JP7623635B2 - Liquid crystal alignment agent for photoalignment method, liquid crystal alignment film, and liquid crystal display element - Google Patents

Description

The present invention relates to a liquid crystal alignment agent for photoalignment, a liquid crystal alignment film, and a liquid crystal display element.

Conventionally, liquid crystal display devices have been widely used as display units for personal computers, smartphones, mobile phones, television receivers, and the like. A liquid crystal display device includes, for example, a liquid crystal layer sandwiched between an element substrate and a color filter substrate, pixel electrodes and a common electrode 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 (Twisted Nematic) method and the VA (Vertical Alignment) method, and horizontal electric field methods such as the IPS (In Plane Switching) method and the FFS (Fringe Field Switching) method are known.

Currently, the most widely used liquid crystal alignment film in the industry is produced by rubbing the surface of a film made of polyamic acid and/or polyimide formed by imidizing it on an electrode substrate in one direction with a cloth such as cotton, nylon, or polyester, which is called a rubbing treatment. The rubbing treatment is a simple and highly productive industrially useful method. However, as liquid crystal display elements become more powerful, more precise, and larger, various problems have become apparent, such as scratches on the surface of the alignment film caused by the rubbing treatment, dust generation, effects due to mechanical force and static electricity, and even non-uniformity within the alignment treatment surface. As an alternative alignment treatment method to the rubbing treatment, a photoalignment method is known in which liquid crystal alignment ability is imparted by irradiating polarized radiation. As for photoalignment methods, methods using photoisomerization reactions, photocrosslinking reactions, photodecomposition reactions, etc. have been proposed (see Non-Patent Document 1 and Patent Document 1).

A liquid crystal alignment film, which is a component of a liquid crystal display element, is a film for uniformly aligning liquid crystals, and liquid crystal alignment is one of its important characteristics. However, liquid crystal alignment films obtained by the photoalignment method tend to have lower liquid crystal alignment properties than liquid crystal alignment films obtained by conventional rubbing treatments, and the range of applications of liquid crystal display devices equipped with such liquid crystal alignment films has been limited.

Japanese Patent Application Publication No. 9-297313

"Functional Materials", November 1997, Vol. 17, No. 11, pp. 13-22

Furthermore, in actual liquid crystal display elements, the twist angle of the liquid crystal varies slightly within the plane of the liquid crystal display element due to manufacturing variations, etc. This in-plane variation then causes the brightness of the liquid crystal display element when displaying black to vary within the plane.
The present invention has been made in consideration of the above circumstances, and has as its object to provide a liquid crystal alignment agent for a photo-alignment method, which can provide a liquid crystal display element having high liquid crystal alignment properties, suppressed brightness variation within the plane during black display, and improved contrast by a photo-alignment method.

The inventors conducted extensive research and discovered that the above problems could be solved by using a liquid crystal alignment agent containing specific components, which led to the completion of the present invention. Specifically, the gist of the present invention is as follows:

At least one repeating unit (a1) selected from the group consisting of repeating units represented by the following formula (1-a) and repeating units represented by the following formula (1-i),
A liquid crystal aligning agent for a photoalignment method, comprising at least one repeating unit (a2) selected from the group consisting of repeating units represented by the following formula (2-a) and repeating units represented by the following formula (2-i), and containing at least one polymer (A) selected from the group consisting of polyimide precursors and imidized polymers thereof, the repeating unit (a1) accounting for 1 to 20 mol % of all repeating units:

（式中、Ｘ_１は下記式（Ｂ）で表される４価の有機基を表し、Ｘ_２は下記式（Ｃ）で表される４価の有機基を表す。Ｒ、Ｚは、それぞれ独立して、水素原子又は炭素数１～６のアルキル基を表す。複数個のＲ及びＺは、それぞれ同一でも異なっていても良い。Ｙ_１、Ｙ_２は、それぞれ独立して、下記式（Ｏ）で表される２価の有機基を表す。）

(In the formula, _X1 represents a tetravalent organic group represented by the following formula (B), and _X2 represents a tetravalent organic group represented by the following formula (C). R and Z each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A plurality of R and Z may be the same or different. _Y1 and _Y2 each independently represent a divalent organic group represented by the following formula (O).

（式中、Ｒ_ｂ１～Ｒ_ｂ４はそれぞれ独立して、水素原子、ハロゲン原子、又は炭素数１～６のアルキル基を表す。Ｌ_１は、単結合、－ＣＨ_２－、－（ＣＨ_２）_ｎ－（ｎは２～１８の整数である。）、又は前記－（ＣＨ_２）_ｎ－の－ＣＨ_２－の少なくとも一部を－Ｏ－、－Ｃ（＝Ｏ）－又は－Ｏ－Ｃ（＝Ｏ）－のいずれかで置き換えた基を表す。Ｒ_ｃ１～Ｒ_ｃ４はそれぞれ独立して、水素原子、ハロゲン原子、炭素数１～６のアルキル基、炭素数２～６のアルケニル基、炭素数２～６のアルキニル基、フッ素原子を含有する炭素数１～６の１価の有機基、又はフェニル基を表し、Ｒ_ｃ１～Ｒ_ｃ４の少なくとも一つは上記定義中の水素原子以外の基を表す。）

(In the formula, R _b1 to R _b4 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms. _{L 1} represents a single bond, -CH ₂ -, -(CH ₂ ) _n - (n is an integer from 2 to 18), or a group in which at least a part of the -CH ₂ - of the -(CH ₂ ) _n - is replaced with any of -O-, -C(═O)-, or -O-C(═O)-. _{R c1} to R _c4 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group, and at least one of R _c1 to R _c4 represents a group other than a hydrogen atom as defined above.)

（Ａｒは、ベンゼン環、ビフェニル構造、又はナフタレン環を表し、２つのＡｒは同一でも異なってもよく、環状の任意の水素原子は１価の有機基で置き換えられてもよい。Ｑ_２は－ＣＨ_２－、－（ＣＨ_２）_ｎ－（ｎは２～１８の整数である。）、又は前記－（ＣＨ_２）_ｎ－の－ＣＨ_２－の少なくとも一部を－Ｏ－、－Ｃ（＝Ｏ）－又は－Ｏ－Ｃ（＝Ｏ）－のいずれかで置き換えた基を表す。ｐは０又は１の整数である。但し、ｐが０である場合、Ａｒはビフェニル構造を表し、ｐが１である場合、２つのＡｒの少なくとも一つはナフタレン環を表す。＊は結合手を表す。）

(Ar represents a benzene ring, a biphenyl structure, or a naphthalene ring, two Ars may be the same or different, and any hydrogen atom in the ring may be replaced by a monovalent organic group. _{Q 2} represents -CH ₂ -, -(CH ₂ ) _n - (n is an integer from 2 to 18), or a group in which at least a part of the -CH ₂ - in the -(CH ₂ ) _n - is replaced by any of -O-, -C(═O)-, or -O-C(═O)-. p is an integer of 0 or 1. However, when p is 0, Ar represents a biphenyl structure, and when p is 1, at least one of the two Ars represents a naphthalene ring. * represents a bond.)

In this specification, * represents a bond in all cases. Boc represents a tert-butoxycarbonyl group. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Examples of carbamate protecting groups include tert-butoxycarbonyl groups and 9-fluorenylmethoxycarbonyl groups.

The liquid crystal alignment agent for photo-alignment method of the present invention has the repeating unit (a1) and the repeating unit (a2), and contains at least one polymer (A) selected from the group consisting of polyimide precursors and imidized polymers thereof, which contains the repeating unit (a1) in an amount of 1 to 20 mol % of the total repeating units. This has the effect of suppressing the variation in brightness within the plane during black display, and enabling a liquid crystal display element with improved contrast to be obtained by the photo-alignment method.

We will now explain the liquid crystal alignment agent for photoalignment method of the present invention (hereinafter also simply referred to as the liquid crystal alignment agent).

<Polymer (A)>
The liquid crystal aligning agent of the present invention contains at least one repeating unit (a1) selected from the group consisting of repeating units represented by the following formula (1-a) and repeating units represented by the following formula (1-i), and at least one repeating unit (a2) selected from the group consisting of repeating units represented by the following formula (2-a) and repeating units represented by the following formula (2-i), and contains at least one polymer (A) selected from the group consisting of polyimide precursors and imidized polymers thereof, the repeating unit (a1) accounting for 1 to 20 mol % of the total repeating units. The polymer (A) may be composed of one type or two or more types.

<Repeating Unit (a1)>
The repeating unit (a1) of the present invention is at least one repeating unit selected from the group consisting of repeating units represented by the following formula (1-a) and repeating units represented by the following formula (1-i):

（式中、Ｘ_１は下記式（Ｂ）で表される４価の有機基を表す。Ｒ、Ｚは、それぞれ独立して、水素原子又は炭素数１～６のアルキル基を表す。２個のＲ及びＺは、それぞれ同一でも異なっていても良い。Ｙ_１は下記式（Ｏ）で表される２価の有機基を表す。）

(In the formula, _X1 represents a tetravalent organic group represented by the following formula (B). R and Z each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Two R's and two Z's may be the same or different. _Y1 represents a divalent organic group represented by the following formula (O).

