TWI842836B - Liquid crystal alignment agent and liquid crystal display element using the same, and compound for making liquid crystal alignment agent - Google Patents

Abstract

A liquid crystal alignment agent characterized by containing the following (A) component, (B) component, and an organic solvent.

(A) Component: at least one type of polymer selected from the group consisting of a polyimide precursor and an imidized polymer of the polyimide precursor.

(B) Component: A compound containing a hydroxyalkylamide group and a structure of the following formula (1).

R ₁ to R ₄ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

Description

Liquid crystal alignment agent and liquid crystal display element using the same, and compound used to manufacture liquid crystal alignment agent

The present invention relates to a liquid crystal alignment agent used in manufacturing a liquid crystal display element, a liquid crystal alignment film obtained from the liquid crystal alignment agent, and a liquid crystal display element using the liquid crystal alignment film.

Liquid crystal display elements are known as lightweight, thin, and low-power display devices. Liquid crystal display elements are composed of a pair of transparent substrates with electrodes to hold a liquid crystal layer. In a liquid crystal display element, the liquid crystal is aligned in a desired state between the substrates, and an organic film containing an organic material is used as a liquid crystal alignment film.

In recent years, high-precision liquid crystal display components used in smart phones or tablet terminals require high display quality, and in addition to the liquid crystal alignment properties, various properties are also required at a high level for the liquid crystal alignment film.

In order to achieve these requirements, the method of adding low molecular weight compounds with various characteristics to the liquid crystal alignment agent used to make the liquid crystal alignment film is widely used. For example, in order to improve the mechanical strength of the obtained liquid crystal alignment film, a liquid crystal alignment agent containing a low molecular weight compound that improves the hardness of the liquid crystal alignment film has been proposed (see patent documents 1, 2). The low molecular weight compound contains a base that causes a crosslinking reaction due to the heating step implemented in the liquid crystal alignment film preparation step, and the polymers are linked to each other by crosslinking, thereby improving the mechanical strength of the obtained liquid crystal alignment film.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2010-544185

[Patent Document 2] Japanese Patent No. 617911

However, as a general issue of the above-mentioned method, one can cite the decrease in liquid crystal alignment. The polymer in the liquid crystal alignment film is three-dimensionally cross-linked, which prevents the liquid crystal from aligning in a fixed direction. In addition, the presence of unreacted low molecular weight compounds may also have an adverse effect on the liquid crystal alignment.

The main purpose of the present invention is to provide a liquid crystal alignment agent that does not reduce the liquid crystal alignment or other properties, but can improve the mechanical strength of the liquid crystal alignment film.

The inventors of the present invention have completed the present invention after careful consideration to solve the above problems. That is, the gist of the present invention is as follows.

1. A liquid crystal alignment agent, characterized by containing the following components (A), (B), and an organic solvent.

(A) Component: at least one type of polymer selected from the group consisting of a polyimide precursor and an imidized polymer of the polyimide precursor.

Component (B): a compound having a hydroxyalkylamide group and a structure of the following formula (1).

R ₁ to R ₄ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and * represents a bond with other atoms.

By using the liquid crystal alignment agent of the present invention, a liquid crystal alignment film can be obtained that can improve the mechanical strength of the liquid crystal alignment film without reducing the liquid crystal alignment or other characteristics.

The reasons why the present invention can achieve the above effects are not fully clear, but are generally considered to be as follows.

The compound of component (B) contained in the liquid crystal alignment agent of the present invention has a structure of a polyimide skeleton as shown in formula (1). Therefore, it is believed that since the compound has a structure similar to the polymer of component (A), it will not hinder the liquid crystal from being aligned along with the polymer. In addition, it is also believed that in the liquid crystal alignment film obtained by the step of aligning the liquid crystal by irradiating polarized ultraviolet light, the cyclobutane structure in formula (1) is decomposed by irradiating polarized ultraviolet light, so it will not hinder the alignment of the liquid crystal.

<Component (A)> The component (A) contained in the liquid crystal alignment agent of the present invention is at least one type of polymer selected from the group consisting of a polyimide precursor and an imidized polymer of the polyimide precursor, and its structure is not particularly limited.

<Tetracarboxylic acid derivative> The polyimide precursor contained in the liquid crystal alignment agent of the present invention is obtained by the reaction of a tetracarboxylic acid derivative and a diamine, and the polyimide is obtained by subjecting the polyimide precursor to imidization. The specific examples of the materials used and the production method are described in detail below.

As the tetracarboxylic acid derivative used as the precursor for producing the polyimide, there can be mentioned not only tetracarboxylic dianhydride but also tetracarboxylic acids, tetracarboxylic acid dihalide compounds, tetracarboxylic acid dialkyl esters, and tetracarboxylic acid dialkyl ester dihalides thereof.

As the tetracarboxylic dianhydride or its derivative, one represented by the following formula (2) is preferred.

In formula (2), the structure of _X1 is not particularly limited. As preferred specific examples, the following formulas (X1-1) to (X1-44) can be cited.

In formula (X1-1) to (X1-4), R ₁₁ to R ₃₁ 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.

As specific examples of formula (X1-1), the following formulas (X1-1-1) to (X1-1-6) can be cited. From the viewpoint of liquid crystal orientation and light sensitivity, (X1-1-1) is particularly preferred.

<Diamine> The diamine used to produce the polyimide precursor is represented by the following formula (3).

In the above formula (3), _A1 and _A2 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.

The structure of _Y1 is not particularly limited. Preferred structures include the following (Y-1) to (Y-182).

In the above formula, Me represents a methyl group, and ^R1 represents a hydrogen atom or a carbon number of 1 to 5 alkyl groups.

