppm)2.81(t，4H)，3.23(broad，4H)，4.48(s，2H)，4.56(s，2H)，5.82(dd，1H)，5.96(d，1H)，6.66(d，1H)，6.77(t，1H)，6.95(q，2H)，7.21(m，2H)。

Synthesis example 2

The synthesis method of the compound represented by the above formula 7 is as follows.

Synthesis of Compound (b):

methyl 3, 5-dinitrobenzoate (MDNBA) (1.1eq, 248.75g) and compound (a) (1.0eq, 244.38g) were placed in a 3L reactor. Subsequently, THF (1038.02g) was added under a nitrogen atmosphere to dissolve MDNBA and the compound (a), followed by mechanical stirring at 200rpm for 10 minutes. Thereafter, N '-Dicyclohexylcarbodiimide (N, N' -Dicyclohexylcarbodiimide, DCC, CAS-538-75-0) (1.1eq, 226.96g) was added, and the reaction vessel wall was washed with THF (129.75 g). At this time, the solution gradually turned from a clear state to a white turbid state. Then, the mixture was stirred for 10 minutes to make the solution uniform white turbid. After a uniform white turbidity was exhibited, 4-dimethylaminopyridine (DMAP, CAS 1122-58-3) (0.1eq, 12.22g) was dissolved in THF (129.75g) and the resulting solution was slowly poured into the reaction kettle at a rate of 5 ml/s. At this point, the solution turned from white turbidity to orange turbidity, and the temperature rose to about 40 ℃. After 8 hours of reaction under a nitrogen atmosphere, the cloudy white urea by-product was filtered off and the filter cake was washed with THF (200g) to make the filter cake white. Thereafter, the filtrate was collected and concentrated to about 1200g, and the resulting concentrate was slowly poured into Isopropanol (IPA) (5200g) to remove excess equivalents of DCC and DMAP. At this time, the compound (b) powder precipitates from THF. Subsequently, the solution in which the compound (b) powder was precipitated was placed in a-20 ℃ refrigerator for 4 hours. Thereafter, filtration was performed, and the compound (b) powder was washed with IPA (200g) to white. Next, IPA on the filter cake was removed using hexane (200g), and high vacuum suction was performed to obtain compound (b) as a white color (yield: 96%).

Then, a mixture of compound (b) powder (300g), THF (540g) and IPA (600g) was added to the reaction vessel and heated to 80 ℃ to dissolve the compound. Stopping heating and naturally returning the temperature after the solution is clear. On the next day, filtration was performed, and after washing with an appropriate amount of IPA and hexane, high vacuum drying was performed to obtain compound (b) as white needle-like crystals (yield: 73%).

Synthesis of a compound represented by formula 7:

in a 3L reactor, compound (b) (113.50g) was dissolved in THF (573.07g), and 5% palladium on carbon catalyst (Pd/C) (5.67g) was added. Then, the mixture was stirred by a mechanical stirrer (stirring speed 200)rpm) under continuous stirring of the resulting mixture, hydrazine (N) was added using a peristaltic pump₂H₄) (113.50g) was slowly dropped at a rate of about 0.05g/s, and the temperature was raised to about 60 ℃. After the addition of hydrazine was completed, the reaction was continued with stirring for 8 hours. At this point, the solution will change from a pale yellow clear solution to a colorless transparent clear solution. Next, Pd/C was filtered off with Celite, and the Celite was washed with THF (200 g). Thereafter, after concentrating the filtrate to 70ml at 45 ℃, the resulting concentrate was poured into IPA (2300g) to remove hydrazine remaining in the solution and obtain a suspended solid. After collecting the white solid by filtration, washing was performed with IPA (200g), and IPA on the filter cake was removed again with hexane (200 g). Next, purification was performed by silica gel column chromatography using ethyl acetate/n-hexane (weight ratio: 1) as an eluent to obtain the compound represented by formula 7 as a powdery solid having an anserine-white color (yield: 43%).¹H NMR(400MHz，CDCl₃)：δ(ppm)2.32(s，3H)，3.51(broad，2H)，3.69(broad，2H)，6.26(s，1H)，6.87(s，1H)，7.23-7.28(m，2H)，7.31-7.37(m，1H)，7.39-7.47(m，2H)，7.54-7.65(m，4H)。

Synthesis example 3

The synthesis method of the compound represented by the above formula 8 is as follows.

