JPS5935433B2 - Tin plating method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a completely new method of tin plating.

In recent years, various plating methods have been proposed as the demand for plating powder increases, and among these plating methods, the substitution plating method is widely used because of its ease of operation. The displacement plating method, which is conventionally known as a powder plating method, involves adding a plating metal-containing solution to a mixed powder of a powder to be plated and a metal powder for reduction, or to the mixing process of the mixed powder while stirring the mixed powder. Alternatively, the powder to be plated and the reducing metal powder are added together or separately into a solution containing the plating metal under stirring.

However, in the above-mentioned substitution plating method, the basis of the reaction is to reduce the metal to be plated with metal powder that is less noble, so standard metals such as gold, platinum, palladium, and silver cannot be used. Powder plating for metals with very noble electrode potentials has good reduction efficiency and plating finish, but it is difficult to plate metal powders with base electrode potentials such as zinc, tin, nickel, and cobalt. In some cases, both the reduction efficiency and the plating finish are poor, making it impractical.

However, recently, as a countermeasure for this problem, when plating nickel, cobalt, zinc, etc., chloride crystal powder of the plating metal is added in the process of mixing the object to be plated with powder of a reducing metal such as magnesium or aluminum, or a mixture of both. A plating method has been proposed in which a small amount of water and/or hydrochloric acid is added after the reaction has started.

However, in any of the above-mentioned plating methods, the reducing metal powder must be more base than the plating metal, so the two metals are necessarily different types, and the treatment of the liquid after plating is a problem. becomes.

For example, when tin plating copper powder, if a tin chloride solution is added to a mixture of copper powder and aluminum powder and plating is performed, a solution containing aluminum chloride and tin chloride will be obtained as a solution after Metsusa treatment according to the reaction formula below. .

Cu+Al+SnC12→Cu-Sn-l-AlCl3
+SnCl2, that is, the solution after the plating process cannot be reused as it is as a tin plating solution for copper powder, so its treatment becomes a problem, and there are also drawbacks such as a low reduction rate of tin.

As a result of various studies on powder plating, the present inventors discovered a completely new method different from conventional substitution methods.

That is, the present invention uses metal powder for plating media that is the same as the plating metal (metal powder of the same type as the metal ion component in the plating solution is hereinafter referred to as metal powder for plating media since plating progresses by adding metal powder). The object of the present invention is to provide a completely conventional and advantageous method of tinning using metals such as:

The present invention will be explained in detail below.

The object to be plated in the present invention is an alloy whose main component is a metal whose standard electrode potential is nobler than that of tin, such as lead-zinc, copper-tin, silver-nickel, palladium-tin, gold-cobalt, etc. Not only binary alloys such as platinum-palladium, but also ternary and multi-component alloys can be used.

Furthermore, in addition to the above-mentioned alloys, it also includes those coated with carbonaceous substances, metal carbides, metal oxides, metal sulfides, nitrides, etc. with the above-mentioned alloys. Note that known techniques such as metal thin layer vapor deposition and palladium precipitation can be applied to this coating treatment. There are no particular restrictions on the shape of these objects to be plated, and powders, wires, plates, etc. may be used as appropriate depending on the purpose and use. The particle size of the tin powder used as the metal powder for the plating medium in the present invention can be selected in consideration of the type and size of the object to be plated, and further the thickness of the plated material.

For example, when brass powder with an average particle size of 40 microns is used as the object to be plated, and the plated material is coated with a coating amount of 30% by weight, the appropriate particle size of the tin is approximately several microns.

The amount of tin powder used may be 1.0 to 1.05 times (by weight) the amount required for plating. The aqueous solution containing tin ions used in the present invention is preferably an aqueous solution of hydrochloric acid, sulfuric acid or nitric acid with a pH of 0.2 to 3, and the amount used is such that the amount of tin in the aqueous solution is in excess of the required amount for plating. You may want to adjust it as you see fit.

In the present invention, tin plating is carried out by heating the object to be plated as described above in the presence of an aqueous solution containing tin powder and tin ions. For example, when using powder as the object to be plated, During the process of mixing the tin powder into the plating body or after mixing the tin powder with the plated body, it is preferable to add the above aqueous solution and heat it with stirring in order to uniformly perform the plating reaction.

The plating reaction is completed by adding an aqueous solution containing tin ions and heating for several minutes.

Note that the heating temperature may be about 80 to 100°C. The plating product after the reaction is filtered to remove the liquid and then washed to recover the tin plating powder.

Since the liquid obtained in the above-mentioned filtration is an aqueous solution containing only tin ions as metal 5 metal ions, it can be directly recycled to the plating process and reused. In the tin plating powder obtained as described above according to the present invention, tin is not deposited on the powder to be plated in the form of particles, and a coating having a substantially uniform thickness is formed.

Although the case where the object to be plated has the shape of powder has been described above, the same can be said of the object to be plated which has the shape of a wire or a plate.

However, in the case of a plate, the plate to be plated is immersed in an aqueous solution containing tin ions in which tin powder is suspended before the heat treatment, and in the case of a powder, there is no need to pass through the plate after the reaction is completed. different.
Although the reaction mechanism in the plating method of the present invention is not yet clear, it is presumed that the tin powder is once dissolved during the reaction process, and tin ions in the aqueous solution are precipitated on the surface of the object to be plated.

As described above, according to the present invention, the liquid after the plating process can be directly recycled to the plating process and reused, so the above-mentioned problems found in the conventional method can be solved.

The present invention will be described in more detail below by way of examples.

Example 1 Brass powder (Cu8O%, Zn2O
%) 109, tin powder with an average particle size of several microns, and 200 ml of a tin chloride aqueous solution with a tin concentration of 509/l were charged into a plating tank (PHO.4 of the charging solution), and heated at 90°C for 5 minutes with stirring. Make it react.

The obtained reaction product is separated, washed with dilute sulfuric acid of pH 2 to 3 until the presence of chloride ions is no longer recognized, washed with water, and then dried. As a result, 13.989 tin plating powder was obtained.

This tin-plated powder had the white luster of tin, and when observed under a microscope, it resembled the powder shape of unplated brass powder, and no fine powder that was thought to be tin powder itself was observed. Since the waste liquid obtained by the above-mentioned filtration is an aqueous tin chloride solution, it is circulated to the plating tank and reused for the plating reaction.

Example 2 200wL1 of tin nitrate aqueous solution with a concentration of 2009/L, 5g of tin powder with an average particle size of several micrometers, and a diameter of 2m7 as the object to be plated.
1L length 4mm bronze wire (Cu85%, Snl5(f)
) 20 pieces were placed in a plating tank, heated to 85° C. with stirring, and plated for 5 minutes.

Claims (1)

[Claims] 1. A tin plating method characterized by heat-treating an object to be plated made of an alloy whose main component is a metal nobler than tin in the presence of an aqueous solution containing silver powder and tin ions.