Liquid crystal alignment agent, method for producing the same, liquid crystal alignment film, and liquid crystal element

Abstract

To provide a liquid crystal alignment agent capable of shortening the duration of gelation in the early stage of the imidization reaction, forming a liquid crystal alignment film with high transmittance, and yielding a liquid crystal element with excellent electrical properties.SOLUTION: The liquid crystal alignment agent comprises a polyimide obtained by imidizing a polyamic acid in the presence of a compound represented by Formula (1). In Formula (1): R1 and R2 are each independently an alkyl group having 3 to 6 carbon atoms; and R3 is an alkyl group having 1 to 6 carbon atoms.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a liquid crystal aligning agent, a method for producing the same, a liquid crystal alignment film, and a liquid crystal element.

Background Art

[0002] A liquid crystal element includes a liquid crystal alignment film having a function of aligning liquid crystal molecules in a liquid crystal layer in a certain direction. The liquid crystal alignment film is generally formed on a substrate by applying a liquid crystal aligning agent in which a polymer component is dissolved in an organic solvent onto the substrate surface and preferably heating it.

[0003] In recent years, large-screen and high-definition liquid crystal televisions have become mainstream, and the popularity of small display terminals such as smartphones and tablet PCs has advanced. The demand for higher quality of liquid crystal elements has been increasing more than ever. The performance of liquid crystal elements (for example, voltage holding ratio and film transmittance) is easily affected by impurities in the liquid crystal elements. In particular, when impurities are present in the liquid crystal alignment film in contact with liquid crystal molecules, there is a risk that the impurities elute into the liquid crystal and cause a deterioration in the performance of the liquid crystal element. Therefore, it is important how to reduce impurities in the liquid crystal alignment film for improving the quality of liquid crystal elements.

[0004] Polyimide has been conventionally used as a polymer component of a liquid crystal aligning agent because of its excellent heat resistance, mechanical properties, electrical properties, oxidation resistance, and hydrolysis resistance. As a method for producing polyimide blended in a liquid crystal aligning agent, a method of imidizing a polyamic acid obtained by polycondensation of a tetracarboxylic dianhydride and a diamine compound in the presence of an imidization catalyst is generally known. Conventionally, amine-based bases such as pyridine and isoquinoline have been used as the imidization catalyst. Also, it has been proposed that by using N-methylpiperidine as the imidization catalyst, a high imidization rate can be achieved and the non-coloring property and low water absorption of the polyimide film can be improved (see Patent Document 1).

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] JP 2010-37401 A Summary of the Invention [Problem to be solved by the invention]

[0006] When pyridine is used as an imidization catalyst in the synthesis of polyimide, there is a problem that the reaction solution is likely to gel at the beginning of the imidization reaction. To prevent gelation, it is possible to increase the reaction temperature, add a solvent, or extend the reaction time. However, there are concerns that the application of these methods will lead to high costs and a large process load.

[0007] When N-methylpiperidine is used as an imidization catalyst, the duration of gelation can be shortened in the early stage of the imidization reaction, and the process load can be reduced. On the other hand, when imidization is performed in the presence of N-methylpiperidine, N-methylpiperidine cannot be sufficiently removed from the reaction solution, and the imidized polymer is prone to coloration. In particular, when used as a liquid crystal alignment agent, there is a concern that impurities may be mixed into the film, causing a decrease in performance, such as a decrease in the voltage retention rate of liquid crystal elements and a decrease in the transmittance of the panel.

[0008] The present invention has been made in consideration of the above problems, and has as its main object to provide a liquid crystal alignment agent that can shorten the duration of gelation in the initial stage of the imidization reaction, form a liquid crystal alignment film with high transmittance, and obtain a liquid crystal element with excellent electrical properties. [Means for solving the problem]

[0009] According to the present invention, the following means are provided. [1] A method for producing a liquid crystal aligning agent, comprising: incorporating a polyimide obtained by imidizing a polyamic acid in the presence of a compound represented by the following formula (1): [ka] (In formula (1), R 1 and R 2 are, independently of each other, alkyl groups having 3 to 6 carbon atoms. R 3 is an alkyl group having 1 to 6 carbon atoms.)

[0010] 〔2〕 A liquid crystal aligning agent containing a polyimide formed by imidizing a polyamic acid in the presence of the compound represented by the above formula (1). 〔3〕 A liquid crystal alignment film formed using the liquid crystal aligning agent of the above 〔2〕. 〔4〕 A liquid crystal element including the liquid crystal alignment film of the above 〔3〕. 〔5〕 A first step of reacting a tetracarboxylic dianhydride with a diamine compound to obtain a polyamic acid, and a second step of imidizing the polyamic acid obtained in the first step, which includes a tetracarboxylic dianhydride containing a monocyclic or condensed cyclic saturated aliphatic ring having 4 to 8 carbon atoms, and in the second step, imidizing the polyamic acid in the presence of the compound represented by the above formula (1), a method for producing a polyimide.

Advantages of the Invention

[0011] According to the liquid crystal aligning agent and its production method of the present invention, the duration of gelation in the initial stage of the imidization reaction can be shortened, a liquid crystal alignment film with high transmittance can be formed, and a liquid crystal element excellent in electrical characteristics can be obtained.

Modes for Carrying Out the Invention

[0012] Hereinafter, matters related to the embodiments of the present disclosure will be described in detail.

[0013] Here, in this specification, the "hydrocarbon group" means a group including a linear hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group. The "linear hydrocarbon group" means a linear hydrocarbon group and a branched hydrocarbon group that do not contain a cyclic structure in the main chain and are composed only of a linear structure. However, it may be saturated or unsaturated. The "alicyclic hydrocarbon group" means a hydrocarbon group that contains only the structure of an alicyclic hydrocarbon as the ring structure and does not contain an aromatic ring structure. However, it is not necessary to be composed only of the structure of an alicyclic hydrocarbon, and those having a linear structure in a part thereof are also included. The "aromatic hydrocarbon group" means a hydrocarbon group that contains an aromatic ring structure as the ring structure. However, it is not necessary to be composed only of the aromatic ring structure, and it may contain a linear structure or the structure of an alicyclic hydrocarbon in a part thereof.

[0014] ≪Liquid Crystal Alignment Agent and Method for Producing the Same≫ The liquid crystal alignment agent and method for producing the same according to the present disclosure will be described. The liquid crystal alignment agent according to the present disclosure contains a polyimide obtained by imidizing a polyamic acid in the presence of a compound represented by the following formula (1) (hereinafter also referred to as "compound (A)"). [Chemical Formula] (In formula (1), R 1 and R 2 are each independently an alkyl group having 3 to 6 carbon atoms. R 3 is an alkyl group having 1 to 6 carbon atoms.)

[0015] Further, the liquid crystal alignment agent according to the present disclosure may contain, together with the polyimide, a component different from the polyimide (hereinafter also referred to as "other components"). Hereinafter, the components contained in the liquid crystal alignment agent according to the present disclosure and other components optionally blended as necessary will be described.

[0016] [Polyimide] The polyimide contained in the liquid crystal aligning agent of the present disclosure can be obtained by dehydrating and ring-closing a polyamic acid in the presence of compound (A) to effect imidization. Specifically, the polyimide contained in the liquid crystal aligning agent of the present disclosure is preferably produced by a method including the following first step and second step. First step: A step of reacting a tetracarboxylic dianhydride with a diamine compound to obtain a polyamic acid Second step: A step of imidizing the polyamic acid obtained in the first step in the presence of compound (A) Hereinafter, each step will be described.

[0017] <First step> · Tetracarboxylic dianhydride Examples of the tetracarboxylic dianhydride used for synthesizing the polyamic acid include aliphatic tetracarboxylic dianhydrides and aromatic tetracarboxylic dianhydrides. Examples of the aliphatic tetracarboxylic dianhydride include chain tetracarboxylic dianhydrides and alicyclic tetracarboxylic dianhydrides.

[0018] Specific examples of the tetracarboxylic dianhydride include, as the chain tetracarboxylic dianhydride, for example, 1,2,3,4-butanetetracarboxylic dianhydride, ethylenediaminetetraacetic dianhydride, etc.; As the alicyclic tetracarboxylic dianhydride, for example, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic dianhydride, 5-(2,5-dioxotetrahydrofuran-3-yl)-3a,4,5,9b-tetrahydronaphtho[1,2-c]furan-1,3-dione, 5-(2,5-dioxotetrahydrofuran-3-yl)-8-methyl-3a,4,5,9b-tetrahydronaphtho[1,2-c]furan-1,3-dione, 3-oxabicyclo[3.2.1]octane-2,4-dione-6-spiro-3'-(tetrahydrofuran-2',5'-dione), 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 3,5,6-tricarboxy-2-carboxymethylnorbornane-2:3,5:6-dianhydride, bicyclo[3.3.0]octane-2,4,6,8-tetracarboxylic 2:4,6:8-dianhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic 2:3,5:6-dianhydride, 4,9-dioxatricyclo[5.3.1.0 2,6 undecane-3,5,8,10-tetraone, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, etc.; As the aromatic tetracarboxylic dianhydride, for example, pyromellitic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, p-phenylenebis(trimellitic monoester anhydride), ethylene glycol bis(anhydrotrimellitate), 1,3-propylene glycol bis(anhydrotrimellitate), 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-biphthalic dianhydride, 4,4'-oxydiphthalic dianhydride, 4,4'-carbonyldiphthalic anhydride, etc. can be respectively mentioned. In addition, the tetracarboxylic dianhydride described in JP-A-2010-97188 can also be used. The tetracarboxylic dianhydride used for the synthesis of the polyamic acid may be one kind or two or more kinds.

[0019] The tetracarboxylic dianhydride preferably contains an aliphatic tetracarboxylic dianhydride, and more preferably contains an alicyclic tetracarboxylic dianhydride, in that a liquid crystal alignment film having good voltage holding characteristics can be obtained. When synthesizing the polyimide, the amount of the alicyclic tetracarboxylic dianhydride used is preferably 20 mol% or more, more preferably 30 mol% or more, and still more preferably 50 mol% or more based on the total amount of the tetracarboxylic dianhydrides constituting the polyimide.

[0020] Among the above, the tetracarboxylic dianhydride used for synthesizing the polyamic acid preferably contains a tetracarboxylic dianhydride having a monocyclic or condensed cyclic saturated aliphatic ring with 4 to 8 carbon atoms. That is, the polyamic acid imidized in the subsequent second step preferably contains a structural unit derived from a tetracarboxylic dianhydride having a monocyclic or condensed cyclic saturated aliphatic ring with 4 to 8 carbon atoms. Specifically, it preferably contains at least one selected from the group consisting of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic dianhydride, 2,4,6,8-tetracarboxybicyclo[3.3.0]octane-2:4,6:8-dianhydride, cyclopentanetetracarboxylic dianhydride, and cyclohexanetetracarboxylic dianhydride.

