JP4120007B2 - Method for producing copper powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a copper powder, and more particularly to a method for producing a copper powder suitably used for a conductive paste used for forming a wiring pattern of a circuit board and forming an external electrode of a chip capacitor.
[0002]
[Prior art]
The copper powder constituting the conductive paste used for forming the wiring pattern of the circuit board and forming the external electrode of the chip capacitor is required to be fine, uniform in particle diameter and excellent in monodispersity. For example, the copper powder used in the conductive paste generally has a particle size of about 1 μm to 10 μm, but recently, there is an increasing demand for a particle size of 1 μm or less.
[0003]
Methods for producing copper powder include mechanical pulverization method, atomization method of spraying molten copper, electrolytic deposition method on cathode, method of heating and reducing copper salt and copper oxide in reducing atmosphere, copper chloride A method of reducing steam with a reducing gas, a method of reducing an aqueous copper salt solution with a reducing agent such as hydrazine, and the like are known. Among these, the wet reduction method in which hydrazine or the like is reduced from an aqueous copper salt solution as a reducing agent is a relatively easy method [see, for example, Patent Document 1].
[0004]
Further, in the wet reduction method, a method of heating and reducing a solid compound composed of a copper oxide, hydroxide or copper salt using a polyol as a solvent (see Patent Document 2 and Patent Document 3) or a similar reaction system Furthermore, a method of adding a monosaccharide or disaccharide as a reducing agent and performing heat reduction [see Patent Document 4] has been proposed as a method for obtaining fine copper powder safely and inexpensively.
[0005]
[Patent Document 1]
JP 57-155302 A [Patent Document 2]
US Pat. No. 4,539,041 [Patent Document 3]
Japanese Patent Publication No. 4-24402 [Patent Document 4]
Japanese Patent Laid-Open No. 11-152506 [0006]
[Problems to be solved by the invention]
However, the wet reduction method using the above polyol is not necessarily satisfactory in terms of the uniformity and monodispersity of the obtained copper powder, and when a copper oxide or hydroxide is used as a raw material, There is a drawback that the particle size of the metal copper powder to be produced varies depending on the particle shape of copper oxide or copper hydroxide or the production method.
[0007]
The present invention has been made to solve the above problems, and provides a method for producing a copper powder having a particle size suitable for producing a conductive paste, particularly a copper powder having a particle size of 0.2 to 8.3 μm. The purpose is that.
[0008]
[Means for Solving the Problems]
As a result of earnest research to solve the above problems, a soluble copper salt and an alkali agent are added to the polyol to form a copper compound such as an oxide, hydroxide, weak acid salt, or organic acid salt in the polyol. Thus, the present inventors have found that a suitable copper powder can be obtained by reduction with a polyol and a saccharide. That is, Claim 1 of the present invention relates to a method for producing a copper powder, wherein ethylene glycol, sodium hydroxide and sucrose are added to cupric sulfate and heated at an arbitrary temperature of 100 to 350 ° C. It has become.
[0009]
A second aspect of the present invention relates to the method for producing a copper powder according to the first aspect, wherein the copper powder has a particle size of 0.2 to 8.3 μm at a cumulative frequency of 50%.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, cupric sulfate, ethylene glycol, sodium hydroxide, and sucrose are mixed and reacted. If described in the order of reaction, cupric sulfate is converted to ethylene glycol. It is mixed with sodium hydroxide and reacted to form copper hydroxide, which is further reduced by adding sucrose as a copper powder precursor (hereinafter collectively referred to as “copper powder precursor”) to form copper metal. It is made up of.
[0011]
The present invention is preferably carried out using ethylene glycol as a solvent in such an amount that can be stirred smoothly throughout the reaction.
In addition to ethylene glycol, it can also be carried out using polyols that are liquid at 100 ° C. or higher, such as diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, glycerin, etc. having two or more alcoholic hydroxyl groups in the molecule, or ethylene You may combine these other polyols in part with glycol. Alternatively, ethylene glycol may be dissolved in another solvent. In the case of using a solvent, it goes without saying that the higher the concentration of ethylene glycol, the more advantageous. However, in practice, 2 mol or more of polyols such as ethylene glycol is required per 1 mol of copper obtained . In the case of a cupric salt and ethylene glycol, at least 2 moles of ethylene glycol are required per mole of cupric sulfate. The solvent may be water, but if water coexists in large quantities, it is disadvantageous in that it is performed under pressure because it is heated to 100 ° C. or higher in the step of performing the reduction reaction. Therefore, a water-soluble solvent having a boiling point of 100 ° C. or higher at normal pressure, such as butyl cellosolve, is preferably selected here.
