JP7448891B2 - Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element - Google Patents

Description

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

A liquid crystal display element is constructed by sandwiching a liquid crystal layer between a pair of transparent substrates provided with electrodes. In the liquid crystal display element, an organic film made of an organic material is used as a liquid crystal alignment film so that the liquid crystal is aligned in a desired state between the substrates. That is, the liquid crystal alignment film is a component of the liquid crystal display element, is formed on the surface of the substrates that sandwich the liquid crystal, and is in contact with the liquid crystal, and plays the role of aligning the liquid crystal in a fixed direction between the substrates. Furthermore, the pretilt angle of the liquid crystal can be controlled by the liquid crystal alignment film. A method is known in which the pretilt angle is lowered mainly by selecting the structure of polyimide (see Patent Documents 1 and 2).

Japanese Patent Application Publication No. 9-188761 Japanese Patent Application Publication No. 10-123532

On the other hand, as the performance of liquid crystal display elements has improved in recent years, in addition to applications such as large-screen, high-definition liquid crystal televisions, they have also been used for in-vehicle applications such as car navigation systems, meter panels, surveillance cameras, and medical camera monitors. Liquid crystal display elements are used in such devices, and due to the demand for viewing angle characteristics, even the rubbing alignment film is required to have a lower pretilt angle than before.

In addition, the viewing angle dependence of color due to the pretilt angle, so-called color shift, has been pointed out as a problem, and in order to solve this problem, an alignment film with a pretilt angle of 1 degree or less is specifically required. .

As a result of various studies to achieve the above object, the inventors have found that a liquid crystal aligning agent having the following configuration is optimal for achieving the above object, and have completed the present invention.

Thus, the present invention is based on the above findings and has the following gist.
A liquid crystal aligning agent containing polyimide which is a reaction product of a diamine component and a tetracarboxylic dianhydride derivative component consisting of at least one selected from aliphatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride. A liquid crystal aligning agent, wherein the diamine component contains at least one diamine selected from diamines having the structure of the following formula [A], and the imidization rate of polyimide is 70% or more.

式中Ｘ_１、Ｘ_２はそれぞれ独立に酸素原子又は硫黄原子であり、Ｒは[－（（ＣＨ_２）_２Ｏ）_ｐ（ＣＨ_２）_２－]で表され、ｐは１から３の整数である。

In the formula, X ₁ and X ₂ are each independently an oxygen atom or a sulfur atom, R is represented by [-((CH ₂ ) ₂ O) _p (CH ₂ ) ₂ -], and p is an integer from 1 to 3. It is.

By using the liquid crystal alignment agent of the present invention, it is possible to obtain a liquid crystal alignment film that satisfies various properties required for a liquid crystal alignment film and provides a low pretilt angle of 1 degree or less.

<Aliphatic, alicyclic tetracarboxylic acid derivatives>
The polyimide contained in the liquid crystal aligning agent of the present invention includes a tetracarboxylic dianhydride derivative component consisting of at least one selected from aliphatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride, and a specific diamine. It is obtained by imidizing a polyimide precursor obtained from a diamine component containing (hereinafter also referred to as a specific polymer). Below, specific examples of the materials used and the manufacturing method will be explained in detail.

Tetracarboxylic acid derivatives used in the production of polyimide precursors include not only tetracarboxylic dianhydride but also its derivatives, such as tetracarboxylic acid, tetracarboxylic dihalide compounds, dialkyl tetracarboxylate esters, and dialkyl tetracarboxylate. Examples include ester dihalides.

Among the aliphatic and alicyclic tetracarboxylic dianhydrides or derivatives thereof, those represented by the following formula (4) are preferred.

式（４）中、Ｘ_１の好ましい構造は、下記式（Ｘ１－１）～（Ｘ１－２４）が挙げられる。

In formula (4), preferred structures of X ₁ include the following formulas (X1-1) to (X1-24).

式（Ｘ１－１）～（Ｘ１－４）において、Ｒ_３～Ｒ_２３は、それぞれ独立して、水素原子、ハロゲン原子、炭素数１～６のアルキル基、炭素数２～６のアルケニル基、炭素数２～６のアルキニル基、フッ素原子を含有する炭素数１～６の１価の有機基、又はフェニル基である。液晶配向性の点から、Ｒ_３～Ｒ_２３は、水素原子、ハロゲン原子、メチル基、又はエチル基が好ましく、水素原子、又はメチル基が好ましい。

In formulas (X1-1) to (X1-4), R ₃ to R ₂₃ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, An alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group. From the viewpoint of liquid crystal orientation, R ₃ to R ₂₃ are preferably a hydrogen atom, a halogen atom, a methyl group, or an ethyl group, and preferably a hydrogen atom or a methyl group.

Specific examples of formula (X1-1) include the following formulas (X1-1-1) to (X1-1-6). From the viewpoint of improving liquid crystal orientation, (X1-1-1) is particularly preferred.

From the viewpoint of obtaining the effects of the present invention, X ₁ is the formula (X1-1-1), (X1-1-2), (X1-9), (X1-10), (X1-21), X1-24) is more preferred.

There may be two or more types of compounds represented by the above formula (4), including the formula (4) in which X ₁ is the above formula (X1-1), and the compound in which X ₁ is the above formula (X1-2) to ( X1-24) and the formula (4).

<Specific diamine>
The diamine component used for manufacturing the polyimide contained in the liquid crystal aligning agent of the present invention contains at least one kind selected from diamines having the structure of the following formula [A].

式中Ｘ_１、Ｘ_２はそれぞれ独立に酸素原子又は硫黄原子であり、Ｒは［－（（ＣＨ_２）_２Ｏ）_ｐ（ＣＨ_２）_２－］で表され、ｐは１から３の整数である。

In the formula, X ₁ and X ₂ are each independently an oxygen atom or a sulfur atom, R is represented by [-((CH ₂ ) ₂ O) _p (CH ₂ ) ₂ -], and p is an integer from 1 to 3. It is.