[0021] ·Diamine compound Examples of the diamine compound include aliphatic diamines, aromatic diamines, diaminoorganosiloxanes, etc. Examples of the aliphatic diamines include chain diamines and alicyclic diamines.

[0022] Specific examples of the diamine compound include, as a chain diamine, metaxylylenediamine, hexamethylenediamine, etc.; as an alicyclic diamine, 1,4-diaminocyclohexane, 4,4'-methylenebis(cyclohexylamine), etc.; and as a diaminoorganosiloxane, 1,3-bis(3-aminopropyl)-tetramethyldisiloxane, etc.

[0023] Examples of the aromatic diamine include p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4-aminophenyl-4-aminobenzoate, 4,4'-diaminoazobenzene, 1,5-bis(4-aminophenoxy)pentane, 1,2-bis(4-aminophenoxy)ethane, 1,3-bis(4-aminophenoxy)propane, 1,6-bis(4-aminophenoxy)hexane, bis[2-(4-aminophenyl)ethyl]hexanedioic acid, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(4-aminophenyl)hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 4,4'-(phenylenediisopropylidene)bisaniline, 1-amino-3-aminomethylbenzene and 4,4'-bis(4-aminophenoxy)biphenyl, an aromatic diamine having a vertical alignment group, an aromatic diamine having a photoalignment group, the following formula (3) [Chemical formula] (In formula (3), R 31 and R 32 are each independently an alkanediyl group. X 31 is -COO-, -NR 33 CO- or -NR 33 CONR 34 -. R 33 and R 34 are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a thermally desorbable group. n1 is an integer of 1 to 3. When n1 is 2 or 3, a plurality of X 31are the same or different, and a plurality of Rs 32 are the same or different.) Examples thereof include compounds represented by the following formulae.

[0024] Examples of the compound represented by the above formula (3) include compounds represented by the following formulae (3-1) to (3-5). [Chemical formula]

[0025] Examples of the aromatic diamine include diamines having a basic moiety (hereinafter also referred to as "basic diamine") and diamines having an acidic moiety (hereinafter also referred to as "acidic diamine"). By introducing a structural unit derived from one or both of the basic diamine and the acidic diamine into the polyimide, the occurrence of afterimages in the liquid crystal element can be reduced. In terms of being able to achieve a higher afterimage reduction effect, the diamine compound used in the synthesis of the polyamic acid preferably contains a structural unit derived from the acidic diamine and a structural unit derived from the basic diamine.

[0026] As the basic diamine, a diamine having at least one nitrogen-containing group selected from the group consisting of a protected primary amino group, a secondary amino group, a protected secondary amino group, a tertiary amino group, and a nitrogen-containing heterocyclic group can be preferably used. Specific examples of the basic diamine include compounds represented by the following formulae (4-1) to (4-33). In the formulae, "Boc" represents a tert-butoxycarbonyl group (the same applies hereinafter). [Chemical formula] [Chemical formula]

[0027] [Chemical formula] [Chemical formula]

Chem.

[0028] Examples of the acidic diamine include diamines having a carboxy group, a sulfo group or a phosphoric acid group, and diamines having a carboxy group can be preferably used. Specific examples of the acidic diamine include compounds represented by each of the following formulas (5-1) to (5-9).

Chem.

[0029] When forming a liquid crystal alignment film for a vertically aligned type and PSA type liquid crystal element, it is preferable to use a diamine having a vertically aligning group (hereinafter also referred to as "side chain diamine") in the synthesis of polyimide. The vertically aligning group referred to here means a group capable of imparting liquid crystal aligning ability to an organic film formed by a liquid crystal aligning agent without light irradiation. Specific examples of the vertically aligning group include, for example, an alkyl group having 4 to 20 carbon atoms, an alkoxy group having 4 to 20 carbon atoms, a fluoroalkyl group having 4 to 20 carbon atoms, a fluoroalkoxy group having 4 to 20 carbon atoms, two or more rings (preferably at least one ring selected from the group consisting of a cyclohexane ring, a benzene ring and a naphthalene ring), a group having a mesogen structure formed by directly bonding or bonding via a divalent linking group (for example, an oxygen atom, -CO-, -COO- or -OCO-), a group having a steroid skeleton, and the like.

[0030] The polyimide preferably contains, as a polymer having a vertically aligning group, a polymer having a partial structure represented by the following formula (6). *-L 1 -R 61 -R 62 -R 63 -R 64 …(6) (In formula (6), L 1 is a single bond, -O-, -CO-, -COO-* 1 , -OCO-* 1 , -NR25 -, -NR 25 -CO-* 1 , -CO-NR 25 -* 1 , an alkane diyl group having 1 to 6 carbon atoms, a divalent group in which a hydrogen atom of an alkane diyl group having 2 to 6 carbon atoms is substituted with a hydroxyl group, -O-R 26 -* 1 , or -R 26 -O-* 1 (provided that R 25 is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms. R 26 is an alkane diyl group having 1 to 3 carbon atoms. "* 1 " represents a bond with R 1 ). R 61 and R 63 are each independently a single bond, a substituted or unsubstituted phenylene group, or a substituted or unsubstituted cycloalkylene group. R 62 is a single bond, a substituted or unsubstituted phenylene group, a substituted or unsubstituted cycloalkylene group, or -R 27 -B 1 -R 28 (provided that R 27 and R 28 are each independently a substituted or unsubstituted phenylene group or cycloalkylene group. B 1 is a single bond, -O-, -COO-* 2 , -OCO-* 2 , -OCH 2 -* 2 , -CH 2 O-* 2 , or an alkane diyl group having 1 to 3 carbon atoms. "* 2 " represents a bond with R 28 ). R 64 is a hydrogen atom, a fluorine atom, a cyano group, CH 3 COO-* 3 ( "* 3 " is R 3a bonding hand to (), an alkyl group having 1 to 18 carbon atoms, a fluoroalkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a fluoroalkoxy group having 1 to 18 carbon atoms, a hydrocarbon group having 17 to 51 carbon atoms having a steroid skeleton, or a monovalent group in which a hydrogen atom of an alkyl group or a fluoroalkyl group having 1 to 18 carbon atoms is substituted with a cyano group. However, R 61 , R 62 and R 63 are all single bonds, or R 61 , R 62 and R 63 only one of them has a ring structure and the number of rings in the ring structure is 1, R 64 is an alkyl group having 4 to 18 carbon atoms, a fluoroalkyl group having 4 to 18 carbon atoms, an alkoxy group having 4 to 18 carbon atoms, a fluoroalkoxy group having 4 to 18 carbon atoms, or a hydrocarbon group having 17 to 51 carbon atoms having a steroid skeleton. "*" represents a bonding hand.)

[0031] In the above formula (6), the alkanediyl group of L 1 is preferably linear. Examples of the monovalent hydrocarbon group having 1 to 10 carbon atoms of R 25 include a chain hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group, and preferably an alkyl group having 1 to 3 carbon atoms. Regarding R 64 , the alkyl group having 1 to 18 carbon atoms, the fluoroalkyl group having 1 to 18 carbon atoms, the alkoxy group having 1 to 18 carbon atoms, the fluoroalkoxy group having 1 to 18 carbon atoms, or the monovalent group in which a hydrogen atom of an alkyl group or a fluoroalkyl group having 1 to 18 carbon atoms is substituted with a cyano group is preferably linear. These groups preferably have 2 to 18 carbon atoms, more preferably 3 to 18 carbon atoms, and still more preferably 4 to 18 carbon atoms. Examples of the hydrocarbon group having 17 to 51 carbon atoms having a steroid skeleton of R 64 include a cholestanyl group, a cholesteryl group, a lanostanyl group, etc.

[0032] From the viewpoint of obtaining a liquid crystal element showing good liquid crystal alignment, the vertical alignment group is R 61 , R62 and R 63 one or more of which has a ring structure, and R 61 , R 62 and R 63 it is preferable that the total number of rings in is 2 or more, and more preferably 2 to 4.

[0033] Specific examples of the vertical alignment group include, for example, groups represented by each of the following formulas (6-1) to (6-10).

Chemical formula

[0034] Specific examples of the side chain diamine include, for example, dodecanoxy-2,4-diaminobenzene, pentadecanoxy-2,4-diaminobenzene, hexadecanoxy-2,4-diaminobenzene, octadecanoxy-2,4-diaminobenzene, pentadecanoxy-2,5-diaminobenzene, octadecanoxy-2,5-diaminobenzene, cholestanyloxy-3,5-diaminobenzene, cholestenyloxy-3,5-diaminobenzene, cholestanyloxy-2,4-diaminobenzene, cholestenyloxy-2,4-diaminobenzene, cholestanyl 3,5-diaminobenzoate, cholestenyl 3,5-diaminobenzoate, lanostanyl 3,5-diaminobenzoate, 3,6-bis(4-aminobenzoyloxy)cholestane, 3,6-bis(4-aminophenoxy)cholestane, 4-(4'-trifluoromethoxybenzoyloxy)cyclohexyl-3,5-diaminobenzoate, 1,1-bis(4-((aminophenyl)methyl)phenyl)-4-butylcyclohexane, cholestan-3-yl 3,5-diaminobenzoate, the following formula (7) [Chemical] (In formula (7), X I and X II are each independently a single bond, -O-, *-COO- or *-OCO- (wherein, “*” represents a bond to the diamino phenyl group side), R I is an alkanediyl group having 1 to 3 carbon atoms, R II is a single bond or an alkanediyl group having 1 to 3 carbon atoms, a is 0 or 1, b is an integer of 0 to 2, c is an integer of 1 to 20, and d is 0 or 1. However, a and b do not become 0 at the same time.) Compounds represented by etc. can be mentioned.

[0035] When synthesizing a polyimide having a vertical alignment group, the amount of the side-chain diamine used is preferably 2 mol% or more, more preferably 6 mol% or more, and still more preferably 10 mol% or more with respect to the total amount of diamines used in the synthesis of the polyimide. Also, from the viewpoint of ensuring solubility, the amount of the side-chain diamine used is preferably 80 mol% or less, more preferably 70 mol% or less, and still more preferably 60 mol% or less with respect to the total amount of diamines used in the synthesis of the polyimide. When synthesizing the polyimide, one kind of side-chain diamine may be used alone, or two or more kinds may be used in combination.

[0036] In addition, when synthesizing the polyimide, as the diamine compound, in addition to the above, the diamines described in JP-A-2010-97188 can be used. The diamine compound constituting the polyimide may be one kind or two or more kinds.

[0037] ·Synthesis of polyamic acid The polyamic acid can be obtained by reacting a tetracarboxylic dianhydride and a diamine compound as described above with a molecular weight regulator as necessary. The usage ratio of the tetracarboxylic dianhydride and the diamine compound used in the synthesis reaction of the polyamic acid is preferably such that the acid anhydride group of the tetracarboxylic dianhydride is 0.2 to 2 equivalents with respect to 1 equivalent of the amino group of the diamine compound.

