JP2016035098A - Silver-coated flake type copper powder and production method of the same, and conductive paste using the silver-coated flake type copper powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silver-coated flake type copper powder that can maintain conductivity even in a paste with a low filler content, a production method of the silver-coated flake type copper powder, and a conductive paste using the silver-coated flake type copper powder.SOLUTION: The silver-coated flake type copper powder comprises silver-coated flake type copper powder particles having silver on at least surfaces thereof and subjected to a flattening treatment. The silver-coated flake type copper powder particles have a circularity coefficient of 0.3 or more and 0.6 or less by the measurement of a scanning electron microscope image, and have an X-ray particle diameter of 10 nm or more and 30 nm or less on an Ag (111) plane and 30 nm or more and 58 nm or less on a Cu (111) plane.SELECTED DRAWING: Figure 2

Description

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

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 parts, 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 the flaky silver powder is expensive because the metal price is higher than the “copper paste” blended with the flaky copper powder, and migration tends to occur. On the other hand, the “copper-based paste” has a drawback in that although it is difficult for migration, 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 further 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 atomizing method is preferred because it is advantageous in terms of price and mass productivity, and silver-coated flaky copper powder obtained by flattening spherical copper powder produced by the atomizing method has been proposed ( (See Patent Document 3).

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

However, according to the study by the present inventors, the silver-coated flaky copper powder by the atomizing method does not have a performance that is sufficiently satisfactory in terms of conductivity. In particular, it has been conceived that further improvement in conductivity is desired in the low filler content conductive paste.
The present invention has been made under the above-mentioned circumstances, and the problem to be solved is a silver-coated flaky copper powder capable of ensuring conductivity even with a low filler content paste, and the silver-coated flakes. And a conductive paste using the silver-coated flaky copper powder.

  In order to solve the above problems, the present inventors have conducted intensive research. And by controlling the shape of the silver-coated flaky copper powder particles, it becomes easy to take contact between the particles of the silver-coated flaky copper powder, and the silver-coated flaky copper powder that can ensure conductivity even with a low filler content paste It was a revolutionary finding that

  Specifically, the circularity coefficient is 0.3 or more and 0.6 or less, the thickness is 0.35 μm or more and 0.70 μm or less, and the particle diameter measured by the X-ray diffraction method (in the present invention) The silver-coated flaky copper powder particles that may be described as “X-ray particle size” are 10 nm to 30 nm in the Ag (111) plane and 30 nm to 58 nm in the Cu (111) plane. The present invention was completed by obtaining the epoch-making knowledge that it is a silver-coated flaky copper powder that facilitates contact between particles and can ensure conductivity even with a low filler content paste.

That is, the first invention for solving the above-described problem is
Silver-coated flaky copper powder containing silver-coated flaky copper powder particles having at least silver on the surface and flattened,
The circularity coefficient by measurement of a scanning electron microscope image of the silver-coated flaky copper powder particles is 0.3 or more and 0.6 or less,
The silver-coated flaky copper powder has an X-ray particle size of 10 nm to 30 nm in the Ag (111) plane and 30 nm to 58 nm in the Cu (111) plane.
The second invention is
The silver-coated flaky copper powder has a thickness of 0.35 μm or more and 0.70 μm or less.
The third invention is
The silver-coated flaky copper powder is characterized in that a product of a circularity coefficient and an aspect ratio measured by a scanning electron microscope image of the silver-coated flaky copper powder particles is 7.5 or more and 15.5 or less. is there.
The fourth invention is:
The aspect ratio (maximum long axis length / average thickness) of the long axis and the average thickness by measurement of a scanning electron microscope image of the silver-coated flaky copper powder particles is 17 or more and 34 or less. And silver-coated flaky copper powder.
The fifth invention is:
The silver-coated flaky copper powder has a BET specific surface area of 0.45 m ² / g or more and 0.65 m ² / g or less.
The sixth invention is:
A silver-coated flaky copper powder having a tap density of 3.5 g / cm ³ or less and 2.0 g / cm ³ or more.
The seventh invention
A flattening treatment step for obtaining a flaky electrolytic copper powder by performing a flattening treatment using an attritor in the presence of water and / or an organic solvent on the electrolytic copper powder having a dendritic shape;
A silver coating step of coating silver on the surface of the flaky electrolytic copper powder obtained by the flattening treatment,
In the flattening treatment, the flattening treatment is performed by setting the value of [amount of electrolytic copper powder (kg) / attritor processing scale (L)] to 0.3 kg / L or more. It is a manufacturing method.
The eighth invention
In the flattening treatment step, the flaky electrolytic copper powder obtained after the flattening treatment is passed through a sieve having an opening of 25 μm.
The ninth invention
In the silver coating step, a wet cake containing water and silver-coated flaky copper powder obtained after the silver-coating reaction is vacuum-dried, which is a method for producing a silver-coated flaky copper powder.
The tenth invention is
A conductive paste containing the silver-coated flaky copper powder according to any one of the first to sixth inventions.

  By using the silver-coated flaky copper powder according to the present invention, it is possible to produce a conductive paste that can ensure conductivity even with a low filler content paste.

It is a flowchart which shows the manufacturing method of the silver covering flaky copper powder which concerns on this invention. 2 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 1. FIG. 4 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 2. FIG. 4 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 3. FIG. 4 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 4. FIG. 6 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 5. FIG. 10 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 6. FIG. 10 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 7. FIG. 10 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 8. FIG. It is a scanning electron microscope image of 1000 times of the silver covering flaky copper powder which concerns on Example 9. FIG. 1 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 10. 3 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Example 11. FIG. It is a 1000 times scanning electron microscope image of the silver covering flaky copper powder which concerns on Example 12. FIG. It is a scanning electron microscope image of 1000 times of the silver covering flaky copper powder which concerns on Example 13. FIG. It is a 1000 times scanning electron microscope image of the silver covering flaky copper powder which concerns on Example 14. FIG. It is a scanning electron microscope image of 1000 times of the silver covering flaky copper powder which concerns on Example 15. FIG. It is a scanning electron microscope image of 1000 times of the silver covering flaky copper powder which concerns on Example 16. FIG. 3 is a scanning electron microscope image of 1000 times the silver-coated copper powder according to Comparative Example 1. FIG. 4 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Comparative Example 2. FIG. It is a scanning electron microscope image of 1000 times of the silver covering copper powder which concerns on the comparative example 3. FIG. 10 is a scanning electron microscope image of 1000 times the silver-coated flaky copper powder according to Comparative Example 4. FIG. It is a scanning electron microscope image of 1000 times the electrolytic copper powder particles having a dendritic shape. It is a scanning electron microscope image of 1000 times of the silver covering flaky copper powder which concerns on Example 17. FIG. It is a scanning electron microscope image of 1000 times of the silver covering flaky copper powder which concerns on Example 18. FIG.

The silver-coated flaky copper powder according to the present invention is a silver-coated flaky copper powder that can ensure conductivity even if it is a low filler content paste.
Hereinafter, “(1) Shape characteristics of silver-coated flaky copper powder particles” according to the present invention will be described, “(2) Method for producing silver-coated flaky copper powder”, and the silver-coated flaky copper powder. “(3) Conductive paste and its manufacturing method” will be described.

(1) Shape characteristics of silver-coated flaky copper powder particles The shape characteristics of silver-coated flaky copper powder particles according to the present invention are described in <1. Circularity coefficient>, <2. X-ray particle size>, <3. Thickness>, <4. Aspect ratio>, <5. Circularity coefficient × aspect ratio>, <6. Maximum axial length>, <7. Maximum axial length / thickness>, <8. BET specific surface area>, <9. Tap density> and <10. The cumulative particle diameter will be described from each viewpoint. A specific method for measuring the shape characteristic will be described in Examples.