[0012]
The cupric sulfate salt may be a hydrate. In addition to cupric sulfate, cupric chloride, cupric acetate and the like can be used.
[0013]
Sodium hydroxide reacts with cupric sulfate in ethylene glycol to produce a copper powder precursor . In addition to sodium hydroxide, alkali metal hydroxide such as potassium hydroxide, alkali metal weak acid salt such as sodium hydrogen carbonate or sodium carbonate, alkali metal organic acid salt such as sodium acetate or sodium succinate, ammonium hydroxide or the like can also be used. . Sodium hydroxide is sufficient to add a theoretical amount or a slightly larger amount necessary for neutralizing cupric sulfate , specifically, at least 1 mol per 1 mol of cupric sulfate. Of sodium hydroxide. If the theoretical amount is greatly exceeded, it is disadvantageous in terms of cost.
[0014]
Sucrose acts as a secondary reducing agent in the present invention, and it is appropriate to add 0.05 to 5 parts by weight with respect to 1 part by weight of the obtained copper. When less than this, the uniformity and dispersibility of the copper powder obtained will become inadequate. On the other hand, if the amount is too high, the viscosity of the reaction solution increases and stirring becomes insufficient, and it takes a lot of time to wash the obtained copper powder, which is disadvantageous from an economical viewpoint. Unexpectedly , sucrose can also be carried out using monosaccharides such as glucose (glucose) and fructose (fructose), disaccharides such as maltose (maltose) and sucrose (sucrose), and water-soluble polysaccharides such as soluble starch .
[0015]
Next, the form which implements the manufacturing method of the copper powder of this invention is demonstrated.
In the present invention, cupric sulfate, ethylene glycol, sodium hydroxide and sucrose are mixed and heated at an arbitrary temperature of 100 to 350 ° C. Sodium hydroxide can be used in an aqueous solution or in crystals. In addition, sucrose may be dissolved in advance in a liquid containing ethylene glycol . Particularly preferably, a cupric sulfate precursor and sodium hydroxide are first added to a liquid containing ethylene glycol to form a copper powder precursor. Subsequently, sucrose is added and the whole is heated at an arbitrary temperature of 100 to 350 ° C. to form a metallic copper powder.
[0016]
When low boiling point components such as water are mixed with cupric sulfate, sodium hydroxide , and sucrose, gradually raise the temperature while removing these low-boiling substances, and finally set it to the prescribed temperature. . The heating time varies depending on the heating temperature and the like, but is typically about 0.5 to 5 hours. Strictly speaking, it is better to determine whether or not the reaction has been completed by taking a sample and performing X-ray diffraction. However, the color of the reaction system changes and the generated water comes out in the form of bubbles. It can be estimated by changing the situation. After completion of the reaction, the mixture is filtered, washed with water and dried to obtain metallic copper powder.
[0017]
The reduction reaction in which the copper powder precursor becomes copper powder occurs with the oxidation reaction of ethylene glycol and sucrose . In ethylene glycol or the like, the terminal hydroxyl group is an oxidation reaction that becomes a carboxyl group via an aldehyde group, and in the case of sucrose , it is an oxidation reaction that becomes an organic acid of a reducing sugar.
[0018]
The present invention is characterized in that a copper powder precursor is deposited in a system in which a reduction reaction is performed, and this is reduced by combining ethylene glycol and sucrose . This copper powder precursor is fine in shape and the surface is in a state where it can be easily reduced. The reduction action by ethylene glycol and sucrose interacts with each other. The produced sodium sulfate conveniently acts as a dispersant that prevents aggregation of copper particles produced by the reduction reaction. Thereby, it is considered that the produced copper powder has a uniform particle size and excellent dispersibility.
[0019]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but these examples are merely illustrative, and the present invention is not limited to these examples.
