JP2002146286A - Coating fluid for forming metal oxide thin film and method for forming metal oxide thin film by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a metal oxide thin film which enables low temperature treatment and continuous treatment, has a wide range of selection of the shape and material of base materials, and particularly excels in the affinity for the surface of an organic polymeric material. SOLUTION: The coating fluid for forming a metal oxide thin film comprises a metal oxide precursor and a substance having a photocatalytic activity. The method for forming the metal oxide thin film comprises coating this coating fluid and then irradiating the coating film with light rays. The metal oxide precursor is not particularly limited if it can be converted to a metal oxide by the hydrolysis condensation reaction and, simultaneously, can be made into a coating fluid, and alkoxides of various metals and their derivatives, nitric acid salts, chlorides, complexes such as acetyl acetonates, and the like, can be used as the metal oxide precursors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating film forming method capable of forming a coating film containing a metal oxide as a main component without restriction of a substrate.

[0002]

2. Description of the Related Art Conventionally, thin films of metals, metal oxides and the like have been deposited by vacuum evaporation, sputtering, ion plating, chemical vapor deposition (CVD), plasma CVD,
It was formed by various methods such as an electrolytic plating method, an electroless plating method, an anodizing method, a baking method, a pyrolysis spray method, a pyrosol method, and a Langmuir method.

In these thin film forming methods, the base material on which a thin film is to be formed needs to be heated to a high temperature, so that the selection range of the base material is narrowed, an expensive apparatus or a method requiring very strict condition control is required. There was a problem with poor productivity due to batch processing.

For example, in the case of forming a transparent electrode thin film, the thermal decomposition spray method is inexpensive, but the use efficiency of the raw material, the nonuniformity of the surface, the response to the increase in size, and the like are inferior. However, there is a problem with the raw materials, and the vapor deposition method and the ion plating method can form a stable film.
The initial cost is large, and it is important to control the film forming conditions in the sputtering method, and both the running cost and the initial cost are expensive.

[0005] On the other hand, in recent years,
Sol using a metal oxide precursor such as a metal alkoxide-
A method for obtaining a metal oxide thin film by a gel method has been energetically studied. Such a method is advantageous in both initial cost and running cost as compared with the above method, and has advantages such as a wide range of metal oxides that can be produced. However, it is difficult to use the coating film formed by the sol-gel method as it is in order to express a precise structure and physical properties, and it is difficult to use a post-treatment step such as baking at a high temperature, or acid, alkali, or catalyst. It is necessary to carry out a chemical conversion reaction using such a method. For this reason, for example, in the most commonly performed high-temperature firing, since the base material used is required to have heat resistance that can withstand high temperatures,
There was a problem that the range of choice of the base material was naturally restricted. Regarding such existing problems, for example, as a method of forming a metal oxide thin film on a substrate having low heat resistance such as plastics, after forming a metal oxide thin film by a sol-gel method, ultraviolet light or Irradiate laser light,
A method for crystallizing a gel (JP-A-5-80205, JP-A-5-107403, JP-A-9-157)
855, JP-A-10-316427, JP-A-11-035710, JP-A-11-0127
No. 45, JP-A-11-250733, JP-A-12-016812, JP-A-12-029326
Publication), a metal oxide gel film of 47 kPa or more, 1MP
a method of obtaining a metal oxide thin film by performing a heat treatment at a relatively low temperature of 60 to 180 ° C. or lower in a steam atmosphere of a or lower (Japanese Patent Laid-Open No. 10-87304), Hydrolysis in the presence of
A method of forming a metal oxide thin film at a low temperature by condensation (JP-A-06-001953, JP-A-08-1996)
-339723, JP-A-08-337775). Since these methods can form a Han family oxide thin film at a relatively low temperature, they can be applied to a substrate having low heat resistance, for example, an organic polymer material such as plastics. Both the precursor sol and the finally formed metal oxide thin film generally have poor affinity with the organic polymer material surface, and the sol has a short pot life of the coating liquid or the substrate surface during coating. There were problems such as repelling and poor coating properties due to poor wettability. In addition, there is a disadvantage that problems such as cracking, poor adhesion and poor adhesion of the thin film to the base material of the finally formed thin film occur. To solve such problems, acid, alkali treatment, plasma treatment,
Flame treatment, physical surface treatment such as sandblasting, etc.
A complicated surface treatment had to be performed in advance.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems and drawbacks of the above-mentioned thin film forming method, which enables low-temperature processing and continuous processing, and allows the selection of the shape and material of the base material. An object of the present invention is to provide a coating liquid, a coating film, and a method for producing the same, which are suitable for producing a thin film which has a wide affinity, particularly, excellent affinity with the surface of an organic polymer material.

