KR102710874B1 - Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element using the same - Google Patents

Abstract

A liquid crystal alignment agent is provided, which enables obtaining a liquid crystal alignment film having good liquid crystal alignment properties, voltage retention, aging resistance, etc.
A liquid crystal alignment agent characterized by containing the following components (A) and (B).
Component (A): A copolymer having a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2).
[Chemical formula 1]

(X ₁ , X ₂ are independently tetravalent organic groups, Y ₁ , Y ₂ are independently divalent organic groups, R ₁ is an alkyl group having 1 to 5 carbon atoms, and A ₁ and A ₂ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms which may have a substituent, an alkenyl group having 2 to 10 carbon atoms, or an alkynyl group having 2 to 10 carbon atoms.)
Component (B): A compound having two or more cross-linking functional groups.

Description

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

The present invention relates to a liquid crystal alignment agent containing a polyamic acid ester-polyamic acid copolymer, a liquid crystal alignment film, and a liquid crystal display element using the same.

Liquid crystal display elements used in liquid crystal televisions, liquid crystal displays, etc., usually have a liquid crystal alignment film formed within the element to control the arrangement of liquid crystals. The liquid crystal alignment film is a film for controlling the alignment of liquid crystal molecules in a certain direction in a liquid crystal display element or a phase difference plate using polymeric liquid crystals. For example, a liquid crystal display element has a structure in which liquid crystal molecules forming a liquid crystal layer are sandwiched between liquid crystal alignment films formed on each surface of a pair of substrates. Then, in the liquid crystal display element, the liquid crystal molecules are aligned in a certain direction accompanied by a pretilt angle by the liquid crystal alignment film, and respond by applying voltage to an electrode formed between the substrate and the liquid crystal alignment film. As a result, the liquid crystal display element displays a desired image by utilizing the alignment change due to the response of the liquid crystal molecules.

As for liquid crystal alignment films, polyimide-based liquid crystal alignment films have been mainly used so far, in which a liquid crystal alignment agent containing a polyimide precursor such as polyamic acid (polyamic acid) or a solution of soluble polyimide as its main component is applied to a glass substrate and then fired.

With the advancement of functionality in liquid crystal display elements, in addition to excellent liquid crystal alignment properties and stable pretilt angle expression, liquid crystal alignment films also have important characteristics such as high voltage retention, low residual charge when DC voltage is applied, and/or rapid relaxation of accumulated residual charge due to DC voltage. Recently, with the goal of power saving in liquid crystal display elements, materials with high voltage retention have been particularly demanded.

In order to meet the above-mentioned requirements, various proposals have been made for polyimide-based liquid crystal alignment films. For example, in addition to polyamic acid or imide-group-containing polyamic acid, a liquid crystal alignment agent containing a tertiary amine of a specific structure has been proposed (see Patent Document 1), and an additive having an isocyanate structure has been proposed (see Patent Document 2).

Meanwhile, it has been reported that a liquid crystal alignment agent using polyamic acid ester as a polymer component constituting the liquid crystal alignment agent has superior liquid crystal alignment stability and voltage maintenance characteristics compared to a liquid crystal alignment agent using polyamic acid because the molecular weight does not decrease due to heat treatment when imidizing it (see Patent Document 3).

(Patent Document 1) Japanese Patent Publication No. Hei 9-316200 (Patent Document 2) WO2014/178406 (Patent Document 3) Japanese Patent Publication No. 2003-26918

However, when a liquid crystal alignment agent with various cross-linking agents added to polyamic acid is used, a liquid crystal display element with excellent voltage retention characteristics is obtained, but there are cases where the liquid crystal alignment property is impaired.

In addition, since a liquid crystal alignment agent using a polyamic acid ester, as described above, provides a liquid crystal display element having superior voltage retention characteristics compared to a liquid crystal alignment agent using a polyamic acid, it was expected that further improvement in voltage retention characteristics would be achieved by adding a cross-linking agent to this, but contrary to expectations, that effect was not obtained.

The present invention aims to provide a liquid crystal alignment agent that obtains a liquid crystal alignment film having good liquid crystal alignment properties, voltage holding ratio (hereinafter also referred to as VHR), and aging resistance.

The inventor of the present invention has conducted a preliminary study and found that the above problem can be solved by using a copolymer of polyamic acid ester and polyamic acid (hereinafter also referred to as a PAE-PAA copolymer) and a crosslinking agent having a specific structure, thereby completing the present invention.

That is, the present invention is based on the above-mentioned knowledge and has the following gist.

1. A liquid crystal alignment agent characterized by containing the following components (A) and (B).

Component (A): A copolymer having a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2).

[Chemical formula 1]

In the above formulas (1) and (2), X ₁ and X ₂ are each independently a tetravalent organic group, Y ₁ and Y ₂ are each independently a divalent organic group, R ₁ is an alkyl group having 1 to 5 carbon atoms, and A ₁ and A ₂ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms which may have a substituent, an alkenyl group having 2 to 10 carbon atoms, or an alkynyl group having 2 to 10 carbon atoms.

Component (B): A compound having two or more cross-linking functional groups.

According to the liquid crystal alignment agent of the present invention, a liquid crystal alignment film having characteristics such as good liquid crystal alignment properties, voltage retention, and aging resistance can be formed. This is thought to be due to the fact that the fine unevenness on the surface of the liquid crystal alignment film formed by the liquid crystal alignment agent of the present invention can be reduced.

＜Component (A): PAE-PAA copolymer＞

The PAE-PAA copolymer used in the present invention is a polyimide precursor for obtaining polyimide, and is a polymer having a site capable of undergoing the imidization reaction shown below by heating.

