JPH0784605B2 - Method for producing fine copper powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing spherical copper fine powder in which particles are monodispersed, which is particularly useful as a copper coating material for forming a thick film conductor of an electronic circuit. It is a thing.

[Conventional technology]

Copper paint is an alternative to the silver or palladium paints currently used to form thick film conductors in electronic circuits.
Recently, it has begun to attract attention. This copper paint is usually 0.2 μm
Copper fine powder having a particle size of up to 10 μm is used, but spherical copper fine powder containing monodispersed particles and less agglomerates and less impurities is desired in order to obtain a dense copper conductor film when a paint is baked. . Further, in order to obtain a dense copper conductor film, two or three kinds of powders having a narrow particle size distribution width may be mixed and used so as to be the closest packing, and the copper powder used for this is spherical. In addition, the powder is required to be a monodispersed powder having a uniform particle size.

Conventionally, various methods have been proposed as a method for producing fine copper powder, but as a method capable of producing a copper powder having a particle size of 0.2 μm to 10 μm, a copper-containing solution containing copper carbonate is mixed with hydrazine or a hydrazine compound, A method in which copper powder is reduced and precipitated by heating this. (JP-A-57-155302) A method of reducing copper oxide with hydrazine and / or a hydrazine compound in an aqueous medium containing a protective colloid. (Special public relations
61-55562) A method for producing copper fine particles by reducing an aqueous solution of copper sulfate using hydrazine as a reducing agent, which is a method of obtaining monodispersed copper fine particles by adding a surfactant to a reaction solution. (JP-A-62-27508, JP-A-62-40302,
JP-A-62-77407 and JP-A-62-77408). However, in these conventional methods (a)
A copper powder that satisfies all the conditions of uniform particle size, (b) monodispersed, (c) few impurities, and (d) spherical shape cannot be obtained.

That is, in the above-mentioned method of reducing copper carbonate with hydrazine, the copper powder agglomerates during precipitation, resulting in an irregular shape.
Further, the method of reducing copper oxide in an aqueous medium containing a protective colloid can prevent aggregation of copper powder to some extent by the protective colloid, but is not satisfactory.
In the experiments conducted by the present inventors, when a powder having an average particle size of 1.5 μm was produced by this method, a powder having a particle size in the range of 0.7 μm to 8 μm was obtained. Further, a problem with this method is that if a protective colloid, that is, a water-soluble polymer compound such as gum arabic remains in the copper powder, it may interfere with the bonding of the copper powders during firing of the thick film conductor, which is not preferable. Is. Further, in the method of reducing an aqueous solution of copper sulfate with hydrazine in the presence of a surfactant, the particle size at the time of precipitation varies for precipitating copper from the aqueous solution. For example, if the average particle size is 2.5 μm, 0.5 μm Powder having a particle size of up to 8 μm is mixed.

[Problems to be Solved by the Present Invention]

The present invention is a production method of reducing a copper compound in an aqueous solution from the advantage of production cost, and a spherical copper fine powder monodispersed even in a short time can be obtained without affecting the particle shape by the reaction time. As a result of various researches on a method for producing a fine copper powder having a narrow particle size distribution range and a particle size that can be freely changed to some extent, it is possible to solve the problem by pre-treating copper oxide with a polyhydric alcohol and reducing it with an aqueous solution containing hydrazine. Heading The present invention has been completed.

[Means for Solving the Problems] That is, the present invention is a method for producing a fine copper powder, which comprises coating the surface of a copper oxide powder with a polyhydric alcohol and then reducing the copper oxide powder with hydrazine. Is.

[Action]

The starting copper compound of the present invention must be copper oxide, and as the copper oxide, either cuprous oxide or cupric oxide can be used, and almost the same results are obtained.

If a copper salt other than copper oxide, such as copper sulfate, copper nitrate, or copper acetate, is used as a starting material, a large amount of non-spherical fine copper powder is deposited, which is not good. Further, when copper hydroxide or copper carbonate is used as a starting material, it is more spheroidized than that using a copper salt, but it contains a lot of irregular powder and has a wider particle size distribution range than when copper oxide is used.

In order to produce spherical copper fine powder with a narrow particle size distribution, it is necessary to use copper oxide as a starting material, but if copper oxide is further used, the particle size of copper fine powder (also called average particle size) can be changed to some extent. be able to. That is, there is a certain degree of correlation between the particle size of the copper oxide powder and the particle size of the precipitated copper fine powder.If the copper oxide powder particle size is large, the copper fine powder also becomes large, and if the copper oxide powder particle size is made small, the copper fine powder also becomes small. Become.

