JP2007292893A - Liquid crystal alignment layer and application liquid for liquid crystal alignment layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal alignment layer by which burning of a screen is hardly caused and to provide an application liquid for forming the liquid crystal alignment layer. <P>SOLUTION: The liquid crystal alignment layer has anisotropic conductivity by making the application liquid for the liquid crystal alignment layer contain diamond fine particles each having a graphite layer into and making the liquid crystal alignment layer contain the diamond fine particles each having the graphite layer. The diamond fine particles are contained in a secondary particle state in the application liquid for the liquid crystal alignment layer and median size of a secondary particle is 0.7 to 2 times as thick as the film thickness of the liquid crystal alignment layer and is 30 to 500 nm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal alignment film and a coating liquid for forming a liquid crystal alignment film.

  2. Description of the Related Art In recent years, liquid crystal display devices are widely used as display means for mobile phones, portable televisions, mobile devices, personal computers, electronic notebooks, electronic game devices, and other electronic devices. In a liquid crystal display device, a glass substrate sandwiching a liquid crystal layer is provided with a transparent electrode for applying a voltage to the liquid crystal layer and a thin film for aligning the liquid crystal, and the voltage is applied to the liquid crystal layer to change the alignment state of the liquid crystal molecules. Display is performed.

  The liquid crystal alignment film is provided on the substrate so as to be in contact with the liquid crystal layer, and in addition to the role of aligning liquid crystal molecules in a certain direction, it also has a role of tilting at a certain angle with respect to the substrate plane (providing a pretilt angle). ing. The liquid crystal alignment film has a great influence on the characteristics of the liquid crystal display device, and is industrially manufactured by a rubbing method in which a film made of polyimide or the like is rubbed in a certain direction with a cloth.

  By the way, while a voltage is applied to the liquid crystal layer by the transparent electrode and an image is displayed on the liquid crystal display device, image sticking may occur on the screen. Burn-in is a phenomenon in which the previous display pattern remains even if the screen is switched when the same pattern is continuously displayed on the liquid crystal display device. It is presumed that this occurs because an ionic impurity contained in the liquid crystal is adsorbed to the liquid crystal alignment film when a voltage is applied between the transparent electrodes of the liquid crystal display device. For this reason, it is considered that image sticking can be reduced by removing the ionic substance in the liquid crystal, but reducing the amount of the ionic substance in the liquid crystal has an industrial limit. On the other hand, the display quality required for a liquid crystal display device is increasing, and a liquid crystal alignment film that hardly causes seizure is desired.

  It is considered that image sticking can also be reduced by making the liquid crystal alignment film have anisotropic conductivity. In other words, it is considered that by applying conductivity in the film thickness direction while not showing conductivity in the planar direction of the film, voltage can be easily applied to the liquid crystal layer and seizure can be prevented. Although the thin film used for the liquid crystal alignment film has no conductivity, the liquid crystal alignment film can have anisotropic conductivity by adding a conductive material thereto. However, it is often undesirable to add a conductive material to the liquid crystal alignment film. This is because the addition of a conductive material may impair the characteristics required for the liquid crystal alignment film. For example, it has the property of being stable with respect to liquid crystal and not changing the properties of the liquid crystal, the property of aligning the liquid crystal without changing the properties of the liquid crystal alignment film itself, and the property of not impairing the transparency required for the liquid crystal alignment film. If it is not a material, it should not be added to the liquid crystal alignment film. Furthermore, since the manufacturing process of the liquid crystal alignment film generally includes a process of applying a solution of a polymer material or a precursor thereof, it is desirable that the conductive material be easily dispersed in this solution.

Japanese Patent Application Laid-Open No. 2003-5187 (Patent Document 1) has a liquid crystal interposed between two substrates for a liquid crystal display device, and has an alignment film on the side of the liquid crystal display device substrate in contact with the liquid crystal. In this liquid crystal display device, a liquid crystal display device satisfying the relationship of 0.98 × R1c > Ra1 when the volume resistance value of the liquid crystal is R1c and the volume resistance value of the alignment film is Ra1 is disclosed. Patent Document 1 discloses a metal such as indium oxide, tin oxide, indium tin oxide, cadmium-doped tin oxide, titanium oxide, titanium dioxide, and zinc oxide in order to bring the volume resistance value of the liquid crystal alignment film into a desired range. It is described that oxide fine particles are added to an alignment film. As described above, since the conductivity of the liquid crystal alignment film is considered to affect the likelihood of image sticking, the volume resistance value of the liquid crystal and the volume resistance value of the alignment film have a desired relationship as described in Patent Document 1. It is considered that seizure can be prevented by satisfying this condition. However, when a liquid crystal display device is used, a large voltage is applied to the liquid crystal and the liquid crystal alignment film. Therefore, when metal oxide fine particles are added to the liquid crystal alignment film as described in Patent Document 1, the liquid crystal display device is used for a long period of time. In the meantime, the metal oxide fine particles may deteriorate the liquid crystal. That is, there is a problem that the liquid crystal alignment film containing metal oxide fine particles is inferior in reliability.

JP2003-5187

  Accordingly, an object of the present invention is to provide a liquid crystal alignment film that has anisotropic conductivity and does not impair the properties of the liquid crystal alignment film, and a coating liquid for forming the liquid crystal alignment film.

  As a result of intensive studies in view of the above object, the present inventors impair the characteristics of the liquid crystal alignment film by making the liquid crystal alignment film provided on the substrate of the liquid crystal display device contain diamond fine particles having a graphite layer. Thus, the present inventors have found that the liquid crystal alignment film can have anisotropic conductivity and have arrived at the present invention.