Preferred specific examples of [A] include diamines of the following formulas [A-1] to [A-4]. These may be used alone or in combination.

The preferred content of the diamine having the structure of the above formula [A] is preferably 40% to 80% of the total diamine components, more preferably 40% to 70%, and still more preferably 40% to 60%.

<Other diamines>
As the diamine component used for producing the polyimide contained in the liquid crystal aligning agent of the present invention, in addition to the diamine having the structure of the above formula [A], various diamines may be used depending on the required characteristics of the liquid crystal aligning agent. I can do it.

Other diamines are represented by the following formula (5).

上記式（５）中、Ａ_１及びＡ_２はそれぞれ独立して、水素原子、又は炭素数１～５のアルキル基、炭素数２～５のアルケニル基、又は炭素数２～５のアルキニル基である。

In the above formula (5), A ₁ and A ₂ are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms. be.

The structure of Y ₁ is not particularly limited. Preferred structures include the following (Y-1) to (Y-182).

上記式中、Ｍｅは、メチル基を表し、Ｒ^１は水素原子または炭素数１～５の炭化水素基を表す。

In the above formula, Me represents a methyl group, and R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms.

From the viewpoint of improving the solubility of the polymer, it is preferable that the structure of any Y ₁ includes a structure represented by the following formula (6).

上記式（６）において、Ｄは、好ましくは１５０℃～２３０℃、より好ましくは１８０℃～２３０℃で脱離し、水素原子に置き換わる熱脱離性基である。上記式（６）で表される構造を含むＹの具体例としては、（Ｙ－１２４）、（Ｙ－１３１）、（Ｙ－１５８）～（Ｙ－１６３）が挙げられる。

In the above formula (6), D is a thermally releasable group that is preferably eliminated at 150° C. to 230° C., more preferably 180° C. to 230° C., and replaced by a hydrogen atom. Specific examples of Y containing the structure represented by the above formula (6) include (Y-124), (Y-131), and (Y-158) to (Y-163).

<Polyamic acid>
The polyamic acid that is the polyimide precursor used in the present invention is specified as a tetracarboxylic dianhydride derivative component consisting of at least one selected from aliphatic tetracarboxylic dianhydrides and alicyclic tetracarboxylic dianhydrides. It is a polyimide precursor obtained from a diamine component containing diamine, and can be produced by the method shown below.

Specifically, a tetracarboxylic dianhydride derivative component consisting of at least one selected from aliphatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride and a diamine component containing a specific diamine are combined into an organic compound. It can be synthesized by reacting in the presence of a solvent at -20°C to 150°C, preferably 0°C to 50°C, for 30 minutes to 24 hours, preferably 1 hour to 12 hours.

The organic solvent used in the above reaction is preferably N,N-dimethylformamide, N-methyl-2-pyrrolidone, or γ-butyrolactone from the viewpoint of solubility of the monomer and polymer, and these may be used alone or in combination of two or more. May be used. The concentration of the polymer is preferably 1% by mass to 30% by mass, more preferably 5% by mass to 20% by mass, from the viewpoints that polymer precipitation is difficult to occur and high molecular weight products are easily obtained.

The polyamic acid obtained as described above can be recovered by injecting the reaction solution into a poor solvent while stirring well to precipitate the polymer. Further, purified polyamic acid powder can be obtained by performing precipitation several times, washing with a poor solvent, and drying at room temperature or by heating. Examples of the poor solvent include, but are not limited to, water, methanol, ethanol, hexane, butyl cellosolve, acetone, toluene, and the like.

<Polyamic acid ester>
Polyamic acid ester, which is one of the polyimide precursors used in the present invention, can be produced by the method (I), (II) or (III) shown below.

(I) When manufactured from polyamic acid
A polyamic acid ester can be synthesized by esterifying a polyamic acid obtained from a tetracarboxylic dianhydride and a diamine. Specifically, the polyamic acid and the esterifying agent are reacted in the presence of an organic solvent at -20°C to 150°C, preferably 0°C to 50°C, for 30 minutes to 24 hours, preferably 1 hour to 4 hours. It can be synthesized by

The esterifying agent is preferably one that can be easily removed by purification, such as N,N-dimethylformamide dimethyl acetal, N,N-dimethylformamide diethyl acetal, N,N-dimethylformamide dipropyl acetal, N,N-dimethylformamide Dineopentyl butyl acetal, N,N-dimethylformamide di-t-butyl acetal, 1-methyl-3-p-tolyltriazene, 1-ethyl-3-p-tolyltriazene, 1-propyl-3-p -tolyltriazene, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, and the like. The amount of the esterifying agent used is preferably 2 mol to 6 mol equivalent per mol of the repeating unit of the polyamic acid.

The solvent used in the above reaction is preferably N,N-dimethylformamide, N-methyl-2-pyrrolidone, or γ-butyrolactone from the viewpoint of polymer solubility, and these may be used alone or in combination of two or more. good. The concentration of the polymer in the reaction solution is preferably 1% by mass to 30% by mass, more preferably 5% by mass to 20% by mass, from the viewpoints that polymer precipitation is unlikely to occur and high molecular weight products are easily obtained.

(II) When manufactured by reaction of tetracarboxylic acid diester dichloride and diamine Polyamic acid ester can be manufactured from tetracarboxylic acid diester dichloride and diamine. Specifically, tetracarboxylic acid diester dichloride and diamine are heated in the presence of a base and an organic solvent at -20°C to 150°C, preferably 0°C to 50°C, for 30 minutes to 24 hours, preferably 1 hour to 4 hours. It can be synthesized by a time reaction.

As the base, pyridine, triethylamine, 4-dimethylaminopyridine, etc. can be used, but pyridine is preferred because the reaction proceeds mildly. The amount of the base to be used is preferably 2 to 4 times the mole of tetracarboxylic acid diester dichloride, from the viewpoint of easy removal and easy obtaining of a high molecular weight product.

