JP3251755B2 - Alumina precursor solution, method for forming alumina thin film using the solution, and alumina thin film formed body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina precursor solution, a method for forming an alumina thin film using the same, and an alumina thin film formed body. Alumina precursor solution capable of efficiently forming an alumina thin film having excellent surface smoothness, high adhesion strength to a substrate, and little deterioration over time, method of forming alumina thin film using the same, and formation of alumina thin film About the body.

[0002]

2. Description of the Related Art In recent years, various studies using metal alkoxides as raw materials have been actively made. This is because metal alkoxides can be easily purified by recrystallization or distillation,
This is because it can be used as a pure starting material, and in the case of a multi-component system, it has several features such as the ability to achieve homogenization at the molecular level in the starting solution. In addition to such high purity and high homogeneity, it also has the characteristic that a dense target product can be obtained at low temperature, so it can be used in various fields such as high-temperature superconductors, ceramics for catalyst carriers, multi-component glass, etc. Applied research is being conducted. On the other hand, the field of thin film formation by dip coating is not an exception, and the use of metal alkoxide as a raw material is being studied.

[0003] By the way, the ceramic film forming technique by dip coating belongs to a chemical film forming method like a spin coating method, in contrast to a physical film forming method such as sputtering, CVD or vacuum evaporation. Things. Among these several chemical film forming methods,
The dip coating method has the advantages that the coating operation is relatively simple, a thin film having a uniform surface and good adhesion is obtained, a large-sized and complicated shape can be coated, and the film can be formed relatively inexpensively. Therefore, taking advantage of these advantages, application to antioxidant films and cutting tools, protective films and electrodes for semiconductors and magnetic materials, electrodes, surface devices, magnetic heads, infrared sensors, Josephson devices, etc., or application research has recently been actively pursued. Has been done.

[0004] In general, a method for preparing a solution used for the dip coating includes, when a metal alkoxide is used as a raw material, a method in which an alkoxide is added to a large amount of water, hydrolyzed, and then dispersed with an acid to obtain a sol; Starting from an alcohol solution of an alkoxide, the method is roughly divided into a method of preparing an alumina precursor solution by hydrolysis and polymerization of a compound in the solution.

In the former method, the properties of the sol obtained vary depending on the type and amount of acid added, and it is important to understand the conditions. Further, for example, when preparing an alumina sol, it is necessary to control the temperature of the water to be hydrolyzed, control the pH, and remove generated alcohol and acid. Heretofore, as the alumina-based dip coating solution for the purpose of forming a film, a solution obtained by diluting a sol obtained by this method with water and alcohol has been generally used.

However, an acid remains in the film obtained by such a dip coating solution due to the production method. Since the acid contains anions such as chloride ion and nitrate ion, there is a possibility that the film is deteriorated due to long-term exposure to ultraviolet rays, and there is a problem in the stability of the film.

On the other hand, in the latter alcohol-based method, in order to prepare a stable solution even after hydrolysis and obtain uniformity of a film obtained by dip coating, hydrolysis of alkoxide is suppressed during sol preparation. For this purpose, a method of adding a stabilizer such as glycols is generally used. When the sol thus prepared is used for film formation, it is considered to increase the viscosity of the solution in order to increase the thickness of the film formed on the substrate. However, with respect to the viscosity of the solution, the range of conditions for obtaining a stable solution is generally narrow when film forming conditions are considered, and thus the film thickness obtained by one film forming is limited. For this reason, there was a problem that dip coating had to be repeated to increase the film thickness.

Further, the conventional substrate for dip coating is limited to glass, and it has been difficult to apply the substrate to other substrates such as stainless steel and resin.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an alumina thin film which has excellent compactness and film surface smoothness, high adhesion strength to a substrate, and little deterioration with time, regardless of the substrate. It is an object of the present invention to provide an alumina precursor solution capable of efficiently forming an alumina film and a method for forming an alumina thin film using the same.

[0010]

Means for Solving the Problems In view of such circumstances, the present inventors have conducted intensive studies and have found that a reaction product of an aluminum alkoxide and water with a β-keto acid compound or a glycol ether compound contains a thickener and a thickener. The present inventors have found that the above-mentioned various problems can be solved by using a composition to which a coupling agent is added, and have completed the present invention.

