JP6096143B2 - Silver-coated flaky copper powder, method for producing the same, and conductive paste - Google Patents

Description

  The present invention relates to a silver-coated flaky copper powder, a method for producing the same, and a conductive paste.

Conventionally, a conductive paste in which silver powder is dispersed in an organic component has been used to form electrodes and circuits such as electronic components, electromagnetic wave shielding films, electromagnetic wave shielding materials, and the like. Among the conductive pastes, resin-cured conductive pastes (see Patent Document 1) are brought into conduction by silver powders contacting each other due to volumetric shrinkage of the resin. As silver powder blended in the resin curable conductive paste, flaky silver powder having a large contact area is used (see Patent Document 2).
However, the “silver paste” blended with flaky silver powder is expensive and prone to migration because the metal price is higher than the “copper paste” blended with flaky copper powder. Further, “copper paste” has a drawback that migration is difficult to occur but it is easily oxidized and conductivity is deteriorated. As one method for overcoming these drawbacks, a silver-coated flaky copper powder in which copper powder is flattened and coated with silver has been proposed.
The copper powder used for the silver-coated flaky copper powder is manufactured by an atomizing method, a wet reduction method, or an electrolysis method. Among these, the atomization method is preferable from the viewpoint of cost and mass productivity, and silver-coated flaky copper powder obtained by flattening spherical copper powder by the atomization method has been proposed (Patent Document 3). reference).
However, the silver-coated flaky copper powder by the atomizing method does not have a sufficiently satisfactory performance in terms of electrical conductivity, particularly in a low filler content paste, and further improvement is desired.

JP 2002-150837 A Japanese Patent No. 3874634 JP 2002-245849 A

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention provides a silver-coated flaky copper powder and a method for producing a silver-coated flaky copper powder that can form a conductive film having excellent conductivity, and conductivity using the silver-coated flaky copper powder. The purpose is to provide a paste.

The silver-coated flaky copper powder of the present invention as a means for solving the problems is a silver-coated flaky copper powder that has at least a surface and is flattened,
The ratio (L / d) of the major axis average length L to the minor axis average length d measured by a scanning electron microscope is 2.5 or more,
The X-ray particle diameter by the X-ray diffraction method is 60 nm or less on the Cu (111) plane.

  According to the present invention, the above conventional problems can be solved, and a silver-coated flaky copper powder and a method for producing a silver-coated flaky copper powder capable of forming a conductive film having excellent conductivity, and the above-mentioned A conductive paste using silver-coated flaky copper powder can be provided.

FIG. 1 is a graph showing the relationship between flake time and X-ray particle size (part 1). FIG. 2 is a graph showing the relationship between flake time and X-ray particle size (part 2). FIG. 3 is an SEM photograph (2,000 times) of the electrolytic copper powder (1). FIG. 4 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 1 produced from the electrolytic copper powder (1) of FIG. FIG. 5 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 2 produced from the electrolytic copper powder (1) of FIG. FIG. 6 is an SEM photograph (2,000 times) of the electrolytic copper powder (2). FIG. 7 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 3 prepared from the electrolytic copper powder (2) of FIG. FIG. 8 is an SEM photograph (2,000 times) of the electrolytic copper powder (3). FIG. 9 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 4 produced from the electrolytic copper powder (3) of FIG. FIG. 10 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 5 produced from the electrolytic copper powder (1) of FIG. FIG. 11 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 6 produced from the electrolytic copper powder (1) of FIG. FIG. 12 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 7 produced from the electrolytic copper powder (1) of FIG. FIG. 13 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 8 produced from the electrolytic copper powder (1) of FIG. 14 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 9 produced from the electrolytic copper powder (1) of FIG. FIG. 15 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 10 produced from the electrolytic copper powder (1) of FIG. FIG. 16 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Example 11 produced from the electrolytic copper powder (1) of FIG. FIG. 17 is an SEM photograph (2,000 times) of the silver-coated atomized copper powder of Comparative Example 1 produced from the atomized copper powder of FIG. 18 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Comparative Example 2 produced from the atomized copper powder of FIG. FIG. 19 is an SEM photograph (2,000 times) of the silver-coated flaky copper powder of Comparative Example 3 produced from the atomized copper powder of FIG. 20 is an SEM photograph (2,000 times) of the silver-coated copper powder of Comparative Example 4 produced from the electrolytic copper powder (1) of FIG. FIG. 21 is a schematic diagram showing an example of particle size measurement of silver-coated flaky copper powder. 22 is a SEM photograph (2,000 times) of the silver-coated copper powder of Example 12 produced from the electrolytic copper powder (3) of FIG. FIG. 23 is an SEM photograph (2,000 times) of atomized copper powder SF-Cu 5 μm.

(Silver-coated flaky copper powder)
The silver-coated flaky copper powder of the present invention is a silver-coated flaky copper powder that has at least silver on the surface and is flattened.
The silver-coated flaky copper powder includes both an aspect in which the copper powder is flattened and then coated with silver, and an aspect in which the powder obtained by coating the copper powder with silver is flattened.
The copper powder used as a raw material for the silver-coated flaky copper powder of the present invention is preferably electrolytic copper powder.

<Electrolytic copper powder>
The electrolytic copper powder is preferably composed of a main trunk and a sub trunk divided into an indefinite shape from the main trunk, and has an indefinite shape having the sub trunk.
The flaky electrolytic copper powder obtained by flattening the irregular-shaped electrolytic copper powder exhibits a shape derived from the main trunk portion of the electrolytic copper powder and the sub trunk portion divided into an irregular shape from the main trunk portion by observation with an electron microscope. In addition, a difference in the shape is recognized from the flaky copper powder obtained by flattening spherical atomized copper powder, wet reduced copper powder or the like. Although the shape of the flaky electrolytic copper powder is a shape derived from the shape of the electrolytic copper powder, it is flat and the shape in the thickness direction is completely different from the electrolytic copper powder, and the horizontal direction is also indefinite. Since the outline is different, it cannot be said that the shape is similar to electrolytic copper powder. Further, there is a difference in the shape of the indefinite shape of the copper powder before flattening and the shape such as flatness and smoothness.
The ratio (L / d) between the major axis average length L and the minor axis average length d of the electrolytic copper powder is preferably 3 or more, and more preferably 3.5 or more. When the main trunk of the electrolytic copper powder used for the flattening treatment is short, or when the branch from the sub trunk and the sub trunk is developed more than the main trunk, the ratio (L / d) is less than 3, In the flaky copper powder after the flattening treatment, the ratio (L / d) is likely to be less than 2.5, the contact probability between the particles may be reduced, and the resistance value of the conductive film may be deteriorated.
The electrolytic copper powder can be produced by an electrolysis method. About the manufacturing method of the electrolytic copper powder by the said electrolysis method, it demonstrates with the manufacturing method of the silver covering flaky copper powder mentioned later.