[0038] Examples of the molecular weight regulator include acid anhydrides such as maleic anhydride, phthalic anhydride, and itaconic anhydride, monoamine compounds such as aniline, cyclohexylamine, and n-butylamine, and monoisocyanate compounds such as phenyl isocyanate and naphthyl isocyanate. The usage ratio of the molecular weight regulator is preferably 20 parts by mass or less with respect to 100 parts by mass in total of the tetracarboxylic dianhydride and diamine compound used.

[0039] The synthesis reaction of the polyamic acid is preferably carried out in an organic solvent. The reaction temperature at this time is preferably -20°C to 150°C, and the reaction time is preferably 0.1 to 24 hours.

[0040] Examples of the organic solvent used in the reaction include aprotic polar solvents, phenolic solvents, alcohols, ketones, esters, ethers, halogenated hydrocarbons, and hydrocarbons. Particularly preferred organic solvents are one or more selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, tetramethylurea, hexamethylphosphortriamide, m-cresol, xylenol, and halogenated phenol used as a solvent, or a mixture of one or more of these and other organic solvents (for example, butyl cellosolve, diethylene glycol diethyl ether, etc.) is preferably used. The usage amount (a) of the organic solvent is preferably such that the total amount (b) of the tetracarboxylic dianhydride and diamine is 0.1 to 50% by mass with respect to the total amount (a + b) of the reaction solution.

[0041] As described above, a reaction solution obtained by dissolving polyamic acid is obtained. In the imidization reaction for obtaining polyimide, this reaction solution may be used as it is, or the imidization reaction may be carried out after isolating the polyamic acid contained in the reaction solution.

[0042] <Second Step> In the second step, it is preferable to obtain a polyimide by dehydrative ring closure of the polyamic acid obtained in the first step in an organic solvent in the presence of compound (A). Specific methods for dehydrative ring closure of the polyamic acid include a method using a dehydrating agent (chemical imidization); a method of heat treatment in a temperature range of 160 to 350 °C (for example, 160 to 220 °C in solution) (thermal imidization); and the like. Further, when obtaining a polyimide with a relatively low imidization rate by chemical imidization, the polyamic acid may be dehydratively ring closed in the presence of compound (A) without using a dehydrating agent.

[0043] In the case of chemical imidization, at least one selected from the group consisting of acid anhydrides, acid chlorides, and carbodiimides can be preferably used as the dehydrating agent. Specific examples thereof include acetic anhydride, propionic anhydride, benzoic anhydride, etc. as acid anhydrides; compounds corresponding to the acid anhydrides exemplified above as acid chlorides; dicyclohexylcarbodiimide, etc. as carbodiimide compounds; and the like can be respectively cited.

[0044] The amount of the dehydrating agent used can be appropriately set according to the desired imidization rate. When using a dehydrating agent, the amount of the dehydrating agent used is usually in the range of 1 to 10 moles, preferably in the range of 1 to 5 moles, per 1 mole of the tetracarboxylic dianhydride used in the synthesis of the polyamic acid. Chemical imidization is preferably carried out at a temperature of 10 °C or higher and 120 °C or lower, more preferably at a temperature of 10 °C or higher and less than 100 °C, and still more preferably at a temperature of 25 °C or higher and 90 °C or lower, from the viewpoint of increasing the reaction rate while suppressing coloring and volatilization of the imidization catalyst.

[0045] In the case of thermal imidization, it is preferable to carry out the reaction while removing the water generated in the dehydration reaction out of the system. At that time, water may be removed by azeotropic distillation using benzene, toluene, xylene, etc. Thermal imidization is preferably carried out at a temperature of 160 °C or higher and 320 °C or lower, more preferably at a temperature of 180 °C or higher and 300 °C or lower.

[0046] As a method of imidization in the second step, imidization can be carried out by heating at a lower temperature, which is preferable in terms of reducing the process load and having a high effect of suppressing coloring. Therefore, chemical imidization is preferably performed by imidizing polyamic acid in the presence of compound (A) and a dehydrating agent.

[0047] In the second step, imidization of polyamic acid is carried out in the presence of compound (A) (a compound represented by the following formula (1)). In this case, compound (A) can function as an imidization catalyst.

Chemical formula

[0048] In the above formula (1), the alkyl group having 3 to 6 carbon atoms represented by R 1 or R 2 , and the alkyl group having 1 to 6 carbon atoms represented by R 3 may be linear or branched. R 1 and R 2 are preferably a linear or branched alkyl group having 3 or 4 carbon atoms, more preferably an isopropyl group. R 3 is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a linear alkyl group having 1 to 4 carbon atoms, and even more preferably a methyl group or an ethyl group.

[0049] The boiling point of compound (A) at 1 atm (hereinafter, also simply referred to as the boiling point) is preferably 100°C or higher and 220°C or lower. When the boiling point of compound (A) is within the above range, the duration of gelation at the initial stage of the imidization reaction can be sufficiently shortened, and compound (A) can be easily removed from the polyimide solution after imidization. As a result, the amount of impurities in the polyimide, which is the final target product, can be minimized as much as possible. For these reasons, the boiling point of compound (A) is more preferably 105°C or higher, and even more preferably 110°C or higher. Also, the boiling point of compound (A) is more preferably 215°C or lower, and even more preferably 210°C or lower.

[0050] Specific examples of compound (A) include N,N - diisopropylethylamine, tripropylamine, tributylamine, and the like.

[0051] In the imidization of the polyamic acid, the amount of compound (A) used is preferably 0.01 to 10 moles, and more preferably 0.1 to 5 moles, per 1 mole of the tetracarboxylic dianhydride used in the synthesis of the polyamic acid.

[0052] Examples of the organic solvent used in the dehydration ring - closing reaction include the same organic solvents as those exemplified for use in the synthesis of the polyamic acid. The reaction temperature of the dehydration ring - closing reaction may be set within the above - mentioned preferred temperature range according to the imidization method. The reaction time is preferably 1.0 to 120 hours.

[0053] After completion of the imidization reaction, it is preferable to remove the imidization catalyst used in the synthesis of the polyimide. The method for removing the imidization catalyst is not particularly limited, and known methods can be appropriately used. Specific examples of the method for removing the imidization catalyst include the solvent replacement method and the reprecipitation method.

[0054] The solvent replacement method is a method in which an organic solvent is added to a solution obtained by an imidization reaction (i.e., a solution containing a polyimide, an organic solvent, and an imidization catalyst) and concentrated by repeating the operation one or more times, thereby distilling off the imidization catalyst. Examples of the organic solvent to be added include the same solvents as those exemplified as the organic solvents used for the synthesis of polyamic acid, and it is preferable to use a solvent having a higher boiling point than the imidization catalyst. The polyimide solution after solvent replacement may be directly used for the preparation of a liquid crystal aligning agent, or may be used for the preparation of a liquid crystal aligning agent after isolating the polyimide.

[0055] The reprecipitation method is a method in which a solution obtained by an imidization reaction is poured into a poor solvent for polyimide (for example, methanol, etc.) to precipitate polyimide, etc., and polyimide, etc. is separated as a solid content by filtration, washing, drying, etc., and the imidization catalyst is removed.

[0056] The polyimide obtained by the above reaction preferably has a weight average molecular weight (Mw) in terms of polystyrene measured by gel permeation chromatography (GPC) of 50,000 to 500,000, more preferably 55,000 to 400,000, and even more preferably 60,000 to 300,000. When the Mw of the polyimide is within the above range, a polyimide capable of sufficiently exhibiting good mechanical properties can be obtained.

[0057] From the viewpoint of obtaining a liquid crystal alignment film excellent in high-temperature resistance and non-coloring property, the imidization rate of the polyimide is preferably 20 to 99%, and more preferably 30 to 90%. The imidization rate is expressed as a percentage of the proportion of the number of imide ring structures to the total of the number of amic acid structures and the number of imide ring structures of the polyimide.

[0058] Here, according to the study by the present inventors, when obtaining a polyamic acid using a compound having a monocyclic or condensed cyclic saturated aliphatic ring with 4 to 8 carbon atoms as the tetracarboxylic dianhydride and imidizing the polyamic acid to produce a polyimide, gelation is likely to occur at the initial stage of the imidization reaction by the addition of an imidization catalyst. On the other hand, by using compound (A) as the imidization catalyst and performing imidization of the polyamic acid in the presence of compound (A), even when the tetracarboxylic dianhydride having the above-mentioned saturated aliphatic ring is used, the time required to eliminate gelation at the initial stage of the imidization reaction can be shortened.

[0059] Further, compound (A) has a structure in which an alkyl group (R 1 , R 2 ) having a relatively large number of carbon atoms is introduced into the nitrogen atom. Therefore, in compound (A), it is considered that while maintaining the basicity of the amine compound, the nucleophilicity of the lone pair of electrons on the nitrogen atom can be reduced. As a result, although not limiting the present disclosure, the generation of impurities due to side reactions between the polyamic acid and its decomposition products, dehydrating agents, etc. present in the imidization reaction system and the imidization catalyst (that is, compound (A)) can be suppressed. As a result, it is considered that the coloring of the obtained polyimide can be reduced and the electrical properties can be improved.

[0060] The content of the polyimide in the liquid crystal aligning agent of the present disclosure is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 20% by mass or more with respect to the total mass of the solid content contained in the liquid crystal aligning agent (the total mass of components other than the solvent of the liquid crystal aligning agent). By setting the content of the polyimide within the above range, it is suitable in that a liquid crystal element capable of sufficiently enhancing the electrical reliability of the liquid crystal alignment film and maintaining good display quality even in a harsh environment such as under high temperature and high humidity can be obtained. Note that the polyimide contained in the liquid crystal aligning agent of the present disclosure may be only one kind or two or more kinds.

[0061] [Other components] Examples of other components that may be incorporated into the liquid crystal aligning agent of the present disclosure include polymers different from polyimide (hereinafter also referred to as "other polymers"), crosslinking agents, solvents, and the like.

[0062] · Other polymers The other polymer may be other than polyimide, and the type of its main skeleton is not particularly limited. Examples of the other polymer include polyamic acid, polyamic acid ester, polyimide, polyorganosiloxane, polyester, polyenamine, polyurea, polyamide, polyamideimide, addition polymer, and the like. In terms of obtaining a liquid crystal element exhibiting excellent voltage holding characteristics, the other polymer is preferably at least one selected from the group consisting of polyamic acid, polyamic acid ester, polyorganosiloxane, and addition polymer, and more preferably at least one selected from the group consisting of polyamic acid, polyorganosiloxane, and addition polymer. Examples of the addition polymer include (meth)acrylic polymers, styrene polymers, maleimide polymers, (meth)acrylic-styrene copolymers, (meth)acrylic-maleimide copolymers, (meth)acrylic-styrene-maleimide copolymers, and styrene-maleimide copolymers.

[0063] When the other polymer is incorporated into the liquid crystal aligning agent, the content of the other polymer is preferably 95 parts by mass or less, more preferably 90 parts by mass or less, based on 100 parts by mass of the polymer component contained in the liquid crystal aligning agent (that is, the total amount of polyimide and the other polymer).