Among them, as the structure of _Y1 , (Y-7), (Y-8), (Y-16), (Y-17), (Y-18), (Y-20), (Y-21) 、(Y-22)、(Y-28)、(Y-35)、(Y-38)、(Y-43)、(Y-48)、(Y-64)、(Y-66)、( Y-71）、(Y-72）、(Y-76）、(Y-77）、(Y-80）、(Y-81）、(Y-82）、(Y-83）、(Y- 156）、(Y-159）、(Y-160）、(Y-161）、(Y-162)(Y-168）、(Y-169）、(Y -170), (Y-171), (Y-173), (Y-175) are preferred, and (Y-7), (Y-8), (Y-16), (Y-17) are particularly preferred. 、(Y-18)、(Y-21)、(Y-22)、(Y-28)、(Y-38)、(Y-64)、(Y-66)、(Y-72)、( Y-76）、(Y-81）、(Y-156）、(Y-159）、(Y-160）、(Y-161）、(Y-162）、(Y-168）、(Y- (Y-169), (Y-170), (Y-171), (Y-173), (Y-175) are preferred.

<Component (B)> The component (B) contained in the liquid crystal alignment agent of the present invention is a compound having a hydroxyalkylamide group and a structure of the following formula (1).

R ₁ to R ₄ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. A hydrogen atom or a methyl group is preferred. * indicates a bond with other atoms.

In the component (B), the compound preferably has two or more hydroxyalkylamide groups. The structure of the compound having two or more hydroxyalkylamide groups is not particularly limited, but from the viewpoint of availability, a preferred example is a compound represented by the following formula (4).

_X2 is an n+1-valent organic group including an aliphatic hydrocarbon group or an aromatic hydrocarbon group having 1 to 20 carbon atoms, n is an integer of 2 to 6, and * indicates a bond with (1).

_R5 and _R6 are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a substituent, an alkenyl group having 2 to 4 carbon atoms which may have a substituent, or an alkynyl group having 2 to 4 carbon atoms which may have a substituent. In addition, at least one of _R5 and _R6 represents a hydroxyl-substituted alkyl group.

In formula (4), from the viewpoint of solubility, n is preferably 2 to 4.

In formula (4), from the viewpoint of reactivity, at least one of _R5 and _R6 is preferably a structure represented by the following formula (5), and more preferably a structure represented by the following formula (6).

In formula (5), R ₇ to R ₁₀ are each independently a hydrogen atom, a alkyl group, or a alkyl group substituted with a hydroxyl group.

Preferred specific examples of the component (B) include the following compounds.

If the amount of component (B) is too much, it will affect the liquid crystal alignment or pre-tilt angle, and if it is too little, the effect of the present invention cannot be achieved. Therefore, the content of component (B) is preferably 3-30% by mass, and more preferably 5-15% by mass, relative to component (A).

<Polyamide> The polyamide used as the polyimide precursor of the present invention can be produced by the method shown below. Specifically, tetracarboxylic dianhydride and diamine can be 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 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 monomers and polymers, and these may be used alone or in combination of two or more. The concentration of the polymer is preferably 1-30% by mass, more preferably 5-20% by mass, from the viewpoint of not easily causing the polymer to precipitate and easily obtaining a high molecular weight product.

The polyamine obtained by the above operation can be recovered by stirring the reaction solution well and injecting a poor solvent to precipitate the polymer. Alternatively, the purified polyamine powder can be obtained by performing precipitation several times, washing with a poor solvent, and drying at room temperature or with heat. The poor solvent is not particularly limited, and examples thereof include water, methanol, ethanol, hexane, butyl solvent, acetone, toluene, and the like.

<Polyamide> The polyamide, which is one of the polyimide precursors used in the present invention, can be produced using the following method (1), (2) or (3).

(1) Production from polyamine Polyamine esters can be synthesized by esterifying polyamine obtained from tetracarboxylic dianhydride and diamine. Specifically, the polyamine and an 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 to 4 hours.

As the esterifying agent, it is preferred that the agent 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 dineopentylbutyl 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-triazine-2-yl)-4-methylmorpholinium chloride, etc. The amount of the esterifying agent used is preferably 2 to 6 molar equivalents relative to 1 mole of the repeating unit of the polyamide.

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 can be used alone or in combination of two or more. The concentration of the polymer in the reaction solution is preferably 1-30 mass %, more preferably 5-20 mass %, from the viewpoint of not easily causing polymer precipitation and easily obtaining a high molecular weight product.

(2) Production by reaction of tetracarboxylic acid diester dichloride and diamine Polyamide can be produced from tetracarboxylic acid diester dichloride and diamine. Specifically, it can be synthesized by reacting tetracarboxylic acid diester dichloride and diamine in the presence of alkali and an organic solvent at -20°C to 150°C, preferably 0°C to 50°C, for 30 minutes to 24 hours, preferably 1 to 4 hours.

The above-mentioned base can be pyridine, triethylamine, 4-dimethylaminopyridine, etc. In order to make the reaction proceed mildly, pyridine is preferred. The amount of the base used is preferably 2 to 4 times the mole of the tetracarboxylic acid diester dichloride from the viewpoint of easy removal and easy acquisition of a high molecular weight body.

The solvent used in the above reaction is preferably N-methyl-2-pyrrolidone or γ-butyrolactone from the viewpoint of solubility of monomers and polymers, and these can be used alone or in combination of two or more. The polymer concentration in the reaction solution is preferably 1-30% by mass, and more preferably 5-20% by mass, from the viewpoint of not easily causing the precipitation of the polymer and easily obtaining a high molecular weight body. In addition, in order to prevent the hydrolysis of the tetracarboxylic acid diester dichloride, the solvent used for synthesizing the polyamic acid ester is preferably dehydrated as much as possible, and preferably in a nitrogen environment to prevent the mixing of external gas.

(3) Production by reaction of tetracarboxylic acid diester and diamine Polyamide ester can be produced by condensation polymerization of tetracarboxylic acid diester and diamine. Specifically, it can be produced by reacting tetracarboxylic acid diester and diamine in the presence of a condensation agent, an alkali, and an organic solvent at 0°C to 150°C, preferably 0°C to 100°C, for 30 minutes to 24 hours, preferably 3 to 15 hours.