  That is, the coating liquid for a liquid crystal alignment film of the present invention contains diamond fine particles having a graphite layer.

  The diamond fine particles are contained in the liquid crystal alignment film coating solution in the form of secondary particles, and the median diameter of the secondary particles is preferably 0.7 to 2 times the film thickness of the liquid crystal alignment film. The median diameter of secondary particles of the diamond fine particles is preferably 30 to 500 nm.

  The liquid crystal alignment film of the present invention is characterized by containing diamond fine particles having a graphite layer.

  It is preferable that the particle diameter of the secondary particles made of the diamond fine particles is 0.7 to 2 times the film thickness of the liquid crystal alignment film. The median diameter of secondary particles of diamond fine particles contained in the liquid crystal alignment film is preferably 30 to 500 nm.

  By applying the liquid crystal alignment film coating liquid of the present invention to a substrate, a liquid crystal alignment film containing diamond fine particles having a graphite layer can be obtained. Even if diamond fine particles having a graphite layer are added to the liquid crystal alignment film, the properties required for the liquid crystal alignment film are not impaired. A liquid crystal alignment film containing diamond fine particles having a graphite layer exhibits anisotropic conductivity.

[1] Coating liquid for liquid crystal alignment film The liquid crystal alignment film is an organic thin film provided on a substrate of a liquid crystal display device to align liquid crystal molecules in a predetermined direction. The liquid crystal alignment film is provided by applying a liquid crystal alignment film coating liquid containing a resin component or the like to a substrate of a liquid crystal display device and curing the liquid.

(1) Diamond fine particles Diamond fine particles are formed by agglomerating at least four, usually several tens to several hundreds of diamond fine particles having a particle size of nanometer order. The median diameter (median value) of the secondary particles of the diamond fine particles is preferably 0.7 to 2 times the film thickness of the liquid crystal alignment film, more preferably 0.75 to 1.8 times, and 0.8 to 1.7 times. Is particularly preferred. If the median diameter of the secondary particles is less than 0.7 times the thickness of the liquid crystal alignment film, the liquid crystal alignment film exhibits sufficient anisotropic conductivity because it is too small with respect to the thickness of the liquid crystal alignment film. Therefore, there are too many diamond fine particles to be added. If the median diameter of the secondary particles is more than 200 nm, the diamond fine particles are likely to be missing from the liquid crystal alignment film because it is too large for the thickness of the liquid crystal alignment film. When a particle size distribution measuring device (for example, HORIBA LB-500 manufactured by Horiba, Ltd.) is used, the diamond fine particle diameter can be measured.

  Of the secondary diamond fine particles, 95% preferably have a particle size in the range of 30 to 100 nm, more preferably substantially free of particles having a particle size of 1000 nm or more and particles having a particle size of 30 nm or less. . The particle size of the secondary particles of the diamond fine particles may be based on the result of dynamic light scattering measurement using an electrophoretic light scattering photometer model ELS-8000. The measurement range of the electrophoretic light scattering method may be 1.4 nm to 5 μm. Particles in this range undergo Brownian motions such as translation, rotation, and refraction in the liquid, and their positions, orientations, and forms are changed over time. The electrophoretic light scattering method uses this phenomenon to measure the particle size from the relationship between the size of particles that settle in the medium and the sedimentation speed. More specifically, when laser light is irradiated onto particles that are in Brownian motion, the light scattered by the particles exhibits a sag corresponding to the particle size of each particle. The particle size can be obtained by observing this fluctuation using the photon detection method and analyzing the result using the photon correlation method (one of the random fluctuation analysis methods; physics and chemistry dictionary). In order to obtain diamond fine particles having a desired secondary particle size, classification may be performed using a centrifugal separator. In this specification, unless otherwise specified, “diamond fine particles” include primary particles and secondary particles.

  Diamond fine particles have the strongest peak at Bragg angle (2θ ± 2 °) of 43.9 ° in X-ray diffraction spectrum (XD) using Cu Kα ray as the source, and at 73.5 ° and 95 °. Preferably it has a characteristic strong peak. Further, it is preferable that there is a strongly distributed halo at a Bragg angle of 17 ° and there is substantially no peak at 26.5 °.

  Since the diamond fine particles have a layer made of graphite on at least a part of the surface, they exhibit conductivity. It can be confirmed that the diamond fine particles have a graphite layer by observing with a transmission electron microscope (TEM). Further, functional groups such as alkyl groups, carboxyl groups, carbonyl groups, hydroxyl groups, nitro groups, and amino groups are bonded to carbon on the surface of the diamond fine particles. Thus, the diamond fine particles having a large number of functional groups on the surface have excellent dispersibility, and if there is no large pH change, they hardly precipitate even after being stored for several months. Such diamond fine particles are called ultra-dispersed diamond.

  The raw material production method is not particularly limited as long as it has a graphite layer and can obtain diamond fine particles having a particle size and an agglomerated state as described above. As a method for synthesizing diamond, an explosion method, a flux method, a high-temperature and high-pressure method, and the like are known. Of these, the explosion method is preferable. The explosion method is a method in which a dynamic impact is applied by exploding an explosive or the like, and a raw material material having a graphite structure is directly converted into particles having a diamond structure to obtain granular diamond. By producing rough diamond (diamond blend, hereinafter referred to as DB) by the blasting method and performing appropriate post-treatment on this, diamond fine particles in a well dispersed state with a narrow particle size distribution can be obtained. Further, the DB that has not been treated after the explosion and the fine particles that are in the course of treatment also have a diamond core and a graphite layer.

