TWI852985B - Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element using the same - Google Patents

Abstract

The present invention provides a liquid crystal alignment agent that can obtain a liquid crystal alignment film that maintains a voltage retention ratio even after being placed in high temperature and high humidity. The liquid crystal alignment agent of the present invention is characterized by containing at least one polymer selected from the group consisting of a polyimide precursor obtained by polymerizing any one of the following diamine components (1) and diamine components (2) with a tetracarboxylic acid component, and a polyimide obtained by imidizing the polyimide precursor. Diamine component (1): a diamine component containing a diamine having a protective group that is thermally replaced with a hydrogen atom and a diamine having a siloxane skeleton. Diamine component (2): a diamine component containing a diamine having a protective group that is thermally replaced with a hydrogen atom and a siloxane skeleton.

Description

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

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

In a liquid crystal display element, the liquid crystal alignment film plays the role of aligning the liquid crystal in a specific direction. Currently, the liquid crystal alignment film mainly uses a polyimide-based liquid crystal alignment film which is prepared by coating a liquid crystal alignment agent with a polyimide precursor such as polyamide or a soluble polyimide solution as the main component on a glass substrate, etc., and then firing it.

With the high functionality of liquid crystal display devices, liquid crystal alignment films are required to exhibit not only excellent liquid crystal alignment or stable pre-tilt angle, but also high voltage holding ratio, less residual charge when DC voltage is applied, and/or rapid relaxation of residual charge accumulated by DC voltage.

In order to respond to the above-mentioned requirements, various proposals have been made. For example, Patent Document 1 proposes a liquid crystal alignment agent composed of an imidized polymer satisfying the following formula (1). [Prior art literature] [Patent literature]

[Patent Document 1] Japanese Patent Application Publication No. 2005-179429

[The problem that the invention wants to solve]

In recent years, as the performance of liquid crystal display elements has improved, liquid crystal display elements have been used in large-screen and high-precision liquid crystal televisions or in-vehicle applications, such as car navigation systems or instrument panels. In addition to good initial characteristics, such applications also require that the voltage retention rate does not easily decrease even after being placed in high temperature and high humidity for a long time.

In addition, when a liquid crystal alignment agent with a high imidization rate is generally used, a high voltage holding rate is easily obtained, but the solubility in the solvent is reduced and when printed on a substrate, polyimide is precipitated due to moisture absorption, which easily causes the varnish to whiten. Therefore, it is also required that the voltage holding rate of the liquid crystal alignment film is not easily reduced even when a liquid crystal alignment agent with a low imidization rate is used.

However, Patent Document 1 does not disclose the voltage retention rate after being placed in high temperature and high humidity. In addition, the example of Patent Document 1 only discloses the case of using a liquid crystal alignment agent with a high imidization rate.

The present invention was completed in view of the above situation. The purpose of the present invention is to provide a liquid crystal alignment agent that can obtain a liquid crystal alignment film that maintains a voltage retention rate even after being placed in high temperature and high humidity. In addition, the purpose of the present invention is to provide a liquid crystal alignment agent that can obtain a liquid crystal alignment film that maintains a voltage retention rate even when the imidization rate is low. [Means for solving the problem]

As a result of careful research to solve the above problems, the inventors of the present invention have found that a liquid crystal alignment agent containing a specific polymer satisfies the above problems. The present invention is based on this insight and has the following as technical requirements. A liquid crystal alignment agent characterized by containing at least one polymer selected from the group consisting of a polyimide precursor obtained by polymerizing any one of the following diamine components (1) and diamine components (2) with a tetracarboxylic acid component, and a polyimide obtained by imidizing the polyimide precursor, Diamine component (1): a diamine component containing a diamine having a protective group that is thermally replaced with a hydrogen atom and a diamine having a siloxane skeleton, Diamine component (2): a diamine component containing a diamine having a protective group that is thermally replaced with a hydrogen atom and a siloxane skeleton. [Effect of the invention]

According to the liquid crystal alignment agent of the present invention, a liquid crystal alignment film that maintains the voltage retention rate can be obtained even after being placed in high temperature and high humidity. Furthermore, according to the liquid crystal alignment agent of the present invention, a liquid crystal alignment film that maintains the voltage retention rate can be obtained even when the imidization rate is low. In addition, the liquid crystal alignment agent of the present invention is also excellent in terms of solubility and sealing adhesion. [Embodiment of the invention]

<Specific polymer> The liquid crystal alignment agent of the present invention contains at least one polymer selected from the group consisting of a polyimide precursor obtained by polymerizing any one of the following diamine components (1) and diamine components (2) with a tetracarboxylic acid component, and a polyimide obtained by imidizing the polyimide precursor (hereinafter also referred to as a specific polymer). Diamine component (1): a diamine component containing a diamine having a protective group that is heat-replaced to a hydrogen atom and a diamine having a siloxane skeleton. Diamine component (2): a diamine component containing a diamine having a protective group that is heat-replaced to a hydrogen atom and a siloxane skeleton.

<Diamine component (1)> Among the diamine components (1), the diamine having a protective group that is heat-replaceable to a hydrogen atom may be, for example, a diamine represented by the following formula [1]. Among the diamine components (1), the diamine having a siloxane skeleton may be, for example, a diamine represented by the following formula [2]. Among the diamine components (1), the diamine having a protective group that is heat-replaceable to a hydrogen atom may be a diamine represented by the following formula [1], and the diamine having a siloxane skeleton may be a diamine represented by the following formula [2].

(Diamine represented by formula [1]) The diamine represented by formula [1] is the following. (In formula [1], ^XD represents an organic group having 1 to 50 carbon atoms and having a structure of at least one selected from the group consisting of the following formula [1a], formula [1b] and formula [1c], and ^A1 and ^A2 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.) (In formula [1a] to formula [1c], ^Xa represents a hydrogen atom or an organic group having 1 to 20 carbon atoms. ^Xd represents a single bond or an organic group having 1 to 20 carbon atoms. ^Xe represents a hydrogen atom or an organic group having 1 to 20 carbon atoms. D represents a protecting group that is heat-replaceable to a hydrogen atom. * represents a bond.)

Here, in the present invention, "protective groups that are replaced by hydrogen atoms by heat" refers to protective groups that are released by heat and replaced by hydrogen atoms. The temperature at which the protective groups are released by heat and replaced by hydrogen atoms is the sintering temperature when making the liquid crystal alignment film, preferably 150-300°C, more preferably 200-270°C. The protective group (D) is preferably a protective group represented by the following formula [P].

(In the formula, ^XA represents a structure selected from the group consisting of the following formulas [a-1] to [a-6], and ^R1 represents an alkylene group having 1 to 5 carbon atoms.)

Specifically, the diamine represented by the formula [1] is preferably a diamine represented by the following formula [1a-1] to [1c-1]. In formula [1a-1], ^X1 represents at least one selected from a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO-, and OCO-. However, ^R1 , ^R2 , and ^R3 each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. In particular, a single bond, -O-, -CONH-, -NHCO-, -COO-, or OCO- is preferred.

In the formula [1a-1], ^X2 represents a single bond or an alkylene group having 1 to 10 carbon atoms. Preferably, it is a single bond or an alkylene group having 1 to 5 carbon atoms. ^Xa represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, more preferably a hydrogen atom or an organic group having 1 to 10 carbon atoms. The organic group having 1 to 10 carbon atoms is preferably -( _CH2 ) _n -COO-tBu (n = an integer of 1 to 5, tBu represents tert-butyl). In the formula [1a-1], ^Xb represents a structure selected from the group consisting of the above formulas [a-1] to [a-6]. In the formula [1a-1], m represents an integer of 1 or 2, and when m is 2, ^Xa has no substituent. p represents an integer of 1 to 4. Preferably, it is 1 to 3 from the viewpoint of raw material availability or ease of synthesis. More preferably, it is 1 to 2. q represents an integer of 1 to 4. Among them, from the viewpoint of raw material availability or ease of synthesis, it is preferably 1 to 3. More preferably, it is 1 to 2.

In formula [1b-1], ^X3 and ^X7 each independently represent a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO-, and at least one organic group selected from the group consisting of OCO-. However, R1, ^R2 , and ^R3 each independently represent a hydrogen atom or an alkylene group having 1 to 3 carbon atoms. Among them, a single bond, -O-, -CONH-, -NHCO-, -COO-, or OCO- is preferred. In formula [ ^1b -1], ^X4 and ^X6 each independently represent a single bond or an alkylene group having 1 to 10 carbon atoms. In particular, a single bond or an alkylene group having 1 to 5 carbon atoms is preferred. ^X5 represents a single bond or an alkylene group having 1 to 10 carbon atoms. Among them, a single bond or an alkylene group having 1 to 5 carbon atoms is preferred. ^Xc represents a structure selected from the group consisting of the above formulas [a-1] to [a-6]. In formula [1b-1], r represents an integer of 1 to 4. From the viewpoint of raw material availability or ease of synthesis, 1 to 3 is preferred. 1 to 2 is more preferred.

In formula [1c-1], ^X8 represents a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO-, and at least one organic group selected from the group consisting of OCO-. However, ^R1 , ^R2 , and ^R3 each independently represent a hydrogen atom or an alkylene group having 1 to 3 carbon atoms. In particular, a single bond, -O-, -CONH-, -NHCO-, -COO-, or OCO- is preferred. In formula [1c-1], ^X9 represents a single bond, an alkylene group having 1 to 10 carbon atoms, preferably a single bond or an alkylene group having 1 to 5 carbon atoms. ^Xd represents a single bond or an organic group having 1 to 20 carbon atoms. Among them, a single bond or an organic group having 1 to 10 carbon atoms is preferred. A single bond or a carbon atom (＞CH-) is more preferred. ^Xe represents a hydrogen atom or an organic group having 1 to 20 carbon atoms. In this case, when ^Xd is a single bond, there is no ^Xe . Among them, a hydrogen atom or NH-COO-tBu (tBu represents tert-butyl) is preferred. In formula [1c-1], ^Xf represents a structure selected from the group consisting of the above formulas [a-1] to [a-6]. n represents an integer of 1 to 4. Among them, from the viewpoint of raw material availability or ease of synthesis, 1 to 3 is preferred, and 1 to 2 is more preferred. s represents an integer of 1 to 4, from the viewpoint of raw material availability or ease of synthesis, 1 to 3 is preferred, and 1 to 2 is more preferred. t represents an integer of 1 to 4, and is preferably 1 to 3, and more preferably 1 to 2, from the viewpoint of raw material availability or ease of synthesis.

