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

Abstract

Provided are: a liquid crystal aligning agent that exhibits good afterimage characteristics even when the light irradiation amount in the alignment treatment based on the photo-alignment method is reduced, in liquid crystal display elements of an IPS driving method or an FFS driving method, a method for producing the same, a liquid crystal alignment film obtained therefrom, and a liquid crystal display element including the same. A liquid crystal aligning agent containing polyimide, the polyimide being an imidized product of a polyimide precursor obtained by a polycondensation reaction of a tetracarboxylic acid component containing a tetracarboxylic dianhydride represented by the following formula (1) or a derivative thereof, and a diamine component containing a first diamine represented by the following formula (3) and a second diamine represented by the following formula (4). (In the formula, X1 is a structure represented by the following formula (X1-1) or (X1-2).) (In the formula, R3 to R 12 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group, provided that at least one of R3 to R6 is a group other than a hydrogen atom as defined above.) (In the formula, each A2 is independently a halogen atom, a hydroxyl group, an amino group, a mercapto group, a nitro group, a phosphoric acid group, or a monovalent organic group having 1 to 20 carbon atoms, and a is an integer of 0 to 4. When there are a plurality of A2, the structures of A2 may be the same or different.)

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 obtained therefrom, and a liquid crystal display element including the obtained liquid crystal alignment film. Background Art

[0002] Liquid crystal display elements used in liquid crystal televisions, liquid crystal displays, etc. generally have a liquid crystal alignment film for controlling the alignment state of liquid crystals in the element. The most commonly used liquid crystal alignment film in the industry at present is produced as follows: a film formed on an electrode substrate and composed of polyamic acid and / or polyimide obtained by imidizing it is subjected to a so-called rubbing treatment, that is, a treatment of rubbing the surface of the film unidirectionally with a cloth such as cotton, nylon, or polyester.

[0003] The rubbing treatment is a simple and industrially useful method with excellent productivity. However, with the high performance, high definition, and large size of liquid crystal display elements, various problems such as scratches on the surface of the alignment film, dust generation, the influence of mechanical force and static electricity generated during the rubbing treatment, and further in-plane non-uniformity of the alignment treatment have become apparent. As a method alternative to the rubbing treatment, a photo-alignment method is known: by irradiating polarized ultraviolet light, the liquid crystal alignment ability is imparted. In the liquid crystal alignment treatment based on the photo-alignment method, treatments using photo-isomerization reaction, photo-crosslinking reaction, photo-decomposition reaction, etc. have been proposed.

[0004] Patent Document 1 proposes the following: using a polyimide film having an alicyclic structure such as a cyclobutane ring in the main chain for the photo-alignment method. Compared with the rubbing treatment method, the obtained liquid crystal alignment film can be expected to improve the contrast and viewing angle characteristics of liquid crystal display elements in the in-plane switching (IPS) driving mode and the fringe field switching (FFS) driving mode. Therefore, it has attracted much attention as a promising liquid crystal alignment treatment method.

[0005] In the liquid crystal alignment film used in liquid crystal display elements in the IPS driving mode and the FFS driving mode, on the basis of basic characteristics such as excellent liquid crystal alignment property and electrical property, an alignment restraining force for suppressing afterimages generated due to long-term driving is required. However, compared with the liquid crystal alignment film obtained by the rubbing treatment, the liquid crystal alignment film obtained by the photo-alignment method has a problem of weak alignment restraining force. Moreover, in the liquid crystal alignment film obtained by the photo-decomposition reaction, low molecular weight components generated by photo-decomposition become a cause of reducing the alignment restraining force, and a method of removing these low molecular weight components by heat treatment or cleaning treatment has been proposed (Patent Document 2).

[0006] However, in the manufacture of liquid crystal display elements, as described above, in order to remove low molecular weight components, it is necessary to add a heat treatment step and a cleaning treatment step, which results in an increase in the manufacturing process of liquid crystal display elements. On the other hand, a method for manufacturing a liquid crystal alignment film has been proposed, which can suppress afterimages caused by long-term driving even with a small number of processes and has no defects caused by low molecular weight components (Patent Document 3).

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 9-297313

[0010] Patent Document 2: Japanese Patent Laid-Open No. 2011-107266

[0011] Patent Document 3: WO2018 / 117239 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] In the case of performing alignment treatment by the photoalignment method, the irradiation amount of light becomes a factor that affects the energy cost and the production speed. Therefore, it is preferable to be able to perform alignment treatment with a small irradiation amount. However, even for a liquid crystal aligning agent that can obtain good afterimage characteristics, when the light irradiation amount is reduced, there is a problem of insufficient afterimage characteristics.

[0014] Therefore, an object of the present invention is to provide a liquid crystal aligning agent that can obtain good afterimage characteristics even when the light irradiation amount in the alignment treatment based on the photoalignment method is reduced, a method for manufacturing the same, a liquid crystal alignment film obtained therefrom, and a liquid crystal display element including the obtained liquid crystal alignment film.

[0015] Solutions for Solving the Problems

[0016] The inventors of the present invention have repeatedly conducted in-depth studies to achieve the above object, and as a result, have found that the above object can be achieved by the invention having the following gist.

[0017] A liquid crystal aligning agent containing polyimide, wherein the polyimide is an imidized product of a polyimide precursor obtained by a polycondensation reaction of a tetracarboxylic acid component containing a tetracarboxylic dianhydride represented by the following formula (1) or a derivative thereof, and a diamine component containing a first diamine represented by the following formula (3) and a second diamine represented by the following formula (4).