Diamond fine particles obtained by the explosion method generally have a density of 3.20 × 10 ³ kg / m ^{3 to} 3.40 × 10 ³ kg / m ³ . The density of amorphous carbon is (1.8 to 2.1) × 10 ³ kg / m ³ , the density of graphite is 2.26 × 10 ³ kg / m ³ , the density of natural diamond is 3.51 × 10 ³ kg / m ³ , and static Since the density of artificial diamond by the pressure application method (non-explosive method) is 3.47 to 3.50, it can be said that the diamond fine particles obtained by the explosion method have a density lower than that of natural diamond or diamond by the static pressure method. it can.

  Next, a method for producing diamond fine particles will be specifically described with an explosion method as an example. Of course, the diamond fine particles contained in the liquid crystal alignment film coating liquid of the present invention are limited to those obtained by this production method. Not.

(A) Explosive-type initial DB manufacturing process An electric detonator is installed in the fuselage, and a steel pipe with a single-sided plug containing explosives is sunk horizontally in water and ice in a pressure vessel made of pure titanium. Examples of preferred explosives include cyclotrimethylenetrinitroamine, cyclotetramethylenetetranitramine, trinitrotoluene, trinitrophenylmethylnitroamine, pentaerythritol tetranitrate, tetranitromethane, and mixtures thereof. An example of a particularly preferred explosive is TNT (trinitrotoluene) / HMX (cyclotetramethylenetetranitramine) = 50/50. When a steel helmet is put on a steel pipe to explode the explosive, an initial DB is generated in the water and ice in the container.

  The initial DB contains a metal component. However, a product obtained by removing the metal component from the initial DB is a preferable diamond fine particle. The DB obtained by removing the metal component from the initial DB has a relatively thick graphite layer on the surface. Such a liquid crystal alignment film containing DB exhibits particularly excellent anisotropic conductivity. The metal component of the initial DB can be removed, for example, by immersing the initial DB in hydrochloric acid. The DB thus obtained is generally composed of a core composed of 50 to 80% by mass of diamond and a 20 to 50% by mass of graphite layer formed on the surface thereof, typically 60 to 80% by mass. Diamond core and 20-40 mass% graphite layer. A particularly preferred DB comprises a 60 to 70% by mass diamond core and a 30 to 40% by mass graphite layer.

(B) Oxidative decomposition treatment process of DB A dispersion of initial DB in 55-56 mass% concentrated HNO ₃ is put in an autoclave, and pressurized and heated. The initial DB can be oxidatively decomposed by applying pressure and heating at 14 atm and 150 to 180 ° C. for 10 to 30 minutes. By this step, carbon-based impurities, inorganic impurities, etc. can be decomposed.

(C) Primary oxidative etching process The dispersion of DB subjected to oxidative decomposition is pressurized and heated. It is preferable to pressurize and heat to about 18 to 200 ° C. In the primary oxidizing etching process step, a part of the graphite covering the DB surface is mainly removed.

(D) Secondary oxidative etching process The secondary oxidative etching process exists mainly in the ion-permeable interface gap between the diamond fine particles constituting the DB aggregate and in the crystal defect portion on the surface of the diamond fine particles that are difficult to remove. This is a process for removing excess graphite. Therefore, the conditions for pressurization and heating need to be stricter than the primary oxidizing etching process. Preferred treatment conditions are about 25 atm and about 230 to 250 ° C. The pH of the liquid to be treated that has been subjected to the secondary oxidizing etching treatment is usually 2.0 to 6.95.

  Setting the pressure and temperature of the oxidative decomposition treatment step, the primary oxidative etching treatment step, and the secondary oxidative etching treatment step to the above ranges is not necessarily a condition to be observed. However, in order to sufficiently remove components that are difficult to remove, it is preferable to increase the pressure and temperature in the order of the steps. On the other hand, the graphite layer of diamond fine particles can be said to be a carbon layer remaining on the surface of the diamond fine particles without being removed by the primary oxidative etching process and the secondary oxidative etching process. In some cases, some of these steps may be omitted, or the pressure and temperature may be reduced.

(E) Neutralization step A basic material which is itself volatile or a volatile decomposition product thereof is added to a nitric acid aqueous solution containing DB subjected to secondary oxidative etching. By adding basic material, the pH of the solution increases from 2-6.95 to 7.05-12. Examples of basic materials are ammonia, hydrazine, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethanolamine, propylamine, isopropylamine, dipropylamine, allylamine, aniline, N, N-dimethylaniline, diisopropylamine And polyalkylene polyamines such as diethylenetriamine and tetraethylenepentamine, 2-ethylhexylamine, cyclohexylamine, piperidine, formamide, N, N-methylformamide and urea.

For example, when ammonia is used as a basic material, it reacts with an acid as shown in the following formula to generate gas.
HNO ₃ + NH ₃ → NH ₄ NO ₃ → N ₂ O + 2H ₂ O
N ₂ O → N ₂ + (O)
3HNO ₃ + NH ₃ → NH ₄ NO ₂ + N ₂ O ₃ + H ₂ O + O ₂ + (O)
NH ₄ NO ₂ → N ₂ + 2H ₂ O
N ₂ O ₃ + NH ₃ → 2N ₂ + 3H ₂ O
N ₂ O ₃ → N ₂ + O ₂ + (O)
NH ₄ NO ₂ + 2NH ₃ → 2N ₂ + H ₂ O + 3H ₂
H ₂ + (O) → H ₂ O
HCl + NaOH → Na ⁺ + Cl ⁻ + H ₂ O
HCl + NH ₃ → NH ₄ ⁺ + Cl ⁻
NH ₄ ⁺ → NH ₃ + H ⁺
H ₂ SO ₄ + 2NH ₃ → N ₂ O + SO ₂ + NO ₂
Since the generated N ₂ , O ₂ , N ₂ O, H ₂ O, H ₂ , and SO ₂ gases can be released out of the system, there is almost no influence on the system by the residue. The amount of ammonia added is preferably 1 to 1.5 equivalents of nitric acid, and more preferably 1.25 equivalents.