In formula [1a-1] to formula [1c-1], A ¹ to A ⁶ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

More specifically, the diamine represented by formula [1] can be exemplified by the diamines represented by the following formulas [1d-1] to [1d-11].

(式[1d-1]~式[1d-5]中，R¹~R⁷各自獨立表示選自由下述式[a-1]~式[a-6]所構成群組中之至少1種的結構，式[1d-1]~式[1d-5]中，A¹~A¹⁰各自獨立表示氫原子或碳數1~5之烷基。式[1d-4]~式[1d-5]中，n1為1~10的整數，n2為1~10的整數，n3為1~10的整數)

(In formula [1d-1] to formula [1d-5], R ¹ to R ⁷ each independently represent at least one structure selected from the group consisting of the following formulas [a-1] to [a-6]; in formula [1d-1] to formula [1d-5], A ¹ to A ¹⁰ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. In formula [1d-4] to formula [1d-5], n1 is an integer of 1 to 10, n2 is an integer of 1 to 10, and n3 is an integer of 1 to 10)

(式[a-2]中，R¹表示碳數1~5之烷基。)

(In formula [a-2], ^R1 represents an alkyl group having 1 to 5 carbon atoms.)

(式[1d-6]~式[1d-9]中，R⁸~R¹⁴各自獨立表示選自由前述式[a-1]~式[a-6]表示之構造所構成群組中之至少1種的結構，式[1d-6]~式[1d-9]中，A¹¹~A¹⁸各自獨立表示氫原子或碳數1~5之烷基)。

(In formulas [1d-6] to [1d-9], R ⁸ to R ¹⁴ each independently represent at least one structure selected from the group consisting of the structures represented by formulas [a-1] to [a-6], and in formulas [1d-6] to [1d-9], A ¹¹ to A ¹⁸ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms).

Among them, the diamine represented by formula [1] is preferably a diamine represented by the aforementioned formula [1d-1] to formula [1d-5].

In addition, the diamine represented by formula [1] can be the diamine represented by the following formula [1d-10] and formula [1d-11].

(式[1d-10]及式[1d-11]中，R¹⁵~R¹⁸各自獨立表示選自由前述式[a-1]~式[a-6]表示之構造所構成群組中之至少1種的結構，式[1d-11]中，A¹⁹ 及A²⁰ 各自獨立表示氫原子或碳數1~5之烷基。)

(In formulas [1d-10] and [1d-11], R ¹⁵ to R ¹⁸ each independently represent at least one structure selected from the group consisting of the structures represented by formulas [a-1] to [a-6], and in formula [1d-11], A ¹⁹ and A ²⁰ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.)

The content of the diamine represented by formula [1] in 100 mol% of the total diamine component is preferably 5 to 70 mol%. Among them, 5 to 30 mol% is more preferred, and 5 to 20 mol% is more preferred. The diamine represented by formula [1] can be used alone or in combination of two or more, depending on the solubility in a solvent of a specific polymer or the coating properties of a liquid crystal alignment agent, the liquid crystal alignment properties when used as a liquid crystal alignment film, the voltage retention rate, the accumulated charge, and other properties.

(Diamine represented by formula [2]) The diamine represented by formula [2] is the following. (In formula [2], _R1 , _R2 , _R3 , and _R4 each independently represent a methyl group or an ethyl group. _X1 and _X2 each independently represent a single bond, -NHCO-, -CONH-, -COO-, or -OCO-. _P1 and _P2 each independently represent _-NH2 , or a structure represented by the following formula [Pa] to [Pb]. n1 and n2 each independently represent an integer of 0 to 6. m represents an integer of 1 to 5. However, the phenyl group in formula [Pa] to [Pb] may be substituted with a halogen.) (In formula [Pa] to formula [Pb], X ^D2 represents an organic group having 1 to 50 carbon atoms and having a structure selected from at least one of the following formulas [2a], [2b], and [2c]. p represents an integer of 0 to 1. * represents a bond.) (In formula [2a] to formula [2c], ^Xa represents a hydrogen atom or an organic group having 1 to 20 carbon atoms. ^Xd represents a single bond or an organic group having 1 to 20 carbon atoms. ^Xe represents a hydrogen atom or an organic group having 1 to 20 carbon atoms. D represents a protecting group that is heat-replaceable to a hydrogen atom. * represents a bond.)

In the above formula [2], R ₁ , R ₂ , R ₃ , and R ₄ are preferably methyl. X ₁ and X ₂ are preferably a single bond, -CONH- or -COO-. P ₁ and P ₂ are preferably -NH ₂ or the formula [2a]. n1 and n2 are preferably 3 or 4. m is preferably 1 or 2, and more preferably 1.

In the diamine represented by the above formula [2], X ^D2 preferably represents a structure selected from the following formulas [2a-1] and [2b-1].

(式[2a-1]中，X¹表示單鍵、碳數1~10之伸烷基、-O-、-N(R¹)-、-CON(R²)-、-N(R³)CO-、-CH₂O-、-COO-及OCO-所構成群組中所選出之至少1種的有機基。但是R¹、R²、R³各自獨立表示氫原子或碳數1~3之烷基。X²表示單鍵、碳數1~10之伸烷基，X^a表示氫原子或碳數1~20之有機基，X^b為與上述式[1a-1]之X^b所定義者相同。m表示1或2之整數，此時，m為2時，X^a表示氫原子。p表示1~4之整數，q表示1~4之整數。

(In formula [2a-1], ^X1 represents a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO-, and OCO-, and at least one organic group selected from the group consisting of. However, ^R1 , ^R2 , and ^R3 each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ^X2 represents a single bond, an alkylene group having 1 to 10 carbon atoms, ^Xa represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, and ^{Xb is} the same as defined in the above formula [1a-1]. m represents an integer of 1 or 2, and when m is 2, ^Xa represents a hydrogen atom. p represents an integer of 1 to 4, and q represents an integer of 1 to 4.

In formula [2b-1], ^X8 represents a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO-, and OCO-. However, ^R1 , ^R2 , and ^R3 each independently represent a hydrogen atom or an alkylene group having 1 to 3 carbon atoms. ^X9 represents a single bond, an alkylene group having 1 to 10 carbon atoms, ^Xd represents a single bond or an organic group having 1 to 20 carbon atoms, ^Xe represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, and ^Xf is the same as defined in formula [1c-1]. ⁿ represents an integer of 1 to 4, s represents an integer of 1 to 4, and t represents an integer of 1 to 4.)

In the formula [2], X ^D2 is more preferably a group represented by the following formula (tB), and more preferably an -N-Boc group.

(A表示單鍵或由碳數1~4之烴基所構成的2價基。)

(A represents a single bond or a divalent group consisting of a carbon number of 1 to 4.)

Preferred examples of diamines represented by formula [2] include the following.

The content of the diamine represented by formula [2] in 100 mol% of the total diamine component is preferably 1 to 50 mol%. Among them, 5 to 30 mol% is preferred, and 5 to 20 mol% is more preferred. The diamine represented by formula [2] can be used alone or in combination of two or more, depending on the solubility in a solvent of a specific polymer or the coating properties of a liquid crystal alignment agent, the liquid crystal alignment properties when used as a liquid crystal alignment film, the voltage retention rate, the stored charge, and other properties.

<Diamine component (2)> Among the diamine components (2), the diamine having a protective group that is heat-replaceable to a hydrogen atom and a siloxane skeleton is, for example, a diamine represented by the following formula [3]. (Diamine represented by formula [3]) The diamine represented by formula [3] is the following. (In formula [3], R ₁ , R ₂ , R ₃ , and R ₄ each independently represent a methyl group or an ethyl group. X represents -NHCO-, -CONH-, -COO-, or -OCO-. X ^D2 is defined in the above formulas [Pa] and [Pb]. n represents an integer of 0 to 6, m represents an integer of 1 to 5. p represents an integer of 0 to 1, and q represents an integer of 0 to 1. However, at least one of p and q represents 1.)

In the above formula [3], X is preferably -CONH- or -COO-. m is preferably 1 or 2, more preferably 1. _{R 1} to R ₄ are preferably methyl groups. n is preferably 1 to 4.

The content of the diamine represented by formula [3] in 100 mol% of the total diamine component is preferably 1 to 50 mol%. Among them, 5 to 30 mol% is preferred, and 5 to 20 mol% is more preferred. The diamine represented by formula [3] can be used alone or in combination of two or more, depending on the solubility in a solvent of a specific polymer or the coating properties of a liquid crystal alignment agent, the liquid crystal alignment properties when used as a liquid crystal alignment film, the voltage retention rate, the stored charge, and other properties.

(Other diamines) In order to obtain the diamine component (1) and the diamine component (2) for the specific polymer, diamines other than the diamines represented by the above formulas [1] to [3] (hereinafter also referred to as other diamines) may be contained. The other diamines include, first, diamines having the following side chain structures.

(Diamines having a specific side chain structure exhibiting vertical alignment) The diamines having a specific side chain structure exhibiting vertical alignment have at least one side chain structure selected from the group represented by the following formulas [S1] to [S3]. The following describes the diamines represented by formulas [S1] to [S3] as examples of diamines having this specific side chain structure.

[A]: A diamine having a specific side chain structure represented by the following formula [S1] In the above formula [S1], ^X1 and ^X2 each independently represent a single bond, -( _CH2 ) _a- (a represents an integer of 1 to 15), -CONH-, -NHCO-, -CON( _CH3 )-, -NH-, -O-, -COO-, -OCO- or -(( _CH2 ) _a1 - _A1 ) _m1- . Wherein, plural a1 each independently represents an integer of 1 to 15. Plural _A1 each independently represents an oxygen atom or -COO-. m1 represents 1 to 2.