[0018]

[0019] Among them, in formula (1), X1 is a structure represented by the following formula (X1-1) or (X1-2).

[0020]

[0021] Among them, in formula (X1-1) and (X1-2), R3 to R 12 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group, provided that at least one of R3 to R6 is a group other than a hydrogen atom as defined above.

[0022]

[0023] Among them, in formula (3) and (4), A2 are each independently a halogen atom, a hydroxyl group, an amino group, a mercapto group, a nitro group, a phosphoric acid group, or a monovalent organic group having 1 to 20 carbon atoms, a is an integer of 0 to 4, and when there are a plurality of A2, the structures of A2 may be the same or different optionally.

[0024] Effects of the Invention

[0025] By using the liquid crystal aligning agent of the present invention, a significant reduction in the amount of light irradiation becomes possible, and a liquid crystal alignment film having good afterimage characteristics can be obtained. In addition, the liquid crystal alignment film obtained from the liquid crystal aligning agent of the present invention has a high yield in the manufacture of liquid crystal panels, and can reduce the afterimage caused by the alternating current driving in the liquid crystal display elements of the IPS driving method and the FFS driving method, and a liquid crystal display element of the IPS driving method and the FFS driving method having excellent afterimage characteristics can be obtained. Detailed Description

[0026] The liquid crystal aligning agent of the present invention is characterized by containing polyimide (hereinafter, also referred to as a specific polymer), and the polyimide is an imide compound of a polyimide precursor obtained by a polycondensation reaction of a tetracarboxylic acid component (hereinafter, also referred to as a tetracarboxylic acid component) containing a tetracarboxylic dianhydride or its derivative having a specific structure and a diamine component (hereinafter, also referred to as a diamine component) containing two diamines having specific structures.

[0027] <Specific Polymer>

[0028] The specific polymer used in the present invention is a polyimide which is an imide compound of a polyimide precursor having a specific structure. As the polyimide precursor, there is no particular limitation as long as it is a polyimide precursor that forms an imide ring by chemical imidization using heating or a catalyst. From the viewpoint of easy imidization by heating or chemical imidization, as the polyimide precursor, polyamic acid or polyamic acid ester is preferred.

[0029] The imidization rate of the polyimide is not particularly limited, and is preferably 10 to 100%, more preferably 50 to 100%, and still more preferably 50 to 80%.

[0030] Hereinafter, each component that is a raw material for obtaining the above-mentioned specific polymer will be described in detail.

[0031] <Tetracarboxylic acid component>

[0032] As the tetracarboxylic acid component used in the polymerization of the specific polymer used in the liquid crystal aligning agent of the present invention, not only tetracarboxylic dianhydride but also tetracarboxylic acid, tetracarboxylic diacyl halide, tetraalkyl ester of tetracarboxylic acid, or tetraalkyl ester dihalide as its derivative can be used.

[0033] The above-mentioned tetracarboxylic dianhydride or its derivative is preferably the one represented by the following formula (1).

[0034]

[0035] Among them, X1 is a structure represented by the following formula (X1-1) or (X1-2).

[0036]

[0037] Among them, R3 to R 12 Each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group. It should be noted that at least one of R3 to R6 is a group other than the hydrogen atom in the above definition.

[0038] From the viewpoint of liquid crystal alignment property, X1 is preferably the above formula (X1-1), more preferably at least one selected from the following formulas (X1-1-1) to (X1-1-5), and particularly preferably the following formula (X1-1-1). The tetracarboxylic dianhydride or its derivative represented by the formula (1) can be used as a mixture of two or more kinds.

[0039]

[0040] The use ratio of the tetracarboxylic dianhydride or its derivative represented by the above formula (1) is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 80 mol% or more based on 1 mol of all the tetracarboxylic acid components used in the specific polymer.

[0041] In addition, in the case where the tetracarboxylic acid component used in the polymerization of the specific polymer described in the present invention further contains the tetracarboxylic dianhydride or its derivative represented by the following formula (2) on the basis of the tetracarboxylic dianhydride or its derivative represented by the above formula (1), it is more preferable from the viewpoints of suppressing bright spots generated by decomposition products and liquid crystal alignment property.

[0042]

[0043] Among them, X2 is selected from the following formulas (X2-1) to (X2-6).

[0044]

[0045] Among them, X2 is preferably the above formula (X2-1), (X2-5) or (X2-6), and particularly preferably the formula (X2-1). The tetracarboxylic dianhydride and its derivatives shown in the formula (2) can be used in a mixture of two or more kinds.

[0046] The usage ratio of the tetracarboxylic dianhydride or its derivatives shown in the above formula (2) is preferably 1 to 30 mol%, more preferably 10 to 30%, and further preferably 10 to 20% relative to 1 mol of all the tetracarboxylic acid components used in the specific polymer.

[0047] The tetracarboxylic dianhydride and its derivatives used in the polymerization of the specific polymer described in the present invention may contain tetracarboxylic dianhydrides or their derivatives other than the above formulas (1) and (2).

[0048] <Diamine>

[0049] The diamine component used in the polymerization of the specific polymer used in the liquid crystal aligning agent of the present invention includes at least one first diamine selected from the diamines shown in the following formula (3) and at least one second diamine selected from the diamines shown in the following formula (4).

[0050]

[0051] Among them, A2 is a halogen atom, a hydroxyl group, an amino group, a mercapto group, a nitro group, a phosphoric acid group, or a monovalent organic group having 1 to 20 carbon atoms, a is an integer of 0 to 4, and when there are a plurality of A2, the structures of A2 are optionally the same or different.

[0052] The following are preferred specific examples of the first diamine shown in the formula (3), but the present invention is not limited to these.