[0064] When imparting liquid crystal aligning ability to the organic film formed using the liquid crystal aligning agent by means of a photo-aligning method, it is preferable that at least a part of the polyimide and the other polymer is a polymer having a photo-aligning group. The photo-aligning group refers to a functional group capable of imparting anisotropy to the film by a photoreaction such as a photo-isomerization reaction, a photo-dimerization reaction, a photo-Fries rearrangement reaction, or a photo-decomposition reaction by light irradiation.

[0065] Specific examples of the photo-aligning group include, for example, an azobenzene-containing group containing an azobenzene or its derivative as a basic skeleton, a cinnamic acid structure-containing group containing cinnamic acid or its derivative (cinnamic acid structure) as a basic skeleton, a chalcone-containing group containing chalcone or its derivative as a basic skeleton, a benzophenone-containing group containing benzophenone or its derivative as a basic skeleton, a coumarin-containing group containing coumarin or its derivative as a basic skeleton, a cyclobutane-containing structure containing cyclobutane or its derivative as a basic skeleton, a stilbene-containing group having stilbene or its derivative as a basic skeleton, a phenylbenzoate-containing group containing phenylbenzoate or its derivative as a basic skeleton, and the like. Among these, the photo-aligning group is preferably at least one selected from the group consisting of an azobenzene-containing group, a cinnamic acid structure-containing group, a chalcone-containing group, a stilbene-containing group, a cyclobutane-containing structure, and a phenylbenzoate-containing group. From the viewpoints of high sensitivity to light and ease of introduction into the polymer, a cinnamic acid structure-containing group or a cyclobutane-containing structure is preferred.

[0066] The main skeleton of the polymer having a photo-aligning group is not particularly limited. From the viewpoint of obtaining a liquid crystal element exhibiting good liquid crystal alignment properties and voltage holding characteristics, it is preferable that other polymers have a photo-aligning group. Specifically, the polymer having a photo-aligning group is more preferably at least one selected from the group consisting of an addition polymer, a polyorganosiloxane, and a polyamic acid.

[0067] The method for synthesizing the polymer having a photo-aligning group is not particularly limited. The polymer having a photo-aligning group can be obtained, for example, by (1) a method of obtaining it by polymerization using a monomer having a photo-aligning group, (2) synthesizing a polymer having a first functional group (for example, an epoxy group) in the side chain, and reacting the first functional group-containing polymer obtained by the synthesis with a reactive compound having a second functional group (for example, a carboxy group) that forms a bond with the first functional group and a photo-aligning group, and the like.

[0068] The content ratio of the photo-aligning group in the polymer can be appropriately set according to the type of the photo-aligning group so as to impart a desired liquid crystal aligning ability to the coating film. For example, in the case of a cinnamic acid structure-containing group, it is preferable that the content ratio of the photo-aligning group be 5 mol% or more, more preferably 10 to 60 mol%, based on all the structural units of the polymer having the photo-aligning group. When the photo-aligning group is a cyclobutane-containing structure, it is preferable that the content ratio of the photo-aligning group be 25 mol% or more, more preferably 40 mol% or more, based on all the constituent units of the polymer having the photo-aligning group. Note that, as the polymer having the photo-aligning group, one kind may be used alone, or two or more kinds may be used in combination.

[0069] · Crosslinking agent The liquid crystal aligning agent of the present disclosure may further contain a crosslinking agent. As the crosslinking agent, a compound having a functional group capable of reacting with an amino group or a carboxy group (hereinafter also referred to as a "crosslinkable group") can be preferably used.

[0070] Preferable specific examples of the crosslinking agent to be contained in the liquid crystal aligning agent of the present disclosure include, as the crosslinkable group, a cyclic ether group, a cyclic thioether group, an isocyanate group, a protected isocyanate group, a methylol group, a protected methylol group, an amino group, a protected amino group, a cyclic carbonate group, a group having a polymerizable carbon-carbon bond, the group "-CR 10 =CR 11 -R 12 -", (wherein R 10 is a monovalent organic group that is eliminated by reaction with an amino group. R 11 is a hydrogen atom or an alkyl group. R 12 is an electron-withdrawing group.), a silanol group, an alkoxysilyl group, a hydroxyalkylamide group, a protected hydroxyalkylamide group, a carboxy group, a protected carboxy group, and a compound having at least one selected from the group consisting of an acid anhydride group.

[0071] Among the above crosslinkable groups, examples of the group having a polymerizable carbon-carbon bond include (meth)acryloyl group, maleimide group, alkenyl group, vinylphenyl group, vinyl ether group, 3-methylenetetrahydrofuran-2(3H)-one-5-yl group, and the like. In the group “-CR 10 =CR 11 -R 12 -”, examples of the monovalent organic group represented by R 10 include, for example, an alkoxy group having 1 to 5 carbon atoms, pyrrolidone-1-yl group, halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom, etc.). Examples of the electron-withdrawing group of R 12 include carbonyl group, sulfonyl group, and the like.

[0072] From the viewpoint of improving the liquid crystal alignment property, voltage holding ratio, and film hardness in a well-balanced manner and suppressing the decrease in reworkability, the number of crosslinkable groups possessed by one molecule of the crosslinking agent is preferably 2 to 12, more preferably 2 to 10. From the viewpoint of maintaining good storage stability and mechanical strength of the film, the molecular weight of the crosslinking agent is preferably 1,500 or less, more preferably 1,200 or less, and still more preferably 800 or less.

[0073] Specific examples of the crosslinking agent include, as the compound having a polymerizable carbon-carbon bond, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate, compounds represented by the following formulas (7-1) to (7-6), etc.; As the compound having a cyclic (thio) ether group, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, triglycidyl isocyanurate, 1,6 - hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, 2,2 - dibromoneopentyl glycol diglycidyl ether, N,N,N’,N’ - tetraglycidyl - m - xylylenediamine, 1,3 - bis(N,N - diglycidylaminomethyl) cyclohexane, N,N,N’,N’ - tetraglycidyl - 4,4’ - diaminodiphenylmethane, N,N - diglycidyl - benzylamine, N,N - diglycidyl - aminomethylcyclohexane, N,N - diglycidyl - cyclohexylamine, etc.; As the compound having an isocyanate group or a protected isocyanate group, compounds represented by the following formulas (7 - 7) to (7 - 11), etc.; As the compound having a methylol group or a protected methylol group, compounds represented by the following formulas (7 - 12) to (7 - 17), etc.; As the compound having a cyclic carbonate group, compounds represented by the following formula (7 - 18) or formula (7 - 19), etc.; Group “-CR 10 =CR 11 -R 12 As the compound having “-”, compounds represented by the following formulas (7 - 20) to (7 - 26), etc.; As the compound having an alkoxysilyl group or a silanol group, 3 - glycidoxypropyltrimethoxysilane, 3 - glycidoxypropyltriethoxysilane, 3 - glycidoxypropylmethyldimethoxysilane, 2 - (3,4 - epoxycyclohexyl) ethyltriethoxysilane, 3 - (meth)acryloxypropyltrimethoxysilane, 3 - (meth)acryloxypropylmethyldimethoxysilane, 3 - (meth)acryloxypropylmethyldiethoxysilane, vinyltriethoxysilane, trimethoxysilylpropyl succinic anhydride, etc.; As the compound having an amino group or a protected amino group, compounds represented by the following formulas (7-27) to (7-31) etc.; As the compound having a hydroxyalkylamide group or a protected hydroxyalkylamide group, compounds represented by the following formulas (7-32) to (7-39) etc.; As the compound having a carboxy group, a protected carboxy group or an acid anhydride group, maleic acid, itaconic acid, trimellitic acid, tetracarboxylic acid, cis-1,2,3,4-tetrahydrophthalic acid, ethylene glycol bistrimellitate, propylene glycol bistrimellitate, 4,4'-oxydiphthalic acid, trimellitic anhydride etc. can be respectively cited. [Chemical formula] [Chemical formula] [Chemical formula] (In formulas (7-7) and (7-8), R 23 is a tert-butoxy group.) [Chemical formula] (In formula (7-16), Ac is an acetyl group.) [Chemical formula] [Chemical formula] [Chemical formula] [Chemical formula]

[0074] When a crosslinking agent is contained in the liquid crystal aligning agent of the present disclosure, from the viewpoint of enhancing the mechanical strength of the liquid crystal alignment film, the content of the crosslinking agent is preferably 0.5 parts by mass or more with respect to 100 parts by mass of the total amount of the polymer components contained in the liquid crystal aligning agent (that is, the total amount of polyimide and other polymers). The content of the crosslinking agent is more preferably 1 part by mass or more, and still more preferably 2 parts by mass or more with respect to 100 parts by mass of the total amount of the polymer components. Further, from the viewpoint of obtaining a liquid crystal element that satisfies the liquid crystal alignment property, voltage holding characteristics, and storage stability, the content of the crosslinking agent is preferably 30 parts by mass or less, and more preferably 20 parts by mass or less with respect to 100 parts by mass of the total amount of the polymer components. As the crosslinking agent, one kind may be used alone, or two or more kinds may be used in combination.

[0075] · Solvent The liquid crystal aligning agent of the present disclosure is preferably prepared as a liquid composition in which polyimide and other components used as necessary are dispersed or dissolved in an appropriate solvent.

[0076] As the solvent, an organic solvent is preferably used. Specific examples thereof include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,2-dimethyl-2-imidazolidinone, 1,3-dimethyl-2-imidazolidinone, phenol, γ-butyrolactone, γ-butyrolactam, N,N-dimethylformamide, N,N-dimethylacetamide, 4-hydroxy-4-methyl-2-pentanone, diacetone alcohol, 1-hexanol, 2-hexanol, propane-1,2-diol, 3-methoxy-1-butanol, ethylene glycol monomethyl ether, methyl lactate, ethyl lactate, butyl lactate, methyl acetate, ethyl acetate, butyl acetate, methyl acetoacetate, ethyl acetoacetate, ethyl propionate, methyl methoxypropionate, ethyl ethoxypropionate, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, ethylene glycol-i-propyl ether, ethylene glycol-n-butyl ether (butyl cellosolve), ethylene glycol dimethyl ether, ethylene glycol 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, diisobutyl ketone, isoamyl propionate, isoamyl isobutyrate, diisopentyl ether, ethylene carbonate, propylene carbonate, propylene glycol monomethyl ether (PGME), diethylene glycol diethyl ether acetate, propylene glycol monomethyl ether acetate (PGMEA), propylene glycol diacetate, cyclopentanone, cyclohexanone and the like. As the solvent, one kind may be used alone or two or more kinds may be used in admixture.

[0077] As other components contained in the liquid crystal aligning agent, in addition to the above, for example, adhesion aids, antioxidants, metal chelate compounds, curing accelerators, surfactants, fillers, dispersants, photosensitizers, etc. can be mentioned. The blending ratio of other components can be appropriately selected according to each compound within the range that does not impair the effects of the present disclosure.

