JP2016125117A - Composite copper particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide composite copper particles conjugated with other metal while the nature of copper as a base material is sufficiently maintained.SOLUTION: Composite copper particles are made up of mother particles containing copper or copper base alloy, and nickel discontinuously covering a surface of the mother particles so that a part of the surface is exposed. The composite copper particles preferably have a flat shape. It is preferable that nickel in a state of fine particles having a particle size of 0.02 μm or more and 0.5 μm or less covers the surface of the mother particles, and nickel covers the mother particles by a quantity smaller than a theoretical complete coverage quantity of the mother particles.SELECTED DRAWING: Figure 1

Description

  The present invention relates to composite copper particles in which nickel is coated on the surface of mother particles containing copper or a copper-based alloy.

  Conventionally, copper powder has been widely used as a raw material for conductive paste. Conductive pastes are widely used because of their ease of handling, from experimental purposes to applications in the electronics industry. In particular, the metal-coated copper powder whose surface is coated with a nickel coat layer, silver coat layer, etc. is processed into a conductive paste and used for circuit formation of printed wiring boards using a screen printing method, various electrical contact portions, etc. It has been applied and used as a material for ensuring electrical continuity. The reason for this is that by coating the surface of the copper particles with metal, the oxidation of copper, which is a metal that easily oxidizes, is suppressed, or the familiarity with other metal materials for making electrical contact is improved. It is to do. Nickel-coated copper powder and silver-coated copper powder are economically advantageous because they are not expensive, unlike metal powders made of only nickel or silver. Therefore, when a conductor is formed with a conductive paste using metal-coated copper powder having excellent conductive properties, a low-resistance conductor can be manufactured at low cost.

  As a prior art regarding metal-coated copper powder, the present applicant previously proposed nickel-coated copper powder in Patent Document 1. This nickel-coated copper powder is one in which palladium is fixed to the surface of copper core particles by a reduction reaction, and electroless nickel plating is applied to the outermost surface to form a nickel-coated layer. According to the technique described in this document, the adhesion and uniformity of nickel plating are improved, and the oxidation resistance of copper powder is improved.

  The present applicant has proposed silver-coated copper powder in Patent Document 2. The silver-coated copper powder described in this document has little change over time in its conductivity even when left in an air atmosphere. Accordingly, when this silver-coated copper powder conductive paste is used, the initial viscosity at the time of processing the conductive paste is reduced, and the change in paste viscosity that changes with time can be reduced.

JP 2006-28630 A JP 2004-52044 A

  The nickel-coated copper powder and silver-coated copper powder described in Patent Documents 1 and 2 are made so that copper is not exposed to the surface by uniformly covering the surface of the copper particles as the core particles with nickel or silver. It is intended to prevent oxidation. However, in order to prevent the copper surface from being exposed, if the amount of nickel or silver is increased, the properties of nickel and silver become prominent in addition to the properties of copper as the base material, and the properties of copper in the particles It will be diminished.

  Accordingly, an object of the present invention is to provide composite copper particles in which the properties of copper as a base material are sufficiently maintained and other metals are combined.

  The present invention provides composite copper particles obtained by discontinuously coating the surface of mother particles containing copper or a copper-based alloy with nickel so that the surface is partially exposed.

  ADVANTAGE OF THE INVENTION According to this invention, the composite copper particle by which nickel was compounded is provided, fully maintaining the property of copper which is a base material.

FIG. 1 is a graph showing measurement results of thermomechanical analysis of particles obtained in Examples and Comparative Examples.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. In the following description, the term “particle” may refer to an individual particle or a powder that is an aggregate of particles, depending on the context. The composite copper particles of the present invention have mother particles and nickel as a coating metal disposed on the surface thereof. Nickel which is a coating metal is directly arranged on the surface of the mother particle. Therefore, no other material is interposed between the mother particles and nickel.