[Chemical formula 2]

(R is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.)

The PAE-PAA copolymer contained in the liquid crystal alignment agent of the present invention has a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2).

[Chemical Formula 3]

[Chemical Formula 4]

In the above formula (1), R ₁ is an alkyl group having 1 to 5 carbon atoms, and from the viewpoint of ease of application to a glass substrate, it is preferably a methyl group or an ethyl group.

In the above formulas (1) and (2), A ₁ and A ₂ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an alkynyl group having 2 to 10 carbon atoms which may have a substituent. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a t-butyl group, a hexyl group, an octyl group, a decyl group, a cyclopentyl group, a cyclohexyl group, a bicyclohexyl group, and the like. Examples of the alkenyl group include those in which one or more CH-CH structures present in an alkyl group are substituted with a C=C structure, and specific examples thereof include a vinyl group, an allyl group, a 1-propenyl group, an isopropenyl group, a 2-butenyl group, a 1,3-butadienyl group, a 2-pentenyl group, a 2-hexenyl group, a cyclopropenyl group, a cyclopentenyl group, and a cyclohexenyl group. Examples of the alkynyl group include those in which one or more CH ₂ -CH ₂ structures present in an alkyl group are substituted with a C≡C structure, and specific examples thereof include an ethynyl group, a 1-propynyl group, and a 2-propynyl group.

The above-mentioned alkyl group, alkenyl group and alkynyl group may have a substituent and may further form a ring structure by the substituent. In addition, forming a ring structure by the substituent means that the substituents or the substituents and a part of the parent skeleton combine to form a ring structure.

Examples of such substituents include a halogen group, a hydroxyl group, a thiol group, a nitro group, an aryl group, an organooxy group, an organothio group, an organosilyl group, an acyl group, an ester group, a thioester group, a phosphate ester group, an amide group, an alkyl group, an alkenyl group, an alkynyl group, etc.

Halogen groups, which are substituents, include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

As an aryl group which is a substituent, a phenyl group can be mentioned. This aryl group may be additionally substituted with another substituent as mentioned above.

As the substituent organooxy group, a structure represented by O-R can be represented. This R may be the same or different, and examples thereof include the above-mentioned alkyl group, alkenyl group, alkynyl group, and aryl group. These R may be further substituted with the above-mentioned substituent. Specific examples of the organooxy group include a methoxy group, an ethoxy group, a propyloxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, and an octyloxy group.

As the substituent organothio group, a structure represented by -S-R can be represented. As this R, the alkyl group, alkenyl group, alkynyl group, aryl group, etc. mentioned above can be exemplified. These R may be further substituted by the above-mentioned substituent. Specific examples of the organothio group include a methylthio group, an ethylthio group, a propylthio group, a butylthio group, a pentylthio group, a hexylthio group, a heptylthio group, an octylthio group, etc.

As the substituent organosilyl group, a structure represented by -Si-(R) ₃ can be represented. This R may be the same or different, and examples thereof include the above-mentioned alkyl group, alkenyl group, alkynyl group, aryl group, etc. These R may be further substituted with the above-mentioned substituent. Specific examples of the organosilyl group include a trimethylsilyl group, a triethylsilyl group, a tripropylsilyl group, a tributylsilyl group, a tripentylsilyl group, a trihexylsilyl group, a pentyldimethylsilyl group, a hexyldimethylsilyl group, etc.

As the substituent acyl group, a structure represented by -C(O)-R can be represented. As this R, the alkyl group, alkenyl group, aryl group, etc. mentioned above can be exemplified. These R may be further substituted with the above-mentioned substituent. Specific examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, a valeryl group, an isovaleryl group, a benzoyl group, etc.

As for the ester group which is a substituent, a structure represented by -C(O)O-R or OC(O)-R can be represented. As for this R, the alkyl group, alkenyl group, alkynyl group, aryl group, etc. mentioned above can be exemplified. These R may be additionally substituted with the substituent mentioned above.

As a substituent thioester group, a structure represented by -C(S)O-R or OC(S)-R can be represented. As this R, the above-mentioned alkyl group, alkenyl group, alkynyl group, aryl group, etc. can be exemplified. These R may be additionally substituted with the above-mentioned substituent.

As a substituent phosphate ester group, a structure represented by -OP(O)-(OR) ₂ can be represented. This R may be the same or different, and examples thereof include the alkyl group, alkenyl group, alkynyl group, aryl group, etc. described above. These R's may be additionally substituted with the substituent described above.

As for the substituent amide group, a structure represented by -C(O) _NH2 , -C(O)NHR, -NHC(O)R, -C(O)N(R) ₂ , or -NRC(O)R can be represented. This R may be the same or different, and examples thereof include the above-mentioned alkyl group, alkenyl group, alkynyl group, aryl group, etc. These R may be additionally substituted with the above-mentioned substituent.

As for the aryl group as a substituent, the same aryl group as described above can be mentioned. This aryl group may be additionally substituted with another substituent as described above.

As the substituent alkyl group, the same alkyl groups as described above can be mentioned. This alkyl group may be additionally substituted with another substituent as described above.

As the substituent alkenyl group, the same alkenyl group as described above can be mentioned. This alkenyl group may be additionally substituted with another substituent as described above.

As the alkynyl group which is a substituent, the same alkynyl group as described above can be mentioned. This alkynyl group may be additionally substituted with another substituent described above.