[0020]
[Example 1] 399 g (1.6 mol) of copper sulfate pentahydrate as a soluble copper salt was dissolved in 2000 mL of ethylene glycol (boiling point 197 ° C.) as a polyol, and 3.2 mol of sodium hydroxide was used as an alkaline agent there. The aqueous solution contained was added to form a suspension solution containing copper hydroxide (copper hydroxide) and sodium sulfate, which is a by-product alkali metal salt. Subsequently, 100 g of this liquid and disaccharide sucrose (weight ratio to the obtained copper powder is 1.0) is put into a 5 L round bottom separable flask and heated at 180 ° C. for 1 hour with stirring. I got a powder.
[0021]
After the obtained copper powder was separated, washed and dried, the particle size distribution was measured and the particle shape was observed with an electron microscope. The result of the particle size distribution measurement is shown in FIG. 1, and the electron micrograph is shown in FIG. From the particle size distribution measurement, it was found that the particle size corresponding to a cumulative frequency of 50% was 3.7 μm and the distribution width was very narrow (uniform particles). Further, from observation of the particle shape with an electron microscope, it was confirmed that the particles had a polyhedral shape with a uniform size and a crystal plane grown.
[0022]
[Reference Example 1] 273 g (1.6 mol) of cupric chloride dihydrate was used as the soluble copper salt, and 100 g of glucose as a monosaccharide (weight ratio to the obtained copper powder was 1.0) as the sugar. Except that, copper powder was prepared in the same manner as in Example 1.
[0023]
As a result of the particle size distribution measurement, it was found that the particle size was 5.4 μm corresponding to a cumulative frequency of 50% and the distribution width was very narrow (uniform particles). Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal planes grown were observed independently (monodispersed).
[0024]
[Reference Example 2] 391 g (1.6 mol) of cupric acetate monohydrate as a soluble copper salt was added to an aqueous solution containing 3.2 mol of sodium hydroxide as an alkaline agent in 3000 mL of ethylene glycol as a polyol. In the same manner as in Example 1, except that copper was used as hydroxide, fructose, which is a monosaccharide, was used as a secondary reducing agent, and the reaction temperature was 130 ° C.
[0025]
As a result of the particle size distribution measurement, it was found that the particle size corresponding to a cumulative frequency of 50% was 0.4 μm and the distribution width was very narrow (uniform particles). Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal planes grown were observed independently (monodispersed).
[0026]
[Reference Example 3] Except that diethylene glycol (boiling point 245 ° C.) was used as the polyol, the reaction temperature was 230 ° C., and the amount of sucrose added was 50 g (weight ratio to the obtained copper powder was 0.5). The same procedure as in Example 1 was performed.
[0027]
As a result of the particle size distribution measurement, it was found that the particle size corresponding to a cumulative frequency of 50% was 0.2 μm and the distribution width was very narrow (uniform particles). Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal planes grown were observed independently (monodispersed).
[0028]
[Reference Example 4] Copper powder was prepared in the same manner as in Example 1 except that soluble starch, which is a polysaccharide, was used as the sugar.
[0029]
As a result of the particle size distribution measurement, it was found that the particle size corresponding to a cumulative frequency of 50% was 4.1 μm and the distribution width was very narrow (uniform particles). Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal planes grown were observed independently (monodispersed).
[0030]
[Reference Example 5] Copper powder was prepared in the same manner as in Example 1 except that glycerol (boiling point: 290 ° C) as a polyol and an aqueous solution containing 1.6 mol of sodium succinate as an alkaline agent were added. Here, it is considered that the copper powder precursor is copper succinate, which is an organic acid salt, and the by-product salt is sodium sulfate.
[0031]
As a result of the particle size distribution measurement, it was found that the particle size was 5.4 μm corresponding to a cumulative frequency of 50% and the distribution width was very narrow (uniform particles). Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal planes grown were observed independently (monodispersed).
[0032]
[Reference Example 6] A copper powder was prepared in the same manner as in Example 1 except that an aqueous solution containing 1.6 mol of sodium carbonate as an alkali agent was added and the heating temperature was 160 ° C.
[0033]
As a result of the particle size distribution measurement, it was found that the particle size was 8.3 μm corresponding to a cumulative frequency of 50% and the distribution width was very narrow (uniform particles). Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal planes grown were observed independently (monodispersed).
[0034]
[Example 2] Copper powder was prepared in the same manner as in Example 1 except that the amount of sucrose added was 10 g (weight ratio to the obtained copper powder was 0.1).
