TW201728761A - Metal composite powder and method for producing same - Google Patents

Abstract

There is prepared a silver-coated copper powder wherein the surface of a copper powder having an average particle diameter of 0.1 to 100 [mu]m is coated with 5 % by weight or more of silver, and the silver-coated copper powder is sprayed into the tail flame region of a thermal plasma to cause silver on the surface of the copper powder to diffuse in the grain boundaries of copper on the inside of the copper powder to produce a metal composite powder wherein the percentage of the area occupied by silver on a cross section of the metal composite powder is 3 to 20 %.

Description

Metal composite powder and its manufacturing method (1)

FIELD OF THE INVENTION The present invention relates generally to a metal composite powder and a method of making the same. Specifically, the present invention relates to a metal composite powder for a conductive paste or the like, and a method for producing the same.

Conventional Art Description Conventionally, in order to form an electrode and an electric wire of an electronic component by a printing method or the like, it is used by mixing a solvent, a resin, a dispersant or the like into a conductive metal powder such as silver or copper powder. One of the conductive pastes is produced.

However, silver powder is expensive because it is a noble metal powder, although it has a very low volume resistance and is a good conductive material. On the other hand, copper powder has a poor storage stability (reliability) than silver powder because it is easily oxidized, although it has a low volume resistance and is a good conductive material.

In order to solve such problems, a copper powder coated with silver is proposed, in which the surface of the copper powder is coated with silver as a metal powder for one of the conductive pastes (see, for example, Japanese Patent Laid-Open Publication No. Cases 2010-174311 and 2010-077495).

However, the silver-coated copper powder disclosed in Japanese Patent Laid-Open Publication Nos. 2010-174311 and 2010-077495, if a portion of the copper surface is not coated with silver, oxidation will proceed from this portion. Therefore, its storage stability (reliability) is insufficient.

In particular, since oxygen easily diffuses in the grain boundary, oxidation proceeds from the particle boundary of copper by diffusion of oxygen along the boundary of the copper particle (particle boundary diffusion).

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to obviate the above problems and to provide a metal composite powder containing copper and silver which can improve its storage stability (reliability) by avoiding oxidation from the boundary of copper particles. And its manufacturing method.

In order to accomplish the foregoing and other objects, the inventors have diligently studied and found that if the copper powder coated with silver coated silver coated copper powder is sprayed into the tail flame region of one of the thermal plasmas, the silver on the surface of the copper powder is By diffusing in the boundary of the copper particles on the inner side of the copper powder, it is possible to produce a metal composite powder which can improve storage stability (reliability) by avoiding oxidation from the boundary of the particles of copper. Therefore, the inventors have completed the present invention.

According to the present invention, there is provided a method for producing a metal composite powder, the method comprising the steps of: preparing a silver coated copper powder, wherein a surface of a copper powder is coated with silver; and coating the silver with silver The copper powder is sprayed into the tail gas region of one of the hot plasmas so that the silver on the surface of the copper powder diffuses into the boundary of the copper particles on the inner side of the copper powder.

In the method for producing a metal composite powder, the tail gas region of the hot plasma preferably has a temperature of 2000 to 5000 K. The copper powder is preferably produced by atomization. The copper powder preferably has an average particle diameter of 0.1 to 100 μm. The silver content is preferably 5% by weight or more with respect to the copper powder coated with silver.

According to the present invention, there is provided a metal composite powder comprising: a copper powder; and silver which is diffused in a copper particle boundary on the inner side of the copper powder. In the metal composite powder, the copper powder preferably has an average particle diameter of 0.1 to 100 μm. The silver content is preferably 5% by weight or more with respect to the metal composite powder. The percentage of a region occupied by silver in one of the cross sections of the metal composite powder is preferably from 3 to 20%.

As used throughout the specification, the expression "average particle diameter of a copper powder" means the cumulative particle diameter corresponding to 50% of the cumulative distribution of copper powder measured by a laser diffraction particle size analyzer (D ₅₀ diameter).