As for the above A ₁ and A ₂ , generally, since introducing a bulky structure may lower the reactivity of the amino group or the liquid crystal orientation, a hydrogen atom or an alkyl group having 1 to 5 carbon atoms that may have a substituent is more preferable, and a hydrogen atom, a methyl group or an ethyl group is particularly preferable.

In the above formulas (1) and (2), if X ₁ and X ₂ are tetravalent organic groups, their structures are not particularly limited, and two or more types may be mixed. Specific examples of X ₁ and X ₂ include X-1 to X-47 shown below. Among them, from the viewpoints of monomer availability, light irradiation sensitivity, and rubbing resistance strength, X ₁ , X ₂ , X-1, X-2, X-3, X-4, X-5, X-6, X-8, X-16, X-19, X-21, X-25, X-26, X-27, X-28, X-32 or X-47 are preferable.

[Chemical Formula 5]

[Chemical formula 6]

[Chemical formula 7]

[Chemical formula 8]

In addition, in formulas (1) and (2), Y ₁ and Y ₂ are divalent organic groups and are not particularly limited. Y ₁ and Y ₂ may be the same or different.

Specific examples of Y ₁ and Y ₂ include the following Y-1 to Y-99. Among them, from the viewpoint of ease of obtaining the monomer, Y-7, Y-8, Y-20, Y-21, Y-22, Y-28, Y-29, Y-30, Y-31, Y-41, Y-43, Y-64, Y-65, Y-66, Y-68, Y-71, Y-72, Y-98 or Y-99 are preferable, and Y-22, Y-28, Y-30, Y-31, Y-72, Y-98, Y-99, Y-100, Y-101, Y-102, Y-103 or Y-104 are more preferable.

[Chemical formula 9]

[Chemical Formula 10]

[Chemical Formula 11]

[Chemical Formula 12]

[Chemical Formula 13]

[Chemical Formula 14]

[Chemical Formula 15]

[Chemical Formula 16]

[Chemical Formula 17]

[Chemical Formula 18]

[Chemical Formula 19]

[Chemical Formula 20]

[Chemical Formula 21]

In the above PAE-PAA copolymer, the (content) ratio of the structural unit represented by formula (1) is preferably 50 to 95 mol%, more preferably 70 to 90 mol%, with respect to the total structural units. In addition, in the above PAE-PAA copolymer, the (content) ratio of the structural unit represented by formula (2) is preferably 5 to 50 mol%, more preferably 10 to 30 mol%, with respect to the total structural units.

＜Method for producing PAE-PAA copolymer＞

The PAE-PAA copolymer of the present invention is produced by the following method.

In the structural unit represented by the above formula (1), a tetracarboxylic acid diester forming X ₁ and a diamine forming Y ₁ and Y ₂ in the above formulas (1) and (2) are subjected to a polycondensation reaction in the presence of a condensing agent, a base and an organic solvent at -20°C to 150°C, preferably 0°C to 50°C, for 30 minutes to 24 hours, preferably 1 to 12 hours, then diphenyl phosphate is added for the purpose of neutralizing the base, and a tetracarboxylic acid or an dianhydride thereof forming X ₂ in the structural unit represented by the above formula (2) is added, and the reaction is further carried out at a temperature of 0°C to 50°C for 30 minutes to 24 hours, preferably 1 to 12 hours, thereby producing the product.

The organic solvent used in the above reaction is preferably N,N-dimethylformamide, N-methyl-2-pyrrolidone, or γ-butyrolactone in view of the solubility of the monomer and the polymer, and these may be used alone or in combination of two or more. The concentration of the polymer is preferably 1 to 30 mass%, more preferably 5 to 20 mass%, from the viewpoints that precipitation of the polymer is unlikely to occur and a high molecular weight body is easily obtained.

Examples of the condensing agent that can be used include triphenylphosphite, dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N,N'-carbonyldiimidazole, dimethoxy-1,3,5-triazinylmethylmorpholinium, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, (2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonic acid diphenyl, and the like. The amount of the condensing agent added is preferably 2 to 3 times molar with respect to the tetracarboxylic acid diester.

As the above base, a tertiary amine such as pyridine or triethylamine can be used. The amount of base added is preferably 2 to 4 times molar with respect to the diamine component from the viewpoint of easy removal and easy acquisition of a high molecular weight body.

The PAE-PAA copolymer obtained as described above can be recovered by precipitating the polymer by injecting the reaction solution into a poor solvent while stirring it well. In addition, by performing precipitation several times, washing with a poor solvent, and drying at room temperature or by heating, a powder of a purified PAE-PAA copolymer can be obtained. The poor solvent is not particularly limited, but may include water, methanol, ethanol, hexane, butyl cellosolve, acetone, toluene, and the like.

The weight average molecular weight of the PAE-PAA copolymer is preferably 10,000 to 305,000, more preferably 10,000 to 210,000. In addition, the number average molecular weight is preferably 5,000 to 152,500, more preferably 10,000 to 105,000.

＜Component (B): Compound containing two or more cross-linking functional groups＞

Component (B) contained in the liquid crystal alignment agent of the present invention is a compound containing two or more crosslinking functional groups.

The crosslinking functional group may include, but is not limited to, at least one selected from the group consisting of a hydroxyl group, a hydroxyalkylamide group, a (meth)acrylate group, a blocked isocyanate group, an oxetane group, and an epoxy group.

Among these, from the viewpoint of improving the availability and voltage maintenance rate, a hydroxyl group, a blocked isocyanate group or an epoxy group is preferable, and a hydroxyl group or an epoxy group is more preferable.

In addition, the compound of component (B) may have two or more of the same cross-linking functional groups in its structure, or may have two or more of two or more different types of cross-linking functional groups.

