JP7786366B2 - Polyimide Varnish - Google Patents

Description

The present invention relates to a polyimide varnish that has a diphenylamine skeleton and can produce a polyimide film with high film transmittance.

Polyimides are widely used as protective materials in the electrical and electronic fields due to their high mechanical strength, heat resistance, and solvent resistance. Specifically, when used as a liquid crystal alignment film for liquid crystal displays, a 0.05 to 0.2 μm thick polyimide coating film is generally formed on a transparent support substrate with a transparent electrode, and a thin polyimide coating film is then formed on various support substrates.
To form a polyimide coating film, a polyimide varnish in which a polyimide (precursor) is dissolved in a suitable organic solvent is generally applied to a supporting substrate by a method such as spin coating, offset printing, gravure printing, flexographic printing, or inkjet printing, followed by a heat treatment.
In recent years, from the viewpoint of imparting various properties to liquid crystal alignment films, polyimides having a diphenylamine skeleton have been proposed in Patent Documents 1 and 2.

WO2004/021076 publication WO2013/008822 publication

It has been revealed that polyimides containing a diphenylamine skeleton tend to produce films with reduced transmittance, and that this is easily affected by the raw material monomers used in the polymerization reaction. The inventors' investigations revealed that polyimides produced using specific alicyclic tetracarboxylic dianhydrides produced films with significantly reduced transmittance. After investigating various causes, it was found that film transmittance decreases when the polyimide (precursor) adopts a specific molecular arrangement. It has also been revealed that the structure of the imide precursor during heat treatment is one of the factors that induces discoloration.

In view of the above circumstances, the object of the present invention is to provide a polyimide varnish that can produce a polyimide film with high film transmittance even when using a polyimide having a diphenylamine skeleton.

As a result of intensive research into achieving the above-mentioned objectives, the inventors discovered that a polyimide varnish containing a specific block copolymer is effective in achieving the above-mentioned objectives, leading to the completion of the present invention.

The present invention is based on this finding and has the following gist.
A polyimide varnish containing at least one block copolymer selected from the group consisting of a polyimide precursor having a block (b1) having a repeating unit represented by the following formula (1) and a block (b2) having a repeating unit represented by the following formula (2), and a polyimide obtained by imidizing the polyimide precursor:
( _X1 represents a tetravalent organic group. _X2 represents a tetravalent organic group derived from an acyclic aliphatic tetracarboxylic dianhydride or a tetravalent organic group represented by the following formula (X2). _Y1 represents a divalent organic group having 3 to 50 carbon atoms and not having a diphenylamine skeleton. _Y2 represents a divalent organic group having a diphenylamine skeleton. Two _R1s and _R2s each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Two _Z1s and _Z2s each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms which may have a substituent, an alkenyl group having 2 to 10 carbon atoms which may have a substituent, an alkynyl group having 2 to 10 carbon atoms which may have a substituent, a tert-butoxycarbonyl group, or a 9-fluorenylmethoxycarbonyl group.)
(R ²¹ to R ²⁴ each independently represent a hydrogen atom, a methyl group, an ethyl group, a propyl group, a chlorine atom, or a phenyl group.)

In this specification, * represents a bond in all cases. Boc represents a tert-butoxycarbonyl group. Furthermore, in this specification, halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

The polyimide varnish of the present invention can obtain a polyimide film with high film transmittance even when a polyimide having a diphenylamine skeleton is used. Furthermore, the polyimide varnish of the present invention can obtain a polyimide film with high film transmittance, while also enabling good polyimide film properties in other respects (e.g., voltage holding ratio, residual DC voltage, afterimage characteristics, rubbing resistance). Furthermore, the present invention provides a method for producing the polyimide varnish.
The mechanism by which the above-described effects of the present invention are obtained is not entirely clear, but the following is thought to be one of the reasons.
That is, the reaction of a diamine component having a diphenylamine skeleton with an acyclic aliphatic tetracarboxylic dianhydride or a specific alicyclic tetracarboxylic dianhydride component proceeds at a relatively low temperature, and therefore coloration due to oxidation of the diamine component in the reaction system can be suppressed compared to a reaction at a high temperature. Furthermore, a film using a polyimide precursor obtained by using a diamine having a diphenylamine skeleton with an acyclic aliphatic tetracarboxylic dianhydride or a specific alicyclic tetracarboxylic dianhydride is easily thermally imidized during heat treatment, and therefore the donor property of the amine can be reduced, and a polyimide film with high film transmittance can be obtained.

FIG. 1 is a diagram showing the transmittance obtained by using the liquid crystal aligning agent (A-1) of Example 1 and the liquid crystal aligning agent (B-1) of Comparative Example 1.

<Block copolymer>
The polyimide varnish of the present invention contains at least one block copolymer selected from the group consisting of a polyimide precursor having a block (b1) having a repeating unit represented by the following formula (1) and a block (b2) having a repeating unit represented by the following formula (2), and a polyimide obtained by imidizing the polyimide precursor: That is, the polyimide varnish of the present invention contains at least one block copolymer selected from the group consisting of a polyimide precursor having the above block (b1) and block (b2) but no imide ring structure, and a polyimide obtained by imidizing the polyimide precursor, the polyimide precursor having the imidized repeating unit represented by the above formula (1), the imidized repeating unit represented by the above formula (2), or another imidized repeating unit.
( _X1 represents a tetravalent organic group. _X2 represents a tetravalent organic group derived from an acyclic aliphatic tetracarboxylic dianhydride or a tetravalent organic group represented by the following formula (X2). _Y1 represents a divalent organic group having 3 to 50 carbon atoms and not having a diphenylamine skeleton. _Y2 represents a divalent organic group having a diphenylamine skeleton. Two _R1s and _R2s each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Two _Z1s and _Z2s each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms which may have a substituent, an alkenyl group having 2 to 10 carbon atoms which may have a substituent, an alkynyl group having 2 to 10 carbon atoms which may have a substituent, a tert-butoxycarbonyl group, or a 9-fluorenylmethoxycarbonyl group.)
(R ²¹ to R ²⁴ each independently represent a hydrogen atom, a methyl group, an ethyl group, a propyl group, a chlorine atom, or a benzene ring.)

In formula (1), _X1 preferably represents a tetravalent organic group derived from a tetracarboxylic dianhydride, and more preferably represents at least one selected from the group consisting of structures represented by the following formulae (X1-1) to (X1-12):

In formula (1), _Y1 preferably represents a divalent organic group having 3 to 50 carbon atoms and having a structure represented by any of the following formulae (S1) to (S3), or a divalent organic group having 3 to 50 carbon atoms and not having a structure represented by any of the formulae (S1) to (S3). Note that, as described above, the divalent organic group having 3 to 50 carbon atoms and having a structure represented by any of the formulae (S1) to (S3) and the divalent organic group having 3 to 50 carbon atoms and not having a structure represented by any of the formulae (S1) to (S3) do not have a diphenylamine skeleton. Specific examples of divalent organic groups having 3 to 50 carbon atoms and not having the structure represented by the formulas (S1) to (S3) include divalent organic groups having a nitrogen-containing heterocycle in the molecule, such as the following formulas (2a-1) to (2a-14), divalent organic groups having radical initiation function, such as the following formulas (2b-1) to (2b-5), divalent organic groups having a carboxy group, such as the following formulas (2c-1) to (2c-2), groups having a group "-N (D) -" (D represents a tert- butoxycarbonyl group), such as the following formulas (2d-1) to (2d-7), groups having photoalignment properties, such as the following formulas (2e-1) to (2e-11), divalent organic groups having an oxygen-containing heterocycle, such as (2f-1) to (2f-3), or divalent organic groups derived from aromatic diamines having no side chain groups having 3 or more carbon atoms, such as the following formulas (2-1) to (2-35).
( ^X1 and ^X2 each independently represent a single bond, -( _CH2 ) _a- (a is an integer of 1 to 15), -CONH-, -NHCO-, -CON( _CH3 )-, -NH-, -O-, -COO-, -OCO-, or -(( _CH2 ) _a1 - _A1 ) _m1- . In these, a1's each independently represent an integer of 1 to 15, _A1 's each independently represent an oxygen atom or -COO-, and _m1 is 1 or 2. ^G1 and ^G2 each independently represent a divalent cyclic group selected from divalent aromatic groups having 6 to 12 carbon atoms and divalent alicyclic groups having 3 to 8 carbon atoms. Any hydrogen atom on the cyclic group may be substituted. m and n each independently represent an integer of 0 to 3, and m+n is 1 to 4. R ¹ represents an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or an alkoxyalkyl group having 2 to 20 carbon atoms, and any hydrogen atom forming R ¹ may be substituted with a fluorine atom. When m, n, and m1 are 2 or more, the multiple occurrences of X ¹ , X ² , G ¹ , G ² , a1, m1, and A ₁ each independently have the definitions above. Examples of the substituent that may be substituted with any hydrogen atom on the cyclic group include a halogen atom, a halogen-atom-containing alkyl group, a halogen-atom-containing alkoxy group, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and a heteroatom-containing group in which any carbon-carbon bond in the halogen-atom-containing alkyl group, halogen-atom-containing alkoxy group, alkyl group, alkoxy group, and alkenyl group is interrupted with an oxygen atom.
( ^X3 represents a single bond, -CONH-, -NHCO-, -CON( _CH3 )-, -NH-, -O-, _-CH2O- , -COO- or -OCO-. ^R2 represents an alkyl group having 1 to 20 carbon atoms or an alkoxyalkyl group having 2 to 20 carbon atoms, and any hydrogen atom forming ^R2 may be substituted with a fluorine atom.)
( ^X4 represents —CONH—, —NHCO—, —O—, —CH ₂ O—, —COO— or —OCO—. ^R3 represents a structure having a steroid skeleton.)