[0053]

[0054] The content of the first diamine shown in the formula (3) is preferably 10 to 50 mol%, more preferably 10 to 30 mol% relative to all the diamine components used in the specific polymer.

[0055] The following are preferred specific examples of the second diamine shown in the formula (4), but the present invention is not limited to these.

[0056]

[0057] The content of the second diamine represented by the formula (4) is preferably 10 to 50 mol%, more preferably 10 to 40 mol%, based on all the diamine components used in the specific polymer.

[0058] The diamine used in the polymerization of the specific polymer contained in the liquid crystal aligning agent of the present invention may include diamines other than the above formulas (3) and (4) (hereinafter, also referred to as other diamines).

[0059] Hereinafter, an example of other diamines is shown, but the present invention is not limited to these.

[0060] m-Phenylenediamine, 4-(2-(methylamino)ethyl)aniline, 3,5-diaminobenzoic acid, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 3,3'-diaminobenzophenone, 1,2-bis(4-aminophenyl)ethane, 1,3-bis(4-aminophenyl)propane, 1,4-bis(4-aminophenyl)butane, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,2-bis(4-aminophenoxy)ethane, 1,2-bis(4-amino-2-methylphenoxy)ethane, 1,3-bis(4-aminophenoxy)propane, 1,4-bis(4-aminophenoxy)butane, 1,5-bis(4-aminophenoxy)pentane, 1,6-bis(4-aminophenoxy)hexane, 4-(2-(4-aminophenoxy)ethoxy)-3-fluoroaniline, bis(2-(4-aminophenoxy)ethyl) ether, 4-amino-4'-(2-(4-aminophenoxy)ethoxy)biphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 1,4-diaminonaphthalene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,7-diaminonaphthalene, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2'-bis(4-aminophenyl)propane, 1,3-bis(4-aminophenethyl)urea, etc.

[0061] Among the above, from the viewpoint of liquid crystal alignment properties, it is preferable to contain 1,2-bis(4-aminophenoxy)ethane. The content of 1,2-bis(4-aminophenoxy)ethane is more preferably 10 to 40 mol% based on all the diamine components used in the specific polymer.

[0062] In addition, from the viewpoints of improving the solvent solubility of the polyimide and making it easier for the specific polymer component to be unevenly present near the surface layer of the liquid crystal alignment film when the liquid crystal aligning agent of the present invention contains a polymer other than the specific polymer, at least one of the diamines represented by the following formula (5) is preferably used as the other diamine.

[0063] H2N-Y1-NH2 (5)

[0064] Among them, Y1 is a divalent organic group containing the structure of the following formula (6).

[0065]

[0066] Among them, D represents a protecting group that leaves upon heating and is replaced by a hydrogen atom, and * represents a connecting site with other structures. Preferred structures for D include tert-butoxycarbonyl.

[0067] Hereinafter, preferred specific examples of the diamine represented by formula (5) are given, but are not limited to these. It should be noted that Boc in the following structures represents tert-butoxycarbonyl.

[0068]

[0069] Regarding the preferred content when using the diamine represented by formula (5), relative to all diamine components used in a specific polymer, the diamine represented by formula (5) is 5 to 30 mol%.

[0070] <Manufacturing methods of polyamide acid esters, polyamic acids, and polyimides>

[0071] The polyamide acid esters, polyamic acids, which are polyimide precursors used in the present invention, and polyimides, which are imidized products of these polyimide precursors, can be synthesized by known methods. As an example, the method described in WO2013 / 157586 can be cited.

[0072] The molecular weight of the specific polymer is not particularly limited as long as it can form a good coating film. For example, in terms of the weight average molecular weight (also referred to as Mw), it is preferably 2000 to 500000, more preferably 5000 to 300000, and further preferably 10000 to 100000. In addition, the number average molecular weight (also referred to as Mn) is preferably 1000 to 250000, more preferably 2500 to 150000, and further preferably 5000 to 50000.

[0073] <Liquid crystal aligning agent>

[0074] The liquid crystal aligning agent of the present invention is a composition containing the above-mentioned specific polymer and an organic solvent, and may contain two or more different structures of specific polymers. In addition, the liquid crystal aligning agent of the present invention may contain polymers other than the specific polymer (hereinafter, also referred to as the second polymer), and various additives.

[0075] When the liquid crystal aligning agent of the present invention contains the second polymer, the ratio of the specific polymer to all polymer components is preferably 5% by mass or more, and as an example, it can be 5 to 95% by mass.

[0076] Examples of the second polymer include polyamic acid, polyimide, polyamic acid ester, polyester, polyamide, polyurea, polyorganosiloxane, cellulose derivative, polyacetal, polystyrene or its derivative, poly(styrene-phenylmaleimide) derivative, poly(meth)acrylate, and the like.

[0077] Particularly preferred as the second polymer is polyamic acid (hereinafter also referred to as the second polyamic acid) obtained from a tetracarboxylic dianhydride component and a diamine component.

[0078] Examples of the tetracarboxylic dianhydride component used to obtain the second polyamic acid include the compounds represented by the following formula (7).

[0079]

[0080] In formula (7), A is a tetravalent organic group, preferably a tetravalent organic group having 4 to 30 carbon atoms. Hereinafter, the structures of preferred A are shown, but the present invention is not limited to these.

