JP2003073584A - Water-soluble coating liquid for forming metal oxide thin film and method for producing ceramic coating film using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating liquid having stable viscosity with time and excellent film-forming property, a water-soluble coating liquid for forming a metal oxide thin film to form a ceramic thin film free from cracks and having excellent surface smoothness and translucency by baking a gel film produced by using the coating liquid and a method for producing a ceramic coating film. SOLUTION: The water-soluble coating liquid for forming a metal oxide thin film is at least composed of a water-soluble metal salt and an organic polymer having amide group and dissolved in water. The production method for the ceramic coating film comprises the use of the solution.

Description

Detailed Description of the Invention

[0001]

The present invention can be used in all fields requiring functional ceramic thin films such as optical, electronic, information, chemical, mechanical, medical, etc., and an aqueous solution of a metal salt is used as a coating liquid. To a method for producing a ceramic coating film.

[0002]

2. Description of the Related Art As a method for producing a ceramic thin film, a method of applying a coating liquid to a substrate by dip coating or spin coating and firing the same has been put into practical use in a wide range in recent years. This method is mainly called a sol-gel method, and in many cases, a coating solution is synthesized by using a metal alkoxide as a starting material, a mainly alcoholic solvent, and It is synthesized by dissolving metal alkoxide.

However, this method has a problem in that (1) the coating liquid uses alcohol as a solvent, and (2) the viscosity of the coating liquid increases with time.

(1) Regarding the problem of using alcohol as a solvent The sol-gel method using a metal alkoxide as a starting material is a method in which metal alkoxide is added to a solution by hydrolysis of the metal alkoxide and subsequent condensation reaction. An inorganic polymer having an oxygen-metal bond (metalloxane bond) as a skeleton is formed into a sol, which is used as a coating liquid. Then, a gel coating film containing the same polymer as a main constituent is formed on the surface of the base material by dip coating or spin coating, and is baked to form a ceramic coating film.

By the way, the metal alkoxide is hydrophobic and immiscible with water. Therefore, in order to allow the hydrolysis reaction to proceed uniformly in the solution without causing precipitation in the solution during the hydrolysis process, it is necessary to use an alcohol miscible with both the metal alkoxide and water as the solvent. That is, it can be said that the sol-gel method using a metal alkoxide as a starting material is a method for producing a ceramic coating film using an alcohol solution of a metal alkoxide as a raw material.

Alcohol is highly volatile and, because it is an organic compound, highly flammable. Alcohols other than ethanol are also harmful to health. Therefore, in carrying out the sol-gel method at the manufacturing site, it is not preferable to use alcohol as a solvent in terms of safety and health management.

On the other hand, water is a non-flammable and unscented substance. Therefore, it has been strongly desired on the manufacturing side to change the solvent of the coating liquid that can be used in the sol-gel method from alcohol to water. However, as described above, since the metal alkoxide and water are immiscible with each other, it has been considered in principle impossible to change the solvent of the coating liquid from alcohol to water.

The sol-gel method starting from a water-soluble metal salt such as a metal nitrate instead of a metal alkoxide has not been proposed so far. However, water is a substance with an exceptionally high surface tension,
It has extremely poor wettability to substrates such as glass, ceramics, and metals. Therefore, a coating solution obtained by simply dissolving a metal salt in water will be repelled even if it is applied to the substrate, forming a firing precursor film. I can't. For this reason,
In order to secure wettability and film-forming property, addition of alcohol such as ethylene glycol has been indispensable until now.

(2) The problem that the viscosity of the coating solution increases with time When a metal alkoxide is used as a starting material, hydrolysis and condensation reactions proceed in the solution, so that an inorganic polymer is formed. Keep growing Therefore, the viscosity of the coating liquid increases with time. Since the thickness of the gel film applied by dip coating or spin coating increases as the viscosity of the coating liquid increases, it is difficult to use one coating liquid for a long time. Therefore, it has been desired to develop a coating liquid that does not change its viscosity with time. Specifically, there are techniques described in the following documents.