<1. Circularity coefficient>
The silver-coated flaky copper powder particles according to the present invention have a circularity coefficient of 0.3 or more and 0.6 or less measured from an electron microscope image. In contrast, in the case of flaky copper powder or silver-coated flaky copper powder obtained by flattening spherical atomized copper powder or wet reduced copper powder according to the prior art, the circularity coefficient is 0.78 or more It is.
Here, the circularity coefficient is a parameter representing “how far the shape of the particle is from the circle”, and is defined by the following Equation 1.
(Circularity coefficient) = (4πS) / (L ² )... Formula 1
However, S: Area of particle, L: Peripheral length of particle Here, the value of the circularity coefficient is 1 when the particle is circular, and becomes smaller than 1 as the particle is far from the circle.
When the circularity coefficient is 0.3 or more and 0.6 or less, a contact portion between the silver-coated flaky copper powders can be sufficiently secured. As a result, it is considered that the conductivity of the conductive film formed by using the conductive paste and using the conductive paste can be sufficiently increased, which is preferable.

  The circularity coefficient of the silver-coated flaky copper powder particles according to the present invention is obtained using a point tool using image analysis software (for example, Mac-View Ver. 4 manufactured by Mountec Co., Ltd.) to a scanning electron microscope image with a magnification of 1000 times. What is necessary is just to obtain | require the value of S and L from the shape data measured using.

<2. X-ray particle size>
In the silver-coated flaky copper powder according to the present invention, the X-ray particle size measured using a calculation software (for example, JADE7 manufactured by Rigaku Corporation) is measured on the Ag (111) plane. It is 10 nm or more and 30 nm or less, preferably 17.5 nm or more and 25 nm or less. Further, the X-ray particle diameter is 30 nm or more and 58 nm or less on the Cu (111) plane, preferably 44 nm or more and 58 nm or less.
If the X-ray particle size on the Cu (111) plane is 58 nm or less, flattening is sufficient and the uniformity of the silver coating is excellent, so that the conductive film formed by blending the silver-coated flaky copper powder It is thought that the resistance value of becomes low.

This is because spherical atomized copper powder particles are easily crushed from random directions depending on the shape, but when electrolytic copper powder particles having a dendritic shape are flattened by an attritor, the shape of the main part or sub-particles is reduced. This is thought to be due to being easily crushed from a specific direction with respect to the executive. Since the degree of collapse in the electrolytic copper powder particles having a dendritic shape varies greatly, it is considered that the number of contact points between the flaky copper powders increases and contributes to improvement in conductivity.
In addition, spherical atomized copper powder particles are not aligned in crystal orientation due to the manufacturing method, but electrolytic copper powder particles having a dendritic shape are mainly connected one after another with the Cu (111) plane in parallel. Since the trunk and the sub-trunk are formed, the horizontal section is the Cu (111) plane. As a result, the electrolytic copper powder particles having a dendritic shape are preferentially crushed in the Cu (111) plane during flattening by an attritor, and as the flattening progresses, X-rays on the Cu (111) plane This is because the value of the particle size is considered to change greatly. And, 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 dendritic shape In the flaky copper powder obtained by flattening the electrolytic copper powder particles having an X-ray particle size of 58 nm or less on the Cu (111) surface, silver substitution reactions occur simultaneously and frequently in the silver coating step described later. This is because the thickness is likely to be uniform and the value of the X-ray particle diameter of silver is considered to be different. Actually, the X-ray particle size of the Ag (111) surface is smaller when the flaky copper powder having an X-ray particle size of 58 nm or less on the Cu (111) surface is coated with silver, and the conductivity of the conductive film is better. It is preferable.

  That is, the X-ray particle size of Cu is considered to affect the level of flattening operation by an attritor. When the X-ray particle size of Cu is 30 nm or more and 58 nm or less, the copper powder is appropriately flattened. It is thought that. When flattening is appropriate, it is considered that values such as thickness, aspect ratio and the like fall within a preferable range in the obtained flaky copper powder. For this reason, it is preferable that it is 30 nm or more in the X-ray particle diameter in Cu (111) surface, Furthermore, it is 44 nm or more and 58 nm or less.

  On the other hand, the X-ray particle size of silver coated in the silver coating step described later on the flaky copper powder subjected to the flattening operation by the attritor described above is generally 10 nm or more and 30 nm or less on the Ag (111) plane. Furthermore, it was found that it was 17.5 nm or more and 25 nm or less.

  From the above, in the silver-coated flaky copper powder according to the present invention, the X-ray particle size by the X-ray diffraction method is 30 nm or more and 58 nm or less, preferably 44 nm or more and 58 nm or less on the Cu (111) plane. It can be understood that the X-ray particle size is 10 nm or more and 30 nm or less, preferably 17.5 nm or more and 25 nm or less in the Ag (111) plane.

<3. Thickness>
The thickness of the silver-coated flaky copper powder particles according to the present invention is 0.35 μm or more and 0.70 μm or less.
The thickness of the silver-coated flaky copper powder particles is the thickness between the two planes produced by flattening treatment in each particle by taking a 1000-fold electron microscope image of the particles.
The thickness is considered to be a parameter indicating the progress of flattening of the silver-coated flaky copper powder particles. And when thickness is 0.35 micrometer or more and 0.70 micrometer or less, since the progress degree of flattening is not enough and has not progressed too much, the contact location of the said silver covering flaky copper powder can fully be ensured. As a result, it is considered that the conductivity of the conductive film formed by using the conductive paste and using the conductive paste can be sufficiently increased, which is preferable.

<4. aspect ratio>
In the silver-coated flaky copper powder particles according to the present invention, the aspect ratio is preferably 17 or more and 34 or less.
Here, the aspect ratio is defined as “maximum length / thickness”.
When the aspect ratio is 17 or more, a sufficient contact area between the silver-coated flaky copper powders can be secured. As a result, it can mix | blend with an electrically conductive paste and can fully make the electroconductivity of the electrically conductive film formed using this electrically conductive paste. If the aspect ratio is 34 or less, it is easy to produce the silver-coated flaky copper powder.

<5. Circularity factor x aspect ratio>
In the silver-coated flaky copper powder particles according to the present invention, the product of the circularity coefficient and the aspect ratio is preferably 7.5 or more and 15.5 or less.
As described above, the circularity coefficient and the aspect ratio are parameters indicating the shape of the silver-coated flaky copper powder particles according to the present invention, and are related to the contact between the silver-coated flaky copper powders. Therefore, when the value of the product of both parameters is 7.5 or more and 15.5 or less, it is considered that the contact portion between the silver-coated flaky copper powders can be sufficiently secured. As a result, it is considered that the conductivity of the conductive film formed by using the conductive paste and using the conductive paste can be sufficiently increased, which is preferable.

<6. Maximum shaft length>
In the silver-coated flaky copper powder according to the present invention, the maximum axial length is a 1000-fold electron microscope image of the silver-coated flaky copper powder. This is the maximum length.

<7. Maximum shaft length / thickness>
In the silver-coated flaky copper powder according to the present invention, when the ratio between the maximum axial length and the thickness is “maximum axial length / thickness”, when the value is within a predetermined range, the silver-coated flaky copper powder Good electrical contact between particles is maintained. The present inventors have found that it is preferable that the ratio value is 17 or more and 34 or less.

<8. BET specific surface area>
In the silver-coated flaky copper powder according to the present invention, the BET specific surface area is preferably 0.45 m ² / g or more and 0.65 m ² / g or less.
The BET specific surface area value is considered to be a parameter indicating the progress of flattening and the surface state of the silver-coated flaky copper powder particles. And when the BET specific surface area value is 0.45 m ² / g or more and 0.65 m ² / g or less, the degree of progress of flattening is not sufficient and does not progress too much. A sufficient contact area can be secured. As a result, it is considered that the conductivity of the conductive film formed by using the conductive paste and using the conductive paste can be sufficiently increased, which is preferable.

