TWI699386B - Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element using the same - Google Patents

Abstract

The present invention provides a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display element that have high liquid crystal alignment and voltage retention, can accelerate the relaxation of residual charges and increase the contrast.

The liquid crystal alignment agent contains polycondensation reaction of a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride of formula (A) and a diamine component containing a diamine of formula (B) polyamide acid and At least one polymer selected from the group of its imidized polymers, and a compound represented by formula (C).

(m is an integer from 1 to 5; X ¹ is an aliphatic hydrocarbon group with 1 to 20 carbon atoms, or an n-valent organic group containing an aromatic hydrocarbon group; n is an integer from 2 to 6; R ¹ and R ² are hydrogen atoms Or optionally substituted alkyl with 1 to 4 carbons, alkenyl with 2 to 4 carbons or alkynyl with 2 to 4 carbons, at least one of R ¹ and R ² is a hydrocarbon group substituted by a hydrocarbon group) .

Description

Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element using the same

The present invention relates to a liquid crystal alignment agent and a liquid crystal alignment film used in a liquid crystal display element of a horizontal electric field driving method driven by applying a parallel electric field to a substrate, and a liquid crystal display element using the liquid crystal alignment agent.

The previous liquid crystal devices are widely used in the display parts of computers, mobile phones, TV cameras, etc. For example, the liquid crystal device is equipped with an alignment film for controlling the alignment of the pixel electrodes, common electrodes and liquid crystal molecules of the liquid crystal layer obtained by applying an electric field to the liquid crystal layer by sandwiching the liquid crystal layer between the element substrate and the filter substrate, and switching supply Thin film transistors (TFT) for electrical signals of pixel electrodes, etc. The known driving methods of liquid crystal molecules include vertical electric field methods such as TN (Twisted Nematic) method and VA (Vertical Alignment) method, and transverse electric field methods such as IPS (In Plane Switching) method and FFS (Fringe Field Switching) method. . Generally, after electrodes are formed on one side of the substrate, the electric field is applied to the horizontal electric field in a direction parallel to the substrate. Compared with the previous vertical electric field in which voltage is applied to the electrodes formed on the upper and lower substrates to drive the liquid crystal, it can have a wider range With viewing angle characteristics, high-quality liquid crystal display elements can be obtained.

Although the liquid crystal cell of the transverse electric field method has excellent viewing angle characteristics, since the electrode portion formed in the substrate is small, the voltage retention rate of the liquid crystal alignment film is weak, and the liquid crystal voltage is insufficient and the display contrast is reduced. In addition, static electricity is easy to accumulate in the liquid crystal cell. Even if the asymmetric voltage generated by driving is applied, electric charge will be accumulated in the liquid crystal cell. The accumulated electric charge will disturb the alignment of the liquid crystal and cause afterimage or burn-in to affect the display. Therefore, the display quality of the liquid crystal element will be significantly reduced. When power is re-energized in this state, flicker (flicker) or the like may occur in the initial stage because the liquid crystal molecules cannot be well controlled. Especially when the horizontal electric field method is compared with the vertical electric field method, the distance between the pixel electrode and the common electrode is shorter, so the electric field acting on the alignment film and the liquid crystal layer is stronger, and this type of problem is likely to be more prominent.

In addition, in the IPS method and FFS driving method, the stability of the liquid crystal alignment is also important in the method of driving the liquid crystal molecules that are horizontally aligned with respect to the substrate by a horizontal electric field. When the stability of the alignment is low, driving the liquid crystal for a long time will not return the liquid crystal to the initial state, which becomes the cause of lower contrast and burn-in.

In order to solve the above-mentioned problem of charge accumulation due to the asymmetry of AC drive, it has been proposed to have a first alignment film formed on the electrode and a polymer formed on the surface of pyromellitic dianhydride and diamine. A liquid crystal display device with a liquid crystal alignment film composed of a second alignment film with a lower resistance than the first alignment film. This method has reported that the asymmetry of AC drive suppresses charge accumulation and accelerates the relaxation of the accumulated charge (patent Literature 1).

Prior art literature Patent literature

Patent Document 1: Japanese Patent Application Publication No. 2013-167782

However, with the high definition of liquid crystal display elements in recent years, the requirements are higher than before. In addition, among the IPS method and FFS driving method, in which liquid crystal molecules aligned parallel to the substrate are driven by a transverse electric field, the alignment stability and electrical reliability of the liquid crystal under severe environments are also important. Therefore, a high-level liquid crystal alignment agent that can meet all these requirements is required.

The purpose of the present invention is to provide liquid crystal display elements of IPS driving mode and FFS driving mode, which can have various particularly important characteristics, namely, higher liquid crystal alignment and higher voltage retention, and acceleration and relaxation factors The residual charge accumulated by DC voltage can be used as a liquid crystal alignment agent for a liquid crystal alignment film with high contrast.

In order to solve the above-mentioned problems, the inventors of the present invention conducted a thorough examination and found a liquid crystal alignment agent that can meet the above-mentioned characteristics at a high level, and completed the present invention.

The present invention is also a liquid crystal alignment agent characterized by containing tetracarboxylic dianhydride containing tetracarboxylic dianhydride represented by the following formula (A) One of at least one selected from the polycondensation reaction of a polycondensation reaction of a component and a diamine component containing a diamine represented by the following formula (B) and the imidized polymer of the polyamide acid A polymer, and a compound represented by the following formula (C).

(In formula (B), m is an integer of 1 to 5).

(In formula (C), X ¹ is an aliphatic hydrocarbon group with 1-20 carbon atoms, or an n-valent organic group containing an aromatic hydrocarbon group, n is an integer of 2-6, and R ¹ and R ² are independently hydrogen Atom, or optionally substituted alkyl with 1 to 4 carbons, alkenyl with 2 to 4 carbons or alkynyl with 2 to 4 carbons, at least one of R ¹ and R ² is a hydrocarbon group substituted by a hydroxy group ).

By using the liquid crystal alignment film obtained from the liquid crystal alignment agent of the present invention, liquid crystal display elements of IPS driving mode and FFS driving mode are available, and have particularly important characteristics, namely, higher liquid crystal alignment and higher voltage retention , And speed up the relaxation of residual electricity accumulated due to DC voltage He is a high-contrast liquid crystal display element.

Although the reason for the aforementioned results obtained by the liquid crystal alignment agent of the present invention has not been determined, it is presumed as follows.

