TWI694095B - Liquid crystal alignment agent for liquid alignment, liquid crystal alignment film, and liquid crystal display element - Google Patents

Abstract

The invention provides a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display that form a liquid crystal alignment film with high anisotropy, good liquid crystal alignment, and higher liquid crystal alignment limiting force by irradiating polarized ultraviolet light with a wavelength of 300 nm or more element.

The liquid crystal alignment agent of the present invention includes a polyimide precursor having a structural unit represented by formula (1) and/or a polyamide imidized polymer of the polyimide precursor.

(X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group represented by the following formula (A), R ₁ and R ₂ are a hydrogen atom, or a C 1-4 alkyl group).

Description

Liquid crystal alignment agent for liquid alignment, liquid crystal alignment film, and liquid crystal display element

The present invention relates to a liquid crystal alignment agent, a liquid crystal alignment film, and a liquid crystal display element provided with the liquid crystal alignment film. More specifically, it is about replacing the rubbing treatment with the photo-alignment treatment, that is, the liquid crystal aligning agent for forming the liquid crystal alignment film endowed with the liquid crystal alignment energy by irradiating polarized ultraviolet light containing ultraviolet rays, and the liquid crystal alignment film thus obtained, and A liquid crystal display element provided with the liquid crystal alignment film.

Liquid crystal display elements used in liquid crystal televisions, liquid crystal displays, etc. are usually provided with liquid crystal alignment films for controlling the liquid crystal alignment state in the elements. At present, the most popular liquid crystal alignment film in the industry is a polyacrylic acid formed by rubbing cotton, nylon, polyester, etc. on the electrode substrate in a certain direction on the electrode substrate and/or the polyimidization of the polyimide. The so-called rubbing treatment on the surface of the film formed by a polyimide-based polymer such as amide imide gives liquid crystal alignment energy.

The rubbing treatment to impart alignment energy to the liquid crystal is an industrially useful method that is simple and excellent in productivity. However, the requirements for high-performance, high-definition, and large-scale liquid crystal display elements are increasing. Various problems such as scratches, dust generation, mechanical force or static electricity caused by the surface of the alignment film, and the unevenness in the alignment treatment surface have become obvious.

As an alternative to the rubbing treatment, a light alignment method that imparts alignment energy to liquid crystals by irradiating polarized radiation is known. As for the alignment treatment by the photo-alignment method, there have been proposed a photo-isomerization reactor, a photo-crosslinking (photo-dimerization) reactor, and a photo-decomposition reactor (see Non-Patent Document 1).

On the other hand, as a polymer for forming a liquid crystal alignment film, when a polyimide-based polymer is used in a liquid crystal alignment film for optical alignment, its availability is expected to be higher than other types due to its high heat resistance. Furthermore, it has been proposed to use a film of a polyimide-based polymer having an alicyclic structure such as a cyclobutane ring in the main chain in the photo-alignment method (refer to Patent Document 1).

[Prior Technical Literature] [Patent Literature]

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

Non-patent literature

Non-Patent Document 1: "Liquid Crystal Optical Alignment Film" Kitowaki, Ichimura, Functional Materials, November 1997, Vol.17 No.11, pages 13-22

Patent Document 1 discloses that a film of a polyimide-based polymer having an alicyclic structure such as cyclobutane obtains high anisotropy by irradiating polarized ultraviolet light near a wavelength of 254 nm with a short-wavelength ultraviolet light, and liquid crystal alignment Liquid crystal alignment film with excellent properties.

However, ultraviolet light near a wavelength of 254 nm has high energy and requires much power for irradiation. Therefore, not only the cost for the optical alignment process becomes large, but also the load on the environment is also large. Moreover, because of the use of short-wavelength ultraviolet rays with strong energy, there is a possibility of damaging the electrodes or thin-film transistors (TFTs) formed on the substrate.

On the other hand, the photo-alignment method using photo-isomerization or photo-dimerization can impart anisotropy by irradiating long-wavelength polarized ultraviolet rays with a wavelength of 300 nm or more. However, in the past, the liquid crystal alignment film obtained by the photo-alignment method of photo-isomerization or photo-dimerization has a weak alignment restriction force, and when used in a liquid crystal display device, there is a problem of afterimages.

The object of the present invention is to provide an anisotropic liquid crystal alignment film by irradiating polarized ultraviolet rays with a wavelength of 300 nm or more to form a liquid crystal alignment with high anisotropy and good liquid crystal alignment, and a higher liquid crystal alignment limiting force The liquid crystal alignment agent of the film, the liquid crystal alignment film thus obtained, and the liquid crystal display element having the liquid crystal alignment film.

After carrying out active research in order to achieve the above object, the present inventors found that the polycondensation reaction of a diamine having a specific structure having a diketone structure between two amine groups by tetracarboxylic dianhydride and/or its derivatives The film obtained by the obtained polyimide precursor and/or the liquid crystal alignment agent containing the imidized polymer of the polyimide precursor can be irradiated by polarized ultraviolet rays including ultraviolet rays with a wavelength of 300 nm or more, Forms optical alignment, high anisotropy and good liquid crystal alignment, and thus has a high liquid crystal alignment limitation Liquid crystal alignment film.

