TWI887964B - Liquid crystal alignment agent for photo-alignment, liquid crystal alignment film and liquid crystal display element - Google Patents

Abstract

A present invention provides a liquid crystal alignment agent for photo-alignment which can lower flicker after high voltage driving, a liquid crystal alignment film formed from said liquid crystal alignment agent, and a liquid crystal display element comprises said liquid crystal alignment film. Said liquid crystal alignment agent for photo-alignment comprises a polymer (A) having a structure represented by formula (I), a polymer (B) having a structure represented by formula (II) and a solvent (C). A definitions of X ₁and X ₂in said formula (I) and X ₃and X ₄in said formula (II) are as stated in a specification and claims respectively. (I)

Description

Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element for photo-alignment method

The present invention relates to a liquid crystal alignment agent for a photo-alignment method, and in particular to a liquid crystal alignment agent for a photo-alignment method capable of reducing flicker after high voltage driving, a liquid crystal alignment film formed by using the liquid crystal alignment agent, and a liquid crystal display element comprising the liquid crystal alignment film.

Generally speaking, a liquid crystal display element may include a liquid crystal layer sandwiched between two glass substrates, a pixel electrode and a common electrode for applying an electric field to the liquid crystal layer, a liquid crystal alignment film for controlling the alignment of liquid crystal molecules in the liquid crystal layer, and a thin film transistor (TFT) for switching the electronic signal supplied to the pixel electrode. As for the driving method of liquid crystal molecules, there are known longitudinal electric field methods such as twisted nematic (TN) method and vertical alignment (VA) method, and transverse electric field methods such as in-plane switching (IPS) method and fringe field switching (FFS) method.

The most popular liquid crystal alignment film in the industry at present is produced by rubbing the surface of a film formed by polyamide and/or polyimide obtained by imidization thereof with cotton cloth, nylon cloth or polyester cloth in one direction. The friction treatment is a simple and highly productive alignment treatment method commonly used in industry. However, in the process of preparing the liquid crystal alignment film, the dust, mechanical force and static electricity generated by the friction treatment will cause defects on the surface of the liquid crystal alignment film, which will lead to various problems such as uneven alignment of the liquid crystal alignment film. Therefore, as an alignment treatment method to replace the friction treatment, there is a known optical alignment method that gives liquid crystal alignment ability by irradiating polarized radiation. In this regard, Japanese Patent Application No. H09-297313 discloses a photo-alignment method for obtaining a liquid crystal alignment film.

In recent years, liquid crystal display elements are often used in medical equipment, aerospace, image processing and industrial control, which require high resolution and fast response time. Liquid crystal display elements used in the above fields need to be able to quickly and accurately display high-resolution images and data, and must also be able to withstand extreme environmental conditions. In this regard, driving liquid crystal display elements with high voltage can allow liquid crystal display elements to provide higher pixel density and faster refresh rate, thereby meeting the needs of the above fields.

However, the liquid crystal display element including the conventional liquid crystal alignment film made by the photo-alignment method has a problem of too high flicker after being driven by a high voltage, so that it cannot meet the application requirements of the industry for liquid crystal display elements.

One aspect of the present invention is to provide a liquid crystal alignment agent for photo-alignment method, which comprises a polymer (A), a polymer (B) and a solvent (C). The liquid crystal alignment film formed by the liquid crystal alignment agent for photo-alignment method can reduce the flicker of the liquid crystal display element after high voltage driving.

Another aspect of the present invention is to provide a liquid crystal alignment film formed by using the liquid crystal alignment agent used in the photo-alignment method as described above.

Another aspect of the present invention is to provide a liquid crystal display element, which includes the liquid crystal alignment film as described above. The liquid crystal display element has a low flicker after high voltage driving.

《Polymer (A)》

The polymer (A) is at least one polymer selected from the group consisting of a polyimide precursor obtained by reacting a tetracarboxylic dianhydride component (a1) and a diamine component (a2), and an imidized polymer of the polyimide precursor. For example, the polymer (A) includes a polyimide precursor having an imide precursor structure such as polyamic acid and polyamic acid ester, and/or an imidized polymer of the polyimide precursor (i.e., polyimide).

The polyimide precursor of the polymer (A) comprises a structure as shown in the following formula (I). (I)

In the formula (I), _X1 is at least one selected from the group consisting of the structures represented by the following formulae (I-1) to (I-7), wherein "*" represents a bonding position. _X2 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. (I-1), (I-2), (I-3), (I-4), (I-5), (I-6), (I-7)

In the formula (I-1), _X11 , _X12 , _X13 and _X14 independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms and containing a fluorine atom, or a phenyl group. In the formula (I-7), _X15 and _X16 independently represent a hydrogen atom or a methyl group.

When the polymer (A) does not contain the polyimide precursor having the structure represented by the formula (I), the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photo-alignment method has poor flicker after high voltage driving.

<Tetracarboxylic dianhydride component (a1)>

In the present invention, the tetracarboxylic dianhydride component (a1) that reacts with the diamine component (a2) may be a tetracarboxylic dianhydride compound, or a tetracarboxylic dianhydride derivative of a tetracarboxylic dianhydride such as a tetracarboxylic dianhydride dihalide, a tetracarboxylic dianhydride dialkyl ester, or a tetracarboxylic dianhydride dialkyl ester dihalide. The tetracarboxylic dianhydride component (a1) may be a single tetracarboxylic dianhydride compound or its derivative, or a combination of a plurality of tetracarboxylic dianhydride compounds may be used.

In some embodiments of the present invention, the tetracarboxylic dianhydride component (a1) comprises an alicyclic tetracarboxylic dianhydride (a1-1) as represented by formula (A11) and other tetracarboxylic dianhydrides (a1-2). (A11)

[Alicyclic tetracarboxylic dianhydride (a1-1) represented by formula (A11)]

The tetracarboxylic dianhydride component (a1) used for reacting with the diamine component (a2) to obtain the polymer (A) comprises an alicyclic tetracarboxylic dianhydride (a1-1) or a derivative thereof as shown in the following formula (A11). The alicyclic tetracarboxylic dianhydride (a1-1) or a derivative thereof as shown in the formula (A11) may be composed of a single tetracarboxylic dianhydride or a derivative thereof, or may be composed of a plurality of tetracarboxylic dianhydrides or derivatives thereof. In the present invention, the alicyclic tetracarboxylic dianhydride (a1-1) as shown in the formula (A11) is, for example, an acid dianhydride obtained by intramolecular dehydration of four carboxyl groups including at least one carboxyl group bonded to an alicyclic structure. However, the four carboxyl groups are not bonded to an aromatic ring. Alternatively, it is not necessary to be composed of only alicyclic structures, and a part of it may have a chain hydrocarbon structure or an aromatic ring structure. Aromatic tetracarboxylic dianhydride is, for example, an acid dianhydride obtained by intramolecular dehydration of four carboxyl groups including at least one carboxyl group bonded to an aromatic ring. However, it is not necessary to be composed of only an aromatic ring structure, and a part of it may have a chain hydrocarbon structure or an alicyclic structure. Non-cyclic aliphatic tetracarboxylic dianhydride is, for example, an acid dianhydride obtained by intramolecular dehydration of four carboxyl groups bonded to a chain hydrocarbon structure. However, it is not necessary to be composed of only alicyclic hydrocarbon structures, and a part of it may have alicyclic structures or an aromatic ring structure. (A11)

In some embodiments of the present invention, in the formula (A11), _X1 is selected from at least one of the group consisting of the structures shown in the following formulas (I-1) to (I-7), and "*" represents a bonding position. (I-1), (I-2), (I-3), (I-4), (I-5), (I-6), (I-7)

In the formula (I-1), _X11 , _X12 , _X13 and _X14 independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms and containing a fluorine atom, or a phenyl group. In the formula (I-7), _X15 and _X16 independently represent a hydrogen atom or a methyl group.

In some embodiments of the present invention, _X1 represents a structure as shown in the following formulas (I-1-1) to (I-1-6). (I-1-1), (I-1-2), (I-1-3), (I-1-4), (I-1-5), (I-1-6)

In some embodiments of the present invention, in order to make the liquid crystal display element including the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photo-alignment method have a lower flicker after high voltage driving, _X1 represents the structure shown in formula (I-1-1).

In some embodiments of the present invention, based on the total usage of the tetracarboxylic dianhydride component (a1) being 100 mol, the usage of the alicyclic tetracarboxylic dianhydride (a1-1) represented by the formula (A11) is 30 mol to 100 mol, preferably, the usage of the alicyclic tetracarboxylic dianhydride (a1-1) represented by the formula (A11) is 40 mol to 100 mol, and more preferably, the usage of the alicyclic tetracarboxylic dianhydride (a1-1) represented by the formula (A11) is 50 mol to 100 mol.

When the tetracarboxylic dianhydride component (a1) does not contain the alicyclic tetracarboxylic dianhydride (a1-1) represented by the formula (A11), the liquid crystal display element including the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photoalignment method has poor flicker after high voltage driving.

﹝Other tetracarboxylic dianhydrides (a1-2)﹞

In some embodiments of the present invention, the other tetracarboxylic dianhydride (a1-2) includes a tetracarboxylic dianhydride compound represented by the following formula (A12) and its derivatives. (A12)

In some embodiments of the present invention, in the formula (A12), X ₁ ′ may represent structures as shown in the following formulas (A12-1) to (A12-32), wherein “*” represents a bonding position. (A12-1), (A12-2), (A12-3), (A12-4), (A12-5), (A12-6), (A12-7), (A12-8), (A12-9), (A12-10), (A12-11), (A12-12), (A12-13), (A12-14), (A12-15), (A12-16), (A12-17), (A12-18), (A12-19), (A12-20), (A12-21), (A12-22), (A12-23), (A12-24), (A12-25), (A12-26), (A12-27), (A12-28), (A12-29), (A12-30), (A12-31), (A12-32)

In the formula (A12-5) and the formula (A12-6), X ₁₁ ' and X ₁₂ ' each independently represent a single bond, -O-, -CO-, -COO-, a phenylene group, a sulfonyl group or an amide group, and a plurality of X ₁₂ ' may be the same as or different from each other. a1 in the formula (A12-5) represents an integer of 0 or 1; a1 in the formula (A12-6) represents an integer of 0 or 1. In the formula (A12-14), X ₁₃ ' each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms and containing a fluorine atom, or a phenyl group, and a plurality of X ₁₃ ' may be the same as or different from each other. From the viewpoint of liquid crystal alignment, preferably, the X ₁₃ ′ independently represents a hydrogen atom, a halogen atom, a methyl group or an ethyl group. More preferably, the X ₁₃ ′ independently represents a hydrogen atom or a methyl group.