[0078] The solid content concentration in the liquid crystal aligning agent (the ratio of the total mass of components other than the 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. The solid content concentration of the liquid crystal aligning agent is preferably in the range of 1 to 10% by mass. When the solid content concentration is 1% by mass or more, the film thickness of the coating film can be sufficiently ensured, and a liquid crystal alignment film showing good liquid crystal alignment properties can be easily obtained. On the other hand, when the solid content concentration is 10% by mass or less, the coating film can be made to have an appropriate thickness, and a liquid crystal alignment film showing good liquid crystal alignment properties can be easily obtained. Also, the viscosity of the liquid crystal aligning agent tends to be appropriate, and the coatability can be improved.

[0079] ≪Liquid Crystal Alignment Film and Liquid Crystal Element≫ The liquid crystal alignment film of the present disclosure is formed by the liquid crystal aligning agent prepared as described above. Also, the liquid crystal element of the present disclosure has a liquid crystal alignment film formed using the liquid crystal aligning agent described above. The operation mode of the liquid crystal in the liquid crystal element is not particularly limited, and for example, it can be applied to various modes such as TN type, STN type, VA type (including VA-MVA type, VA-PVA type, etc.), IPS (In-Plane Switching) type, FFS (Fringe Field Switching) type, OCB (Optically Compensated Bend) type, PSA type (Polymer Sustained Alignment). The liquid crystal element can be manufactured, for example, by a method including the following steps 1 to 3. The substrate used in step 1 differs depending on the desired operation mode. Steps 2 and 3 are common to each operation mode.

[0080] <Step 1: Formation of Coating Film> First, a liquid crystal aligning agent is applied onto a substrate, and preferably, a coating film is formed on the substrate by heating the coating surface. As the substrate, for example, glass such as float glass and soda glass; or a transparent substrate made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polyethersulfone, polycarbonate, poly(alicyclic olefin) can be used. When manufacturing a TN-type, STN-type, or VA-type liquid crystal element, two substrates provided with a patterned transparent conductive film are used. On the other hand, when manufacturing an IPS-type or FFS-type liquid crystal element, a substrate provided with electrodes patterned in a comb shape and a counter substrate without electrodes are used. As the transparent conductive film, a NESA film (registered trademark of PPG Industries, Inc., USA) made of tin oxide (SnO 2 ), an ITO film made of indium oxide - tin oxide (In 2 O 3 -SnO 2 ), etc. can be used. The application of the liquid crystal aligning agent onto the substrate is preferably performed on the substrate surface by an offset printing method, a flexographic printing method, a spin coating method, a roll coater method, or an inkjet printing method.

[0081] After applying the liquid crystal aligning agent, preheating (pre-bake) is preferably performed for the purpose of preventing dripping of the applied liquid crystal aligning agent. The pre-bake temperature is preferably 30 to 200°C, and the pre-bake time is preferably 0.25 to 10 minutes. Then, a baking (post-bake) process is performed for the purpose of removing the solvent in the applied liquid crystal aligning agent, etc. The baking temperature (post-bake temperature) at this time is preferably 80 to 250°C, more preferably 80 to 200°C. The post-bake time is preferably 5 to 200 minutes. The thickness of the film thus formed is preferably 0.001 to 1 μm.

[0082] <Process 2: Alignment treatment> When manufacturing a TN-type, STN-type, IPS-type, or FFS-type liquid crystal element, a process for imparting liquid crystal alignment ability (alignment process) is performed on the coating film formed in the above step 1. As a result, the alignment ability of the liquid crystal molecules is imparted to the coating film, forming a liquid crystal alignment film. As the alignment process, for example, a rubbing process in which the coating film formed on the substrate is rubbed in a certain direction with a roll wrapped with a cloth made of fibers such as nylon, rayon, or cotton, or an optical alignment process in which the coating film formed on the substrate is irradiated with light to impart liquid crystal alignment ability to the coating film can be used. On the other hand, when manufacturing a vertical alignment (VA)-type liquid crystal element, the coating film formed in the above step 1 can be used as the liquid crystal alignment film as it is. Further, in order to further enhance the liquid crystal alignment ability, the coating film may be subjected to an alignment process. A liquid crystal alignment film suitable for a vertical alignment type liquid crystal element is also suitable for a PSA-type liquid crystal element.

[0083] In the optical alignment process, the light irradiation can be performed by a method of irradiating the coating film after the post-bake process, a method of irradiating the coating film after the pre-bake process and before the post-bake process, a method of irradiating the coating film during heating of the coating film in at least one of the pre-bake process and the post-bake process, and the like. As the radiation for irradiating the coating film, for example, ultraviolet rays and visible light including light with a wavelength of 150 to 800 nm can be used. Preferably, it is ultraviolet light including light with a wavelength of 200 to 400 nm. When the radiation is polarized light, it may be linearly polarized light or partially polarized light. When the radiation used is linearly polarized light or partially polarized light, the irradiation may be performed from a direction perpendicular to the substrate surface, from an oblique direction, or a combination of these. In the case of non-polarized radiation, the irradiation direction is an oblique direction.

[0084] Examples of the light source to be used include a low-pressure mercury lamp, a high-pressure mercury lamp, a deuterium lamp, a metal halide lamp, an argon resonance lamp, a xenon lamp, an excimer laser, and the like. The irradiation amount of the radiation on the substrate surface is preferably 400 to 50,000 J / m 2 and more preferably 1,000 to 20,000 J / m 2This is the case. After light irradiation for imparting alignment ability, a treatment of cleaning the substrate surface using, for example, water, an organic solvent (e.g., methanol, isopropyl alcohol, 1-methoxy-2-propanol acetate, butyl cellosolve, ethyl lactate, etc.) or a mixture thereof, or a treatment of heating the substrate may be performed.

[0085] <Step 3: Construction of liquid crystal cell> Prepare two substrates on which the liquid crystal alignment film has been formed as described above, and manufacture a liquid crystal cell such that liquid crystal is disposed adjacent to the liquid crystal alignment film between the two substrates. To manufacture a liquid crystal cell, for example, two substrates are disposed opposite to each other with a gap therebetween such that the liquid crystal alignment films face each other, the peripheral portions of the two substrates are bonded together with a sealing agent, and liquid crystal is injected and filled into the cell gap surrounded by the substrate surface and the sealing agent, and the injection holes are sealed. Examples thereof include a method of injecting and filling liquid crystal and sealing the injection holes, and a method by the ODF method. As the sealing agent, an epoxy resin containing a curing agent and aluminum oxide spheres as spacers can be used. Examples of the liquid crystal include nematic liquid crystal and smectic liquid crystal, and among them, nematic liquid crystal is preferable. In the PSA mode, a liquid crystal cell is constructed by disposing a photopolymerizable compound together with liquid crystal between two substrates, and after the construction of the liquid crystal cell, a treatment of irradiating the liquid crystal cell with light in a state where a voltage is applied between the conductive films of a pair of substrates is performed.

[0086] When manufacturing a PSA-type liquid crystal element, the liquid crystal element can be manufactured by a method including the following steps [1] to [3]. [1] A step of applying the liquid crystal aligning agent of the present disclosure onto each of the conductive films of a pair of substrates having conductive films to form a coating film. [2] A step of constructing a liquid crystal cell by disposing a pair of substrates coated with the liquid crystal aligning agent such that the coating films face each other with a liquid crystal layer interposed therebetween. [3] A step of irradiating the liquid crystal cell with light in a state where a voltage is applied between the conductive films.

[0087] Specifically, first, a liquid crystal cell is constructed in the same manner as in the above-described Steps 1 to 3, except that a photopolymerizable compound is injected or dropped together with the liquid crystal between a pair of substrates having conductive films. As the photopolymerizable compound, conventionally known compounds can be used. Preferably, it is a polyfunctional (meth)acrylic compound.

[0088] After constructing the liquid crystal cell, the liquid crystal cell is irradiated with light while a voltage is applied between the conductive films of the pair of substrates (Step [3]). The voltage applied here can be, for example, a direct current or an alternating current of 5 to 50 V. As the light to be irradiated, for example, ultraviolet rays and visible rays including light having a wavelength of 150 to 800 nm can be used. Among these, ultraviolet rays including light having a wavelength of 300 to 400 nm are preferable. As the light source of the irradiated light, for example, a low-pressure mercury lamp, a high-pressure mercury lamp, a deuterium lamp, a metal halide lamp, an argon resonance lamp, a xenon lamp, an excimer laser, etc. can be used. The irradiation amount of light is preferably 1,000 to 200,000 J / m 2 and more preferably 1,000 to 100,000 J / m 2 .

[0089] For each mode of the liquid crystal cell, subsequently, if necessary, a polarizing plate is bonded to the outer surface of the liquid crystal cell to obtain a liquid crystal element. Examples of the polarizing plate include a polarizing plate in which a polarizing film called an "H film" that absorbs iodine while stretching and orienting polyvinyl alcohol is sandwiched between cellulose acetate protective films, or a polarizing plate composed of the H film itself.

[0090] The liquid crystal element of the present disclosure can be effectively applied to various uses. Specifically, for example, it can be applied to various display devices such as watches, portable game machines, word processors, notebook personal computers, car navigation systems, camcorders, PDAs, digital cameras, mobile phones, smartphones, various monitors, liquid crystal TVs, information displays, etc., and to light control films, retardation films, etc.