As a compound containing two or more hydroxyl groups, for example, a compound represented by the following formula (3) can be mentioned.

[Chemical Formula 22]

In the above formula (3), X ₃ is an n-valent organic group containing an aliphatic hydrocarbon group having 1 to 20 carbon atoms, or an aromatic hydrocarbon group. Among them, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms is preferable. R ₂ and R ₃ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a substituent, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, and at least one of R ₂ and R ₃ is represented by the following formula (4), but it is preferable that both R ₂ and R ₃ are represented by the following formula (4). n is an integer of 2 to 6, and particularly preferably 2.

[Chemical Formula 23]

In the above formula (4), R ₄ to R ₇ are each independently a hydrogen atom, a hydrocarbon group, or a hydrocarbon group substituted with a hydroxyl group, and a hydrogen atom is preferred.

_X3 is preferably an aliphatic hydrocarbon group from the viewpoints of liquid crystal orientation and solubility, as described above, and is more preferably a group having 1 to 10 carbon atoms. n represents an integer from 2 to 6, but from the viewpoint of solubility, n is preferably 2 to 4.

As compounds containing two or more hydroxyl groups, the following compounds can be specifically exemplified.

[Chemical Formula 24]

As a compound containing two or more block isocyanate groups, a compound represented by the following formula (5) can be exemplified.

[Chemical Formula 25]

In formula (5), Z is, each independently, an alkyl group having 1 to 3 carbon atoms, a hydroxyl group, or an organic group represented by formula (6) below, and at least one of Z is an organic group represented by formula (6) below.

[Chemical Formula 26]

As compounds containing two or more block isocyanate groups, the following compounds can be specifically exemplified.

[Chemical formula 27]

As compounds containing two or more block isocyanate groups other than those in the above formula (7), the following compounds can be exemplified.

[Chemical formula 28]

As compounds containing two or more epoxy groups, the following compounds can be specifically exemplified.

[Chemical Formula 29]

[Chemical formula 30]

As compounds containing two or more (meth)acrylate groups, the following compounds can be specifically exemplified.

[Chemical Formula 31]

As compounds having two or more cross-linking functionalities, the following compounds can also be exemplified.

[Chemical formula 32]

The compound of component (B) is preferably contained in an amount of 1 to 30 wt%, more preferably 3 to 15 wt%, relative to component (A) in the liquid crystal alignment agent of the present invention.

＜Liquid crystal orientation agent＞

The liquid crystal alignment agent of the present invention is in the form of a solution in which the above-mentioned PAE-PAA copolymer and a compound containing two or more crosslinkable functional groups are dissolved in an organic solvent. When each component is synthesized in an organic solvent, the resulting reaction solution may be used as is, or may be a solution obtained by diluting this reaction solution with an appropriate solvent. In addition, when each component is obtained as a powder, this may be dissolved in an organic solvent to form a solution.

In the liquid crystal alignment agent of the present invention, the content (concentration) of the polymer component containing the PAE-PAA copolymer can be appropriately changed depending on the setting of the thickness of the polyimide film to be formed. From the viewpoint of forming a uniform and defect-free coating film, the content of the polymer component with respect to the organic solvent is preferably 0.5 mass% or more, and from the viewpoint of the storage stability of the solution, it is preferably 15 mass% or less, more preferably 1 to 10 mass%.

In this case, a concentrated solution of the polymer may be prepared in advance, and when using this concentrated solution as a liquid crystal alignment agent, it may be diluted. The concentration of this concentrated solution of the polymer component is preferably 10 to 30 mass%, and more preferably 10 to 15 mass%. In addition, when dissolving the powder of the polymer component in an organic solvent to prepare a solution, it may be heated. The heating temperature is preferably 20 to 150°C, and particularly preferably 20 to 80°C.

The organic solvent contained in the liquid crystal alignment agent of the present invention is not particularly limited as long as the polymer component is uniformly dissolved. Specific examples thereof include 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-dimethyl-imidazolidinone, 3-methoxy-N,N-dimethylpropanamide, and the like. These may be used alone or in mixtures of two or more. In addition, even if it is a solvent that cannot uniformly dissolve the polymer component alone, as long as it is within a range in which the polymer is not precipitated, it may be mixed with the organic solvent mentioned above.

The liquid crystal alignment agent of the present invention may contain, in addition to an organic solvent for dissolving the polymer component, a solvent for improving the uniformity of the coating film when applying the liquid crystal alignment agent to a substrate. Such a solvent is generally a solvent having a lower surface tension than the organic solvent. Specific examples thereof include ethyl cellosolve, butyl cellosolve, butyl cellosolve acetate, 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, dipropylene glycol, 2-(2-ethoxypropoxy)propanol, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, and isoamyl lactate. Two or more of these solvents may be used in combination.

In addition to the above, the liquid crystal alignment agent of the present invention may contain various additives such as compounds that improve film thickness uniformity or surface smoothness when the liquid crystal alignment agent is applied, a silane coupling agent, or a cross-linking agent.

Compounds that improve the uniformity of film thickness or surface smoothness include fluorine-based surfactants, silicone-based surfactants, and nonionic surfactants.

More specifically, examples thereof include F-Top (Trade names of Tochem Products Co., Ltd., EF301, EF303, EF352), Megapack (Trade names of Dainippon Ink Co., Ltd., F171, F173, R-30), Fluoride (Trade names of Sumitomo 3M Co., Ltd., FC430, FC431), Asahi Guard (Trade names of Asahi Glass Co., Ltd., AG710), and Surflon (Trade names of Asahi Glass Co., Ltd., S-382, SC101, SC102, SC103, SC104, SC105, SC106).

