JPH04325608A - Production of copper powder - Google Patents

Abstract

PURPOSE:To easily obtain a copper powder high in aspect ratio by reducing the crystallite of copper oxide in a reducing gas atmosphere while substantially maintaining its shape. CONSTITUTION:Copper is oxidized to form the needle, wedge or axeshaped crystallite of copper oxide. The crystallite is reduced in a reducing gas atmosphere while substantially maintaining its shape, and a fine copper powder having several mum length of long side and submicron thickness is formed. Hydrogen, carbon monoxide, their mixture or a reducing compd. capable of being gasified such as hydrazine are used as the reducing gas. The reduction is preferably conducted at 50-300 deg.C.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a novel method for producing copper powder having a length or long side of ~ several μm and a diameter or thickness of submicron or less, and is used in conductive coatings, powder metallurgy, and anti-fungal applications. ,
It can be suitably used for various other uses.

0002

[Prior Art] Conventionally, methods for producing copper powder include electrolytic method,
Atomization methods, mechanical pulverization, etc. are known and are mainly used for applications such as powder metallurgy. Copper powder produced by these methods has a large particle size, and although it has become possible to obtain finer copper powder by controlling manufacturing conditions and sorting, the productivity is low and there is a limit to miniaturization. there were. In addition, in fields such as conductive paints, powders with high aspect ratios such as scales or needles are used in combination with regular powders, but copper powders do not have high aspect ratios, and silver powders It has been difficult to produce good electrically conductive paints such as these.

0003

[Problems to be Solved by the Invention] The present inventor first attempted to chemically oxidize the surface of the inner layer copper foil in order to improve the interlayer adhesion of the inner layer board of a multilayer printed wiring board, thereby eliminating fine needles and wedges. ,
By forming irregularities in the shape of an axe, etc., and reducing them in a vapor phase to produce metallic copper that substantially retains these irregularities, we can create multilayer boards without "halos" or "pink rings" during the through-hole plating process. I found a way to manufacture it. Furthermore, upon studying this method, it was discovered that this method could be applied to the production of copper powder in the shape of fine needles, wedges, axes, etc., leading to the present invention.

0004

[Means for Solving the Problems] That is, the present invention oxidizes copper to form needle-, wedge-, or ax-shaped copper oxide microcrystals, and converts the copper oxide microcrystals into copper oxide microcrystals in an atmosphere in the presence of a reducing gas. A method for producing copper powder, which is characterized in that the reducing gas is hydrogen, carbon monoxide, or a mixture thereof, and the reducing gas is hydrogen, carbon monoxide, or a mixture thereof. , is a method for producing copper powder using a reducing compound gas.

The present invention will be explained below. Considering the purity of the copper powder to be produced, the copper of the present invention is preferably of higher purity, and its form is not particularly limited,
Various materials such as sheets, foils, powders, and wires can be used, and the most suitable one is selected mainly in consideration of the relationship with the manufacturing method of needle-, wedge-, or ax-shaped copper oxide crystals. In particular, a method of using powder on the order of μm and completely oxidizing it to form all copper oxide crystals is highly productive and preferred.

[0006] A method of oxidizing copper to convert it into copper oxide crystals is also known, and various methods can be selected, but from the viewpoint of the morphology of the obtained copper oxide crystals, it is difficult to use the inner layer copper foil of the multilayer board. Those used to form fine irregularities on the surface by oxidation treatment can be suitably used to obtain copper oxide with a high aspect ratio. Specific examples of these include, but are not limited to, the following, and known methods can be used. ■． Sodium hydroxide (NaOH (15g/liter))/sodium hypochlorite (NaClO2 (31g/liter))
liter))/sodium phosphate (15g/liter)
, 70-100°C, 0.5-10 minutes. ■． Copper sulfate (50g/liter)/sodium chloride (
200g/liter), 40-80℃, 3-15 minutes. ■． Acetic acid (20g/liter)/Ammonium chloride (
20g/liter)/copper acetate (10g/liter), 3
0-80℃, 1-10 minutes. ■． Copper acetate (10g/liter)/Copper sulfate (24g/liter)
liter)/barium sulfide (24g/liter)/ammonium chloride (24g/liter), 40-50℃,
1 to 10 minutes. ■． Copper sulfate (25g/liter)/Nickel sulfate (2
5g/liter)/potassium chlorate (25g/liter), 70-90°C, 1-10 minutes. ■． Potassium persulfate (20g/liter)/sodium hydroxide (50g/liter), 50-80℃, 1-
3 minutes.

[0007] Among the methods for forming the brown or black finely uneven copper oxide film described above, the method that has been put into practical use involves lamination molding of the obtained copper oxide film itself or a product that has been reduced in a liquid phase. This is a suitable condition that shows strong adhesive strength when However, the present invention does not use these copper oxide films, but uses fine copper oxide crystals separated from copper, and performs vapor phase reduction to obtain copper powder. Therefore, the adhesion strength as an oxidized film is irrelevant, and conditions are selected that produce copper oxide crystals with a higher aspect ratio that are easier to separate, that is, conditions that produce copper oxide crystals that have greater unevenness and are easier to peel off. Usually, it is preferable to select harsher conditions such as higher temperature and longer time.

