JPH0774364B2 - 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 in order to obtain a dense copper conductor film when a paint is baked, spherical fine copper powder with monodispersed particles and less impurities is desired. There is. 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, an organic compound such as gum arabic remains in the copper powder, the firing atmosphere is deteriorated during firing of the thick film conductor, which is not preferable for forming a thick film. Further, in the method of reducing an aqueous solution of copper sulfate with hydrazine in the presence of a surfactant, copper is deposited from a water-soluble copper compound, so that the grain size at the time of deposition varies, for example, an average grain size of 2.5 μm so
Powder with a particle size of 0.5 μm 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, to obtain spherical copper fine powder monodispersed even in a short time without affecting the particle shape by the reaction time, Furthermore, 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 a certain extent, the problem can be solved by pre-treating copper oxide with a silane coupling agent and reducing it with an aqueous solution containing hydrazine. The inventors have found that and completed the present invention.

[Means for solving 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 silane coupling agent and then reducing the copper oxide powder with hydrazine.

[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 carbide is used as a starting material, it is more spheroidized than that using a copper salt, but it is not good because it contains a larger amount of irregular powder and has a wider particle size distribution 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 silane coupling agent, by going through this step,
Even if the copper oxide powder particle size is increased, no coarse agglomerates are present, and even if a small copper oxide powder is used, it does not form a fine colloidal form, and a copper fine powder having a uniform particle size can be obtained.

The silane coupling agent in the present invention is an organosilicon compound and has a chemical structural formula represented by the general formula YRSiX ₃ . Here, Y is an organic functional group such as a vinyl group or an amino group. R is an alkyl group and X is a hydrolyzable group such as methoxy group and ethoxy group. The silane coupling agent used for producing the fine copper powder forming the thick film conductor of the electronic circuit is preferably one which does not contain S and Cl in its chemical structure and does not react violently with water.

A hydrolyzable group having a chloro group reacts violently with water and is not good.

The silane coupling agent is vinyl-tris (β-methovyethexy) silane. Γ-Glycidoxypropyltrimethoxysilane. Γ-Aminopropyltriethoxysilane. N-β- (Aminoethyl) -γ-aminopropyl trimethoxy.
silane. γ-Ureidopropyltriethoxysilane. and the like are suitable. The amount of silane coupling agent is 0.5 wt% by weight with respect to copper oxide
There is an effect, and up to 20 wt% is an appropriate amount, and addition of more than this is not effective and is not economical.

As a method of coating copper oxide with a silane coupling agent, the silane coupling agent may be directly added to copper oxide or an aqueous solution or alcohol solution of the silane coupling agent may be added, followed by stirring, mixing or pulverizing.

When the silane coupling agent is used as an aqueous solution or an alcohol solution, the surface of the copper oxide powder can be quickly and uniformly coated. However, if the concentration of the silane coupling agent in the water or alcohol solution is low, the effect of the silane coupling agent decreases. Therefore, when making the water or alcohol solution, it is preferable to add 20 wt% or more of the silane coupling agent.

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 silane coupling agent on the surface of copper oxide while crushing is important in producing fine copper powder having a small particle size. When the copper oxide powder becomes small, it becomes difficult to uniformly form the coating of the silane coupling agent, and the effect of the present invention may not be sufficiently obtained. In particular, when trying to obtain a small copper fine powder using a small copper oxide powder, a silane coupling agent is added to a large copper oxide, and a small copper oxide powder uniformly coated while being crushed is used. It is a good method to easily 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 besides hydrazine include formaldehyde, glucose, hypophosphorous acid, sodium borohydride, etc., but the reducing power is weak and copper oxide cannot be reduced to metallic copper, or even if it is reduced and precipitated, the particle size distribution is wide. Only irregularly 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 to copper oxide is 10 by weight
A reduction reaction is observed from wt%, but the reaction proceeds faster and the reaction ends 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 silane coupling agent should be an amount that allows the copper oxide to be stirred well, and is preferably about 50 times the volume of the copper oxide, but the stirring operation was not performed. The case is not particularly limited.