That is, the present invention provides an alumina precursor containing (A) a reaction product of an aluminum alkoxide with water and a β-keto acid compound or a glycol ether compound, (B) a thickener, and (C) a coupling agent. It provides a solution. The present invention also provides a method for forming an alumina thin film, which is characterized by dip-coating a substrate using the alumina precursor solution, and an alumina thin film formed body obtained by the method.

In order to prepare the reactant (A) used in the alumina precursor solution of the present invention, first, (1) aluminum alkoxide, (2) β-keto acid compound or glycol ether compound and if necessary (3) Prepare a mixture of alcohols.

The aluminum alkoxide used here includes, for example, aluminum ethoxide, aluminum propoxide, aluminum isopropoxide, aluminum butoxide, aluminum isobutoxide,
1-6 carbon atoms such as aluminum secondary butoxide
And various aluminum alkoxides of the above alkyl group.

Examples of the β-keto acid compound include alkanoyl acetates having 5 to 16 carbon atoms in total, and specifically, acetoacetate such as methyl acetoacetate, ethyl acetoacetate and butyl acetoacetate. No. Examples of the glycol ether compound include a monoether, diether or monoether alkanoate of a glycol having 2 to 6 carbon atoms.
-Methoxyethanol (ethylene glycol monomethyl ether), 2-ethoxyethanol (ethylene glycol monoethyl ether), 2-isopropoxyethanol (ethylene glycol monoisopropyl ether), 1-acetoxy-2-methoxyethanol (ethylene glycol monomethyl ether acetate) , 1-
Acetoxy-2-butoxyethanol (ethylene glycol monobutyl ether acetate) and the like can be mentioned.
The β-keto acid compound or glycol ether compound is preferably added in an equimolar amount or more, particularly 2 to 10 times by mole, with respect to the concentration of the aluminum alkoxide in order to suppress gelation of the aluminum alkoxide during the hydrolysis reaction. .

The alcohol is blended for the purpose of dissolving the mixed liquid having the above structure. For example, when 2-methoxyethanol or the like is used as the glycol ether compound, the alcohol itself has a dissolving effect. As such, the addition of alcohol is not necessary unless there is another purpose. Except for such cases, the dissolution of the mixed liquid
An alcohol is added. At this time, it is particularly preferable to use an alcohol having 4 or less carbon atoms. This is to prevent the boiling point from increasing with an increase in the number of carbon atoms. That is, as the boiling point rises, in the drying and heat treatment steps of the substrate after coating, there is a concern that cracks may occur in the thin film due to the evaporation of alcohol.

Next, water is added to the above mixed solution to cause a reaction. Water is added for hydrolysis, and it is preferable to add water in a molar amount of 1/2 to 3 times the aluminum alkoxide in order to maintain the stability of the solution. The hydrolysis reaction should be at least 3 to promote sufficient reaction.
The reaction is preferably performed for 0 minutes or more. Further, the heating reaction for the purpose of accelerating the reaction between the aluminum alkoxide and the β-keto acid compound or glycol ether compound is preferably performed by heating at 75 ° C. or more and refluxing for 60 minutes or more.

The reaction in these series of operations is as follows. First, water reacts with the alkoxyl group of the aluminum alkoxide. This reacts with the β-keto acid compound or glycol ether compound to form an alkoxide precursor. This is a dip coating solution that is hardly hydrolyzed by atmospheric moisture and stable for a long period of time.

The thickener (B) is added mainly for the purpose of improving the strength of the alumina thin film. It is considered that the improvement of the strength of the thin film is caused by entanglement between the alkoxide precursors, that is, by exhibiting an entangled structure such as a network structure at the time of gelation. In addition, since such a structure is exhibited, cracks due to evaporation of a solvent, which often occur in the heat treatment of the substrate after coating, can be suppressed, and as a result, the strength of the thin film is maintained. The thickener (B) is also effective for improving the thickness of a single coating. That is, there is a limit to the film thickness obtained by one film formation. Therefore, in order to increase the film thickness, dip coating generally has to be repeated. Here, several factors are related to the film growth, and one of the factors having a large influence is the viscosity of the solution. That is, if the viscosity of the solution increases, the thickness of the film formed on the substrate can be increased. The thickener has the effect of increasing the viscosity of the solution, and therefore, improves the film thickness in one coating. As such a thickener, various types can be used, and for example, a cellulose compound such as hydroxypropylcellulose or polyethylene glycol is preferable. In addition, it is preferable to add these thickeners in the range of 0.1 to 1.0% by weight based on the reactant (A). If the thickener is added in an amount exceeding 1% by weight, gelation may occur, which is not preferable.

