WO2020040091A1 - Liquid crystal alignment agent, production method thereof, liquid crystal alignment film, and liquid crystal display element - Google Patents

Abstract

A liquid crystal alignment agent is provided which, even when reducing the light irradiation amount in alignment treatment by the photo-alignment method, enables obtaining excellent afterimage characteristics in an IPS-driven or FFS-driven liquid crystal display element; a production method of the liquid crystal alignment agent, a liquid crystal alignment film obtained therefrom, and a liquid crystal display element provided therewith are also provided. This liquid crystal alignment agent contains a polyimide, which is the imidized product of a polyimide precursor obtained from a polycondensation reaction of: a tetracarboxylic acid component that contains tetracarboxylic dianhydride represented by formula (1), or a derivative thereof; and a diamine component that contains a first diamine represented by formula (3) and a second diamine represented by formula (4). (X₁ is a structure represented by formula (X1-1) or (X1-2).) (R₃-R₁₂ are independently a hydrogen atom, a halogen atom, an alkyl group of 1-6 carbons, an alkenyl group of 2-6 carbons, an alkynyl group of 2-6 carbons, a monovalent organic group of 1-6 carbons containing a fluorine atom, or a phenyl group, but at least one of R₃-R₆ is a group in the aforementioned definition other than a hydrogen atom.) (The A₂'s are independently a halogen atom, a hydroxyl group, an amino group, a thiol group, a nitro group, a phosphate group, or a monovalent organic group of 1-20 carbons, a is an integer 0-4, if there are multiple A₂'s, then the structure of the A₂'s may be the same or different.)

Description

Liquid crystal alignment agent, method for producing the same, liquid crystal alignment film, and liquid crystal display element

The present invention relates to a liquid crystal alignment agent, a method for producing the same, a liquid crystal alignment film obtained therefrom, and a liquid crystal display device including the obtained liquid crystal alignment film.

(4) A liquid crystal display element used for a liquid crystal television, a liquid crystal display, or the like usually has a liquid crystal alignment film for controlling an alignment state of liquid crystal provided in the element. At present, the most widely used liquid crystal alignment film in the industry is to coat the surface of a film made of polyamic acid and / or polyimide obtained by imidizing the same with a cloth of cotton, nylon, polyester or the like. It is manufactured by performing a process of rubbing in a direction, a so-called rubbing process.

Rubbing treatment is a simple and industrially useful method with excellent productivity. However, with the high performance, high definition, and large size of the liquid crystal display device, scratches and dust on the surface of the alignment film generated by the rubbing process, the effects of mechanical force and static electricity, and the surface of the alignment process Various problems such as internal non-uniformity have been clarified. As an alternative to the rubbing treatment, a photo-alignment method for imparting liquid crystal alignment ability by irradiating polarized ultraviolet light is known. As the liquid crystal alignment treatment by the photo-alignment method, those using a photoisomerization reaction, those using a photocrosslinking reaction, those using a photolysis reaction, and the like have been proposed.

Patent Document 1 proposes using a polyimide film having an alicyclic structure such as a cyclobutane ring in a main chain for a photo-alignment method. In this optical alignment method, the obtained liquid crystal alignment film can be expected to improve the contrast and the viewing angle characteristics of a liquid crystal display element of an IPS driving method or a fringe field switching (hereinafter, FFS) driving method, as compared with the rubbing treatment method. Therefore, it attracted attention as a promising liquid crystal alignment treatment method.

The liquid crystal alignment film used for the IPS drive type or FFS drive type liquid crystal display element has not only basic characteristics such as excellent liquid crystal alignment and electrical characteristics but also an alignment regulating force for suppressing an afterimage generated by long-term driving. However, the liquid crystal alignment film obtained by the photo-alignment method has a problem that the alignment control force is weaker than the liquid crystal alignment film obtained by the rubbing treatment. In the liquid crystal alignment film obtained by utilizing the photodecomposition reaction, the low molecular weight component generated by photolysis is considered to be a cause of lowering the alignment regulating force, and the low molecular weight component is removed by heat treatment or cleaning treatment. A method has been proposed (Patent Document 2).

However, in the production of the liquid crystal display element, it is necessary to add a heat treatment step and a cleaning treatment step in order to remove the low molecular weight components as described above, which leads to an increase in the production steps of the liquid crystal display element. Was. On the other hand, a method of manufacturing a liquid crystal alignment film has been proposed in which afterimages due to long-term driving can be suppressed even with a small number of steps, and there is no problem caused by low molecular weight components (Patent Document 3).

Japanese Patent Application Laid-Open No. 9-297313 Japanese Patent Application Laid-Open No. 2011-107266 WO2018 / 117239

(4) When the alignment treatment is performed by the photo-alignment method, the irradiation amount of light is a factor that affects the energy cost and the production speed. However, there is a problem that even if the liquid crystal aligning agent provides good afterimage characteristics, the afterimage characteristics become insufficient when the light irradiation amount is reduced.

Accordingly, an object of the present invention is to provide a liquid crystal aligning agent capable of obtaining good afterimage characteristics even when the light irradiation amount in the alignment treatment by the optical alignment method is reduced, and obtaining a stable liquid crystal aligning ability of good quality, and its production. It is an object of the present invention to provide a method, a liquid crystal alignment film obtained therefrom, and a liquid crystal display device provided with the obtained liquid crystal alignment film.

