JP2008050650A - Method for producing copper powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing extremely fine, spherical copper powder having excellent oxidation resistance and uniform grain sizes. <P>SOLUTION: In the method for producing copper powder where a copper salt aqueous solution is mixed with alkali hydroxide and reducing sugar, thereby producing cuprous oxide, and the cuprous oxide is reduced with a hydrazine based reducing agent, hereby obtaining metal copper, a water soluble silver salt is beforehand dissolved into the copper salt aqueous solution, and thereafter, the alkali hydroxide and the reducing sugar are mixed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a fine copper powder, and in particular, a method for producing a spherical highly dispersible copper powder with little aggregation useful as a conductive filler such as a conductor paste for electronics, a conductive paint, and a conductive adhesive. About.

  Copper powder is inexpensive and highly conductive, so in the electronics field, thick film conductor paste, conductive paint, conductive ink, conductive adhesive, etc. for forming conductor circuits, electrodes of electronic components, electromagnetic shielding layers, etc. It is widely used as a conductive filler (hereinafter collectively referred to as “conductor paste”). In such applications, mainly spherical, polygonal, granular, dendritic or flaky copper powder is used depending on the application and purpose.

  Here, in recent years, with the miniaturization and high performance of electronic components, there has been a demand for a conductive paste capable of forming a high-definition conductor pattern and a very thin and dense electrode layer with high accuracy. For this reason, there is a demand for a spherical copper powder that is fine, has a uniform size and shape, has little aggregation, and is excellent in dispersibility in a conductor paste. Moreover, since copper powder is generally easy to oxidize in air | atmosphere, it is calculated | required that it is excellent in oxidation resistance.

One method for producing such copper powder is to reduce cuprous oxide (Cu ₂ O) with a hydrazine-based reducing agent, or to produce copper hydroxide by adding an alkali hydroxide to an aqueous copper salt solution. There is known a method of reducing this with a reducing sugar to produce cuprous oxide and reducing the obtained cuprous oxide with a hydrazine-based reducing agent (see Patent Documents 1 to 3). These methods are widely adopted because fine copper powder having a relatively uniform particle size can be obtained.
JP-A-2-294414 JP-A-4-116109 JP-A-5-221737

  However, the methods described in Patent Documents 2 to 3 have a problem that the obtained copper powder has a relatively large particle size, and a copper powder of 0.5 μm or less cannot be obtained. On the other hand, in the method described in Patent Document 1, an extremely fine copper powder is obtained, but the copper fine particles are fused with each other, so that the dispersibility in the conductive paste is deteriorated, or irregularly shaped particles or coarse particles are mixed. As a result, there is a problem that it is difficult to obtain spherical particles having a uniform particle size. Further, since the fine copper powder has high activity and is very easy to oxidize, it is oxidized immediately after the copper powder is generated and separated and / or during storage, and there is a problem that it is difficult to handle so as not to lower the conductivity.

  In particular, in order to form a fine conductor pattern (for example, a high-definition conductor pattern having a pattern width and pattern interval of 100 μm or less) or a thin and highly conductive electrode layer using a conductor paste It is necessary to use a spherical copper powder that is extremely fine and has excellent conductive performance. For this purpose, it is desirable to use a copper fine powder having an average particle size of 0.5 μm or less, more preferably 0.1 μm or less, and excellent dispersibility and oxidation resistance. Then, there existed a problem that it was difficult to obtain the spherical copper fine powder suitable for such a use with few aggregation and stable conductive performance with sufficient reproducibility.

  In addition, among the organic complexing agents used in the methods described in Patent Documents 1 to 3, the resulting copper particles and compounds are made and bonded firmly, and are not removed by washing or the like. May remain. Thus, the conductive paste manufactured using copper powder with organic substances firmly bonded to the surface is hard to decompose and remove organic substances when baked in a non-oxidizing atmosphere, and becomes a carbonaceous residue. May be adversely affected.

  The object of the present invention is a spherical non-aggregated copper powder that is suitable as a conductive filler such as a conductor paste, is extremely fine, has excellent oxidation resistance, and has a uniform particle size (preferably an average particle size of 0.5 μm or less). Another object of the present invention is to provide a method of manufacturing by a simple process. Another object of the present invention is to efficiently produce a fine, finely dispersed copper powder with good dispersibility, without using a complexing agent that tends to remain in the resulting copper powder.

In order to solve the above problem, the invention according to claim 1 is:
In the method for producing copper powder, a cuprous oxide is produced by mixing an alkali hydroxide and a reducing sugar in a copper salt aqueous solution, and the cuprous oxide is reduced with a hydrazine-based reducing agent to obtain metallic copper.
A water-soluble silver salt is previously dissolved in the copper salt aqueous solution, and then the alkali hydroxide and the reducing sugar are mixed.