In formula (1), from the viewpoint of increasing the transmittance of the resulting polyimide film, at least one of _Y1 is preferably a divalent organic group having a structure represented by any of formulas (S1) to (S3), a divalent organic group having a nitrogen-containing heterocycle in the molecule, or a divalent organic group represented by any of formulas (2-1) to (2-35). Specific examples of the divalent organic group having a structure represented by any of formulas (S1) to (S3) above include groups obtained by removing two amino groups from diamines represented by formulas (Ys-1) to (Ys-13) below.

(In the formula, X ^v1 to X ^v4 and X ^p1 to X ^p8 each independently represent —(CH ₂ ) _a — (a is an integer of 1 to 15), —CONH—, —NHCO—, —CO—N(CH ₃ )—, —NH—, —O—, —CH ₂ O—, —CH ₂ —OCO—, —COO—, or —OCO—; X ^v5 represents —O—, —CH ₂ O—, —CH ₂ —OCO—, —COO—, or —OCO—; X ^v6 to X ^v7 and X ^s1 to X ^s4 each independently represent —O—, —CH ₂ O—, —COO—, or —OCO—; and _{X a} to X _f each independently represent a single bond, —O—, —NH—, or —O—(CH ₂ ) _m represents —O—, and R ^v1 to R ^v4 and R ^1a to R ^1h each independently represent —C _n H _2n+1 (n is an integer of 1 to 20) or —O—C _n H _2n+1 (n is an integer of 2 to 20). m represents an integer of 1 to 8.

In formula (1), preferably, two R ₁ 's each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Preferably, two Z ₁ 's each independently represent a hydrogen atom or a methyl group.

In formula (1), each of X ₁ , Y ₁ , R ₁ and Z ₁ may be one type or two or more types.
The block (b1) having the repeating unit represented by formula (1) may have any repeating unit other than the repeating unit represented by formula (1).
The content of the repeating unit represented by formula (1) is preferably 5 to 90 mol %, more preferably 10 to 80 mol %, and particularly preferably 20 to 70 mol %, based on the total repeating units contained in block (b1) and block (b2).

In formula (2), the "acyclic aliphatic tetracarboxylic acid dianhydride" of _X2 is an acid dianhydride obtained by intramolecular dehydration of four carboxy groups bonded to a chain hydrocarbon structure. However, it does not have to be composed only of a chain hydrocarbon structure, and may partially contain an alicyclic structure or an aromatic ring structure.
Specific examples of the "acyclic aliphatic tetracarboxylic acid dianhydride" include the following compound (T _2a ).
(X _2a represents at least one selected from the group consisting of structures represented by the following formulas (X _2a -1) to (X _2a -5).)

In formula (2), _X2 preferably represents at least one selected from the group consisting of structures represented by the following formulae (X2-1) to (X2-4).

In formula (2), _Y2 preferably represents a structure represented by the following formula (d2).
(A ₁ represents a single bond, —NR— (R represents a hydrogen atom or a monovalent organic group), —O—, —C(═O)—, —C(═O)NR— (R represents a hydrogen atom or a monovalent organic group), —C(═O)O—, or a divalent organic group. R ₁ and R ₂ each independently represent a hydrogen atom or a monovalent organic group. When n is 2, multiple A _1s and R _2s each independently have the above definition.)

Examples of the divalent organic group for _A1 include _-CH2- , -C( _CH3 ) _2- , an alkylene group having 2 to 20 carbon atoms, and a divalent organic group in which some of the methylene groups in the alkylene group have been replaced with -NR- (R represents a hydrogen atom or a monovalent organic group), -O-, -C(=O)-, -C(=O)NR- (R represents a hydrogen atom or a monovalent organic group), or -C(=O)O-.

Examples of the monovalent organic group in formula (d2) include alkyl groups having 1 to 10 carbon atoms, such as methyl and ethyl groups; alkyl groups having 1 to 10 carbon atoms and containing a halogen atom, such as trifluoroalkyl groups; alkoxyalkyl groups having 1 to 10 carbon atoms; groups containing a thermally eliminable group; and groups in which some of the methylene groups in the alkyl group have been replaced with -O-, -C(=O)-, or -C(=O)NR- (where R represents a hydrogen atom or a methyl group) (excluding the above-mentioned groups containing a thermally eliminable group). Examples of groups containing a thermally eliminable group include carbamate protecting groups such as tert-butoxycarbonyl (Boc), benzyloxycarbonyl, 9-fluorenylmethyloxycarbonyl, and allyloxycarbonyl; and groups in which some of the hydrogen atoms in the alkyl group have been replaced with the group "*-O-E" (where E represents a hydrogen atom or a carbamate protecting group).

More preferred structures for _Y2 include the following formulae (d2-1) to (d2-13).

In formula (2), preferably, two _R2s each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Preferably, two _Z2s each independently represent a hydrogen atom or a methyl group.

In formula (2), X ₂ , Y ₂ , R ₂ and Z ₂ may each be one type or two or more types.
The block (b2) having the repeating unit represented by formula (2) may have any repeating unit other than the repeating unit represented by formula (2).
The content of the repeating unit represented by formula (2) is preferably 5 to 90 mol %, more preferably 10 to 80 mol %, and particularly preferably 20 to 70 mol %, based on the total repeating units contained in block (b1) and block (b2).

The ratio of the total number of moles of repeating units represented by formula (1) to the total number of moles of repeating units represented by formula (2) per molecule of the block copolymer of the present invention is preferably 9:1 to 1:9, more preferably 8:2 to 2:8, and particularly preferably 7:3 to 3:7.
When the ratio of the total number of moles of repeating units is within this range, the film is excellent in terms of achieving high transmittance.
The block copolymer of the present invention may have any repeating unit other than the block (b1) having the repeating unit represented by formula (1) and the block (b2) having the repeating unit represented by formula (2).

<Production of Polyimide Precursor (Polyamic Acid)>
The polyimide precursor used in the present invention includes polyamic acid, polyamic acid ester, and the like.

The polyamic acid, which is a polyimide precursor used in the present invention, can be produced, for example, by a production method including the following steps (I) and (II): step (I) of reacting a tetracarboxylic acid component containing a tetracarboxylic acid dianhydride represented by the following formula (1-T) or a derivative thereof with a diamine component containing a diamine represented by the following formula (1-D) to obtain a block (b1);
Step (II) of adding a tetracarboxylic acid component containing a tetracarboxylic dianhydride represented by the following formula (2-T) or a derivative thereof and a diamine component containing a diamine represented by the following formula (2-D) to the block (b1) and reacting them to obtain a polyimide precursor containing the block (b1) and the block (b2).
(X ₁ , X ₂ , Y ₁ , and Y ₂ are the same as defined in formulas (1) and (2).)

In the above, examples of derivatives of tetracarboxylic dianhydrides include tetracarboxylic acids, tetracarboxylic dihalides, tetracarboxylic diester dichlorides, tetracarboxylic diesters, etc.

The reaction temperature in step (II) is preferably lower than the reaction temperature in step (I), more preferably at least 10° C. lower than the reaction temperature in step (I), and particularly preferably at least 20° C. lower than the reaction temperature in step (I). A polyimide varnish containing a block copolymer obtained by reaction within the above range can produce a polyimide film with high film transmittance because high temperatures are not required for heating and oxidation during the reaction can be suppressed.
Preferably, the reaction temperature in the step (I) is 0 to 150° C., and the reaction temperature in the step (II) is −20 to 130° C. More preferably, the reaction temperature in the step (I) is 5 to 100° C., and the reaction temperature in the step (II) is −5 to 80° C.

The tetracarboxylic acid component in step (I) may contain any tetracarboxylic acid dianhydride or derivative thereof other than the tetracarboxylic acid dianhydride represented by formula (1-T) or a derivative thereof, but preferably consists of the tetracarboxylic acid dianhydride represented by formula (1-T) or a derivative thereof.
The diamine component in step (I) may contain any diamine other than the diamine represented by formula (1-D) above, but preferably consists of the diamine represented by formula (1-D) above.
The tetracarboxylic acid component in step (II) may contain any tetracarboxylic acid dianhydride or derivative thereof other than the tetracarboxylic acid dianhydride represented by the formula (2-T) or a derivative thereof, but preferably consists of the tetracarboxylic acid dianhydride represented by the formula (2-T) or a derivative thereof.
The diamine component in step (II) may contain any diamine other than the diamine represented by formula (2-D) above, but preferably consists of the diamine represented by formula (2-D) above.