(1) H, Kozuka and M, Kajimura, J, AmCer
am.soc, 83, 1056 (2000). (Kotsuka) This reference describes that one coating operation is performed by a sol-gel method using a metal alkoxide / metal acetate dropping solution containing polypinylpyrrolidone. It has been reported that a crack-free BaTiO ₃ thin film having a thickness of 0.2 μm can be prepared. However, in this method, alcohol is used as a solvent, and the viscosity of the sol rapidly increases with time, and the sol gels in a few hours, which makes practical application difficult.

<2) Toshio Tsuchiya, Atsushi Koizumi, Journal of the Ceramic Society of Japan, 98 (9), 1011 (199)
0). In this document, tin (II) chloride and antimony (III) chloride were dissolved in diethylene glycol in the presence of hydrochloric acid to prepare a coating solution, and an antimony-doped tin oxide thin film was prepared on a quartz glass substrate by dip coating. Diethylene glycol is a kind of alcohol, and using it as a solvent was indispensable for film formation.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a coating liquid having a small change in viscosity with time and having a good film-forming property.
By firing a gel film produced by using this as a coating liquid, a ceramic thin film having a metal oxide thin film for forming a ceramic thin film having no cracks, excellent surface smoothness, and translucency can be obtained. A method of manufacturing a membrane is provided.

[0013]

That is, the above object is achieved by the following constitution of the present invention. (1) A water-soluble coating solution for forming a metal oxide thin film, wherein at least a water-soluble metal salt and an organic polymer having an amide group are dissolved in water. (2) The water-soluble metal salt is a water-soluble coating for forming a metal oxide thin film according to (1), which is one or more of lead sulfate, nitrate, oxychloride, carboxylate, and halide. liquid. (3) The organic polymer having an amide group is one or more of polyacrylamide, polyvinylacetamide, and polyvinylpyrrolidone. The water-soluble coating for forming a metal oxide thin film according to (1) or (2) above. liquid. (4) A method for producing a ceramic coating film, wherein the water-soluble coating liquid for forming a metal oxide thin film according to any one of (1) to (3) above is applied onto a substrate and fired to obtain a ceramic coating film.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The water-soluble coating solution for forming a metal oxide thin film of the present invention is one in which a water-soluble metal salt and an organic polymer having an amide group are dissolved in water.

By coating such a coating solution on a substrate and baking (heat treatment), it is possible to easily obtain a ceramic coating film having no cracks, excellent surface smoothness and translucency. .

As the ceramic coating film obtained with the coating liquid of the present invention, there is no crack in the coating film and surface smoothness and translucency can be obtained.
It is particularly effective to use it for a ceramic oxide dielectric film.

For example, Al ₂ O ₃ , MgO, SiO ₂ , Y ₂
O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , TiO ₂ , ZnO, Zr
Single oxides such as O ₂ , BaTiO ₃ , SrTiO ₃ and P
An oxide-based ceramic coating film such as a complex oxide such as b (Zr _1-x Ti _x ) O ₃ can be obtained.

The coating liquid of the present invention does not contain alcohol as a solvent. That is, it does not contain a component having both volatility and flammability. Further, since the inorganic polymer is not produced by the hydrolysis / condensation reaction of the metal alkoxide, the viscosity of these coating solutions does not change with time.

The water-soluble metal salt used in the coating liquid is
The material is not particularly limited as long as it is water-soluble, and a material containing necessary components may be selected and used depending on the ceramic coating film to be formed. Specifically, sulfate, nitrate, oxychloride, or acetate,
Examples thereof include carboxylic acid salts such as ammonium lactate and halides such as chlorides and iodides.
These may be used alone or in combination of two or more. When a plurality of types are used, the mixing ratio is arbitrary.