Therefore, the present invention has been completed based on the above-mentioned novel insights, and provides a liquid crystal alignment agent characterized by including a polyimide precursor having a structural unit represented by the following formula (1) and the polyimide At least one polymer selected from the group consisting of precursor imidized polymers,

(X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group represented by the following formula (A), R ₁ and R ₂ are a hydrogen atom, or a C 1-4 alkyl group),

The liquid crystal alignment agent of the present invention can form a liquid crystal alignment film with high anisotropy, excellent liquid crystal alignment and alignment restricting power by irradiating polarized ultraviolet light including ultraviolet light with a wavelength of 300 to 400 nm. Use this When a liquid crystal alignment film is used as a liquid crystal display element, a liquid crystal display element excellent in afterimage characteristics is obtained.

The polarized ultraviolet light used in the light alignment treatment in the liquid crystal alignment agent of the present invention is not a short wavelength in the past, but a longer polarized ultraviolet light with a wavelength of more than 300mm can be used, so the power used for the light alignment treatment is small, and the Environmental load. Moreover, because of the use of long-wavelength ultraviolet rays with weak energy, damage to the electrodes or TFTs formed on the substrate can be reduced.

In the photo-alignment process of the film obtained by the liquid crystal aligning agent of this invention, although it is not necessarily clear why the above-mentioned excellent effect can be obtained, it is considered as follows. The polyimide precursor of the polymer contained in the liquid crystal alignment agent of the present invention and/or its imidized polymer has a diketo structure in its main chain, and when the polymer having a diketo structure is irradiated with polarized ultraviolet light It is considered that only the aromatic ring bonded to the diketone portion of the molecular chain whose long axis direction is parallel to the polarization direction absorbs light, and excites and moves the energy to perform the following cracking reaction and impart anisotropy.

<Polyimide Precursor and Polyimide>

The liquid crystal alignment agent of the present invention contains a polyimide precursor having a structural unit represented by the following formula (1) and the polyimide precursor of the polyimide At least one polymer selected from the group consisting of chemical polymers.

In the above formula (1), X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group represented by the following formula (A), R ₁ and R ₂ are a hydrogen atom, or a C 1-4 alkyl group, It is preferably a hydrogen atom.

In the above formula (A), one or both of the benzene rings may have a substituent formed by (Z) _m . Here, Z is preferably an alkyl group having 1 to 4 carbon atoms, and m is 1 to 4, preferably an integer of 1 or 2.

In formula (1), the bonding site of the nitrogen atom of Y ₁ represented by formula (A) may be either ortho, meta, or para, but preferably para.

X ₁ in the above formula (1) is not particularly limited as long as it is a tetravalent organic group, but it is preferably a tetravalent organic group derived from a tetracarboxylic acid derivative.

In the polyimide precursor, X ₁ may also be present in mixture of two or more. If a specific example of X ₁ is illustrated, the structure of the following formulas (X-1) to (X-43) will be listed. Among them, from the viewpoint of availability, X _{1 is} preferably (X-1) to (X-14).

R ₅ to R ₈ in formula (X-1) are each independently hydrogen atom, halogen atom, alkyl group having 1 to 6 carbon atoms, alkenyl group having 2 to 6 carbon atoms, alkynyl group having 2 to 6 carbon atoms, or Phenyl. When R ₅ to R ₈ are of a bulky structure, there is a possibility of lowering the alignment of the liquid crystal, so it is more preferably a hydrogen atom, a methyl group or an ethyl group, and preferably a hydrogen atom or a methyl group.

Y ₁ in the above formula (1) is preferably a divalent organic group derived from the following diamine compound.

In addition, the polyimide precursor of the present invention may include a structural unit represented by the following formula (10) in addition to the structural unit represented by the above formula (1).

In formula (10), R ₄ has the same definition as R _{1 in} the above formula (1). In formula (10), X ₂ is a tetravalent organic group, and the preferred examples include the same definition as X ₁ in formula (1). Z ₁ and Z _{2 are} each independently a hydrogen atom, or a C 1-10 alkyl group, a C 2-10 alkenyl group, or a C 2-10 alkynyl group which may have a substituent.

Specific examples of the alkyl group having 1 to 10 carbon atoms include methyl, ethyl, propyl, butyl, tertiary butyl, hexyl, octyl, decyl, cyclopentyl, cyclohexyl, and dicyclohexyl groups.

The above alkenyl group having 2 to 10 carbon atoms is exemplified by replacing one or more CH ₂ -CH ₂ existing in the above alkyl group with CH=CH. More specific examples include vinyl, allyl, 1-propenyl, isopropenyl, 2-butenyl, 1,3-butadienyl, 2-pentenyl, 2-hexenyl, cyclopropenyl , Cyclopentenyl, cyclohexenyl, etc.

The above alkynyl groups having 2 to 10 carbon atoms are exemplified by replacing one or more CH ₂ -CH ₂ present in the above alkyl group with C≡C, and more specifically exemplified by ethynyl, 1-propynyl, and 2-propene Alkynyl and so on.