Invention of Claim 2 is a manufacturing method of the copper powder of Claim 1,
The water-soluble silver salt is dissolved so that silver is 0.1 to 5 mol% in terms of atoms with respect to copper atoms in the copper salt aqueous solution.

  In the present invention, when forming cuprous oxide from an aqueous copper salt solution, a water-soluble silver salt is previously dissolved in the aqueous copper salt solution, and mixed with an alkali hydroxide and a reducing sugar to precipitate the cuprous oxide, which is hydrazine-based. By reducing with a reducing agent, a fine spherical particle with a particle size of approximately 0.02 to 0.5 μm observed with a scanning electron microscope (SEM) is suppressed without using a complexing agent that tends to remain. Copper powder can be produced. Moreover, although the copper powder obtained in this way is fine, it has good oxidation resistance and thus has excellent storage stability and is easy to handle. In addition, since the degree of oxidation is small, it is possible to obtain a copper powder having excellent conductive performance.

  Below, one Embodiment of the manufacturing method of the copper powder which concerns on this invention is described.

  First, a water-soluble silver salt is added and dissolved in an aqueous copper salt solution, and this is reacted with an alkali hydroxide and a reducing sugar to reduce and precipitate cuprous oxide. When adding alkali hydroxide and reducing sugar to an aqueous copper salt solution, there is no restriction on the order of addition of alkali hydroxide and reducing sugar. Even if reducing sugar is added after adding alkali hydroxide, water after adding reducing sugar is added. An alkali oxide may be added. Alternatively, a mixed solution of alkali hydroxide and reducing sugar is prepared in advance, and both may be added simultaneously. Alternatively, a reducing sugar solution may be used as a mother liquor, and an aqueous copper salt solution in which a silver salt is previously dissolved and an alkali hydroxide may be added thereto.

  The copper salt used in the present invention can be applied as long as it is a water-soluble copper compound and does not contain an anion that forms an insoluble precipitate with silver. It is preferable to use possible copper sulfate, copper nitrate, copper acetate and the like. The concentration of the aqueous copper salt solution is usually 10 to 40% by weight, although it depends on the type of copper salt. When the copper salt concentration is less than 10% by weight, the production efficiency is low, and when the concentration is higher than 40% by weight, the reaction tends to be non-uniform, and it becomes difficult to produce a copper powder that is fine and suppressed in aggregation.

  The silver salt used in the present invention is not particularly limited as long as it is water-soluble, but for example, nitrate is preferable. Specifically, for example, metal silver, silver oxide, silver carbonate or the like dissolved in nitric acid or the like can be used. The addition amount of the silver salt is preferably 0.1 to 5 mol% with respect to copper atoms in terms of silver atoms. When the addition amount is less than 0.1 mol%, the effect of obtaining a fine and uniform spherical copper powder is small. On the other hand, when the addition amount is more than 5 mol%, the target copper powder can be obtained, but a large amount of expensive silver is used, which is undesirable in terms of cost.

  There is no restriction | limiting in particular in the alkali hydroxide used by this invention, Although an alkali metal hydroxide, ammonium hydroxide, etc. can be used, Sodium hydroxide and potassium hydroxide are used suitably especially. The alkali hydroxide may be added as a solid to the copper salt aqueous solution or may be added as an aqueous solution. In this invention, it is thought that copper hydroxide produces | generates prior to the reduction | restoration to cuprous oxide by adding alkali hydroxide to copper salt aqueous solution. The addition amount of the alkali hydroxide is preferably in the range of 1 to 1.5 times the equivalent to the copper salt, and in particular, added so that the pH after addition of the alkali hydroxide is in the range of 8 to 13. preferable. If the pH is less than 8, a large amount of unreacted copper ions remain in the waste liquid, and the reduction reaction to cuprous oxide by reducing sugars may not proceed sufficiently. If the pH is higher than 13, the effect of the present invention is not impaired, but the cost increases because the amount of alkali hydroxide used increases, and when excessively added alkali metal ions remain, the conductor paste There is a risk of damaging the characteristics.

  The reducing sugar used in the present invention is not particularly limited, and reducing sugars such as glucose, fructose, and lactose can be appropriately used. The reducing sugar may be added as a solid to the copper salt aqueous solution, but may be added in advance as an aqueous solution. Moreover, it is preferable to add reducing sugar in the range of 1-2 times the reaction equivalent with respect to copper salt. If the amount added is less than an equivalent amount, the reduction reaction to cuprous oxide may not proceed sufficiently. On the other hand, if the amount added is more than twice the equivalent amount, the treatment of the waste liquid becomes complicated and the cost increases.