In some specific examples of the present invention, the formula (A12-5) and the formula (A12-6) include but are not limited to the structures shown below. , , , , , , , , , , , , , , ,

The other tetracarboxylic dianhydride (a1-2) may be used alone or in combination of two or more.

In some embodiments of the present invention, based on the total usage of the tetracarboxylic dianhydride component (a1) being 100 mol, the usage of the other tetracarboxylic dianhydride (a1-2) is 0 mol to 70 mol, preferably, the usage of the other tetracarboxylic dianhydride (a1-2) is 0 mol to 60 mol, and more preferably, the usage of the other tetracarboxylic dianhydride (a1-2) is 0 mol to 50 mol.

<Diamine component (a2)>

The diamine component (a2) includes a diamine compound (a2-1) represented by the following formula (A21). (A21)

When the diamine component (a2) does not include the diamine compound (a2-1) represented by the formula (A21), the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photoalignment method has poor flicker after high voltage driving.

In some embodiments of the present invention, based on the total usage of the diamine component (a2) being 100 mol, the usage of the diamine compound (a2-1) is 5 mol to 60 mol, preferably, the usage of the diamine compound (a2-1) is 7 mol to 50 mol, and more preferably, the usage of the diamine compound (a2-1) is 10 mol to 45 mol.

In some embodiments of the present invention, the diamine component (a2) may optionally include a diamine compound (a2-2), a diamine compound (a2-3) and other diamine compounds (a2-4).

[Diamine compound (a2-2)]

In some embodiments of the present invention, the diamine compound (a2-2) is selected from diamine compounds represented by the following formula (A22-1) or formula (A22-2). (A22-1) (A22-2)

In some embodiments of the present invention, in the formula (A22-1), Y ₂₁ represents a divalent organic group as shown in the following formula (A22-3). A plurality of Y _22s each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. In the formula (A22-2), a plurality of Y _23s each independently represents a divalent organic group as shown in the following formula (A22-3'). (A22-3) (A22-3')

In the formula (A22-3), Ar independently represents a divalent benzene ring or a naphthyl ring, and the hydrogen atom of the benzene ring or the naphthyl ring may be substituted by a monovalent substituent or not; Y ₂₁ ' represents -(CH ₂ ) _n -, n represents an integer from 2 to 18, and at least one -CH ₂ - in -(CH ₂ ) _n - may be substituted by -O-, -C(=O)- or -OC(=O)- or not; p1 represents an integer of 0 or 1; "*" represents a bonding position.

In the formula (A22-3'), Ar' independently represents a divalent benzene ring or a biphenyl structure, and the hydrogen atom of the benzene ring or the biphenyl structure may be substituted by a monovalent substituent group or may not be substituted; Y ₂₃ ' represents -(CH ₂ ) _n -, n represents an integer from 2 to 18, and at least one -CH ₂ - in -(CH ₂ ) _n - may be substituted by -O-, -C(=O)- or -OC(=O)- or may not be substituted; p2 represents an integer of 0 or 1; "*" represents a bonding position.

In some embodiments of the present invention, the monovalent substituent group of the benzene ring, the biphenyl structure, or the naphthyl ring may be, for example, a halogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a fluoroalkyl group having 1 to 10 carbon atoms, a fluoroalkenyl group having 2 to 10 carbon atoms, a fluoroalkoxy group having 1 to 10 carbon atoms, a carboxyl group, a hydroxyl group, an alkoxycarbonyl group having 1 to 10 carbon atoms, a cyano group, or a nitro group.

In some embodiments of the present invention, from the perspective of improving the alignment of liquid crystal, preferably, the divalent organic group represented by formula (A22-3) includes groups represented by the following formulas (A22-3-1) to (A22-3-14), wherein "*" represents the bonding position. (A22-3-1), (A22-3-2), (A22-3-3), (A22-3-4), (A22-3-5), (A22-3-6), (A22-3-7), (A22-3-8), (A22-3-9), (A22-3-10), (A22-3-11), (A22-3-12), (A22-3-13), (A22-3-14)

In the formula (A22-3-13), the multiple m's independently represent integers from 1 to 3.

In some embodiments of the present invention, from the viewpoint of improving the alignment of liquid crystal, preferably, the divalent organic group represented by the formula (A22-3') includes the groups represented by the above formulas (A22-3-7) to (A22-3-14).

In some embodiments of the present invention, when the diamine compound (a2-2) is selected from a plurality of diamine compounds as shown in formula (A22-1), preferably, the diamine compound (a2-2) is selected from a combination of a diamine compound in which Y ₂₁ in the formula (A22-1) represents a diamine compound of the formula (A22-3-1) to the formula (A22-3-12) and a diamine compound in which Y ₂₁ in the formula (A22-1) represents a diamine compound of the formula (A22-3-13) to the formula (A22-3-14).

In some specific examples of the present invention, the diamine compound represented by formula (A22-2) includes but is not limited to the diamine compounds represented by the following formulas (A22-2-1) to (A22-2-5). (A22-2-1), (A22-2-2), (A22-2-3), (A22-2-4), (A22-2-5)

The diamine compound (a2-2) may be used alone or in combination of two or more.

In some embodiments of the present invention, based on the total usage of the diamine component (a2) being 100 mol, the usage of the diamine compound (a2-2) may be 15 mol to 60 mol, preferably, the usage of the diamine compound (a2-2) is 20 mol to 55 mol, and more preferably, the usage of the diamine compound (a2-2) is 30 mol to 50 mol.

[Diamine compound (a2-3)]

In some embodiments of the present invention, from the viewpoint of improving the voltage retention rate of the liquid crystal display element, the molecular structure of the polymer (A) may selectively have an -N(D)- group (wherein D represents a carbamate-based protective group). The polymer (A) having an -N(D)- group can be obtained by a method in which a monomer having an -N(D)- group is used as at least a part of the reaction raw material, or by a method in which the monomer having an -N(D)- group is used as a capping agent described later. In some specific examples of the present invention, the monomer having an -N(D)- group is, for example, a diamine compound (a2-3) having an -N(D)- group. For example, the carbamate-based protective group includes but is not limited to a tert-butyloxycarbonyl group and a 9-fluorenylmethoxycarbonyl group.

In some embodiments of the present invention, preferably, the diamine compound (a2-3) having an -N(D)- group is selected from diamine compounds having at least one aromatic group such as a benzene ring. More preferably, the diamine compound (a2-3) having an -N(D)- group is selected from diamine compounds having at least one aromatic group such as a benzene ring, and the residue other than the substituent (D) has a carbon number of 6 to 30. In some specific examples of the present invention, the diamine compound (a2-3) having an -N(D)- group is, for example but not limited to, a diamine compound represented by the following formula (A23-1) to formula (A23-10). (A23-1), (A23-2), (A23-3), (A23-4), (A23-5), (A23-6), (A23-7), (A23-8), (A23-9), (A23-10)

The diamine compound (a2-3) may be used alone or in combination of two or more.

In some embodiments of the present invention, based on the total usage of the diamine component (a2) being 100 mol, the usage of the diamine compound (a2-3) may be 5 mol to 45 mol, preferably, the usage of the diamine compound (a2-3) is 7 mol to 35 mol, and more preferably, the usage of the diamine compound (a2-3) is 10 mol to 30 mol.

﹝Other diamine compounds (a2-4)﹞

In addition to the aforementioned diamine compound represented by the formula (A21), the diamine compound (a2-2) represented by the formula (A22-1) or the formula (A22-2), and the diamine compound (a2-3), the diamine component (a2) used to obtain the polymer (A) may optionally include other diamine compounds (a2-4). For example, the other diamine compound (a2-4) includes but is not limited to: 4,4'-diaminoazobenzene or diamine compounds represented by the following formulas (A24-1) to (A24-3) and other diamine compounds having a photoalignment group; 2,4-diaminophenol, 3,5-diaminophenol, 3,5-diaminobenzyl alcohol, 2,4-diaminobenzyl alcohol or 4,6-diaminoresorcinol; 2,4-diaminoazobenzene; Benzoic acid, 2,5-diaminobenzoic acid, 3,5-diaminobenzoic acid or a diamine compound having a carboxyl group such as a diamine compound represented by the following formula (A24-4) to (A24-7); 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ketone, 1,4-bis(4-aminobenzyl)benzene, 4,4'-diaminodiphenyl Aminodiphenyl ether, 1-(4-aminophenyl)-1,3,3-trimethyl-1H-dihydroindene-5-amine or 1-(4-aminophenyl)-2,3-dihydro-1,3,3-trimethyl-1H-indene-6-amine; diamine compounds having a urea bond such as diamine compounds represented by the following formulas (A24-8) to (A24-10); diamine compounds having a urea bond such as diamine compounds represented by the following formulas (A24-11) to (A24-13); Diamine compounds having an amide bond; diamine compounds having a photopolymerizable group at the end such as 2-(2,4-diaminophenoxy)ethyl methacrylate or 2,4-diamino-N,N-diallylaniline; diamine compounds having a siloxane bond, such as 3-bis(3-aminopropyl)-tetramethyldisiloxane; diamine compounds having an oxazoline structure such as diamine compounds represented by the following formulas (A24-14) to (A24-15). (A24-1), (A24-2), (A24-3), (A24-4), (A24-5), (A24-6), (A24-7), (A24-8), (A24-9), (A24-10), (A24-11), (A24-12), (A24-13), (A24-14), (A24-15)

In the formula (A24-4), _Y41 represents _a single bond, _-CH2- , -C2H4-, -C( _CH3 ) _2- , _-CF2- , -C(CF3) _2- , -O-, -CO-, -NH-, -N( _CH3 ) _- , -CONH-, -NHCO-, -CH2O-, -OCH2-, -COO-, _-OCO- , -CON( _CH3 )- or -N( _CH3 )CO-; m1 and m2 each independently represent an integer of 0 to 4, and (m1+ _m2 ) represents an integer of 1 to 4. In the formula (A24-5) _, m3 and m4 each independently represent an integer of 1 to 5. In the formula (A24-6), _Y42 represents a linear or branched alkyl group having 1 to 5 carbon atoms; m5 represents an integer from 1 to 5. In the formula (A25-7), _Y43 and _Y44 each independently represent _a single bond, _-CH2- , -C2H4-, -C( _CH3 ) _2- , _-CF2- , -C( _CF3 ) _2- , -O- _, -CO-, -NH-, -N( _CH3 )-, -CONH-, -NHCO-, _-CH2O- , _-OCH2- , -COO-, -OCO-, -CON( _CH3 )- or -N( _CH3 )CO-; m6 represents an integer from 1 to 4.