The alkyl group having 1 to 10 carbon atoms, the alkenyl group having 2 to 10 carbon atoms and the alkynyl group having 2 to 10 carbon atoms may have a substituent if they have 1 to 10 carbon atoms or 2 to 10 carbon atoms, and may further have a substituent Form a ring structure. In addition, the so-called ring structure system is formed by the substituents, and the substituents or a part of the parent skeleton is bonded to form a ring structure.

Examples of the substituent include halogen group, hydroxyl group, thiol group, nitro group, aryl group, organic oxygen group, organic sulfur group, organosilyl group, amide group, ester group, thioester group, phosphate group, amide group Amino, alkyl, alkenyl, alkynyl, etc.

In the polyimide precursor, Z ₁ and Z _{2 are} more preferably a hydrogen atom or a C 1-5 alkyl group which may have a substituent, and most preferably a hydrogen atom, a methyl group or an ethyl group. Generally, when a large-volume structure is introduced, there is a possibility that the reactivity of the amine group or the liquid crystal alignment will decrease.

In the above formula (10), Y ₂ is a divalent organic group, and specific examples thereof are given by the following formulas (Y-1) to (Y-114). In addition, in the polyimide precursor, Y ₂ may be mixed in two or more kinds.

Among them, in order to obtain good liquid crystal alignment, it is preferable to use diamine that forms polyimide with high linearity. Therefore, from the viewpoint of liquid crystal alignment, Y _{2 is} preferably Y-7, Y-10, Y-11, Y-12, Y-13, Y-21, Y-22, Y-23, Y-25, Y-26, Y-27, Y-41, Y-42, Y-43, Y-44, Y-45, Y-46, Y-48, Y-61, Y-63, Y-64, Y- 71, Y-72, Y-73, Y-74, Y-75, or Y-98.

In addition, when increasing the pretilt angle, it is preferable to use a diamine having a structure in which the side chain has a long-chain alkyl group, an aromatic ring, an aliphatic ring, a steroid skeleton, or a combination of these. Therefore, from the viewpoint of the pretilt angle, Y _{2 is} preferably Y-76, Y-77, Y-78, Y-79, Y-80, Y-81, Y-82, Y-83, Y-84, Y -85, Y-86, Y-87, Y-88, Y-89, Y-90, Y-91, Y-92, Y-93, Y-94, Y-95, Y-96, or Y- 97.

When the liquid crystal alignment agent of the present invention contains the structural unit represented by the above formula (10), when the ratio of the structural unit represented by the formula (10) is high, there may be polarized ultraviolet rays including ultraviolet rays with a wavelength of 300 to 400 nm. The possibility of tropism, so the ratio of structural units expressed by formula (10) is preferably 0 to 70 mol%, more preferably 0 to 55 mol% relative to 1 mol of all structural units. That is, the content of the structural unit represented by formula (1) is preferably 30 to 100 mol%, more preferably 45 to 100 mol%.

<Manufacturing method of polyamic acid>

The polyamic acid of the polyimide precursor used in the present invention can form the tetracarboxylic acid or its dianhydride of X ₁ in the structural unit of the above formula (1) in the presence of an organic solvent, and form the diamine of Y ₁ The reaction is obtained.

The organic solvent used in the above reaction is not particularly limited as long as it can dissolve the generated polyamide acid. Specific examples are N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, dimethyl碸, γ-butyrolactone, etc. In addition, when the solubility of the polyimide precursor is high, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone or the following formula (D- 1) Organic solvent represented by formula (D-3).

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

These can be used alone or mixed. In addition, even if it is a solvent which cannot dissolve the polyamic acid alone, it can be mixed and used in the above solvent in a range where the polyamic acid is not precipitated. In addition, the moisture in the organic solvent hinders the polymerization reaction and further causes the hydrolysis of the produced polyamic acid. Therefore, it is preferable to use one that dehydrates the organic solvent as much as possible.

The method of mixing and reacting the diamine component and the tetracarboxylic dianhydride in the organic solvent is exemplified by stirring the solution in which the diamine is dispersed or dissolved in the organic solvent, and the tetracarboxylic dianhydride is added directly or dispersed or dissolved in the organic solvent Method, on the contrary, diamine is added to disperse or dissolve the tetracarboxylic dianhydride The method in a solution in an organic solvent, the method in which tetracarboxylic dianhydride and diamine are alternately or simultaneously added in an organic solvent, etc. may be any of these methods.

The temperature during the synthesis of the above-mentioned polyamide can be selected from the range of -20 to 150°C, preferably -5 to 100°C, and more preferably 0 to 80°C. Moreover, the reaction time can be arbitrarily selected in a range longer than the time for stabilizing the polymerization of the polyamic acid, but it is preferably 30 minutes to 24 hours, more preferably 1 to 12 hours. Moreover, the reaction can be carried out at any concentration, but when the concentration of the diamine component of the raw material and the tetracarboxylic dianhydride is too low, it is difficult to obtain a high molecular weight polymer, and when the concentration is too high, the viscosity of the reaction solution becomes too high to be difficult It is uniformly stirred, so it is preferably 1-50% by mass, more preferably 5-20% by mass. It is also possible to proceed at a high concentration in the initial stage of the reaction, and then add an organic solvent.