(F) Decantation process Water is added to the suspension containing the diamond fine particles and decanted sufficiently. The decantation operation is preferably performed three times or more.

(G) Washing step Nitric acid is added to the decanted diamond particle suspension and stirred. For stirring, a mechanical stirrer, a magnetic stirrer or the like can be used. After washing, leave to separate into upper layer drainage and lower layer suspension. Since the diamond fine particles are contained in the lower layer suspension, the upper layer drainage liquid is removed. For example, when 50 kg of nitric acid aqueous solution is added to 1 kg of diamond fine particle-containing liquid, the upper layer drainage and the lower layer suspension are not clearly separated into layers, but the volume of the lower layer suspension containing diamond particles is the same as that of the upper layer drainage. It is about 1/4 of the capacity. In the upper layer drainage liquid, diamond-shaped ultra-fine particles having a diameter of about 1.2 to 2.0 nm may exist, but it is not essential to collect these ultra-fine particles. This is because the ultra-fine particles are likely to agglomerate due to the inclusion of impurities in the liquid layer, and it is easy to produce defective fine particles that cannot be decomposed by mechanical pressure, so that it is difficult to obtain diamond fine particles exhibiting good dispersibility even when collected. .

(H) Centrifugation step Centrifugal dehydration of the diamond fine particle suspension is performed using an ultra-high speed centrifuge. The rotation speed is preferably 10,000 to 30,000 RPM, more preferably about 20,000 RPM.

(I) Step of Preparing Suspension Containing Diamond Fine Particles It is preferable to mix the diamond fine particles and the dispersion medium so as to prevent the diamond fine particles from aggregating excessively. The concentration of the diamond fine particles may be in a range where the diamond fine particles are in a dispersed state. In the preparation of the coating liquid for a liquid crystal alignment film (5) described later, the concentration of diamond fine particles that easily brings the concentration of diamond fine particles to a desired range is generally 0.01 to 16%, preferably 0.1 to 12%, preferably 0.1 to 10%. Is more preferable. If the concentration exceeds 16%, the storage stability of the suspension is often hindered. The pH of the suspension is preferably adjusted to 4.0 to 10.0, more preferably pH 5.0 to 8.0, and particularly preferably pH 6.0 to 7.5.

(2) Resin Component Any resin component that is generally used as a resin constituting the liquid crystal alignment film or a precursor thereof can be used as the resin component of the coating liquid for liquid crystal alignment film of the present invention. The resin may be photosensitive or non-photosensitive. Examples of preferable resins include polyimide resins, polyamide resins, and polyvinyl alcohol resins. However, a polyimide resin is preferable in terms of heat resistance and reliability of the liquid crystal alignment film.

  The polyimide resin used for the liquid crystal alignment film is not particularly limited, but usually a polyamic acid mainly composed of a structural unit represented by the following general formula (1) is heated or imidized by an appropriate catalyst. Those are preferred.

(In the above general formula (1), n is 1 or 2, R ₁ represents a trivalent or tetravalent organic group having at least 2 carbon atoms, and R ₂ represents 2 having at least 2 carbon atoms. Valent organic group.)

R _{1 which} is preferable from the viewpoint of heat resistance contains a cyclic hydrocarbon, an aromatic ring or an aromatic heterocyclic ring, has 6 to 30 carbon atoms, and is a trivalent or tetravalent group. Examples of R ₁ are derived from phenyl, biphenyl, terphenyl, naphthalene, perylene, diphenyl ether, diphenylsulfone, diphenylpropane, benzophenone, biphenyltrifluoropropane, cyclobutyl, and cyclopentyl. Groups.

From the viewpoint of heat resistance, preferred R ₂ contains a cyclic hydrocarbon, an aromatic ring or an aromatic heterocycle, has 6 to 30 carbon atoms, and is a divalent group. Examples of R ₂ are derived from phenyl, biphenyl, terphenyl, naphthalene, perylene, diphenyl ether, diphenylsulfone, diphenylpropane, benzophenone, biphenyltrifluoropropane, diphenylmethane, and cyclohexylmethane. Group, but is not limited thereto. R ₁ and R ₂ may have one of these preferred groups, or each may have two or more.

  Diamond fine particles may be added to a commercially available composition or coating solution for forming a liquid crystal alignment film. Examples of commercially available liquid crystal alignment film compositions or liquid crystal alignment film coating solutions include SE-130, SE-150, SE-2110, SE-410, SE-610, SE-1180, SE manufactured by Nissan Chemical Industries, Ltd. -2170, SE-1211, SE-3140, SE-3210, SE-3310, SE-3510, SE-5291, SE-6210, SE-7492, SE-7992, SE-7511L, SE-8192L, RN-1322 RN-1332, RN-1349, RN-1358, RN-1386, RN-1417, RN-1436, RN-1450 and RN-1477, PIA-5140, PIA-5150, PIA-5310, manufactured by Chisso Corporation, PIA-X322, PIA-2024, PIA-2700, PIA-2800, PIA-2900, PIA-2942, PIA-2945 and PIA-2710, AL1000, AL1068, AL1072, AL1077, AL1F00, AL3000 manufactured by JSR Corporation, AL4000, AL5000, AL6000, AL 000, AL8000, JALS-146, JALS-212, JALS-246, JALS-406, JALS-445, JALS-469, JALS-550, JALS-552, JALS-553, JALS-555, JALS-556, JALS- 566, JALS-725, JALS-1082, JALS-1085, and JALS-1216. The composition for liquid crystal aligning film or the coating liquid for liquid crystal aligning film may be used independently, 2 or more types may be mixed and another resin component may be added suitably.

