JP7351295B2 - Liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display element using the same - Google Patents

Description

The present invention relates to a liquid crystal aligning agent, a liquid crystal aligning film, and a liquid crystal display element using the same, using a novel polymer.

Liquid crystal display elements are widely used as display units in personal computers, mobile phones, smartphones, televisions, and the like. A liquid crystal display element includes, for example, a liquid crystal layer sandwiched between an element substrate and a color filter substrate, a pixel electrode and a common electrode that apply an electric field to the liquid crystal layer, an alignment film that controls the orientation of liquid crystal molecules in the liquid crystal layer, It includes a thin film transistor (TFT) and the like for switching electrical signals supplied to the pixel electrodes. As methods for driving liquid crystal molecules, vertical electric field methods such as TN method and VA method, and transverse electric field methods such as IPS method and FFS method are known. The horizontal electric field method, in which an electrode is formed only on one side of the substrate and an electric field is applied in a direction parallel to the substrate, has a wider field area than the conventional vertical electric field method, in which voltage is applied to electrodes formed on the upper and lower substrates to drive the liquid crystal. It is known as a liquid crystal display element that has viewing angle characteristics and is capable of high-quality display.

Although transverse electric field type liquid crystal cells have excellent viewing angle characteristics, since there are few electrodes formed in the substrate, if the voltage holding rate is low, sufficient voltage will not be applied to the liquid crystal, resulting in a decrease in display contrast. Furthermore, if the stability of liquid crystal alignment is low, the liquid crystal will not return to its initial state when driven for a long time, causing a decrease in contrast and afterimages, so stability of liquid crystal alignment is important. Furthermore, static electricity tends to accumulate in the liquid crystal cell, and the application of positive and negative asymmetric voltages caused by driving also accumulates charges in the liquid crystal cell, and these accumulated charges affect the display as disturbances in liquid crystal alignment and afterimages. , which significantly deteriorates the display quality of the liquid crystal element.
In recent years, with the introduction of HDR (High Dynamic Range) to meet the demand for high contrast, backlights with higher brightness than before have been used.

Although Patent Document 1 discloses a liquid crystal aligning agent containing a specific structure and compound, there is no description regarding resistance to backlight. In addition, Patent Documents 2 and 3 disclose liquid crystal aligning agents containing specific structures, and there are descriptions regarding backlight resistance of VHR (Voltage Holding Ratio), but there is no mention of accumulated charge, and conventional techniques It was difficult to fully satisfy the required characteristics.

International Publication Publication WO2016/063834 pamphlet International Publication Publication WO2014/104015 pamphlet International Publication Publication WO2015/119168 Pamphlet

The present invention provides a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display element that can obtain a liquid crystal alignment film in which accumulated charges are quickly relaxed and the amount of accumulated charges does not easily change even when irradiated with a backlight. The task is to

（Ｒ^１は、水素、炭素数１～４を有する、アルキル基、アルケニル基、アルコキシ基、フルオロアルキル基、フルオロアルケニル基若しくはフルオロアルコキシ基を表し、２つのＲ^１は、同じでも異なっていてもよいが、それらの少なくとも１つは水素ではない。＊は他の基に結合する部位を示す。ベンゼン環の任意の水素原子は一価の有機基で置換されていてもよい。）As a result of intensive studies to solve the above problems, the present inventors discovered that various properties can be simultaneously improved by introducing a specific structure into the polymer contained in the liquid crystal aligning agent. Completed the invention.
The present invention is based on this knowledge and has the following gist.
A liquid crystal aligning agent characterized by containing a polymer obtained from a diamine having the structure of the following formula (1) and an organic solvent.

(R ¹ represents hydrogen, an alkyl group, an alkenyl group, an alkoxy group, a fluoroalkyl group, a fluoroalkenyl group, or a fluoroalkoxy group having 1 to 4 carbon atoms, and two R ¹ 's may be the same or different. (However, at least one of them is not hydrogen. * indicates a bonding site to another group. Any hydrogen atom in the benzene ring may be substituted with a monovalent organic group.)

According to the present invention, a liquid crystal aligning agent, a liquid crystal aligning film, and a liquid crystal display element are obtained, which can provide a liquid crystal aligning film in which accumulated charges are quickly relaxed and the amount of accumulated charges hardly changes even when irradiated with a backlight. It will be done.

<Specific diamine>
The liquid crystal aligning agent of the present invention is a liquid crystal aligning agent containing a novel polymer obtained from a diamine (hereinafter also referred to as specific diamine) having a structure represented by the following formula (1).

In the above formula (1), R ¹ is as defined above, and is preferably an alkyl group having 1 to 5 carbon atoms, particularly preferably a methyl group.
From the viewpoint of steric hindrance, the bond between the benzene ring and the nitrogen atom in formula (1) is preferably as shown in formula (1-1).

The above-mentioned specific diamine can be represented by, for example, the following formula (1-2), particularly preferably a diamine represented by the following formula (1-3), and more preferably a diamine represented by the formula (1-4). Diamines are more preferred.

The definition of R ¹ is the same as in the case of formula (1) above, and Q ¹ and Q ² are each independently a single bond or a divalent organic group, that is, Q ¹ and Q ² are mutually exclusive. It may have a different structure. Furthermore, the two Q ² in formula (1-4) may have different structures. Furthermore, any hydrogen atom of the benzene ring may be substituted with a monovalent organic group as in the case of formula (1) above.