In the production reaction of polyamic acid, the ratio of the number of moles of tetracarboxylic dianhydride to the number of moles of the diamine component is preferably 0.8 to 1.2. As in the normal polycondensation reaction, the closer the molar ratio is to 1.0, the larger the molecular weight of the produced polyamic acid.

The polyamic acid obtained as described above can be poured into a weak solvent while sufficiently stirring the reaction solution to precipitate and recover the polymer. Furthermore, after several precipitations, washing with a weak solvent, and drying at room temperature or by heating, purified polyamic acid powder can be obtained. The weak solvent is not particularly limited, and examples thereof include water, methanol, ethanol, 2-propanol, hexane, butyl cellosolvin, acetone, toluene, and the like, preferably water, methanol, ethanol, 2-propanol, and the like.

"Manufacture of Polyamide"

The polyamide ester of the polyimide precursor of the present invention can be produced by the production method of [1], [2] or [3] shown below.

[1] Manufactured from polyamide

Polyamide can be produced by esterifying the polyamide produced as described above. Specifically, in the presence of an organic solvent, the polyamic acid and the esterifying agent are reacted at -20 to 150°C, preferably 0 to 50°C, for 30 minutes to 24 hours, preferably 1 to 4 hours.

The esterifying agent is preferably one that can be easily removed by purification, and is exemplified by N,N-dimethylformamide dimethyl acetal, N,N-dimethylformamide diethyl acetal, N,N -Dimethylformamide dipropyl acetal, N,N-dimethylformamide dineopentylbutyl acetal, N,N-dimethylformamide dithird butyl acetal, 1-methyl-3-p-tolyltriazene, 1-ethyl-3-p-tolyltriazene, 1-propyl-3-p-tolyltriazene, 4-(4, 6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, etc. The addition amount of the esterifying agent is preferably 2 to 6 moles, and more preferably 2 to 4 moles relative to 1 mole of the repeating unit of the polyamic acid.

Organic solvents are exemplified by N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethyl Ethylacetamide, dimethyl sulfoxide or 1,3-dimethyl-imidazolidinone. In addition, when the solvent solubility of the polyimide precursor is high, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone or the above formula (D -1) ~ Solvent represented by formula (D-3).

These organic solvents can be used alone or in combination. Furthermore, even if it is a solvent that does not dissolve the precursor of polyimide, The polyimide precursor may be mixed and used in the aforementioned organic solvent within the range of precipitation. In addition, the moisture in the organic solvent will hinder the polymerization reaction, and further cause the hydrolysis of the produced polyimide precursor, so the solvent is preferably used after dehydration and drying.

The organic solvent used in the above reaction is preferably N,N-dimethylformamide, N-methyl-2-pyrrolidone, or γ-butyrolactone in terms of the solubility of the polymer. Use 1 type or mix 2 or more types. The concentration at the time of manufacturing is preferably 1 to 30% by mass, more preferably 5 to 20% by mass in terms of not easily causing precipitation of the polymer and easily obtaining a high molecular weight body.

[2] Case produced by the reaction of tetracarboxylic acid ester dichloride and diamine

Polyamide ester structural units from the above formula (1) is formed of X ₁ of the tetracarboxylic acid diester dichloride is formed with a diamine component containing a diamine of Y of _a compound to be manufactured.

Specifically, the tetracarboxylic acid diester dichloride and diamine can be reacted in the presence of an alkali and an organic solvent at -20 to 150°C, preferably 0 to 50°C for 30 minutes to 24 hours, preferably 1 to Manufactured in 4 hours.

Pyridine, triethylamine, 4-dimethylaminopyridine and the like can be used as the aforementioned base, but pyridine is preferred in order to stabilize the reaction. The amount of alkali added is an amount that can be easily removed, and from the viewpoint of easily obtaining a high molecular weight body, it is preferably 1 to 8 times moles, more preferably 2 to 4 times moles relative to the tetracarboxylic acid diester dichloride.

The organic solvent used in the above reaction is preferably N-methyl-2-pyrrolidone or γ-butyrolactone in terms of the solubility of the monomer and the polymer, and these can be used alone or in combination of two or more. use. Polymer concentration The degree is preferably from 1 to 30% by mass, and more preferably from 5 to 20% by mass from the viewpoint of not easily causing precipitation of the polymer and easily obtaining a high molecular weight body.

In addition, in order to prevent the hydrolysis of the tetracarboxylic acid diester dichloride, the organic solvent used in the production of the polyamide is preferably dehydrated as much as possible, and the reaction is preferably in a nitrogen atmosphere to prevent the mixing of outside air.

[3] Manufactured from tetracarboxylic acid diester and diamine

Polyamide can be produced by polycondensation of a tetracarboxylic acid diester forming X ₁ in the structural unit of the above formula (1) and a diamine component containing a diamine compound forming Y ₁ .