(3) Solvent Any liquid that can disperse the resin component and the fine diamond particles can be used as a solvent for the liquid crystal alignment film coating liquid. Diamond fine particles tend to be easily dispersed in a polar solvent. Examples of solvents for the liquid crystal alignment film coating solution include alcohols such as ethanol, methanol, isobutanol, and 3-methyl-3-methoxybutanol, ketones such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, diethyl ether, isopropyl ether, and tetrahydrofuran. , Ethers such as dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethyl acetate, n-butyl acetate, 3-methoxy-3-methylbutyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate , Ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol Monoethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, esters such as γ-butyrolactone, amides such as N, N-dimethylformamide, N, N-dimethylacetamide, 2-pyrrolidone, N- Examples include pyrrolidones such as methyl pyrrolidone, water and butyl cellosolve.

(4) Other components In order to improve the coatability, a surfactant may be added to the liquid crystal alignment film coating solution. The addition amount of the surfactant is preferably 10 parts by mass or less and more preferably 1 part by mass or less with respect to 100 parts by mass of the resin component.

  Specific examples of the surfactant include silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, alkyl, fluorine-modified silicone oil, polyether, alcohol-modified silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, phenol, carboxy, Modified silicone oils such as mercapto-modified silicone oils, anionic surfactants such as ammonium lauryl sulfate and polyoxyethylene alkyl ether sulfate triethanolamine, cationic surfactants such as lauryltrimethylammonium chloride, lauryldimethylamine oxide, lauryl carboxy Amphoteric surfactants such as methylhydroxyethyl imidazolium betaine, polyoxyethylene lauryl ether, polyoxyethylene Nonionic surfactants such as emissions stearyl ether and sorbitan monostearate and the like. Only one surfactant may be added, or two or more surfactants may be added.

(5) Preparation of coating liquid for liquid crystal alignment film In order to prepare a coating liquid for liquid crystal alignment film, generally, a suspension of diamond fine particles and a solution containing a resin component and the like are mixed. When the temperature of the solution containing the resin component is increased, polymerization may start. On the other hand, when the temperature of the diamond fine particles is decreased, the particles are aggregated too much. Therefore, it is preferable that the solution containing the resin component is stored at a low temperature until just before mixing, and the suspension of the diamond fine particles is stored at a high temperature. Specifically, before mixing, the solution containing the resin component is preferably stored at 10 ° C. or lower, and more preferably stored at 5 ° C. or lower. The suspension of diamond fine particles is preferably stored at 0 ° C. or higher, and more preferably stored at 5 ° C. or higher.

The content of the diamond fine particles is preferably 0.01 to 20 parts by mass, more preferably 0.03 to 15 parts by mass, and preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the resin component of the liquid crystal alignment film coating liquid. It is particularly preferred. When the content of the diamond fine particles is less than 0.01 parts by mass, the conductivity in the film thickness direction of the liquid crystal alignment film to be formed is too small. If the content of the diamond fine particles is larger than 20 parts by mass, the alignment characteristics of the liquid crystal may be poor. When the diamond fine particles contain graphite at a relatively high mass ratio (for example, DB), the diamond fine particles have particularly large conductivity, so even if the amount of diamond fine particles contained in the liquid crystal alignment film coating liquid is relatively small. A liquid crystal alignment film exhibiting desirable anisotropic conductivity can be formed. For example, about 0.01-3 mass parts may be sufficient with respect to 100 mass parts of resin components of the coating liquid for liquid crystal aligning films.
The concentration of the resin component varies depending on the resin, but in any case, the concentration of the resin component may be a general concentration in the liquid crystal alignment film coating solution.

  A mixture of diamond fine particles, resin component, additive and solvent is stirred. When diamond fine particles are difficult to disperse, it is preferable to irradiate this mixture with ultrasonic waves. It is preferable to irradiate 1 to 100 kHz ultrasonic waves for about 1 to 100 minutes, and more preferable to irradiate 5 to 50 kHz ultrasonic waves for about 5 to 30 minutes. Even when diamond fine particles are added to a commercially available liquid crystal alignment film composition or liquid crystal alignment film coating solution, the diamond fine particles can be sufficiently dispersed in a solvent by stirring and / or ultrasonically irradiating the mixture. .

  In order to obtain a coating liquid for a liquid crystal alignment film containing diamond fine particles having a desired particle diameter, the diamond fine particles were dispersed by irradiating ultrasonic waves (ultrasonic dispersion) to a diamond fine particle added with a dispersion medium. Thereafter, classification is performed using a centrifuge or the like. The rotational speed of the centrifuge is preferably 5000 to 30000 rpm, and more preferably 5000 to 20000 rpm. When the centrifugal separation treatment is performed for 5 to 60 minutes, preferably 10 to 50 minutes, the solid content settles. Therefore, a solvent or a commercially available alignment film coating liquid (or a commercially available alignment film composition) is added to the dispersion liquid excluding the sediment. And agitation and / or ultrasonic irradiation. When the ultrasonic dispersion treatment and / or the centrifugal separation treatment are performed under appropriate conditions, a coating liquid for a liquid crystal alignment film containing diamond fine particles having a desired particle diameter in a good dispersion state can be obtained.