<X-ray particle size>
About the silver coating flake copper powder after carrying out silver coating to the various copper powder produced by the Example and comparative example which are shown in Table 1-Table 4 mentioned later, X-ray particle size is measured by the said X-ray diffraction method, X-ray particle The relationship between the diameter and the flake time is shown in FIGS.
From FIG. 1 and FIG. 2, the silver-coated flaky copper powder of the present invention has an X-ray particle size of 600 Å (60 nm) or less on the Cu (111) plane and 460 以下 (46 nm) or less. Preferably, it is 420 mm (42 nm) or less. The X-ray particle size is preferably 190 mm (19 nm) or less on the Ag (111) plane.
When the X-ray particle size on the Cu (111) surface exceeds 600 mm (60 nm), the flattening is insufficient, the uniformity of the silver coating is poor, and the conductivity formed by blending the silver-coated flaky copper powder. The resistance value of the film may not be lowered.
This is because spherical atomized copper powder tends to be crushed from a random direction depending on its shape, but when the indefinite shape of electrolytic copper powder is flattened, the shape causes the main trunk and sub trunk from a specific direction. It is thought that it is easy to be crushed. In addition, the spherical atomized copper powder does not have the same crystal orientation because of its manufacturing method, but the indeterminate shaped electrolytic copper powder forms a main trunk and a sub trunk by successively connecting the Cu (111) planes in parallel. Therefore, the horizontal cross section is the Cu (111) plane. As a result, the irregularly shaped electrolytic copper powder is preferentially crushed in the Cu (111) surface during flattening, and the value of the X-ray particle size of the Cu (111) surface changes greatly as the flattening progresses. Conceivable. From the crystal orientation of the surface and the shape of the main trunk and sub trunk resulting from the flattening of the main trunk and sub trunk (the substitution reaction is thought to start easily from the irregularities on the outer periphery), the electrolysis of indefinite shape The flaky copper powder that flattened the copper powder and made the X-ray particle size on the Cu (111) surface 600 nm (60 nm) or less is likely to have a uniform silver coating thickness due to simultaneous occurrence of silver substitution reactions. It is considered that a difference occurs in the value of the X-ray particle diameter of silver. In fact, the silver coated flaky copper powder with a small X-ray particle size on the Cu (111) surface has a smaller X-ray particle size on the Ag (111) surface, and a powder with a particle size of 190 mm (19 nm) or less is obtained. The conductivity of the resulting conductive film is favorable, which is preferable.

Here, the X-ray particle size can be calculated from the half-value width of the diffraction peak of the crystal plane of each particle by the X-ray diffraction method based on the following apparatus and conditions.
[XRD equipment, conditions]
・ SmartLab X-ray Diffractometer manufactured by Rigaku Corporation
-X-ray used: CuKα (wavelength = 1.5405 mm)
Ag (111) plane: 2θ = 35 ° -40 °
Cu (111) plane: 2θ = 41 ° to 47 °
Cu (200) plane: 2θ = 47.5 ° to 52.5 °
Scanning was performed at a scanning speed of 5 ° / min, and after removing the Kα2 component, the angle 2θ, intensity, and half width of each diffraction peak were measured.
The X-ray particle diameter (crystallite diameter) can be calculated from Scherrer's equation = 0.94 × wavelength / half width / cos θ.

The ratio (L / d) of the major axis average length L to the minor axis average length d of the silver-coated flaky copper powder is 2.5 or more, and preferably 3 to 5.
When the ratio (L / d) is less than 2.5, the probability of contact between particles may be reduced, and the resistance value of the conductive film may be deteriorated.
Further, the aspect ratio (L / t) between the long axis average length L and the average thickness t of the silver-coated flaky copper powder is preferably 8 or more, more preferably 10 to 300, and still more preferably 10 to 100. .
When the aspect ratio (L / t) is less than 8, the contact area between the silver-coated flaky copper powders is not sufficient, and the conductive formed by using the conductive paste blended with the conductive paste. The conductivity of the film may not be sufficiently high, and if it exceeds 300, it may be difficult to produce the silver-coated flaky copper powder.

The “major axis average length L”, “minor axis average length d”, and “average thickness t” in the ratio (L / d) and aspect ratio (L / t) are the scanning electron microscope (SEM). It can be measured by observing the SEM photograph. In that case, the reference | standard of whether to put each silver covering flaky copper powder in a measuring object is that a boundary is clear as one particle.
For each particle of the silver-coated flaky copper powder, the longest straight line is taken as the major axis, the length is measured as the “major axis length” L, and the portion that has the major axis and can be approximated by a rectangle It is assumed to be a senior executive. Then, the longest length d in the direction perpendicular to the major axis of the particle is measured as the “short axis length”, and this d is larger than the length of the main trunk in the direction perpendicular to the major axis of the main trunk, When there is a portion protruding from the main trunk portion in a direction perpendicular to the major axis direction with respect to the main trunk portion, that portion is set as a sub trunk portion. The major axis L ′ and the minor axis d ′ are measured for each of the main trunk portion and the sub trunk portion. Note that the directions defined by the sub trunk L ′ and d ′ are not the long and short but the major axis direction and the minor axis direction of the main trunk unit (see FIG. 21). L of each particle is L ′ of the main trunk, and d of each particle is “d ′ of the main trunk d + the largest d ′ of the sub trunks projecting to one side perpendicular to the main trunk + the vertical of the main trunk It can be defined by the maximum d ′ ”of the sub-trunk projecting to the other side of the direction.
Furthermore, the “thickness” of the main part of each silver-coated flaky copper powder is measured for 10 silver-coated flaky copper powders having a clear boundary with a horizontal surface being observed as a side surface. .
From the above, “long axis length”, “short axis length” for 100 silver-coated flaky copper powders, and “thickness” for 10 silver-coated flaky copper powders, The average major axis length L, the minor axis average length d, and the average thickness t can be obtained.