The other diamine compound (a2-4) may be used alone or in combination of two or more.

In some embodiments of the present invention, based on the total usage of the diamine component (a2) being 100 mol, the usage of the other diamine compound (a2-4) may be 0 mol to 50 mol, preferably, the usage of the other diamine compound (a2-4) is 0 mol to 40 mol, and more preferably, the usage of the other diamine compound (a2-4) is 0 mol to 30 mol.

《Polymer (B)》

The polymer (B) is at least one polymer selected from the group consisting of a polyimide precursor obtained by reacting a tetracarboxylic dianhydride component (b1) and a diamine component (b2) not containing the above-mentioned specific diamine compound, and an imidized polymer (i.e., polyimide) of the polyimide precursor. For example, specific examples of the polyimide precursor include polyamic acid or polyamic acid ester. The polymer (B) can be used alone or in combination of multiple types.

The polyimide precursor of the polymer (B) comprises a structure represented by the following formula (II). (II)

In the formula (II), X ₃ represents a tetravalent organic group; X ₄ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

When the polymer (B) does not contain the polyimide precursor having the structure represented by the formula (II), the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photo-alignment method has poor flicker after high voltage driving.

In some embodiments of the present invention, the usage ratio of the polymer (A) to the polymer (B) (i.e., the mass ratio of [polymer (A)]/[polymer (B)]) may be 10/90 to 90/10, preferably, the usage ratio of the polymer (A) to the polymer (B) is 20/80 to 90/10, and more preferably, the usage ratio of the polymer (A) to the polymer (B) is 20/80 to 80/20.

<Tetracarboxylic dianhydride component (b1)>

The tetracarboxylic dianhydride component (b1) used for reacting with the diamine component (b2) to obtain the polymer (B) includes but is not limited to a non-cyclic aliphatic tetracarboxylic dianhydride compound, an alicyclic tetracarboxylic dianhydride compound, an aromatic tetracarboxylic dianhydride compound, or derivatives of these compounds. Specific examples of the non-cyclic aliphatic tetracarboxylic dianhydride compound, the alicyclic tetracarboxylic dianhydride compound and the aromatic tetracarboxylic dianhydride compound include the tetracarboxylic dianhydride compounds exemplified for the polymer (A). Preferably, the tetracarboxylic dianhydride component (b1) includes an alicyclic tetracarboxylic dianhydride or a derivative thereof as represented by the formula (A11), or a tetracarboxylic dianhydride compound or a derivative thereof as represented by the formula (A12) and X ₁ ' represents a structure represented by the formula (A12-1) to the formula (A12-6). The tetracarboxylic dianhydride component (b1) may be used alone or in combination of two or more.

In some embodiments of the present invention, preferably, the tetracarboxylic dianhydride component (b1) comprises a tetracarboxylic dianhydride compound as shown in the formula (A12) and X ₁ ' represents a structure shown in the following formula (III) [hereinafter referred to as tetracarboxylic dianhydride compound (b1-1)]. (III)

In the formula (III), Z ₁₁ represents a single bond; and "*" represents a bonding position.

When the tetracarboxylic dianhydride component (b1) comprises a tetracarboxylic dianhydride compound having a structure as shown in the formula (III), a liquid crystal display element comprising a liquid crystal alignment film formed by the liquid crystal alignment agent for photoalignment has a lower flicker after high voltage driving.

The tetracarboxylic dianhydride compound (b1-1) may be used alone or in combination of two or more.

In some embodiments of the present invention, preferably, the tetracarboxylic dianhydride component (b1) comprises a tetracarboxylic dianhydride compound represented by the following formula (IV). (IV)

In some embodiments of the present invention, based on the total usage of the tetracarboxylic dianhydride component (b1) being 100 mol, the usage of the tetracarboxylic dianhydride compound (b1-1) may be 30 mol to 100 mol, preferably, the usage of the tetracarboxylic dianhydride compound (b1-1) is 40 mol to 100 mol, and more preferably, the usage of the tetracarboxylic dianhydride compound (b1-1) is 50 mol to 100 mol.

<Diamine component (b2)>

In some embodiments of the present invention, the diamine component (b2) used to react with the tetracarboxylic dianhydride component (b1) to obtain the polymer (B) comprises a diamine compound (b2-1) represented by the following formula (B21). (B21)

In some embodiments of the present invention, the diamine component (b2) further includes but is not limited to the diamine component (a2), or a diamine compound having at least one nitrogen-containing atom structure selected from the group consisting of a nitrogen-containing heterocyclic ring, a diamine group and a tertiary amine group [hereinafter referred to as diamine compound (b2-2)], but the diamine component (b2) does not include the diamine compound (a2-1).

The diamine component (b2) may be used alone or in combination of two or more.

When the diamine component (b2) does not include the diamine compound (b2-1) represented by the formula (B21), the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photoalignment method has poor flicker after high voltage driving.

In some embodiments of the present invention, based on the total usage of the diamine component (b2) being 100 mol, the usage of the diamine compound (b2-1) is 3 mol to 100 mol, preferably, the usage of the diamine compound (b2-1) is 5 mol to 100 mol, and more preferably, the usage of the diamine compound (b2-1) is 7 mol to 100 mol.

[Diamine compound (b2-2)]

In some embodiments of the present invention, the diamine compound (b2-2) may have a heterocyclic ring containing a nitrogen atom, such as pyrrole, imidazole, pyrazole, triazole, pyridine, pyrimidine, pyrimidine, pyrimidine, pyrimidine, indole, benzimidazole, purine, quinoline, isoquinoline, azidine, quinazoline, pyrimidine, tririmidine, carbazole, acridine, piperidine, piperidine, pyrrolidine or hexamethyleneimine, etc. Preferably, the heterocyclic ring containing a nitrogen atom is pyridine, pyrimidine, pyrimidine, piperidine, piperidine, quinoline, carbazole or acridine.

In some embodiments of the present invention, the diamine compound (b2-2) may include a diamine group and a tertiary amine group as shown in the following formula (B22). (B22)

In the formula (B22), Z represents a hydrogen atom or an alkyl group, a cycloalkyl group or an aryl group having 1 to 10 carbon atoms; "*" represents the bonding position to the alkyl group.

In some embodiments of the present invention, the alkyl represented by Z includes, but is not limited to, methyl, ethyl or propyl; the cycloalkyl represented by Z includes, but is not limited to, cyclohexyl; the aryl represented by Z includes, but is not limited to, phenyl or tolyl. Preferably, Z is a hydrogen atom or a methyl group.

In some embodiments of the present invention, specific examples of the diamine compound (b2-2) include: 2,6-diaminopyridine, 3,4-diaminopyridine, 2,4-diaminopyrimidine, 3,6-diaminocarbazole, N-methyl-3,6-diaminocarbazole, 1,4-bis-(4-aminophenyl)-piperidinium, 3,6-diaminoacridine, N-ethyl-3,6-diaminocarbazole, N-phenyl-3,6-diaminocarbazole, diamine compounds represented by the following formulas (B22-1) to (B22-8), or diamine compounds represented by the following formulas (B22-9) to (B22-26). (B22-1), (B22-2), (B22-3), (B22-4), (B22-5), (B22-6), (B22-7), (B22-8), (B22-9), (B22-10), (B22-11), (B22-12), (B22-13), (B22-14), (B22-15), (B22-16), (B22-17), (B22-18), (B22-19), (B22-20), (B22-21), (B22-22), (B22-23), (B22-24), (B22-25), (B22-26)

The diamine compound (b2-2) may be used alone or in combination of two or more.

In some embodiments of the present invention, based on the total usage of the diamine component (b2) being 100 mol, the usage of the diamine compound (b2-2) may be 3 mol to 90 mol, preferably, the usage of the diamine compound (b2-2) is 5 mol to 80 mol, and more preferably, the usage of the diamine compound (b2-2) is 7 mol to 70 mol.

In some embodiments of the present invention, when the diamine component (b2) includes the diamine compound (b2-2) having at least one nitrogen-containing atom structure selected from the group consisting of a heterocyclic ring containing nitrogen atoms, a diamine group and a tertiary amine group, the liquid crystal display element including the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photoalignment method has a lower flicker after high-voltage driving.

《Polymer production method》

The polymer (A) can be produced by reacting the tetracarboxylic dianhydride component (a1) and the diamine component (a2) in a solvent (polycondensation), and the polymer (B) can be produced by reacting the tetracarboxylic dianhydride component (b1) and the diamine component (b2) in a solvent (polycondensation). When a portion of the polymer (A) or the polymer (B) has an acylamidic acid structure, for example, the tetracarboxylic dianhydride component (a1) is reacted with the diamine component (a2), or the tetracarboxylic dianhydride component (b1) is reacted with the diamine component (b2) to obtain a polymer having an acylamidic acid structure (i.e., polyacylamidic acid). The solvent is not particularly limited, and it only needs to be able to dissolve the formed polymer. For example, specific examples of the solvent include but are not limited to N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide or 1,3-dimethyl-2-imidazolidinone. In some specific examples of the present invention, when the solvent solubility of the polymer (A) or the polymer (B) is high, the solvent includes methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone, or a solvent as shown in the following formula (D-1) to formula (D-3). (D-1), (D-2), (D-3)

In the formula (D-1), Z ₁ represents an alkyl group having 1 to 3 carbon atoms. In the formula (D-2), Z ₂ represents an alkyl group having 1 to 3 carbon atoms. In the formula (D-3), Z ₃ represents an alkyl group having 1 to 4 carbon atoms.