In the liquid crystal alignment film obtained from the liquid crystal alignment agent of the present invention, the polymer main chain constituting it has a soft structure that can be fully extended by rubbing treatment and an aromatic functional group that can fully interact with liquid crystal molecules. It has high liquid crystal orientation. In addition, the compound represented by the formula (C) reacts with the carboxyl group in the polymer during firing, thereby improving heat resistance. Therefore, during firing, the amount of decomposition products generated by the liquid crystal alignment film can be suppressed, and the voltage retention rate is higher . In addition, the reaction between the compound represented by formula (C) and the carboxyl group of the polymer can increase the hardness of the film by forming a cross-linked structure in the polymer, and is not easily affected by the rubbing cloth during rubbing treatment. Therefore, the liquid crystal alignment is used The liquid crystal display element of the film can suppress the decrease in contrast due to friction. In addition, since the polymer main chain of the liquid crystal alignment film of the present invention has an expanded π-electron conjugated structure, the volume resistance value is low, and it is inferred that it can accelerate the relaxation of the residual charge accumulated by the DC voltage.

Form of invention <Polyamic acid and the imidized polymer of the polyamic acid>

The liquid crystal alignment agent of the present invention is a polycondensation reaction of a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride of the following formula (A) and a diamine component containing a diamine represented by the following formula (B) Polymerization of at least one selected from the group of the obtained polyamide and the imidized polymer of the polyamide And the compound represented by the following formula (C).

In formula (B), m is 1 to 5, preferably an integer of 1 to 3.

In the formula, X ¹ is an aliphatic hydrocarbon group with 1 to 20 carbons, or an n-valent organic group containing an aromatic hydrocarbon group, preferably an aliphatic hydrocarbon group with 1 to 5 carbons. n is 2-6, preferably an integer of 3-4. R ¹ and R ² are independently hydrogen atoms, or a hydrocarbon group formed by an alkyl group with 1 to 4 carbons, an alkenyl group with 2 to 4 carbons, or alkynyl group with 2 to 4 carbons which may have substituents, Preferably, it is an alkyl group having 1 to 4 carbon atoms which may have a substituent. In addition, at least one of R ¹ and R ² is a hydrocarbon group substituted with a hydroxy group, preferably a hydroxyethyl group.

<Tetracarboxylic dianhydride component>

The tetracarboxylic dianhydride component used for producing the liquid crystal alignment agent of the present invention contains the tetracarboxylic dianhydride represented by the above formula (A). The ratio of tetracarboxylic dianhydride represented by formula (A) to 1 mol of all tetracarboxylic dianhydrides is 20 to 80 mol%, preferably 30 to 70 mol%, preferably 40 to 60 mol%, more preferably 40 to 50 mol%.

<Other tetracarboxylic dianhydrides>

The tetracarboxylic dianhydride component used in the production of the liquid crystal alignment agent of the present invention may contain the tetracarboxylic dianhydride represented by the following formula (1) in addition to the tetracarboxylic dianhydride represented by the above formula (A) .

In formula (1), X is a tetravalent organic group, and its structure is not particularly limited. A specific example is the structure of the following formulas (X-1) to (X-42).

In the formula (X-1), R ₃ to R ₆ are independently hydrogen atoms, alkyl groups having 1 to 6 carbon atoms, or phenyl groups, preferably hydrogen atoms or methyl groups.

Among tetracarboxylic dianhydrides, at least one tetracarboxylic dianhydride selected from the group of structures represented by the following formula (2) is preferred from the viewpoint of the availability of the compound.

(In formula (2), X ₁ is at least one selected from the group of structures represented by the above formulas (X-1) to (X-14)).

In order to further improve the reliability of the obtained liquid crystal alignment film, it is preferably a structure formed only by aliphatic groups such as (X-1)~(X-7) or (X-11), more preferably (X-1) The structure represented. In addition, in order to obtain good liquid crystal alignment, X _{1 is} particularly preferably the following formula (X1-1) or (X1-2).

The ratio of the tetracarboxylic dianhydride represented by formula (1) to 1 mol% of all tetracarboxylic dianhydrides is preferably 30~70 mol%, 40-60 mol% is more preferred, more preferably 50 ~60 mol%.

<Diamine component>

The diamine component used in the present invention contains the diamine represented by the above formula (B). In formula (B), m is an integer of 1 to 5, preferably an integer of 1 to 3.

In addition to the diamine of formula (B), the aforementioned diamine component preferably contains at least one diamine selected from the group of structures of the following formulas (YD-1) to (YD-5).

In the formula (YD-1), A ₁ is a heterocyclic ring containing a nitrogen atom with 3 to 15 carbons, and Z ₁ is a hydrogen atom, or a hydrocarbon group with 1 to 20 carbons that may have a substituent.

In the formula (YD-2), W ₁ is a hydrocarbon group with 1 to 10 carbons, and A ₂ is a monovalent organic group with 3 to 15 carbons with a heterocyclic ring containing a nitrogen atom, or a fatty group with 1 to 6 carbons. Disubstituted amino group substituted by a group.

In the formula (YD-3), W ₂ is a divalent organic group with 6 to 15 carbons and 1 or 2 benzene rings, W ₃ is an alkylene or biphenylene group with 2 to 5 carbons, Z ₂ is a hydrogen atom, an alkyl group with 1 to 5 carbon atoms, or a benzene ring, and a is an integer of 0 to 1.

In the formula (YD-4), A ₃ is a heterocyclic ring containing a nitrogen atom with 3 to 15 carbon atoms.

In the formula (YD-5), A ₄ is a heterocyclic ring containing a nitrogen atom with 3 to 15 carbon atoms, and W ₅ is an alkylene group with 2 to 5 carbon atoms.

In formulas (YD-1), (YD-2), (YD-4) and (YD-5), A ₁ , A ₂ , A ₃ , and A ₄ are heterocyclic rings containing nitrogen atoms with 3 to 15 carbon atoms There are no special restrictions. For example, pyrrolidine, pyrrole, imidazole, pyrazole, oxazole, thiazole, piperidine, piperazine, pyridine, pyrazine, indole, benzimidazole, quinoline, isoquinoline, etc., preferably piperazine, piperidine , Indole, benzimidazole, imidazole, carbazole or pyridine.

A specific example is a divalent organic group having a nitrogen atom represented by the following formulas (YD-6) to (YD-21). It can suppress the accumulation of electric charge due to AC driving, more preferably formula (YD-14) ~ formula (YD-21), particularly preferably (YD-14) or (YD-18).

In formulas (YD-14) and (YD-21), j is an integer of 0-3, preferably 0-1.

In formula (YD-17), h is an integer of 1 to 3, preferably 2 to 3.

