JP2007188845A - Conductive powder, conductive paste and electrical circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve electrical resistance characteristics for conductive powder made of coating powder equipped with a conductive coating on the surface of a core material. <P>SOLUTION: The conductive powder contains spherical conductive coating particles with an aspect ratio of 1.0 to 1.5 and flat conductive coating particles with an aspect ratio of 5.0 to 20.0, and also, the spherical conductive coating particles and the flat conductive coating particles are equipped with conductive coating layers made of the same composition on the surface of a core material made of the same or different materials. Without thickening the conductive coating layers, the excellent electric resistance characteristics can be realized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a conductive powder that can be used as a constituent material such as a conductive paste, and more particularly to a conductive powder made of a coated powder having a conductive coating layer on the surface of a core material.

  Since noble metals such as gold, silver, palladium, and platinum are excellent in conductivity, they are used as main constituent materials of various conductive materials such as anisotropic conductive films, conductive pastes, and conductive adhesives. For example, a noble metal particle is mixed with a binder and a solvent to form a conductive paste, and a circuit pattern is printed on the substrate using this conductive paste and baked to form a printed wiring board or an electric circuit of an electronic component. be able to.

  Since noble metals such as gold, silver, palladium, and platinum are very expensive, conductive powder called coating powder, which is obtained by plating a noble metal film on the surface of core material particles by electroless plating or the like, has been developed and used. . For example, Patent Document 1 discloses conductive particles including core particles made of a metal having a relatively high melting point and a coating layer formed around the metal and having a relatively low melting point.

  In addition, conductive powder made of spherical noble metal particles is generally used for conventional conductive pastes, but conductive powder made of spherical noble metal particles may be entangled with each other. For this reason, there are problems such that the fluidity is too large when the paste is used or used as a paste, and it is difficult to apply the conductive paste to a uniform thickness. Therefore, it has been proposed to mix particles of different shapes, such as mixing spherical particles and flaky particles. For example, Patent Document 2 discloses a conductive paste containing a metal powder obtained by mixing a powder made of a polygonal plate and a powder made of spherical particles. In Patent Document 3, in a conductive paste containing conductive powder having an aspect ratio of 5 or more, conductive powder having an aspect ratio of 3 or less, a binder and a solvent, the binder is contained in an amount of 20 to 50% by volume based on the solid content of the conductive paste. An electrically conductive paste is disclosed. Patent Document 4 discloses that a spherical powder having a minute particle diameter is added to a flake-shaped metal powder.

JP 2002-334614 A JP 2003-59337 A JP-A-10-64331 JP 2005-8930 A

  An object of the present invention is to provide an electrically conductive powder that can improve the electrically conductive powder made of a coated powder and can realize an excellent electrically conductive performance at low cost.

  In recent years, with the miniaturization of electronic components, fine pitches and small areas of electrodes and the like have advanced, and more excellent conductive performance has been demanded. Therefore, if the film thickness of the conductive coating layer is increased, the merit in terms of cost is diluted. Therefore, an object of the present invention is to provide a conductive powder that can realize excellent electrical resistance characteristics without increasing the thickness of the conductive coating layer.

  The present invention comprises spherical conductive coat particles having an aspect ratio of 1.0 to 1.5 and flat conductive coat particles having an aspect ratio of 5.0 to 20.0, and these spherical conductive coat particles and The flat conductive coat particle proposes a conductive powder comprising a conductive coat layer having the same composition on the surface of a core material made of the same or different material.

  Thus, by mixing the spherical conductive coat particles and the flat conductive coat particles, excellent electrical resistance characteristics can be realized while maintaining the dispersibility of the conductive coat particles. Moreover, by mixing spherical conductive coat particles having a conductive coat layer having the same composition and flat conductive coat particles, for example, when the conductive paste is prepared and cured, the spherical conductive coat particles and A conductive network having the same composition is formed between the flat conductive coat particles, and even more excellent electrical resistance characteristics can be realized without increasing the thickness of the conductive coat layer.