The solvent may be used alone or in combination. Furthermore, even if the solvent cannot dissolve the polymer (A) or the polymer (B), it may be mixed with the solvent to the extent that the polymer (A) or the polymer (B) produced does not precipitate. When the tetracarboxylic dianhydride component (a1) reacts with the diamine component (a2) in the solvent, or when the tetracarboxylic dianhydride component (b1) reacts with the diamine component (b2) in the solvent, the reaction can be carried out at any concentration. Preferably, the total concentration of the tetracarboxylic dianhydride component (a1) and the diamine component (a2) is 1 wt % to 50 wt %, or the total concentration of the tetracarboxylic dianhydride component (b1) and the diamine component (b2) is 1 wt % to 50 wt %. More preferably, the total concentration of the tetracarboxylic dianhydride component (a1) and the diamine component (a2) is 5 wt % to 30 wt %, or the total concentration of the tetracarboxylic dianhydride component (b1) and the diamine component (b2) is 5 wt % to 30 wt %. The reaction can also be carried out at a high concentration at the beginning, and then the solvent can be added additionally. When the reaction is carried out, preferably, the total molar ratio of the diamine component (a2) to the total molar ratio of the tetracarboxylic dianhydride component (a1) is 0.8 to 1.2, or the total molar ratio of the diamine component (b2) to the total molar ratio of the tetracarboxylic dianhydride component (b1) is 0.8 to 1.2. Similar to the general polycondensation reaction, the closer the total molar ratio is to 1.0, the greater the molecular weight of the polymer (A) or the polymer (B) formed.

A polymer having an acylamidate structure can be obtained, for example, by the following known methods: (1) a method in which the polyacylamidate obtained by the above method is further reacted with an esterifying agent, (2) a method in which a tetracarboxylic acid diester compound is reacted with a diamine compound, or (3) a method in which a tetracarboxylic acid diester dihalide is reacted with a diamine compound.

The imidized polymer in the polymer (A) or the polymer (B) contained in the liquid crystal alignment agent for the photo-alignment method of the present invention is obtained, for example, by ring-closing the polymer having an acylamidic acid structure. In the imidized polymer, the ring-closing ratio (also referred to as the imidization ratio) of the functional group possessed by the acylamidic acid group or its derivative is not necessarily 100%, and the imidization ratio can be arbitrarily adjusted according to the use and/or purpose.

The method for obtaining the imidized polymer includes, for example, directly heating the solution containing the polymer having an amide structure obtained by the above reaction for thermal imidization, or adding a catalyst to the solution containing the polymer having an amide structure for catalytic imidization. When thermal imidization is performed in the solution containing the polymer having an amide structure, preferably, the reaction temperature is 100° C. to 400° C., more preferably, the reaction temperature is 120° C. to 250° C. When thermal imidization is performed, preferably, water generated by the imidization reaction is discharged from the reaction system.

The catalytic imidization is carried out, for example, by adding an alkaline catalyst and an acid anhydride to a solution containing the polymer having an amide structure, preferably with stirring at -20°C to 250°C, more preferably with stirring at 0°C to 180°C. The amount of the alkaline catalyst added is preferably 0.5 to 30 times the molar equivalent of the amide group, and more preferably 2 to 20 times; the amount of the acid anhydride added is preferably 1 to 50 times the molar equivalent of the amide group, and more preferably 3 to 30 times. Specific examples of the alkaline catalyst include but are not limited to pyridine, triethylamine, trimethylamine, tributylamine or trioctylamine. Among them, pyridine is ideal because it has a moderate alkalinity that allows the reaction to proceed. Specific examples of the acid anhydride include but are not limited to acetic anhydride, trimellitic anhydride or pyromellitic anhydride. Among them, if acetic anhydride is used, purification after the reaction is easier, so it is more ideal. The imidization rate of the catalytic imidization can be controlled by adjusting the amount of catalyst, reaction temperature and/or reaction time.

When the imidized polymer is recovered from the reaction solution of the thermal imidization or the catalytic imidization, the reaction solution is put into a solvent and precipitated. The solvent used for precipitation includes, but is not limited to, methanol, ethanol, isopropanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, toluene, benzene or water. After filtering and recovering the polymer precipitated in the solvent, it can be dried at normal pressure or reduced pressure, at room temperature or by heating. Alternatively, the polymer recovered by precipitation is dissolved again in the solvent used for precipitation, and re-precipitated and recovered. This operation is repeated 2 to 10 times to reduce impurities in the polymer. The solvent used for the precipitation is, for example, alcohol or ketone. If three or more selected solvents are used, the efficiency of purification can be further improved, which is more ideal.

Solution Viscosity and Molecular Weight of Polymers

When the solution containing the polymer (A) or the polymer (B) is prepared to contain 10 wt% to 15 wt% of the polymer (A) or the polymer (B), the viscosity of the solution containing the polymer (A) or the polymer (B) of the present invention is not particularly limited. Based on the viewpoint of easier operation, the viscosity of the solution containing the polymer (A) or the polymer (B) is, for example, 10 mPa·s to 1000 mPa·s. The viscosity (mPa·s) of the solution containing the polymer (A) or the polymer (B) is a value measured at 25° C. using a good solvent for the polymer (A) or the polymer (B) (e.g., γ-butyrolactone or N-methyl-2-pyrrolidone, etc.) to prepare a solution containing 10 wt% to 15 wt% of the polymer (A) or the polymer (B) using an E-type rotational viscometer.

The weight average molecular weight (Mw) of the polymer (A) or the polymer (B) of the present invention measured by gel permeation chromatography (GPC) in terms of polystyrene is preferably 1,000 to 500,000, and more preferably 2,000 to 500,000. In addition, the molecular weight distribution ( _{Mw / Mn} ) represented by the ratio of Mw to the number average molecular weight ( _{Mn )} in terms of polystyrene measured by GPC is preferably 15 or less, and more preferably 10 or less. When the weight average molecular weight of the polymer (A) or the polymer (B) is within the above weight average molecular weight range, it can ensure good alignment and stability of the liquid crystal display element.

《Capping agent》

In some embodiments of the present invention, when synthesizing the polymer (A) or the polymer (B) of the present invention, the tetracarboxylic dianhydride component (a1) and the diamine component (a2), or the tetracarboxylic dianhydride component (b1) and the diamine component (b2) as described above, and a suitable end-capping agent can be used to synthesize an end-sealed polymer. The end-sealed polymer has the effect of improving the film hardness of the liquid crystal alignment film obtained by coating, and improving the sealing properties of the sealant and the liquid crystal alignment film. The end of the polymer (A) or the polymer (B) of the present invention may, for example, contain an amino group, a carboxyl group, an anhydride group or a derivative thereof. The amino group, the carboxyl group, the anhydride group or a derivative thereof can be obtained by a general condensation reaction, or by using the end-capping agent described later to seal the end. Similarly, the aforementioned derivatives can be obtained, for example, by using the following blocking agent.

For example, the end-capping agent includes, but is not limited to, acetic anhydride, maleic anhydride, neddic anhydride, phthalic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride, 3-hydroxyphthalic anhydride, trimellitic anhydride, 3-((3-trimethoxysilyl)propyl)-3,4-dihydrofuran-2,5-dione, 4,5,6,7-tetrafluoroisobenzofuran-1,3-dione or 4-ethynylphthalic anhydride; dibutyl dicarbonate or diallyl dicarbonate; Carbonic acid diester compounds; chlorocarbonyl compounds such as acrylyl chloride, methacrylic chloride or nicotinyl chloride; monoamine compounds such as aniline, 2-aminophenol, 3-aminophenol, 4-aminosalicylic acid, 5-aminosalicylic acid, 6-aminosalicylic acid, 2-aminobenzoic acid, 3-aminobenzoic acid, 4-aminobenzoic acid, cyclohexylamine, n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine or n-octylamine; monoisocyanate compounds such as ethyl isocyanate, phenyl isocyanate or naphthyl isocyanate, etc.

The blocking agent may be used alone or in combination of two or more.

In some embodiments of the present invention, based on the total usage of the diamine component (a2) or the diamine component (b2) being 100 mol parts, the usage of the end-capping agent is preferably 0.01 mol parts to 20 mol parts, more preferably, the usage of the end-capping agent is 0.01 mol parts to 10 mol parts.

《Other polymers》

In some embodiments of the present invention, the liquid crystal alignment agent used in the photo-alignment method of the present invention may selectively include other polymers. The types of other polymers include, but are not limited to, polyesters, polyamides, polyureas, polyorganosiloxanes, cellulose derivatives, polyacetals, polystyrene or its derivatives, poly(styrene-phenylmaleimide) derivatives, or poly(meth)acrylates.

Solvent (C)

From the perspective of forming a uniform film, the liquid crystal alignment agent used in the photo-alignment method is in the form of a coating liquid to produce a liquid crystal alignment film. Based on the set coating thickness to be formed, the concentrations of the polymer (A) and the polymer (B) in the liquid crystal alignment agent used in the photo-alignment method can be appropriately changed. From the perspective of forming a uniform and defect-free coating, the total concentration of the polymers in the liquid crystal alignment agent used in the photo-alignment method is preferably greater than 1wt%. From the perspective of the storage stability of the solution, the total concentration of the polymers in the liquid crystal alignment agent used in the photo-alignment method is preferably less than 10wt%. The ideal total concentration of the polymers can be 2wt% to 8wt%. The content of the polymer in the liquid crystal alignment agent used in the photo-alignment method can be appropriately changed by the coating method of the liquid crystal alignment agent and/or the film thickness of the desired liquid crystal alignment film. Preferably, the content of the polymer (A) is 2wt% to 10wt%, and more preferably, the content of the polymer (A) is 3wt% to 7wt%.

The solvent (C) contained in the liquid crystal alignment agent used in the photo-alignment method is not particularly limited, and it only needs to be able to dissolve the polymer uniformly. Specific examples of the solvent (C) may include, but are not limited to, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethyllactamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylsulfoxide, γ-butyrolactone, γ-valerolactone, 1,3-dimethyl-2-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide, The solvent (C) is preferably N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropionamide, 3-butoxy-N,N-dimethylpropionamide or γ-butyrolactone. In some embodiments of the present invention, the total usage of the solvent (C) in the liquid crystal alignment agent used in the photo-alignment method is 100wt%, the usage of the good solvent is 20wt% to 99wt%, preferably, the usage of the good solvent is 20wt% to 90wt%, and more preferably, the usage of the good solvent is 30wt% to 80wt%.