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that the above object can be achieved by the invention having the following gist.
A tetracarboxylic acid component containing a tetracarboxylic dianhydride represented by the following formula (1) or a derivative thereof, a first diamine represented by the following formula (3), and a first diamine represented by the following formula (4) A liquid crystal aligning agent comprising a polyimide which is an imidized product of a polyimide precursor obtained from a polycondensation reaction with a diamine component containing a second diamine.

In the formula (1), _{X 1} is a structure represented by the following formula (X1-1) or (Xl-2).

However, in the formulas (X1-1) and (X1-2), R ₃ to R ₁₂ each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkenyl having 2 to 6 carbon atoms. A alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group, wherein at least one of R ₃ to R ₆ is hydrogen as defined above. It is a group other than an atom.

In the formulas (3) and (4), A ₂ is independently a halogen atom, a hydroxyl group, an amino group, a thiol group, a nitro group, a phosphate group, or a monovalent organic group having 1 to 20 carbon atoms. a group, a is an integer of 0 to 4, when a ₂ there are multiple structures of a ₂ may be the same or different.

(4) The liquid crystal aligning agent of the present invention makes it possible to greatly reduce the amount of light irradiation, and to obtain a liquid crystal aligning film having good afterimage characteristics. Further, the liquid crystal alignment film obtained from the liquid crystal alignment agent of the present invention has a high yield in manufacturing a liquid crystal panel, and can reduce an afterimage due to AC driving generated in a liquid crystal display element of an IPS drive system or an FFS drive system. A liquid crystal display device of the IPS drive system or the FFS drive system having excellent afterimage characteristics can be obtained.

The liquid crystal aligning agent of the present invention comprises a tetracarboxylic acid component containing a tetracarboxylic dianhydride having a specific structure or a derivative thereof (hereinafter, also referred to as a tetracarboxylic acid component) and a diamine having two specific structures. It is characterized by containing a polyimide (hereinafter, also referred to as a specific polymer), which is an imidized product of a polyimide precursor obtained from a polycondensation reaction with a contained diamine component (hereinafter, also referred to as a diamine component).

<Specific polymer>
The specific polymer used in the present invention is a polyimide which is an imidized product of a polyimide precursor having a specific structure. The polyimide precursor is not particularly limited as long as it is a polyimide precursor that forms an imide ring by heating or chemically imidizing with a catalyst. As the polyimide precursor, a polyamic acid or a polyamic acid ester is preferable from the viewpoint that imidization by heating or chemical imidization easily proceeds.

The imidation ratio of the polyimide is not particularly limited, but is preferably 10 to 100%, more preferably 50 to 100%, and further preferably 50 to 80%.
Hereinafter, each component as a raw material for obtaining the specific polymer will be described in detail.

<Tetracarboxylic acid component>
The tetracarboxylic acid component used in the polymerization of the specific polymer used in the liquid crystal alignment agent of the present invention includes not only tetracarboxylic dianhydride, but also derivatives thereof such as tetracarboxylic acid, tetracarboxylic dihalide, and tetracarboxylic acid. Dialkyl esters or tetracarboxylic acid dialkyl ester dihalides can also be used.

The above tetracarboxylic dianhydride or its derivative is preferably represented by the following formula (1).

However, _{X 1} is a structure represented by the following formula (X1-1) or (Xl-2).

However, R ₃ to R ₁₂ each independently contain 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, and a fluorine atom. A monovalent organic group having 1 to 6 carbon atoms, or a phenyl group. In addition, at least one of R ₃ to R ₆ is a group other than a hydrogen atom in the above definition.

From the viewpoint of liquid crystal alignment, X ₁ is preferably the above formula (X1-1), more preferably at least one selected from the following formulas (X1-1-1) to (X1-1-5), The following formula (X1-1-1) is particularly preferred. The tetracarboxylic dianhydride represented by the formula (1) or a derivative thereof may be used as a mixture of two or more.

The use ratio of the tetracarboxylic dianhydride or its derivative represented by the above formula (1) is preferably at least 50 mol%, more preferably at least 70 mol%, based on 1 mol of all the tetracarboxylic acid components used in the specific polymer. Is more preferable, and 80 mol% or more is further preferable.

Further, the tetracarboxylic acid component used for the polymerization of the specific polymer according to the present invention may be represented by the following formula (2) in addition to the tetracarboxylic dianhydride represented by the above formula (1) or a derivative thereof. It is more preferable to contain a tetracarboxylic dianhydride or a derivative thereof, from the viewpoints of suppression of luminescent spots due to decomposition products and liquid crystal alignment.

However, _{X 2} is selected from the following formulas (X2-1) ~ (X2-6).

Among them, X ₂ is preferably the above formula (X2-1), (X2-5), or (X2-6), and particularly preferably the formula (X2-1). The tetracarboxylic dianhydrides represented by the formula (2) and derivatives thereof may be used as a mixture of two or more.

The use ratio of the tetracarboxylic dianhydride or its derivative represented by the above formula (2) is preferably 1 to 30 mol%, preferably 10 to 30 mol%, per 1 mol of all the tetracarboxylic acid components used in the specific polymer. % Is more preferable, and 10 to 20% is still more preferable.

The tetracarboxylic dianhydride and its derivative used for the polymerization of the specific polymer according to the present invention may contain a tetracarboxylic dianhydride other than the above formulas (1) and (2) or a derivative thereof. Good.