Among them, from the viewpoint of raw material availability or ease of synthesis, ^X1 and ^X2 are each independently a single bond, -( _CH2 ) _a- (a represents an integer of 1 to 15), -O-, _-CH2O- or -COO-, and more preferably a single bond, -( _CH2 ) _a- (a represents an integer of 1 to 10), -O-, _-CH2O- or -COO-.

In the above formula [S1], ^G1 and ^G2 each independently represent a divalent cyclic group selected from the group consisting of a divalent aromatic group having 6 to 12 carbon atoms and a divalent alicyclic group having 3 to 8 carbon atoms. Any hydrogen atom on the cyclic group may be substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorinated alkyl group having 1 to 3 carbon atoms, a fluorinated alkoxy group having 1 to 3 carbon atoms, or a fluorine atom. m and n each independently represent an integer of 0 to 3, and the total of m and n is 1 to 4.

In the above formula [S1], ^R1 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. Any hydrogen forming ^R1 may be substituted with fluorine. Examples of divalent aromatic groups having 6 to 12 carbon atoms include phenylene, biphenylene, and naphthylene. Examples of divalent alicyclic groups having 3 to 8 carbon atoms include cyclopropylene, cyclohexylene, and the like.

Therefore, the preferred specific examples of the above formula [S1] can be listed as the following formulas [S1-x1] to [S1-x7].

In the above formulas [S1-x1] to [S1-x7], R ¹ is the same as in the above formula [S1]. X ^p represents -(CH ₂ ) _a - (a represents an integer of 1 to 15), -CONH-, -NHCO-, -CON(CH ₃ )-, -NH-, -O-, -CH ₂ O-, -COO- or -OCO-. A ₁ represents an oxygen atom or -COO-* (the bond with "*" is bonded to (CH ₂ ) _a2 ). A ₂ represents an oxygen atom or *-COO- (the bond with "*" is bonded to (CH ₂ ) _a2 ). a ₁ represents an integer of 0 or 1, and a ₂ represents an integer of 2 to 10. Cy represents a 1,4-cyclohexylene group or a 1,4-phenylene group.

[B]: A diamine having a specific side chain structure represented by the following formula [S2] In the above formula [S2], ^X3 represents a single bond, -CONH-, -NHCO-, -CON( _CH3 )-, -NH-, -O-, _-CH2O- , -COO- or -OCO-. From the viewpoint of the liquid crystal alignment property of the liquid crystal alignment agent, ^X3 is preferably -CONH-, -NHCO-, -O-, _-CH2O- , -COO- or -OCO-.

In the above formula [S2], ^R2 represents an alkyl group having 1 to 20 carbon atoms or an alkoxyalkyl group having 2 to 20 carbon atoms. Any hydrogen forming ^R2 may be substituted by fluorine. From the viewpoint of the liquid crystal alignment property of the liquid crystal alignment agent, ^R2 is preferably an alkyl group having 3 to 20 carbon atoms or an alkoxyalkyl group having 2 to 20 carbon atoms.

[C]: A diamine having a specific side chain structure represented by the following formula [S3] In the above formula [S3], ^X4 represents -CONH-, -NHCO-, -O-, -COO- or -OCO-. ^R3 represents a structure having a steroid skeleton. The steroid skeleton here is a skeleton represented by the following formula (st) having three six-membered rings and one five-membered ring bonded thereto.

Examples of the above formula [S3] include the following formula [S3-x].

In the above formula [S3-x], X represents the above formula [X1] or [X2]. In addition, Col represents at least one selected from the group consisting of the above formulas [Col1] to [Col3], and G represents at least one selected from the group consisting of the above formulas [G1] to [G4]. * represents a site bonded to another group.

Preferred combinations of X, Col and G in the above formula [S3-x] include, for example, the following combinations. That is, [X1] and [Col1] and [G1], [X1] and [Col1] and [G2], [X1] and [Col2] and [G1], [X1] and [Col2] and [G2], [X1] and [Col3] and [G2], [X1] and [Col3] and [G1], [X2] and [Col1] and [G2], [X2] and [Col2] and [G2], [X2] and [Col2] and [G1], [X2] and [Col3] and [G2], [X2] and [Col1] and [G1].

In addition, specific examples of the above formula [S3] include the structure of the steroid compound described in paragraph [0024] of Japanese Patent Application Laid-Open No. 4-281427 after removing the hydroxyl group, the structure of the steroid compound described in paragraph [0030] of the same publication after removing the acid chloride group, the structure of the steroid compound described in paragraph [0038] of the same publication after removing the amine group, the structure of the steroid compound described in paragraph [0042] of the same publication after removing the halogen group, and the structures described in paragraphs [0018] to [0022] of Japanese Patent Application Laid-Open No. 8-146421.

Furthermore, as a representative example of a steroid skeleton, cholesterol (a combination of [Col1] and [G2] in the above formula [S3-x]) can be listed, but a steroid skeleton that does not contain the cholesterol can also be used. That is, as a diamine having a steroid skeleton, for example, 3,5-diaminobenzoic acid cholesterol ester can be listed, but it can also be a diamine component that does not contain a diamine having the cholesterol skeleton. Furthermore, a diamine having a specific side chain structure can also be used that does not contain an amide at the connection position between the diamine and the side chain. By using such a diamine, in the present embodiment, a diamine component that does not contain a diamine having a cholesterol skeleton can be used to provide a liquid crystal alignment film or a liquid crystal display element that can ensure a high voltage retention rate over a long period of time.

Furthermore, the diamine having the side chain structure represented by the above formulas [S1] to [S3] is represented by the following formulas [1-S1] to [1-S3], respectively. In the above formula [1-S1], ^X1 , ^X2 , ^G1 , ^G2 , ^R1 , m and n are the same as in the above formula [S1]. In the above formula [1-S2], ^X3 and ^R2 are the same as in the above formula [S2]. In the above formula [1-S3], ^X4 and ^R3 are the same as in the above formula [S3].

(Diamine having a characteristic side chain structure of a di-lateral chain type exhibiting vertical alignment) The diamine having a characteristic side chain structure of a di-lateral chain type exhibiting vertical alignment is represented by the following formula [N1], for example.

In the above formula [N1], X represents a divalent organic group consisting of a single bond, -O-, -C(CH ₃ ) ₂ -, -NH-, -CO-, -NHCO-, -COO-, -(CH ₂ ) _m -, -SO ₂ -, or an arbitrary combination thereof. Among them, X preferably represents a single bond, -O-, -NH-, or -O-(CH ₂ ) _m -O-. Examples of "an arbitrary combination thereof" include -O-(CH ₂ ) _m -O-, -OC(CH ₃ ) ₂ -, -CO-(CH ₂ ) _m -, -NH-(CH ₂ ) _m -, -SO ₂ -(CH ₂ ) _m -, -CONH-(CH ₂ ) _m -, -CONH-(CH ₂ ) _m -NHCO-, -COO-(CH ₂ ) _m -OCO-, and the like. m represents an integer of 1 to 8. In the above formula [N1], two Ys each independently represent the structure of the following formula [1-1].

In the above formula [1-1], ^Y1 and ^Y3 each independently represent a single bond, -( _CH2 ) _a- (a represents an integer of 1 to 15), -O-, _-CH2O- , -COO- or -OCO-. ^Y2 represents a single bond or -( _CH2 ) _b- (b represents an integer of 1 to 15). However, when ^Y1 or ^Y3 is a single bond or represents -( _CH2 ) _a- , ^Y2 represents a single bond. Furthermore, when ^Y1 represents -O-, _-CH2O- , -COO- or -OCO-, and/or ^Y3 represents -O-, _-CH2O- , -COO- or -OCO-, ^Y2 represents a single bond or -( _CH2 ) _b- . In formula [1-1], ^Y4 represents a divalent cyclic group selected from at least one of the group consisting of a benzene ring, a cyclohexane ring and a heterocyclic ring, or a divalent organic group having 17 to 51 carbon atoms and a steroid skeleton. Any hydrogen atom forming the cyclic group may be substituted with an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorinated alkyl group having 1 to 3 carbon atoms, a fluorinated alkoxy group having 1 to 3 carbon atoms, or a fluorine atom.

In the above formula [1-1], Y ⁵ represents at least one cyclic group selected from the group consisting of a benzene ring, a cyclohexane ring and a heterocyclic ring. Any hydrogen atom forming the cyclic group may be substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorinated alkyl group having 1 to 3 carbon atoms, a fluorinated alkoxy group having 1 to 3 carbon atoms or a fluorine atom. In the above formula [1-1], Y ⁶ represents at least one group selected from the group consisting of an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a fluorinated alkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms and a fluorinated alkoxy group having 1 to 18 carbon atoms. n represents an integer of 0 to 4.

In the above formula [N1], the position of Y relative to X may be the meta position or the ortho position, but is preferably the ortho position. That is, the above formula [N1] is preferably the following formula [1'].

In the above formula [N1], the positions of the two amino groups (-NH ₂ ) may be at any position on the benzene ring, but are preferably at the positions represented by the following formulas [1]-a1 to [1]-a3, and more preferably, the following formula [1]-a1. In the following formulas, X is the same as in the above formula [N1]. In the following formulas [1]-a1 to [1]-a3, the positions of the two amino groups are described, and the symbol Y represented in the above formula [N1] is omitted.

Therefore, based on the above formulas [1'] and [1]-a1 to [1]-a3, the above formula [N1] is preferably any structure selected from the group consisting of the following formulas [1]-a1-1 to [1]-a3-2, and more preferably a structure represented by the following formula [1]-a1-1. In the following formulas, X and Y are the same as in the case of formula [N1].

Examples of the above formula [1-1] include the following formulas [1-1]-1 to [1-1]-22. Among them, the above example of the formula [1-1] is preferably the following formulas [1-1]-1 to [1-1]-4, [1-1]-8 or [1-1]-10. In the following formulas, * represents the bonding position with the phenyl group in the above formulas [1], [1'] and [1]-a1 to [1]-a3.