In the polyamide acid and polyamide acid imidization polymer of the present invention, at least one diamine selected from the group of structures of the above formulas (YD-1) to (YD-5), The ratio of 1 mole relative to the total diamine is preferably 10 to 80 mole%, more preferably 20 to 60 mole%, and more preferably 30 to 50 mole%.

<Other Diamines>

The polyamide acid contained in the liquid crystal alignment agent of the present invention is in addition to the diamine represented by the above formula (B), and at least one selected from the group of the above formula (YD-1)~(YD-5) In addition to amines, diamines represented by the following formula (3) can be used. In the following formula (3), Y ₂ is a divalent organic group, and its structure is not limited, and two or more types can be used in combination. The specific examples are the following (Y-1) to (Y-102).

[Chemistry 14] H ₂ NY ₂ -NH ₂ (3)

Among them, in order to obtain good liquid crystal alignment, diamines with higher linearity are preferred, and Y _{2 is more} preferably Y-7, Y-21~Y-23, Y-25~Y-27, Y-43~Y -46, Y-48, Y-63, Y-71, Y-73~Y-75, Y-98~Y-101 or Y-102.

The ratio of the diamine represented by the formula (3) to 1 mol% of all diamines is preferably 0-40 mol%, preferably 0-25 mol%, more preferably 0-15 mol%.

<Compound represented by formula (C)>

The liquid crystal alignment agent of the present invention contains a compound represented by the following formula (C) (hereinafter also referred to as a specific compound).

In the above formula (C), X ¹ is an aliphatic hydrocarbon group with 1 to 20 carbons, or an n-valent organic group containing an aromatic hydrocarbon group, n is an integer of 2 to 6, and R ¹ and R ² are each independent hydrogen Atoms, or optionally substituted alkyl groups with 1 to 4 carbons, alkenyl groups with 2 to 4 carbons, or alkynyl groups with 2 to 4 carbons. At least one of R ¹ and R ² represents Hydrocarbyl substituted by hydroxy.

Among them, from the viewpoint of liquid crystal orientation, the atom directly bonded to the carbonyl group in X ¹ of formula (C) is preferably a carbon atom that does not form an aromatic ring.

In formula (C), n represents an integer of 2-6. From the viewpoint of solubility, n is preferably 2 to 4.

In formula (C), R ¹ and R ² are independently hydrogen atoms, or optionally substituted alkyl groups with 1 to 4 carbons, alkenyl groups with 2 to 4 carbons, or alkynes with 2 to 4 carbons. At least one of R ¹ and R ² represents a hydrocarbon group substituted by a hydroxy group. Among them, from the viewpoint of reactivity, at least one of R ¹ and R ² is preferably a structure represented by the following formula (3), and more preferably a structure represented by the following formula (4).

In formula (3), R ³ to R ⁶ represent any of a hydrogen atom, a hydrocarbon group, or a hydrocarbon group substituted with a hydroxyl group.

Preferred specific examples of the above-mentioned specific compound include the following compound (C-1).

When the content of the specific compound in the liquid crystal alignment agent is too large, it will affect the liquid crystal alignment and pretilt angle, and when it is too small, the effect of the present invention cannot be obtained. Therefore, the content of the specific compound relative to the polymer of the component (A) in the liquid crystal alignment agent is preferably 0.1-20% by mass, more preferably 1-10% by mass.

<Manufacturing method of polyamide acid>

The polyimide precursor of the polyimide used in the present invention can be produced by the following method. Specifically, it can be achieved by reacting tetracarboxylic dianhydride and diamine at -20~150°C, preferably 0~50°C in the presence of an organic solvent, for 30 minutes to 24 hours, preferably 1 to 12 hours. Got.

The organic solvent used in the above reaction is preferably N,N-dimethylformamide, N-methyl-2-pyrrolidone, γ-butyrolactone, etc. in terms of the solubility of monomers and polymers. Use alone or in combination of two or more.

The concentration of the polymer in the reaction system is less likely to cause polymer precipitation, and from the viewpoint that a high molecular weight body is easily obtained, it is preferably 1-30% by mass, more preferably 5-20% by mass.

The polyamide acid obtained above can be recovered by injecting the polymer into a weak solvent while fully stirring the reaction solution. In addition, after precipitation for several times, it is washed with a weak solvent, and then dried at room temperature or by heating to obtain a refined polyamide acid powder. The weak solvent is not particularly limited. For example, water, methanol, ethanol, 2-propanol, hexane, butyl cellosolve, acetone, toluene, etc., preferably water, methanol, ethanol, 2-propanol, etc.

<Manufacturing Method of Polyimide>

The polyimide used in the present invention can be obtained by imidizing the aforementioned polyimide.

When producing polyimide from polyamic acid, it is simpler to perform chemical imidization by adding a catalyst to the diamine component and reacting with tetracarboxylic dianhydride in the aforementioned polyimide solution. The chemical imidization is preferable because the imidization reaction can be carried out at a relatively low temperature, and the process of imidization is not easy to reduce the molecular weight of the polymer.

Chemical imidization can be carried out by stirring the polymer to be imidized in the presence of a basic catalyst and acid anhydride in an organic solvent. As the organic solvent, the solvent used in the aforementioned polymerization reaction can be used. Alkaline catalysts such as pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine, etc. Among them, it is preferable that pyridine possesses a moderate alkalinity during the reaction. Furthermore, acid anhydrides such as acetic anhydride, trimellitic anhydride, pyromellitic anhydride, etc., among them, it is preferable that acetic anhydride is used for easy purification after the reaction is completed.

The temperature during the imidization reaction is -20~140°C, preferably 0~100°C, and the reaction time can be 1~100 hours. The amount of alkaline catalyst is 0.5 to 30 times mol of polyamide acid group, preferably 2 to 20 times mol, and the amount of acid anhydride is 1 to 50 times mol of polyamide acid group, preferably 3~30 times mole. The imidization rate of the obtained polymer can be controlled by adjusting the amount of catalyst, temperature and reaction time.

After the imidization reaction of polyamide acid, the added catalyst will remain in the solution. Therefore, it is preferable to recover the obtained imidization polymer by the following method and then dissolve it in an organic solvent to obtain The liquid crystal alignment agent of the present invention.

Fully stir the polyimide solution obtained above and inject it into a weak solvent to precipitate the polymer. After several times of precipitation, it is washed with a weak solvent, and then dried at room temperature or by heating to obtain a refined polymer powder.

The aforementioned weak solvent is not particularly limited, for example, methanol, 2-propanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, benzene, etc., preferably Methanol, ethanol, 2-propanol, acetone, etc.

