KR20230057342A - Silver-coated flaky copper powder and its manufacturing method - Google Patents

Abstract

When the volume cumulative particle size at 90% by volume by laser diffraction scattering particle size distribution measurement is D ₉₀ (μm) and the cumulative volume particle size at 10% by volume is D ₁₀ (μm), The value of lightness L* for the degree of dispersion defined by D ₉₀ /D ₁₀ is 13 or more. processing the dispersion liquid containing the copper base powder and the first complexing agent by means of a media agitating mill device to transform the copper base particles constituting the copper base powder into flakes; Silver-coated flakes by treating the copper base powder containing the copper base particles transformed into flakes with an aqueous solution containing silver ions and a second complexing agent to deposit silver on the surface of the copper base particles. manufacture copper powder.

Description

Silver-coated flaky copper powder and its manufacturing method

This invention relates to silver-coated flaky copper powder and its manufacturing method.

Since the flaky copper particles have a large specific surface area due to their shape and the particles easily come into contact with each other, it is easy to impart conductivity to the resin by adding them to the resin. However, copper is easily oxidized, and as a result, there is a drawback that the electrical resistance of copper particles tends to increase. For the purpose of supplementing this drawback, various techniques have been proposed to suppress the increase in electrical resistance of the particles by coating the surfaces of the copper particles with silver, which is a metal having lower electrical resistance than copper.

For example, Patent Documents 1 to 3 propose a silver-coated flaky copper powder containing silver-coated flaky copper particles having silver on the surface and subjected to a flattening process.

Japanese Unexamined Patent Publication No. 2010-275638 Japanese Unexamined Patent Publication No. 2015-71818 Japanese Unexamined Patent Publication No. 2016-35098

According to the techniques described in Patent Literatures 1 to 3, the electrolytic copper powder is flattened using a grinding device such as an attritor, and then the surface of the copper powder is coated with silver by displacement plating. However, the silver-coated flaky copper powder obtained by this method has a problem that silver coating is not uniform and the surface of the copper powder is in a partially exposed state. This subject is remarkable especially when the thickness of the electrolytic copper powder after flattening is thin. When the silver-coated flaky copper powder in such a coated state is mixed with a resin, copper is easily eluted in the resin, and due to this, the resin is easily deteriorated with time.

Therefore, the subject of this invention is providing the silver-coated flaky copper powder which can eliminate the various faults which the prior art mentioned above has, and its manufacturing method.

The present invention is a silver-coated flaky copper powder containing silver-coated flaky copper particles having silver on at least the surface,

The volume cumulative particle size of the silver-coated flaky copper powder at a cumulative volume of 90% by volume by laser diffraction scattering particle size distribution measurement is set to D ₉₀ (μm), and the cumulative volume particle size at 10% by volume of the cumulative volume When D ₁₀ (㎛),

The above object is solved by providing a silver-coated flaky copper powder having a value of lightness L* of the silver-coated flaky copper powder with respect to the degree of dispersion defined by D ₉₀ /D ₁₀ of 13 or more.

Further, the present invention treats a dispersion liquid containing copper mother powder and a first complexing agent with a media agitating mill device to transform the copper mother particles constituting the copper mother powder into flakes,

Silver-coated flaky copper, wherein the copper base powder containing the copper base particles transformed into flakes is treated with an aqueous solution containing silver ions and a second complexing agent to deposit silver on the surface of the copper base particles. It is to provide a method for producing the powder.

Hereinafter, the present invention will be described based on its preferred embodiments.

The present invention relates to a silver-coated copper powder which is an aggregate of silver-coated copper particles having silver on at least the surface of copper particles as a base material. Silver-coated copper particles have one of the characteristics in their appearance. In detail, the silver-coated copper particles have a flaky shape. Therefore, in the following description, silver-coated copper particles are referred to as "silver-coated flaky copper particles", and silver-coated copper powder is referred to as "silver-coated flaky copper powder".

In this specification, "flake shape" has the same meaning as "flat shape" or "flaky shape", and means that the particles are in the shape of a thin plate. Flake-shaped particles are specified by their aspect ratio. The aspect ratio refers to the value of D/T, which is the ratio of the major diameter D on the plate surface when the flaky particles are viewed in plan to the thickness T of the flaky particles. The major axis D in the plate surface refers to the length of the longest line segment among the line segments crossing the plate surface. In the present invention, the aspect ratio of the silver-coated flaky copper particles is preferably 5 or more and 160 or less, and is 10 or more and 160 or less, from the viewpoint of being able to impart high conductivity when the silver-coated flaky copper powder is added to resin. is more preferably 10 or more and 140 or less, still more preferably 15 or more and 140 or less, still more preferably 20 or more and 140 or less, particularly preferably 30 or more and 120 or less, particularly preferably 30 or more and 80 or less .

The aspect ratio is calculated by measuring the major diameter D and thickness T of one particle and calculating the D/T value for 50 or more particles.

The measuring method of major diameter D and thickness T is as follows.

