JP2011204667A - Method of manufacturing titanium-oxide-based transparent conductive substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a transparent conductive substrate forming a titanium-oxide-based transparent conductive substrate having excellent conductivity by a simple applying method with a specific coating liquid for a transparent conductive film.SOLUTION: The method of manufacturing a titanium-oxide-based transparent conductive substrate includes applying an coating liquid containing a titanium compound and a niobium compound on a transparent substrate and annealing the substrate under a reducing atmosphere within 24 hours after the application so as to form a transparent conductive film composed of niobium-doped titanium oxide on the transparent substrate. The coating liquid contains a titanium compound, a niobium compound, an inorganic acid, water and an alcohol.

Description

  The present invention relates to a method for producing a transparent conductive substrate provided with a titanium oxide-based transparent conductive film having good conductivity.

  Conventionally, indium tin oxide (ITO) films have been widely used as transparent conductive substrates used in solar cells and liquid crystal display devices. However, there is a possibility that the raw material In may be depleted, and the search for a material that can replace ITO in terms of resources and costs has become an issue. A titanium oxide transparent conductive material doped with niobium or tantalum is known as a kind of transparent conductive material expected as a substitute for ITO.

A transparent conductive substrate provided with a titanium oxide-based transparent conductive film and a method for producing the transparent conductive substrate and a peroxylated reaction product obtained by reacting a titanium compound with hydrogen peroxide and a niobium compound or a tantalum compound with hydrogen peroxide. After applying the precursor solution containing the reaction product formed on the transparent substrate, annealing is performed in a reducing atmosphere to form a transparent conductive film made of titanium oxide doped with niobium or tantalum. A method has been proposed (see Patent Document 1). In this manufacturing method, a transparent conductive substrate having a resistivity of the order of 10 ⁻³ Ω · cm can be produced.
However, since the coating liquid that is the precursor liquid uses a peroxy complex of titanium and niobium, the storage stability of the coating liquid at room temperature is extremely low, and the degree of condensation is constantly increasing due to thermal decomposition of the peroxy precursor. And may change. That is, there is a problem that the coating solution cannot be stably stored at room temperature.

  In other words, it is known that peroxy complexes have low thermal stability, so if they are not cooled sufficiently, they thicken and condensation occurs and the polymer precipitates as particles, that is, the degree of polymerization tends to increase. (See Patent Document 2).

On the other hand, a so-called sol-gel method in which a titanium oxide thin film is formed by adding hydrolysis, condensation reaction and dehydration reaction by adding an acid, water, and alcohol to a titanium organic compound as a starting material is a promising film formation method. Are known. For example, a method for producing a titanium oxide thin film using a titanium sol containing a titanium organic compound, water, acid, and alcohol as a coating solution has been proposed (see Patent Document 3).
However, in Patent Document 3, it is possible to produce a stable titanium sol that does not generate precipitates or gels, and it is possible to produce a titanium oxide thin film, but no proposal has been made to produce a film that exhibits conductivity.

In addition, a solution or dispersion containing a titanium compound and a transition element compound is applied onto a substrate, then baked to form a transparent film of titanium oxide doped with a transition element, and then the transparent film is reduced. A method of manufacturing a transparent conductive film by heat treatment in an atmosphere has been proposed (see Patent Document 4).
However, the transparent conductive film obtained by the method described in Patent Document 4 has a resistivity on the order of at most 10 ^-2 Ω · cm. Therefore, it is desired to form a transparent conductive film having higher conductivity.

JP 2009-1335096 A Japanese Patent Laid-Open No. 62-252319 JP-A-5-59562 JP 2008-288196 A

  The subject of this invention is providing the manufacturing method of the transparent conductive substrate which can form the titanium oxide type transparent conductive film which has the outstanding electroconductivity with a simple coating method.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, the present invention has the following configuration.