Synthesis of Compound (d):

compound (d) was synthesized in the same procedure as compound (b) and was obtained by substituting compound (c) for compound (a) as a synthetic starting material to give compound (d) as a white product (yield: 96%).

Synthesis of a compound represented by formula 8:

in a 3L reactor, compound (d) (259.51g) was dissolved in THF (1341.14g), and 5% palladium on carbon catalyst (Pd/C) (12.98g) was added. Then, under continuous stirring of the resulting mixture by a mechanical stirrer (stirring speed of 200rpm), hydrazine (N) was added by a peristaltic pump₂H₄) (259.51g) at a rate of about 0.05g/sSlowly dropping and raising the temperature to about 60 ℃. After the addition of hydrazine was completed, the reaction was continued with stirring for 8 hours. At this point, the solution will change from a pale yellow clear solution to a colorless transparent clear solution. Next, Pd/C was filtered off with Celite, and the Celite was washed with THF (200 g). Thereafter, after concentrating the filtrate to 150ml at 45 ℃, the resulting concentrate was poured into IPA (5300g) to remove the hydrazine remaining in the solution, and a suspended solid was obtained. After collecting the white solid by filtration, washing was performed with IPA (200g), and IPA on the filter cake was removed again with hexane (200 g). Then, high vacuum suction was performed to obtain the compound represented by formula 8 as a powder (yield: 92%).¹H NMR(400MHz，CDCl₃)：δ(ppm)0.70-1.50(m，18H)，1.67-1.81(m，7H)，2.09(m，1H)，2.18(s，3H)，3.55(broad，4H)，4.82(m，1H)，6.14(s，1H)，6.51(s，1H)。

< preparation of liquid Crystal alignment agent, liquid Crystal alignment film and liquid Crystal display device >

Example 1

A1000 ml three-port reaction kettle is taken, wherein one port is a thermometer inserting pipe, the other port is a feeding pipe, a glass plug is used for plugging after feeding, and the other port is used for stirring by stirring blades. Then, the compound represented by the aforementioned formula 6 (70mmole) prepared in Synthesis example 1 and p-phenylenediamine (PPDA) were placed in a three-port reaction vessel and dissolved in N-methyl-2-pyrrolidone (NMP) (150 mL). Then, the compound represented by the above formula 2 was added (200mmole) to carry out polymerization, NMP was further added to a solid content of 15 wt%, and after reaction at 30 ℃ for 8 hours, a polyamic acid solution having a solid content of 15 wt% was obtained. Then, the stirring blade was removed, and the mixture was stirred with a magnet and charged into an H-glass tube for imidization. Thereafter, toluene (45g) was charged into the three-port reaction tank, and heating and stirring were carried out at 130 ℃ for 4 hours to dehydrate and cyclize the polyamic acid into a polyimide. And then, after the temperature is raised to 200 ℃ for reaction for 1 hour, collecting and removing the added toluene and at least 5.76g of water removed by imidization reaction in an H-shaped glass tube to obtain a copolymer solution of polyamic acid and polyimide, wherein the imidization rate is 80% and the solid content is 15 wt%. Thereafter, the copolymer solution of polyamic acid and polyimide was diluted with a mixed solvent of NMP/diethylene glycol monobutyl ether (weight ratio 1: 1) to a solid content of 6.6 wt% to obtain the liquid crystal aligning agent of example 1.

