JP2818785B2 - Method of forming silica coating on metal substrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a silica coating on a metal substrate, and more particularly, to a method for forming a uniform silica coating on the surface of a metal substrate such as a stainless steel plate. And a method for coating.

[Prior art and its disadvantages] For the purpose of improving alkali resistance, heat resistance and corrosion resistance of various metal base materials, and controlling electric characteristics, etc.
Research has been conducted to form a silica coating on the surface of a metal substrate. (For example, The Ceramic Society of Japan 97
[1] 91-94, 1989) These methods relate to a technique of coating a metal base material with a glass thin film by a so-called sol-gel method using alkoxysilane as a raw material.
This is a highly practical method from an industrial point of view.

However, when forming a silica coating, it is required that the silica coating has no pinholes, has a uniform thickness over the entire surface, and has high adhesion strength to a metal substrate. It is very difficult to form a film. Therefore, according to the above document, a method is disclosed in which a special type of raw material such as monomethyl-triethoxysilane is used and phosphoric acid is used as a hydrolysis catalyst. It was difficult to obtain an excellent silica coating.

[Problems and Solutions to the Invention] In view of the above-mentioned circumstances, the present inventor utilizes a silica sol obtained by hydrolyzing tetra-lower alkoxysilane, makes it adhere well to the surface of the metal substrate, and forms a pinhole. After extensive investigations on the method of forming a uniform silica thin film without, the amount of water in the mixture when forming the silica sol and the pH in the system at this time have an important effect on the formation of the thin film, In addition, it has been found that the speed of pulling the metal base material from the mixture after the immersion treatment in the silica sol is also important. Then, as a result of continued study based on this finding, it was confirmed that the object of the present invention was achieved by adjusting these conditions to a specific range, and the present invention was completed.

That is, the gist of the present invention is that a tetra-lower alkoxysilane is a mixture of 5 to 40% by volume of a lower aliphatic alcohol and 1 to 30% by volume of water with respect to the alkoxysilane, and the pH of the system is adjusted to hydrochloric acid. The silica sol is formed by adjusting the temperature to 20 to 70 ° C. and adjusting the temperature to 20 to 70 ° C., and then immersing the pre-washed metal substrate in the mixture, and then dipping the metal in the mixture by dipping. The substrate is pulled up perpendicular to the liquid surface at a speed of 0.05 to 10 mm / sec to form a silica film on the surface of the metal substrate, and drying the silica film on the metal substrate. Lies in the method of formation.

 Hereinafter, the present invention will be described in detail.

The tetra-lower alkoxysilane targeted in the present invention has the following general formula (Wherein, R1 to R4 represent the same or different lower alkyl groups), and usually, there are tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane and the like in which R1 to R4 are the same alkyl group. Among them, tetraethoxysilane is preferable.

In the present invention, the alkoxysilane is mixed with a specific amount of a lower aliphatic alcohol and water.Examples of the lower aliphatic alcohol include methanol, ethanol, n-propanol, iso-propanol, n-butanol and mixtures thereof. No. However, it is usually preferable to use an alcohol having the same carbon number as the alkoxy group of the alkoxysilane. For example, when using tetraethoxysilane, ethanol is preferred. The amount of the alcohol used is 5 to the alkoxysilane.
-40% by volume, preferably 10-30% by volume. On the other hand, the amount of water used is 1 to 30% by volume, preferably 5 to 20% by volume, based on the alkoxysilane. Further, the usage ratio of water to the alcohol is usually 30 to 70% by volume, preferably 40 to 60% by volume. In the present invention, the proportions of the alcohol and water used are important, and in any case, a good silica coating cannot be obtained if the amount is more than the above range or less than the above range.

The tetra-lower alkoxysilane mixed with the lower aliphatic alcohol and water is hydrolyzed to produce a silica sol. In the present invention, it is important to adjust the pH at this time to 1 to 3 with hydrochloric acid. If an acid other than hydrochloric acid (for example,
PH adjustment with sulfuric acid, phosphoric acid, etc.)
If the range is out of the above range, it is not possible to obtain silica having excellent adhesion to a metal substrate. In addition, it is required that the above-mentioned water use range is included, including the amount of water added with hydrochloric acid. In addition, the solification temperature is 20 to 70 ° C., preferably 30 to 50 ° C. If this temperature is too low, hydrolysis does not proceed well, while if it is too high, the reaction rate is high and the silica sol becomes unstable. Is not preferred. The time until the completion of the sol formation varies depending on the conditions, but is usually about 0.5 to 3 hours. In the present invention, it is desirable that the concentration of the silica sol in the above mixture is usually in the range of 10 to 20% by weight.

In the present invention, the metal substrate is immersed in a mixed solution containing the silica sol prepared as described above, and a silica coating is formed on the surface thereof by a dipping method. Particularly preferred after 10 to 20 days. Examples of the metal substrate targeted in the present invention include those usually made of metal such as stainless steel, iron plate (cold rolled steel plate), aluminum, and copper. Among them, stainless steel is most preferable. The shape of the metal substrate is not particularly limited, but usually a plate-like material is preferred.