<Diamine>
The diamine component used in the polymerization of the specific polymer used in the liquid crystal aligning agent of the present invention includes at least one first diamine selected from diamines represented by the following formula (3) and a first diamine represented by the following formula (4). And at least one second diamine selected from the diamines represented.

Wherein A ₂ is a halogen atom, a hydroxyl group, an amino group, a thiol group, a nitro group, a phosphate group, or a monovalent organic group having 1 to 20 carbon atoms, a is an integer of 0 to 4, When a plurality of A ₂ are present, the structures of A ₂ may be the same or different.

Preferred specific examples of the first diamine represented by the formula (3) are shown below, but the present invention is not limited thereto.

The content of the first diamine represented by the formula (3) is preferably from 10 to 50 mol%, more preferably from 10 to 30 mol%, based on all diamine components used in the specific polymer.

Preferred specific examples of the second diamine represented by the formula (4) are shown below, but the present invention is not limited thereto.

The content of the second diamine represented by the formula (4) is preferably from 10 to 50 mol%, more preferably from 10 to 40 mol%, based on all diamine components used in the specific polymer.

The diamine used for the polymerization of the specific polymer contained in the liquid crystal aligning agent of the present invention may include a diamine other than the above formulas (3) and (4) (hereinafter, also referred to as other diamines).
Examples of other diamines are shown below, but the present invention is not limited thereto.

m-phenylenediamine, 4- (2- (methylamino) ethyl) aniline, 3,5-diaminobenzoic acid, 4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 4,4′-diaminobenzophenone, 3,3′-diaminobenzophenone, 1,2-bis (4-aminophenyl) ethane, 1,3-bis (4-aminophenyl) propane, 1,4-bis (4-aminophenyl) butane, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,2-bis (4-aminophenoxy) Ethane, 1,2-bis (4-amino-2-methylphenoxy) ethane, 1,3-bis (4-aminophenoxy) Lopan, 1,4-bis (4-aminophenoxy) butane, 1,5-bis (4-aminophenoxy) pentane, 1,6-bis (4-aminophenoxy) hexane, 4- (2- (4- Aminophenoxy) ethoxy) -3-fluoroaniline, di (2- (4-aminophenoxy) ethyl) ether, 4-amino-4 ′-(2- (4-aminophenoxy) ethoxy) biphenyl, 2,2′- Dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 1,4-diaminonaphthalene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,7- Diaminonaphthalene, 2,2'-bis [4- (4-aminophenoxy) phenyl] propane, 2,2'-bis [4- (4-aminophenoxy) phenyl] hex Safluoropropane, 2,2'-bis (4-aminophenyl) propane, 1,3-bis (4-aminophenethyl) urea and the like.

か Among the above, it is preferable to include 1,2-bis (4-aminophenoxy) ethane from the viewpoint of liquid crystal alignment. The content of 1,2-bis (4-aminophenoxy) ethane is more preferably from 10 to 40 mol% based on all diamine components used in the specific polymer.

In addition, from the viewpoint of improving the solvent solubility of polyimide, the specific polymer component tends to be unevenly distributed near the surface layer of the liquid crystal alignment film when a polymer other than the specific polymer is contained in the liquid crystal alignment agent of the present invention. It is preferable to use at least one diamine represented by the following formula (5) as another diamine.

Here, Y ₁ is a divalent organic group having the structure of the following formula (6).

Here, D represents a protecting group which is eliminated by heating and is replaced by a hydrogen atom, and * represents a connection point with another structure. The preferred structure of D includes a t-butoxycarbonyl group.
Preferred specific examples of the diamine represented by the formula (5) are shown below, but it should not be construed that the invention is limited thereto. Boc in the following structure represents a t-butoxycarbonyl group.

好 ま し い When the diamine represented by the formula (5) is used, the preferable content is 5 to 30 mol% of the diamine represented by the formula (5) based on all diamine components used for the specific polymer.

<Method for producing polyamic acid ester, polyamic acid and polyimide>
The polyamic acid ester and the polyamic acid which are the polyimide precursors used in the present invention, and the polyimide which is an imidized product of these polyimide precursors can be synthesized by a known method. One example is the method described in WO2013 / 157586.
The molecular weight of the specific polymer is not particularly limited as long as a good coating can be formed. For example, the weight average molecular weight (Mw) is preferably from 2,000 to 500,000, more preferably from 5,000 to 300,000, and still more preferably from 10,000 to 100,000. The number average molecular weight (Mn) is preferably from 1,000 to 250,000, more preferably from 2,500 to 150,000, and still more preferably from 5,000 to 50,000. 000.

<Liquid crystal aligning agent>
The liquid crystal aligning agent of the present invention is a composition containing the above specific polymer and an organic solvent, and may contain two or more kinds of specific polymers having different structures. Further, the liquid crystal alignment agent of the present invention may contain a polymer other than the specific polymer (hereinafter, also referred to as a second polymer) and various additives.
When the liquid crystal aligning agent of the present invention contains the second polymer, the ratio of the specific polymer to all polymer components is preferably 5% by mass or more, and an example thereof is 5 to 95% by mass.