The polyamic acid, which is a polyimide precursor used in the present invention, can also be produced, for example, by a production method including the following steps (III) to (V).
a step (III) of reacting a tetracarboxylic acid component containing a tetracarboxylic dianhydride represented by the following formula (1-T) or a derivative thereof with a diamine component containing a diamine represented by the following formula (1-D) to obtain a block (b1);
a step (IV) of reacting a tetracarboxylic acid component containing a tetracarboxylic acid dianhydride represented by the following formula (2-T) or a derivative thereof with a diamine component containing a diamine represented by the following formula (2-D) to obtain a block (b2);
Step (V) of coupling the block (b1) obtained in step (III) with the block (b2) obtained in step (IV) to obtain a polyimide precursor containing the block (b1) and the block (b2).
(X ₁ , X ₂ , Y ₁ , and Y ₂ are the same as defined in formulas (1) and (2).)

The reaction temperature in step (IV) is preferably lower than the reaction temperature in step (III), more preferably at least 10° C. lower than the reaction temperature in step (III), and particularly preferably at least 20° C. lower than the reaction temperature in step (III). A polyimide varnish containing a block copolymer obtained by reaction within the above range can produce a polyimide film with high film transmittance because high temperatures are not required for heating and oxidation during the reaction can be suppressed.
Preferably, the reaction temperature in the step (III) is 0 to 150° C., and the reaction temperature in the step (IV) is −20 to 130° C. More preferably, the reaction temperature in the step (III) is 5 to 100° C., and the reaction temperature in the step (IV) is −5 to 80° C.

The tetracarboxylic acid component in step (III) may contain any tetracarboxylic acid dianhydride or derivative thereof other than the tetracarboxylic acid dianhydride represented by formula (1-T) or a derivative thereof, but preferably consists of the tetracarboxylic acid dianhydride represented by formula (1-T) or a derivative thereof.
The diamine component in step (III) may contain any diamine other than the diamine represented by formula (1-D) above, but preferably consists of the diamine represented by formula (1-D) above.
The tetracarboxylic acid component in the step (IV) may contain any tetracarboxylic acid dianhydride or derivative thereof other than the tetracarboxylic acid dianhydride represented by the formula (2-T) or a derivative thereof, but preferably consists of the tetracarboxylic acid dianhydride represented by the formula (2-T) or a derivative thereof.
The diamine component in step (IV) may contain any diamine other than the diamine represented by formula (2-D) above, but preferably consists of the diamine represented by formula (2-D) above.

The method for coupling block (b1) and block (b2) in step (V) is not particularly limited, but examples include: (1) a method in which, when the termini of blocks (b1) and (b2) are acid anhydride groups or derivatives thereof, a diamine is added and further reacted; (2) a method in which, when the termini of blocks (b1) and (b2) are amine terminals, a tetracarboxylic acid dianhydride or a derivative thereof is added and further reacted; and (3) a method in which, when blocks (b1) and (b2) have both an acid anhydride group or a derivative thereof and an amine terminal, block (b1) and block (b2) are reacted.

The reaction between the diamine component and the tetracarboxylic acid component is usually carried out in an organic solvent. The organic solvent used in this reaction is not particularly limited as long as it dissolves the produced polyimide precursor. Specific examples of organic solvents used in the reaction include, but are not limited to, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and 1,3-dimethyl-2-imidazolidinone.
When the polyimide precursor has high solubility, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone, or an organic solvent represented by the following formulas [D-1] to [D-3] can be used.
In formula [D-1], ^D1 represents an alkyl group having 1 to 3 carbon atoms, in formula [D-2], ^D2 represents an alkyl group having 1 to 3 carbon atoms, and in formula [D-3], ^D3 represents an alkyl group having 1 to 4 carbon atoms.
These organic solvents may be used alone or in combination. Furthermore, even if a solvent does not dissolve the polyimide precursor, it may be mixed with the above-mentioned solvent to the extent that the resulting polyimide precursor does not precipitate.

The concentration of polyamic acid in the reaction system is preferably 1 to 30% by mass, more preferably 5 to 20% by mass, as this makes it less likely for polymer precipitation to occur and makes it easier to obtain a high molecular weight product.

The polyamic acid obtained as described above can be recovered by pouring the reaction solution into a poor solvent while stirring thoroughly, thereby precipitating the polymer. Alternatively, purified polyamic acid powder can be obtained by repeating the precipitation process several times, washing with a poor solvent, and then drying at room temperature or by heating. The poor solvent is not particularly limited, but examples include water, methanol, ethanol, hexane, butyl cellosolve, acetone, and toluene.

<Production of Polyimide Precursor (Polyamic Acid Ester)>
The polyamic acid ester, which is the polyimide precursor used in the present invention, can be produced, for example, by (1) an esterification reaction of a polyamic acid using an esterifying agent, (2) a reaction of a tetracarboxylic acid diester dichloride with a diamine, or (3) a polycondensation reaction of a tetracarboxylic acid diester with a diamine. The production methods (2) and (3) can be carried out in accordance with the production of polyamic acid described above.

Among the above three production methods, the above production method (1) or (2) is particularly preferred because it allows the production of a high molecular weight polyamic acid ester.
The polyamic acid ester solution obtained as described above can be poured into a poor solvent while being thoroughly stirred to precipitate the polymer. Precipitation is carried out several times, and the resulting solution is washed with a poor solvent, followed by drying at room temperature or by heating to obtain a purified polyamic acid ester powder. The poor solvent is not particularly limited, but examples thereof include water, methanol, ethanol, hexane, butyl cellosolve, acetone, and toluene.

<Production of Polyimide>
The polyimide used in the present invention can be produced by imidizing the above-mentioned polyimide precursor.
In the polyimide used in the present invention, the ring closure rate (also called imidization rate) of the amic acid groups does not necessarily need to be 100%, and can be adjusted as desired depending on the application and purpose.
For example, the imidization rate of the polyimide may be 20 to 100%, 50 to 99%, or 70 to 99%, from the viewpoint of increasing the solubility of the polyimide varnish.

Imidization can be carried out by stirring the polyamic acid to be imidized in an organic solvent in the presence of a basic catalyst and an acid anhydride. The organic solvent can be the same as that used in the polymerization reaction described above. Examples of basic catalysts include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Among these, pyridine is preferred because it has the appropriate basicity to promote the reaction. Examples of acid anhydrides include acetic anhydride, trimellitic anhydride, and pyromellitic anhydride. Acetic anhydride is preferred because it facilitates purification after the reaction is complete.

The temperature for the above imidization reaction is -20 to 140°C, preferably 0 to 100°C, and the reaction time is 0.5 to 100 hours, preferably 1 to 80 hours. The amount of basic catalyst is 0.5 to 30 times by mole, preferably 2 to 20 times by mole, the amount of amic acid, and the amount of acid anhydride is 1 to 50 times by mole, preferably 3 to 30 times by mole, the amount of amic acid. The imidization rate of the resulting polymer can be controlled by adjusting the amount of catalyst, temperature, and reaction time.

Since the added catalyst and the like remain in the solution after the imidization reaction of the polyimide precursor, it is preferable to recover the obtained imidized polymer by the means described below, redissolve it in an organic solvent, and use it as a component of the liquid crystal aligning agent of the present invention.
The polyimide solution obtained as described above can be poured into a poor solvent while being thoroughly stirred to precipitate the polymer. The precipitation is repeated several times, and the resulting solution is washed with a poor solvent and then dried at room temperature or by heating to obtain a purified polyimide powder.
The poor solvent is not particularly limited, but examples thereof include methanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, and benzene.

<Polyimide varnish>
The polyimide varnish of the present invention contains the above-described block copolymer. The content of the block copolymer in the polyimide varnish can be appropriately changed depending on the thickness of the polyimide film to be formed. From the viewpoint of forming a uniform and defect-free coating film, the content of the block copolymer is preferably 1 to 10% by mass, more preferably 2 to 9% by mass, and particularly preferably 2 to 7% by mass of the entire liquid crystal aligning agent.
The polyimide varnish of the present invention preferably further contains at least one polymer (P) selected from the group consisting of polyimide precursors having a repeating unit represented by the following formula (3) and polyimides obtained by imidizing the polyimide precursors:
( _X3 represents a tetravalent organic group, preferably a tetravalent organic group derived from a tetracarboxylic dianhydride. _Y3 represents a divalent organic group derived from a diamine, preferably a divalent organic group having 3 to 50 carbon atoms and not having a diphenylamine skeleton. _R3 and _Z3 are synonymous with _R1 and _Z1 in formula (1). Two _R3s and two _Z3s each independently have the above definition.)
The polymer (P) preferably does not have a diphenylamine skeleton. By further containing the polymer (P), the properties of the polyimide varnish of the present invention (for example, the voltage holding ratio and rubbing resistance of a liquid crystal alignment film obtained from the polyimide varnish) can be improved.
When the polyimide varnish of the present invention contains polymer (P), the content ratio of at least one block copolymer (hereinafter also referred to as block copolymer (b)) selected from the group consisting of polyimide precursors having the above block (b1) and the above block (b2) and polyimides obtained by imidizing the polyimide precursors to polymer (P) may be, in terms of the mass ratio of [block copolymer (b)]/[polymer (P)], 10/90 to 90/10, 20/80 to 90/10, or 20/80 to 80/20.