（式中、Ｒ_ｂ１～Ｒ_ｂ４はそれぞれ独立して、水素原子、ハロゲン原子、又は炭素数１～６のアルキル基を表す。Ｌ_１は、単結合、－ＣＨ_２－、－（ＣＨ_２）_ｎ－（ｎは２～１８の整数である。）、又は前記－（ＣＨ_２）_ｎ－の－ＣＨ_２－の少なくとも一部を－Ｏ－、－Ｃ（＝Ｏ）－又は－Ｏ－Ｃ（＝Ｏ）－のいずれかで置き換えた基を表す。）

(In the formula, R _b1 to R _b4 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms. _{L 1} represents a single bond, -CH ₂ -, -(CH ₂ ) _n - (n is an integer of 2 to 18), or a group in which at least a portion of the -CH ₂ - of the -(CH ₂ ) _n - is replaced with any of -O-, -C(═O)-, or -O-C(═O)-.)

（Ａｒは、ベンゼン環、ビフェニル構造、又はナフタレン環を表し、２つのＡｒは同一でも異なってもよく、環状の任意の水素原子は１価の有機基で置き換えられてもよい。Ｑ_２は－ＣＨ_２－、－（ＣＨ_２）_ｎ－（ｎは２～１８の整数である。）、又は前記－（ＣＨ_２）_ｎ－の－ＣＨ_２－の少なくとも一部を－Ｏ－、－Ｃ（＝Ｏ）－又は－Ｏ－Ｃ（＝Ｏ）－のいずれかで置き換えた基を表す。ｐは０又は１の整数である。但し、ｐが０である場合、Ａｒはビフェニル構造を表し、ｐが１である場合、２つのＡｒの少なくとも一つはナフタレン環を表す。）

(Ar represents a benzene ring, a biphenyl structure, or a naphthalene ring, the two Ars may be the same or different, and any hydrogen atom in the ring may be replaced by a monovalent organic group. _{Q 2} represents -CH ₂ -, -(CH ₂ ) _n - (n is an integer from 2 to 18), or a group in which at least a part of the -CH ₂ - in the -(CH ₂ ) _n - is replaced by any of -O-, -C(═O)-, or -O-C(═O)-. p is an integer of 0 or 1. However, when p is 0, Ar represents a biphenyl structure, and when p is 1, at least one of the two Ars represents a naphthalene ring.)

Preferred examples of L ₁ are a single bond, —CH ₂ — or —(CH ₂ ) _n — (n is an integer of 2 to 18) from the viewpoint of efficiently obtaining the effects of the present invention.
A preferred example of R _b1 to R _b4 is a hydrogen atom, from the viewpoint of efficiently obtaining the effects of the present invention.

From the viewpoint of improving liquid crystal alignment, the tetravalent organic group represented by the formula (B) is preferably a tetravalent organic group represented by the following formulas (b-1) to (b-2).

Preferred examples of the divalent organic group represented by the formula (O) are the divalent organic groups represented by the following formulas (o-1) to (o-7), from the viewpoint of efficiently obtaining the effects of the present invention.

<Repeating unit (a2)>
The repeating unit (a2) of the present invention is at least one repeating unit selected from the group consisting of repeating units represented by the following formula (2-a) and repeating units represented by the following formula (2-i):

（式中、Ｘ_２は下記式（Ｃ）で表される４価の有機基を表す。Ｒ、Ｚは、それぞれ独立して、水素原子又は炭素数１～６のアルキル基を表す。２個のＲ及びＺは、それぞれ同一でも異なっていても良い。Ｙ_２は好ましい具体例を含め上記Ｙ_１と同義である。）

(In the formula, _X2 represents a tetravalent organic group represented by the following formula (C). R and Z each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Two R and Z may be the same or different. _Y2 has the same meaning as _Y1 above, including preferred specific examples.)

（式中、Ｒ_ｃ１～Ｒ_ｃ４はそれぞれ独立して、水素原子、ハロゲン原子、炭素数１～６のアルキル基、炭素数２～６のアルケニル基、炭素数２～６のアルキニル基、フッ素原子を含有する炭素数１～６の１価の有機基、又はフェニル基を表し、Ｒ_ｃ１～Ｒ_ｃ４の少なくとも一つは上記定義中の水素原子以外の基を表す。）

(In the formula, R _c1 to R _c4 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group, and at least one of R _c1 to R _c4 represents a group other than a hydrogen atom as defined above.)

Examples of the tetravalent organic group represented by formula (C) include tetravalent organic groups represented by the following formulas (Xc-1) to (Xc-6). Among these, (Xc-1) is preferred from the viewpoint of enhancing liquid crystal alignment.

<Repeating unit (a3)>
The polymer (A) may be at least one selected from the group consisting of polyimide precursors having, in addition to the repeating units (a1) and (a2), at least one repeating unit (a3) selected from the group consisting of repeating units represented by the following formula (3-a) and repeating units represented by the following formula (3-i), and imidized polymers thereof:

（式中、Ｘ_３は４価の有機基を表し、Ｙ_３は下記式（３ｄ）で表される２価の有機基を表す。Ｒ、Ｚは、前記式（１－ａ）と同義である。）

(In the formula, _X3 represents a tetravalent organic group, and _Y3 represents a divalent organic group represented by the following formula (3d). R and Z are the same as those in the formula (1-a).)

（Ａｒ_３は、ベンゼン環、又はビフェニル構造を表し、２つのＡｒ_３は同一でも異なってもよく、上記環上の任意の水素原子は１価の有機基で置き換えられてもよい。Ｑ_３は－（ＣＨ_２）_ｎ－（ｎは２～１８の整数である。）、又は前記－（ＣＨ_２）_ｎ－の－ＣＨ_２－の少なくとも一部を－Ｏ－、－Ｃ（＝Ｏ）－又は－Ｏ－Ｃ（＝Ｏ）－のいずれかで置き換えた基を表す。）

(Ar ₃ represents a benzene ring or a biphenyl structure, two Ar _3s may be the same or different, and any hydrogen atom on the ring may be replaced with a monovalent organic group. Q ₃ represents -(CH ₂ ) _n - (n is an integer of 2 to 18), or a group in which at least a portion of the -CH ₂ - of the -(CH ₂ ) _n - is replaced with any of -O-, -C(═O)-, or -O-C(═O)-.)

Examples of the divalent organic group represented by formula (3d) include, but are not limited to, divalent organic groups represented by the following formulas (3d-1) to (3d-8):

The polymer (A) may be at least one selected from the group consisting of polyimide precursors having repeating units (a1) and (a2) as well as at least one type of repeating unit (a4) selected from the group consisting of repeating units represented by the following formula (4-a) and repeating units represented by the following formula (4-i), and imidized polymers thereof.

（式中、Ｒ、Ｚは、前記式（１－ａ）と同義である。Ｘ_４は４価の有機基を表し、Ｙ_４は基「－Ｎ（Ｄ）－（Ｄはカルバメート系保護基を表す。）」を分子内に有する炭素数６～３０の２価の有機基を表す。）

(In the formula, R and Z are the same as those in the formula (1-a). _X4 represents a tetravalent organic group, and _Y4 represents a divalent organic group having 6 to 30 carbon atoms and containing a group "-N(D)- (D represents a carbamate protecting group)" in the molecule.)

Specific examples of the divalent organic group having 6 to 30 carbon atoms and having a group "-N(D)- (D represents a carbamate protecting group)" in the molecule in _Y4 include a divalent organic group having a partial structure represented by the following formula (4-1) or a divalent organic group represented by the following formula (4-2).

In the formula, _Q5 is a single bond, -( _CH2 ) _n- (n is an integer of 1 to 20), or a group in which _{any -CH2-} of -( _CH2 ) _n- is replaced with -O-, -COO-, -OCO-, _-NQ9- , _-NQ9- CO-, -CO- _NQ9- , _-NQ9 -CO- _NQ10- , _-NQ9- COO- or -O-COO-, _Q9 and _Q10 each independently represent a hydrogen atom or a monovalent organic group, _Q6 and _Q7 each independently represent -H, a group having -NHD, or a group having -N(D) ₂ . _Q8 represents a group having -NHD, or a group having -N(D) ₂ . D represents a carbamate protecting group. However, at least one of Q ₅ , Q ₆ and Q ₇ has a carbamate-based protecting group in the group. Specific examples of the monovalent organic group in _{Q 9} and Q ₁₀ include an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, an alkyl group having 1 to 6 carbon atoms containing a fluorine atom, the above-mentioned carbamate-based protecting group, and an alkoxyalkyl group having 1 to 6 carbon atoms.

Here, examples of _Y4 include structures represented by the following formulae (Y4-1) to (Y4-4), but are not limited thereto.