The ratio (A / B) between the measured area A of the silver-coated flaky copper powder and the virtual rectangular conversion area B of the silver-coated flaky copper powder is preferably 0.8 or less, 0.5 to 0.75. Is more preferable.
The ratio A / B is a simple indicator as to how far the silver-coated flaky copper powder is from a rectangle (cuboid) or whether voids exist outside the particles, and particles having the same weight in the conductive film It is considered that there is a correlation with the ease of contact between particles in the presence of water, ie, conductivity.
When the ratio (A / B) exceeds 0.8, particularly in a conductive film having a low filler content, the distance between particles increases, the contact probability decreases, and the conductivity may deteriorate.
The measured area A of each particle is defined as A = Σ (L ′ × d ′). Each particle is regarded as a rectangular aggregate of a main trunk and a sub trunk (there are a plurality of sub trunks for one particle), and the respective areas are totaled. Further, the virtual rectangle conversion area B is defined as B = L × d with respect to the longest length L in the major axis direction of each particle and the maximum length d in the direction perpendicular thereto. Thereby, the ratio (A / B) of the virtual rectangle conversion area and the measured area can be obtained.

BET specific surface area of the silver-coated flaky copper powder is ^preferably from ^{0.4m 2 / g~4m 2 / g,} 0.5m 2 /g~1.5m 2 / g is more preferable. When the BET specific surface area exceeds 4 m ² / g, handling properties and productivity may be deteriorated, and conductivity of the conductive film may be deteriorated.
The BET specific surface area is, for example, MONOSORB (manufactured by Yuasa Ionics Co., Ltd.), He: 70%, N ₂ : 30% carrier gas, 3 g of sample is put in a cell, and deaeration is performed at 60 ° C. for 10 minutes. After performing, it can be measured by the BET one point method.

The tap density of the silver-coated flaky copper powder is preferably from 4g / cm ³ or less, 3 g / cm ³ or less is more preferable.
The tap density can be measured using, for example, a tap specific gravity measuring instrument (Shibayama Kagaku Co., Ltd., Casa specific gravity measuring instrument SS-DA-2 type).

The cumulative 50% particle size (D50) in the mass-based particle size distribution measured by the laser diffraction particle size distribution measurement method of the silver-coated flaky copper powder is preferably 3 μm to 20 μm, more preferably 7 μm to 15 μm.
The cumulative 50% particle diameter (D50) can be measured using, for example, a microtrack particle size distribution measuring device (Honeywell-Nikkiso Co., Ltd., 9320HRA (X-100)).

From the value obtained by multiplying the BET specific surface area by the X-ray particle size of the Ag (111) plane, the volume of the single crystal layer of the silver coating can be evaluated. When evaluating the volume for the single crystal layer of the silver coating, 1 × 10 ⁻⁵ m ³ / g or more is preferable. When the flaky copper powder having a small X-ray particle size on the Cu (111) surface is coated with silver, the X-ray particle size on the Ag (111) surface is also small, and the resulting conductive film has better conductivity. Compared with atomized copper powder or flaky copper powder having a short flattening time, the volume of the single crystal layer of the silver coating is increased. This is because the small X-ray grain size of the Ag (111) plane does not make it difficult for the crystal growth of Ag to progress, but the percentage of nucleation increases, and the Ag substitution reaction progresses simultaneously and frequently. Can think. Therefore, it can be expected that not only the volume of the single crystal is large, but also the thickness of the silver coating is relatively uniform.

(Method for producing silver-coated flaky copper powder)
The method for producing a silver-coated flaky copper powder according to the present invention includes a step of flattening the electrolytic copper powder (flattening step) and a step of coating the surface of the flaky electrolytic copper powder after the flattening treatment (silver coating). Step), and preferably includes an electrolytic copper powder preparation step, and further includes other steps as necessary.
Depending on the purpose, the electrolytic copper powder may be flattened after first being coated with silver.

<Electrolytic copper powder production process>
The electrolytic copper powder production step is a step of producing electrolytic copper powder by electrolysis.
As the electrolysis method, for example, an anode and a cathode are immersed in a sulfuric acid acidic electrolyte solution containing copper ions, a direct current is passed through the electrolysis, and copper is deposited in a powder form on the cathode surface. And a method of producing electrolytic copper powder through a sieving step and the like, if necessary.
If necessary, surface treatment may be performed with a triazole-based substance such as benzotriazole as an antioxidant treatment.

<Flatening process>
The flattening step is a step of flattening electrolytic copper powder in which the ratio (L / d) of the major axis average length L to the minor axis average length d measured by a scanning electron microscope is 3 or more. .
There is no restriction | limiting in particular as an apparatus which performs the said flattening process, According to the objective, it can select suitably, For example, media-type mills, such as a rolling ball mill, an attritor, and SC mill (Pulverizing mill with a ball and beads) Etc. In addition, as a device for performing the flattening treatment, a commercially available device can be used as it is.

When performing the flattening treatment, it is preferable to carry out the treatment by adding a solvent to the copper powder. When the flattening treatment is performed without adding the solvent, the flaky copper powder aggregates during the treatment, the particle size becomes excessive, and the aspect ratio may not be a sufficiently large value. When the viscosity of the solvent is high, flattening may not progress sufficiently.
There is no restriction | limiting in particular as said solvent, According to the objective, it can select suitably, For example, water, an organic solvent, etc. are mentioned.
There is no restriction | limiting in particular as said organic solvent, Although it can select suitably according to the objective, For example, the organic solvent of molecular weight 200 or less is preferable, and the alcohol of molecular weight 200 or less is more preferable. Examples of the alcohol having a molecular weight of 200 or less include methanol, ethanol, propanol, or a mixture thereof.
There is no restriction | limiting in particular as the addition amount of the said solvent added at the time of the said flattening process, Although it can select suitably according to the objective, 0.1 times-3 times by mass with respect to the copper powder to flatten processing Is preferred. If the addition amount is less than 0.1 times, the effect of solvent addition may be insufficient, and if it exceeds 3 times, a sufficient aspect ratio may not be obtained.