  Among them, the conductive powder obtained by mixing spherical core particles and flat core particles and forming a conductive coat layer on the surface of the mixed core particles is the conductive powder of the present invention. Is particularly preferred. By mixing the spherical core particles and the flat core particles in this way, and forming the conductive coat layer on the surface of each of the mixed core particles, the spherical conductive coat particles and the flat conductive particles are formed. Since the conductive coating layer of the conductive coating particles can be formed with the same composition and the same film thickness, the conductive coating particles and the conductive conductive particles having the same composition and uniform thickness between the flat conductive coating particles. A network is formed, and even more excellent electrical resistance characteristics can be realized.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, although embodiment of this invention is explained in full detail, the scope of the present invention is not limited to the following embodiment.
In this specification, “X to Y” (X and Y are arbitrary numbers) means “X or more and Y or less” unless otherwise specified, and “preferably larger than X, Y It includes the meaning of “smaller”.

  The conductive powder of this embodiment contains spherical conductive coat particles (also referred to as “spherical conductive coat particles”) and flat conductive coat particles (“flat conductive coat particles”) in a mixed state. Conductive powder.

  Both spherical conductive coat particles and flat conductive coat particles are particles having a laminated structure in which a conductive coat layer is provided on the surface of a core material. The conductive coat layer may be formed on the outermost surface, and an intermediate layer may be provided between the core material and the conductive coat layer. This intermediate layer may be provided with a catalyst layer made of Sn—Pd catalyst or Pd chloride catalyst, for example, in order to further stabilize the conductive coating layer. However, the present invention is not limited to this.

The core material of the spherical conductive coat particle and the flat conductive coat particle is not particularly limited, and may be, for example, inorganic particles made of metal or ceramics, or organic particles made of resin. Specific examples of the nonmetal include ceramics such as barium sulfate, calcium carbonate, zinc oxide, and alumina.
When metal particles are used as the core material, it is preferable to select a metal that is difficult to form a solid solution with the material of the conductive coating layer.
The core material of the spherical conductive coat particle and the core material of the flat conductive coat particle may be the same material or different materials.

The conductive coating layer of the spherical conductive coat particle and the flat conductive coat particle is not particularly limited as long as it has a conductive composition. For example, a noble metal such as gold, silver, platinum, palladium, or an alloy thereof can be used as a main component.
The composition of the conductive coat layer of the spherical conductive coat particles and the conductive coat layer of the flat conductive coat particles are preferably the same. When the conductive coating layer has the same composition, for example, when a conductive paste is prepared and cured, a uniform conductive network having the same composition is formed between the spherical conductive coating particles and the flat conductive coating particles. The electrical resistance characteristics can be enhanced without increasing the thickness of the conductive coating layer formed.

The film thickness of the conductive coat layer depends on the composition of the conductive coat layer, but it is preferable that both the spherical conductive coat particles and the flat conductive coat particles are 0.01 μm to 0.8 μm. Among these, when the main component of the conductive coating layer is gold, platinum, palladium, rhodium or an alloy thereof, it is preferably 0.01 μm to 0.08 μm, and the main component of the conductive coating layer is silver or this. In the case of an alloy, it is preferably 0.1 μm to 0.8 μm. If the thickness is smaller than these ranges, excellent conductive properties cannot be obtained and the resistance becomes high. On the other hand, if it is thicker than these ranges, the cost merit becomes dilute. The advantage of the present invention is that excellent electrical resistance characteristics can be realized without increasing the thickness of the conductive coating layer in the coating powder.
In addition, from the viewpoint of forming a uniform conductive network between the spherical conductive coat particles and the flat conductive coat particles, the film thickness of the conductive coat layer of the spherical conductive coat particles and the flat conductive coat particles is It is preferable that they are substantially the same.

(Spherical conductive coated particles)
The spherical conductive coat particle is a spherical particle having a conductive coat layer on the surface of the core material particle, and has an aspect ratio of 1.0 to 1.5, particularly 1.0 to 1.4, particularly 1. It is preferably 0 to 1.3. When the aspect ratio is 1.0 to 1.5, a conductive network can be efficiently formed between the flat conductive coat particles and the conductivity can be increased.
The particle diameter of the spherical conductive coat particles is preferably 1 μm to 20 μm, more preferably 1.5 μm to 18 μm, still more preferably 2 μm to 15 μm, as the center particle diameter (D50).

The “aspect ratio” refers to the ratio between the longest diameter and the shortest diameter of each particle (longest diameter / shortest diameter). In the case of flat particles, it refers to the ratio of the longest diameter to the thickness of each particle (longest diameter / thickness).
Moreover, the center particle diameter (D50) in this invention is the center particle diameter (D50) measured with the laser scattering type particle size distribution measuring apparatus.

(Flat conductive coated particles)
The flat conductive coat particle is a flat particle having a conductive coat layer on the surface of the core material particle, and has an aspect ratio of 5.0 to 20.0, particularly 7.0 to 18.0, In particular, it is preferably 8.0 to 15.0. When the aspect ratio is less than 5.0, it becomes impossible to efficiently form a conductive network between the spherical conductive coat particles, and it becomes difficult to increase the conductivity. On the other hand, if it is larger than 20.0, it may be disadvantageous in terms of cost although it depends on the center particle size ratio.
The particle size of the flat conductive coat particles is preferably 1.2 μm to 25 μm, more preferably 1.8 μm to 22 μm, and even more preferably 2.5 μm to 18 μm, as the center particle size (D50).

  Here, the “flat shape” comprehensively includes shapes having a large difference between the longest diameter and the shortest diameter, and includes shapes such as a flat plate shape, a flake shape, a rod shape, and a flake shape.

  The ratio of the aspect ratio of the flat conductive coat particle to the aspect ratio of the spherical conductive coat particle (: aspect ratio ratio) is preferably 2 to 20, particularly 3 to 15, particularly 5 to 13. More preferably.

(Conductive powder (mixed powder))
The particle size of the mixed powder of flat conductive coat particles and spherical conductive coat particles is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less, as the center particle size (D50).

  The center particle diameter ratio between the flat conductive coat particles and the spherical conductive coat particles is preferably (flat conductive coat particles D50 / spherical conductive coat particles D50) = 1.2 to 10, more preferably. It is 1.3-9, More preferably, it is 1.4-8.

The mixing ratio of the flat conductive coat particles and the spherical conductive coat particles is preferably (flat conductive coat particles / spherical conductive coat particles) = 1.0 to 12, particularly 1.1. ˜11, especially 1.2˜10 is preferred.
By making the mixing ratio of flat conductive coat particles / spherical conductive coat particles 1.0 to 12, it is possible to enjoy the advantage that excellent electrical resistance characteristics can be realized without increasing the thickness of the conductive coat layer. can do.

  In addition, the electroconductive powder of this embodiment may contain other components (particles) other than the spherical electroconductive coat particle and the flat electroconductive coat particle as long as the effects of the present invention are not impaired.

(Production method)
The conductive powder of this embodiment can be manufactured as follows. However, it is not limited to the following manufacturing method.

  That is, the conductive powder of the present embodiment is manufactured by mixing spherical core particles and flat core particles, and forming a conductive coat layer on the surface of each mixed core particle. Is preferred. If manufactured in this way, the conductive coating layers of the spherical conductive coating particles and the flat conductive coating particles can be formed with the same composition and the same film thickness. For example, a conductive paste was prepared and cured. Sometimes it is possible to form a uniform conductive network with the same composition and the same thickness between the spherical conductive coat particles and the flat conductive coat particles, so that the electric resistance characteristics can be achieved without increasing the thickness of the conductive coat layer. Can be increased. On the other hand, when the conductive coating layer is formed and then mixed, the flat particles and spherical particles each form an aggregate, and the spherical conductive coating particles and the flat conductive coating particles are uniformly mixed. In addition, it is difficult to cause problems in electrode applications with fine pitches.

The spherical core material particles preferably have an aspect ratio of 1.0 to 1.5, particularly 1.0 to 1.4, and more preferably 1.0 to 1.3, according to the spherical conductive coat particles.
The particle diameter of the spherical core particles is preferably 1 μm to 20 μm, more preferably 1.5 μm to 18 μm, still more preferably 2 μm to 15 μm, as the center particle diameter (D50).
Such spherical core particles can be obtained by known methods such as various atomizing methods, but are not limited to this method.

On the other hand, the flat core material particles preferably have an aspect ratio of 5 to 20, particularly 7 to 18, especially 8 to 15, in accordance with the flat conductive coat particles.
The particle diameter of the flat core particles is preferably 1.2 μm to 25 μm, more preferably 1.8 μm to 22 μm, and even more preferably 2.5 μm to 18 μm, as the center particle diameter (D50).
Such flat core particles can be obtained by a general mechanical processing technique, but are not limited to this method.

  The ratio of the aspect ratio of the flat core particles to the aspect ratio of the spherical core particles (: aspect ratio) is preferably 2 to 20, particularly 3 to 15, and especially 5 to 13. Is more preferable.

  The mixing ratio of the spherical core material particles to the flat core material particles is preferably a mass ratio of (flat core material / spherical core material) = 1.0 to 12, particularly 1.1 to 11. Among these, 1.2 to 10 is particularly preferable.

  When the spherical core material particles and the flat core material particles are mixed, it is preferably added to a dispersion medium, for example, water, and mixed by stirring to form a slurry. In particular, when plating the conductive coating layer by the substitution method, it is preferable to mix and slurry in the catalyst activation treatment when plating the conductive coating layer by the reduction treatment or acid cleaning treatment, or when the conductive coating layer is plated by the reduction method. .

The method for forming the conductive coating layer on the surface of the spherical core particles and the flat core particles is not particularly limited, but various plating methods can be employed. When the core particle is a metal particle, either a substitution method or a reduction method can be employed. When the core material is non-metallic, it is necessary to adopt a reduction method.
A commercially available plating solution can also be used when the conductive coating layer is plated by a substitution method.
When the conductive coating layer is plated by the reduction method, it is preferable to perform activation by imparting Pd to the surface of the core material.

In addition, it is preferable to use a Sn—Pd catalyst or a Pd chloride catalyst depending on the material of the core material when plating. In addition, the oxide layer on the surface of the core material is obtained by performing a reduction treatment using a reducing agent such as hydrazine or sodium borohydride (SBH) or an acid treatment using an acid such as sulfuric acid before plating. Is preferably removed.
It is preferable to mix the spherical core material particles and the flat core material particles from the pretreatment stage of the plating process.
Moreover, when electroless plating is performed, it is preferable to separate the solid and liquid after the treatment and dry in an atmosphere of 50 to 80 ° C.
In addition, after forming the conductive coat layer on the surface of the core material particles, when the particles are aggregated, it is preferable to perform a dispersion treatment using an ultrasonic wave, a homogenizer, or the like.

(Use)
Since the conductive powder of the present invention is excellent in conductive properties, it can be suitably used as a main constituent material of various conductive materials such as anisotropic conductive films, conductive pastes, and conductive adhesives.
For example, in order to prepare a conductive paste, the conductive powder of the present invention can be mixed with a binder and a solvent, and further, if necessary, a curing agent, a coupling agent, a corrosion inhibitor, etc., to produce a conductive paste. .
In this case, examples of the binder include liquid epoxy resins, phenol resins, unsaturated polyester resins, and the like, but are not limited thereto.
Examples of the solvent include terpineol, ethyl carbitol, carbitol acetate, butyl cellosolve and the like.
Examples of the curing agent include 2-ethyl 4-methylimidazole.
Examples of the corrosion inhibitor include benzothiazole and benzimidazole.

  The conductive paste can be used to form a circuit pattern on a substrate to form various electric circuits. For example, it is possible to form a printed wiring board, an electric circuit of various electronic components, external electrodes, and the like by applying or printing on a fired substrate or an unfired substrate, heating, pressurizing and baking as necessary.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Measurement of particle aspect ratio>
The photograph of 1200 times was taken with a transmission electron microscope (TEM), the longest diameter of arbitrary 100 particles was measured, and the average long diameter (A) was obtained. In addition, the measurement sample was filled with an epoxy resin, and the cross section of the powder filled with resin was polished stepwise using a water-resistant sandpaper P400, P800, P1500, and a pure alumina powder 20% slurry, followed by a scanning electron microscope (SEM). ) Was taken 1000 times, the shortest diameter of any 100 particles was measured, and the average short diameter (B) was determined. Then, the aspect ratio (A / B) was calculated from (A) and (B) thus obtained.
In the case of flat particles, the thickness of arbitrary 100 particles was measured, the average thickness (B) was determined, and the aspect ratio (A / B) was calculated.

<Center particle size measurement method>
Take a small amount of the powder to be measured in a beaker, add 2 or 3 drops of 3% Triton X solution (Kanto Chemical), and mix with the powder, then add 0.1% SN Dispersant 41 solution (San Nopco) 50mL Then, using a ultrasonic disperser TIPφ20 (Nippon Seiki Seisakusho, OUTPUT: 8, TUNING: 5), dispersion treatment was performed for 2 minutes to prepare a measurement sample. The center particle size (D50) of this measurement sample was determined using a laser diffraction / scattering particle size distribution analyzer MT3300 (manufactured by Nikkiso).

<Evaluation of conductivity (specific resistance) of conductive paste>
Ethylcellulose: terpineol: powder was mixed at a mass ratio of 2:28:70, mixed with a three roll mill, and then a 1 cm × 5 cm strip pattern was printed on a glass plate by screen printing. The paste was dried at 70 ° C. for 60 minutes in the air, then cured at 150 ° C. for 39 minutes, and the electrical resistance was measured with a digital voltmeter (manufactured by Yokogawa Electronics Works) to determine the specific resistance.
Also, measure the film thickness with a micrometer,
Specific resistance (Ω · cm) = width (cm) × film thickness (μm) × resistance (Ω) / (length (cm) × 10 ⁴ )
The conductivity (specific resistance) of the conductive paste was calculated by the following formula.

Example 1
(1) Pretreatment of core material Flat nickel powder made of flat nickel particles (Mitsui Metals, D50: 12.2 μm, aspect ratio: 10.4) 30 g and spherical nickel powder made of spherical nickel particles (Inco Corporation) Manufactured, D50: 6.9 μm, aspect ratio: 1.2) 6 g was put into 500 mL of pure water kept at 40 ° C. and stirred for 5 minutes to make a slurry. Next, 5 g of SBH was added, and the reduction treatment was performed while maintaining stirring for 30 minutes. Then, after separating into solid and liquid with a Buchner funnel and washing with 500 mL of pure water, 100 mL of methanol was added and dehydration was performed to obtain cake-like mixed particles (core material). The moisture of the obtained cake was measured and weighed 30 g in terms of dry powder.

(2) Electroless plating treatment 1200 mL of pure water was heated to 80 ° C., 69 mL of electroless plating solution (Muden Gold) manufactured by Okuno Pharmaceutical Co., Ltd. was added, and then 7.56 g of potassium gold cyanide was added. Next, the cake-like mixed particles (core material) obtained above are put into a slurry, and after stirring for 30 minutes, the mixture is solid-liquid separated, washed with 1000 mL of warm pure water, and methanol while sucking. 100 mL and 100 mL of acetone were sequentially added to perform dehydration treatment. The obtained cake was transferred to a stainless steel vat, held in a 70 ° C. atmosphere for 12 hours and dried to obtain a conductive powder.

  While measuring the specific resistance (ohm * cm) of the obtained electroconductive powder, the aspect ratio, the film thickness of the electroconductive coating layer, etc. were calculated and shown in Table 1 and Table 2.

The gold film thickness, that is, the film thickness (A) of the conductive coating layer was calculated by the following calculation formula. The same applies below.
Film thickness (A) = {noble metal content / (noble metal specific gravity × 100)} / {core specific surface area × (1−noble metal content / 100)}
The “core material specific surface area” in the above formula is an arithmetic average value obtained by multiplying the core material specific surface areas of the core material flat particles and the core material spherical particles by the mass ratio.

The mass ratio (flat / spherical) between the flat conductive coat particles and the spherical conductive coat particles was calculated by the following formula. The same applies below.
Flat conductive coat particle mass / spherical conductive coat particle mass = {core material flat particle mass + (noble metal specific gravity × film thickness (A) × core flat particle specific surface area × core flat particle mass)} / {Mass of core material spherical particles + (noble metal specific gravity x film thickness (A) x core material spherical particle specific surface area x core material spherical particle mass)}

(Example 2)
The same treatment as in Example 1 was performed using 24 g of the same flat nickel powder as in Example 1 and 12 g of the spherical nickel powder to obtain a conductive powder.

  While measuring the specific resistance (Ω · cm) of the obtained conductive powder, the film thickness of the conductive coating layer, the aspect ratio, the mass ratio of the flat conductive coated particles to the spherical conductive coated particles (flat / Sphere) etc. were calculated and shown in Tables 1 and 2.

(Example 3)
The same treatment as in Example 1 was performed using 32 g of flat nickel powder similar to that in Example 1 and 4 g of spherical nickel powder to obtain a conductive powder.

  The specific resistance (Ω · cm) of the obtained conductive powder was measured, and the aspect ratio, the film thickness of the conductive coating layer, and the mass ratio of the flat conductive coating particles to the spherical conductive coating particles (flat / Sphere) etc. were calculated and shown in Tables 1 and 2.

Example 4
Flat nickel powder made of flat nickel particles (Mitsui Metals, D50: 9.8 μm, aspect ratio: 6.5) and spherical nickel powder made of spherical nickel particles (Inco, D50: 6.9 μm) , Aspect ratio: 1.2) Using 6 g, the same treatment as in Example 1 was performed to obtain a conductive powder.

  The specific resistance (Ω · cm) of the obtained conductive powder was measured, and the aspect ratio, the film thickness of the conductive coating layer, and the mass ratio of the flat conductive coating particles to the spherical conductive coating particles (flat / Sphere) etc. were calculated and shown in Tables 1 and 2.

(Example 5)
Flat nickel powder composed of flat nickel particles (Mitsui Metals, D50: 14.4 μm, aspect ratio: 15.3) and spherical nickel powder composed of spherical nickel particles (Inco, D50: 6.9 μm) , Aspect ratio: 1.2) Using 6 g, the same treatment as in Example 1 was performed to obtain a conductive powder.

  The specific resistance (Ω · cm) of the obtained conductive powder was measured, and the aspect ratio, the film thickness of the conductive coating layer, and the mass ratio of the flat conductive coating particles to the spherical conductive coating particles (flat / Sphere) etc. were calculated and shown in Tables 1 and 2.

(Example 6)
Flat nickel powder made of flat nickel particles (Mitsui Metals, D50: 4.9 μm, aspect ratio: 9.5) and spherical nickel powder made of spherical nickel particles (Mitsui Metals, D50: 2.6 μm) , Aspect ratio: 1.1) Using 6 g, the same treatment as in Example 1 was performed to obtain a conductive powder.

  The specific resistance (Ω · cm) of the obtained conductive powder was measured, and the aspect ratio, the film thickness of the conductive coating layer, and the mass ratio of the flat conductive coating particles to the spherical conductive coating particles (flat / Sphere) etc. were calculated and shown in Tables 1 and 2.

(Example 7)
(1) Pretreatment of core material Flat alumina bar powder made of flat barium sulfate powder made of flat barium sulfate particles (manufactured by Sakai Chemical Co., Ltd., D50: 8.5 μm, aspect ratio: 9.1) and spherical alumina particles 6 g (D50: 2.5 μm, aspect ratio: 1.5) was prepared.
15 mL of 17.5 mL of hydrochloric acid, and OPC-80 catalyst (Okuno Pharmaceutical Co., Ltd.) with Sn salt content of 35% were added to 140 mL of pure water, and the liquid temperature was kept at 40 ° C. Thereafter, the flat barium sulfate powder and the spherical alumina powder were added thereto to make a slurry, followed by stirring for 15 minutes to carry out a catalytic activity treatment.
The treated slurry was filtered with a Buchner funnel, washed with 400 mL of pure water, filtered again, and dehydrated to obtain a catalyst active treated cake.

