JPS6026155B2 - Method of forming corrosion-resistant film - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of forming a novel corrosion-resistant coating.

Specifically, it is a method in which a sodium silicate solution on the surface of a protective substrate is reacted with a key acid or an acidic metal salt solution to form a corrosion-resistant film made of silicon dioxide on the surface of the protective substrate. The film formed by the method of the present invention has excellent acid resistance, heat resistance, and weather resistance. Conventionally, various methods have been adopted for forming films for the purpose of corrosion prevention or rust prevention.

Typical examples include the electrical corrosion protection method, the environmental isolation method, and the paint method. From another perspective, there are two methods of film formation: one using an organic coating and the other using an inorganic coating. However, although the former is beautiful and effective for a short time after the coating is formed, it generally reduces its mechanical strength due to oxidation due to oxygen, deterioration due to moisture, the action of corrosive gases or liquids, the influence of temperature, etc., and causes peeling of the coating film. There are few that can withstand long-term use because they may become damaged or partially damaged. Furthermore, although an alkali silicate coating is known as a typical inorganic coating, it cannot be said to be fully satisfactory in terms of acid resistance, heat resistance, and weather resistance. The present inventor has conducted repeated research on a method for forming a film that is simple and inexpensive and has acid resistance, heat resistance, and toughness resistance, and is stable over a long period of time.

As a result, they discovered that by decomposing a specific sodium silicate solution on the surface of a protective substrate with hydrogen acid or an acidic metal salt solution, a delicate and strong film was formed on the surface of the substrate, and the present invention was completed. I ended up letting it happen. In the present invention, after applying a sodium silicate solution having a molar ratio of Si02/Na20 of 3.0 to 4.5 on the surface of a protective substrate, a sodium silicate solution and a mineral salt solution are then applied. This is a method for forming a corrosion-resistant film in which a film made of silicon dioxide is formed on the surface of the protective substrate by reacting with an acid and/or an acidic metal salt solution.

In addition, the present invention provides a method for reacting the key acid and/or acidic metal salt solution with the sodium silicate solution using a compound selected from the group consisting of alkali metal sulfates, magnesium sulfate, aluminum hydroxide, aluminum oxide, silica-containing substances, and hydrated silicic acid. A preferred embodiment of the method is also provided in which a silicon dioxide film is rapidly formed by the presence of at least one decomposition regulating additive. The protective substrate to which the present invention can be applied is not particularly limited, as long as it can form a dense silicon dioxide film on the surface of the substrate.

In general, metal materials widely used as industrial materials, such as iron, nickel, aluminum, titanium, etc., are most effectively applied. In addition to metal materials, synthetic resin materials, wood, etc. can also be used, but wood is water permeable during the reaction, making it difficult to form a uniform film, and the effectiveness of the formed film cannot be expected for a sufficiently long period of time. In such cases, it is preferable to apply the present invention after applying a known coating such as an organic coating or paint treatment. The sodium silicate solution used in the present invention is generally used as an aqueous solution, and its properties are such that the molar ratio of Si02/Na20 is 3.
It is preferable to select from the range of 0 to 4.5. The Si02/
If the molar ratio of Na20 is less than 3.0, the reaction rate is low and it is difficult to carry out the reaction industrially.On the other hand, if it exceeds 4.5, the sodium silicate itself may become unstable and a good film may not be formed. So I don't like it. Therefore, if the Si02/Na20 molar ratio of the sodium silicate solution to be used is outside the above range, it is preferable to adjust the molar ratio in advance using known means.

For example, if the molar ratio is less than 3.0, Si02,
A means for adjusting the molar ratio by mixing silicate clay or the like and heating and melting the mixture, or a means for adjusting the molar ratio by mixing and melting NaOH when the molar ratio is larger than 4.5 may be used. The concentration of the sodium silicate IJum solution used is not particularly limited as long as the sodium silicate remains liquid under the reaction conditions.
Generally 1 to 10% by weight in terms of Si02, preferably 3 to 10% by weight
A range of 6% by weight is best used.

As the mineral acid used in the present invention, sulfuric acid, hydrochloric acid, nitric acid, etc., which are known to decompose sodium silicate and produce silicon dioxide, can be used without particular limitation.