The reduction reaction can be observed at room temperature, but the reaction rate is slow and it takes a long time to complete the reaction, so it is better to heat it to 60 ° 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 it to 60 ° C. or higher, 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 silane coupling agent is dispersed in an aqueous solution, suspended, and hydrazine is added with stirring,
When 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 silane coupling agent, but it is considered as follows.

The silane coupling agent coated on the surface of the copper oxide powder is hydrolyzed to silanol and forms a siloxane bond on the surface of the copper oxide.

Up to now, it has been said that in order to obtain monodisperse spherical fine copper powder, the copper ion concentration should be lowered and the reaction should be carried out slowly. That is, when the copper ion concentration is increased or the reaction rate is increased, many copper nuclei are generated at one time, and the nuclei agglomerate with each other at the growth stage, resulting in irregularly shaped fine copper powder.

It is considered that the siloxane bond formed on the copper oxide surface prevents the aqueous solution from approaching to some extent, and controls the copper ion concentration in the aqueous solution so as not to exceed a certain level even in the presence of the reducing agent.

In other words, it is considered that the concentration of copper ion in the aqueous solution is controlled from the early stage of the reaction to near the end of the reaction to prevent many nuclei from forming and aggregating at once.

The smaller the nucleus grows, the faster it grows, and the larger the nucleus grows slower.Therefore, the diameter of the copper fine powder obtained is very uniform even if the nucleation continues continuously from the initial reaction to the end of the reaction. It will be a complete set.

It is considered that the silane coupling agent does not prevent the fine particles of copper reduced and precipitated from sticking to each other, but has the effect of controlling the concentration of copper ions in the reaction solution to obtain monodispersed spherical copper fine powder.

〔Example〕

 Examples of the present invention will be shown below.

Example (1) To 50 g of cupric oxide having an average particle size of 10 μm, 5 g of silane coupling agent Vinyl-tris (β-methoxyethoxy) silane was added,
Stir and mix with a mixer for 10 minutes, then add 500cc
50 g of hydrazine monohydrate was added while stirring and dispersing in an aqueous solution of, and gradually warmed to 70 ° C. after 15 minutes. When the suspension was kept at 70 ° C for 15 minutes, 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 1.5 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was very small at 0.12% and the amount of Si was also extremely small at 0.003%.

Example (2) Using the same cupric oxide as in Example (1), only a silane coupling agent for surface-treating cupric oxide was used. Γ-Glycidoxypro
Fine copper powder was obtained in the same manner as in Example (1) except that pyltrimethoxysilane was used instead.

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 particle size of 1 μm to 1.5 μm and no aggregation, and the oxygen content was 0.13%, which was very small.

Example (3) Using the same cupric oxide as in Example (1), only the silane coupling agent for surface-treating cupric oxide was γ-Aminopropylt.
Fine copper powder was obtained in the same manner as in Example (1) except that riethoxysilane was used.

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 1.5 μm, which were uniform and non-aggregated monodispersed spherical powders, and the oxygen content was 0.14%, which was very small.

Example (4) The same cupric oxide as in Example (1) was used, and only the silane coupling agent for surface-treating cupric oxide was N-β- (Aminoe
Fine copper powder was obtained in the same manner as in Example (1) except that thyl) -γ-aminopropyltrimethoyxsilane was used.

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 particle size of 1 μm to 1.5 μm and no aggregation, and the oxygen content was 0.13%, which was very small.

Example (5) Using the same cupric oxide as in Example (1), only the silane coupling agent for surface-treating cupric oxide is γ-Ureidopropyl.
Fine copper powder was obtained in the same manner as in Example (1) except that triethoxysilane was used.

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 1.5 μm, which were uniform and non-aggregated monodispersed spherical powders, and the oxygen content was 0.14%, which was very small.

Example (6) Using 100 g of cupric oxide having the same average particle size of 10 μm as in Example (1), a silane coupling agent γ-Aminopropyltriethoxy was used.
0.5 g of silane was added, and the particles were crushed for 30 minutes with an attritor using a 5 mmφ stainless ball as a crushing medium. The average particle size of the crushed cupric oxide 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 pulverized, is dispersed and suspended in 500 cc of an aqueous solution, and then 50 g of hydrazine monohydrate is added with stirring. After 15 minutes, the temperature reaches 70 ° C. It was gradually heated. Suspension at 70 ℃, 15
After holding for a minute, 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.