The solvent used in the above reaction is preferably N-methyl-2-pyrrolidone or γ-butyrolactone from the viewpoint of solubility of the monomer and polymer, and these may be used alone or in combination of two or more. The polymer concentration in the reaction solution is preferably 1% by mass to 30% by mass, more preferably 5% by mass to 20% by mass, from the viewpoints that polymer precipitation is unlikely to occur and high molecular weight products are easily obtained. Furthermore, in order to prevent hydrolysis of the tetracarboxylic acid diester dichloride, the solvent used in the synthesis of the polyamic acid ester is preferably as dehydrated as possible, and preferably in a nitrogen atmosphere to prevent outside air from entering.

(III) When manufactured by reaction of tetracarboxylic acid diester and diamine Polyamic acid ester can be manufactured by polycondensing tetracarboxylic acid diester and diamine. Specifically, a tetracarboxylic acid diester and a diamine are heated in the presence of a condensing agent, a base, and an organic solvent at 0°C to 150°C, preferably 0°C to 100°C, for 30 minutes to 24 hours, preferably for 3 hours to It can be produced by reacting for 15 hours.

The condensing agent includes triphenyl phosphite, dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-carbonyldiimidazole, dimethoxy-1,3,5-triazimide. Nylmethylmorpholinium, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, O-(benzotriazol-1-yl)-N,N , N',N'-tetramethyluronium hexafluorophosphate, diphenyl (2,3-dihydro-2-thioxo-3-benzooxazolyl)phosphonate, and the like can be used. The amount of the condensing agent added is preferably 2 to 3 times the molar amount of the tetracarboxylic acid diester.

Tertiary amines such as pyridine and triethylamine can be used as the base. The amount of the base to be used is preferably 2 to 4 times the mole of the diamine component, from the viewpoint of easy removal and easy obtaining of a high molecular weight product.

Moreover, in the above reaction, the reaction proceeds efficiently by adding a Lewis acid as an additive. As the Lewis acid, lithium halides such as lithium chloride and lithium bromide are preferred. The amount of Lewis acid added is preferably 0 to 1.0 times the mole of the diamine component.

Among the above three methods for producing a polyamic acid ester, the above method (II) is particularly preferable for the above (I) because a high molecular weight polyamic acid ester is obtained.

The polyamic acid ester solution obtained as described above can be poured into a poor solvent while stirring well to precipitate the polymer. After performing precipitation several times and washing with a poor solvent, a purified polyamic acid ester powder can be obtained by drying at room temperature or by heating. Examples of the poor solvent include, but are not limited to, water, methanol, ethanol, hexane, butyl cellosolve, acetone, toluene, and the like.

<Polyimide>
The polyimide used in the present invention can be produced by imidizing the polyamic acid or polyamic acid ester. The imidization rate of the polyimide used in the present invention is preferably 70% to 99% from the viewpoint of electrical properties. When producing polyimide from a polyamic acid ester, chemical imidization is easily carried out by adding a basic catalyst to the polyamic acid ester solution or a polyamic acid solution obtained by dissolving the polyamic acid ester resin powder in an organic solvent. Chemical imidization is preferable because the imidization reaction proceeds at a relatively low temperature and the molecular weight of the polymer is less likely to decrease during the imidization process.

Chemical imidization can be carried out by stirring the polyamic acid or polyamic acid ester to be imidized in an organic solvent in the presence of a basic catalyst and an acid anhydride. As the organic solvent, the solvent used in the polymerization reaction described above can be used. Examples of the basic catalyst include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Among these, pyridine is preferable because it has an appropriate basicity to allow the reaction to proceed. Further, examples of the acid anhydride include acetic anhydride, trimellitic anhydride, pyromellitic anhydride, etc. Among them, acetic anhydride is preferably used because it facilitates purification after the reaction is completed.

The temperature for carrying out the imidization reaction is, for example, -20°C to 120°C, preferably 0°C to 100°C, and the reaction time can be carried out for 1 hour to 100 hours. The amount of the basic catalyst is 0.5 to 30 times the mole of the amic acid group, preferably 2 to 20 times the mole, and the amount of the acid anhydride is 1 to 50 times the mole of the amic acid group. Preferably it is 3 to 30 times the mole. The imidization rate of the resulting polymer can be controlled by adjusting the amount of catalyst, temperature, and reaction time.

Since the added catalyst remains in the solution after the imidization reaction of polyamic acid ester or polyamic acid, the resulting imidized polymer is recovered by the method described below and redissolved in an organic solvent. Therefore, it is preferable to use the liquid crystal aligning agent of the present invention.

The polyimide solution obtained as described above can be poured into a poor solvent with thorough stirring to precipitate the polymer. After performing precipitation several times and washing with a poor solvent, a purified polyamic acid ester powder can be obtained by drying at room temperature or by heating.

Examples of the poor solvent include, but are not limited to, methanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, benzene, and the like.

<Liquid crystal alignment agent>
The liquid crystal aligning agent of the present invention has the form of a solution in which a polymer including a specific polymer is dissolved in an organic solvent. The weight average molecular weight of the polyimide precursor and polyimide according to the present invention is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and still more preferably 10,000 to 100. ,000. Further, the number average molecular weight is preferably 1,000 to 250,000, more preferably 2,500 to 150,000, and even more preferably 5,000 to 50,000.

The content of the specific polymer in the liquid crystal aligning agent of the present invention is preferably 2% by mass to 10% by mass, more preferably 3% by mass to 8% by mass.

In addition to the specific polymer, the liquid crystal aligning agent of the present invention may contain polyamic acid, which is a reaction product of any tetracarboxylic acid derivative component and any diamine component.

Further, when the liquid crystal aligning agent contains the polyamic acid, the proportion thereof is preferably 10 parts by mass to 900 parts by mass, more preferably 25 parts by mass to 700 parts by mass, based on 100 parts by mass of polyimide.