The usage ratio of these surfactants is preferably 0.01 to 2 parts by mass, more preferably 0.01 to 1 part by mass, per 100 parts by mass of the resin component contained in the liquid crystal alignment agent.

Silane coupling agents are added for the purpose of improving the adhesion between the substrate on which the liquid crystal alignment agent is applied and the liquid crystal alignment film formed thereon. For example, the following various silane coupling agents can be given as specific examples, but are not limited thereto.

Amine-based silanes such as 3-aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-phenylaminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and 3-aminopropyldiethoxymethylsilane; Vinyl-based silanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, vinylmethyldimethoxysilane, vinyltriacetoxysilane, vinyltriisopropoxysilane, allyltrimethoxysilane, and p-styryltrimethoxysilane; Epoxy types such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; Methacryl types such as 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane; Acrylic types such as 3-acryloxypropyltrimethoxysilane; Ureide types such as 3-ureidopropyltriethoxysilane; Sulfide types such as bis(3-(triethoxysilyl)propyl)disulfide, bis(3-(triethoxysilyl)propyl)tetrasulfide; Mercapto systems such as 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-octanoylthio-1-propyltriethoxysilane; isocyanate systems such as 3-isocyanatepropyltriethoxysilane and 3-isocyanatepropyltrimethoxysilane; aldehyde systems such as triethoxysilylbutyraldehyde; carbamate systems such as triethoxysilylpropylmethylcarbamate and (3-triethoxysilylpropyl)-t-butylcarbamate.

The amount of silane coupling agent added is preferably 0.01 to 5.0 wt%, more preferably 0.1 to 1.0 wt%, based on the solid content of the polymer, because if the amount is too large, unreacted matter may have a negative effect on liquid crystal orientation, and if the amount is too small, no effect on adhesion is observed.

In the liquid crystal alignment film of the present invention, an imidization accelerator may be added to efficiently promote imidization of the PAE-PAA copolymer or polyamic acid ester when firing the film.

＜Liquid crystal alignment film＞

The liquid crystal alignment film of the present invention is a film obtained by applying the liquid crystal alignment agent of the present invention to a substrate, drying if necessary, and then firing. The substrate on which the liquid crystal alignment agent of the present invention is applied is not particularly limited as long as it is a highly transparent substrate, and for example, in addition to a glass substrate, a plastic substrate such as an acrylic substrate or a polycarbonate substrate can be used. When the liquid crystal alignment agent of the present invention is used in the manufacture of a liquid crystal display element, it is preferable to form the liquid crystal alignment film using a substrate on which an ITO (Indium Tin Oxide) electrode, etc. for driving a liquid crystal is formed. In addition, when manufacturing a reflective liquid crystal display element, an opaque substrate such as a silicon wafer can be used as long as it is only on one side of the substrate, and in this case, the electrode can be made of a material that reflects light such as aluminum.

Examples of methods for applying the liquid crystal alignment agent of the present invention onto a substrate include screen printing, offset printing, flexographic printing, or inkjet printing. Other methods for applying include dip coating, roll coater coating, slit coater coating, spinner coating, or spray coating, and these may be used depending on the purpose.

The coating film is dried at 50 to 120°C for 1 to 10 minutes to sufficiently remove the organic solvent usually contained therein, and then fired at 150 to 300°C for 5 to 120 minutes. The thickness of the coating film after firing is not particularly limited, but if it is too thin, the reliability of the liquid crystal display element may be lowered, so it is 5 to 300 nm, preferably 10 to 200 nm.

Methods for aligning the obtained liquid crystal alignment film include a rubbing method and a photoalignment method.

The rubbing treatment of the film surface formed on the substrate can be performed using an existing rubbing device. The rubbing cloth material at this time may include cotton, rayon, nylon, etc. The conditions for the rubbing treatment are generally a rotation speed of 300 to 2000 rpm, a transmission speed of 5 to 100 mm/s, and a pressing amount of 0.1 to 1.0 mm. After that, residues generated by the rubbing are removed by ultrasonic cleaning using pure water or alcohol.

As a photoalignment treatment method, a method can be exemplified in which the surface of the coating film is irradiated with radiation biased in a certain direction, and in some cases, additionally heat-treated at a temperature of 150 to 250°C to impart liquid crystal alignment ability. As the radiation, ultraviolet rays and visible light having a wavelength of 100 to 800 nm can be used. Among these, ultraviolet rays having a wavelength of 100 to 400 nm are preferable, and those having a wavelength of 200 to 400 nm are particularly preferable. In addition, in order to improve the liquid crystal alignment ability, the coating film substrate may be heated at 50 to 250°C while irradiating with radiation. The irradiation dose of the radiation is preferably 1 to 10,000 mJ/cm2, and particularly preferably 100 to 5,000 mJ/cm2.

＜Liquid crystal display element＞

The liquid crystal display element of the present invention is obtained by obtaining a substrate with a liquid crystal alignment film from the liquid crystal alignment agent of the present invention by the above-described method, and then manufacturing a liquid crystal cell by a known method to form a liquid crystal display element.

An example of a method for manufacturing a liquid crystal display element is as follows. First, a pair of substrates on which a liquid crystal alignment film is formed are prepared, and they are installed so that the rubbing direction is at an arbitrary angle of 0˚ to 270˚ with a spacer of preferably 1 to 30 ㎛, more preferably 2 to 10 ㎛ between them, and the periphery is fixed with a sealant. Next, a liquid crystal is injected between the substrates and sealed. There is no particular limitation on the method for sealing the liquid crystal, and examples thereof include a vacuum method in which the inside of the manufactured liquid crystal cell is reduced in pressure and then the liquid crystal is injected, and a dropping method in which the liquid crystal is dropped and then sealed.

