JP7469744B2 - Liquid crystal alignment agent, liquid crystal alignment film using the same, and liquid crystal display element - Google Patents

Description

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

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

A liquid crystal display element is composed of a liquid crystal layer sandwiched between a pair of transparent substrates each equipped with an electrode. A liquid crystal alignment film for controlling the alignment state of the liquid crystal is usually provided on the surface of the substrate that contacts the liquid crystal. As the liquid crystal alignment film, a polyimide-based liquid crystal alignment film is mainly used, which is formed by applying a liquid crystal alignment agent, the main component of which is a solution of a polyimide precursor such as polyamic acid (also called polyamic acid) or a soluble polyimide, to a substrate or the like and baking the applied liquid crystal alignment film.
As liquid crystal display elements become higher definition, there are demands for suppressing contrast degradation and reducing image retention in liquid crystal display elements. In response to these demands, it is becoming increasingly important for liquid crystal alignment films to have properties such as high voltage retention, suppression of image retention caused by AC drive, and little residual charge when a DC voltage is applied, in addition to excellent liquid crystal alignment properties and stable pretilt angle expression ability.
In order to meet such requirements, techniques have been proposed for modifying the ends of polyamic acid or polyimide with various structures for polyimide-based liquid crystal alignment films. For example, imidized polymers modified at the ends by reacting with monoacid anhydrides, monoamine compounds, and monoisocyanate compounds have been proposed to achieve improved liquid crystal alignment, high pretilt angles, short image retention erasing times, and high reliability (see Patent Document 1).

JP 2001-296525 A

However, in recent years, there has been a demand for further improvements in the characteristics of high-definition LCD elements for mobile phones and tablet devices, the market share of which has been rapidly expanding. In particular, there is a demand for high reliability at low cost.
To obtain high reliability, it is common to use a liquid crystal alignment agent using a soluble polyimide, but the production of a soluble polyimide requires the modification of polyamic acid, which is more expensive than the production of polyamic acid. However, liquid crystal alignment films using polyamic acid are less reliable than those using soluble polyimide.

The main object of the present invention is to provide a liquid crystal alignment agent that has reliability equal to or greater than that of soluble polyimide, specifically, high voltage holding ratio characteristics, even when using polyamic acid.

The present inventors have conducted extensive research 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 aligning agent comprising at least one member selected from the group consisting of polyamic acids and polyimides having the following formula (1):

In the formula, R ₁ represents a trialkylsilyl group.

By using the liquid crystal alignment agent of the present invention, it is possible to obtain a liquid crystal alignment agent that has reliability equal to or greater than that of soluble polyimide, specifically, high voltage holding ratio characteristics, even when using polyamic acid, without using complicated manufacturing processes such as those for polyamic acid esters or soluble polyimides. The same effect can be obtained when the present invention is applied to soluble polyimide.

The liquid crystal alignment agent of the present invention contains at least one of a polyamic acid having the structure of the following formula (1) and its imidized product, a polyimide.

In the formula, _R1 represents a trialkylsilyl group. Specific examples include structures of the following formulae (1-1) to (1-4). * represents a bond. A t-butylsilyl group is more preferred.

To introduce such a structure into polyimide, a method is used in which a silylating agent is used during and after the polymerization of the polyimide precursor. The silylating agent used in the present invention can be any commercially available silylating agent that can introduce a trialkylsilyl group, but it is preferable to use a compound selected from the following formulas (S-1) to (S-5). More preferably, it is (S-1) or (S-2).

<Tetracarboxylic acid derivatives>
The polyimide contained in the liquid crystal aligning agent of the present invention is obtained by imidizing a polyimide precursor obtained by reacting a tetracarboxylic acid derivative with a diamine. Specific examples of the materials used and the production method are described in detail below.

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

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

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

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 alignment, R ₃ to R ₂₃ are preferably a hydrogen atom, a halogen atom, a methyl group, or an ethyl group, and more preferably a hydrogen atom or a methyl group.

Specific examples of formula (X1-1) include the following formulas (X1-1-1) to (X1-1-6). From the viewpoint of liquid crystal alignment, (X1-1-1) is particularly preferred.

<Diamine>
The diamine used in the production of the polyimide precursor is represented by the following formula (2).

In the above formula (2), A ₁ and A ₂ each independently represent 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. Preferred structures include the following (Y-1) to (Y-177).

In the above formula, Me represents a methyl group, and ^R1 represents a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms.