Major axis D: After photographing a sample at an arbitrary magnification with an electron microscope, the major axis is measured using image analysis particle size distribution measurement software (Mac-View, manufactured by Mounttech Co., Ltd.).

Thickness T: The sample is resin-embedded, and end-face processing is performed with a cross-section polisher. After that, it is measured at an arbitrary magnification using an electron microscope, and then measured in the same way as the major diameter D.

The shape of the silver-coated flaky copper particle when viewed in plan view, ie, the shape of the plate surface, is not particularly limited. Among these shapes, a substantially circular one is preferable from the viewpoint of being able to provide high conductivity when the silver-coated flaky copper powder is added to the resin.

When the shape of the plate surface of the silver-coated flaky copper particles is substantially circular, the circularity of the plate surface is preferably 0.60 or more and 0.95 or less, more preferably 0.65 or more and 0.90 or less, and still more preferably 0.65 or more and 0.85 or less. Circularity is defined as 4πS/L ² where S is the area of the plate surface and L is the circumferential length of the plate surface. The circularity is taken as the arithmetic average value of the values measured for 50 or more particles.

The specific measurement method of circularity is as follows.

It measures using image analysis particle size distribution measuring software (Mac-View by Mount Tech Co., Ltd.). Using this software, the contours of more than 50 samples are modeled, and the area within the contours is calculated. Calculate the equivalent circle diameter from the area and average it.

In the silver-coated flaky copper particles, when a part of the surface of the flaky copper particles as the base material is exposed, that is, when the silver coating is non-uniform, when the silver-coated flaky copper powder is mixed with a resin, copper The resin may be denatured due to contact with the resin. Therefore, as for the silver-coated flaky copper particle, it is preferable that the surface of the flaky copper particle as a base material is coated with silver as uniformly as possible. In particular, it is preferable from the viewpoint of economy that the surfaces of the flaky copper particles are uniformly coated with the smallest amount of silver as possible.

The silver coating state in the silver-coated flaky copper particles can be evaluated by the value of lightness L* of the silver-coated flaky copper powder. This reason is that the brightness of silver itself is higher than the brightness of copper itself. However, as a result of investigation by the present inventors, even if the surface of the flaky copper particles is coated with silver with a large thickness to increase the brightness, not only is it economically disadvantageous, but also the dispersibility of the silver-coated flaky copper powder in the resin is reduced. Turned out. Therefore, it cannot be said that the said silver-coated flaky copper powder is a preferable thing only for the reason that the value of lightness L* of silver-coated flaky copper powder is high.

From the viewpoint of preventing denaturation of the resin when mixed with the resin and improving the dispersibility in the resin, the inventors of the present invention conducted intensive studies and found that the value of D ₉₀ /D ₁₀ for the silver-coated flaky copper powder and the lightness L* It has been found to be advantageous to employ the ratio of the values of as a measure. D ₉₀ refers to the volume cumulative particle size (μm) in a cumulative volume of 90% by volume by a laser diffraction scattering particle size distribution measurement method, and D ₁₀ refers to a volume cumulative particle size in a cumulative volume of 10% by volume by the same measurement method ( μm). In addition, the value of D ₉₀ /D ₁₀ is a value that becomes a measure of the particle size distribution of powder and is generally called dispersion. The smaller the value of the degree of dispersion, the lower the degree of particle aggregation and the sharper the particle size distribution of the powder. Therefore, the larger the value of L*/dispersion, the more uniform the coating with silver and the lower the degree of aggregation of the silver-coated flaky copper powder.

In the silver-coated flaky copper powder of this invention, it is preferable that it is 13 or more, as for the value of L*/dispersion degree, it is more preferable that it is 14 or more, and it is still more preferable that it is 15 or more. The larger the value of L*/dispersion, the better, but when the value is as large as 25, the desired effect of the present invention is sufficiently exhibited.

The value of L*/dispersion is preferably as described above, and the value of L* itself is preferably 70 or more, more preferably 73 or more, and even more preferably 76 or more from the viewpoint of uniform coating with silver. do. The silver-coated flaky copper powder having such an L* value can be manufactured by the method described later. There is no particular restriction on the upper limit of L*, and the closer to 100, the better. However, when the value of L* is as large as about 86, the intended effect of the present invention is sufficiently exhibited. The value of L* is obtained by using a diffuse illumination vertical light receiving method described in JIS Z 8722 (compliance with geometric condition c/including specular reflection light), for example, using a color difference meter (CR-400) manufactured by Konica Minolta Co., Ltd. It is measured.

On the other hand, the value of the degree of dispersion is preferably 5.3 or less, particularly 5.0 or less, and particularly 4.5 or less from the viewpoint of enhancing the dispersibility of the silver-coated flaky copper powder in the resin. The silver-coated flaky copper powder having such a dispersion degree can be manufactured by the method mentioned later. There is no particular restriction on the lower limit of the degree of dispersion, and the closer to 1, the better. However, when the value of the degree of dispersion is as small as about 3.0, the desired effect of the present invention is fully exhibited.