According to the present invention, there can be provided a metal composite powder containing copper and silver, which can improve its storage stability (reliability) by avoiding oxidation from the boundary of copper particles, and a method for producing the same.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a method for producing a metal composite powder according to the present invention, wherein a surface of a copper powder is sprayed with a silver-coated powder coated with silver. In one of the hot plasma regions, the silver on the surface of the copper powder is diffused into the boundary of the copper particles on the inner side of the copper powder.

Although the copper powder as a raw material can be produced by a wet reduction method, an electrolysis method, a vapor phase method, or the like, it is preferably produced by a so-called atomization method (such as a gas atomization method or a water atomization method). ), which is used to rapidly cool and solidify copper which is melted at a temperature not lower than its melting temperature to produce a fine powder by causing molten copper to fall from a portion below a feed tank. A high pressure gas or high pressure water collides with it. In particular, if the copper powder is produced by a so-called water atomization method for spraying a high-pressure water, it is possible to obtain a copper powder having a small particle size, and thus, since copper powder is used for preparing a conductive paste, By increasing the number of contact points between the copper powder particles, the conductivity of the conductive paste can be improved.

The average particle diameter of the copper powder is preferably in the range of from 0.1 μm to 100 μm, more preferably in the range of from 0.5 μm to 20 μm, and most preferably in the range of from 1 μm to 10 μm. If the average particle diameter of the copper powder is less than 0.1 μm, it is not preferable because it has a bad influence on the conductivity of the copper powder coated with silver. On the other hand, if the average particle diameter of copper exceeds 100 μm, it is not preferable because it is difficult to form a fine electric wire.

As a method for coating a copper powder with silver, silver may be deposited on the surface of the copper powder by using a substitution method using a substitution reaction for replacing silver with silver, or by a reduction method using a reducing agent. The method above. For example, a method of depositing silver on a surface of a copper powder while stirring a solution containing one of copper powder and silver ions in a solvent, or a method of containing copper powder and an organic material in a solvent while stirring may be used. A method of depositing silver on the surface of a copper powder when the solution contains a mixed solution of silver ions and a solution of one of the organic materials in a solvent.

As the solvent, water, an organic solvent, or a mixed solvent of these may be used. If a solvent is prepared by mixing water with an organic solvent, it is used at room temperature (20 to 30 ° C) as one of the liquid organic solvents, and the mixing ratio of water and organic solvent can be determined according to the organic solvent used. Adjust appropriately. When water is used as a solvent, distilled water, ion-exchanged water, industrial water, or the like can be used unless there is a possibility that impurities are mixed therein.

As a raw material of silver, silver nitrate having high solubility for water and many organic solvents is preferably used because silver ions are required to be present in a solution. In order to carry out the reaction of coating copper powder with silver as uniformly as possible (silver coating reaction), it is preferably prepared by dissolving silver nitrate in a solvent (water, an organic solvent, or a mixed solvent thereof). One of the silver nitrate solutions, not the solid silver nitrate. The amount of the silver nitrate solution used, the concentration of silver nitrate in the silver nitrate solution, and the amount of the organic solvent can be determined depending on the desired amount of the silver-containing layer.

In order to form silver more uniformly, a chelating agent may be added to the solution. As the chelating agent, a chelating agent having a high misalignment stability constant with respect to copper ions or the like is preferably used in order to avoid reprecipitation of copper ions or the like, which is formed as a by-product by a substitution reaction of silver ions in place of metal copper. In particular, the chelating agent is preferably selected in view of the mismatching stability constant with respect to copper because the copper powder as the core of the copper powder coated with silver contains copper as a main constituent element. In particular, as the chelating agent, one selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), aminodiacetic acid, diethylenetriamine, triethylenediamine, and the like Chelating agent.

In order to carry out the silver coating reaction stably and safely, a pH buffer may be added to the solution. As the pH buffer, ammonium carbonate, ammonium hydrogencarbonate, ammonia water, sodium hydrogencarbonate or the like can be used.