As the second polymer, polyamic acid, polyimide, polyamic acid ester, polyester, polyamide, polyurea, polyorganosiloxane, cellulose derivative, polyacetal, polystyrene or its derivative, poly (styrene-phenylmaleimide) derivative, poly (meth) Acrylate and the like can be mentioned.
In particular, a polyamic acid obtained from a tetracarboxylic dianhydride component and a diamine component (hereinafter, also referred to as a second polyamic acid) is preferable as the second polymer.

テ ト ラ Examples of the tetracarboxylic dianhydride component for obtaining the second polyamic acid include a compound represented by the following formula (7).

However, in the formula (7), A is a tetravalent organic group, preferably a tetravalent organic group having 4 to 30 carbon atoms. Hereinafter, preferred structures of A are shown, but the present invention is not limited thereto.

Of the above structures, (A-1) and (A-2) are preferable from the viewpoint of further improving photo-alignment, (A-4) is preferable from the viewpoint of improving the relaxation rate of accumulated charge, and (A-4) is preferable. -15) to (A-17) are preferable from the viewpoints of further improving the liquid crystal alignment and improving the relaxation rate of accumulated charge. As the tetracarboxylic dianhydride component for obtaining the second polyamic acid, two or more kinds of tetracarboxylic dianhydrides may be used in combination.

Examples of the diamine component for obtaining the second polyamic acid include a diamine represented by the formula (3), a diamine represented by the formula (4), and other diamines exemplified above. .
It is preferable to use at least one of the diamines represented by the following formula (8) from the viewpoint of improving the relaxation rate of the accumulated charge. As the diamine component for obtaining the second polyamic acid, two or more diamines may be used in combination.

In the formula (8), Y ₂ is a divalent organic group having a nitrogen atom bonded to an aromatic group or having a nitrogen-containing aromatic heterocycle.
Preferred structures of Y ₂ are shown below, but the invention is not limited thereto.

分子 The molecular weight of the second polyamic acid is not particularly limited. For example, the Mw is 2,000 to 500,000, preferably 5,000 to 300,000, more preferably 10,000 to 100,000. Further, Mn is 1,000 to 250,000, preferably 2,500 to 150,000, and more preferably 5,000 to 50,000.

The concentration of the polymer in the liquid crystal aligning agent of the present invention can be appropriately changed by setting the thickness of the coating film to be formed, but is 1% by mass or more from the viewpoint of forming a uniform and defect-free coating film. Is preferable, and from the viewpoint of storage stability of the solution, the content is preferably 10% by mass or less. A particularly preferred concentration of the polymer is 2 to 8% by mass.

有機 The organic solvent contained in the liquid crystal aligning agent of the present invention is not particularly limited as long as the polymer component is uniformly dissolved. Specific examples thereof include N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-methylcaprolactam, Examples thereof include 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl sulfone, γ-butyrolactone, 1,3-dimethyl-imidazolidinone, and 3-methoxy-N, N-dimethylpropanamide. These may be used alone or in combination of two or more. In addition, even if the solvent alone cannot dissolve the polymer component uniformly, it may be mixed with the above organic solvent as long as the polymer is not precipitated.

液晶 The liquid crystal aligning agent of the present invention may contain a solvent for improving the uniformity of the coating when the liquid crystal aligning agent is applied to the substrate, in addition to the organic solvent for dissolving the polymer component. As such a solvent, a solvent having a lower surface tension than the above-mentioned organic solvent is generally used. Specific examples thereof include ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, ethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, and 1-butoxy-2-propanol. , 1-phenoxy-2-propanol, propylene glycol monoacetate, propylene glycol diacetate, propylene glycol-1-monomethyl ether-2-acetate, propylene glycol-1-monoethyl ether-2-acetate, butyl cellosolve acetate, dipropylene glycol , 2- (2-ethoxypropoxy) propanol, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, isobutyl lactate Glycol ester and the like. These solvents may be used in combination of two or more.

In addition to the above, the liquid crystal aligning agent of the present invention includes a dielectric or conductive substance for changing electric properties such as a dielectric constant and conductivity of the liquid crystal alignment film, and a purpose of improving adhesion between the liquid crystal alignment film and the substrate. A silane coupling agent, a cross-linkable compound for the purpose of increasing the hardness and compactness of the liquid crystal alignment film, and an imidization for the purpose of efficiently progressing the imidization of polyamic acid when firing the coating film. An accelerator or the like may be added.

<Production method of liquid crystal alignment film>
The method for producing a liquid crystal alignment film using the liquid crystal alignment agent of the present invention is not particularly limited, but the excellent properties possessed by the liquid crystal alignment agent of the present invention are produced by the following steps (A) to (D). Can be exhibited more effectively.
Step (A): a step of applying the liquid crystal aligning agent of the present invention onto a substrate.
Step (B): a step of heating the applied liquid crystal aligning agent at a temperature at which thermal imidization does not substantially proceed to obtain a film.
Step (C): a step of irradiating the film obtained in step (B) with polarized ultraviolet light.
Step (D): a step of baking the film obtained in step (C) at a temperature of 100 ° C. or higher and higher than that of step (B).

