JP4599585B2 - Method for forming alignment film and method for manufacturing liquid crystal display device - Google Patents

Description

  The present invention relates to an alignment control film for liquid crystal used when manufacturing a liquid crystal device such as a liquid crystal display panel or a liquid crystal projector.

  2. Description of the Related Art Conventionally, alignment films that align liquid crystal molecules in a certain direction have been used in TN (Twisted Nematic) type and VA (Vertically Aligned) type liquid crystal display devices. The alignment film of the prior art is formed by forming a resin film having molecular orientation such as polyimide resin on a substrate, rubbing (rubbing) the surface and performing an alignment treatment, and then liquid crystal on the alignment-treated surface. It is common to arrange the layers.

  However, in the rubbing process, since the surface of the alignment film is rubbed using a cloth roll or a brush, various dusts are likely to be generated. Also, dust is generated due to wear of a machine used for rubbing.

  Therefore, a cleaning process for removing such dust is also required. In addition, the rubbing process causes not only uneven alignment but also a problem that static electricity generated during rubbing destroys the TFT element. Due to the generated static electricity, a partial decrease in the charge retention rate on the surface of the alignment control film and the seizure of foreign matter are inevitable. Further, the rubbing conditions of the stepped portion and the flat portion are different, resulting in nonuniformity of the alignment regulating force and tilt angle, and nonuniformity becomes a problem.

Furthermore, when the resin film described above is used for the alignment film, the light transmittance is poor and the contrast of light and dark is inferior. In addition, it has a disadvantage that the heat-resistant temperature is low.
In order to solve this problem, a liquid crystal alignment control film using an organic porous film is known instead of a resin film (see, for example, Patent Document 1). This alignment film randomly aligns liquid crystal molecules. Therefore, light leakage occurs at least when no voltage is applied. For this reason, black display is difficult to appear and the contrast ratio is lowered. Further, since the organic porous film is a kind of organic film, there is a problem that it is weak in heat resistance.

In order to solve the above problems, for example, an inorganic porous alignment control film for liquid crystals (inorganic alignment film) using ISM-1.5, which is an inorganic porous material made by ULVAC, has been developed (for example, Patent Documents). 2).
This inorganic porous material has pores on the order of nanometers, and an inorganic alignment film can be formed by applying and drying this inorganic porous material by a solution coating method. That is, the alignment film can be manufactured without performing the rubbing process, which is a conventional alignment control technique.

By not performing the rubbing treatment, problems such as the destruction of TFT and uneven alignment due to dust generation and charging can be solved. Further, by adopting an inorganic porous film, it has a heat-resistant temperature (400 ° C. or higher) higher than that of a glass substrate for liquid crystal panels, and further has excellent permeability. However, a liquid crystal panel using this inorganic alignment film has a problem that liquid crystal molecules are not aligned when heated.
Japanese Patent Application Laid-Open No. 07-204513 JP 2004-069870 A

  The present invention has been created to solve the above-described disadvantages of the prior art, and an object of the present invention is to produce a liquid crystal alignment film having a high alignment regulating force and to improve the heat resistance of the liquid crystal device.

  As a result of intensive studies by the present inventors, it has been found that when the porosity of the inorganic alignment film is 29% or more, the alignment film exhibits practically sufficient liquid crystal alignment. Furthermore, when the upper limit of the porosity of the inorganic alignment film was examined, if the porosity of the inorganic alignment film was 70% or less, the alignment of the liquid crystal molecules was maintained even when the liquid crystal panel was heated. I found out that

  When an inorganic alignment film (Japanese Patent Application Laid-Open No. 2004-069870) is formed using the above-described inorganic porous material, the porosity thereof is about 70% to 80%. As a result of further examination of a method of forming an alignment film having a porosity of 70% or less, an alignment film is produced using a raw material solution containing 0.01 to 0.25 mol of surfactant with respect to 1 mol of the inorganic-containing material. It was found that the porosity was 70% or less.