The liquid crystal aligning agent of example 1 was coated on a glass substrate by a roll printer. Then, after prebaking at 85 ℃ for 135 seconds, reheating to 230 ℃ and solid baking for 30 minutes were carried out to obtain the liquid crystal alignment film of example 1, wherein the thickness was

A pair of substrates having the liquid crystal alignment film of example 1 was combined with a liquid crystal liquid in a conventional manner to obtain the liquid crystal display element of example 1 including a pair of the liquid crystal alignment films of example 1, a liquid crystal layer interposed between the pair of liquid crystal alignment films, and a pair of electrode layers respectively disposed on the liquid crystal layer sides of the pair of liquid crystal alignment films, wherein the liquid crystal liquid/liquid crystal layer includes liquid crystal molecules (MJ 012008 manufactured by Merck corporation) and a polymerizable monomer containing a bisacryloyl in an amount of 3000ppm with respect to 100% by mass of the liquid crystal molecules, and the structure is as follows.

Thereafter, the liquid crystal display element of example 1 was applied with a voltage of 18V and simultaneously irradiated with 8520mJ/cm²The ultraviolet light energy is used to make the polymerization monomer in the liquid crystal layer carry out cross-linking reaction, and a layer of acrylic polymer film is formed on the pair of liquid crystal alignment films, so as to provide a stable pretilt angle. Finally, the liquid crystal display element of example 1 was completed after the voltage was released.

Example 2 to example 4

The liquid crystal alignment agents, the liquid crystal alignment films, and the liquid crystal display devices of examples 2 to 4 were respectively prepared in the same steps as example 1, and were different in that: the kind of diamine component and the amount thereof used for preparing the copolymer solution of polyamic acid and polyimide were changed as shown in table 1. The results of the evaluations performed in the above evaluation methods are shown in table 3.

Comparative examples 1 to 2

The liquid crystal aligning agents, the liquid crystal alignment films, and the liquid crystal display devices of comparative examples 1 to 2 were respectively prepared in the same steps as example 1, and were different in that: the kind of diamine component and the amount thereof used for preparing the copolymer solution of polyamic acid and polyimide were changed as shown in table 1.

Comparative examples 3 to 4

The liquid crystal aligning agents, the liquid crystal alignment films, and the liquid crystal display devices of comparative examples 3 to 4 were respectively prepared in the same steps as example 1, except that: the kinds and the amounts of the components used and the kinds of the tetracarboxylic dianhydride components were changed as shown in Table 1. Specifically, the structure of VA2 in table 1 is as follows:

and the structure of C16 is as follows:

then, the liquid crystal aligning agents of examples 1 to 4 and comparative examples 1 to 4 were evaluated for coatability, respectively; the liquid crystal alignment films of examples 1 to 4 and comparative examples 1 to 4 were evaluated for wettability, respectively; the liquid crystal display elements of examples 1 to 4 and comparative examples 1 to 4 were evaluated for a pretilt angle (PTA), a Voltage Holding Ratio (VHR), and a residual direct current Voltage (RDC), respectively; and the surface distribution profile (morphology) and the surface roughness (roughness) of the acrylic polymer thin films in the liquid crystal display elements of examples 1 to 4 and comparative examples 1 to 4 were evaluated by a Scanning Electron Microscope (SEM) and an Atomic Force Microscope (AFM), respectively. The above-described evaluation methods are explained below, and the evaluation results are shown in table 1.

Coatability

The liquid crystal aligning agents of examples 1 to 4 and comparative examples 1 to 4 were coated on the glass substrates, respectively, by a roll printer to form thin films. Then, after 10 minutes, nitrogen was blown through the films. And then, moving the glass substrate coated with the films to a pre-baking platform for curing, and pre-baking at the temperature of 85 ℃ for 135 seconds. Finally, the presence or absence of the deposition of these films was observed by an optical microscope. If no precipitation is observed, the determination is good, and if precipitation is observed, the determination is bad. It should be noted that if the coating property is determined to be poor, the subsequent evaluation of the wettability of the liquid crystal alignment film and the evaluation of the pretilt angle, the voltage holding ratio, the residual dc voltage, the surface distribution configuration and the surface roughness of the liquid crystal display device are not performed.

