KR102813565B1 - Liquid crystal alignment agent and liquid crystal alignment film and liquid crystal display element using the same - Google Patents

Abstract

식 중 R₁ 은, 트리알킬실릴기를 나타낸다.A liquid crystal alignment agent containing at least one polyamic acid and polyimide having a structure represented by the following formula (1).

In the formula, R ₁ represents a trialkylsilyl group.

Description

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

The present invention relates to a liquid crystal alignment agent used in the manufacture of a liquid crystal display element, a liquid crystal alignment film obtained from the liquid crystal alignment agent, and a liquid crystal display element using the liquid crystal alignment film.

Liquid crystal display elements are known as lightweight, thin, and low-power consumption display devices.

Liquid crystal display elements are composed of a pair of transparent substrates having electrodes to sandwich a liquid crystal layer. On the surface of the substrate that comes into contact with the liquid crystal, a liquid crystal alignment film is usually formed to control the arrangement of the liquid crystal. As the liquid crystal alignment film, a polyimide-based liquid crystal alignment film is mainly used, which is made by applying a liquid crystal alignment agent containing a polyimide precursor such as polyamic acid (also called polyamic acid) or a solution of a soluble polyimide as a main component to a substrate, etc., and then firing it.

With the advancement of high definition liquid crystal display elements, demands are being made for suppressing the reduction in contrast of liquid crystal display elements and reducing afterimages. Accordingly, liquid crystal alignment films are becoming increasingly important for having, in addition to excellent liquid crystal alignment properties and stable pretilt angle expression ability, high voltage retention, suppression of afterimages caused by AC driving, and low residual charge when DC voltage is applied.

In order to meet such demands, technologies for modifying the terminals of polyamic acid or polyimide with various structures have been proposed as liquid crystal alignment films of polyimide systems. For example, in order to achieve improved liquid crystal alignment properties, high pretilt angles, small afterimage erasing time, and high reliability, imidized polymers modified at the terminals by reacting with monoacid anhydrides, monoamine compounds, and monoisocyanate compounds have been proposed (see Patent Document 1).

Japanese Patent Publication No. 2001-296525

However, in recent years, for high-definition liquid crystal display elements for mobile phones and tablet terminals, which have been rapidly expanding their share, further improvement in characteristics is required. In particular, achieving high reliability at low cost is required.

To obtain high reliability, it is common to use a liquid crystal alignment agent using available polyimide, but the production of available polyimide requires modification of polyamic acid, and is more expensive than the production of polyamic acid. However, liquid crystal alignment films using polyamic acid have a point of inferior reliability compared to films using available polyimide.

The main purpose of the present invention is to provide a liquid crystal alignment agent having reliability equal to or higher than that of available polyimide, specifically, high voltage retention characteristics, even when using polyamic acid.

The inventors of the present invention have conducted thorough studies to solve the above problems and have completed the present invention. That is, the gist of the present invention is as follows.

1. A liquid crystal alignment agent containing at least one selected from polyamic acid and polyimide having a structure represented by the following formula (1).

[Chemical Formula 1]

In the formula, R ₁ represents a trialkylsilyl group.

By using the liquid crystal alignment agent of the present invention, a liquid crystal alignment agent having reliability equivalent to or higher than that of a soluble polyimide, specifically, high voltage retention characteristics, can be obtained even when using polyamic acid without using a complex manufacturing process such as polyamic acid ester or soluble polyimide. In addition, even when the present invention is applied to a soluble polyimide, the same effect can be obtained.

The liquid crystal alignment agent of the present invention contains at least one kind of polyamic acid having a structure represented by the following formula (1) and a polyimide which is an imide thereof.

[Chemical formula 2]

In the formula, R ₁ represents a trialkylsilyl group. Specific examples thereof include structures of the following formulas (1-1) to (1-4). * represents a bond. More preferably, it is a t-butylsilyl group.

[Chemical Formula 3]

In order to introduce such a structure into a polyimide, a method of using a silylating agent is used during and after the polymerization of the polyimide precursor. As the silylating agent used in the present invention, any commercially available silylating agent can be used as long as it can introduce a trialkylsilyl group, but among these, it is preferable to use a compound selected from the following formulae (S-1) to (S-5). More preferably, they are (S-1) and (S-2).

[Chemical Formula 4]

＜Tetracarboxylic acid derivatives＞

The polyimide contained in the liquid crystal alignment agent of the present invention is obtained by imidizing a polyimide precursor obtained from the reaction of a tetracarboxylic acid derivative and a diamine. Specific examples of the materials used and the manufacturing method are described in detail below.

Tetracarboxylic acid derivatives used in the production of polyimide precursors include not only tetracarboxylic dianhydride but also its derivatives, such as tetracarboxylic acid, tetracarboxylic acid dihalide compounds, tetracarboxylic acid dialkyl esters, and tetracarboxylic acid dialkyl ester dihalides.