  When precipitating cuprous oxide in the present invention, it is desirable to heat the reaction solution to about 40 to 80 ° C. in order to efficiently advance the reduction reaction to cuprous oxide. In this case, the aqueous copper salt solution may be heated in advance before adding the alkali hydroxide and / or reducing sugar, or the heating may be started after adding the alkali hydroxide and / or reducing sugar. When it is lower than 40 ° C., there is a possibility that the reduction reaction to cuprous oxide does not proceed sufficiently even if an equivalent or more reducing sugar is added to the copper salt.

  Subsequently, a hydrazine-based reducing agent is added to the thus obtained cuprous oxide slurry for reduction to produce metallic copper to obtain copper powder. At this time, if unreacted copper salt or reducing sugar remains excessively, the reduction reaction from cuprous oxide to copper may not proceed sufficiently. After separating copper, it is preferable to re-disperse in water to make a slurry, and to add a hydrazine-based reducing agent to the slurry to advance the reduction reaction. The removal amount of the reaction solution is not limited because it varies depending on the concentration of the reaction solution, but it is usually desirable to remove a solution portion of 80% by volume or more with respect to the cuprous oxide slurry. There is no particular limitation on the method for removing the solution part. For example, a method of removing the supernatant after allowing the precipitated cuprous oxide precipitate to settle and a method of performing solid-liquid separation by filtration are preferable examples. Can be mentioned.

  As the hydrazine reducing agent used in the present invention, hydrazine, hydrated hydrazine, hydrazine sulfate, hydrazine carbonate, hydrazine hydrochloride and the like can be used. The hydrazine-based reducing agent is added to the cuprous oxide slurry as it is or as an aqueous solution in advance. The hydrazine-based reducing agent is preferably added in the range of 1 to 1.9 times the reaction equivalent. If the addition amount of the hydrazine-based reducing agent is less than the equivalent, the reduction reaction to copper may not proceed sufficiently. On the other hand, the amount of hydrazine reducing agent added may exceed 1.9 times the equivalent, but the cost increases and the treatment of the waste liquid becomes complicated.

  In order to efficiently proceed the reduction reaction from cuprous oxide to metallic copper, it is desirable that the slurry containing cuprous oxide is heated to 50 to 90 ° C. during the reduction. In this case, the cuprous oxide slurry may be heated in advance before adding the hydrazine-based reducing agent, or heating may be started after adding the hydrazine-based reducing agent.

  Further, when adding a hydrazine-based reducing agent, it is preferable to add an antifoaming agent in order to suppress rapid foaming caused by the reduction reaction. Thereby, copper powder can be manufactured with a smaller reaction volume, and the manufacturing efficiency per volume can be improved. The antifoaming agent is not limited as long as it is water-soluble, and organic antifoaming agents such as silicone antifoaming agents, surfactants, polyethers and higher alcohols can be used.

  As described above, in the present invention, copper powder is produced in the presence of a minute amount of a water-soluble silver salt, whereby a copper powder that is extremely fine and suppressed in aggregation is obtained. Although this mechanism is not necessarily clear, each of the process of producing copper hydroxide by alkali hydroxide, the process of producing cuprous oxide by reducing sugar, and the process of producing metal copper from cuprous oxide by adding a hydrazine reducing agent. In the process, it is considered that a small amount of silver oxide or metallic silver produced from a silver salt and coexisting in the reaction solution may inhibit grain growth of copper hydroxide, cuprous oxide and metallic copper. Moreover, the oxidation resistance of the produced copper powder is improved, and a copper powder having good storage stability and easy handling can be obtained despite being extremely fine.

  In addition, in order to further improve the oxidation resistance and the dispersion stability in the conductor paste, the produced copper powder may be subjected to a surface treatment by a usual method using various surface treatment agents. As the surface treatment agent, known ones that are generally used can be applied. Examples thereof include silane compounds such as triazoles, fatty acids, aliphatic amines, aliphatic amides, and silane coupling agents. The amount of the surface treatment agent is in a normal range, and is desirably 0.05 to 3.0% by weight with respect to the copper powder. When the amount of the surface treatment agent is less than 0.05% by weight, the effect of improving the oxidation resistance and the dispersion stability in the paste is insufficient. On the other hand, when the amount of the surface treatment agent exceeds 3.0% by weight, there is a risk of adversely affecting electrical characteristics.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In the following examples, the average particle diameter is an average value calculated from the particle diameters of 100 independent particles randomly selected in an image of an arbitrary field of view observed by SEM.