The polymer (A) may be at least one selected from the group consisting of polyimide precursors having repeating units (a1) and (a2) as well as at least one type of repeating unit (a5) selected from the group consisting of repeating units represented by the following formula (5-a) and repeating units represented by the following formula (5-i), and imidized polymers thereof.

式（５－ａ）及び式（５－ｉ）中、Ｒ、Ｚは、前記式（１－ａ）と同義である。Ｘ_５は４価の有機基を表し、Ｙ_５は２価の有機基を表す。但し、Ｙ_５は前記式（３ｄ）で表される２価の有機基、又は基「－Ｎ（Ｄ）－（Ｄはカルバメート系保護基を表す。）」を分子内に有する炭素数６～３０の２価の有機基以外の構造を表し、Ｘ_５が前記式（Ｂ）で表される４価の有機基又は前記式（Ｃ）で表される４価の有機基と同義である場合は、Ｙ_５は前記式（Ｏ）で表される２価の有機基以外の構造を表す。

In formula (5-a) and formula (5-i), R and Z are the same as those in formula (1-a). _X5 represents a tetravalent organic group, and _Y5 represents a divalent organic group. However, _Y5 represents a structure other than the divalent organic group represented by formula (3d) or the divalent organic group having 6 to 30 carbon atoms and having a group "-N(D)- (D represents a carbamate-based protecting group)" in the molecule, and when _X5 is the same as the tetravalent organic group represented by formula (B) or the tetravalent organic group represented by formula (C), _Y5 represents a structure other than the divalent organic group represented by formula (O).

In formula (5-a) and formula (5-i), Y Specific examples of _{No. 5} include p-phenylenediamine, 2,3,5,6-tetramethyl-p-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, m-phenylenediamine, 2,4-dimethyl-m-phenylenediamine, 2,5-diaminotoluene, 2,6-diaminotoluene, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-difluoro-4,4'-diaminobiphenyl, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,4'-diaminobiphenyl, 3,3'-diaminobiphenyl, 2,2'-diaminobiphenyl, 2,3'-diaminobiphenyl, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,4 Examples of the divalent organic groups include divalent organic groups obtained by removing two amino groups from aromatic diamines such as 1,4-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-diaminobenzanilide, 4,4'-diaminoazobenzene, 1,5-diaminonaphthalene, 1,6-diaminonaphthalene, 1,7-diaminonaphthalene, 2,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,7-diaminonaphthalene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenyl)benzene, 1,3-bis(4-aminophenyl)benzene, and 1,4-bis(4-aminobenzyl)benzene, as well as divalent organic groups exemplified by _Y6 described later.

The structure of the tetravalent organic group of X ₃ , X ₄ and X ₅ is not particularly limited, and any structure can be independently selected. Preferred specific examples include the following formulae (X1-1) to (X1-44).

式（Ｘ１－１）～（Ｘ１－４）において、Ｒ^３～Ｒ^２３は、それぞれ独立して、水素原子、ハロゲン原子、炭素数１～６のアルキル基、炭素数２～６のアルケニル基、炭素数２～６のアルキニル基、フッ素原子を含有する炭素数１～６の１価の有機基、又はフェニル基である。液晶配向性の点から、Ｒ^３～Ｒ^２３は、水素原子、ハロゲン原子、メチル基、又はエチル基が好ましく、水素原子、又はメチル基がより好ましい。

In formulae (X1-1) to (X1-4), R ³ to R ²³ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group. From the viewpoint of liquid crystal alignment, R ³ to R ²³ are preferably a hydrogen atom, a halogen atom, a methyl group, or an ethyl group, and more preferably a hydrogen atom or a methyl group.

Specific examples of formula (X1-1) include the following formulas (X1-1-1) to (X1-1-6). From the viewpoints of liquid crystal alignment and photoreaction sensitivity, (X1-1-1) to (X1-1-2) are more preferred, with (X1-1-2) being particularly preferred.

In order to obtain the effects of the present invention satisfactorily, it is preferable that polymer (A) contains repeating unit (a1) in an amount of 1 to 20 mol % of the total repeating units, and more preferably 1 to 15 mol %.

In order to obtain the effects of the present invention satisfactorily, it is preferable that the sum of repeating units (a1) and repeating units (a2) in polymer (A) is 5 mol % or more of the total repeating units, and more preferably 10 mol % or more.

From the viewpoint of obtaining the effects of the present invention well, the polymer (A) preferably contains 1 to 95 mol %, more preferably 1 to 90 mol %, and even more preferably 5 to 90 mol % of the repeating units (a3) based on the total repeating units. In this case, the sum of the repeating units (a1) and (a2) is preferably 99 mol % or less, more preferably 95 mol % or less.

In order to obtain the effects of the present invention satisfactorily, it is preferable that polymer (A) contains repeating unit (a4) in an amount of 1 to 40 mol % of the total repeating units, more preferably 1 to 30 mol %, and even more preferably 1 to 25 mol %.

<Polymer (B)>
The liquid crystal aligning agent of the present invention may contain a polymer (B) having a repeating unit represented by the following formula (6) from the viewpoint of reducing residual images derived from residual DC. The polymer (B) does not have the repeating unit (a1) and the repeating unit (a2) in the same molecule. The polymer (B) may be composed of one or more types, and the repeating units constituting the polymer (B) may be composed of one or more types.

（Ｘ_６は４価の有機基であり、Ｙ_６は、２価の有機基である。Ｒ_、Ｚは、式（１－ａ）と同義である。）

( _X6 is a tetravalent organic group, and _Y6 is a divalent organic group. R _and Z are the same as in formula (1-a).)

Examples of the tetravalent organic group in formula _X6 include a tetravalent organic group derived from an acyclic aliphatic tetracarboxylic dianhydride, a tetravalent organic group derived from an alicyclic tetracarboxylic dianhydride, a tetravalent organic group derived from an aromatic tetracarboxylic dianhydride, etc. Specific examples of the tetravalent organic group derived from an acyclic aliphatic tetracarboxylic dianhydride and the tetravalent organic group derived from an alicyclic tetracarboxylic dianhydride include structures selected from the following formulae (x-1) to (x-13).

（上記式（ｘ－１）～（ｘ－１３）中、Ｒ^１～Ｒ^４は、それぞれ独立して、水素原子、ハロゲン原子、炭素数１～６のアルキル基、炭素数２～６のアルケニル基、炭素数２～６のアルキニル基、フッ素原子を有する炭素数１～６の１価の有機基又はフェニル基を表す。Ｒ^５及びＲ^６は、それぞれ独立して、水素原子又はメチル基を表す。）

(In the above formulas (x-1) to (x-13), R ¹ to R ⁴ each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms and a fluorine atom, or a phenyl group. ^{R 5} and R ⁶ each independently represent a hydrogen atom or a methyl group.)

The above formula (x-1) is preferably selected from the group consisting of the following formulas (x1-1) to (x1-6).

上記式（ｘ１－１）～（ｘ１－６）において、＊１は一方の酸無水物基に結合する結合手を表し、また、＊２は他方の酸無水物基に結合する結合手を表す。

In the above formulae (x1-1) to (x1-6), *1 represents a bond bonded to one acid anhydride group, and *2 represents a bond bonded to the other acid anhydride group.

Aromatic tetracarboxylic acid dianhydrides are acid dianhydrides obtained by intramolecular dehydration of a carboxy group bonded to an aromatic ring such as a benzene ring or a naphthalene ring. Specific examples include the tetravalent organic groups represented by the above formulas (X1-28) to (X1-40).

The divalent organic group in the formula _Y6 includes a diamine having at least one nitrogen atom-containing structure (hereinafter also referred to as a nitrogen atom-containing structure) selected from the group consisting of a nitrogen atom-containing heterocycle, a secondary amino group, and a tertiary amino group, 2,4-diaminophenol, 3,5-diaminophenol, 3,5-diaminobenzyl alcohol, 2,4-diaminobenzyl alcohol, 4,6-diaminoresorcinol, 2,4-diaminobenzoic acid, 2,5-diaminobenzoic acid, 3,5-diaminobenzoic acid, and the compounds represented by the following formulae (3b-1) to (3b-4): diamines having a carboxy group such as the diamine compounds mentioned above, 4-(2-(methylamino)ethyl)aniline, 4-(2-aminoethyl)aniline, 4,4'-diaminodiphenylmethane, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylether, 4,4'-diaminobenzanilide, 4,4'-diaminoazobenzene, 1-(4-aminophenyl)-1,3,3-trimethyl-1H-indan-5-amine, 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-indan-5-amine, diamines having a photopolymerizable group at the end, such as 2-(2,4-diaminophenoxy)ethyl methacrylate and 2,4-diamino-N,N-diallylaniline; cholestanyloxy-3,5-diaminobenzene; cholestanyloxy-3,5-diaminobenzene; cholestanyloxy-2,4-diaminobenzene; cholestanyl 3,5-diaminobenzoate; cholestanyl 3,5-diaminobenzoate; cholestanyl 3,5-diaminobenzoate; lano 3,5-diaminobenzoate; stannyl, 3,6-bis(4-aminobenzoyloxy)cholestane or other diamines having a steroid skeleton, diamines represented by the following formulas (V-1) to (V-8), diamines having a siloxane bond such as 1,3-bis(3-aminopropyl)-tetramethyldisiloxane, divalent organic groups obtained by removing two amino groups from diamines such as diamines having an oxazoline structure such as the following formulas (Ox-1) to (Ox-2), and groups represented by any of the formulas (Y-1) to (Y-167) described in WO 2018/117239.