Among them, the structure of _Y1 is preferably (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) to (Y-56), (Y-61), and (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- Preferred are (Y-173), (Y-175), (Y-178) to (Y-182), and particularly preferred are (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) to (Y-56), (Y-61), and (Y-64). ) to (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), and (Y-178) to (Y-182) are preferred.

<Production of polyimide precursor-polyamic acid>
The polyamic acid, which is the polyimide precursor used in the present invention, can be produced by the following method.

Specifically, the compound can be synthesized by reacting a tetracarboxylic dianhydride with a 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 between the diamine component and the tetracarboxylic acid component is usually carried out in a solvent. The solvent used in this reaction is not particularly limited as long as it dissolves the polyimide precursor produced. Specific examples of solvents used in the reaction are listed below, but are not limited to these examples. For example, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, or 1,3-dimethyl-imidazolidinone can be mentioned.

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

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. Furthermore, even if the solvent does not dissolve the polyimide precursor, it may be mixed with the above solvent to the extent that the generated polyimide precursor does not precipitate. Furthermore, 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 from 1 to 30% by mass, and more preferably from 5 to 20% by mass, from the viewpoints that precipitation of the polymer is unlikely to occur and a high molecular weight polymer is easily obtained.
When the silylating agent is introduced during or after the polymerization of the polyimide precursor, the amount of the silylating agent introduced 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, to obtain a silylated polyimide precursor.
During the reaction, it is preferable to replace the atmosphere in the system with nitrogen in order to prevent oxidation of the diamine portion in the polyamic acid, and it is also preferable to install a reflux device in order to maintain the temperature in the system.

The polyamic acid obtained as described above can be recovered by injecting the reaction solution into the poor solvent described below while thoroughly stirring it, thereby precipitating the polymer. In addition, the precipitation can be carried out several times, washed with the poor solvent, and then dried at room temperature or by heating to obtain a purified polyamic acid powder. The poor solvent is not particularly limited, but examples include water, methanol, ethanol, hexane, butyl cellosolve, acetone, and toluene.

<Polyimide>
The polyimide used in the present invention can be produced by imidizing the above-mentioned polyamic acid or polyamic acid ester.

Alternatively, the liquid crystal alignment agent can be produced by imidizing a non-silylated polyamic acid using the method described below, dissolving the isolated imidized polymer in a solvent, and introducing a silylation agent when producing the liquid crystal alignment agent.

When producing polyimide from polyamic acid, a simple method is chemical imidization, in which a catalyst is added to a solution of the polyamic acid obtained by reacting a diamine component with a tetracarboxylic dianhydride. Chemical imidization is preferable because the imidization reaction proceeds at a relatively low temperature and the molecular weight of the polymer is less likely 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. The solvent can be the same as that used in the polymerization reaction described above. Examples of basic catalysts include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Among these, pyridine is preferred because it has an appropriate basicity for promoting the reaction. Examples of acid anhydrides include acetic anhydride, trimellitic anhydride, and pyromellitic anhydride. Among these, acetic anhydride is preferred because it facilitates purification after the reaction.

The temperature for the imidization reaction 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, the amic acid group, and the amount of the acid anhydride is 1 to 50 molar times, preferably 3 to 30 molar times, the amic acid group. The imidization rate of the resulting polymer can be controlled by adjusting the amount of catalyst, temperature, reaction time, etc.

When producing polyimide from polyamic acid ester, a simple method is chemical imidization in which a basic catalyst is added to the polyamic acid ester solution or to a polyamic acid solution obtained by dissolving 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 less likely 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. The solvent can be the same as that used in the polymerization reaction described above. Examples of basic catalysts include pyridine, triethylamine, trimethylamine, tributylamine, and trioctylamine. Among these, triethylamine is preferred because it is sufficiently basic to promote the reaction.

The temperature for the imidization reaction 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 basic catalyst is 0.5 to 30 molar times, preferably 2 to 20 molar times, the amount of amic acid ester groups.

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

Since the added catalyst and other substances remain in the solution after the imidization reaction, it is preferable to recover the resulting imidized polymer by the means described below and redissolve it in a solvent to obtain the liquid crystal alignment agent of the present invention.