Specifically, the tetracarboxylic acid diester and diamine are reacted in the presence of a condensing agent, an alkali and an organic solvent at 0 to 150°C, preferably 0 to 100°C for 30 minutes to 24 hours, preferably 3 to 15 Made in hours.

As the aforementioned condensing agent, 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'-tetra Methylurea tetrafluoroborate, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethylurea hexafluorophosphate, (2,3-dihydro- 2-thio-3-benzoxazolyl)phosphonic acid diphenyl ester and the like. The addition amount of the condensing agent is preferably 2 to 3 times moles, more preferably 2 to 2.5 times moles relative to the tetracarboxylic acid diester.

As the aforementioned base, tertiary amines such as pyridine and triethylamine can be used. The amount of alkali added is an amount that can be easily removed, and from the viewpoint of easily obtaining a high molecular weight body, it is preferably 2 to 4 times the molar amount, more preferably 2 to 3 times the molar amount of the diamine component. ear.

In addition, in the above reaction, by adding a Lewis acid as an additive, the reaction proceeds efficiently. The Lewis acid is preferably a lithium halide such as lithium chloride or lithium bromide. The amount of Lewis acid added is preferably 0.1 to 10.0 times the molar amount of the diamine component, more preferably 2.0 to 3.0 times the molar amount.

Among the above three methods of producing polyamides, in order to obtain high molecular weight polyamides, the method of [1] or [2] above is preferred.

The solution of the polyamic acid ester obtained as described above can precipitate a polymer by injecting a weak solvent with sufficient stirring. Precipitation is carried out several times, washed with a weak solvent, and dried at room temperature or heating to obtain a powder of purified polyamide. The weak solvent is not particularly limited, and examples thereof include water, methanol, ethanol, hexane, butyl cellosolve, acetone, and toluene.

<Manufacturing method of polyimide>

The polyimide used in the present invention can be produced by amidating the aforementioned polyimide precursor, imide.

In the polyimide of the present invention, the ring-closing rate (amidation rate) of the amide acid group or amide group need not necessarily be 100%, as long as it can be arbitrarily adjusted according to the use or purpose.

The method for closing the ring of the polyimide precursor is exemplified by thermal imidization of heating the polyimide precursor without using a catalyst, and catalyst imidization using a catalyst.

When the polyimide precursor is thermally imidized, the polyimide precursor is preferably The solution of the flooding substance is heated to 100-400°C, preferably 120-250°C, and the water or alcohol produced by the amide imidization reaction is discharged to the outside of the system.

The catalyst imidization of the polyimide precursor can be performed by adding an alkaline catalyst and an acid anhydride to the polyamic acid solution and stirring at -20 to 250°C, preferably 0 to 180°C. The amount of the alkaline catalyst is 0.5 to 30 mole times of the amide acid group, preferably 2 to 20 mole times, and the amount of the acid anhydride is 1 to 50 mole times of the amide acid group, preferably 3 to 30 mole times.

Examples of the basic catalyst include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Among them, pyridine is preferable because it has a moderate alkalinity for the reaction to proceed.

Examples of the acid anhydride include acetic anhydride, trimellitic anhydride, and pyromellitic anhydride. Among them, when acetic anhydride is used, the purification after the reaction is easier, so it is preferable. The rate of acetimidation of catalyst imidate can be controlled by adjusting the amount of catalyst, reaction temperature and reaction time.

When recovering the polymer component from the reaction solution of polyimide, it is sufficient to deposit the reaction solution in a weak solvent. Examples of the weak solvent used for precipitation include methanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, benzene, and water. After the polymer precipitated by inputting the weak solvent is recovered by filtration, it is preferably dried under normal pressure or reduced pressure at normal temperature or under heating.

<Liquid crystal alignment agent>

The liquid crystal alignment agent of the present invention is a coating liquid for preparing a liquid crystal alignment film, and its main component is a composition containing a polymer for forming a resin film and an organic solvent for dissolving the polymer. The molecular weight of the polymer is by weight The quantity average molecular weight is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and still more preferably 10,000 to 100,000. Moreover, the number average molecular weight is preferably 1,000 to 250,000, more preferably 2,500 to 150,000, and still more preferably 5,000 to 50,000.

The polymer concentration in the liquid crystal alignment agent in the present invention can be appropriately changed according to the thickness setting of the coating film to be formed, but from the viewpoint of forming a uniform and defect-free coating film, it is preferably 1% by mass or more, based on the preservation of the solution The viewpoint of stability is preferably 10% by mass or less. The best polymer concentration is 2-8% by mass.

The above-mentioned resin components may be all polymers of the present invention, and polymers other than the polymer of the present invention may be mixed. The other polymer is exemplified by polyimide precursors or polyimide obtained by using a diamine compound other than 4,4'-diaminobiphenyl amide (DAB) as a diamine component.

The organic solvent contained in the liquid crystal alignment agent of the present invention is not particularly limited as long as it can dissolve the polymer component uniformly. Specific examples 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 sulfoxide, γ- Butyrolactone, 1,3-dimethyl-imidazolidinone, 3-methoxy-N,N-dimethylpropionamide, etc. One of these may be used alone, or two or more of them may be used in combination. In addition, even if the solvent alone cannot dissolve the polymer component uniformly, it can be mixed in the above-mentioned organic solvent as long as the polymer is not precipitated.