  Copper particles or copper-based alloy particles are used as the mother particles. When copper particles are used as the mother particles, the copper particles consist only of copper and the remaining inevitable impurities. When copper-based alloy particles are used as the mother particles, the particles are preferably made of a copper-based alloy containing nickel, for example. The copper-based alloy contains nickel as an alloy component, and may contain other elements as alloy components in addition to these alloy components. Examples of such elements include silicon, phosphorus, and aluminum. In the copper base alloy, the proportion of all alloy components including nickel depends on the specific use of the composite copper particles of the present invention, but from the viewpoint of not impairing the properties of copper, the mass of the copper base alloy It is preferably 0.05% by mass or more and 40% by mass or less, and more preferably 0.1% by mass or more and 30% by mass or less.

  As will be described later, since nickel is unevenly arranged on the surface of the mother particle, the shape of the composite copper particle reflects the shape of the mother particle. For example, if the shape of the mother particle is flat, the shape of the composite copper particle is also flat. If the shape of the mother particles is spherical, the shape of the composite copper particles is also spherical. The shape of the composite copper particle depends on its specific application, and examples thereof include a flat shape, a spherical shape, a needle shape, and a dendritic shape. In particular, a flat shape or a spherical shape is preferable, and a flat shape (flakes) is preferable because the effect of discontinuously disposing nickel as a coating metal is particularly noticeable.

  Similar to the shape described above, the size of the composite copper particles reflects the size of the mother particles. Due to the fact that the amount of nickel disposed on the surface of the mother particles is smaller, the size of the composite copper particles is slightly larger than the size of the mother particles. When the composite copper particles are flat, for example, the plate diameter is preferably 0.05 μm or more and 20 μm or less, and more preferably 0.1 μm or more and 10 μm or less. The plate thickness is preferably from 0.01 μm to 10 μm, and more preferably from 0.05 μm to 5 μm. On the other hand, when the composite copper particles are spherical, the particle size is preferably 0.05 μm or more and 10 μm or less, and more preferably 0.1 μm or more and 5 μm or less.

The plate diameter of the flat composite copper particles is measured from the major axis of the plate surface of the particles in the photograph after taking a photograph of the particles using a scanning electron microscope (SEM). The plate thickness is similarly measured from the length in the direction perpendicular to the plate surface of the particles in the photo after taking a photo using a scanning electron microscope (SEM). On the other hand, the particle size of the composite copper particles spherical is defined as the volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measuring method.

  If the shape of the mother particle is spherical, it can be produced, for example, by a wet reduction method or an atomization method. In the case of a flat shape, spherical mother particles can be produced by plastic deformation by flattening using a media mill or the like. In the case of a dendritic shape, it can be produced by an electrolytic method.

  Nickel is used as the coating metal disposed on the surface of the mother particle. By using nickel as the coating metal, the familiarity between the composite copper particles and the target site to which the composite copper particles are applied is improved, and it is possible to effectively suppress the occurrence of inconveniences such as a decrease in conductivity. it can.

  Nickel, which is a coating metal, discontinuously coats the surface of the mother particle. The discontinuous coating means that nickel is arranged on the surface so that the surface of the mother particle is exposed to the outside. Examples of the discontinuous coating form of nickel include a sea-island structure in which nickel is arranged in a scattered manner on the surface of the base particle. That is, the surface of the mother particle corresponds to the sea, and nickel corresponds to the island. As another discontinuous coating form, there is a form in which nickel is arranged in a network on the surface of the base particle, and the surface of the base particle is exposed in a section defined by the network.

The composite copper particles of the present invention are essentially made of copper or a copper-based alloy that constitutes the mother particles by discontinuously coating the surface with nickel as a coating metal so that the surfaces of the mother particles are exposed. The advantage of being coated with nickel, which is a coating metal, can be exhibited without diminishing the properties possessed. From this viewpoint, it is preferable that the coating of the mother particles with nickel is performed in an amount smaller than the theoretical complete coating amount of the mother particles. The full coverage theoretical amount of the mother particle, assuming a mean diameter of the particles covering the surface of the mother particle as a coating thickness, mass W of nickel when fully coated _N and the base material mass W _M and the ratio W _N / is the amount that is defined in the W _M. The coating amount of nickel is preferably 0.01% or more and 90% or less, and more preferably 0.01% or more and 80% or less with respect to the theoretical complete coating amount of the mother particles. By covering the surface of the base particle discontinuously with such an amount, the advantage of being covered with the cover metal can be further exhibited without further impairing the properties of the base particle. it can.