Preferred examples of the specific diamine include diamines represented by the following formulas (2-1), (2-2), or (2-3).

In the above formula, the definition of R ¹ is the same as in the above formula (1), R ² is a single bond or a structure represented by the following formula (3), and n represents an integer from 1 to 3. . Any hydrogen atom of the benzene ring may be substituted with a monovalent organic group.

In the above formula, R ³ is a single bond, -O-, -COO-, -OCO-, -(CH ₂ ) _l -, -O(CH ₂ ) _m O-, -CONR-, and -NRCO- It represents a selected divalent organic group, and k represents an integer of 1 to 5. Note that R represents hydrogen or a monovalent organic group, and l and m represent integers of 1 to 5. Such a monovalent organic group is preferably an alkyl group having 1 to 3 carbon atoms. * ₁ represents a site that binds to the benzene ring in formulas (2-1) to (2-3), and * ₂ represents a site that binds to the amino group in formulas (2-1) to (2-3). Represents a part.

Specific examples include, but are not limited to, the following. Among these, formulas (2-1-1) to (2-1-6), formula (2-1-15), and formula (2-1-16) are preferable from the viewpoint of alleviation of accumulated charge; Formula (2-1-1), formula (2-1-2), formula (2-1-15), and formula (2-1-16) are particularly preferred from the viewpoint of compatibility with properties.

<Method for synthesizing specific diamine>
Below, a method for obtaining a specific diamine will be explained using a diamine of the following formula (2-1-1) as an example.

The method for synthesizing the specific diamine of the present invention is not particularly limited, but for example, a dinitro compound (2-1-N) which is a precursor of the diamine of formula (2-1-1) above is synthesized, and the nitro group is One way is to give back.

The catalyst used in the above reduction reaction is preferably a commercially available metal supported on activated carbon, such as palladium-activated carbon, platinum-activated carbon, rhodium-activated carbon, and the like. The catalyst does not necessarily have to be an activated carbon-supported metal catalyst, such as palladium hydroxide, platinum oxide, or Raney nickel. Palladium-activated carbon, which is commonly used, is preferred because it gives good results.

In order to make the reduction reaction proceed more effectively, the reaction may be carried out in the presence of activated carbon. At this time, the amount of activated carbon used is not particularly limited, but is preferably in the range of 1 to 30% by mass, more preferably 10 to 20% by mass, based on the dinitro compound X1. For similar reasons, the reaction may also be carried out under pressure. In this case, in order to avoid reduction of benzene nuclei, the reaction is preferably carried out at a pressure of up to 20 atm, more preferably up to 10 atm.

The solvent can be used without any restriction as long as it does not react with each raw material. For example, aprotic polar organic solvents (dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dimethyl acetate (DMAc), N-methylpyrrolidone (NMP), etc.), ethers (diethyl ether ( _Et2O ), diisopropyl (i-Pr ₂ O), tetrabutyl methyl ether (TBME), cyclopentyl methyl ether (CPME), tetrahydrofuran (THF), dioxane, etc.); aliphatic hydrocarbons (pentane, hexane, heptane, petroleum ether, etc.); Aromatic hydrocarbons (benzene, toluene, xylene, mesitylene, chlorobenzene, dichlorobenzene, nitrobenzene, tetralin, etc.); Halogenated hydrocarbons (chloroform, dichloromethane, carbon tetrachloride, dichloroethane, etc.); Lower fatty acid esters (methyl acetate, etc.) , ethyl acetate, butyl acetate, methyl propionate, etc.); nitriles (acetonitrile, propionitrile, butyronitrile, etc.); and the like can be used.

These solvents can be appropriately selected in consideration of the ease with which the reaction occurs, and can be used alone or in a mixture of two or more. If necessary, the solvent can be dried using an appropriate dehydrating agent or drying agent and used as a non-aqueous solvent.
The amount of the solvent used (reaction concentration) is not particularly limited, but it is usually 0.1 to 10 times the amount by mass, preferably 0.5 to 30 times the amount by mass, and more preferably 1 to 10 times the amount by mass of the dinitro compound. It's double. The reaction temperature is not particularly limited, but is usually in the range from -100°C to the boiling point of the solvent used, preferably -50 to 150°C. The reaction time is usually 0.05 to 350 hours, preferably 0.5 to 100 hours.

The dinitro compound (2-1-N) can be synthesized by a known reaction using, for example, 4-bromonitrobenzene and a corresponding amine according to the reaction formula below.

<Specific polymer>
The polymer contained in the liquid crystal aligning agent of the present invention is a polymer obtained using the above-mentioned specific diamine. Specific examples include polyamic acid, polyamic acid ester, polyimide, polyurea, polyamide, etc., but from the viewpoint of use as a liquid crystal aligning agent, a polyimide precursor having a structural unit represented by the following formula (4), and/or at least one kind of polymer selected from polyimide which is an imidized product thereof (hereinafter also referred to as a specific polymer) is more preferable.

In the above formula, X ¹ is a tetravalent organic group derived from a tetracarboxylic acid derivative, and Y ¹ is a divalent organic group derived from a specific diamine. R ⁵ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. From the viewpoint of ease of imidization by heating, R ⁵ is preferably a hydrogen atom, a methyl group, or an ethyl group.

