JP7652237B2 - Compound - Google Patents

Description

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

Liquid crystal display elements are known as display devices that are lightweight, thin, and consume little power. Liquid crystal display elements are constructed by sandwiching a liquid crystal layer between a pair of transparent substrates equipped with electrodes. In liquid crystal display elements, 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.
In recent years, high display quality is required for high-definition liquid crystal display elements for smartphones and tablet terminals, and liquid crystal alignment films are also required to have various other properties at a high level in addition to liquid crystal alignment ability.

To meet these requirements, a method of adding low molecular weight compounds with various properties to a liquid crystal alignment agent for producing a liquid crystal alignment film is widely used. For example, in order to improve the mechanical strength of the resulting 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 and 2). This low molecular weight compound contains a group that undergoes a crosslinking reaction during the heating step carried out in the liquid crystal alignment film production process, and the crosslinking connects the polymers together, thereby improving the mechanical strength of the resulting liquid crystal alignment film.

JP 2010-544185 A Patent No. 617911

However, a common problem with the above method is the deterioration of liquid crystal alignment. The polymer in the liquid crystal alignment film is crosslinked three-dimensionally, which prevents the liquid crystal from aligning in a certain direction. In addition, the presence of unreacted low-molecular-weight compounds can also have a negative effect on liquid crystal alignment.

The main object of the present invention is to provide a liquid crystal alignment agent that can improve the mechanical strength of a liquid crystal alignment film without deteriorating the liquid crystal alignment property or other properties.

The present inventors have conducted extensive research to solve the above problems and have completed the present invention. That is, the gist of the present invention is as follows.
1. A liquid crystal aligning agent comprising the following components (A) and (B), and an organic solvent:

Component (A): At least one polymer selected from the group consisting of polyimide precursors and imidized polymers of the polyimide precursors.

Component (B): A compound having a group containing a hydroxyalkylamide group and a structure represented by 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 to another atom.

By using the liquid crystal alignment agent of the present invention, it is possible to obtain a liquid crystal alignment film with improved mechanical strength without compromising the liquid crystal alignment properties or other characteristics.

It is not entirely clear why the present invention achieves the above-mentioned effects, but it is generally believed to be as follows.

The compound of component (B) contained in the liquid crystal alignment agent of the present invention has a polyimide skeleton structure as shown in formula (1). In this way, since the compound has a structure similar to the polymer of component (A), it is thought that it does not hinder the alignment of the liquid crystal along the polymer. Furthermore, in the liquid crystal alignment film obtained in the process of aligning the liquid crystal by irradiating with polarized ultraviolet light, the cyclobutane structure in formula (1) is decomposed by the irradiation of polarized ultraviolet light, so it is thought that it does not hinder the alignment of the liquid crystal.

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

<Tetracarboxylic acid derivatives>
The polyimide precursor contained in the liquid crystal aligning agent of the present invention is obtained by reacting a tetracarboxylic acid derivative with a diamine, and the polyimide is obtained by imidizing the polyimide precursor. Specific examples of the materials used and the production method are described in detail below.

Tetracarboxylic acid derivatives used in the production of polyimide precursors include not only tetracarboxylic acid dianhydrides, but also their derivatives, such as tetracarboxylic acids, tetracarboxylic acid dihalide compounds, tetracarboxylic acid dialkyl esters, and tetracarboxylic acid dialkyl ester dihalides.

Among the tetracarboxylic dianhydrides and derivatives thereof, those represented by the following formula (2) are preferred.

In formula (2), the structure of _X1 is not particularly limited. Preferred specific examples include the following formulae (X1-1) to (X1-44).

In formulas (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 containing 1 to 6 carbon atoms and containing a fluorine atom, or a phenyl group. From the viewpoint of liquid crystal alignment, R ₃ to R ₂₃ are preferably a hydrogen atom, a halogen atom, a methyl group, or an ethyl group, and more 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 viewpoints of liquid crystal alignment and photoreaction sensitivity, (X1-1-1) is particularly preferred.

<Diamine>
The diamine used in the production of the polyimide precursor is represented by the following formula (3).

In the above formula (3), A ₁ and A ₂ each independently represent 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 Y ₁ 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 hydrocarbon group having 1 to 5 carbon atoms.