Hereinafter, each of the steps (A) to (D) will be described in more detail.
<Step (A)>
The substrate on which the liquid crystal aligning agent of the present invention is applied is not particularly limited as long as it is a substrate having high transparency, and a plastic substrate such as an acrylic substrate or a polycarbonate substrate can be used together with a glass substrate and a silicon nitride substrate. At that time, it is preferable to use a substrate on which an ITO electrode or the like for driving the liquid crystal is formed in terms of simplification of the process. In the case of a reflection type liquid crystal display device, an opaque material such as a silicon wafer can be used if only one substrate is used. In this case, a material that reflects light such as aluminum can be used for the electrode.
The method of applying the liquid crystal aligning agent is not particularly limited, but a method of performing screen printing, offset printing, flexographic printing, an inkjet method, or the like is generally used. Other coating methods include a dip method, a roll coater method, a slit coater method, a spinner method, a spray method and the like, and these may be used according to the purpose.

<Step (B)>
Step (B) is a step of heating the liquid crystal aligning agent applied on the substrate under the condition that thermal imidization does not substantially proceed to form a film. After the liquid crystal aligning agent is applied on the substrate, the solvent is evaporated by a heating means such as a hot plate, a heat circulation type oven, or an IR (infrared) type oven to form a film. In this step, any temperature and time can be selected as long as the organic solvent contained in the liquid crystal aligning agent can be removed under the condition that thermal imidization does not substantially proceed. Usually, heating at 50 to 150 ° C. for 1 to 10 minutes is preferable to sufficiently remove the contained solvent, and heating at 50 to 120 ° C. for 1 to 5 minutes is more preferable.

<Step (C)>
Step (C) is a step of irradiating polarized ultraviolet light to the film obtained in step (B). As the ultraviolet rays, those having a wavelength of 200 to 400 nm are preferable, and those having a wavelength of 200 to 300 nm are more preferable. In order to improve the liquid crystal alignment, the substrate coated with the liquid crystal alignment agent may be irradiated with ultraviolet rays while being heated at 50 to 250 ° C. The irradiation amount of the ultraviolet ray is, for example, 1 to 2,000 mJ / cm ² , preferably 10 to 1,000 mJ / cm ² , and more preferably 100 to 600 mJ / cm ² . Further, it is preferable that the polarized ultraviolet light has a higher extinction ratio because higher anisotropy can be imparted thereto. Specifically, the extinction ratio of the linearly polarized ultraviolet light is preferably 10: 1 or more, and more preferably 20: 1 or more.

<Step (D)>
Step (D) is a step of baking the film irradiated with the ultraviolet light in step (C). Specifically, this is a step of firing at a temperature of 100 ° C. or higher and higher than the temperature heated in step (B). The firing temperature is not particularly limited as long as it is 100 ° C. or higher and higher than the heating temperature in step (B), but is preferably 150 to 300 ° C., more preferably 150 to 250 ° C., and further preferably 200 to 250 ° C. . The firing time is preferably from 5 to 120 minutes, more preferably from 5 to 60 minutes, even more preferably from 5 to 30 minutes. If the thickness of the liquid crystal alignment film after firing is too small, the reliability of the liquid crystal display element may be reduced. Therefore, the thickness is preferably from 5 to 300 nm, more preferably from 10 to 200 nm.

The liquid crystal alignment film of the present invention is suitable as a liquid crystal alignment film of a liquid crystal display device of a lateral electric field type such as an IPS type or an FFS type, and is particularly useful as a liquid crystal alignment film of an FFS type liquid crystal display device. The liquid crystal display element is manufactured by obtaining a substrate with a liquid crystal alignment film obtained from the liquid crystal alignment agent of the present invention, manufacturing a liquid crystal cell by a known method, and using the liquid crystal cell.

(4) 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 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 forming an image display may be used.

Specifically, a transparent glass substrate is 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 so that a desired image can be displayed. Next, an insulating film is provided on each substrate so as to cover the common electrode and the segment electrodes. The insulating film can be, for example, a SiO ₂ —TiO ₂ film formed by a sol-gel method.

(4) Next, a liquid crystal alignment film is formed on each substrate, and the other substrate is superimposed on one substrate so that the surfaces of the liquid crystal alignment films face each other, and the periphery is bonded with a sealant. Usually, it is preferable that a spacer is mixed in the sealant in order to control the gap between the substrates. Further, it is preferable that spacers for controlling the gap between the substrates are sprayed on the in-plane portion where the sealant is not provided. Part of the sealant is provided with an opening through which liquid crystal can be filled from the outside. Next, a liquid crystal material is injected into a space surrounded by the two substrates and the sealant through an opening provided in the sealant, and then the opening is sealed with an adhesive. For the injection, a vacuum injection method may be used, or a method utilizing a capillary phenomenon in the atmosphere may be used. As the liquid crystal material, either a positive liquid crystal material or a negative liquid crystal material may be used. Next, a polarizing plate is installed. Specifically, a pair of polarizing plates is attached to surfaces of the two substrates opposite to the liquid crystal layer.

As described above, according to the liquid crystal alignment agent of the present invention, an afterimage due to long-term AC driving generated in a liquid crystal display device of an IPS drive system or an FFS drive system can be suppressed, and the brightness generated by the remaining low molecular weight compound can be suppressed. It is possible to obtain a liquid crystal alignment film which has no problems such as points and can be manufactured in a smaller number of steps than in the related art.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not construed as being limited thereto.
The abbreviations of the compounds and the methods for measuring the respective properties are as follows. Note that all numerical values and units in the following are based on mass unless otherwise specified.
NMP: N-methyl-2-pyrrolidone, GBL: γ-butyrolactone,
BCS: butyl cellosolve,

However, in the above formula, Boc represents a t-butoxycarbonyl group.