[0035]
As a result of the particle size distribution measurement, it was found that the particle size corresponding to a cumulative frequency of 50% was 3.3 μm and the distribution width was very narrow (uniform particles). Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal planes grown were observed independently (monodispersed).
[0036]
[Comparative Example 1] When performed in the same manner as in Example 1 except that the alkaline agent was not added, solid particles were not obtained.
[0037]
[Comparative Example 2] 395 g (1.6 mol) of copper sulfate pentahydrate as a soluble copper salt was dissolved in 2000 mL of pure water, and an aqueous solution containing 3.2 mol of sodium hydroxide was added thereto as an alkaline agent. A suspension containing copper hydroxide (copper hydroxide) and sodium sulfate, which is a by-product alkali metal salt, was prepared. Next, copper hydroxide as a solid phase is recovered from this suspension by filtration, washed with water to remove sodium sulfate as a by-product alkali metal salt, and then suspended again in 2000 mL of ethylene glycol as a polyol. Made cloudy. Subsequently, in the same manner as in Example 1, 100 g of this liquid and sucrose as a disaccharide were put into a 5 L round bottom separable flask and heated at 180 ° C. for 1 hour to prepare copper powder.
[0038]
The result of the particle size distribution measurement is shown in FIG. From this result, although the particle size corresponding to the cumulative frequency of 50% is 2.5 μm, there are a distribution centered around 0.2 μm and a distribution centered around 3 μm, and particles with a very wide distribution width ( Non-uniform particles).
[0039]
[Comparative Example 3] The same operation as in Example 1 was performed except that water was used as a solvent, 300 g of glucose was used as a sugar, and the heating temperature was 90 ° C. As a result of powder X-ray diffraction analysis, the obtained solid particles were cuprous oxide (Cu ₂ O).
[0040]
[Comparative Example 4] The same procedure as in Example 1 was carried out except that 391 g (1.6 mol) of cupric acetate monohydrate was used as the soluble copper salt, and no alkaline agent and sugar were added. The obtained copper powder formed an aggregate having a diameter of 1 to 5 mm.
[0041]
[Comparative Example 5] The same procedure as in Example 1 was performed except that 127 g (1.6 mol) of copper oxide (CuO) having a particle diameter of 150 µm or less was used as a copper source, and no alkali agent was added. The particle size distribution measurement result of the obtained copper particles is shown in FIG. From this result, it was found that the particle size corresponding to a cumulative frequency of 50% was 17.0 μm, and the particles had a wide distribution width (non-uniform particles).
[0042]
[Comparative Example 6] The same operation as in Example 1 was performed except that sucrose was not added. As a result of the particle size distribution measurement, the obtained copper particles were found to be particles (nonuniform particles) having a particle size corresponding to a cumulative frequency of 50% of 13.2 μm and a wide distribution width as in Comparative Example 4. .
[0043]
【The invention's effect】
According to the present invention, it is possible to produce a copper powder having a particle size suitable for producing a conductive paste, particularly a copper powder having a particle size of 0.2 to 8.3 μm, and at the same time, the particle size is uniform and excellent in monodispersity. Copper powder. This conductive paste from the copper powder is suitable for use in forming a wiring pattern on a circuit board and forming an external electrode of a chip capacitor.
[Brief description of the drawings]
1 is a measurement result of particle size distribution of the powder obtained in Example 1. FIG.
FIG. 2 is a particle size distribution measurement result of the powders obtained in Comparative Examples 2 and 5.
3 is a scanning electron micrograph of the powder obtained in Example 1. FIG.

Claims (2)

A method for producing copper powder from cupric sulfate, wherein at least 2 mol of ethylene glycol and 1 mol of cupric sulfate are added to 1 mol of cupric sulfate, 1 mol of cupric sulfate. On the other hand, at least 1 mol of sodium hydroxide is mixed to form copper hydroxide, and then 0.05 to 5 parts by weight of sucrose is added to 1 part by weight of the obtained copper powder. A method for producing copper powder, characterized by heating at an arbitrary temperature.   2. The method for producing copper powder according to claim 1, wherein a particle diameter of the copper powder at a cumulative frequency of 50% is 0.2 to 8.3 μm.

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