[0091] According to the present disclosure described above, the following means are provided. 〔Means 1〕A method for producing a liquid crystal aligning agent, which comprises incorporating a polyimide obtained by imidizing a polyamic acid in the presence of a compound represented by the above formula (1). 〔Means 2〕The method for producing a liquid crystal aligning agent according to 〔Means 1〕, wherein the polyamic acid contains a structural unit derived from a tetracarboxylic dianhydride having a monocyclic or condensed saturated aliphatic ring having 4 to 8 carbon atoms. 〔Means 3〕The method for producing a liquid crystal aligning agent according to 〔Means 1〕 or 〔Means 2〕, wherein the boiling point of the compound represented by the above formula (1) at 1 atm is 100 °C or higher and 220 °C or lower. 〔Means 4〕The method for producing a liquid crystal aligning agent according to any one of 〔Means 1〕 to 〔Means 3〕, wherein the imidization of the polyamic acid is carried out at a temperature of 10 °C or higher and lower than 100 °C. 〔Means 5〕The method for producing a liquid crystal aligning agent according to any one of 〔Means 1〕 to 〔Means 4〕, wherein the imidization of the polyamic acid is carried out in the presence of at least one dehydrating agent selected from the group consisting of acid anhydrides, acid chlorides, and carbodiimides and the compound represented by the above formula (1). 〔Means 6〕The method for producing a liquid crystal aligning agent according to any one of 〔Means 1〕 to 〔Means 5〕, which further contains a polymer different from the polyimide. 〔Means 7〕A cyclic ether group, a cyclic thioether group, an isocyanate group, a protected isocyanate group, a methylol group, a protected methylol group, an amino group, a protected amino group, a cyclic carbonate group, a group having a polymerizable carbon-carbon bond, the group “-CR 10 =CR 11 -R 12 -” (wherein R 10 is a monovalent organic group that is eliminated by reaction with an amino group. R 11 is a hydrogen atom or an alkyl group. R 12 is an electron-withdrawing group.), a silanol group, an alkoxysilyl group, a hydroxyalkylamide group, a protected hydroxyalkylamide group, a carboxy group, a protected carboxy group, and an acid anhydride group, and further contains a compound having a total of two or more of at least one group selected from the group consisting of these groups. The method for producing a liquid crystal aligning agent according to any one of 〔Means 1〕 to 〔Means 6〕. 〔Means 8〕A liquid crystal aligning agent containing a polyimide obtained by imidizing a polyamic acid in the presence of the compound represented by the above formula (1). 〔Means 9〕The liquid crystal aligning agent according to 〔Means 8〕, wherein the polyimide contains a structural unit derived from a tetracarboxylic acid derivative having a monocyclic or condensed cyclic saturated aliphatic ring having 4 to 8 carbon atoms. 〔Means 10〕The liquid crystal aligning agent according to 〔Means 8〕 or 〔Means 9〕, further containing a polymer different from the polyimide. 〔Means 11〕Furthermore, a cyclic ether group, a cyclic thioether group, an isocyanate group, a protected isocyanate group, a methylol group, a protected methylol group, an amino group, a protected amino group, a cyclic carbonate group, a group having a polymerizable carbon-carbon bond, the group "-CR 10 =CR 11 -R 12 -」(However, R 10 is a monovalent organic group that is eliminated by reaction with an amino group. R 11 is a hydrogen atom or an alkyl group. R 12 is an electron-withdrawing group.), A silanol group, an alkoxysilyl group, a hydroxyalkylamide group, a protected hydroxyalkylamide group, a carboxy group, a protected carboxy group, and a liquid crystal aligning agent according to any one of 〔Means 8〕 to 〔Means 10〕 containing at least two compounds selected from the group consisting of acid anhydride groups in total. 〔Means 12〕A liquid crystal alignment film formed using the liquid crystal aligning agent according to any one of 〔Means 8〕 to 〔Means 11〕. 〔Means 13〕A liquid crystal element including the liquid crystal alignment film of 〔Means 12〕. 〔Means 14〕A first step of reacting a tetracarboxylic dianhydride and a diamine compound to obtain a polyamic acid, and a second step of imidizing the polyamic acid obtained in the first step, wherein the tetracarboxylic dianhydride includes a tetracarboxylic dianhydride having a monocyclic or condensed cyclic saturated aliphatic ring having 4 to 8 carbon atoms, and in the second step, the polyamic acid is imidized in the presence of the compound represented by the above formula (1). A method for producing a polyimide.

Example

[0092] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples.

[0093] In the following examples, the solution viscosity, weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer, and the imidization rate of the polyimide were measured by the following methods. <Solution viscosity of polymer> The solution viscosity of the polymer was measured at 25 °C using an E-type viscometer. <Weight average molecular weight (Mw) and number average molecular weight (Mn)> Mw and Mn were measured under the following conditions by gel permeation chromatography (GPC). The molecular weight distribution (Mw / Mn) was calculated from the obtained Mw and Mn. Apparatus: "GPC-101" manufactured by Showa Denko K.K. GPC columns: "GPC-KF-801", "GPC-KF-802", "GPC-KF-803" and "GPC-KF-804" manufactured by Shimadzu GL Sciences Inc. were connected. Mobile phase: Tetrahydrofuran (THF) Column temperature: 40 °C Flow rate: 1.0 mL / min Sample concentration: 1.0 mass% Sample injection volume: 100 μL Detector: Differential refractometer Standard substance: Monodisperse polystyrene <Imidization rate of polyimide> The polyimide solution was poured into pure water, and the obtained precipitate was sufficiently dried under reduced pressure at room temperature, then dissolved in deuterated dimethyl sulfoxide, and at room temperature using tetramethylsilane as a reference substance. 1 1H-NMR measurement was performed. The obtained 1 From the 1H-NMR spectrum, the imidization rate [%] was determined by the following formula (1). Imidization rate [%] = (1 - (β 1 / (β 2 × α))) × 100 …(1) (In formula (1), β 1 is the peak area derived from the proton of the NH group appearing around 10 ppm in chemical shift, and β 2is the peak area derived from other protons, and α is the ratio of the number of other protons to one proton of the NH group in the precursor (polyamic acid) of the polymer.)

[0094] The abbreviations of the compounds used in the following examples are shown below. For convenience, hereinafter, "the compound represented by the formula (X)" may be simply referred to as "compound (X)". "Parts" and "%" in the examples and comparative examples are based on mass unless otherwise specified.)

[0095] · Tetracarboxylic dianhydride

Chemical formula

[0096] · Diamine compound

Chemical formula

Chemical formula

Chemical formula

[0097] · Polymerizable carbon-carbon bond-containing monomer

Chemical formula

[0098] · Alkoxysilane monomer and carboxylic acid

Chemical formula

[0099] · Crosslinking agent

Chemical formula

[0100] · Imidization catalyst

Chemical formula

[0101] The boiling points of the imidization catalysts used in the following Examples and Comparative Examples are shown in Table 1. [Table 1]

[0102] [Synthesis of Polymer] 1. Synthesis of Polyamic Acid [Synthesis Example 1] 100 mol parts of compound (TA-1) as a tetracarboxylic dianhydride, 20 mol parts of compound (DA-1), 50 mol parts of compound (DC-1), and 30 mol parts of compound (DD-1) were dissolved in N-methyl-2-pyrrolidone (NMP), and reacted at 60°C for 6 hours to obtain a solution containing 20% by mass of polyamic acid (this is referred to as polymer (PAA-1)).

[0103] [Synthesis Examples 2 to 18] The same operations as in Synthesis Example 1 were carried out except that the types and amounts of the tetracarboxylic dianhydride and diamine compound used were changed as shown in Table 2, and polyamic acids (polymers (PAA-2) to polymer (PAA-18)) were obtained. In Table 2, the numerical values of the tetracarboxylic dianhydride represent the ratio (molar ratio) of each compound to the total amount of 100 mol parts of the tetracarboxylic dianhydride used in the synthesis of the polyamic acid. The numerical values of the diamine compound represent the ratio (molar ratio) of each compound to the total amount of 100 mol parts of the diamine compound used in the synthesis of the polyamic acid.

[0104] [Table 2]

[0105] 2. Synthesis of Polyimide [Synthesis Example 19] A 100 mL three-necked flask equipped with a reflux tube and a stir bar (oval strong magnetic stir bar 10×20 mm SCS1020V) was charged with a polyamic acid (PAA-1) solution, and then NMP was added to make a solution with a polyamic acid concentration of 10% by mass. To this solution, N,N-diisopropylethylamine (compound (BA-1)) was added in an amount of 1.8 molar equivalents relative to the amide groups of the polyamic acid, and acetic anhydride (Ac 2 O) was added in an amount of 1.2 molar equivalents relative to the amide groups of the polyamic acid. The reaction vessel was heated to 60 °C in an oil bath, and a dehydration ring-closure reaction was carried out for 4 hours while rotating the stir bar at 500 rpm using a magnetic stirrer (AMG-S manufactured by ASH). After the dehydration ring-closure reaction, the solvent was replaced by repeating the operation of adding fresh NMP and then concentrating with an evaporator (N-1300 manufactured by EYELA). As a result, a solution containing 15% by mass of polyimide (referred to as polymer (PI-1) hereinafter) with an imidization rate of about 58% (hereinafter, also simply referred to as "polyimide solution") was obtained.

[0106] [Synthesis Examples 20 to 44] The same operations as in Synthesis Example 19 were carried out except that the type and amount of the polyamic acid, imidization catalyst, the amount of the dehydrating agent, and the reaction temperature for imidization were changed as shown in Table 3, and polyimides (polymers (PI-2) to polymer (PI-26)) were obtained. In Table 3, the amounts of the imidization catalyst and the dehydrating agent represent the amounts (unit: molar equivalent) relative to the amide groups of the polyamic acid. In Table 3, the notation "Ac2O" represents acetic anhydride. The notation "-" indicates that the corresponding component was not used.

[0107] [Table 3]

[0108] 3. Synthesis of Polyorganosiloxane [Synthesis Example 45] Into a 1000 mL three-necked flask, 100.0 g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (Compound (S-1)), 500 g of methyl isobutyl ketone, and 10.0 g of triethylamine were charged and mixed at room temperature. Next, 100 g of deionized water was added dropwise from a dropping funnel over 30 minutes, and then the reaction was carried out at 80 °C for 6 hours while mixing under reflux. After completion of the reaction, the organic layer was taken out, washed with a 0.2 mass% aqueous ammonium nitrate solution until the water became neutral after washing, and then the solvent and water were distilled off under reduced pressure. An appropriate amount of methyl isobutyl ketone was added to obtain a 50 mass% solution of a polymer (ESSQ-1) which is a polyorganosiloxane having an epoxy group. Into a 500 mL three-necked flask, 3.10 g of Compound (S-2) (20 mol% based on the amount of epoxy groups in the polymer (ESSQ-1)), 3.24 g of Compound (S-3) (10 mol% based on the amount of epoxy groups in the polymer (ESSQ-1)), 1.00 g of tetrabutylammonium bromide, 20.0 g of the polymer (ESSQ-1) - containing solution, and 290.0 g of methyl isobutyl ketone were added, and the mixture was stirred at 90 °C for 18 hours. After cooling to room temperature, the liquid separation washing operation with distilled water was repeated 10 times. Then, the organic layer was recovered, and concentration and NMP dilution were repeated twice with a rotary evaporator, and then adjusted with NMP so that the solid content concentration became 10 mass% to obtain an NMP solution of a polyorganosiloxane (this is designated as polymer (PSQ-1)).

[0109] 4. Synthesis of Styrene-Maleimide Copolymer [Synthesis Example 46] Under nitrogen, 18.7 mmol of compound (M-2), 18.7 mmol of compound (M-4), 10.6 mmol of compound (M-6), and 5.3 mmol of compound (M-7) were added as polymerization monomers to a 100 mL two-necked flask, 0.98 g of 2,2'-azobis(2,4-dimethylvaleronitrile) was added as a radical polymerization initiator, and 50 mL of N-methyl-2-pyrrolidone (NMP) was added as a solvent. Polymerization was carried out at 70 °C for 6 hours. After reprecipitation in methanol, the precipitate was filtered and vacuum-dried at room temperature for 8 hours to obtain a styrene-maleimide copolymer (designated as polymer (MI-1)) as an addition polymer. The weight average molecular weight (Mw) measured by GPC in terms of polystyrene was 35,000, and the molecular weight distribution (Mw / Mn) was 2.

[0110] [Synthesis Example 47] The same procedure as in Synthesis Example 46 was carried out except that the types and amounts of the polymerization monomers used were changed as shown in Table 4 to obtain an addition polymer (polymer (MI-2)).

