JP2004225087A - Method for manufacturing copper powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a copper powder which has a uniform particle size, is superior in monodispersibility, and is suitable particularly for manufacturing a conductive paste. <P>SOLUTION: This manufacturing method comprises adding a copper salt soluble in the below-described liquid (e.g. cupric sulfate, cupric chloride, or cupric acetate), an alkaline agent (e.g. a hydroxide, a weak acid salt, or an organic acid salt of an alkali metal or ammonium), and a saccharide (e.g. a monosaccharide, a disaccharide or a water-soluble polysaccharide) to a liquid containing a polyol (e.g. a glycol or glycerin) and heating the resultant liquid at an arbitrary temperature between 100°C and 350°C. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention is suitable for a method for producing a copper powder, and more particularly, for a conductive paste used for forming a wiring pattern on a circuit board and forming an external electrode of a chip capacitor, having a uniform particle size and excellent monodispersity. The present invention relates to a method for producing copper powder.
[0002]
[Prior art]
Copper powder constituting a conductive paste used for forming a wiring pattern of a circuit board or forming an external electrode of a chip capacitor is required to be fine particles having a uniform particle diameter and excellent monodispersity. For example, copper powder used for the conductive paste generally has a particle size of about 1 μm to 10 μm, but recently, the demand for a particle size of 1 μm or less has been increasing.
[0003]
Methods for producing copper powder include mechanical pulverization, atomization by spraying molten copper, electrolytic deposition on the cathode, heat reduction of copper salts and copper oxides in a reducing atmosphere, and copper chloride. A method of reducing steam with a reducing gas and a method of reducing an aqueous copper salt solution with a reducing agent such as hydrazine are known. Among these, the wet reduction method of reducing hydrazine or the like as a reducing agent from an aqueous solution of a copper salt is a relatively easy method (for example, see Patent Document 1).
[0004]
Further, in a wet reduction method, a method of heating and reducing a solid compound composed of a copper oxide, a hydroxide or a copper salt using a polyol as a solvent (see Patent Documents 2 and 3), or in a similar reaction system Furthermore, a method of adding a monosaccharide or disaccharide as a reducing agent and reducing by heating (see Patent Document 4) has been proposed as a method for obtaining fine copper powder safely and at low cost.
[0005]
[Patent Document 1]
JP-A-57-155302 [Patent Document 2]
US Patent No. 4539041 [Patent Document 3]
Japanese Patent Publication No. 4-24402 [Patent Document 4]
JP-A-11-152506
[Problems to be solved by the invention]
However, the wet reduction method using the 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 produced metal copper powder differs depending on the particle shape of the copper oxide or copper hydroxide or the difference in the manufacturing method, and the wet-type The metal copper powder produced in the reduction also has the disadvantage that the uniformity is poor and the dispersibility is not high.
[0007]
The present invention has been made in order to solve these problems, and it is an object of the present invention to provide a method for producing a copper powder having a uniform particle diameter and excellent monodispersibility, and particularly suitable for producing a conductive paste. .
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, in the polyol, a soluble copper salt, an alkali agent is added to the polyol to form a copper compound such as an oxide, a hydroxide, a weak acid salt, an organic acid salt, and the state The present inventors have found that a suitable copper powder can be obtained by reducing with a polyol and a saccharide in the present invention, and have accomplished the present invention. That is, claim 1 of the present invention relates to a method for producing a copper powder, wherein a soluble copper salt, an alkali agent and a saccharide are added to a liquid containing a polyol, and the liquid is heated at an arbitrary temperature of 100 to 350 ° C. It consists of doing.
[0009]
A second aspect of the present invention relates to the method for producing copper powder according to the first aspect, wherein a soluble copper salt and an alkali agent are added to a liquid containing a polyol to convert copper into an oxide, a hydroxide, or a weak acid salt. , An organic acid salt or a mixture thereof, and then adding a saccharide.
[0010]
Claim 3 of the present invention relates to the method for producing copper powder according to claim 1 or 2, wherein the polyol is one or two selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and glycerin. That is all.
[0011]
Claim 4 of the present invention relates to the method for producing copper powder according to claim 1 or 2, wherein the soluble copper salt is one or more selected from cupric sulfate, cupric chloride and cupric acetate. It is.
[0012]
Claim 5 of the present invention relates to the method for producing copper powder according to claim 1 or 2, wherein the alkali agent is one or more selected from hydroxides, weak acid salts and organic acid salts of alkali metals and ammonium. It is.
[0013]
Claim 6 of the present invention relates to the method for producing copper powder according to claim 1 or 2, wherein the saccharide is one or more selected from monosaccharides, disaccharides and water-soluble polysaccharides.