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

D in the above formulas (B-1) to (B-17) is each independently a tert-butoxycarbonyl group or a 9-fluorenylmethoxycarbonyl group. The multiple Ds present in formulas (B-14) to (B-17) may be the same or different. The higher the basicity after deprotection by heating, the more effective it is at promoting the imidization of the polyamic acid ester and polyamic acid. Therefore, from the viewpoint of further enhancing the thermal imidization promotion effect, (B-14) to (B-17) are preferred, and among these, (B-17) is particularly preferred.

Since the added catalyst and the like remain in the solution after the imidization reaction of the polyamic acid or polyamic acid ester, it is preferable to recover the obtained imidized polymer by the means described below and re-dissolve it in a solvent to obtain the liquid crystal aligning agent of the present invention.
The polyimide solution obtained as described above can be poured into the following poor solvent while being thoroughly stirred to precipitate the polymer. The precipitation is carried out several times, washed with the poor solvent, and then dried at room temperature or by heating to obtain a purified powder of polyamic acid ester.

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

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

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

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

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

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

The molecular weight of the specific structure 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 weight average molecular weight. 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 changed as appropriate depending on the thickness of the coating film to be formed, but from the viewpoint of forming a uniform and defect-free coating film, it is preferable that the concentration is 1% by mass or more, and from the viewpoint of storage stability of the solution, it is preferable that the concentration is 10% by mass or less. Particularly preferable is 3 to 6.5% by 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 dissolves the specific structure polymer uniformly.

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

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

Furthermore, when the polymer of the present invention has high solubility in a solvent, 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% by mass of the total solvent contained in the liquid crystal alignment agent. Of these, 20 to 90% by mass is more preferable. More preferably, it is 30 to 80% by mass.

The liquid crystal alignment agent of the present invention can use a solvent (also called a poor solvent) that improves the coating properties and surface smoothness of the liquid crystal alignment film when the liquid crystal alignment agent is applied, as long as the effect of the present invention is not impaired. Specific examples of poor solvents are listed below, but are 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 ethyl ether, diethylene glycol dibutyl ether, 2-pentanone, 3-pentanone, 2-hexanone, 2-heptanone, 4-heptanone, 3-ethoxybutyl acetate, 1-methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, ethylene glycol monoacetate, ethylene glycol diacetate, propylene carbonate, ethylene carbonate, 2-(methoxy methoxy)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 Examples of the solvent include 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 ethyl 3-ethoxypropionate, ethyl 3-methoxypropionate, 3-ethoxypropionic acid, 3-methoxypropionic acid, propyl 3-methoxypropionate, butyl 3-methoxypropionate, methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate, isoamyl lactate, and the solvents represented by the formulas [D-1] to [D-3] above.

Among these, 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 poor solvent preferably accounts for 1 to 80% by mass of the total solvent contained in the liquid crystal alignment agent, more preferably 10 to 80% by mass, and even more preferably 20 to 70% by mass.

In addition to the above, the liquid crystal alignment agent of the present invention may contain, within the scope of the invention, polymers other than those described in the present invention, dielectric or conductive substances for the purpose of changing the electrical properties of the liquid crystal alignment film, such as the dielectric constant or conductivity, silane coupling agents for the purpose of improving adhesion between the liquid crystal alignment film and the substrate, crosslinking compounds for the purpose of increasing the hardness and density of the film when made into a liquid crystal alignment film, and imidization accelerators for the purpose of efficiently promoting imidization by heating the polyimide precursor 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 horizontal alignment type or vertical alignment type liquid crystal alignment film, and is particularly suitable for vertical alignment type liquid crystal display elements such as VA type or PSA mode. The method for forming the liquid crystal alignment film of the present invention is to first apply the above liquid crystal alignment agent to a substrate, dry and bake to obtain a coating film. The substrate to 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 plastic substrates such as glass substrates, silicon nitride substrates, acrylic substrates, and polycarbonate substrates can be used. Furthermore, it is preferable to use a substrate on which an ITO electrode or the like for driving 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 for only one substrate, and the electrode in this case can be made of a light-reflecting material such as aluminum.

Examples of the method for applying the liquid crystal alignment agent of the present invention include spin coating, printing, and inkjet methods. The temperature and time for the drying and baking process after applying the liquid crystal alignment agent of the present invention can be selected as desired. In general, in order to thoroughly remove the solvent contained, the coating is dried at 50 to 120°C, preferably 60 to 100°C, for 1 to 10 minutes, preferably 2 to 5 minutes, and then baked 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 is 5 to 300 nm, preferably 10 to 200 nm, since if it is too thin, the reliability of the liquid crystal display element may decrease.