（式（３ｂ－１）中、Ａ^１は単結合、－ＣＨ_２－、－Ｃ_２Ｈ_４－、－Ｃ（ＣＨ_３）_２－、－ＣＦ_２－、－Ｃ（ＣＦ_３）_２－、－Ｏ－、－ＣＯ－、－ＮＨ－、－Ｎ（ＣＨ_３）－、－ＣＯＮＨ－、－ＮＨＣＯ－、－ＣＨ_２Ｏ－、－ＯＣＨ_２－、－ＣＯＯ－、－ＯＣＯ－、－ＣＯＮ（ＣＨ_３）－又はＮ（ＣＨ_３）ＣＯ－を示し、ｍ１及びｍ２はそれぞれ独立して、０～４の整数を示し、かつｍ１＋ｍ２は１～４の整数を示す。式（３ｂ－２）中、ｍ３及びｍ４はそれぞれ独立して、１～５の整数を示す。式（３ｂ－３）中、Ａ^２は炭素数１～５の直鎖又は分岐アルキル基を示し、ｍ５は１～５の整数を示す。式（３ｂ－４）中、Ａ^３及びＡ^４はそれぞれ独立して、単結合、－ＣＨ_２－、－Ｃ_２Ｈ_４－、－Ｃ（ＣＨ_３）_２－、－ＣＦ_２－、－Ｃ（ＣＦ_３）_２－、－Ｏ－、－ＣＯ－、－ＮＨ－、－Ｎ（ＣＨ_３）－、－ＣＯＮＨ－、－ＮＨＣＯ－、－ＣＨ_２Ｏ－、－ＯＣＨ_２－、－ＣＯＯ－、－ＯＣＯ－、－ＣＯＮ（ＣＨ_３）－又は－Ｎ（ＣＨ_３）ＣＯ－を示し、ｍ６は１～４の整数を示す。）

(In formula (3b-1), A ¹ represents a single bond, —CH ₂ —, —C ₂ H ₄ —, —C(CH ₃ ) ₂ —, —CF ₂ —, —C(CF ₃ ) ₂ —, —O—, —CO—, —NH—, —N(CH ₃ )—, —CONH—, —NHCO—, —CH ₂ O—, —OCH ₂ —, —COO—, —OCO—, —CON(CH ₃ )— or N(CH ₃ )CO—; m1 and m2 each independently represent an integer of 0 to 4, and m1+m2 represents an integer of 1 to 4; in formula (3b-2), m3 and m4 each independently represent an integer of 1 to 5; in formula (3b-3), A In formula (3b-4), A ³ and A ⁴ each independently represent a single bond, —CH ₂ —, —C ₂ H ₄ —, —C(CH ₃ ) ₂ —, —CF ₂ —, —C(CF ₃ ) ^{2 —} , _—O— , —CO—, —NH—, —N(CH 3 )—, —CONH—, —NHCO—, —CH ₂ O—, _{—OCH 2} —, —COO—, —OCO—, —CON(CH ₃ )— or —N(CH ₃ )CO—, and m6 represents an integer from 1 to 4.

（Ｘ^ｖ１～Ｘ^ｖ４、Ｘ^ｐ１～Ｘ^ｐ２は、それぞれ独立に、－（ＣＨ_２）_ａ－（ａは１～１５の整数である。）、－ＣＯＮＨ－、－ＮＨＣＯ－、－ＣＯＮ（ＣＨ_３）－、－ＮＨ－、－Ｏ－、－ＣＨ_２Ｏ－、－ＣＨ_２ＯＣＯ－、－ＣＯＯ－、又は－ＯＣＯ－を表し、Ｘ^ｖ５は－Ｏ－、－ＣＨ_２Ｏ－、－ＣＨ_２ＯＣＯ－、－ＣＯＯ－、又は－ＯＣＯ－を表す。Ｘ_ａは、単結合、－Ｏ－、－ＮＨ－、－Ｏ－（ＣＨ_２）_ｍ－Ｏ－（ｍは１～６の整数を表す。）を表し、Ｒ^ｖ１～Ｒ^ｖ４、Ｒ^１ａ～Ｒ^１ｂは、それぞれ独立に、炭素数１～２０のアルキル基、炭素数１～２０のアルコキシ基又は炭素数２～２０のアルコキシアルキル基を表す。Ｘ^Ｖ７～Ｘ^Ｖ８は、それぞれ独立に、－Ｏ－、－ＣＨ_２Ｏ－、－ＣＯＯ－又は－ＯＣＯ－を表す。）

(X ^v1 to X ^v4 and X ^p1 to X ^p2 each independently represent -(CH ₂ ) _a - (a is an integer of 1 to 15), -CONH-, -NHCO-, -CON(CH ₃ )-, -NH-, -O-, -CH ₂ O-, -CH ₂ OCO-, -COO-, or -OCO-; X ^v5 represents -O-, -CH ₂ O-, -CH ₂ OCO-, -COO-, or -OCO-; X _a represents a single bond, -O-, -NH-, or -O-(CH ₂ ) _m -O- (m is an integer of 1 to 6); R ^v1 to R ^v4 and R ^1a to R Each of ^1b independently represents an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or an alkoxyalkyl group having 2 to 20 carbon atoms. Each of X ^V7 to X ^V8 independently represents -O-, -CH ₂ O-, -COO-, or -OCO-.

Examples of the nitrogen atom-containing heterocycle include pyrrole, imidazole, pyrazole, triazole, pyridine, pyrimidine, pyridazine, pyrazine, indole, benzimidazole, purine, quinoline, isoquinoline, naphthyridine, quinoxaline, phthalazine, triazine, carbazole, acridine, piperidine, piperazine, pyrrolidine, hexamethyleneimine, etc. Among these, pyridine, pyrimidine, pyrazine, piperidine, piperazine, quinoline, carbazole, and acridine are preferred.

The secondary amino group and tertiary amino group that may be possessed by the diamine having a nitrogen atom-containing structure are represented, for example, by the following formula (n).

上記式（ｎ）において、Ｒは，水素原子又は炭素数１～１０の１価の炭化水素基を表す。「＊１」は、炭化水素基に結合する結合手を表す。

In the above formula (n), R represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms. "*1" represents a bond bonded to the hydrocarbon group.

Examples of the monovalent hydrocarbon group of the above formula R include alkyl groups such as methyl, ethyl, and propyl; cycloalkyl groups such as cyclohexyl; and aryl groups such as phenyl and methylphenyl. R is preferably a hydrogen atom or a methyl group.

Specific examples of diamines having a nitrogen atom-containing structure include, for example, 2,6-diaminopyridine, 3,4-diaminopyridine, 2,4-diaminopyrimidine, 3,6-diaminocarbazole, N-methyl-3,6-diaminocarbazole, 1,4-bis-(4-aminophenyl)piperazine, 3,6-diaminoacridine, N-ethyl-3,6-diaminocarbazole, N-phenyl-3,6-diaminocarbazole, N,N'-bis(4-aminophenyl)benzidine, N,N'-bis(4-aminophenyl)-N,N'-dimethylbenzidine, 4,4'-diaminodiphenylamine, N,N-bis(4-aminophenyl)-methylamine, and compounds represented by the following formulas (z-1) to (z-23).

From the viewpoint of reducing the afterimage caused by residual DC, the polymer (B) is preferably a polymer containing a repeating unit in which _Y6 is a divalent organic group (collectively referred to as a specific divalent organic group) selected from the group consisting of diamines having a nitrogen atom-containing structure, 2,4-diaminophenol, 3,5-diaminophenol, 3,5-diaminobenzyl alcohol, 2,4-diaminobenzyl alcohol, 4,6-diaminoresorcinol, the above diamines having a carboxy group, or the above diamines having a urea bond, from which two amino groups have been removed.

From the viewpoint of reducing afterimages derived from residual DC, the polymer (B) may contain repeating units in which _Y6 is the specific divalent organic group in an amount of 1 mol % or more, or 5 mol % or more, of all repeating units contained in the polymer (B).

From the viewpoint of minimizing afterimages caused by residual DC, the content ratio of polymer (A) to polymer (B) may be 10/90 to 90/10 in terms of the mass ratio of [polymer (A)]/[polymer (B)], or may be 20/80 to 90/10, or may be 20/80 to 80/20.