Among tetracarboxylic acid dianhydrides or derivatives thereof, those represented by the following formula (3) are preferable.

[Chemical Formula 5]

In formula (3), the structure of X ₁ is not particularly limited as long as it is a tetravalent organic group. Preferable specific examples include the following formulas (X1-1) to (X1-44). From the viewpoint of liquid crystal orientation, X ₁ is preferably (X1-1) to (X1-3), (X1-5), (X1-7) to (X1-10), (X1-18), (X1-24), (X1-27) to (X1-43).

[Chemical formula 6]

[Chemical formula 7]

[Chemical formula 8]

[Chemical formula 9]

[Chemical Formula 10]

[Chemical Formula 11]

In formulas (X1-1) to (X1-4), R ₃ to R ₂₃ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, a monovalent organic group having 1 to 6 carbon atoms containing a fluorine atom, or a phenyl group. From the viewpoint of liquid crystal orientation, R ₃ to R ₂₃ are preferably a hydrogen atom, a halogen atom, a methyl group, or an ethyl group, and a hydrogen atom or a methyl group is preferable.

Specific examples of formula (X1-1) include the following formulas (X1-1-1) to (X1-1-6). In terms of liquid crystal orientation, (X1-1-1) is particularly preferable.

[Chemical Formula 12]

＜Diamine＞

The diamine used in the manufacture of polyimide precursor is represented by the following formula (2).

[Chemical Formula 13]

In the above formula (2), A ₁ and A ₂ are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms.

The structure of Y ₁ is not particularly limited. Preferable structures include the following (Y-1) to (Y-177).

[Chemical Formula 14]

[Chemical Formula 15]

[Chemical Formula 16]

[Chemical Formula 17]

[Chemical Formula 18]

[Chemical Formula 19]

[Chemical formula 20]

[Chemical Formula 21]

[Chemical Formula 22]

[Chemical Formula 23]

[Chemical Formula 24]

[Chemical Formula 25]

[Chemical Formula 26]

[Chemical Formula 27]

[Chemical Formula 28]

[Chemical Formula 29]

[Chemical formula 30]

[Chemical Formula 31]

[Chemical formula 32]

[Chemical formula 33]

In the above formula, Me represents a methyl group, and R ¹ represents a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms.

[Chemical Formula 34]

Among them, the structure of Y ₁ includes (Y-7), (Y-8), (Y-16), (Y-17), (Y-18), (Y-20), (Y-21), (Y-22), (Y-27), (Y-28), (Y-29), (Y-35), (Y-37), (Y-38), (Y-43), (Y-48), (Y-53) ~ (Y-56), (Y-61), (Y-64) ~ (Y-66), (Y-69), (Y-71), (Y-72), (Y-76), (Y-77), (Y-80), (Y-81), (Y-82), (Y-83), (Y-156), (Y-159), (Y-160), (Y-161), (Y-162), (Y-168), (Y-169), (Y-170), (Y-171), (Y-173), (Y-175), (Y-178) to (Y-182) are preferred, especially (Y-7), (Y-8), (Y-16), (Y-17), (Y-18), (Y-21), (Y-22), (Y-27), (Y-28), (Y-29), (Y-37), (Y-38), (Y-53) ~ (Y-56), (Y-61), (Y-64) ~ (Y-66), (Y-69), (Y-72), (Y-76), (Y-81), (Y-156), (Y-159), (Y-160), (Y-161), (Y-162), (Y-168), (Y-169), (Y-170), (Y-171), (Y-173), (Y-175), (Y-178) ∼ (Y-182) are preferred.

＜Manufacture of polyimide precursor-polyamic acid＞

Polyamic acid, which is a polyimide precursor used in the present invention, can be manufactured by the following method.

Specifically, it can be synthesized by reacting tetracarboxylic dianhydride and diamine in the presence of a solvent at -20 to 150°C, preferably 0 to 50°C, for 30 minutes to 24 hours, preferably 1 to 12 hours.

The reaction of the diamine component and the tetracarboxylic acid component is usually carried out in a solvent. The solvent used at that time is not particularly limited as long as the produced polyimide precursor is soluble. Specific examples of the solvent used in the reaction are given below, but the solvent is not limited to these examples. For example, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, or 1,3-dimethyl-imidazolidinone can be given.

In addition, when the solubility of the polyimide precursor is high, methyl ethyl ketone, cyclohexanone, cyclopentanone, 4-hydroxy-4-methyl-2-pentanone, or a solvent represented by the following formulae [D-1] to [D-3] can be used.

[Chemical Formula 35]

In formula [D-1], D ¹ represents an alkyl group having 1 to 3 carbon atoms, in formula [D-2], D ² represents an alkyl group having 1 to 3 carbon atoms, and in formula [D-3], D ³ represents an alkyl group having 1 to 4 carbon atoms.