<Liquid crystal alignment agent>

The liquid crystal alignment agent of the present invention has a solution form in which polymer components are dissolved in an organic solvent. In the molecular weight of the polymer, the weight average molecular weight is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and more preferably 10,000 to 100,000. Furthermore, the number average molecular weight is preferably 1,000 to 250,000, more preferably 2,500 to 150,000, and more preferably 5,000 to 50,000.

The concentration of the polymer in the liquid crystal alignment agent of the present invention can be appropriately changed according to the thickness of the coating film to be formed. However, from the viewpoint of forming a uniform and defect-free coating film, it is preferably 1% by mass or more, and from the viewpoint of the storage stability of the solution Preferably it is 10 mass% or less. The concentration of the polymer is particularly preferably 2-8% by mass.

The organic solvent contained in the liquid crystal alignment agent may be a substance that can uniformly dissolve the polymer component, and is not particularly limited. Specifically, for example, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl -2-pyrrolidone, N-methylcaprolactam, 2-pyrrole Alkanone, N-vinyl-2-pyrrolidone, dimethyl sulfide, dimethyl sulfide, γ-butyrolactone, 1,3-dimethyl-imidazolinone, 3-methoxy-N,N -Dimethyl acrylamide and so on. These can be used alone or in combination of two or more kinds. In addition, even if it is a solvent that cannot uniformly dissolve the polymer component when it is alone, it can be mixed with the above-mentioned organic solvent within the range where the polymer does not precipitate.

In addition to the organic solvent for dissolving the polymer component, the liquid crystal alignment agent of the present invention may contain a solvent for improving the uniformity of the coating film when the liquid crystal alignment agent is applied to the substrate. Such solvents generally use solvents with a lower surface tension than the above-mentioned organic solvents. 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, 1-butoxy-2-propanol, 1-phenoxy-2-propanol, propylene glycol monoacetate, propylene glycol diacetate, propylene glycol-1-mono Methyl 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, isoamyl lactate, etc. These solvents can be used in combination of two or more kinds.

In addition to the above, the liquid crystal alignment agent of the present invention can be added with polymers other than the polyimide precursor and polyimide polymer of the present invention within the range that does not impair the effects of the present invention, and the purpose is to change the liquid crystal alignment film. A dielectric or conductive material with electrical properties such as dielectric constant and conductivity, a silane coupling agent for improving the adhesion between the liquid crystal alignment film and the substrate, and the purpose of improving the hardness and fineness of the film when used as a liquid crystal alignment film The cross-linking compound, and the purpose is to efficiently carry out the polyamide acid when baking the coating film Imidization accelerator, etc.

<Method of Manufacturing Liquid Crystal Alignment Film>

The liquid crystal alignment film of the present invention is a film obtained by coating the above-mentioned liquid crystal alignment agent on a substrate, drying and baking. The substrate coated with the liquid crystal alignment agent of the present invention can be a highly transparent substrate, and is not particularly limited. Plastic substrates such as glass substrates, silicon nitride substrates, acrylic substrates, polycarbonate substrates, etc. can be used, and the steps are simplified From this point of view, it is preferable to use a substrate on which ITO electrodes for driving liquid crystals are formed. In addition, in reflective liquid crystal display elements, opaque materials such as silicon wafers can be used for only one side of the substrate, and light-reflecting materials such as aluminum can be used for the electrodes in this case.

The coating method of the liquid crystal alignment agent of the present invention is, for example, a spin coating method, a printing method, an inkjet printing method, and the like. Any temperature and time can be selected for the drying and firing steps after coating the liquid crystal alignment agent of the present invention. Generally, in order to fully remove the organic solvent contained, it is preferably dried at 50~120°C for 1~10 minutes, and preferably baked at 150~300°C for 5~120 minutes. The thickness of the coating film after firing is not particularly limited. If it is too thin, the reliability of the liquid crystal display element will be reduced, so it is 5~300nm, preferably 10~200nm.

The method of aligning the obtained liquid crystal alignment film may be a rubbing method, a photo-alignment method, etc.

For the rubbing treatment of the liquid crystal alignment film, an existing rubbing device can be used. At this time, the material of the friction cloth is cotton, rayon, nylon, etc.

A specific example of the photo-alignment treatment method is a method of irradiating the surface of the coating film with radiation polarized in a certain direction, and then heating it at a temperature of 150-250°C depending on the situation, to impart alignment energy to the liquid crystal. The radiation can use ultraviolet rays and visible rays with a wavelength of 100 to 800 nm. Among them, ultraviolet rays having a wavelength of 100 to 400 nm are preferred, and those having a wavelength of 200 to 400 nm are particularly preferred. In addition, in order to improve the orientation of the liquid crystal, the coated substrate may be heated at 50 to 250°C while irradiating radiation. The irradiation amount of the aforementioned radiation is preferably 1 to 10,000 mJ/cm ² , particularly preferably 100 to 5,000 mJ/cm ² . The liquid crystal alignment film obtained above can stabilize the alignment of liquid crystal molecules in a certain direction.

Next, the above-mentioned film irradiated with polarized radiation can be used, and it contains at least one solvent selected from the group of water and organic solvents for contact treatment.

The solvent used in the contact treatment may be a solvent that can dissolve the decomposed product generated by irradiation with light, and is not particularly limited. For example, water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, 1-methoxy-2-propanol, 1-methoxy-2-propanol acetate, butyl cellosolve , Ethyl lactate, methyl lactate, diacetone alcohol, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, propyl acetate, butyl acetate, cyclohexyl acetate, etc. These solvents can be used in combination of two or more kinds.

From the viewpoint of versatility and safety, the above-mentioned solvent is more preferably at least one selected from the group consisting of water, 2-propanol, 1-methoxy-2-propanol, and ethyl lactate. Particularly preferred is 1-methoxy-2-propanol or ethyl lactate.

In the present invention, the contact treatment between the film irradiated with polarized radiation and the solution containing the organic solvent may be immersion treatment, spray treatment, etc., and it is preferable to perform treatment such that the film and the liquid can be fully contacted. among them It is also better to immerse the film in a solution containing an organic solvent for 10 seconds to 1 hour, more preferably 1 to 30 minutes. The contact treatment may be at room temperature or under heating, but is preferably carried out at 10 to 80°C, and more preferably at 20 to 50°C. In addition, if necessary, ultrasonic waves can be implemented to improve contact.

In order to remove the organic solvent in the used solution after the above-mentioned contact treatment, either water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone and other low-boiling solvents can be used for cleaning and drying. Or both.

In addition, the above-mentioned film after solvent contact treatment can be heated above 150°C in order to dry the solvent and realign the molecular chains in the film.