In formula (3), _X3 preferably represents at least one selected from the group consisting of structures represented by the following formulae ( _X3-1 ) to (X3-18), and the above formulae ( _X2a -1) to (X2a-2), and ( _X2a -5). Preferred specific examples of formula (X3-13) below include structures represented by the above formulae (X2-1) to (X2-4).
(R ³¹ to R ³⁴ each independently represent a hydrogen atom, a methyl group, an ethyl group, a propyl group, a chlorine atom, or a benzene ring. j and k each independently represent 0 or 1. A ₁ and A ₂ each independently represent a single bond, —O—, —CO—, —COO—, a phenylene group, a sulfonyl group, or an amido group. Two A _2s each independently have the above definition.)
Preferred specific examples of (X3-17) and (X3-18) include the following formulae (X3-19) to (X3-34).

In formula (3), _Y3 preferably represents at least one selected from the group consisting of the structures represented by _Y1 above.

In formula (3), preferably, two _R3s each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Preferably, two _Z3s each independently represent a hydrogen atom or an alkyl group having 1 carbon atom.

In formula (3), X ₃ , Y ₃ , R ₃ and Z ₃ may each be one type or two or more types.

The polyimide precursor preferably comprises a repeating unit represented by the formula (3).
In the polymer (P), the sum of the repeating unit (3) and the imidized structural unit of the repeating unit (3) is more preferably 10 to 100 mol %, and even more preferably 15 to 100 mol %, of all repeating units.
In particular, the sum of the repeating unit (3) in which X ₃ in the above formula (3) is (X3-1) to (X3-11), (X3-13) (more preferably (X2-1) to (X2-4)), or (X _2a -1) to (X _2a -2) and the imidized structural unit of the repeating unit (3) is more preferably 10 to 100 mol %, and even more preferably 15 to 100 mol %, of all repeating units.
The polyimide varnish of the present invention further contains the polymer (P), which has the effect of providing a high voltage holding ratio and good orientation.

The polyimide varnish of the present invention can be prepared, for example, by dispersing or dissolving the block copolymer of the present invention, and, if necessary, the polymer (P) and other components, in an organic solvent.
Examples of other components include antioxidants (phenolic, phosphite, thioether, etc.), ultraviolet absorbers, hindered amine light stabilizers, nucleating agents, resin additives (fillers, talc, glass fibers, etc.), flame retardants, processability improvers/lubricants, etc.

Examples of the organic solvent include lactone solvents such as γ-valerolactone and γ-butyrolactone; lactam solvents such as γ-butyrolactam; amide solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide; 4-hydroxy-4-methyl-2-pentanone, 2,6-dimethyl-4-heptanone (diisobutyl ketone), methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, isoamyl lactate, n-butyl acetate, propylene glycol monoethyl ether acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, ethylene glycol monomethyl ether, ethylene glycol ethyl ether, ethylene glycol monobutyl ether, ethylene glycol-n-propyl ether, ethylene glycol-i-propyl ether, ethylene glycol-n-butyl ether (butyl cellosolve), ethylene glycol dimethyl ether, ethylene glycol monoethyl ether acetate ... monoethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monoethyl Examples of suitable solvents include propylene glycol butyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monobutyl ether, propylene glycol diacetate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, isoamyl propionate, isoamyl isobutyrate, diisopropyl ether, diisopentyl ether; carbonate solvents such as ethylene carbonate and propylene carbonate, 1-hexanol, cyclohexanol, 1,2-ethanediol, diisobutylcarbinol (2,6-dimethyl-4-heptanol), etc. These can be used alone or in combination of two or more.

Preferred solvent combinations include N-methyl-2-pyrrolidone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone and propylene glycol monobutyl ether, N-ethyl-2-pyrrolidone and propylene glycol monobutyl ether, and N-methyl-2-pyrrolidone, γ-butyrolactone and 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-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 methyl 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 Examples of suitable solvents include N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether, and diisopropyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether, and diisobutylcarbinol, N-methyl-2-pyrrolidone, γ-butyrolactone, and dipropylene glycol dimethyl ether, and N-methyl-2-pyrrolidone, propylene glycol monobutyl ether, and dipropylene glycol dimethyl ether. The type and content of such solvents are appropriately selected depending on the coating device, coating conditions, coating environment, etc. of the liquid crystal alignment agent.

<Liquid crystal alignment agent>
The liquid crystal aligning agent of the present invention is preferably prepared as a coating solution suitable for forming a liquid crystal alignment film. The liquid crystal aligning agent of the present invention can be prepared, for example, by dispersing or dissolving the polyimide varnish of the present invention and, if necessary, other components in an organic solvent.
Examples of other components include a crosslinkable compound, a functional silane compound, a surfactant, a compound having a photopolymerizable group, and an organic solvent.

Crosslinkable compounds can be used to increase the strength of the liquid crystal alignment film. Examples of such crosslinkable compounds include compounds having an isocyanate group or a cyclocarbonate group, or compounds having at least one group selected from the group consisting of lower alkoxyalkyl groups, as described in paragraphs [0109] to [0113] of International Publication WO2016/047771, as well as compounds having a blocked isocyanate group.

Blocked isocyanate compounds are commercially available, and examples that can be used include Coronate AP Stable M, Coronate 2503, 2515, 2507, 2513, 2555, and Millionate MS-50 (all manufactured by Nippon Polyurethane Industry Co., Ltd.), and Takenate B-830, B-815N, B-820NSU, B-842N, B-846N, B-870N, B-874N, and B-882N (all manufactured by Mitsui Chemicals, Inc.).

Specific examples of preferred crosslinkable compounds include compounds represented by the following formulae (CL-1) to (CL-11).

The above are examples of crosslinkable compounds, and the present invention is not limited to these. Furthermore, the crosslinkable compounds used in the liquid crystal aligning agent of the present invention may be one type or a combination of two or more types.

The content of other crosslinkable compounds in the liquid crystal aligning agent of the present invention is 0.1 to 150 parts by mass, or 0.1 to 100 parts by mass, or 1 to 50 parts by mass, per 100 parts by mass of all polymer components.

Functional silane compounds can be used to improve adhesion between the liquid crystal alignment film and the underlying substrate. Specific examples include the silane compounds described in paragraph [0019] of International Publication No. 2014/119682. The content of the functional silane compound is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, per 100 parts by mass of all polymer components.

Surfactants can be used to improve the uniformity of the film thickness and surface smoothness of the liquid crystal alignment film. Examples of such compounds include fluorine-based surfactants, silicone-based surfactants, and nonionic surfactants. Specific examples of these surfactants include those described in paragraph [0117] of International Publication WO2016/047771. The amount of surfactant used is preferably 0.01 to 2 parts by mass, more preferably 0.01 to 1 part by mass, per 100 parts by mass of all polymer components contained in the liquid crystal alignment agent.

Examples of compounds having a photopolymerizable group include compounds having one or more polymerizable unsaturated groups, such as acrylate groups or methacrylate groups, within the molecule, such as compounds represented by the following formulas (M-1) to (M-7).

Furthermore, the liquid crystal aligning agent of the present invention can contain nitrogen-containing heterocyclic amine compounds represented by formulas [M1] to [M156], more preferably 3-picolylamine and 4-picolylamine, as described in paragraphs [0194] to [0200] of International Publication WO 2011/132751 (published October 27, 2011), as compounds that promote charge transfer in the liquid crystal alignment film and thereby promote charge drainage from the device. These amine compounds may be added directly to the liquid crystal aligning agent, but are preferably added after being prepared into a solution with a concentration of 0.1 to 10% by mass, preferably 1 to 7% by mass. There are no particular restrictions on the solvent used, as long as it dissolves the polyimide varnish.

When the liquid crystal aligning agent of the present invention contains polyamic acid, polyamic acid ester, or polyamic acid-polyamic acid ester copolymer, an imidization accelerator or the like may be added to efficiently promote imidization by heating when baking the coating film.

Examples of organic solvents contained in the liquid crystal aligning agent of the present invention include lactone solvents such as γ-valerolactone and γ-butyrolactone; lactam solvents such as γ-butyrolactam, N-methyl-2-pyrrolidone, and N-ethyl-2-pyrrolidone; amide solvents such as N,N-dimethylformamide and N,N-dimethylacetamide; 4-hydroxy-4-methyl-2-pentanone, 2,6-dimethyl-4-heptanone, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, isoamyl lactate, n-butyl acetate, propylene glycol monoethyl ether acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, ethylene glycol monomethyl ether, ethylene glycol ethyl ether, ethylene glycol monobutyl ether, ethylene glycol-n-propyl ether, ethylene glycol-i-propyl ether, ethylene glycol-n-butyl ether (butyl cellosolve), ethylene glycol dimethyl ether, ethylene glycol Examples of suitable solvents include glycerol ethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monobutyl ether, propylene glycol diacetate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, isoamyl propionate, isoamyl isobutyrate, diisopropyl ether, diisopentyl ether; carbonate solvents such as ethylene carbonate and propylene carbonate, 1-hexanol, cyclohexanol, 1,2-ethanediol, 2,6-dimethyl-4-heptanol, etc. These can be used alone or in combination of two or more.