Wettability-contact Angle

The liquid crystal liquid used for manufacturing the liquid crystal display element described above was dropped on the liquid crystal alignment films of examples 1 to 4 and comparative examples 1 to 4, on which the heat baking was completed. After the liquid crystal liquid did not flow, the contact angle between the liquid crystal liquid and the liquid crystal alignment film was measured using a contact angle measuring instrument (model: DSA100, manufactured by KRUSS Co., Ltd.) and the surface energy thereof was calculated. It is worth mentioning that when a liquid contacts a surface, the shape of the liquid changes due to the characteristics of the surface. Further, when the liquid spreads on the surface to wet the surface, the contact angle between the surface and the liquid is small, that is, the wettability between the surface and the liquid is high. Specifically, the contact angle of the liquid crystal is determined to be good if it is 15 degrees or less, good if it is 15 degrees to 17 degrees, and poor if it is 17 degrees or more.

Pretilt angle (PTA)

With respect to the liquid Crystal display devices of examples 1 to 4 and comparative examples 1 to 4, the pretilt angle of the liquid Crystal molecules in the liquid Crystal layer was measured by a Crystal Rotation Method (Crystal Rotation Method), respectively. Specifically, the tilt angles of the liquid crystal display elements are obtained by rotating the directions of the liquid crystal display elements to change the incident angle of the laser beam and by changing the phase retardation (phase retardation) of the light passing through the liquid crystal display elements. If the pretilt angle is 89 degrees or more, it is judged as good, if the pretilt angle is between 89 degrees and 87 degrees, it is judged as good, and if the pretilt angle is 87 degrees or less, it is judged as bad.

Voltage Holding Ratio (VHR)

Direct currents (charging voltage of 5V, operating frequency of 0.6Hz, pulse width of 60 μ sec) were applied to the liquid crystal display elements of examples 1 to 4 and comparative examples 1 to 4, respectively, at an ambient temperature of 60 ℃ to measure the voltage holding ratio of each liquid crystal display element. In detail, a very small current and a very low drain voltage were measured using a liquid crystal physical parameter measuring instrument (model: ALCT-IV1, manufactured by INSTEC corporation) to evaluate a voltage holding ratio at a voltage of 5V. If the voltage holding ratio is 80% or more, it is judged as good, if the voltage holding ratio is 80% to 70%, it is judged as good, and if the voltage holding ratio is 70% or less, it is judged as bad.

Residual direct current voltage (RDC)

Direct current (charging voltage of 5V, operation frequency of 0.6Hz, pulse width of 60 μ sec) was applied to the liquid crystal display elements of examples 1 to 4 and comparative examples 1 to 4, respectively, at an ambient temperature of 60 ℃ for 1 hour, followed by discharging for 1 second, and after 10 minutes, the residual direct current voltage value (V) was recorded. If the residual direct current voltage value is less than or equal to 1.0V, the judgment is good, if the residual direct current voltage value is between 1.0V and 1.5V, and if the residual direct current voltage value is greater than or equal to 1.5V, the judgment is bad.

Evaluation of surface Profile-Scanning Electron Microscope (SEM)

First, the two substrates in the liquid crystal display elements of examples 1 to 4 and comparative examples 1 to 4 were detached and separated, respectively. Then, the liquid crystal layer in each liquid crystal display element was removed by washing with water and alcohol, and the washing was repeated 3 times and then the substrate was blow-dried with nitrogen, wherein the acrylic polymer thin film formed on the liquid crystal alignment film remained on the substrate. Next, the surface distribution configuration of each acrylic polymer film was observed by means of a scanning electron microscope (model: S-4700FE-SEM, manufactured by Hitachi corporation). If the surface distribution configuration of the acrylic polymer film is consistent in growth size state and uniformity and has no obvious difference, the acrylic polymer film is judged to be excellent, as shown in fig. 1; and if the distribution configuration of the surface of the acrylic polymer film shows a significant difference between the growth size state and the uniformity, the film is determined to be bad, as shown in fig. 2.