The ball (media) is not particularly limited as long as it is a ball (media) having a diameter of 0.1 mm to 3 mm and a spherical shape, and can be appropriately selected according to the purpose. When the diameter of the ball (media) is less than 0.1 mm, the separation efficiency may be reduced due to clogging of the media when separating the flaky copper powder and the media after the flattening treatment, When it exceeds 3 mm, the particle size of the obtained flaky copper powder may become excessive.
There is no restriction | limiting in particular as a material of the said ball | bowl (media), According to the objective, it can select suitably, For example, metals, such as stainless steel (SUS), ceramics, such as an alumina and a zirconia, etc. are mentioned. Among these, stainless steel (SUS) is particularly preferable in view of product contamination.
There is no restriction | limiting in particular as addition amount at the time of the flattening process of the said ball | bowl (media), Although it can select suitably according to the objective, 1-50 times by mass with respect to the copper powder to flatten a process. preferable. When the addition amount is less than 1 time, a sufficient aspect ratio may not be obtained, and when it exceeds 50 times, the amount of copper powder that can be flattened at one time decreases, and the processing cost increases. Sometimes.

The treatment time for the flattening treatment is not particularly limited, and can be appropriately selected according to the addition amount of the flaking apparatus, the balls, and the copper powder. Considering productivity, it is preferably 10 minutes to 300 minutes. For example, when a 5 L attritor is used, it is preferably 10 minutes to 180 minutes, and more preferably 60 minutes to 150 minutes. If the treatment time is less than 10 minutes, flattening tends to be insufficient, and depending on the combination of the ratio of balls, powder, solvent, and the capacity of the treatment tank, if the treatment time exceeds 180 minutes, the flattening proceeds too much. The BET specific surface area is increased, and the electric resistance is easily increased when a conductive paste is easily formed.
In the flattening process, it is not necessary to flatten all of the input copper powder, and copper powder that has not been flattened after the flattening process may be mixed. If at least one of the above flaky copper powders is formed on the supplied copper powder before and after the flattening process, it can be said that the flattening process has been performed.

In order to improve the dispersibility of the obtained flaky copper powder, it is preferable to add 0.1% by mass to 5% by mass of the dispersant with respect to the copper powder to be flattened. There is no restriction | limiting in particular as said dispersing agent, According to the objective, it can select suitably, For example, a fatty acid, fatty acid salt, surfactant, an organic metal, a chelate formation agent, a protective colloid etc. are mentioned. Of these, fatty acids are particularly preferred. The fatty acid is not particularly limited and may be appropriately selected depending on the intended purpose.For example, propionic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylic acid, oleic acid, Examples thereof include linoleic acid, arachidonic acid, ricinoleic acid, and mixtures thereof. In addition, the said dispersing agent can also be added with a solvent instead of adding a dispersing agent to the copper powder before a flattening process. The dispersant may be added to the copper powder before the flattening step, and the dispersant may be added together with the solvent in the flattening step.
However, if the dispersibility of the flaky copper powder is sufficient, it is possible not to add a dispersant in the flaking process. If a large amount of the dispersant is present on the surface, the silver coating in the silver coating step described later may be non-uniform, and in some cases, it is necessary to remove the dispersant before the silver coating step.

<Silver coating process>
The silver coating step is a step of coating silver on the surface of the flaky electrolytic copper powder after the flattening treatment.
As a method for coating the surface of the flaky electrolytic copper powder with silver, for example, there are two kinds of methods, a reduction method and a substitution method.
The reduction method is a method in which fine particles of silver reduced with a reducing agent are densely coated on the surface of copper powder particles (see, for example, JP-A-2000-248303).
In the substitution method, at the interface of the copper powder particles, silver ions exchange electrons with metallic copper, silver ions are reduced to metallic silver, and instead metallic copper is oxidized into copper ions, In this method, the surface layer of the copper powder particles is a silver layer (see, for example, JP-A-2006-161081).
Among these, the substitution method is preferable in terms of uniformity of silver coating and adhesion of the silver layer to the copper surface.

  In the substitution method, when the silver coating reaction is performed, first, the copper powder raw material is put in the liquid before adding the silver salt and stirred, and then the silver powder is sufficiently dispersed in the liquid. It is preferable to add a liquid containing a salt. The reaction temperature is not particularly limited as long as the reaction solution does not solidify or evaporate, and can be appropriately selected according to the purpose, but can be set at 20 ° C to 80 ° C. The reaction time varies depending on the silver coating amount and the reaction temperature, but can be set in the range of 1 minute to 5 hours.

  As a reaction solution for performing the silver coating reaction, an aqueous solution containing water or an organic solvent or an emulsion composed of an organic solvent phase and an aqueous solvent phase is used. When using an organic solvent with a high solubility in water, a uniform mixed solution is obtained. However, in the case of an organic solvent with a low solubility, the aqueous phase and the organic solvent phase are separated in a stationary state. The silver coating reaction is carried out in the state where is formed. By using these reaction liquids, the flaky copper powder can be subjected to the silver coating reaction as it is without removing the auxiliary added at the time of flattening.

  As the organic solvent, alcohols, ketones, aldehydes, and ethers having compatibility with water and solubility of silver salts (mainly silver nitrate) can be used. Examples of the organic solvent include methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-methylpropanol, 3-methylpropanol, 1,1-dimethylethanol, ethylene glycol, diethylene glycol, triethylene glycol, and glycerin. Carbitol, methyl carbitol, butyl carbitol, cellosolve, methyl cellosolve, butyl cellosolve, terpineol, formaldehyde, acetaldehyde, acetone, methyl ethyl ketone, methyl ether, ethyl ether, methyl ethyl ether and the like. These may be used individually by 1 type and may use 2 or more types together. Among these, when using an organic solvent as a single reaction solution without containing water, a polyhydric alcohol capable of directly dissolving a silver salt is preferable, specifically, ethylene glycol, diethylene glycol, glycerin, etc. Is mentioned.

  When silver coating is performed in a mixed solution of an organic solvent and water or in an emulsion, it is necessary to use a liquid that is liquid at room temperature (20 ° C. to 30 ° C.) as the organic solvent. The mixing ratio of the water and the organic solvent can be appropriately adjusted depending on the organic solvent used. As the water mixed with the organic solvent, any of distilled water, ion-exchanged water, industrial water, etc. may be used as long as there is no risk of impurities being mixed.

  As a silver raw material used for the silver coating reaction, it is necessary to make silver ions exist in the liquid. Therefore, it is preferable to use silver nitrate having solubility in water or many organic solvents. In order to realize as uniform a covering reaction as possible, it is preferable to use silver nitrate solution in which silver nitrate is dissolved in an aqueous solution, an organic solvent, or a mixed solution of water and an organic solvent without adding silver nitrate in a solid state. Depending on the target silver coating amount, the concentration of the silver nitrate solution to be used, the amount of the organic solvent, and the amount of the silver nitrate solution to be used can be determined.