The heating temperature is preferably 150~300°C. Although the realignment of the molecular chains can be promoted at higher temperatures, excessively high temperatures may be accompanied by decomposition of the molecular chains. Therefore, the heating temperature is more preferably 180~250℃, particularly preferably 200~230℃.

If the heating time is too short, the effect of the present invention may not be obtained, but if the heating time is too long, the molecular chain may be decomposed. Therefore, it is preferably 10 seconds to 30 minutes, more preferably 1 to 10 minutes.

The liquid crystal alignment film of the present invention is suitable for the liquid crystal alignment film of the liquid crystal display element of the horizontal electric field mode such as IPS driving mode and FFS driving mode, and is particularly suitable for the liquid crystal alignment film of the liquid crystal display element of the FFS driving mode.

<Liquid crystal display element>

The liquid crystal display element of the present invention is produced by a known method after obtaining a substrate with a liquid crystal alignment film obtained by using the liquid crystal alignment agent of the present invention The liquid crystal cell is obtained by using the liquid crystal cell again.

A liquid crystal display element with a passive matrix structure as an example of a manufacturing method of a liquid crystal cell will be described. In addition, a liquid crystal display element with a movable matrix structure such as a switching element such as TFT (Thin Film Transistor) can be provided for each pixel portion constituting the image display.

First, a transparent glass substrate is prepared, a common electrode is set on one substrate, and a node electrode is set on the other substrate. The electrodes can be ITO electrodes, for example, to draw a desired image display. Secondly, an insulating film covering the common electrode and the node electrode is provided on each substrate. The insulating film may be, for example, a film made of SiO ₂ -TiO ₂ formed by a sol-gel method.

Secondly, the liquid crystal alignment film of the present invention is formed on each substrate.

Then, one substrate and the other substrate are superimposed in a way that the alignment film surfaces face each other, and then the surroundings are connected with a sealing material. In addition, in order to control the substrate gap, the spacer is generally injected into the sealing material. Also, even if it is an in-plane part where no sealing material is provided, it is better to spread the spacer for substrate gap control. A part of the sealing material may be provided with an opening filled with liquid crystal from the outside.

Next, the liquid crystal material is injected into the space surrounded by the two substrates and the sealing material through the opening provided in the sealing material. After that, the opening is sealed with an adhesive. Vacuum injection method or capillary phenomenon in the atmosphere can be used for injection. The liquid crystal material can use any one of a positive type liquid crystal material and a negative type liquid crystal material. Secondly, set the polarizing plate. Specifically, a pair of polarizing plates are attached to the opposite side surfaces of the liquid crystal layer in the two substrates. Through the above steps, the liquid crystal display device of the present invention is obtained. Since the liquid crystal display element uses the liquid crystal alignment film obtained in the present invention as the liquid crystal alignment film, it is excellent Good afterimage characteristics, suitable for large-screen and high-definition LCD TVs, etc.

[Example]

Hereinafter, the present invention will be specifically described with examples. In addition, the present invention is not limited to these embodiments. The codes used below are as follows.

NMP: N-methyl-2-pyrrolidone

GBL: γ-butyrolactone

BCS: Butyl Cellosolve

Acid dianhydride (A): Tetracarboxylic dianhydride of the following formula (A)

Acid dianhydride (B): Tetracarboxylic dianhydride of the following formula (B)

Acid dianhydride (C): Tetracarboxylic dianhydride of the following formula (C)

DA-1: Diamine of the following formula (DA-1)

DA-2: Diamine of the following formula (DA-2)

Specific compound A: The following compound (Primid XL552, manufactured by Yems Corporation)

The following is the measurement method of various characteristics.

[Viscosity]

The E-type viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.) was used for measurement with a sample volume of 1.1 mL, a tapered rotor TE-1 (1°34', R24), and a temperature of 25°C.

[Molecular weight]

It is measured using a GPC (normal temperature gel permeation chromatography) device, and the number average molecular weight (Mn) and weight average molecular weight (Mw) are calculated with polyethylene glycol and polyethylene oxide conversion values.

GPC device: manufactured by Shodex (GPC-101)

Column: manufactured by Shodex (in-line KD803, KD805)

Column temperature: 50℃

Eluent: N,N-dimethylformamide (additive is lithium bromide-hydrate (LiBr.H ₂ O) 30mmol/L (liter), phosphoric anhydride crystal (o-phosphoric acid) 30mmol/L, tetrahydrofuran (THF) 10ml/L)

Flow rate: 1.0ml/min

Standard samples for making calibration lines: Tosoh Corporation’s TSK standard polyethylene oxide (weight average molecular weight (Mw) approximately 900,000, 150,000, 100,000, 30,000), and Polyman’s polyethylene glycol (maximum molecular weight ( Mp) about 12,000, 4,000, 1,000). In order to avoid peak overlap during the measurement, the four samples of 900,000, 100,000, 12,000, and 1,000 were mixed, and the three samples of 150,000, 30,000, and 4,000 were mixed.

[Making LCD cell]

Fabricate a liquid crystal cell with a structure of FFS type liquid crystal display element.

On the prepared glass substrate with electrodes (length 30mm×width 50mm×thickness 0.7mm), an ITO electrode with a coating pattern as the first layer to constitute the counter electrode was formed. A SiN (silicon nitride) film formed by the CVD method as a second layer is formed on the counter electrode for the first layer. The SiN film used for the second layer has a thickness of 500 nm and functions as an interlayer insulating film. It is formed on the SiN film for the second layer as the third layer. After drawing the ITO film, the formed comb-shaped pixel electrodes are arranged to form the first pixel and the second image. The two kinds of pixels. The size of each pixel is approximately 10mm in length and 5mm in width. At this time, the counter electrode of the first layer and the pixel electrode of the third layer are electrically insulated by the SiN film for the second layer.

The pixel electrode of the third layer has a comb-tooth shape composed of a plurality of arranged U-shaped electrode elements with a curved central part. The width of each electrode element in the short direction is 3 μm, and the interval between electrode elements is 6 μm. Since the pixel electrode forming each pixel is composed of a plurality of arranged electrode elements with a curved central part, the shape of each pixel is not a rectangular shape, but the same as the electrode element, it has a central curved part, which is similar The shape of "ㄑ" in thick characters. In addition, each pixel system is divided into upper and lower areas with its central curved portion as a boundary, and has a first area on the upper side of the curved portion and a second area on the lower side.