When a silver coating reaction is carried out, a solution containing one of the silver salts is preferably added to a solution in which the copper powder is after the copper powder is placed therein and before the silver salt is added thereto The solution was sufficiently dispersed. The reaction temperature of the silver coating reaction may be a temperature which does not cause the reaction solution to solidify or evaporate. The reaction temperature is preferably set to 10 to 40 ° C, and more preferably 15 to 35 ° C. The reaction time can be set to range from 1 minute to 5 hours, even if it is changed depending on the amount of silver coated and the reaction temperature.

The amount of silver (coating amount) relative to the copper powder coated with silver is preferably 5% by weight or more, more preferably from 7% by weight to 50% by weight, more preferably from 8% by weight to It is in the range of 40% by weight, and most preferably ranges from 9% by weight to 20% by weight. If the amount of silver is less than 5% by weight, it is not preferred because it has a bad influence on the conductivity of the silver-coated copper powder. On the other hand, if the amount of silver exceeds 50% by weight, it is not preferable because the cost is high due to an increase in the amount of silver used.

The silver-coated copper powder thus obtained is sprayed to the end of the hot plasma to be heat treated to diffuse the silver on the surface of the copper powder to the grain boundary of the copper on the inner side of the copper powder. Since the plasma flame uses a clean gas, it is impossible to adhere impurities to the silver coated copper powder sprayed into the hot plasma tail flame. The time during which heat is applied to the silver-coated copper powder by the tail region of the hot plasma is a short period of time, so that the silver-coated copper powder can be prevented from coalescing.

A typical method for producing ultrafine particles (nanoparticles) by directly feeding a raw material into a plasma flame by using a hot plasma, the raw material being in a high temperature region of not less than 10,000 ° C of the plasma flame. Immediately heated to several thousand degrees Celsius, decomposed into atoms and/or groups, rapidly cooled to about 1,000 ° C in a downstream low temperature region, a uniform nucleation occurs, and ultrafine particles are synthesized. However, in a preferred embodiment of the method for producing a metal composite powder according to the present invention, the silver coated copper powder is fed into the plasma tail flame region having a temperature of 2000 to 5000 K, thus The silver-coated copper powder has a lower melting point of silver than the copper melt diffusion when it passes through the plasma tail flame region for a short period of time. Therefore, when the shape of the copper powder as the core of the copper powder coated with silver is maintained to some extent, the silver on the surface of the copper powder is diffused into the grain boundary of copper on the inner side of the copper powder. Further, the silver on the surface of the copper powder is preferably diffused into the grain boundary of the copper on the inner side of the copper powder to reach 1/3 or more of the diameter of the copper powder particles from the surface of the copper powder, and more preferably It diffuses into the entire grain boundary of the copper on the inside of the copper powder.

Spraying the silver coated copper powder into the tail gas region of the hot plasma can be carried out by a hot plasma device. In order to feed the silver-coated copper powder to the tail gas region of the hot plasma having a temperature of 2000 to 5000 K by a hot plasma device, the output of the plasma device is preferably 2 to 10 kW, more preferably 4 to 8 kW, and the best is 5 to 7 kW. The flow rate of the argon gas for the plasma is preferably from 5 to 40 liters/min, and more preferably from 15 to 25 liters/min. The flow rate of the carrier nitrogen for providing the silver-coated copper powder is preferably from 0 to 3 liters/min, and more preferably from 0 to 0.5 liters/min. The pressure in the apparatus is preferably from 0 to 100 kPa, and more preferably from 50 to 100 kPa. The amount of the silver-coated copper powder supplied is preferably from 0.1 to 400 g/min, and more preferably from 100 to 400 g/min.

In the above preferred embodiment for producing a metal composite powder according to the present invention, a metal composite powder in which silver is diffused on the boundary of copper particles on the inner side of a copper powder can be produced. The silver content relative to the metal composite powder may be 5% by weight or more (preferably 7 to 50% by weight, more preferably 8 to 40% by weight, and most preferably 9 to 20% by weight). The percentage of a region occupied by silver in one of the cross sections of the metal composite powder may be 3 to 20% (preferably 8 to 20%).