<Methods of producing polyamic acid, polyamic acid ester, and polyimide>
The polyimide precursors, ie, polyamic acid ester, polyamic acid and polyimide, used in the present invention can be synthesized by known methods such as those described in WO 2013/157586.
Specifically, it is synthesized by reacting a diamine component with a tetracarboxylic acid derivative component in a solvent (condensation polymerization). The tetracarboxylic acid derivative component may be tetracarboxylic acid dianhydride or a derivative thereof (tetracarboxylic acid dihalide, tetracarboxylic acid diester, or tetracarboxylic acid diester dihalide). When the polymer (A) or (B) contains an amic acid structure in a part thereof, for example, a polymer having an amic acid structure (polyamic acid) can be obtained by reacting a tetracarboxylic acid dianhydride component with a diamine component. The solvent is not particularly limited as long as it dissolves the produced polymer.

The diamine component and the tetracarboxylic acid derivative component for obtaining the polyimide precursor of the polymer (A) are selected and used according to the repeating units represented by the above-mentioned formula (1-a) and formula (2-a) contained in the polymer (A) and, if necessary, the repeating units represented by the formula (3-a), formula (4-a), and formula (5-a) so as to obtain the structure of such repeating units.
For example, when the polymer (A) has a repeating unit represented by formula (1-a), a diamine having a structure of -N(Z)-Y ₁ -N(Z)- (wherein Y ₁ and Z are defined as above) is used as the diamine component, and a tetracarboxylic acid derivative having a structure represented by the following formula is used as the tetracarboxylic acid derivative component.

（Ｘ_１の定義は上記と同じである。）

( _X1 is defined as above.)

Polyamic acid esters can be obtained by known methods, such as, for example, [I] a method of reacting the polyamic acid obtained by the above-mentioned method with an esterifying agent, [II] a method of reacting a tetracarboxylic acid diester with a diamine, or [III] a method of reacting a tetracarboxylic acid diester dihalide with a diamine.

Methods for obtaining polyimide include thermal imidization in which a solution containing a polyimide precursor such as polyamic acid or polyamic acid ester obtained by the above reaction is heated as is, and catalytic imidization in which a catalyst is added to the above solution.
In the polyimide used in the present invention, the ring closure rate of the amic acid groups (also called the imidization rate) does not necessarily need to be 100%, and can be arbitrarily adjusted depending on the application or purpose.
For example, the imidization rate of the polyimide may be 20 to 100%, 50 to 99%, or 70 to 99%, from the viewpoint of increasing the solubility of the polyimide varnish.

<Polymer solution viscosity and molecular weight>
The polyamic acid, polyamic acid ester, and polyimide used in the present invention preferably have a solution viscosity of, for example, 10 to 1000 mPa·s when made into a solution of 10 to 15% by mass from the viewpoint of workability, but are not particularly limited thereto. The solution viscosity (mPa·s) of the above polymer is a value measured at 25° C. using an E-type rotational viscometer for a polymer solution of 10 to 15% by mass prepared using a good solvent for the polymer (e.g., γ-butyrolactone, N-methyl-2-pyrrolidone, etc.).

The polystyrene-equivalent weight average molecular weight (Mw) of the above polyamic acid, polyamic acid ester, and polyimide measured by gel permeation chromatography (GPC) is preferably 1,000 to 500,000, and more preferably 2,000 to 300,000. The molecular weight distribution (Mw/Mn), expressed as the ratio of Mw to the polystyrene-equivalent number average molecular weight (Mn) measured by GPC, is preferably 15 or less, and more preferably 10 or less. Having the molecular weight within this range ensures good alignment and stability of the liquid crystal display element.

<Liquid crystal alignment agent>
The liquid crystal aligning agent of the present invention contains a polymer (A) and, if necessary, a polymer (B). The liquid crystal aligning agent of the present invention may contain other polymers in addition to the polymer (A) and the polymer (B). Examples of the other polymers include polyesters, polyamides, polyureas, polyorganosiloxanes, cellulose derivatives, polyacetals, polystyrene or derivatives thereof, poly(styrene-phenylmaleimide) derivatives, and poly(meth)acrylates.

The liquid crystal alignment agent is used to prepare a liquid crystal alignment film, and takes the form of a coating liquid from the viewpoint of forming a uniform thin film. The liquid crystal alignment agent of the present invention is also preferably a coating liquid containing the above-mentioned polymer component and an organic solvent. In this case, the concentration of the polymer in the liquid crystal alignment agent can be appropriately changed depending on the thickness of the coating film to be formed. From the viewpoint of forming a uniform and defect-free coating film, 1% by mass or more is preferable, and from the viewpoint of storage stability of the solution, 10% by mass or less is preferable. A particularly preferable polymer concentration is 2 to 8% by mass.

The organic solvent contained in the liquid crystal alignment agent is not particularly limited as long as it dissolves the polymer components uniformly. Specific examples thereof include N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethyllactamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-(n-butyl)-2-pyrrolidone, N-(tert-butyl)-2-pyrrolidone, N-(n-pentyl)-2-pyrrolidone, N-methoxypropyl-2-pyrrolidone, N-ethoxyethyl-2-pyrrolidone, N-methoxybutyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, γ-valerolactone, 1,3-dimethyl-2-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide (collectively referred to as "good solvents"). Among them, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide or γ-butyrolactone is preferred. The content of the good solvent is preferably 20 to 99% by mass, more preferably 20 to 90% by mass, and particularly preferably 30 to 80% by mass, of the total solvent contained in the liquid crystal alignment agent.

In addition, it is preferable to use a mixed solvent containing the above-mentioned solvent and a solvent (also called a poor solvent) that improves the coatability and surface smoothness of the coating film when applying the liquid crystal alignment agent. Specific examples of organic solvents to be used in combination are listed below, but are not limited to these.

For example, diisopropyl ether, diisobutyl ether, diisobutyl carbinol (2,6-dimethyl-4-heptanol), 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, 3-ethoxybutyl acetate, 1-methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, ethylene glycol monoacetate, ethylene glycol diacetate, propylene carbonate, ethylene carbonate, ethylene glycol monobutyl ether, ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, propylene glycol monobutyl ether, 1-(2-butoxyethoxy)-2 -propanol, 2-(2-butoxyethoxy)-1-propanol, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, diethylene glycol acetate, propylene glycol diacetate, n-butyl acetate, propylene glycol monoethyl ether acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, propyl 3-methoxypropionate, butyl 3-methoxypropionate, n-butyl lactate, isoamyl lactate, diethylene glycol monoethyl ether, diisobutyl ketone (2,6-dimethyl-4-heptanone), and the like.

Among these, diisobutyl carbinol, propylene glycol monobutyl ether, propylene glycol diacetate, diethylene glycol diethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, or diisobutyl ketone are preferred.

Preferred solvent combinations of good and poor solvents include N-methyl-2-pyrrolidone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone and propylene glycol monobutyl ether, N-ethyl-2-pyrrolidone and propylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone, 4-hydroxy-4-methyl-2-pentanone and diethylene glycol diethyl ether, and N-methyl-2-pyrrolidone and γ-butyrolactone. Examples of the poor solvent include propylene glycol monobutyl ether and 2,6-dimethyl-4-heptanone, N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether and diisopropyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether and 2,6-dimethyl-4-heptanol, N-methyl-2-pyrrolidone, γ-butyrolactone and dipropylene glycol dimethyl ether, and N-methyl-2-pyrrolidone, propylene glycol monobutyl ether and dipropylene glycol dimethyl ether. The content of the poor solvent is preferably 1 to 80% by mass of the total solvent contained in the liquid crystal alignment agent, more preferably 10 to 80% by mass, and particularly preferably 20 to 70% by mass. The type and content of the poor solvent are appropriately selected depending on the coating device, coating conditions, coating environment, etc. of the liquid crystal alignment agent.

The liquid crystal alignment agent of the present invention may additionally contain components other than the polymer component and the organic solvent (hereinafter also referred to as additive components). Such additive components include adhesion assistants for increasing the adhesion between the liquid crystal alignment film and the substrate or between the liquid crystal alignment film and the sealant, compounds for increasing the strength of the liquid crystal alignment film (hereinafter also referred to as cross-linking compounds), compounds for promoting imidization, and dielectrics and conductive substances for adjusting the dielectric constant and electrical resistance of the liquid crystal alignment film.

From the viewpoint of exhibiting good resistance to AC afterimages and highly improving film strength, the crosslinkable compound may be a compound having at least one group selected from the group consisting of an oxiranyl group, an oxetanyl group, a protected isocyanate group, a protected isothiocyanate group, a group containing an oxazoline ring structure, a group containing a Meldrum's acid structure, a cyclocarbonate group, and a group represented by formula (d), or a compound selected from compounds represented by the following formula (e) (hereinafter, these are also collectively referred to as compound (C)).