Among them, Y The structures of ₁ are (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, particularly (Y-7), (Y-8), (Y-16), (Y-17), (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-169), (Y-170), (Y-171), (Y-173), and (Y-175) are preferred.

<Component (B)>
The component (B) contained in the liquid crystal aligning agent of the present invention is a compound having a group 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.
A hydrogen atom or a methyl group is preferable. * represents a bond to another atom.

In the (B) component, it is preferable that the component has two or more hydroxyalkylamide groups. The structure of the group 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 containing an aliphatic hydrocarbon group having 1 to 20 carbon atoms or an aromatic hydrocarbon group, n is an integer of 2 to 6, and * represents a bond to (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. At least one of _R5 and _R6 represents a hydrocarbon group substituted with a hydroxy group.

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

In formula (4), at least one of _R5 and _R6 is preferably a structure represented by the following formula (5) from the viewpoint of reactivity, 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 hydrocarbon group, or a hydrocarbon group substituted with a hydroxyl group.

Specific examples of preferred components (B) include the following compounds:

If the amount of component (B) is too large, it will affect the liquid crystal alignment and pretilt angle, and if the amount is too small, the effects of the present invention will not be obtained. Therefore, the content of component (B) is preferably 3 to 30% by mass, and more preferably 5 to 15% by mass, relative to component (A).

<Polyamic Acid>
The polyamic acid, which is a polyimide precursor used in the present invention, can be produced by the following method: Specifically, it can be synthesized by reacting a tetracarboxylic dianhydride with a diamine 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 in terms of the solubility of the monomer and polymer, and these may be used alone or in combination of two or more. The concentration of the polymer is preferably 1 to 30% by mass, more preferably 5 to 20% by mass, from the viewpoints that precipitation of the polymer is unlikely to occur and that a high molecular weight product is easily obtained.

The polyamic acid obtained as described above can be recovered by injecting the reaction solution into a poor solvent while thoroughly stirring it to precipitate the polymer. Alternatively, the precipitation can be carried out several times, washed with a poor solvent, and then dried at room temperature or by heating to obtain a purified polyamic acid powder. The poor solvent is not particularly limited, but examples include water, methanol, ethanol, hexane, butyl cellosolve, acetone, and toluene.

<Polyamic acid ester>
The polyamic acid ester, which is one of the polyimide precursors used in the present invention, can be produced by the following method (1), (2) or (3).

(1) Production from polyamic acid
The polyamic acid ester can be synthesized by esterifying a polyamic acid obtained from a tetracarboxylic dianhydride and a diamine, specifically by reacting a polyamic acid with an esterifying agent 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.

The esterification agent is preferably one that can be easily removed by purification, and examples of such an agent include 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, and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride. The amount of the esterification agent used is preferably 2 to 6 molar equivalents per mole 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 in terms of the solubility of the polymer, and these may be used alone or in combination of two or more. The concentration of the polymer in the reaction solution is preferably 1 to 30% by mass, more preferably 5 to 20% by mass, from the viewpoints that precipitation of the polymer is unlikely to occur and that a high molecular weight product is easily obtained.

(2) Production by reaction of tetracarboxylic acid diester dichloride with diamine Polyamic acid ester can be produced from tetracarboxylic acid diester dichloride and diamine. Specifically, it can be synthesized by reacting tetracarboxylic acid diester dichloride with diamine 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 to 4 hours.

The base may be pyridine, triethylamine, 4-dimethylaminopyridine, etc., but pyridine is preferred because the reaction proceeds mildly. The amount of base used is preferably 2 to 4 times the molar amount of tetracarboxylic acid diester dichloride, from the viewpoints that it is an amount that can be easily removed and that it is easy to obtain a high molecular weight product.

The solvent used in the above reaction is preferably N-methyl-2-pyrrolidone or γ-butyrolactone in terms of the solubility of the monomer and polymer, and these may be used alone or in a mixture of two or more. The polymer concentration in the reaction solution is preferably 1 to 30% by mass, more preferably 5 to 20% by mass, from the viewpoint of preventing precipitation of the polymer and facilitating the production of a high molecular weight product. In addition, in order to prevent hydrolysis of the tetracarboxylic acid diester dichloride, it is preferable that the solvent used in the synthesis of the polyamic acid ester is as dehydrated as possible, and it is preferable to use a nitrogen atmosphere to prevent the inclusion of outside air.