[viscosity]
The measurement was performed using an E-type viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.) at a sample amount of 1.1 mL, a cone rotor TE-1 (1 ° 34 ′, R24) and a temperature of 25 ° C.

[Molecular weight]
The measurement was performed using a GPC (normal temperature gel permeation chromatography) apparatus, and Mn and Mw were calculated in terms of polyethylene glycol and polyethylene oxide.
GPC apparatus: Shodex (GPC-101), Column: Shodex (KD803, KD805 in series), Column temperature: 50 ° C., Eluent: N, N-dimethylformamide (lithium bromide-water as an additive) 30 mmol / L of hydrate (LiBr.H ₂ O), 30 mmol / L of phosphoric acid / anhydrous crystals (o-phosphoric acid), 10 ml / L of tetrahydrofuran (THF), flow rate: 1.0 ml / min. Standard sample: TSK standard polyethylene oxide (weight average molecular weight (Mw)) manufactured by Tosoh Corporation about 900,000, 150,000, 100,000, 30,000) and polyethylene glycol manufactured by Polymer Laboratory (peak top molecular weight ( Mp) about 12,000, 4,000, 1,000). For the measurement, in order to avoid overlapping peaks, a sample in which four types of 900,000, 100,000, 12,000, and 1,000 were mixed and three types of 150,000, 30,000, and 4,000 were used. Two samples of the mixed sample were measured separately.

<Measurement of imidation ratio>
20 mg of the polyimide powder is placed in an NMR sample tube (NMR sampling tube standard, φ5 (manufactured by Kusano Science Co., Ltd.)), and deuterated dimethyl sulfoxide (DMSO-d6, a mixture of 0.05% TMS (tetramethylsilane)) (0.1%) 53 ml) and sonicated to dissolve completely. The solution was subjected to proton NMR measurement at 500 MHz using an NMR measuring device (JNW-ECA500) (manufactured by JEOL Datum). The imidation ratio is determined by determining a proton derived from a structure that does not change before and after imidation as a reference proton. The peak integrated value of this proton and the proton peak derived from the NH group of the amic acid appearing in the vicinity of 9.5 ppm to 10.0 ppm are determined. It was determined by the following equation using the integrated value.
Imidation ratio (%) = (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 value of the peak of the reference proton, α is the NH of the amic acid in the case of polyamic acid (imidation ratio is 0%). This is the ratio of the number of reference protons to one group proton.

[Configuration of FFS driving liquid crystal cell]
The liquid crystal cell for the fringe field switching (FFS) mode has a FOP (Finger on Plate) electrode layer formed on the surface, which includes a planar common electrode, an insulating layer, and a comb-shaped pixel electrode. One set of the first glass substrate and the second glass substrate having a columnar spacer having a height of 4 μm on the front surface and an ITO film formed on the back surface for antistatic were formed. The above-mentioned pixel electrode has a comb-like shape in which a plurality of electrode elements having a width of 3 μm and having a central portion bent at an inner angle of 160 ° are arranged in parallel at intervals of 6 μm, and one pixel includes: A first region and a second region are provided on a line connecting the bent portions of the plurality of electrode elements.
Note that the liquid crystal alignment film formed on the first glass substrate is subjected to an alignment process so that the direction that equally divides the internal angle of the pixel bent portion is orthogonal to the liquid crystal alignment direction, and the liquid crystal alignment film formed on the second glass substrate is formed. When the liquid crystal cell is manufactured, the film is subjected to an alignment treatment such that the alignment direction of the liquid crystal on the first substrate and the alignment direction of the liquid crystal on the second substrate match.

A liquid crystal aligning agent filtered through a filter having a pore size of 1.0 μm was applied to each surface of the above-mentioned pair of glass substrates by spin coating, and dried on a hot plate at 80 ° C. for 2 minutes. After that, the coating film surface is irradiated with a predetermined amount of ultraviolet light having a wavelength of 254 nm, which is linearly polarized light having an extinction ratio of 26: 1, through a polarizing plate, and then baked in a hot air circulating oven at 230 ° C. for 30 minutes. A substrate with an alignment film was obtained.
Next, a sealant was printed on one of the pair of glass substrates provided with a liquid crystal alignment film, the other substrate was bonded so that the liquid crystal alignment film surfaces faced, and the sealant was cured to produce an empty cell. Liquid crystal MLC-3019 (manufactured by Merck) was injected into the 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 evaluated for afterimage characteristics.

[Afterimage evaluation by long-term AC drive]
An AC voltage of ± 5 V at a frequency of 60 Hz was applied to the FFS-driven liquid crystal cell manufactured above under a constant temperature environment of 60 ° C. for 120 hours. Thereafter, the pixel electrode of the liquid crystal cell and the counter electrode were short-circuited and left at room temperature for one day.
With respect to the liquid crystal cell subjected to the above processing, the deviation between the alignment direction of the liquid crystal in the first region and the alignment direction of the liquid crystal in the second region of the pixel in a state where no voltage was applied was calculated as an angle.
Specifically, a liquid crystal cell is installed between two polarizing plates arranged so that the polarization axes are orthogonal to each other, the backlight is turned on, and the liquid crystal cell is set so that the transmitted light intensity in the first region of the pixel is minimized. Was adjusted, and then the rotation angle required when the liquid crystal cell was rotated such that the transmitted light intensity in the second region of the pixel was minimized was determined.
It can be said that the residual image characteristics by the long-term AC driving are better as the value of the rotation angle is smaller. When the value of the angle Δ of the liquid crystal cell was 0.1 ° or less, it was evaluated as “good”.