The purpose of adding the coupling agent (C) is to improve the strength of the formed film and the adhesion to the substrate. The addition of the coupling agent (C) improves the strength of the film because the silicon or titanium contained in the coupling agent (C) reacts with the aluminum precursor in the film to partially improve A.
It is considered that the region of l-O-Si or Al-O-Ti bond is formed, so that the strength of the film can be increased. The addition of the coupling agent (C) is also effective in increasing the water repellency of the formed thin film. As the coupling agent (C) to be added, various types can be used. In particular, a silane coupling agent and a titanate coupling agent are used to improve the strength of the film and the adhesion between the film and the substrate. It is effective. Here, as the silane coupling agent, a vinyl type, an epoxy type, and an amino type can be used. As the titanate-based coupling agent, amine-based,
Carboxylic acid type, acrylic type, phenyl type and the like can be used. Specifically, examples of the silane coupling agent include vinyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane. As a titanate coupling agent, isopropyl tri (N-
(Aminoethyl-aminoethyl) titanate, isopropyl triisostearoyl titanate, isopropyl trioctanoyl titanate, isopropyl isostearyl diacryl titanate, isopropyl tricumylphenyl titanate, and the like. The amount of the coupling agent (C) to be added is 0.1-1.
It is preferably 0% by weight. 1% by weight
If it exceeds, gelation may occur, which is not preferable.

As described above, a solution (alumina precursor solution) obtained by adding a thickener and a coupling agent to the reactant (A) (alkoxide precursor solution) is used as a dip coating agent to form a film. , Excellent film strength,
In addition, an alumina thin film having a large thickness can be obtained. In particular, the compounding of the thickener and the coupling agent can enhance the adhesion of the thin film to be formed to the substrate, and dip coating on stainless steel and resin, which has been considered difficult, has become possible. . In particular, dip coating on polyethylene or polyethylene terephthalate resin has been almost impossible in the past, but the present invention has made it possible to form a strong alumina thin film on such a resin. Was.

Dip coating using the composition of the present invention may be carried out according to a conventional method. For example, a substrate may be dipped in the composition of the present invention and then heat-treated for 0.5 to 2 hours. The heating temperature varies depending on the base material, and is 200 to 600 ° C. for metal, 200 to 600 ° C. for glass, and 80 to 130 for resin.
C is preferred. The above operation may be repeated as necessary to obtain a desired film thickness.

[0022]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.
Hereinafter, "%" indicates% by weight.

Example 1 0.1 mol / l of aluminum isopropoxide (purity: 99.9%) was added to 1 l of isopropanol and water (0.1%).
1 mol / l) and ethyl acetoacetate (0.3 mol / l)
And dissolved under reflux at 80 ° C. for 2 hours. To this, hydroxypropyl cellulose and isopropyl tri (N-aminoethyl-aminoethyl) titanate were added at 0.2% each, and reacted for 1 hour to obtain an alumina precursor solution.

A stainless steel (SUS-30) was added to this solution.
4) Dip-coated on heat-resistant glass and resin (polyethylene, polyethylene terephthalate, acrylic). The heat treatment temperature was 500 ° C. for stainless steel and heat resistant glass, and 100 to 120 ° C. for resin. The heat treatment was performed for 1 hour, and the coating was performed 1 to 5 times.

As a result of observing the state of the film after film formation, no cracks or the like were observed in any of the substrates, and it was confirmed that the film was sound.

When the thickness of the alumina film in one coating was measured, the thickness was about 0.1 μm for stainless steel and heat-resistant glass, and the thickness increased in proportion to the number of coatings. 0.5 μm. on the other hand,
In the case of the resin, the thickness was 0.05 μm each time, and an alumina film of about 0.3 μm was formed by five coatings.
The strength of each film was 61.78 Hv in Vickers hardness in the case of a heat-resistant glass substrate.

Subsequently, the obtained alumina film was irradiated with a 500 W xenon lamp, and the deterioration time of the film was examined. At this time, the experimental conditions were as follows: a temperature of 25 ° C., an irradiation distance of the xenon lamp of 15 cm, a light intensity of 1.9 mW / cm ² , of the xenon lamp irradiation light, light having a wavelength of 300 nm or less was cut by Pyrex glass, and the light energy was The distribution can be approximated to sunlight. As a result of conducting a continuous irradiation experiment for three months under the above conditions, cracks and the like did not occur at all in any of the films, indicating soundness.