Preferred solvent combinations include N-methyl-2-pyrrolidone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone and ethylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone and propylene glycol monobutyl ether, N-ethyl-2-pyrrolidone and propylene glycol monobutyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone, 4-hydroxy-4-methyl-2-pentanone and diethylene glycol Lithium diethyl ether, N-ethyl-2-pyrrolidone, N-methyl-2-pyrrolidone, and 4-hydroxy-4-methyl-2-pentanone, N-methyl-2-pyrrolidone, 4-hydroxy-4-methyl-2-pentanone, and 2,6-dimethyl-4-heptanone, 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 2,6-dimethyl-4-heptanone, γ-butyrolactone, 4-hydroxy-4-methyl-2-pentanone, and propylene glycol diacetate, N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether, and 2,6-dimethyl-4-heptanone, N-methyl Examples of suitable solvents include N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether, and diisopropyl ether, N-methyl-2-pyrrolidone, γ-butyrolactone, propylene glycol monobutyl ether, and 2,6-dimethyl-4-heptanol, N-methyl-2-pyrrolidone, γ-butyrolactone, and dipropylene glycol dimethyl ether, and N-methyl-2-pyrrolidone, propylene glycol monobutyl ether, and dipropylene glycol dimethyl ether. The type and content of such solvents are appropriately selected depending on the coating device, coating conditions, coating environment, etc. of the liquid crystal alignment agent.

The solid content concentration in the liquid crystal aligning agent (the ratio of the total mass of the components other than the organic solvent of the liquid crystal aligning agent to the total mass of the liquid crystal aligning agent) is appropriately selected in consideration of viscosity, volatility, etc., and is preferably in the range of 1 to 10 mass%.
The particularly preferred range of solid content varies depending on the method used to apply the liquid crystal alignment agent to the substrate. For example, when using a spin coating method, a solid content of 1.5 to 4.5 mass% is particularly preferred. When using a printing method, a solid content of 3 to 9 mass% is particularly preferred, thereby resulting in a solution viscosity of 12 to 50 mPa·s. When using an inkjet method, a solid content of 1 to 5 mass% is particularly preferred, thereby resulting in a solution viscosity of 3 to 15 mPa·s.

<Liquid crystal alignment film/liquid crystal display element>
The liquid crystal alignment film of the present invention is obtained from the liquid crystal aligning agent. The liquid crystal alignment film of the present invention can be used for horizontal alignment or vertical alignment. Vertical alignment liquid crystal alignment films are particularly suitable for vertical alignment liquid crystal display elements such as VA or PSA modes. More preferably, the vertical alignment liquid crystal alignment film can be used for liquid crystal display elements obtained by a manufacturing method of a liquid crystal display element, which comprises applying a coating film to a pair of substrates having conductive films, arranging the coating films opposite each other with a layer of liquid crystal molecules interposed therebetween to form a liquid crystal cell, and irradiating the liquid crystal cell with light while applying a voltage between the conductive films of the pair of substrates. More specifically, the liquid crystal display element is a PSA mode liquid crystal display element or an SC-PVA mode liquid crystal display element, which will be described later. The liquid crystal display element of the present invention comprises the liquid crystal alignment film. The liquid crystal display element of the present invention can be manufactured, for example, by a method including the following steps (1) to (3) or (1) to (4).
(1) Step of applying the liquid crystal aligning agent to a substrate: The liquid crystal aligning agent of the present invention is applied to one side of a substrate provided with a patterned transparent conductive film by an appropriate application method, such as a roll coater method, a spin coat method, a printing method, or an inkjet method. The substrate is not particularly limited as long as it is highly transparent, and plastic substrates such as acrylic substrates and polycarbonate substrates can be used in addition to glass substrates and silicon nitride substrates. In addition, in a reflective liquid crystal display element, an opaque material such as a silicon wafer can be used for only one substrate, and in this case, a light-reflecting material such as aluminum can also be used for the electrode.
(2) Step of Baking the Coating After applying the liquid crystal alignment agent, preliminary heating (pre-baking) is preferably performed first for the purpose of preventing dripping of the applied alignment agent. The pre-baking temperature is preferably 30 to 200°C, more preferably 40 to 150°C, and particularly preferably 40 to 100°C. The pre-baking time is preferably 0.25 to 10 minutes, more preferably 0.5 to 5 minutes. Then, a heating (post-baking) step is preferably performed.
The post-baking temperature is preferably 80 to 300° C., more preferably 120 to 250° C. The post-baking time is preferably 5 to 200 minutes, more preferably 10 to 100 minutes. The film thickness of the film thus formed is preferably 5 to 300 nm, more preferably 10 to 200 nm.

The coating film formed in step (1) above can be used as is as a liquid crystal alignment film, but it may also be subjected to an alignment ability-imparting treatment. Examples of alignment ability-imparting treatments include rubbing the coating film in a certain direction with a roll wrapped around a cloth made of fibers such as nylon, rayon, or cotton, and photoalignment treatment in which the coating film is irradiated with polarized or unpolarized radiation.

In the photo-alignment treatment, the radiation to be irradiated onto the coating film can be, for example, ultraviolet light and visible light containing light with a wavelength of 150 to 800 nm. When the radiation is polarized, it may be linearly polarized or partially polarized. Furthermore, when the radiation used is linearly polarized or partially polarized, the radiation may be applied from a direction perpendicular to the substrate surface, from an oblique direction, or a combination of these. When irradiating with unpolarized radiation, the irradiation direction is an oblique direction.
(3) Step of Forming a Liquid Crystal Layer (3-1) In the Case of a VA-Type Liquid Crystal Display Element Two substrates on which a liquid crystal alignment film has been formed as described above are prepared, and liquid crystal is placed between the two substrates arranged opposite each other. Specifically, the following two methods can be mentioned. The first method is a conventionally known method. First, the two substrates are arranged opposite each other with a gap (cell gap) between them so that the liquid crystal alignment films face each other. Next, the peripheries of the two substrates are bonded together using a sealant, and a liquid crystal composition is injected and filled into the substrate surfaces and the cell gap defined by the sealant so that it comes into contact with the film surface, and then the injection hole is sealed.

The second method is called the ODF (One Drop Fill) method. A UV-curable sealant, for example, is applied to a predetermined location on one of two substrates with a liquid crystal alignment film formed thereon, and liquid crystal composition is then dropped onto several predetermined locations on the liquid crystal alignment film surface. The other substrate is then attached so that the liquid crystal alignment film faces the other, and the liquid crystal composition is spread over the entire surface of the substrate and brought into contact with the film surface. The entire surface of the substrate is then irradiated with UV light to cure the sealant. In either method, it is desirable to further heat the substrate to a temperature at which the liquid crystal composition is in an isotropic phase, and then slowly cool it to room temperature to remove flow alignment that occurs during liquid crystal filling.

(3-2) In the case of producing a PSA type liquid crystal display element, the process is the same as in (3-1) above, except that a liquid crystal composition containing a polymerizable compound is injected or dropped. Examples of the polymerizable compound include the polymerizable compounds represented by the formulas (M-1) to (M-7) above.
(3-3) In the case where a coating film is formed on a substrate using a liquid crystal aligning agent containing a compound having a polymerizable group, a method for producing a liquid crystal display element may be employed, which involves the same process as in (3-1) above, followed by a step of irradiating with ultraviolet light, as described below. This method, similar to the production of the PSA-type liquid crystal display element, allows for the production of a liquid crystal display element with excellent response speed with a low light exposure dose. The compound having a polymerizable group may be a compound having one or more polymerizable unsaturated groups, such as acrylate groups or methacrylate groups, in the molecule, as represented by the formulas (M-1) to (M-7). The content of the compound is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of all polymer components. The polymerizable group may also be contained in the polymer used in the liquid crystal aligning agent. Examples of such polymers include polymers obtained by reacting a diamine component containing a diamine having the photopolymerizable group at its terminal.

(4) Step of Irradiating Ultraviolet Light: The liquid crystal cell is irradiated with light while a voltage is applied between the conductive films of the pair of substrates obtained in step (3-2) or (3-3) above. The voltage applied here can be, for example, 5 to 50 V DC or AC. The irradiated light can be, for example, ultraviolet light and visible light containing light with a wavelength of 150 to 800 nm, but ultraviolet light containing light with a wavelength of 300 to 400 nm is preferred. Examples of light sources that can be used for the irradiated light include low-pressure mercury lamps, high-pressure mercury lamps, deuterium lamps, metal halide lamps, argon resonance lamps, xenon lamps, and excimer lasers. The light irradiation dose is preferably 1,000 to 200,000 J/ ^m² , more preferably 1,000 to 100,000 J/ ^m² .

A liquid crystal display element can then be obtained by laminating a polarizing plate to the outer surface of the liquid crystal cell. Examples of polarizing plates that can be laminated to the outer surface of the liquid crystal cell include polarizing plates in which a polarizing film called an "H film," made by stretching and aligning polyvinyl alcohol and absorbing iodine, is sandwiched between cellulose acetate protective films, or polarizing plates made of the H film itself.

The liquid crystal display element of the present invention can be effectively applied to a variety of devices, such as watches, portable games, word processors, notebook computers, car navigation systems, camcorders, PDAs, digital cameras, mobile phones, smartphones, various monitors, LCD televisions, and information displays.