[0111] [Table 4]

[0112] 5. Evaluation [Examples 1 to 16, Comparative Examples 1 to 10] Regarding the polyimides produced in Synthesis Examples 19 to 44, the time from when gelation occurred with the addition of an imidization catalyst during the production of the polyimide until the gelation was resolved (hereinafter referred to as the "gelation duration"), the degree of reduction of the imidization catalyst after removing the imidization catalyst by the solvent substitution method (hereinafter referred to as the "catalyst removability"), and the film transmittance were evaluated. The evaluation results are shown in Table 5.

[0113] 〈Evaluation of Gelation Duration〉 In each synthesis example, after adding an imidization catalyst into the reaction vessel, the time t (min) from when the rotation of the stirrer chip completely stopped due to gelation until the stirrer chip started rotating again was measured with a stopwatch. When t ≤ 10, it was rated as "good (◎)"; when 10 < t ≤ 30, it was rated as "acceptable (○)"; when 30 < t, it was rated as "poor (×)".

[0114] 〈Evaluation of Catalyst Removability〉 The concentration of the imidization catalyst in the polyimide solution obtained in each synthesis example was measured by gas chromatography (column: manufactured by Agilent, hP-5MS UI (inner diameter) 0.25 mm × (length) 30 m (film thickness) 0.25 μm, 50 °C to 325 °C (10 °C / min), 5 min hold / carrier gas: helium / detector: MS FID). The measurement of the imidization catalyst concentration in the polyimide solution was performed by preparing a calibration curve of the imidization catalyst in advance and quantifying it by the external standard method (absolute calibration curve method). When the concentration of the imidization catalyst remaining in the polyimide solution obtained in each synthesis example was c (ppm), when c ≤ 100, it was rated as "good (○)"; when 100 < c, it was rated as "poor (×)".

[0115] 〈Evaluation of Membrane Permeability〉 NMP and butyl cellosolve (BC) were added to the polyimide solution obtained in each synthesis example to prepare a solution with a solvent composition of NMP / BC = 50 / 50 (mass ratio) and a solid content concentration of 4.0 mass%. By filtering this solution through a filter with a pore size of 0.2 μm, liquid crystal alignment agents (AL-1 to Al-16, AR-1 to AR-10) were prepared. Subsequently, the liquid crystal aligning agent was applied onto a quartz substrate using a spin coater, heated on a hot plate at 70°C for 200 seconds, and then heated in an oven at 230°C with the inside of the oven replaced with nitrogen for 20 minutes to form a coating film with an average film thickness of 100 nm. Regarding the coating film formed on the quartz substrate, an absorption spectrum in the ultraviolet-visible light region was measured using an ultraviolet-visible near-infrared spectrophotometer (manufactured by JASCO Corporation, product name "V-670"), and the transmittance at 400 nm (this is referred to as "transmittance measurement value UV-AL") was obtained. In the measurement, P-polarization was used with a polarizing filter, and the incident angle to the substrate was set to the Brewster angle to suppress the influence of reflection. Also, the transmittance measurement value UV-AL was determined using the same type of quartz substrate without a coating film as a reference. Separately, for each example and comparative example, the same type of polyamic acid was used (for example, in Example 1, polymer (PAA-1) was used as the polyamic acid, and in Example 3, polymer (PAA-2) was used as the polyamic acid). The same operations as in Synthesis Example 1 were performed except that the imidization catalyst used for the imidization of the polyamic acid was 2.0 molar equivalents of pyridine and the dehydrating agent was 2.0 molar equivalents of acetic anhydride to synthesize polyimide. Also, the same operations as above were performed except that the synthesized polyimide was used, and the transmittance at 400 nm of the coating film formed on the quartz substrate (this is referred to as "transmittance control value UV-ref") was determined and used as a reference. For each example and comparative example, the transmittance difference ΔUV was obtained by subtracting the transmittance control value UV-ref from the transmittance measurement value UV-AL, and the film transmittance was evaluated based on the transmittance difference ΔUV. The evaluation was as follows: when ΔUV was 0.5% or more, it was rated as "good (◎)"; when it was greater than 0% and less than 0.5%, it was rated as "acceptable (○)"; when it was 0% or less, it was rated as "unacceptable (×)".

[0116] [Table 5]

[0117] [Example 17: PSA-Type Liquid Crystal Display Element] (1) Preparation of Liquid Crystal Aligning Agent To a solution containing 25 parts by mass of the polymer (PI-1) obtained in Synthesis Example 19, 70 parts by mass of the polymer (PAA-13) obtained in Synthesis Example 13, 5 parts by mass of the polymer (MI-1), 10 parts by mass of the additive (AD-2), and NMP and butyl cellosolve (BC) as solvents were added to obtain a solution with a solvent composition of NMP / BC = 50 / 50 (mass ratio) and a solid content concentration of 4.0% by mass. This solution was filtered through a filter with a pore size of 0.2 μm to prepare a liquid crystal aligning agent (AL-17).

[0118] (2) Preparation of Liquid Crystal Composition To 10 g of a nematic liquid crystal (manufactured by Merck, MLC-6608), 5% by mass of a liquid crystalline compound represented by the following formula (L1-1) and 0.3% by mass of a photopolymerizable compound represented by the following formula (L2-1) were added and mixed to obtain a liquid crystal composition LC1. [Chemical formula]

[0119] (3) Manufacture of PSA-Type Liquid Crystal Display Element After storing the liquid crystal aligning agent (AL-17) prepared in (1) above in a freezer at -15°C for 7 days, it was thawed at room temperature. The thawed liquid crystal aligning agent (AL-17) was applied onto each electrode surface of two glass substrates each having a conductive film composed of an ITO electrode patterned in a slit shape using a liquid crystal alignment film printer (manufactured by Nippon Shashin Printing Co., Ltd.), heated (pre-baked) on a hot plate at 80°C for 2 minutes to remove the solvent, and then heated (post-baked) on a hot plate at 230°C for 10 minutes to form a coating film with an average film thickness of 0.06 μm. The coating film was subjected to ultrasonic cleaning in ultrapure water for 1 minute and then dried in a 100°C clean oven for 10 minutes to obtain a pair (two sheets) of substrates having liquid crystal alignment films. The pattern of the electrodes used was the same type of pattern as the electrode pattern in the PSA mode. Next, an epoxy resin adhesive containing aluminum oxide spheres with a diameter of 5.5 μm was applied to the outer edge of the surface having the liquid crystal alignment film of one of the pair of substrates. Then, the substrates were overlapped so that the liquid crystal alignment film surfaces faced each other, pressed together, and the adhesive was cured. Next, the liquid crystal composition LC1 prepared in (b) above was filled between the pair of substrates through the liquid crystal injection port. Then, the liquid crystal cell was manufactured by sealing the liquid crystal injection port with an acrylic-based photocurable adhesive. Thereafter, an alternating current of 10 V at a frequency of 60 Hz was applied between the conductive films of the liquid crystal cell. While the liquid crystal was being driven, ultraviolet rays were irradiated using an ultraviolet irradiation device with a metal halide lamp as the light source at an irradiation dose of 100,000 J / m 2 The irradiation dose was measured using a photometer measured based on a wavelength of 365 nm. Thereafter, polarizing plates were attached to both outer surfaces of the substrates such that their polarization directions were orthogonal to each other and formed an angle of 45° with the projection direction of the optical axis of the ultraviolet rays of the liquid crystal alignment film onto the substrate surface, thereby manufacturing a PSA-type liquid crystal display element.

[0120] (4) Evaluation of voltage holding characteristics The voltage holding ratio (VHR) of the PSA-type liquid crystal display element manufactured in (3) above was measured, and this value was designated as the VHR measurement value VHR-AL. The measurement of the voltage holding ratio was performed using a VHR-1 manufactured by Toyo Technica Co., Ltd. Separately, for each example and comparative example, the same type of polyamic acid was used. The same operations as in Synthesis Example 1 were performed except that the imidization catalyst used for imidizing the polyamic acid was 2.0 molar equivalents of pyridine and the dehydrating agent was 2.0 molar equivalents of acetic anhydride to synthesize polyimide. Also, a PSA-type liquid crystal display element was manufactured by performing the same operations as in (1) to (3) above except that the synthesized polyimide was used, and the voltage holding ratio (VHR) was measured. This value was designated as the VHR control value VHR-ref. For each of the examples and comparative examples, the difference ΔVHR in VHR was obtained by subtracting the VHR control value VHR-ref from the VHR measurement value VHR-AL, and the voltage holding characteristics were evaluated based on ΔVHR. The evaluation was defined as "good (◎)" when ΔVHR was greater than 5.0%, "acceptable (○)" when it was greater than 0% and less than or equal to 5.0%, and "poor (×)" when it was less than or equal to 0%. As a result, the voltage holding characteristics of this example were evaluated as "good (◎)".

[0121] [Examples 18 to 23, 31 and Comparative Examples 11, 12, 17, 20] Liquid crystal aligning agents (AL-18) to (AL-23), (AL-31), (AR-11), (AR-12), (AR-17) and (AR-20) were prepared with the same solvent composition and solid content concentration as in Example 17, except that the composition of the liquid crystal aligning agent was changed as shown in Table 6. Further, using each liquid crystal aligning agent, a PSA-type liquid crystal display element was manufactured in the same manner as in Example 17, and the voltage holding characteristics were evaluated. The results are shown in Table 6. In Table 6, the numerical values in parentheses for each component in the aligning agent composition represent the blending amount (parts by mass). In the table, a blank indicates that the compound was not used.

[0122] [Example 24: FFS-type liquid crystal display element using the photo-alignment method] (1) Preparation of liquid crystal aligning agent A liquid crystal aligning agent (AL-24) was prepared with the same solvent composition and solid content concentration as in Example 17, except that the composition of the liquid crystal aligning agent was changed as shown in Table 6.