In the liquid crystal alignment agent of the present invention, except for In addition to the organic solvent in which the components are dissolved, a solvent for improving the uniformity of the coating film when the liquid crystal alignment agent is applied on the substrate may also be included. The solvent generally uses a low surface tension solvent. Specific examples 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 may be used in combination.

The weak solvent is a weak solvent with low solubility of the resin. These solvents are preferably 5 to 60% by mass of the organic solvent contained in the liquid crystal alignment agent, more preferably 10 to 50% by mass.

In addition to the above, the liquid crystal alignment agent of the present invention may contain a polymer other than the polymer of the present invention, a dielectric substance or a conductive substance for changing the electrical characteristics such as the dielectric constant or conductivity of the liquid crystal alignment film, and for improving Silane coupling agent for the adhesion between the liquid crystal alignment film and the substrate, a cross-linking compound to increase the hardness or density of the film when the liquid crystal alignment film is formed, and to make the polyimide precursor when the coating film is fired An amide imidization accelerator that effectively proceeds imidate.

When the compound containing a functional silane or the compound containing an epoxy group is contained, the amount thereof is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, and most preferably 1 to 10 relative to 100 parts by mass of the resin component. Quality parts.

When the surfactant is contained, its amount is 100 parts by mass relative to the resin component It is preferably 0.01 to 2 parts by mass, and more preferably 0.01 to 1 part by mass.

<Liquid crystal alignment film>

The liquid crystal alignment film of the present invention is obtained by irradiating substantially linearly polarized ultraviolet rays including ultraviolet rays with a wavelength of 300 to 400 nm to a film obtained from the liquid crystal alignment agent of the present invention. Generally, a coating is formed by applying a liquid crystal alignment agent on a substrate, and before or after firing, the coating surface can be irradiated with the above ultraviolet rays. The coating is preferably dried before firing or before irradiation with ultraviolet rays.

The substrate coated with the liquid crystal alignment agent is preferably a substrate with high transparency, and a plastic substrate such as a glass substrate, a silicon nitride substrate, an acrylic substrate, and a polycarbonate substrate can be used. When using a substrate formed with ITO electrodes or the like for liquid crystal driving, it is preferable in view of simplification of the manufacturing process. In addition, in a reflective liquid crystal display device, an opaque substance such as a silicon wafer can also be used as a single-sided substrate. In this case, an electrode such as aluminum may be used to reflect light.

The coating method of the liquid crystal alignment agent of the present invention is exemplified by spin coating method, printing method, inkjet method and the like.

The drying and firing steps of the film of the liquid crystal alignment agent are used to polyimide the polyimide precursor and convert it to an imide polymer, so any temperature and time can be selected. Generally, in order to fully remove the organic solvent contained, it is preferably dried at 50 to 120°C for 1 to 10 minutes, and then, preferably fired at 150 to 300°C for 5 to 120 minutes.

Although the film thickness after firing is not particularly limited, there will be a liquid crystal display when it is too thin When the reliability of the device is reduced, it is preferably 5 to 300 nm, and more preferably 10 to 200 nm.

For the irradiation of ultraviolet rays, it is preferable to use ultraviolet rays including a wavelength of 300 to 400 nm, preferably 310 to 380 nm, polarized in a certain direction on the surface of the aforementioned coating. The total irradiation amount of ultraviolet rays also varies with the content of the polymer contained in the liquid crystal alignment agent or the thickness of the film, but it is preferably 1 to 10,000 mJ/cm ² , more preferably 100 to 5,000 mJ/cm ² , and most preferably It is 400~5,000mJ/cm ² .

<Liquid crystal display element>

The liquid crystal display element of the present invention is obtained after obtaining the substrate with the above-mentioned liquid crystal alignment film, making a liquid crystal cell by a known method, and using the liquid crystal cell as a liquid crystal display element.

An example of a method for manufacturing a liquid crystal cell is described by taking a passive matrix structured liquid crystal display device as an example. Alternatively, a liquid crystal display element of an active matrix structure in which a switching element such as a TFT (Thin Film Transistor) is provided on each pixel portion constituting an image display.

First, a substrate made of transparent glass is prepared, a common electrode is provided on one of the substrates, and a segmented electrode is provided on the other substrate. These electrodes can be, for example, ITO electrodes, and can be patterned in a desired image display manner. Next, an insulating film is provided on each substrate so as to cover the common electrode and the segment electrode. The insulating film may be a film made of SiO ₂ -TiO ₂ formed by the solution gel method.

The liquid crystal alignment film of the present invention is formed on each substrate. Pick up In order to make the alignment film surfaces face each other, the other substrate is overlapped on the other substrate, and the periphery is sealed with the sealing material. In order to control the substrate gap in the sealing material, a separator is usually mixed. Moreover, it is preferable to also spread a spacer for controlling the substrate gap inside the surface where the sealing material is not provided. An opening that can be filled with liquid crystal from the outside is provided on a part of the sealing material.