  The proportion of nickel in the composite copper particles is 0.01% by mass or more and 90% by mass or less, provided that the ratio of the coating amount of the coated particle to the theoretical total coating amount of the mother particle is within the above range. It is more preferable that it is 0.01 mass% or more and 80 mass% or less. The proportion of nickel in the composite copper particles can be measured by examining the nickel mass increase rate by inductively coupled plasma emission spectroscopy (ICP-AES) for the particles before and after coating.

  The nickel is preferably disposed on the surface of the mother particle in a state where a plurality of fine nickel particles are deposited. By arranging nickel in such a state, nickel on the surface exhibits partial oxidation resistance without impairing the characteristics of the mother particles during sintering, which is preferable. In particular, nickel is preferably in the state of fine particles having a particle diameter of 0.001 μm or more and 0.5 μm or less, particularly 0.01 μm or more and 0.3 μm or less, since the advantageous effects described above become more remarkable.

  The particle diameter of the nickel fine particles can be measured by taking a photograph of the particles using a field emission scanning electron microscope (FE-SEM) and then using the image analysis type particle size distribution measurement software Mac view. The equivalent circle diameter is calculated based on the perimeter determined by image analysis. As the magnification of FE-SEM, an optimum magnification according to the particle size is selected in the range of 5000 times to 15000 times. In principle, software settings for image analysis are the initial conditions, and image capture is manually selected. The number of particles to be measured is 500 [piece / field of view] or more and 600 [piece / field of view] or less. The particle size data is the Heywood diameter. The distribution format is volume distribution.

  Nickel can be arranged on the surface of the mother particle by a method such as plating or mechanochemical. Among these methods, it is preferable to dispose nickel on the surface of the mother particles by a plating method, particularly an electroless plating method from the viewpoint that the covering power and the covering amount can be easily controlled.

  Next, the suitable manufacturing method of the composite copper particle of this invention is demonstrated. The composite copper particles are preferably manufactured by, for example, manufacturing mother particles by a predetermined method and disposing nickel as a coating metal on the surface of the obtained mother particles. In the following description, the case where the composite copper particles include mother particles made of copper and have a flat shape will be described as an example.

  First, copper mother particles are produced. For the production of the mother particles, for example, a wet reduction method or an atomization method can be used. When the wet reduction method is used, copper particles can be obtained by reducing copper compounds such as copper acetate and copper sulfate in a wet manner using various reducing agents such as hydrazine. When using the atomization method, copper particles can be obtained by using a molten copper and spraying the molten metal.

  The copper particles obtained by the above method are generally spherical. Flat copper particles are produced from the spherical copper particles. In order to produce flat particles from spherical particles, for example, a method of applying an external force to the spherical particles and plastically deforming them to make them flat can be suitably used. As a means for performing plastic deformation, for example, a method using a media mill can be mentioned. Specifically, the copper particles can be wet processed using a bead mill or a sand mill. In the case of using a bead mill, as the beads, for example, those made of ceramics such as zirconia or alumina, metal, glass or the like can be used. The bead diameter depends on the particle diameter of the copper particles, but generally 0.01 mm or more and 0.5 mm or less, particularly 0.05 mm or more and 0.3 mm or less can be used. As a slurry used for wet-treating copper particles, a slurry using water as a medium or a slurry using an organic solvent such as alcohol as a medium can be used.

  When flat mother particles are obtained by the above method, nickel is placed on the surface of the mother particles. The arrangement of nickel can be performed by plating, for example. Alternatively, a method may be employed in which nickel fine particles are mechanically collided with the mother particles and the nickel fine particles are embedded in the surfaces of the mother particles.

