JP4106460B2 - Method for producing copper powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is suitable for a copper powder manufacturing method, more specifically, a conductive paste used for forming a wiring pattern of a circuit board and forming an external electrode of a chip capacitor with a uniform particle size and excellent monodispersibility. The present invention relates to a method for producing copper powder.
[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]
In addition, a method of heating and reducing a solid compound composed of a copper oxide, hydroxide, or copper salt using a polyol as a solvent in a wet reduction method (see, for example, Patent Document 2 and Patent Document 3), or a copper oxide When the powder is suspended in a polyol solution to make copper powder, the acidic components such as sulfate radical, hydrochloric acid radical, and nitrate radical other than the oxide of copper are neutralized so that the shape of the copper powder changes from spherical to polyhedral. There has been proposed a method [see Patent Document 4] that suppresses the monodispersibility of the copper powder from being changed to make it easy to aggregate. In addition, a method has been proposed in which fine copper powder is obtained safely and inexpensively by a method in which a monosaccharide or disaccharide is further added as a reducing agent in the reaction system and heated and reduced (for example, see Patent Document 5).
[0005]
[Patent Document 1]
JP 57-155302 A [Patent Document 2]
U.S. Pat.No. 4,539,041,
[Patent Document 3]
Japanese Patent Publication No. 4-24402 [Patent Document 4]
JP-A-10-330809 (page 3)
[Patent Document 5]
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 always satisfactory in terms of uniformity and monodispersity of the obtained copper powder. For example, when copper oxide or hydroxide is used as a raw material, the particle size of the copper oxide or copper hydroxide, or the particle size of the metal copper powder produced differs depending on the manufacturing method, The copper metal powder produced in the reduction also has the disadvantages of poor uniformity and not high dispersibility.
[0007]
The present invention has been made to solve these problems, and an object of the present invention is to provide a method for producing a copper powder having a uniform particle size and excellent monodispersity, and particularly suitable for producing a conductive paste. .
[0008]
[Means for Solving the Problems]
As a result of diligent research to solve the above problems, a conventional copper is used as a copper compound in a method of suspending a copper compound in a polyol solution and heating to produce a copper powder. The present inventors have found that a copper powder that is uniform and highly dispersible can be obtained as compared with the case where the oxide or hydroxide is used as a feedstock. That is, the invention of claim 1 relates to a method for producing copper powder, which comprises suspending basic copper carbonate in a liquid containing a polyol and heating it at an arbitrary temperature of 150 to 350 ° C.
[0009]
Invention of Claim 2 concerns the manufacturing method of the copper powder of Claim 1, Comprising: The said polyol is 1 type (s) or 2 or more types chosen from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and glycerin. is there.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Basic copper carbonate is a general term for compounds containing a part of hydroxide in copper carbonate, and is obtained by adding alkali carbonate to a copper (II) salt aqueous solution. The composition of the amount of hydroxide varies depending on the production conditions. It becomes. Basic copper carbonate used in the present invention was precipitated by mixing an aqueous solution of alkali metal, alkaline earth metal carbonate, or ammonium carbonate in an aqueous solution of copper sulfate, copper chloride, or copper nitrate in the neutral region or more. Although the reaction product is obtained by filtration and separation, it may be commercially available as basic copper carbonate.
[0011]
The polyol used in the present invention is a compound having two or more alcoholic hydroxyl groups in the molecule. Specifically, it is ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, or glycerin. One species may be used alone, or two or more species may be combined. The present invention is preferably carried out using a polyol as a solvent in such an amount that can be stirred smoothly throughout the reaction, and a polyol that is liquid at 150 ° C. or higher is preferably selected. Alternatively, the polyol may be dissolved in another solvent. In the case of using other solvents, it goes without saying that the higher the concentration of the polyol, the more advantageous, but in practice, 2 mol or more of the polyol is necessary for 1 mol of the obtained copper. Here, the solvent may be water, but if a large amount of water coexists, the reduction reaction is performed by heating to 150 ° C. or higher, and in that case, there are disadvantages such as performing under pressure. Therefore, the solvent used here is preferably a water-soluble solvent having a normal pressure and a boiling point of 150 ° C. or higher, such as butyl cellosolve.
[0012]
In carrying out the present invention, first, basic copper carbonate is suspended in a liquid containing a polyol. Basic copper carbonate is more advantageous as it is finer, and usually has a particle size of 10 μm or less. Next, the suspension is stirred at an arbitrary temperature of 150 to 350 ° C.
[0013]
The heating time varies depending on the heating temperature, the type and amount of polyol, and is typically about 0.5 to 5 hours. Strictly speaking, it is better to determine that the reaction has completely terminated by taking a sample and performing X-ray diffraction. However, it can be estimated by changing the color of the reaction system, no foaming, etc. it can. After completion of the reaction, the mixture is filtered, washed with water and dried to obtain metallic copper powder.
[0014]