Next, the liquid crystal material is injected into the space surrounded by the two substrates and the sealing material through the opening provided in the sealing material. Subsequently, the opening is sealed with an adhesive. The injection method can be a vacuum injection method or a method using capillary phenomenon in the atmosphere. Next, the polarizing plate is installed. Specifically, a pair of polarizing plates are bonded to the surfaces of the two substrates opposite to the liquid crystal layer. Through the above steps, a liquid crystal display element is obtained. Since this liquid crystal display element uses the liquid crystal alignment film of the present invention as a liquid crystal alignment film, it is excellent in afterimage characteristics and can be preferably used for a large-screen high-definition liquid crystal TV and the like.

Examples

The following examples illustrate the present invention more specifically, but the present invention is not limited thereto.

The abbreviation of the compound and the measuring method of each characteristic are as follows.

NMP: N-methyl-2-pyrrolidone, BCS: butyl cellosolve

<Diamine>

<Tetracarboxylic dianhydride>

[Viscosity]

The viscosity of the polyamic acid solution was measured using an E-type viscometer TVE-22H (manufactured by Toki Industry Co., Ltd.), a sample volume of 1.1 mL, a conical rotor TE-1 (1°34', R24), and a temperature of 25°C.

[Determination of solid content concentration]

The calculation of the solid content concentration of the polyamic acid solution is as follows Row. Measure about 1.1g of the polyamic acid solution in the aluminum cup No. 2 (manufactured by AS ONE) with a hand, and heat it at 200°C for 2 hours in an oven (DNF400, manufactured by Yamato), at room temperature Leave it for 5 minutes to measure the weight of the solid content remaining in the aluminum cup. The solid content concentration was calculated from the value of the solid content weight and the original solution weight.

<Synthesis Example 1>

Using 1.95 g of CBDA as the tetracarboxylic dianhydride component and 2.40 g of DAB as the diamine component, the NMP 17.22 g was reacted at 60° C. for 18 hours to obtain a polyamic acid solution having a solid content concentration of 20% by mass ( PAA-1).

<Synthesis Examples 2-6>

In addition to using the raw materials and specifications shown in Table 1, the same procedure as in Synthesis Example 1 was carried out to obtain various polyamic acid solutions (PAA-2 to PAA-6) having a solid content concentration of 20% by mass. In addition, when PAA-5 and PAA-6 are obtained, two kinds of diamines are added without a special time difference.

(Example 1)

BCS 6.0 g and NMP 8.0 g were added to 6.0 g of the polyamic acid solution (PAA-1) obtained in Synthesis Example 1, and stirred at room temperature for 1 hour to obtain a polymer solution having a solid content concentration of 6.0% by mass. The polymer solution is a liquid crystal alignment agent (A1) used directly to form a liquid crystal alignment film.

(Examples 2-6)

Using the polyamic acid solutions (PAA-2) to (PAA-6) shown in Table 2, as in Example 1, the solvent BCS/NMP ratio (g/g) was 8.0/12.0 to obtain a solid The liquid crystal alignment agents (A2 to A6) of Examples 2 to 6 having a component concentration of 6.0% by mass.

[Production of liquid crystal cells and evaluation of liquid crystal alignment 1]

Using the liquid crystal alignment agents (A1 to A6) obtained in the examples, the liquid crystal cells were produced in the order shown below. The substrate is a glass substrate with a size of 30 mm × 40 mm and a thickness of 1.1 mm. The ITO film is applied only to one side of the substrate. Spin-coat each liquid crystal alignment agent (A1~A6) on the substrate. Next, it was dried with a 70°C hot plate for 90 seconds, and fired with a 230°C hot plate for 10 minutes to form a liquid crystal alignment film with a film thickness of 100 nm. Next, the coating film surface was irradiated with ultraviolet rays at 313 nm for 23 seconds to 233 seconds through a polarizing plate to obtain a substrate with a liquid crystal alignment film. The ultraviolet irradiation amount is set to 100 to 1000 mJ/cm ² . The opposite substrate is also produced in the same operation.

After spreading a spacer with a thickness of 4 μm on the surface of the liquid crystal alignment film of a substrate, a sealant (XN-1500T, manufactured by Kyoritsu Chemical Co., Ltd.) was printed on the liquid crystal alignment film. Next, another substrate (counter substrate) was bonded face-to-face with a liquid crystal alignment film so that the alignment direction became 0°, and then the sealant was thermally cured (150° C.) to produce cells. After injecting liquid crystal (MLC-2041, manufactured by Merck) into the hollow cell by a reduced pressure injection method, the injection port was sealed to prepare a liquid crystal cell. Subsequently, the liquid crystal cell was heated in an oven at 120°C for 1 hour, and then returned to normal temperature.

While illuminating with backlight, the alignment state of the liquid crystal of the liquid crystal cell produced above was observed while being sandwiched between two polarizing plates. The results are shown in Table 3. In Table 3, when the liquid crystal cell was observed while rotating in parallel with the backlight, those who did not observe poor liquid crystal alignment were noted as "○", and those who observed white spots or bright spots were noted as "△".