In order to form the silver coating layer more uniformly, a chelating agent may be added to a reaction liquid (mixed solution or emulsion) containing an organic solvent. As the chelating agent, those having a high complex stability constant with copper ions are preferred so that copper ions by-produced by substitution reaction between silver ions and metallic copper do not reprecipitate. Examples of the chelating agent include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid, diethylenetriamine, triethylenediamine, or salts thereof.
In performing the silver coating reaction stably and safely, a pH buffer may be added. Examples of the pH buffering agent include ammonium carbonate, ammonium hydrogen carbonate, aqueous ammonia, sodium hydrogen carbonate, and the like.

The ratio of silver to copper covering the flaky electrolytic copper powder (silver coating amount) is preferably 0.3% by mass to 30% by mass. If the silver coating amount is less than 0.3% by mass, the volume resistivity may not be sufficiently reduced. If the silver coating amount exceeds 30% by mass, there is a large difference in the volume resistivity reduction effect. However, the cost increases as the proportion of silver increases.
The silver coating amount can be determined, for example, by dissolving silver-coated flaky copper powder with nitric acid, adding hydrochloric acid, drying the resulting silver chloride precipitate, and measuring the weight.

<Other processes>
As said other process, a washing | cleaning, a drying process, etc. are mentioned, for example.
-Cleaning and drying process-
The said washing | cleaning and drying process is a process of solid-liquid-separating the obtained silver covering flaky copper powder, washing | cleaning as needed, and drying.
There is no restriction | limiting in particular as said washing | cleaning and drying, The well-known method with respect to copper powder can be used suitably, You may disintegrate after drying.

  The obtained silver-coated flaky copper powder is preferably used by blending with the conductive paste described below.

(Conductive paste)
The conductive paste of the present invention contains the silver-coated flaky copper powder of the present invention, preferably a resin and a solvent, and further contains other components as necessary.
Examples of the conductive paste include a resin curable paste.
The content of the silver-coated flaky copper powder in the conductive paste is not particularly limited and can be appropriately selected depending on the purpose.

<Resin>
There is no restriction | limiting in particular as said resin, According to the objective, it can select suitably, For example, an epoxy resin, an acrylic resin, a polyester resin, a polyimide resin, a polyurethane resin, a phenoxy resin, a silicone resin etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.

<Solvent>
The solvent is not particularly limited and may be appropriately selected depending on the intended purpose. For example, toluene, methyl ethyl ketone, methyl isobutyl ketone, tetradecane, tetralin, propyl alcohol, isopropyl alcohol, terpineol, ethyl carbitol, butyl carbitol Ethyl carbitol acetate, butyl carbitol acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, diethylene glycol acetate mono-n-ethyl ether, and the like. These may be used individually by 1 type and may use 2 or more types together.

<Other ingredients>
Examples of the other components include surfactants, glass frit, dispersants, viscosity modifiers, and the like.

  There is no restriction | limiting in particular as a preparation method of the said electrically conductive paste, According to the objective, it can select suitably, For example, the said silver covering flaky copper powder of this invention, the said resin, the said solvent, and as needed The other components can be produced by mixing using, for example, ultrasonic dispersion, a disper, a three-roll mill, a ball mill, a bead mill, a twin-screw kneader, a self-revolving stirrer, and the like.

There is no restriction | limiting in particular as a viscosity of the said electrically conductive paste, Although it can select suitably according to the objective, 5 Pa * s-100 Pa * s are preferable at 25 degreeC. When the viscosity of the conductive paste is less than 5 Pa · s, “bleeding” may occur during printing, and when it exceeds 100 Pa · s, uneven printing may occur.
The volume resistivity of the conductive paste is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 2 × 10 ⁻² Ω · cm or less, and more preferably 5 × 10 ⁻⁴ Ω · cm or less. Preferably, it is 3.3 × 10 ⁻⁵ Ω · cm or less. When the volume resistivity is 2 × 10 ⁻² Ω · cm or less, a conductive paste having an extremely low volume resistivity can be realized.
The volume resistivity can be measured using, for example, a digital multimeter (manufactured by ADVANTEST, R6551).

  The conductive paste containing the silver-coated flaky copper powder of the present invention is directly or directly on various substrates such as silicon wafers for solar cells, films for touch panels, and glass for EL elements, if necessary. On the transparent conductive film provided with a transparent conductive film, a conductive coating film can be formed by coating or printing. For example, current collecting electrodes of solar cells, external electrodes of chip-type electronic components, RFID, electromagnetic waves It is suitably used for electrodes such as shield, vibrator adhesion, membrane switch, electroluminescence, or electrical wiring.

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

Silver-coated copper powder was produced as follows. Moreover, the electrically conductive paste was produced using the obtained silver covering copper powder. Moreover, the said electrically conductive paste was apply | coated and the electrically conductive film was formed by heat-processing.
BET specific surface area, particle size distribution (D10, D50, and D90), ratio (L / d) and aspect ratio (L / t), tap density, X-ray particle size, area ratio (A / B) of the silver-coated copper powder ) And the method for measuring the silver coating amount are as follows.

<Measurement method of BET specific surface area>
The BET specific surface area of the silver-coated copper powder is MONOSORB (manufactured by Yuasa Ionics Co., Ltd.), He: 70%, N ₂ : 30% carrier gas is used, and 3 g of the silver-coated copper powder is put into the cell for deaeration. After performing at 60 degreeC for 10 minute (s), it measured by the BET 1 point method.

<Measuring method of particle size distribution (D10, D50, and D90)>
The particle size distribution of the silver-coated copper powder is determined by adding 0.3 g of silver-coated copper powder to 30 mL of isopropanol using a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Nikkiso Co., Ltd., MICROTORAC HRA), and subjecting it to ultrasonic dispersion treatment for 5 minutes. A sample was prepared and the particle size was measured in total reflection mode. From the cumulative mass distribution obtained by measurement, values of cumulative 10 mass% particle diameter (D10), cumulative 50 mass% particle diameter (D50), and cumulative 90 mass% particle diameter (D90) were determined.

<Measurement of tap density>
The tap density is measured using a tap density measuring device (Shibayama Kagaku Co., Ltd., Casa specific gravity measuring device SS-DA-2), 15 g of silver-coated copper powder is weighed, put into a container (20 mL test tube), and a drop of 20 mm. And tapped 1,000 times, and calculated from tap density = sample weight (15 g) / sample volume after tapping.