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 particle size of 0.5 μm to 0.8 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) Using 100 g of cupric oxide having the same average particle size of 10 μm as in Example (1), a silane coupling agent γ-Aminopropyltriethoxy was used.
5 g of silane was added and crushed for 180 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 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, and then 50 g of vidrazine monohydrate was added with stirring, and after 20 minutes, the mixture was gradually heated to 60 ° C. Suspension at 60 ℃, 2
After holding for 0 minutes, the reaction was completed and copper fine powder was deposited.
After filtering with an aspirator, washing with acetone, then at 20 ℃
And dried naturally.

37 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 0.5 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was a very small amount of 0.19%.

Example (8) 5 g of silane coupling agent Vinyl-tris (β-methoxyethoxy) silane 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.
After dispersing and suspending in an aqueous solution of c, 50 g of vidrazine monohydrate was added with stirring, and after 15 minutes, the mixture was gradually heated to 60 ° C. When the suspension was kept at 60 ° C for 15 minutes, 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 grain shape, it was a monodispersed spherical powder having a uniform size of 2 μm to 2.5 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was a very small amount of 0.11%.

Example (9) To 50 g of cuprous oxide having an average particle size of 10 μm, 5 g of a silane coupling agent γ-Aminopropyltriethoxysilane was added and mixed by stirring for 10 minutes with a mixer, and then dispersed and suspended in an aqueous solution of 500 cc in total amount and then stirred. While adding 25 g of vidrazine monohydrate, 15 minutes later, the mixture was gradually heated to 60 ° C. The reaction starts gradually when the temperature of the suspension rises above 40 ° C,
Precipitation of copper was clearly observed at 60 ° C, and the reaction was completed after 30 minutes, and fine copper 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%.

Example (10) To 50 g of cupric oxide having an average particle size of 10 μm, a mixed solution of silane coupling agent Vinyl-tris (β-methoxyethoxy) silane 2 g and water 3 g was added, and mixed by stirring for 10 minutes with a mixer, and then the whole amount was added. Disperse and suspend in 500 cc of aqueous solution, then add 50 g of hydrazine monohydrate with stirring, and after 15 minutes, add 70
The mixture was gradually warmed up to ℃. When the suspension was kept at 70 ° C for 15 minutes, 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 1.5 μm and no aggregation. As a result of measuring the amount of oxygen as an impurity, it was a very small amount of 0.13%.

Example (10) The same cupric oxide as in Example (10) was used, and only the silane coupling agent for surface-treating cupric oxide was γ-Glycidoxypro.
Fine copper powder was obtained in the same manner as in Example (10) except that a mixed solution of 2 g of pyltrimethoxysilane and 3 g of ethanol was used.

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 1.5 μm, which were uniform and non-aggregated monodispersed spherical powders, and the oxygen content was 0.14%, which was very small.

Example (12) Using the same cupric oxide as in Example (10), only a silane coupling agent for surface-treating cupric oxide was used. Γ-Aminopropylt
Fine copper powder was obtained in the same manner as in Example (10) except that the mixed solution of 2 g of riethoxysilane and 3 g of ethylene glycol was used.

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 1.5 μm and no aggregation, and the oxygen content was 0.15%, which was very small.

〔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 silane coupling agent and then reducing the copper oxide powder with hydrazine. 2. The surface of the copper oxide powder is charged into a silane cup by charging a copper oxide powder and a silane coupling agent or an aqueous solution or an alcohol solution of the silane coupling agent into a mixer or a pulverizer and performing a mixing or pulverizing operation. The method for producing a fine copper powder according to claim 1, characterized in that the fine copper powder is coated with a ring agent. 3. A copper oxide powder coated with a silane coupling agent is dispersed in water, and the hydrazine or hydrazine aqueous solution is added to the copper oxide powder while stirring to reduce the copper oxide powder. 2. The method for producing a fine copper powder according to item 1 or 2. 4. A copper oxide powder coated with a silane coupling agent in a state of being dispersed in water, hydrazine or an aqueous solution of hydrazine is added with stirring, and then the mixed suspension is heated to give the copper oxide powder. The method for producing a fine copper powder according to claim 3, wherein the copper fine powder is reduced.