（Ｒ_２及びＲ_３は、それぞれ独立に水素原子、炭素数１～３のアルキル基又は「＊－ＣＨ_２－ＯＨ」である。Ａは芳香環を有する（ｍ＋ｎ）価の有機基を表す。ｍは１～６の整数を表し、ｎは０～４の整数を表す。Ｒは、水素原子又は炭素数１～５のアルキル基を表す。上記Ａの芳香環上の水素原子は、ハロゲン原子、炭素数１～６のアルキル基、炭素数２～６のアルケニル基、炭素数２～６のアルキニル基、フッ素原子を含有する炭素数１～６の１価の有機基などの１価の有機基で置き換えられてもよい。）

( _R2 and _R3 are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or "* _-CH2 -OH". A represents an (m+n)-valent organic group having an aromatic ring. m represents an integer of 1 to 6, and n represents an integer of 0 to 4. R represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. The hydrogen atom on the aromatic ring of A may be replaced with a monovalent organic group such as a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, or a monovalent organic group having 1 to 6 carbon atoms and containing a fluorine atom.)

Specific examples of compounds having an oxiranyl group include compounds having two or more oxiranyl groups, such as the compounds described in paragraph [0037] of JP-A-10-338880 and compounds having a triazine ring skeleton described in WO 2017/170483. Among these, compounds containing nitrogen atoms, such as N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, N,N,N',N'-tetraglycidyl-p-phenylenediamine, and compounds represented by the following formulas (r-1) to (r-3), may be used.

Specific examples of compounds having an oxetanyl group include compounds having two or more oxetanyl groups, such as those described in paragraphs [0170] to [0175] of WO 2011/132751.

Specific examples of compounds having a protected isocyanate group include compounds having two or more protected isocyanate groups described in paragraphs [0046] to [0047] of JP 2014-224978 A, and compounds having three or more protected isocyanate groups described in paragraphs [0119] to [0120] of WO 2015/141598 A, and may be compounds represented by the following formulae (bi-1) to (bi-3).

Specific examples of compounds having a protected isothiocyanate group include compounds having two or more protected isothiocyanate groups, as described in JP 2016-200798 A.

Specific examples of compounds having a group containing an oxazoline ring structure include compounds containing two or more oxazoline ring structures, as described in paragraph [0115] of JP 2007-286597 A.

Specific examples of compounds having a group containing a Meldrum's acid structure include compounds having two or more Meldrum's acid structures, as described in International Publication No. 2012/091088.

Specific examples of compounds having a cyclocarbonate group include the compounds described in WO 2011/155577.

Examples of the alkyl group having 1 to 3 carbon atoms for R ₂ and R ₃ in the group represented by formula (d) include a methyl group, an ethyl group, and a propyl group.

Specific examples of the compound having a group represented by formula (d) include compounds having two or more groups represented by formula (d) described in WO 2015/072554 and paragraph [0058] of JP 2016-118753 A, and compounds described in JP 2016-200798 A, and may be compounds represented by the following formulae (hd-1) to (hd-8).

In the formula (e), the (m+n)-valent organic group having an aromatic ring in A includes an (m+n)-valent aromatic hydrocarbon group having 6 to 30 carbon atoms, an (m+n)-valent organic group to which an aromatic hydrocarbon group having 6 to 30 carbon atoms is bonded directly or via a linking group, and an (m+n)-valent group having an aromatic heterocycle. Examples of the aromatic hydrocarbon include benzene and naphthalene. Examples of the aromatic heterocycle include a pyrrole ring, an imidazole ring, a pyrazole ring, a pyridine ring, a pyrimidine ring, a quinoline ring, an isoquinoline ring, a carbazole ring, a pyridazine ring, a pyrazine ring, a benzimidazole ring, an indole ring, a quinoxaline ring, and an acridine ring. Examples of the linking group include an alkylene group having 1 to 10 carbon atoms, -NR- (wherein R represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms), a group in which one hydrogen atom has been removed from the alkylene group, and a divalent or trivalent cyclohexane ring. Any hydrogen atom in the alkylene group may be substituted with a fluorine atom or an organic group such as a trifluoromethyl group. Specific examples of the compound represented by formula (e) include the compounds described in WO 2010/074269 and the compounds represented by the following formulas (e-1) to (e-10).

The above compounds are examples of crosslinkable compounds, and are not limited thereto. For example, components other than those described above are disclosed on pages 53 [0105] to 55 [0116] of WO 2015/060357. Two or more types of crosslinkable compounds may be combined.

The content of the crosslinkable compound in the liquid crystal alignment agent of the present invention is preferably 0.5 to 20 parts by mass per 100 parts by mass of the polymer component contained in the liquid crystal alignment agent, and more preferably 1 to 15 parts by mass from the viewpoint of proceeding with the crosslinking reaction and exhibiting good resistance to AC afterimages.

Examples of the adhesion aid include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyldiethoxymethylsilane, 2-aminopropyltrimethoxysilane, 2-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, N-ethoxycarbonyl-3-aminopropyltrimethoxysilane, N-ethoxycarbonyl-3-aminopropyltrimethoxysilane, and N-ethoxycarbonyl-3-aminopropyltrimethoxysilane. N-trimethoxysilylpropyltriethylenetriamine, N-trimethoxysilylpropyltriethylenetriamine, 10-trimethoxysilyl-1,4,7-triazadecane, 10-triethoxysilyl-1,4,7-triazadecane, 9-trimethoxysilyl-3,6-diazanonyl acetate, 9-triethoxysilyl-3,6-diazanonyl acetate, N-benzyl-3-aminopropyltrimethoxysilane, N-benzyl-3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltriethoxysilane Aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane, N-bis(oxyethylene)-3-aminopropyltrimethoxysilane, N-bis(oxyethylene)-3-aminopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane Examples of silane coupling agents include silane coupling agents such as xysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane. When using a silane coupling agent, from the viewpoint of exhibiting good resistance to AC afterimages, it is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, relative to 100 parts by mass of the polymer component contained in the liquid crystal alignment agent.

As the compound for promoting the imidization, a compound having a basic site (e.g., a primary amino group, an aliphatic heterocycle (e.g., a pyrrolidine skeleton), an aromatic heterocycle (e.g., an imidazole ring, an indole ring), or a guanidino group, etc.) (excluding the crosslinking compound and the adhesion aid) or a compound that generates the basic site when baked is preferable. A compound that generates the basic site when baked is more preferable, and a preferred example of the compound is an amino acid in which some or all of the basic sites of the amino acid are protected. Specific examples of the amino acid include glycine, alanine, cysteine, methionine, asparagine, glutamine, valine, leucine, phenylalanine, tyrosine, tryptophan, proline, hydroxyproline, arginine, histidine, lysine, and ornithine. A more preferred example of the compound for promoting the imidization is N-α-(9-fluorenylmethoxycarbonyl)-N-τ-(tert-butoxycarbonyl)-L-histidine.

<Method of manufacturing liquid crystal alignment film>
The method for producing a liquid crystal alignment film using the liquid crystal alignment agent of the present invention is characterized by sequentially carrying out the steps of applying the above-mentioned liquid crystal alignment agent (step (1)), baking the applied liquid crystal alignment agent (step (2)), irradiating the film obtained in step (2) with polarized ultraviolet light (step (3)), and baking the film obtained in step (3) at a temperature of 100° C. or higher and at a temperature higher than that of step (2) (step (4)).

<Step (1)>
The substrate to which the liquid crystal alignment agent used in the present invention is applied is not particularly limited as long as it is a highly transparent substrate, and a glass substrate, a silicon nitride substrate, an acrylic substrate, a plastic substrate such as a polycarbonate substrate, etc. can also be used. In this case, it is preferable to use a substrate on which an ITO electrode for driving the liquid crystal is formed from the viewpoint 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 also be used for the electrode.

The method for applying the liquid crystal alignment agent is not particularly limited, but in industry, screen printing, offset printing, flexographic printing, or inkjet printing are commonly used. Other application methods include the dip method, roll coater method, slit coater method, spinner method, and spray method, and these may be used depending on the purpose.

<Step (2)>
Step (2) is a step of baking the liquid crystal alignment agent applied on the substrate to form a film. After the liquid crystal alignment agent is applied on the substrate, the solvent can be evaporated or the amic acid or amic acid ester in the polymer can be thermally imidized by a heating means such as a hot plate, a heat circulation type oven, or an IR (infrared) type oven. The drying and baking steps after the application of the liquid crystal alignment agent of the present invention can be performed at any temperature and time, and may be performed multiple times. The baking temperature can be, for example, 40 to 150°C. From the viewpoint of shortening the process, it may be performed at 40 to 120°C. The baking time is not particularly limited, but may be 1 to 10 minutes or 1 to 5 minutes. When the amic acid or amic acid ester in the polymer is thermally imidized, a baking step can be performed at a temperature range of, for example, 190 to 250°C or 200 to 240°C after the above baking step. The baking time is not particularly limited, but may be 5 to 40 minutes or 5 to 30 minutes.

<Step (3)>
Step (3) is a step of irradiating the film obtained in step (2) with polarized ultraviolet light. The wavelength of the ultraviolet light is preferably 200 to 400 nm, and more preferably, ultraviolet light having a wavelength of 200 to 300 nm. In order to improve the liquid crystal alignment, the substrate coated with the liquid crystal alignment film may be irradiated with ultraviolet light while being heated at 50 to 250°C. The irradiation dose of the ultraviolet light is preferably 1 to 10,000 mJ/ ^cm2 , and more preferably 100 to 5,000 mJ/ ^cm2 . The liquid crystal alignment film thus prepared can stably align liquid crystal molecules in a certain direction.