The value of dispersion degree is computable with the following method, for example. A small amount of silver-coated flaky copper powder was placed in a beaker, 2 or 3 drops of a 3% by mass Triton X solution (manufactured by Kanto Chemical Co., Ltd.) were added, and after mixing with the powder, a 0.1% by mass SN Dispersant 41 solution ( 50 mL of San Nopco Co., Ltd.) is added. Thereafter, using an ultrasonic disperser TIPφ20 (manufactured by Nippon Seiki Seisakusho, OUTPUT: 8, TUNING: 5), dispersion treatment is carried out for 2 minutes to prepare a sample for measurement. The particle size distribution of this sample for measurement is measured using a laser diffraction scattering type particle size distribution analyzer MT3300 (manufactured by Microtrac Bell Co., Ltd.), and values of D ₉₀ and D ₁₀ are obtained. The degree of dispersion is calculated from these values.

From the viewpoint of preventing denaturation of the resin when mixed with the resin and enhancing the dispersibility in the resin, the ratio of the thickness T (μm) of the silver-coated flaky copper particles to D ₅₀ (μm) is employed as a measure It has also been found to be advantageous as a result of examination by the present inventors. D ₅₀ refers to the cumulative volume particle diameter (μm) in 50% by volume of the cumulative volume according to the laser diffraction scattering particle size distribution measurement method. In this invention, it is preferable that the value of T/ _D50 is 0.04 or less, and it is more preferable that it is 0.03 or less. On the other hand, the value of T/D ₅₀ is preferably 0.005 or more, more preferably 0.01 or more, and still more preferably 0.01 or more and 0.02 or less. The value of T/D ₅₀ means that the thickness T of the silver-coated flaky copper particles is small with respect to the particle size D ₅₀ when the particle size D ₅₀ is fixed and considered. When the thickness is too small, the surface area of the particles becomes too large, and the reactivity with the resin becomes strong. The silver-coated flaky copper powder means that it is effective for preventing modification with the resin when this is mixed with the resin and effective for improving the dispersibility in the resin. In general, in order to reduce the thickness T, an external force is applied to the copper hair powder as a raw material for a long time to deform it sufficiently _flat . In other words, reducing the thickness T and decreasing D ₅₀ have a contradictory relationship. However, in this invention, it became possible to make thickness T small, suppressing the increase of _D50 by flake-forming copper hair powder by the method mentioned later.

The thinner the thickness T, the more preferable it is, specifically, 0.5 μm or less, particularly 0.3 μm or less, particularly 0.25 μm or less, particularly preferably 0.20 μm or less. Although there is no particular restriction on the lower limit of the thickness T, as long as the thickness T is as small as 0.10 μm, the desired effect of the present invention is sufficiently exhibited.

On the other hand, the value of D ₅₀ is preferably 7 μm or more and 17 μm or less, more preferably 8 μm or more and 16 μm or less, from the viewpoint of enhancing the dispersibility of the silver-coated flaky copper powder in resin. It is further more preferable that it is micrometer or less. The value of D ₅₀ can be measured by the method similar to the above-mentioned measurement of dispersion degree.

As described above, the silver-coated flaky copper powder of the present invention has a low degree of aggregation, that is, a small value of the above-mentioned dispersity (D ₉₀ /D ₁₀ ). Therefore, in the silver-coated flaky copper powder of this invention, it is preferable that the values of _D90 and _D10 do not become large apart from the value of _D50 . From this point of view, the value of D ₉₀ is preferably 15 μm or more and 35 μm or less, more preferably 16 μm or more and 31 μm or less, and still more preferably 17 μm or more and 30.5 μm or less. On the other hand, the value of D ₁₀ is preferably 3.0 μm or more and 8.0 μm or less, more preferably 3.9 μm or more and 7.0 μm or less, and still more preferably 5.0 μm or more and 6.2 μm or less.

As described above, in the silver-coated flaky copper powder of the present invention, the thickness of the silver-coated flaky copper particles constituting the same is thin, and the degree of aggregation of the particles is low. Owing to this, the silver-coated flaky copper powder of the present invention has a low tap density. Specifically, the tap density of the silver-coated flaky copper powder of the present invention is preferably 0.5 g/cm 3 or more and 2.5 g/cm 3 or less, more preferably 0.5 g/cm 3 or more and 2.0 g/cm 3 or less, and furthermore It is preferably 0.7 g/cm 3 or more and 2.0 g/cm 3 or less, more preferably 0.7 g/cm 3 or more and 1.8 g/cm 3 or less, still more preferably 0.7 g/cm 3 or more and 1.5 g/cm 3 or less, particularly preferably Preferably, it is 0.8 g/cm 3 or more and 1.3 g/cm 3 or less. A tap density is measured based on JIS Z 2512.