The ^above -mentioned They are selected as appropriate, and two or more types may be present in the same polymer.
Specific examples of X ¹ include structures of formulas (X-1) to (X-46) published on pages 13 to 14 of International Publication No. 2015/119168.

Preferred examples of X ¹ (A-1) to (A-21) are shown below, but the invention is not limited thereto.

Among the above, (A-1) and (A-2) are particularly preferred from the viewpoint of further improving the film hardness, and (A-4) is particularly preferred from the viewpoint of further improving the relaxation rate of accumulated charges. A-15) to (A-17) are particularly preferred from the viewpoint of further improving the liquid crystal orientation and the relaxation rate of accumulated charges.

<Other structural units>
In addition to the structural unit represented by formula (4), the polyimide precursor may have a structural unit represented by formula (5) below.

X ² is the same as the definition of X ¹ in the above formula (4). Specific examples of X ² include the same ones as exemplified for X ¹ in formula (4), including preferred examples. Each of R ⁶ is the same as the definition of R ⁵ in the above formula (4). R ⁷ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Moreover, it is preferable that at least one of the two R ^7s is a hydrogen atom.

Further, Y ² is a divalent organic group derived from a diamine that does not include the structure represented by formula (1) in the main chain direction, and its structure is not particularly limited. ^Y2 is determined as appropriate depending on the degree of required properties, such as the solubility of the polymer in a solvent, the applicability of the liquid crystal alignment agent, the alignment of the liquid crystal when used as a liquid crystal alignment film, the voltage holding rate, and the accumulated charge. selected, and two or more types may be mixed in the same polymer.

To give specific examples of Y ² , the structure of formula (2) published on page 4 of International Publication No. 2015/119168, and the structure of formula (Y-1) ~ ( published on pages 8 to 12) Structures of Y-97), (Y-101) to (Y-118); divalent organic group obtained by removing two amino groups from formula (2), published on page 6 of International Publication No. 2013/008906 ; Divalent organic group obtained by removing two amino groups from formula (1) published on page 8 of International Publication Publication 2015/122413; Formula (3) published on page 8 of International Publication Publication 2015/060360 Structure: Divalent organic group obtained by removing two amino groups from the formula (1) described on page 8 of Japanese Patent Publication No. 2012-173514; Formula ( Examples include divalent organic groups obtained by removing two amino groups from A) to (F).

Preferred structures of Y ² , formulas (B-1) to (B-20), are shown below, but the present invention is not limited thereto.

Among the above structures, (B-28) and (B-29) are particularly preferable from the viewpoint of further improving the film hardness, and (B-1) to (B-3) are particularly preferable from the viewpoint of further improving the liquid crystal orientation. (B-14) to (B-18) and (B-27) are particularly preferable from the perspective of further improving the relaxation rate of accumulated charge, and (B-26) is particularly preferable from the perspective of further improving the relaxation rate of accumulated charges. This is preferable from the viewpoint of further improving the ratio.

When the polyimide precursor contains a structural unit represented by formula (5) in addition to the structural unit represented by formula (4), the structural unit represented by formula (4) is the structural unit represented by formula (4). It is preferably 10 mol % or more, more preferably 20 mol % or more, particularly preferably 30 mol % or more based on the total of formula (5).
The weight average molecular weight (Mw) of the polyimide precursor used in the present invention is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and even more preferably 10,000 to 100. ,000.

<Polyimide>
Polyimide among the specific polymers is obtained by ring-closing polyimide precursors represented by formulas (4) and (5). The imidization rate in this case does not necessarily have to be 100%, and can be arbitrarily adjusted depending on the use and purpose.
Known methods can be used to imidize the polyimide precursor. Chemical imidization, which involves adding a basic catalyst to a solution of a polyimide precursor, is simple. 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 performed by stirring the polyimide precursor in an organic solvent in the presence of a basic catalyst. As the organic solvent, the solvent used in the polymerization reaction described above can be used. Examples of the basic catalyst include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Among these, triethylamine is preferred because it has sufficient basicity to advance the reaction.
The temperature during the imidization reaction is -20 to 140°C, preferably 0 to 100°C, and the reaction time is preferably 1 to 100 hours. The amount of the basic catalyst is 0.5 to 30 times, preferably 2 to 20 times by mole, the amount of the amic acid ester group. The imidization rate of the obtained polymer can be controlled by adjusting the amount of catalyst, temperature, reaction time, etc. Since the added catalyst and the like remain in the solution after the imidization reaction, the obtained imidized polymer is recovered by the means described below and redissolved in an organic solvent to form the liquid crystal alignment of the present invention. It is preferable to use it as an agent.

Since the added catalyst, etc. remain in the solution after the imidization reaction of the polyimide precursor, the resulting imidized polymer is recovered by the method described below, redissolved in an organic solvent, and then processed into the present invention. It is preferable to use it as a liquid crystal aligning agent of the invention.
The polyimide solution obtained as described above can be poured into a poor solvent with thorough stirring to precipitate the polymer. A purified polyimide powder can be obtained by performing precipitation several times, washing with a poor solvent, and drying at room temperature or by heating.
Examples of the poor solvent include, but are not limited to, methanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, benzene, and the like.