A higher extinction ratio for polarized UV light is preferable because it can provide higher anisotropy. Specifically, the extinction ratio for linearly polarized UV light is preferably 10:1 or greater, and more preferably 20:1 or greater.

<Step (4)>
Step (4) is a step of baking the film obtained in step (3) at 100° C. or higher and at a temperature higher than that in step (2). The baking temperature is not particularly limited as long as it is 100° C. or higher and higher than the baking temperature in step (2), but is preferably 150 to 300° C., more preferably 150 to 250° C., and even more preferably 200 to 250° C. The baking time is preferably 5 to 120 minutes, more preferably 5 to 60 minutes, and even more preferably 5 to 30 minutes.

If the thickness of the liquid crystal alignment film after baking is too thin, the reliability of the liquid crystal display element may decrease, so a thickness of 5 to 300 nm is preferable, and 10 to 200 nm is more preferable.

Furthermore, after performing either step (3) or (4), the obtained liquid crystal alignment film can be subjected to a contact treatment using water or a solvent.

The solvent used in the contact treatment is not particularly limited as long as it dissolves the decomposition products generated from the liquid crystal alignment film by irradiation with ultraviolet light. Specific examples include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, 1-methoxy-2-propanol, 1-methoxy-2-propanol acetate, butyl cellosolve, ethyl lactate, methyl lactate, diacetone alcohol, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, propyl acetate, butyl acetate, and cyclohexyl acetate. Among these, water, 2-propanol, 1-methoxy-2-propanol, and ethyl lactate are preferred from the viewpoint of versatility and solvent safety. Water, 1-methoxy-2-propanol, and ethyl lactate are more preferred. The solvent may be one type or a combination of two or more types.

The above-mentioned contact treatment, i.e., treatment with water or a solvent on the liquid crystal alignment film irradiated with polarized ultraviolet light, includes immersion treatment and spray treatment (also called spray treatment). The treatment time in these treatments is preferably 10 seconds to 1 hour from the viewpoint of efficiently dissolving the decomposition products generated from the liquid crystal alignment film by ultraviolet light. In particular, immersion treatment for 1 to 30 minutes is preferable. The solvent during the contact treatment may be at room temperature or heated, but is preferably 10 to 80°C, and more preferably 20 to 50°C. In addition, ultrasonic treatment or the like may be performed as necessary from the viewpoint of the solubility of the decomposition products.

After the contact treatment, it is preferable to rinse the liquid crystal alignment film with a low boiling point solvent such as water, methanol, ethanol, 2-propanol, acetone, or methyl ethyl ketone (also called rinsing), and then bake the liquid crystal alignment film. In this case, either rinsing or baking may be performed, or both may be performed. The baking temperature is preferably 150 to 300°C. Of these, 180 to 250°C is more preferable, and 200 to 230°C is even more preferable. The baking time is preferably 10 seconds to 30 minutes, and of these, 1 to 10 minutes is more preferable.

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

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

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

Next, a liquid crystal alignment film is formed on each substrate, and one substrate is superimposed on the other substrate so that the liquid crystal alignment film faces each other, and the periphery is bonded with a sealant. Spacers are usually mixed into the sealant in order to control the gap between the substrates, and it is also preferable to disperse spacers for controlling the gap between the substrates in the in-plane portion where the sealant is not provided. An opening is provided in a part of the sealant so that liquid crystal material can be filled from the outside. Next, liquid crystal material is injected into the space surrounded by the two substrates and the sealant through the opening provided in the sealant, and then this opening is sealed with an adhesive. For injection, a vacuum injection method or a method utilizing capillary action in the atmosphere may be used. The liquid crystal material may be either a positive type liquid crystal material or a negative type liquid crystal material. Next, a polarizing plate is installed. Specifically, a pair of polarizing plates are attached to the surface opposite to the liquid crystal layer of the two substrates.

By using the manufacturing method of the present invention, it is possible to suppress image retention caused by long-term AC driving in liquid crystal display elements using the IPS drive system or FFS drive system. Furthermore, by baking in a temperature range of 40 to 150°C in step (2) and then carrying out step (3), a liquid crystal alignment film can be obtained with fewer steps than in the past. The liquid crystal alignment agent of the present invention can be particularly preferably used in a manufacturing method for a liquid crystal alignment film including a step of baking in a temperature range of 40 to 150°C in step (2) and then carrying out step (3).

(solvent)
NMP: N-methyl-2-pyrrolidone BCS: Butyl cellosolve (diamine)
DA-1 to DA-9: Compounds (tetracarboxylic dianhydrides) represented by the following formulas (DA-1) to (DA-9), respectively.
CA-1 to CA-5: Compounds (additives) represented by the following formulas (CA-1) to (CA-5), respectively.
C-1: 2,2'-bis(4-hydroxy-3,5-dihydroxymethylphenyl)propane (compound represented by the following formula (C-1))
S-1: Compound represented by the following formula (S-1) F-1: Compound represented by the following formula (F-1)

（Ｆｍｏｃは、９－フルオレニルメチルオキシカルボニル基を表す。）

(Fmoc represents a 9-fluorenylmethyloxycarbonyl group.)

<Measurement of Viscosity>
The measurements were performed 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.

<Measurement of imidization rate>
20 mg of polyimide powder was placed in an NMR sample tube (NMR sampling tube standard, φ5 (Kusano Scientific Co., Ltd.)), deuterated dimethyl sulfoxide (DMSO-d6, 0.05% TMS (tetramethylsilane) mixture) (0.53 mL) was added, and the mixture was sonicated to completely dissolve. This solution was measured for proton NMR at 500 MHz using an NMR measurement device (JNW-ECA500) (JEOL Datum Co., Ltd.). The imidization rate was calculated by the following formula, using a proton derived from a structure that does not change before and after imidization as a reference proton, and the peak integrated value of this proton and the proton peak integrated value derived from the NH group of the amic acid that appears around 9.5 ppm to 10.0 ppm.
Imidization rate (%)=(1−α·x/y)×100
In the above formula, x is the integrated value of the proton peak derived from the NH group of the amic acid, y is the integrated value of the peak of the reference proton, and α is the ratio of the number of the reference protons to one NH group proton of the amic acid in the case of polyamic acid (imidization rate 0%).

[Polymer synthesis example]
<Synthesis Example 1>
4.95 g (20.3 mmol) of DA-1, 5.30 g (18.0 mmol) of DA-2, and 1.60 g (6.75 mmol) of DA-3 were weighed out into a 200 mL four-neck flask equipped with a stirrer and a nitrogen inlet tube, and NMP was added to the mixture so that the concentration was 12% by mass, and the mixture was stirred and dissolved while feeding nitrogen. While stirring this diamine solution, 9.28 g (41.4 mmol) of CA-1 was added, and NMP was added to the mixture so that the concentration was 12% by mass, and the mixture was stirred at 40° C. for 24 hours to obtain a polyamic acid solution.
35 g (8.9 mmol) of the obtained polyamic acid solution was taken in a 100 mL four-neck flask equipped with a stirrer and a nitrogen inlet tube, 11.7 g of NMP was added, and the mixture was stirred for 30 minutes. 2.74 g of acetic anhydride (3 equivalents relative to the molar amount of polyamic acid) and 0.71 g of pyridine (equivalent to the molar amount of polyamic acid) were added to the obtained polyamic acid solution, and the mixture was heated at 50 ° C. for 3 hours to perform chemical imidization. The obtained reaction solution was poured into 150 mL of methanol while stirring, and the precipitate was filtered off. The same operation was carried out twice to wash the resin powder, and then the resin powder was dried at 60 ° C. for 12 hours to obtain a polyimide resin powder. The imidization rate of this polyimide resin powder was 75%. 3.60 g of the obtained polyimide resin powder was taken in a 100 mL Erlenmeyer flask, NMP was added so that the solid concentration was 12%, and the mixture was stirred and dissolved at 70 ° C. for 24 hours to obtain a polyimide solution (PI-1).

<Synthesis Examples 2 to 10>
Polyimide solutions (PI-2) to (PI-10) were obtained in the same manner as in Synthesis Example 1, except that the types and amounts of monomers used were changed as shown in Table 1 below. In Table 1, the numbers in parentheses indicate the blending ratio (parts by mole) of each compound relative to 100 parts by mole of the total amount of tetracarboxylic acid derivatives used in the synthesis for the tetracarboxylic acid components, and the blending ratio (parts by mole) of each compound relative to 100 parts by mole of the total amount of diamines used in the synthesis for the diamine components. The organic solvents indicate the blending ratio (parts by mass) of each organic solvent relative to 100 parts by mass of the total amount of organic solvents used in the preparation of the polyimide solutions.
<Synthesis Example 11>
In a 200 mL four-neck flask equipped with a stirrer and a nitrogen inlet tube, 3.37 g (8.0 mmol) of DA-7, 2.39 g (8.0 mmol) of DA-8, and 4.78 g (24.0 mmol) of DA-9 were weighed out, NMP was added so that the concentration was 12 mass%, and the mixture was stirred and dissolved while feeding nitrogen. While stirring this diamine solution, 11.3 g (38.5 mmol) of CA-5 was added, NMP was added so that the concentration was 12 mass%, and the mixture was stirred at 70 ° C. for 24 hours to obtain a polyamic acid solution (PAA-1).