(6) Liquid crystal alignment film A layer made of a liquid crystal alignment film coating solution is provided on a substrate having electrodes. Examples of a method of providing a layer made of a liquid crystal alignment film coating solution on a substrate include flexographic printing, spin coating, roll coating, slit die coating, and silk printing. This layer is dried, fired or irradiated with light as necessary. For example, when the coating liquid for liquid crystal aligning film contains polyamic acid, it is set as polyimide by heating a board | substrate, spin-drying | dehydrating and ring-closing polyamic acid. When soluble polyimide is contained, a polyimide thin film is formed by evaporating the solvent. In order to obtain a liquid crystal alignment film, the thin film is generally subjected to an alignment treatment such as rubbing. However, the rubbing treatment may not be required depending on the application, such as for vertical alignment liquid crystal.

  A liquid crystal alignment film containing diamond fine particles exhibits excellent anisotropic conductivity. That is, since a film having low conductivity (for example, a film made of polyimide) contains conductive fine particles having a size close to the film thickness, the conductivity in the plane direction of the film is low, but the film thickness direction Is highly conductive. Diamond is basically non-conductive because it is a covalently bonded carbon, but since a conductive layer containing graphite or the like is formed on the surface of diamond fine particles, a liquid crystal alignment film containing diamond fine particles is Excellent anisotropic conductivity. Among them, since DB has a relatively thick graphite layer and exhibits high conductivity, the liquid crystal alignment film containing DB exhibits particularly excellent anisotropic conductivity. It is preferable that the liquid crystal alignment film exhibits excellent anisotropic conductivity from the viewpoint of reducing the driving power of the liquid crystal display device in addition to preventing liquid crystal burn-in.

  The film thickness of the liquid crystal alignment film is preferably 30 to 200 nm, and more preferably 60 to 130 nm. If the thickness of the liquid crystal alignment film is greater than 200 nm, the voltage loss due to the liquid crystal alignment film is too large, which is not preferable from the viewpoint of driving the liquid crystal display device. Also, it is not preferred that the liquid crystal alignment film is thinner than 30 nm because the ability to align the liquid crystal is too low.

  The pretilt angle, voltage holding ratio, surface energy, etc. of the liquid crystal alignment film containing the diamond fine particles are not substantially different from those not containing. Further, the liquid crystal alignment film containing diamond fine particles tends to exhibit a residual DC smaller than the liquid crystal alignment film not containing. It is known that the residual DC of the liquid crystal alignment film serves as an index of the image sticking property of the liquid crystal display device, and even if the residual DC is slightly small, it has a high effect in preventing image sticking. Therefore, it is presumed that the liquid crystal alignment film containing the diamond fine particles hardly causes image sticking.

[2] Liquid crystal display device The substrate of the liquid crystal display device is not particularly limited and may be a general one. Examples of the substrate of the liquid crystal display device include quartz glass, borosilicate glass, aluminosilicate glass, inorganic glass such as soda lime glass whose surface is coated with silica, and a transparent substrate such as a plastic film or sheet.

  The liquid crystal is not particularly limited, and can be selected according to a volume resistance value, a display method, a driving method, and the like. Examples of liquid crystals that can provide good display include nematic liquid crystals and smectic liquid crystals. The nematic liquid crystal may have a positive dielectric anisotropy or a negative one depending on the display method. Smectic liquid crystals include ferroelectric liquid crystals, antiferroelectric liquid crystals, thresholdless antiferroelectric liquid crystals, and the like.

  As a method for producing a liquid crystal cell, a substrate having an electrode and an alignment film formed on the surface is bonded to face each other, the inside of the obtained cell (between two substrates) is decompressed, and the cell is immersed in liquid crystal Is mentioned. As a method used for manufacturing a large liquid crystal element, there is a “drop injection” method in which a liquid crystal is dropped on an alignment film formed on a substrate and then the substrate is bonded. In any case, the liquid crystal alignment film of the present invention can be provided on the substrate.

  In order to obtain a color liquid crystal display device, a substrate in which electrodes are formed on a color filter having a colored layer and a black matrix layer is used. In addition to the auxiliary capacitance electrode and the pixel electrode, a thin film transistor (TFT) element, a gate electrode, a signal line, and the like are provided on the substrate of the liquid crystal display device facing the color filter. A liquid crystal display device is completed when a polarizing plate is bonded to the outside of the substrate and an IC driver or the like is provided.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1
(a) Preparation of coating liquid for liquid crystal alignment layer Diamond fine particles (Vision Development Co., Ltd., product name UDD-V101) 1.5 g, mixed solvent (N-methyl-2-pyrrolidone 30% by mass, ethylene glycol monobutyl ether 30% by mass) And 40% by mass of γ-butyrolactone) was added, and the mixture was stirred for 20 minutes using a magnetic stirrer. This was irradiated with ultrasonic waves (20 kHz, 100 W) for 10 minutes and then centrifuged (5000 rpm, 10 minutes, room temperature 15 ° C.) to obtain diamond fine particles having a median diameter of secondary particles of 115 nm. The median diameter of the diamond fine particles was measured on a volume basis, and a dynamic light scattering particle size distribution measuring device (HORIBA LB-500, manufactured by Horiba, Ltd.) was used.

  Diamond fine particles (median diameter 115 nm) obtained in Example 1 (a) were added to a commercially available liquid crystal alignment film material (PIA-2942 manufactured by Chisso Corporation) to obtain a coating liquid for liquid crystal alignment film. The content of the diamond fine particles was 10% by mass with respect to the solid component of the commercially available liquid crystal alignment film material.