<9. Tap density〉
In the silver-coated flaky copper powder according to the present invention, the tap density is preferably 3.5 g / cm ³ or less and 2.0 g / cm ³ or more.
When the tap density is in the range of 3.5 g / cm ³ or less and 2.0 g / cm ³ or more, the handleability and productivity are excellent, and the conductivity of the conductive film is kept high.

<10. Cumulative particle size>
In the silver-coated flaky copper powder according to the present invention, the cumulative 50% particle size (D50) in the volume-based particle size distribution by the laser diffraction particle size distribution measurement method is preferably 7 μm or more and 13 μm or less.

(2) Method for producing silver-coated flaky copper powder The silver-coated flaky copper powder according to the present invention comprises a step of flattening electrolytic copper powder particles having a dendritic shape (flattening step), and a flattening treatment. It is manufactured through a step of coating silver on the surface of the later flaky electrolytic copper powder particles (silver coating step) and, if necessary, other steps.
If desired, the flattening step can be performed after the silver coating step is first performed on the electrolytic copper powder particles having a dendritic shape.
Hereinafter, with reference to FIG. 1 which is a flowchart showing a method for producing a silver-coated flaky copper powder according to the present invention, <1. Electrolytic copper powder particles having a dendritic shape>, <2. Flattening step>, <3. Silver coating step> and <4. Other steps> will be described in order of the method for producing silver-coated flaky copper powder according to the present invention.

<1. Electrolytic copper powder particles having a dendritic shape>
FIG. 22 shows a scanning electron microscope image of 1000 times in an example of the electrolytic copper powder particles having a dendritic shape according to the present invention.
As is clear from FIG. 22, the electrolytic copper powder particles having a dendritic shape according to the present invention have an indefinite shape including a main trunk portion and a branch portion branched from the main trunk portion into an indefinite shape. Yes.

  Commercially available electrolytic copper powder can be used as the electrolytic copper powder << 1 >> having a dendritic shape according to the present invention. For example, Fukuda Metal Foil Powder Co., Ltd. FCC-115, JX Nippon Mining & Metals Co., Ltd. # 51-R (A), etc. can be mentioned as preferred examples.

  Also, 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 electrolyte to conduct electrolysis, and copper is deposited in the form of powder on the cathode surface. The electrolytic copper powder having a dendritic shape according to the present invention can also be produced by scraping off, collecting, washing, drying, and performing a sieving step as necessary. If necessary, the electrolytic copper powder having a dendritic shape may be surface-treated with a triazole-based substance such as benzotriazole as an antioxidant treatment.

<2. Flattening process>
In the flattening step, the electrolytic copper powder << 1 >> having a dendritic shape is flattened << 5 >>, so that the circularity coefficient is 0.3 to 0.6 and the thickness is 0.35 μm to 0 This is a step of obtaining flaky electrolytic copper powder << 10 >> of 70 μm or less.
An attritor is used as an apparatus for performing the flattening process. The attritor can use a commercially available apparatus as it is.

  When performing the flattening treatment, the attritor is loaded with electrolytic copper powder having a dendritic shape, a ball, and a solvent (water and / or organic solvent) << 4 >>. The inventors have a circularity coefficient value of 0.3 to 0.6, an X-ray particle size of 10 nm to 30 nm on the Ag (111) plane, and 30 nm to 58 nm on the Cu (111) plane. In obtaining silver-coated flaky copper powder particles having a value, it was found that the value of [electrolytic copper powder amount (kg) / attritor processing scale (L)] is preferably 0.3 kg / L or more. .

  In addition, when the processing scale of the attritor becomes large, for example, 10L or more, only the operation of the attritor causes a particle accumulation due to sedimentation of particles at the bottom portion, resulting in dead space, and flattening of the electrolytic copper powder is uneven It is possible to become. Therefore, it is also preferable to extract a part of the slurry from the bottom of the attritor and re-inject it from the top of the attritor with a circulation pump. It is considered that uniform flattening of the electrolytic copper powder can be promoted by using the circulation pump to circulate the slurry. The pressure of the circulation pump may be 0.3 MPa or more in terms of gauge pressure.

By performing the flattening operation described above, when the ball (media) loaded in the attritor flattens the electrolytic copper powder << 1 >> having a dendritic shape, the ball is electrolyzed. It is considered that the impact force applied to the copper powder particles is made uniform, and the local temperature rise is mitigated by the impact. As a result, the silver-coated flaky copper powder after the flattening treatment has an X-ray particle size of 30 nm or more and 58 nm or less on the Cu (111) plane and 10 nm or more on the Ag (111) plane by the X-ray diffraction method. It is thought that it may be 30 nm or less. Further, in the silver-coated flaky copper powder after the flattening treatment, the BET specific surface area is 0.45 m ² / g or more and 0.65 m ² / g or less, and the tap density is 3.5 g / cm ³ or less 2.0 g. / Cm ³ or more.

As the solvent, water and / or an organic solvent are used. Specifically, water, an organic solvent, a solution containing water and an organic solvent, or an emulsion containing an organic solvent phase and an aqueous solvent phase is used. I can do it. As the organic solvent, an organic solvent having a molecular weight of 200 or less is preferable, and an alcohol having a molecular weight of 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.
In the flattening treatment, the amount of the solvent to be mixed and stirred << 3 >> with the electrolytic copper powder having a dendritic shape is 0.1 to 3 times by mass with respect to the copper powder to be flattened. Is preferred. If the addition amount is 0.1 times or more, the effect of solvent addition is obtained, and if it is 3 times or less, flaky electrolytic copper powder << 10 >> can be obtained while avoiding saturation of the addition effect. .
Furthermore, in the flattening treatment, a solvent that is mixed and stirred with the electrolytic copper powder is circulated by a circulation pump. The flow of the solvent circulates to mitigate the effect of local temperature rise due to the mutual collision of balls and electrolytic copper powder particles, and in addition, the effect of particles staying in part due to sedimentation, etc. This is because the values of the X-ray particle size, the BET specific surface area, and the tap density are considered to be stable.

  The ball (media) loaded in the attritor is not particularly limited as long as it is a ball 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 is 0.1 mm or more, clogging of the ball does not occur when the flake-shaped copper powder and the ball are separated << 6 >> after the flattening treatment, and separation efficiency is ensured. On the other hand, if the diameter of the ball is 3 mm or less, the particle diameter of the obtained flaky copper powder is preferable because it does not become excessive.

  There is no restriction | limiting in particular as a material of the said ball | bowl, 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.

  The amount of the ball added during the flattening treatment is not particularly limited and may be appropriately selected depending on the purpose. However, the copper powder to be flattened may have a weight ratio of 1 to 50 parts by weight. Is preferred. When the added amount of the balls is 1 part by weight or more, a sufficient flattening effect can be obtained in the flaky copper powder after flattening. If the said addition amount is 50 weight part or less, the quantity of the copper powder which can be flattened at once can be ensured, and it is preferable from a viewpoint of processing cost.

The treatment time of the flattening treatment is not particularly limited, and can be appropriately selected according to the specifications (capacity) of the attritor and the added amounts of balls and copper powder. Considering productivity, it is preferably 10 minutes or more and 300 minutes or less. For example, when an attritor with a capacity of 5 L is used, it is preferably 10 minutes or more and 180 minutes or less, and more preferably 60 minutes or more and 150 minutes or less. If the said processing time is 10 minutes or more, flattening of copper powder will fully advance. On the other hand, if the treatment time is 180 minutes or less, it is possible to avoid excessive progress of flattening of the copper powder.
For example, when an attritor having a capacity of 100 L is used, it is preferably 100 minutes or longer and 300 minutes or shorter, and more preferably 180 minutes or longer and 240 minutes or shorter.
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 the flaky copper powder is partly formed before and after the flattening process, it can be said that the flattening process has been performed.