[0014]
Claim 7 of the present invention relates to the method for producing copper powder according to claim 1 or 2, wherein the saccharide is added in an amount of 0.05 to 5 parts by weight based on 1 part by weight of the obtained copper powder. .
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is to react a soluble copper salt, an alkali agent, and a saccharide with respect to the liquid in the liquid containing the polyol. The precursor of copper powder such as copper oxide, hydroxide, weak acid salt, organic acid salt or a mixture thereof by reacting a soluble copper salt with an alkali agent (hereinafter collectively referred to as “copper powder precursor”) And then reducing it with polyols and sugars to form metallic copper.
[0016]
The polyol used in the present invention is a compound having two or more alcoholic hydroxyl groups in the molecule. Specific examples thereof include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and glycerin. Species may be used alone or in combination of two or more. The present invention is preferably carried out by using a polyol as a solvent in such an amount that stirring can be carried out smoothly throughout the reaction, and a polyol that is liquid at 100 ° C. or higher is preferably selected. Alternatively, the reaction may be performed by dissolving the polyol in another solvent. In the case of using a solvent, it goes without saying that the higher the concentration of the polyol is, the more advantageous it is. However, practically, 2 mol or more of the polyol is required for 1 mol of the obtained copper. The solvent may be water, but if water coexists in a large amount, it is disadvantageous in that it is heated to 100 ° C. or higher in the step of performing the reduction reaction, and is performed under pressure. Therefore, as the solvent, a water-soluble solvent having a boiling point of 100 ° C. or more at normal pressure, such as butyl cellosolve, is preferably selected.
[0017]
The soluble copper salt is a copper salt that is soluble in the polyol, specifically, for example, cupric sulfate, cupric chloride or cupric acetate, or a hydrate thereof. Good. One soluble copper salt may be used alone, or two or more soluble copper salts may be used in combination.
[0018]
The alkali agent reacts with a soluble copper salt in a liquid containing a polyol to generate a copper powder precursor. To be specific, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, Examples thereof include a weak acid salt of an alkali metal such as sodium hydrogen or sodium carbonate, an organic acid salt of an alkali metal such as sodium acetate and sodium succinate, and ammonium hydroxide. The stoichiometric amount necessary for neutralizing the soluble copper salt or a slightly larger amount of the alkali agent is sufficient. Exceeding the stoichiometric amount is disadvantageous in terms of cost, while lowering the amount lowers the recovery rate of copper powder.
[0019]
On the other hand, a reaction between the alkali agent and the soluble copper salt generates a copper powder precursor, and at the same time, generates an alkali metal salt or an ammonium salt. The alkali metal salt or ammonium salt is determined depending on the type of the alkali agent and the soluble copper salt used, and includes sodium sulfate, sodium chloride, sodium acetate, potassium sulfate, potassium chloride, ammonium sulfate, ammonium acetate, ammonium chloride and the like.
[0020]
Saccharides act as secondary reducing agents in the present invention, and specific examples include monosaccharides such as glucose (glucose) and fructose (fructose); disaccharides such as maltose (maltose) and sucrose (sucrose); It is a water-soluble polysaccharide such as starch. It is appropriate to add 0.05 to 5 parts by weight of the saccharide to 1 part by weight of the obtained copper. If the amount is less than this, the obtained copper powder becomes insufficient in uniformity and dispersibility. On the other hand, if the amount is too large, the viscosity of the reaction solution increases and stirring becomes insufficient, and a large amount of time is required for washing the obtained copper powder, and it is economically disadvantageous.
[0021]
Next, an embodiment of a method for producing a copper powder of the present invention will be described.
The present invention comprises adding a soluble copper salt, an alkali agent, and a saccharide to a liquid containing a polyol and heating the liquid at an arbitrary temperature of 100 to 350 ° C. The alkaline agent can be used in the form of an aqueous solution or crystals. The saccharide may be dissolved in a liquid containing a polyol in advance. Particularly preferably, first, a soluble copper salt and an alkali agent are added to a liquid containing a polyol to form a copper powder precursor. At the same time, an alkali metal salt or an ammonium salt is also generated. Next, saccharides are added and the whole is heated at an arbitrary temperature of 100 to 350 ° C. to obtain metallic copper powder. The heating temperature is preferably equal to or lower than the boiling point of the liquid containing the polyol at normal pressure, but when the boiling point of the liquid containing the polyol is low, the heating can be performed under pressure.