[0007]

The present invention has the following arrangement to solve the above-mentioned problems. "A coating liquid for forming a metal oxide thin film, comprising a metal oxide precursor and a substance having photocatalytic activity, and characterized by being produced by applying the coating liquid to a substrate and then irradiating it with light. Method for producing metal oxide thin film. "

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is well known that when a substance having photocatalytic activity is irradiated with light having a wavelength having energy equal to or larger than its band gap, electrons and holes are generated by photoexcitation. The concept of the present invention is to form a metal oxide metal oxide film on a substrate by utilizing the decomposition of organic substances by the strong reducing power and oxidizing power of the electrons and holes.

Therefore, it is possible to continuously apply a coating solution containing a metal oxide precursor and a substance having photocatalytic activity to a substrate, dry the substrate, and irradiate light, thereby forming a metal oxide film at low cost. it can.

The metal oxide precursor in the present invention can be converted into a metal oxide by a hydrolysis-condensation reaction.
There is no particular limitation as long as the coating liquid can be formed, and alkoxides and derivatives of various metals, complexes of nitrate, chloride, acetylacetonate and the like can be used.

As the metal species, Al, B, Ba, Bi, C
a, Ce, Co, Dy, Er, Fe, Ga, Ge, H
f, In, K, La, Li, Mg, Mn, Mo, Nb,
P, Pb, Pr, Sb, Si, Sm, Sn, Sr, T
a, Ti, V, W, Y, Zn, Zr, etc., and alkoxides and halides, and other derivatives and complexes can be used. Preferable examples include, for example, alkyl silanes such as tetraethoxysilane, methyltrimethoxysilane, and methyltriethoxysilane, tetraisopropyl titanate, tetranormal butyl titanate, butyl titanate dimer, and tetra (2-ethylhexyl)
Titanate, titanium tetraacetylacetonate, isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, tetraisopropyl bis (dioctyl phosphite) titanate, tetra (2,2-diallyloxymethyl-) 1-butyl) bis (ditridecyl) phosphite titanate, bis (dioctylpyrophosphate) oxyacetate titanate, bis (dioctylpyrophosphate) ethylene titanate, isopropyltrioctanoyl titanate, isopropyldimethacrylyl isostearyl titanate, isopropyl isostearyl diacryl titanate , Isopropyl tri (dioctyl phosphate) Organic titanate compounds such as isopropyltricumylphenyltitanate, isopropyltri (n-aminoethyl-aminoethyl) titanate, dicumylphenyloxyacetate titanate, diisostearoylethylene titanate, zirconium normal propylate, zirconium normal butyrate, zirconium Tetraacetylacetonate, zirconium acetylacetonate bisethylacetonate,
Zirconium acetate, zirconium oxalate,
Organic zirconium compounds such as zirconium lactate,
Triisopropoxyindium, tetra-n-butoxytin and the like.

These metal oxide precursors can be applied as they are with a substance having photocatalytic activity. However, from the viewpoints of the stability of the coating solution, workability during coating and coatability, an organic component is used. It is preferable that they coexist. In this case, an organic surfactant capable of decomposing an organic component by a later photocatalyst, a protective colloid, or another organic polymer-based binder can coexist, but has an organic structure site as described below. It is preferred to have a metal oxide precursor.

The metal oxide precursor having an organic structural site is produced by hydrolyzing and condensing the above hydrolyzable metal compound in the presence of a polyhydric alcohol. When a metal oxide precursor having is used, not only is it easy to prepare a coating liquid in various solvents because of having an organic structural site, but also has excellent affinity with the organic polymer-based substrate surface, A coating film having excellent film-forming properties, adhesion to a substrate, and coating film strength before light irradiation can be obtained. In addition, since it has moderate hygroscopicity even after being formed into a coating film, activation of water molecules is caused by the photocatalyst, active oxygen species having strong oxidizing power such as hydroxyl radicals are easily generated, and organic components are decomposed. Can also be provided.