The invention according to claim 1 made on the basis of such knowledge is a method of forming an alignment film that forms an alignment film in which liquid crystal molecules in the liquid crystal material are aligned when the liquid crystal material is brought into contact with the surface. An interface containing any one selected from the group consisting of an inorganic-containing material which is an organic silane, alkyltrimethylammonium chloride, alkyltrimethylammonium bromide, alkyldimethylethylammonium chloride, and alkyldimethylethylammonium bromide And applying a raw material liquid containing 0.01 to 0.25 mol of the surfactant with respect to 1 mol of the inorganic-containing material to form a coating layer. The coating layer is heated to hydrolyze the inorganic-containing material to form an alignment film containing the inorganic material as a main component. A method of forming the alignment film.
Invention of Claim 2 is the formation method of the alignment film of Claim 1 , Comprising: The said organic silane is a formation method of the alignment film containing either one or both of tetraethoxysilane and tetramethoxysilane. is there.
Invention of Claim 3 is the formation method of the oriented film of any one of Claim 1 or Claim 2 , Comprising: The heating of the said coating layer raises the said coating layer to 180 degreeC or more and 400 degrees C or less. This is a method of forming an alignment film to be heated.
Invention of Claim 4 is the formation method of the oriented film of any one of Claim 1 thru | or 3 , Comprising: The formation of the said coating layer is the film thickness of the said coating layer, forming the said raw material liquid. This is a method of forming an alignment film to be applied to be 1 μm or less.
According to a fifth aspect of the invention, after forming an orientation film in the manufacturing method of the alignment film according to any one of claims 1 to 4, placing the liquid crystal on the alignment layer surface, thereby orienting the liquid crystal It is a manufacturing method of a liquid crystal display device.

  Since the alignment film of the present invention is made of an inorganic material, the heat resistance is higher than when the alignment film is made of a resin film. Since the alignment film of the present invention has liquid crystal alignment even without rubbing treatment, not only the number of steps that do not require rubbing treatment is reduced, but also contaminants such as dust generated by rubbing treatment are added to the liquid crystal display device. Hard to mix. Further, since the alignment film is not charged by the rubbing treatment, the TFT provided on the substrate is not destroyed. The process of heating the coating layer of the raw material liquid can be performed not only in a vacuum atmosphere but also in an air atmosphere. If the heating process is performed in an air atmosphere, a vacuum exhaust device is not required, and the tact surface and cost are reduced. Is also excellent. The alignment film of the present invention has higher light transmittance than the alignment film made of a resin film, and the amount of light emitted to the outside of the liquid crystal display device increases, so that the contrast between light and dark is high.

Hereinafter, embodiments of the present invention will be described.
0.01 mol or more and 0.25 mol of alkyltrimethyl halide surfactant which is a cationic surfactant per 1 mol of TEOS (tetraethoxysilane, Si (OC ₂ H ₅ ) ₄ ) which is a liquid inorganic material The porous material precursor solution is prepared by adding water and further adding either water or acid or alkali. The porous material precursor solution is diluted with a diluent solvent to prepare a raw material liquid.

  Reference numeral 11 in FIG. 1A denotes a substrate made of a transparent glass substrate. A transparent conductive film such as ITO (indium tin oxide) is patterned on the surface of the substrate 11 to form an electrode film 12. ing. On the surface of the substrate 11 on which the electrode film 12 is disposed, the above-described raw material liquid is applied by a spin coating method to form a coating layer 13 having a thickness of 1 μm or less (FIG. 1B).

When the whole is heated to a temperature of 180 ° C. or higher and 400 ° C. or lower using an infrared heating furnace or the like, the TEOS, which is an inorganic-containing material, is hydrolyzed by reacting with an acid or alkali in the coating layer. Some silicon oxide (SiO ₂ ) is deposited, and a film of an inorganic material grows. At this time, since the surfactant, water, and solvent in the coating layer 13 are evaporated by heating, voids are formed in the inorganic material film.

  Reference numeral 15 in FIG. 1C denotes an alignment film made of an inorganic material film. In the alignment film 15, voids having a pore size of nanometer units are formed, and the porosity of the alignment film 15 is 29. % To 70%.

  Two substrates 11 and 21 having the same alignment films 15 and 25 formed in the above-described steps are manufactured, and the alignment films 15 and 25 are not rubbed, and the liquid crystal display device indicated by reference numeral 10 in FIG. Is made.

  In the liquid crystal display device 10, the two substrates 11 and 21 are arranged at a predetermined distance with a spacer (not shown) in a state where the surfaces on which the alignment films 12 and 22 are formed face each other. Liquid crystal is disposed in the space between the substrates 11 and 21 to form a liquid crystal layer 31, and the liquid crystal layer 31 is sealed by a sealing layer 33 disposed at the edge portions of the alignment films 15 and 25. .

  Here, the liquid crystal layer 31 is composed of nematic liquid crystal, and in the OFF state in which no voltage is applied between the opposing electrode films 12 and 22, the liquid crystal molecules in the liquid crystal layer 31 have a molecular major axis of the substrate 11. In the ON state in which a voltage is applied between the opposing electrode films 12 and 22, the vertical alignment of the liquid crystal molecules is broken. Therefore, in the ON state, light incident on the liquid crystal layer 31 travels straight without being polarized, and in the OFF state, it is polarized by the liquid crystal layer 31.