<Liquid crystal alignment agent>
Although the liquid crystal aligning agent of the present invention contains a specific polymer, it may contain two or more types of specific polymers having different structures. Moreover, in addition to the specific polymer, other polymers may be contained. Other types of polymers include polyamic acids, polyimides, polyamic acid esters, polyesters, polyamides, polyureas, polyorganosiloxanes, cellulose derivatives, polyacetals, polystyrene or its derivatives, poly(styrene-phenylmaleimide) derivatives, poly(meth) ) acrylate, etc. Further, it may contain a polyimide selected from a polyimide precursor represented by the above formula (5) and/or a polyimide obtained by imidizing the polyimide precursor.

When the liquid crystal aligning agent of the present invention contains other polymers, the ratio of the specific polymer to the total polymer components is preferably 5% by mass or more, more preferably 5 to 95% by mass.
A liquid crystal aligning agent is used for producing a liquid crystal aligning film, and generally takes the form of a coating liquid from the viewpoint of forming a uniform thin film. Also in the liquid crystal aligning agent of the present invention, it is preferable that it is a coating liquid containing the above-described polymer component and an organic solvent that dissolves this polymer component. At that time, the concentration of the polymer in the liquid crystal aligning agent can be changed as appropriate depending on the thickness of the coating film to be formed. From the viewpoint of forming a uniform and defect-free coating film, the content is preferably 1% by mass or more, and from the viewpoint of storage stability of the solution, the content is preferably 10% by mass or less. Particularly preferred polymer concentrations are 2 to 8% by weight.

The organic solvent contained in the liquid crystal aligning agent is not particularly limited as long as the polymer component is uniformly dissolved therein. Specific examples include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylsulfoxide, γ-butyrolactone, 1,3-dimethyl -Imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, etc. may be mentioned. Among them, it is preferable to use N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone.

In addition, the organic solvent contained in the liquid crystal aligning agent is a mixed solvent containing the above solvents and a solvent that improves the coating properties and surface smoothness of the coating film when applying the liquid crystal aligning agent. Generally, such a mixed solvent is suitably used in the liquid crystal aligning agent of the present invention. Specific examples of organic solvents used in combination are listed below, 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-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentane Diol, 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, 4-hydroxy-4-methyl-2-pentanone, 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-(methoxymethoxy)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 mono Ethyl 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 monoethyl acetate, methyl pyruvate, pyruvic acid Ethyl, methyl 3-methoxypropionate, methylethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, 3-ethoxypropionic acid, 3-methoxypropionic acid, propyl 3-methoxypropionate, butyl 3-methoxypropionate, Examples include methyl lactate, ethyl ester, n-propyl ester, n-butyl ester, isoamyl lactate, and solvents represented by the following formulas [D-1] to [D-3].

In formula [D-1], D ¹ represents an alkyl group having 1 to 3 carbon atoms, in formula [D-2], D ² represents an alkyl group having 1 to 3 carbon atoms, and in formula [D-3] Among them, D ³ represents an alkyl group having 1 to 4 carbon atoms. Among them, 1-hexanol, cyclohexanol, 1,2-ethanediol, 1,2-propanediol, propylene glycol monobutyl ether, diethylene glycol diethyl ether, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monobutyl ether or Dipropylene glycol dimethyl ether is preferred. The type and content of such a solvent are appropriately selected depending on the liquid crystal aligning agent coating device, coating conditions, coating environment, and the like.

The liquid crystal aligning agent of the present invention may additionally contain components other than the polymer component and the organic solvent. Such additional components include an adhesion aid to improve the adhesion between the liquid crystal alignment film and the substrate and the adhesion between the liquid crystal alignment film and the sealing material, a crosslinking agent to increase the strength of the liquid crystal alignment film, and a liquid crystal alignment agent. Examples include dielectric materials and conductive materials for adjusting the dielectric constant and electrical resistance of the film. Specific examples of these additional components are disclosed in various known documents regarding liquid crystal aligning agents, but one example is WO 2015/060357, pages 53 [0105] to 55 [ 0116] and the like.

<Liquid crystal alignment film>
The liquid crystal aligning film of the present invention is obtained from the liquid crystal aligning agent of the present invention. An example of a method for obtaining a liquid crystal alignment film from a liquid crystal alignment agent is to apply a liquid crystal alignment agent in the form of a coating liquid to a substrate, dry it, and bake it, then apply a rubbing treatment or photo alignment treatment to the resulting film. An example of this method is to perform an orientation treatment.
The substrate to which the liquid crystal alignment agent is applied is not particularly limited as long as it is a highly transparent substrate, and a glass substrate, a silicon nitride substrate, a plastic substrate such as an acrylic substrate or a polycarbonate substrate, etc. can also be used. In this case, it is preferable to use a substrate on which ITO electrodes and the like for driving the liquid crystal are formed, from the viewpoint of process simplification. Furthermore, in a reflective liquid crystal display element, an opaque material such as a silicon wafer can be used as long as only one substrate is used, and a material that reflects light such as aluminum can also be used for the electrodes in this case.

The method for applying the liquid crystal aligning agent is not particularly limited, but screen printing, offset printing, flexographic printing, inkjet methods, etc. are commonly used industrially. Other coating methods include a dip method, a roll coater method, a slit coater method, a spinner method, and a spray method, and these may be used depending on the purpose.
After applying the liquid crystal aligning agent onto the substrate, the solvent is evaporated and baked using a heating means such as a hot plate, a thermal circulation oven, or an IR (infrared) oven. Any temperature and time can be selected for the drying and baking steps after applying the liquid crystal aligning agent. Usually, in order to sufficiently remove the contained solvent, conditions include firing at 50 to 120°C for 1 to 10 minutes, and then firing at 150 to 300°C for 5 to 120 minutes.