  For the purpose of improving the dispersibility of the obtained flaky copper powder, it is also preferable to add a dispersant in an amount of 0.1% by mass to 5% by mass with respect to the copper powder to be flattened. There is no restriction | limiting in particular as the said dispersing agent, According to the objective, it can select suitably, For example, a fatty acid, a 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. On the other hand, the dispersant may be added to the copper powder before the flattening treatment, and the dispersant may be added together with the solvent in the flattening treatment.

  However, if the dispersibility of the flaky copper powder is sufficient, it is of course possible not to add a dispersant in the flattening treatment. In addition, when a large amount of the dispersant is present on the surface of the flaky copper powder, removal of the dispersant before the silver coating step described later prevents the silver coating in the silver coating step. It can avoid becoming uniform.

When the flattening process is completed, the flaky copper powder and the ball are separated, and the flaky copper powder is dried << 7 >> to obtain the flaky electrolytic copper powder << 10 >> according to the present invention.
At this time, coarse particles are removed by passing the dried flaky electrolytic copper powder through a sieve having an opening of 25 μm, and the obtained flaky electrolytic copper powder is subjected to a silver coating step described later. Is a preferred configuration from the viewpoint of increasing the uniformity of silver coating on the flaky electrolytic copper powder by removing the agglomerated particles.

<3. 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.
Examples of the method for coating the surface of the flaky electrolytic copper powder according to the present invention with silver include two types of methods, ie, a reduction method and a substitution method.
The reduction method is a method in which the surface of copper powder particles is finely coated with silver fine particles reduced with a reducing agent (see, for example, JP 2000-248303 A).
On the other hand, at the interface of the copper powder particles, the silver ion exchanges electrons with metallic copper, the silver ions are reduced to metallic silver, and the metallic copper is oxidized to copper ions instead. In this method, the surface layer of the copper powder particles is a silver layer (see, for example, JP-A-2006-161081).
When both methods are compared, the substitution method is preferable from the viewpoint of uniformity of silver coating and adhesion of the silver layer to the copper surface.

The silver coating reaction on the flaky electrolytic copper powder by the substitution method will be described.
First, as a surface treatment agent for flaky electrolytic copper powder, an aqueous solution containing a chelating agent << 8 >> (for example, EDTA · 4Na · 4H ₂ O) and a pH buffering agent << 9 >> (for example, ammonium carbonate). The liquid temperature was adjusted to 10 to 80 ° C. << 11 >>. Then, flaky electrolytic copper powder << 10 >> was added to the surface treatment agent and mixed and stirred << 12 >> to obtain a flaky electrolytic copper powder dispersion. This flaky copper powder dispersion was temperature-controlled and maintained <13> at a temperature of 10 ° C. to 80 ° C. for 1 minute to 5 hours in a dry nitrogen gas atmosphere.

  On the other hand, a reaction solution for silver coating reaction was prepared. The reaction solution for performing the silver coating reaction is a silver salt << 16 >> and a solvent << 17 >>, and water and / or an organic solvent are used as the solvent. Specifically, water, an organic solvent, water and an organic solvent are used. A solution containing a solvent or an emulsion containing an organic solvent phase and an aqueous solvent phase can be used. At this time, when an organic solvent having a high solubility in water is used as the solvent, the reaction solution becomes a uniform mixed solution. However, in the case of an organic solvent having a low solubility, the aqueous phase and the organic solvent phase are stationary. Therefore, the silver coating reaction is performed in a state where an emulsion is formed by stirring the liquid. By using these reaction liquids, the flaky electrolytic copper powder << 10 >> can be used as it is without removing the auxiliary agent such as the dispersant added during the above-mentioned flattening treatment << 5 >>. It can also be subjected to a coating reaction.

As the organic solvent, alcohols, ketones, aldehydes, and ethers having compatibility with water and solubility of silver salts (mainly silver nitrate) can be preferably 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.
On the other hand, when water is not contained and an organic solvent is used as a single solvent, a polyhydric alcohol capable of directly dissolving a silver salt is preferable. Specific examples include ethylene glycol, diethylene glycol, and glycerin.

  When silver coating is performed using a mixed solution of the organic solvent and water described above or an emulsion, the organic solvent may be a liquid at room temperature (specifically, 10 ° C. to 30 ° C.). preferable. 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 the silver salt (silver raw material) used for the silver coating reaction, it is preferable to use silver nitrate having solubility in water and many organic solvents because silver ions need to be present in the reaction solution. In order to realize a coating reaction that is as uniform 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. 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 appropriately determined according to the target silver coating amount.

In order to form a silver coating layer more uniformly, a chelating agent << 14 >> is added and mixed in a reaction solution (mixed solution, emulsion, or organic solvent) for silver coating reaction << 18 >>, and dissolved or emulsified. << 19 >> 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 thereof include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid, diethylenetriamine, triethylenediamine, or salts thereof.
In order to carry out the silver coating reaction stably and safely, a pH buffering agent <15> may be further added to and mixed with the reaction solution for carrying out the silver coating reaction to dissolve or emulsify <19>. Examples of the pH buffering agent include ammonium carbonate, ammonium hydrogen carbonate, aqueous ammonia, sodium hydrogen carbonate, and the like.

After the temperature of the reaction solution for carrying out the silver coating reaction is adjusted to 10 to 80 ° C. << 20 >>, it is added and mixed <21> to the flaky electrolytic copper powder dispersion, ripened <22>, and flaky electrolytic copper powder The surface is coated with silver to obtain a dispersion of silver-coated flaky copper powder.
The ratio of silver covering the flaky electrolytic copper powder to the copper (silver coating amount) is preferably 0.3% by mass or more and 30% by mass or less. When the silver coating amount is 0.3% by mass or more, the volume resistivity can be sufficiently reduced. On the other hand, if it is 30 mass% or less, the raw material cost of silver can be reduced.
The silver coating amount can be determined, for example, by dissolving silver-coated flaky copper powder with nitric acid and then adding hydrochloric acid, drying the resulting silver chloride precipitate, and measuring the weight.

<4. Other processes>
It is also preferable to add the stearic acid emulsion << 23 >> to the aged silver-coated flaky copper powder dispersion and continue the stirring to perform the surface treatment << 24 >> on the silver-coated flaky copper powder.
Examples of other processes include a cleaning process << 25 >> and a drying process << 26 >>.
The washing step and the drying step are steps in which the obtained silver-coated flaky copper powder is solid-liquid separated, washed and dried.
There is no restriction | limiting in particular in the said washing | cleaning process, The well-known method with respect to copper powder can be used suitably.
On the other hand, the drying process is not particularly limited, but is preferably vacuum drying at a temperature of 10 to 120 ° C. and an atmospheric pressure of 0 to 750 mmHg.
This is because the aggregation of the silver-coated flaky copper powder during drying is suppressed.
After the drying, crushing << 27 >> may be performed, and the silver-coated flaky copper powder << 28 >> according to the present invention can be obtained. Of course, after crushing << 27 >>, it is also preferable to appropriately carry out a sieving step to remove coarse particles.