[0081]

[0082]

[0083] In the above structures, from the viewpoint of further improving the photoalignment property, (A-1) and (A-2) are preferred; from the viewpoint of improving the relaxation rate of charge accumulation, (A-4) is preferred; from the viewpoints of further improving the liquid crystal alignment property and improving the relaxation rate of charge accumulation, (A-15) to (A-17) are preferred, and the like. The tetracarboxylic dianhydride component used to obtain the second polyamic acid can be used in combination of two or more tetracarboxylic dianhydrides.

[0084] Examples of the diamine component used to obtain the second polyamic acid include the diamines represented by the aforementioned formula (3), the diamines represented by the aforementioned formula (4), and other diamines exemplified above.

[0085] In addition, from the viewpoint of improving the relaxation rate of charge accumulation, it is preferred to use at least one of the diamines represented by the following formula (8). The diamine component used to obtain the second polyamic acid can be used in combination of two or more diamines.

[0086] H2N-Y2-NH2 (8)

[0087] In formula (8), Y2 is a divalent organic group having a nitrogen atom bonded to an aromatic group or a nitrogen-containing aromatic heterocycle.

[0088] Hereinafter, the structures of preferred Y2 are shown, but the present invention is not limited to these.

[0089]

[0090] The molecular weight of the second polyamic acid is not particularly limited. For example, Mw is 2,000 to 500,000, preferably 5,000 to 300,000, and more preferably 10,000 to 100,000. In addition, Mn is 1,000 to 250,000, preferably 2,500 to 150,000, and more preferably 5,000 to 50,000.

[0091] The concentration of the polymer in the liquid crystal aligning agent of the present invention can be appropriately changed by setting the thickness of the coating film to be formed. From the aspect of forming a uniform and defect-free coating film, it is preferably 1% by mass or more, and from the aspect of the storage stability of the solution, it is preferably set to 10% by mass or less. The particularly preferred concentration of the polymer is 2 to 8% by mass.

[0092] The organic solvent contained in the liquid crystal aligning agent of the present invention is not particularly limited as long as the polymer component is uniformly dissolved. If specific examples are listed, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-methylcaprolactam, 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl sulfone, γ-butyrolactone, 1,3-dimethylimidazolidinone, 3-methoxy-N,N-dimethylpropanamide, etc. can be cited. They can be used alone or in combination of two or more. In addition, in the case of a single solvent, even if it is a solvent that cannot uniformly dissolve the polymer component, as long as it is within the range where the polymer does not precipitate, it can be mixed in the above organic solvent.

[0093] In addition to the organic solvent for dissolving the polymer component, the liquid crystal aligning agent of the present invention may further contain a solvent for improving the coating film uniformity when the liquid crystal aligning agent is coated on a substrate. The above solvent is usually a solvent having a surface tension lower than that of the above organic solvent. Specific examples thereof include ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, ethyl carbitol acetate, ethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol, 1-phenoxy-2-propanol, propylene glycol monoacetate, propylene glycol diacetate, propylene glycol-1-monomethyl ether-2-acetate, propylene glycol-1-monoethyl ether-2-acetate, butyl cellosolve acetate, dipropylene glycol, 2-(2-ethoxypropoxy)propanol, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, isoamyl lactate, etc. Two or more of these solvents can be used in combination.

[0094] In the liquid crystal aligning agent of the present invention, in addition to the above, the following can be added: a dielectric or a conductive substance for the purpose of changing electrical properties such as the dielectric constant and conductivity of the liquid crystal alignment film, a silane coupling agent for the purpose of improving the adhesion between the liquid crystal alignment film and the substrate, a crosslinkable compound for the purpose of increasing the hardness and density of the film when forming the liquid crystal alignment film, and an imidization accelerator for the purpose of promoting the imidization of polyamic acid well when firing the coating film, etc.

[0095] <Manufacturing method of liquid crystal alignment film>

[0096] The manufacturing method of the liquid crystal alignment film using the liquid crystal aligning agent of the present invention is not particularly limited, and it can be manufactured by the following steps (A) to (D), thereby more effectively exerting the excellent characteristics of the liquid crystal aligning agent of the present invention.

[0097] Step (A): A step of coating the liquid crystal aligning agent of the present invention on a substrate.

[0098] Step (B): A step of heating the coated liquid crystal aligning agent at a temperature at which thermal imidization is substantially not performed to obtain a film.

[0099] Step (C): A step of irradiating polarized ultraviolet light on the film obtained in step (B).

[0100] Step (D): A step of firing the film obtained in step (C) at 100°C or higher and at a temperature higher than that in step (B).

[0101] Hereinafter, each of the steps (A) to (D) will be described in more detail.

[0102] <Step (A)>

[0103] As the substrate for coating the liquid crystal aligning agent of the present invention, there is no particular limitation as long as it is a substrate with high transparency, and glass substrates, silicon nitride substrates, and plastic substrates such as acrylic substrates and polycarbonate substrates can be used. At this time, from the aspect of simplifying the process, it is preferable to use a substrate formed with an ITO electrode or the like for driving liquid crystals. In addition, in a reflective liquid crystal display element, if only one-sided substrate is formed, an opaque substance such as a silicon wafer can also be used, and in this case, a light-reflecting material such as aluminum can be used for the electrode.

[0104] The coating method of the liquid crystal aligning agent is not particularly limited, and it is usually a method performed by screen printing, offset printing, flexographic printing, or inkjet method, etc. As other coating methods, there are dipping method, roll coater method, slot coater method, spinner method, spraying method, etc., and they can be used according to the purpose.