<Measurement of X-ray particle size>
The X-ray particle size was calculated from the half-value width of the diffraction peak of the crystal plane of the silver-coated copper powder by the X-ray diffraction method with the following apparatus and conditions.
[XRD equipment, conditions]
・ SmartLab X-ray Diffractometer manufactured by Rigaku Corporation
-X-ray used: CuKα (wavelength = 1.5405 mm)
Ag (111) plane: 2θ = 35 ° -40 °
Cu (111) plane: 2θ = 41 ° to 47 °
Cu (200) plane: 2θ = 47.5 ° to 52.5 °
-After scanning at a scan speed of 5 ° / min and removing the Kα2 component, the angle 2θ, intensity, and half width of each peak were measured.
The X-ray particle size (crystallite size) was calculated by the Scherrer equation = 0.94 × wavelength / half-value width / cos θ.

<Method for Measuring Ratio (L / d) and Aspect Ratio (L / t)>
The “major axis average length L”, “minor axis average length d”, and “average thickness T” in the ratio (L / d) and aspect ratio (L / t) are the scanning electron microscope (SEM). It was measured by observing the SEM photograph. In that case, the reference | standard of whether to put each silver covering copper powder in a measuring object is that a boundary is clear as one particle.
For each particle of the silver-coated copper powder, the longest straight line is taken as the major axis, the length is measured as the “major axis length” L, and the portion that has the major axis and can be approximated by a rectangle is the main trunk. To do. Then, the longest length d in the direction perpendicular to the major axis of the particle is measured as the “short axis length”, and this d is larger than the length of the main trunk in the direction perpendicular to the major axis of the main trunk, When there is a portion protruding from the main trunk portion in a direction perpendicular to the major axis direction with respect to the main trunk portion, that portion is set as a sub trunk portion. The major axis L ′ and the minor axis d ′ are measured for each of the main trunk portion and the sub trunk portion. Note that the directions defined by the sub trunk L ′ and d ′ are not the long and short but the major axis direction and the minor axis direction of the main trunk unit (see FIG. 21). L of each particle is L ′ of the main trunk, and d of each particle is “d ′ of the main trunk d + the largest d ′ of the sub trunks projecting to one side perpendicular to the main trunk + the vertical of the main trunk It can be defined by the maximum d ′ ”of the sub-trunk projecting to the other side of the direction.
About 100 silver-coated copper powders, “major axis length”, “minor axis length”, and “thickness” were measured, and “average major axis length L”, “minor axis average length d”, and “ The average thickness t ”was determined.

<Area ratio (A / B)>
The measured area A of each particle of the silver-coated copper powder is defined as A = Σ (L ′ × d ′). Each particle is regarded as a rectangular aggregate of a main trunk and a sub trunk (there are a plurality of sub trunks for one particle), and the respective areas are totaled. Further, the virtual rectangle conversion area B is defined as B = L × d with respect to the longest length L in the major axis direction of each particle and the maximum length d in the direction perpendicular thereto. From this, the ratio (A / B) of the virtual rectangle conversion area and the measured area was obtained.

<Measurement of silver coating amount>
The silver coating amount was obtained by dissolving the silver-coated copper powder with nitric acid, adding hydrochloric acid, drying the resulting silver chloride precipitate, and measuring the weight to determine the actual silver coating amount.

Example 1
<Preparation of silver-coated flaky copper powder>
-Electrolytic copper powder (1)-
As electrolytic copper powder (1), JX Nippon Mining & Metals # 51-R (A) was prepared.
The electrolytic copper powder (1) was observed at a magnification of 2,000 using a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-6100). The obtained SEM photograph is shown in FIG.
When an SEM photograph of the electrolytic copper powder (1) is observed, the long axis average length is 8.89 μm, the short axis average length is 2.10 μm, L / d is 4.23, and the particle average thickness is 2.10 μm. The aspect ratio was 4.23, and the ratio (A / B) of the measured area A to the virtual rectangle conversion area B was 0.65.

-Flattening process-
The electrolytic copper powder (1) 1,254g and Neoethanol P-7 (manufactured by Daishin Chemical Co., Ltd.) 624g together with 10.5 kg of SUS balls (diameter 1.6 mm), Attritor (manufactured by Nippon Coke Industries, Ltd .: MA- 1SE-X, capacity 5L), and a flattening treatment was performed under the conditions of a rotation speed of 360 rpm and a treatment time of 60 minutes to obtain a flaky copper powder slurry. After separating the flaky copper powder slurry and the SUS ball, the wet cake obtained by filtration was vacuum dried at 70 ° C. to obtain flaky copper powder.

-Silver coating process-
185 g of ammonium carbonate and 1,167 g of ethylenediaminetetraacetic acid tetrasodium salt solution (EDTA · 4Na · 4H ₂ O, concentration 50% by mass) were dissolved in 741 g of pure water, and the liquid temperature was adjusted to 35 ° C. This solution was mixed with an aqueous silver nitrate solution containing 61.8 g of silver to prepare a silver complex salt solution. Further, after dissolving 9.1 g of ammonium carbonate and 113 g of 50 mass% aqueous solution of EDTA · 4Na · 4H ₂ O in 1,404 g of pure water, 350 g of the flake copper powder was added and stirred to obtain a flaky copper powder dispersion. Got ready. The liquid temperature of this flaky copper powder dispersion was adjusted to 35 ° C. in a dry nitrogen gas atmosphere, the silver complex salt solution was added to carry out the silver coating reaction, and the mixture was held for 30 minutes with stirring. 5.7 g of a stearic acid emulsion containing 15% by weight of stearic acid was added, and stirring was continued for 5 minutes to perform surface treatment on the silver-coated copper powder.
The obtained silver-coated flake copper powder is filtered, washed with ion-exchanged water, further washed with isopropanol, and the resulting wet cake is vacuum-dried at 70 ° C. to obtain the silver-coated flake-like copper powder of Example 1 Got.
The SEM photograph of the obtained silver-coated flaky copper powder of Example 1 with a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-6100) is shown in FIG.
Various properties of the obtained silver-coated flaky copper powder of Example 1 were evaluated. The results are shown in Tables 2-4.