The aforementioned condensation agent may be triphenylphosphite, dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-carbonyldiimidazole, dimethoxy-1,3,5-triazinylmethylmorpholinium, O-(benzotriazole-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, O-(benzotriazole-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, (2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonic acid diphenyl ester, etc. The amount of the condensation agent added is preferably 2 to 3 times the molar amount relative to the tetracarboxylic acid diester.

The aforementioned alkali may be a tertiary amine such as pyridine, triethylamine, etc. The amount of the alkali used is preferably 2 to 4 times the mole of the diamine component from the viewpoint of easy removal and easy acquisition of a high molecular weight.

In the above reaction, the reaction can be efficiently carried out 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 the Lewis acid added is preferably 0 to 1.0 times the mole of the diamine component.

Among the above three methods for producing polyamide esters, the method (1) or (2) is particularly preferred because it can produce polyamide esters with high molecular weight.

The polyamic acid ester solution obtained by the above operation can be stirred well and injected into a poor solvent to precipitate the polymer. After several precipitations and washing with a poor solvent, the purified polyamic acid ester powder can be obtained by drying at room temperature or by heating. The poor solvent is not particularly limited, and examples thereof include water, methanol, ethanol, hexane, butyl solvent, acetone, toluene, etc.

<Polyimide> The polyimide used in the present invention can be produced by imidizing the aforementioned polyamic acid or polyamic acid ester. The imidization rate of the polyimide used in the present invention is not limited to 100%. From the viewpoint of electrical properties, 20 to 99% is preferred. In the case of producing polyimide from polyamic acid ester, chemical imidization in which an alkaline catalyst is added to the polyamic acid solution obtained by dissolving the aforementioned polyamic acid ester solution or polyamic acid ester resin powder in an organic solvent is simple. Chemical imidization is preferred because the imidization reaction is carried out at a relatively low temperature and the molecular weight of the polymer is not easily reduced during the imidization process.

Chemical imidization can be carried out by stirring the polyamide acid or polyamide ester to be imidized in an organic solvent in the presence of an alkaline catalyst and an acid anhydride. In addition, at this time, by reacting the compounds shown in (R-1) to (R-2) below, a polyimide precursor with a specific structure introduced at the end can be obtained. As an organic solvent, a solvent used in the aforementioned polymerization reaction can be used. As an alkaline catalyst, pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine, etc. can be cited. Among them, pyridine is preferred because it has an alkalinity suitable for the reaction. In addition, examples of acid anhydrides include anhydrous acetic acid, anhydrous trimellitic acid, anhydrous pyromellitic acid, etc. Among them, the use of anhydrous acetic acid is preferred because purification after the reaction is easy. Generally, in the case of conventional polyimide, if anhydrous acetic acid is used, an acetyl group is generated as the main chain terminal. In contrast, the present invention can suppress acetylation.

R ₂₂ and R ₂₂ ′ represent a monovalent organic group, and specific examples thereof include methyl, ethyl, propyl, 2,2,2-trichloroethyl, 2-trimethylsilylethyl, 1,1-dimethylpropynyl, 1-methyl-1-phenylethyl, 1-methyl-1-(4-biphenylyl)ethyl, 1,1-dimethyl-2-haloethyl, 1,1-dimethyl-2-cyanoethyl, tert-butyl, cyclobutyl, 1-methylcyclobutyl, 1-adamantyl, vinyl, allyl, cinnamyl, 8-quinolyl, N-hydroxypiperidinyl, benzyl, p-nitrobenzyl, 3,4-dimethoxy-6-nitrobenzyl, 2,4-dichlorobenzyl, and 9-fluoromethyl.

The temperature during the imidization reaction is, for example, -20°C to 120°C, preferably 0°C to 100°C, and the reaction time can be 1 to 100 hours. The amount of the alkaline catalyst is 0.5 to 30 mole times of the amide group, preferably 2 to 20 mole times, and the amount of the acid anhydride is 1 to 50 mole times of the amide group, preferably 3 to 30 mole times. The imidization rate of the obtained polymer can be controlled by adjusting the amount of the catalyst, the temperature, and the reaction time.

Since the solution after the imidization reaction of polyamic acid ester or polyamic acid will retain the added catalyst, etc., it is best to recover the imidized polymer by the means described below and then dissolve it in an organic solvent to make the liquid crystal alignment agent of this invention.

The polyimide solution obtained by the above operation is stirred well and injected with a poor solvent at the same time, so that the polymer can be precipitated several times and washed with a poor solvent, and then dried at room temperature or by heating to obtain a purified polyamide powder.

The aforementioned poor solvent is not particularly limited, and examples thereof include methanol, acetone, hexane, butyl cellulose, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, benzene, and the like.

<Liquid crystal alignment agent> The liquid crystal alignment agent used in the present invention has the form of a solution in which the aforementioned (A) component is selected from at least one polymer group consisting of a polyimide precursor and an imidized polymer of the polyimide precursor (hereinafter referred to as a polymer of a specific structure), and the (B) component is a compound having a hydroxyalkylamide group dissolved in a solvent.

The molecular weight of the specific structural polymer is preferably 2,000-500,000, more preferably 5,000-300,000, and more preferably 10,000-100,000 in terms of weight average molecular weight. In addition, the number average molecular weight is preferably 1,000-250,000, more preferably 2,500-150,000, and more preferably 5,000-50,000.

The concentration of the polymer in the liquid crystal alignment agent of the present invention can be appropriately changed according to the setting of the coating thickness to be formed. From the perspective of forming a uniform and defect-free coating, it is preferably 1% by mass or more, and from the perspective of the storage stability of the solution, it is preferably 10% by mass or less. The most preferred concentration is 3-6.5% by mass.