The silver-coated flaky copper powder according to the present invention obtained by subjecting the electrolytic copper powder having a dendritic shape to a silver coating treatment and a flattening treatment is an electrolytic copper having a silver shape at least on the surface and having a dendritic shape. This is a silver-coated flaky copper powder obtained by adding a flattening treatment to the powder.
However, after the silver-coated flaky copper powder is flattened with an electrolytic copper powder having a dendritic shape, the silver is coated, and the electrolytic copper powder having a dendritic shape is coated with silver. Thereafter, any of flattening processing is included.
According to an electron microscope observation (see FIGS. 2 to 17 described later), it has a shape derived from the main trunk portion and the branch portion of the electrolytic copper powder having a dendritic shape. That is, a noticeable difference in shape is recognized from the conventional flaky copper powder and silver-coated flaky copper powder obtained by flattening spherical atomized copper powder, wet reduced copper powder, and the like.

(3) Conductive paste and production method thereof The obtained silver-coated flaky copper powder is preferably used by blending with the conductive paste described below.
Examples of the conductive paste according to the present invention include a resin curable paste, and the content of the silver-coated flaky copper powder in the conductive paste is not particularly limited and should be appropriately selected according to the purpose. Can do. In addition to the silver-coated flaky copper powder, the conductive paste contains a resin and a solvent, and further contains other components as desired.
The conductive paste according to the present invention will be described in the following <1. Resin>, <2. Solvent>, <3. Other components>, <4. Manufacturing method of conductive paste>, <5. The characteristics will be described in the order of the characteristics of the conductive paste>.

<1. resin>
There is no restriction | limiting in particular in resin contained in the electrically conductive paste which concerns on this invention, 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, and the like can be given. These may be used individually by 1 type and may use 2 or more types together.

<2. solvent>
There is no restriction | limiting in particular as a solvent contained in the electrically conductive paste which concerns on this invention, According to the objective, it can select suitably. 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, Examples include 3-pentanediol monoisobutyrate and acetic acid diethylene glycol mono-n-ethyl ether. These may be used individually by 1 type and may use 2 or more types together.

<3. Other ingredients>
Examples of other components contained in the conductive paste according to the present invention include surfactants, glass frit, dispersants, viscosity modifiers, and the like.

<4. Method for producing conductive paste>
There is no restriction | limiting in particular in the manufacturing method of the electrically conductive paste which concerns on this invention, According to the objective, it can select suitably. For example, the silver-coated flaky copper powder according to the present invention, the resin, the solvent, and, if necessary, the other components, for example, ultrasonic dispersion, disperser, three-roll mill, ball mill, bead mill, two It can be manufactured by mixing using a shaft kneader, a self-revolving stirrer or the like.

<5. Characteristics of conductive paste>
There is no restriction | limiting in particular in the viscosity of the electrically conductive paste which concerns on this invention, Although it can select suitably according to the objective, 5 Pa.s or more and 100 Pa.s or less are preferable at 25 degreeC. When the viscosity of the conductive paste is 5 Pa · s or more, “bleeding” does not occur during printing. If the viscosity is 100 Pa · s or less, it is possible to avoid unevenness during printing.

The volume resistivity of the conductive paste according to the present invention is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 5 × 10 ⁻⁴ Ω · cm or less, more preferably 2.4 × 10. ^-4 Ω · cm or less. When the volume resistivity is 5 × 10 ⁻⁴ Ω · cm or less, a conductive paste having an extremely low volume resistivity can be realized.
The volume resistivity can be measured by using, for example, DIGITAL MULTITIMER (ADVANTEST, AD7451A).

  The conductive paste according to the present invention can ensure conductivity even if it is a low filler content paste. As a result, for example, directly on the various substrates such as a silicon wafer for solar cells, a film for touch panel, glass for EL elements, or on the transparent conductive film further provided with a transparent conductive film on the substrate as necessary, A conductive coating can be formed by coating or printing. Specifically, for example, it is suitably used for a current collecting electrode of a solar battery cell, an external electrode of a chip-type electronic component, an RFID, an electromagnetic wave shield, a vibrator adhesive, a membrane switch, an electroluminescence electrode, or an electrical wiring application. .

Examples of the present invention will be described below, but the present invention is not limited to these examples.
Example 1
About Example 1, (1) electrolytic copper powder, (2) flattening step, (3) silver coating step, (4) measurement of characteristic values of silver-coated flaky copper powder, (5) manufacturing process of conductive paste (6) Volume resistivity of the conductive film will be described in this order.

(1) Electrolytic copper powder As electrolytic copper powder, Fukuda Metal Foil Powder Industry Co., Ltd. FCC-115 was prepared.

(2) Flattening step 30.66 kg of the electrolytic copper powder and Solmix AP-7 (manufactured by Nippon Alcohol Sales Co., Ltd., ethanol 85.5% by mass, IPA 5% by mass, n-propyl alcohol 9.5% by mass) ) 17.77 kg was loaded together with 185.8 kg of SUS balls (diameter 1.6 mm) into an attritor (Nippon Coke Kogyo Co., Ltd., MA15SE, capacity 100 L).
As a result, the value of [amount of electrolytic copper powder (kg) / attritor processing scale (L)] was 0.307 kg / L.
The electrolytic copper powder was flattened under the conditions of a rotation speed of the attritor of 195 rpm, a circulation pump pressure of 0.4 Mpa, and a treatment time of 180 minutes, to obtain a flaky copper powder slurry. After separating the flaky copper powder slurry and the SUS ball, the wet cake obtained by filtering the flaky copper powder slurry was vacuum dried at 70 ° C. to obtain flaky copper powder.

(3) Silver coating step 175.0 g of ammonium carbonate and 735.0 g of ethylenediaminetetraacetic acid tetrasodium salt (EDTA · 4Na · 4H ₂ O) 50% by mass solution were dissolved in 118.4 g of pure water to obtain a solution, and the liquid temperature Was adjusted to 35 ° C.
The solution was mixed with an aqueous silver nitrate solution containing 38.89 g of silver to prepare a silver complex salt solution.
Moreover, after dissolving 9.1 g of ammonium carbonate and 112.6 g of a 50 mass% solution of EDTA · 4Na · 4H ₂ O in 1441.1 g of pure water, 350.0 g of the flake copper powder was added and stirred. A flaky copper 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. The stearic acid emulsion 11.3g of 15 mass% stearic acid was added, and stirring was continued for 5 minutes, and surface treatment to the silver coating flake copper powder was performed.
The obtained silver-coated flake copper powder was filtered and washed with ion exchange water, and the obtained wet cake was dried at 120 ° C. in a nitrogen atmosphere to obtain a dried product. The dried agglomerate of the obtained dried product was pulverized by a sample mill (KII WR-1 type, manufactured by Fuji Paudal Co., Ltd.), and passed through a sieve having an opening of 25 μm to obtain a silver-coated flaky copper powder according to Example 1. (In the present invention, the silver coating step is referred to as “silver coating step (A)”).
About the above operation, processing scale of attritor, original powder (electrolytic copper powder) name, original powder (electrolytic copper powder) amount, electrolytic copper powder amount (kg) / attritor processing scale (L), attritor processing Time, used ball diameter, ball filling ratio in attritor, used solvent name, electrolytic copper powder amount / slurry amount = electrolytic copper powder amount / (electrolytic copper powder amount + solvent amount), ball mass / electrolytic copper powder amount, atto The lighter rotation speed, circulation pump pressure, and silver coating process type are listed in Table 1 (hereinafter the same applies to Examples 2 to 18 and Comparative Examples 1 to 4).
A scanning electron micrograph of 1000 times of the silver-coated flaky copper powder according to Example 1 is shown in FIG.

(4) Measurement of characteristic value of silver-coated flaky copper powder With respect to the obtained silver-coated flaky copper powder according to Example 1, <1. Circularity coefficient>, <2. X-ray particle size>, <3. Thickness>, <4. Aspect ratio>, <5. Circularity coefficient × aspect ratio>, <6. Maximum axial length>, <7. Each characteristic value of Axis Length Maximum Length / Thickness> was measured, and the results are shown in Table 2. <8. BET specific surface area>, <9. Tap density>, <10. Cumulative particle diameter>, <11. The oxygen content, carbon content, silver coating amount> were measured, and the results are shown in Tables 2 and 3. (The same applies to Examples 2 to 18 and Comparative Examples 1 to 4 below.)
This will be described below.

