JPS5818992B2 - galvanizing method - Google Patents

Description

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

In recent years, various plating methods have been proposed as the demand for plating powder has increased, and among these, the plating method based on the substitution 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 liquid to a mixed powder of a powder to be plated and a metal powder for reduction, or in the process of mixing these powders, while stirring the mixed powder. Alternatively, the powder to be plated and the reducing metal powder are added together with a stirring knife or separately in a pot into a solution containing plating metal.

However, in the plating method using the above-mentioned substitution method, the basic reaction is to reduce the metal to be plated with metal powder that is less noble.
In powder plating for metals such as Pd and Ag, whose standard electrode potential is extremely sensitive, both reduction efficiency and finish are good, but Z ns S n + N t
*When plating metal powder with a base electrode potential such as Cos, both the reduction efficiency and the plating finish are poor, making it impractical.

Recently, however, as a countermeasure to this problem, metal powders such as Ni and Co have been added to base metals such as Mg, A,! A plating method has been proposed in which chloride crystal powder of the plating metal is added during the process of mixing with the throat-reducing metal powder or to a mixture of the two, and after the reaction has started, a small amount of water and/or hydrochloric acid is added.

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 therefore the treatment of the liquid after plating is a problem. Become.

For example, when plating copper powder with zinc, if a zinc chloride solution is added to a mixture of copper powder and aluminum powder as a reducing metal powder, a solution containing aluminum chloride and zinc chloride will form according to the reaction equation below. It will be obtained as a liquid after plating treatment.

Cu+A! +Zn(J'2-)Cu-Zn+A, IC
, ff 3 + ZnCl2 That is, the above-mentioned plating solution cannot be reused as it is as a zinc plating solution for copper powder, so its treatment becomes a problem and there are drawbacks such as a low reduction rate of zinc.

As a result of various studies regarding galvanizing powder, the inventors of the present invention have discovered a completely new method that is different from conventional substitution methods.

That is, the present invention uses metal powder of the same type as the plating metal as a metal powder for plating medium (because plating progresses by adding metal powder, metal powder of the same type as the metal ion component in the plating solution is referred to as metal powder for plating medium). The object is to provide an entirely new and advantageous galvanizing method for use.

The present invention will be explained in detail below.

The object to be plated in the present invention is a metal that has a higher ionization tendency than zinc, such as Au sAgjPt.
In addition to metals such as s Cu+ Fe and Nip Co, it also includes those pre-coated with metals more harmful than zinc, such as carbonaceous substances, metal carbides, metal oxides, and metal nitrides.

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;
Powder, fiber, plate, etc. are used as appropriate depending on the purpose and use.

The particle size of the zinc 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, as well as the plating thickness thereof.

For example, using copper powder with an average particle size of 40μ as the object to be plated,
When plating 28% by weight on this, the particle size of the zinc is suitably on the order of several microns.

The amount of zinc powder used may be 1.0 to 1.05 times (by weight) the amount required for plating.

The aqueous solution containing zinc ions used in the present invention is preferably a hydrochloric acid, sulfuric acid or nitric acid aqueous solution, such as a zinc chloride aqueous solution, with a pH of 2 to 3. It is best to adjust the amount of zinc so that it is in excess of the required amount of plating.

In the present invention, the object to be plated as described above is galvanized by heat treatment in the presence of an aqueous solution containing zinc powder and zinc ions. For example, when powder is used as the object to be plated, π is It is preferable to add the above aqueous solution during the process of mixing the zinc powder to the plating powder or after mixing the zinc powder to the powder to be plated, and heat it while stirring to uniformly perform the plating reaction.

The plating reaction in the present invention can be completed by adding an aqueous solution containing zinc ions as described above and heating at a temperature of 80° C. to 100° C. for several minutes.

That is, according to the present invention, there is no need for heating at high temperatures to melt the zinc powder applied to the object to be plated, which is required in the prior art.

After the reaction has been completed, the plating product is filtered to remove liquid, and then washed with dilute sulfuric acid to recover galvanized powder.

It should be noted that if this cleaning is performed with hydrochloric acid, a sparingly soluble zinc compound may be generated and the galvanized coating may be destroyed.

Since the liquid obtained by the above-mentioned offshore filtration is an aqueous solution containing zinc ions, it can be recycled as is and reused in the plating process.

According to the present invention, the zinc-plated powder obtained as described above does not deposit zinc on the powder to be plated in the form of particles.
A coating with a fairly uniform thickness forms.

Although the case where the object to be plated is powder has been described above, the same applies to objects which are fibrous or liquid.

However, in the case of a liquid, the object to be plated is immersed in a liquid solution containing zinc ions in which zinc powder is suspended before the heat treatment, and that rinsing after the reaction is not necessary is different from the case of a powder.

Although the reaction mechanism in the plating method of the present invention is not yet clear, it is presumed that the zinc powder is once dissolved during the reaction process, and the zinc ions in the aqueous solution are deposited on the surface of the object to be plated.

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

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

Example 1 10 g of copper powder with an average particle size of 40 μm, 4 g of zinc powder with an average particle size of several μm, and 5 oj/l of zinc.

200 mt of zinc chloride aqueous solution was charged into a plating tank (pH of the solution was 2 to 3), and heated at 90° C. for 5 minutes with stirring to react.

The resulting reaction product was separated and diluted with sulfuric acid (pH 2-3).
After cleaning with water until the presence of chlorine ions is no longer recognized, dry.

As a result, 13.98.9% galvanized powder was obtained.

This galvanized powder has the white luster of zinc, and when observed using a microscope F, it resembled the square shape of the copper powder before coating, and no fine particles that were thought to be the zinc powder itself were observed.

Since the E solution obtained by the above filtration is a zinc chloride water core solution, it is circulated to the above plating tank and reused for the plating reaction.

Example 2 20nl of zinc sulfate aqueous solution with a concentration of 200g/l, 2.0fir of zinc powder with an average particle size of several microns, and 20 nickel wires with a diameter of 2 mm and a length of 4 mm as objects to be plated were placed in a plating tank and stirred. It was heated to 85°C and plated for 5 minutes.

From then on, the same operations as in Example 1 were performed.

The plated body thus obtained had a beautiful galvanized surface that could not be seen at all under a 400x microscope.

Example 3 To 250 ml of zinc sulfate aqueous solution with a concentration of 2009/l, 2.0 jir of zinc powder with an average particle size of several microns was added and heated to 80°C [-then stirred while stirring]. sa5crn
A copper plate with a thickness of 2 ml and 1 m was immersed for 5 minutes and galvanized.

The resulting galvanized copper plate had a uniformly plated surface, and no copper base surface was visible even under a microscope.

The average plating thickness measured with an electronic film thickness meter was about 0.1 μm.

Claims (1)

[Claims] 1. A galvanizing method characterized by heat-treating an object to be plated at a temperature of 80° C. to 100° C. in the presence of an aqueous solution containing zinc powder and zinc ions.