These solvents may be used alone or in combination. In addition, even if it is a solvent that does not dissolve the polyimide precursor, it may be used by mixing it with the solvent as long as the generated polyimide precursor is not precipitated. In addition, since moisture in the solvent inhibits the polymerization reaction and further causes hydrolysis of the generated polyimide precursor, it is preferable to use a solvent that has been dehydrated and dried.

The concentration of the polyamic acid polymer in the reaction system is preferably 1 to 30 mass%, more preferably 5 to 20 mass%, from the viewpoint that precipitation of the polymer is unlikely to occur and that a high molecular weight polymer is easily obtained.

When a silylating agent is introduced during and after the polymerization of the polyimide precursor, the amount of introduction is preferably 25 to 100 mol%, particularly preferably 75 to 100 mol%, based on the amount of carboxylic acid in the polyimide precursor. After the introduction of the silylating agent, the mixture is stirred at 5°C to 60°C, preferably 40°C to 80°C, for 1 to 30 hours, preferably 6 to 24 hours, thereby obtaining a silylated polyimide precursor.

In addition, during the reaction, it is desirable to substitute the inside of the system with nitrogen to prevent oxidation of the diamine portion in the polyamic acid, and it is also desirable to install a reflux device to avoid changing the temperature inside the system.

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

＜Polyimide＞

The polyimide used in the present invention can be manufactured by imidizing the above-mentioned polyamic acid or polyamic acid ester.

In addition, it can also be produced by imidizing a non-silylated polyamic acid by the method described below, dissolving the isolated imidized polymer in a solvent, and introducing a silylating agent when producing a liquid crystal alignment agent.

When manufacturing polyimide from polyamic acid, chemical imidization is simple by adding a catalyst to a solution of the polyamic acid obtained by the reaction of a diamine component and tetracarboxylic dianhydride. Chemical imidization is preferable because the imidization reaction proceeds at a relatively low temperature and the molecular weight of the polymer is unlikely to decrease during the imidization process.

Chemical imidization can be carried out by stirring the polyamic acid to be imidized in a solvent in the presence of a basic catalyst and an acid anhydride. As the solvent, the solvent used in the polymerization reaction described above can be used. Examples of the basic catalyst include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Among them, pyridine is preferable because it has an appropriate basicity for promoting the reaction. In addition, examples of the acid anhydride include acetic anhydride, trimellitic anhydride, and pyromellitic anhydride, and among them, acetic anhydride is preferable because purification after the completion of the reaction is easy.

The temperature at which the imidization reaction is performed is -20 to 140°C, preferably 0 to 100°C, and the reaction time is 1 to 100 hours, preferably 1 to 5 hours.

The amount of the basic catalyst is 0.5 to 30 molar times, preferably 2 to 20 molar times, of the amic acid group, and the amount of the acid anhydride is 1 to 50 molar times, preferably 3 to 30 molar times, of the amic acid group. The imidization degree of the obtained polymer can be controlled by adjusting the amount of catalyst, temperature, reaction time, etc.

When manufacturing a polyimide with a polyamic acid ester, chemical imidization is simple by adding a basic catalyst to the polyamic acid solution obtained by dissolving the polyamic acid ester solution or polyamic acid ester resin powder in a solvent. Chemical imidization is preferable because the imidization reaction proceeds at a relatively low temperature and the molecular weight of the polymer is unlikely to decrease during the imidization process.

Chemical imidization can be carried out by stirring the polyamic acid ester to be imidized in a solvent in the presence of a basic catalyst. As the solvent, the solvent used in the polymerization reaction described above can be used. As the basic catalyst, pyridine, triethylamine, trimethylamine, tributylamine, trioctylamine, etc. Among them, triethylamine is preferable because it has sufficient basicity to proceed with the reaction.

The temperature at which the imidization reaction is performed is -20 to 140°C, preferably 0 to 100°C, and the reaction time is 1 to 100 hours, preferably 1 to 5 hours.

The amount of the basic catalyst is 0.5 to 30 mole times, preferably 2 to 20 mole times, of the amic acid ester group.

The imidization degree of the obtained polymer can be controlled by adjusting the amount of catalyst, temperature, reaction time, etc.

Since the solution after the imidization reaction contains the added catalyst, etc., it is preferable to recover the obtained imidized polymer by the means described below, re-dissolve it in a solvent, and use it as the liquid crystal alignment agent of the present invention.

In addition, in the imidization reaction of polyamic acid or polyamic acid ester, an imidization accelerator can be used. Specific examples of the imidization accelerator are shown below, but are not limited to these.

[Chemical formula 36]

In the above formulas (B-1) to (B-17), D is each independently a tert-butoxycarbonyl group or a 9-fluorenylmethoxycarbonyl group. A plurality of Ds present in formulas (B-14) to (B-17) may be the same or different. The higher the basicity after deprotection by heating, the higher the imidization promoting effect of the polyamic acid ester and the polyamic acid. Therefore, (B-14) to (B-17) are preferable in that the thermal imidization promoting effect is further increased, and among them, (B-17) is particularly preferable.