<1. Circularity coefficient>
The degree of separation of the shape of the silver-coated flaky copper powder particles according to the present invention from the circle is evaluated using the circularity coefficient.

  Specifically, it is convenient to take a 1000-fold scanning electron microscope image of the silver-coated flaky copper powder according to the present invention and obtain the electron microscope image by applying commercially available image analysis software. As the commercially available image analysis software, in this example, using the image analysis type particle size distribution measurement software “Mac-View Ver. 4” manufactured by Mountec Co., Ltd., from shape data measured using a point tool, S , L was determined.

<2. X-ray particle size>
In the present invention, the calculation peak (JADE7 manufactured by Rigaku Corporation) is used to smooth the diffraction peak obtained by the X-ray diffraction method, and background removal and Kα2 removal are performed using cubic approximation. After the above, peak separation was performed. And the value of the crystallite diameter obtained with the said calculation software was made into the X-ray particle size.
・ RINT-ULtimaIII made by Rigaku Corporation
-X-ray used: CoKα (wavelength = 1.7889 mm)
Scanning range: 2θ = 10 ° to 100 °
-Scanning at scan speed = 2 ° / min-Calculation software: JADE7 manufactured by Rigaku Corporation

<3. Thickness>
The thickness of the silver-coated flaky copper powder according to the present invention is the length between two planes produced by a flattening treatment in each particle by taking a scanning electron microscope image of the silver-coated flaky copper powder 1000 times. The thickness of each particle is measured.
Similar to the circularity coefficient described above, it is convenient to obtain by applying commercially available image analysis software, and in this embodiment, the image analysis type particle size distribution measurement software “Mac-View Ver. Was measured using the two-point designation of the length tool.

<4. aspect ratio>
In the silver-coated flaky copper powder according to the present invention, the aspect ratio is defined as “maximum length / thickness (based on the major axis)”.
It is convenient to obtain the above-described maximum length and thickness and obtain them by calculation.

<5. Circularity factor x aspect ratio>
It is convenient to obtain the above-described circularity coefficient and aspect ratio by calculation.

<6. Maximum shaft length>
A 1000-times scanning electron microscope image of the silver-coated flaky copper powder according to the present invention is taken, and for each particle, the longest straight line is defined as the axial length, and the length is defined as the maximum axial length.
(The actual maximum axial length is not measured, but the value automatically calculated in the software from the particle shape measured by tracing the edge of the particle with a point tool. The description “measured” is “the maximum axial length”.)
Similar to the circularity coefficient described above, it is convenient to obtain by applying commercially available image analysis software, and in this embodiment, the image analysis type particle size distribution measurement software “Mac-View Ver. And measured using a point tool.

<7. Maximum shaft length / thickness>
It is convenient to obtain the above-described maximum axial length and thickness and obtain them by calculation.

<8. BET specific surface area>
The BET specific surface area value of the silver-coated flaky copper powder according to the present invention was determined by the BET method using a BET specific surface area measuring apparatus (manufactured by Your Sonics Co., Ltd .: 4 Sorb US).

<9. Tap density>
A method for measuring the tap density of the silver-coated flaky copper powder according to the present invention will be described.
A sample is loaded into a mold with a lid whose weight and profile are known (the height of the mold when the mold is empty is h0 (μm) and the weight of the blank is w0 (mg)), and the lid Place the mold on the micrometer. Next, the mold is compressed by turning the anvil of the micrometer, and the ratchet of the anvil is clicked five times. The height of the mold at that time is read, and this height is defined as h1 (μm). On the other hand, the weight of the mold including the sample is measured, and the weight is defined as w1 (mg). And the tap density was calculated | required from Formula 2 from the value of w0, w1, h0, h1. Incidentally, 36.6 is a coefficient.
Tap density = 36.6 × (w1−w0) ÷ (h1−h0) g / cm ³ Equation 2
(For details, refer to JP 2007-263860 A.)

<10. Cumulative particle size>
The cumulative particle size on the volume basis of the silver-coated flaky copper powder according to the present invention was measured by a laser diffraction particle size distribution device (manufactured by SYMPATEC, HEROS particle size distribution measurement device, HELOS & RODOS). In addition, the lens used for the measurement was appropriately changed according to the particle diameter.

<11. Oxygen content, carbon content, silver coverage>
The oxygen content in the silver-coated flaky copper powder according to the present invention was measured with an oxygen / nitrogen analyzer (manufactured by LECO: TC-436), and the carbon content was measured using a carbon / sulfur analyzer (manufactured by Horiba: EMIA- 220V).
The silver coating amount in the silver-coated flaky copper powder according to the present invention is determined by adding hydrochloric acid after dissolving the silver-coated copper powder with nitric acid, drying the resulting silver chloride precipitate, and measuring the weight. The measured value of the silver coating amount in the silver-coated flaky copper powder was determined.

An example of a method for measuring the Ag content of the silver-coated flaky copper powder according to the present invention will be specifically described.
2 g of a sample is weighed and transferred to a beaker while being rinsed with pure water, and then 10 ml of nitric acid is added and dissolved by heating. After allowing to cool, the solution is filtered to remove floating organic components, and a filtrate is obtained. 100 ml of pure water is added to the filtrate, 6 ml of HCl is added and stirred sufficiently, and further HCl is added. Then, HCl is added until no new AgCl can be precipitated, and then heating and aging are performed until the solution becomes transparent. Thereafter, the mixture was filtered through a glass fiber filter (weight is W1 (g)), and the collected AgCl precipitate was dried at 110 ° C. for 3 hours by a dryer. After allowing to cool, the glass fiber filter and the collected AgCl were weighed together, and the weight was defined as W2 (g).
From the values of W1 and W2, the Ag content was determined from Equation 3.
Ag (mass%) = (W2−W1) / initial sample amount (g) × 0.7526 × 100 Formula 3

(5) Manufacturing process of conductive paste About the manufacturing process of the conductive paste which concerns on Example 1, <1. Composition of conductive paste>, <2. Step of kneading conductive paste>, <3. The conductive paste printing step will be described in this order.
(The same applies to Examples 2 to 18 and Comparative Examples 1 to 4 below.)

<1. Composition of conductive paste>
The obtained silver-coated flaky copper powder according to Example 1, a polyester resin, and a solvent were mixed in the following composition.
-60 parts by mass of silver-coated flaky copper powder-12 parts by mass of polyester resin (Toyobo Co., Ltd., Byron 200)-Solvent: Diethylene glycol acetate mono-n-ethyl ether (Wako Pure Chemical Industries, Ltd., ECA) 28 masses Part

<2. Conductive paste kneading process>
The obtained mixture was kneaded by using a vacuum stirring and defoaming mixer (manufactured by EME, Inc., V-mini300) twice at 1400 rpm for 30 seconds to conduct the conductive paste according to Example 1. Got.

<3. Printing process of conductive paste>
After the produced conductive paste according to Example 1 was printed on an alumina substrate by a screen printing method (in a pattern having a line width of 500 μm and a line length of 37.5 mm), the obtained alumina substrate was subjected to an atmospheric circulation dryer. Was subjected to heat treatment at 130 ° C. for 30 minutes to form a conductive film.