The metal oxide precursor having the organic structure site is produced by bringing the above-mentioned hydrolyzable metal compound into contact with a solution containing a polyhydric alcohol, whereby the hydrolysis and condensation reactions proceed. At that time, it is preferable that water necessary for the hydrolysis of the organometallic compound coexist in the solution containing the polyhydric alcohol, and it is also preferable to add a catalyst for promoting the hydrolysis and condensation reaction. As the catalyst, hydrochloric acid, nitric acid, sulfuric acid, inorganic acids such as phosphoric acid, formic acid, acetic acid,
Organic acids such as propionic acid, oxalic acid, sulfonic acid, acetic anhydride and benzoic acid, and amines such as ammonia, monomethylamine, dimethylamine, monoethylamine, diethylamine, ethylenediamine, 2-aminoethanol and triethanolamine can be used. is there. Among them, ammonia is preferred because it is low in toxicity, easy to remove and inexpensive, and a commercially available 28% aqueous ammonia solution can be used. Polyhydric alcohols include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylene glycol, neopentyl glycol, cyclohexanedimethanol, glycerin, diethylene glycol,
Pentaerythritol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can be mentioned, and they are used alone or as a mixture. Also,
In addition to polyhydric alcohol, water, methanol, ethanol,
Monoalcohols such as isopropanol, n-propanol, butanol, dioxane, methyl cellosolve, γ
-Butyrolactone, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 2-aminoethanol, triethanolamine, triethylamine, acetone, methyl ethyl ketone, methyl isobutyl ketone, N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide,
A solvent compatible with the polyhydric alcohol used, such as dimethyl sulfoxide and tetrahydrofuran, may be mixed. The amount of the polyhydric alcohol to be used is preferably at least equimolar to the metal alkoxide, more preferably at least twice the molar amount.

The metal oxide precursor having an organic structure site prepared in this manner is measured by a differential thermogravimetric simultaneous measuring device or the like. (The ratio to the weight of the charged sample) is preferably 5% or more. It is more preferably at least 10%. If the heating weight loss rate is less than 5%, problems such as poor stability as a coating liquid, poor affinity with the base material and poor coating in the coating film forming process before light irradiation occur, and the effects of the present invention are recognized. There may not be.

Next, the substance having photocatalytic activity used in the present invention will be described. Examples of the substance having photocatalytic activity include known metal compound semiconductors such as titanium oxide, zinc oxide, tungsten oxide, iron oxide, and strontium titanate, and tris (2,2′-bipyridine) ruthenium (II).
A complex or the like can be used, and among them, titanium oxide is preferable since it is inexpensive and has photocatalytic activity with relatively low energy. V, Fe, Co, Ni, C
a metal and / or a metal compound selected from u, Zn, Ru, Rh, Pd, Ag, Pt, and Au is adsorbed or carried on the inside and / or on the surface, and if necessary, heated,
Reduced ones can also be used.

The coating liquid in the present invention contains the substance having photocatalytic activity and the metal oxide precursor as essential components. The weight ratio of the metal oxide precursor to the substance having photocatalytic activity is 99.9. : 0.1 to 50:50. When the amount of the substance having photocatalytic activity is too small, the decomposition of the target organic substance becomes insufficient, and the hardness and adhesion of the metal oxide film tend to be insufficient. Conversely, if the amount is too large, the performance of the target metal oxide film is adversely affected, and when the substrate is plastic, the substrate itself is oxidized, which causes deterioration of the substrate.
However, for example, when the substance having photocatalytic activity does not adversely affect the physical properties of the finally obtained thin film,
For example, when a titanium oxide precursor is used as a metal oxide precursor to form a titanium oxide film, it goes without saying that adding a substance having photocatalytic activity beyond this range is also effective. When the metal oxide precursor itself has photocatalytic activity, it can be used alone as a coating liquid.

The coating liquid containing the metal oxide precursor and the substance having photocatalytic activity does not need to use a solvent as long as the metal oxide precursor is a liquid, but is diluted with a solvent from the viewpoint of workability. You can do it. The solvent is not particularly limited as long as it can dissolve or disperse the metal oxide precursor, and is appropriately selected depending on the coating method and the type of the metal oxide precursor, and is not limited at all. From the viewpoint of workability and reduction of environmental load, alcohols such as water, ethanol, and isopropanol are preferable. Also, surfactants, leveling agents, defoamers, stabilizers, for the purpose of improving coatability and film strength,
Various additives such as thickeners and binders can also be used. Depending on the desired film properties, various fine particles, conductive agent,
It is also possible to add pigments and the like.