Among these, sulfuric acid and hydrochloric acid are favorably used in industrial scale implementation from the viewpoint of both workability and reactivity. Further, in the present invention, an acidic metal salt solution can be used as a decomposing agent for sodium silicate in addition to the above-mentioned mineral acid.

The acidic metal salt solution is not particularly limited as long as it has the ability to decompose sodium silicate, and any known solution can be used, that is, one whose aqueous solution exhibits acidity, but generally it is a solution containing dissolved alkali acid phosphate, aluminum sulfate, etc. Aqueous solutions exhibiting acidity can be used satisfactorily. When using only these acidic metal salt solutions as a decomposing agent for sodium silicate, it is necessary to use a large amount of energy depending on the amount of sodium silicate used.
In such a case, the mineral acid and acidic metal salt solution may be used together. In the present invention, the reaction between sodium oxalate and stannic acid can be carried out as long as the reaction is carried out by sequentially applying stannic acid and/or an acidic metal salt solution to the surface of the protective substrate. The reaction conditions of Kosanku can be adopted.

However, since the specificity of the silicon dioxide film obtained may vary depending on the reaction conditions, it is preferable to determine the reaction conditions in advance as necessary. Examples of reaction conditions that are generally well employed are 25 to 120°C, preferably 60°C.
It is best to apply hydric acid to the reaction solution under heating at a temperature of 12 pi or less and under normal pressure or increased pressure so that the bait of the reaction solution is in the range of 3 to 7, preferably 3.5 to 5.0. . It is necessary to adjust the thickness of the film depending on the usage environment of the film protection base material of the present invention, and when using it under harsh conditions, it is even better to divide the film formation treatment into several times. Forms a strong film with superior properties. Furthermore, in the practice of the present invention, electrolyte substances such as sodium sulfate, sodium chloride, or sodium nitrate are produced as by-products in the reaction between sodium oxalate and halogen acid, and these electrolyte substances have the effect of promoting the production of silicon dioxide. This is a factor that makes the present invention advantageous. Therefore, it is also a good means to make these electrolyte substances exist in advance, if necessary. Generally, sodium silicate is originally a stable substance, but it tends to become unstable when certain impurities are mixed in.

The present invention also provides a technique for rapidly forming a deposited film of silicon dioxide by effectively utilizing this property and providing a specific additive. The decomposition control aids used in the present invention are alkali metal sulfates such as sodium sulfate and potassium sulfate; magnesium sulfate; aluminum hydroxide; aluminum oxide; silica-containing substances such as clay and silica sand, or hydrated silicic acid.

Among these, sodium sulfate and hydrated silicic acid are components produced by the reaction of sodium silicate and hydrogenated acid depending on the type of key acid used, but they are more effective if they are present in advance during the reaction. In addition, metal carbonates and chlorides generally exist as substances that destabilize sodium silicate, but when these are used, gaseous substances are generated by reaction, and this gas becomes a source of damage to the silicon dioxide film, causing the coating film to deteriorate. cannot be used in the present invention because it cannot be made dense. The amount of decomposition aid used in the present invention is not particularly limited and may be used appropriately as necessary, but if used in large amounts it may cause uneven coating film formation, so in general, sodium silicate is used. It is preferable to select from the range of 1 to 3% by weight, preferably 5 to 2% by weight. Generally, the mineral acid and/or acidic metal salt solution used in the reaction of the present invention may be applied in an amount sufficient to decompose the sodium silicate used, as in the above-mentioned range. If the substances remain, the strength of the formed film will decrease.

Therefore, in general, an amount slightly larger than the theoretically necessary amount of acid to decompose sodium silicate is used, and the pH of the reaction solution after the reaction is completed.
It is preferable to set H to such an extent that it exhibits acidity. After the reaction of forming a silicon dioxide film on the surface of the protective substrate is completed, moisture is dried to form a film with excellent acid resistance, chemical resistance, and weather resistance.

The drying may be carried out naturally or by heating, if necessary. EXAMPLES In order to explain the present invention more specifically, Examples and Comparative Examples will be described below, but the present invention is not limited to these Examples.