At the grain boundary, the crystal arrangement is in chaos and the oxygen is easily diffused, so the oxidation proceeds from the particle boundary of copper by the diffusion of oxygen along the boundary of the copper particles (particle boundary diffusion). However, in the metal composite powder according to the present invention, silver is diffused in the boundary of the copper particles on the inner side of the copper powder, and is filled in the boundary of the copper particles on the inner side of the copper powder. Therefore, oxidation from the boundary of the copper particles can be suppressed, so that a metal composite powder having high oxidation resistance can be provided.

An example of a metal composite powder and a method for producing the same according to the present invention will be described in detail below. Comparative example

One of commercially available copper powders (spherical atomized copper powder manufactured by Nippon Atomized Metal Powders Corporation having a purity of 99.9% by weight and an average particle diameter of 5 μm) was prepared by atomization.

It was also prepared to obtain one solution (solution 1) by dissolving 2.6 kg of ammonium carbonate in 450 kg of pure water, and by adding 92 kg of an aqueous solution of silver nitrate containing 16.904 kg of silver to 319 kg. One solution (solution 2) was obtained by dissolving EDTA-4Na (43%) and 76 kg of ammonium carbonate in 284 kg of pure water to obtain one solution.

Then, 100 kg of the above copper powder was added to the solution 1 in a nitrogen atmosphere, and when the solution was stirred, the temperature of the solution was raised to 35 °C. Then, the solution 2 was added to a solution containing copper dispersed therein, and stirred for 30 minutes.

Thereafter, one of the solid components obtained by filtration is washed with ion-exchanged water until a transparent filtrate is obtained, and then the washed solid component is vacuum dried at 70 ° C to obtain a silver-coated copper powder (one silver) Coated copper powder).

A section of the silver-coated copper powder thus obtained was produced by a cross-section polisher (CP) which was observed by a field emission scanning electron microscope (FE-SEM). The composition image (COMPO image) of the BE mode of the cross section of the silver-coated copper powder observed in this observation is shown in Fig. 1. In this COMPO image, since the brightness is brighter when the atomic weight is larger, the silver display is brighter than copper, so the brighter portion corresponds to silver, and the dark portion corresponds to copper. The silver coated copper powder obtained in this comparative example can be seen from the COMPO image, and the copper powder is coated with silver. Further, the black line observed on the inner side of the copper powder as the core of the copper powder coated with silver showed the grain boundary of copper.

Then, a thermogravimetric/differential thermal analyzer (TG-DTA apparatus) (Thermo Plus EVO2 TG-8120 manufactured by Rigaku Co., Ltd.) was used to carry out the 40 mg of the silver-coated copper powder obtained from the self-obtained The TG-DTA measurement of the silver-coated copper powder was carried out from the room temperature by increasing the temperature at a temperature of 10 ° C/min while flowing air at a flow rate of 200 ml/min. 25 ° C) increased to 400 ° C. The measurement results are shown in Figure 4. Each weight of the silver-coated copper powder obtained at temperatures of 200 ° C, 250 ° C, 300 ° C, 350 ° C, and 400 ° C from the measurement with respect to the weight of the silver-coated copper powder before heating Storage stability (reliability) of silver-coated copper powder based on the weight increase rate (%) of the difference between the weight of the silver-coated copper powder before heating (weight by heating) It is evaluated by evaluating the high temperature stability (related to oxidation) of silver coated copper powder in air, which assumes that all the weight increased by heating is increased by oxidation of silver coated copper powder. weight. As a result, the weight gain rates at 200 ° C, 250 ° C, 300 ° C, 350 ° C, and 400 ° C were 0.16%, 0.46%, 1.27%, 3.80%, and 6.54%, respectively. The TG-DTA measurement of the silver-coated copper powder obtained in this comparative example showed an exothermic peak (and an increase in weight due to oxidation).