[Example 1]
After dissolving 450 g of copper sulfate pentahydrate and 2 g of silver nitrate (0.65 mol% with respect to copper in terms of silver atom) in 1500 g of distilled water heated to 55 ° C. in advance, 280 g of potassium hydroxide (equivalent) Was added) and 250 g of glucose (1.6 times the equivalent) was added to obtain a cuprous oxide precipitate. After completion of the reaction, the cuprous oxide was separated, and distilled water was added and redispersed to obtain a cuprous oxide slurry having a total amount of 500 mL. This cuprous oxide slurry was heated to 60 ° C., and a reducing agent solution obtained by diluting 30 mL of an 80% aqueous solution of hydrazine with 70 mL of distilled water was added to reduce the cuprous oxide, thereby producing a copper powder slurry. The obtained slurry was filtered and sufficiently washed with distilled water to obtain a copper powder. Next, the obtained copper powder was dispersed in an aqueous solution containing an aliphatic amine, filtered again, and dried to perform surface treatment.

  When the X-ray diffraction pattern of the powder obtained using an X-ray diffractometer (manufactured by Rigaku Corporation) was observed, a pattern almost identical to that of metallic copper was obtained, and peaks attributed to silver and copper oxide were observed. Was not.

  In addition, the powder obtained using SEM (manufactured by Hitachi, Ltd.) was observed, and the fine particles having an average particle size of about 0.25 μm and a particle size in the range of about 0.15 to 0.3 μm were obtained. It was confirmed that the copper powder was spherical. Moreover, the fusion | melting of particle | grains was hardly seen but it was a thing close to monodispersion. The obtained SEM image is shown in FIG.

[Example 2]
A copper powder was obtained in the same manner as in Example 1 except that the amount of silver nitrate was 3 g (0.97 mol% based on copper in terms of silver atoms).

  When the X-ray diffraction pattern of the obtained powder was observed, almost the same pattern as that of metallic copper was obtained as in Example 1. SEM observation confirms that the copper powder is close to monodisperse consisting of spherical fine particles with an average particle size of approximately 0.15 μm and a particle size of approximately 0.1 to 0.2 μm. did.

[Example 3]
A copper powder was obtained in the same manner as in Example 1 except that the amount of silver nitrate was 6 g (2.0 mol% based on copper in terms of silver atoms).

  When the X-ray diffraction pattern of the obtained powder was observed, almost the same pattern as that of metallic copper was obtained as in Example 1. SEM observation confirms that the copper powder is close to monodisperse, consisting of spherical fine particles with an average particle size of approximately 0.09 μm within a particle size range of 0.05 to 0.15 μm. did.

[Comparative Example 1]
A copper powder was obtained in the same manner as in Example 1 except that silver nitrate was not added.

  When an X-ray diffraction pattern of the obtained powder was observed, a copper oxide peak was observed in addition to the metal copper peak. By SEM observation, it was confirmed that the powder was a copper powder composed of particles having an average particle size of about 0.42 μm and a variation in size and shape within a range of about 0.1 to 1.0 μm. The obtained SEM image is shown in FIG.

[Comparative Example 2]
A copper powder was produced in the same manner as in Example 1 except that 13.5 g of amine acetate was added to the copper salt aqueous solution instead of silver nitrate.

  From the X-ray diffraction pattern of the obtained powder, a trace of copper oxide was observed in addition to metallic copper. By SEM observation, it was observed that the particles were aggregated and coarsened by a large number of particles having a size of about 0.6 to 1.0 μm.

[Comparative Example 3]
A copper powder was produced in the same manner as in Example 1 except that 3.0 g of ethylenediamine and 0.3 g of hydroxyethylcellulose were added to the copper salt aqueous solution instead of silver nitrate.

  When the X-ray diffraction pattern of the obtained powder was observed, a trace of copper oxide was observed in addition to copper metal. By SEM observation, it was observed that plate-like particles having a size of about 1.0 μm were mixed in addition to the spherical particles of 0.2 to 0.5 μm.

2 is a SEM image of the powder obtained in Example 1. 2 is a SEM image of the powder obtained in Comparative Example 1.

Claims (2)

In the method for producing copper powder, a cuprous oxide is produced by mixing an alkali hydroxide and a reducing sugar in a copper salt aqueous solution, and the cuprous oxide is reduced with a hydrazine-based reducing agent to obtain metallic copper.
A method for producing a copper powder, comprising dissolving a water-soluble silver salt in the copper salt aqueous solution in advance and then mixing the alkali hydroxide and the reducing sugar.   The said water-soluble silver salt is dissolved so that silver may become 0.1-5 mol% in conversion of an atom with respect to the copper atom in the said copper salt aqueous solution, The manufacture of the copper powder of Claim 1 characterized by the above-mentioned. Method.