Since the solution after the imidization reaction of the polyamic acid or polyamic acid ester contains the added catalyst, etc., it is preferable to recover the obtained imidized polymer by the means described below, re-dissolve it in a solvent, and use it as the liquid crystal alignment agent of the present invention.

The polyimide solution obtained as described above can be injected into the following poor solvent while stirring well to precipitate a polymer. After performing precipitation several times and washing with the poor solvent, the solution can be dried at room temperature or by heating to obtain a powder of purified polyamic acid ester.

Examples of solvents include, but are not limited to, methanol, acetone, hexane, butyl cellosolve, heptane, methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene, benzene, etc.

When the obtained polyimide powder is re-dissolved in a solvent, the solvent (also called a good solvent) is not particularly limited as long as a specific structural polymer is uniformly dissolved. Examples thereof include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, 1,3-dimethyl-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, or 4-hydroxy-4-methyl-2-pentanone.

Among them, it is preferable to use N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone.

The temperature during re-dissolution is preferably 5°C to 80°C, more preferably 20°C to 50°C. The stirring time for re-dissolution is preferably 30 minutes to 50 hours, more preferably 3 hours to 12 hours.

When re-dissolving non-silylated polyimide powder, a silylated polyimide solution can be obtained by introducing a silylating agent during stirring during re-dissolution. After introducing the silylating agent, a silylated polyimide solution is obtained by stirring at 5°C to 60°C, preferably 40°C to 80°C, for 1 to 30 hours, preferably 6 to 24 hours.

＜Liquid crystal orientation agent＞

The liquid crystal alignment agent used in the present invention has a form of a solution in which at least one selected from polyamic acid and polyimide having the structure of the above formula (1) is dissolved in a solvent.

The molecular weight of the specific structural polymer is preferably 2,000 to 500,000, more preferably 5,000 to 300,000, and even more preferably 10,000 to 100,000, in terms of a weight average molecular weight. In addition, the number average molecular weight is preferably 1,000 to 250,000, more preferably 2,500 to 150,000, and even more preferably 5,000 to 50,000.

The concentration of the polymer in the liquid crystal alignment agent of the present invention can be appropriately changed depending on the setting of the thickness of the coating film to be formed. However, from the viewpoint of forming a uniform and defect-free coating film, it is preferably 1 mass% or more, and from the viewpoint of the storage stability of the solution, it is preferably 10 mass% or less. It is particularly preferably 3 to 6.5 mass%.

The solvent (also called a good solvent) contained in the liquid crystal alignment agent of the present invention is not particularly limited as long as it uniformly dissolves a specific structural polymer.

Examples thereof include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, 1,3-dimethyl-imidazolidinone, methyl ethyl ketone, cyclohexanone, cyclopentanone, or 4-hydroxy-4-methyl-2-pentanone.

Among them, it is preferable to use N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or γ-butyrolactone.

In addition, when the solubility of the polymer of the present invention in a solvent is high, it is preferable to use a solvent represented by the above formulas [D-1] to [D-3].

The good solvent in the liquid crystal alignment agent of the present invention is preferably 20 to 99 mass% of the total solvent contained in the liquid crystal alignment agent. Among them, 20 to 90 mass% is preferable. More preferably, 30 to 80 mass% is more preferable.

The liquid crystal alignment agent of the present invention can use a solvent (also called a poor solvent) that improves the film properties or surface smoothness of a liquid crystal alignment film when the liquid crystal alignment agent is applied, as long as the effects of the present invention are not impaired. Specific examples of poor solvents are given below, but the present invention is not limited to these examples.

For example, ethanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, isopentyl alcohol, tert-pentyl alcohol, 3-methyl-2-butanol, neopentyl alcohol, 1-hexanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, cyclohexanol, 1-methylcyclohexanol, 2-methylcyclohexanol, 3-methylcyclohexanol, 1,2-Ethanediol, 1,2-Propanediol, 1,3-Propanediol, 1,2-Butanediol, 1,3-Butanediol, 1,4-Butanediol, 2,3-Butanediol, 1,5-Pentanediol, 2-Methyl-2,4-Pentanediol, 2-Ethyl-1,3-Hexanediol, Dipropyl Ether, Dibutyl Ether, Dihexyl Ether, Dioxane, Ethylene Glycol Dimethyl Ether, Ethylene Glycol Diethyl Ether, Ethylene Glycol Dibutyl Ether, 1,2-Butoxyethane, Diethylene Glycol Dimethyl Ether, Diethylene Glycol Diethyl Ether, Diethylene Glycol Methyl Ether, Diethylene Glycol Dibutyl Ether, 2-Pentanone, 3-Pentanone, 2-Hexanone, 2-Heptanone, 4-Heptanone, 3-Ethoxybutylacetate, 1-Methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, ethylene glycol monoacetate, ethylene glycol diacetate, propylene carbonate, ethylene carbonate, 2-(methoxymethoxy)ethanol, ethylene glycol monobutyl ether, ethylene glycol monoisoamyl ether, ethylene glycol monohexyl ether, 2-(hexyloxy)ethanol, furfuryl alcohol, diethylene glycol, propylene glycol, propylene glycol monobutyl ether, 1-(butoxyethoxy)propanol, propylene glycol monomethyl ether acetate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, Ethylene glycol monobutyl ether acetate, ethylene glycol monoacetate, ethylene glycol diacetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 2-(2-ethoxyethoxy)ethyl acetate, diethylene glycol acetate, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, n-butyl acetate, propylene glycol monoethyl ether acetate, methyl pyruvate, ethyl pyruvate, methyl 3-methoxypropionate, methyl 3-ethoxypropionate ethyl, 3-methoxypropionate, 3-ethoxypropionic acid, 3-methoxypropionic acid, propyl 3-methoxypropionate, butyl 3-methoxypropionate, Examples thereof include lactic acid methyl ester, lactic acid ethyl ester, lactic acid n-propyl ester, lactic acid n-butyl ester, lactic acid isoamyl ester, and solvents represented by the above formulae [D-1] to [D-3].