A COMPO image of a cross section of the silver-coated copper powder shown in Fig. 1 and a particle analysis software (Region Adviser manufactured by SYSTEM IN FRONTIER INC.) were used to carry out the cross section of the silver-coated copper powder of this comparative example. Image analysis. In this image analysis, after performing the date smoothing of the COMPO image, in the automatic contrast/brightness control part (ACB), the contrast is set to 100 and the brightness is controlled between 60 and 100, and One of the binary system coding systems (to construct the histogram of the luminance value on the image, and the one-way processing of the image based on the trend of the histogram) is implemented by a region division . As a result, the silver percentage (the amount of silver in the cross section) relative to the entire cross-sectional area of the copper powder coated with silver was 3.85%, which was smaller than the silver content (11.06%). Further, the silver content in the silver-coated copper powder of this comparative example was obtained as follows. First, 5.0 g of silver-coated copper powder was added to 40 ml of an aqueous solution of nitric acid, which was prepared by diluting an aqueous solution of nitric acid having a specific gravity of 1.38 in a volume ratio of 1:1 with pure water, and the solution was The silver coated copper powder was completely dissolved therein by boiling with a heater. Thereafter, an aqueous solution of hydrochloric acid is gradually added by gradually diluting a monohydrochloric acid aqueous solution having a specific gravity of 1.18 with a volume ratio of 1:1 in pure water, and the copper powder coated with silver is completely dissolved therein. The aqueous solution described above precipitates silver chloride and the aqueous hydrochloric acid solution is added until the silver chloride-free precipitate is produced. The silver content is calculated from the weight of the obtained silver chloride to obtain the silver content in the silver-coated copper powder. example

The silver-coated copper powder obtained in the comparative example was sprayed by a thermoelectric plasma apparatus (Nanoparticle Synthesis Experimental Apparatus manufactured by JEOL Ltd.) into a heat-oxidation tail flame region to obtain heat treatment. A metal composite powder. The plasma tail flame region is purple, so it can be judged that the temperature is 3000 to 5000 K. For this procedure, the output of the hot plasma device is 6 kW. The flow rate of the argon gas for the plasma was 20 liters/min, and the flow rate of the carrier nitrogen for supplying the silver-coated copper powder was 2 liters/min. The pressure in this apparatus was 50 kPa and the amount of silver coated copper powder supplied was 2.5 g/min.

After a section of the thus obtained metal composite powder was produced by a cross-section polisher (CP), the cross section was observed by a field emission scanning electron microscope (FE-SEM). The COMPO image of the cross section of the observed metal composite powder is shown in Fig. 2. From this COMPO image, the metal composite powder obtained in this example can be seen, and silver diffuses in the entire grain boundary of copper on the inner side of the copper powder even if the surface of the copper powder is not coated with silver.

Then, the cross section of the metal composite powder obtained in this example was observed by an energy dispersive X-ray spectrometer (EDS) and a launch Auger electron spectrometer (FE-AES). The mapped image of the cross section of the observed metal composite powder is shown in Fig. 3. From this mapping image, it can also be seen that silver diffuses in the boundary of the copper particles.

Regarding the obtained metal composite powder, the TG-DTA measurement was carried out by the same method as in the comparative example. The measurement results are shown in Fig. 5. The weight of each metal composite powder obtained from the weight of the metal composite powder before heating, measured at temperatures of 200 ° C, 250 ° C, 300 ° C, 350 ° C, and 400 ° C, and the weight of the metal composite powder before heating Based on the ratio (%) of the weight gain obtained by the increase in weight by heating, the storage stability (reliability) of the metal composite powder is evaluated by the high temperature stability of the metal composite powder in air (for oxidation) As assessed, it is assumed that all of the weight increased by heating is increased by oxidation of the metal composite powder. As a result, the weight gain rates at 200 ° C, 250 ° C, 300 ° C, 350 ° C, and 400 ° C were 0.42%, 0.73%, 1.38%, 2.44%, and 3.99%, respectively. From these results, it can be seen that the high-temperature stability (with respect to oxidation) of the metal composite powder in air is improved, so the storage stability (reliability) of the metal composite powder is improved because of the high temperature of the metal composite powder obtained in this example. The weight increase rate was smaller than that of the silver-coated copper powder obtained in the comparative example. Further, the TG-DTA measurement of the metal composite powder obtained in this example showed no exothermic peak (and an increase in weight due to oxidation).