The solvent (also called good solvent) contained in the liquid crystal alignment agent of the present invention is not particularly limited as long as it can uniformly dissolve the polymer with a specific structure.

For example, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone or 4-hydroxy-4-methyl-2-pentanone.

Among them, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone is preferably used.

Furthermore, when the polymer of the present invention has high solubility in a solvent, it is preferred to use a solvent represented by the following formula [D-1] to [D-3]. (D ¹ to D ³ represent an alkyl group having 1 to 6 carbon atoms.)

The good solvent in the liquid crystal alignment agent of the present invention is preferably 20-99 mass % of the total solvent contained in the liquid crystal alignment agent. Among them, 20-90 mass % is also preferred. More preferably, it is 30-80 mass %.

As long as the effects of the present invention are not impaired, the liquid crystal alignment agent of the present invention may use a solvent (also called a poor solvent) that improves the coating properties or surface smoothness of the liquid crystal alignment film when the liquid crystal alignment agent is applied. The following examples are specific examples of poor solvents, but the invention is not limited to these examples.

For example, ethanol, 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-propylene glycol, 1,3-propylene glycol, 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 Diethyl Ether, Diethylene Glycol Methyl Ether, Diethylene Glycol Dibutyl Ether, 2-Pentanone, 3-Pentanone, 2-Hexanone, 2-Heptanone, 4-Heptanone, 3-Ethoxybutyl Acetate, 1-Methylpentyl Acetate, 2-Ethylbutyl Acetate, 2-Ethylhexyl Acetate, Ethylene Glycol Monoacetate, Ethylene Glycol diacetate, propylene carbonate, ethyl carbonate, 2-(methoxymethoxy)ethanol, ethylene glycol monobutyl ether, ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, 2-(hexyloxy)ethanol, sugar alcohol, diethylene glycol, propylene glycol, propylene glycol monobutyl ether, 1-(butoxyethoxy)propanol, propylene glycol monomethyl ether acetate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene 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, 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, ethyl lactate, methyl acetate, ethyl acetate, n-butyl acetate, propylene glycol acetate monoethyl ether, 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 lactate, isoamyl lactate, solvents represented by the above formulas [D-1] to [D-3], and the like.

Among them, 1-hexanol, cyclohexanol, 1,2-ethylene glycol, 1,2-propylene glycol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether or dipropylene glycol dimethyl ether is preferably used.

The amount of the poor solvent is preferably 1-80 mass % of the total amount of the solvent contained in the liquid crystal alignment agent, more preferably 10-80 mass % and even more preferably 20-70 mass %.

As long as the scope of the effect of the present invention is not impaired, in addition to the above, the liquid crystal alignment agent of the present invention may also include polymers other than the polymers described in the present invention, dielectrics or conductive substances for the purpose of changing the electrical properties of the liquid crystal alignment film such as the dielectric constant or conductivity, silane coupling agents for the purpose of improving the adhesion between the liquid crystal alignment film and the substrate, cross-linking compounds for the purpose of increasing the film hardness or density when the liquid crystal alignment film is made, and imidization promoters for the purpose of making the imidization caused by heating the polyimide precursor when firing the coating film.

<Liquid crystal alignment film> <Method for manufacturing liquid crystal alignment film> The liquid crystal alignment film of the present invention is a film obtained by applying the above-mentioned liquid crystal alignment agent on a substrate, drying it, and then firing it. The substrate on which the liquid crystal alignment 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, polycarbonate substrates, etc. can be used. In addition, from the perspective of simplifying the process, it is preferred to use a substrate formed with an ITO electrode for driving the liquid crystal. In addition, in a reflective liquid crystal display element, if it is only used on a single-sided substrate, an opaque object such as a silicon wafer can also be used, and the electrode at this time can also use a light-reflecting material such as aluminum.

As the coating method of the liquid crystal alignment agent of the present invention, there can be cited a spin coating method, a printing method, an ink jet method, etc. The drying and firing steps after coating the liquid crystal alignment agent of the present invention can be selected at any temperature and time. Usually, in order to fully remove the contained solvent, it is dried at 50~120℃, preferably at 60~100℃, for 1~10 minutes, preferably at 2~5 minutes, and then fired at 150~300℃, preferably at 200~240℃, for 5~120 minutes, preferably at 10~30 minutes. There is no particular limit to the thickness of the coating after firing. If it is too thin, the reliability of the liquid crystal display element will be reduced, so it is preferably 5~300nm, preferably 10~200nm.

As a method of applying an alignment treatment to the obtained liquid crystal alignment film, there can be cited a rubbing method, a photo-alignment treatment method, and the like.

Friction treatment can be performed using existing friction devices. The materials of the friction cloth at this time include cotton, nylon, rayon, etc. The friction treatment conditions are generally a rotation speed of 300~2000 rpm, a conveying speed of 5~100mm/s, and an injection amount of 0.1~1.0mm. Afterwards, pure water or alcohol is used to remove the residues generated by friction through ultrasonic cleaning.

As a specific example of the photo-alignment treatment method, there can be cited a method in which the surface of the aforementioned coating is irradiated with radiation that has been polarized into a fixed direction, and depending on the circumstances, a heat treatment is performed at a temperature of 150~250°C to impart liquid crystal alignment ability. As radiation, ultraviolet light and visible light with a wavelength of 100~800nm can be used. Among them, ultraviolet light with a wavelength of 100~400nm is preferred, and ultraviolet light with a wavelength of 200~400nm is particularly preferred. In addition, in order to improve the alignment of the liquid crystal, the coated substrate can be heated at 50~250°C and irradiated with radiation at the same time. The irradiation amount of the aforementioned radiation is preferably 1~10,000mJ/ ^cm2 , and is particularly preferably 100~5,000mJ/ ^cm2 . The liquid crystal alignment film manufactured by the above operation can stably align the liquid crystal molecules in a fixed direction.