Since the diamine component contains a di-chain diamine having a specific structure, it can form a liquid crystal alignment film that does not reduce the ability of the liquid crystal to align vertically even when it is placed under excessive heating. In addition, since the diamine component contains the di-chain diamine, it can form a liquid crystal alignment film that does not reduce the ability of the liquid crystal to align vertically when a foreign object contacts the film and is damaged. That is, since the diamine component contains the di-chain diamine, a liquid crystal alignment agent that can obtain a liquid crystal alignment film with various excellent characteristics as described above can be provided.

Furthermore, other diamines include, secondly, diamines represented by the following general formula (Y).

In the above formula (Y), _A1 and _A2 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms. From the perspective of liquid crystal orientation, _A1 and _A2 are preferably hydrogen atoms or methyl groups. If the structure of _Y1 is exemplified, it is shown in the following formulas (Y-1) to (Y-68).

(Boc in the formula represents tert-butyloxycarbonyl. * represents a bond.)

In addition, other diamines include the third diamine having a thiophene or furan structure described in International Publication No. WO2018/092759, preferably a diamine having a structure represented by the following formula (sf); ( _Y1 represents a sulfur atom or an oxygen atom, _R2 each independently represents a single bond or a group "*1- ^R5 -Ph-*2", ^R5 represents a group selected from a single bond, -O-, -COO-, -OCO-, -( _CH2 ) _1- , -O( _CH2 ) _m O-, -CONH-, and a divalent organic group (l, m represent integers of 1 to 5) in the group consisting of -NHCO-, *1 represents a site bonded to the benzene ring in the formula (pn), and *2 represents a site bonded to the amine group in the formula (pn). Ph represents a phenylene group. n represents 1 to 3), diaminoorganosiloxanes such as 2,3-diaminopyridine, 2,6-diaminopyridine, 3,4-diaminopyridine, 2,4-diaminopyrimidine, 1,3-bis(3-aminopropyl)-tetramethyldisiloxane, aliphatic diamines such as m-xylene diamine, alicyclic diamines such as 4,4-methylenebis(cyclohexylamine), etc. Other diamines may be used alone or in combination of two or more.

(Tetracarboxylic acid component) In order to obtain the tetracarboxylic acid component for the specific polymer, the tetracarboxylic dianhydride represented by the following formula [4] or its derivatives (tetracarboxylic acid, tetracarboxylic acid dihalide, tetracarboxylic acid dialkyl ester, or tetracarboxylic acid dialkyl ester dihalide) (these are collectively referred to as specific tetracarboxylic acids) can be used.

(式[4]中，Z¹表示選自由下述式[4a]~式[4q]所構成群組中之至少1種的結構。)

(In formula [4], ^Z1 represents at least one structure selected from the group consisting of the following formulas [4a] to [4q].)

In formula [4a], Z ¹ to Z ⁴ each independently represent a hydrogen atom, a methyl group, an ethyl group, a propyl group, a chlorine atom or a benzene ring. Z ⁵ and Z ⁶ each independently represent a hydrogen atom or a methyl group.

Among ^Z1 in formula [4], tetracarboxylic dianhydride and tetracarboxylic acid derivatives thereof having a structure represented by formula [4a], formula [4c] to [4g], formula [4k] to [4m] or formula [4p] are preferred from the viewpoint of ease of synthesis or ease of polymerization reactivity when producing a polymer. More preferred are tetracarboxylic dianhydride and tetracarboxylic acid derivatives thereof having a structure represented by formula [4a], formula [4e] to [4g], formula [41], formula [4m] or formula [4p]. Particularly preferred are tetracarboxylic dianhydride and tetracarboxylic acid derivatives thereof having a structure represented by formula [4a], formula [4e], formula [4f], formula [41], formula [4m] or formula [4p].

More specifically, it is preferred to use the following formula [4a-1] or formula [4a-2].

In the total tetracarboxylic acid component 100 mol%, the specific tetracarboxylic acid is preferably 50~100 mol%. Among them, it is preferably 70~100 mol%. More preferably, it is 80~100 mol%.

Specific tetracarboxylic acids can be used alone or in combination of two or more, depending on the solubility in the solvent of the specific polymer or the coating properties of the liquid crystal alignment agent, the liquid crystal alignment properties when used as a liquid crystal alignment film, the voltage retention rate, the stored charge and other properties.

In order to obtain a tetracarboxylic acid component for a specific polymer, a tetracarboxylic acid other than the above-mentioned specific tetracarboxylic acid (hereinafter also referred to as other tetracarboxylic acids) may be contained.

Examples of other tetracarboxylic acids include the following tetracarboxylic acid compounds, tetracarboxylic dianhydrides, tetracarboxylic acid dihalide compounds, tetracarboxylic acid dialkyl ester compounds, and tetracarboxylic acid dialkyl ester dihalide compounds.

That is, other tetracarboxylic acids include 1,2,5,6-naphthalenetetracarboxylic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 1,2,5,6-anthracenetetracarboxylic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 2,3,3',4-biphenyltetracarboxylic acid, bis(3,4-dicarboxyphenyl)ether, 3,3',4,4'-benzophenonetetracarboxylic acid, bis(3,4-dicarboxyphenyl)sulfone, bis(3,4-dicarboxyphenyl)methane, 2,2-bis(3,4-dicarboxyphenyl) Propane, 1,1,1,3,3,3-hexafluoro-2,2-bis(3,4-dicarboxyphenyl)propane, bis(3,4-dicarboxyphenyl)dimethylsilane, bis(3,4-dicarboxyphenyl)diphenylsilane, 2,3,4,5-pyridinetetracarboxylic acid, 2,6-bis(3,4-dicarboxyphenyl)pyridine, 3,3',4,4'-diphenylsulfonatetetracarboxylic acid, 3,4,9,10-perylenetetracarboxylic acid or 1,3-diphenyl-1,2,3,4-cyclobutanetetracarboxylic acid, etc. Other tetracarboxylic acids can be used alone or in combination of two or more, depending on the solubility in a solvent of a specific polymer or the coating property of a liquid crystal alignment agent, the liquid crystal alignment property when used as a liquid crystal alignment film, the voltage retention rate, the stored charge, and other characteristics.

<Method for producing a specific polymer> The specific polymer is at least one selected from the group consisting of a polyimide precursor obtained by polymerizing a diamine component and a tetracarboxylic acid component, and a polyimide obtained by imidizing the polyimide precursor.

The reaction of the diamine component and the tetracarboxylic acid component is usually carried out in a solvent. The solvent used at this time is not particularly limited as long as it dissolves the generated polyimide precursor. Specific examples of solvents used in the reaction are listed below, but are not limited to these examples. For example, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, dimethyl sulfoxide, or 1,3-dimethyl-imidazolidinone can be listed. When the solvent solubility of the polyimide precursor is high, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone, or ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol propyl ether, etc. can be used.

These solvents may be used alone or in combination. In addition, even if the solvent does not dissolve the polyimide precursor, it may be mixed with the above-mentioned solvents as long as the generated polyimide precursor does not precipitate. In addition, the water in the solvent will hinder the polymerization reaction and become the cause of hydrolysis of the generated polyimide precursor, so it is better to use a solvent that has been dehydrated and dried.

When the diamine component and the tetracarboxylic acid component are reacted in a solvent, there can be listed a method in which a solution in which the diamine component is dispersed or dissolved in the solvent is stirred, and the tetracarboxylic acid component is added directly or dispersed or dissolved in the solvent; conversely, a method in which the diamine component is added to a solution in which the tetracarboxylic acid component is dispersed or dissolved in the solvent; a method in which the diamine component and the tetracarboxylic acid component are alternately added to the reaction system, and any of these methods can be used. Furthermore, when a plurality of diamine components or tetracarboxylic acid components are used for the reaction, they may be reacted in a premixed state, or they may be reacted in sequence individually. Furthermore, low molecular weight products that have been reacted individually may be mixed and reacted to form a polymer.

The temperature for polymerizing the diamine component and the tetracarboxylic acid component can be selected from any temperature of -20 to 150°C, but preferably from -5 to 100°C. The reaction can be carried out at any concentration, but if the concentration is too low, it becomes difficult to obtain a high molecular weight polymer, and if the concentration is too high, the viscosity of the reaction solution becomes too high, and uniform stirring becomes difficult. Therefore, the concentration of the polymer is preferably 1 to 50% by mass, and more preferably 5 to 30% by mass. The reaction can be carried out at a high concentration in the initial stage, and then the solvent is added. In the polymerization reaction to obtain the polyimide precursor, the ratio of the total molar number of the tetracarboxylic acid component to the total molar number of the diamine component is preferably 0.8 to 1.2. Similar to a conventional polymerization reaction, the closer this molar ratio is to 1.0, the larger the molecular weight of the resulting polyimide precursor becomes.

Polyimide is obtained by ring-closing a polyimide precursor. In this polyimide, the ring-closing ratio of the amide group (also called imidization ratio) does not necessarily need to be 100% and can be adjusted arbitrarily according to the use or purpose. The method of imidizing the polyimide precursor can be exemplified by thermal imidization in which a solution of the polyimide precursor is heated or catalytic imidization in which a catalyst is added to the solution of the polyimide precursor.

The temperature of the thermal imidization of the polyimide precursor in the solution is preferably 100-400°C, more preferably 120-250°C, while the water generated by the imidization reaction is discharged out of the system. The catalytic imidization of the polyimide precursor is carried out by adding an alkaline catalyst and anhydride to the solution of the polyimide precursor and stirring at -20-250°C, preferably 0-180°C.

The amount of alkaline catalyst is preferably 0.5 to 30 mole times of the amide group, more preferably 2 to 20 mole times, and the amount of acid anhydride is preferably 1 to 50 mole times of the amide group, more preferably 3 to 30 mole times. As alkaline catalysts, pyridine, triethylamine, trimethylamine, tributylamine or trioctylamine can be listed. Among them, pyridine is preferred because it has the appropriate alkalinity required for the reaction. As acid anhydrides, acetic anhydride, trimellitic anhydride, pyromellitic anhydride, etc. can be listed. In particular, if acetic anhydride is used, purification after the reaction becomes easy, so it is preferred. The imidization rate caused by catalyst imidization can be controlled by adjusting the amount of catalyst, reaction temperature, and reaction time.