Example 1 A 5% by weight aqueous solution of sodium silicate with a Si02/Na20 molar ratio of 3.21 was added to 15 ml of an aqueous solution with a Na20 equivalent concentration of 5% by weight. ×50
The material was applied to four skin stainless steel (BUS27) material test combs and treated as follows.

A: 48 at room temperature (2000) after applying sodium silicate solution
Dry for an hour.

B: After applying the sodium silicate solution, it was dried at 100° C. for 2 hours.

C: After applying the sodium silicate solution, it was dried at 100°C for 2 hours, then 5% sulfuric acid was applied with a brush and left for 10 minutes, then washed with water and dried at room temperature (20q0) for 2 hours.

D: After coating the sodium silicate solution, the pH of the coating solution is 3.
．． 5% sulfuric acid was added so that the value was 5 to 4 and maintained at 9000.

When the pH of the coating solution started to decrease from 3.5 to 4.0, the addition of sulfuric acid was stopped and the solution was dried at room temperature (20 qo) for 2 hours. The test combs of A to ○ were suspended in the dilute sulfuric acid solution of solution 2 and left for 7 hours. In A and B, rust developed after several hours, and rust was deposited on the entire surface after 7 hours. After 7 hours of heating, rust appeared on almost the entire surface of C. However, the Nagaza D test bar did not rust at all and remained in the same condition as the original. Example 2 The same treatment was carried out as in Example 1 except that hydrochloric acid and phosphoric acid were used instead of sulfuric acid in the treatment of test group D.

After drying, the same test as in Example 1 was carried out, and as a result, no rust developed even after 7 hours. Example 3 The same treatment as in Example 1 Test Birch D was carried out except that the SiQ/Na20 molar ratio of the sodium silicate solution in Example 1 was changed as shown in Table 1.

The same test as in Example 1 was conducted on the dried test birch, and the results are shown in Table 1. Table 1 M. 1 and earth. 6 shows the results for a test bar that was subjected to the same treatment for comparison. Table 1 Example 4 Example 1 The same treatment as in Example 1 was carried out except that an acidic sodium phosphate solution was used instead of sulfuric acid in the treatment of test comb D. As a result, 7 young There was no rust even after hours.

Example 5 Si02/Na20 molar ratio 3.2, Na20 equivalent concentration 4
% sodium silicate dilute solution, 1.0 part of aluminum sulfate (AI2(S04)3) is mixed with respect to 100 parts of the solution, and further hydrated silicic acid (Tokuyama Soda trade name: Tokusil N)
R) was mixed at 10% with respect to sodium silicate.

This melting agent was applied to an iron rod measuring 15 sides x 5 ribs. The coating solution was maintained at 100 oo and a dilute sulfuric acid solution was added so that the pH became 3 to 4.5, and when the pH started to become lower than 3.0, the addition of the sulfuric acid solution was stopped. Thereafter, it was dried at 100° C. for 2 hours to obtain a film-forming test bar. The film-forming test rod was subjected to the same test as in Example 1, and as a result, no specular formation was observed even after 7 hours. Example 6 The same treatment as in Example 5 was carried out except that the substances shown in Table 2 were used in place of the hydrated silicic acid in Example 5, and aluminum sulfate was not mixed at all.

The results were as shown in Table 2. Table 2 Example 7 SiQ/N is also ○ Sodium silicate with a molar ratio of 3.21 100
The same hydrous silicic acid used in Example 5 was added to CC and melted in an autoclave to obtain a molar ratio of sodium silicate.

Using this solution, the same treatment as for the test bar ○ in Example 1 was performed. Further, as a result of conducting the same test as in Example 1, no rust was observed. Example 8 Aluminum-coated iron bamboo (15 fences ◇ x 50 ribs) was prepared with a Si02/Na20 molar ratio of 3.3 and a Na20 equivalent of 5 (
% by weight sodium silicate solution.

Claims (1)

[Claims] 1 After applying a sodium silicate solution with a molar ratio of SiO_2/Na_2O of 3.0 to 4.5 on the surface of the protective base material, a mineral acid and/or an acidic metal salt solution is applied, and the sodium silicate solution and the mineral acid and/or A method for forming a corrosion-resistant film, which comprises reacting with an acidic metal salt solution to form a film similar to silicon dioxide on the surface of the protective substrate.