[0022]
When components having a low boiling point, such as water, are mixed together with soluble copper salts, alkaline agents, saccharides, etc., the temperature is gradually raised while removing these low-boiling substances, so as to finally reach a predetermined temperature. The heating time varies depending on the heating temperature, the type and amount of the polyol, the type and amount of the saccharide, and the like, but is typically about 0.5 to 5 hours. Strictly speaking, it is better to determine whether the reaction is complete by taking a part of the sample and conducting X-ray diffraction. However, it is important to note that the color of the reaction system changes and the generated water comes out as bubbles. It can be estimated from a change in the situation, such as disappearance. After completion of the reaction, the mixture is filtered, washed with water and dried to obtain metallic copper powder.
[0023]
The reduction reaction of the copper powder precursor into copper powder occurs along with the oxidation reaction between the polyol and the saccharide. In the case of a polyol, this is an oxidation reaction in which a terminal hydroxyl group becomes a carboxyl group via an aldehyde group, and in the case of a saccharide, it is an oxidation reaction in which a reducing sugar becomes an organic acid.
[0024]
The present invention is characterized in that a copper powder precursor is precipitated in a system in which a reduction reaction is performed, and this is reduced in the presence of an alkali metal salt or an ammonium salt by combining a polyol and a saccharide. This copper powder precursor is fine in shape and the surface is in a state where it can be easily reduced, the reducing action by the polyol and the saccharide interact with each other, and further, it is a by-product when the copper powder precursor is generated An alkali metal salt or an ammonium salt advantageously acts as a dispersant that prevents aggregation of copper particles generated by a reduction reaction. It is considered that this resulted in a uniform copper powder particle diameter and excellent dispersibility.
[0025]
【Example】
Hereinafter, the present invention will be described specifically with reference to examples. However, these examples are merely examples, and the present invention is not limited to these examples.
[0026]
[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 alkali agent. The aqueous solution contained was added to obtain a suspension containing copper hydroxide (copper hydroxide) and sodium sulfate which is an alkali metal salt by-produced. Subsequently, this solution and 100 g of sucrose (a weight ratio with respect to the obtained copper powder), which is a disaccharide, were put into a 5 L round bottom separable flask, and heated at 180 ° C. for 1 hour with stirring to obtain copper. Powder was obtained.
[0027]
After separating, washing and drying the obtained copper powder, 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 particles had a particle size corresponding to a cumulative frequency of 50% of 3.7 μm and had a very narrow distribution width (uniform particles). Further, from observation of the particle shape by an electron microscope, it was confirmed that polyhedral particles of a uniform size with crystal faces grown were independent (monodispersed).
[0028]
[Example 2] 273 g (1.6 mol) of cupric chloride dihydrate was used as a soluble copper salt, and 100 g of glucose (a weight ratio to the obtained copper powder was 1.0) which was a monosaccharide was used as a sugar. A copper powder was prepared in the same manner as in Example 1 except for the above.
[0029]
As a result of the particle size distribution measurement, it was found that the particles (uniform particles) having a particle size corresponding to the cumulative frequency of 50% and having a very narrow distribution width of 5.4 μm. Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal faces grown were observed independently (monodispersed).
[0030]
[Example 3] An aqueous solution containing 391 g (1.6 mol) of cupric acetate monohydrate as a soluble copper salt in 3.2 mL of ethylene glycol as a polyol and 3.2 mol of sodium hydroxide as an alkali agent was added. The procedure was performed in the same manner as in Example 1 except that copper was used as a hydroxide, fructose as a monosaccharide was used as a sub-reducing agent, and the reaction temperature was set at 130 ° C.
[0031]
As a result of the particle size distribution measurement, it was found that the particles had a particle size corresponding to a cumulative frequency of 50% of 0.4 μm and had a very narrow distribution width (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 faces grown were observed independently (monodispersed).
[0032]
Example 4 Except that the reaction temperature was 230 ° C. using diethylene glycol (boiling point: 245 ° C.) as the polyol, and the amount of sucrose added was 50 g (the weight ratio to the obtained copper powder was 0.5). , And in the same manner as in Example 1.
[0033]
As a result of the particle size distribution measurement, it was found that the particles had a particle size corresponding to a cumulative frequency of 50% of 0.2 μm and had a very narrow distribution width (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 faces grown were observed independently (monodispersed).
[0034]
Example 5 A copper powder was prepared in the same manner as in Example 1, except that soluble starch, which is a polysaccharide, was used as the saccharide.
[0035]
As a result of the particle size distribution measurement, it was found that the particles (homogeneous particles) having a particle size corresponding to the cumulative frequency of 50% of 4.1 μm and having a very narrow distribution width were obtained. Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal faces grown were observed independently (monodispersed).
[0036]
Example 6 A copper powder was prepared in the same manner as in Example 1, except that an aqueous solution containing glycerin (boiling point: 290 ° C.) as a polyol and 1.6 mol of sodium succinate as an alkaline agent was added. Here, the precursor of the copper powder is considered to be copper succinate, which is an organic acid salt, and the by-produced salt is sodium sulfate.