In the silver-coated flaky copper powder of this invention, it is preferable that the surface of the flaky copper particle which is a base material is coated with silver as thinly and uniformly as possible. Therefore, it is undesirable to make high the ratio of silver in the silver-coated flaky copper powder of this invention. Specifically, the ratio of silver in the silver-coated flaky copper powder of the present invention is 5 mass% or more and 20 mass% or less, more preferably 7 mass% or more and 16 mass% or less, still more preferably 9 mass% It is % or more and 14 mass % or less. The ratio of silver in the silver-coated flaky copper powder can be measured by ICP emission spectrometry.

Next, the suitable manufacturing method of the silver-coated flaky copper powder of this invention is demonstrated. The production method of the present invention is broadly divided into a process of forming flakes of copper particles as a base material and a process of coating flaky copper particles with silver.

In the flake forming step, the dispersion liquid containing the copper base powder and the first complexing agent is treated with a medium stirring mill device to deform the copper base particles constituting the copper base powder into flakes.

In the silver coating step, copper base powder containing copper base particles deformed into flakes is treated with an aqueous solution containing silver ions and a second complexing agent to deposit silver on the surfaces of the copper base particles.

Hereinafter, each process is demonstrated.

In the flaking process of copper hair powder, an external force is applied to copper hair powder having a shape other than flake shape to deform the copper hair powder into a flat shape. Examples of the copper mother powder include spherical copper hair powder manufactured by a wet reduction method, electrolytic copper hair powder obtained by electrolyzing an electrolyte solution containing copper ions, and spherical copper hair powder manufactured by an atomization method. Among these copper base powders, it is preferable to flake the dendrite-like copper base powder produced by the electrolytic method from the viewpoint of being able to smoothly manufacture a flaky copper powder having a small thickness.

In the case of using dendrite-like copper particles produced by the electrolysis method as the mother powder, pulverizing the dendrite-like copper particles prior to flaking makes it possible to more smoothly produce flaky copper powder having a small thickness preferred in The means of pulverization is not particularly limited, and examples thereof include disc type, roller type, cylinder type, impact type, jet type, and high-speed rotation type pulverization method. Also, either dry grinding or wet grinding may be used. From the viewpoint of reliably separating the branch portion and the stem portion of the dendrite-like copper particles, it is preferable to perform dry grinding. For dry grinding, it is preferable to use, for example, a jet mill of a collision plate type or a jet mill of a type in which particles collide with each other.

From the viewpoint of obtaining flaky copper particles having a desired particle diameter and thickness, the particle size D ₅₀ of the copper particles after grinding is preferably 2 μm or more and 8 μm or less, more preferably 3 μm or more and 7 μm or less, and 4 μm or more 6 μm. It is further more preferable that it is micrometer or less.

Next, flake formation of copper particles as a base material is performed. For flake formation, media agitation mills such as bead mills, ball mills, and attritors can be used.

Prior to flake formation using a media stirring mill, copper particles are dispersed in a liquid medium to prepare a dispersion. As a liquid medium used for preparation of a dispersion liquid, water and an organic solvent are mentioned, for example. A mixed solvent of water and an organic solvent may also be used. Examples of organic solvents include lower monoalcohols having 1 to 4 carbon atoms such as methanol and ethanol; lower polyhydric alcohols having 1 to 4 carbon atoms such as ethylene glycol; lower carboxylic acids having 1 to 4 carbon atoms; A lower amine having 1 to 4 carbon atoms and the like can be used alone or in combination of two or more. Among these liquid media, it is preferable to use an organic solvent from the viewpoint of increasing the dispersibility of the copper particles in the dispersion and increasing the quality stability during treatment with a medium stirring mill. It is preferable to use especially lower alcohols, such as methanol, from the viewpoint that volatilization of the medium is easy and that the medium is difficult to remain in the target flaky copper particles.

The concentration of the copper particles in the dispersion is preferably 10% by mass or more and 60% by mass or less, and preferably 20% by mass or more and 50% by mass or less, from the viewpoint of productivity and prevention of generation of coarse particles.

To prepare the dispersion, it is sufficient to simply mix the copper particles and the liquid medium. Depending on the case, you may prepare a dispersion liquid using the stirring dispersion apparatus. Examples of such a device include a fluid mill and T.K. Filmix (registered trademark) manufactured by Primix Co., Ltd.

In this manufacturing method, it is preferable to contain the first complexing agent in the dispersion. Aggregation of copper particles during flaking is effectively suppressed by the action of the first complexing agent. In addition, the oxide present on the surface of the copper particle is removed by the first complexing agent, and the surface of the flaky copper particle can be coated with silver thinly and uniformly. From this point of view, the concentration of the first complexing agent contained in the dispersion is preferably 0.1% by mass or more and 40% by mass or less, and is 0.5% by mass or more, on condition that the concentration of the copper particles in the dispersion is in the above-mentioned range. It is more preferable that it is 20 mass % or less, and it is still more preferable that it is 1 mass % or more and 10 mass % or less.

