JPS5935991B2 - Corrosion prevention treatment method for metal surfaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for anticorrosion treatment of metal surfaces.

Corrosion prevention methods for the surface of metal substrates can be roughly classified industrially into methods of metal plating the metal substrate to be treated and methods of painting the metal substrate to be treated.

Among these metal plating methods, zinc plating is relatively often used, so to explain this example, in order to improve the corrosion resistance of the plated surface after galvanizing, chromate treatment is further applied. is customary. However, there is a concern that the waste liquid discharged from chromate chemical conversion treatment may cause pollution problems.
Research has been conducted to develop a treatment method that can replace chromate treatment, but an effective treatment method has not yet been found. On the other hand, in a metal coating treatment method, in order to improve the adhesion of the coating, it has become common industrially to form a phosphate film on the surface of the metal substrate to be treated as a pretreatment step. However, phosphate coatings have the disadvantage that they are inferior to chromate coatings in terms of corrosion resistance, and painting them is generally time-consuming and depending on the intended use of the HL product, some metal parts may be unsuitable for painting. be. The present inventors have conducted intensive research to form a chemical conversion film with good corrosion resistance on the surface of a metal substrate using a treatment agent that does not cause pollution and a simple treatment method, and as a result, the present invention has been achieved.

That is, the present invention includes a primary treatment in which a metal substrate to be treated is immersed in an acidic solution prepared by adding nitric acid or a nitrate to an aqueous solution of a water-soluble metal salt containing or not containing a silicic acid compound, and then washed with water; This is a method for anticorrosion treatment of a metal surface, which comprises a secondary treatment in which the obtained metal substrate is immersed in a silicic acid colloid or silicic acid compound aqueous solution and then dried without washing with water. In the present invention, steel plates, zinc plates, galvanized plates, tin-lead alloy plates, etc. are used as the metal substrates, and water-soluble metal salts for the primary treatment of these substrates include iron, aluminum, zinc, nickel, cobalt, etc. Metal sulfates, nitrates, phosphates, fluorides or organic acid salts are used, each at a concentration of 10 to 200 f.
t/ι, and when using industrial nitric acid with a concentration of 62%, it is 2 to 20 cc/4! , the added ray treatment solution should be acidic, preferably with a pH of 4 or less.

When adding a silicate compound to this primary treatment liquid, add sodium silicate, potassium silicate, lithium silicate, etc. to a concentration of 3 to 50 ft/t. Preferably the pH is 4 or less.
Note that adding an appropriate amount of malonic acid to the primary treatment solution has the advantage of slightly improving corrosion resistance.Next, the silicic acid colloid solution used in the secondary treatment is 10 to 300 ft/ι, and the silicic acid compound is 10-200ft of acid soda, potassium silicate, lithium silicate, ethyl silicate, etc.
/ι is used.

In carrying out the present invention, the metal substrate whose surface has been cleaned is immersed in the primary treatment liquid at room temperature for 5 seconds or more, and then taken out L-1.
Leave it in the air for 0 seconds or more and then wash it with water.

Next, the primary treated metal substrate is immersed in the secondary treatment solution at room temperature for 5 seconds or more, then taken out and washed at a temperature of 50~50°C to speed up drying without washing.
Dry with hot air at 200℃. Although the formation mechanism and composition of the chemical conversion film in the present invention are not clear, metal oxides, hydroxides, and other water-soluble metal salts are formed on the surface of the metal substrate by the primary treatment, and these are converted into silicic acid colloids or by the secondary treatment. It is presumed that it is fixed to the metal substrate surface by silicate. According to the present invention, a chemical conversion coating that is stable and has excellent corrosion resistance can be formed on the surface of a metal substrate through a simple treatment. In particular, when a silicate compound is added to the primary treatment solution, the chemical conversion coating can be formed on the surface of a metal substrate. Stability and corrosion resistance can be further improved.

In the examples shown below, the corrosion resistance test for the film formed on the product was conducted using the salt spray test method specified in JIS Z-2371, and the comparison was made based on the number of hours until the area of rust on the metal surface to be treated reached a factor of 10 of the total surface area. I judged it. In addition, when the metal substrate to be chemically treated was iron, red rust was evaluated, and when the metal substrate was galvanized, white rust was evaluated. Example 1 Primary treatment: Degreased and cleaned iron plate was heated with 25 tons of aluminum sulfate.
The sample was immersed in an aqueous solution containing 10 cc of 62% monosulfuric acid/5 t of 4-malonic acid/I for 15 seconds at room temperature, left in the air for 60 seconds, and then washed with water.