All the polymer components in the liquid crystal aligning agent of the present invention may be mixed with other polymers. Other polymers include cellulose polymers, acrylic polymers, methacrylic polymers, polystyrene, polyamides, polysiloxanes, and the like. The content of other polymers is preferably 0.5 parts by mass to 15 parts by mass, more preferably 1 part by mass to 10 parts by mass, based on a total of 100 parts by mass of polyimide and polyamic acid.

The concentration of the polymer in the liquid crystal aligning agent used in the present invention can be changed as appropriate depending on the thickness of the coating film to be formed, but from the viewpoint of forming a uniform and defect-free coating film, it is necessary to % or more, and from the viewpoint of storage stability of the solution, 10% by weight or less is preferable.

The solvent in the liquid crystal alignment agent of the present invention is a solvent that dissolves the polyimide precursor and polyimide (also referred to as a good solvent), or a solvent that improves the coating properties and surface smoothness of the liquid crystal alignment film when the liquid crystal alignment agent is applied. (also referred to as a poor solvent) is preferably used. Specific examples of other solvents are listed below, but the solvent is not limited to these examples.

Specific examples of good solvents include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, γ-butyrolactone, γ-valerolactone, 1,3-dimethylimidazolidinone, Examples include N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, methyl ethyl ketone, cyclohexanone, cyclopentanone, 3-methoxy N,N-dimethylpropanamide or 4-hydroxy-4-methyl-2-pentanone. be able to.

Specific examples of poor solvents include 1-butoxy-2-propanol, 2-butoxy-1-propanol, 2-propoxyethanol, 2-(2-propoxyethoxy)ethanol, 1-propoxy-2-propanolethanol, and isopropyl alcohol. , 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol, tert-pentyl alcohol, 3 -Methyl-2-butanol, neopentyl alcohol, 1-hexanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3 -Heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, cyclohexanol, 1-methylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, 1,2-ethanediol, 1,2 -Propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-methyl- 2,4-pentanediol, 2-ethyl-1,3-hexanediol, dipropyl ether, dibutyl ether, dihexyl ether, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, 1,2-butoxyethane , diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, 2-pentanone, 3-pentanone, 2-hexanone, 2-heptanone, 4-heptanone, 3-ethoxybutyl acetate, 1-methylpentyl acetate, 2-ethyl Butyl acetate, 2-ethylhexyl acetate, ethylene glycol monoacetate, ethylene glycol diacetate, propylene carbonate, ethylene carbonate, 2-(methoxymethoxy)ethanol, butyl cellosolve, ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, 2-(hexyloxy)ethanol, furfuryl alcohol, diethylene glycol, propylene glycol, 1-(butoxyethoxy)propanol, propylene glycol monomethyl ether acetate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, Propylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monoacetate, ethylene glycol diacetate, diethylene glycol monoethyl ether acetate, propylene glycol diacetate diisopentyl ether, diethylene glycol monobutyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, diethylene glycol acetate, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, methyl lactate, lactic acid Ethyl, methyl acetate, ethyl acetate, n-butyl acetate, propylene glycol monoethyl acetate, methyl pyruvate, ethyl pyruvate, methyl 3-methoxypropionate, methyl ethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, 3-ethoxypropionic acid, 3-methoxypropionic acid, propyl 3-methoxypropionate, butyl 3-methoxypropionate, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl ester, isoamyl lactate, Examples include diisobutyl ketone and ethyl carbitol.

Moreover, as a poor solvent, a solvent represented by the following formula, and a specific example, diisobutylcarbinol is also preferably used.

Ｒ_２４、Ｒ_２５はそれぞれ独立して、直鎖又は分岐の、炭素数１～８のアルキル基である。但し、Ｒ_２４とＲ_２５の炭素数の合計は３より大きい整数である。

R _{24 and} R ₂₅ are each independently a linear or branched alkyl group having 1 to 8 carbon atoms. However, the total number of carbon atoms in R ₂₄ and R ₂₅ is an integer greater than 3.

In addition, as the poor solvent, when the polyimide precursor and polyimide contained in the liquid crystal aligning agent have high solubility in the solvent, solvents represented by the following formulas [D-1] to [D-3] are preferable. .

式［Ｄ－１］中、Ｄ^１は炭素数１～３のアルキル基を示し、式［Ｄ－２］中、Ｄ^２は炭素数１～３のアルキル基を示し、式［Ｄ－３］中、Ｄ^３は炭素数１～４のアルキル基を示す。

In formula [D-1], D ¹ represents an alkyl group having 1 to 3 carbon atoms, in formula [D-2], D ² represents an alkyl group having 1 to 3 carbon atoms, and in formula [D-3] Among them, D ³ represents an alkyl group having 1 to 4 carbon atoms.

Examples of solvent combinations of good and poor solvents include N-methyl-2-pyrrolidone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone, and ethylene glycol monobutyl ether from the viewpoint of good printability. , N-methyl-2-pyrrolidone and γ-butyrolactone and propylene glycol monobutyl ether, N-ethyl-2-pyrrolidone and propylene glycol monobutyl ether, N-methyl-2-pyrrolidone and γ-butyrolactone and 4-hydroxy-4-methyl -2-pentanone and diethylene glycol diethyl ether, N-methyl-2-pyrrolidone and γ-butyrolactone, propylene glycol monobutyl ether and 2,6-dimethyl-4-heptanone, N-methyl-2-pyrrolidone and γ-butyrolactone and propylene glycol Monobutyl ether and diisopropyl ether, N-methyl-2-pyrrolidone and γ-butyrolactone and propylene glycol monobutyl ether and 2,6-dimethyl-4-heptanol, N-methyl-2-pyrrolidone and γ-butyrolactone and dipropylene glycol dimethyl ether, N-methyl-2-pyrrolidone and propylene glycol monobutyl ether and dipropylene glycol dimethyl ether, N-ethyl-2-pyrrolidone and propylene glycol monobutyl ether and dipropylene glycol dimethyl ether, N-methyl-2-pyrrolidone and propylene glycol monobutyl ether and dipropylene glycol dimethyl ether Examples include combinations of propylene glycol monomethyl ether and the like. The amount of these poor solvents is preferably 1 to 80% by weight, more preferably 10 to 80% by weight, and particularly preferably 20 to 70% by weight of the total solvent contained in the liquid crystal aligning agent. The type and content of the solvent are appropriately selected depending on the liquid crystal aligning agent coating device, coating conditions, coating environment, and the like.