  (1) A coating solution containing a titanium compound, niobium compound, inorganic acid, water and alcohol is applied onto a transparent substrate, and within 24 hours after coating, annealing is performed by heating in a reducing atmosphere, and niobium is doped. A method for producing a transparent conductive substrate, comprising: forming a transparent conductive film made of titanium oxide on a transparent substrate.

  (2) The coating liquid contains titanium alkoxide as the titanium compound, niobium alkoxide as the niobium compound, at least one selected from the group consisting of hydrochloric acid and nitric acid as the inorganic acid, and ethanol as the alcohol. The manufacturing method of the transparent conductive substrate as described in (1).

  (3) The manufacturing method of the transparent conductive substrate as described in said (1) or (2) whose molar ratio of niobium / titanium in a coating liquid is 0.01-0.7.

  (4) The method for producing a transparent conductive substrate according to any one of (1) to (3) above, wherein the heating temperature of the annealing treatment in a reducing atmosphere is 350 to 1000 ° C.

  (5) The transparent conductive substrate obtained by the method in any one of said (1)-(4).

According to the present invention, niobium having an excellent conductivity of 10 ⁻³ Ω · cm or less on a transparent substrate by a simple coating method using a specific transparent conductive film-forming coating solution. There is an effect that a transparent conductive film made of titanium oxide doped with can be formed.

  In the method for producing a transparent conductive substrate of the present invention, first, as a film forming material, a coating solution is obtained in which an inorganic acid and water are added to an alcohol solution in which a titanium compound and a niobium compound are dissolved. The obtained coating liquid can produce a low-resistance conductive film even after long-term storage in the atmosphere. The titanium compound and niobium compound contained in this coating solution are metal oxide precursors that become titanium oxide doped with niobium by heating. In the present invention, the film formation is performed with a metal oxide in which pentavalent niobium belonging to group VA of the periodic table is doped with titanium oxide, thereby exhibiting good conductivity.

  The coating solution may be obtained by sequentially dissolving a titanium compound and a niobium compound in alcohol at a desired ratio, or a mixture obtained by previously mixing a titanium compound and a niobium compound at a desired ratio in alcohol. What was obtained by making it melt | dissolve may be used.

  In obtaining the coating solution, the mixing ratio of the titanium compound and the niobium compound is not particularly limited, but the niobium / titanium molar ratio in the finally formed titanium oxide film is 0.01 to 0.7. You can do it. If the niobium content is less than this range, the doping effect becomes insufficient and the conductivity may be lowered. On the other hand, even if the niobium content is more than this range, there is a possibility that the conductivity is lowered and the transparency of the film is lowered.

  The alcohol that can be used in the coating solution is not particularly limited, but in view of the decrease in conductivity due to contamination with impurities, it is preferable to use alcohol with a small amount of residual carbon or a mixed solvent thereof when forming a film. preferable. Therefore, it is desirable to use an alcohol having a certain degree of volatility. Specifically, for example, methanol, ethanol, propanol, butanol, 3-methoxy-1-butanol, diacetone alcohol, 2-ethoxyethanol, etc. 6 aliphatic lower alcohols.

The titanium compound is not particularly limited as long as it contains Ti atoms as a titanium source. For example, titanium chloride (titanium dichloride, titanium trichloride, titanium tetrachloride, etc.), titanium alkoxide (methoxide, ethoxide, isopropoxide). Etc.), titanyl sulfate, metallic titanium, titanium hydroxide (ortho titanic acid etc.), titanium oxysulfate and the like can be used.
The niobium compound is not particularly limited as long as it contains an Nb atom as a niobium source. For example, niobium chloride, niobium alkoxide (methoxide, ethoxide, etc.), niobium metal, niobium hydroxide, and the like can be used.
Of the above, titanium alkoxide and niobium alkoxide are unstable substances that react immediately upon contact with moisture, and thus are preferably handled in a dry (low humidity) atmosphere.

  As the inorganic acid, hydrochloric acid, nitric acid and the like can be used, but hydrochloric acid is preferable. Water is usually contained in the coating solution as an aqueous solution of an inorganic acid, but may be added separately from the inorganic acid.