For example, when forming an Al ₂ O ₃ film, aluminum bromide hexahydrate, aluminum oxychloride nonahydrate, aluminum hydroxide chloride dihydrate, aluminum iodide hexahydrate, aluminum lactate , Aluminum nitrate 9
A hydrate, aluminum sulfate, etc. are mentioned.

When forming a Y ₂ O ₃ film, yttrium bromide, yttrium chloride, yttrium nitrate hexahydrate,
Examples thereof include yttrium nitrate octahydrate.

Niobium bromide (V) can be used when forming the Nb ₂ O ₅ film, and tantalum fluoride (V) can be used when forming the Ta ₂ O ₅ film.

When forming the ZnO film, zinc acetate dihydrate, zinc oxychloride, zinc chloride, zinc formate dihydrate, zinc iodide, zinc nitrate, zinc sulfate and the like can be mentioned.

When forming the SiO ₂ film, silicon fluoride,
It is possible to use silicon tetrachloride, silicon acetate, etc.
Examples of the gO film include magnesium bromide, magnesium oxychloride hexahydrate, magnesium chloride, magnesium iodide, magnesium nitrate, magnesium sulfate and the like.

When forming a TiO ₂ film, (C
_{H 3 CH (O) CO 2} NH 4) 2 Ti (OH) 2, Ti
(SO ₄ ) ₂ and TiCl ₄ are preferably used, and ZrO ₂
When forming a film, ZrCl ₂ O can be used.

Further, when forming the composite oxide thin film, a plurality of metal salts may be used.

For example, when forming a BaTiO ₃ thin film,
Ba (CH ₃ COO) ₂ may be used as the Ba source, and the metal salt of Ti used for forming the TiO ₂ film may be used as the Ti source.

Similarly, as the Sr source for forming the SrTiO ₃ thin film, strontium halides such as strontium oxychloride, strontium chloride, strontium bromide, strontium fluoride and strontium iodide, and strontium nitrate and strontium hydroxide. Can be used, and the metal salt of Ti used for forming the TiO ₂ film can be used as the Ti source.

Further, PbTiO ₃ and Pb (Zr _1-x T
i _x) when forming a thin film of O _3, etc., as Pb source, lead acetate, lead citrate trihydrate, lactic lead, lead carboxylate or lead bromide such as formate salts of lead, lead chloride, oxy Using lead chloride etc.,
As the Ti and Zr sources, the metal sources used to form the TiO ₂ and ZrO ₂ films may be used.

Also, in the case of a superconducting composite oxide such as YBa ₂ Cu ₃ O _7-x, copper (II) sulfate, copper (II) nitrate, copper (II) chloride, copper bromide (II) is used as a Cu source. ), Copper oxydide (I
I) hexahydrate, copper (II) acetate monohydrate, copper (II) formate
The above-mentioned substances may be used as the Y and Ba sources by using copper carboxylates and the like.

The metal salt concentration in the aqueous solution is preferably in the range of 10 ^-2 to 10 ¹ mol / L in total of metal salts.

The organic polymer added to the solution is not particularly limited as long as it has an amide group and is water-soluble. Specifically, polyacrylamide, polyvinylacetamide, polyvinylpyrrolidone, etc. can be mentioned. These may be used alone or in combination of two or more. When a plurality of types are used, the mixing ratio is arbitrary.

By having an amide group in the organic polymer,
A coordination bond is formed between the amide group and the metal atom, a polymer complex is formed in the solution, and the formation of this polymer complex improves the film forming property.

The total amount of the organic polymer to be added is preferably in the range of 0.1 to 4 in terms of molar ratio with respect to the metal element in terms of monomer.

The metal salt and the organic polymer are dissolved in water to obtain a coating liquid. The liquid temperature at the time of adjusting the coating liquid is preferably in the range of 10 to 100 ° C.