Moreover, the liquid crystal aligning agent of the present invention is a crosslinkable compound having an epoxy group, an isocyanate group, an oxetane group, or a cyclocarbonate group, a hydroxyl group, a hydroxyalkyl group, and a lower alkoxyalkyl group. It may contain a crosslinkable compound having a group or a crosslinkable compound having a polymerizable unsaturated bond.

As such a crosslinking compound, various known compounds can be used depending on the purpose. The following compounds are preferably used.

The content of the crosslinkable compound is preferably 0.1 parts by mass to 150 parts by mass based on 100 parts by mass of all polymer components. Among these, in order for the crosslinking reaction to proceed and exhibit the desired effect, the amount is preferably from 0.1 parts by weight to 100 parts by weight, and more preferably from 1 part by weight to 50 parts by weight.

The liquid crystal aligning agent of the present invention can contain a compound that improves the uniformity of the film thickness and surface smoothness of the liquid crystal aligning film when the liquid crystal aligning agent is applied.

Examples of compounds that improve the uniformity of film thickness and surface smoothness of the liquid crystal alignment film include fluorine-based surfactants, silicone-based surfactants, and nonionic surfactants.

The amount of surfactant used is preferably 0.01 parts by mass to 2 parts by mass, more preferably 0.01 parts by mass to 1 part by mass, based on 100 parts by mass of all polymer components contained in the liquid crystal aligning agent. Department.

It also contains a silane coupling agent for the purpose of improving the adhesion between the liquid crystal alignment film and the substrate, and an imidization promoter for the purpose of efficiently promoting imidization by heating the polyimide precursor when baking the coating film. You can force it.
Examples of the silane coupling agent include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldiethoxymethylsilane, 2-aminopropyltrimethoxysilane, 2-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, N-ethoxycarbonyl-3-aminopropyltrimethoxysilane, N-ethoxycarbonyl-3-aminopropyltriethoxysilane, N-triethoxysilylpropyltriethylenetriamine, N-trimethoxysilylpropyltriethylenetriamine, N-bis( oxyethylene)-3-aminopropyltrimethoxysilane, N-bis(oxyethylene)-3-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltri Methoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane , 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, Tris-( Examples include silane coupling agents such as trimethoxysilylpropyl) isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane. The amount of these silane coupling agents used is preferably 0.1 to 30 parts by mass, and 0.1 to 20 parts by mass, based on 100 parts by mass of the polymer component contained in the liquid crystal aligning agent, from the viewpoint of improving liquid crystal alignment. Parts by mass are more preferred.

<Liquid crystal alignment film, liquid crystal display element>
The liquid crystal aligning film of the present invention is a film obtained by applying the above-mentioned liquid crystal aligning agent to a substrate, drying, and baking. The substrate to which the liquid crystal aligning agent of the present invention is applied is not particularly limited as long as it is a highly transparent substrate, and plastic substrates such as glass substrates, silicon nitride substrates, acrylic substrates, and polycarbonate substrates can also be used. In this case, it is preferable to use a substrate on which ITO electrodes and the like for driving the liquid crystal are formed, from the viewpoint of process simplification. Further, in a reflective liquid crystal display element, an opaque material such as a silicon wafer can be used for only one substrate, and in this case, a material that reflects light such as aluminum can also be used for the electrodes.

Industrially, the liquid crystal aligning agent is generally applied by screen printing, offset printing, flexographic printing, or inkjet method, and other methods include dip method, roll coater method, and slit coater method. method, spinner method, spray method, etc. are known.

After applying the liquid crystal aligning agent onto the substrate, the solvent can be evaporated using a heating means such as a hot plate, a thermal circulation type oven, or an IR (infrared ray) type oven to form a liquid crystal aligning film. Any temperature and time can be selected for the drying and baking steps after applying the liquid crystal aligning agent. Usually, the conditions include baking at 50° C. to 120° C. for 1 minute to 10 minutes, and then baking at 150° C. to 300° C. for 5 minutes to 120 minutes to sufficiently remove the contained solvent. The thickness of the liquid crystal alignment film after firing is preferably 5 nm to 300 nm, more preferably 10 nm to 200 nm, since the reliability of the liquid crystal display element may decrease if it is too thin.

The liquid crystal aligning agent of the present invention can be coated on a substrate, baked, and then subjected to alignment treatment such as rubbing treatment or photo alignment treatment, and can be used as a liquid crystal alignment film without alignment treatment in vertical alignment applications. Known methods and devices can be used for alignment treatment such as rubbing treatment and photo alignment treatment.

As an example of a method for manufacturing a liquid crystal cell, a liquid crystal display element having a passive matrix structure will be described as an example. Note that a liquid crystal display element having an active matrix structure in which a switching element such as a TFT (Thin Film Transistor) is provided in each pixel portion constituting an image display may be used.

Specifically, transparent glass substrates are prepared, and a common electrode is provided on one substrate and a segment electrode is provided on the other substrate. These electrodes can be, for example, ITO electrodes, and are patterned to display a desired image. Next, an insulating film is provided on each substrate so as to cover the common electrode and the segment electrode. The insulating film can be, for example, a SiO ₂ -TiO ₂ film formed by a sol-gel method.