As a method for applying such a coating liquid, a generally known method can be applied. Examples include spin coating, dip coating, spray coating, die coating, bar coating, roll coating, reverse roll coating, blade coating, screen printing, gravure printing, and the like.

In the present invention, a step of irradiating the coating film after application of the coating liquid with light having a wavelength having energy equal to or larger than the band gap of a substance having photocatalytic activity to decompose the organic substance of the metal oxide precursor is included. As the light, a light ray including ultraviolet rays is preferable. For example, sunlight, a fluorescent lamp, a black light, a chemical lamp, a mercury lamp, a xenon lamp, or the like can be used as a light source. In particular, light containing near-ultraviolet light of 300 to 400 nm is preferable.

Since the present invention does not require high-temperature sintering, the substrate can be selected from a wide range of choices, such as an organic polymer substrate or an inorganic substrate, without limitation. For example, plastic sheet, film, fiber, non-woven fabric, carbon fiber, wood, glass,
Ceramics, metals and the like can be applied without limitation as long as they can be applied and can be irradiated with light irrespective of their material, shape and processing state.
Naturally, if the substrate has excellent heat resistance, it can be fired at a high temperature.

The present invention can form a metal oxide thin film at low cost and can be applied to products in all fields where a thin film needs to be provided. For example, imparting magnetism, imparting gas barrier properties, preventing oxidation, imparting conductivity, imparting insulating properties, shielding electromagnetic waves,
UV shielding, anti-reflection, heat ray reflection, anti-static, surface heating,
Improving scratch resistance, imparting water repellency, imparting hydrophilicity, imparting antibacterial properties,
Can be used for antifouling, water and air treatment, etc.
Integrated circuits such as memory ICs, microprocessors, logic ICs, recording media such as hard disks, floppy disks, optical disks, and video tapes, semiconductor lasers, image sensors, thin film sensors, magnetic sensors, humidity sensors, temperature sensors, magnetic heads, capacitors, Transparent conductive film, anti-reflection film, CRT, LCD, LE
D, it can be used to manufacture members such as plasma displays and electroluminescent displays. In addition, by using the concept of the present invention, not only the formation of a metal oxide film, but also a material that is not decomposed by photoirradiation by coexisting a substance that is not decomposed by a photocatalyst (or a precursor thereof) and a substance that is decomposed, , That is, it can be applied as a kind of photolithography.

[0023]

The present invention will be described in more detail with reference to the following Examples, which are not intended to limit the scope of the present invention.

The reflectance is "U-341" manufactured by Hitachi, Ltd.
It was measured with a type 0 self-recording spectrophotometer. Pencil hardness is JIS K
It measured according to the pencil scratch value measurement method (hand scratch method) of -5400. For chemical resistance, the coating film was immersed in a 5% aqueous solution of sodium hydroxide, and the change in appearance was visually observed. The evaluation results are summarized in Table 1.

[0025]

[Table 1]

Example 1 In a reaction vessel equipped with a thermometer and a stirrer, 100
g, glycerin 33 g, tetraisopropoxy titanium 5
0 g was added and the mixture was stirred for 30 minutes. After adding 18 g of 28% ammonia water and stirring for 30 minutes, 900 g of water was further added.
Was added. After continuing stirring for 1 hour, ethanol, isopropyl alcohol and ammonia were removed by distillation under reduced pressure to obtain an aqueous dispersion of a titanium oxide precursor. To this, 6 g of a photocatalyst aqueous titanium oxide dispersion “STS-21” (manufactured by Ishihara Techno Co., Ltd.) was added to prepare a coating liquid. Apply this coating solution to a glass plate
The solution was applied with a spin coater of 000 rpm, dried at 100 ° C., and irradiated with ultraviolet rays for 30 minutes at an irradiation distance of 10 cm using a Toshiba germicidal lamp “GL4” as a light source. F of coating film after irradiation
By T-IR measurement, the absorption peak derived from the organic component (3000
-2800 cm-1 and 1200-1000 cm-1) were confirmed to have disappeared.

Example 2 Example 2 was repeated except that no photocatalytic titanium oxide was added. By FT-IR measurement of the coating film after light irradiation, the absorption peak derived from the organic component (3000-2800 cm-1,
And 1200-1000 cm-1) disappeared.