Since the higher the extinction ratio of polarized ultraviolet light is, the higher the anisotropy can be given, a higher extinction ratio is preferred. Specifically, the extinction ratio of linearly polarized ultraviolet light is preferably above 10:1, and more preferably above 20:1.

The film irradiated with polarized radiation may then be contact treated with a solvent comprising at least one selected from the group consisting of water and organic solvents.

The solvent used in the contact treatment is not particularly limited as long as it can dissolve the decomposition products generated by light irradiation. Specific examples include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, 1-methoxy-2-propanol, 1-methoxy-2-propanol acetate, butyl solvent, ethyl lactate, methyl lactate, diacetone alcohol, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, propyl acetate, butyl acetate, cyclohexyl acetate, and the like. Two or more of these solvents may be used in combination.

From the perspective of versatility or safety, at least one solvent selected from the group consisting of water, 2-propanol, 1-methoxy-2-propanol and ethyl lactate is preferred. Water, 2-propane, or a mixed solvent of water and 2-propanol is particularly preferred.

In the present invention, the contact treatment between the film irradiated with polarized radiation and the solution containing a solvent is carried out by a method such as immersion treatment, spraying treatment, etc., so that the film and the liquid are in ideal and sufficient contact. Among them, the method of immersion treatment in the solution containing a solvent is preferably carried out for 10 seconds to 1 hour, and more preferably for 1 to 30 minutes. The contact treatment can be carried out at room temperature or heated, preferably at 10 to 80°C, and more preferably at 20 to 50°C. In addition, if necessary, a means of improving contact such as ultrasound can be applied.

After the contact treatment, either washing (wetting) with a low-boiling-point solvent such as water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, or the like or drying, or both, may be performed for the purpose of removing the solvent in the solution used.

Furthermore, the film that has been contact-treated with a solution containing a solvent may be heated at a temperature above 150° C. for the purpose of drying the solvent and realigning the molecular chains in the film.

The heating temperature is preferably 150~300℃. The higher the temperature, the more the molecular chain realignment is promoted, but when the temperature is too high, there is a concern that the molecular chain will decompose. Therefore, the heating temperature is preferably 180~250℃, and particularly preferably 200~230℃.

If the heating time is too short, the molecular chain realignment effect may not be achieved, and if it is too long, the molecular chain may be decomposed. Therefore, 10 seconds to 30 minutes is preferred, and 1 to 10 minutes is more preferred.

<Liquid crystal display element> The liquid crystal display element of the present invention is characterized by having a liquid crystal alignment film obtained by the above-mentioned liquid crystal alignment film manufacturing method.

The liquid crystal display device of the present invention is obtained by using the liquid crystal alignment agent of the present invention to obtain a substrate with a liquid crystal alignment film by the aforementioned method for manufacturing a liquid crystal alignment film, and then manufacturing a liquid crystal unit by a known method, and using the liquid crystal unit to manufacture the liquid crystal display device.

As an example of a method for manufacturing a liquid crystal cell, a liquid crystal display element with a passive matrix structure is used for explanation. Alternatively, a liquid crystal display element with 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.

First, prepare transparent glass substrates, set a common electrode on one side of the substrate, and set segment electrodes on the other side of the substrate. These electrodes can be made of, for example, ITO electrodes, and patterned to produce the desired image display. Next, set an insulating film on each substrate in a manner covering the common electrode and the segment electrodes. The insulating film can be made of, for example, a film containing _SiO2 - _TiO2 formed by a sol-gel method.

Next, the liquid crystal alignment film of the present invention is formed on each substrate. Next, the alignment film surfaces of one side substrate and the other side substrate are overlapped in a manner that they face each other, and the periphery is connected with a sealant. In order to control the gap between the substrates, a spacer can usually be mixed in advance in the sealant. In addition, it is also preferred to pre-distribute the spacer for controlling the gap between the substrates in the surface where the sealant is not provided. A part of the sealant is pre-provided with an opening that can be filled with liquid crystal from the outside.

Next, the liquid crystal material is injected into the space surrounded by the two substrates and the sealant through the opening provided on the sealant. Afterwards, the opening is sealed with an adhesive. The injection can be performed by a vacuum injection method or by a method utilizing the capillary phenomenon in the atmosphere. Next, the polarizing plate is installed. Specifically, a pair of polarizing plates are attached to the surface opposite to the liquid crystal layer of the two substrates. The liquid crystal display element of the present invention is obtained by the above steps.

In the present invention, as the sealant, for example, a resin having a reactive group such as an epoxy group, an acryl group, a (meth)acryl group, a hydroxyl group, an allyl group, an acetyl group, etc., which is cured by irradiation with ultraviolet light or heating, can be used. In particular, a curing resin having both an epoxy group and a (meth)acryl group as reactive groups is preferably used.

In order to improve adhesion and moisture resistance, the sealant of the present invention may also be mixed with an inorganic filler. The inorganic filler that can be used is not particularly limited, and specifically includes spherical silica, molten silica, crystalline silica, titanium oxide, titanium black, silicon carbide, silicon nitride, boron nitride, calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, mica, talc, clay, aluminum oxide, magnesium oxide, zirconium oxide, aluminum hydroxide, calcium silicate, aluminum silicate, lithium aluminum silicate, zirconium silicate, barium titanium oxide, glass fiber, carbon fiber, molybdenum disulfide, sponge, etc. Preferred examples include spherical silica, molten silica, crystalline silica, titanium oxide, titanium black, silicon nitride, boron nitride, calcium carbonate, barium sulfate, calcium sulfate, mica, talc, clay, aluminum oxide, aluminum hydroxide, calcium silicate, or aluminum silicate. The aforementioned inorganic fillers may also be used in combination of two or more. [Example]

The following examples are given to illustrate the present invention in more detail, but the present invention is not limited thereto. The abbreviations of the following compounds and the measurement methods of the properties are as follows. NMP: N-methyl-2-pyrrolidone GBL: γ-butyl lactone BCS: butyl cellosolve THF: tetrahydrofuran DMF: N,N-dimethylformamide

< ^1HNMR measurement> Apparatus: Fourier transform superconducting nuclear magnetic resonance apparatus (FT-NMR) "AVANCE 3" (manufactured by BRUKER) 500MHz. Solvent: deuterated chloroform ( _CDCl3 ) or deuterated N,N-dimethylsulfoxide ([ _D6 ]-DMSO). Standard substance: tetramethylsilane (TMS).