The thickness of the liquid crystal alignment film after firing is not particularly limited, but if it is too thin, the reliability of the liquid crystal display element may decrease, so it is preferably 5 to 300 nm, more preferably 10 to 200 nm.
The liquid crystal alignment film of the present invention is suitable as a liquid crystal alignment film for a horizontal electric field type liquid crystal display element such as an IPS type or an FFS type, and is particularly useful as a liquid crystal alignment film for an FFS type liquid crystal display element.

<Liquid crystal display element>
The liquid crystal display element of the present invention is obtained by obtaining a substrate with a liquid crystal alignment film obtained from the above-mentioned liquid crystal aligning agent, then producing a liquid crystal cell by a known method, and using the liquid crystal cell to form an element.
As an example of a method for manufacturing a liquid crystal cell, a liquid crystal display element having a passive matrix structure will be described as an example. Note that it may be an active matrix liquid crystal display element in which a switching element such as a TFT (Thin Film Transistor) is provided in each pixel portion constituting an image display.

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

Next, an ultraviolet curable sealing material, for example, was placed at a predetermined location on one of the two substrates on which the liquid crystal alignment film was formed, and liquid crystals were further placed at several predetermined locations on the surface of the liquid crystal alignment film. After that, the other substrate is attached and pressure-bonded so that the liquid crystal alignment films face each other, and the liquid crystal is spread out in front of the liquid crystal alignment film.The entire surface of the substrate is irradiated with ultraviolet rays to harden the sealing material. Get a cell.
Alternatively, as a step after forming a liquid crystal alignment film on the substrate, when placing a sealant at a predetermined location on one substrate, an opening that can be filled with liquid crystal from the outside is provided, and the liquid crystal is filled with the liquid crystal. After bonding the substrates together without arranging them, a liquid crystal material is injected into the liquid crystal cell through an opening provided in the sealing material, and then this opening is sealed with an adhesive to obtain a liquid crystal cell. The liquid crystal material may be injected by a vacuum injection method or by a method utilizing capillary action in the atmosphere.

In any of the above methods, in order to secure the space in which the liquid crystal material is filled in the liquid crystal cell, columnar projections are provided on one substrate, spacers are sprinkled on one substrate, or sealing material is It is preferable to take measures such as mixing a spacer into the material or combining these methods.
Examples of the above-mentioned liquid crystal materials include nematic liquid crystals and smectic liquid crystals, among which nematic liquid crystals are preferred, and either positive-type liquid crystal materials or negative-type liquid crystal materials may be used. Next, a polarizing plate is installed. Specifically, it is preferable to attach a pair of polarizing plates to the surfaces of the two substrates opposite to the liquid crystal layer.

In addition, the liquid crystal alignment film and liquid crystal display element of the present invention are not limited to the above description as long as the liquid crystal aligning agent of the present invention is used, and even those produced by other known methods may be used. good. The process of obtaining a liquid crystal display element from a liquid crystal aligning agent is disclosed, for example, in paragraphs 0074 on page 17 to paragraph 0081 on page 19 of Japanese Patent Application Publication No. 2015-135393.

The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.
In addition, the abbreviations of compounds and solvents are as follows.
NMP: N-methyl-2-pyrrolidone, GBL: γ-butyrolactone,
BCS: butyl cellosolve, DA-1 to DA-9: compounds with the following structural formula,
CA-1, CA-2: Compounds with the following structural formula,
AD-1: 3-glycidoxypropyltriethoxysilane AD-2, AD-3: Compounds with the following structural formula

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

<Measurement of imidization rate>
The imidization rate of polyimide was measured as follows. 30 mg of polyimide powder was placed in an NMR (nuclear magnetic resonance) sample tube (NMR sampling tube standard, φ5, manufactured by Kusano Scientific Co., Ltd.), and deuterated dimethyl sulfoxide (DMSO-d6, 0.05% by mass TMS (tetramethylsilane) was mixed with the tube. 0.53 ml of the product was added and completely dissolved by applying ultrasonic waves.Proton NMR of this solution was measured at 500 MHz using an NMR measuring machine (JNW-ECA500, manufactured by JEOL Datum Co., Ltd.).The imidization rate was , a proton derived from a structure that does not change before and after imidization is determined as a reference proton, and the peak integrated value of this proton and the proton peak integrated value derived from the NH group of amic acid appearing around 9.5 ppm to 10.0 ppm are calculated. It was calculated using the following formula.
Imidization rate (%) = (1-α・x/y)×100
In the above formula, x is the integrated value of the proton peak derived from the NH group of the amic acid, y is the integrated peak value of the standard proton, and α is the NH of the amic acid in the case of polyamic acid (imidization rate is 0%). It is the ratio of the number of reference protons to one base proton.