Next, a liquid crystal alignment film is formed on each substrate, one substrate is stacked on the other substrate so that the surfaces of the liquid crystal alignment films face each other, and the periphery is bonded with a sealant. In order to control the gap between the substrates, a spacer is usually mixed into the sealant, and it is preferable that spacers for controlling the gap between the substrates are also sprinkled on the in-plane portion where the sealant is not provided. A portion of the sealant is provided with an opening that can be filled with liquid crystal from the outside. Next, a liquid crystal material is injected into a space surrounded by the two substrates and the sealant through an opening provided in the sealant, and then this opening is sealed with an adhesive. For injection, a vacuum injection method may be used, or a method utilizing capillary action in the atmosphere may be used. The liquid crystal material may be either a positive type liquid crystal material or a negative type liquid crystal material, but a negative type liquid crystal material is preferred. Next, a polarizing plate is installed. Specifically, a pair of polarizing plates is attached to the surfaces of the two substrates opposite to the liquid crystal layer.

The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. In addition, the abbreviations of compounds and solvents are as follows.
NMP: N-methyl-2-pyrrolidone GBL: γ-butyrolactone BCS: Butyl cellosolve DA-1: A compound represented by the following structural formula. (Compound of formula (1))
DA-2: A compound represented by the following structural formula. (Compound of formula (2))
DA-3: A compound shown by the following structural formula.
DA-4: A compound represented by the following structural formula.
CA-1: A compound represented by the following structural formula.
(BDA: 1,2,3,4-butanetetracarboxylic dianhydride)
CA-2: A compound represented by the following structural formula.
(CBDA: 1,2,3,4,-cyclobutanetetracarboxylic dianhydride)
AD-1: 3-glycidoxypropyltriethoxysilane

<Viscosity>
In the synthesis example, the viscosity of the polymer solution was measured using an E-type viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.), sample volume 1.1 mL, cone rotor TE-1 (1° 34', R24), and temperature 25. Measured at °C.

<Measurement of imidization rate of polyimide>
The imidization rate of polyimide in the synthesis example was measured as follows. 30 mg of polyimide powder was placed in an NMR (nuclear magnetic resonance) sample tube (NMR sampling tube standard, φ5 (manufactured by Kusano Kagaku)), and deuterated dimethyl sulfoxide (DMSO-d6, 0.05% by mass TMS (tetramethylsilane)) was added. Mixed product) (0.53 ml) was added and completely dissolved by applying ultrasound. This solution was subjected to proton NMR measurement at 500 MHz using an NMR measuring device (JNW-ECA500) (manufactured by JEOL Datum). The imidization rate is determined using a proton derived from a structure that does not change before and after imidization as a reference proton, and the peak integrated value of this proton and the proton peak derived from the NH group of the amic acid that appears around 9.5 ppm to 10.0 ppm. It was calculated using the following formula using the integrated value.

Imidization rate (%) = (1-α・x/y)×100
In the above formula, x is the integrated value of the proton peak derived from the NH group of amic acid, y is the integrated peak value of the standard proton, and α is one NH group proton of the amic acid in the case of polyamic acid (imidization rate is 0%). This is the ratio of the number of standard protons to the standard proton.

(Synthesis example 1)
According to the following reaction formula, compound [DA-1] was synthesized via compound [1] and compound [2].

Synthesis of Compound [1] In dimethylformamide (400 g), 4-fluoronitrobenzene (50.0 g, 354 mmol), hydroquinone (78.0 g), and potassium carbonate (73.4 g) were added and stirred at 80°C for 2 hours. . After cooling to room temperature, the reaction solution was poured into pure water (800 g) and stirred to precipitate crystals. After filtering the crystals, methanol (1200 g) was added to the filtrate, stirred, filtered, and the filtrate was concentrated to obtain a crude product (40 g). After adding ethanol (320 g) to the crude product and heating and stirring at 80° C., pure water (400 g) was added and stirred to precipitate crystals. Compound [1] was obtained by filtering the crystals and drying the filtrate (yield: 34.5 g, yield: 42%, ocher crystals).
1H-NMR (400MHz, DMSO-d6, δppm): 9.60(br, 1H), 8.22(d, 2H, J = 9.6 Hz), 7.04(d, 2H, J = 9.6 Hz), 7.02(d, 2H, J = 9.0 Hz), 6.85(d, 2H, J = 9.0 Hz).

Synthesis of Compound [2] In dimethylformamide (276 g), diethylene glycol ditosylate (30.2 g, 72.8 mmol), compound [1] (34.5 g), and potassium carbonate (30.2 g) were added, and the mixture was heated at 80°C. Stirred for 15 hours. After cooling to room temperature, pure water (552 g) was added and stirred, resulting in a viscous material at the bottom of the flask. After removing the supernatant by decantation, methanol (100 g) was added and stirred, and the supernatant was removed by decantation again. When methanol (100 g) was added to the remaining viscous material and stirred, the viscous material gradually solidified. A crude product (35.5 g) was obtained by crushing and stirring the lumps, filtration, and drying the filtrate. Dimethylformamide (71 g) was added to the crude product, heated and stirred at 80° C., and then methanol (142 g) was added to precipitate crystals. The mixture was cooled to room temperature, filtered, and the filtered product was dried. The obtained crystals were recrystallized again from dimethylformamide-methanol, and the filter residue was washed as a slurry with methanol (100 g), filtered, and the filter residue was dried to obtain compound [2] (yield: 24. 9 g, yield: 64%, light brown crystals).
1H-NMR (400MHz, DMSO-d6, δppm): 8.23(d, 4H, J = 9.6 Hz), 7.14(d, 4H, J= 9.2 Hz), 7.16-7.04(m, 8H), 4.17-4.14( m, 4H), 3.86-3.83(m, 4H).