In some embodiments of the present invention, the solvent (C) in the liquid crystal alignment agent for photo-alignment method is preferably a mixed solvent of the good solvent and a solvent (also called a poor solvent) that can improve the coating property of the liquid crystal alignment agent for photo-alignment method and the surface smoothness of the coating film. The specific poor solvent used in combination can be, for example, but not limited to, the solvent described below. In some embodiments of the present invention, the total amount of the solvent (C) in the liquid crystal alignment agent for the photo-alignment method is 100wt%, preferably, the amount of the poor solvent is 1wt% to 80wt%, more preferably, the amount of the poor solvent is 10wt% to 80wt%, and particularly preferably, the amount of the poor solvent is 20wt% to 70wt%. The type and amount of the poor solvent can be appropriately selected according to the coating device, coating conditions and/or coating environment of the liquid crystal alignment agent for the photo-alignment method.

For example, the poor solvent may be, 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, ethyl carbonate, ethylene glycol monobutyl ether (butyl celoxylate), ethylene glycol monoisopentyl ether, ethylene glycol monohexyl ether, propylene glycol monobutyl ether, 1-(2-butoxyethoxy) )-2-propanol, 2-(2-butoxyethoxy)-1-propanol, propylene glycol monomethyl ether acetate, propylene glycol diacetate, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, diethylene glycol acetate, propylene glycol diacetate, n-butyl acetate, propylene glycol monoethyl ether acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, propyl 3-methoxypropionate, butyl 3-methoxypropionate, n-butyl lactate, isoamyl lactate, diethylene glycol monoethyl ether, or diisobutyl ketone (2,6-dimethyl-4-heptanone), etc. Preferably, the poor solvent is diisobutyl carbinol, propylene glycol monobutyl ether, propylene glycol diacetate, diethylene glycol diethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether acetate, or diisobutyl ketone.

In some embodiments of the present invention, the solvent combination of the good solvent and the poor solvent is preferably, for example, but not limited to, 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-ethyl-2-pyrrolidone and 4-hydroxy-4-methyl-2-pentanone; N-ethyl-2-pyrrolidone and propylene glycol diacetate; N,N-dimethyl lactamide and diisobutyl ketone; N-methyl-2-pyrrolidone and ethyl 3-ethoxypropionate; N-ethyl-2-pyrrolidone and ethyl 3-ethoxypropionate; N- Methyl-2-pyrrolidone and ethylene glycol monobutyl ether acetate; N-ethyl-2-pyrrolidone and dipropylene glycol dimethyl ether; N,N-dimethyl lactamide and ethylene glycol monobutyl ether; N,N-dimethyl lactamide and propylene glycol diacetate; N-ethyl-2-pyrrolidone and diethylene glycol diethyl ether; N,N-dimethyl lactamide and diethylene glycol diethyl ether; N-methyl-2-pyrrolidone, γ-butyrolactone, 4-hydroxy-4-methyl-2-pentanone and diethylene glycol diethyl ether; N-ethyl-2-pyrrolidone, N-methyl-2-pyrrolidone and 4-hydroxy-4-methyl-2-pentanone; N-ethyl-2-pyrrolidone, 4-hydroxy-4-methyl-2-pentanone and propylene glycol monobutyl ether; N-methyl- 2-pyrrolidone, 4-hydroxy-4-methyl-2-pentanone and diisobutyl ketone; N-methyl-2-pyrrolidone, 4-hydroxy-4-methyl-2-pentanone and dipropylene glycol monomethyl ether; N-methyl-2-pyrrolidone, 4-hydroxy-4-methyl-2-pentanone and propylene glycol monobutyl ether; N-methyl-2-pyrrolidone, 4-hydroxy-4-methyl-2-pentanone and propylene glycol diacetate; γ-butyrolactone, 4-hydroxy-4-methyl-2-pentanone and diisobutyl ketone; γ-butyrolactone, 4-hydroxy-4-methyl-2-pentanone and propylene glycol diacetate; N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether and diisobutyl ketone; N-methyl-2-pyrrolidone, γ-butyrolactone Lactone and propylene glycol monobutyl ether and diisopropyl ether; N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether and diisobutyl carbinol; N-methyl-2-pyrrolidone, γ-butyrolactone and dipropylene glycol dimethyl ether; N-methyl-2-pyrrolidone, propylene glycol monobutyl ether and dipropylene glycol dimethyl ether; N-ethyl-2-pyrrolidone, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether; N-ethyl-2-pyrrolidone, propylene glycol monobutyl ether and propylene glycol diacetate; N-ethyl-2-pyrrolidone, propylene glycol monobutyl ether and diisobutyl ketone; N-ethyl-2-pyrrolidone, γ-butyrolactone and diisobutyl ketone; or N-ethyl-2-pyrrolidone, N,N-dimethyllactamide and diisobutyl ketone, etc.

The solvent (C) may be used alone or in combination of two or more.

In some embodiments of the present invention, based on the total usage of the polymer (A) and the polymer (B) being 100 parts by weight, the usage of the solvent (C) is 800 to 4000 parts by weight, preferably, the usage of the solvent (C) is 900 to 3500 parts by weight, and more preferably, the usage of the solvent (C) is 1000 to 3000 parts by weight.

Additive ingredients

In some embodiments of the present invention, the liquid crystal alignment agent used in the photo-alignment method of the present invention may also selectively add components other than the polymer (A), the polymer (B) and the solvent (C) (hereinafter referred to as additive components). The additive components include, but are not limited to: a bonding aid for improving the adhesion between the liquid crystal alignment film and the substrate or the adhesion between the liquid crystal alignment film and the sealant, a compound for improving the strength of the liquid crystal alignment film (hereinafter referred to as a cross-linking compound), a compound for promoting imidization, a dielectric or conductive substance for adjusting the dielectric constant or resistance of the liquid crystal alignment film, etc.

〈Sealing aid〉

The adhesion aid is, for example, 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-aminopropyl diethoxymethyl silane, 2-aminopropyl trimethoxysilane, 2-aminopropyl triethoxysilane, N-(2-aminoethyl)-3-aminopropyl trimethoxysilane, N-(2-aminoethyl)-3-aminopropyl methyl dimethoxysilane, 3-ureidopropyl trimethoxysilane, 3-ureidopropyl triethoxysilane, N-ethoxycarbonyl-3-aminopropyl trimethoxysilane, N-ethoxycarbonyl-3-aminopropyl triethoxysilane, N-triethoxysilylpropyl triethyl triamine, N-trimethoxysilylpropyl triethyl triamine, vinyl trimethoxysilane, Silane, vinyl triethoxysilane, 2-(3,4-epoxyhexyl)ethyl trimethoxysilane, 3-glycidoxypropyl methyl dimethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl methyl diethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-methacryloyloxypropyl methyl dimethoxysilane Silane coupling agents include 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris(3-trimethoxysilylpropyl)isocyanurate, and 3-isocyanatepropyltriethoxysilane. In some embodiments of the present invention, when the bonding aid is used, based on the viewpoint of exhibiting good resistance to AC afterimage, relative to the total usage of the polymer (A) and the polymer (B) in the liquid crystal alignment agent for the photoalignment method being 100 parts by weight, preferably, the usage of the bonding aid is 0.1 parts by weight to 30 parts by weight, and more preferably, the usage of the bonding aid is 0.1 parts by weight to 20 parts by weight.

〈Cross-linking compounds〉

From the viewpoint of exhibiting good resistance to AC afterimage and effectively improving film strength, the crosslinking compound may be a compound having an ethylene oxide group, a propylene oxide group, at least one group selected from the group consisting of a group represented by the following formula (E1) and a group represented by the following formula (E2), or a compound selected from the compound represented by the following formula (E3). (E1) (E2) (E3)

In the formula (E1), _G1 and _G2 each independently represent a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or -CH2 _- OH. In the formula (E2), _G3 represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms. _G4 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms. In the formula (E3), _G5 represents a (g1+g2)-valent organic group containing an aromatic ring. _G6 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. g1 represents an integer from 1 to 6, and g2 represents an integer from 0 to 4.

In some embodiments of the present invention, in the formula (E3), the (g1+g2)-valent organic group having an aromatic ring represented by _G5 can be a (g1+g2)-valent aromatic alkyl group having 6 to 30 carbon atoms, a (g1+g2)-valent organic group formed by directly or intermittently bonding an aromatic alkyl group having 6 to 30 carbon atoms to a linking group, or a (g1+g2)-valent group having an aromatic heterocyclic ring. The aromatic alkyl group is, for example, a phenyl group or a naphthyl group. The aromatic heterocyclic ring can be exemplified by the above-mentioned specific aromatic heterocyclic ring containing a nitrogen atom. The linking group can be an alkylene group having 1 to 10 carbon atoms or a group in which a hydrogen atom is removed from the alkylene group, or a divalent or trivalent cyclohexane group. Wherein, any hydrogen atom of the alkylene group may be substituted by a fluorine atom or an organic group such as trifluoromethyl. In the formula (E3), the alkyl group with 1 to 5 carbon atoms represented by _G6 may be methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl or n-pentyl.

﹝Compounds with ethylene oxide groups﹞

In some embodiments of the present invention, specific examples of compounds having an ethylene oxide group include N,N,N',N'-tetraethylene oxide propyl-m-xylene diamine, 1,3-bis(N,N-diethylene oxide propylaminomethyl)cyclohexane, N,N,N',N'-tetraethylene oxide propyl-4,4'-diaminodiphenylmethane, N,N,N',N'-tetraethylene oxide propyl-p-phenylenediamine, and compounds containing nitrogen atoms such as those shown in the following formulas (E4) to (E6). (E4), (E5), (E6)

﹝Compounds with propylene oxide group﹞

In some embodiments of the present invention, specific examples of the compound having an propylene oxide group include compounds represented by the following formula (E7) to formula (E16). (E7), (E8), (E9), (E10), (E11), (E12), (E13), (E14), (E15), (E16)

In the formula (E15), R represents , where "*" represents the key position.