[0123] (2) Manufacture of FFS-type liquid crystal cell using the photo-alignment method The liquid crystal aligning agent (AL-24) prepared above was stored in a freezer at -15°C for 7 days and then thawed at room temperature. A glass substrate (first substrate) with a flat electrode, an insulating layer, and a comb-shaped electrode laminated in this order on one side, and a counter glass substrate (second substrate) without an electrode were prepared. The thawed liquid crystal aligning agent (AL-24) was applied to the electrode formation surface of the first substrate and one substrate surface of the second substrate using a spinner, and heated (pre-baked) on a hot plate at 80°C for 1 minute. Then, drying (post-baking) was performed in an oven at 230°C with the inside of the oven replaced with nitrogen for 30 minutes to form a coating film with an average film thickness of 0.1 μm. The obtained coating film was irradiated with ultraviolet light containing a linearly polarized emission line of 254 nm using an Hg-Xe lamp 2 from the substrate normal direction to perform photo-alignment treatment. The irradiation amount was a value measured using a light meter measured based on a wavelength of 254 nm. Next, the coating film subjected to the photo-alignment treatment was heated in a clean oven at 230°C for 30 minutes to perform heat treatment to form a liquid crystal alignment film. Next, for one of the pair of substrates on which the liquid crystal alignment film was formed, an epoxy resin adhesive containing aluminum oxide spheres with a diameter of 3.5 μm was applied by screen printing to the outer edge of the surface having the liquid crystal alignment film. Then, the substrates were overlapped and pressed so that the projection direction of the polarization axis on the substrate surface during light irradiation was anti-parallel, and the adhesive was thermally cured at 150°C for 1 hour. Next, a negative-type liquid crystal (manufactured by Merck, MLC-6608) was filled between the pair of substrates through a liquid crystal injection port, and then the liquid crystal injection port was sealed with an epoxy-based adhesive to obtain a liquid crystal cell. Further, in order to remove the flow alignment during liquid crystal injection, this was heated at 120°C and then gradually cooled to room temperature. Then, polarizing plates were bonded to both outer surfaces of the substrates in the liquid crystal cell to obtain a liquid crystal display element. Also, by performing the above series of operations while changing the ultraviolet light irradiation amount after post-baking in the range of 100 to 10,000 J / m 2 respectively, three or more liquid crystal display elements with different ultraviolet light irradiation amounts were manufactured, and the liquid crystal display element with the exposure amount (optimum exposure amount) showing the best alignment characteristics was used for the evaluation of the voltage holding characteristics.

[0124] (3) Evaluation of voltage holding characteristics Regarding the FFS-type liquid crystal cell manufactured by the photo-alignment method in the above (2), the voltage holding characteristics were evaluated in the same manner as in Example 17. The results are shown in Table 6.

[0125] [Examples 25 to 27, Comparative Examples 13, 14, 18, 19] Liquid crystal aligning agents (AL-25) to (AL-27), (AR-13), (AR-14), (AR-18), and (AR-19) were prepared with the same solvent composition and solid content concentration as in Example 17, except that the composition of the liquid crystal aligning agent was changed as shown in Table 6. Further, using each liquid crystal aligning agent, an FFS liquid crystal display element was manufactured by the photo-alignment method in the same manner as in Example 24, and the voltage holding characteristics were evaluated. The results are shown in Table 6.

[0126] [Example 28: FFS-type liquid crystal display element using the rubbing method] (1) Preparation of liquid crystal aligning agent A liquid crystal aligning agent (AL-28) was prepared with the same solvent composition and solid content concentration as in Example 17, except that the composition of the liquid crystal aligning agent was changed as shown in Table 6.

[0127] (2) Manufacture of FFS-type liquid crystal display element using the rubbing method The liquid crystal aligning agent (AL-28) prepared above was stored in a freezer at -15°C for 7 days and then thawed at room temperature. A glass substrate (first substrate) with a flat electrode, an insulating layer, and a comb-shaped electrode laminated on one side in this order, and a counter glass substrate (second substrate) without an electrode were prepared. The thawed liquid crystal aligning agent was applied to each of the electrode formation surface of the first substrate and one substrate surface of the second substrate using a spinner, and pre-baked on a hot plate at 80°C for 1 minute. Then, it was heated at 230°C for 1 hour in an oven with the inside replaced by nitrogen to form a coating film with a film thickness of 0.1 μm. The coating film was subjected to a rubbing treatment with a rubbing machine having a roll wrapped with a nylon cloth at a roll rotation speed of 1000 rpm, a stage moving speed of 2.5 cm / second, and a brush pressing length of 0.4 mm. Then, ultrasonic cleaning was performed in ultrapure water for 1 minute, and then dried in a 100°C clean oven for 10 minutes to obtain a pair of substrates having liquid crystal alignment films. An epoxy resin adhesive containing aluminum oxide spheres with a diameter of 3.5 μm was applied by screen printing to the outer periphery of the surface of one of the pair of substrates having a liquid crystal alignment film. Then, the substrates were overlapped and pressure-bonded so that the liquid crystal alignment film surfaces faced each other, and the adhesive was cured. Next, a nematic liquid crystal (manufactured by Merck, MLC-6608) was filled between the pair of substrates through a liquid crystal injection port. Then, the liquid crystal injection port was sealed with an acrylic-based photocurable adhesive, and polarizing plates were bonded to both outer surfaces of the substrates to manufacture a rubbing FFS type liquid crystal display element.

[0128] (3) Evaluation of voltage holding characteristics Regarding the FFS type liquid crystal cell manufactured by the rubbing method in (2) above, the voltage holding characteristics were evaluated in the same manner as in Example 17 above. The results are shown in Table 6.

[0129] [Examples 29, 30 and Comparative Examples 15, 16] Liquid crystal aligning agents (AL-29), (AL-30), (AR-15) and (AR-16) were prepared with the same solvent composition and solid content concentration as in Example 17, except that the composition of the liquid crystal aligning agent was changed as shown in Table 6. Further, using each liquid crystal aligning agent, an FFS type liquid crystal display element was manufactured by the rubbing method in the same manner as in Example 28, and the voltage holding characteristics were evaluated. The results are shown in Table 6.

[0130]

Table 6

[0131] As is clear from the results in Table 5, by synthesizing polyimide using the compounds (compounds (BA-1) to (BA-3)) represented by the above formula (1) as imidization catalysts, the time from the occurrence of gelation to the disappearance of gelation could be shortened in comparison with the case where compound (BA-4) or compound (BA-6) was used as the imidization catalyst. In particular, when compound (BA-1) was used, the time until the gelation disappeared could be further shortened. Further, by using compounds (BA-1) to (BA-3) as the imidization catalyst, the coloring of the polyimide could be reduced, and a liquid crystal alignment film with a high film transmittance could be formed. When polyimide was synthesized without using an imidization catalyst, gelation occurred for a long time during imidization (Comparative Example 10), and the results were inferior to those of Examples 1 to 16.

[0132] Also, as shown in Table 6, by using the polyimide obtained by using the compounds (compounds (BA-1) to (BA-3)) represented by the above formula (1) as the polymer component of the liquid crystal aligning agent, a liquid crystal element excellent in voltage holding ratio could be obtained in comparison with the case where compounds (BA-4) to (BA-7) were used as the imidization catalyst. In particular, when compound (BA-1) was used, the improvement effect on the voltage holding ratio was high and excellent.

[0133] From the above results, it was clarified that the polyimide imidized using the compound represented by the above formula (1) could shorten the duration of gelation after the addition of the imidization catalyst, and could reduce the process load of the imidization step. Further, according to the liquid crystal aligning agent containing polyimide imidized using the compound represented by the above formula (1), it was possible to reduce the mixing of the imidization catalyst that could become an impurity, to form a liquid crystal alignment film excellent in non-coloring property, and to obtain a liquid crystal element excellent in electrical characteristics.

Claims

1. A method for producing a liquid crystal aligning agent, comprising incorporating a polyimide obtained by imidizing a polyamic acid in the presence of a compound represented by the following formula (1). 【Chemical 1】 (In formula (1), R １ and R ２ are, independently of each other, alkyl groups having 3 to 6 carbon atoms. R ３ is an alkyl group having 1 to 6 carbon atoms.)

2. The method for producing a liquid crystal aligning agent according to claim 1, wherein the polyamic acid contains a structural unit derived from a tetracarboxylic dianhydride having a monocyclic or condensed saturated aliphatic ring having 4 to 8 carbon atoms.

3. The method for producing a liquid crystal aligning agent according to claim 1 or 2, wherein the compound represented by the above formula (1) has a boiling point at 1 atm of 100°C or higher and 220°C or lower.

4. The method for producing a liquid crystal aligning agent according to claim 1 or 2, wherein the imidization of the polyamic acid is carried out at a temperature of 10°C or higher and lower than 100°C.

5. The method for producing a liquid crystal aligning agent according to claim 1 or 2, wherein the imidization of the polyamic acid is carried out in the presence of at least one dehydrating agent selected from the group consisting of acid anhydrides, acid chlorides, and carbodiimides and the compound represented by the above formula (1).

6. The method for producing a liquid crystal aligning agent according to claim 1 or 2, further comprising incorporating a polymer different from the polyimide.

7. A cyclic ether group, a cyclic thioether group, an isocyanate group, a protected isocyanate group, a methylol group, a protected methylol group, an amino group, a protected amino group, a cyclic carbonate group, a group having a polymerizable carbon-carbon bond, the group “—CR １０ =CR １１ —R １２ —” (wherein R １０ is a monovalent organic group that is eliminated by reaction with an amino group. R １１ is a hydrogen atom or an alkyl group. R １２ is an electron-withdrawing group.), a silanol group, an alkoxysilyl group, a hydroxyalkylamide group, a protected hydroxyalkylamide group, a carboxy group, a protected carboxy group, and an acid anhydride group, and further contains a compound having at least two of the groups selected from the group consisting of, the method for producing a liquid crystal aligning agent according to claim 1 or 2.

8. A liquid crystal aligning agent containing a polyimide obtained by imidizing a polyamic acid in the presence of a compound represented by the following formula (1). [Chemical 2] (In formula (1), R １ and R ２ are, independently of each other, an alkyl group having 3 to 6 carbon atoms. R ３ is an alkyl group having 1 to 6 carbon atoms.)

9. The liquid crystal aligning agent according to claim 8, wherein the polyimide contains a structural unit derived from a tetracarboxylic acid derivative having a monocyclic or condensed saturated aliphatic ring having 4 to 8 carbon atoms.

10. The liquid crystal aligning agent according to claim 8, further comprising a polymer different from the polyimide.

11. Furthermore, an annular ether group, an annular thioether group, an isocyanate group, a protected isocyanate group, a methylol group, a protected methylol group, an amino group, a protected amino group, an annular carbonate group, a group having a polymerizable carbon-carbon bond, a group “—CR １０ =CR １１ —R １２ —” (wherein R １０ is a monovalent organic group that is eliminated by reaction with an amino group. R １１ is a hydrogen atom or an alkyl group. R １２ is an electron-withdrawing group.), a silanol group, an alkoxysilyl group, a hydroxyalkylamide group, a protected hydroxyalkylamide group, a carboxy group, a protected carboxy group, and at least one group selected from the group consisting of acid anhydride groups, and containing a compound having a total of two or more such groups, the liquid crystal aligning agent according to claim 8.

12. A liquid crystal alignment film formed using the liquid crystal aligning agent according to any one of claims 8 to 11.

13. A liquid crystal element including the liquid crystal alignment film according to claim 12.

14. A first step of reacting a tetracarboxylic dianhydride and a diamine compound to obtain a polyamic acid, a second step of imidizing the polyamic acid obtained in the first step, including the tetracarboxylic dianhydride includes a tetracarboxylic dianhydride having a monocyclic or condensed saturated aliphatic ring having 4 to 8 carbon atoms, in the second step, a method for producing a polyimide, wherein the polyamic acid is imidized in the presence of a compound represented by the following formula (1). [Chemical Formula 3] (In formula (1), R １ and R ２ are each independently an alkyl group having 3 to 6 carbon atoms. R ３ is an alkyl group having 1 to 6 carbon atoms.)

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