(6) Volume resistivity of electrically conductive film The electrically conductive paste which concerns on Example 1 was printed on the alumina substrate, and the volume resistivity of the electrically conductive film obtained by heat-processing was measured as follows.
(The same applies to Examples 2 to 18 and Comparative Examples 1 to 4 below.)
The volume resistivity of the conductive film was determined by measuring the line resistance of the obtained conductive film with DIGITAL MULTITIMER (ADVANTEST, AD7451A). On the other hand, the film thickness of the obtained conductive film was measured with a surface roughness shape measuring instrument (Surfcom 1500DX type manufactured by Tokyo Seimitsu Co., Ltd.). And the volume resistivity in the electrically conductive film was computed by Formula 4.
Volume resistivity (Ω · cm) = line resistance (Ω) × film thickness (cm) × line width (cm) / line length (cm)... Formula 4
The measurement results of the obtained volume resistivity are shown in Table 4. (The same applies to Examples 2 to 18 and Comparative Examples 1 to 4 below.)

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

(Example 2)
In the flattening treatment step, the same operation as in Example 1 was performed except that the rotation speed of the attritor was changed to 227 rpm, and the silver-coated flaky copper powder, the conductive paste, and the conductive film according to Example 2 were obtained. .
The measurement results of the volume resistivity in the operation and the silver-coated flaky copper powder and conductive film according to Example 2 are shown in Tables 1 to 4.
And the scanning electron micrograph of 1000 time of the silver covering flaky copper powder which concerns on Example 2 is shown in FIG. Hereinafter, also in Examples 3-18, 1000 times the scanning electron micrographs of the silver-coated flaky copper powder according to each Example are shown in FIGS.

(Example 3)
In the flattening process, the same operation as in Example 1 was performed except that the amount of electrolytic copper powder was 35.7 kg and the rotation speed of the attritor was 227 rpm, and the silver-coated flaky copper powder according to Example 3 A conductive paste and a conductive film were obtained.
At this time, the value of [amount of electrolytic copper powder (kg) / processing scale of attritor (L)] was 0.357 kg / L.

Example 4
In the flattening treatment step, the same operation as in Example 1 was performed except that the rotation speed of the attritor was set to 227 rpm and the pressure of the circulation pump was set to 0.55 MPa. A conductive paste and a conductive film were obtained.

(Example 5)
In the flattening treatment step, the same operation as in Example 1 was performed except that the rotation speed of the attritor was changed to 227 rpm.

In the silver coating process, 35.00 kg of ammonium carbonate and 147.00 kg of 50% by mass ethylenediaminetetraacetic acid tetrasodium salt (EDTA.4Na.4H ₂ O) were dissolved in 225.68 kg of pure water, and the liquid temperature was adjusted to 35 ° C. did. 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 is filtered, washed with ion-exchanged water, the obtained wet cake is dried at 120 ° C. in a nitrogen atmosphere, and passed through a sieve having an opening of 25 μm according to Example 5. Silver-coated flaky copper powder was obtained (in the present invention, the silver coating step is referred to as “silver coating step (B)”).
Except for this, the same operations as in Example 1 were performed to obtain a conductive paste and a conductive film according to Example 5.

(Example 6)
In the flattening treatment step, the same operation as in Example 1 was performed except that the rotation speed of the attritor was changed to 227 rpm.

In the silver coating process, 35.00 kg of ammonium carbonate and 147.00 kg of 50% by mass ethylenediaminetetraacetic acid tetrasodium salt (EDTA.4Na.4H ₂ O) were dissolved in 225.68 kg of pure water, and the liquid temperature was adjusted to 35 ° C. did. 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 dry agglomeration was pulverized by Type 1), and the silver-coated flaky copper powder according to Example 6 was obtained through a sieve having an opening of 25 μm (in the present invention, the silver coating step is referred to as “silver coating step (C)”). .)
Except for this, the same operation as in Example 1 was performed to obtain a conductive paste and a conductive film according to Example 6.

(Example 7)
In the flattening process, the same operation as in Example 1 was performed except that the processing time by the attritor was set to 240 minutes, and the silver-coated flaky copper powder, the conductive paste, and the conductive film according to Example 7 were obtained. It was.

(Example 8)
In the flattening treatment step, the same operation as in Example 1 was performed except that the rotation speed of the attritor was set to 170 rpm, and the silver-coated flaky copper powder, the conductive paste, and the conductive film according to Example 8 were obtained. .

Example 9
In the flattening treatment step, the silver coated flaky copper powder according to Example 9 was performed by performing the same operation as in Example 1 except that the treatment time by the attritor was 240 minutes and the rotation speed of the attritor was 170 rpm. A conductive paste and a conductive film were obtained.

(Example 10)
In the flattening process, the same operation as in Example 1 was performed except that the processing time by the attritor was 240 minutes and the rotation speed of the attritor was 170 rpm.

<Silver coating process>
In the silver coating step, the “silver coating step (C)” described in Example 6 was performed to obtain a silver-coated flaky copper powder according to Example 10.
Except for this, the same operations as in Example 1 were performed to obtain a conductive paste and a conductive film according to Example 10.

(Example 11)
In the flattening treatment step, the same operation as in Example 1 was performed except that the rotation speed of the attritor was set to 150 rpm, and the silver-coated flaky copper powder, the conductive paste, and the conductive film according to Example 11 were obtained. .

(Example 12)
In the flattening treatment step, the silver coated flaky copper powder according to Example 12 was performed by performing the same operation as in Example 1 except that the treatment time by the attritor was 240 minutes and the rotation speed of the attritor was 150 rpm. A conductive paste and a conductive film were obtained.

(Example 13)
In the flattening treatment step, the same operation as in Example 1 was performed except that the pressure of the circulation pump was changed to 0.55 MPa to obtain a silver-coated flaky copper powder, a conductive paste, and a conductive film according to Example 13. It was.

(Example 14)
In the flattening process, the same operation as in Example 1 was performed except that the processing time by the attritor was 240 minutes and the pressure of the circulation pump was 0.55 MPa, and the silver-coated flaky copper powder according to Example 14 A conductive paste and a conductive film were obtained.

(Example 15)
In the flattening process, the same operation as in Example 1 was performed except that the processing time by the attritor was 240 minutes, the rotation speed of the attritor was 170 rpm, and the pressure of the circulation pump was 0.55 MPa. A silver-coated flaky copper powder, a conductive paste, and a conductive film were obtained.

(Example 16)
In the flattening treatment process, the processing scale of the attritor is 5.4 L, and electrolytic copper powder is # 51-R (A) manufactured by Fukuda Metal Foil Powder Industry Co., Ltd. The processing time with a lighter was 120 minutes, the ball filling rate was 45.02 vol%, the rotation speed of the attritor was 360 rpm, and the processing scale of the attritor was 5.4 L. The same operation as in Example 1 was performed to obtain a silver-coated flaky copper powder, a conductive paste, and a conductive film according to Example 16.
At this time, the value of [amount of electrolytic copper powder (kg) / processing scale of attritor (L)] was 0.345 kg / L.

(Example 17)
In the silver coating step, the obtained wet cake was vacuum-dried at 70 ° C. to obtain a dried product, and then the same operation as in Example 9 was performed to obtain a silver-coated flaky copper powder according to Example 17, conductive Conductive paste and conductive film were obtained.

(Example 18)
The same operation as in Example 9 was performed except that the flaky copper powder obtained by performing the same flattening treatment step as in Example 9 was changed to a flaky copper powder through a sieve having an opening of 25 μm. A silver-coated flaky copper powder, a conductive paste, and a conductive film according to Example 18 were obtained.

