JPH0688780B2 - Aluminum oxide precursor gel and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precursor gel-like material for producing a transparent aluminum oxide thin film which can be stored for a long period of time and a method for producing the same.

[0002]

2. Description of the Related Art Aluminum oxide thin films have been used for various purposes as heat-resistant, chemical-resistant and wear-resistant protective films. The transparent thin film is used as a non-reflective film and an infrared transmitting film. As a method of manufacturing this aluminum oxide thin film, a method of applying a solution containing a metal alkoxide to a molded article to form an oxide thin film is proposed because of its advantages such as high productivity and low device cost. .

However, since the aluminum alkoxide hydrolyzes very rapidly, the stability of the solution against water and moisture is poor, and as shown in the following formula, it is easily hydrolyzed to form aluminum hydroxide and precipitate. To do.

[0004]

Embedded image Al (OR ′) ₃ + 3H ₂ O → Al (OH) ₃ + 3R′OH (1)

Therefore, it was difficult to obtain a uniform and transparent coating layer when the solution was coated. Therefore, by strictly controlling the moisture at the time of application or by substituting the alkoxy group of the alkoxide with a chelating agent such as acetylacetone, hydrolysis is remarkably suppressed to prepare a transparent sol solution, and the solution is stabilized. A method was proposed.

However, since the thin film formed by using this solution is not sufficiently hydrolyzed, it contains a large amount of unreacted alkoxy groups and chelates substituted with alkoxy groups and is heated to form an oxide thin film. If you get, pinholes and cracks that occur due to the decomposition of those groups,
There is a problem that a dense film cannot be formed.

Further, even if the hydrolysis is suppressed by the above method, the solution containing the aluminum alkoxide having an unreacted alkoxy group is hydrolyzed if left in the atmosphere for a long time. The result is a change in the viscosity of the solution and the formation of a precipitate. Therefore, in order to store this solution for a long period of time, there is a problem that a solution storage device whose atmosphere is controlled is necessary.

[0008]

The problem to be solved by the present invention is that the aluminum oxide precursor for preparing a transparent thin film prepared from an aluminum alkoxide is not stable in moisture, and moreover, it is difficult to form an oxide thin film. At this time, a large amount of residual organic matter that causes pinholes and cracks is present in the precursor. Furthermore, another problem to be solved is that the aluminum oxide precursor prepared by the conventional method has a large amount of unreacted alkoxy groups, and thus lacks stability and cannot be stored for a long period of time. is there.

[0009]

As means for solving the above problems, in the present invention, by reacting an aluminum alkoxide with a carboxylic acid and substituting a part of the alkoxy group of the alkoxide with an OCOR group, The rate of hydrolysis is controlled and the slow hydrolysis-polycondensation of the compound, as represented by the formula below, results in a precipitation product from formula (1) above due to fast hydrolysis if not controlled. Is a completely different, non-reacted alkoxy group-free Al-O-Al bond-containing transparent aluminum oxide-based precursor polymer gel.

[0010]

[Chemical 2]

By using the solid polymer gel-like material, it was possible to achieve the object of obtaining an aluminum oxide precursor which is extremely stable against moisture in the air for a long period of time.
Further, the solution in which this gel-like material is dissolved is also very stable, and by applying this solution, the purpose of obtaining a transparent aluminum oxide thin film with almost no residual organic matter was realized.

[0012]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to Examples.

[0013]

Example 1 0.5 m of aluminum i-propoxide
It was dissolved in i-butyl alcohol so as to be ol / liter and refluxed. While stirring this solution in a beaker, acetic acid (acetic acid / aluminum alkoxide = 1.5
[Mol ratio]) and water (water / aluminum alkoxide =
0.5 [mol ratio]) of the mixed solution was added dropwise, and then stirring was continued for 1 hour. The beaker was sealed with a film and allowed to stand. By the reaction of acetic acid and the alkoxy group of the alkoxide and hydrolysis-polycondensation, a polymer having an OCOCH ₃ group in the side chain and having an Al-O-Al bond as the main chain is formed,
The viscosity of the solution rapidly increased with time, and after mixing, it gelled while remaining transparent within a few hours to obtain an aluminum oxide precursor gel. When the beaker containing this gel-like material was left as it was, the gel-like material did not change at all even after 3 months.