(b) Formation of Liquid Crystal Alignment Film A glass substrate provided with an ITO layer by sputtering is spin-coated with the liquid crystal alignment film coating solution obtained in Example 1 (a) and fired (after 3 minutes at 80 ° C., 230 For 30 minutes). The film thickness was 80 nm. FIG. 1 is an SEM photograph (10,000 times) of the film after firing. The white spots in the SEM photograph are diamond fine particles, the slightly light gray part behind is the substrate, and the black part is the ITO film. Next, the film is rubbed (pushing 0.4 mm) using rayon cloth (YA-18R), and then irradiated with ultrasonic waves (34 kHz, 50 W) for 10 minutes while immersed in ultrapure water. The membrane was washed. SEM photographs were taken after rubbing, but there was almost no difference from before rubbing, and no diamond particles were observed.

(c) Formation of liquid crystal cell Two substrates having the liquid crystal alignment film obtained in Example 1 (b) were opposed to each other so that the rubbing direction was anti-parallel, and bonded so that the cell gap was 7 μm. After evacuating the substrate, a liquid crystal (liquid crystal for SNT manufactured by Chisso Corporation, product name PIA-2942) was added to obtain a liquid crystal cell.

(d) Measurement The pretilt angle of the alignment film was measured by a crystal rotation method and found to be 4.4 °. In addition, 50 mV, 1 kHz alternating current and 0.0039 Hz direct current triangular wave were superimposed on the liquid crystal cell, and the residual DC voltage was measured. The residual DC voltage was measured as described in “Science and Technology Bulletin EID91-111” (Miyake et al., Page 19). In addition, the voltage holding ratio was measured by the method described in “Preliminary Collection of 14th Liquid Crystal Panel Discussion” (Mizushima et al., P. 78). When measuring the voltage holding ratio, the frequency was 30 Hz and the wave height was ± 4.5 V. The measurement results are shown in Table 1 and FIGS. The contact angle was measured by Kyowa Interface Science Co., Ltd. CA-V contact angle meter, and the surface energy was obtained. The results are shown in Table 2.

Example 2
A coating liquid for a liquid crystal alignment film was prepared in the same manner as in Example 1 except that the content of the diamond fine particles was 0.3 mass% with respect to the solid component of the commercially available liquid crystal alignment film material. The pretilt angle, voltage holding ratio, residual DC voltage and surface energy were measured. The measurement results are shown in Tables 1 and 2 and FIGS.

Example 3
DB [diamond: graphite = 65: 35 (mass ratio), Vision Development Co., Ltd., product name DB-V101] is dispersed in a mixed solvent, the median diameter of DB secondary particles is 144 nm, and the DB mixture is contained. A coating liquid for a liquid crystal alignment film was prepared in the same manner as in Example 1 except that the amount was 0.33% by mass with respect to the solid component of the commercially available liquid crystal alignment film material. The voltage holding ratio, residual DC voltage and surface energy were measured. The measurement results are shown in Tables 1 and 2 and FIGS.

Example 4
Diamond fine particles (product name: UDD-V102, manufactured by Vision Development Co., Ltd.) are dispersed in a mixed solvent, the median diameter of the secondary particles of diamond fine particles is 99 nm, and the content of diamond fine particles is a solid component of a commercially available liquid crystal alignment film material. A liquid crystal alignment film coating solution was prepared in the same manner as in Example 1 except that the amount was 0.34% by mass. A liquid crystal cell was prepared, and the pretilt angle, voltage holding ratio, residual DC voltage, and surface energy of the liquid crystal cell were measured. did. The measurement results are shown in Tables 1 and 2 and FIGS.

Comparative Example 1
A liquid crystal alignment film coating solution was prepared in the same manner as in Example 1 except that a film made of a commercially available liquid crystal alignment film material (manufactured by Chisso Corporation, PIA-2942) was formed on the substrate surface without adding diamond fine particles. A liquid crystal cell was prepared, and the pretilt angle, voltage holding ratio, residual DC, and surface energy of the liquid crystal cell were measured. The measurement results are shown in Tables 1 and 2 and FIGS.

  Although the pretilt angle of Example 1 was 1 ° smaller than that of Comparative Example 1, it is not problematic in practical use. The pretilt angles of Examples 1 to 3 were almost the same as those of Comparative Example 1. The voltage holding ratios of Examples 1 and 2 were slightly larger than those of Comparative Example 1, and the voltage holding ratio of Example 3 was small. However, neither of them was a practical problem. Regarding the residual DC, Example 1 had a small initial value, and Example 3 was quickly relaxed. All of these can be said to be favorable trends for preventing seizure. The surface energy of any of Examples 1 to 4 was not inferior to that of Comparative Example 1.

Example 5
(a) Preparation of coating liquid for liquid crystal alignment film Diamond dispersion in water (diamond fine particle concentration 2.2 mass%, manufactured by Vision Development Co., Ltd., product name UDD-V101) in 50 mL mixed solvent (N-methyl-2-pyrrolidone) (Containing 35% by mass, 35% by mass of ethylene glycol monobutyl ether and 30% by mass of γ-butyrolactone) was added, and the mixture was stirred for 20 minutes using a magnetic stirrer. This was irradiated with ultrasonic waves (20 kHz, 100 W) for 10 minutes and then centrifuged (5000 rpm, 10 minutes, room temperature 15 ° C.). Collect only the precipitated solid, add 50 mL of the same mixed solvent as above, stir again, irradiate with ultrasound (20 kHz, 100 W, 10 minutes), and centrifuge (5000 rpm, 10 minutes, room temperature) 15 ° C). The precipitated solid content is recovered, and the operations of adding a mixed solvent, stirring, ultrasonic irradiation and centrifugation are repeated twice, and the secondary particle size of the obtained diamond fine particles is measured in the same manner as in Example 1 (a). As a result, the median diameter was 109 nm.