Secondary treatment: 10'-% of the chemical iron plate obtained in the secondary treatment
- It was immersed in a No. 3 sodium silicate aqueous solution for 60 seconds at room temperature and then dried with hot air for 10 minutes without washing with water. When the corrosion resistance of the obtained product was tested, it took 6 hours for the incidence of red rust to reach 10q1I. In addition, in the above primary treatment,
When the same amount of stannous sulfate, cobalt sulfate, or zinc sulfate was used as a substitute for aluminum sulfate o, and other conditions were kept the same, a product with almost the same effect as above was obtained. Example 2 Primary treatment: A degreased and cleaned iron plate was immersed in an aqueous solution containing aluminum sulfate 50 ft/m, 62% mononitric acid 10 cc/lithium musilicate 5 ft/ι and malonic acid 5 ft/ι for 30 seconds at room temperature, and then left in air for 60 seconds. , then washed with water.

Secondary treatment: 110% of the chemical iron plate obtained by secondary treatment
After being immersed in No. 1 sodium silicate aqueous solution for 60 seconds at room temperature, it was dried with hot air for 10 minutes without washing with water.

When the corrosion resistance of the obtained product was tested, it took 9 hours for the incidence of red rust to reach 10%.

- Example 3 Primary treatment: A cleaned galvanized steel sheet was immersed in an aqueous solution of 50 ft/m of zinc nitrate and 10 CC/t of 62% mononitric acid at room temperature for 15 seconds, left in the air for 60 seconds, and then washed with water.

Secondary treatment: The chemically galvanized steel sheet obtained by the secondary treatment was immersed in a 10% monoethylsilicate alcohol aqueous solution for 60 seconds at room temperature, and then dried with hot air for 10 minutes without washing with water.

When the corrosion resistance of the obtained product was tested, it took 98 hours for the incidence of white rust to reach 10%.

Example 4 Primary treatment: A cleaned galvanized steel sheet was immersed for 15 seconds at room temperature in an aqueous solution containing 50 ft/mu of ferrous sulfate, 2 CC/t of 62% mononitric acid, 2 t of ammonium nitrate/5'/ι of sodium musilicate, and then immersed in air at room temperature. It was left in the water for 60 seconds and then washed with water.

Secondary treatment: The chemically galvanized steel sheet obtained by the secondary treatment was immersed in a 10% No. 3 sodium silicate aqueous solution for 60 seconds at room temperature, and then dried with hot air for 10 minutes without washing with water.

When the corrosion resistance of the obtained product was tested, it took 145 hours for the incidence of white rust to reach 10%.

Example 5 Primary treatment: A galvanized steel plate is immersed in 0.5% mononitric acid, and after activation, nickel sulfate is added at 20t/m6.
It was immersed in an aqueous solution containing 4 cc of 2%-HNO3/Musnotex 0 (manufactured by Nissan Chemical, silicate colloid) 50 V1 at 25° C. for 20 seconds, left in the air for 90 seconds, and then washed with water.

Secondary treatment: The chemically treated galvanized steel sheet obtained by the secondary treatment is immersed in an aqueous solution containing 200ff/ι of Snowtex 20 (manufactured by Nissan Chemical, silicate colloid) at 25°C for 30 seconds, and then heated to 100°C without rinsing with water. It was dried with hot air for 5 minutes.

Treatment effect: - When a corrosion resistance test was conducted on the product obtained through the secondary treatment and the secondary treatment, it took 102 hours for the white rust growth rate to reach 10%.

Furthermore, if the same amount of aluminum sulfate, stannous sulfate, cobalt sulfate, or zinc sulfate is used as a substitute for nickel sulfate in the above primary treatment, and the other conditions are the same, a product with almost the same effect as above can be obtained. It was done. As a comparative example, when a corrosion resistance test was conducted on a degreased and cleaned iron plate, the incidence of red rust was 10% within one hour.

Claims (1)

[Scope of Claims] 1. A primary treatment in which the metal substrate to be treated is immersed in an acidic solution prepared by adding nitric acid or nitrate to an aqueous solution of a water-soluble metal salt, and then washed with water, and the metal substrate obtained in the primary treatment is treated with a silicate colloid. 1. A method for anticorrosion treatment of metal surfaces, comprising a secondary treatment of immersing the metal in a solution or an aqueous silicate compound solution and then drying without rinsing with water. 2. A primary treatment in which the metal substrate to be treated is immersed in an acidic solution containing nitric acid or a nitrate added to an aqueous solution containing a water-soluble metal salt and a silicate compound, and then washed with water, and a silicate colloid is applied to the metal substrate obtained in the primary treatment. 1. A method for anticorrosion treatment of metal surfaces, comprising a secondary treatment of immersing the metal in a solution or an aqueous silicate compound solution and then drying without rinsing with water.