Polarizing plates 17 and 27 are disposed on the surfaces of the substrates 11 and 21 opposite to the electrode films 12 and 22, respectively, and the light from the backlight 30 is applied to one polarizing plate 17.
As described above, the substrates 11 and 21 and the electrode films 12 and 22 are transparent, and the alignment films 15 and 25 formed according to the present invention are also highly transparent. The polarized light is transmitted through the substrate 11, the electrode film 12, and the alignment film 15 and is incident on the liquid crystal layer 31. The light that has passed through the liquid crystal layer 31 is transmitted through the alignment film 25, the electrode film 12, and the substrate 11, and Incident on the polarizing plate 27.

  Since the polarizing plates 17 and 27 are oriented so that the polarization directions are orthogonal to each other, the light traveling straight through the liquid crystal layer 31 is absorbed by the polarizing plate 27, but the light polarized by the liquid crystal layer 31 passes through the polarizing plate 27. pass. Accordingly, light is emitted outside the liquid crystal display device 10 in the ON state, and no light is emitted outside the liquid crystal display device 10 in the OFF state.

  In the liquid crystal display device 10 of the present invention, since the alignment films 15 and 25 are made of an inorganic material, the heat resistance is higher than when the alignment film is made of a resin film as in the conventional liquid crystal display device. Yes.

  If the alignment regulating force of the alignment film is low, the liquid crystal may be repelled when the liquid crystal temperature is increased, and the liquid crystal alignment may be lost. In the liquid crystal display device 10 of the present invention, since the alignment films 15 and 25 have a porosity of 29% or more and 70% or less, the alignment regulating force of the alignment films 15 and 25 is increased. Even when 10 is heated, the liquid crystal orientation does not collapse.

<Example 1>
A porous material precursor solution to which a surfactant is added in an amount of 0.01 mol to 0.25 mol with respect to 1 mol of TEOS is diluted 10-fold (weight ratio) with a solvent, respectively. A raw material solution was prepared.

  In Example 1, Examples 2 to 4 and Comparative Examples 1 and 2 described later, CTACL (cetyltrimethylammonium chloride) was used as the surfactant, and ethanol was used as the solvent.

  Each raw material liquid was spin-coated on a silicon substrate at 2000 revolutions per second and baked at 400 ° C. in a vacuum of 1 Pa to obtain a porous film of Example 1. When the refractive index and the porosity were measured for each porous film of Example 1, the refractive index was 1.152 to 1.354, and the porosity was 29% to 70%.

The porosity X is determined from the following formula (1), where the refractive index of air is 1, the refractive index of glass is 1.5, and the proportions are proportionally distributed, and the respective contents are X and 1-X. It was.
Formula (1): A = 1 * X + 1.5 * (1-X)
(A in the above formula (1) indicates the measured refractive index.)

  Next, the porous film of Example 1 described above is formed as the alignment films 15 and 25 on the surface of the substrates 11 and 21 on which the ITO film is formed, and the thickness between the two substrates 11 and 21 is 5 μm. The liquid crystal panels were prepared by injecting nematic liquid crystal and the liquid crystal molecules were confirmed to be vertically aligned in each liquid crystal panel.

<Example 2>
The porous material precursor solution used in Example 1 was diluted with a solvent to prepare a plurality of types of raw material liquids with different amounts of surfactant added. These raw material liquids were applied to a silicon substrate under the same conditions as in Example 1, and then fired at 400 ° C. in atmospheric pressure to produce the porous film of Example 2. The refractive index of each porous film and the empty The porosity was measured. The measurement results are shown in Table 1 below together with the addition amount of the surfactant.

As apparent from Table 1 above, the porous membrane of Example 2 has a porosity in the range of 34% to 68% and a refractive index in the range of 1.162 to 1.332, It was confirmed that the larger the amount added, the higher the porosity, and the higher the porosity, the lower the refractive index.
Therefore, if the addition amount of the surfactant is adjusted, it is possible not only to increase the orientation regulating force by controlling the porosity of the porous film but also to adjust the refractive index.

  Moreover, when the porous film of Example 2 was formed as an alignment film on the same substrate as that used in Example 1, and a liquid crystal panel was produced under the same conditions as in Example 1, the vertical alignment of the liquid crystal molecules in each liquid crystal panel. Was confirmed.

