JPS595668B2 - Method for forming an insulating oxide film on copper or copper alloy - Google Patents

Description

Detailed Description of the Invention The present invention involves immersing copper or copper alloy in a mixed aqueous solution of sodium chlorite (NaCl02) and sodium hydroxide (NaOH) to form an electrically insulating oxide film on its surface. It's about how to do it.

A method of forming an oxide film, that is, a thin black cupric oxide (CuO) film on the surface of copper or copper alloy using a mixed aqueous solution of sodium chlorite and sodium hydroxide, is a method using a so-called copper black dyeing solution. is already known as. The present inventors conducted various studies on the oxide film formed in this manner.

According to them, this film grows to a thickness of about 1 to 2 microns at most, but it has strong adhesion to the underlying metal and is durable, and its electrical dielectric strength is also affected by the amount of chemicals in the solution and the amount of chemicals in the solution. It has been found that by optimally controlling conditions such as the amount of copper ions eluted in the test and the bath temperature of the solution, it is possible to stably obtain a value of several tens of volts. The present invention was made through the above process, and in order to obtain an electrically insulating oxide film with a relatively high dielectric strength voltage and a stable property in an oxidation treatment solution using a mixture of sodium chlorite and sodium hydroxide, Ingredient amount, blending ratio, amount of eluted copper ions,
This specifies a specific range for oxidation treatment temperature, etc.

The characteristics of the present invention are that the total amount of sodium chlorite and sodium hydroxide is 10 to 500 y/l, and the mixing ratio of sodium chlorite and sodium hydroxide is 5/10 to 1.
0/1, the amount of eluted copper ions in the solution is set to 3 to 100 ppm, and the bath temperature of the solution is set to 80 ° C. or higher,
The purpose is to form an electrically insulating oxide film with high dielectric strength and stability.

Next, the present invention will be explained in more detail.

Describing the process of forming an oxide film using a mixed aqueous solution of sodium chlorite and sodium hydroxide, since the aqueous solution is a strong alkaline bath with sodium hydroxide, it is thought to be caused by the following reaction.

From the above reaction, as is clear from reaction formula (4), copper is directly oxidized to cupric oxide by sodium chlorite.

This is the formation of the first oxide film. The cupric oxide thus produced also becomes a sodium-copper complex ion (Na2CUO2) with sodium hydroxide, as shown in reaction formula (5). This reaction is reversible. When this complex ion is hydrolyzed, a second oxide film is regenerated. Through such hydrolysis, a thin film of cupric oxide with excellent adhesiveness is formed. It is thought that due to the hydrolysis of this complex ion, the surface of the film is acicular and exhibits a velvety state. Next, the reason why various conditions are limited to predetermined ranges in the present invention will be described.

First, the total amount of sodium chlorite and sodium hydroxide (NaClO2+NaOH) is 10 to 500.
The reason why the range is 7/e is that if this total amount is less than 10f7/e, for example, when the blending ratio of sodium chlorite and sodium hydroxide (NaClO2/NaOH) is a value of 1 that satisfies that condition. Even in this case, the surface of the copper or copper alloy is only slightly discolored to brown, but the oxidation reaction does not proceed completely, and an oxide film with excellent insulation properties is not produced.

On the other hand, when the total amount of chemicals exceeds 500 t/e, the oxidation reaction progresses rapidly, but the generation of complex ions and hydrolysis by sodium hydroxide occur vigorously and unevenly, resulting in an oxide film. This is because the adhesion of the material is considerably reduced, and at the same time, the surface tends to become rough and rough. Further, the blending ratio of the above sodium chlorite and sodium hydroxide used in the present invention is 5/10 to 10/
The reason for setting the ratio to be 1 is because if this ratio is less than 5/10, the surface of the copper or copper alloy will be completely gray and no insulating oxide film will be formed.

In other words, if there is too much sodium hydroxide, the formation of the first oxide film before hydrolysis will not proceed smoothly as shown in reaction formula (4). Conversely, if this ratio exceeds 10/1, the surface of the copper or copper alloy will appear brown or brown. In other words, even if the amount of sodium hydroxide is too small, the formation of complex ions by sodium hydroxide and its hydrolysis as shown in reaction formula (5) will not proceed smoothly, resulting in needle-like formation due to the hydrolysis of these complex ions. This is because the formation of a secondary oxide film exhibiting a velvety state cannot be expected. Therefore, it becomes impossible to form an oxide film with excellent electrical insulation properties. Furthermore, in the aqueous solution of the invention, copper ions (Cu2+) are eluted during the generation of cupric oxide and the hydrolysis of complex ions as shown in reaction formulas (4) and (5) above. However, since the amount of eluted copper ions greatly affects film formation, it is necessary to limit this amount.