[0105] <Step (B)>

[0106] Step (B) is a step of heating the liquid crystal aligning agent coated on the substrate to form a film under conditions where thermal imidization is substantially not performed. After the liquid crystal aligning agent is coated on the substrate, heating means such as a hot plate, a thermal cycle oven, an IR (infrared) oven, etc. are used to evaporate the solvent to form a film. In this step, any temperature and time can be selected as long as the organic solvent contained in the liquid crystal aligning agent can be removed under conditions where thermal imidization is substantially not performed. Generally, in order to sufficiently remove the contained solvent, it is preferably heated at 50 to 150 °C for 1 to 10 minutes, more preferably heated at 50 to 120 °C for 1 to 5 minutes.

[0107] <Step (C)>

[0108] Step (C) is a step of irradiating polarized ultraviolet rays on the film obtained in Step (B). As the ultraviolet rays, those having a wavelength of 200 to 400 nm are preferred, and among them, those having a wavelength of 200 to 300 nm are more preferred. In order to improve the liquid crystal alignment property, ultraviolet rays can be irradiated while heating the substrate after coating the liquid crystal aligning agent at 50 to 250 °C. As the irradiation amount of the aforementioned ultraviolet rays, for example, it is 1 to 2000 mJ / cm 2 , preferably 10 to 1000 mJ / cm 2 , more preferably 100 to 600 mJ / cm 2 . In addition, the higher the extinction ratio of the polarized ultraviolet rays, the higher the anisotropy can be imparted, so it is preferred. Specifically, the extinction ratio of the ultraviolet rays linearly polarized is preferably 10:1 or more, more preferably 20:1 or more.

[0109] <Step (D)>

[0110] Step (D) is a step of firing the film irradiated with ultraviolet rays in Step (C). Specifically, it is a step of firing at a temperature of 100 °C or higher and higher than the temperature at which heating is performed in Step (B). The firing temperature is not particularly limited as long as it is 100 °C or higher and higher than the heating temperature in Step (B), preferably 150 to 300 °C, more preferably 150 to 250 °C, and further preferably 200 to 250 °C. The firing time is preferably 5 to 120 minutes, more preferably 5 to 60 minutes, and further preferably 5 to 30 minutes. If the thickness of the liquid crystal alignment film after firing is too thin, the reliability of the liquid crystal display element sometimes decreases, so it is preferably 5 to 300 nm, more preferably 10 to 200 nm.

[0111] The liquid crystal alignment film of the present invention is suitable as a liquid crystal alignment film for liquid crystal display elements of a horizontal electric field mode such as an IPS mode or an FFS mode, and is particularly useful as a liquid crystal alignment film for a liquid crystal display element of an FFS mode. A liquid crystal display element can be fabricated as follows: After obtaining a substrate with a liquid crystal alignment film obtained from the liquid crystal aligning agent of the present invention, a liquid crystal cell is fabricated by a known method, and the liquid crystal display element is fabricated using this liquid crystal cell.

[0112] As an example of a method for fabricating a liquid crystal cell, a liquid crystal display element with a passive matrix structure is taken as an example for explanation. It should be noted that it can be a liquid crystal display element with an active matrix structure in which switching elements such as TFTs (Thin Film Transistors) are provided in each pixel portion constituting the image display.

[0113] Specifically, a transparent glass substrate is prepared. A common electrode is provided on one substrate, and a segment electrode is provided on the other substrate. These electrodes can be formed as ITO electrodes, for example, and patterned in a manner capable of performing a desired image display. Next, an insulating film is provided on each substrate to cover the common electrode and the segment electrode. The insulating film can be formed as a SiO2-TiO2 film by the sol-gel method, for example.

[0114] Next, a liquid crystal alignment film is formed on each substrate. One substrate is overlapped with the other substrate so that the liquid crystal alignment films face each other, and the periphery is bonded with a sealant. In order to control the substrate gap, spacers are usually preferably premixed in the sealant in advance. In addition, it is preferable to also scatter spacers for controlling the substrate gap in the in-plane portion where the sealant is not provided. An opening for filling liquid crystal from the outside is provided in advance in a part of the sealant. Next, through the opening provided in the sealant, a liquid crystal material is injected into the space surrounded by the two substrates and the sealant. After that, the opening is sealed with an adhesive. The injection can use a vacuum injection method or a method utilizing capillary action in the atmosphere. As the liquid crystal material, either a positive-type liquid crystal material or a negative-type liquid crystal material can be used. Next, polarizers are provided. Specifically, a pair of polarizers are adhered to the surfaces on the opposite sides of the liquid crystal layer of the two substrates.

[0115] As described above, by using the liquid crystal aligning agent of the present invention, a liquid crystal alignment film can be obtained that can suppress afterimages caused by long-term AC driving in liquid crystal display elements of the IPS driving mode and the FFS driving mode, has no defects such as bright spots caused by the residue of low-molecular-weight compounds, and can be manufactured with fewer process steps than in the past.

[0116] Examples

[0117] Examples are listed below to further specifically illustrate the present invention, but the present invention is not limited to this interpretation.

[0118] The abbreviations of the compounds below and the measurement methods for each property are as described below. It should be noted that the values and units below are based on mass unless otherwise specified.

[0119] NMP: N-methyl-2-pyrrolidone, GBL: γ-butyrolactone,

[0120] BCS: butyl cellosolve,

[0121]

[0122] Among them, in the above formula, Boc represents tert-butoxycarbonyl.

[0123]

[0124] [Viscosity]

[0125] Measured using an E-type viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.) at a sample volume of 1.1 mL, a conical rotor TE-1 (1°34’, R24), and a temperature of 25 °C.

[0126] [Molecular weight]

[0127] Measured using a GPC (gel permeation chromatography at room temperature) device, and Mn and Mw are calculated in terms of polyethylene glycol and polyethylene oxide conversion values.