The present invention will be described in further detail below based on examples, but the present invention is not limited to these examples in any way.
<Synthesis of Liquid Crystal Alignment Agent>
The abbreviations used in the preparation of the liquid crystal alignment agent below are as follows:
(Tetracarboxylic acid dianhydride)
BODA: bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic dianhydride CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride BDA: meso-butane-1,2,3,4-tetracarboxylic dianhydride (diamine)
(Additives)
(solvent)
NMP: N-methyl-2-pyrrolidone, BCS: butyl cellosolve

<Molecular weight measurement>
Measurement equipment: room temperature gel permeation chromatography (GPC) (SSC-7200) manufactured by Senshu Scientific Co., Ltd.; Column: Shodex column (KD-803, KD-805 in series); Column temperature: 50°C; Eluent: N,N-dimethylformamide (additives: lithium bromide monohydrate (LiBr.H ₂ O) 30 mmol/L, phosphoric acid anhydrous crystal (o-phosphoric acid) 30 mmol/L, tetrahydrofuran (THF) 10 ml/L); Flow rate: 1.0 mL/min;
Standard samples for preparing a calibration curve: TSK standard polyethylene oxide (molecular weights: approximately 900,000, 150,000, 100,000, and 30,000) manufactured by Tosoh Corporation, and polyethylene glycol (molecular weights: approximately 12,000, 4,000, and 1,000) manufactured by Polymer Laboratory.

<Measurement of imidization rate>
20 mg of polyimide powder was placed in an NMR sample tube (Kusano Scientific NMR Sampling Tube Standard φ5), 1.0 mL of deuterated dimethyl sulfoxide (DMSO-d ₆ , 0.05% TMS mixture) was added, and the mixture was sonicated to completely dissolve the powder. This solution was subjected to 500 MHz proton NMR measurement using a JEOL Datum NMR spectrometer (JNW-ECA500).
The chemical imidization ratio was determined by the following formula, using a proton derived from a structure that remains unchanged before and after imidization as a reference proton, and the peak integrated value of this proton and the peak integrated value of a proton derived from the NH group of the amic acid that appears around 9.5 to 10.0 ppm: where x is the peak integrated value of the proton derived from the NH group of the amic acid, y is the peak integrated value of the reference proton, and α is the ratio of the number of reference protons to one proton of the NH group of the amic acid in the case of polyamic acid (imidization ratio 0%).
Imidization rate (%) = (1 - α x/y) x 100

<Synthesis Example 1>
BODA (1.75 g, 7.0 mmol) and DA-5 (1.66 g, 8.4 mmol) were dissolved in NMP (13.7 g) and reacted at 60° C. for 3 hours, after which DA-1 (1.12 g, 5.6 mmol) and NMP (4.5 g) were added and dissolved, and CBDA (1.31 g, 6.7 mmol) and NMP (5.3 g) were added and reacted at 40° C. for 4 hours to obtain polyamic acid solution (1). The number average molecular weight Mn of this polyamic acid was 10,200, and the weight average molecular weight Mw was 38,400.
<Synthesis Example 2>
BODA (1.88 g, 7.5 mmol), DA-3 (0.65 g, 6.0 mmol), and DA-4 (1.18 g, 3.0 mmol) were dissolved in NMP (14.8 g) and reacted at 60°C for 3 hours. DA-1 (1.20 g, 6.0 mmol) and NMP (4.8 g) were then added and dissolved, and CBDA (1.41 g, 7.2 mmol) and NMP (5.6 g) were added. The mixture was reacted at 40°C for 4 hours to obtain polyamic acid solution (2). The Mn of this polyamic acid was 11,200 and the Mw was 25,800.

<Synthesis Example 3>
BODA (0.75 g, 3.0 mmol) and DA-5 (2.08 g, 10.5 mmol) were dissolved in NMP (11.3 g) and reacted at 60° C. for 3 hours, after which DA-2 (0.96 g, 4.5 mmol) and NMP (3.8 g) were added and dissolved, and CBDA (2.18 g, 11.1 mmol) and NMP (8.7 g) were added and reacted at 40° C. for 4 hours to obtain polyamic acid solution (3). The Mn of this polyamic acid was 10,600 and the Mw was 28,700.
<Synthesis Example 4>
BODA (2.50 g, 10.0 mmol), DA-5 (0.99 g, 5.0 mmol), DA-6 (0.66 g, 2.0 mmol), DA-7 (1.42 g, 6.0 mmol) and DA-4 (2.76 g, 7.0 mmol) were dissolved in NMP (33.4 g) and reacted at 60 ° C. for 3 hours, after which CBDA (1.92 g, 9.8 mmol) and NMP (7.7 g) were added and reacted at 40 ° C. for 4 hours to obtain a polyamic acid solution. After diluting this polyamic acid solution (25 g) with NMP to 6.5 mass%, acetic anhydride (4.96 g) and pyridine (1.53 g) were added as imidization catalysts and the mixture was reacted at 50 ° C. for 3 hours. This reaction solution was added to methanol (334 g), and the resulting precipitate was filtered off. The precipitate was washed with methanol and dried under reduced pressure at 60°C to obtain a polyimide powder. The imidization rate of this polyimide was 59%, with an Mn of 12,500 and an Mw of 42,300. NMP (28.0 g) was added to the obtained polyimide powder (2.0 g) and dissolved by stirring at 70°C for 15 hours. BCS (20.0 g) was added to this solution to obtain a polyimide solution (1).
<Synthesis Example 5>
BDA (2.58 g, 13.0 mmol), DA-8 (3.42 g, 14.0 mmol), and DA-9 (3.34 g, 6.0 mmol) were dissolved in NMP (52.9 g) and reacted at 50 ° C. for 2 hours. Then, CBDA (1.33 g, 6.8 mmol) and NMP (7.6 g) were added, and the mixture was reacted at 40 ° C. for 4 hours to obtain a polyamic acid solution. This polyamic acid solution (25 g) was diluted to 6.5 mass % with NMP, and then acetic anhydride (3.59 g) and pyridine (1.11 g) were added as imidization catalysts, and the mixture was reacted at 40 ° C. for 2.5 hours. This reaction solution was added to methanol (250 g), and the resulting precipitate was filtered off. This precipitate was washed with methanol and dried under reduced pressure at 60 ° C. to obtain a polyimide powder. The imidization rate of this polyimide was 65%, with an Mn of 11,200 and an Mw of 38,100. NMP (28.0 g) was added to the obtained polyimide powder (2.0 g) and dissolved by stirring at 70° C. for 15 hours. BCS (20.0 g) was added to this solution to obtain polyimide solution (2).

Comparative Synthesis Example 1
BODA (1.75 g, 7.0 mmol), DA-5 (1.66 g, 8.4 mmol), and DA-1 (1.12 g, 5.6 mmol) were dissolved in NMP (18.1 g) and reacted at 60°C for 3 hours, after which CBDA (1.31 g, 6.7 mmol) and NMP (5.2 g) were added and reacted at 40°C for 4 hours to obtain polyamic acid solution (4). The Mn of this polyamic acid was 11,100 and the Mw was 31,900.
Comparative Synthesis Example 2
BODA (1.88 g, 7.5 mmol), DA-3 (0.65 g, 6.0 mmol), DA-4 (1.18 g, 3.0 mmol), and DA-1 (1.20 g, 6.0 mmol) were dissolved in NMP (19.6 g) and reacted at 60°C for 3 hours, after which CBDA (1.41 g, 7.2 mmol) and NMP (5.5 g) were added and reacted at 40°C for 4 hours to obtain polyamic acid solution (5). The Mn of this polyamic acid was 10,000 and the Mw was 20,200.

Comparative Synthesis Example 3
BODA (0.75 g, 3.0 mmol), DA-5 (2.08 g, 10.5 mmol), and DA-2 (0.96 g, 4.5 mmol) were dissolved in NMP (15.2 g) and reacted at 60°C for 3 hours, after which CBDA (2.18 g, 11.1 mmol) and NMP (8.7 g) were added and reacted at 40°C for 4 hours to obtain polyamic acid solution (6). The Mn of this polyamic acid was 9,400 and the Mw was 34,200.

The specifications of each polymer obtained in the above synthesis example and comparative synthesis example are as shown in Table 1 below.

<Preparation of Liquid Crystal Alignment Agent>
In Examples and Comparative Examples, examples of preparation of liquid crystal alignment agents are described. Liquid crystal display elements were produced using the liquid crystal alignment agents obtained in Examples and Comparative Examples, and various evaluations were carried out.
[Example 1]
NMP (16.0 g) and BCS (16.0 g) were added to the polyamic acid solution (1) (8.0 g) obtained in Synthesis Example 1, and the mixture was stirred at room temperature for 2 hours to obtain a liquid crystal aligning agent (A-1).
[Examples 2 and 3, Comparative Examples 1 to 3]
Liquid crystal aligning agents (A-2), (A-3), (B-1) to (B-3) of Examples 2 and 3 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the polyamic acid solutions (2) to (6) were used instead of the polyamic acid solution (1).