  A commercially available liquid crystal alignment film material (PIA-2942 manufactured by Chisso Corporation) was added to the diamond fine particles having a median diameter of 109 nm obtained as described above to obtain a liquid crystal alignment film coating solution. The content of the diamond fine particles was 9.9% by mass with respect to the solid component of the commercially available liquid crystal alignment film material.

(b) Formation of liquid crystal alignment film A liquid crystal alignment film was formed in the same manner as in Example 1 (b) except that the liquid crystal alignment film coating solution obtained in Example 5 (a) was used. . The thickness of the liquid crystal alignment film was 80 nm.

(c) Formation of liquid crystal cell A liquid crystal cell was obtained in the same manner as in Example 1 (c) except that two substrates having a liquid crystal alignment film obtained in Example 5 (b) were used.

(d) Measurement The pretilt angle, voltage holding ratio, residual DC, and surface energy of the liquid crystal cell of Example 5 were measured in the same manner as in Example 1 (d). The measurement results are shown in Tables 3 and 4 and FIGS.

Example 6
A liquid crystal alignment film coating solution was prepared in the same manner as in Example 5 except that the content of the diamond fine particles was 0.99% by mass with respect to the solid component of the commercially available liquid crystal alignment film material. The pretilt angle, voltage holding ratio, residual DC and surface energy were measured. The measurement results are shown in Tables 3 and 4 and FIGS.

Example 7
A liquid crystal alignment film coating solution was prepared in the same manner as in Example 5 except that the content of the diamond fine particles was 0.3% by mass with respect to the solid component of the commercially available liquid crystal alignment film material. The pretilt angle, voltage holding ratio, residual DC and surface energy were measured. The measurement results are shown in Tables 3 and 4 and FIGS.

Example 8
DB [Diamond: Graphite = 65: 35 (mass ratio), Vision Development Co., Ltd., product name DB-V101] is dispersed in a mixed solvent, the median diameter of DB secondary particles is 157 nm, and the DB content is commercially available. A liquid crystal alignment film coating solution was prepared in the same manner as in Example 5 except that the solid component of the liquid crystal alignment film material was 1.17% by mass, a liquid crystal cell was prepared, and the pretilt angle, voltage holding ratio, Residual DC and surface energy were measured. The measurement results are shown in Tables 3 and 4 and FIGS.

Example 9
A liquid crystal alignment film coating solution was prepared in the same manner as in Example 5 except that the DB content was 0.33 mass% with respect to the solid component of the commercially available liquid crystal alignment film material. Angle, voltage holding ratio, residual DC and surface energy were measured. The measurement results are shown in Tables 3 and 4 and FIGS.

Comparative Example 2
A liquid crystal alignment film coating solution was prepared in the same manner as in Example 5 except that a film made of a commercially available liquid crystal alignment film material (manufactured by Chisso Corporation, PIA-2942) was formed on the substrate without adding diamond fine particles. A liquid crystal cell was prepared, and the pretilt angle, voltage holding ratio, residual DC, and surface energy of the liquid crystal cell were measured. The measurement results are shown in Tables 3 and 4 and FIGS.

  As can be seen from Tables 3 and 4, the pretilt angles and voltage holding ratios of Examples 5 to 9 were almost the same as those of Comparative Example 2. On the other hand, the residual DC is smaller than that of Comparative Example 2, and Examples 5 to 9 are considered to hardly cause seizure.

It is a SEM photograph (1000 times) of the film | membrane (before rubbing) which apply | coated the coating liquid for liquid crystal aligning films of Examples 1-4 and the comparative example 1, and baked. 4 is a graph showing pretilt angles of liquid crystal alignment films of Examples 1 to 4 and Comparative Example 1. 4 is a graph showing voltage holding ratios of liquid crystal alignment films of Examples 1 to 4 and Comparative Example 1. 4 is a graph showing residual DC of liquid crystal alignment films of Examples 1 to 4 and Comparative Example 1. It is a graph which shows the pretilt angle of the liquid crystal aligning film of Examples 5-9 and the comparative example 2. FIG. It is a graph which shows the voltage holding ratio of the liquid crystal aligning film of Examples 5-9 and Comparative Example 2. It is a graph which shows residual DC of the liquid crystal aligning film of Examples 5-9 and the comparative example 2. FIG.

Claims (6)

  A coating liquid for a liquid crystal alignment film, comprising diamond fine particles having a graphite layer.   2. The liquid crystal alignment film coating liquid according to claim 1, wherein the median diameter of secondary particles of the diamond fine particles is 0.7 to 2 times the film thickness of the liquid crystal alignment film. .   3. The liquid crystal alignment film coating liquid according to claim 1, wherein the median diameter of secondary particles of the diamond fine particles is 30 to 500 nm.   A liquid crystal alignment film comprising diamond fine particles having a graphite layer.   5. The liquid crystal alignment film according to claim 4, wherein the median diameter of the secondary particles made of the diamond fine particles is 0.7 to 2 times the film thickness of the liquid crystal alignment film. 6. The liquid crystal alignment film according to claim 4, wherein the median diameter of secondary particles of the diamond fine particles is 30 to 500 nm.