<Example 3>
Of the porous material precursor solution used in Example 2 above, a porous material precursor solution in which the amount of surfactant added to 1 mol of TEOS was 0.25 mol was diluted with a solvent to prepare a raw material solution, When the raw material liquid was applied on a silicon substrate under the same conditions as in Example 1 and baked at 180 ° C. in atmospheric pressure, a porous film having a refractive index of 1.206 and a porosity of 59% was obtained. . When this porous film was formed as an alignment film on the same substrates 11 and 21 used in Example 1, and a liquid crystal panel was produced under the same conditions as in Example 1, vertical alignment of liquid crystal molecules was confirmed.

<Example 4>
Porous material precursor solutions with different amounts of surfactant added were diluted with ethanol to prepare a plurality of types of raw material solutions. Each raw material liquid was spin-coated at different rotation speeds to form a coating layer (500 to 4000 revolutions per second), and fired at 400 ° C. in atmospheric pressure to form a porous film. The film thickness of each porous film is shown in the graph of FIG. 3 together with the spin speed.

  In addition, the numerical value of CTACL in FIG. 3 is a value obtained by dividing the number of moles of CTACL by the number of moles of TEOS and multiplying by 100 (unit%), and the dilution factor in FIG. 3 indicates the porous material precursor solution. It is the dilution factor (weight ratio) when diluted with a solvent.

  As is clear from FIG. 3, the film thickness of the porous film produced using the raw material liquid of Example 5 is in the range of 60 nm to 350 nm, and the alignment film 15 is increased by increasing the number of spin coat rotations. , 25 can be reduced.

  When the porous film of Example 4 was formed as an alignment film on the same substrate as that used in Example 1, and a liquid crystal panel was produced under the same conditions as in Example 1, the liquid crystal molecules were aligned vertically in each liquid crystal panel. confirmed.

<Comparative Example 1>
An alignment film having a porosity of 71% or more is formed on the substrate used in Example 1 by using a porous material precursor solution in which the amount of surfactant added relative to 1 mol of TEOS is 0.26 mol or more. A liquid crystal panel of Comparative Example 1 was produced under the same conditions as in Example 1.

<Comparative example 2>
An alignment film having a porosity of less than 29% is formed on the substrate used in Example 1, using a porous material precursor solution in which the amount of surfactant added relative to 1 mol of TEOS is less than 0.01 mol. A liquid crystal panel of Comparative Example 2 was produced under the same conditions as in 1.

As a result of confirming the orientation of the liquid crystals of the liquid crystal panels of Comparative Examples 1 and 2, Comparative Example 2 had a weaker alignment regulating force than it was practically insufficient.
In Comparative Example 1, the alignment regulating force was practically sufficient, but when the liquid crystal panel was heated, the alignment of the liquid crystal was disturbed when the liquid crystal temperature reached 60 ° C.

  On the other hand, the liquid crystal panel 10 produced in Examples 1 to 4 described above has a strong alignment regulating force for liquid crystal, and no change was observed in the liquid crystal alignment even when the liquid crystal temperature was raised to 60 ° C.

  The above describes the case where the raw material liquid is applied by the spin coating method. However, the present invention is not limited to this, and the wire bar coating method, the blade coating may be used as long as a coating layer having a thickness of 1 μm or less can be formed. Various coating methods such as a method can be used.

  The thickness of the alignment films 15 and 25 is not particularly limited, but the thickness is preferably 1 μm or less. If the film thickness of the coating layer 13 when the raw material liquid is applied is 1 μm or less, the film thickness of the alignment films 15 and 25 can be 1 μm or less.

The firing condition is not limited to firing in the air, but may be a firing treatment in a vacuum. In addition, when oxidation of the substrate 11 and the electrode film 12 becomes a problem, an inert gas (He gas, Ar gas, N ₂ gas, etc.) is supplied to the substrate 11 on which the coating layer 13 is formed. You may perform a baking process in atmosphere.

  Regarding the temperature and time of the firing conditions, any temperature and time may be used as long as the solvent, water, pore-forming substance and the like in the solution can be evaporated. Preferably, the baking is performed from 180 ° C. at which the pore-forming substance and other organic materials evaporate to 400 ° C. which is lower than the heat resistant temperature of the liquid crystal panel substrate. The inorganic porous alignment film obtained after firing may be water repellent or hydrophilic.

  As a porous material precursor solution, for example, based on a product containing TEOS and a surfactant, such as trade name “ISM-2” manufactured by ULVAC, Inc., the addition amount of the surfactant is 0.01 mol or more and 0.25. Although what was adjusted to the mole or less is mentioned, it will not be limited to this as long as it can form a porous film that the porosity becomes 29% or more and 70% or less. Further, the raw material liquid may be prepared by diluting the porous material precursor solution with an appropriate solvent, or the porous material precursor solution may be used as it is without being diluted.