(3) Production by reaction of tetracarboxylic acid diester with diamine Polyamic acid ester can be produced by polycondensation of tetracarboxylic acid diester with diamine. Specifically, it can be produced by reacting tetracarboxylic acid diester with diamine 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 3 to 15 hours.

The condensing agent may be triphenyl phosphite, dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-carbonyldiimidazole, dimethoxy-1,3,5-triazinylmethylmorpholinium, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, (2,3-dihydro-2-thioxo-3-benzoxazolyl)diphenylphosphonate, or the like. The amount of the condensing agent added is preferably 2 to 3 times the molar amount of the tetracarboxylic acid diester.

The base can be a tertiary amine such as pyridine or triethylamine. The amount of base used is preferably 2 to 4 times the molar amount of the diamine component, from the viewpoints that it is an amount that can be easily removed and that it is easy to obtain a high molecular weight product.

In addition, the reaction proceeds more 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 molar amount of the diamine component.

Among the three methods for producing polyamic acid esters, the methods (1) and (2) are particularly preferred because they produce high molecular weight polyamic acid esters.

The polyamic acid ester solution obtained as described above can be poured into a poor solvent while being thoroughly stirred to precipitate the polymer. Precipitation can be carried out several times, washed with a poor solvent, and then dried at room temperature or by heating to obtain a purified polyamic acid ester powder. The poor solvent is not particularly limited, but examples include water, methanol, ethanol, hexane, butyl cellosolve, acetone, and toluene.

<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 not limited to 100%. From the viewpoint of electrical properties, it is preferably 20 to 99%. When producing a polyimide from a polyamic acid ester, chemical imidization is convenient, in which a basic catalyst is added to the polyamic acid ester solution or a polyamic acid solution obtained by dissolving a 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. In addition, by reacting the compounds shown in (R-1) to (R-2) below, a polyimide precursor having a specific structure introduced at the end can be obtained. The organic solvent can be the solvent used in the polymerization reaction described above. Examples of basic catalysts include pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine, etc. Among them, pyridine is preferable because it has a suitable basicity for promoting the reaction. Examples of acid anhydrides include acetic anhydride, trimellitic anhydride, pyromellitic anhydride, etc. Among them, acetic anhydride is preferable because it makes purification after the reaction easy. Normally, in the case of conventional polyimides, acetyl groups are generated at the main chain end when acetic anhydride is used, but the present invention can suppress acetylation.

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

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

Since the added catalyst and the like remain in the solution after the imidization reaction of the polyamic acid ester or polyamic acid, it is preferable to recover the obtained imidized polymer by the means described below and redissolve it in an organic solvent to obtain the liquid crystal alignment agent of the present invention.

The polyimide solution obtained as described above can be poured into a poor solvent while being thoroughly stirred to precipitate the polymer. Precipitation can be carried out several times, and after washing with a poor solvent, a purified polyamic acid ester powder can be obtained by drying at room temperature or by heating.

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

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

The molecular weight of the specific structure polymer is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and even more preferably 10,000 to 100,000, in terms of weight average molecular weight. 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 concentration of the polymer in the liquid crystal alignment agent of 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 preferably 1% by mass or more, and from the viewpoint of storage stability of the solution, it is preferably 10% by mass or less. Particularly preferably, it is 3 to 6.5% by mass.

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

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

Among these, it is preferable to use N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone.

（Ｄ^１～Ｄ^３は炭素数１～６のアルキル基を表す。） Furthermore, when the polymer of the present invention has high solubility in a solvent, it is preferable to use a solvent represented by the following formulas [D-1] to [D-3].

(D ¹ to D ³ each 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 to 99% by mass of the total solvent contained in the liquid crystal alignment agent. Of these, 20 to 90% by mass is more preferable. More preferably, it is 30 to 80% by mass.

The liquid crystal alignment agent of the present invention can use a solvent (also called a poor solvent) that improves the coating properties and surface smoothness of the liquid crystal alignment film when the liquid crystal alignment agent is applied, as long as the effect of the present invention is not impaired. Specific examples of poor solvents are listed below, but are 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-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 diethyl 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-ethylbutyl acetate, 2-ethylhexyl acetate, ethylene glycol monoacetate, ethylene glycol diacetate, propylene carbonate, ethylene carbonate, 2-(methoxy methoxy)ethanol, ethylene glycol monobutyl ether, ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, 2-(hexyloxy)ethanol, furfuryl 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 Examples of the solvent include 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 monoethyl ether 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 lactate, isoamyl lactate, and the solvents represented by the formulas [D-1] to [D-3] above.