The copper oxide crystals obtained above are usually purified by washing with water if necessary, dried, and then subjected to the gas phase reduction of the present invention. The reducing gas atmosphere of the present invention is: (1). Reducing gases such as hydrogen and carbon monoxide, ■. Hydrazine, other gasifiable reducing compounds, or ■. This is a gaseous atmosphere that simultaneously contains (1) and (2). First, the method of supplying these reducing gases is not particularly limited, and for example, the method of supplying the above gas (①) in a cylinder, the method of supplying the above gas (②) by electrolysis, catalytic pyrolysis, etc. Further, it is possible to carry out the method by supplying a compound gas by promoting the vaporization of a reducing compound with a non-oxidizing or reducing gas.

Compounds that can be used to generate reducing gases such as hydrogen and carbon monoxide through catalytic thermal decomposition include methanol, ethanol, propanol,
Lower alcohols such as butanol; aldehydes or their derivatives such as formaldehyde, paraformaldehyde, and trioxane; lower carboxylic acids such as formic acid, formic acid esters, and acetic acid; ammonia, hydrazine; methylamine, ethylamine, diethylamine, methylhydrazine, and other nitrogen-containing Examples include lower amines and hydrazine derivatives; metal hydrides and organometallic compounds such as calcium hydrite, boron hydrite, and methyl boron, and are not particularly limited in use in the present invention. Among these, lower alcohols, lower carboxylic acids, ammonia and the like are preferred from the viewpoint of ease of handling, safety, presence or absence of waste, price, etc. Compounds that can be suitably used to supply reducing compound gas include hydrazines such as hydrazine and methylhydrazine; formic acid and compounds that generate formic acid by thermal decomposition, and formic acid gas is copper oxide. It decomposes into hydrogen and carbon dioxide when it comes into contact with copper or metal, so it can be used effectively.

[0010] Next, the reduction temperature may be selected as long as it does not cause sintering of the copper produced by the reduction, that is, the appearance of copper oxide changes and becomes more aggregated, or does not occur at all. , usually 50℃~300℃
°C, preferably 80 °C to 200 °C, especially 10 °C
From the viewpoint of continuous production, the temperature is preferably selected from the range of 0 to 150° C., and the processing time is preferably selected from the range of 1 minute to 12 hours, preferably 2 to 60 minutes. In particular, when hydrazine is used as the reducing compound gas, the reduction rate tends to become too high because this compound has the ability to reduce copper oxide to metallic copper even at room temperature. If the reduction rate is too fast, copper tends to condense due to heat generation, and the produced water may form an extremely fine thin film in which the reduction reaction may proceed. In this case, since the morphology of the copper oxide crystal is destroyed, it is preferable to reduce the concentration of hydrazine.

[0011]

[Examples] The present invention will be explained in more detail below with reference to Examples. Example 1 A rolled copper foil with a thickness of 70 μm was used, and this was treated with NaOH (
15g/liter)/sodium hypochlorite (31g/liter)
The foil was treated with an aqueous solution of sodium phosphate (15 g/liter) at 90°C for 10 minutes, washed with water to obtain a double-sided black oxidized copper foil, and dried at 200°C. Next, scrape the surface with a spatula, and the maximum length or width is about 3 μm.
A copper oxide crystal powder was obtained. This copper oxide crystal powder is placed in a dryer that can be vacuum-suctioned, and the inside of the dryer is vacuumed while raising the temperature, nitrogen gas is introduced, and after vacuum suction is performed again, nitrogen gas containing 5% hydrogen gas is introduced. 160℃,
Reduction was performed for 30 minutes. Thereafter, the inside of the dryer was vacuum-suctioned, and nitrogen gas containing a trace amount of oxygen was introduced to perform gradual oxidation, and then the reduced copper powder was cooled and taken out from the dryer. This copper powder is a slightly pale black color, has an oxygen content of 2.7%, and its shape is a mixture of needles, wedges, axes, scales, etc. with a maximum length or width of about 2 μm. Met.

Example 2 In Example 1, hydrazine was used as the reducing gas.
Using nitrogen gas containing mmHg, the temperature was set to 120℃, 10
It was the same except that it was set to 1 minute. The obtained copper powder has a slightly pale black color, an oxygen content of 3.1%, and a fine shape consisting of a mixture of needles, wedges, axes, scales, etc., with a maximum length or width of about 2 μm. It was copper powder.

[0013]

[Effects of the Invention] From the above detailed description and examples, the copper powder produced by the production method of the present invention has an aspect ratio that is unprecedented. This production method is achieved by combining a conventionally known method with the gas phase reduction developed by the present inventors, and is easily implemented, and has extremely high industrial significance. It is.

Claims (1)

[Claims] Claim 1: Copper is oxidized to produce needle-, wedge-, or ax-shaped copper oxide microcrystals, and the copper oxide microcrystals are substantially maintained in the shape of the copper oxide microcrystals in an atmosphere in the presence of a reducing gas. A method for producing copper powder characterized by gas phase reduction.Claim 2. A method for producing copper powder according to claim 1, wherein the reducing gas is hydrogen, carbon monoxide, or a mixture thereof.Claim 3
The method for producing copper powder according to claim 1, wherein the reducing gas is a reducing compound gas.