Conventionally, when copper hair powder is flaked by a media stirring mill, aggregation of copper particles constituting the copper hair powder is often suppressed by making a dispersion liquid containing the copper hair powder contain a fatty acid. However, when a fatty acid is used, since the fatty acid adheres to and remains on the surface of the copper particle after flaking, it is necessary to remove the fatty acid prior to coating the surface of the copper particle after flaking with silver. In order to remove fatty acids, there was a problem that a degreasing step was required and the number of steps increased, and a problem that the surface of the copper particles was oxidized by the degreasing step. In contrast, such a problem does not occur according to the present production method in which the dispersion liquid does not contain a fatty acid and instead contains the first complexing agent.

The first complexing agent may be a single-located agent or may be a multi-located agent such as two-located, tri-located, and tetra-located. Citric acid, ascorbic acid, ethylenediamine tetraacetate, etc. are mentioned as a 1st complexing agent from a viewpoint of the height of coordination with copper. These complexing agents may be used individually by 1 type, and may be used in combination of 2 or more type. Among these complexing agents, it is preferable to use ethylenediamine tetraacetate from the viewpoint of effectively suppressing aggregation of copper particles in the flaking step.

In the flake forming process, the dispersion liquid and pulverization media are put into a medium agitation mill and mixed and agitated.

It is preferable that the diameter of grinding media is 0.1 mm or more and 1 mm or less. The material of the grinding media is generally zirconia or alumina.

What is necessary is just to adjust suitably so that the target flaky copper powder may be obtained for the operating time, rotational speed, number of passes, etc. of the media stirring mill device.

After the copper base particles constituting the copper base powder have been deformed into flakes in this way, a silver coating step is performed next. In the silver coating step, as described above, the copper base powder containing the copper base particles deformed into flakes is treated with an aqueous solution containing silver ions and a second complexing agent. It is preferable that this process includes process 1 and process 2 below.

[Process 1]

Substitution plating is performed by bringing silver ions and flaky copper particles into contact in water to deposit silver on the surface of the flaky copper particles. Precursor particles are obtained by this precipitation.

[Process 2]

The precursor particles obtained in Process 1, silver ions, and a reducing agent for the silver ions are brought into contact in water to further deposit silver on the surface of the precursor particles.

The silver ion used in the process 1 and the process 2 is produced|generated from the silver compound used as a silver source. As a silver compound, water-soluble silver compounds, such as silver nitrate, can be used, for example. The concentration of silver ions in water is preferably set to 0.01 to 10 mol/L, particularly 0.04 to 2.0 mol/L, from the viewpoint of allowing a preferable amount of silver to precipitate on the surface of the flaky copper particles.

In Treatment 1, the amount of the flaky copper particles in water is 1 to 1000 g/L, particularly 50 to 500 g/L, so that silver in a preferable amount can be deposited on the surface of the flaky copper particles. preferred in

In Process 1, there is no particular restriction on the order of adding the flaky copper particles and silver ions. For example, flaky copper particles and silver ions can be simultaneously added to water. From the viewpoint of ease of control of silver deposition by displacement plating, it is preferable to prepare a dispersion by previously dispersing flaky copper particles in water, and to add a silver compound serving as a silver source to the dispersion. In this case, the dispersion may be at room temperature or in the temperature range of 0 to 80°C.

Prior to the addition of the silver compound, it is preferable to add the second complexing agent in the dispersion to control reduction of silver. Examples of the second complexing agent include ethylenediamine tetraacetate, triethylenediamine, iminodiacetic acid and salts thereof, citric acid and salts thereof, and tartaric acid and salts thereof.

The first complexing agent described above and the second complexing agent described above may be of the same kind or different kinds, but from the viewpoint of matching the stability constants of the complex, the first complexing agent and the second complexing agent are of the same kind. It is desirable to be In particular, both the first complexing agent and the second complexing agent are ethylenediaminetetraacetate from the viewpoint of effectively suppressing aggregation of copper particles in the flaking step and from the viewpoint of thinly and uniformly coating silver in the silver coating step. It is desirable to be

It is preferable to perform addition of the silver compound in the process 1 in the state of aqueous solution. This aqueous solution may be added in a lump in the dispersion, or may be added continuously or discontinuously over a predetermined period of time. It is preferable to add the aqueous solution of the silver compound to the dispersion over a predetermined period of time from the viewpoint of facilitating the control of the substitution plating reaction.

In Treatment 1, it is preferable to irradiate the dispersion with ultrasonic waves before adding the silver compound to the dispersion or simultaneously with the addition. The dispersion of the flaky copper particles in the dispersion is promoted by the irradiation of ultrasonic waves, so that the uniform coating of the flaky copper particles with silver tends to occur. When irradiated with ultrasonic waves, there is a certain effect, but in particular, the frequency is preferably 200 kHz or less, and more preferably 45 kHz or less. A lower limit of 10 kHz is sufficient.

In process 1, silver precipitates on the surface of the flaky copper particle by the displacement plating mentioned above, and precursor particle|grains are obtained. The amount of precipitation of silver in the precursor particles is 0.1 to 50% by mass, particularly 1 to 10% by mass of the amount of silver in the finally obtained silver-coated flaky copper powder, so that a thin and uniform silver coating can be formed. It is desirable in that it can be

Process 2 will be described next. In Treatment 2, silver ions and a reducing agent for silver ions are added to the dispersion containing the precursor particles obtained in Treatment 1. In this case, the precursor particles obtained in Treatment 1 may be once solid-liquid separated and then dispersed in water to form a dispersion, or the dispersion of precursor particles obtained in Treatment 1 may be directly used in Treatment 2. In the case of the latter, the silver ions added in the treatment 1 may or may not remain in the dispersion.