Among these, it is preferable to use 1-hexanol, cyclohexanol, 1,2-ethanediol, 1,2-propanediol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, or dipropylene glycol dimethyl ether.

The poor solvent preferably accounts for 1 to 80% by mass of the total solvent contained in the liquid crystal alignment agent, more preferably 10 to 80% by mass, and even more preferably 20 to 70% by mass.

In addition to the above, the liquid crystal alignment agent of the present invention may contain, within the scope of the invention, polymers other than those described in the present invention, dielectric or conductive substances for changing the electrical properties of the liquid crystal alignment film, such as the dielectric constant or conductivity, silane coupling agents for improving the adhesion between the liquid crystal alignment film and the substrate, crosslinking compounds for increasing the hardness and density of the film when made into a liquid crystal alignment film, and imidization promoters for efficiently promoting imidization by heating the polyimide precursor when baking the coating film.

<Liquid crystal alignment film>
<Method of manufacturing liquid crystal alignment film>
The liquid crystal alignment film of the present invention is a film obtained by applying the liquid crystal alignment agent to a substrate, drying and baking. The substrate to 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 glass substrates, silicon nitride substrates, acrylic substrates, polycarbonate substrates and other plastic substrates can be used. Furthermore, from the viewpoint of simplifying the process, it is preferable to use a substrate on which an ITO electrode or the like for driving liquid crystal is formed. In addition, 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 light-reflecting material such as aluminum can be used for the electrode.

Methods for applying the liquid crystal alignment agent of the present invention include spin coating, printing, and inkjet methods. The temperature and time for the drying and baking steps after applying the liquid crystal alignment agent of the present invention can be selected as desired. In general, in order to thoroughly remove the solvent contained, the coating is dried at 50 to 120°C, preferably 60 to 100°C, for 1 to 10 minutes, preferably 2 to 5 minutes, and then baked at 150 to 300°C, preferably 200 to 240°C, for 5 to 120 minutes, preferably 10 to 30 minutes. The thickness of the coating film after baking is not particularly limited, but is 5 to 300 nm, preferably 10 to 200 nm, since if it is too thin, the reliability of the liquid crystal display element may decrease.

Methods for performing alignment treatment on the obtained liquid crystal alignment film include rubbing and photoalignment.

The rubbing process can be carried out using existing rubbing equipment. Examples of materials for the rubbing cloth include cotton, nylon, and rayon. The conditions generally used for the rubbing process are a rotation speed of 300 to 2000 rpm, a feed speed of 5 to 100 mm/s, and a push-in amount of 0.1 to 1.0 mm. After that, the residues generated by rubbing are removed by ultrasonic cleaning using pure water or alcohol.

A specific example of the photo-alignment treatment method is a method in which the coating surface is irradiated with radiation polarized in a certain direction, and in some cases, further heat-treated at a temperature of 150 to 250°C to impart liquid crystal alignment ability. As the radiation, ultraviolet rays having a wavelength of 100 to 800 nm and visible light can be used. Among these, ultraviolet rays having a wavelength of 100 to 400 nm are preferred, and ultraviolet rays having a wavelength of 200 to 400 nm are particularly preferred. In addition, in order to improve the liquid crystal alignment property, the coating substrate may be irradiated with radiation while being heated at 50 to 250°C. The radiation dose is preferably 1 to 10,000 mJ/ ^cm2 , and particularly preferably 100 to 5,000 mJ/ ^cm2 . The liquid crystal alignment film prepared as described above can stably align liquid crystal molecules in a certain direction.

The higher the extinction ratio of the polarized UV light, the higher the anisotropy that can be imparted, which is preferable. Specifically, the extinction ratio of linearly polarized UV light is preferably 10:1 or greater, and more preferably 20:1 or greater.

The film irradiated with polarized radiation may then be contact-treated with a solvent containing 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 dissolves 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 cellosolve, ethyl lactate, methyl lactate, diacetone alcohol, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, propyl acetate, butyl acetate, and cyclohexyl acetate. Two or more of these solvents may be used in combination.