The imidization rate of the polyimide precursor or the imidized polymer thereof of the present invention is preferably 1-95%, more preferably 20% to 80%, and even more preferably 40% to 70%.

When the generated polyimide precursor or its imide polymer is recovered from the reaction solution, the reaction solution can be put into a solvent to precipitate. The solvent used for precipitation can be methanol, ethanol, isopropanol, acetone, hexane, butyl solvent, heptane, methyl ethyl ketone, methyl isobutyl ketone, toluene, benzene, water, etc. After the polymer put into the solvent to precipitate is filtered and recovered, it can be dried at normal pressure or reduced pressure, at room temperature or by heating. In addition, if the polymer recovered after precipitation is dissolved in a solvent again, and the operation of re-precipitation and recovery is repeated 2 to 10 times, the impurities in the polymer can be reduced. The solvent at this time can be, for example, alcohols, ketones, hydrocarbons, etc. It is preferred to use three or more solvents selected from these, because the efficiency of purification can be further improved.

In the present invention, when the polyimide precursor is polyamide alkyl ester, the specific method for producing the polyimide precursor may include, for example, the method described in paragraphs [0054] to [0062] of International Publication No. WO2011-115077.

<Liquid crystal alignment agent> The content of the specific polymer in the liquid crystal alignment agent of the present invention is preferably 2 to 10% by mass, and more preferably 3 to 8% by mass.

The liquid crystal alignment agent of the present invention may also contain other polymers besides the specific polymer. Examples of other polymers include cellulose polymers, acrylic polymers, methacrylic polymers, polystyrene, polyamide, polysiloxane, etc. The content of other polymers is preferably 0.5 to 15 parts by mass, and more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the specific polymer.

In addition, the liquid crystal alignment agent usually contains an organic solvent, and the content of the organic solvent is preferably 70~99.9% by mass relative to the liquid crystal alignment agent. This content can be appropriately changed by the coating method of the liquid crystal alignment agent or the film thickness of the intended liquid crystal alignment film. The organic solvent used in the liquid crystal alignment agent is preferably a solvent that dissolves a specific polymer (also called a good solvent). For example, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylsulfoxide, γ-butyrolactone, 1,3-dimethyl-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, etc. Among them, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide or γ-butyrolactone is preferably used.

The good solvent in the liquid crystal alignment agent of the present invention is preferably 20-99 mass % of the total solvent contained in the liquid crystal alignment agent, more preferably 20-90 mass %, and particularly preferably 30-80 mass %.

The liquid crystal alignment agent of the present invention can use a solvent (also called a weak solvent) that improves the coating properties or surface smoothness of the liquid crystal alignment film when the liquid crystal alignment agent is applied. The specific examples are listed below. 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 monoisopentyl ether, ethylene glycol monohexyl ether, propylene glycol monobutyl ether, 1-(2-butoxyethoxy)-2-propanol, 2-(2- propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monobutyl ether acetate, ethylene glycol monoacetate, ethylene glycol diacetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, diethylene glycol acetate, 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 them, the preferred solvent combinations include N-methyl-2-pyrrolidone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone and γ-butyrolactone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone and γ-butyrolactone and propylene glycol monobutyl ether, N-ethyl-2-pyrrolidone and propylene glycol monobutyl ether, N-methyl-2-pyrrolidone and γ-butyrolactone and 4-hydroxy-4-methyl-2-pentanone and diethyl Glycol diethyl ether, N-methyl-2-pyrrolidone and γ-butyrolactone and propylene glycol monobutyl ether and 2,6-dimethyl-4-heptanone, N-methyl-2-pyrrolidone and γ-butyrolactone and propylene glycol monobutyl ether and diisopropyl ether, N-methyl-2-pyrrolidone and γ-butyrolactone and propylene glycol monobutyl ether and 2,6-dimethyl-4-heptanol, N-methyl-2-pyrrolidone and γ-butyrolactone and dipropylene glycol dimethyl ether, etc. Such weak solvents are preferably 1-80% by mass of the total solvent contained in the liquid crystal alignment agent, more preferably 10-80% by mass, and particularly preferably 20-70% by mass. The type and content of the solvent can be appropriately selected according to the coating equipment, coating conditions, coating environment, etc. of the liquid crystal alignment agent.

The liquid crystal alignment agent of the present invention may also contain a dielectric for changing the electrical properties of the liquid crystal alignment film, such as the dielectric constant or conductivity, a silane coupling agent for improving the adhesion between the liquid crystal alignment film and the substrate, a cross-linking compound for improving the hardness or density of the film when used as a liquid crystal alignment film, and even an imidization accelerator for efficiently carrying out the imidization of the polyimide precursor by heating when the coating is sintered.

Compounds for improving the adhesion between the liquid crystal alignment film and the substrate include functional silane compounds or compounds containing epoxy groups, such as 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl methyl diethoxysilane, 2-aminopropyl trimethoxysilane, 2-aminopropyl triethoxysilane, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, N-(2- Aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, N-ethoxycarbonyl-3-aminopropyltrimethoxysilane, N-ethoxycarbonyl-3-aminopropyltriethoxysilane, N-triethoxysilylpropyltriethylenetriamine, N-trimethoxysilylpropyltriethylenetriamine, 10-trimethoxysilyl-1,4,7-triazadecane, 10-triethoxysilyl-1,4,7-triazadecane, 9-trimethoxysilyl-3,6-dimethoxysilane Azononyl acetate, 9-triethoxysilyl-3,6-diazononyl acetate, N-benzyl-3-aminopropyl trimethoxysilane, N-benzyl-3-aminopropyl triethoxysilane, N-phenyl-3-aminopropyl trimethoxysilane, N-phenyl-3-aminopropyl triethoxysilane, N-bis(oxyethylene)-3-aminopropyl trimethoxysilane, N-bis(oxyethylene)-3-aminopropyl triethoxysilane, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether Glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerol diglycidyl ether, 2,2-dibromoneopentyl glycol diglycidyl ether, 1,3,5,6-tetraglycidyl-2,4-hexanediol, N,N,N',N',-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, or N,N,N',N',-tetraglycidyl-4,4'-diaminodiphenylmethane, etc.

Furthermore, in order to improve the mechanical strength of the liquid crystal alignment film, the following additives (CL-1) to (CL-15) may be added to the liquid crystal alignment agent of the present invention.

The amount of the additive is preferably 0.1-30 parts by weight, more preferably 0.5-20 parts by weight, relative to 100 parts by weight of the polymer component contained in the liquid crystal alignment agent.

<Method for manufacturing liquid crystal alignment film> The liquid crystal alignment film is obtained by applying the above-mentioned liquid crystal alignment agent on a substrate to form a film, preferably drying it, and then firing it. The substrate is preferably a highly transparent substrate, and its material can be glass, ceramics such as silicon nitride, plastics such as acrylic or polycarbonate substrates, etc. From the perspective of simplifying the steps, it is better to use a substrate formed with an ITO (Indium Tin Oxide) electrode for driving the liquid crystal as a substrate. In addition, when the reflective liquid crystal display element is a single-sided substrate, an opaque material such as a silicon wafer can also be used, and this electrode can also use a light-reflecting material such as aluminum.

The method of forming a film on a substrate from a liquid crystal alignment agent can be industrially used by screen printing, lithography, relief printing, inkjet method, etc., and also by immersion method, roll coating method, slit coating method, spin coating method, spray method, etc., which can be used according to the purpose. After the film of the liquid crystal alignment agent is formed on the substrate, the film is dried by heating means such as a heating plate, a heat cycle oven, an IR (infrared) oven, etc., preferably at 30~120℃, more preferably at 50~120℃, preferably for 1 minute to 10 minutes, more preferably for 1 minute to 5 minutes, so that the solvent evaporates.

When the imide precursor in the polymer is thermally imidized, the film obtained from the liquid crystal alignment agent is then calcined by the same heating method as the above-mentioned drying treatment, preferably at 120-250°C, more preferably at 150-230°C. The calcination time varies depending on the calcination temperature, preferably 5 minutes to 1 hour, more preferably 5 minutes to 40 minutes.

The thickness of the film after the above-mentioned sintering treatment is not particularly limited. If it is too thin, the reliability of the liquid crystal display element may sometimes be reduced. If it is too thick, the resistance of the resulting liquid crystal alignment film becomes larger. Therefore, it is preferably 5~300nm, and more preferably 10~200nm.

After the above-mentioned sintering treatment, the obtained film is subjected to an alignment treatment. The alignment treatment method may include a rubbing treatment method, a photo-alignment treatment method, and the like.

A specific example of the photo-alignment treatment is to irradiate the surface of the aforementioned film with radiation polarized in a certain direction. The radiation can be ultraviolet light or visible light with a wavelength of 100~800nm. Among them, ultraviolet light with a wavelength of 100~400nm is preferred, and ultraviolet light with a wavelength of 200~400nm is more preferred. In order to improve the alignment of the liquid crystal, the substrate coated with the liquid crystal alignment film can be heated at 50~250℃ while irradiating with ultraviolet light. In addition, the irradiation amount of the aforementioned radiation is preferably 1~10,000mJ/ ^cm2 . Among them, 100~5,000mJ/ ^cm2 is preferred. The liquid crystal alignment film produced in this way can make the liquid crystal molecules stably align in a specific direction. The higher the extinction ratio of the polarized ultraviolet light, the higher the anisotropy can be given, so it is better. Specifically, the extinction ratio of the linearly polarized ultraviolet light is preferably 10:1 or more, and more preferably 20:1 or more.

The film subjected to the above-mentioned alignment treatment may be subjected to at least one treatment selected from the group consisting of a heat treatment and a contact treatment caused by a solvent. The heat treatment after the alignment treatment may be performed by the same heating means as the above-mentioned drying treatment or sintering treatment, preferably at 180-250°C, more preferably at 180-230°C. When the temperature of the heat treatment is performed within the above-mentioned range, the contrast of the liquid crystal display element obtained by the prepared liquid crystal alignment film can be improved. The time of the heat treatment varies depending on the heating temperature, preferably 5 minutes to 1 hour, more preferably 5 to 40 minutes.