  There is no restriction | limiting in particular in the solid content concentration of the said coating liquid, What is necessary is just a solid content concentration which does not precipitate and gelatinize an oxide or a hydroxide. The solid content concentration may be appropriately selected in consideration of the film thickness finally formed by the selected solvent and coating method, and is usually 1 to 30% by weight, preferably about 5 to 30% by weight. In addition, solid content concentration here means the ratio (weight%) which the total weight of the titanium compound and niobium compound used when obtaining a precursor liquid accounts to the total weight of a coating liquid.

In obtaining the coating solution, the molar ratio of water / solid content (sum of titanium compound and niobium compound) in the coating solution is 0.1 to 10, preferably 0.1 to 5, more preferably 0.1 to 3. By setting the equivalent ratio of water / inorganic acid to 2 to 40, preferably 2 to 20, more preferably 2 to 10, precipitation of titanium oxide, titanium hydroxide, niobium oxide and niobium hydroxide and Since the formation of gel can be prevented, a transparent coating solution can be obtained. By setting the molar ratio of water / solid content (sum of titanium compound and niobium compound) and the equivalent ratio of water / inorganic acid in the coating solution to the above ranges, a coating solution having no viscosity change for one month or more can be prepared.
In addition, since an exothermic reaction usually occurs due to the addition of an inorganic acid, the temperature of the coating solution when adding an inorganic acid is 20 ° C. or lower, preferably 10 ° C. or lower, more preferably 5 ° C. or lower, in order to reduce the influence of heat generation. It is desirable to make it.

  In the method for producing a transparent conductive substrate of the present invention, next, the obtained coating solution is applied onto a transparent substrate and annealed under specific conditions. The transparent substrate is not particularly limited as long as it can maintain its shape at the heating temperature in the annealing process to which heat is applied and has transparency. For example, inorganic materials such as various glasses, thermoplastic resins and thermosetting resins (for example, epoxy resin, polymethyl methacrylate, polycarbonate, polystyrene, polyethylene sulfide, polyethersulfone, polyolefin, polyethylene terephthalate, polyethylene naphthalate, triacetyl cellulose) Further, a plate-like material, a sheet-like material, a film-like material or the like formed of a polymer material such as plastics such as polyimide) can be used. However, it is more preferable to use inorganic materials such as various glasses because annealing is performed at a relatively high temperature. In general, the visible light transmittance of the transparent substrate is preferably 90% or more, and more preferably 95% or more.

  There is no particular limitation on the coating method when the coating solution is applied onto the transparent substrate, and any conventionally known method can be adopted as long as it is a method capable of uniformly wet coating, for example, a capillary coating method, a spin coating method, and the like. A slit die coating method, a spray coating method, a dip coating method, a roll coating method, a screen printing method, a flexographic printing method, a bar coater method and the like can be employed.

  When applying the coating solution, the coating amount is not particularly limited. For example, the thickness of the finally formed film (dry film thickness) may be 10 nm to 300 nm. If the dry film thickness that is finally formed is smaller than the above range, there may be a place that is difficult to apply partially or a place that is not actually applied, such as when there is unevenness on the substrate, If it is larger than the above range, the transparency may be lowered. In addition, when apply | coating a precursor liquid to the above thickness, you may make it carry out by one application | coating operation | work, and may be performed in multiple times.

In the present invention, the substrate after coating is annealed by heating in a reducing atmosphere within 24 hours after coating. As a result, the niobium-doped titanium oxide forming the film becomes an amorphous phase, and with the subsequent crystal transition to the anatase phase, oxygen deficiency occurs in the crystal phase, and high conductivity can be expressed. When the annealing treatment is performed 24 hours after the application to the substrate, it is difficult to develop high conductivity.
The term “within 24 hours after coating” includes the case where the annealing treatment is performed immediately after coating.