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

In the present invention, the contact treatment between the film irradiated with polarized radiation and the solution containing a solvent is preferably carried out by a method such as immersion treatment or spraying treatment that brings the film into sufficient contact with the liquid. Among these, a method of immersion treatment in a solution containing a solvent for preferably 10 seconds to 1 hour, more preferably 1 to 30 minutes, is preferred. The contact treatment may be carried out at room temperature or heated, but is preferably carried out at 10 to 80°C, more preferably 20 to 50°C. Furthermore, a means for enhancing contact, such as ultrasound, may be applied as necessary.

After the contact treatment, in order to remove the solvent in the solution used, rinsing with a low boiling point solvent such as water, methanol, ethanol, 2-propanol, acetone, or methyl ethyl ketone and/or drying may be performed.

Furthermore, the membrane that has been contact-treated with a solution containing a solvent may be heated to 150°C or higher to dry the solvent and reorient the molecular chains in the membrane.

The heating temperature is preferably 150 to 300°C. The higher the temperature, the more the reorientation of the molecular chains is promoted, but if the temperature is too high, there is a risk of the molecular chains being decomposed. Therefore, the heating temperature is more preferably 180 to 250°C, and particularly preferably 200 to 230°C.

If the heating time is too short, the molecular chain reorientation effect may not be achieved, and if it is too long, the molecular chains may decompose, so a heating time of 10 seconds to 30 minutes is preferable, and 1 to 10 minutes is more preferable.

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

The liquid crystal display element of the present invention is produced by obtaining a substrate with a liquid crystal alignment film from the liquid crystal alignment agent of the present invention by the method for producing a liquid crystal alignment film, and then producing a liquid crystal cell by a known method, and using the liquid crystal cell to produce a liquid crystal display element.

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

First, 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 may be, for example, ITO electrodes, and are patterned so as 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 may be, for example, a film made of SiO ₂ -TiO ₂ formed by the sol-gel method.

Next, the liquid crystal alignment film of the present invention is formed on each substrate. Next, one substrate is superimposed on the other substrate so that the alignment film surfaces face each other, and the periphery is bonded with a sealant. Spacers are usually mixed into the sealant to control the gap between the substrates. It is also preferable to disperse spacers for controlling the gap between the substrates even in the in-plane parts where no sealant is provided. An opening is provided in part of the sealant so that liquid crystal can be filled from the outside.

Next, liquid crystal material is injected into the space surrounded by the two substrates and the sealant through an opening in the sealant. This opening is then sealed with adhesive. The injection may be performed using a vacuum injection method or a method utilizing capillary action in the atmosphere. Next, polarizing plates are installed. Specifically, a pair of polarizing plates are attached to the surfaces of the two substrates opposite the liquid crystal layer. Through the above steps, the liquid crystal display element of the present invention is obtained.

In the present invention, the sealant used is a resin that has reactive groups such as epoxy groups, acryloyl groups, (meth)acryloyl groups, hydroxyl groups, allyl groups, and acetyl groups, and that is cured by ultraviolet light irradiation or heating. In particular, it is preferable to use a curable resin system that has both epoxy and (meth)acryloyl reactive groups.

The sealing agent of the present invention may contain an inorganic filler for the purpose of improving adhesion and moisture resistance. The inorganic filler that can be used is not particularly limited, but specific examples include spherical silica, fused silica, crystalline silica, titanium oxide, titanium black, silicon carbide, silicon nitride, boron nitride, calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, mica, talc, clay, alumina, magnesium oxide, zirconium oxide, aluminum hydroxide, calcium silicate, aluminum silicate, lithium aluminum silicate, zirconium silicate, barium titanate, glass fiber, carbon fiber, molybdenum disulfide, asbestos, etc. Preferred examples include spherical silica, fused silica, crystalline silica, titanium oxide, titanium black, silicon nitride, boron nitride, calcium carbonate, barium sulfate, calcium sulfate, mica, talc, clay, alumina, aluminum hydroxide, calcium silicate, and aluminum silicate. The inorganic fillers may be used in combination of two or more.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. In the following, the abbreviations of compounds and the measuring methods of each property are as follows.
NMP: N-methyl-2-pyrrolidone GBL: γ-butyrolactone BCS: butyl cellosolve THF: tetrahydrofuran DMF: N,N-dimethylformamide

< ^1H NMR Measurement>
Apparatus: Fourier transform superconducting nuclear magnetic resonance apparatus (FT-NMR) "AVANCE 3" (manufactured by BRUKER) 500 MHz.
Solvent: deuterated chloroform (CDCl ₃ ) or deuterated N,N-dimethylsulfoxide ([D ₆ ]-DMSO).
Standard substance: tetramethylsilane (TMS).