Further, copper oxide has a large copper content in the compound as compared with other copper compounds, and is also inexpensive as a raw material for depositing copper powder.

In the present invention, through the step of coating the surface of the copper oxide powder with a polyhydric alcohol, by going through this step, there is no coarse agglomerates even if the powder particle size of the copper oxide is increased, and a small copper oxide powder Does not produce a fine colloidal form,
A fine copper powder having a uniform particle size is obtained.

Suitable polyhydric alcohols are ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol and glycerin. The amount of polyhydric alcohol added is effective from 0.5 wt% to copper oxide by weight, and up to 20 wt% is an appropriate amount, and addition of more than this is not economical and is not economical.

It should be noted that monodispersed spherical copper fine powder cannot be obtained with monohydric alcohol.

As a method of coating the copper oxide with the polyhydric alcohol, the polyhydric alcohol may be added to the copper oxide and mixed by stirring or pulverized.

As a mixer in the case of stirring and mixing, an ordinary mixer, kneader or the like can be used. When the crushing is performed while crushing, a ball mill, an attritor, a vibration mill, or the like is used as a crushing medium. If a crusher is used, the crushing and coating treatment can be efficiently performed.

In the present invention, forming a coating of a polyhydric alcohol on the surface of copper oxide while pulverizing is important when producing a fine copper powder having a small particle size.

When the copper oxide powder becomes small, it becomes difficult to uniformly form a coating of polyhydric alcohol, and the effect of the present invention may not be sufficiently obtained. In particular, when a small copper fine powder is to be obtained using a small copper oxide powder, a polyhydric alcohol is added to the large copper oxide, and a small copper oxide powder uniformly coated while being crushed is used. This is a better method because it is easy to obtain a uniform spherical copper fine powder having a uniform particle size.

As the reducing agent used in the present invention, hydrazine and hydrazine hydrate are suitable, and hydrazine compounds such as hydrazine hydrochloride and hydrazine sulfate can also be used, but they are not preferred because of problems in washing.

Other reducing agents than hydrazine include formaldehyde, glucose, hypophosphorous acid, sodium borohydride, etc., but their reducing power is weak and copper oxide cannot be reduced to metallic copper. Only regular shaped copper powder can be obtained.

The amount of hydrazine as a reducing agent is also related to the amount of aqueous solution, but it is basically determined by the amount of copper oxide. The amount of hydrazine with respect to copper oxide by weight shows a reduction reaction from 10 wt%, but the reaction proceeds faster and the reaction is completed in a short time when 50 wt% or more is added. It should be noted that the reaction proceeds faster as the amount of hydrazine added increases, but it becomes the same even if 200 wt% or more is added, which is not economical.

The amount of the aqueous solution for dispersing and suspending the copper oxide coated with the polyhydric alcohol may be an amount that allows the copper oxide to be well stirred, and is preferably about 50 times the copper oxide volume, but when the stirring operation is not performed. Is not particularly limited.

The temperature at which the reduction reaction starts is from about 40 ° C, but since it takes a long time to complete the reaction, it is better to heat it to 60 ° C or higher. When heated above 70 ° C, the reaction heat will naturally
Since the temperature rises to 100 ° C, it is not necessary to heat at 70 ° C or higher.

In order to obtain the copper fine powder in a short time, it is preferable to increase the amount of hydrazine and heat up to 70 ° C, and the copper fine powder obtained by this does not have an irregular shape.

The reaction vessel used for carrying out the present invention is preferably equipped with a stirrer, and the reaction vessel is preferably made of glass to prevent elution of impurities, but may be made of stainless steel or a vessel coated with Teflon.

Explaining the reduction process of the copper fine powder in the method of the present invention, copper oxide coated with a polyhydric alcohol is dispersed and suspended in an aqueous solution, hydrazine is added with stirring, and the mixture is gradually heated to the reduction reaction temperature. The black or reddish brown suspension gradually becomes red and changes to copper color. When this is left to stand, fine copper powder settles in the lower part, and the upper part becomes a colorless and transparent liquid. The precipitated fine copper powder is taken out, washed with an organic solvent such as alcohol or acetone, and dried by an ordinary method to obtain monodispersed spherical fine copper powder having a particle size of 10 μm or less.