Comparative Example 1 The same operation as in Example 1 was carried out except that no ultraviolet ray was irradiated. In the FT-IR measurement of the coating film, it was confirmed that absorption peaks (3000-2800 cm-1 and 1200-1000 cm-1) derived from organic components were present.

Example 3 Ethanol 100 was added to a reaction vessel equipped with a thermometer and a stirrer.
g, 100 g of ethylene glycol and 50 g of tetra-n-butoxyzirconium were added and stirred for 30 minutes. there,
18 g of 1N hydrochloric acid was added and stirred for 60 minutes. After removing ethanol and n-butyl alcohol by distillation under reduced pressure, 800 g of water was added to obtain an aqueous dispersion of a zirconium oxide precursor. To this, a photocatalyst titanium oxide aqueous dispersion "STS
Then, 8 g of -01 "(manufactured by Ishihara Techno Co., Ltd.) was added to obtain a coating solution.
pm), dried at 100 ° C., and irradiated with 3 ultraviolet rays at an irradiation distance of 10 cm using a Toshiba germicidal lamp “GL4” as a light source.
Irradiated for 0 minutes. By FT-IR measurement of the coating film after irradiation,
Absorption peaks derived from organic components (3000-2800cm-1 and 120
0-1000 cm-1) has disappeared.

Comparative Example 2 The same operation as in Example 3 was carried out except that no ultraviolet ray was irradiated. In the FT-IR measurement of the coating film, it was confirmed that absorption peaks (3000-2800 cm-1 and 1200-1000 cm-1) derived from organic components were present.

Example 4 Ethanol 100 was placed in a reaction vessel equipped with a thermometer and a stirrer.
g, glycerin 26 g, tetraisopropoxy tin 50
g was added and stirred for 30 minutes. There, 14 g of 28% ammonia water was added, and after stirring for 30 minutes, 500 g of water was further added. After continuing stirring for 1 hour, ethanol, isopropyl alcohol and ammonia were removed by distillation under reduced pressure to obtain an aqueous dispersion of a titanium oxide precursor. To this, 3 g of an aqueous dispersion of photocatalyst titanium oxide "STS-21" (manufactured by Ishihara Techno Co., Ltd.) was added to obtain a coating liquid. The coating solution was applied to a glass plate with a spin coater (2000 rpm), dried at 100 ° C., and irradiated with ultraviolet light for 30 minutes at an irradiation distance of 10 cm using a Toshiba germicidal lamp “GL4” as a light source. F of coating film after irradiation
By T-IR measurement, the absorption peak derived from the organic component (3000
-2800 cm-1 and 1200-1000 cm-1) were confirmed to have disappeared.

Comparative Example 3 The same operation as in Example 4 was carried out except that no ultraviolet ray was irradiated. In the FT-IR measurement of the coating film, it was confirmed that absorption peaks (3000-2800 cm-1 and 1200-1000 cm-1) derived from organic components were present.

[0033]

According to the present invention, the use of a coating liquid containing a metal oxide precursor and a substance having photocatalytic activity enables low-temperature processing and continuous processing, and also allows the selection of the shape and material of the base material. It is possible to provide a metal oxide thin film and a method for producing a metal thin film that are broad and particularly excellent in affinity with an organic polymer material surface.

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Claims (7)

[Claims] 1. A coating liquid for forming a metal oxide thin film, comprising a metal oxide precursor and a substance having photocatalytic activity. 2. The coating liquid for forming a metal oxide thin film according to claim 1, wherein the metal oxide precursor has an organic structure in the molecule. 3. The metal oxide thin film according to claim 1, wherein the metal oxide precursor is produced by hydrolyzing and condensing a hydrolyzable metal compound in the presence of a polyhydric alcohol. Coating liquid. 4. A metal oxide precursor having a temperature of 200 ° C. to 600 ° C.
2. The coating liquid for forming a metal oxide thin film according to claim 1, wherein a weight loss rate by heating at 5 [deg.] C. is 5% or more. 5. The coating liquid for forming a metal oxide thin film according to claim 1, wherein the metal oxide precursor has photocatalytic activity. 6. A method for producing a metal oxide thin film, which is produced by applying the coating liquid for forming a metal oxide thin film according to claim 1 to a substrate and then irradiating the substrate with light. 7. A metal oxide thin film produced by the method for producing a coating film according to claim 6, comprising a metal oxide as a main component.