[Example 4]
The polyimide solution (1) (3.0 g) obtained in Synthesis Example 4, the liquid crystal aligning agent (A-1) (7.0 g) obtained in Example 1 and AD-1 (0.04 g) were mixed to obtain a liquid crystal aligning agent (C-1).
[Examples 5 and 6, Comparative Examples 4 to 6]
The liquid crystal aligning agents (C-2), (C-3), (D-1) to (D-3) of Examples 5 and 6 and Comparative Examples 4 to 6 were obtained in the same manner as in Example 4, except that the liquid crystal aligning agents (A-2), (A-3), (B-1) to (B-3) were used instead of the liquid crystal aligning agent (A-1).
[Example 7]
The polyimide solution (2) (3.0 g) obtained in Synthesis Example 5 and the liquid crystal aligning agent (A-1) (7.0 g) obtained in Example 1 were mixed to obtain a liquid crystal aligning agent (C-4).
[Example 8, Comparative Examples 7 and 8]
The liquid crystal aligning agents (C-5), (D-4) and (D-5) of Example 8 and Comparative Examples 7 and 8 were obtained in the same manner as in Example 7, except that the liquid crystal aligning agents (A-3), (B-1) and (B-3) were used instead of the liquid crystal aligning agent (A-1).

The liquid crystal alignment agents (A-1) to (A-3), (B-1) to (B-3), (C-1) to (C-5), and (D-1) to (D-5) obtained as described above were found to be homogeneous solutions, with no abnormalities such as turbidity or precipitation observed. Using the obtained liquid crystal alignment agents, evaluation of transmittance, preparation of liquid crystal cells, evaluation of voltage holding ratio, and evaluation of residual DC voltage were carried out.

[Transmittance Evaluation]
The liquid crystal alignment agents (A-1) to (A-3), (C-1) to (C-5), (B-1) to (B-3), and (D-1) to (D-5) obtained in the examples and comparative examples were spin-coated onto a quartz substrate and dried on a hot plate at 70 °C for 90 seconds. This was then baked for 20 minutes in an IR (infrared) oven at 230 °C to form a coating film with a thickness of 100 nm, yielding a substrate with a liquid crystal alignment film. This liquid crystal alignment film-coated substrate was placed on the inside, and another quartz substrate was sandwiched between them with a refractive index liquid (Shimadzu Device Manufacturing Co., Ltd., contact liquid) to prevent light interference. Transmittance was evaluated using a UV-3600 (Shimadzu Corporation) measuring device at 25 °C and a scanning wavelength of 380 to 800 nm. A reference was used in this case, with the refractive index liquid sandwiched between two uncoated quartz substrates. The evaluation was based on the transmittance at a wavelength of 580 nm, and the values are shown in Table 2 below, and an example of the relationship between wavelength and transmittance is shown in FIG.

[Preparation of Liquid Crystal Display Elements for Evaluation of Voltage Holding Ratio and Residual DC Characteristics]
Liquid crystal cells were prepared using the liquid crystal alignment agents (A-1) to (A-3), (C-1) to (C-3), (B-1) to (B-3), and (D-1) to (D-3) obtained in the examples and comparative examples, according to the procedure described below. The liquid crystal alignment agent was spin-coated onto a glass substrate with an ITO electrode, dried on a hot plate at 70°C for 90 seconds, and then baked in an IR oven at 230°C for 20 minutes to form a liquid crystal alignment film with a thickness of 100 nm. Two substrates with this liquid crystal alignment film were prepared, and 4 μm diameter bead spacers (manufactured by JGC Catalysts and Chemicals, Shinshikyu, SW-D1) were applied to one of the liquid crystal alignment films, followed by printing with a thermosetting sealant (manufactured by Mitsui Chemicals, XN-1500T). Next, the surface of the other substrate on which the liquid crystal alignment film had been formed was facing inward, and the sealant was then cured to prepare an empty cell. Liquid crystal MLC-3023 (manufactured by Merck) was injected into this empty cell by a vacuum injection method to prepare a liquid crystal cell. Next, with a DC voltage of 15 V applied to this liquid crystal cell, UV light was irradiated from the outside of the liquid crystal cell at 10 J/ ^cm² through a 325 nm or less cut filter. The UV illuminance was measured using a UV-MO3A manufactured by ORC Corporation. Thereafter, in order to deactivate any unreacted polymerizable compound remaining in the liquid crystal cell, the liquid crystal cell was irradiated with UV (UV lamp: FLR40SUV32/A-1) for 30 minutes using a UV-FL irradiation device manufactured by Toshiba Lighting & Technology Corporation without applying voltage.

[Fabrication of Liquid Crystal Display Elements for Evaluating Afterimage Characteristics]
Liquid crystal cells were prepared using the liquid crystal alignment agents (A-2), (C-1) to (C-3), (B-2), and (D-1) to (D-3) obtained in the examples and comparative examples according to the following procedure. The liquid crystal alignment agent was spin-coated onto the ITO surface of an ITO electrode substrate (length: 35 mm, width: 30 mm, thickness: 0.7 mm) with an ITO electrode pattern having a pixel size of 200 μm × 600 μm and a line/space of 3 μm each, and a glass substrate (length: 35 mm, width: 30 mm, thickness: 0.7 mm) with an ITO electrode patterned with 3.2 μm-high photospacers. The substrate was then dried on a hot plate at 70 ° C for 90 seconds, and then baked in an IR oven at 230 ° C for 20 minutes to form a liquid crystal alignment film with a thickness of 100 nm. The ITO electrode substrate on which this ITO electrode pattern is formed is divided into four areas in a cross-checkered pattern, so that each of the four areas can be driven separately.
Next, a sealant (Mitsui Chemicals, Inc., XN-1500T) was printed on the other substrate. The other substrate was then bonded to the first substrate with the side on which the liquid crystal alignment film had been formed facing inward, and the sealant was cured to create an empty cell. Liquid crystal MLC-3023 (Merck & Co., Inc.) was injected into this empty cell by a reduced pressure injection method to create a liquid crystal cell. With a DC voltage of 15 V applied to the liquid crystal cell, the cell was irradiated from the outside with 10 J/ ^cm² of UV light passed through a 325 nm or less cut filter. The UV irradiance was measured using a UV-MO3A manufactured by ORC Corporation. Thereafter, in order to deactivate any unreacted polymerizable compound remaining in the liquid crystal cell, the cell was irradiated with UV (UV lamp: FLR40SUV32/A-1) for 30 minutes using a UV-FL irradiation device manufactured by Toshiba Lighting & Technology Corporation without applying voltage.

[Evaluation of Voltage Holding Ratio]
The voltage holding ratio was measured using a liquid crystal cell for evaluating the voltage holding ratio after UV irradiation. A voltage of 1 V was applied for 60 μs in a hot air circulating oven at 60°C, and the voltage was measured 16.67 msec later, and the voltage holding ratio was calculated as the amount of voltage that could be held. A VHR-1 manufactured by Toyo Corporation was used to measure the voltage holding ratio. The values are shown in Table 2 below.
[Evaluation of Residual DC Voltage]
A 30 Hz, 7.8 Vpp square wave voltage superimposed with a DC voltage of 2 V was applied to the liquid crystal cell for voltage holding ratio evaluation prepared above at 25° C. for 100 hours, and the voltage remaining in the liquid crystal cell (residual DC voltage) after 1 hour from the DC voltage cutoff was measured by the flicker elimination method. The values are shown in Table 2 below.

[Afterimage characteristics]
Using the liquid crystal cell for evaluating image retention characteristics prepared above, an AC voltage of 60 Hz and 20 Vp-p was applied to two diagonal areas of the four pixel areas, and the cell was driven at a temperature of 25°C for 168 hours. After that, all four pixel areas were driven with an AC voltage of 5 Vp-p, and the brightness difference between the pixels was visually observed. A state in which the brightness difference was almost undetectable was considered good, and the evaluation results are shown in Table 2.

[Rubbing resistance]
The liquid crystal alignment agents (C-4), (C-5), (B-1), (B-3), (D-4), and (D-5) obtained in the examples and comparative examples were spin-coated onto the ITO surface of a glass substrate with an ITO electrode attached to the entire surface, and then temporarily dried on a hot plate at 70 °C for 90 seconds. The substrate was then baked in an IR oven at 230 °C for 20 minutes to form a coating film with a thickness of 100 nm, yielding a substrate with a liquid crystal alignment film. This liquid crystal alignment film was rubbed with a rayon cloth (roller diameter: 120 mm, roller rotation speed: 1000 rpm, movement speed: 20 mm/sec, indentation length: 0.6 mm). The substrate was observed under a microscope, and those with no rubbing streaks on the film surface were rated as "good" and those with streaks were rated as "poor." The results are shown in Table 2.

As shown in Table 2 and Figure 1, the transmittance evaluation results using the liquid crystal alignment agents (A-1) to (A-3) and (C-1) to (C-5) obtained in Examples 1 to 8 show that liquid crystal alignment films with higher transmittance can be obtained compared to the transmittance evaluation results using the corresponding liquid crystal alignment agents (B-1) to (B-3) and (D-1) to (D-5) obtained in Comparative Examples 1 to 8. Note that a 1% difference in transmittance is significant in the art. Meanwhile, evaluations of voltage holding ratio, residual DC voltage, afterimage characteristics, and rubbing resistance show that liquid crystal alignment films with similar characteristics can be obtained.