[0037]
As a result of the particle size distribution measurement, it was found that the particles (uniform particles) having a particle size corresponding to the cumulative frequency of 50% and having a very narrow distribution width of 5.4 μm. Further, when the particle shape was observed with an electron microscope, as in Example 1, polyhedral particles of a uniform size with crystal faces grown were observed independently (monodispersed).
[0038]
Example 7 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 was added as an alkali agent and the heating temperature was set to 160 ° C.
[0039]
As a result of the particle size distribution measurement, it was found that the particles had a particle size corresponding to a cumulative frequency of 50% of 8.3 μm and had a very narrow distribution width (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 faces grown were observed independently (monodispersed).
[0040]
Example 8 A copper powder was prepared in the same manner as in Example 1 except that the amount of sucrose added was 10 g (the weight ratio to the obtained copper powder was 0.1).
[0041]
As a result of the particle size distribution measurement, it was found that the particles had a particle size corresponding to a cumulative frequency of 50% of 3.3 μm and had a very narrow distribution width (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 faces grown were observed independently (monodispersed).
[0042]
[Comparative Example 1] The same operation as in Example 1 was carried out except that the alkali agent was not added, and no solid particles were obtained.
[0043]
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 as an alkali agent was added thereto. A suspension solution containing copper hydroxide (copper hydroxide) and sodium sulfate as a by-product alkali metal salt was prepared. Next, the solid phase copper hydroxide is recovered from the suspension by filtration, washed with water to remove sodium sulfate which is a by-product alkali metal salt, and suspended again in 2000 mL of ethylene glycol as a polyol. Turned cloudy. Subsequently, in the same manner as in Example 1, this liquid and 100 g of sucrose, which is a disaccharide, were placed in a 5 L round bottom separable flask and heated at 180 ° C. for 1 hour to prepare copper powder.
[0044]
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 at around 0.2 μm and a distribution centered at around 3 μm, and particles having a very wide distribution width ( (Heterogeneous particles).
[0045]
Comparative Example 3 The same operation as in Example 1 was carried out except that the heating temperature was 90 ° C. using water as the solvent and glucose 300 g as the sugar. As a result of powder X-ray diffraction analysis, the obtained solid particles were cuprous oxide (Cu ₂ O).
[0046]
[Comparative Example 4] The procedure of Example 1 was repeated, except that 391 g (1.6 mol) of cupric acetate monohydrate was used as a soluble copper salt, and no alkali agent or sugar was added. The obtained copper powder formed an aggregate having a diameter of 1 to 5 mm.
[0047]
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. FIG. 2 shows the results of measuring the particle size distribution of the obtained copper particles. From these results, it was found that the particles corresponded to a cumulative frequency of 50% and had a particle size of 17.0 μm and a wide distribution width (uneven particles).
[0048]
[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% and a wide distribution width of 13.2 μm, as in Comparative Example 4. .
[0049]
【The invention's effect】
According to the present invention, it is possible to produce a copper powder having a uniform particle diameter and excellent monodispersity as compared with the conventional method. This is more suitable for a conductive paste used for forming a wiring pattern on a circuit board or forming an external electrode of a chip capacitor.
[Brief description of the drawings]
FIG. 1 shows the results of measuring the particle size distribution of the powder obtained in Example 1.
FIG. 2 shows the results of measuring the particle size distribution of the powders obtained in Comparative Examples 2 and 5.
FIG. 3 is a scanning electron micrograph of the powder obtained in Example 1.

Claims (7)

A method for producing a copper powder, comprising adding a soluble copper salt, an alkali agent and a saccharide to a liquid containing a polyol and heating the liquid at an arbitrary temperature of 100 to 350 ° C. In a liquid containing a polyol, a soluble copper salt and an alkali agent are added to the liquid to convert copper into an oxide, a hydroxide, a weak acid salt, an organic acid salt or a mixture thereof, and then a saccharide is added. The method for producing copper powder according to claim 1, wherein: The method for producing a copper powder according to claim 1, wherein the polyol is at least one selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and glycerin. 4. The method for producing copper powder according to claim 1, wherein the soluble copper salt is at least one selected from cupric sulfate, cupric chloride, and cupric acetate. 4. The method for producing copper powder according to claim 1 or 2, wherein the alkali agent is one or more selected from hydroxides, weak acid salts, and organic acid salts of alkali metals and ammonium. The method for producing copper powder according to claim 1, wherein the saccharide is one or more selected from a monosaccharide, a disaccharide, and a water-soluble polysaccharide. The method for producing copper powder according to claim 1 or 2, wherein the saccharide is added in an amount of 0.05 to 5 parts by weight based on 1 part by weight of the obtained copper powder.

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