Synthesis of [DA-1] In tetrahydrofuran (200 g), compound [2] (24.9 g, 46.8 mmol) and 5% palladium on carbon (2.5 g) were added, and after 18 hours at room temperature under a hydrogen atmosphere, The mixture was stirred at 40°C for 6 hours. After purging with nitrogen, the catalyst was filtered and the filtrate was concentrated to obtain a crude product (22.3 g). Ethyl acetate (23 g) was added to the crude product, and the mixture was heated and dissolved at 70° C., and then hexane (45 g) was added and cooled to room temperature. After oiling out, the mixture solidified. Compound [DA-1] was obtained by crushing the lumps, stirring, filtering, and drying the filtrate (yield: 21.2 g, yield: 96%, white crystals).
1H-NMR (400MHz, DMSO-d6, δppm): 6.88(d, 4H, J = 9.2 Hz), 6.80(d, 4H, J = 9.2 Hz), 6.70(d, 4H, J = 9.2 Hz), 6.55 (d, 4H, J = 9.2 Hz), 4.91(br, 4H), 4.06-4.03(m, 4H), 3.79-3.76(m, 4H).

(Synthesis example 2)
(Example)
In a 50 mL eggplant flask equipped with a stirrer and a nitrogen inlet tube, add 3.90 g (8.3 mmol) of DA-1, 1.79 g (4.5 mmol) of DA-3, and 1.25 g (2.5 mmol) of DA-4. 3 mmol) was weighed out, 27.3 g of NMP was added, and the mixture was stirred and dissolved while supplying nitrogen. While stirring this diamine solution under water cooling, 1.93 g (9.8 mmol) of CA-1 was added, and further 7.7 g of NMP was added, followed by stirring at 50° C. for 6 hours under a nitrogen atmosphere. Furthermore, 1.0 g (5.1 mmol) of CA-2 was added, and further 3.8 g of NMP was added, and the mixture was stirred for 2 hours at 23°C under a nitrogen atmosphere. I got it.

20 g of this polyamic acid solution was placed in a 100 mL Erlenmeyer flask containing a stirring bar, 13.3 g of NMP, 1.86 g of acetic anhydride, and 0.48 g of pyridine were added, and after stirring at room temperature for 30 minutes, The reaction was carried out at ℃ for 3 hours. This reaction solution was poured into 125 g of methanol, and the resulting precipitate was filtered off. This precipitate was washed with methanol and then dried under reduced pressure at a temperature of 80°C to obtain polyimide powder (imidation rate: 85%).

Furthermore, 2.4 g of this polyimide powder was taken into a 50 mL eggplant flask containing a stirrer, 17.6 g of NMP was added, and the mixture was stirred at 50°C for 24 hours to dissolve the polyimide solution SPI-A1. I got it.

(Synthesis example 3)
(Example)
In a 100 mL eggplant flask equipped with a stirrer and a nitrogen inlet tube, add 5.55 g (19.3 mmol) of DA-2, 4.18 g (10.5 mmol) of DA-3, and 2.92 g (5.5 mmol) of DA-4. 3 mmol) was weighed out, 50.6 g of NMP was added, and the mixture was stirred and dissolved while supplying nitrogen. While stirring this diamine solution under water cooling, 4.51 g (22.8 mmol) of CA-1 was added, and further 18.0 g of NMP was added, followed by stirring at 50° C. for 6 hours under a nitrogen atmosphere. Furthermore, 2.26 g (11.5 mmol) of CA-2 was added, and further 8.8 g of NMP was added, and the mixture was stirred for 2 hours at 23°C under a nitrogen atmosphere. I got it.

30.0 g of this polyamic acid solution was taken into a 100 mL Erlenmeyer flask containing a stirring bar, 20.0 g of NMP, 3.31 g of acetic anhydride, and 0.86 g of pyridine were added, and the mixture was stirred at room temperature for 30 minutes. , and reacted at 55°C for 3 hours. This reaction solution was poured into 190 g of methanol, and the resulting precipitate was filtered off. This precipitate was washed with methanol and then dried under reduced pressure at a temperature of 80°C to obtain polyimide powder (imidation rate: 84%).

Furthermore, 3.0 g of this polyimide powder was taken into a 50 mL eggplant flask containing a stirrer, 22.0 g of NMP was added, and the mixture was stirred at 50°C for 24 hours to dissolve the polyimide solution SPI-A2. I got it.

(Synthesis example 4)
(Comparative example)
20.0 g of the polyamic acid solution PAA-B1 obtained in Synthesis Example 2 was taken, 13.3 g of NMP, 1.86 g of acetic anhydride, and 0.48 g of pyridine were added, and after stirring at room temperature for 30 minutes, The reaction was carried out at 55°C for 1 hour and 30 minutes. This reaction solution was poured into 125 g of methanol, and the resulting precipitate was filtered off. This precipitate was washed with methanol and then dried under reduced pressure at a temperature of 80° C. to obtain polyimide powder (imidation rate: 55%).

Furthermore, 2.4 g of this polyimide powder was taken into a 50 mL eggplant flask containing a stirring bar, 17.6 g of NMP was added, and the mixture was stirred at 50°C for 24 hours to dissolve the polyimide solution SPI-B1. I got it.

(Synthesis example 5)
(Comparative example)
30.0 g of the polyamic acid solution PAA-B1 obtained in Synthesis Example 2 was taken, 20.0 g of NMP, 3.31 g of acetic anhydride, and 0.86 g of pyridine were added, and after stirring at room temperature for 30 minutes, The reaction was carried out at 55°C for 1 hour and 30 minutes. This reaction solution was poured into 190 g of methanol, and the resulting precipitate was filtered off. This precipitate was washed with methanol and then dried under reduced pressure at a temperature of 80° C. to obtain polyimide powder (imidation rate: 54%).

Furthermore, 3.0 g of this polyimide powder was taken into a 50 mL eggplant flask containing a stirrer, 22.0 g of NMP was added, and the mixture was stirred at 50°C for 24 hours to dissolve the polyimide solution SPI-B2. I got it.

(Examples 1 and 2)
To the polyimide solutions obtained in Synthesis Examples 2 and 3, an NMP solution containing 1% by weight of NMP, GBL, BCS, and AD-1 was added with stirring so that the composition was as shown in Table 1 below, and then The liquid crystal aligning agents of Examples 1 and 2 were obtained by stirring at room temperature for 2 hours.