The coating film formed as above can be used as it is as a liquid crystal alignment film, but it may also be subjected to an alignment treatment. Methods for the alignment treatment include rubbing and photoalignment.

The rubbing process can be carried out using existing rubbing equipment. Examples of materials for the rubbing cloth include cotton, nylon, and rayon. The conditions generally used for the rubbing process are a rotation speed of 300 to 2000 rpm, a feed speed of 5 to 100 mm/s, and a push-in depth of 0.1 to 1.0 mm. After that, any residues generated by rubbing are removed by ultrasonic cleaning using pure water or alcohol.

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

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

(1) In the case of a VA-type liquid crystal display element, two substrates on which a liquid crystal alignment film is formed as described above are prepared, and liquid crystal is placed between the two substrates arranged opposite to each other. Specifically, the following two methods can be mentioned. The first method is a conventionally known method. First, the two substrates are arranged opposite to each other with a gap (cell gap) between them so that the liquid crystal alignment films face each other. Next, the peripheries 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 partitioned by the sealant to come into contact with the film surface, and then the injection hole is sealed.
The second method is a method called ODF (One Drop Fill) method. For example, a UV-curable sealant is applied to a predetermined location on one of the two substrates on which a liquid crystal alignment film is formed, and a liquid crystal composition is dropped at a predetermined number of locations on the liquid crystal alignment film surface. Thereafter, the other substrate is bonded so that the liquid crystal alignment film faces the other substrate, and the liquid crystal composition is spread over the entire surface of the substrate to contact the film surface. Next, the entire surface of the substrate is irradiated with UV light to cure the sealant. In either method, it is preferable to remove the flow alignment during liquid crystal filling by heating the substrate to a temperature at which the liquid crystal composition used has an isotropic phase and then slowly cooling to room temperature.

(2) In the case of producing a PSA type liquid crystal display element, the same procedure as in (1) above is followed except that a liquid crystal composition containing a polymerizable compound is injected or dropped. Examples of the polymerizable compound include those represented by the following formulae (M-1) to (M-7).

(3) In the case where a coating film is formed on a substrate using a liquid crystal alignment agent containing a compound having a polymerizable group After the above-mentioned (1), a method of manufacturing a liquid crystal display element through a step of irradiating ultraviolet light 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 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 in the molecule, such as acrylate groups or methacrylate groups, as represented by the above formulas (M-1) to (M-7), and the content thereof is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, relative to 100 parts by mass of all polymer components. In addition, the polymerizable group may be possessed by a polymer used in the polymer composition, and an example of such a polymer includes a polymer obtained by using a diamine component containing a diamine having a photopolymerizable group at its terminal in a reaction.

(4) Step of irradiating ultraviolet light The liquid crystal cell is irradiated with light while a voltage is applied between the conductive films of the pair of substrates obtained in (2) or (3) above. The voltage applied here can be, for example, 5 to 50 V DC or AC. The light to be irradiated can be, for example, ultraviolet light and visible light containing light with a wavelength of 150 to 800 nm, but ultraviolet light containing light with a wavelength of 300 to 400 nm is preferred. The light source for the irradiation light can be, 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. The amount of light irradiation is preferably 1,000 to 200,000 J/m ² , more preferably 1,000 to 100,000 J/m ² .

A liquid crystal display element can be obtained by attaching a polarizing plate to the outer surface of the liquid crystal cell. Examples of polarizing plates that can be attached to the outer surface of the liquid crystal cell include a polarizing film called an "H film" made by stretching and aligning polyvinyl alcohol and absorbing iodine, sandwiched between cellulose acetate protective films, and 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, for example, various display devices such as watches, portable games, word processors, notebook computers, car navigation systems, camcorders, PDAs, digital cameras, mobile phones, smartphones, various monitors, liquid crystal televisions, and information displays.