[Preparation of liquid crystal alignment agent]
<Comparative Example 1>
The polyimide solution (PI-1) obtained in Synthesis Example 1, NMP, and BCS were added to a sample tube containing a stirrer, and S-1, C-1, and F-1 were added in amounts of 1 part by mass, 10 parts by mass, and 15 parts by mass, respectively, relative to 100 parts by mass of polymer solid content, and the mixture was stirred for 30 minutes. After stirring, a liquid crystal alignment agent (R1) was obtained in which the solid content concentration of the polyimide solution (PI-1) was 6% by mass and the solvent composition was NMP:BCS=80:20 by mass ratio.

<Comparative Examples 2 to 5, Examples 1 to 12>
Liquid crystal alignment agents (R2) to (R5), (1) to (12) were obtained in the same manner as in Comparative Example 1, except that the polymer components used were changed as shown in Table 2 below. In Table 2, the numbers in parentheses indicate the blending ratio (parts by mass) of each polymer component or additive relative to 100 parts by mass of the total of the polymer components used in the preparation of the liquid crystal alignment agent, for the polymer and additive, respectively. For the organic solvent, the numbers indicate the blending ratio (parts by mass) of each organic solvent relative to 100 parts by mass of the total amount of the organic solvent in the liquid crystal alignment agent.

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 3.5 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 inner angle of 160° at the center are arranged in parallel with a gap 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 substrate coincides with the alignment direction of the liquid crystal on the second substrate when the liquid crystal cell is fabricated.

[Preparation of Liquid Crystal Cell]
A liquid crystal alignment agent filtered through a filter with a pore size of 1.0 μm was applied by spin coating to the surface of each of the above glass substrates, and dried for 2 minutes on a hot plate at 80° C. After that, the coating surface was irradiated with 150 to 350 mJ/ ^cm2 of linearly polarized ultraviolet light with an extinction ratio of 26:1 and a wavelength of 254 nm through a polarizing plate, and then baked for 30 minutes in a hot air circulation oven at 230° C. to obtain two substrates with a liquid crystal alignment film having a thickness of 100 nm.
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 (Mitsui Chemicals, Inc., XN-1500T) was cured to prepare an empty cell. Liquid crystal (Merck, Inc., MLC-3019) 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 (hereinafter, this treatment is also referred to as ISO treatment), and left overnight before being used for each evaluation.

<Evaluation of Liquid Crystal Alignment>
The liquid crystal cells before the ISO treatment were used and the evaluation was performed by defining those with initial flow alignment as "bad" and those without initial flow alignment as "good".
<Evaluation of in-plane uniformity of contrast>
The twist angle of the liquid crystal display element was evaluated using an OPTIPRO-micro manufactured by Shintech Co., Ltd. The fabricated liquid crystal cell was placed on a measurement stage, and 20 points within the first pixel plane were measured without applying voltage, and the standard deviation was calculated. The evaluation was performed by defining a twist angle standard deviation of 0.5 or more as "poor" and a twist angle standard deviation of less than 0.5 as "good."

<Voltage holding ratio evaluation>
The liquid crystal cell prepared above was subjected to a voltage of 1 V for 60 microseconds at 60° C., and the voltage retention rate after 1,000 milliseconds was measured using an apparatus manufactured by Toyo Corporation. In this case, a voltage retention rate of 90% or more was defined as "good", and a voltage retention rate of less than 90% was defined as "poor".

<Evaluation Results>
Table 3 shows the evaluation results of the liquid crystal display devices obtained by using the liquid crystal alignment agents (1) to (12) and (R1) to (R5) obtained in the above Examples 1 to 12 and Comparative Examples 1 to 5.

Claims (12)

At least one repeating unit (a1) selected from the group consisting of repeating units represented by the following formula (1-a) and repeating units represented by the following formula (1-i),
A liquid crystal aligning agent for a photoalignment method, comprising at least one repeating unit (a2) selected from the group consisting of repeating units represented by the following formula (2-a) and repeating units represented by the following formula (2-i), and containing at least one polymer (A) selected from the group consisting of polyimide precursors and imidized polymers thereof, the repeating unit (a1) accounting for 1 to 20 mol % of all repeating units:

(In the formula, _X1 represents a tetravalent organic group represented by the following formula (B), and _X2 represents a tetravalent organic group represented by the following formula (C). R and Z each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A plurality of R and Z may be the same or different. _Y1 and _Y2 each independently represent a divalent organic group represented by the following formula (O).

(In the formula, R _b1 to R _b4 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms. _{L 1} represents a single bond, -CH ₂ -, -(CH ₂ ) _n - (n is an integer from 2 to 18), or a group in which at least a part of the -CH ₂ - of the -(CH ₂ ) _n - is replaced with any of -O-, -C(═O)-, or -O-C(═O)-. _{R c1} to R _c4 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group, and at least one of R _c1 to R _c4 represents a group other than a hydrogen atom as defined above.)

(Ar represents a benzene ring, a biphenyl structure, or a naphthalene ring, two Ars may be the same or different, and any hydrogen atom in the ring may be replaced by a monovalent organic group. _Q2 represents _-CH2- , -( _CH2 ) _n- (n is an integer from 2 to 18), or a group in which at least a part of the _-CH2- in the -( _CH2 ) _n- is replaced by any of -O-, -C(=O)- or -O-C(=O)-. p is an integer of 1, and at least one of the two Ars represents a naphthalene ring. * represents a bond.) The liquid crystal aligning agent for photoalignment method according to claim 1, wherein the tetravalent organic group represented by the formula (B) is a tetravalent organic group represented by the following formulas (b-1) to (b-2):

(* represents a bond.) The liquid crystal aligning agent for photoalignment method according to claim 1 or 2, wherein the divalent organic group represented by the formula (O) is a divalent organic group represented by the following formulas (o-1) to (o-6) :

The polymer (A) has at least one repeating unit (a3) selected from the group consisting of a repeating unit represented by the following formula (3-a) and a repeating unit represented by the following formula (3-i): The liquid crystal aligning agent for photoalignment method according to any one of claims 1 to 3.

(In the formula, _X3 represents a tetravalent organic group, and _Y3 represents a divalent organic group represented by the following formula (3d). R and Z are the same as those in the formula (1-a).)

(Ar ₃ represents a benzene ring or a biphenyl structure, two Ars may be the same or different, and any hydrogen atom on the ring may be replaced with a monovalent organic group. Q ₃ represents -(CH ₂ ) _n - (n is an integer from 2 to 18), or a group in which at least a part of the -CH ₂ - of the -(CH ₂ ) _n - is replaced with any of -O-, -C(═O)-, or -O-C(═O)-. * represents a bond.) The polymer (A) has at least one repeating unit (a4) selected from the group consisting of a repeating unit represented by the following formula (4-a) and a repeating unit represented by the following formula (4-i): The liquid crystal aligning agent for photoalignment method according to any one of claims 1 to 4.

(In the formula, R and Z are the same as those in the formula (1-a). _X4 represents a tetravalent organic group, and _Y4 represents a divalent organic group having 6 to 30 carbon atoms and containing a group "-N(D)- (D represents a carbamate protecting group)" in the molecule.) The liquid crystal aligning agent for photoalignment method according to claim 5, wherein _Y4 is a structure represented by the following formulas (Y4-1) to (Y4-4).

(Boc represents a tert-butoxycarbonyl group.) A liquid crystal alignment film obtained from the liquid crystal alignment agent for photoalignment method according to any one of claims 1 to 6. A liquid crystal display element comprising the liquid crystal alignment film according to claim 7. A method for producing a liquid crystal alignment film, comprising the following steps (1) to (3):
Step (1): A step of applying the liquid crystal aligning agent for photoalignment method according to any one of claims 1 to 6 onto a substrate.
Step (2): A step of heating the applied liquid crystal alignment agent for photoalignment method to obtain a film.
Step (3): A step of irradiating the film obtained in step (2) with polarized ultraviolet light. The method for producing a liquid crystal alignment film according to claim 9, further comprising the following step (4):
Step (4): A step of baking the film obtained in step (3) at a temperature of 100° C. or higher and higher than that in step (2). The method for producing a liquid crystal alignment film according to claim 9 or 10, wherein the step (2) is a step of obtaining a film by heating at a temperature range of 40 to 180°C. A liquid crystal display element having a liquid crystal alignment film obtained by the method for producing a liquid crystal alignment film according to any one of claims 9 to 11.