The solvent used in the contact treatment caused by the above-mentioned solvent is not particularly limited as long as it is a solvent that dissolves impurities attached to the liquid crystal alignment film. Specific examples include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, 1-methoxy-2-propanol, 1-methoxy-2-propanol acetate, butyl cellulose, ethyl lactate, methyl lactate, diacetone alcohol, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, propyl acetate, butyl acetate, cyclohexyl acetate, etc. Among them, from the perspective of versatility or safety of the solvent, water, 2-propanol, 1-methoxy-2-propanol or ethyl lactate are preferred. Water, 1-methoxy-2-propanol or ethyl lactate are more preferred. These solvents can be one or more than two.

The contact treatment may be immersion treatment or spray treatment (also referred to as spray treatment). The treatment time in such treatment is preferably 10 seconds to 1 hour, and in particular, immersion treatment may be performed for 1 to 30 minutes. The temperature during the contact treatment may be room temperature or heated, preferably 10 to 80°C, and may be 20 to 50°C. During the contact treatment, ultrasonic treatment may be performed if necessary.

After the above-mentioned contact treatment, rinsing or drying may be performed by a low boiling point solvent such as water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, etc. At this time, either rinsing or drying may be performed, or both may be performed. The drying temperature is preferably 50-150°C, and 80-120°C may be listed. In addition, the drying time is preferably 10 seconds to 30 minutes, and more preferably 1-10 minutes.

After the contact treatment with the solvent, the heat treatment after the alignment treatment can be applied. In this way, a liquid crystal alignment film with excellent liquid crystal alignment can be obtained.

<Liquid crystal display element> The liquid crystal alignment film of the present invention can be applied to various drive modes such as TN mode, STN mode, IPS mode, FFS mode, VA mode, MVA mode, PSA mode, etc., and is suitable as a liquid crystal alignment film for a liquid crystal display element of a transverse electric field mode such as IPS mode or FFS mode, and can be used in particular for a liquid crystal display element of FFS mode. The liquid crystal display element of the present invention is obtained by obtaining a substrate with a liquid crystal alignment film obtained from the above-mentioned liquid crystal alignment agent, and then using a known method to make a crystal cell (liquid crystal cell) and use the crystal cell as an element. As an example of a method for making a crystal cell, a liquid crystal display element of a passive matrix structure is taken as an example. In addition, it can also be a liquid crystal display element of an active matrix structure in which a switching element such as TFT (Thin Film Transistor) is provided in each pixel portion constituting an image display.

Specifically, transparent glass substrates are prepared, a common electrode is set on one of the substrates, and a segment electrode is set on the other substrate. These electrodes, for example, can be ITO electrodes, and can be patterned to display the desired image. Then, an insulating film is set on each substrate so as to cover the common electrode and the segment electrode. The insulating film can be, for example, a film made of _SiO2 - _TiO2 formed by a sol-gel method. Next, under the conditions as described above, a liquid crystal alignment film is formed on each substrate, and one of the substrates is overlapped with the other substrate in a manner that the liquid crystal alignment film surfaces face each other, and the periphery is connected with a sealant. In order to control the gap between the substrates, it is usually better to mix the sealant with a spacer in advance. In addition, it is also preferred to pre-distribute spacers for controlling the gap between the substrates in the surface where the sealant is not provided. A portion of the sealant is pre-provided with an opening that can be filled with liquid crystal from the outside.

Then, the liquid crystal material is injected into the space surrounded by the two substrates and the sealant through the opening provided in the sealant. Then, the opening is sealed with a sealant. When injecting, a vacuum injection method, a method utilizing the capillary phenomenon in the atmosphere, or an ODF (One Drop Fill) method can be used. The liquid crystal material can use either positive or negative dielectric anisotropy. In the present invention, from the perspective of liquid crystal alignment, liquid crystals with negative dielectric anisotropy are preferred and can be used separately according to the purpose. After the liquid crystal material is injected into the liquid crystal cell, a polarizing plate is provided. Specifically, it is preferred to adhere a pair of polarizing plates to the surfaces of the two substrates on the opposite side of the liquid crystal layer.

[Example]

The present invention is described in more detail below with reference to Examples, but the present invention is not limited to these Examples. The abbreviations of the compounds used are as follows.

(Diamine component) (Tetracarboxylic acid component) (Solvent) NMP: N-methyl-2-pyrrolidone BCS: Ethylene glycol monobutyl ether

<Measurement of Molecular Weight of Polyimide> The molecular weight of polyimide was measured as follows using a room temperature gel permeation chromatography (GPC) apparatus (SSC-7200) manufactured by SENSHU Scientific Co., Ltd. and columns (KD-803, KD-805) manufactured by Shodex Corporation. Column temperature: 50°C Solvent: N,N'-dimethylformamide (additives: lithium bromide monohydrate (LiBr･H ₂ O) 30mmol/L, phosphoric acid･anhydrous crystals (o-phosphoric acid) 30mmol/L, tetrahydrofuran (THF) 10ml/L) Flow rate: 1.0ml/min Standard samples for calibration curve preparation: TSK standard polyethylene oxide manufactured by Tosoh Corporation (molecular weight approximately 9,000,000, 150,000, 100,000, 30,000), and polyethylene glycol manufactured by Polymer Laboratories (molecular weight approximately 12,000, 4,000, 1,000).

<Determination of imidization rate> Place 20 mg of polyimide powder in an NMR sample tube (NMR sampling tube standard φ5 manufactured by Kusano Scientific Co., Ltd.), add 0.53 ml of deuterated dimethyl sulfoxide (DMSO-d ₆ , 0.05% TMS mixture), and apply ultrasound to completely dissolve. This solution is measured by 500 MHz proton NMR using an NMR analyzer (JNW-ECA500) manufactured by JEOL Datum Co., Ltd. The imidization rate is determined by using the proton from the structure that does not change before and after imidization as the reference proton, and the peak integral value of this proton and the proton peak integral value from the NH group of acylamine appearing around 9.5~10.0 ppm are used to calculate the following formula. Imidization rate (%) = (1-α･x/y) × 100

<Synthesis of polyimide polymer> <Synthesis Example 1> D1 (9.14 g), DA-1 (4.68 g, 0.3 molar ratio relative to the total diamine component), DA-2 (3.25 g, 0.4 molar ratio relative to the total diamine component), DA-3 (1.95 g, 0.2 molar ratio relative to the total diamine component), DA-4 (1.02 g, 0.1 molar ratio relative to the total diamine component) were mixed in NMP solvent (80.17 g) and reacted at 60°C for 12 hours to obtain a polyimide solution. NMP (103.85 g) was added to the polyamide solution (50.0 g) and diluted to 6.5% by mass. Acetic anhydride (20.84 g) and pyridine (3.23 g) were added as imidization catalysts and reacted at 80°C for 5 hours. The reaction solution was put into methanol (622.70 g) and the obtained precipitate was filtered. The precipitate was washed with methanol and dried under reduced pressure at 60°C to obtain polyimide powder (A). The imidization rate of the polyimide was 72%, Mn was 11,800, and Mw was 41,800.

<Synthesis Examples 2 to 4, Comparative Synthesis Examples 1 and 2> In Synthesis Example 1, except that the materials and proportions were changed to the same as Tables 1 and 2, the polyimide powders (B to D) of Synthesis Examples 2 to 4 and the polyimide powders (E and F) of Comparative Synthesis Examples 1 and 2 were obtained in the same manner as Synthesis Example 1. <Synthesis Example 5> D2 (5.12 g), DA-7 (3.26 g, 0.4 molar ratio relative to the total diamine component), DA-8 (3.97 g, 0.4 molar ratio relative to the total diamine component), and DA-9 (3.24 g, 0.2 molar ratio relative to the total diamine component) were mixed in NMP solvent (62.43 g), reacted at 60°C for 3 hours, cooled to room temperature, and D3 (3.86 g) and NMP solvent (15.44 g) were added, and reacted at 40°C for 12 hours to obtain a polyamide solution (G). The Mn of this polyamide solution (G) was 10,600 and the Mw was 35,700.

In Table 1, the right side of the bracket after the name of the diamine component indicates the molar ratio of each diamine used in the reaction relative to the total diamine components.

<Example 1> NMP (44.0 g) was added to the polyimide powder (A) (6.0 g) obtained in Synthesis Example 1, and the mixture was stirred at 70°C for 40 hours to dissolve. BCS (50.0 g) was added to the solution and stirred for 5 hours to obtain the liquid crystal alignment agent [1] of Example 1. No abnormalities such as turbidity or precipitation were observed in the liquid crystal alignment agent, confirming that the resin component was uniformly dissolved. <Examples 2 to 4, Comparative Examples 1 and 2> In Example 1, except that the polyimide material was changed as shown in Table 3, the alignment treatment agents [2] to [4] of Examples 2 to 4 and the liquid crystal alignment agents [5] and [6] of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1. No abnormalities such as turbidity or precipitation were observed in these liquid crystal alignment agents, confirming that the resin components were uniformly dissolved. <Example 5> NMP (29.0 g) was added to the polyamide solution (G) (21.0 g) obtained in Synthesis Example 5, and the mixture was stirred for 30 minutes. BCS (35.0 g) was added, and the mixture was stirred for another 30 minutes. Liquid crystal alignment agent [1] (30.0 g) was added, and the mixture was stirred for 5 hours, thereby obtaining the liquid crystal alignment agent [7] of Example 5. No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent, confirming that the resin components were uniformly dissolved.