Hereinafter, synthesis examples of polyamic acid and polyimide will be described.
<Synthesis example 1>
In a 300 mL four-necked flask equipped with a stirrer and a nitrogen inlet tube, 5.86 g (24.0 mmol) of DA-1, 1.73 g (16.0 mmol) of DA-2, and 5.53 g of DA-3 ( 24.0 mmol) and 3.79 g (16.0 mmol) of DA-4 were weighed, and 197.2 g of NMP was added, and the mixture was stirred and dissolved while supplying nitrogen. While stirring the diamine solution, 14.88 g (66.4 mmol) of CA-1 and 3.00 g (12.0 mmol) of CA-2 were added, and the mixture was stirred at 40 ° C. for 24 hours, and the polyamic acid solution (A- 1) (viscosity: 425 mPa · s) was obtained. Mn of the polyamic acid was 11,000 and Mw was 29000.

<Synthesis Examples 2 to 6>
Except that the diamine component, the tetracarboxylic acid component, and NMP shown in Table 1 below were used and the reaction was carried out at the reaction temperature, the reaction was carried out in the same manner as in Synthesis Example 1 to obtain a polyamic acid solution (A- 2) to (A-4), (B-1) and (B-2) were obtained. The viscosity and Mn / Mw of the obtained polyamic acid are shown in Table 1 below.
The polyamic acid concentrations in the polyamic acid solutions obtained in Synthesis Examples 1 to 6 were all 15% by mass.

<Synthesis Example 7>
100 g of the obtained polyamic acid solution (A-1) was placed in a 300 mL four-necked flask equipped with a stirrer and a nitrogen inlet tube, 50 g of NMP was added, and the mixture was stirred for 30 minutes. 17.60 g of acetic anhydride and 5.50 g of pyridine were added to the obtained polyamic acid solution, and the mixture was heated at 50 ° C. for 3 hours to perform chemical imidization.
The obtained reaction solution was poured into 600 ml of methanol with stirring, the deposited precipitate was collected by filtration, and the same operation was performed twice to wash the resin powder, followed by drying at 60 ° C. for 12 hours. Thus, a polyimide resin powder was obtained. The imidation ratio of this polyimide resin powder was 73%, Mn = 12600, Mw = 33900. 3.60 g of the obtained polyimide resin powder was placed in a 100-ml Erlenmeyer flask, 26.4 g of NMP was added so that the solid concentration became 12%, and the mixture was stirred at 70 ° C. for 24 hours to dissolve the polyimide solution (A-1-). PI) was obtained (see Table 2 below).
In Table 2, the concentration (% by mass) under the imidization conditions represents the concentration of the polymer in the solution in the imidization reaction.

<Synthesis Examples 8 to 10>
A polyimide solution (A-2-PI) to (A-4) shown in Table 2 below was obtained by performing a chemical imidization operation in the same manner as in Synthesis Example 7 except that acetic anhydride and pyridine shown in Table 2 below were used. -PI). The imidation ratio and Mn / Mw of the obtained polyimide are shown in Table 2 below.

<Example 1>
50 g of 4.0 g of the 12% by weight polyimide solution (A-1-PI) obtained in Synthesis Example 7 and 4.8 g of the 15% by weight polyamic acid solution (B-1) obtained in Synthesis Example 5 In a flask, 3.24 g of NMP, 3.96 g of GBL and 4.00 g of BCS were added and mixed at 25 ° C. for 8 hours to obtain a liquid crystal aligning agent (1) (see Table 3 below). No abnormality such as turbidity or precipitation was observed in this liquid crystal aligning agent, and it was confirmed that the solution was a uniform solution.
In Table 3, A / B indicates the mass% ratio of the polyimide solution / polyamic acid solution, and the solid content ratio (mass%) indicates the content ratio of the polymer in the liquid crystal aligning agent.

<Examples 2 to 4, Comparative Example 1>
Liquid crystal alignment agents (2) to (5) were obtained in the same manner as in Example 1 except that the polyamic acid solution and the polyimide solution shown in Table 3 below were used. No abnormality such as turbidity or precipitation was observed in these liquid crystal aligning agents, and it was confirmed that the liquid crystal aligning agent was a uniform solution.

<Example 11>
The afterimage characteristics were evaluated in accordance with the above-mentioned "afterimage evaluation by long-term AC drive". That is, after the liquid crystal aligning agent (1) obtained in Example 1 was filtered through a filter having a pore size of 1.0 μm, the prepared electrode-coated substrate and a 4 μm-high columnar column having an ITO film formed on the back surface were prepared. It was applied to a glass substrate having a spacer by spin coating. After drying on a hot plate at 80 ° C. for 5 minutes, the coated surface is irradiated with a linearly polarized ultraviolet ray having a wavelength of 254 nm having 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. Thus, a substrate with a liquid crystal alignment film was obtained.
A pair of the obtained two substrates was used as a set, a sealant was printed on the substrates, and another substrate was bonded so that the liquid crystal alignment films faced each other so that the alignment direction was 0 °. The agent was cured to produce an empty cell. Liquid crystal MLC-3019 (manufactured by Merck) was injected into the 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 and left overnight, and an afterimage was evaluated by long-term AC driving.
The value (°) of the angle Δ of the liquid crystal cell after the long-term AC driving is as shown in Table 4 below, that is, the angle Δ of the liquid crystal cell when the irradiation amount of the ultraviolet light is 0.15 J / cm ^2. Is 0.08 °, the value of the angle Δ of the liquid crystal cell at 0.20 J / cm ² is 0.09 °, and the value of the angle Δ of the liquid crystal cell at 0.25 J / cm ² Was 0.09 °. In each case, since the minimum value of the angle Δ was less than 0.10 °, good liquid crystal alignment was obtained by using the liquid crystal alignment agent (1).