(Examples 2-11 and Comparative Examples 1-4)
-Production of silver-coated copper powder-
In Example 1, the silver covering copper powder of Examples 2-11 and Comparative Examples 1-4 was produced like Example 1 except having changed the quantity and conditions as shown in Table 1.
In addition, when the target value of the silver coating amount is 10% by mass with respect to the target value of 15% by mass of the silver coating amount, the purity of the ammonium carbonate and ethylenediaminetetraacetic acid tetrasodium salt solution in the silver complex salt solution of Example 1 The amount dissolved in water is changed to 175 g and 735 g, and the silver content of the added silver nitrate is changed to 38.9 g. Further, the amount of stearic acid emulsion added was appropriately adjusted according to the specific surface area before silver coating. Example 2 was 9.0 g, Example 3 was 9.0 g, and Example 4 was 9. 0 g, Example 5 5.7 g, Example 6 5.7 g, Example 7 5.7 g, Example 8 9.0 g, Example 9 11.3 g, Example 10 13.6 g, Example 11 was 9.0 g, Comparative Example 2 was 6.8 g, Comparative Example 3 was 6.8 g, and Comparative Example 4 was 5.7 g.
In addition, the electrolytic copper powder (2) used in Example 3, the electrolytic copper powder (3) used in Example 4, and the atomized copper powder used in Comparative Examples 1 to 3 are as shown below. Moreover, the crushing in the comparative example 3 was performed by Melita Japan Co., Ltd. select grind MJ-518.
The SEM photograph of the obtained silver covering copper powder of Examples 2-11 was shown in FIGS.
Various properties of the obtained silver-coated copper powders of Examples 2 to 11 and Comparative Examples 1 to 4 were evaluated. The results are shown in Tables 2-4.

-Electrolytic copper powder (2)-
As the electrolytic copper powder (2), FCC-TBX manufactured by Fukuda Metal Foil Industry Co., Ltd. was used.
The electrolytic copper powder (2) was observed at a magnification of 2,000 using a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-6100). The obtained SEM photograph is shown in FIG.
When an SEM photograph of the electrolytic copper powder (2) was observed, the long axis average length was 5.73 μm, the short axis average length was 1.85 μm, L / d was 3.10, and the particle average thickness was 1.85 μm. Yes, the aspect ratio was 3.10, and the ratio (A / B) of the measured area A to the virtual rectangle conversion area B was 0.78.

-Electrolytic copper (3)-
As electrolytic copper powder (3), FCC-115 manufactured by Fukuda Metal Foil Industry Co., Ltd. was used.
The electrolytic copper powder (3) was observed at a magnification of 2,000 using a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-6100). The obtained SEM photograph is shown in FIG.
When an SEM photograph of the electrolytic copper powder (3) was observed, the major axis average length was 7.81 μm, the minor axis average length was 2.06 μm, L / d was 3.80, and the particle average thickness was 2.06 μm. Yes, the aspect ratio was 3.80, and the ratio (A / B) of the measured area A to the virtual rectangle conversion area B was 0.68.

-Atomized copper powder-
As atomized copper powder, SF-Cu 5 μm manufactured by Nippon Atomizing Co., Ltd. was used. The atomized copper powder was observed at a magnification of 2,000 using a scanning electron microscope (SEM, manufactured by JEOL Ltd., JSM-6100). The obtained SEM photograph is shown in FIG.

(Example 12)
<Preparation of silver-coated flaky copper powder>
-Electrolytic copper powder (3)-
FCC-115 manufactured by Fukuda Metal Foil Powder Co., Ltd. was prepared as the electrolytic copper powder (3) (see FIG. 8).

-Flattening process-
The electrolytic copper powder (3) 30.66 kg and Solmix AP-7 (manufactured by Nippon Alcohol Sales Co., Ltd.) 17.77 kg together with SUS ball (diameter 1.6 mm) 185.8 kg, attritor (manufactured by Nippon Coke Industries, Ltd., MA15SE, capacity 100L), and a flattening treatment was performed under the conditions of a rotation speed of 170 rpm and a treatment time of 240 minutes to obtain a flaky copper powder slurry. After separating the flaky copper powder slurry and the SUS ball, the wet cake obtained by filtration was vacuum dried at 70 ° C. to obtain flaky copper powder.

-Silver coating process-
Ammonium carbonate (35.00 kg) and ethylenediaminetetraacetic acid tetrasodium salt (EDTA · 4Na · 4H ₂ O) solution (147.00 kg) were dissolved in pure water (225.68 kg), and the liquid temperature was adjusted to 35 ° C. This solution was mixed with an aqueous silver nitrate solution containing 7.778 kg of silver to prepare a silver complex salt solution. Further, after dissolving 1.82 kg of ammonium carbonate and 22.52 kg of a 50 mass% solution of EDTA · 4Na · 4H ₂ O in 288.23 kg of pure water, 70.00 kg of the flake copper powder was added and stirred, and the flaky copper was added. A powder dispersion was prepared. The liquid temperature of this flaky copper powder dispersion was adjusted to 35 ° C. in a dry nitrogen gas atmosphere, the silver complex salt solution was added to carry out the silver coating reaction, and the mixture was held for 30 minutes with stirring. 2.26 kg of a stearic acid emulsion containing 15% by mass of stearic acid was added, and stirring was continued for 5 minutes to perform surface treatment on the silver-coated flake copper powder.
The obtained silver-coated flake copper powder was filtered and washed with ion-exchanged water. The obtained wet cake was dried at 120 ° C. in a nitrogen atmosphere, and a sample mill (KII WR-, manufactured by Fuji Powder Co., Ltd.) was obtained. The dried agglomerates were crushed by Type 1), and the silver-coated flaky copper powder of Example 12 was obtained through a sieve having an opening of 25 μm. The SEM photograph of the obtained silver-coated copper powder of Example 12 is shown in FIG.

* In the numerical values shown in Table 4 for BET specific surface area x X-ray particle size (Ag (111) plane), the symbol “E” is the “exponential” with the following numerical value as the base. The numerical value represented by the exponential function with the base 10 is multiplied by the numerical value before “E”. For example, “1.0E-05” indicates “1.0 × 10 ⁻⁵ ”.

<Preparation of conductive paste>
Next, each silver covering copper powder, polyester resin, and solvent of Examples 1-12 and Comparative Examples 1-4 which were produced were mixed with the following composition and content, and 3 rolls (Otto Herman company make, EXAKT80S). Kneading by passing the roll gap through 100 μm to 20 μm, adding a solvent as appropriate, and adding a viscosity of about 8 Pa · s (value at 1 rpm with a Brookfield viscometer DV-III URTRA). The conductive pastes of Examples and Comparative Examples were obtained.
[Composition and content]
Each silver-coated copper powder: 60 parts by mass Polyester resin (byron 200, manufactured by Toyobo Co., Ltd.): 12 parts by mass Solvent [ECA (acetic acid diethylene glycol mono-n-ethyl ether), Wako Pure Chemical Industries, Ltd. [Made by]] 28 parts by mass

Next, a film of the produced conductive paste was formed on the alumina substrate by screen printing. Screen printing conditions are as follows.
[Printing conditions]
-Printing device: MT-320T manufactured by Microtech
-Printing conditions: Squeegee pressure was 0.18 MPa, and the film was formed into a circuit having a width of 500 μm and a length of 37.5 mm.
The obtained film was heat-treated at 130 ° C. for 30 minutes using an air circulation dryer to produce a conductive film.
About the obtained electrically conductive film, average thickness and volume resistivity were measured as follows. The results are shown in Table 5.

<Average thickness of conductive film>
Each of the obtained conductive films was measured using a surface roughness meter (SE-30D, manufactured by Kosaka Laboratory Ltd.) between the portion where the film was not printed on the polyethylene terephthalate (PET) film and the portion of the conductive film. The average thickness of the conductive film was measured by measuring the step.

<Volume resistivity of conductive film>
The resistance value at the position of the length (interval) of each conductive film was measured using a digital multimeter (manufactured by ADVANTEST, R6551). The volume of the conductive film was determined from the size (average thickness, width, length) of each conductive film, and the volume resistivity was determined from the volume and the measured resistance value.

* In the numerical values shown for volume resistivity in Table 5, the symbol “E” indicates that the next numerical value is a “power index” with 10 as the base, and is an exponential function with 10 as the base. Indicates that the numerical value represented is multiplied by the numerical value before “E”. For example, “1.0E-04” indicates “1.0 × 10 ⁻⁴ ”.

From the above results, it can be seen that the volume resistivity of the silver-coated flake copper powder obtained by flattening the electrolytic copper powder is lower than that of the silver-coated flake copper powder obtained by flattening the atomized copper powder. Further, from the comparison between Comparative Example 4 and Examples 1 to 12, it can be seen that as the electrolytic copper powder is flattened, the Cu (111) surface changes greatly and the X-ray particle size becomes smaller (half-value width becomes larger).
The volume resistivity at flattening time BET specific surface area of 120 min to 150 min 0.7m ² /g~0.9m ² / g, the ratio (L / d) is 3.3 or more ranges of electrolytic copper powder The tendency of the rate to become the minimum was shown.
In addition, Example 12 differs from Example 3 in that the flake apparatus scale is large, but the powder has a slightly larger specific surface area, both silver and copper have a smaller X-ray particle size, and an aspect ratio. small. The film characteristic is large in volume resistivity. It was found that the degree of flattening was slightly smaller depending on the equipment scale and conditions.

  The conductive paste containing the silver-coated flaky copper powder of the present invention is directly or directly on various substrates such as silicon wafers for solar cells, films for touch panels, and glass for EL elements, if necessary. On the transparent conductive film provided with a transparent conductive film, a conductive coating film can be formed by coating or printing. For example, current collecting electrodes of solar cells, external electrodes of chip-type electronic components, RFID, electromagnetic waves It is suitably used for electrodes such as shield, vibrator adhesion, membrane switch, electroluminescence, or electrical wiring.

As an aspect of this invention, it is as follows, for example.
<1> A silver-coated flaky copper powder having at least silver on the surface and flattened,
The ratio (L / d) of the major axis average length L to the minor axis average length d measured by a scanning electron microscope is 2.5 or more,
The silver-coated flaky copper powder is characterized in that an X-ray particle diameter by an X-ray diffraction method is 60 nm or less on a Cu (111) plane.
<2> The silver-coated flaky copper powder according to <1>, wherein the X-ray particle size is 19 nm or less on the Ag (111) plane.
<3> The silver according to any one of <1> to <2>, wherein an aspect ratio (L / t) between a major axis average length L measured by a scanning electron microscope and an average thickness t is 8 or more. Coated flaky copper powder.
<4> The ratio (A / B) between the actual measurement area A of the silver-coated flaky copper powder and the virtual rectangular conversion area B of the silver-coated flaky copper powder measured by a scanning electron microscope is 0.8 or less. The silver-coated flaky copper powder according to any one of <1> to <3>.
<5> Any one of <1> to <4>, wherein the silver-coated flaky copper powder is obtained by coating silver on a surface of a flaky copper powder obtained by flattening an electrolytic copper powder obtained by an electrolysis method. The silver-coated flaky copper powder described in 1.
<6> A step of flattening an electrolytic copper powder having a ratio (L / d) of the major axis average length L to the minor axis average length d of 3 or more measured by a scanning electron microscope,
A step of coating silver on the surface of the flaky electrolytic copper powder obtained by the flattening treatment,
It is a manufacturing method of the silver covering flaky copper powder characterized by including.
<7> A conductive paste comprising the silver-coated flaky copper powder according to any one of <1> to <5>.

Claims (5)

A silver-coated flaky copper powder which have a silver at least on the surface,
The ratio (L / d) of the major axis average length L to the minor axis average length d measured by a scanning electron microscope is 2.5 or more,
X-ray particle diameter by X-ray diffraction method, in the Cu (111) surface state, and are less 60 nm,
The measured area A of the silver-coated flaky copper powder by measurement of scanning electron microscope, a ratio of the imaginary rectangle conversion area B of the silver-coated flaky copper powder (A / B) is 0.8 or less der Rukoto A silver-coated flaky copper powder.   The silver-coated flaky copper powder according to claim 1, wherein the X-ray particle size is 19 nm or less on the Ag (111) plane.   3. The silver-coated flaky copper powder according to claim 1, wherein an aspect ratio (L / t) between a major axis average length L and an average thickness t measured by a scanning electron microscope is 8 or more. A step of flattening an electrolytic copper powder having a ratio (L / d) of a major axis average length L measured by a scanning electron microscope to a minor axis average length d of 3 or more;
A step of obtaining silver-coated flaky copper powder according to any one of claims 1 to 3 by coating silver on the surface of the flaky electrolytic copper powder obtained by the flattening treatment,
A method for producing a silver-coated flaky copper powder, comprising: A conductive paste comprising the silver-coated flaky copper powder according to claim 1.