Silver ions added in Treatment 2 are generated from a water-soluble silver compound in the same manner as in Treatment 1. The silver compound is preferably added to the dispersion in the form of an aqueous solution. The concentration of silver ions in the aqueous solution is preferably 0.01 to 10 mol/L, more preferably 0.1 to 2.0 mol/L. 0.1 to 55 parts by mass, in particular 0.1 to 55 parts by mass, based on 100 parts by mass of the precursor particles in the dispersion liquid containing the precursor particles of 1 to 1000 g/L, particularly 50 to 500 g/L, of an aqueous solution having silver ions at a concentration in this range. It is preferable to add 1 to 25 parts by mass from the viewpoint of being able to form a thin and uniform silver coating.

As the reducing agent added in Treatment 2, a reducing agent having a level of reducing power capable of simultaneously advancing silver substitution plating and reduction plating is used. By using such a reducing agent, a thin and uniform silver coating can be formed smoothly. If a reducing agent with strong reducing properties is used, reduction plating proceeds unilaterally, making it difficult to form a silver coating having a target structure. On the other hand, if a reducing agent with weak reducibility is used, reduction plating of silver ions is difficult to proceed, and it is also not easy to form a silver coating having a target structure due to this. From the viewpoints above, it is preferable to use an organic reducing agent that exhibits acidity when dissolved in water as the reducing agent. Specifically, there are formic acid, oxalic acid, L-ascorbic acid, erythorbic acid, formaldehyde and the like. These organic reducing agents may be used individually by 1 type, or may be used in combination of 2 or more types. Especially, it is preferable to use L-ascorbic acid. "Acidity" as used herein means that an aqueous solution obtained by dissolving 0.1 mol of an organic reducing agent in 1000 g of water has a pH of 1 to 6 at 25°C.

The addition amount of the reducing agent is preferably 0.5 to 5.0 equivalents, particularly 1.0 to 2.0 equivalents, relative to the silver ions in the aqueous solution to be added, in view of facilitating simultaneous silver substitution plating and reduction plating.

The order in which the reducing agent and silver ions are added to the dispersion containing the precursor particles is not particularly limited. From the viewpoint of controlling the reduction of silver ions and forming a thin and uniform silver coating, it is preferable to add silver ions after adding a reducing agent to the dispersion. The silver compound serving as a silver source may be added in a lump in the dispersion liquid, or may be added continuously or discontinuously over a predetermined period of time. From the viewpoint of easy control of the reduction of silver ions, it is preferable to add the silver compound to the dispersion in the form of an aqueous solution over a predetermined period of time.

In Process 2, when silver substitution plating and reduction plating are performed simultaneously, the dispersion may be maintained at room temperature or heated in a temperature range of 0 to 80°C.

As in the case of Treatment 1, in Treatment 2, it is preferable to irradiate the dispersion with ultrasonic waves before or simultaneously with the addition of the reducing agent to the dispersion. The dispersion of the precursor particles in the dispersion liquid is promoted by the irradiation of ultrasonic waves, and the uniform coating of the precursor particles with silver tends to occur. When irradiated with ultrasonic waves, there is a certain effect, but in particular, the frequency is preferably 200 kHz or less, and more preferably 45 kHz or less. A lower limit of 10 kHz is sufficient.

The silver-coated flaky copper powder thus obtained is suitably used in the state of a conductive composition containing the copper powder and resin. For example, a conductive paste can be formed by mixing silver-coated flaky copper powder with a resin, an organic solvent, and a glass frit. Alternatively, a conductive ink can be obtained by mixing silver-coated flaky copper powder with an organic solvent or the like. By applying the conductive paste or conductive ink obtained in this way to the surface of the object to be applied, a conductive film having a desired pattern can be obtained.

In the silver-coated flaky copper powder of the present invention, since the coating of silver is thin and uniform, elution of copper is effectively suppressed in the conductive composition of the silver-coated flaky copper powder. As a result, denaturation of the resin contained in the conductive composition is suppressed.

Moreover, since the degree of aggregation is low, the silver-coated flaky copper powder of this invention has favorable dispersibility in a conductive composition. Therefore, the conductive film obtained from the conductive composition has high conductivity.

Example

Hereinafter, the present invention will be described in more detail by examples. However, the scope of the present invention is not limited to these examples. Unless otherwise indicated, "%" and "part" mean "mass %" and "part by mass", respectively.