The present invention will be described in more detail below with reference to examples. However, the present invention should not be construed as being limited to these examples. The abbreviations of the compounds used are shown below.
(Specific diamine)
DBA: 3,5-diaminobenzoic acid 3AMPDA: 3,5-diamino-N-(pyridin-3-ylmethyl)benzamide DA-1: Compound represented by formula [DA-1] (diamine having a specific side chain structure)

(Tetracarboxylic acid component)
PMDA: Pyromellitic anhydride Compounds represented by the following [D1] to [D2] D1: 1,2,3,4-cyclobutanetetracarboxylic dianhydride D2: Bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic dianhydride (silylation agent component)
Compounds represented by the following formulas [S-1] to [S-5] (silylation agents)

(solvent)
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 examples was measured as follows using a room temperature gel permeation chromatography (GPC) apparatus (SSC-7200) manufactured by Senshu Scientific Co., Ltd. and columns (KD-803, KD-805) manufactured by Shodex.
Column temperature: 50 ° C.
Eluent: N,N'-dimethylformamide (additives: lithium bromide hydrate (LiBr.HO) 30mmol/L, phosphoric acid anhydrous crystal (o-phosphoric acid) 30mmol/L, tetrahydrofuran (THF) 10ml/L)
Flow rate: 1.0 ml/min. Standard samples for preparing calibration curves: TSK standard polyethylene oxide (molecular weights: approximately 9,000,000, 150,000, 100,000, 30,000) manufactured by Tosoh Corporation, and polyethylene glycol (molecular weights: approximately 12,000, 4,000, 1,000) manufactured by Polymer Laboratory.

<Measurement of imidization rate>
The imidization rate of the polyimide in the synthesis examples was measured as follows: 20 mg of polyimide powder was placed in an NMR sample tube (Kusano Scientific NMR Sampling Tube Standard φ5), and 0.53 ml of deuterated dimethyl sulfoxide (DMSO-d ₆ , 0.05% TMS mixture) was added to completely dissolve the polyimide.

This solution was subjected to 500 MHz proton NMR measurement using an NMR measuring device (JNW-ECA500) manufactured by JEOL Datum Co., Ltd. The imidization rate was calculated by the following formula using a proton derived from a structure that does not change before and after imidization as a reference proton and the peak integrated value of this proton and the proton peak integrated value derived from the NH group of the amic acid appearing in the vicinity of 9.5 to 10.0 ppm.
Imidization rate (%)=(1−α·x/y)×100

<Synthesis of polyimide polymer>
<Synthesis Example 1>
In a 100 ml four-neck flask equipped with a stirrer and a nitrogen inlet 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 out and diluted with NMP to a solid content 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 content concentration of 20%, and heated and stirred at 60 ° C. for 1 hour. The resulting reaction solution was cooled to 17 ° C. or less, and then 1.96 g (8.99 mmol) of PMDA was added, diluted with 20% NMP, and stirred at room temperature for 5 hours. Finally, 5.11 g (26.1 mmol) of D1 was diluted with NMP to a solid content concentration of 20%, and heated and stirred at 40 ° C. for 6 hours. The resulting polymerization solution was cooled to room temperature to obtain a polyamic acid polymerization solution (PAA-1).

<Synthesis Example 2>
NMP (103.85 g) was added to PAA-1 (50.0 g) and diluted to 6.5% by mass, and then acetic anhydride (6.67 g) and pyridine (2.58 g) were added as imidization catalysts and reacted at 70° C. for 3 hours. This reaction solution was poured into methanol (570.9 g) and the resulting precipitate was filtered off. This 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 rate 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>
1.75 g of S-1 was added to PAA-1 (10.0 g), and the mixture was heated and stirred at 50° C. for 12 hours to obtain a polyamic acid silyl ester polymerization liquid. (PASE-1)

<Synthesis Example 4-7>
Polyamic acid silyl ester polymerization solutions were obtained by the same treatment as 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 in Synthesis Example 3. (PASE-2 to PASE-5)

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 the mixture was stirred at 25° C. for 5 hours. This resulted in the liquid crystal alignment agent [1] of Example 1. 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.

<Example 2-5>
NMP (14.0 g) and BCS (8.0 g) were added to the polyamic acid silyl ester polymerization solution (PASE-2 to PASE-5) (6.0 g) obtained in Synthesis Example 4-7, and the mixture was stirred at 25° C. for 5 hours. This resulted in the liquid crystal alignment agent [2-5] of Example 2-5. 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.

<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 the mixture was stirred at 25° C. for 5 hours. This resulted in the production of a liquid crystal alignment agent of Comparative Example 1. No abnormalities such as turbidity or precipitation were observed in this liquid crystal alignment agent, and it was confirmed that the resin components were uniformly dissolved.