[viscosity]
The viscosity of the polyimide and polyamic acid solutions was measured using an E-type viscometer (VE-22H, manufactured by Toki Sangyo Co., Ltd.) with a sample amount of 1.1 mL, a cone rotor TE-1 (1°34′, R24), and a temperature of 25°C.

[Measurement of imidization rate]
20 mg of polyimide powder was placed in an NMR sample tube (Kusano Scientific NMR Sampling Tube Standard φ5), 0.53 ml of deuterated dimethyl sulfoxide (DMSO-d6, 0.05% TMS (tetramethylsilane) mixture) was added, and the mixture was sonicated to completely dissolve. This solution was measured for proton NMR at 500 MHz using a JEOL Datum NMR analyzer (JNW-ECA500). The imidization rate was calculated by the following formula, 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 integrated value derived from the NH group of the amic acid that appears around 9.5 to 10.0 ppm.

Imidation rate (%) = (1-α x/y) x 100

[Preparation of Liquid Crystal Cell]
A liquid crystal cell having the structure of an FFS mode liquid crystal display element was prepared.
First, a substrate with electrodes was prepared. The substrate was a rectangular glass plate measuring 30 mm x 50 mm and having a thickness of 0.7 mm. An ITO electrode having a solid pattern was formed on the substrate as a first layer, which constitutes an opposing electrode. A SiN (silicon nitride) film formed by a CVD method was formed as a second layer on the first layer opposing electrode. The thickness of the second layer SiN film was 500 nm, and it functions as an interlayer insulating film. A comb-shaped pixel electrode formed by patterning an ITO film as a third layer was arranged on the second layer SiN film, forming two pixels, a first pixel and a second pixel. The size of each pixel was 10 mm long and about 5 mm wide. At this time, the first layer opposing electrode and the third layer pixel electrode were electrically insulated by the action of the second layer SiN film.

The pixel electrodes in the third layer have a comb-like shape consisting of multiple electrode elements arranged in a "L" shape with a bent central portion. The width of each electrode element in the short direction is 3 μm, and the distance between the electrode elements is 6 μm. Because the pixel electrodes that form each pixel are arranged in multiple electrode elements arranged in a "L" shape with a bent central portion, the shape of each pixel is not rectangular, but has a shape similar to a bold "L" shape that is bent in the center like the electrode elements. Each pixel is divided into upper and lower parts by the bent central portion, and has a first region above the bent portion and a second region below the bent portion.

Comparing the first and second regions of each pixel, the directions in which the electrode elements of the pixel electrodes that make them up are different. That is, based on the rubbing direction of the liquid crystal alignment film described below, the electrode elements of the pixel electrode in the first region of the pixel are formed to form an angle of +10° (clockwise), and the electrode elements of the pixel electrode in the second region of the pixel are formed to form an angle of -10° (clockwise). That is, the first and second regions of each pixel are configured so that the directions of rotational movement (in-plane switching) of the liquid crystal within the substrate surface induced by the application of a voltage between the pixel electrode and the opposing electrode are opposite to each other.

Next, the obtained liquid crystal alignment agent was filtered through a filter with a pore size of 1.0 μm, and then applied by spin coating to the prepared substrate with the electrode and a glass substrate having a columnar spacer with a height of 4 μm on the back surface of which an ITO film was formed. After drying for 2 minutes on a hot plate at 80 ° C., baking was performed for 30 minutes at 230 ° C. using an IR oven to form a coating film with a thickness of 100 nm. The coating surface was irradiated with polarized ultraviolet light so as to be 300 mJ / cm ² , and an alignment treatment was performed. The coating surface was again baked for 30 minutes at 230 ° C. using an IR oven to obtain a substrate with a liquid crystal alignment film. The above two substrates were combined into a set, a sealant was printed on the substrate, and the other substrate was attached so that the alignment direction of the liquid crystal alignment film surface facing each other was 0 °, and then the sealant was cured to prepare an empty cell. Liquid crystal MLC-3019 (manufactured by Merck) was injected into this empty cell by a reduced pressure injection method, and the injection port was sealed to obtain an FFS drive liquid crystal cell. Thereafter, the obtained liquid crystal cell was heated at 110° C. for 1 hour and left overnight before being used for evaluation of afterimages.