[0014]

Example 2 0.5 m of aluminum i-propoxide
It was dissolved in n-butyl alcohol so as to be ol / liter and refluxed. While stirring this solution in a beaker, acetic acid (acetic acid / aluminum alkoxide = 2 [m
ol ratio]) and water (water / aluminum alkoxide = 1)
The [mol ratio]) mixed solution was added dropwise and stirred. The reaction of acetic acid with the alkoxy group of the alkoxide, and further by hydrolysis-polycondensation, has an OCOCH ₃ group in the side chain,
A polymer having an —O—Al bond as the main chain was formed, the viscosity of the solution rapidly increased, and gelled within 30 minutes after mixing.
The transparent aluminum oxide precursor polymer had no change in transparency even in the air, and no precipitation was observed.

[0015]

Example 3 A gelled product was prepared under the same conditions as in Example 1 except that n-butyric acid was used as the carboxylic acid instead of acetic acid. Even after the mixed solution of n-butyric acid and water was added dropwise to the alkoxide solution, the solution was transparent. After several weeks, the solution gelled, and a transparent aluminum oxide precursor gel was obtained. When the number of carbon atoms in the carboxylic acid is increased, hydrolysis is further suppressed, resulting in a longer gelation time. However, the transparency was the same as when acetic acid was used, and no precipitation was observed.

[0016]

[Reference Example] Using the transparent aluminum oxide precursor gels obtained in Examples 1 and 2, i-butyl alcohol: gel was weighed to be 2: 1 [weight ratio],
The gel material was mixed with i-butyl alcohol. And
The gel was completely dissolved by heating at 70 ° C or lower.
These solutions are applied on a glass substrate, and the temperature is kept at 500 ° C and 8
By heat treatment at 00 ° C., a transparent and dense aluminum oxide thin film was obtained. The crystal phase of the thin film obtained at 500 ° C. was γ-aluminum oxide, and the crystal phase of the thin film obtained at 800 ° C. was α-aluminum oxide. Also,
When the solution thus prepared was left in the atmosphere for 6 months, no change in viscosity or change in precipitation was observed.

[0017]

INDUSTRIAL APPLICABILITY As described in the above examples, in the present invention, the addition of carboxylic acid suppresses the hydrolysis, and a sufficient hydrolysis-polycondensation is slowly carried out, whereby the aluminum alkoxide of By suppressing the formation of aluminum hydroxide precipitate due to fast hydrolysis, forming a transparent aluminum oxide precursor gel-like material having an Al-O-Al network and containing almost no unreacted alkoxy groups, it has been impossible to achieve conventional methods. It has become possible to store the precursor, which was not affected by atmospheric moisture, stably for a long period of time. Further, as described in Reference Example, by dissolving the gel-like material of the present invention in an organic solvent, it is possible to easily obtain a highly stable solution for producing a transparent thin film, which was difficult by the conventional method. It has become possible. Furthermore, by applying this solution to a molded product and baking it, a dense and transparent aluminum oxide thin film, which was difficult due to the effect of residual organic substances, was obtained from the conventional thin film forming solution. This greatly expands the application as an optical material.

Claims (3)

[Claims] 1. A polymer having an Al-O-Al bond as a main chain and having an OCOR group (wherein R represents a linear or branched alkyl group having 1 to 4 carbon atoms) in a side chain. ,
Transparent aluminum oxide precursor gel. 2. Al (OR ′) ₃ and RCOOH (wherein R ′ represents a linear or branched alkyl group having 2 to 5 carbon atoms) and water are mixed and reacted in an organic solvent. The method for producing an aluminum oxide precursor gel-like product according to claim 1, which is characterized by the above-mentioned. 3. The method according to claim 2, wherein the organic solvent is an alcohol having 1 to 5 carbon atoms.