<Preparation of Liquid Crystal Cell>
The liquid crystal alignment agent obtained above was spin-coated on the ITO surface of an alkali-free glass substrate (length 30 mm, width 40 mm, thickness 0.7 mm) with ITO that had been washed with pure water and IPA (isopropyl alcohol), and baked on a hot plate at 70° C. for 90 seconds, and then baked in an infrared heating furnace at 230° C. for 20 minutes to prepare a polyimide-coated substrate with a film thickness of 100 nm.

Two polyimide-coated substrates were prepared using the above method, 4 μm bead spacers were sprayed onto the liquid crystal alignment film surface of one of the substrates, and then a thermosetting sealant (XN-1500T manufactured by Kyoritsu Chemical Co., Ltd.) was printed on top of the bead spacers. The other substrate was then attached to the previous substrate with the side on which the liquid crystal alignment film was formed facing inward, and the sealant was cured to prepare an empty cell. PSA polymerizable compound-containing liquid crystal MLC-3023 (product name manufactured by Merck & Co., Ltd.) was injected into this empty cell by the reduced pressure injection method to prepare a liquid crystal cell. The voltage retention rate of this liquid crystal cell was measured.

Next, with a DC voltage of 15 V applied to the liquid crystal cell, the liquid crystal cell was irradiated with 7 J/ ^cm2 UV light through a 325 nm cut filter from the outside (also referred to as a primary PSA treatment). The UV illuminance was measured using a UV-MO3A manufactured by ORC Corporation.

After that, in order to inactivate any unreacted polymerizable compound remaining in the liquid crystal cell, the cell was irradiated with UV (UV lamp: FLR40SUV32/A-1) for 30 minutes with no voltage applied using a UV-FL irradiation device manufactured by Toshiba Lighting & Technology Corporation (referred to as secondary PSA treatment). The voltage retention rate was then measured.

<Evaluation of Voltage Holding Ratio>
Using the liquid crystal cell prepared above, a voltage of 1 V was applied for 60 μs in a hot air circulating oven at 60° C., and the voltages were measured after 16.67 msec and 1667 msec, respectively, and the extent to which the voltage was maintained was calculated as the voltage retention rate. To measure the voltage retention rate, a VHR-1 manufactured by Toyo Corporation was used.

As shown in the table, PASE silyl esterified with a silylating agent showed a good voltage retention rate compared to the comparative examples, and PASE-1 and PASE-2, which have a tert-butyl group, showed particularly good voltage retention rates.

<Evaluation of Solubility>
BCS was dropped into 1 g of the liquid crystal alignment agent of each of Examples 3 to 7 and Comparative Example 1 obtained above while stirring, and the solubility was calculated from the weight of the solution that became cloudy according to the following formula.
The evaluation results are shown in the table below.
Solubility = (amount of BCS in liquid crystal alignment agent + amount of BCS dropped) / (amount of liquid crystal alignment agent + amount of BCS dropped)

Although the liquid crystal alignment film obtained from the liquid crystal alignment agent of the present invention uses polyamic acid, it has reliability equal to or higher than that of soluble polyimide, specifically, high voltage holding ratio characteristics. Therefore, it can be used in a wide range of liquid crystal display elements that require high display quality.

Claims (8)

A liquid crystal aligning agent comprising at least one of a polyamic acid and a polyimide having the structure of the following formula (1), wherein the polyamic acid is a reaction product of a polyamic acid and a silylating agent :

In the formula, R ₁ represents a t-butylsilyl group. The liquid crystal aligning agent according to claim 1 , wherein the silylating agent is at least one selected from the following (S-1) to (S-2):

The liquid crystal aligning agent according to claim 1 or 2 , comprising a polyamic acid having the structure of formula (1). The liquid crystal aligning agent according to any one of claims 1 to 3, characterized in that the polyamic acid and polyimide are obtained by a reaction between a tetracarboxylic acid derivative and a diamine, and the tetracarboxylic acid derivative is a tetracarboxylic acid dianhydride represented by the following formula ( 3 ):

( _X1 represents a tetravalent organic group.) The liquid crystal aligning agent according to claim 4 , wherein the X ₁ is selected from the following formula (X1-8):

The liquid crystal aligning agent according to any one of claims 1 to 5, characterized in that the polyamic acid and polyimide are obtained by a reaction between a tetracarboxylic acid derivative and a diamine, and 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 each independently represent 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 _Y1 is selected from the following:

A liquid crystal alignment film obtained from the liquid crystal aligning agent according to any one of claims 1 to 6 . A liquid crystal display device comprising the liquid crystal alignment film according to claim 7 .