[Viscosity] The viscosity of polyimide and polyamide solutions was measured using an E-type viscometer (VE-22H manufactured by Toki Sangyo Co., Ltd.) with a sample volume of 1.1 mL and a conical rotor TE-1 (1˚34’, R24) at a temperature of 25°C.

[Measurement of imidization rate] Put 20 mg of polyimide powder in an NMR sample tube (NMR sample tube standard φ5 manufactured by Kusano Scientific Co., Ltd.), add 0.53 ml of deuterated dimethyl sulfoxide (DMSO-d6, 0.05% TMS (tetramethylsilane) mixture), and apply ultrasound to completely dissolve it. Use an NMR measurement device (JNW-ECA500) manufactured by JEOL Data Corporation to measure the 500 MHz proton NMR of the solution. The imidization rate is determined by using the peak cumulative value of the proton derived from the structure that does not change before and after imidization as the reference proton and the peak cumulative value of the proton derived from the NH group of the amide appearing around 9.5 to 10.0 ppm, and is calculated by the following formula.

Imidization rate (%) = (1-α・x／y) × 100

[Production of Liquid Crystal Cell] Production of a liquid crystal cell having a structure of a FFS mode liquid crystal display element. First, prepare a substrate with electrodes. The substrate is a glass plate with a rectangular shape of 30mm×50mm and a thickness of 0.7mm. An ITO electrode with a solid pattern constituting a counter electrode is formed on the substrate as the first layer. A SiN (silicon nitride) film formed by CVD is formed on the counter electrode of the first layer as the second layer. The film thickness of the second layer of SiN film is 500nm, and it functions as an interlayer insulating film. A comb-shaped pixel electrode formed by arranging a patterned ITO film on the second layer of SiN film is formed as the third layer, and then two pixels, the first pixel and the second pixel, are formed. The size of each pixel is 10 mm in length and about 5 mm in width. At this time, the counter electrode of the first layer and the pixel electrode of the third layer are electrically insulated by the action of the SiN film of the second layer.

The pixel electrode of the third layer has a comb-like shape composed of a plurality of electrode elements arranged in a central portion bent into a < shape. The width of each electrode element in the short side direction is 3μm, and the interval between the electrode elements is 6μm. Since the pixel electrode forming each pixel is composed of a plurality of electrode elements arranged in a central portion bent into a < shape, the shape of each pixel is not a rectangle, but has a shape similar to a bold "<" that is bent in the central portion like the electrode elements. Moreover, each pixel is divided into upper and lower parts with the bent portion in the center as the boundary, and has a first area on the upper side of the bent portion and a second area on the lower side.

If the first area and the second area of each pixel are compared, the formation directions of the electrode elements constituting the pixel electrodes are different. That is, when the rubbing direction of the liquid crystal alignment film described later is used as a reference, the electrode elements of the pixel electrodes in the first area of the pixel are formed in a manner to become an angle of +10˚ (clockwise), and the electrode elements of the pixel electrodes in the second area of the pixel are formed in a manner to become an angle of -10˚ (clockwise). That is, in the first area and the second area of each pixel, the directions of the rotation of the liquid crystal in the substrate surface (in-plane switching) excited by applying a voltage between the pixel electrode and the counter electrode are formed in opposite directions.

Next, the obtained liquid crystal alignment agent is filtered with a filter of 1.0 μm in aperture, and then applied to the above-mentioned substrate with electrodes and a glass substrate with a columnar spacer having a height of 4 μm and an ITO film formed on the inner surface by a rotary coating. After drying on a heating plate at 80°C for 2 minutes, it is baked at 230°C for 30 minutes using an IR oven to form a coating with a thickness of 100 nm. The coating surface is irradiated with polarized ultraviolet light at a rate of 300 mJ/ ^cm2 to give an alignment treatment. The substrate with a liquid crystal alignment film is baked again at 230°C for 30 minutes using an IR oven. The above two substrates were used as a set, and a sealant was printed on the substrates. After the other substrate was laminated in a manner that the liquid crystal alignment film surfaces faced each other and the alignment direction was 0°, the sealant was cured to produce an empty cell. Liquid crystal MLC-3019 (Merck) was injected into the empty cell by the reduced pressure injection method and the injection port was sealed to obtain an FFS-driven liquid crystal cell. Afterwards, the obtained liquid crystal cell was heated at 110°C for 1 hour, left overnight, and used for afterimage evaluation.

Since AD-3 and AD-4 are novel compounds that have not been documented, their synthesis examples are described below. (Synthesis Example 1: Synthesis of AD-3)