Comparing the first area and the second area of each pixel, it turns out that the electrode elements constituting the pixel electrodes have different formation directions. That is, when the rubbing direction of the liquid crystal alignment film described later is used as a reference, in the first area of the pixel, the electrode elements of the pixel electrode are formed at an angle of +10° (clock rotation), and in the second area of the pixel, The electrode elements of the pixel electrode are formed at an angle of -10° (clock rotation). That is, the first area and the second area of each pixel are such that the directions of the rotation (in-plane switching) of the liquid crystal in the surface of the substrate induced by the voltage applied between the pixel electrode and the counter electrode are opposite to each other. The way the direction is composed.

Secondly, the obtained liquid crystal alignment agent was filtered with a 1.0μm filter, and then it was spin-coated on the prepared substrate with electrodes and formed on the back of the glass substrate with a columnar spacer with a height of 4μm. On the board. After drying on a hot plate at 80°C for 5 minutes, it is fired in a hot air circulating oven at 230°C for 20 minutes to form a coating film with a thickness of 100 nm. The coating film surface is subjected to alignment treatment such as rubbing and polarized ultraviolet irradiation to obtain a substrate with a liquid crystal alignment film. Using the above two substrates as a set, after printing the sealant on one substrate, the other substrate is bonded so that the relative alignment direction of the liquid crystal alignment film surface is 0°, and then the sealant is hardened to make an empty cell. The liquid crystal MLC-2041 (manufactured by Merco) 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 110° C. for 1 hour, and left overnight for each evaluation.

[Assess liquid crystal orientation]

Under a constant temperature environment of 60°C, an AC voltage with a frequency of 30 Hz and a relative light transmittance of 100% was applied to the liquid crystal cell obtained by the above-mentioned manufacturing method for 168 hours. After that, the pixel electrode and the counter electrode of the liquid crystal cell were short-circuited, and they were left directly at room temperature for one day. After placement, the liquid crystal cell is placed between two polarizing plates arranged orthogonally to the polarization axis, the backlight is turned on under no applied voltage, and the arrangement angle of the liquid crystal cell is adjusted to the minimum brightness of light transmission. Furthermore, the rotation angle when the liquid crystal cell is rotated from the angle where the second area of the first pixel is the darkest to the angle where the first area is the darkest is calculated as the angle Δ. Similarly, compare the second area of the second pixel with the first area to calculate the same angle △. Then, the average value of the angle Δ between the first pixel and the second pixel is calculated as the angle Δ of the liquid crystal cell, and the liquid crystal alignment is evaluated with this value. That is, a small value of the angle Δ indicates that the liquid crystal alignment is good. [Evaluation of voltage holding rate (VHR) (backlight aging resistance (voltage holding rate 1))]

On the prepared glass substrate with electrodes (length 30mm×width 50mm×thickness 0.7mm), an ITO electrode with a film thickness of 35nm was formed. The electrode was a strip pattern with a length of 40mm and a width of 10mm. Secondly, the liquid crystal alignment agent was filtered with a 1.0 μm filter, and then it was spin-coated on the prepared substrate with electrodes. After drying on a hot plate at 50°C for 5 minutes, it is fired in an IR oven at 230°C for 20 minutes to form a coating film with a thickness of 100nm, and a substrate with a liquid crystal alignment film is obtained. After rubbing the liquid crystal alignment film with rayon (roller diameter: 120mm, roll rotation number: 1000rpm, moving speed: 20mm/sec, pressing length: 0.4mm), the liquid crystal alignment film is irradiated in pure water with ultrasonic waves for 1 minute to clean it, and then blown After removing the water droplets, dry at 80°C for 15 minutes to obtain a substrate with a liquid crystal alignment film.

Prepare two substrates with liquid crystal alignment film mentioned above, spread the 4μm spacer on the liquid crystal alignment film surface of one of them, and print the sealant on top of it, and then use the rubbing direction as the opposite direction and the film surface facing each other Attach another substrate in a way. Next, the sealant is hardened to make an empty cell. The liquid crystal MLC-2041 (manufactured by Merco) was injected into the empty cell by a reduced pressure injection method, and the injection port was sealed to obtain a liquid crystal cell. Secondly, the obtained liquid crystal cell was heated at 110°C for 1 hour and placed at 23°C for the next night to obtain a VHR measurement cell. Secondly, the unit was aged for 72 hours under an LED light source (1000cd) in an oven at 70°C.

After 72 hours of backlight aging, apply a voltage of 1V for 60μsec to the unit at a temperature of 60℃, measure the voltage after 100msec, and then How much voltage can be maintained as VHR, and use this value to evaluate the backlight aging resistance of VHR. That is, when the VHR value is large, it indicates that the VHR has good backlight aging resistance.

[Assess black level]

After fabricating the liquid crystal cell with the above (making the liquid crystal cell), it is placed between the two polarizing plates arranged in a way that the polarization axis system is orthogonal, and the backlight is turned on in a state where no voltage is applied. At the same time, the arrangement angle of the liquid crystal cell is adjusted to make The transmitted light has the smallest brightness. While observing the LCD unit with a digital CCD camera "C8800-21C" manufactured by Hamamatsu Corporation, use the company's analysis software "ExDcam Image capture Software" to digitize the brightness of the captured image. When the brightness value of the liquid crystal cell is 500 to 600, it is regarded as "good", the above is regarded as "bad".

[Relief characteristics of accumulated charge]

After fabricating the liquid crystal cell as above (making the liquid crystal cell), it is placed between the two polarizing plates arranged orthogonally to the polarization axis system. When the pixel electrode and the counter electrode are short-circuited and the same potential, the two The LED backlight is illuminated under the polarizing plate, and the angle of the liquid crystal unit is adjusted at the same time, so that the light transmission brightness of the LED backlight measured above the two polarizing plates is the smallest.

Next, a rectangular wave with a frequency of 30 Hz was applied to the liquid crystal cell, and the V-T characteristics (voltage-transmittance characteristics) at a temperature of 23°C were measured at the same time, and then an AC voltage with a relative transmittance of 23% was calculated. Next, apply an AC voltage with a relative light transmittance of 23% and a rectangular wave with a frequency of 30 Hz. 5 After minutes, superimpose +1.0V DC voltage and drive for 30 minutes. After that, the DC voltage was cut off, and only an AC voltage with a relative light transmittance of 23% and a rectangular wave with a frequency of 30 Hz was applied for 20 minutes.

Accelerating the relaxation of the accumulated charge will also accelerate the accumulation of charge in the liquid crystal cell when the DC voltage is superimposed. Therefore, the relaxation characteristic of the accumulated charge is that the current relative light transmittance of the superimposed DC voltage is 30% or more after 30 minutes. When the relative light transmittance drops to less than 28%, it is defined as a "good" evaluation method. Under superimposed DC voltage, even after 30 minutes, the relative light transmittance has not fallen below 28%, it is defined as "bad" evaluation method.

(Synthesis example 1)

After measuring 79.4g (0.33mol) of DA-1 in a 3L four-necked flask with a stirring device under nitrogen environment, measure 64.8g (0.33mol) of DA-2, then add 911g of NMP and 911g of GBL, and send it Stir and dissolve while adding nitrogen. While stirring the diamine solution, add 65.0g (0.33mol) of acid dianhydride (C). After stirring for 2 hours at room temperature, add 86.1g (0.29mol) of acid dianhydride (A), followed by 390g The NMP and 390g of GBL were stirred at 40°C for 30 hours under a nitrogen environment to obtain a polyamide acid solution (PAA-1). The viscosity of the polyamide acid solution at a temperature of 25°C is 215mPa. s. The Mn of the polyamide acid is 15,773, and the Mw is 31,242.

(Synthesis example 2)

Measure 95.3 g in a 3L four-neck flask with a stirring device under nitrogen environment After (0.39mol) DA-1, weigh 51.8g (0.26mol) DA-2, add 939g NMP and 939g GBL, and stir to dissolve while feeding nitrogen. While stirring the diamine solution, add 65.0g (0.33mol) of acid dianhydride (C). After stirring for 2 hours at room temperature, add 86.1g (0.29mol) of acid dianhydride (A), 402g of NMP and 402g The GBL was stirred at 40°C for 30 hours in a nitrogen environment to obtain a polyamide acid solution (PAA-2). The viscosity of the polyamide acid solution at a temperature of 25°C is 221mPa. s. The Mn of the polyamic acid is 14,773, and the Mw is 32,212.

(Synthesis example 3)

After measuring 79.4g (0.33mol) of DA-1 in a 3L four-necked flask with a stirring device under nitrogen environment, measure 64.8g (0.33mol) of DA-2, then add 859g of NMP and 859g of GBL, and send it Stir and dissolve while adding nitrogen. While stirring the diamine solution, add 65.0g (0.33mol) of acid dianhydride (C). After stirring for 2 hours at room temperature, add 63.8g (0.29mol) of acid dianhydride (B), 369g of NMP and 369g The GBL was stirred at 40°C for 30 hours under a nitrogen environment to obtain a polyamide acid solution (PAA-3). The viscosity of the polyamide acid solution at a temperature of 25°C is 207mPa. s. The Mn of the polyamide is 13,853, and the Mw is 28,251.

(Synthesis example 4)

After measuring 79.4g (0.33mol) of DA-1 in a 3L four-necked flask with a stirring device under nitrogen environment, measure 64.8g (0.33mol) of DA-2, then add 839g of NMP and 839g of GBL, and send it Stir while adding nitrogen Mix to dissolve. While stirring the diamine solution, 122.3g (0.62mol) of acid dianhydride (C), 360g of NMP and 360g of GBL were added, and after stirring at 40°C for 30 hours under a nitrogen environment, a polyamide acid solution (PAA- 4). The viscosity of the polyamic acid solution at a temperature of 25°C is 212mPa. s. The Mn of this polyamic acid is 14,255, and the Mw is 28,373.

(Synthesis Example 5)

After weighing 129.5g (0.65mol) of DA-2 in a 3L four-necked flask with a stirring device in a nitrogen environment, add 884g of NMP and 884g of GBL, and stir to dissolve while feeding nitrogen. While stirring the diamine solution, add 65.0g (0.33mol) of acid dianhydride (C). After stirring for 2 hours at room temperature, add 86.1g (0.29mol) of acid dianhydride (A), 379g of NMP and 379g The GBL was stirred at 40°C for 30 hours under a nitrogen environment to obtain a polyamide acid solution (PAA-5). The viscosity of the polyamic acid solution at a temperature of 25°C is 225mPa. s. The Mn of the polyamide acid is 12,799, and the Mw is 33,192.

(Synthesis Example 6)

After measuring 91.6g (0.38mol) of DA-1 in a 3L four-necked flask with a stirring device in a nitrogen environment, measure 74.7g (0.38mol) of DA-2, then add 661g of NMP and 661g of GBL, and send it Stir and dissolve while adding nitrogen. While stirring the diamine solution, add 67.7g (0.35mol) of acid dianhydride (C). After stirring for 2 hours at room temperature, add 99.3g (0.34mol) of acid dianhydride (A), 283g of NMP and 283g Of GBL, stirring at 40°C for 30 hours in a nitrogen environment, to obtain a polyamide acid solution (PAA-6). The viscosity of the polyamide acid solution at a temperature of 25°C is 583mPa. s. The Mn of the polyamide acid is 11,141, and the Mw is 21,889.

(Synthesis Example 7)

After measuring 73.3g (0.30mol) of DA-1 in a 3L four-neck flask with a stirring device under nitrogen environment, measure 59.8g (0.30mol) of DA-2, then add 674g of NMP and 674g of GBL, and send it Stir and dissolve while adding nitrogen. While stirring the diamine solution, add 50.0g (0.26mol) of acid dianhydride (C). After stirring for 2 hours at room temperature, add 79.4g (0.27mol) of acid dianhydride (A), 288g of NMP and 288g The GBL was stirred at 40°C for 30 hours under a nitrogen environment to obtain a polyamide acid solution (PAA-7). The viscosity of the polyamide acid solution at a temperature of 25°C is 117mPa. s. The Mn of the polyamide acid is 8,953, and the Mw is 19,521.

(Example 1)

A 5L Erlenmeyer flask with a stir bar was used to aliquot 1861 g of the polyamide acid solution (PAA-1) obtained in Synthesis Example 1, and then add 578 g of NMP and 1.8 g of 3-glycidoxypropyl triethoxy Hydroxysilane, 5.4g of specific compound A, 122g of GBL, and 642g of BCS were stirred with a magnetic stirrer for 2 hours to obtain a liquid crystal alignment agent (A-1).

(Example 2)

Use a 5L Erlenmeyer flask with a stir bar to aliquot 1861g of Synthesis Example 2 After the obtained polyamide acid solution (PAA-2), 578g of NMP, 1.8g of 3-glycidoxypropyltriethoxysilane, 5.4g of specific compound A, 122g of GBL and 642g of BCS was stirred with a magnetic stirrer for 2 hours to obtain a liquid crystal alignment agent (A-2).

(Example 3)

Take 371 g of the polyamide acid solution (PAA-6) obtained in Synthesis Example 6 in a 3L Erlenmeyer flask with a stir bar, and add 84.6 g of NMP and 0.53 g of 3-glycidoxypropyl triethyl The oxysilane, 1.6 g of specific compound A, 201 g of GBL and 165 g of BCS were stirred with a magnetic stirrer for 2 hours to obtain a liquid crystal alignment agent (A-3).

(Example 4)

In a 2L Erlenmeyer flask into which a stir bar was placed, 213 g of the polyamide acid solution (PAA-7) obtained in Synthesis Example 7 was aliquoted, and 101 g of NMP and 0.25 g of 3-glycidoxypropyl triethoxy were added. Hydroxysilane, 0.74g of specific compound A, 146g of GBL, and 109g of BCS were stirred with a magnetic stirrer for 2 hours to obtain a liquid crystal alignment agent (A-4).

(Comparative example 1)

A 5L Erlenmeyer flask with a stir bar was used to aliquot 1861 g of the polyamide acid solution (PAA-3) obtained in Synthesis Example 3, and then add 578 g of NMP and 1.8 g of 3-glycidoxypropyl triethoxy Silane, 5.4g of specific compound A, 122g of GBL and 642g of BCS, stirred with a magnetic stirrer After 2 hours, the liquid crystal alignment agent (B-1) was obtained.

(Comparative example 2)

A 5L Erlenmeyer flask with a stir bar was used to aliquot 1861 g of the polyamide acid solution (PAA-4) obtained in Synthesis Example 4, and then add 578 g of NMP and 1.8 g of 3-glycidoxypropyl triethoxy Hydroxysilane, 5.4g of specific compound A, 122g of GBL and 642g of BCS were stirred with a magnetic stirrer for 2 hours to obtain a liquid crystal alignment agent (B-2).

(Comparative example 3)

A 5L Erlenmeyer flask with a stir bar was used to aliquot 1861 g of the polyamide acid solution (PAA-5) obtained in Synthesis Example 5, and then 578 g of NMP and 1.8 g of 3-glycidoxypropyl triethoxy were added. Hydroxysilane, 5.4g of specific compound A, 122g of GBL and 642g of BCS were stirred with a magnetic stirrer for 2 hours to obtain a liquid crystal alignment agent (B-3).

(Comparative Example 4)

A 5L Erlenmeyer flask with a stir bar was used to aliquot 1861g of the polyamide acid solution (PAA-1) obtained in Synthesis Example 1, and then add 583g of NMP and 1.8g of 3-glycidoxypropyl triethoxy The base silane, 122 g of GBL and 642 g of BCS were stirred with a magnetic stirrer for 2 hours to obtain a liquid crystal alignment agent (B-4).

Industrial use possibility

The liquid crystal alignment film obtained from the liquid crystal alignment agent of the present invention is particularly suitable for the liquid crystal alignment film of the liquid crystal display element of the IPS driving mode or the FFS driving mode and the liquid crystal TV.

Also, citing the Japanese patent application 2014-213835 filed on October 20, 2014, and the Japanese patent application 2015-032093 filed on February 20, 2015, the entire contents of the specification, application scope and abstract description, And it is included in the disclosure in the specification of the present invention.

Claims (10)

A liquid crystal alignment agent characterized by polycondensation of a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride of the following formula (A) and a diamine component containing a diamine represented by the following formula (B) At least one polymer selected from the group of the polyamide acid obtained by the reaction and the imidization polymer of the polyamide acid, and the compound represented by the following formula (C),

(In formula (B), m is an integer from 1 to 5)

(In formula (C), X ¹ is an n-valent organic group containing an aliphatic hydrocarbon group with 1 to 20 carbon atoms, n is an integer of 2 to 6, and R ¹ and R ² are independent hydrogen atoms, or may have The substituent is a hydrocarbon group formed by an alkyl group with 1 to 4 carbons, an alkenyl group with 2 to 4 carbons, or alkynyl group with 2 to 4 carbons. At least one of R ¹ and R ² is a hydrocarbon group substituted by a hydroxy group) . The liquid crystal alignment agent of claim 1, wherein 20-80 mole% of the aforementioned tetracarboxylic dianhydride component is the tetracarboxylic dianhydride of formula (A). The liquid crystal alignment agent of claim 1 or 2, wherein 20-80 mole% of the aforementioned diamine component is a diamine of formula (B). The liquid crystal alignment agent of claim 1 or 2, wherein the aforementioned diamine component is a diamine containing at least one selected from the group of structures of the following formulas (YD-1) to (YD-5),

(In formula (YD-1), A ₁ is a heterocyclic ring containing a nitrogen atom with 3 to 15 carbon atoms, and Z ₁ is a hydrogen atom, or a hydrocarbon group with 1 to 20 carbon atoms that may have a substituent; formula (YD-2 In ), W ₁ is a hydrocarbon group with 1 to 10 carbons, and A ₂ is a monovalent organic group with 3 to 15 carbons and a heterocyclic ring containing a nitrogen atom, or substituted by an aliphatic group with 1 to 6 carbons Disubstituted amino group; in formula (YD-3), W ₂ is a divalent organic group with 6 to 15 carbons and 1 or 2 benzene rings, and W ₃ is an alkylene group with 2 to 5 carbons or Biphenyl, Z ₂ is a hydrogen atom, an alkyl group with 1 to 5 carbons, or a benzene ring, a is an integer of 0 to 1; in formula (YD-4), A ₃ is a carbon containing 3 to 15 A heterocyclic ring with a nitrogen atom; in formula (YD-5), A ₄ is a heterocyclic ring containing a nitrogen atom with 3 to 15 carbon atoms, and W ₅ is an alkylene group with 2 to 5 carbon atoms. The liquid crystal alignment agent of claim 1 or 2, wherein the aforementioned diamine component is selected from the group of divalent organic groups having the structure of the following formula (YD-6)~(YD-21) At least one,

(In formula (YD-17), h is an integer from 1 to 3, and in formulas (YD-14) and (YD-21), j is an integer from 1 to 3). The liquid crystal alignment agent of claim 1 or 2, wherein the content of the compound represented by the above formula (C) relative to the polymer of the component (A) is 0.1-20% by mass. The liquid crystal alignment agent of claim 1 or 2, wherein the compound represented by the above formula (C) is a compound represented by the following formula (C-1),

A liquid crystal alignment film, which is obtained by coating the liquid crystal alignment agent according to any one of claims 1 to 7 and then firing. A liquid crystal display element including the liquid crystal alignment film as claimed in claim 8. Such as the liquid crystal display element of claim 9, which is an IPS driving method or an FFS driving method.