[0128] GPC device: manufactured by Shodex Co., Ltd. (GPC-101), column: manufactured by Shodex Co., Ltd. (series of KD803 and KD805), column temperature: 50 °C, eluent: N,N-dimethylformamide (lithium bromide hydrate (LiBr·H2O) as an additive is 30 mmol / L, phosphoric acid anhydrous crystal (orthophosphoric acid) is 30 mmol / L, tetrahydrofuran (THF) is 10 ml / L), flow rate: 1.0 ml / minute

[0129] Standard samples for making the standard curve: TSK standard polyethylene oxide manufactured by Tosoh Corporation (weight-average molecular weight (Mw): approximately 900,000, 150,000, 100,000, 30,000), and polyethylene glycol manufactured by Polymer Laboratories Limited (peak molecular weight (Mp) approximately 12,000, 4,000, 1,000). During the measurement, in order to avoid peak overlap, two samples were measured separately, one mixed with the four samples of 900,000, 100,000, 12,000, and 1,000, and the other mixed with the three samples of 150,000, 30,000, and 4,000.

[0130] <Measurement of imidization rate>

[0131] 20 mg of polyimide powder was added to an NMR sample tube (an NMR standard sampling tube, φ5 (manufactured by Kusano Kagaku Co., Ltd.)), and deuterated dimethyl sulfoxide (DMSO-d6, a 0.05% TMS (tetramethylsilane) mixture (0.53 ml)) was added, and ultrasonic waves were applied to completely dissolve it. For this solution, proton NMR at 500 MHz was measured using an NMR measuring machine (JNW-ECA500) (manufactured by JEOL DATUM LTD.). The imidization rate was calculated as follows: Protons derived from a structure that did not change before and after imidization were determined as reference protons, and using the peak integration value of this proton and the peak integration value of the protons of the NH group of amic acid that appeared around 9.5 ppm to 10.0 ppm, it was calculated using the following formula.

[0132] Imidization rate (%) = (1 - α·x / y) × 100

[0133] In the above formula, x is the peak integration value of the protons of the NH group of amic acid, y is the peak integration value of the reference protons, and α is the ratio of the number of reference protons to one NH group proton of amic acid in the case of polyamic acid (imidization rate of 0%).

[0134] [Configuration of FFS-driven liquid crystal cell]

[0135] In a liquid crystal cell for the Fringe Field Switching (FFS) mode, a first glass substrate having an FOP (Finger on Plate) electrode layer formed on the surface and composed of a planar common electrode - insulating layer - comb-shaped pixel electrode, and a second glass substrate having columnar spacers with a height of 4 μm on the surface and an ITO film for antistatic formed on the back surface are used as a set. The pixel electrode has a comb shape in which electrode elements with a width of 3 μm bent at an inner angle of 160° within the central part are arranged in parallel with a 6-μm interval, and one pixel has a first region and a second region with a line connecting the bent parts of multiple electrode elements as a boundary.

[0136] It should be noted that the liquid crystal alignment film formed on the first glass substrate is aligned in such a way that the direction bisecting the inner angle of the pixel bent part is orthogonal to the liquid crystal alignment direction, and the liquid crystal alignment film formed on the second glass substrate is aligned in such a way that the liquid crystal alignment direction on the first substrate is the same as the liquid crystal alignment direction on the second substrate when the liquid crystal cell is fabricated.

[0137] On each surface of the above-mentioned set of glass substrates, a liquid crystal aligning agent filtered by a filter with a pore diameter of 1.0 μm for spin coating was applied and dried on a hot plate at 80 °C for 2 minutes. After that, ultraviolet light with a wavelength of 254 nm and linearly polarized with an extinction ratio of 26:1 was irradiated onto the coated surface through a polarizer. Then, firing was carried out in a hot air circulation oven at 230 °C for 30 minutes to obtain a substrate with a liquid crystal alignment film having a film thickness of 100 nm.

[0138] Next, a sealant was printed on one of the above-mentioned set of glass substrates with a liquid crystal alignment film, and the other substrate was bonded with the liquid crystal alignment film surfaces facing each other to cure the sealant, thereby fabricating an empty cell. By the reduced-pressure injection method, liquid crystal MLC-3019 (manufactured by Merck KGaA) was injected into the empty cell, and the injection port was sealed to obtain an FFS-driven liquid crystal cell. After that, the obtained liquid crystal cell was heated at 120 °C for 1 hour, and after standing overnight, evaluation of the afterimage characteristics was performed.

[0139] [Evaluation of afterimage caused by long-term AC driving]

[0140] For the FFS-driven liquid crystal cell fabricated above, an AC voltage of ±5 V was applied at a frequency of 60 Hz for 120 hours in a constant-temperature environment at 60 °C. After that, a state in which the pixel electrode and the counter electrode of the liquid crystal cell were short-circuited was formed, and it was directly left at room temperature for one day.

[0141] Regarding the liquid crystal cell that had undergone the above treatment, the deviation between the liquid crystal alignment directions of the first region and the second region of the pixel in the non-applied voltage state was calculated at an angle.

[0142] Specifically, the liquid crystal cell was placed between two polarizers arranged with their polarization axes orthogonal, the backlight was lit, and the arrangement angle of the liquid crystal cell was adjusted so that the transmitted light intensity of the first region of the pixel became minimum. Then, the rotation angle required to rotate the liquid crystal cell so that the transmitted light intensity of the second region of the pixel became minimum was obtained.

[0143] The smaller the value of this rotation angle, the better the afterimage characteristics caused by long-term AC driving can be said to be. When the value of the angle Δ of the liquid crystal cell is 0.1° or less, it is evaluated as "good".