Comparative Example 1 0.1 mol / l of aluminum isopropoxide (purity: 99.9%) was added to 1 l of isopropanol and water (0.1%).
1 mol / l) and ethyl acetoacetate (0.3 mol / l).
1) and dissolved under reflux at 80 ° C. for 2 hours.
This was further reacted for 1 hour to obtain an alkoxide precursor solution.

The solution was made of stainless steel (SUS-30).
4) Dip-coated on heat-resistant glass and resin (polyethylene, polyethylene terephthalate, acrylic). The heat treatment temperature was 500 ° C. for stainless steel and heat resistant glass, and 100 to 120 ° C. for resin. The heat treatment was performed for 1 hour, and the coating was performed 1 to 5 times.

As a result of observing the state of the film after film formation, a good thin film was formed on the heat-resistant glass in appearance, but cracks and peeling were observed in the alumina film with respect to stainless steel and any resin. Was. In particular, the resin was only partially formed, and a remarkable crack was also observed in the portion where the film was formed.

When the thickness of the alumina film in one coating was measured, the thickness was about 0.05 μm for stainless steel and heat-resistant glass, and the thickness increased in proportion to the number of coatings. 0.3 μm. On the other hand, in the case of the resin, as a result of measurement at the portion where the film is formed, the result was 0.01 to 0.03 μm at one time, and an alumina film of about 0.1 to 0.2 μm was formed by five coatings. . As for the strength of the film, in the case of a heat-resistant glass substrate, the Vickers hardness was 28.94 Hv, which was only 30% or more of that of Example 1.

Subsequently, an irradiation experiment using a xenon lamp similar to that in Example 1 was performed. Here, only the heat resistant glass on which a relatively good film was formed was subjected to the test. As a result, 1
By continuous irradiation for months, the film having an area ratio of 50% or more was peeled off, and cracks were found in the remaining film.

Example 2 0.1 mol / l of aluminum isopropoxide (purity: 99.9%) was dispersed in 1 l of 2-methoxyethanol and water (0.1 mol / l), and the mixture was dispersed at 80 ° C. for 2 hours. Dissolved at reflux. To this, hydroxypropylcellulose and isopropyl tri (N-aminoethyl-aminoethyl) titanate were added in an amount of 0.2%, respectively, and reacted for 1 hour to obtain an alumina precursor solution.

A stainless steel (SUS-30) was added to this solution.
4) Dip-coated on heat-resistant glass and resin (polyethylene, polyethylene terephthalate, acrylic). The heat treatment temperature was 500 ° C. for stainless steel and heat resistant glass, and 100 to 120 ° C. for resin. The heat treatment time was 1 hour, and the coating was performed up to 1 to 5 times.

As a result of observing the state of the film after film formation, no cracks or the like were observed in any of the substrates, and it was confirmed that the film was sound.

When the thickness of the alumina film in one coating was measured, the thickness was about 0.2 μm for stainless steel and heat-resistant glass, and the thickness increased in proportion to the number of coatings. 0.0 μm. on the other hand,
In the case of resin, the thickness was 0.1 μm each time, and an alumina film of about 0.6 μm was formed by five coatings. The strength of each film was 80.64 Hv in Vickers hardness in the case of a heat-resistant glass substrate.

Subsequently, an irradiation experiment using a xenon lamp similar to that in Example 1 was performed. As a result, as in Example 1, even after continuous irradiation for three months, each film almost maintained the initial state, and it was recognized that the film was sound.

Comparative Example 2 0.1 mol / l of aluminum isopropoxide (purity: 99.9%) was dispersed in 1 liter of 2-methoxyethanol and water (0.1 mol / l), and the mixture was dispersed at 80 ° C. for 2 hours. Dissolved at reflux. The mixture was further reacted for 1 hour to obtain an alkoxide precursor solution.

The solution was made of stainless steel (SUS-30).
4) Dip-coated on heat-resistant glass and resin (polyethylene, polyethylene terephthalate, acrylic). The heat treatment temperature was 500 ° C. for stainless steel and heat resistant glass, and 100 to 120 ° C. for resin. The heat treatment was performed for 1 hour, and the coating was performed 1 to 5 times.

As a result of observing the state of the film after film formation, good film formation on heat-resistant glass was confirmed, but cracks and peeling were observed in stainless steel and any resin. In particular, the resin was only partially formed, and a remarkable crack was also observed in the portion where the film was formed.