(Comparative Examples 1 to 4)
An NMP solution containing 1% by weight of NMP, GBL, BCS, and AD-1 was added to the polyamic acid solutions obtained in Synthesis Examples 2 and 3 and the polyimide solutions obtained in Synthesis Examples 4 and 5 according to the table below. The liquid crystal aligning agents of Comparative Examples 1 to 4 were obtained by adding the mixture with stirring to obtain the composition shown in 2 and further stirring at room temperature for 2 hours.

Below, a method for manufacturing a liquid crystal cell for evaluating the pretilt angle will be shown.
[Preparation of liquid crystal cell]
First, a substrate with electrodes was prepared. The substrate is a glass substrate with a size of 30 mm x 40 mm and a thickness of 1.1 mm. An ITO electrode with a thickness of 35 nm is formed on the substrate, and the electrode has a stripe pattern of 40 mm in length and 10 mm in width.

Next, the liquid crystal aligning agent was filtered through a filter with a pore size of 1.0 μm, and then applied to the prepared electrode-equipped substrate by spin coating. After drying on a hot plate at 80° C. for 2 minutes, baking was performed in an IR oven at 230° C. for 20 minutes to form a coating film with a thickness of 100 nm to obtain a substrate with a liquid crystal alignment film. After rubbing this liquid crystal alignment film with a rayon cloth (roller diameter: 120 mm, roller rotation speed: 1000 rpm, moving speed: 20 mm/sec, pushing length: 0.4 mm), it was irradiated with ultrasonic waves for 1 minute in pure water. After washing with water and removing water droplets with air blowing, the substrate was dried at 80° C. for 10 minutes to obtain a substrate with a liquid crystal alignment film. Prepare two substrates with this liquid crystal alignment film, sprinkle 4 μm spacers on the surface of one of the liquid crystal alignment films, print a sealant on top of it, and rub the other substrate in the opposite direction. , and after laminating them so that the membrane surfaces faced each other, the sealant was cured to create an empty cell. Liquid crystal MLC-3019 (manufactured by Merck & Co., Ltd.) was injected into this empty cell by a reduced pressure injection method, and the injection port was sealed to obtain a liquid crystal cell. Thereafter, the obtained liquid crystal cell was heated at 120° C. for 1 hour and left at 23° C. overnight before being used for each evaluation.

<Pretilt angle>
The pretilt angle within the liquid crystal cell 1 was evaluated using an AxoScan Mueller matrix polarimeter manufactured by Optometrics.

Table 3 below shows the results of pretilt angles conducted as described above for liquid crystal display elements using each of the liquid crystal alignment agents of Examples 1 and 2 and Comparative Examples 1 to 4.

It can be seen that the liquid crystal display element using the liquid crystal aligning agent of the example of the present invention has a low pretilt angle and excellent viewing angle characteristics.

By using the liquid crystal alignment agent of the present invention, it is possible to obtain a liquid crystal alignment film that satisfies various properties required for a liquid crystal alignment film and provides a low pretilt angle of 1 degree or less.

Claims (11)

The alignment film contains polyimide which is a reaction product of a tetracarboxylic dianhydride derivative component consisting of at least one selected from aliphatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride and a diamine component; A liquid crystal aligning agent with a pretilt angle of 1 degree or less , the diamine component containing at least one diamine selected from diamines having the structure of the following formula [A], and the imidization rate of polyimide is 70% or more. , liquid crystal alignment agent.

In the formula, X ₁ and X ₂ are each independently an oxygen atom or a sulfur atom, R is represented by [-((CH ₂ ) ₂ O) _p (CH ₂ ) ₂ -], and p is an integer from 1 to 3. It is. The liquid crystal aligning agent according to claim 1, wherein the diamine having the structure of the formula [A] is at least one selected from the following formulas [A-1] to [A-4].

The liquid crystal aligning agent according to claim 1 or 2, wherein the diamine having the structure of formula [A] accounts for 40% to 80% of the total diamine component. The liquid crystal aligning agent according to any one of claims 1 to 3, wherein the diamine component further contains a diamine having a structure of the following formula (6) in its structure.

In the above formula (6), D is a thermally releasable group that is eliminated at 150° C. to 230° C. and replaced by a hydrogen atom. The liquid crystal aligning agent according to claim 4, wherein the diamine having the structure of formula (6) is at least one selected from the following diamines.

In the formula, n is an integer from 1 to 12. The liquid crystal aligning agent according to any one of claims 1 to 5, wherein the aliphatic tetracarboxylic dianhydride and the alicyclic tetracarboxylic dianhydride are represented by the following formula (4).

In the formula, X ₁ is a structure selected from the following structures.

A liquid crystal aligning agent containing polyimide which is a reaction product of a diamine component and a tetracarboxylic dianhydride derivative component consisting of at least one selected from aliphatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride. and the diamine component contains at least one selected from the formulas [A-1] to [A-3], the imidization rate of the polyimide is 70% or more, and the diamine component has the formula [A-1] to [A-3]. When containing formula [A-2], the aliphatic tetracarboxylic dianhydride and alicyclic tetracarboxylic dianhydride are represented by the following formula (4), according to claim 6. The liquid crystal alignment agent described.

In the formula, X ₁ is a structure selected from the following structures.

The liquid crystal aligning agent according to claim 7, wherein the diamine component further contains a diamine having a structure of the following formula (6) in its structure.

In the above formula (6), D is a thermally releasable group that is eliminated at 150° C. to 230° C. and replaced by a hydrogen atom. Furthermore, the liquid crystal aligning agent of any one of Claims 1-8 containing polyamic acid which is a reaction product of a tetracarboxylic dianhydride derivative and a diamine. A liquid crystal aligning film obtained from the liquid crystal aligning agent according to any one of claims 1 to 9. A liquid crystal display element comprising the liquid crystal alignment film according to claim 10.