[0144] Hereinafter, synthesis examples of polyamic acid and polyimide are shown.

[0145] <Synthesis Example 1>

[0146] In a 300 mL four-necked flask equipped with a stirring device and a nitrogen inlet tube, 5.86 g (24.0 mmol) of DA-1, 1.73 g (16.0 mmol) of DA-2, 5.53 g (24.0 mmol) of DA-3, and 3.79 g (16.0 mmol) of DA-4 were measured, and 197.2 g of NMP was added. While introducing nitrogen, the mixture was stirred until dissolved. While stirring the diamine solution, 14.88 g (66.4 mmol) of CA-1 and 3.00 g (12.0 mmol) of CA-2 were added, and the mixture was stirred at 40 °C for 24 hours to obtain a polyamic acid solution (A-1) (viscosity: 425 mPa·s). The Mn of the polyamic acid was 11000 and the Mw was 29000.

[0147] <Synthesis Examples 2-6>

[0148] Using the diamine component, tetracarboxylic acid component, and NMP shown in Table 1 below, and carrying out the reaction at the reaction temperature, and otherwise carrying out the same as in Synthesis Example 1, polyamic acid solutions (A-2) to (A-4), (B-1), and (B-2) shown in Table 1 below were obtained. The viscosities and Mn / Mw of the obtained polyamic acids are shown in Table 1 below.

[0149] It should be noted that the concentration of the polyamic acid in the polyamic acid solutions obtained in Synthesis Examples 1 to 6 was 15% by mass.

[0150] [Table 1]

[0151]

[0152] <Synthesis Example 7>

[0153] In a 300 mL four-necked flask equipped with a stirring device and a nitrogen inlet tube, 100 g of the obtained polyamic acid solution (A-1) was taken, 50 g of NMP was added, and the mixture was stirred for 30 minutes. In the obtained polyamic acid solution, 17.60 g of acetic anhydride and 5.50 g of pyridine were added, and the mixture was heated at 50 °C for 3 hours for chemical imidization.

[0154] While stirring, the obtained reaction solution was poured into 600 ml of methanol, and the precipitated precipitate was filtered. The same operation was carried out 2 times, and after washing the resin powder, it was dried at 60 °C for 12 hours to obtain a polyimide resin powder. The imidization rate of the polyimide resin powder was 73%, Mn = 12600, Mw = 33900. 3.60 g of the obtained polyimide resin powder was taken into a 100 ml Erlenmeyer flask, 26.4 g of NMP was added so that the solid component concentration became 12%, and the mixture was stirred at 70 °C for 24 hours to dissolve it, obtaining a polyimide solution (A-1-PI) (refer to Table 2 below).

[0155] It should be noted that in Table 2, the concentration (mass%) under the imidization conditions represents the polymer concentration in the solution during the imidization reaction.

[0156] <Synthesis Examples 8 - 10>

[0157] Using acetic anhydride and pyridine shown in Table 2 below, and otherwise performing the chemical imidization operation in the same manner as in Synthesis Example 7, polyimide solutions (A - 2 - PI) to (A - 4 - PI) shown in Table 2 below were obtained. The imidization rate and Mn / Mw of the obtained polyimides are shown in Table 2 below.

[0158] [Table 2]

[0159]

[0160] <Example 1>

[0161] 4.0 g of the 12 mass% polyimide solution (A - 1 - PI) obtained in Synthesis Example 7 and 4.8 g of the 15 mass% polyamic acid solution (B - 1) obtained in Synthesis Example 5 were taken into a 50 ml Erlenmeyer flask, 3.24 g of NMP, 3.96 g of GBL, and 4.00 g of BCS were added, and they were mixed at 25°C for 8 hours to obtain a liquid crystal aligning agent (1) (refer to Table 3 below). No abnormalities such as turbidity or precipitation were observed in this liquid crystal aligning agent, and it was confirmed to be a homogeneous solution.

[0162] It should be noted that in Table 3, A / B represents the mass% ratio of the polyimide solution to the polyamic acid solution, and the solid content ratio (mass%) represents the content ratio of the polymer in the liquid crystal aligning agent.

[0163] <Examples 2 - 4, Comparative Example 1>

[0164] Using the polyamic acid solutions and polyimide solutions shown in Table 3 below, and otherwise performing the same operations as in Example 1, liquid crystal aligning agents (2) to (5) were obtained. No abnormalities such as turbidity or precipitation were observed in these liquid crystal aligning agents, and it was confirmed to be a homogeneous solution.

[0165] [Table 3]

[0166]

[0167] <Example 11>

[0168] Evaluate the afterimage characteristics based on the above [evaluation of afterimage caused by long-term AC driving]. That is, the liquid crystal aligning agent (1) obtained in Example 1 was filtered through a filter with a pore size of 1.0 μm, and then spin-coated on the above-mentioned electrode-bearing substrate and a glass substrate with an ITO film formed on the back and columnar spacers with a height of 4 μm. After drying on a hot plate at 80 °C for 5 minutes, ultraviolet light with a wavelength of 254 nm and linearly polarized with an extinction ratio of 26:1 was irradiated on the coated film surface through a polarizer, and then fired in a hot air circulation oven at 230 °C for 30 minutes to obtain a substrate with a liquid crystal alignment film.