Among them, it is preferable to use 1-hexanol, cyclohexanol, 1,2-ethanediol, 1,2-propanediol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether or dipropylene glycol dimethyl ether.

The empty solvent is preferably 1 to 80 mass% of the total solvent contained in the liquid crystal alignment agent, more preferably 10 to 80 mass%, and still more preferably 20 to 70 mass%.

In addition to the above, the liquid crystal alignment agent of the present invention may further contain, as long as the effects of the present invention are not impaired, a polymer other than the polymer described in the present invention, a dielectric or conductive material for changing electrical properties such as permittivity or conductivity of the liquid crystal alignment film, a silane coupling agent for improving adhesion between the liquid crystal alignment film and the substrate, a crosslinking compound for increasing the hardness or density of the film when formed into a liquid crystal alignment film, and further an imidization accelerator for efficiently promoting imidization of the polyimide precursor by heating when baking the coating film.

＜Liquid crystal alignment film＞

＜Liquid crystal display element＞

The liquid crystal alignment film of the present invention can be used for a horizontal alignment type or a vertical alignment type liquid crystal alignment film, but among them, it is a preferable liquid crystal alignment film for a vertical alignment type liquid crystal display element such as a VA mode or PSA mode. As a method for forming the liquid crystal alignment film of the present invention, first, the liquid crystal alignment agent is applied to a substrate, dried, and baked to obtain a coating film. 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 a plastic substrate such as a glass substrate, a silicon nitride substrate, an acrylic substrate, a polycarbonate substrate, or the like can be used. In addition, it is preferable to use a substrate on which an ITO electrode or the like for driving a liquid crystal is formed from the viewpoint of simplifying the process. In addition, in a reflective liquid crystal display element, an opaque material such as a silicon wafer can be used as long as it is only one-sided substrate, and in this case, a material that reflects light such as aluminum can also be used as the electrode.

Examples of methods for applying the liquid crystal alignment agent of the present invention include a spin coating method, a printing method, an inkjet method, and the like. The drying and baking processes after applying the liquid crystal alignment agent of the present invention can select any temperature and time. Typically, in order to sufficiently remove the contained solvent, drying is performed at 50 to 120°C, preferably 60 to 100°C, for 1 to 10 minutes, preferably 2 to 5 minutes, and then baking is performed at 150 to 300°C, preferably 200 to 240°C, for 5 to 120 minutes, preferably 10 to 30 minutes. The thickness of the coating film after baking is not particularly limited, but if it is too thin, the reliability of the liquid crystal display element may be lowered, and therefore, it is 5 to 300 nm, preferably 10 to 200 nm.

The film formed above can be used as a liquid crystal alignment film as it is, but an alignment treatment may also be performed on the film. Examples of the alignment treatment method include a rubbing method and an optical alignment treatment method.

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

In the light alignment treatment, as radiation to be irradiated to the coating film, for example, ultraviolet rays and visible light containing light having a wavelength of 150 to 800 nm can be used. When the radiation is polarized, it may be linearly polarized or partially polarized. In addition, when the radiation used is linearly polarized or partially polarized, the irradiation may be performed from a direction perpendicular to the substrate surface, from a diagonal direction, or a combination of these. When irradiating with non-polarized radiation, the direction of the irradiation is diagonal.

Next, the liquid crystal display device of the present invention can be manufactured by any of the following methods: a combination of process (1), process (2) and process (4), or a combination of process (3) and process (4).

(1) In case of VA type liquid crystal display element

As described above, two substrates having liquid crystal alignment films formed thereon are prepared, and a liquid crystal is placed between the two substrates that are positioned opposite each other. Specifically, the following two methods can be cited. The first method is a method that has been known in the past. First, two substrates are positioned opposite each other with a gap (cell gap) between them so that their respective liquid crystal alignment films face each other. Next, the peripheral portions of the two substrates are bonded together using a sealant, and a liquid crystal composition is injected and filled into the substrate surfaces and the cell gap defined by the sealant to contact the film surface, and then the injection hole is sealed.