[Example]

The present invention is specifically described below by way of examples, but the present invention is not to be construed as being limited to these. The abbreviations for compounds used hereinafter and the methods for measuring each characteristic are as follows.

＜Monomer＞

1,3DMCBDE-Cl: Dimethyl 1,3-bis(chlorocarbonyl)-1,3-dimethylcyclobutane-2,4-dicarboxylate

1,3DMCBDA: 1,3-Dimethyl1,2,3,4cyclobutanetetracarboxylic acid dianhydride

PMDA: Pyromellitic dianhydride

PMDE-me: 2,5-Bis(methoxycarbonyl)benzene-1,4dicarboxylic acid

CBDE: 2,4-Bis(methoxycarbonyl)cyclobutane1,3-dicarboxylic acid

CBDA: 1,2,3,4-Cyclobutanetetracarboxylic acid dianhydride

DADPA: 4,4'-Diaminodiphenylamine

p-PDA: p-phenylenediamine

DBOP: Diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl) phosphonate

[Chemical formula 33]

＜Solvent＞

NMP: N-Methyl-2-pyrrolidone

BCS: Butyl Cellosolve

GBL: γ-butyrolactone

＜Viscosity＞

The viscosity of the polymer solution was measured using an E-type viscometer TVE-22H (manufactured by Toki Sangyo Co., Ltd.) with a sample volume of 1.1 ml, cone rotor TE-1 (1˚34', R24), and a temperature of 25°C.

＜Molecular weight＞

The molecular weight of the polymer was measured by a GPC (Gel Permeation Chromatography) device, and the number average molecular weight (hereinafter also referred to as Mn) and the weight average molecular weight (hereinafter also referred to as Mw) were calculated in terms of polyethylene glycol and polyethylene oxide.

GPC device: manufactured by Shodex (GPC-101)

Column: Shodex Manufacturing (KD803, KD805 series)

Column temperature: 50℃

Eluent: N,N-dimethylformamide (containing 30 mmol/ℓ of lithium bromide hydrate (LiBr _H2O ) as additives, 30 mmol/ℓ of phosphoric acid anhydrous crystals (o-phosphoric acid), and 10 mL/ℓ of tetrahydrofuran (THF))

Flow rate: 1.0 ㎖/min

Standard samples for creating a calibration curve: TSK standard polyethylene oxide manufactured by Tosoh Corporation (weight average molecular weight (Mw) approx. 900,000, 150,000, 100,000, 30,000), and polyethylene glycol manufactured by Polymer Laboratory Co. (peak top molecular weight (Mp) approx. 12,000, 4,000, 1,000). In order to avoid overlapping peaks, measurements were performed separately on two samples: a mixed sample of four types of 900,000, 100,000, 12,000, 1,000, and a mixed sample of three types of 150,000, 30,000, 4,000.

(Synthesis Example 1)

In a 2 ℓ four-necked flask equipped with a stirring device and a nitrogen inlet tube, 1.30 g (12.02 mmol) of p-PDA, 1.76 g (7.21 mmol) of DA-A, and 1.64 g (4.81 mmol) of DA-B were placed, and 46.10 g of NMP, 106.9 g of GBL, and 3.58 g (0.44 mmol) of pyridine were added and dissolved. Next, 1.07 g (4.81 mmol) of 1,3DMCBDA was added while stirring the solution, and the mixture was reacted for 5 hours under water cooling. To the solution thus obtained, 6.02 g (18.5 mmol) of 1,3DMCBDE-Cl was added, and the mixture was reacted for an additional 14 hours under water cooling.

To the obtained polyamic acid ester-polyamic acid copolymer solution, 2.39 g (2.64 mmol) of acryloyl chloride was added, and further, after reacting for 4 hours, this solution was poured into 1061 mL of isopropanol with stirring, and the precipitated white precipitate was filtered out. Subsequently, 2655 mL of isopropanol was used in five divided portions to wash, and by drying, white polyamic acid ester-polyamic acid copolymer resin powder (PWD-1) was obtained. The molecular weight of this polyamic acid ester-polyamic acid copolymer was Mn = 13,493 and Mw = 27,207.

The polyamic acid ester-polyamic acid copolymer resin powder (PWD-1) obtained above was dissolved in GBL to obtain a polyamic acid ester-polyamic acid copolymer solution (Copolymer-1) having a solid content concentration of 12 mass%.

(Synthesis Example 2)

In a 200 mL four-necked flask equipped with a stirring device and a nitrogen inlet tube, 8.40 g (3.23 mmol) of CBDE, 5.57 g (2.28 mmol) of DA-A, and 3.03 g (1.52 mmol) of DADPA were placed, and 106.57 g of NMP and 6.92 g (6.84 mmol) of triethylamine were added to dissolve them. Next, 24.77 g (6.46 mmol) of DBOP was added to the solution while stirring, and the reaction was carried out under water cooling for 5 hours. After this, while further stirring the solution, 1.90 g (0.76 mmol) of diphenyl phosphate, 1.08 g (0.49 mmol) of PMDA, and 22.84 g of NMP were added, and the reaction was performed again for 5 hours under water cooling.