When the thickness of the alumina film in one coating was measured, the thickness was about 0.1 μm for stainless steel and heat-resistant glass, and the thickness increased in proportion to the number of coatings. 0.5 μm. on the other hand,
As for the resin, as a result of measurement at the portion where the film was formed, each time it was about 0.05 μm, and an alumina film of about 0.2 to 0.3 μm was formed by five coatings. In the case of a heat-resistant glass substrate, the film strength was 24.85 Hv in Vickers hardness, which was significantly lower than that in Example 2.

Subsequently, an irradiation experiment using a xenon lamp similar to that in Example 1 was performed. Here, only the heat resistant glass on which a relatively good film was formed was subjected to the test. As a result, 1
By continuous irradiation for months, 70% or more of the film in the area ratio was peeled off, and cracks were found in the remaining film.

Example 3 0.1 mol / l of aluminum isopropoxide (purity: 99.9%) was added to 1 l of isopropanol, ethyl acetoacetate (0.3 mol / l) and water (0.1 mol / l).
And dissolved under reflux at 80 ° C. for 2 hours. To this, polyethylene glycol and γ-glycidoxypropyltrimethoxysilane were each added in an amount of 0.2%, and reacted for 1 hour to obtain an alkoxide precursor solution.

A stainless steel (SUS-30) was added to this solution.
4) Dip-coated on heat-resistant glass and resin (polyethylene, polyethylene terephthalate, acrylic). The heat treatment temperature was 500 ° C. for stainless steel and heat resistant glass, and 100 to 120 ° C. for resin. The heat treatment time was 1 hour, and the coating was performed up to 1 to 5 times.

As a result of observing the state of the film after film formation, no crack or the like was observed at all for any of the substrates, and it was confirmed that the film was sound.

When the thickness of the alumina film in one coating was measured, the thickness was about 0.2 μm for stainless steel and heat-resistant glass, and the thickness increased in proportion to the number of coatings. 0.0 μm. on the other hand,
In the case of resin, the thickness was 0.1 μm each time, and an alumina film of about 0.5 μm was formed by five coatings. In the case of a heat-resistant glass substrate, the strength of each film was 70.04 Hv in Vickers hardness.

Subsequently, an irradiation experiment using a xenon lamp similar to that in Example 1 was performed. As a result, as in Example 1, even after continuous irradiation for three months, each film almost maintained the initial state, and it was recognized that the film was sound.

As is clear from the above results, it is understood that a film having good properties can be formed by the thin film forming method of the present invention using the alumina precursor solution of the present invention.

[0049]

By using the alumina precursor solution of the present invention, it is possible to efficiently form an alumina thin film having a high adhesion strength to any substrate, a dense, smooth surface, and stable over time. it can.

Continued on the front page (72) Inventor Norifumi Nagata 2-4-2, Daisaku, Sakura City, Chiba Prefecture Onoda Cement Co., Ltd. Central Research Laboratory (72) Inventor Shinji Iguchi 2-4-2, Daisaku, Sakura City, Chiba Prefecture Onoda Inside the Central Research Institute of Cement Co., Ltd. (72) Masayuki Watanabe 2-4-2 Daisaku, Sakura City, Chiba Pref. Inside the Central Research Laboratory of Onoda Cement Co., Ltd. (56) References JP-A-1-257663 (JP, A) JP-A-5-70122 (JP, A) JP-A-5-247657 (JP, A) JP-A-4-213602 (JP, A) JP-A-1-298017 (JP, A) JP-A-2-254176 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 18/12

Claims (6)

(57) [Claims] 1. An alumina precursor solution containing (A) a reaction product of an aluminum alkoxide, water and a β-keto acid compound or a glycol ether compound, (B) a thickener, and (C) a coupling agent. 2. The alumina precursor solution according to claim 1, wherein the coupling agent (C) is a silane coupling agent or a titanate coupling agent. 3. A method for forming an alumina thin film, comprising dip-coating a substrate using the alumina precursor solution according to claim 1 or 2. 4. The method for forming an alumina thin film according to claim 3, wherein the substrate is metal, glass or resin. 5. An alumina thin film-formed body obtained by dip-coating a substrate using the alumina precursor solution according to claim 1 or 2. 6. The alumina thin film-formed body according to claim 5, wherein the substrate is metal, glass or resin.