  The diluting solvent is not limited to ethanol, and various alcohols such as isopropyl alcohol, methanol, and butanol can be used. These alcohols may be used alone or in combination of two or more. . The dilution solvent is added to adjust the concentration of the entire reaction solution, and is added in an adjusted amount so that it can be easily applied according to the viscosity of the reaction solution.

  The hydrolysis of the inorganic-containing material may be performed by acid or alkali. For the hydrolysis, inorganic acids such as nitric acid and hydrochloric acid, organic acids such as formic acid, ammonia and the like are used. Alkali can be used.

  When acid or alkali is added to the raw material liquid to hydrolyze the organic silane, if the amount of acid or alkali added to 1 mol of the organic silane is less than 0.5 mol, the hydrolysis proceeds extremely slowly. If the amount exceeds mol, the organic silane is not hydrolyzed and the raw material liquid is solidified. Therefore, the amount added is preferably 0.5 mol or more and 1.5 mol or less with respect to 1 mol of the organic silane. Moreover, it is preferable that content of water with respect to 1 mol of organosilanes is 8 mol or more and 15 mol or less.

  Although the kind of surfactant used in the present invention is not particularly limited, it is preferable to use a cationic surfactant. Examples of surfactants other than CTACL include lauryltrimethylammonium chloride, n-hexadecyltrimethylammonium chloride, Use alkyltrimethylammonium bromide, cetyltrimethylammonium bromide, stearyltrimethylammonium chloride, alkyldimethylethylammonium chloride, alkyldimethylethylammonium bromide, cetyldimethylethylammonium bromide, octadecyldimethylethylammonium bromide, methyldodecylbenzyltrimethylammonium chloride, etc. Can do. These surfactants may be used alone or in combination of two or more.

The material constituting the electrode film 12 is not limited to ITO, but includes tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), cadmium oxide (CdO), or one or more of these. Various transparent conductive materials such as cadmium oxide-tin oxide (Cd ₂ SnO ₄ : CTO), cadmium oxide-zinc oxide (CZT), and indium oxide-zinc oxide (IZO) may be used.

The organic silane used for the inorganic-containing material is not particularly limited as long as it can be hydrolyzed, but tetraalkoxysilane is preferably used. In the present invention, it is more preferable to use TEOS and TMOS (tetramethoxysilane, Si (OCH ₃ ) ₄ ) among tetraalkoxysilanes. TEOS and TMOS may be used alone, or TEOS and TMOS may be used together. The same raw material liquid may be used.
The substrates 11 and 21 are not limited to glass substrates as long as they have high translucency, and substrates made of a transparent resin film can also be used.

(A)-(c): Sectional drawing explaining an example of the manufacturing process of the oriented film of this invention Sectional drawing explaining an example of the liquid crystal display device of this invention A graph explaining the relationship between the film thickness of the alignment film and the spin speed

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Liquid crystal display device 11, 21 ... Substrate 12, 22 ... Electrode film 13 ... Coating layer 15, 25 ... Orientation film 31 ... Liquid crystal layer

Claims (5)

An alignment film forming method for forming an alignment film in which liquid crystal molecules in the liquid crystal material are aligned when a liquid crystal material is brought into contact with the surface,
An inorganic-containing material that is an organosilane ;
Contains an alkyl trimethyl ammonium chloride, alkyl trimethyl ammonium bromide, alkyl dimethyl ethyl ammonium chloride, a surfactant containing any one selected from the group consisting of alkyl dimethyl ethyl ammonium bromide, and the interface The raw material liquid in which the content of the activator is 0.01 mol or more and 0.25 mol or less with respect to 1 mol of the inorganic-containing material is applied to the substrate surface to form a coating layer,
A method for forming an alignment film, wherein the coating layer is heated to hydrolyze the inorganic-containing material to form an alignment film containing the inorganic material as a main component. The organosilane, and tetraethoxysilane, a method of forming the alignment film according to claim 1, further comprising either one or both of tetramethoxysilane. The heating of the coated layer, forming method of claim 1 or the alignment film of any one of claims 2 to the temperature of the said coating layer below 400 ° C. 180 ° C. or higher. The formation of the coating layer, the raw material liquid, the method of forming the alignment film according to any one of claims 1 to 3 film thickness of the coating layer is applied so as to be 1μm or less. After forming an alignment film by the manufacturing method of the alignment film of any one of Claim 1 thru | or 4 ,
A method for manufacturing a liquid crystal display device, wherein a liquid crystal is arranged on a surface of the alignment film and the liquid crystal is aligned.

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