The present invention is characterized by using basic copper carbonate. The reduction reaction from basic copper carbonate to metallic copper occurs with an oxidation reaction in which the terminal hydroxyl group of the polyol becomes a carboxyl group via an aldehyde group. Basic copper carbonate is easily decomposed by heat in a liquid containing a polyol, and immediately undergoes a reduction reaction with the polyol from the state, so that the generated copper metal particles are considered to be small and uniform. Moreover, since it is basic copper carbonate, it is also advantageous that the influence of the monodispersibility reduction and agglomeration of copper powder caused by sulfate radical, hydrochloric acid radical, nitrate radical, etc., pointed out in Patent Document 4 can be avoided.
[0015]
In the present invention, a saccharide can be further added to the polyol to promote the reduction reaction.
[0016]
【Example】
Unless otherwise stated, the basic copper carbonate in the examples is obtained by mixing 2 L of 1.6 mol / L aqueous copper sulfate solution and 1.6 mol / L aqueous sodium carbonate solution at 70 to 80 ° C. with PH = 7 or more. The reaction product was separated and thoroughly washed with water.
[0017]
Example 1 Basic copper carbonate and 2 kg of ethylene glycol (boiling point 197 ° C.) as a polyol were put into a 5 L round bottom separable flask and heated at 180 ° C. for 1 hour with stirring to prepare copper powder. After separating, washing and drying the obtained copper powder, the particle size distribution was measured and the particles were observed with a scanning electron microscope.
[0018]
FIG. 1 shows the particle size distribution of the obtained copper powder. Since the slope of the graph shown in FIG. 1 is large, it can be seen that the distribution width is a very narrow particle (uniform particle). The particle size corresponding to a cumulative frequency of 50% was 3.5 μm.
[0019]
FIG. 2 shows an electron micrograph of the obtained copper powder. When the particle shape is observed, it is observed that the polyhedral particles having a uniform crystal size and grown are independent (monodispersed).
[0020]
[Example 2] Copper powder was prepared in the same manner as in Example 1 except that triethylene glycol (boiling point 285 ° C) was used as the polyol and the heating temperature was 250 ° C. As a result of measuring the particle size distribution of the obtained body powder, 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). 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).
[0021]
[Example 3] Similar to Example 1, except that 0.383 kg of a reagent manufactured by Kishida Chemical Co., Ltd. (1.6 mol as CuCO ₃ · Cu (OH) ₂ · H ₂ O) was used as basic copper carbonate. A copper powder was prepared. As a result of measuring the particle size distribution of the obtained body powder, it was found that the particle size corresponding to a cumulative frequency of 50% was 3.6 μm and the distribution width was very narrow (uniform particles). 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).
[0022]
[Example 4] Copper powder was prepared in the same manner as in Example 1 except that glycerin (boiling point: 290 ° C) as a polyol, heating temperature: 160 ° C, and reaction time: 3 hours. As a result of measuring the particle size distribution of the obtained body powder, it was found that the particle size corresponding to a cumulative frequency of 50% was 4.6 μm, and the distribution width was very narrow (uniform particles). 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).
[0023]
[Comparative Example 1] The same procedure as in Example 1 was conducted except that 0.254 kg (3.2 mol) of cupric oxide (special grade reagent by Hanai Tesque Co., Ltd.) was used instead of basic copper carbonate. The obtained powder was a mixture of copper (Cu), cuprous oxide (Cu ₂ O) and cupric oxide (CuO) by an X-ray diffraction method, and was found to be insufficiently reduced.
[0024]
[Comparative Example 2] Example 1 except that 0.798 kg (3.2 mol) of copper sulfate pentahydrate instead of basic copper carbonate, 4 kg of ethylene glycol as a polyol, and 7 hours of reaction time were used. And performed in the same manner. The obtained solid was black and was identified by X-ray diffraction. As a result, cuprous oxide was mainly contained and copper was contained only a little. The liquid phase after the reaction was colored dark green, suggesting that unreacted copper compound remained.
[0025]
[Comparative Example 3] Except for 0.546 kg (3.2 mol) of cupric chloride dihydrate instead of basic copper carbonate, 4 kg of ethylene glycol as a polyol, and a reaction time of 7 hours. Performed as in Example 1. The resulting solid was white and was identified by cuprous chloride as identified by X-ray diffraction.
[0026]
[Comparative Example 4] The same procedure as in Example 1 was conducted except that 0.639 kg (3.2 mol) of cupric acetate monohydrate and 4 kg of ethylene glycol as the polyol were used instead of basic copper carbonate. . The obtained copper powder formed an aggregate having a diameter of 1 to 5 mm.
[0027]
[Comparative Example 5] The same operation as in Example 1 was performed except that the heating temperature was 140 ° C and the reaction time was 10 hours. As a result of powder X-ray diffraction analysis, the obtained solid particles were basic copper carbonate.
[0028]
【The invention's effect】
According to the present invention, a copper powder having a uniform particle diameter and excellent monodispersity can be produced. This is suitable for the production of a conductive paste used for forming a wiring pattern of a circuit board and forming an external electrode of a chip capacitor.
[Brief description of the drawings]
1 is a particle size distribution measurement result of the copper powder obtained in Example 1. FIG.
2 is an electron micrograph of the copper powder obtained in Example 1. FIG.

Claims (2)

A method for producing a copper powder, characterized in that basic copper carbonate is suspended in a liquid containing a polyol and heated at an arbitrary temperature of 150 to 350 ° C. The method for producing copper powder according to claim 1, wherein the polyol is one or more selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and glycerin.

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