Evaluation of surface roughness-Atomic Force Microscope (AFM)

First, the two substrates in the liquid crystal display elements of examples 1 to 4 and comparative examples 1 to 4 were detached and separated, respectively. Then, the liquid crystal layer in each liquid crystal display element was removed by washing with water and alcohol, and the washing was repeated 3 times and then the substrate was blow-dried with nitrogen, wherein the acrylic polymer thin film formed on the liquid crystal alignment film remained on the substrate. Next, the surface roughness Ra (nm) of each acrylic polymer film was measured in a Tapping mode (Tapping mode) with a scanning frequency of 0.4Hz at an area of 5 μm x5 μm using an atomic force microscope (model: Dimension Icon AFM, manufactured by BRUKER). In the evaluation, the surface was judged to be flat if the surface roughness Ra was 2nm or less, and was judged to be rough if the surface roughness Ra was 2nm or more.

As can be seen from table 1, the liquid crystal alignment agent of the present invention, which includes a polymer obtained by reacting a diamine component containing at least one of the compounds represented by formulas 6, 7 and 8 and a tetracarboxylic dianhydride component containing the compound represented by formula 2, has good coatability, and the formed liquid crystal alignment film has good wettability with the liquid crystal layer. Furthermore, the liquid crystal display device of the invention not only has good voltage holding ratio, lower residual direct current voltage and good vertical alignment capability, but also has excellent surface uniformity and flatness of the acrylic polymer film formed on the liquid crystal alignment film by the polymerizable monomer, which means that the polymerizable monomer can be uniformly dispersed on the liquid crystal alignment film before polymerization reaction. Therefore, the liquid crystal display element of the invention not only can avoid the problem of point-like color phase unevenness caused by uneven alignment, but also has the advantages of high response speed, good electrical performance and the like, thereby having good display quality.

In contrast to comparative examples 3 and 4, the tetracarboxylic dianhydride component does not contain the compound represented by formula 2, and thus the liquid crystal aligning agents of comparative examples 3 and 4 do not have good coatability. Further, the liquid crystal aligning agent of comparative example 3, which does not contain the compound represented by formula 2 in the tetracarboxylic dianhydride component, has no good coatability even if the diamine component contains at least one of the compounds represented by formulae 6, 7 and 8.

In contrast to comparative examples 1 and 2, the liquid crystal alignment films of comparative examples 1 and 2, in which the tetracarboxylic dianhydride component contains the compound represented by formula 2 and the diamine component does not contain the compounds represented by formulae 6, 7, and 8, did not have good wettability to the liquid crystal layer and the polymerizable monomer was not uniformly dispersed thereon.

Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention.

Claims

1. A liquid crystal alignment agent comprising:

a solvent, a water-soluble organic solvent,

wherein the diamine component is selected from at least one of the compounds represented by formula 7 and formula 8:

and the tetracarboxylic dianhydride component comprises a compound represented by formula 2:

wherein the content of the compound represented by formula 2 is 50 mol% or more based on the total mole number of the tetracarboxylic dianhydride component.

2. A liquid crystal alignment agent comprising:

a solvent, a water-soluble organic solvent,

wherein the diamine component is selected from compounds represented by formula 6:

3. The liquid crystal aligning agent according to claim 1 or 2, wherein the content of the compound represented by formula 6, 7, or 8 is 1 mol% or more based on the total mole number of the diamine component.

4. The liquid crystal aligning agent according to claim 1 or 2, wherein the tetracarboxylic dianhydride component further comprises at least one selected from the group consisting of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride, tetrahydronaphthalene dianhydride, 3 ', 4,4 ' -biphenyltetracarboxylic dianhydride, 4,4 ' -oxydiphthalic anhydride, and 3,3 ', 4,4 ' -benzophenonetetracarboxylic dianhydride.

5. The liquid crystal aligning agent of claim 1 or 2, wherein the polymer comprises polyamic acid, polyimide, a copolymer of polyamic acid and polyimide, or a mixture of polyamic acid and polyimide.

6. A liquid crystal alignment film made of the liquid crystal aligning agent according to any one of claims 1 to 5.

7. A liquid crystal display element comprising:

a liquid crystal alignment film according to claim 6; and