4-aminophenylacetic acid (10.6 g, 70 mmol), DAH-1 (7.5 g, 33.6 mmol), and acetic acid (120 g) were placed in a 500 mL four-necked flask and stirred under reflux. After the reaction was completed, the reaction solution was poured into pure water (800 g) and the precipitate was separated by filtration. THF (120 g) was added to the obtained crude product and repulp washing was performed at room temperature to obtain 32.6 g of [AD-3-1]. [AD-3-1] (30.0 g, 61 mmol), bis[2-(trimethylsilyloxy)ethyl]amine (45.8 g, 184 mmol), diphenyl (2,3-dihydro-2-thione-3-benzoxazolyl)phosphonate (47.0 g, 122 mmol), triethylamine (45.8 g, 184 mmol), and NMP (450 g) were placed in a 2 L four-necked flask and stirred at room temperature. After the reaction was completed, the reaction solution was poured into a 0.5 mol/L aqueous hydrochloric acid solution (2500 g) and the precipitate was separated by filtration. Methanol (300 g) was added to the obtained crude product and the product was washed with heavy slurry at room temperature to obtain 30.3 g of [AD-3] (white solid). The results of ¹ H-NMR of the target product are shown below. From this result, it was confirmed that the obtained solid was the target [AD-3]. ¹ H NMR (500 MHz, [D ₆ ]-DMSO): δ7.32-7.38 (m,8H), 4.92-4.95 (t,2H), 4.69-4.72 (t,2H), 3.82 (s,4H), 3.55-3.59 (m,6H), 3.47-3.52 (m,8H), 3.36-3.39 (m,4H), 1.40 (s,6H)

(Synthesis Example 2: Synthesis of AD-4)

4-aminobenzoic acid (32.9 g, 24 mmol), DAH-1 (26.9 g, 12 mmol), and AcOH (540 g) were placed in a 2 L four-necked flask and stirred under reflux. After the reaction was completed, the reaction solution was poured into pure water (3500 g) and the precipitate was separated by filtration. Methanol (1200 g) was added to the obtained crude product and the heavy slurry was washed at room temperature to obtain 40.4 g of [AD-4-1].

[AD-4-1] (40.4 g, 87 mmol), bis[2-(trimethylsilyloxy)ethyl]amine (76.0 g, 305 mmol), diphenyl(2,3-hydro-2-thioxo-3-benzoxazolyl)phosphonate (83.7 g, 218 mmol), triethylamine (30.9 g, 305 mmol), and NMP (400 g) were placed in a 1 L four-necked flask and stirred at room temperature. After the reaction was completed, the reaction solution was poured into methanol (600 g), and the precipitate was separated by filtration. Methanol (500 g) was added to the obtained crude product, trifluoroacetic acid (7 g) was added to make it acidic, and the precipitate was separated by filtration. Furthermore, DMF (400 g) was added to the crude product and completely dissolved at 50°C, and then the insoluble matter was separated by filtration. The obtained filtrate was poured into ethyl acetate (2500 g), and the precipitate was separated by filtration and dried to obtain 48.8 g of [AD-4] (white solid). The result of ¹ H-NMR of the target product is shown below. From this result, it was confirmed that the obtained solid was the target [AD-4]. ¹ H NMR (500 MHz, [D ₆ ]-DMSO): δ7.56-7.58 (d, 4H), 7.48-7.50 (d, 4H), 4.84-4.87 (t, 4H), 3.61-3.65 (m, 6H), 3.55-3.56 (d, 4H), 3.48-3.50 (d, 4H), 3.35 (s, 4H), 1.42 (s, 6H)

(Production Example 1) DA-1 (1.08 g, 10 mmol), DA-2 (3.66 g, 15 mmol), DA-3 (4.81 g, 15 mmol), and DA-4 (3.41 g, 10 mmol) were added to a 200 ml four-necked flask equipped with a stirring device and a nitrogen inlet tube, and then 132 g of NMP was added, and nitrogen was transported and stirred to dissolve. The diamine solution was stirred and DAH-1 (10.54 g, 47 mmol) was added at the same time. After adding 40.3 g of NMP, the mixture was stirred at 40°C for 12 hours to obtain a polyamide solution (PAA-1) having a resin solid content of 12 mass %. The viscosity of the polyamide solution at 25°C was 380 mPa･s.

60.0 g of the obtained polyamide solution (PAA-1) was weighed and placed in a 200 ml Erlenmeyer flask. 20.0 g of NMP was added thereto, followed by 4.56 g of anhydrous acetic acid and 1.18 g of pyridine, and the mixture was reacted at 55°C for 3 hours. The reaction solution was poured into 300 g of methanol, and the resulting precipitate was separated by filtration. The precipitate was washed with methanol, and dried under reduced pressure at 80°C to obtain a polyimide powder. The imidization rate of the polyimide was 66%. A polyimide solution (SPI-1) was obtained by adding 26.4 g of NMP to 3.6 g of the obtained polyimide powder and stirring at 70°C for 20 hours to dissolve the mixture.

(Production Example 2) Into a 100 mL four-necked flask equipped with a stirring device and a nitrogen inlet tube, 3.99 g (20 mmol) of DA-5 and 1.49 g (5 mmol) of DA-6 were weighed and placed, and then 78 g of NMP was added, and nitrogen was supplied and stirred to dissolve. While stirring the diamine solution, 6.77 g (23 mmol) of DAH-2 was added, and NMP was added so that the solid content concentration became 12 mass %, and stirred at 70°C for 20 hours to obtain a polyamide solution (PAA-2) (viscosity: 420 mPa･s).

(Comparative Example 1) Into a 50 mL Erlenmeyer flask with a stirrer, 5.63 g of the polyimide solution (SPI-1) obtained in Preparation Example 1 was measured and placed. 3.34 g of NMP, 2.03 g of GBL, 3.00 g of BCS, and 1.01 g of a 10% NMP solution of AD-1 were added, and stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-1).

(Comparative Example 2) Into a 50 mL Erlenmeyer flask with a stirrer, 5.63 g of the polyimide solution (SPI-1) obtained in Preparation Example 1 was measured and placed. 3.34 g of NMP, 2.03 g of GBL, 3.00 g of BCS, and 1.01 g of a 10% NMP solution of AD-2 were added, and stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-2).

(Example 1) Into a 50 mL Erlenmeyer flask with a stirrer, 5.63 g of the polyimide solution (SPI-1) obtained in Preparation Example 1 was measured and placed. 3.34 g of NMP, 2.03 g of GBL, 3.00 g of BCS, and 1.01 g of a 10% NMP solution of AD-3 were added, and stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-3).