[Example 1]

(1) Manufacture of electrolytic copper powder

In an electrolytic cell of 2.5 m × 1.1 m × 1.5 m (approximately 4 m 3), nine negative electrode plates and insoluble positive electrode plates (DSE (manufactured by Permelec Electrode Co., Ltd.)) of each size (1.0 m × 1.0 m) are placed at a distance between electrodes. It was installed by hanging it so that it was 5 cm. A copper sulfate solution as an electrolytic solution was circulated through the electrolytic cell at 20 L/min. A positive electrode and a negative electrode were immersed in this electrolyte solution, and electrolysis was performed by applying a direct current thereto to deposit powdery copper on the surface of the negative electrode.

Electrolysis was performed for 40 minutes by adjusting the copper ion concentration of the circulating electrolyte to 5 g/L, the sulfuric acid (H ₂ SO ₄ ) concentration to 100 g/L, and the current density to 100 A/m 2 .

The copper precipitated on the surface of the negative electrode was mechanically scraped off and recovered, and then washed to obtain a water-containing copper powder cake. This cake was dispersed in 3 L of water, stirred for 10 minutes, filtered through a Buchner funnel, washed, and dried at 80° C. for 6 hours under reduced pressure (1×10 ^-3 Pa) to obtain electrolytic copper powder.

(2) grinding of electrolytic copper powder

The electrolytic copper powder is pulverized by a collision plate-type jet mill (IDS type jet mill, IDS-5 manufactured by Nippon Pneumatic Kogyo Co., Ltd.) under conditions of a pulverization pressure of 6 kgf/cm 2 and a feed rate of 6.7 kg/hr. did Particle size D ₅₀ of the copper powder after grinding was 4.5 µm.

(3) Flakes

3 kg of electrolytic copper powder after pulverization, 9 kg of methanol, and 1 kg of disodium ethylenediamine tetraacetate (hereinafter also referred to as "EDTA2Na") were mixed to prepare a methanol dispersion of the copper powder. 12 kg of this dispersion was placed in Star Mill (registered trademark) LMZ, which is a bead mill manufactured by Ashizawa Finetech Co., Ltd., and further 4.85 kg of zirconia beads having a diameter of 0.2 mm were placed. The bead mill was operated over 180 minutes to flake the copper powder. Thereafter, after separating the dispersion liquid and the beads by filtration, the dispersion liquid was left still to precipitate the flaky copper particles. The supernatant was removed and filtered to obtain flaky copper particles. Subsequently, the flaky copper particles were washed with water, and subsequently, washing with methanol was repeated twice.

(4) Silver coating

Into 500 mL of pure water heated to 40°C, 100 g of flaky copper particles were introduced to obtain a dispersion. While stirring the dispersion, 4.3 g of EDTA2Na was added and dissolved. Furthermore, substitution plating was performed by continuously adding 48 mL of a 0.44 mol/L silver nitrate aqueous solution to this dispersion over 6 minutes, silver was precipitated on the surface of the flaky copper particles, and precursor particles were obtained. At this time, ultrasonic waves (100W, 28 kHz) were irradiated to the dispersion.

Next, L-ascorbic acid as a reducing agent was added to the dispersion and dissolved. Furthermore, 192 mL of 0.44 mol/L silver nitrate aqueous solution was continuously added to the dispersion over 24 minutes. Thereby, reduction plating and displacement plating were simultaneously advanced, silver was further deposited on the surface of the precursor particles, and the target silver-coated flaky copper powder was obtained. Ultrasound irradiation was continued during this time.

[Examples 2 to 8]

Except having adopted the conditions shown in the following Table 1, it carried out similarly to Example 1, and manufactured the silver-coated flaky copper powder.

[Comparative Example 1]

In the flake formation step in Example 1, EDTA2Na was not used, and the flake formation time was 20 minutes. In addition, ultrasonic wave irradiation was not performed in the silver coating process. Except these, it carried out similarly to Example 1, and manufactured the silver-coated flaky copper powder.

[Evaluation 1]

For the silver-coated flaky copper powders obtained in Examples and Comparative Examples, the particle size distribution, lightness, circularity of the plate surface of the particles, thickness of the particles, tap density, and silver content were measured by the methods described above. Their results are shown in Table 2 below.

[Evaluation 2]

Conductive compositions were prepared using the silver-coated flaky copper powder obtained in Examples and Comparative Examples.

An epoxy resin (EPICLON850 manufactured by DIC) and butylcarbitol were mixed at a mass ratio of 35:65, and silver-coated flaky copper powder was added thereto so as to be 70% in concentration to prepare a paste-like conductive composition.

A conductive composition was coated on one side of a polyethylene terephthalate (PET) film using a bar coater. The coating width was 200 mm. The gap of the bar coater was set to 30 μm.

The formed coating film was dried over 60 minutes within a 90 degreeC vacuum dryer. Then, the PET film on which the coating film was formed was sandwiched between sheets, and vacuum pressing was performed under conditions of 160°C and 20 kN. About the sample obtained in this way, the thickness of the conductive film was measured using the micrometer (Nikon digital micrometer MF-501). In addition, the resistance value of the conductive film was measured. The resistance value was measured by the four-probe method using a resistivity meter (Mitsubishi Chemical MCP-T600). The results are shown in Table 2.