In addition, the second method is a technique called the ODF (One Drop Fill) method. For example, an ultraviolet light-curable sealant is applied to a predetermined location on one of the two substrates on which a liquid crystal alignment film has been formed, and a liquid crystal composition is further dropped onto predetermined points on the surface of the liquid crystal alignment film. Thereafter, the other substrate is bonded so that the liquid crystal alignment films face each other, and the liquid crystal composition is pressed and spread over the entire surface of the substrates to contact the film surface. Subsequently, ultraviolet light is irradiated over the entire surface of the substrates to harden the sealant. In either method, it is preferable to further remove the flow alignment during liquid crystal filling by heating the liquid crystal composition used to a temperature at which it takes an isotropic phase and then slowly cooling it to room temperature.

(2) When manufacturing PSA type liquid crystal display elements

The same procedure as (1) above is followed, except that a liquid crystal composition containing a polymerizable compound is injected or dropped. As the polymerizable compound, polymerizable compounds represented by the following formulae (M-1) to (M-7) can be exemplified.

[Chemical Formula 37]

(3) When a film is formed on a substrate using a liquid crystal alignment agent containing a compound having a polymerizable group

After the same as (1) above, a method of manufacturing a liquid crystal display element through a process of irradiating ultraviolet rays as described later may be adopted. According to this method, as in the case of manufacturing the PSA type liquid crystal display element, a liquid crystal display element having an excellent response speed can be obtained with a small amount of light irradiation. The compound having a polymerizable group may be a compound having one or more polymerizable unsaturated groups such as acrylate groups or methacrylate groups represented by the formulas (M-1) to (M-7) in the molecule, and the content thereof is preferably 0.1 to 30 parts by mass, and more preferably 1 to 20 parts by mass, with respect to 100 parts by mass of the total polymer components. In addition, the polymerizable group may be present in a polymer used in the polymer composition, and examples of such a polymer include a polymer obtained by using a diamine component including a diamine having a photopolymerizable group at a terminal for the reaction.

(4) Process of irradiating ultraviolet rays

A voltage is applied between the conductive films of a pair of substrates obtained in the above (2) or (3), and light is irradiated onto the liquid crystal cell. The voltage applied here can be, for example, a direct current or an alternating current of 5 to 50 V. In addition, as the light to be irradiated, for example, ultraviolet light and visible light containing light having a wavelength of 150 to 800 nm can be used, but ultraviolet light containing light having a wavelength of 300 to 400 nm is preferable. As the light source of the irradiation light, for example, a low-pressure mercury lamp, a high-pressure mercury lamp, a deuterium lamp, a metal halide lamp, an argon resonance lamp, a xenon lamp, an excimer laser, or the like can be used. The amount of light irradiated is preferably 1,000 to 200,000 J/m2, and more preferably 1,000 to 100,000 J/m2.

And, by bonding a polarizing plate to the outer surface of the liquid crystal cell, a liquid crystal display element can be obtained. As a polarizing plate bonded to the outer surface of the liquid crystal cell, there can be mentioned a polarizing plate in which a polarizing film called an "H film", which is made by stretching and orienting polyvinyl alcohol and absorbing iodine, is sandwiched between a cellulose acetate protective film, or a polarizing plate made of the H film itself.

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

Example

The present invention will be described more specifically by way of examples below. However, the present invention is not limited to these examples. The abbreviations for the compounds used are shown below.

(certain diamines)

DBA: 3,5-Diaminobenzoic acid

3AMPDA: 3,5-Diamino-N-(pyridin-3-ylmethyl)benzamide

DA-1: A compound represented by the formula [DA-1] (diamine having a specific side chain structure)

[Chemical formula 38]

(Tetracarboxylic acid component)

PMDA: Pyromellitic anhydride

Compounds represented by [D1] to [D2] below

D1: 1,2,3,4-Cyclobutanetetracarboxylic dianhydride

D2: Bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic dianhydride

(Silylating agent component)

Compounds (silylating agents) represented by the following formulas [S-1] to [S-5]

[Chemical Formula 39]

(menstruum)

NMP: N-Methyl-2-pyrrolidone

BCS: Ethylene Glycol Monobutyl Ether

＜Measurement of molecular weight of polyimide＞

The molecular weight of the polyimide in the synthesis example was measured as follows using a room temperature gel permeation chromatography (GPC) apparatus (SSC-7200) manufactured by Senshu Scientific Co., Ltd. and a column (KD-803, KD-805) manufactured by Shodex.