  When nickel is disposed by plating, displacement plating utilizing a difference in ionization tendency can be performed. Instead of or in addition to this, electroless plating using a reducing agent can be performed.

  The amount of nickel disposed on the surface of the flat mother particle is set such that a part of the surface of the mother particle is exposed and nickel is discontinuously present on the surface of the mother particle. The amount of nickel disposed may be adjusted, for example, by adjusting the plating time when using the above-described plating. When a method of mechanically colliding nickel fine particles is used, for example, the amount of fine particles to be collided may be adjusted.

  The intended composite copper particles are obtained as described above. The composite copper particles thus obtained are used in the state of a conductive composition such as a conductive paste or a conductive ink. When used in the state of a conductive paste, for example, the composite copper particles of the present invention are mixed with various vehicles, glass frit and the like to form a composition. When used in the state of a conductive ink, for example, the composite copper particles of the present invention are mixed with various organic solvents, a viscosity modifier, a surface tension modifier and the like to form a composition. These conductive compositions can be used as external electrode materials for various electronic devices such as active devices such as surface-mount ICs, transistors and FETs, and passive devices such as chip resistors, chip inductors and chip capacitors. Further, it is used as a conductive material for establishing electrical continuity between the external electrodes of these various electronic elements and the printed wiring board. It is used as a conductive material for establishing electrical continuity between electrodes of various electronic elements such as active elements and passive elements and a printed wiring board. Alternatively, it is used as an internal electrode of an electronic element, for example, an internal electrode of a multilayer ceramic chip capacitor.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
As a raw material for the mother particles, 1100Y, which is a spherical copper particle manufactured by Mitsui Metal Mining Co., Ltd., was used. The copper particles had a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measurement method was 1.2 [mu] m. 1 kg of the copper particles and 5 kg of methanol were mixed to form a slurry, and the slurry was put into a dyno mill which is a medium dispersion mill. Further, a darno mill was used as a media mill, and zirconia beads having a diameter of 0.2 mm were adjusted to a filling rate of 70%. The dyno mill was operated for 30 minutes to plastically deform the copper particles and flatten them.

  Nickel was discontinuously arranged on the surface of the flat mother particles thus obtained by electroless plating. Specifically, 1 kg of flat mother particles was used and put into 5 L of pure water to form a slurry. In this slurry, 40 mL of Melplate, Activator 352 manufactured by Meltex was added. Furthermore, 40 mL of hydrazine hydrate was added to the slurry. Subsequently, a nickel plating solution (0.48 L of Ni-426A manufactured by Meltex Co., plus 0.48 L of Ni-426B) was added to perform electroless plating of nickel. The amount of nickel deposited was adjusted by adjusting the plating time. In this way, the intended composite copper particles were obtained.

When the obtained composite copper particles were observed with a scanning electron microscope, the overall shape was flat, nickel was dispersed and arranged in an island shape on the surface of the copper mother particles, and a part of the surface of the mother particles was It was exposed. The composite copper particles, a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measurement method was 2.3 .mu.m. The plate diameter of the flat composite copper particles was 1.4 μm, and the plate thickness was 0.2 μm. Nickel covered the surface of the mother particle in the form of fine particles having a particle diameter of 0.1 μm. The coating of the copper base particles with nickel was 12% with respect to the theoretical complete coverage of the base particles.

[Example 2]
In Example 1, the amount of nickel electroless plating was increased to obtain composite copper particles. The composite copper particles, a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measurement method was 2.3 .mu.m. The plate diameter of the flat composite copper particles was 1.4 μm, and the plate thickness was 0.2 μm. Nickel covered the surface of the mother particle in the form of fine particles having a particle diameter of 0.05 μm. The coating of the copper base particles with nickel was 20% with respect to the theoretical complete coverage of the base particles.

Example 3
In Example 1, the amount of nickel electroless plating was increased to obtain composite copper particles. The composite copper particles, a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measurement method was 2.3 .mu.m. Nickel covered the surface of the mother particle in the form of fine particles having a particle diameter of 0.05 μm. The coating of the copper base particles with nickel was 40% with respect to the theoretical complete coverage of the base particles.