  There is no particular limitation on the reducing atmosphere in the annealing treatment, and for example, nitrogen, carbon monoxide, argon plasma, hydrogen plasma, hydrogen, vacuum, ammonia, inert gas (such as argon), or a mixed gas thereof. A general reducing atmosphere such as an atmosphere may be used. Preferably, a hydrogen atmosphere (preferably 100% hydrogen gas atmosphere) that is a strongly reducing atmosphere is employed.

  The heating temperature in the annealing process may be a temperature at which the crystal phase of the niobium-doped titanium oxide coated on the substrate can be changed to an anatase type that expresses high conductivity, depending on the content ratio of niobium, etc. What is necessary is just to set suitably. The temperature required to change to the anatase crystal phase increases as the amount of niobium doped into titanium oxide increases, and the heating temperature in the annealing treatment is usually 350 ° C. or higher, preferably 400 ° C. or higher, more preferably It is 500 ° C. or higher.

  The upper limit of the heating temperature of the annealing treatment may be less than the temperature at which the anatase crystal phase starts to change to a rutile crystal phase with low conductivity. However, when oxygen deficiency is introduced, it tends to change to a rutile phase having a high resistance value, but in the present invention, niobium doped in titanium oxide stabilizes the anatase phase even if oxygen deficiency is introduced. Because of its action, there is almost no risk of phase transition to the rutile crystal phase and a decrease in conductivity. Therefore, when it is desired to further improve the conductive characteristics, the annealing temperature is desirably set in a high temperature range of 600 ° C. or less, preferably with a high temperature of 1000 ° C. at which the conductive characteristics tend to be high as the upper limit.

  Specifically, when the content ratio of niobium (the content ratio of niobium in the formed transparent conductive film) is 20 mol%, the annealing temperature is 600 ° C. and the heating time is about 30 minutes. A transparent conductive film can be obtained. In addition to the above, the heat resistance temperature of the transparent substrate to be used is also taken into consideration when setting the heating temperature for the annealing treatment. For example, when alkali-free glass is used as the transparent substrate, since the softening point is 975 ° C., it is usually used at 950 ° C. or less, preferably 800 ° C. or less.

  The annealing time (heating time) may be appropriately set according to the heating temperature or the like, but is usually about 1 minute to 1 hour, preferably about 3 minutes to 30 minutes.

  If the coating liquid is applied on a transparent substrate and then allowed to stand at room temperature for 24 hours or more before the annealing treatment in the reducing atmosphere, the resistance value of the obtained transparent conductive film tends to increase. This is because the titanium and niobium precursors coated on the transparent base material undergoes condensation by thermal decomposition on the substrate, and the polymer precipitates as large particles, reducing the uniformity of the film. As a result, it is estimated that the conductivity is lowered. Therefore, in order to obtain good conductivity, the standing time at room temperature after applying the coating solution and before annealing in a reducing atmosphere is preferably within 24 hours, and preferably within 20 hours. More preferred.

By the method as described above, a transparent conductive film made of titanium oxide doped with niobium is formed on a transparent substrate. This transparent conductive film is a thin film having an anatase-type crystal phase and made of a polycrystal of niobium-doped titanium oxide, and exhibits high conductivity. Specifically, the transparent conductive substrate obtained by the production method of the present invention has a resistivity of 10 ⁻³ Ω · cm or less. Further, the transmittance of the transparent conductive substrate obtained by the present invention is usually 65% or more, preferably 70% or more, more preferably 75% or more in the visible region. In addition, a resistivity can be measured by the method mentioned later in an Example, for example.

  The transparent conductive substrate obtained by the production method of the present invention is, for example, a touch panel, a liquid crystal display, an LED (light emitting element), an organic EL display, a flexible display, a display electrode such as a plasma display, a solar cell electrode, or a window glass. It is suitably used for applications such as heat ray reflective films and antistatic films. Furthermore, the transparent conductivity obtained by the production method of the present invention is effective as an antistatic film having an antireflection function, taking advantage of its high refractive index.