Column temperature: 50℃

Eluent: N,N'-dimethylformamide (as additives, lithium bromide hydrate (LiBr H ₂ O) 30 mmol/ℓ, phosphoric acid anhydrous crystal (o-phosphoric acid) 30 mmol/ℓ, tetrahydrofuran (THF) 10 mL/ℓ)

Flow rate: 1.0 ㎖/min

Standard samples for preparing calibration curves: TSK standard polyethylene oxide manufactured by Tosoh Corporation (molecular weights: approximately 9,000,000, 150,000, 100,000, 30,000), and polyethylene glycol manufactured by Polymer Laboratories (molecular weights: approximately 12,000, 4,000, 1,000).

＜Measurement of imidization rate＞

The imidization degree of polyimide in the synthesis example was measured as follows. 20 mg of polyimide powder was placed in an NMR sample tube (Kusano Scientific NMR sampling tube standard φ5), 0.53 mL of deuterated dimethyl sulfoxide (DMSO-d ₆ , 0.05% TMS mixture) was added, and the mixture was completely dissolved.

This solution was subjected to proton NMR measurement at 500 MHz using an NMR meter (JNW-ECA500) manufactured by Nippon Electronic Datum Co., Ltd. The imidization degree was determined by using a proton derived from a structure that does not change before and after imidization as a reference proton, and using the peak integration value of this proton and the peak integration value of the proton derived from the NH group of the amic acid appearing around 9.5 to 10.0 ppm, it was calculated by the following formula.

Imidation rate (%) = (1 - α x/y) × 100

＜Synthesis of polyimide polymers＞

＜Synthesis Example 1＞

In a 100 mL four-necked flask equipped with a stirring device and a nitrogen introduction tube, 2.74 g (18.0 mmol) of DBA, 3.27 g (13.5 mmol) of 3AMPDA, and 5.14 g (13.5 mmol) of DA-1 were weighed and added, and the mixture was diluted with NMP to a solid concentration of 20%. After stirring at room temperature for 30 minutes, 2.25 g (8.99 mmol) of D2 was added, and the mixture was diluted again with NMP to a solid concentration of 20%, and heated and stirred at 60°C for 1 hour. After the obtained reaction solution was cooled to 17°C or lower, 1.96 g (8.99 mmol) of PMDA was added, diluted with 20% NMP, and stirred at room temperature for 5 hours. Finally, D1 was diluted with 5.11 g (26.1 mmol) of NMP to a solid concentration of 20%, and stirred and heated at 40°C for 6 hours. The obtained polymer solution was cooled to room temperature, thereby obtaining a polyamic acid polymer solution (PAA-1).

＜Synthesis Example 2＞

NMP (103.85 g) was added to PAA-1 (50.0 g), diluted to 6.5 mass%, and then acetic anhydride (6.67 g) and pyridine (2.58 g) as imidization catalysts were added, and the mixture was reacted at 70°C for 3 hours. This reaction solution was poured into methanol (570.9 g), and the obtained precipitate was separated by filtration. The precipitate was washed with methanol and dried under reduced pressure at 60°C, to obtain polyimide powder (SPI-1) of Synthesis Example 1. The imidization degree of this polyimide was 72%, the number average molecular weight was 11,800, and the weight average molecular weight was 41,800.

＜Synthesis Example 3＞

By adding 1.75 g of S-1 to PAA-1 (10.0 g) and heating and stirring at 50°C for 12 hours, a polyamic acid silyl ester polymerization solution (PASE-1) was obtained.

＜Synthesis Example 4-7＞

In Synthesis Example 3, except that S-2 to S-5 were added in the amounts shown in the table below instead of S-1, polyamic acid silyl ester polymerization solutions (PASE-2 to PASE-5) were obtained through the same treatment as in Synthesis Example 3.

＜Example 1＞

NMP (14.0 g) and BCS (8.0 g) were added to the polyamic acid silyl ester polymerization solution (PASE-1) (6.0 g) obtained in Synthesis Example 3, and stirred at 25°C for 5 hours. Thus, the liquid crystal alignment agent [1] of Example 1 was obtained. No abnormalities such as turbidity or precipitation were observed in the liquid crystal alignment agent, and it was confirmed that the resin component was uniformly dissolved.

＜Example 2-5＞

To the polyamic acid silyl ester polymerization solution (PASE-2 to PASE-5) (6.0 g) obtained in Synthesis Example 4-7, NMP (14.0 g) and BCS (8.0 g) were added, and the mixture was stirred at 25°C for 5 hours. Thus, the liquid crystal alignment agent [2-5] of Example 2-5 was obtained. No abnormalities such as turbidity or precipitation were observed in the liquid crystal alignment agent, and it was confirmed that the resin component was uniformly dissolved.

＜Comparative Example 1＞

NMP (14.0 g) and BCS (8.0 g) were added to the polyamic acid polymerization solution (PAA-1) (6.0 g) obtained in Synthesis Example 1, and stirred at 25°C for 5 hours. Thus, the liquid crystal alignment agent of Comparative Example 1 was obtained. No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent, and it was confirmed that the resin component was uniformly dissolved.