Since AD-3 and AD-4 are novel compounds with no literature registration, 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 charged into a 500 mL four-neck flask and stirred under reflux. After completion of the reaction, the reaction solution was poured into pure water (800 g) and the precipitate was filtered off. THF (120 g) was added to the obtained crude product, and the mixture was repulped and washed 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), (2,3-dihydro-2-thioxo-3-benzoxazolyl)diphenylphosphonate (47.0 g, 122 mmol), triethylamine (45.8 g, 184 mmol), and NMP (450 g) were charged into a 2 L four-neck flask and stirred at room temperature. After completion of the reaction, the reaction solution was poured into a 0.5 mol/L-hydrochloric acid aqueous solution (2500 g), and the precipitate was filtered off. Methanol (300 g) was added to the obtained crude product, and the mixture was repulped and washed 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 these results, 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 charged into a 2 L four-neck flask and stirred under reflux. After the reaction was completed, the reaction solution was poured into pure water (3500 g) and the precipitate was filtered off. Methanol (1200 g) was added to the obtained crude product, which was then repulped and 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), (2,3-dihydro-2-thioxo-3-benzoxazolyl)diphenylphosphonate (83.7 g, 218 mmol), triethylamine (30.9 g, 305 mmol), and NMP (400 g) were charged into a 1 L four-neck flask and stirred at room temperature. After the reaction was completed, the reaction solution was poured into methanol (600 g) and the precipitate was filtered off. Methanol (500 g) was added to the obtained crude product, trifluoroacetic acid (7 g) was added to make it acidic, and the precipitate was filtered off. Furthermore, DMF (400 g) was added to the crude product and completely dissolved at 50° C., and the insoluble matter was filtered off. The obtained filtrate was poured into ethyl acetate (2500 g), and the precipitate was filtered off and dried to obtain 48.8 g of [AD-4] (white solid). The results of ¹ H-NMR of the target product are shown below. From these results, 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-neck flask equipped with a stirrer and a nitrogen inlet tube, and then 132 g of NMP was added and stirred while feeding nitrogen to dissolve. DAH-1 (10.54 g, 47 mmol) was added while stirring this diamine solution, and 40.3 g of NMP was added, and then the mixture was further stirred at 40° C. for 12 hours to obtain a polyamic acid solution (PAA-1) with a resin solids concentration of 12% by mass. The viscosity of this polyamic acid solution at 25° C. was 380 mPa·s.

60.0 g of the resulting polyamic acid solution (PAA-1) was dispensed into a 200 ml Erlenmeyer flask, and 20.0 g of NMP was added, followed by 4.56 g of acetic anhydride and 1.18 g of pyridine, and the mixture was allowed to react at 55°C for 3 hours. This reaction solution was poured into 300 g of methanol, and the resulting precipitate was filtered off. This precipitate was washed with methanol and dried under reduced pressure at 80°C to obtain polyimide powder. The imidization rate of this polyimide was 66%. 26.4 g of NMP was added to 3.6 g of the resulting polyimide powder, and the mixture was stirred at 70°C for 20 hours to dissolve, yielding a polyimide solution (SPI-1).

(Production Example 2)
3.99 g (20 mmol) of DA-5 and 1.49 g (5 mmol) of DA-6 were weighed out into a 100 mL four-neck flask equipped with a stirrer and a nitrogen inlet tube, and then 78 g of NMP was added and stirred to dissolve while feeding nitrogen. 6.77 g (23 mmol) of DAH-2 was added while stirring this diamine solution, and NMP was further added so that the solid concentration became 12 mass%, and the mixture was stirred at 70° C. for 20 hours to obtain a polyamic acid solution (PAA-2) (viscosity: 420 mPa s).