The obtained polyamic acid ester-polyamic acid copolymer solution was added to 2000 mL of isopropanol with stirring, the precipitated white precipitate was filtered out, and subsequently washed using 407.83 mL of methanol in four portions, and dried to obtain a white polyamic acid ester-polyamic acid copolymer resin powder (PWD-2).

The polyamic acid ester-polyamic acid copolymer resin powder (PWD-2) obtained above was dissolved in NMP to obtain a polyamic acid ester-polyamic acid copolymer solution (Copolymer-2) having a solid content concentration of 12 mass%.

(Comparative synthesis example 1)

In a 2 ℓ 4-necked flask equipped with a stirring device and a nitrogen inlet tube, 10.00 g (92.4 mmol) of p-PDA, 13.60 g (55.5 mmol) of DA-A, and 12.60 g (37.0 mmol) of DA-B were placed, and 379.00 g of NMP, 1023.00 g of GBL, and 34.60 g (0.43 mmol) of pyridine were added and dissolved. Next, 58.30 g (179.4 mmol) of 1,3DMCBDE-Cl was added while stirring the solution, and the reaction was carried out under water cooling for 14 hours.

To the obtained polyamic acid solution, 2.41 g (26.6 mmol) of acryloyl chloride was added, and further, after reacting for 4 hours, this solution was poured into 8653 mL of isopropanol with stirring, and the precipitated white precipitate was filtered out. Subsequently, 21635 mL of isopropanol was used in five divided portions to wash, and by drying, a white polyamic acid ester resin powder (PWD-3) was obtained. The molecular weight of this polyamic acid ester was Mn = 24,366 and Mw = 54,808.

The polyamic acid ester resin powder (PWD-3) obtained above was dissolved in GBL to obtain a polyamic acid ester solution (PAE-1) having a solid content concentration of 12 mass%.

(Comparative synthesis example 2)

In a 15 ℓ four-necked flask equipped with a stirring device and a nitrogen introduction tube, 761.05 g (1.75 mol) of p-PDA, 256.50 g (1.05 mol) of DA-A, and 258.56 g (0.7 mol) of DA-B were placed, and 9671.41 g of NMP was added to dissolve them. Next, 761.05 g (3.39 mol) of 1,3DMCBDA was added to the solution while stirring, and the solution was diluted with NMP so that the solid content concentration of the solution became 12%. The solution was reacted under water cooling for 14 hours to obtain a polyamic acid solution (PAA-1). The molecular weight of this polyamic acid was Mn = 14,366 and Mw = 28,508.

(Example 1)

In a 20 mL sample tube containing a stirrer, 5.50 g of the polyamic acid ester-polyamic acid copolymer solution (Copolymer-1) obtained in Synthesis Example 1 was placed, and 0.28 g of an NMP (10 mass% dilution) solution of AD-A, further 0.55 g of a 3-glycidoxypropylmethyldiethoxysilane solution diluted to 1.0 mass% with NMP, and 1.70 g of NMP were added. Thereafter, 2.00 g of BCS was added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain a liquid crystal alignment agent (A-1). The viscosity of (A-1) was 35 mPa·S. No precipitation of solids was observed when the liquid crystal alignment agent (A-1) was stored at -20°C for one week, indicating that it was a uniform solution.

(Example 2)

In a 20 mL sample tube containing a stirrer, 7.50 g of the polyamic acid ester-polyamic acid copolymer solution (Copolymer-2) obtained in Synthesis Example 2 was placed, 0.45 g of an NMP (10 mass% dilution) solution of AD-A, further 0.9 g of a 3-glycidoxypropylmethyldiethoxysilane solution diluted to 1.0 mass% with NMP, and 3.12 g of NMP were added. Thereafter, 3.00 g of BCS was added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain a liquid crystal alignment agent (A-2). The viscosity of (A-2) was 37 mPa·S. When the liquid crystal alignment agent (A-2) was stored at -20°C for one week, no precipitation of solids was observed, indicating that it was a uniform solution.

(Comparative Example 1)

In a 20 mL sample tube containing a stirrer, 7.50 g of the polyamic acid ester solution (PAE-1) obtained in Comparative Synthesis Example 1 was placed, 0.45 g of an NMP (10 mass% dilution) solution of AD-A, 0.90 g of a 3-glycidoxypropylmethyldiethoxysilane solution diluted to 1.0 mass% with NMP, and 2.48 g of NMP were added. Thereafter, 3.00 g of BCS was added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain a liquid crystal alignment agent (B-1). The viscosity of (B-1) was 32 mPa·S. When the liquid crystal alignment agent (B-1) was stored at -20°C for one week, no precipitation of solids was observed, indicating that it was a uniform solution.

(Comparative Example 2)

In a 20 mL sample tube containing a stirrer, 8.21 g of the polyamic acid solution (PAA-1) obtained in Comparative Synthesis Example 2 was placed, 0.45 g of an NMP (10 mass% dilution) solution of AD-A, 0.90 g of a 3-glycidoxypropylmethyldiethoxysilane solution diluted to 1.0 mass% with NMP, and 3.12 g of NMP were added. Thereafter, 3.00 g of BCS was added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain a liquid crystal alignment agent (B-2). The viscosity of (B-2) was 35 mPa·S. When the liquid crystal alignment agent (B-2) was stored at -20°C for one week, no precipitation of solids was observed, indicating that it was a uniform solution.

