JPH026836B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for preventing oxidation of copper powder.

Copper powder is dispersed in an organic varnish together with glass frit to form a paste, which is applied onto a ceramic substrate by coating or printing, dried, and fired in a non-oxidizing atmosphere. It is used as a thick copper coating for electrodes, conductive circuit patterns, etc.

In performing such utilization, it is important not to oxidize the copper powder. This is because as the oxidation of copper powder progresses, printability becomes difficult when it is made into a paste, and as a result of baking, an increase in resistivity is observed, as well as deterioration of solderability and adhesive strength. It was accompanied by

Therefore, it is necessary to immediately perform oxidation prevention treatment after producing copper powder, and up to now the following oxidation prevention treatment has been performed.

In other words, the conventional oxidation prevention treatment method for copper powder is to immerse the copper powder in a 10% alcohol solution of H ₃ BO ₃ for about 1 hour, then separate the copper powder from the alcohol solution and soak it at a temperature of about 200°C. This method involves heat treatment for 10 to 20 minutes. The surface of the copper powder obtained by this method is covered with boron (B), and it can be said that it has an excellent antioxidation effect. However, the heat treatment temperature is specified at approximately 200°C, and the heat treatment temperature must be strictly controlled. This is because the melting point of boron is specified to be in the range of 184 to 186°C, and to cover the surface of the copper powder with boron as the boron melts, it is specified to be about 200°C. If the heat treatment temperature is less than 180°C, boron will not be melted and the surface of the copper powder will not be sufficiently coated, while if it exceeds 200°C, the copper powder will be oxidized.

Therefore, the present invention provides a method for carrying out the oxidation prevention treatment of copper powder easily.

Further, the present invention provides a method for preventing oxidation of copper powder, which prevents oxidation of the copper powder and enables long-term storage.

That is, the gist of the present invention is a method for preventing oxidation of copper powder, which is characterized by bringing copper powder into contact with a halogenated hydrocarbon compound or acetone, thereby preventing oxidation of the copper powder.

Examples of the halogenated hydrocarbon compound used in this invention include trichlorethylene, perchlorethylene, chlorofluorocarbon, and chlorobenzene.

By contacting the copper powder with a halogenated hydrocarbon compound or acetone, the copper powder becomes stable and difficult to be oxidized by the poisoning effect of the halogenated hydrocarbon compound or acetone. To explain this using dichlorodifluoromethane among chlorofluorocarbons as an example, dichlorodifluoromethane has the following structure and has a lone pair of electrons.

_{Dichlorodifluoromethane} : _CCl2F2 That is, Cl and F have free electrons in their outer shells, and these electrons react with the catalyst and exhibit toxicity.

On the other hand, copper powder has the property of easily reacting with oxygen in the air and has catalytic activity. When dichlorodifluoromethane comes into contact with such copper powder, dichlorodifluoromethane has catalytic toxicity, so it reacts with the copper powder and eliminates the catalytic active sites of the copper powder, causing oxidation of the copper powder. Measures will be taken to prevent this. Similar effects are also seen with other halogenated hydrocarbon compounds and acetone.
Performs a similar action. The contact of the copper powder with the halogenated hydrocarbon compound or acetone is preferably carried out quickly after the copper powder is produced by a molten metal pulverization method, a mechanical pulverization method, an electrolytic method, or a reduction precipitation method.

The method of contacting the copper powder with the halogenated hydrocarbon compound or acetone is to immerse the copper powder in a solution of the halogenated hydrocarbon compound or acetone, or to spray and apply the halogenated hydrocarbon compound or acetone onto the copper powder. There are also methods of exposing to vapor of a halogenated hydrocarbon compound or acetone, and any method may be used.

It is permissible to carry out a heat treatment after contacting the copper powder with the halogenated hydrocarbon compound or acetone. This is to ensure that the copper powder is prevented from oxidizing after the surface of the copper powder is brought into contact with the halogenated hydrocarbon compound or acetone. The heat treatment is performed in a natural atmosphere, and it is sufficient to perform the heat treatment at a temperature in the range of 30 to 50°C, and the heat treatment at a low temperature can reliably perform the antioxidation treatment.

Further, the heat treatment time is not particularly limited, but the treatment can be performed for about 10 to 50 minutes.