It is necessary to wash and degrease the surface of the metal base material in advance. This washing method usually includes washing with an organic solvent such as benzene, washing with a caustic aqueous solution, acid washing with sulfuric acid or the like, a combination thereof, and water washing. The metal substrate after these washings needs to be sufficiently washed with water in the final step and then dried.

When the metal substrate is immersed in the mixed solution containing silica sol, it is usually preferable that the metal substrate is immersed almost vertically and pulled up almost vertically. The temperature during the immersion process is
Usually, 5 to 40 ° C., and this immersion time is usually 0.25 to
It is 2 hours, preferably 0.5 to 1 hour. If the immersion time is too short, it is not possible to form a uniform silica coating on the surface of the metal substrate, and if it is too long, the quality of the metal substrate surface or, in some cases, the state of silica gel changes, so it is preferable. Absent. By this treatment, the silica sol adheres to the surface of the metal substrate, and a uniform silica coating is formed on the entire surface.

The metal substrate after the immersion treatment is pulled up from the mixed solution, but the pulling speed at this time is important, and in the present invention, 0.05 to 10 mm / sec perpendicular to the liquid surface, preferably 0.1 to 5 mm.
It is necessary to adjust the speed to mm / sec. In short, it is necessary to pull up the silica component uniformly adhered to the surface of the metal substrate while keeping the silica component as it is, and for that purpose, a controlled pulling speed is required.

The raised metal substrate is then, for example, 110-300
By drying at a temperature of ° C., the silica component is completely fixed on the surface of the metal substrate. This drying time is usually
It takes about 10 to 60 minutes.

In this way, a metal substrate having a silica coating formed on the surface can be obtained, and the thickness of the silica coating can be generally adjusted in the range of 0.8 to 2 microns.

[Effect of the Invention] According to the method of the present invention, a silica coating having a uniform thickness without pinholes can be easily formed on the surface of a metal substrate. Further, the adhesion strength of the silica coating to the metal substrate is excellent. Further, in the present invention, a silica film having a small amount of silanol groups (OH groups) is obtained, probably because of the small amount of water used. Therefore, the metal substrate having a silica coating obtained by the present invention is excellent in chemical resistance and peeling resistance, and is highly useful in various fields.

[Examples] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the description of the following examples as long as it does not exceed the gist.

Example 1 A mixture having the following composition was prepared by adjusting the pH of the mixture to 2 with hydrochloric acid. Tetraethoxysilane 5 parts by volume ethanol 1 〃 water 0.5 後 After uniformly mixing the mixture, the mixture was allowed to stand at a temperature of 50 to 60 ° C. Generate silica sol (silica sol concentration
15%), and after 15 days, then the su washed
Vertically immerse all s304 stainless steel plates (30 mm x 20 mm x 0.5 mm) and hold them at a temperature of 25 ° C for 30 minutes.
The stainless plate was pulled up at a speed of sec and dried at a temperature of 170 ° C. for 30 minutes to obtain a stainless plate on which a silica coating was formed.

Analysis of the stainless steel plate with this silica coating using a scanning electron microscope, electron beam microanalyzer, and FT-IR spectrum confirmed that a uniform silica coating without any pinholes was coated on the entire surface of the stainless steel plate. The thickness of the silica coating was measured to be 0.5 μm.

 The stainless plate was washed in the following order.

Wipe with benzene impregnated cloth Wash with benzene Wash with 2% aqueous sodium hydroxide solution Wash with distilled water Wash with 10% sulfuric acid Wash with distilled water Dry (110 ° C x 30 min) Example 2 After mixing this mixture uniformly, the mixture was allowed to stand at a temperature of 50 to 60 ° C. to form a silica sol (silica sol concentration).
15%), and after 15 days, all of the iron plates (cold rolled steel plates) (150 mm × 70 mm × 1 mm) pre-washed were immersed vertically and kept at a temperature of 25 ° C. for 30 minutes. mm /
The iron plate was pulled up at a speed of sec and dried at a temperature of 170 ° C. for 30 minutes to obtain an iron plate on which a silica coating was formed.

As a result of analyzing the iron plate having the silica coating with a scanning electron microscope, an electron beam microanalyzer, and FT-IR spectrum, it was confirmed that a uniform silica coating without any pinholes was coated on the entire surface of the iron plate. When the thickness of the silica coating was measured, it was 0.5 μm.

 The cleaning of the iron plate was performed in the following order.

Cleaning with benzene impregnated cloth Cleaning with benzene Cleaning with 2% aqueous sodium hydroxide solution Cleaning with distilled water Cleaning with 2% sulfuric acid Cleaning with distilled water

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C01B 13/12 C23C 20/08

Claims (1)

(57) [Claims] 1. A tetra-lower alkoxysilane is a mixture of 5 to 40% by volume of a lower aliphatic alcohol and 1 to 30% by volume of water with respect to the alkoxysilane, and the pH of the system is adjusted to 1 with hydrochloric acid. Adjust to ~ 3 and set the temperature to 20
A silica sol is produced by adjusting the temperature to ~ 70 ° C, and then, after immersing the pre-washed metal substrate in the mixture, the metal substrate is dipped into the mixture by a dipping method in a direction perpendicular to the liquid surface by 0.05 d. A method for forming a silica film on a metal substrate, comprising: forming a silica film on the surface of a metal substrate at a speed of about 10 mm / sec; and drying the silica film.