  In the production method of the present invention described above, the coating liquid is applied directly on the transparent substrate. However, in the use of a transparent electrode such as a device such as a liquid crystal display, a colored film ( An intermediate film such as a color filter) may be interposed, and the precursor liquid may be applied directly on the intermediate film. In this manner, an intermediate film is interposed between the transparent substrate and the transparent conductive film. Included in the present invention.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by this Example.
In addition, in each Example, the viscosity change of the coating liquid and the physical properties of the transparent conductive substrate were measured by the following methods.

<Sheet resistance (surface resistance)>
Sheet resistance (Ω / □) was measured by a four-terminal four-probe method using a resistivity meter (“LORESTA-GP, MCP-T160” manufactured by Mitsubishi Chemical Corporation). Specifically, four needle electrodes were placed in a straight line on the sample, a constant current was passed between the two outer probes, and the potential difference generated between the two inner probes was measured to determine the resistance. The measurement was performed at 9 points on a 5 cm square film-formed substrate, and the average of the measured values was taken as the resistance value of the film.

<Resistivity (specific resistance)>
The resistivity (Ω · cm) was calculated by multiplying the sheet resistance and the film thickness (cm).

<Transmissivity>
The transmittance was measured in a wavelength range of 190 nm to 2700 nm using an ultraviolet-visible-near infrared spectrophotometer (“V-670” manufactured by JASCO Corporation).

<Observation of film surface>
The observation of the film surface was performed using an electrolytic emission electron microscope (FE-SEM).

Example 1
First, in a nitrogen atmosphere, 2.00 g of titanium tetraisopropoxide and 0.56 g of niobium ethoxide were dissolved in 27.68 g of dehydrated ethanol to obtain an ethanol solution in which the alkoxide was dissolved. After the flask containing the solution was cooled to 2 ° C. with ice water, 0.32 g of 35% by weight hydrochloric acid was added to the solution all at once with stirring. The addition of hydrochloric acid caused a sudden rise in the internal temperature of the solution. Controlled not to. After completion of the addition of hydrochloric acid, the rise in the internal temperature was stopped, and when the liquid temperature reached 2 ° C. again, it was removed from the ice bath and returned to room temperature. During this time, stirring was performed. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 8.4% by weight was prepared.
This coating solution was applied once on a transparent substrate {non-alkali glass (Corning Corporation 1737), 5 cm square, thickness 0.7 mm} with a spin coater to a dry film thickness of 60 nm, and immediately hydrogenated. An annealing treatment was performed at 600 ° C. for 30 minutes in a 100% reducing atmosphere to obtain a transparent conductive substrate.
The obtained transparent conductive substrate had a sheet resistance of 290Ω / □, a resistivity of 1.74 × 10 ⁻³ Ω · cm, and a transmittance of 70% in the visible region and 60% in the infrared region. When the crystal structure of the conductive film in this transparent substrate was observed by FE-SEM, it was a polycrystal of titanium oxide doped with niobium having one grain of 500 nm.

(Example 2)
In a nitrogen atmosphere, 2.00 g of titanium tetraisopropoxide and 0.56 g of niobium ethoxide were dissolved in 27.68 g of 2-ethoxyethanol to obtain an alcohol solution in which the alkoxide was dissolved. After the flask containing the solution was cooled to 2 ° C. with ice water, 0.32 g of 35% by weight hydrochloric acid was added to the solution all at once with stirring. The addition of hydrochloric acid caused a sudden rise in the internal temperature of the solution. Controlled not to. After completion of the addition of hydrochloric acid, the rise in the internal temperature was stopped, and when the liquid temperature reached 2 ° C. again, it was removed from the ice bath and returned to room temperature. During this time, stirring was performed. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 8.4% by weight was prepared.
This coating solution was applied once on the same transparent substrate as in Example 1 with a spin coater so that the dry film thickness was 60 nm, and immediately annealed at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen. And a transparent conductive substrate was obtained.
The sheet resistance of the obtained transparent conductive substrate was 1137Ω / □, the resistivity was 6.82 × 10 ⁻³ Ω · cm, and the transmittance was 70% in the visible region and 80% in the infrared region.