It has not been fully clarified that monodispersed spherical fine copper powder can be obtained even if the reaction rate is increased by using copper oxide coated with a polyhydric alcohol, but it is considered as follows.

It is presumed that the polyhydric alcohol coated on the surface of the copper oxide powder forms a copper compound with the copper oxide and the polyhydric alcohol is not immediately dissolved and dispersed in water even when the copper compound is dispersed in water. Therefore, it is considered that the copper that is reduced and precipitated by hydrazine is prevented from coming into contact with other precipitated copper by the polyhydric alcohol in the vicinity, and a monodispersed spherical copper fine powder is obtained.

This is presumed from the fact that even if the polyhydric alcohol is added to the aqueous solution in the same amount as the amount of copper powder, only aggregated irregularly shaped copper powder is obtained.

In order to obtain monodispersed spherical copper fine powder, there was only a method of decreasing the copper ion concentration and slowly precipitating,
In polyhydric alcohol, even with high copper ion concentration,
Since copper nuclei are deposited only at regular intervals due to slow migration of copper ions, they will not stick to each other in subsequent reduction and deposition of copper, and monodispersed spherical copper fine powder will be obtained even if the reaction rate is fast. .

〔Example〕

 Examples of the present invention will be shown below.

Example (1) 5 g of ethylene glycol was added to 50 g of cupric oxide having an average particle size of 10 μm, and the mixture was stirred and mixed with a mixer for 10 minutes, and then the whole amount was dispersed and suspended in an aqueous solution of 500 cc, and then hydrazine 1 water was added with stirring. 50 g of the Japanese product was added, and after 15 minutes, the mixture was gradually heated to 70 ° C. When the suspension temperature was close to 70 ° C., a rapid reaction occurred, and after 10 minutes, the liquid temperature was raised to 90 ° C. and, at the same time, the reaction was completed and copper fine powder was deposited.

After filtering with an aspirator, washing with acetone, then at 20 ℃
And dried naturally.

39 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the grain shape, it was a monodispersed spherical powder having a uniform size of 1 μm to 2 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was a very small amount of 0.13%.

Example (2) Copper fine powder was prepared in the same manner as in Example (1) except that the same cupric oxide as in Example (1) was used and only the polyhydric alcohol for surface treatment of cupric oxide was changed to diethylene glycol. Obtained.

39 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the grain shape, it was a monodispersed spherical powder having a uniform size of 1 μm to 2 μm and no aggregation, and the oxygen content was 0.14%, which was very small.

Example (3) The same copper as in Example (1) was used except that the same cupric oxide as in Example (1) was used and only the polyhydric alcohol for surface treatment of cupric oxide was changed to triethylene glycol. A powder was obtained.

39 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the grain shape, the particles were 1 μm to 2 μm and were a uniform monodispersed spherical powder without agglomeration, and the oxygen content was very small at 0.15%.

Example (4) Copper was used in the same manner as in Example (1) except that the same cupric oxide as in Example (1) was used and only the polyhydric alcohol for surface treatment of cupric oxide was changed to polyethylene glycol # 300. A fine powder was obtained.

39 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the particle shape, it was a monodispersed spherical powder having a uniform size of 1 μm to 2 μm and no aggregation, and the oxygen amount was 0.13%, which was very small.

Example (5) Copper fine powder was prepared in the same manner as in Example (1) except that the same cupric oxide as in Example (1) was used and only the polyhydric alcohol for surface treatment of cupric oxide was changed to glycerin. Obtained.

39 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the grain shape, the particles were 1 μm to 2 μm and were a uniform monodispersed spherical powder without agglomeration, and the oxygen content was very small at 0.15%.

Example (6) Using 100 g of cupric oxide having the same average particle diameter of 10 μm as in Example (1), 0.5 g of ethylene glycol was added, and crushed for 30 minutes with an attritor using a 5 mmφ stainless ball as a crushing medium. The average particle size of the cupric oxide after pulverization was 5 μm.

In this way, 50 g of cupric oxide having an average particle size of 5 μm, which has been surface-treated while being crushed, is dispersed and suspended in a 500 cc aqueous solution, and then 50 g of vitrazine monohydrate is added with stirring, and after 15 minutes, the temperature becomes 70 ° C. It was gradually heated. When the suspension temperature was close to 70 ° C., a rapid reaction occurred, and after 10 minutes, the liquid temperature was raised to 92 ° C. and, at the same time, the reaction was terminated and copper fine powder was deposited. It was filtered with an aspirator, washed with acetone, and then naturally dried at 20 ° C.