The copper powder thus obtained is used, for example, to prepare a conductive paste.

As an example of preparing this conductive paste, it can be obtained by mixing it with a thermosetting resin such as epoxy or phenol. This conductive paste is applied to a substrate by means such as coating or printing, and then cured by applying heat, thereby making it possible to use it as a conductive portion of a thick film circuit.

In the above example, the use as a low-temperature baking type was explained, but it is also possible to use it as a high-temperature baking type.

In other words, a thick copper coating can be obtained by applying a paste made of copper powder, glass frit, and organic varnish onto a ceramic substrate by a method such as printing, and then baking it at a temperature of, for example, 900°C. It will be done. The baking atmosphere at this time is a non-oxidizing atmosphere such as nitrogen to prevent oxidation of the copper. Further, as for the glass frit, for example, a zinc borosilicate type glass frit which does not contain Pb is used, which can be heat treated in a non-oxidizing atmosphere.

Hereinafter, this invention will be explained in detail according to examples.

Example 1 10 g of copper powder with a diameter of 1 to 5 μm was prepared and immersed in a chlorofluorocarbon solution for about 1 minute.

The copper powder was then separated from this chlorofluorocarbon solution and heat treated at 40° C. for 30 minutes in natural atmosphere.

When the obtained copper powder was left at room temperature in a natural atmosphere, no oxidation of the copper powder was observed even after 500 hours, indicating that it had an anti-oxidation effect.

Further, when this copper powder was subjected to forced oxidation treatment at a temperature of 150° C. in a natural atmosphere, it was found that oxidation did not proceed even after 30 minutes, indicating that the effects of the present invention were obtained.

Next, the copper powder obtained according to Example 1 above
A paste made by mixing 75 g of epoxy resin and 25 g of epoxy resin was printed on an alumina substrate and heat-treated at 150°C. The resistance value of the copper film obtained at this time was 3 Ω/cm ² and could be used as a conductive part of a circuit pattern.

Example 2 10 g of copper powder with a diameter of 1 to 5 μm was prepared and immersed in an acetone solution for about 1 minute.

The copper powder was then filtered from the acetone solution and heat treated at 40° C. for 30 minutes in natural atmosphere.

When the obtained copper powder was left at room temperature in a natural atmosphere, no oxidation of the copper powder was observed even after 500 hours, indicating that it had an anti-oxidation effect.

Further, when this copper powder was subjected to forced oxidation treatment at a temperature of 150° C. in a natural atmosphere, it was found that oxidation did not proceed even after 30 minutes, indicating that the effects of the present invention were obtained.

In addition, in the above-mentioned example, dichlorodifluoromethane and acetone, which are a type of halogenated hydrocarbon compound, were explained, but in addition, trichlorethylene, perchloroethylene, chlorobenzene, etc., which are halogenated hydrocarbon compounds, were explained. Of course, the same effect can also be obtained.

As described above, according to the present invention, by bringing the copper powder into contact with a halogenated hydrocarbon compound or acetone, the oxidation prevention treatment of the copper powder can be achieved, and the oxidation prevention of the copper powder can be achieved with a simple treatment. Therefore, when forming a thick copper coating using this copper powder, there is no need to take precautions to prevent oxidation, and it is convenient to handle during use. Further, if the treatment according to the present invention is performed, oxidation will not proceed even if the product is left in a natural atmosphere, so long-term storage is possible. Further, in order to ensure the prevention of oxidation of the copper powder, it is subjected to heat treatment, and this heat treatment also has the effect of being carried out at a low temperature.

Claims (1)

[Scope of Claims] 1. A method for preventing oxidation of copper powder, which comprises bringing copper powder into contact with a halogenated hydrocarbon compound or acetone, thereby preventing oxidation of the copper powder. 2. The method for preventing oxidation of copper powder according to claim 1, wherein the halogenated hydrocarbon compound is any one of trichlorethylene, perchlorethylene, chlorofluorocarbon, and chlorobenzene. 3. The method for preventing oxidation of copper powder according to claim 1, wherein the method of bringing the copper powder into contact with a halogenated hydrocarbon compound or acetone is any one of coating, spraying, dipping, and vapor phase deposition.