[Compounds having a group represented by formula (E1)]

In some embodiments of the present invention, specific examples of the compound having a group represented by formula (E1) include compounds represented by the following formulas (E1-1) to (E1-12). (E1-1), (E1-2), (E1-3), (E1-4), (E1-5), (E1-6), (E1-7), (E1-8), (E1-9), (E1-10), (E1-11), (E1-12)

[Compounds having a group represented by formula (E2)]

In some embodiments of the present invention, specific examples of the compound having a group represented by formula (E2) include compounds represented by the following formulas (E2-1) to (E2-4). (E2-1), (E2-2), (E2-3), (E2-4)

[Compounds having a group represented by formula (E3)]

In some embodiments of the present invention, specific examples of the compound having a group represented by formula (E3) may be compounds represented by the following formulas (E3-1) to (E3-10). (E3-1), (E3-2), (E3-3), (E3-4), (E3-5), (E3-6), (E3-7), (E3-8), (E3-9), (E3-10)

In some embodiments of the present invention, based on the total usage of the polymer (A) and the polymer (B) in the liquid crystal alignment agent for the photo-alignment method being 100 parts by weight, preferably, the usage of the crosslinking compound is 0.5 to 20 parts by weight. Based on the viewpoint of the crosslinking reaction and the good resistance to AC afterimage, more preferably, the usage of the crosslinking compound is 1 to 15 parts by weight.

〈Compounds for promoting imidization〉

In some embodiments of the present invention, the compound used to promote imidization is preferably a compound having a basic site [e.g., a primary amine group, an aliphatic heterocycle (e.g., a pyrrolidine skeleton), an aromatic heterocycle (e.g., an imidazole ring or an indole ring), or a guanidine group, etc.] (except for the above-mentioned adhesion aid and the cross-linking compound), or a compound that generates the basic site when calcined. More preferably, the compound used to promote imidization is a compound that generates the basic site when calcined, and a specific example thereof may be an amino acid in which a part or all of the basic site of the amino acid is protected. Specific examples of the above amino acids include glycine, alanine, cysteine, methionine, asparagine, glutamine, valine, leucine, phenylalanine, tyrosine, tryptophan, proline, hydroxyproline, arginine, histidine, lysine, or ornithine. For the purpose of promoting the formation of an acylated compound, a more preferred specific example of the compound for promoting acylation is N-α-(9-fluorenylmethoxycarbonyl)-N-τ-(tert-butyloxycarbonyl)-L-histidine.

《Method for producing liquid crystal alignment film and liquid crystal display element》

The liquid crystal alignment film of the present invention is obtained by the liquid crystal alignment agent used in the optical alignment method as described above. The liquid crystal alignment film of the present invention can be used as a horizontal alignment type or a vertical alignment type (VA type) liquid crystal alignment film. Preferably, the liquid crystal alignment film of the present invention is suitable for being used as a liquid crystal alignment film of a horizontal alignment type liquid crystal display element such as an IPS method or a FFS method. The liquid crystal display element of the present invention has the above-mentioned liquid crystal alignment film. The liquid crystal display element of the present invention can be manufactured, for example, by the following method of steps (1) to (4) or steps (1) to (2) and step (4).

〈Step (1): Applying a liquid crystal alignment agent on a substrate〉

The liquid crystal alignment agent used in the photo-alignment method of the present invention is applied on one side of a substrate provided with a patterned transparent conductive film by using a suitable coating method such as roller coating, spin coating, printing or inkjet coating. There is no particular limitation on the substrate, and it only needs to be a highly transparent substrate. A glass substrate or a silicon nitride substrate can also be used together with a plastic substrate such as an acrylic substrate or a polycarbonate substrate. Secondly, in a reflective liquid crystal display element, if it is only a single-sided substrate, an opaque material such as a silicon wafer can also be used, and the electrode used can also be a material that can reflect light such as aluminum. Furthermore, when manufacturing IPS type or FFS type liquid crystal elements, the comb-tooth type uses an electrode substrate composed of a patterned transparent conductive film or metal film and an opposite substrate without an electrode.

The method of coating the liquid crystal alignment agent for the photo-alignment method on the substrate and forming a film can be listed as screen printing, lithography, flexographic printing, inkjet method or inkjet coating method, etc. Among them, the film forming method is preferably coating by inkjet method.

〈Step (2): Calcination of the coated liquid crystal alignment agent〉

Step (2) is a step of calcining the liquid crystal alignment agent for photo-alignment method coated on the substrate to form a film. After the liquid crystal alignment agent for photo-alignment method is coated on the substrate, the solvent (C) in the liquid crystal alignment agent for photo-alignment method can be evaporated by heating means such as a hot plate, a heat circulation oven or an IR (infrared) oven, or thermal imidization of polyamine or polyamine ester can be performed. The drying step and calcining step performed after the liquid crystal alignment agent for photo-alignment method of the present invention has been coated can be selected at any temperature and time, and multiple drying steps or calcining steps can be performed. The temperature of the drying step may be, for example, 40°C to 180°C. From the viewpoint of shortening the treatment, it may be performed at 40°C to 150°C. The time of the drying step is not particularly limited, and it may be, for example, 1 minute to 10 minutes or 1 minute to 5 minutes. When thermal imidization of polyamine or polyamine ester is performed, after the drying step, the calcination step may be further performed at a temperature of, for example, 150°C to 300°C or 150°C to 250°C. The time of the calcination step is not particularly limited, and it may be 5 minutes to 40 minutes or 5 minutes to 30 minutes. If the film after calcination is too thin, the reliability of the liquid crystal display element will be reduced, so the thickness of the film after calcination is preferably 5nm to 300nm, and more preferably, the thickness of the film after calcination is 10nm to 200nm.

〈Step (3): performing an alignment treatment on the film obtained in step (2)〉

Step (3) is to perform an alignment treatment on the film obtained in step (2) as appropriate. In other words, in a horizontal alignment type liquid crystal display element such as the IPS mode or the FFS mode, the film obtained in step (2) is subjected to an alignment treatment to be given an alignment capability. On the other hand, in a vertical alignment type liquid crystal display element such as the VA mode or the PSA mode, the film obtained in step (2) can be used directly as a liquid crystal alignment film, but the film obtained in step (2) can also be subjected to an alignment treatment to be given an alignment capability. The alignment treatment of the liquid crystal alignment film can be exemplified by a friction treatment method or a photo-alignment treatment method, and the photo-alignment treatment method is preferred. The photo-alignment treatment method may include irradiating the surface of the film obtained in step (2) with radiation that has been deflected in a certain direction, and heating it at a temperature of 150° C. to 250° C. to impart liquid crystal alignment (also known as liquid crystal alignment ability). The radiation may be ultraviolet light or visible light with a wavelength of 100 nm to 800 nm. The radiation is preferably ultraviolet light with a wavelength of 100 nm to 400 nm, and more preferably ultraviolet light with a wavelength of 200 nm to 400 nm.

The radiation irradiation amount may be 1mJ/ ^cm2 to 10,000mJ/ ^cm2 , preferably 100mJ/ ^cm2 to 5,000mJ/ ^cm2 , more preferably 100mJ/ ^cm2 to 1500mJ/ ^cm2 , and particularly preferably 100mJ/ ^cm2 to 1000mJ/ ^cm2 . When a general liquid crystal alignment agent is used, the light irradiation amount of the alignment treatment is 100mJ/ ^cm2 to 5000mJ/ ^cm2 , but the liquid crystal alignment agent used in the photo-alignment method of the present invention can still obtain a liquid crystal alignment film in which the variation (non-uniformity) of the liquid crystal alignment in the film surface is effectively suppressed even if the light irradiation amount of the alignment treatment is reduced. When irradiating radiation, in order to improve the liquid crystal alignment, the substrate having the film obtained in step (2) formed on the surface can be heated at 50°C to 250°C while irradiating. The liquid crystal alignment film produced in this way can make the liquid crystal molecules stably align in a certain direction. Secondly, the liquid crystal alignment film irradiated with polarized radiation in the above method can be contact-treated with a solvent, or the liquid crystal alignment film irradiated with radiation can be heated.

The solvent used in the contact treatment is not particularly limited, and it only needs to be able to dissolve the decomposition products generated from the film-like material obtained in the step (2) after irradiation. Specific examples of the solvent used in the contact treatment include water, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, 1-methoxy-2-propanol, 1-methoxy-2-propanol acetate, butyl celecoxib, ethyl lactate, methyl lactate, diacetone alcohol, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, propyl acetate, butyl acetate, or cyclohexyl acetate. Among them, based on the viewpoint of versatility and safety, preferably, the solvent used in the contact treatment is water, 2-propanol, 1-methoxy-2-propanol or ethyl lactate, and more preferably, the solvent used in the contact treatment is water, 1-methoxy-2-propanol or ethyl lactate. The solvent used in the contact treatment can be used alone or in combination.

The temperature for heat treatment of the liquid crystal alignment film irradiated with radiation is preferably 50° C. to 300° C., and more preferably 120° C. to 250° C. The time for heat treatment is preferably 1 minute to 30 minutes.

<Step (4): Making a liquid crystal cell>

Prepare two substrates with liquid crystal alignment films formed on their surfaces, and arrange liquid crystal between the two substrates facing each other. For example, the following two methods can be listed. The first method is to arrange the two substrates facing each other with a gap (cell gap) between them in a way that the liquid crystal alignment films face each other. Then, the periphery of the two substrates is bonded with a sealant, and then the liquid crystal composition is injected into the cell gap separated by the substrate surface and the sealant, and after it contacts the film surface, the injection hole is sealed.

The second method is called ODF (One Drop Fill). A sealant such as a UV-curable sealant is applied to a predetermined position on one of the two substrates with a liquid crystal alignment film formed on the surface, and then a liquid crystal composition is dropped at a plurality of predetermined positions on the surface of the liquid crystal alignment film. Then, the other substrate is attached in a manner that the liquid crystal alignment films face each other, and the liquid crystal composition is pushed onto the entire surface of the liquid crystal alignment film so that it contacts the film surface of the other liquid crystal alignment film. Then, ultraviolet light is irradiated onto the entire surface of the substrate to cure the sealant. When performing any of the aforementioned methods, it is preferred to further heat the liquid crystal composition used to a temperature at which it becomes an isotropic phase, and then slowly cool it to room temperature to remove the flow alignment during liquid crystal filling. Secondly, when the liquid crystal alignment film is subjected to rubbing treatment, the two substrates are arranged so that the rubbing directions of the liquid crystal alignment films are at a predetermined angle to each other, for example, orthogonal or antiparallel. The sealant may be, for example, an epoxy resin containing a hardener and aluminum oxide balls as spacers. The liquid crystal composition may be nematic liquid crystal and lamellar liquid crystal, and preferably nematic liquid crystal.