Furthermore, the liquid crystal display elements using the liquid crystal alignment agents (C-1) to (C-3) exhibited higher voltage retention characteristics than the liquid crystal display elements using the liquid crystal alignment agents (A-1) to (A-3). That is, by mixing the polyimide solution (1) that does not have a diphenylamine skeleton, a liquid crystal alignment film having high transmittance can be obtained, and a liquid crystal display element having a high voltage retention ratio can be obtained.
Furthermore, the liquid crystal display elements using the liquid crystal alignment agents (C-4) and (C-5) exhibited good rubbing resistance. That is, by mixing the polyimide solution (2) having no diphenylamine skeleton, a liquid crystal alignment film having high transmittance can be obtained, and a liquid crystal display element exhibiting good rubbing resistance can be obtained.

The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2020-044505, filed on March 13, 2020, are hereby incorporated by reference as part of the disclosure of the specification of the present invention.

Claims (18)

A polyimide varnish containing at least one block copolymer selected from the group consisting of a polyimide precursor having a block (b1) having a repeating unit represented by the following formula (1) and a block (b2) having a repeating unit represented by the following formula (2), and a polyimide obtained by imidizing the polyimide precursor:
( _X1 represents at least one selected from the group consisting of structures represented by the following formulas (X1-1) to (X1-4), (X1-7), (X1-9), and (X1-11). _X2 represents a tetravalent organic group represented by the following formula (X2). _Y1 represents a divalent organic group of 3 to 50 carbon atoms that does not have a diphenylamine skeleton. _Y2 represents a divalent organic group that has a diphenylamine skeleton. Two _R1s and _R2s each independently represent a hydrogen atom or an alkyl group of 1 to 4 carbon atoms, and two _Z1s and _Z2s each independently represent a hydrogen atom, an alkyl group of 1 to 10 carbon atoms that may have a substituent, an alkenyl group of 2 to 10 carbon atoms that may have a substituent, an alkynyl group of 2 to 10 carbon atoms that may have a substituent, a tert-butoxycarbonyl group, or a 9-fluorenylmethoxycarbonyl group.)
(R ²¹ to R ²⁴ each independently represent a hydrogen atom, a methyl group, an ethyl group, a propyl group, a chlorine atom, or a phenyl group.) The polyimide varnish according to claim 1, wherein in formula (1), Y ₁ represents at least one selected from the group consisting of divalent organic groups having 3 to 50 carbon atoms and having a structure represented by any of the following formulae (S1) to (S3), and divalent organic groups having 3 to 50 carbon atoms and not having a structure represented by any of the following formulae (S1) to (S3) (provided that the divalent organic groups having 3 to 50 carbon atoms and having a structure represented by any of the formulae (S1) to (S3) and the divalent organic groups having 3 to 50 carbon atoms and not having a structure represented by any of the formulae (S1) to (S3) do not have a diphenylamine skeleton).
( ^X1 and ^X2 each independently represent a single bond, -( _CH2 ) _a- (a is an integer of 1 to 15), -CONH-, -NHCO-, -CON( _CH3 )-, -NH-, -O-, -COO-, -OCO-, or -(( _CH2 ) _a1 - _A1 ) _m1- . In these, a1's each independently represent an integer of 1 to 15, _A1 's each independently represent an oxygen atom or -COO-, and m1 is 1 or 2. ^G1 and ^G2 each independently represent a divalent cyclic group selected from divalent aromatic groups having 6 to 12 carbon atoms and divalent alicyclic groups having 3 to 8 carbon atoms. Any hydrogen atom on the cyclic group may be substituted. m and n each independently represent an integer of 0 to 3, and m+n is 1 to 4. R ¹ represents an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or an alkoxyalkyl group having 2 to 20 carbon atoms, and any hydrogen atom forming R ¹ may be substituted with a fluorine atom. When m, n, and m1 are 2 or more, the multiple occurrences of X ¹ , X ² , G ¹ , G ² , a1, m1, and A ₁ each independently have the above definition.
( ^X3 represents a single bond, -CONH-, -NHCO-, -CON( _CH3 )-, -NH-, -O-, _-CH2O- , -COO- or -OCO-. ^R2 represents an alkyl group having 1 to 20 carbon atoms or an alkoxyalkyl group having 2 to 20 carbon atoms, and any hydrogen atom forming ^R2 may be substituted with a fluorine atom.)
( ^X4 represents —CONH—, —NHCO—, —O—, —CH ₂ O—, —COO— or —OCO—. ^R3 represents a structure having a steroid skeleton.) The polyimide varnish according to claim 2, wherein in formula (1), at least one of Y ₁ represents a divalent organic group having 3 to 50 carbon atoms and having a structure represented by any one of formulas (S1) to (S3). 4. The polyimide varnish according to claim 2, wherein in formula (1), at least one of Y ₁ represents a divalent organic group having 3 to 50 carbon atoms and not having any of the structures represented by formulas (S1) to (S3). The polyimide varnish according to claim 2 or 4, wherein the divalent organic group having 3 to 50 carbon atoms and not having a structure represented by any of formulas (S1) to (S3) is a divalent organic group having a nitrogen-containing heterocycle in the molecule, a divalent organic group having radical initiation functionality, a divalent organic group having a carboxyl group, a group having the group "-N(D)-" (D represents a tert-butoxycarbonyl group), a group having photoalignment properties, a divalent organic group having an oxygen-containing heterocycle, or a divalent organic group derived from an aromatic diamine that does not have a side chain group having 3 or more carbon atoms. The polyimide varnish according to any one of claims 1 to 5, wherein in formula (2), _X2 represents at least one selected from the group consisting of structures represented by the following formulas (X2-1) to (X2-4):
The polyimide varnish according to any one of claims 1 to 6, wherein in formula (2), Y ₂ represents a structure represented by the following formula (d2):
(A ₁ represents a single bond, —NR— (R represents a hydrogen atom or a monovalent organic group), —O—, —C(═O)—, —C(═O)NR— (R represents a hydrogen atom or a monovalent organic group), —C(═O)O—, or a divalent organic group. R ₁ and R ₂ each independently represent a hydrogen atom or a monovalent organic group. When n is 2, multiple A _1s and R _2s each independently have the above definition.) The polyimide varnish according to any one of claims 1 to 7, wherein the ratio of the total number of moles of repeating units represented by formula (1) to the total number of moles of repeating units represented by formula (2) per molecule of the block copolymer is 1:9 to 9:1. The polyimide varnish according to any one of claims 1 to 8, further comprising at least one polymer (P) selected from the group consisting of a polyimide precursor having a repeating unit represented by the following formula (3) and a polyimide obtained by imidizing the polyimide precursor:
( _X3 represents a tetravalent organic group derived from a tetracarboxylic dianhydride. _Y3 represents a divalent organic group having 3 to 50 carbon atoms and not having a diphenylamine skeleton. _R3 and _Z3 are synonymous with _R1 and _Z1 in formula (1). Two _R3s and _{two Z3s} each independently have the above definition.) The polyimide varnish according to claim 9, wherein the polymer (P) does not have a diphenylamine skeleton. A method for producing the polyimide varnish according to any one of claims 1 to 10,
a step (I) of reacting a tetracarboxylic acid component containing a tetracarboxylic acid dianhydride represented by the following formula (1-T) or a derivative thereof with a diamine component containing a diamine represented by the following formula (1-D) to obtain a block (b1);
a step (II) of adding a tetracarboxylic acid component containing a tetracarboxylic dianhydride represented by the following formula (2-T) or a derivative thereof and a diamine component containing a diamine represented by the following formula (2-D) to the block (b1) and reacting them to obtain a polyimide precursor having the block (b1) and the block (b2);
A method for producing a polyimide varnish comprising the steps of:
(X ₁ , X ₂ , Y ₁ , and Y ₂ are the same as defined in formulas (1) and (2).) The method for producing a polyimide varnish according to claim 11, wherein the reaction temperature in step (II) is lower than the reaction temperature in step (I). A method for producing the polyimide varnish according to any one of claims 1 to 10,
a step (III) of reacting a tetracarboxylic acid component containing a tetracarboxylic dianhydride represented by the following formula (1-T) or a derivative thereof with a diamine component containing a diamine represented by the following formula (1-D) to obtain a block (b1);
a step (IV) of reacting a tetracarboxylic acid component containing a tetracarboxylic acid dianhydride represented by the following formula (2-T) or a derivative thereof with a diamine component containing a diamine represented by the following formula (2-D) to obtain a block (b2);
a step (V) of coupling the block (b1) obtained in the step (III) with the block (b2) obtained in the step (IV) to obtain a polyimide precursor having the block (b1) and the block (b2);
A method for producing a polyimide varnish comprising the steps of:
(X ₁ , X ₂ , Y ₁ , and Y ₂ are the same as defined in formulas (1) and (2).) The method for producing a polyimide varnish according to claim 13, wherein the reaction temperature in step (IV) is lower than the reaction temperature in step (III). A liquid crystal alignment agent obtained from the polyimide varnish described in any one of claims 1 to 10. A liquid crystal alignment film formed using the liquid crystal alignment agent described in claim 15. A liquid crystal display element comprising the liquid crystal alignment film according to claim 16. A method for manufacturing a liquid crystal display element, comprising: applying the liquid crystal aligning agent according to claim 15 onto a pair of substrates having conductive films to form coating films; arranging the coating films so as to face each other with a layer of liquid crystal molecules interposed therebetween to form a liquid crystal cell; and irradiating the liquid crystal cell with light while applying a voltage between the conductive films of the pair of substrates.