(2) Electroless plating treatment 45.5 g of silver nitrate was dissolved in 385 mL of pure water, 60 mL of 25% aqueous ammonia was added, and 25 g of ammonium sulfate was further added to prepare a silver ammine complex aqueous solution adjusted to pH 9.4.
To this silver ammine complex aqueous solution, the total amount of the catalyst active-treated cake was added and stirred and dispersed at 40 ° C. for 5 minutes to obtain a reaction slurry. Then, a reducing agent solution in which 4 mL of hydrazine-hydrate was dissolved in 320 mL of pure water was quantitatively added to this reaction slurry in 100 minutes, and after complete addition, the mixture was stirred for 7 minutes. The silver coat reaction on the material was terminated. Subsequently, this slurry was filtered with a Buchner funnel, and washed at 70 ° C. with 1000 mL of pure water. Further, 100 mL of methanol and 100 mL of acetone were sequentially added while sucking to perform dehydration treatment. The obtained cake was transferred to a stainless steel vat, held in a 70 ° C. atmosphere for 12 hours and dried to obtain a conductive powder.

  The specific resistance (Ω · cm) of the obtained conductive powder was measured, and the aspect ratio, the film thickness of the conductive coating layer, and the mass ratio of the flat conductive coating particles to the spherical conductive coating particles (flat / Sphere) etc. were calculated and shown in Tables 1 and 2.

(Comparative Example 1)
Only the flat nickel powder 36g similar to Example 1 was used, and the process similar to Example 1 was performed, and the electroconductive powder was obtained.
While measuring the specific resistance (ohm * cm) of the obtained electroconductive powder, the film thickness etc. of the electroconductive coating layer were computed and it showed in Table 1 and Table 2.

(Comparative Example 2)
Using only the spherical nickel powder 36g similar to Example 1, the process similar to Example 1 was performed and the electroconductive powder was obtained.
While measuring the specific resistance (ohm * cm) of the obtained electroconductive powder, the film thickness etc. of the electroconductive coating layer were computed and it showed in Table 1 and Table 2.

(Comparative Example 3)
Using only the flat nickel powder 36g similar to Example 6, the process similar to Example 1 was performed and the electroconductive powder was obtained.
While measuring the specific resistance (ohm * cm) of the obtained electroconductive powder, the film thickness etc. of the electroconductive coating layer were computed and it showed in Table 1 and Table 2.

(Comparative Example 4)
Using only the same flat barium sulfate powder 36g as in Example 7, the same treatment as in Example 7 was performed to obtain a conductive powder.
While measuring the specific resistance (ohm * cm) of the obtained electroconductive powder, the film thickness etc. of the electroconductive coating layer were computed and it showed in Table 1 and Table 2.

The center particle size ratio in Table 2 indicates the ratio of the center particle size after coating to the center particle size before coating. When the noble metal film is coated, each particle is likely to aggregate, so this ratio can be said to indicate the degree of aggregation.
From Table 1 and Table 2, the specific resistance is remarkably lowered by mixing spherical conductive coat particles and flat conductive coat particles as in Examples 1 to 7 as compared with Comparative Examples 1 to 4. I found that I could do it.

Claims (7)

  Spherical conductive coat particles having an aspect ratio of 1.0 to 1.5 and flat conductive coat particles having an aspect ratio of 5.0 to 20.0, and the spherical conductive coat particles and the flat conductive The coated particle is a conductive powder comprising a conductive coating layer having the same composition on the surface of a core material made of the same or different material.   2. The conductive powder according to claim 1, obtained by mixing spherical core particles and flat core particles in a dispersion medium, and forming a conductive coating layer on the surface of the mixed core particles. .   The spherical core material particles and the flat core material particles are mixed in a dispersion medium, and the surface of the mixed core material particles is pretreated to form a conductive coating layer. 2. The conductive powder according to 2.   4. The conductive powder according to claim 1, wherein the film thickness of the conductive coating layer of the spherical conductive coat particle and the flat conductive coat particle is 0.01 μm to 0.8 μm.   The conductive powder according to any one of claims 1 to 4, wherein the conductive coating layer contains, as a main component, any one of gold, silver, platinum, palladium, rhodium, and alloys thereof.   A conductive paste using the conductive powder according to claim 1.   An electric circuit obtained by forming a circuit pattern on the surface of a substrate using the conductive paste according to claim 6.