If necessary, a polarizing plate can be attached to the outer surface of the liquid crystal cell to obtain a liquid crystal display element. The polarizing plate attached to the outer surface of the liquid crystal cell can be a polarizing film called "H film" that stretches polyvinyl alcohol and absorbs iodine at the same time. It can be a polarizing plate sandwiched by a cellulose acetate protective film, or a polarizing plate composed of the H film itself.

The effect of the present invention is that the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photo-alignment method of the present invention can effectively reduce the flicker degree of the liquid crystal display element after high-voltage driving by using the polymer (A) prepared by the polyimide precursor of the structure represented by the formula (I) and the polymer (B) prepared by using the polyimide precursor of the structure represented by the formula (II).

《Preparation of polymer (A)》

[Preparation Example A-1] Polymer (A)

A nitrogen inlet, a stirrer, a condenser and a thermometer were installed on a 500 ml four-necked conical flask, and nitrogen was introduced. Then, 0.80 g (0.0025 mol) of compound (a2-1-1), 7.15 g (0.025 mol) of compound (a2-2-1), 7.74 g (0.0175 mol) of compound (a2-3-1), 1.00 g (0.005 mol) of compound (a2-4-2) and 80 g of N-methyl-2-pyrrolidone (hereinafter referred to as NMP) were added and stirred at room temperature until dissolved. Next, 3.36 g (0.015 mol) of compound (a1-1-1), 7.56 g (0.035 mol) of compound (a1-2-1) and 20 g of NMP were added, and the mixture was reacted at room temperature for 2 hours to obtain a reaction solution. The reaction solution was poured into 1500 ml of water to precipitate a polymer, and filtered to obtain a filter cake. Then, the filter cake was washed with methanol and then filtered, and the washing and filtering steps were repeated three times to obtain a crude product. Thereafter, the crude product was placed in a vacuum oven and dried at a temperature of 60°C to obtain a polymer (A).

[Preparation Examples A-2 to A-6 and Comparative Preparation Examples A'-1 to A'-2]  Polymer (A)

Preparation Examples A-2 to A-6 and Comparative Preparation Examples A’-1 to A’-2 are used to prepare polymer (A) by a method similar to that of Preparation Example A-1, except that the types and amounts of the components are changed in Preparation Examples A-2 to A-6 and Comparative Preparation Examples A’-1 to A’-2, as shown in Table 1.

《Preparation of polymer (B)》

[Preparation Examples B-1 to B-4 and Comparative Preparation Examples B'-1 to B'-2]  Polymer (B)

Preparation Examples B-1 to B-4 and Comparative Preparation Examples B’-1 to B’-2 are used to prepare polymer (B) by a method similar to that of Preparation Example A-1, except that the types and amounts of the components are changed in Preparation Examples B-1 to B-4 and Comparative Preparation Examples B’-1 to B’-2, as shown in Table 2.

[Example 1] Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element for optical alignment method

Weigh 50 parts by weight of the polymer (A) of Preparation Example A-4, 50 parts by weight of the polymer (B) of Preparation Example B-4, and 800 parts by weight of NMP [as a solvent (C)], and stir and mix them at room temperature to prepare a liquid crystal alignment agent for the photoalignment method.

The liquid crystal alignment agent used in the photo-alignment method is rotationally coated on a glass substrate, and a pixel electrode is formed on the glass substrate, wherein the pixel electrode is an IPS driving electrode having a pair of ITO electrodes (electrode width is 10μm, electrode spacing is 10μm, and electrode height is 50nm), and the pair of ITO electrodes have a comb-like shape respectively, and the comb-like parts of each other are configured in a separated and interlocking manner. Then, the glass substrate coated with the liquid crystal alignment agent for the photo-alignment method was dried on a heating plate at 80°C for 3 minutes, and then baked in a hot air circulation oven at 250°C for 30 minutes to form a film with a thickness of 100 nm of the liquid crystal alignment agent for the photo-alignment method.

The film is irradiated with ultraviolet light of 254 nm through a polarizing plate, and then baked in a hot air circulation oven at 250° C. for 30 minutes to form a liquid crystal alignment film on the film, thereby obtaining a first composite substrate having the liquid crystal alignment film and the glass substrate. Similarly, a glass substrate without electrodes and having columnar spacers of 4 μm in height is taken as an opposing substrate, and a liquid crystal alignment agent for the optical alignment method is coated on the opposing substrate, and the liquid crystal alignment agent for the optical alignment method is formed into a film, and then an alignment treatment is applied to the film to form a liquid crystal alignment film on the film, thereby obtaining a second composite substrate including the liquid crystal alignment film and the opposing substrate.

The first composite substrate and the second composite substrate are used as a set, and a sealant is printed on one of them, and the other is bonded in a manner that the liquid crystal alignment film faces each other and the alignment direction is 0°, and then the sealant is hardened to produce an empty cell. This empty cell is injected with liquid crystal MLC-2041 (Merck) by a reduced pressure injection method, and the injection port is sealed to produce a liquid crystal display element. The liquid crystal display element is evaluated by the following evaluation method, and the results are shown in Table 3.

[Examples 2 to 12 and Comparative Examples 1 to 4] Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element for optical alignment method

Examples 2 to 12 and Comparative Examples 1 to 4 are used to obtain a liquid crystal alignment agent, a liquid crystal alignment film and a liquid crystal display element for the optical alignment method by a method similar to that of Example 1, with the difference being that Examples 2 to 12 and Comparative Examples 1 to 4 change the type and amount of polymer (A) and polymer (B) in the liquid crystal alignment agent for the optical alignment method, as shown in Tables 3 to 4.

[Evaluation Items]

The following description takes the liquid crystal display element of Example 1 as an example, and the liquid crystal display elements of other Examples 2 to 12 and Comparative Examples 1 to 4 are carried out in the same manner.

《Flicker degree after high voltage drive》

The liquid crystal display element of Example 1 is placed between two polarizing plates whose polarization axes are arranged in a vertically crossed manner. The LED backlight source is lit without applying voltage, and the arrangement angle of the liquid crystal display element of Example 1 is adjusted so that the brightness of the transmitted light reaches the minimum state. Then, an alternating voltage with a frequency of 30 Hz is applied to the liquid crystal display element of Example 1, and the V-T curve (voltage-transmittance curve) is measured at the same time, and the alternating voltages with relative transmittances of 23% and 100% are calculated as driving voltages.

The method for measuring the flicker degree of the liquid crystal display element of Example 1 after high-voltage driving is, under the temperature condition that the temperature of the liquid crystal display element of Example 1 is 23°C, the turned-on LED backlight source is turned off, after being placed in a light-proof state for 72 hours, the LED backlight source is turned on again, and at the same time when the LED backlight source starts to be turned on, an AC voltage with a relative transmittance of 100% and a frequency of 30 Hz is applied to the liquid crystal display element of Example 1, so that after the liquid crystal display element of Example 1 is driven for 24 hours, an AC voltage with a relative transmittance of 23% and a frequency of 30 Hz is applied to the liquid crystal display element of Example 1, and the flicker amplitude of the liquid crystal display element of Example 1 is tracked. The flicker amplitude of the liquid crystal display element of the embodiment 1 is obtained by using a data acquisition/data recording switching device 34970A (manufactured by Agilent technologies) connected to a photodiode and an I-V conversion amplifier to read the brightness value of the liquid crystal display element of the embodiment 1 through two polarizing plates. The flicker degree (FL) of the liquid crystal display element of the embodiment 1 is calculated according to the following formula (V) using the flicker amplitude and the brightness value. Flicker degree (FL, %) = [Flicker amplitude/(2×brightness value)]×100%        Formula (V)

Among them, the lower the flicker (FL), the better the quality of the LCD display element. The judgment standard of flicker is as follows. ※: FL＜3%. ◎: 3%≦FL＜3.5%. ○: 3.5%≦FL＜4%. △: 4%≦FL＜5%. ╳: FL≧5%.

Table 1 Unit: mole% Preparation example Comparison of preparation examples A-1 A-2 A-3 A-4 A-5 A-6 A'-1 A'-2 Tetracarboxylic dianhydride component (a1) a1-1-1 30 100 70 -- -- -- 30 -- a1-1-2 -- -- -- -- 40 10 -- 40 a1-1-3 -- -- -- 50 -- 20 -- -- a1-2-1 70 -- 30 50 -- 70 70 -- a1-2-2 -- -- -- -- 60 -- -- 60 Diamine component (a2) a2-1-1 5 25 40 60 30 20 -- -- a2-2-1 50 -- -- -- -- 30 55 30 a2-2-2 -- 40 -- -- 35 -- -- 35 a2-2-3 -- 20 -- -- -- 10 -- -- a2-2-4 -- -- 35 -- -- -- -- -- a2-2-5 -- -- -- -- -- -- -- -- a2-3-1 35 -- -- -- 30 -- 35 30 a2-3-2 -- 15 -- 5 -- 40 -- -- a2-4-1 -- -- -- 35 5 -- -- 5 a2-4-2 10 -- 25 -- -- -- 10 -- Note: "--" means not added. a1-1-1: a1-1-2: a1-1-3: a1-2-1: a1-2-2: a2-1-1: a2-2-1: a2-2-2: a2-2-3: a2-2-4: p-phenylenediamine a2-2-5: a2-3-1: a2-3-2: a2-4-1: 4,4'-diaminodiphenylmethane a2-4-2: 4,4'-diaminodiphenyl ether