(Example 3)

The liquid crystal alignment agent (A-1) obtained in Example 1 was filtered through a 1.0 μm filter, spin-coated on a glass substrate with a transparent electrode, and dried on a hot plate at a temperature of 80 °C for 5 minutes. Thereafter, the film was baked for 10 minutes in a hot air circulation oven at a temperature of 230 °C, thereby obtaining an imidized film with a film thickness of 100 nm. The baked film was irradiated with 254 nm ultraviolet rays at 250 mJ/cm2 through a polarizing plate, thereby obtaining a substrate with a liquid crystal alignment film.

In order to evaluate the electrical characteristics of the liquid crystal cell, two substrates with the above liquid crystal alignment film were prepared, and a 6 μm spacer was spread on one of the liquid crystal alignment films. A sealant was printed thereon, and another substrate was attached with the liquid crystal alignment film surfaces facing each other and the light alignment directions being orthogonal, and then the sealant was cured to create a blank cell. Liquid crystal ML-7026-100 (manufactured by Merck Japan) was injected into this blank cell by a reduced pressure injection method, and the injection port was sealed to obtain an IPS liquid crystal cell. This liquid crystal cell was heat-treated at 120°C for 30 minutes, and then cooled to room temperature. The cell was observed, and the alignment was found to be good.

＜Measurement of voltage maintenance ratio＞

A voltage of 1 V was applied to the above liquid crystal cell for 60 ㎲ at a temperature of 60 ℃, and the voltage after 500 ㎳ was measured to calculate the voltage maintenance rate to what extent the voltage could be maintained.

As a result, the voltage retention rate at 60°C of the alignment film 1 composed of the alignment agent (A-1) was 85.4%.

(Example 4)

Using the liquid crystal alignment agent of the present invention obtained in Synthesis Example 2, the same evaluation as in Example 3 was performed, but rubbing treatment using alignment-treated rayon cloth (roll diameter 120 mm, rotational speed 1000 rpm, moving speed 20 mm/sec, pressing length 0.3 mm) was performed. The results are described in Table 1 below.

(Comparative Example 3)

Using the liquid crystal alignment agent of the present invention obtained in Comparative Example 1, the same evaluation as in Example 3 was performed. The results are described in Table 1 below.

(Comparative Example 4)

Using the liquid crystal alignment agent of the present invention obtained in Comparative Example 1, the same evaluation as in Example 3 was performed, however, light irradiation was performed by irradiating 500 mJ/cm2 of 254 nm ultraviolet rays through a polarizing plate.

The results of Examples 3 and 4 and Comparative Examples 3 and 4 are described in Table 1 below.

Industrial applicability

A liquid crystal alignment film formed using the liquid crystal alignment agent of the present invention not only has improved liquid crystal alignment properties, but also has improved electrical characteristics such as voltage retention and residual DC voltage. As a result, it is widely useful for TN elements, STN elements, TFT liquid crystal elements, and further, vertically aligned liquid crystal display elements.

In addition, the entirety of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2015-236340, filed on December 3, 2015, is incorporated herein by reference and is incorporated herein as the disclosure of the specification of the present invention.

Claims (12)

A liquid crystal alignment agent characterized by containing the following components (A) and (B).
Component (A): A copolymer having a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2).
[Chemical Formula 1]

(X ₁ and X ₂ are each independently a tetravalent organic group. Y ₁ and Y ₂ are each independently a divalent organic group. R ₁ is an alkyl group having 1 to 5 carbon atoms. A ₁ and A ₂ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an alkynyl group having 2 to 10 carbon atoms which may have a substituent.)
Component (B): A compound having two or more functional groups selected from a hydroxyl group, a hydroxyalkylamide group, and a blocked isocyanate group. In paragraph 1,
A liquid crystal alignment agent, wherein the above component (B) is a compound represented by the following formula (3).
[Chemical formula 2]

(X ₃ is an n-valent organic group containing an aliphatic hydrocarbon group having 1 to 20 carbon atoms, or an aromatic hydrocarbon group. R ₂ and R ₃ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms which may have a substituent, and at least one of R ₂ and R ₃ is represented by the following formula (4). n is an integer of 2 to 6.)
[Chemical Formula 3]

(R ₄ to R ₇ are each independently a hydrogen atom, a hydrocarbon group, or a hydrocarbon group substituted with a hydroxy group.) In claim 1 or 2,
A liquid crystal alignment agent, wherein the copolymer of the above component (A) has 50 to 95 mol% of the structural unit represented by formula (1) and 5 to 50 mol% of the structural unit represented by formula (2) with respect to the total structural units it has. In claim 1 or 2,
A liquid crystal alignment agent, wherein the content of the above component (B) is 1 to 30 wt% with respect to component (A). In claim 1 or 2,
Additionally, a liquid crystal alignment agent containing an organic solvent, wherein the total content of the component (A) and the component (B) is 0.5 to 15 mass% with respect to the organic solvent. In claim 1 or 2,
A liquid crystal alignment agent, wherein in the above formulas (1) and (2), X ₁ and X ₂ are each independently at least one selected from a group consisting of structures represented by the following formulas.
[Chemical Formula 4]
In claim 1 or 2,
A liquid crystal alignment agent, wherein in the above formulas (1) and (2), Y ₁ and Y ₂ are each independently at least one selected from a group consisting of structures represented by the following formulas.
[Chemical Formula 5]
In claim 1 or 2,
A liquid crystal alignment agent, wherein the above block isocyanate group is an organic group represented by the following formula (6).
[Chemical formula 6]
In the second paragraph,
A liquid crystal alignment agent, wherein the compound represented by the above formula (3) is the following compound.
[Chemical formula 7]
A liquid crystal alignment film obtained from the liquid crystal alignment agent described in claim 1 or 2. A liquid crystal display element having a liquid crystal alignment film as described in claim 10. delete