Example 4
Electroless plating of the same amount of nickel as in Example 1 was performed on the surface of the spherical copper particles that did not flatten the copper particles to obtain composite copper particles. The composite copper particles, a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measurement method was 1.2 [mu] m. Nickel covered the surface of the mother particle in the form of fine particles having a particle diameter of 0.05 μm. The coating of the copper base particles with nickel was 12% with respect to the theoretical complete coverage of the base particles.

[Comparative Example 1]
The flat mother particles themselves made of copper obtained in Example 1 were used as Comparative Example 1. Cumulative volume particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measuring method was 2.1 .mu.m.

[Comparative Example 2]
In Example 1, the amount of electroless plating of nickel was increased, and nickel was disposed over the entire surface of flat mother particles made of copper to obtain composite copper particles. The composite copper particles, a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measurement method was 2.5 [mu] m. Nickel covered the surface of the mother particle in the form of fine particles having a particle diameter of 0.05 μm. The coverage of the copper base particles with nickel was 159% with respect to the theoretical complete coverage of the base particles.

[Comparative Example 3]
Nickel particles 2015RS manufactured by Mitsui Mining & Smelting Co., Ltd. were used as comparative examples as completely coated particles. The composite copper particles, a volume cumulative particle diameter D ₅₀ in the cumulative volume 50% by volume by laser diffraction scattering particle size distribution measurement method was 1.7 [mu] m.

[Evaluation]
About the particle | grains obtained by the Example and the comparative example, the measurement of the thermogravimetric (TG) and the thermomechanical analysis (TMA) was performed. The measurement was performed in the atmosphere. The heating rate was 10 ° C./min. For TG, the temperature at which the mass of the sample increased by 0.75% was measured and used as a measure of oxidation resistance. The results are shown in Table 1 below. For TMA, the temperature when shrinking by 5% was measured and used as a measure of heat shrinkability. The results are shown in Table 1 below. Moreover, about TMA, the graph of the measurement result was shown in FIG. 1 (however, except Example 4).

  As is clear from the results shown in Table 1, it can be seen that the composite copper particles obtained in each Example show both the behavior of copper and nickel. Specifically, it can be seen that it exhibits high conductivity equivalent to that of Comparative Example 1 that is copper particles and high oxidation resistance that is equivalent to that of Comparative Example 3 that is nickel particles. Moreover, the composite copper particle obtained by each Example shows the intermediate | middle property of copper and nickel regarding heat shrinkability. On the other hand, the composite copper particles of Comparative Example 2 in which the entire surface of the mother particles made of copper is coated with nickel are not exposed to copper on the surface, so the oxidation resistance is high but the conductivity is inferior. It turns out that it shows the behavior close to the comparative example 3 which is particle | grains.

Claims (9)

  Composite copper particles obtained by discontinuously coating the surface of mother particles containing copper with nickel so that the surface is partially exposed.   Composite copper particles obtained by discontinuously coating the surface of mother particles containing a copper-based alloy with nickel so that the surface is partially exposed.   The composite copper particle according to claim 1, wherein the mother particle is composed of only copper and the balance inevitable impurities.   The composite copper particle according to any one of claims 1 to 3, wherein the composite copper particle has a flat shape and has a plate diameter of 0.05 µm to 20 µm.   The composite copper particle according to any one of claims 1 to 3, wherein the composite copper particle has a spherical shape. Nickel covers the surface of the mother particles in the form of fine particles having a particle diameter of 0.001 μm or more and 0.5 μm or less,
The composite copper particles according to any one of claims 1 to 5, wherein the base particles are coated with nickel in an amount smaller than a theoretically-covered amount of the base particles.   The composite copper particle according to claim 6, wherein nickel particles deposited by electroless plating cover the surface of the mother particle.   The electroconductive composition containing the composite copper particle as described in any one of Claims 1 thru | or 7.   The conductive composition according to claim 8, which is a conductive paste or a conductive ink.

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