[0169] Take the above-mentioned 2 obtained substrates as a group, print a sealant on the substrates, bond another substrate with the liquid crystal alignment film surface facing each other and the alignment direction being 0°, and then cure the sealant to fabricate an empty cell. By the vacuum injection method, liquid crystal MLC-3019 (manufactured by Merck & Co., Inc.) was injected into the empty cell, and the injection port was sealed to obtain an FFS-driven liquid crystal cell. After that, the obtained liquid crystal cell was heated at 120 °C for 1 hour and left overnight to conduct the evaluation of afterimage caused by long-term AC driving.

[0170] The value (°) of the angle Δ of the liquid crystal cell after long-term AC driving is shown in Table 4 below. That is, the irradiation amount of the above-mentioned ultraviolet light is 0.15 J / cm 2 and the value of the angle Δ of the liquid crystal cell is 0.08 °, 0.20 J / cm 2 and the value of the angle Δ of the liquid crystal cell is 0.09 °, 0.25 J / cm 2 and the value of the angle Δ of the liquid crystal cell is 0.09 °. The minimum values of the angle Δ are all lower than 0.10 °. Therefore, good liquid crystal alignment properties were obtained using the liquid crystal aligning agent (1).

[0171] <Examples 12 to 14 and Comparative Example 11>

[0172] In Examples 12 to 14 and Comparative Example 11, each liquid crystal aligning agent shown in Table 4 below was used instead of the liquid crystal aligning agent (1). Except for this, FFS-driven liquid crystal cells were fabricated using exactly the same method as in Example 11, and the evaluation of afterimage caused by long-term AC driving was conducted.

[0173] For each of Examples 12 to 14 and Comparative Example 11, the value (°) of the angle Δ of the liquid crystal cell after long-term AC driving under each different irradiation amount of ultraviolet light is shown in Table 4.

[0174] [Table 4]

[0175]

[0176] As shown in Table 4, in Examples 11 to 14, for the ultraviolet irradiation amount of 200 J / cm with an angle Δ (deg.) of 0.1° or less 2 even with such a small polarized ultraviolet irradiation amount as described above, the angle Δ becomes optimal. Due to the above-mentioned excellent afterimage characteristics, it can be seen that the production time of the liquid crystal display element is significantly shortened.

[0177] Industrial Applicability

[0178] The liquid crystal aligning agent of the present invention is useful for forming a liquid crystal alignment film in a wide range of liquid crystal display elements such as the IPS driving method and the FFS driving method.

[0179] It should be noted that the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2018-154228 filed on August 20, 2018 are incorporated herein by reference as the disclosure of the specification of the present invention.

Claims

1. A liquid crystal aligning agent containing polyimide, wherein the polyimide is an imidized product of a polyimide precursor obtained by polycondensation reaction of a tetracarboxylic acid component containing a tetracarboxylic dianhydride or its derivative represented by the following formula (1) and a diamine component containing a first diamine represented by the following formula (3), a second diamine represented by the following formula (4), and a diamine represented by the following formula (5). Wherein, X1 has the structure represented by the following formula (X1-1), wherein R3 to R6 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group, provided that at least one of R3 to R6 is a group other than the hydrogen atom defined above, wherein A2 are each independently a halogen atom, a hydroxyl group, an amino group, a mercapto group, a nitro group, a phosphoric acid group, or a monovalent organic group having 1 to 20 carbon atoms, a is an integer of 0 to 4, and when there are a plurality of A2, the structures of A2 may be the same or different optionally; In formula (5), Y1 is a divalent organic group having the structure of the above formula (6), D represents a protecting group that is removed by heating and replaced by a hydrogen atom, and * represents a connecting site to other structures; wherein the tetracarboxylic acid component further contains a tetracarboxylic dianhydride represented by the following formula (2) or a derivative thereof, wherein X2 has the structure of the following formula (X2-1), The content of the tetracarboxylic dianhydride or its derivative represented by formula (1) is 50 mol% or more based on the tetracarboxylic acid component, The content of the tetracarboxylic dianhydride or its derivative represented by formula (2) is 1 to 30 mol% based on the tetracarboxylic acid component, The content of the first diamine represented by formula (3) is 10 to 50 mol% based on the diamine component, The content of the second diamine represented by formula (4) is 10 to 50 mol% based on the diamine component, The content of the diamine represented by formula (5) is 5 to 30 mol% based on the diamine component.

2. The liquid crystal aligning agent according to claim 1, wherein, X1 in the formula (1) is at least one selected from the following formulas (X1-1-1) to (X1-1-5), 3. The liquid crystal aligning agent according to claim 1 or 2, wherein, The first diamine represented by formula (3) is the diamine represented by the following formula, 4. The liquid crystal aligning agent according to claim 1 or 2, wherein, The second diamine represented by formula (4) is the diamine represented by the following formula, 5. A liquid crystal alignment film obtained by using the liquid crystal aligning agent according to any one of claims 1 to 4.

6. A liquid crystal display element comprising the liquid crystal alignment film according to claim 5.

7. A method for manufacturing a liquid crystal alignment film, comprising the following steps (A), (B), (C), and (D). Step (A): A step of coating the liquid crystal aligning agent according to any one of claims 1 to 4 on a substrate. Step (B): A step of heating the coated liquid crystal aligning agent under conditions where substantial thermal imidization does not occur to obtain a film; Step (C): A step of irradiating polarized ultraviolet rays onto the film obtained in step (B); Step (D): A step of firing the film obtained in step (C) at 100°C or higher and at a temperature higher than that in step (B).

8. The method for manufacturing a liquid crystal aligning film according to claim 7, wherein In the step (B), heating is carried out at 50°C to 150°C.

9. The method for manufacturing a liquid crystal aligning film according to claim 7 or 8, wherein In the step (D), the film is fired at 150 to 300°C.

Images