(Example 3)
In a nitrogen atmosphere, 4.03 g of titanium tetraisopropoxide and 1.13 g of niobium ethoxide were dissolved in 55.36 g of dehydrated ethanol to obtain an ethanol solution in which the alkoxide was dissolved. After the flask containing the solution was cooled to 2 ° C. with ice water, 0.57 g of nitric acid having a concentration of 69% by weight and then 0.24 g of ultrapure water were added all at once to the solution with stirring. The internal temperature was controlled so as not to occur. After completion of the addition of nitric acid, the rise in the internal temperature stopped, and when the liquid temperature reached 2 ° C. again, it was removed from the ice bath and returned to room temperature. During this time, stirring was performed. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 8.4% by weight was prepared.
This coating solution was applied once on the same transparent substrate as in Example 1 with a spin coater so that the dry film thickness was 60 nm, and immediately annealed at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen. And a transparent conductive substrate was obtained.
The obtained transparent conductive substrate had a sheet resistance of 931 Ω / □, a resistivity of 5.59 × 10 ⁻³ Ω · cm, and a transmittance of 70% in the visible region and 65% in the infrared region.

Example 4
In a nitrogen atmosphere, 4.00 g of titanium tetraisopropoxide and 0.80 g of niobium ethoxide were dissolved in 51.90 g of dehydrated ethanol to obtain an ethanol solution in which the alkoxide was dissolved. After the flask containing the solution was cooled to 2 ° C. with ice water, 0.61 g of 35% by weight hydrochloric acid was added to the solution all at once with stirring. The addition of hydrochloric acid caused a sudden rise in the internal temperature of the solution. Controlled not to. After completion of the addition of hydrochloric acid, the rise in the internal temperature was stopped, and when the liquid temperature reached 2 ° C. again, it was removed from the ice bath and returned to room temperature. During this time, stirring was performed. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 85: 15 (molar ratio) and a solid content concentration of 8.4% by weight was prepared.
This coating solution was applied once on the same transparent substrate as in Example 1 with a spin coater so that the dry film thickness was 60 nm, and immediately annealed at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen. And a transparent conductive substrate was obtained.
The sheet resistance of the obtained transparent conductive substrate was 540.9Ω / □, the resistivity was 3.25 × 10 ⁻³ Ω · cm, and the transmittance was 70% in the visible region and 65% in the infrared region. .

(Example 5)
In a nitrogen atmosphere, 2.00 g of titanium tetraisopropoxide and 0.96 g of niobium ethoxide were dissolved in 32.00 g of dehydrated ethanol to obtain an ethanol solution in which the alkoxide was dissolved. After the flask containing the solution was cooled to 2 ° C. with ice water, 0.37 g of hydrochloric acid having a concentration of 35% by weight was added all at once to the solution while stirring. The addition of hydrochloric acid caused a sudden rise in the internal temperature of the solution. Controlled not to. After completion of the addition of hydrochloric acid, the rise in the internal temperature was stopped, and when the liquid temperature reached 2 ° C. again, it was removed from the ice bath and returned to room temperature. During this time, stirring was performed. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 70: 30 (molar ratio) and a solid content concentration of 8.4% by weight was prepared.
This coating solution was applied once on the same transparent substrate as in Example 1 with a spin coater so that the dry film thickness was 60 nm, and immediately annealed at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen. And a transparent conductive substrate was obtained.
The obtained transparent conductive substrate had a sheet resistance of 365.5 Ω / □, a resistivity of 2.19 × 10 ⁻³ Ω · cm, and a transmittance of 70% in the visible region and 65% in the infrared region. It was.