(Synthesis example 1)

Synthesis of Compound [1] DA-1 (50.0 g, 234 mmol) was placed in tetrahydrofuran (500 g) and dimethylformamide (125 g), and trifluoroacetic anhydride (103 g) was added dropwise over 1 hour under ice cooling. After the dropwise addition was completed, the mixture was stirred at room temperature for 30 minutes. After most of the tetrahydrofuran was distilled off under reduced pressure, ethyl acetate (300 mL) was added, washed three times with saturated aqueous sodium bicarbonate solution (250 mL), washed with saturated brine (250 mL), dehydrated with sodium sulfate, and the filtrate Compound [1] was obtained by concentrating (yield: 76.5 g, yield: 81%, blue-white crystals).
1H-NMR (400MHz, DMSO-d6, δppm): 11.16(s, 2H), 7.57(d, 4H, J = 9.2 Hz), 7.04(d, 4H, J = 9.2 Hz), 3.26(s, 3H) .

Synthesis of Compound [2] Compound [1] (76.5 g, 189 mmol), potassium carbonate (78.4 g), and methyl iodide (80.5 g) were added to acetonitrile (300 g), and the mixture was stirred at room temperature for 68 hours. . The crystals were separated by filtration and the filtered material was dried to obtain Compound [2] (yield: 83.3 g, crude yield: 102%, pale white crystals). The next step was carried out using compound [2] as a crude product.
1H-NMR (400MHz, DMSO-d6, δppm): 7.35(d, 4H, J = 8.8 Hz), 7.09(d, 4H, J = 8.8 Hz), 3.32(s, 3H), 3.27(s, 6H) .

Synthesis of Compound [3] Compound [2] (83.3 g) and potassium carbonate (52.2 g) were added to methanol (416 g) and pure water (208 g), and the mixture was stirred at 70° C. for 2 hours. After about 70% of methanol was distilled off under reduced pressure, pure water (300 g) and ethyl acetate (400 g) were added, and the organic layer was separated and extracted. The mixture was separated and washed with pure water (200 g), dehydrated with sodium sulfate, and the filtrate was concentrated to obtain a crude product. Isopropyl alcohol (168 g) was added to the crude product, and the mixture was completely dissolved at 75° C., then cooled, filtered, and the filtrate was dried to obtain compound [3] (yield: 27.0 g, Yield: 59% (based on compound [1], gray crystals).
1H-NMR (400MHz, DMSO-d6, δppm): 6.69(d, 4H, J = 8.8 Hz), 6.45(d, 4H, J = 8.8 Hz), 5.22-5.19(m, 2H), 3.02(s, 3H), 2.62(d, 6H, J = 5.2Hz).

Synthesis of compound [4] In NMP (350 g), compound [3] (35.0 g), 4-bromonitrobenzene (61.5 g), potassium phosphate (92.3 g), palladium acetate (0.65 g), and Bis[2-(diphenylphosphino)phenyl]ether (1.56 g) was added and stirred at 100°C for 2 hours. After the reaction solution was cooled, it was poured into pure water (1400 g), stirred at room temperature, and then filtered. The filtrate was washed as a slurry with a mixed solvent of pure water (175 g) and ethyl acetate (350 g), and then filtered, the slurry was washed with methanol (350 g), filtered, and the filtrate was dried to obtain a crude product. Ta. Dimethylformamide (235 g) was added to this crude product, and the mixture was stirred at 100° C., then methanol (336 g) was added, cooled, filtered, and the filtered product was dried. Dimethylformamide (230 g) was added again and the mixture was stirred at 100° C., and methanol (336 g) was added to the filtrate which was filtered while hot, followed by cooling and filtration. The filtrate was slurried washed with methanol (200 g) and dried to obtain compound [4] (yield: 56.7 g, yield: 81%, ocher crystals).
1H-NMR (400MHz, DMSO-d6, δppm): 8.06(d, 4H, J = 9.6 Hz), 7.25(d, 4H, J = 8.8 Hz), 7.17(d, 4H, J = 8.8 Hz), 6.76 (d, 4H, J = 9.6 Hz), 3.37(s, 6H), 3.34(s, 3H).

Synthesis of [DA-2] In dimethylformamide (360 g), compound [4] (36.0 g, 74.5 mmol) and 5% palladium carbon (3.6 g) were charged, and in an autoclave under a 0.4 MPa hydrogen atmosphere, The mixture was stirred at 40°C for 12 hours. After hot filtration of the catalyst at 80° C., the total internal weight was reduced to 189 g by vacuum concentration. After completely dissolving at 100°C, methanol (220g) was added to precipitate crystals, stirred at room temperature, filtered, and dried to obtain compound [DA-2] (yield: 23.5g, Yield: 74%, light brown crystals).
1H-NMR (400MHz, DMSO-d6, δppm): 6.77(d, 4H, J = 8.8 Hz), 6.74(d, 4H, J = 9.2 Hz), 6.62(d, 4H, J = 9.2 Hz), 6.54 (d, 4H, J = 8.8 Hz), 4.88(br, 4H), 3.08(s, 3H), 3.07(s, 6H).

(Synthesis example 2)
In a 50 mL eggplant flask equipped with a stirrer and a nitrogen inlet tube, add 2.03 g (4.8 mmol) of DA-2, 0.96 g (4.8 mmol) of DA-3, and 0.72 g (2 mmol) of DA-4. 0.4 mmol) was weighed out, 35.0 g of NMP was added, and the mixture was stirred and dissolved while supplying nitrogen. While stirring this diamine solution under water cooling, 3.22 g (10.9 mmol) of CA-1 was added, and further 15.0 g of NMP was added, and the mixture was stirred at 70°C for 11 hours under a nitrogen atmosphere to form a polymer solution A-1. (Viscosity: 390 mPa·s) was obtained.