Table 2 Unit: mole% Preparation example Comparison of preparation examples B-1 B-2 B-3 B-4 B'-1 B'-2 Tetracarboxylic dianhydride component (b1) b1-1-1 100 -- -- -- 100 -- b1-1-2 -- 50 -- -- -- -- b1-1-3 -- -- 30 -- -- -- b1-2-1 -- 50 -- 100 -- 100 b1-2-2 -- -- 70 -- -- -- Diamine component (b2) b2-1-1 3 40 70 100 -- -- b2-2-1 60 -- -- -- 60 -- b2-2-2 -- 40 -- -- -- -- b2-2-3 -- -- 10 -- -- -- b2-2-4 -- -- -- -- -- -- b2-2-5 -- 10 -- -- -- -- b2-3-1 37 -- 20 -- 40 100 b2-3-2 -- 10 -- -- -- -- Note: "--" means not added. b1-1-1: b1-1-2: b1-1-3: b1-2-1: b1-2-2: b2-1-1: b2-2-1: b2-2-2: b2-2-3: b2-2-4: b2-2-5: b2-3-1: 4,4'-diaminodiphenylmethane b2-3-2: 4,4'-diaminodiphenyl ether

Table 3 Unit: weight Embodiment 1 2 3 4 5 6 7 8 9 10 11 12 Polymer (A) Preparation example A-1 -- -- -- 50 -- -- 50 -- -- -- -- -- A-2 -- -- -- -- 50 -- -- 30 -- -- -- -- A-3 -- -- -- -- -- 50 -- 20 50 -- -- -- A-4 50 -- -- -- -- -- -- -- -- 50 -- 10 A-5 -- 50 -- -- -- -- -- -- -- -- 50 -- A-6 -- -- 50 -- -- -- -- -- -- -- -- 40 Polymer (B) Preparation example B-1 -- -- -- -- -- -- 50 -- 20 50 -- -- B-2 -- -- -- -- -- -- -- 50 -- -- 40 -- B-3 -- -- -- -- -- -- -- -- 30 -- 10 50 B-4 50 50 50 50 50 50 -- -- -- -- -- -- Flicker after high voltage drive ○ ○ ○ ◎ ◎ ◎ ※ ※ ※ ◎ ◎ ◎ Note: "--" means not added.

Table 4 Unit: weight Comparative example 1 2 3 4 Polymer (A) Preparation example A-1 -- -- 50 -- A-2 -- 50 -- -- A-3 -- -- -- -- A-4 -- -- -- -- A-5 -- -- -- -- A-6 -- -- -- -- Comparison of preparation examples A'-1 -- -- -- 50 A'-2 50 -- -- -- Polymer (B) Preparation example B-1 -- -- -- 50 B-2 -- -- -- -- B-3 -- -- -- -- B-4 50 -- -- -- Comparison of preparation examples B'-1 -- -- 50 -- B'-2 -- 50 -- -- Flicker after high voltage drive ╳ ╳ ╳ ╳ Note: "--" means not added.

Referring to Tables 1 to 3, Preparation Examples A-1 to A-6 use compound a2-1-1 to prepare polymer (A), that is, Preparation Examples A-1 to A-6 use diamine compound (a2-1) to prepare polymer (A), and Preparation Examples B-1 to B-4 use compound b2-1-1 to prepare polymer (B), that is, Preparation Examples B-1 to B-4 use diamine compound (b2-1) to prepare polymer (B). Therefore, the liquid crystal used in the photoalignment method of Examples 1 to 12 is The alignment agent is added to the polymers (A) of Preparation Examples A-1 to A-6 and the polymers (B) of Preparation Examples B-1 to B-4. Therefore, the liquid crystal alignment film formed by the liquid crystal alignment agent used in the optical alignment method of Examples 1 to 12 can give the liquid crystal display element a high-voltage-driven post-flicker degree of less than 4%. That is to say, the liquid crystal alignment film formed by the liquid crystal alignment agent used in the optical alignment method of Examples 1 to 12 can effectively reduce the high-voltage-driven post-flicker degree of the liquid crystal display element.

Furthermore, the liquid crystal alignment agent used in the photo-alignment method of Examples 4 to 6 is added with a polymer (A) of at least one of Preparation Examples A-1 to A-3, and the polymers (A) of Preparation Examples A-1 to A-3 are particularly prepared using compound a1-1-1. Therefore, the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photo-alignment method of Examples 4 to 6 can further reduce the flicker after high-voltage driving of the liquid crystal display element, so the liquid crystal display element of Examples 4 to 6 has a flicker after high-voltage driving of less than 3.5%. The liquid crystal alignment agent used in the photo-alignment method of Examples 10 to 12 is prepared by adding a polymer (B) of at least one of Preparation Examples B-1 to B-3, and the polymers (B) of Preparation Examples B-1 to B-3 are particularly prepared by using compounds b1-1-1 to b1-1-3 in combination with compounds b2-2-1 to b2-2-5, that is, they are prepared by using a tetracarboxylic dianhydride compound (b1-1) in combination with a diamine compound (b2-2). Therefore, the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photo-alignment method of Examples 10 to 12 can further reduce the flicker degree of the liquid crystal display element after high-voltage driving, so the liquid crystal display element of Examples 10 to 12 has a flicker degree after high-voltage driving of less than 3.5%.

Furthermore, the liquid crystal alignment agent used in the photo-alignment method of Examples 7 to 9 is prepared by combining the polymer (A) of at least one of Examples A-1 to A-3 with the polymer (B) of at least one of Examples B-1 to B-3. Therefore, the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photo-alignment method of Examples 7 to 9 can further reduce the flicker degree of the liquid crystal display element after high-voltage driving. Therefore, the liquid crystal display element of Examples 7 to 9 has a flicker degree after high-voltage driving of less than 3%.

Referring to Tables 1 to 2 and Table 4, in contrast to Comparative Examples 1 to 4, the liquid crystal alignment agents used in the optical alignment method of Comparative Examples 1 and 4 are respectively added with the polymer (A) of Comparative Preparation Example A’-2 and the polymer (A) of Comparative Preparation Example A’-1, and neither the polymer (A) of Comparative Preparation Example A’-2 nor the polymer (A) of Comparative Preparation Example A’-1 are prepared using compound a2-1-1, that is, neither Comparative Preparation Example A’-2 nor Comparative Preparation Example A’-1 uses diamine compound (a2-1) to prepare polymer (A), so the flicker degree of the liquid crystal display elements of Comparative Examples 1 and 4 after high voltage driving is more than 5%. The liquid crystal alignment agents used in the photoalignment method of Comparative Examples 2 and 3 are respectively added with the polymer (B) of Comparative Preparation Example B’-2 and the polymer (B) of Comparative Preparation Example B’-1, and neither the polymer (B) of Comparative Preparation Example B’-2 nor the polymer (B) of Comparative Preparation Example B’-1 are prepared using compound b2-1-1, that is, neither Comparative Preparation Example B’-2 nor Comparative Preparation Example B’-1 uses diamine compound (b2-1) to prepare polymer (B), so the flicker degree of the liquid crystal display elements of Comparative Examples 2 and 3 after high voltage driving is greater than 5%.

In summary, the liquid crystal alignment film formed by the liquid crystal alignment agent used in the photo-alignment method of the present invention by using the polymer (A) prepared by the polyimide precursor having the structure represented by the formula (I) and the polymer (B) prepared by using the polyimide precursor having the structure represented by the formula (II) can effectively reduce the flicker degree of the liquid crystal display element after high-voltage driving, so the purpose of the present invention can be achieved.

However, the above is only an embodiment of the present invention and should not be used to limit the scope of implementation of the present invention. All simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the patent specification are still within the scope of the present patent.

Claims (9)

A liquid crystal alignment agent for photo-alignment method, comprising: a polymer (A), at least one polymer selected from the group consisting of a polyimide precursor and an imidized polymer of the polyimide precursor, wherein the polyimide precursor of the polymer (A) comprises a structure represented by the following formula (I): (I) In the formula (I), _X1 is at least one selected from the group consisting of the structures represented by the following formulae (I-1) to (I-7), wherein "*" represents a bonding position; _X2 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; (I-1), (I-2), (I-3), (I-4), (I-5), (I-6), (I-7); in the formula (I-1), _X11 , _X12 , _X13 and _X14 independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms and containing a fluorine atom, or a phenyl group; and in the formula (I-7), _X15 and _X16 independently represent a hydrogen atom or a methyl group; a polymer (B), at least one polymer selected from the group consisting of a polyimide precursor and an imidized polymer of the polyimide precursor, wherein the polyimide precursor of the polymer (B) comprises a structure represented by the following formula (II): (II) In the formula (II), X ₃ represents a tetravalent organic group; X ₄ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and a solvent (C). The liquid crystal alignment agent for photo-alignment method as described in claim 1, wherein the polymer (A) is obtained by reacting a tetracarboxylic dianhydride component (a1) and a diamine component (a2), and the diamine component (a2) comprises a compound of the following formula (A21): (A21). The liquid crystal alignment agent for photo-alignment method as described in claim 1, wherein the polymer (B) is obtained by reacting a tetracarboxylic dianhydride component (b1) and a diamine component (b2), and the diamine component (b2) comprises a compound of the following formula (B21): (B21). The liquid crystal alignment agent for photo-alignment method as described in claim 1, wherein _X1 represents a structure shown in the following formula (I-1-1) to formula (I-1-6): (I-1-1), (I-1-2), (I-1-3), (I-1-4), (I-1-5), (I-1-6). The liquid crystal alignment agent for photo-alignment method as described in claim 4, wherein _X1 represents a structure as shown in formula (I-1-1): (I-1-1). The liquid crystal alignment agent for photo-alignment method as described in claim 1, wherein the polymer (B) is obtained by reacting a tetracarboxylic dianhydride component (b1) and a diamine component (b2), and the tetracarboxylic dianhydride component (b1) comprises a structure shown in the following formula (III): (III) In the formula (III), Z ₁₁ represents a single bond; and “*” represents a bonding position. A liquid crystal alignment agent for photo-alignment method as described in claim 1, wherein the polyimide precursor of the polymer (B) is obtained by reacting a tetracarboxylic dianhydride component (b1) and a diamine component (b2), and the diamine component (b2) contains a diamine compound having at least one nitrogen-containing atom structure selected from the group consisting of a nitrogen-containing heterocyclic ring, a diamine group and a tertiary amine group. A liquid crystal alignment film is formed using a liquid crystal alignment agent used in a photo-alignment method as described in any one of claims 1 to 7. A liquid crystal display element comprises a liquid crystal alignment film as described in claim 8.