Unlike the coating solution containing a metal alkoxide, the coating solution of the present invention uses a water-soluble metal salt as a metal source and contains a water-soluble polymer having an amide group, so that the reaction proceeds in the solution. It is possible to maintain the viscosity during adjustment over a long period of time. Specifically, it can be stored for 100 hours or more, particularly 1000 hours or more, and can withstand long-time transportation and storage, which can greatly contribute to improvement in productivity and cost reduction.

The prepared coating liquid is applied onto a base material to form a gel coating film. The coating liquid can be applied to the substrate by a method such as dipping, spinning, spraying, or laminar coating.

The obtained gel coating film is baked (heat treated) to form a ceramic coating film.

The temperature during firing (heat treatment) is preferably 500 to 1000 ° C., and particularly 600 to 900 ° C. The atmosphere during firing may be air or an oxidizing atmosphere such as oxygen. The firing time is usually 5 minutes to 10 hours, particularly about 10 minutes to 30 minutes.

If it is desired to make the fired film dense, heat treatment may be performed before the main firing in the cases such as the above. The temperature during such heat treatment is preferably 1
The temperature is from 00 to 400 ° C, especially from 300 to 400 ° C. The atmosphere during heat treatment may be the same as that during firing.
The treatment time is usually 5 min to 8 hours, especially 10 to 6
It is about 0 min.

The coating liquid of the present invention has low flammability because it does not contain a solvent such as highly flammable alcohol, and is more safe than conventional coating liquids containing alcohol. For this reason, for example, the solution is sprayed on a substrate heated to 300 ° C. or higher, or is supplied onto the substrate in the form of an aerosol formed by using an ultrasonic atomizing method, and at the same time as coating, the coating film is baked or baked. It can be more safely used in the so-called spray pyrolysis method in which the previous heat treatment is performed.

The sol-gel film obtained by the coating liquid of the present invention has a sufficient film thickness. Specifically 0.0
A film having a thickness of 5 μm or more, particularly 0.1 μm or more can be obtained. Moreover, the obtained film is dense and has no cracks.

The oxide thin film of the present invention can be used for various purposes. Specifically, it can be used for applications that require a high dielectric constant and high refractive index and a film thickness on the order of sub μm to μm. That is, an electronic device using a high dielectric or ferroelectric thin film or a thick film, for example, a laminated ceramic capacitor, a hybrid IC circuit, a composite LC network circuit, a capacitor dielectric layer formation of a ceramic LCR built-in multilayer substrate, or a thin film EL. It can be used as a dielectric layer of an element, and is also preferably used in a field requiring a thin plate of piezoelectric ceramics such as a piezoelectric layer for a small actuator, a piezoelectric speaker, and a pyroelectric body of a pyroelectric sensor.

Further, since it is possible to form a dense and crack-free film, it is possible to have a good light-transmitting property, and it can be used as an optical thin film, for example, as a film usually used as an antireflection film, an infrared reflection film or a transmission film. It is also effective to apply to light emitting devices and displays. Further, it can be easily applied to the formation of an oxide conductive film or a transparent conductive film.

[0045]

EXAMPLES Example 1 Preparation of a TiO ₂ coating solution from an aqueous solution containing titanium sulfate and polyvinylpyrrolidone.

As shown in Table 1, 40 g of an aqueous solution of titanium sulfate (manufactured by Wako Pure Chemical Industries, containing 30 wt% of Ti (SO ₄ ) _{2 and} containing 13 wt% of sulfuric acid) at room temperature, polyvinylpyrrolidone (manufactured by Tokyo Kasei Co., average Molecular weight 10,000) 2.78g
Then, a solution containing 20.8 g of water was prepared as a coating solution.

[0047]

[Table 1]

Using this coating solution, the substrate was pulled up at a speed of 3 cm / min by dip coating to a thickness of 1.
A gel coating film was prepared on a 2 mm quartz glass substrate, and this was applied at 100 ° C for 10 minutes and then at 700 ° C for 10 minutes.
TiO with a film thickness of 0.1 μm by heat treatment at min
_{2 A} ceramic coating film was obtained.