(Synthesis example 3)
In a 50 mL eggplant flask equipped with a stirrer and a nitrogen inlet tube, add 1.02 g (4.8 mmol) of DA-1, 0.96 g (4.8 mmol) of DA-3, and 0.72 g (2 g of DA-4). .4 mmol) was weighed out, 30.5 g of NMP was added, and the mixture was stirred and dissolved while supplying nitrogen. While stirring this diamine solution under water cooling, 3.39 g (11.5 mmol) of CA-1 was added, and further 13.1 g of NMP was added, and the mixture was stirred at 70°C for 5 hours under a nitrogen atmosphere to form a polymer solution B-1. (Viscosity: 420 mPa·s) was obtained.

(Synthesis example 4)
In a 100 mL eggplant flask equipped with a stirrer and nitrogen inlet tube, add 1.67 g (8.4 mmol) of DA-3, 1.25 g (4.2 mmol) of DA-4, and 3.54 g (5.5 g) of DA-5. .24 mmol) was weighed out, 63.3 g of NMP was added, and the mixture was stirred and dissolved while supplying nitrogen. While stirring this diamine solution under water cooling, 5.98 g (20.3 mmol) of CA-1 was added, and further 27.1 g of NMP was added, and the mixture was stirred at 70°C for 10 hours under a nitrogen atmosphere to form a polymer solution B-2. (Viscosity: 500 mPa·s) was obtained.

(Synthesis example 5)
In a 3L four-neck flask equipped with a stirrer and a nitrogen inlet tube, add 17.3 g (159 mmol) of DA-6, 58.6 g (240 mmol) of DA-7, 76.8 g (240 mmol) of DA-8, and diamine DA. 54.6 g (160 mmol) of -9 was weighed out, 2458 g of NMP was added thereto, and the mixture was stirred and dissolved while supplying nitrogen. While stirring this diamine solution, 171 g (764 mmol) of CA-2 was added, and further NMP was added so that the solid content concentration was 12% by mass, and the mixture was stirred at 40°C for 20 hours. Viscosity: 426 mPa·s) was obtained.
2250 g of this polyamic acid solution was collected, 750 g of NMP was added, 171 g of acetic anhydride and 35.4 g of pyridine were added, and the mixture was reacted at 55° C. for 3 hours. This reaction solution was poured into 9620 g of methanol, and the generated precipitate was filtered off. This precipitate was washed with methanol and dried under reduced pressure at 60°C to obtain a polyimide powder. The imidization rate of this polyimide was 66%. 440 g of NMP and 440 g of GBL were added to 120 g of the obtained polyimide powder and dissolved by stirring at 70° C. for 20 hours to obtain a polymer solution C-1.

(Examples 1 and 2) and (Comparative Examples 1 and 2)
NMP, GBL, BCS, AD- A GBL solution containing 1% by weight of 1, an NMP solution containing 10% by weight of AD-2, and AD-3 were added with stirring so that the composition was as shown in Table 1 below, and the mixture was further stirred at room temperature for 2 hours. By this, liquid crystal aligning agents of Examples 1 and 2 and Comparative Examples 1 and 2 were obtained.

Using the liquid crystal aligning agent obtained above, an FFS drive liquid crystal cell was produced according to the procedure shown below, and the backlight aging resistance of the DC accumulation amount was evaluated.
[Configuration of FFS drive liquid crystal cell]
A liquid crystal cell for fringe field switching (FFS) mode has a FOP (Finger on Plate) electrode layer formed on its surface, which consists of a planar common electrode, an insulating layer, and a comb-shaped pixel electrode. A pair of the glass substrate No. 1 and a second glass substrate having columnar spacers with a height of 4 μm on the front surface and an ITO film for preventing static electricity formed on the back surface were made into a set. The above pixel electrode has a comb-teeth shape in which a plurality of electrode elements each having a width of 3 μm and whose central portion is bent at an internal angle of 160° are arranged in parallel with an interval of 6 μm. It has a first region and a second region separated by a line connecting the bent portions of the plurality of electrode elements.
The liquid crystal alignment film formed on the first glass substrate is aligned so that the direction that equally divides the internal angle of the pixel bend and the alignment direction of the liquid crystal are perpendicular to each other, and the liquid crystal alignment film formed on the second glass substrate is The film is aligned so that the alignment direction of the liquid crystal on the first substrate matches the alignment direction of the liquid crystal on the second substrate when the liquid crystal cell is produced.

[Preparation of liquid crystal cell]
A liquid crystal aligning agent filtered through a filter with a pore size of 1.0 μm was applied on the surface of each of the above pair of glass substrates by spin coating, and dried on a hot plate at 80° C. for 2 minutes. After that, the coated film surface was irradiated with a predetermined amount of linearly polarized ultraviolet light with a wavelength of 254 nm with an extinction ratio of 26:1 through a polarizing plate, and then baked in a hot air circulation oven at 230°C for 30 minutes to form a liquid crystal film with a thickness of 100 nm. A substrate with an alignment film was obtained.
Next, a sealant was printed on one of the above-mentioned pair of glass substrates with a liquid crystal alignment film, and the other substrate was bonded so that the liquid crystal alignment film surfaces faced each other, and the sealant was cured to prepare an empty cell. Liquid crystal MLC-3019 (manufactured by Merck & Co., Ltd.) was injected into this empty cell by a reduced pressure injection method, and the injection port was sealed to obtain an FFS-driven liquid crystal cell. Thereafter, the obtained liquid crystal cell was heated at 120° C. for 1 hour, left overnight, and then the afterimage characteristics were evaluated.
This liquid crystal cell had no defects in liquid crystal alignment, and the liquid crystal alignment state was good.