<Production of Liquid Crystal Cell> The liquid crystal alignment agents of Examples 1 to 5 and Comparative Examples 1 and 2 were respectively rotationally coated on the ITO surface of an ITO-attached glass substrate (30 mm long, 40 mm wide, 0.7 mm thick) washed with pure water and IPA (isopropyl alcohol), and then fired at 70°C for 90 seconds with a heating plate, and then fired at 230°C for 20 minutes in an infrared heating furnace to produce a polyimide-coated substrate with a film thickness of 100 nm. Two polyimide-coated substrates were produced by the above method, and 4 μm spherical spacers were sprinkled on the liquid crystal alignment film surface of one of the substrates, and a thermosetting sealant (XN-1500T manufactured by Kyoritsu Chemical Co., Ltd.) was printed thereon. Next, the other substrate with the liquid crystal alignment film formed on the inner side is bonded to the previous substrate, and the sealant is hardened to make an empty cell. Liquid crystal MLC-3023 (trade name of Merck) containing a polymerizable compound for PSA is injected into the empty cell by the reduced pressure injection method to make a liquid crystal cell. The voltage retention of the liquid crystal cell is measured.

Next, while applying a DC voltage of 15V to the liquid crystal cell, 10J/ ^cm2 of UV through a 325nm cutoff filter was irradiated from the outside of the liquid crystal cell (also referred to as the first PSA treatment). The UV irradiance was measured using UV-MO3A manufactured by ORC. Then, in order to inactivate the unreacted polymerizable compound remaining in the liquid crystal cell, UV (UV lamp: FLR40SUV32/A-1) was irradiated for 30 minutes using a UV-FL irradiation device manufactured by Toshiba Lighting and Technology without applying a voltage (also referred to as the second PSA treatment). Then, the voltage holding ratio was measured.

<Evaluation of voltage retention> Using the above-made liquid crystal cell, a voltage of 1V was applied for 60μs in a hot air circulation oven at 60℃, and then the voltage was measured after 1667msec. The voltage retention was calculated as the voltage retention. The voltage retention was measured using VHR-1 manufactured by TOYO Corporation. <Evaluation of high temperature and high humidity resistance> The above-made liquid crystal cell was placed in a constant temperature and humidity chamber (PR-2KP manufactured by ESPEC) at a temperature of 85℃ and a humidity of 85% for 7 days, and then the voltage retention was measured. The difference between the voltage retention measured here and the voltage retention after the second PSA treatment was taken as the VHR change.

As shown in Table 3, in Comparative Examples 1 and 2, the VHR after the second PSA treatment is lower than 86%, but in Examples 1 to 5, it is above 86%. In addition, in Comparative Examples 1 and 2, the VHR changes greatly by more than 65% when the liquid crystal cell is placed under high temperature and high humidity, but in Examples 1 to 5, it is confirmed that the VHR changes can be less than 50%.

<Preparation of liquid crystal cells for tilt angle evaluation> The liquid crystal alignment agents of Examples 1 to 5 and Comparative Examples 1 and 2 were respectively applied by rotation on the ITO surface of a 3.5×3mm ITO electrode substrate (35mm long, 30mm wide, 0.5mm thick) with an ITO electrode pattern of 200μm×600μm pixel size and line width/pitch of 3μm, and a glass substrate (35mm long, 30mm wide, 0.7mm thick) with an ITO electrode patterned with a photo spacer of 3.2μm in height. Then, it was fired at 70°C for 90 seconds on a heating plate, and then fired in an infrared furnace at 230°C for 20 minutes or 60 minutes to produce a polyimide coated substrate with a film thickness of 100nm. In addition, the ITO electrode substrate formed with this ITO electrode pattern is divided into 4 cross-check patterns, and each of the 4 areas can be driven separately.

Two polyimide coated substrates were prepared by the above method, and a thermosetting sealant (XN-1500T manufactured by Kyoritsu Chemical Co., Ltd.) was printed thereon. Next, the surface of the other substrate on which the liquid crystal alignment film was formed was placed inside, and after being bonded to the previous substrate, the sealant was cured to produce an empty cell. Liquid crystal MLC-3023 (trade name manufactured by Merck) containing a polymerizable compound for PSA was injected into the empty cell by the reduced pressure injection method to produce a liquid crystal cell. The voltage retention rate of the liquid crystal cell was measured. Next, while a DC voltage of 15V was applied to the liquid crystal cell, 10J/ ^cm2 of UV through a 325nm cutoff filter was irradiated from the outside of the liquid crystal cell (also referred to as a 1st PSA treatment). In addition, the UV illumination was measured using UV-MO3A manufactured by ORC. Then, in order to inactivate the unreacted polymerizable compound remaining in the liquid crystal cell, UV (UV lamp: FLR40SUV32/A-1) was irradiated for 30 minutes using a UV-FL irradiation device manufactured by Toshiba Lighting and Technology without applying voltage (referred to as the second PSA treatment). Then, the tilt angle was measured.

<Evaluation of pre-tilt angle> The pre-tilt angle of the liquid crystal cell prepared above was measured using an LCD analyzer (LCA-LUV42A manufactured by Meiling Technica). The pre-tilt angle difference was obtained by subtracting the pre-tilt angle of the polyimide coated substrate calcined in an infrared heating furnace at 230°C for 20 minutes from the pre-tilt angle of the polyimide coated substrate calcined for 60 minutes. The evaluation results are shown in Table 4.

As shown in Table 4, the pre-tilt angle difference of Comparative Example 1 without the introduction of the siloxane skeleton is 2.0°, while the pre-tilt angle difference of Examples 1 to 5 can be set to be less than 0.4°.

<Evaluation of solubility> BCS was dripped into 10g of the liquid crystal alignment agent of Examples 1 to 5 and Comparative Examples 1 and 2 respectively, and the solubility was calculated from the weight of the white turbidity using the following formula. The evaluation results are shown in Table 5. Solubility (%) = (amount of BCS in the liquid crystal alignment agent + amount of BCS dripped) / (amount of liquid crystal alignment agent + amount of BCS dripped) × 100

<Preparation of Sealing Adhesion Test Substrate> The liquid crystal alignment agents of Examples 1 to 5 and Comparative Examples 1 and 2 were respectively applied by rotation on the ITO surface of an ITO-attached glass substrate (length 30 mm, width 40 mm, thickness 0.7 mm) cleaned with pure water and IPA (isopropyl alcohol), and then fired at 70°C for 90 seconds with a heating plate, and then fired at 230°C for 20 minutes in an infrared heating furnace to prepare a polyimide-coated substrate with a film thickness of 100 nm. Two polyimide-coated substrates were prepared by the above method, and 4μm spherical spacers were sprinkled on the liquid crystal alignment film surface of one of the substrates, and then a sealant (XN-1500T manufactured by Kyoritsu Chemical Co., Ltd.) was dripped. Next, the two substrates were bonded together with the liquid crystal alignment film surface of the other substrate as the inner side, so that the overlapping width of the substrates became 1 cm and the diameter of the sealant became a circle close to 3 mm. After the two bonded polyimide coated substrates were fixed, they were baked in a hot air circulation oven at 150°C for 1 hour to produce samples for adhesion evaluation.

<Evaluation of Sealing Adhesion> The above-mentioned sample for adhesion evaluation was fixed to the lower part of the three-point bending fixture (interval 64cm) of the table-top precision universal testing machine (made by Shimadzu Corporation, AGS-X 500N), and after fixing the substrate for adhesion evaluation, it was pressed from the upper part of the center of the substrate at a speed of 5mm/min, and the force (N) during peeling was measured. The peeling force (N) measured by the above method was divided by the diameter of the sealant to evaluate the sealing adhesion. The sealing evaluation results are shown in Table 5.

As shown in Table 5, it was confirmed that the solubility was less than 60% in Comparative Examples 1 and 2, but was more than 60% in Examples 1 to 5. The sealing tightness was also confirmed to be less than 2 N/mm in Comparative Examples 1 and 2, but was more than 2.5 N/mm in Examples 1 to 5.

In addition, the entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2019-021819 filed on February 8, 2019 are cited herein and incorporated as a disclosure of the specification of the present invention.

Claims (14)

A liquid crystal alignment agent, characterized in that it contains at least one polymer selected from the group consisting of a polyimide precursor obtained by polymerizing any one of the following diamine components (1) and diamine components (2) with a tetracarboxylic acid component, and a polyimide obtained by imidizing the polyimide precursor, wherein the diamine component (1) is a diamine component containing a diamine having a protective group that is heat-replaceable to a hydrogen atom and a diamine having a siloxane skeleton, and the diamine component (2) is a diamine component containing a diamine having a protective group that is heat-replaceable to a hydrogen atom and a siloxane skeleton, wherein the diamine having a protective group that is heat-replaceable to a hydrogen atom in the diamine component (1) is a diamine represented by the following formula [1],

(In formula [1], ^XD represents an organic group having 1 to 50 carbon atoms and having a structure selected from at least one of the following formulas [1a], [1b], and [1c], and ^A1 and ^A2 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms)

(In formulas [1a] to [1c], ^Xa represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, ^Xd represents a single bond or an organic group having 1 to 20 carbon atoms, ^Xe represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, D represents a protective group that is heat-replaceable to a hydrogen atom, and * represents a bond) wherein the content of the diamine represented by the above formula [1] is 5 to 70 mol% in 100 mol% of the total diamine component. The liquid crystal alignment agent of claim 1, wherein the diamine having a siloxane skeleton in the diamine component (1) is a diamine represented by the following formula [2]:

(In formula [2], _R1 , _R2 , _R3 , and _R4 each independently represent a methyl group or an ethyl group, _X1 and _X2 each independently represent a single bond, -NHCO-, -CONH-, -COO-, or -OCO-; _P1 and _P2 each independently represent _-NH2 , or a structure represented by the following formula [Pa] to [Pb], n1 and n2 each independently represent an integer of 0 to 6, and m represents an integer of 1 to 5, but the phenyl group in formula [Pa] to [Pb] may be substituted with a halogen)

(In formula [Pa] to formula [Pb], X ^D2 represents an organic group having 1 to 50 carbon atoms and having a structure of at least one selected from the group consisting of the following formula [2a], formula [2b] and formula [2c], p represents an integer of 0 to 1, and * represents a bond)