An SEM photograph of the obtained coating film is shown in FIG. 1, a visible ultraviolet absorption spectrum is shown in FIG. 2, and an X-ray diffraction pattern is shown in FIG. As shown in the SEM photograph of FIG. 1, the fired film had a dense cross section and a smooth surface, and as seen in the visible ultraviolet absorption spectrum of FIG. 2, the fired film showed good visible light transmittance. . As seen in the X-ray diffraction pattern of FIG. 3, the rutile phase and the anatase phase were mixed in the baked film.

[0050] Example 2 Preparation of TlO ₂ coating liquid from the water溶汲containing titanium sulfate and poly pin sulfonyl acetamide.

As shown in Table 1, at room temperature, 41.5 g of an aqueous solution of titanium sulfate (manufactured by Wako Pure Chemical Industries, containing 30 wt% of Ti (SO ₄ ) _{2 and} containing 13 wt% of sulfuric acid), an aqueous solution of polyvinylacetamide (Showa Denko KK) GE-191LL, containing 40 wt% polyvinylacetamide, average molecular weight 30,000
0) Prepare a melted night consisting of 11.0 g and 68.0 g of water,
It was coating night.

Using this coating solution, a gel coating film was prepared on a glass substrate in the same manner as in Example 1,
Heat treatment was performed to obtain a TiO ₂ ceramic coating film having a thickness of 0.07 μm.

The visible-ultraviolet absorption spectrum of the coating film thus obtained is shown in FIG. 2, and the X-ray diffraction pattern thereof is shown in FIG. The fired film had a smooth surface and exhibited good visible light transmittance as seen in the visible ultraviolet absorption spectrum of FIG. Moreover, it was found from the X-ray diffraction pattern of FIG. 3 that the fired film was composed of a rutile phase.

Example 3 Preparation of a TiO ₂ coating film from an aqueous solution containing titanium tetrachloride and polyvinylpyrrolidone.

As shown in Table 1, an aqueous titanium chloride solution (manufactured by Wako Pure Chemical Industries, containing 16 to 17 wt% of Ti, C
11.52 wt%) 14.52 g, polyvinylpyrrolidone (Tokyo Kasei Co., Ltd., average molecular weight 10,000) 2.78 g
A solution of 40.6 g of water was prepared as a coating solution.

Using this coating solution, a gel coating film was prepared on a glass substrate in the same manner as in Example 1,
This was heat-treated at 700 ° C. for 10 minutes to obtain a TiO ₂ ceramic coating film having a film thickness of 0.1 μm. As seen in the visible-ultraviolet absorption spectrum shown in FIG. 4, the baked film exhibited good visible light transmittance.

Example 4 Preparation of a ZrO ₂ coating film from an aqueous solution containing zirconium oxychloride and polyvinyl hyrrolidone.

As shown in Table 1, 16.1 g of zirconium oxychloride octahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) at room temperature,
Polyvinylpyrrolidone (Tokyo Kasei Co., average molecular weight 1
50,000) 7.1 g and water 50.0 g to prepare a coating solution.

Using this coating solution, a gel coating film was prepared on a glass substrate in the same manner as in Example 1,
By heat treatment, a ZrO ₂ ceramic coating film having a film thickness of 0.08 μm was obtained.

The visible-ultraviolet absorption spectrum and the X-ray diffraction pattern of the obtained coating film are shown in FIG. 2 and FIG. 3, respectively. The fired film had a smooth surface and exhibited good visible light transmittance as seen in the visible ultraviolet absorption spectrum of FIG. In addition, a cubic zirconia phase (and an orthorhombic zirconia phase) and a monoclinic zirconia phase were found in the X-ray diffraction pattern of the fired film shown in FIG.

Example 5 Preparation of a ZrO ₂ coating film from an aqueous solution containing zirconium oxychloride and polyacrylamide.