(Comparative Example 1)
5.63 g of the polyimide solution (SPI-1) obtained in Production Example 1 was weighed out into a 50 mL Erlenmeyer flask containing a stirrer. 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 the mixture was stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-1).

(Comparative Example 2)
5.63 g of the polyimide solution (SPI-1) obtained in Production Example 1 was weighed out into a 50 mL Erlenmeyer flask containing a stirrer. 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 the mixture was stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-2).

Example 1
5.63 g of the polyimide solution (SPI-1) obtained in Production Example 1 was weighed out into a 50 mL Erlenmeyer flask containing a stirrer. 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 the mixture was stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-3).

Example 2
5.63 g of the polyimide solution (SPI-1) obtained in Production Example 1 was weighed out into a 50 mL Erlenmeyer flask containing a stirrer. 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 the mixture was stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-4).

Example 3
In a 50 mL Erlenmeyer flask containing a stirrer, 1.13 g of the polyimide solution (SPI-1) obtained in Production Example 1 was weighed out, and 4.50 g of the polyamic acid solution (PAA-2) obtained in Production Example 2 was added. Furthermore, 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 the mixture was stirred overnight with a magnetic stirrer to obtain a liquid crystal alignment agent (AL-5).

[Evaluation of image lag due to long-term AC drive]
Using the above liquid crystal cell, an AC voltage of ±5 V at a frequency of 30 Hz was applied for 120 hours in a constant temperature environment of 60° C. Thereafter, the pixel electrode and the counter electrode of the liquid crystal cell were shorted, and the liquid crystal cell was left at room temperature for one day.

After leaving it, the liquid crystal cell was placed between two polarizing plates arranged so that the polarization axes were perpendicular to each other, and the backlight was turned on with no voltage applied, and the arrangement angle of the liquid crystal cell was adjusted so that the brightness of the transmitted light was minimized. Then, the rotation angle when the liquid crystal cell was rotated from the angle at which the second region of the first pixel was the darkest to the angle at which the first region was the darkest was calculated as the angle Δ. Similarly, the second region and the first region of the second pixel were compared, and the same angle Δ was calculated. Then, the average value of the angle Δ values of the first pixel and the second pixel was calculated as the angle Δ of the liquid crystal cell.
The angle Δ of the liquid crystal cell obtained above was evaluated as "x" when it was 0.15° or more, and as "good" when it was less than 0.15°.

(Comparative Examples 3 and 4, Examples 4, 5, and 6)
The obtained liquid crystal alignment agents (AL-1, AL-2, AL-3, AL-4, AL-5) were subjected to a long-term AC drive image retention evaluation as described above. That is, liquid crystal cells having the configuration of an FFS mode liquid crystal display element were prepared as described above using the liquid crystal alignment agents (AL-1, AL-2, AL-3, AL-4, AL-5), and the FFS drive liquid crystal cells were subjected to a long-term AC drive image retention evaluation. The results are summarized in Table 1 below.

[Membrane strength evaluation]
The liquid crystal alignment agent was applied by spin coating to the ITO surface of a glass substrate with an ITO electrode on the entire surface. After drying for 2 minutes on a hot plate at 80 ° C, it was baked at 230 ° C for 30 minutes using an IR oven to form a coating film with a thickness of 100 nm. The coating surface was irradiated with polarized ultraviolet light at 300 mJ / cm ² to perform an alignment treatment. It was baked again at 230 ° C for 30 minutes using an IR oven to obtain a substrate with a liquid crystal alignment film. This liquid crystal alignment film was rubbed with a rayon cloth (roller diameter: 120 mm, roller rotation speed: 1000 rpm, moving speed: 20 mm / sec, indentation length: 0.6 mm). The substrate was observed under a microscope, and those that did not have rubbing streaks on the film surface were evaluated as "◯", and those that had streaks were evaluated as "X".

(Comparative Examples 5 and 6, Examples 7, 8, and 9)
The above-mentioned film strength evaluation was carried out for the obtained liquid crystal alignment agents (AL-1, AL-2, AL-3, AL-4, and AL-5). The results are summarized in Table 2 below.

The above results are summarized in Table 3 below.

As shown in Table 3, the liquid crystal alignment agents AD-3 and AD-4, which have both an imide ring structure and an alkylamide structure, were able to achieve both good alignment and high rubbing resistance.

Claims (1)

Any of the following compounds: