JP7571730B2 - Liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display element using the same - Google Patents

Description

The present invention relates to a liquid crystal alignment agent, a liquid crystal alignment film obtained using this liquid crystal alignment agent, and a liquid crystal display element having the obtained liquid crystal alignment film.

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

Although the liquid crystal cell of the horizontal electric field type has excellent viewing angle characteristics, the electrode portion formed in the substrate is small, so if the voltage retention rate is low, the liquid crystal does not receive sufficient voltage and the display contrast decreases. In addition, if the stability of the liquid crystal orientation is low, the liquid crystal will not return to its initial state when driven for a long time, which causes a decrease in contrast and afterimages, so the stability of the liquid crystal orientation is important. Furthermore, static electricity is easily accumulated in the liquid crystal cell, and charges are accumulated in the liquid crystal cell even when the positive and negative asymmetric voltages generated by driving are applied, and these accumulated charges affect the display as liquid crystal orientation disturbances and afterimages, significantly reducing the display quality of the liquid crystal element. In addition, charges are accumulated when the backlight light is irradiated on the liquid crystal cell immediately after driving, causing problems such as afterimages even when driven for a short time and flickering during driving.

Patent Document 1 discloses a liquid crystal alignment agent containing a polymer obtained by polycondensing a specific diamine and an aliphatic tetracarboxylic acid derivative as a liquid crystal alignment agent that has excellent voltage retention and reduced charge accumulation when used in such in-plane switching mode liquid crystal display elements. However, as liquid crystal display elements become more powerful, the properties required of liquid crystal alignment films are becoming more stringent, and it is difficult for these conventional technologies to fully satisfy all the required properties.

International Publication WO2004/021076 Pamphlet

The present invention aims to provide a liquid crystal alignment agent capable of obtaining a liquid crystal alignment film that has excellent stability in liquid crystal alignment and is less susceptible to flicker during operation, a liquid crystal alignment film obtained from the liquid crystal alignment agent, and a liquid crystal display element equipped with the obtained liquid crystal alignment film.

As a result of extensive research into solving the above problems, the inventors discovered that the above problems could be improved by introducing multiple specific structures into the polymer contained in the liquid crystal alignment agent, and thus completed the present invention.

The present invention is based on these findings and has the following gist.
A liquid crystal aligning agent comprising the following polymer (A) and polymer (B):
Polymer (A): A polyamic acid obtained by polycondensation of a diamine component including a first diamine represented by the following formula (1), a second diamine represented by the following formula (2), and a third diamine represented by the following formula (3), and a tetracarboxylic dianhydride having an alicyclic structure.
(In formula (3), n1 and n2 each independently represent an integer of 1 to 3.)
Polymer (B): A polyamic acid obtained by polycondensation of a diamine component that does not simultaneously contain a first diamine represented by the formula (1), a second diamine represented by the formula (2), and a third diamine represented by the formula (3), and a tetracarboxylic dianhydride.

FIG. 1 is a schematic cross-sectional view showing an example of a horizontal electric field liquid crystal display element. FIG. 11 is a schematic cross-sectional view showing another example of a horizontal electric field liquid crystal display element.

The liquid crystal aligning agent of the present invention contains the polymer (A) and the polymer (B) described below.
<Polymer (A)>
The polymer (A) used in the present invention is a polyamic acid obtained by polycondensation of a diamine component including a first diamine represented by the following formula (1), a second diamine represented by the following formula (2), and a third diamine represented by the following formula (3), and a tetracarboxylic acid dianhydride having an alicyclic structure.

In formula (3), n1 and n2 each independently represent an integer of 1 to 3.

The content ratio of the diamines of the above formulae (1) to (3) in polymer (A) is not particularly limited, but it is preferable that the diamine of formula (1) is 10 to 70 mol %, the diamine of formula (2) is 10 to 70 mol %, and the diamine of formula (3) is 5 to 50 mol % relative to the total diamine components constituting polymer (A).

The diamine component of polymer (A) may contain diamines other than those of formulas (1) to (3) above. The content of diamines other than those of formulas (1) to (3) is preferably 50 mol % or less, more preferably 30 mol % or less, of the total diamine components constituting polymer (A).

In the polymer (A), the structure of the tetracarboxylic dianhydride having an alicyclic structure is not particularly limited. In addition, the structure of the tetracarboxylic dianhydride having an alicyclic structure in the polymer (A) may be one type, or two or more types may be mixed.

Preferred structures of the tetracarboxylic dianhydride having an alicyclic structure in the polymer (A) are shown below, but the present invention is not limited to these.

The polymer (A) used in the present invention may be a polymer whose main chain end is modified with a compound that is monofunctional with respect to the tetracarboxylic acid derivative component and/or the diamine component. Examples of the monofunctional compound include monoamines, monoisocyanates, compounds having one acid anhydride group, and compounds having one acid chloride group.

The molecular weight of polymer (A) is not particularly limited as long as a good coating film can be formed, but for example, the weight average molecular weight is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and even more preferably 10,000 to 100,000. The number average molecular weight is preferably 1,000 to 250,000, more preferably 2,500 to 150,000, and even more preferably 5,000 to 50,000.

<Polymer (B)>
The polymer (B) used in the present invention is a polyamic acid obtained by polycondensation of a diamine component that does not simultaneously contain the first diamine represented by the formula (1), the second diamine represented by the formula (2), and the third diamine represented by the formula (3), and a tetracarboxylic dianhydride.
The polymer (B) is a polymer different from the polymer (A). Therefore, the polymer (B) is specified to be a polyamic acid obtained by using a diamine component that does not simultaneously contain a first diamine represented by formula (1), a second diamine represented by formula (2), and a third diamine represented by formula (3).

The diamine contained in the diamine component of the polymer (B) may be a compound represented by the following formula (4).
In formula (4), _Y1 represents a divalent organic group, and two R each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

The diamine component in polymer (B) may be one type of diamine, or may be a mixture of two or more types of diamines, but does not simultaneously contain the first diamine represented by formula (1), the second diamine represented by formula (2), and the third diamine represented by formula (3). It is preferable that the diamine component of polymer (B) does not contain any of the diamines represented by formulas (1) to (3).

Regarding the compound represented by the formula (4), structures of _Y1 in particularly preferred compounds as the diamine component of the polymer (B) are shown below, but the present invention is not limited thereto.

The compound of formula (4) in which Y ₁ is any of the above structures may be present alone or in combination of two or more kinds in the diamine component of polymer (B).
It is also preferred that the compound of formula (4) in which Y ₁ is any one of the following structures is additionally included.
In the above, Boc represents a group represented by the following formula:

In the polymer (B), the structure of the tetracarboxylic dianhydride is not particularly limited. In addition, the structure of the tetracarboxylic dianhydride in the polymer (B) may be one type, or two or more types may be mixed.

Preferred structures of the tetracarboxylic dianhydride in the polymer (B) are shown below, but the present invention is not limited to these.

The polymer (B) used in the present invention may be a polymer whose main chain end is modified with a compound that is monofunctional with respect to the tetracarboxylic acid derivative component and/or the diamine component. Examples of the monofunctional compound include monoamines, monoisocyanates, compounds having one acid anhydride group, and compounds having one acid chloride group.

The molecular weight of polymer (B) is not particularly limited as long as a good coating film can be formed, but for example, the weight average molecular weight is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and even more preferably 10,000 to 100,000. The number average molecular weight is preferably 1,000 to 250,000, more preferably 2,500 to 150,000, and even more preferably 5,000 to 50,000.

<Liquid crystal alignment agent>
In the liquid crystal aligning agent of the present invention, the blending ratio of the polymer (A) and the polymer (B) is not particularly limited, but the content of the polymer (A) is preferably 50 to 90 mass%, more preferably 60 to 80 mass%, based on the total of the polymer (A) and the polymer (B).

The liquid crystal alignment agent of the present invention may contain other polymers in addition to polymer (A) and polymer (B). The main skeleton of the other polymers is not particularly limited, but examples thereof include polymers having a main skeleton of polyamic acid, polyamic acid ester, polyimide, polysiloxane, polyester, cellulose derivative, polyacetal, polystyrene derivative, poly(styrene-maleimide) derivative, poly(meth)acrylate, etc.

The liquid crystal alignment agent of the present invention may contain components other than the polymer. Examples of components other than the polymer include dielectric or conductive substances for changing the electrical properties of the liquid crystal alignment film, such as the dielectric constant and conductivity, silane coupling agents for improving adhesion between the liquid crystal alignment film and the substrate, crosslinking compounds for increasing the hardness and density of the film when made into a liquid crystal alignment film, and imidization promoters for efficiently promoting imidization of polyamic acid when the coating film is baked.

The liquid crystal alignment agent of the present invention is used to prepare a liquid crystal alignment film, and from the viewpoint of forming a uniform thin film, it is preferable that the liquid crystal alignment agent is a coating solution in which the above components are dissolved in an organic solvent. The concentration of the polymer in the liquid crystal alignment agent is appropriately changed depending on the coating device used and the thickness of the liquid crystal alignment film to be obtained. From the viewpoint of forming a uniform and defect-free coating film, it is preferable that the concentration is 1% by mass or more, and from the viewpoint of storage stability of the solution, it is preferable that the concentration is 10% by mass or less. A particularly preferable concentration of the polymer is 2 to 8% by mass.

The organic solvent used in the coating solution is not particularly limited as long as it dissolves the polymer component uniformly. Specific examples include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylsulfoxide, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone, methyl ethyl ketone, cyclohexanone, and cyclopentanone. Of these, it is preferable to use N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone. Two or more of these solvents may be used in combination.

In addition, in compositions intended for forming coating films, it is common to use mixed solvents containing, in addition to the above-mentioned solvents, a solvent that improves the coating properties and the smoothness of the coating surface, and such mixed solvents are preferably used in the liquid crystal alignment agent of the present invention. Specific examples of organic solvents to be mixed are listed below, but are not limited to these examples.

For example, ethanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol, tert-pentyl alcohol, 3-methyl-2-butanol, neopentyl alcohol, 1-hexanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-ethyl -1-butanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, cyclohexanol, 1-methylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3 -butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, dipropyl ether, dibutyl ether, dihexyl ether, 1,4-dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, 1,2-butoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, 4-hydroxy-4-methyl-2-pentanone, diethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, 2-pentanone, 3-pentanone, 2-hexanone, 2-heptanone, 4-heptanone, 3-ethoxybutyl acetate, 1-methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, ethylene glycol monoacetate, ethylene glycol diacetate, propylene Carbonate, ethylene carbonate, 2-(methoxymethoxy)ethanol, ethylene glycol monobutyl ether, ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, 2-(hexyloxy)ethanol, furfuryl alcohol, diethylene glycol, propylene glycol, propylene glycol monobutyl ether, 1-(butoxyethoxy)propanol, propylene glycol monomethyl ether acetate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monoacetate, ethylene glycol Examples of the solvent include butyl ether acetate, ...

(R in formula [D-1] and formula [D-2] represents an alkyl group having 1 to 3 carbon atoms, and R in formula [D-3] represents an alkyl group having 1 to 4 carbon atoms.)

Among the above, 1-hexanol, cyclohexanol, 1,2-ethanediol, 1,2-propanediol, propylene glycol monobutyl ether, diethylene glycol diethyl ether, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monobutyl ether, or dipropylene glycol dimethyl ether is preferred. The type and content of such a solvent are appropriately selected depending on the coating device, coating conditions, coating environment, etc. of the liquid crystal alignment agent. In addition, two or more of these solvents may be used in combination.

<Liquid crystal alignment film>
The liquid crystal alignment film of the present invention is obtained from the liquid crystal alignment agent of the present invention. One example of a method for obtaining a liquid crystal alignment film from a liquid crystal alignment agent is to apply a liquid crystal alignment agent in the form of a coating liquid to a substrate, dry, and bake the resulting film, and then perform an alignment treatment by a rubbing treatment method or a photo-alignment treatment method.

The substrate to which the liquid crystal alignment agent is applied is not particularly limited, and a glass substrate, a silicon nitride substrate, or a plastic substrate such as an acrylic substrate or a polycarbonate substrate can be used. In this case, it is preferable to use a substrate on which an ITO electrode for driving the liquid crystal is formed in terms of simplifying the process. In addition, in a reflective liquid crystal display element, an opaque material such as a silicon wafer can be used for only one substrate, and in this case, a light-reflecting material such as aluminum can be used for the electrode.
The method of applying the liquid crystal alignment agent is not particularly limited, but industrially, screen printing, offset printing, flexographic printing, inkjet printing, etc. are generally used. Other application methods include a dip method, a roll coater method, a slit coater method, a spinner method, a spray method, etc., and these may be used depending on the purpose.

After the liquid crystal alignment agent is applied to the substrate, the solvent is evaporated and the substrate is baked by a heating means such as a hot plate, a heat circulation oven, or an IR (infrared) oven. The temperature and time for the drying and baking process after the liquid crystal alignment agent is applied can be selected as desired. Usually, the substrate is baked at 50 to 120° C. for 1 to 10 minutes, and then baked at 150 to 300° C. for 5 to 120 minutes in order to sufficiently remove the solvent contained therein.
The thickness of the liquid crystal alignment film after baking is not particularly limited, but if it is too thin, the reliability of the liquid crystal display element may decrease, so that the thickness is preferably 5 to 300 nm, more preferably 10 to 200 nm.
The liquid crystal alignment film of the present invention is suitable as a liquid crystal alignment film for a liquid crystal display element of a horizontal electric field type such as an IPS type or an FFS type, and is particularly useful as a liquid crystal alignment film for a liquid crystal display element of an FFS type.

<Liquid crystal display element>
The liquid crystal display element of the present invention is obtained by preparing a substrate having a liquid crystal alignment film obtained from the above liquid crystal aligning agent, and then preparing a liquid crystal cell by a known method, and using the liquid crystal cell to form an element.
An example of a method for producing a liquid crystal cell will be given below, but the present invention is not limited to this.

First, a set of substrates is prepared on which electrodes for driving the liquid crystal are formed. These electrodes can be, for example, ITO electrodes, and are patterned to display the desired image. In addition, a switching element such as a TFT (Thin Film Transistor) may be provided in each pixel portion that constitutes the image display. A liquid crystal alignment film is formed on the substrates as described above.

Next, a sealant, for example an ultraviolet-curable sealant, is placed at a predetermined location on one of the two substrates on which the liquid crystal alignment film is formed, and liquid crystal is placed at several predetermined locations on the liquid crystal alignment film surface.The other substrate is then attached and pressed together so that the liquid crystal alignment film faces the other substrate, spreading the liquid crystal over the entire surface of the liquid crystal alignment film.Then, ultraviolet light is irradiated onto the entire surface of the substrate to cure the sealant, thereby obtaining a liquid crystal cell.
Alternatively, as a process after forming a liquid crystal alignment film on the substrate, when placing a sealant at a predetermined position on one of the substrates, an opening into which liquid crystal can be filled from the outside is provided, and after bonding the substrates together without placing liquid crystal, liquid crystal material is injected into the liquid crystal cell through the opening provided in the sealant, and then this opening is sealed with an adhesive to obtain a liquid crystal cell. The liquid crystal material can be injected by a vacuum injection method or a method utilizing capillary action in the atmosphere.
In any of the above methods, in order to secure space within the liquid crystal cell into which the liquid crystal material is filled, it is preferable to take measures such as providing columnar protrusions on one of the substrates, scattering spacers on one of the substrates, mixing spacers into the sealing agent, or a combination of these.

The liquid crystal material may be nematic liquid crystal or smectic liquid crystal, of which nematic liquid crystal is preferred, and either positive or negative liquid crystal material may be used. Next, polarizing plates are installed. Specifically, it is preferred to attach a pair of polarizing plates to the surfaces of the two substrates opposite the liquid crystal layer.

FIG. 1 is a schematic cross-sectional view showing an example of a horizontal electric field liquid crystal display element, which is an example of an IPS mode liquid crystal display element.
In the lateral electric field liquid crystal display element 1 illustrated in Fig. 1, liquid crystal 3 is sandwiched between a comb-tooth electrode substrate 2 having a liquid crystal alignment film 2c and a counter substrate 4 having a liquid crystal alignment film 4a. The comb-tooth electrode substrate 2 has a base material 2a, a plurality of linear electrodes 2b formed on the base material 2a and arranged in a comb-tooth shape, and a liquid crystal alignment film 2c formed on the base material 2a so as to cover the linear electrodes 2b. The counter substrate 4 has a base material 4b and a liquid crystal alignment film 4a formed on the base material 4b. At least one of the liquid crystal alignment film 2c and the liquid crystal alignment film 4a is the liquid crystal alignment film of the present invention.
In this IPS LCD element 1, when a voltage is applied to the linear electrodes 2b, an electric field is generated between the linear electrodes 2b as indicated by electric force lines L.

FIG. 2 is a schematic cross-sectional view showing another example of a horizontal electric field liquid crystal display element, which is an example of an FFS mode liquid crystal display element.
In the lateral electric field liquid crystal display element 1 illustrated in Fig. 2, liquid crystal 3 is sandwiched between a comb-tooth electrode substrate 2 having a liquid crystal alignment film 2h and a counter substrate 4 having a liquid crystal alignment film 4a. The comb-tooth electrode substrate 2 has a base material 2d, a plane electrode 2e formed on the base material 2d, an insulating film 2f formed on the plane electrode 2e, a plurality of linear electrodes 2g formed on the insulating film 2f and arranged in a comb-tooth shape, and a liquid crystal alignment film 2h formed on the insulating film 2f so as to cover the linear electrodes 2g. The counter substrate 4 has a base material 4b and a liquid crystal alignment film 4a formed on the base material 4b. At least one of the liquid crystal alignment film 2h and the liquid crystal alignment film 4a is the liquid crystal alignment film of the present invention.
In this IPS LCD element 1, when a voltage is applied to the plane electrodes 2e and the linear electrodes 2g, an electric field is generated between the plane electrodes 2e and the linear electrodes 2g as indicated by electric field lines L.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The abbreviations for compounds and solvents, and the method for evaluating the properties are as follows:

NMP: N-methyl-2-pyrrolidone GBL: γ-butyrolactone BCS: butyl cellosolve DA-1 to DA-9: compounds of the following structural formulae CA-1 and CA-2: compounds of the following structural formulae AD-1 and AD-2: compounds of the following structural formulae

[Viscosity measurement]
In the following synthesis examples, the viscosity of the polymer solution was measured using an E-type viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.) with a sample amount of 1.1 mL, a cone rotor TE-1 (1°34′, R24), and a temperature of 25°C.

<Synthesis of Polymer>
(Synthesis Example 1)
DA-1 (99.63 g, 500 mmol), DA-2 (106.64 g, 500 mmol), and DA-3 (74.60 g, 250 mmol) were added to a 5000 mL separable flask equipped with a stirrer and a nitrogen inlet tube, and then NMP (3663.6 g) was added and stirred and dissolved while feeding nitrogen. While stirring this solution, CA-1 (228 g, 1163 mmol) and NMP (915.8 g) were added, and the mixture was stirred at 23° C. for 2 hours to obtain an NMP solution of polyamic acid (PAA-A1). The viscosity of this polyamic acid solution was 91 mPa·s.

(Synthesis Example 2)
DA-4 (0.54 g, 4.99 mmol), DA-5 (1.83 g, 7.49 mmol), DA-6 (2.40 g, 7.49 mmol), and DA-7 (1.99 g, 4.99 mmol) were added to a 100 mL four-neck flask equipped with a stirrer and a nitrogen inlet tube, and then NMP (68.43 g) was added and stirred while feeding nitrogen to dissolve. While stirring this solution, CA-2 (5.31 g, 23.7 mmol) and NMP (20.12 g) were added, and the mixture was further stirred at 50° C. for 12 hours to obtain a solution of polyamic acid (PAA-B1). The viscosity of this polyamic acid solution was 402 mPa·s.

(Synthesis Example 3)
DA-4 (17.3 g, 160 mmol), DA-5 (58.6 g, 240 mmol), DA-6 (76.9 g, 240 mmol), and DA-8 (54.6 g, 160 mmol) were added to a 3000 mL separable flask equipped with a stirrer and a nitrogen inlet tube, and then NMP (1944 g) was added and stirred and dissolved while feeding nitrogen. While stirring this solution, CA-2 (171 g, 764 mmol) and NMP (833 g) were added, and the mixture was further stirred at 50° C. for 12 hours to obtain a solution of polyamic acid (PAA-B2). The viscosity of this polyamic acid solution was 426 mPa·s.

Comparative Synthesis Example 1
DA-1 (4.14 g, 20.78 mmol) and DA-9 (1.03 g, 5.20 mmol) were added to a 100 mL four-neck flask equipped with a stirrer and a nitrogen inlet tube, and then NMP (71.22 g) was added and dissolved by stirring while feeding nitrogen. CA-1 (4.72 g, 24.1 mmol) and NMP (10 g) were added while stirring this solution, and then the mixture was further stirred at 23° C. for 2 hours to obtain a solution of polyamic acid (PAA-C1). The viscosity of this polyamic acid solution was 130 mPa·s.

Comparative Synthesis Example 2
DA-1 (3.99 g, 20.03 mmol) and DA-3 (1.49 g, 4.99 mmol) were added to a 100 mL four-neck flask equipped with a stirrer and a nitrogen inlet tube, and then NMP (71.91 g) was added and dissolved by stirring while feeding nitrogen. CA-1 (4.51 g, 23.00 mmol) and NMP (10 g) were added while stirring this solution, and then further stirred at 23° C. for 2 hours to obtain a solution of polyamic acid (PAA-C2). The viscosity of this polyamic acid solution was 134 mPa·s.

Comparative Synthesis Example 3
Acetic anhydride and pyridine were added to a solution of polyamic acid (PAA-B2) obtained in the same manner as in Synthesis Example 3, and the mixture was reacted at 55°C for 3 hours. This reaction solution was poured into methanol, and the resulting precipitate was separated by filtration. This precipitate was washed with methanol and dried under reduced pressure at 60°C to obtain a polyimide (SPI-1) powder. The imidization rate of this polyimide was 66%. NMP and GBL were added to the obtained polyimide (SPI-1) powder, and the mixture was stirred at 70°C for 20 hours to dissolve the polyimide (SPI-1) solution.

Examples and Comparative Examples
The polymer solutions obtained in Synthesis Examples 1 to 3 and Comparative Synthesis Examples 1 to 3, AD-1, AD-2, and the solvents shown in Table 1 were mixed and stirred at room temperature for 2 hours to obtain liquid crystal alignment agents having the compositions shown below (the numbers in the lower row indicate mass %).

Using the liquid crystal alignment agent obtained as described above, an FFS-driven liquid crystal cell was fabricated using the procedure described below, and its characteristics were evaluated.

[Configuration of FFS driving liquid crystal cell]
The liquid crystal cell for Fringe Field Switching (FFS) mode is a set of a first glass substrate on which an FOP (Finger on Plate) electrode layer consisting of a surface-shaped common electrode, an insulating layer, and a comb-shaped pixel electrode is formed on the surface, and a second glass substrate on which a columnar spacer having a height of 4 μm is formed on the surface and an ITO film for preventing static electricity is formed on the back surface. The pixel electrode has a comb-like shape in which a plurality of electrode elements each having a width of 3 μm and bent at an internal angle of 160° at the center are arranged in parallel at intervals of 6 μm, and one pixel has a first region and a second region with a line connecting the bent parts of the plurality of electrode elements as a boundary.
The liquid crystal alignment film formed on the first glass substrate is oriented so that the direction dividing the interior angles of the pixel bends is perpendicular to the alignment direction of the liquid crystal, and the liquid crystal alignment film formed on the second glass substrate is oriented so that the alignment direction of the liquid crystal on the first glass substrate coincides with the alignment direction of the liquid crystal on the second glass substrate when the liquid crystal cell is fabricated.

[Preparation of Liquid Crystal Cell]
The liquid crystal alignment agent was filtered through a filter with a pore size of 1.0 μm, and then spin-coated on the electrode-attached substrate (first glass substrate) and the opposing substrate (second glass substrate). The substrate was then dried on a hot plate at 80° C. for 5 minutes, and then baked at 230° C. for 20 minutes to obtain a coating film with a thickness of 100 nm, thereby obtaining a polyimide film on each substrate. The coating surface was irradiated with 300 mJ/cm ² of linearly polarized ultraviolet light with a wavelength of 254 nm and an extinction ratio of 26:1 through a polarizing plate. The substrate was then baked at 230° C. for 20 minutes to obtain a substrate with a liquid crystal alignment film.
Next, a sealant was printed on one of the pair of substrates with liquid crystal alignment film, and the other substrate was attached so that the liquid crystal alignment film faces each other, and the sealant was cured to prepare an empty cell. Liquid crystal (MLC-3019, manufactured by Merck) was vacuum-injected into this empty cell at room temperature by a reduced pressure injection method, and the injection port was sealed to obtain an FFS drive liquid crystal cell. The obtained liquid crystal cell was then heated at 120°C for 1 hour and left overnight before being used for each evaluation.

<Evaluation of Liquid Crystal Alignment Stability>
An AC voltage of ±5 V at a frequency of 60 Hz was applied to the FFS driving liquid crystal cell prepared above for 120 hours in a constant temperature environment of 60° C. Thereafter, the pixel electrode and the counter electrode of the liquid crystal cell were shorted, and the cell was left at room temperature for one day.
For the liquid crystal cell that had been subjected to the above-mentioned treatment, the deviation between the alignment direction of the liquid crystal in the first region of the pixel and the alignment direction of the liquid crystal in the second region in the absence of applied voltage was calculated as an angle.
Specifically, a liquid crystal cell was placed between two polarizing plates arranged so that their polarization axes were perpendicular to each other, the backlight was turned on, and the angle of the liquid crystal cell was adjusted so that the transmitted light intensity of the first region of the pixel was minimized.Then, the rotation angle required to rotate the liquid crystal cell so that the transmitted light intensity of the second region of the pixel was minimized was determined.
The smaller the rotation angle, the better the stability of the liquid crystal alignment. The stability of the liquid crystal alignment was evaluated by defining it as "good" when the rotation angle was maintained at 0.20 degrees or less, and "poor" when the rotation angle exceeded 0.20 degrees.

<Evaluation of flicker that occurs during operation>
The liquid crystal cell prepared above was placed between two polarizing plates arranged so that the polarization axes were perpendicular to each other, and the LED backlight was turned on in a state where no voltage was applied, and the arrangement angle of the liquid crystal cell was adjusted so that the brightness of the transmitted light was minimized. Next, a VT curve (voltage-transmittance curve) was measured while applying an AC voltage of 30 Hz to the liquid crystal cell, and the AC voltage at which the relative transmittance was 23% was calculated as the driving voltage.

In the measurement of flicker, the LED backlight that had been turned on was once turned off and left in the dark for 72 hours, and then the LED backlight was turned on again, and at the same time as the backlight started to be turned on, an AC voltage of 30 Hz frequency at which the relative transmittance was 23% was applied to drive the liquid crystal cell for 60 minutes to track the flicker amplitude. The flicker amplitude was measured by reading the transmitted light of the LED backlight that had passed through two polarizing plates and the liquid crystal cell between them using a data acquisition/data logger switch unit 34970A (manufactured by Agilent Technologies) connected via a photodiode and an I-V conversion amplifier. The value calculated based on this data using the following formula was taken as the flicker level.
Flicker level (%) = {flicker amplitude/(2 x z)} x 100

In the above formula, z is the luminance value read by the data acquisition/data logger switch unit 34970A when driven with an AC voltage of 30 Hz at which the relative transmittance is 23%.
Flicker was evaluated as "○" when the flicker level was maintained below 2% for 60 minutes from the start of lighting the LED backlight and application of AC voltage, and as "×" when the flicker level reached 2% or more within 60 minutes.
The evaluation of the flicker level according to the above-mentioned method was carried out under a temperature condition in which the temperature of the liquid crystal cell was 23°C.

<Evaluation Results>
The results of evaluation of the stability of liquid crystal alignment and flicker occurring during operation carried out on the liquid crystal display elements using the liquid crystal alignment agents of the above Examples and Comparative Examples are shown in the table below.

The liquid crystal alignment agent of the present invention is widely used in liquid crystal display elements of vertical electric field types such as TN type and VA type, and particularly in horizontal electric field types such as IPS type and FFS type.

REFERENCE SIGNS LIST 1 lateral electric field liquid crystal display element 2 comb-tooth electrode substrate 2a substrate 2b linear electrode 2c liquid crystal alignment film 2d substrate 2e plane electrode 2f insulating film 2g linear electrode 2h liquid crystal alignment film 3 liquid crystal 4 opposing substrate 4a liquid crystal alignment film 4b substrate L electric field line

Claims (4)

A liquid crystal aligning agent comprising the following polymer (A) and polymer (B):
Polymer (A): A polyamic acid obtained by polycondensation of only a diamine component including a first diamine represented by the following formula (1), a second diamine represented by the following formula (2), and a third diamine represented by the following formula (3), and a tetracarboxylic acid dianhydride having an alicyclic structure.
(In formula (3), n1 and n2 each independently represent an integer of 1 to 3.)
Polymer (B): A polyamic acid obtained by polycondensation of a diamine component that does not simultaneously contain a first diamine represented by the formula (1), a second diamine represented by the formula (2), and a third diamine represented by the formula (3), and a tetracarboxylic dianhydride. The liquid crystal aligning agent according to claim 1, wherein the tetracarboxylic dianhydride having an alicyclic structure in the polymer (A) is at least one selected from the following:
A liquid crystal alignment film obtained from the liquid crystal alignment agent according to claim 1 or 2. A liquid crystal display element having the liquid crystal alignment film according to claim 3.