(Example 6)
Titanium tetraisopropoxide (2.00 g) and niobium ethoxide (0.56 g) were dissolved in 22.70 g of ethanol in an air atmosphere to obtain an ethanol solution in which the alkoxide was dissolved. Subsequently, 0.32 g of hydrochloric acid having a concentration of 35% by weight was added all at once with stirring. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 10% by weight was prepared.
This coating solution was spin coated (150 rpm × 5 sec, then 800 rpm × 20 sec) on the same transparent substrate as in Example 1, and immediately annealed at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen. A transparent conductive substrate was obtained.
The sheet resistance of the obtained transparent conductive substrate was 202.8Ω / □, the resistivity was 1.5 × 10 ⁻³ Ω · cm, and the transmittance was 70% in the visible region and 60% in the infrared region. .

(Example 7)
In an air atmosphere, 2.00 g of titanium tetraisopropoxide and 0.56 g of niobium ethoxide were dissolved in 14.18 g of ethanol to obtain an ethanol solution in which the alkoxide was dissolved. Subsequently, 0.32 g of hydrochloric acid having a concentration of 35% by weight was added all at once with stirring. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 15% by weight was prepared.
This coating solution was spin coated (150 rpm × 5 sec, then 800 rpm × 20 sec) on the same transparent substrate as in Example 1, and immediately annealed at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen. A transparent conductive substrate was obtained.
The sheet resistance of the obtained transparent conductive substrate was 203.9Ω / □, the resistivity was 2.3 × 10 ⁻³ Ω · cm, and the transmittance was 75% in the visible region and 50% in the infrared region. .

(Example 8)
In an air atmosphere, 4.00 g of titanium tetraisopropoxide and 1.12 g of niobium ethoxide were dissolved in 55.36 g of ethanol to obtain an ethanol solution in which the alkoxide was dissolved. Subsequently, 0.64 g of hydrochloric acid having a concentration of 35% by weight was added all at once with stirring. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 8.4% by weight was prepared.
This coating solution was applied once by spin coating on the same transparent substrate as in Example 1 so that the dry thick film had a thickness of 60 nm, and immediately annealed at 600 ° C. for 60 minutes in a reducing atmosphere of 3% hydrogen. And a transparent conductive substrate was obtained.
The sheet resistance of the obtained transparent conductive substrate was 1171 Ω / □, the resistivity was 7.0 × 10 ⁻³ Ω · cm, and the transmittance was 70% in the visible region and 70% in the infrared region.

Example 9
In an air atmosphere, 2.00 g of titanium tetraisopropoxide and 0.56 g of niobium ethoxide were dissolved in 13.50 g of 3-methoxy-1-butanol to obtain a solution in which the alkoxide was dissolved. Subsequently, 0.32 g of hydrochloric acid having a concentration of 35% by weight was added all at once with stirring. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 16% by weight was prepared.
This coating solution is spin-coated (800 rpm × 60 sec) on the same transparent substrate as in Example 1, and immediately subjected to an annealing treatment at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen to obtain a transparent conductive substrate. Got.
The obtained transparent conductive substrate had a sheet resistance of 679 Ω / □, a resistivity of 3.2 × 10 ⁻³ Ω · cm, and a transmittance of 70% in the visible region and 70% in the infrared region.

(Example 10)
In an air atmosphere, 2.00 g of titanium tetraisopropoxide and 0.56 g of niobium ethoxide were dissolved in 6.80 g of 3-methoxy-1-butanol to obtain a solution in which the alkoxide was dissolved. Subsequently, 0.32 g of hydrochloric acid having a concentration of 35% by weight was added all at once with stirring. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 26% by weight was prepared.
This coating solution is spin-coated (800 rpm × 60 sec) on the same transparent substrate as in Example 1, and immediately subjected to an annealing treatment at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen to obtain a transparent conductive substrate. Got.
The obtained transparent conductive substrate had a sheet resistance of 485 Ω / □, a resistivity of 5.1 × 10 ⁻³ Ω · cm, and a transmittance of 70% in the visible region and 70% in the infrared region.