[Backlight aging resistance of DC storage amount]
The above liquid crystal cell is installed between two polarizing plates arranged so that the polarization axes are perpendicular to each other, and with the pixel electrode and the counter electrode short-circuited to have the same potential, the LED back is illuminated from below the two polarizing plates. The liquid crystal cell was irradiated with light, and the angle of the liquid crystal cell was adjusted so that the brightness of the transmitted light from the LED backlight measured on the two polarizing plates was minimized.
Next, a VT curve (voltage-transmittance curve) was measured while applying an AC voltage with a frequency of 30 Hz to this liquid crystal cell, and the AC voltage at which the relative transmittance was 23% or 100% was calculated as the driving voltage. The temperature of the liquid crystal cell was raised to 60° C., and a 20 mV square wave was applied at a frequency of 1 kHz for 30 minutes.
Thereafter, AC driving with a relative transmittance of 100% was applied for 30 minutes, and while measuring the minimum offset voltage value every 3 minutes during that time, the amount of change from the start of measurement until 30 minutes later was calculated as the initial DC accumulation amount.

Furthermore, the sample was left on the LED backlight panel for 24 hours, and the minimum offset voltage value was measured in the same manner as above, which was defined as the DC accumulation amount after aging. The smaller the difference between this accumulated amount and the initial DC accumulated amount, the better the backlight aging resistance.
Table 2 below shows the evaluation results of the DC accumulation amount carried out as described above for the liquid crystal display elements using each of the liquid crystal alignment agents of Examples 1 and 2 and Comparative Examples 1 and 2.

It can be seen that the liquid crystal display elements using the liquid crystal aligning agents of Examples 1 and 2 of the present invention have a small change in DC accumulation amount due to backlight irradiation and have good backlight aging resistance.

The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2018-074928 filed on April 9, 2018 are cited here as disclosure of the specification of the present invention. , is something to be taken in.

Claims (9)

A diamine having a structure represented by the following formula (1) and represented by the following formula (2-1), formula (2-2), or formula (2-3) and a tetracarboxylic dianhydride; A liquid crystal aligning agent characterized by containing at least one polymer selected from the group consisting of a polyimide precursor which is a polycondensate thereof and a polyimide which is an imidized product thereof, and an organic solvent.

(R ¹ represents hydrogen, an alkyl group, an alkenyl group, an alkoxy group, a fluoroalkyl group, a fluoroalkenyl group, or a fluoroalkoxy group having 1 to 4 carbon atoms, and two R ¹ 's may be the same or different. (However, at least one of them is not hydrogen. * indicates a bonding site to another group. Any hydrogen atom in the benzene ring may be substituted with a monovalent organic group.)

(The definition of R ¹ is the same as the above formula (1), R ² represents a single bond or a structure represented by the following formula (3), and n represents an integer of 1 to 3. Any hydrogen atom may be substituted with a monovalent organic group.

(R ³ is a single bond, -O-, -COO-, -OCO-, -(CH ₂ ) _l -, -O(CH ₂ ) _m O-, -CONR-, and -NRCO- 2 represents a valent organic group, k represents an integer of 1 to 5. R represents hydrogen or a monovalent organic group, l and m represent an integer of 1 to 5. * ₁ represents formula (2-1) ~Represents the site that binds to the benzene ring in formula (2-3), and * ₂ represents the site that binds to the amino group in formula (2-1) ~ formula (2-3).)) The liquid crystal aligning agent according to claim 1, wherein R ¹ in the formula (1), formula (2-1), formula (2-2), and formula (2-3) is hydrogen or a methyl group. The liquid crystal aligning agent according to claim 1 or 2, wherein the polyimide precursor has a structural unit represented by the following formula (4).

(X ¹ is a tetravalent organic group derived from a tetracarboxylic acid derivative, Y ¹ has a structure represented by the above formula (1), and has the structure represented by the above formula (2-1), formula (2-2) , or a divalent organic group derived from a diamine represented by formula (2-3), and R ⁵ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.) The liquid crystal aligning agent according to claim 3, wherein in the formula (4), X ¹ is at least one selected from the group consisting of the following (A-1) to (A-21).

The liquid crystal aligning agent according to claim 3 or 4, wherein the polymer having the structural unit represented by the formula (4) is contained in an amount of 10 mol% or more based on the total polymer contained in the liquid crystal aligning agent. The liquid crystal aligning agent according to any one of claims 1 to 5, wherein the organic solvent contains at least one selected from the group consisting of 4-hydroxy-4-methyl-2-pentanone and diethylene glycol diethyl ether. A liquid crystal aligning film obtained from the liquid crystal aligning agent according to any one of claims 1 to 5 . A liquid crystal display element comprising the liquid crystal alignment film according to claim 7. 9. The liquid crystal display element according to claim 8, wherein the liquid crystal display element is of a transverse electric field drive type.