By limiting the amount of eluted copper ions in this way, the chemical reaction (1)-{5) described above is carried out smoothly and sufficiently at the interface between the surface of the copper or copper alloy and the oxidation treatment solution, and the adhesion is particularly good. Moreover, it becomes possible to form a homogeneous electrically insulating oxide film. Here, the range is set to 3 to 100 ppm because
When the amount of eluted copper ions is less than 3 ppm, for example when the treatment solution is completely new and the bath has just been set up, the interfacial reaction cannot start instantaneously, and good adhesion may not occur during short-time treatment. This is because an oxide film cannot be formed. On the other hand, when the amount of eluted copper ions exceeds 100 ppm, the treated aqueous solution becomes more blue and the reactions of the above reaction formulas (4) and (5) are chemically suppressed. This is because no film is formed. Next, the temperature of the treatment liquid in the present invention needs to be 80° C. or higher in order to obtain a high quality and highly efficient electrically insulating oxide film.

In other words, when the liquid temperature is less than 80°C, the reaction formula (4),
This is because the reaction (5) is not carried out sufficiently and a complete electrically insulating oxide film is not produced. The processing time of the present invention carried out under the above conditions is not particularly limited, but is preferably 1 minute or more and 30 minutes or less.

Next, an example will be described.

2.0mmφ soft electric copper wire with trichlorethylene,
After thoroughly cleaning the surface using ultrasonic waves, prepare a bath of first-grade reagent sodium chlorite and sodium hydroxide in demineralized water in a 2e stainless steel container, heat, and use the following conditions under the following table. Oxide film generation treatment was performed for 3 minutes each.

Thereafter, it was washed with water and dried, and its electrical insulation properties and appearance were observed. The results were as shown in the following table. In addition, in the table, the dielectric strength voltage indicating the electrical insulation property is n=5 among the values of the two-layer breakdown voltage (AC breakdown) due to two strands.
The average value of 20V or more is represented by ◯, and the value less than 20V is represented by ×, and the electrical insulation properties are classified.

Appearance was judged by three people, with rank A being a pure black appearance, rank B being a gray or bluish appearance, and rank C being hardly oxidized or red even if oxidized. Indicates a case where the color is brown or brownish. Under these conditions, the amount of copper ions eluted in the treatment solution was adjusted by dissolving a fixed amount of cupric oxide as a reagent. From this table, the total amount of sodium chlorite and sodium hydroxide is in the range of 10 to 500 t/e, the mixing ratio of sodium chlorite and sodium hydroxide is in the range of 5/10 to 10/1, and the amount of eluted copper ions. is in the range of 3 to 100 ppm, and the solution temperature is 80°C or higher, the oxide film exhibits the jet black appearance that occurs when the film is sufficiently formed, and at the same time has excellent electrical insulation properties with high dielectric strength voltage. It can be seen that it is formed by

The soft electrical copper wire on which the electrically insulating oxide film is formed in this way can be used, for example, in general windings with excellent insulation properties.

As is clear from the above description, according to the present invention, in the method of immersing copper or copper alloy in a mixed aqueous solution of sodium chlorite and sodium hydroxide to form an electrically insulating oxide film on its surface, The total amount of chemicals, compounding ratio, amount of eluted copper ions, oxidation treatment temperature, etc. are set within specific optimal ranges, so the product has a black appearance, good adhesion, is thick, homogeneous, and has a relatively high dielectric strength. It is possible to obtain an excellent electrically insulating oxide film that has a high and stable needle shape and a velvety state.

Claims (1)

[Claims] 1. In a method of immersing copper or copper alloy in a mixed aqueous solution of sodium chlorite and sodium hydroxide to form an electrically insulating oxide film on its surface, the total amount of sodium chlorite and sodium hydroxide is 500g/l,
The blending ratio of sodium chlorite and sodium hydroxide is 5.
/10 to 10/1, the amount of eluted copper ions in the solution is 3 to 10
1. A method for forming an insulating oxide film on copper or a copper alloy, characterized in that the solution is set at 0 ppm and the bath temperature of the solution is 80° C. or higher.