(Example 2) Into a 50 mL Erlenmeyer flask with a stirrer, 5.63 g of the polyimide solution (SPI-1) obtained in Preparation Example 1 was measured and placed. 3.34 g of NMP, 2.03 g of GBL, 3.00 g of BCS, and 1.01 g of a 10% NMP solution of AD-4 were added, and stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-4).

(Example 3) Into a 50 mL Erlenmeyer flask with a stirrer, 1.13 g of the polyimide solution (SPI-1) obtained in Preparation Example 1 was measured and added, and 4.50 g of the polyamide solution (PAA-2) obtained in Preparation Example 2 was added. 0.86 g of NMP, 4.50 g of GBL, 3.00 g of BCS, and 1.01 g of a 10% NMP solution of AD-3 were added, and stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-5).

[Evaluation of afterimages caused by long-term AC drive] Using the above-mentioned liquid crystal unit, an AC voltage of ±5V with a frequency of 30Hz was applied for 120 hours in a constant temperature environment of 60℃. Afterwards, the pixel electrode and the counter electrode of the liquid crystal unit were short-circuited and placed directly at room temperature for one day.

After placement, the liquid crystal unit is set between two polarizing plates whose polarization axes are arranged in an orthogonal manner, and the backlight is pre-lit without applying voltage, and the configuration angle of the liquid crystal unit is adjusted so that the brightness of the transmitted light becomes the smallest. Then, the rotation angle of the liquid crystal unit from the angle at which the second area of the first pixel becomes the darkest to the angle at which the first area becomes the darkest is calculated as angle Δ. The second pixel is also compared with the first area in the same way, and the same angle Δ is calculated. Then, the average value of the angle Δ values of the first pixel and the second pixel is calculated as the angle Δ of the liquid crystal unit. The angle Δ of the liquid crystal unit obtained above is rated as "×" if it is 0.15˚ or more, and "0" if it is less than 0.15˚.

(Comparison Examples 3, 4, Implementation Examples 4, 5, 6) For the obtained liquid crystal alignment agents (AL-1, AL-2, AL-3, AL-4, AL-5), the afterimage caused by long-term AC driving was evaluated by the above-mentioned operation. That is, using the liquid crystal alignment agents (AL-1, AL-2, AL-3, AL-4, AL-5), the above-mentioned operations were performed respectively to produce a liquid crystal unit having a structure of a FFS mode liquid crystal display element, and the afterimage caused by long-term AC driving was evaluated for the FFS-driven liquid crystal unit. The results are summarized in the following Table 1.

[Evaluation of film strength] The liquid crystal alignment agent was applied to the ITO surface of the glass substrate with ITO electrodes attached to the entire surface by the spin coating method. After drying on a heating plate at 80°C for 2 minutes, it was baked at 230°C for 30 minutes using an IR oven to form a coating with a thickness of 100nm. The coated surface was irradiated with polarized ultraviolet light at a rate of 300mJ/ ^cm2 to give an alignment treatment. The IR oven was used again to bake at 230°C for 30 minutes to obtain a substrate with a liquid crystal alignment film. The liquid crystal alignment film was rubbed using rayon cloth (roller diameter: 120mm, roller rotation number: 1000rpm, movement speed: 20mm/sec, injection length: 0.6mm). The substrate was observed under a microscope, and the film surface was rated as "0" if no scratches were found due to friction, and rated as "×" if scratches were found.

(Comparative Examples 5, 6, Implementation Examples 7, 8, 9) The obtained liquid crystal alignment agents (AL-1, AL-2, AL-3, AL-4, AL-5) were subjected to the above-mentioned film strength evaluation. The results are summarized in the following Table 2.

The above results are summarized in the following Table 3.

As shown in Table 3, the liquid crystal alignment agents AD-3 and AD-4, which have both an imide ring skeleton and an alkylamide skeleton, can have both good alignment and high friction resistance.

Claims (11)

A liquid crystal alignment agent is characterized by comprising the following components (A), (B), and an organic solvent; (A) component: at least one type of polymer selected from the group consisting of a polyimide precursor and an imidized polymer of the polyimide precursor; (B) component: a compound having a hydroxyalkylamide group and a structure of the following formula (1);

R ₁ to R ₄ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and * represents a bond with other atoms. The liquid crystal alignment agent of claim 1, wherein component (B) is a compound having two or more hydroxyalkylamide groups. The liquid crystal alignment agent of claim 1 contains 0.1-20% by mass of component (B) relative to component (A). The liquid crystal alignment agent of claim 1, wherein the group having two or more hydroxyalkylamide groups in component (B) is represented by the following formula (4);

_X2 is an n+1-valent organic group including an aliphatic alkyl group or an aromatic alkyl group having 1 to 20 carbon atoms, n is an integer of 2 to 6, and * represents a bond with (1); _R5 and _R6 are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a substituent, an alkenyl group having 2 to 4 carbon atoms which may have a substituent, or an alkynyl group having 2 to 4 carbon atoms which may have a substituent; and at least one of _R5 and _R6 has a hydroxyl group as a substituent. The liquid crystal alignment agent of claim 4, wherein at least one of _R5 and _R6 is represented by the following formula (5);

R ₇ to R ₁₀ are each independently a hydrogen atom, a alkyl group, or a alkyl group substituted with a hydroxyl group. The liquid crystal aligner of claim 4, wherein the atom in _X2 that is directly bonded to the carbonyl group is a carbon atom that forms an aromatic ring. The liquid crystal aligner of claim 4, wherein _R5 and _R6 are compounds represented by the following formula (6);

The liquid crystal alignment agent of any one of claims 1 to 7, wherein component (B) is any one of the following compounds;

A liquid crystal alignment film obtained from a liquid crystal alignment agent as described in any one of claims 1 to 8. A liquid crystal display element having a liquid crystal alignment film as claimed in claim 9. A compound as follows;