＜Manufacturing of liquid crystal cells＞

The liquid crystal alignment agent obtained above was spin-coated on the ITO surface of an ITO-attached alkali-free glass substrate (30 mm in length, 40 mm in width, and 0.7 mm in thickness) washed with pure water and IPA (isopropyl alcohol), respectively, and baked on a hot plate at 70°C for 90 seconds, and then baked in an infrared heater at 230°C for 20 minutes to manufacture a polyimide-coated substrate having a film thickness of 100 nm.

By the above method, two polyimide-coated substrates were manufactured, and a 4 ㎛ bead spacer was spread on the liquid crystal alignment film surface of one substrate, and then a thermosetting sealant (XN-1500T manufactured by Kyoritsu Chemical Co., Ltd.) was printed from thereon. Next, the surface of the other substrate on the side where the liquid crystal alignment film was formed was turned inward, and it was bonded to the previous substrate, and then the sealant was cured to manufacture an empty cell. A liquid crystal MLC-3023 (trade name manufactured by Merck & Co., Ltd.) containing a polymerizable compound for PSA was injected into the empty cell by a reduced pressure injection method, and a liquid crystal cell was manufactured. The voltage retention ratio of the liquid crystal cell was measured.

Next, while applying a DC voltage of 15 V to the liquid crystal cell, UV passing through a 325 nm cut filter was irradiated at 7 J/cm2 from the outside of the liquid crystal cell (also called primary PSA treatment). In addition, the UV illuminance was measured using UV-MO3A manufactured by ORC.

Thereafter, in order to inactivate the unreacted polymerizable compound remaining in the liquid crystal cell, UV (UV lamp: FLR40SUV32/A-1) was irradiated for 30 minutes (referred to as secondary PSA treatment) using a UV-FL irradiation device manufactured by Toshiba Lightec Co., Ltd. without applying voltage, and the voltage retention ratio was then measured.

＜Evaluation of voltage maintenance rate＞

Using the liquid crystal cell manufactured above, a voltage of 1 V was applied for 60 ㎲ in a hot air circulation oven at 60 ℃, and the voltage after 16.67 msec and 1667 msec was measured respectively, and the extent to which the voltage was maintained was calculated as the voltage retention rate. For the measurement of the voltage retention rate, VHR-1 manufactured by Toyo Technica Co., Ltd. was used.

As shown in the table, PASE silylated with a silylating agent exhibited good voltage retention compared to the comparative examples, and in particular, the voltage retention was good for PASE-1 and PASE-2 having a Tert-Butyl group.

＜Evaluation of solubility＞

While stirring 1 g of the liquid crystal alignment agent of Examples 3-7 and Comparative Example 1 obtained above, BCS was added dropwise to each, and the solubility was calculated by the following formula from the weight that became cloudy.

The evaluation results are shown in the table below.

Solubility = (amount of BCS in the liquid crystal alignment agent + amount of BCS dropped) / (amount of liquid crystal alignment agent + amount of BCS dropped)

Industrial applicability

The liquid crystal alignment film obtained from the liquid crystal alignment agent of the present invention has reliability equal to or higher than that of available polyimide, and specifically, high voltage retention characteristics, despite using polyamic acid. Therefore, it can be used in a wide range of liquid crystal display elements requiring high display quality.

Claims (11)

Containing at least one type of polyamic acid and polyimide having a structure of the following formula (1),
A liquid crystal alignment agent, wherein the above polyamic acid is a reaction product of polyamic acid and a silylating agent.

In the formula, R ₁ represents a t-butyldimethylsilyl group. In paragraph 1,
A liquid crystal alignment agent, wherein the above-mentioned silylating agent is at least one selected from the following (S-1) to (S-2).
In the second paragraph,
A liquid crystal alignment agent, wherein the liquid crystal alignment agent contains a polyamic acid having a structure of the above formula (1). In paragraph 1,
A liquid crystal alignment agent, characterized in that the above polyamic acid and polyimide are obtained from the reaction of a tetracarboxylic acid derivative and a diamine, and the tetracarboxylic acid derivative is a tetracarboxylic dianhydride represented by the following formula (3).

(X ₁ represents a 4-valent organic group.) In paragraph 4,
The above X ₁ is a liquid crystal alignment agent selected from the following formula (X1-8).
In paragraph 1,
A liquid crystal alignment agent, characterized in that the above polyamic acid and polyimide are obtained from the reaction of a tetracarboxylic acid derivative and a diamine, wherein the diamine is a diamine represented by the following formula (2) or 3,5-diamino-N-(pyridin-3-ylmethyl)benzamide.

(In formula (2), A ₁ and A ₂ are each independently a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an alkynyl group having 2 to 5 carbon atoms.
The structure of Y ₁ is selected from the following.)







A liquid crystal alignment film obtained from the liquid crystal alignment agent described in any one of claims 1 to 6. A liquid crystal display device having a liquid crystal alignment film as described in claim 7. delete delete delete