[Manufacture of liquid crystal cells and evaluation of liquid crystal alignment 2]

Using the liquid crystal alignment agents (A1 to A6) obtained in each example, the liquid crystal cells were produced in the order shown below. The substrate is a glass substrate with a size of 30 mm × 40 mm and a thickness of 1.1 mm. The ITO film is applied to only one side of the substrate. The liquid crystal alignment agents (A1 to A6) were spin-coated on the substrate. Next, it was dried with a 70°C hot plate for 90 seconds, and the coated film surface was irradiated with 313 nm ultraviolet rays for 23 seconds to 233 seconds through the polarizing plate. The irradiation amount of ultraviolet rays is set to 100~1000mJ/cm ² . It was fired on a hot plate at 230°C for 10 minutes to form a liquid crystal alignment film with a thickness of 100 nm. The opposite substrate is also produced by the same operation.

After spreading a spacer with a thickness of 4 μm on the surface of the liquid crystal alignment film of a substrate, a sealant (XN-1500T, manufactured by Kyoritsu Chemical Co., Ltd.) was printed on the liquid crystal alignment film. Next, the other substrate (counter substrate) was bonded face-to-face with a liquid crystal alignment film so that the alignment direction became 0°, and then the sealant was thermally cured to produce cells. After injecting liquid crystal (MLC-2041, manufactured by Merck) into the hollow cell by a reduced pressure injection method, the injection port was sealed to prepare a liquid crystal cell. Subsequently, the liquid crystal cell was heated in an oven at 120°C for 1 hour After that, return to normal temperature.

While illuminating with backlight, the alignment state of the liquid crystal of the liquid crystal cell produced above was observed while being sandwiched between two polarizing plates. The results are shown in Table 4. In Table 4, when the liquid crystal cell was observed while rotating in parallel with the backlight, those who did not observe poor liquid crystal alignment were noted as "○", and those who observed white spots or bright spots were noted as "△".

[Industry availability]

The liquid crystal alignment film obtained from the liquid crystal alignment agent of the present invention can be widely used in TN devices, STN devices, TFT devices, and further in vertical alignment type liquid crystal display devices. In particular, it is useful for liquid crystal display elements or liquid crystal TVs driven by IPS or FFS (Fringe Field Switching).

In addition, the entire contents of the specification, patent application scope and abstract of Japanese Patent Application No. 2014-148082 filed on July 18, 2014 are incorporated herein and incorporated as disclosure of the specification of the present invention.

Claims (10)

A liquid crystal alignment agent characterized in that it comprises at least one selected from the group consisting of a polyimide precursor having a structural unit represented by the following formula (1) and a polyamide imide polymer of the polyimide precursor A polymer,

(X ₁ is a tetravalent organic group, Y ₁ is a divalent organic group represented by the following formula (A), R ₁ and R ₂ are a hydrogen atom, or a C 1-4 alkyl group),

The liquid crystal alignment agent according to claim 1, wherein in the aforementioned formula (1), R ₂ is a hydrogen atom. As in the liquid crystal alignment agent of claim 1 or 2, in the aforementioned formula (1), the bonding site of Y ₁ to the nitrogen atom represented by formula (A) is para-position. For the liquid crystal alignment agent of claim 1 or 2, wherein X ₁ in the aforementioned formula (1) is at least one selected from the group consisting of structures represented by the following formulas (X-1) to (X-14),

(R ₅ , R ₆ , R ₇ and R _{8 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, or benzene base). The liquid crystal alignment agent according to claim 1 or 2, wherein the aforementioned X ₁ is a tetravalent organic group derived from a tetracarboxylic acid derivative, and Y ₁ is derived from 4,4′-diaminobiphenyl benzoyl amide (DAB) 2-valent organic radical. The liquid crystal alignment agent according to claim 1 or 2, wherein the aforementioned polyimide precursor further has a structural unit represented by the following formula (10),

(X ₂ is a tetravalent organic group, Y ₂ is a divalent organic group, R ₄ is a hydrogen atom, or a C 1-4 alkyl group, Z ₁ and Z _{2 are} each independently a hydrogen atom or may have a substituent (C1-C10 alkyl, C2-C10 alkenyl or C2-C10 alkynyl). A method for manufacturing a liquid crystal alignment film, characterized in that a film is formed from the liquid crystal alignment agent according to any one of claims 1 to 6, and before or after firing, the film is irradiated with ultraviolet rays containing a wavelength of 300 to 400 nm Polarized ultraviolet rays. The method for manufacturing a liquid crystal alignment film according to claim 7, wherein polarized ultraviolet rays of 1 to 10,000 mJ/cm ^{2 are} irradiated. A liquid crystal alignment film is a film obtained by the liquid crystal alignment agent according to any one of claims 1 to 6, which is irradiated with polarized ultraviolet rays including ultraviolet rays with a wavelength of 300 to 400 nm before or after firing the film. A liquid crystal display element having the liquid crystal alignment film according to claim 9.