As shown in Table 1, 16.1 g of zirconium oxychloride octahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) at room temperature,
Aqueous polyacrylamide solution (manufactured by Aldrich, containing 50 wt% of polyacrylamide, average molecular weight 10,000)
A solution consisting of 7.1 g and 43.8 g of water was prepared as a coating solution.

Using this coating solution, a gel coating film was prepared on a glass substrate in the same manner as in Example 1,
By heat treatment, a ZrO ₂ ceramic coating film having a thickness of 0.09 μm was obtained.

The visible-ultraviolet absorption spectrum and the X-ray diffraction pattern of the obtained coating film are shown in FIG. 2 and FIG. 3, respectively. The fired film has a dense cross section and a smooth surface.
As shown in the visible-ultraviolet absorption spectrum of FIG. 2, it showed good visible light transmittance. A cubic zirconia phase (and an orthorhombic zirconia phase) was found in the X-ray diffraction pattern of the fired film shown in FIG.

Example 6 Ba from an aqueous solution containing titanium bisammonium lactate and polyvinylpyrrolidone
Preparation of TiO ₃ coating film.

As shown in Table 1, at room temperature, an aqueous solution of titanium bisammonium lactate dihydroxide (Titanium bisammonium lactate dihydroxide 50 manufactured by Aldrich) was used.
wt%) 24.77 g, polyvinylpyrrolidone (Tokyo Kasei Co., Ltd., average molecular weight 10,000) 2.341 g, barium acetate 10.757 g, and water 2.973 g to prepare a coating solution.

Using this coating solution, a gel coating film was prepared on a glass substrate in the same manner as in Example 1,
By heat-treating this at 700 ° C for 10 minutes,
A transparent BaTiO ₃ ceramic coating film having a thickness of 0.35 μm was obtained.

The X-ray diffraction pattern of the obtained coating film is shown in FIG. As seen in this X-ray diffraction pattern, the fired film was a BaTiO ₃ single phase.

[0069]

As described above, according to the present invention, a coating liquid having a small change in viscosity with time and having a good film-forming property, and a gel film produced by using the coating liquid as a coating liquid are fired without cracks. It is possible to provide a water-soluble coating liquid for forming a metal oxide thin film and a method for producing a ceramic coating film, which is capable of obtaining a ceramic thin film having excellent surface smoothness and translucency.

[Brief description of drawings]

FIG. 1 is a surface S of a ceramic thin film formed in Example 1.
It is an EM photograph.

FIG. 2 is a diagram showing visible-ultraviolet absorption spectra of the ceramic thin films obtained in Examples 1, 2, 4, and 5.

FIG. 3 is a view showing an X-ray diffraction pattern of the ceramic thin films obtained in Examples 1, 2, 4, and 5.

FIG. 4 is a view showing a visible-ultraviolet absorption spectrum of the ceramic thin film obtained in Example 3.

5 is a diagram showing an X-ray diffraction pattern of the ceramic thin film obtained in Example 6. FIG.

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Claims (4)

[Claims] 1. A water-soluble coating liquid for forming a metal oxide thin film, wherein at least a water-soluble metal salt and an organic polymer having an amide group are dissolved in water. 2. The water-soluble metal salt is lead sulfate, nitrate,
The water-soluble coating liquid for forming a metal oxide thin film according to claim 1, which is one kind or two or more kinds selected from an oxychloride, a carboxylate, and a halide. 3. The water-soluble coating liquid for forming a metal oxide thin film according to claim 1, wherein the organic polymer having an amide group is one or more of polyacrylamide, polyvinylacetamide, and polyvinylpyrrolidone. . 4. A method for producing a ceramic coating film, which comprises applying the water-soluble coating liquid for forming a metal oxide thin film according to any one of claims 1 to 3 on a base material and firing the coating liquid to obtain a ceramic coating film.