(In formula [2a] to formula [2c], ^Xa represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, ^Xd represents a single bond or an organic group having 1 to 20 carbon atoms, ^Xe represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, D represents a protecting group that is heat-replaceable to a hydrogen atom, and * represents a bond). The liquid crystal alignment agent of claim 1, wherein the diamine represented by the aforementioned formula [1] is at least one diamine selected from the group consisting of the following formulas [1a-1] to [1c-1],

(In formula [1a-1], ^X1 represents a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO- and OCO-, wherein ^R1 , ^R2 and ^R3 each independently represent a hydrogen atom or an alkylene group having 1 to 3 carbon atoms, ^X2 represents a single bond, an alkylene group having 1 to 10 carbon atoms, ^Xa represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, ^Xb represents a structure selected from the group consisting of the following formulas [a-1] to [a-6], m represents an integer of 1 or 2, and when m is 2, ^Xa represents a hydrogen atom, p represents an integer of 1 to 4, and q represents an integer of 1 to 4, In formula [1b-1], X ^X3 and ^X7 each independently represent a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO- and OCO-, but ^R1 , ^R2 and ^R3 each independently represent a hydrogen atom or an alkylene group having 1 to 3 carbon atoms, ^X4 and ^X6 each independently represent a single bond or an alkylene group having 1 to 10 carbon atoms, ^X5 represents a single bond or an alkylene group having 1 to 10 carbon atoms, ^Xc represents a structure selected from the group consisting of the following formulae [a-1] to [a-6], r represents an integer of 1 to 4, and in formula [1c-1], ^X8 represents a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N(R1)-, -CON(R2)-, -N( ^R3) CO-, -CH2O-, -COO- and OCO- )-, -CON(R ² )-, -N(R ³ )CO-, -CH ₂ O-, -COO- and OCO-, wherein R ¹ , R ² and R ³ each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, X ⁹ represents a single bond or an alkylene group having 1 to 10 carbon atoms, X ^d represents a single bond or an organic group having 1 to 20 carbon atoms, X ^e represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, X ^f represents a structure selected from the group consisting of the following formulae [a-1] to [a-6], n represents an integer of 1 to 4, s represents an integer of 1 to 4, t represents an integer of 1 to 4, and in formulae [1a-1] to [1c-1], A ¹ to A ⁶ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms)

( ^R1 represents an alkyl group having 1 to 5 carbon atoms). The liquid crystal alignment agent of claim 3, wherein the diamine represented by the aforementioned formula [1a-1] to formula [1c-1] is at least one diamine selected from the group consisting of the following formula [1d-1] to formula [1d-5],

(In formula [1d-1] to formula [1d-5], R ¹ to R ⁷ each independently represent at least one structure selected from the group consisting of the following formulas [a-1] to [a-6]; in formula [1d-1] to formula [1d-5], A ¹ to A ¹⁰ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms; in formula [1d-4] to formula [1d-5], n1 is an integer of 1 to 10, n2 is an integer of 1 to 10, and n3 is an integer of 1 to 10)

(In formula [a-2], R ¹ represents an alkyl group having 1 to 5 carbon atoms). As in claim 2, the liquid crystal alignment agent, wherein in the diamine represented by the aforementioned formula [2], m represents 1. The liquid crystal aligner of claim 2, wherein in the diamine represented by the aforementioned formula [2], X ^D2 represents a structure selected from the following formulas [2a-1] and [2b-1],

(In formula [2a-1], ^X1 represents a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO- and OCO-, wherein ^R1 , ^R2 and ^R3 each independently represent a hydrogen atom or an alkylene group having 1 to 3 carbon atoms, ^X2 represents a single bond, an alkylene group having 1 to 10 carbon atoms, ^Xa represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, ^Xb represents a structure selected from the group consisting of formula [a-1] to formula [a-6] of claim 3, and m represents an integer of 1 or 2. In this case, when m is 2, X ^a represents a hydrogen atom, p represents an integer of 1 to 4, q represents an integer of 1 to 4, in formula [2b-1], ^X8 represents a single bond, an alkylene group having 1 to 10 carbon atoms, -O-, -N( ^R1 )-, -CON( ^R2 )-, -N( ^R3 )CO-, _-CH2O- , -COO- and OCO-, but ^R1 , ^R2 and ^R3 each independently represent a hydrogen atom or an alkylene group having 1 to 3 carbon atoms, ^X9 represents a single bond, an alkylene group having 1 to 10 carbon atoms, ^Xd represents a single bond or an organic group having 1 to 20 carbon atoms, ^Xe represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, and ^Xf is the same as X in the above formula [1c-1] ^f is defined the same way, n represents an integer from 1 to 4, s represents an integer from 1 to 4, and t represents an integer from 1 to 4). The liquid crystal alignment agent of claim 2, wherein the diamine represented by the aforementioned formula [2] is represented by the following formula:

The liquid crystal alignment agent of claim 1, wherein in the diamine component (2), the diamine having a protective group that is heat-replaceable to a hydrogen atom and a siloxane skeleton is a diamine represented by the following formula [3],

(In formula [3], R ₁ , R ₂ , R ₃ , and R ₄ each independently represent a methyl group or an ethyl group, X represents -NHCO-, -CONH-, -COO-, or -OCO-; X ^D2 is defined by formulas [Pa] and [Pb] of claim 2, n represents an integer of 0 to 6, m represents an integer of 1 to 5, p represents an integer of 0 to 1, and q represents an integer of 0 to 1, but at least one of p and q represents 1). The liquid crystal alignment agent of any one of claims 1 to 4, wherein the tetracarboxylic acid component is a tetracarboxylic acid compound represented by the following formula [4]:

(Z represents at least one structure selected from the group consisting of the following formula [4a] to formula [4q])

(In formula [4a], Z ¹ to Z ⁴ each independently represent a hydrogen atom, a methyl group, an ethyl group, a propyl group, a chlorine atom or a benzene ring; in formula [4g], Z ⁵ and Z ⁶ each independently represent a hydrogen atom or a methyl group). A liquid crystal alignment agent as claimed in any one of claims 1 to 4, wherein the diamine component (1) and the diamine component (2) further contain at least one diamine selected from the group consisting of diamines having specific side chain structures represented by the following formulas [S1] to [S3] and di-side chain diamines represented by the following formula [N1],

(In the above formula [S1], ^G1 and ^G2 each independently represent a divalent cyclic group selected from the group consisting of a divalent aromatic group having 6 to 12 carbon atoms and a divalent alicyclic group having 3 to 8 carbon atoms, any hydrogen atom on the cyclic group may be substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorinated alkyl group having 1 to 3 carbon atoms, a fluorinated alkoxy group having 1 to 3 carbon atoms, or a fluorine atom, m and n each independently represent an integer of 0 to 3, and the total of m and n is 1 to 4, ^X1 and ^X2 each independently represent a single bond, -( _CH2 ) _a- (a represents an integer of 1 to 15), -CONH-, -NHCO-, -CON( _CH3 )-, -NH-, -O-, -COO-, -OCO- or -(( _CH2 ) _a1 - _A1 ) _m1- , R ¹ 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, wherein each of the plural a1s independently represents an integer of 1 to 15, each of the plural _A1s independently represents an oxygen atom or -COO-; m1 represents 1 to 2) ─X ³ －R ² [S2] (In the above formula [S2], X ³ represents a single bond, -CONH-, -NHCO-, -CON(CH ₃ )-, -NH-, -O-, -CH ₂ O-, -COO-, or -OCO-; R ² represents an alkyl group having 1 to 20 carbon atoms, or an alkoxyalkyl group having 2 to 20 carbon atoms) ─X ⁴ －R ³ [S3] (In the above formula [S3], X ⁴ represents -CONH-, -NHCO-, -O-, -COO-, or -OCO-; R ³ represents a structure having a steroid skeleton)

(In the above formula [N1], X represents a divalent organic group selected from a single bond, -O-, -C(CH ₃ ) ₂ -, -NH-, -CO-, -NHCO-, -COO-, -(CH ₂ ) _m -, -SO ₂ - or any combination thereof, m represents an integer of 1 to 8, and Y each independently represents a structure of the following formula [1-1])

(In the above formula [1-1], ^Y1 and ^Y3 each independently represent a single bond, -( _CH2 ) _a- (a represents an integer of 1 to 15), -O-, _-CH2O- , -COO- or -OCO-; ^Y2 represents a single bond or -( _CH2 ) _b- (b represents an integer of 1 to 15), but when ^Y1 or ^Y3 represents a single bond or -( _CH2 ) _a- , ^Y2 represents a single bond; and when ^Y1 represents -O-, _-CH2O- , -COO- or -OCO-, and/or ^Y3 represents -O-, _-CH2O- , -COO- or -OCO-, ^Y2 represents a single bond or -(CH2)b-, Y3 represents a single bond or -( _CH2 ) _b- . ^Y4 represents at least one divalent cyclic group selected from the group consisting of a benzene ring, a cyclohexane ring and a heterocyclic ring, or a divalent organic group having 17 to 51 carbon atoms and having a steroid skeleton, and any hydrogen atom forming the cyclic group may be substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorinated alkyl group having 1 to 3 carbon atoms, a fluorinated alkoxy group having 1 to 3 carbon atoms, or a fluorine atom, ^Y5 represents at least one cyclic group selected from the group consisting of a benzene ring, a cyclohexane ring and a heterocyclic ring, and any hydrogen atom forming the cyclic group may be substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorinated alkyl group having 1 to 3 carbon atoms, a fluorinated alkoxy group having 1 to 3 carbon atoms, or a fluorine atom, and Y ⁶ represents at least one selected from the group consisting of an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a fluorinated alkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, and a fluorinated alkoxy group having 1 to 18 carbon atoms; and n represents an integer of 0 to 4). For example, in the liquid crystal alignment agent of claim 2, the content of the diamine represented by the above formula [2] is 1 to 50 mol% in the total diamine component of 100 mol%. A liquid crystal alignment agent as claimed in any one of claims 1 to 4, wherein the imidization rate of the polyimide contained in the aforementioned polymer is 1 to 95%. A liquid crystal alignment film obtained from a liquid crystal alignment agent as described in any one of claims 1 to 12. A liquid crystal display element having a liquid crystal alignment film as claimed in claim 13.