39 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the grain shape, it was a monodispersed spherical powder having a uniform size of 0.5 μm to 1 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was a very small amount of 0.19%.

Example (7) 100 g of cupric oxide having the same average particle size of 10 μm as in Example (1) was used, 5 g of ethylene glycol was added, and the mixture was ground for 180 minutes with an attritor using a 5 mmφ stainless ball as a grinding medium. The average particle size of the cupric oxide after pulverization was 0.5 μm.

An average particle size of 0.5 μm, which was surface-treated while being crushed in this way
50 g of cupric oxide was dispersed and suspended in a 500 cc aqueous solution, 50 g of vitrazine monohydrate was added with stirring, and the mixture was gradually heated to 70 ° C. after 15 minutes. When the suspension temperature was close to 70 ° C., a rapid reaction occurred, and after 10 minutes, the liquid temperature was raised to 95 ° C. and, at the same time, the reaction was terminated and copper fine powder was precipitated. It was filtered with an aspirator, washed with acetone, and then naturally dried at 20 ° C.

39 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the grain shape, it was a monodispersed spherical powder having a uniform size of 0.3 μm to 0.6 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was a very small amount of 0.19%.

Example (8) 5 g of ethylene glycol was added to 50 g of cuprous oxide having an average particle size of 10 μm, and the mixture was stirred and mixed with a mixer for 10 minutes. Then, the whole amount was dispersed and suspended in an aqueous solution of 500 cc, and then vitrazine 1 was stirred. 50 g of the hydrate was added, and 15 minutes later, the mixture was gradually heated to 70 ° C. When the suspension temperature was close to 70 ° C., a rapid reaction occurred, and after 10 minutes, the liquid temperature was raised to 90 ° C. and, at the same time, the reaction was completed and copper fine powder was deposited. It was filtered with an aspirator, washed with acetone, and then naturally dried at 20 ° C.

44 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the particle shape, it was a monodispersed spherical powder having a uniform size of 2 μm to 3 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was a very small amount of 0.11%.

Example (9) To 50 g of cuprous oxide having an average particle size of 10 μm, 5 g of glycerin was added, and the mixture was stirred and mixed with a mixer for 10 minutes.
25 g of bitrazine monohydrate was added while being dispersed and suspended in a 0 cc aqueous solution, and the mixture was gradually heated to 60 ° C. after 15 minutes. When the temperature of the suspension reached 40 ° C or higher, the reaction gradually started, and when it reached 60 ° C, the precipitation of copper was clearly observed. After 30 minutes, the reaction was completed and copper fine powder was precipitated. It was filtered with an aspirator, washed with acetone, and then naturally dried at 20 ° C.

44 g of copper fine powder was obtained, the particle size of the powder under an electron microscope,
As for the grain shape, it was a monodispersed spherical powder having a uniform size of 4 μm to 5 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was a very small amount of 0.10%.

〔The invention's effect〕

As described above, according to the present invention, monodispersed spherical copper fine powder having a narrow particle size distribution width can be produced in a short time and at low cost.

The spherical copper fine powder obtained by the present invention is particularly suitable for a copper coating which forms a denser thick-film conductor, and has high purity, so that it is also useful for various catalysts.

Claims (4)

[Claims] 1. A method for producing a fine copper powder, which comprises coating the surface of a copper oxide powder with a polyhydric alcohol and then reducing the copper oxide powder with hydrazine. 2. A copper oxide powder and a polyhydric alcohol are charged into a mixer or a crusher, and a mixing or crushing operation is performed to coat the surface of the copper oxide powder with the polyhydric alcohol. 2. The method for producing a fine copper powder according to item 1. 3. A copper oxide powder coated with a polyhydric alcohol is dispersed in water to add hydrazine or an aqueous hydrazine solution while stirring to reduce the copper oxide powder. The method for producing a fine copper powder according to claim 1 or 2. 4. A copper oxide powder coated with a polyhydric alcohol is dispersed in water, hydrazine or an aqueous solution of hydrazine is added thereto with stirring, and then the mixed suspension is heated to obtain the copper oxide powder. The method for producing a fine copper powder according to claim 3, characterized in that the copper fine powder is reduced.