Fig. 2 shows a COMPO image of a cross section of a metal composite powder and a particle analysis software (Region Adviser manufactured by SYSTEM IN FRONTIER INC.) used to carry out image analysis of a cross section of the metal composite powder of this example. As a result, the percentage of silver (the amount of silver in the cross section) with respect to the entire cross-sectional area of the metal composite powder was 12.00%, which was larger than the silver content (10.92%). Further, the silver content in the metal composite powder of this example was obtained as follows. First, 5.0 g of the metal composite powder was added to 5 ml of an aqueous solution of nitric acid prepared by diluting an aqueous solution of nitric acid having a specific gravity of 1.38 in a volume ratio of 1:1 with pure water, and the solution was passed through a heater. Boiling causes the metal composite powder to be completely dissolved therein. Thereafter, one filtrate is obtained by filtration to have a fixed volume by adding pure water thereto, and the silver content in the metal composite powder is emitted by a spectrophotometric analyzer by an inductively coupled plasma (ICP) ( Quantitative analysis of iCAP 6300) manufactured by Thermo Scientific.

Although the present invention has been disclosed in its preferred embodiments, it is understood that the invention may be embodied in various forms without departing from the principles of the invention. Therefore, the present invention is intended to be understood to include all possible embodiments and modifications of the illustrated embodiments, which may be practiced without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description of the preferred embodiments of the invention. However, the drawings are not intended to be limited to a particular embodiment, but are intended to be In the schema:

Figure 1 is an image of one of the BE (backscattered electron) modes obtained by observing a cross section of a silver-coated copper powder in a comparative example by a single emission scanning electron microscope (FE-SEM) (COMPO) image);

2 is a COMPO image obtained by observing a cross section of one of the metal composite powders by FE-SEM observation;

3 is a map image obtained by observing a section of the metal composite powder obtained by the example by an energy dispersive X-ray spectrometer (EDS) and a launch Auger electron spectroscopy (FE-AES);

4 is a graph showing measurement results of thermogravimetric differential analysis (TG-DTA) of silver-coated copper powder obtained in a comparative example; and

Fig. 5 is a graph showing the measurement results of TG-DTA of the metal composite powder obtained in the example.

Claims (9)

A method for producing a metal composite powder, the method comprising the steps of: providing a silver coated copper powder, wherein a surface of a copper powder is coated with silver; and spraying the silver coated copper powder to In a region of the tail gas of a thermal plasma, silver on the surface of the copper powder is diffused into a grain boundary of copper on the inner side of the copper powder. A method for producing a metal composite powder according to claim 1, wherein the tail gas region of the hot plasma has a temperature of 2000 to 5000 K. A method for producing a metal composite powder according to claim 1, wherein the copper powder is produced by atomization. A method for producing a metal composite powder according to claim 1, wherein the copper powder has an average particle diameter of 0.1 to 100 μm. A method for producing a metal composite powder according to claim 1, wherein the silver content is not less than 5% by weight with respect to the silver-coated copper powder. A metal composite powder comprising: a copper powder; and silver dispersed in a particle boundary of copper on the inner side of the copper powder. The metal composite powder of claim 6, wherein the copper powder has an average particle diameter of 0.1 to 100 μm. The metal composite powder according to claim 6, wherein the silver content is not less than 5% by weight with respect to the metal composite powder. The metal composite powder according to claim 6, wherein a percentage of a region occupied by silver on one of the cross sections of the metal composite powder is 3 to 20%.