[Evaluation 3]

About the silver-coated flaky copper powder obtained by the Example and the comparative example, the elution amount of copper ion was measured.

A dispersion liquid was prepared by mixing 0.2 g of silver-coated flaky copper powder, 10 mL of 15% concentration hydrochloric acid, and 2 mL of methanol. This dispersion liquid was left still for 10 minutes in a 25 degreeC environment. Then, the dispersion liquid was filtered, and the concentration of copper ions contained in the filtrate was measured by ICP emission spectrometry. The results are shown in Table 2.

As is clear from the results shown in Table 2, the conductive film formed using the silver-coated flaky copper powder obtained in each Example has higher conductivity than the conductive film formed using the silver-coated flaky copper powder obtained in Comparative Example. Able to know.

Moreover, it turns out that the elution of copper ion is suppressed in the silver-coated flaky copper powder obtained by each Example rather than the silver-coated flaky copper powder obtained by the comparative example.

According to the present invention, when mixed with a resin, the silver-coated flaky copper powder has good dispersibility in the resin, suppresses deterioration of the resin, and can reduce the electrical resistance of a film formed of the resin. and a manufacturing method thereof is provided.

Claims (16)

A silver-coated flaky copper powder containing silver-coated flaky copper particles having silver on at least the surface,
The volume cumulative particle size of the silver-coated flaky copper powder at a cumulative volume of 90% by volume by laser diffraction scattering particle size distribution measurement is set to D ₉₀ (μm), and the cumulative volume particle size at 10% by volume of the cumulative volume When D ₁₀ (㎛),
The silver-coated flaky copper powder, wherein the value of lightness L* of the silver-coated flaky copper powder with respect to the degree of dispersion defined by D ₉₀ /D ₁₀ is 13 or more. A silver-coated flaky copper powder containing silver-coated flaky copper particles having silver on at least the surface,
The volume cumulative particle size of the silver-coated flaky copper powder in a cumulative volume of 50% by volume by laser diffraction scattering particle size distribution measurement is D ₅₀ (μm), and the thickness of the silver-coated flaky copper particle is T (μm),
The silver-coated flaky copper powder whose value of thickness T is 0.04 or less with respect to particle diameter _D50 . According to claim 1 or 2,
The silver-coated flaky copper powder whose thickness T of the said silver-coated flaky copper particle is 0.1 micrometer or more and 0.5 micrometer or less. According to claim 3,
The silver-coated flaky copper powder whose thickness T of the said silver-coated flaky copper particle is 0.1 micrometer or more and 0.3 micrometer or less. According to any one of claims 1 to 4,
The silver-coated flaky copper powder whose tap density is 0.5 g/cm<3> or more and 2.5 g/cm<3> or less. According to any one of claims 1 to 5,
The silver-coated flaky copper powder whose silver ratio is 5 mass % or more and 20 mass % or less. According to any one of claims 1 to 6,
The silver-coated flaky copper powder whose circularity of the said silver-coated flaky copper particle is 0.60 or more and 0.95 or less. According to any one of claims 1 to 7,
The silver-coated flaky copper powder whose lightness L* is 70 or more and 86 or less. According to any one of claims 1 to 8,
The volume cumulative particle diameter D ₉₀ of the silver-coated flaky copper powder in a cumulative volume of 90% by volume by laser diffraction scattering particle size distribution analysis is 15 µm or more and 35 µm or less. Silver-coated flaky copper powder. According to any one of claims 1 to 9,
A silver-coated flaky copper powder in which the volume cumulative particle diameter D ₁₀ of the silver-coated flaky copper powder in a cumulative volume of 10% by volume by a laser diffraction scattering particle size distribution measuring method is 3 μm or more and 8 μm or less. According to claim 10,
A silver-coated flaky copper powder having a degree of dispersion defined by D ₉₀ /D ₁₀ of 3.0 or more and 5.3 or less. According to any one of claims 1 to 11,
The volume cumulative particle size D ₅₀ of the silver-coated flaky copper powder in a cumulative volume of 50% by volume by a laser diffraction scattering particle size distribution measurement method is 7 µm or more and 17 µm or less. Silver-coated flaky copper powder. The dispersion liquid containing the copper mother powder and the first complexing agent is treated by a media agitating mill device to transform the copper mother particles constituting the copper mother powder into flakes;
Silver-coated flaky copper, wherein the copper base powder containing the copper base particles transformed into flakes is treated with an aqueous solution containing silver ions and a second complexing agent to deposit silver on the surface of the copper base particles. Method for preparing the powder. According to claim 13,
The manufacturing method in which a 1st complexing agent and a 2nd complexing agent are the thing of the same kind or a thing of a different kind. According to claim 14,
The manufacturing method in which both a 1st complexing agent and a 2nd complexing agent are ethylenediamine tetraacetate. According to any one of claims 13 to 15,
The manufacturing method in which the said copper hair powder is an electrolytic copper powder obtained by electrolyzing the electrolyte solution containing copper ion.