<Examples 12 to 14 and Comparative Example 11>
In Examples 12 to 14 and Comparative Example 11 in place of the liquid crystal aligning agent (1), each of the liquid crystal aligning agents shown in Table 4 below was used. A cell was fabricated, and an afterimage was evaluated by long-term AC driving.
Table 4 shows the value (°) of the angle Δ of the liquid crystal cell after long-term AC driving for each of the irradiation amounts of the ultraviolet rays for Examples 12 to 14 and Comparative Example 11.

As shown in Table 4, in Examples 11 to 14, the angle Δ (deg.) Is best when the polarized ultraviolet ray irradiation amount is as small as 200 mJ / cm ² or less so that the angle Δ (deg.) Is 0.1 ° or less. Becomes It can be seen that such good afterimage characteristics are excellent in shortening the production time of the liquid crystal display device.

The liquid crystal alignment agent of the present invention is useful for forming a liquid crystal alignment film in a wide range of liquid crystal display devices such as an IPS drive system and an FFS drive system.
The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2018-154228 filed on Aug. 20, 2018 are cited herein as the disclosure of the specification of the present invention. , Is to take in.

Claims (13)

1. A tetracarboxylic acid component containing a tetracarboxylic dianhydride represented by the following formula (1) or a derivative thereof, a first diamine represented by the following formula (3), and a first diamine represented by the following formula (4) A liquid crystal aligning agent comprising a polyimide which is an imidized product of a polyimide precursor obtained from a polycondensation reaction with a diamine component containing a second diamine.
   

   

   (Wherein, _{X 1} is a structure represented by the following formula (X1-1) or (Xl-2).)
   

   

   (However, R ₃ to R ₁₂ each independently represent 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 fluorine atom Which is a monovalent organic group having 1 to 6 carbon atoms or a phenyl group, wherein at least one of R ₃ to R ₆ is a group other than a hydrogen atom as defined above.)
   

   

   (However, A ₂ is independently a halogen atom, a hydroxyl group, an amino group, a thiol group, a nitro group, a phosphate group, or a monovalent organic group having 1 to 20 carbon atoms, and a is 0 to 4 of an integer, if a ₂ there are multiple structures of a ₂ may be the same or different.)
2. 2. The liquid crystal aligning agent according to claim 1, wherein X ₁ in the formula (1) is at least one selected from the following formulas (X1-1-1) to (X1-1-5).
   

   
3. The liquid crystal aligning agent according to claim 1, wherein the first diamine represented by the formula (3) is a diamine represented by the following formula.
   

   
4. 4. The liquid crystal aligning agent according to claim 1, wherein the first diamine represented by the formula (4) is a diamine represented by the following formula.
   

   
5. The liquid crystal aligning agent according to any one of claims 1 to 4, wherein the first diamine represented by the formula (3) is contained in an amount of 10 to 50 mol% based on the diamine component.
6. The liquid crystal aligning agent according to any one of claims 1 to 5, wherein the second diamine represented by the formula (4) is contained in an amount of 10 to 50 mol% based on the diamine component.
7. 7. The liquid crystal aligning agent according to claim 1, wherein the tetracarboxylic acid component further contains a tetracarboxylic dianhydride represented by the following formula (2) or a derivative thereof.
   

   

   (However, X ₂ is a structure selected from the following formulas (X2-1) to (X2-6).)
   

   
8. The liquid crystal aligning agent according to claim 7, wherein the tetracarboxylic dianhydride represented by the formula (2) or a derivative thereof is contained in an amount of 1 to 30 mol% based on the tetracarboxylic acid component.
9. (8) A liquid crystal alignment film obtained by using the liquid crystal alignment agent according to any one of (1) to (8).
10. A liquid crystal display device comprising the liquid crystal alignment film according to claim 9.
11. A method for producing a liquid crystal alignment film, comprising the following steps (A), (B), (C) and (D).
    Step (A): a step of applying the liquid crystal aligning agent according to any one of claims 1 to 8 on a substrate.
    Step (B): a step of heating the applied liquid crystal alignment agent under conditions under which thermal imidization does not substantially proceed to obtain a film.
    Step (C): a step of irradiating the film obtained in step (B) with polarized ultraviolet light.
    Step (D): a step of baking the film obtained in step (C) at a temperature of 100 ° C. or higher and higher than that of step (B).
12. 12. The method for producing a liquid crystal alignment film according to claim 11, wherein in the step (B), heating is performed at 50 ° C. to 150 ° C.
13. 13. The method for producing a liquid crystal alignment film according to claim 11, wherein in the step (D), the film is fired at 150 to 300 ° C.