(Example 11)
In an air atmosphere, 2.00 g of titanium tetraisopropoxide and 0.56 g of niobium ethoxide were dissolved in 27.68 g of ethanol to obtain an ethanol solution in which the alkoxide was dissolved. Subsequently, 0.32 g of hydrochloric acid having a concentration of 35% by weight was added all at once with stirring. By preparing the coating solution under these conditions, a coating solution having titanium: niobium = 80: 20 (molar ratio) and a solid content concentration of 8.4% by weight was prepared.
This coating solution is spin-coated (800 rpm × 60 sec) on the same transparent substrate as in Example 1, and immediately subjected to an annealing treatment at 500 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen to obtain a transparent conductive substrate. Got.
The sheet resistance of the obtained transparent conductive substrate was 825Ω / □, the resistivity was 4.9 × 10 ⁻³ Ω · cm, and the transmittance was 70% in the visible region and 75% in the infrared region.

(Test Example 1)
After the coating, the storage stability of the coating film before the annealing treatment was evaluated, that is, the coating solution obtained in Example 1 was spin coated on the same transparent substrate as in Example 1 so that the dry film thickness was 60 nm. After coating once and providing the following standing time at room temperature, an annealing treatment was performed at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen to obtain a transparent conductive substrate. Regardless of the aging time before annealing of the obtained transparent conductive substrate, it was 70% in the visible region and 60% in the infrared region. Table 1 shows the sheet resistance (film average) and resistivity at each storage time.

表１から明らかなように、塗布後２４時間以内、とりわけ１７時間以内にアニール処理を施すことにより、低抵抗の透明導電性膜を透明基板上に形成することができることがわかる。

As is apparent from Table 1, it can be seen that a low resistance transparent conductive film can be formed on a transparent substrate by performing an annealing treatment within 24 hours, especially within 17 hours after coating.

(Test Example 2)
The holding stability of the coating solution was evaluated, that is, the coating solution obtained in Example 1 was provided with the holding time shown below in the atmosphere, and then the dry film thickness was 60 nm on the same transparent substrate as in Example 1. It applied once with the spin coater so that it might become. Immediately after coating, annealing was performed at 600 ° C. for 30 minutes in a reducing atmosphere of 100% hydrogen to obtain a transparent conductive substrate. Regardless of the retention time of the coating solution in the atmosphere, it was 70% in the visible region and 60% in the infrared region. Table 2 shows the sheet resistance (film average) and resistivity at each storage time.

表２から明らかなように、本発明における塗布液は保存安定性に優れ、大気下での長い保存時間を設けた後も低抵抗な透明導電性膜を透明基板上に形成することができることがわかる。

As is apparent from Table 2, the coating liquid in the present invention is excellent in storage stability, and can form a low-resistance transparent conductive film on a transparent substrate even after providing a long storage time in the atmosphere. Recognize.

  As is clear from the above examples, according to the present invention, it is possible to produce a transparent conductive film having a stable conductive property as a coating liquid for forming a transparent conductive film on a substrate. The value is great.

Claims (5)

  A coating solution containing a titanium compound, niobium compound, inorganic acid, water and alcohol was applied on a transparent substrate, and within 24 hours after coating, annealing was performed by heating in a reducing atmosphere, and niobium was doped. A method for producing a transparent conductive substrate, comprising forming a transparent conductive film made of titanium oxide on a transparent substrate.   The transparent coating according to claim 1, wherein the coating solution contains titanium alkoxide as the titanium compound, niobium alkoxide as the niobium compound, at least one selected from the group consisting of hydrochloric acid and nitric acid as the inorganic acid, and ethanol as the alcohol. A method for manufacturing a conductive substrate.   The method for producing a transparent conductive substrate according to claim 1 or 2, wherein the niobium / titanium molar ratio in the coating solution is 0.01 to 0.7.   The method for producing a transparent conductive substrate according to any one of claims 1 to 3, wherein a heating temperature of the annealing treatment in a reducing atmosphere is 350 to 1000 ° C.   The transparent conductive substrate obtained by the method in any one of Claims 1-4.