(Comparative Example 1)
In the silver coating step, 393.0 g of ammonium carbonate and 1268.7 g of ethylenediaminetetraacetic acid tetrasodium salt (EDTA · 4Na · 4H ₂ O) 50% by mass solution were dissolved in 1458.7 g of pure water, and the liquid temperature was adjusted to 25 ° C. did. This solution was mixed with an aqueous silver nitrate solution containing 55.56 g of silver to prepare a silver complex salt solution. Further, after the 50 wt% solution 576.2g of ammonium carbonate 356.9g and EDTA · 4Na · 4H ₂ O dissolved in pure water 5031.1G, spherical copper powder D50 particle size of 6.4μm by Heroes 500. 0 g was added and stirred to prepare a spherical copper powder dispersion. The liquid temperature of this spherical copper powder dispersion was adjusted to 25 ° 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. The stearic acid emulsion 4.6g of 15 mass% stearic acid was added, and stirring was continued for 30 minutes, and the surface treatment to the silver coating spherical copper powder was performed.
The obtained silver-coated spherical copper powder was filtered, washed with ion-exchanged water, and the obtained wet cake was dried at 120 ° C. in a nitrogen atmosphere and passed through a sieve having an opening of 32 μm. The same operation as in Example 1 was performed to obtain a silver-coated spherical copper powder, a conductive paste, and a conductive film according to Comparative Example 1.
And the scanning electron micrograph of 1000 time of the silver covering copper powder which concerns on the comparative example 1 is shown in FIG.

(Comparative Example 2)
In the silver coating step, 393.0 g of ammonium carbonate and 1268.7 g of ethylenediaminetetraacetic acid tetrasodium salt (EDTA · 4Na · 4H ₂ O) 50% by mass solution were dissolved in 1458.7 g of pure water to obtain a solution, and the liquid temperature was adjusted. Adjusted to 25 ° C. This solution was mixed with an aqueous silver nitrate solution containing 55.56 g of silver to prepare a silver complex salt solution.
Further, 356.9 g of ammonium carbonate and 576.2 g of a 50 mass% solution of EDTA · 4Na · 4H ₂ O were dissolved in 5031.1 g of pure water, and then 200 g of IPA was added to obtain a solution. To the solution was added 500.0 g of flaky copper powder obtained by flattening spherical copper powder having a D50 particle size of 13.97 μm as measured by Heros, followed by stirring to prepare a flaky copper powder dispersion.
The liquid temperature of the flaky copper powder dispersion was adjusted to 25 ° C. in a dry nitrogen gas atmosphere, and then the silver complex salt solution was added to carry out a silver coating reaction, which was held for 30 minutes with stirring. Next, 4.6 g of a stearic acid emulsion containing 15% by mass of stearic acid was added thereto, and stirring was continued for 30 minutes to perform surface treatment on the silver-coated flaky copper powder.
The obtained silver-coated flaky copper powder was filtered, washed with ion-exchanged water, the obtained wet cake was dried at 120 ° C. in a nitrogen atmosphere, and passed through a sieve having an opening of 32 μm. The same operation as in Example 1 was performed to obtain a silver-coated flaky copper powder, a conductive paste, and a conductive film according to Comparative Example 2.
And the scanning electron micrograph of 1000 time of the silver covering flaky copper powder which concerns on the comparative example 2 is shown in FIG.

(Comparative Example 3)
In the silver coating step, 196.5 g of ammonium carbonate and 634.5 g of ethylenediaminetetraacetic acid tetrasodium salt (EDTA · 4Na · 4H ₂ O) 50% by mass solution were dissolved in 729.4 g of pure water to obtain a solution. The temperature was adjusted to 25 ° C. This solution was mixed with an aqueous silver nitrate solution containing 27.78 g of silver to prepare a silver complex salt solution.
In addition, 178.5 g of ammonium carbonate and 288.1 g of a 50 mass% solution of EDTA · 4Na · 4H ₂ O were dissolved in 2315.5 g of pure water, and then 200 g of IPA was added to obtain a solution. To this solution, 250.0 g of Fukuda Metal Foil Powder Co., Ltd. FCC-115 was added and stirred to prepare a dendritic copper powder dispersion.
The liquid temperature of this dendritic copper powder dispersion was adjusted to 25 ° C. in a dry nitrogen gas atmosphere, and the silver complex salt solution was added to carry out the silver coating reaction, and the mixture was held for 30 minutes with stirring. Next, 2.0 g of a stearic acid emulsion containing 15% by mass of stearic acid was added, and stirring was continued for 30 minutes to perform surface treatment on the silver-coated dendritic copper powder.
The obtained silver-coated dendritic copper powder was filtered, washed with ion-exchanged water, the obtained wet cake was dried at 120 ° C. in a nitrogen atmosphere, and passed through a sieve having an opening of 32 μm. The same operation as in Example 1 was performed to obtain a silver-coated dendritic copper powder, a conductive paste, and a conductive film according to Comparative Example 3.
And the scanning electron micrograph of 1000 time of the silver covering copper powder which concerns on the comparative example 3 is shown in FIG.

(Comparative Example 4)
In the flattening treatment step, the same operation as in Example 1 was performed except that the amount of electrolytic copper powder was 25 kg and the treatment time with an attritor was 210 minutes, and the silver-coated flaky copper powder according to Comparative Example 4 A conductive paste and a conductive film were obtained.
At this time, the value of [amount of electrolytic copper powder (kg) / processing scale of attritor (L)] was 0.250 kg / L.
And the scanning electron micrograph of 1000 time of the silver covering flaky copper powder which concerns on the comparative example 4 is shown in FIG.

(Summary)
From the above results, the silver-coated flaky copper powder according to the present invention of Examples 1 to 18 has a silver-coated flaky copper powder particle that has at least silver on the surface and is flattened. The copper powder has a circularity coefficient of 0.3 or more and 0.6 or less, a thickness of 0.35 μm or more and 0.70 μm or less, and an X-ray particle size of 10 nm or more on the Ag (111) plane. It was 30 nm or less, and was 30 nm or more and 58 nm or less on the Cu (111) plane. And the silver covering flaky copper powder which concerns on this invention which has the said structure has low volume resistivity as shown in Table 4, and filler (silver covering copper powder for conductive paste) content is as low as 60 mass%. It can be understood that even a conductive paste having a filler content has a volume resistivity equivalent to that of a conductive paste according to the prior art having a filler content of 80% by mass or more.
That is, it can be understood that the silver-coated flaky copper powder according to the present invention is a silver-coated flaky copper powder that can ensure conductivity even in a paste with a low filler content.

In contrast, in the silver-coated flaky copper powder according to the conventional techniques of Comparative Examples 1 to 3, Comparative Example 1 does not satisfy the circularity coefficient and thickness, Comparative Example 2 does not satisfy the circularity coefficient, and Comparative Example 3 Does not meet the thickness.
On the other hand, although it is the same method as the manufacturing method of the present invention, in the flattening treatment, the value of [electrolytic copper powder amount (kg) / attritor treatment scale (L)] is 0.25. In the silver-coated flaky copper powder, the thickness did not satisfy 0.35 μm or more and 0.70 μm or less. As a result, as shown in Table 4, the volume resistivity was higher than those of Examples 1-18.

  Since the conductive paste containing the silver-coated flaky copper powder according to the present invention can be a low filler content paste, for example, on various substrates such as silicon wafers for solar cells, films for touch panels, glass for EL elements, etc. The conductive coating film can be formed by coating or printing directly or on the transparent conductive film further provided with a transparent conductive film on the substrate, if necessary. As a result, for example, it is suitably used for a current collecting electrode of a solar battery cell, an external electrode of a chip-type electronic component, an RFID, an electromagnetic wave shield, a vibrator adhesive, a membrane switch, an electroluminescence electrode, or an electrical wiring application.

Claims (10)

Silver-coated flaky copper powder containing silver-coated flaky copper powder particles having at least silver on the surface and flattened,
The circularity coefficient by measurement of a scanning electron microscope image of the silver-coated flaky copper powder particles is 0.3 or more and 0.6 or less,
A silver-coated flaky copper powder having an X-ray particle size of 10 nm to 30 nm in the Ag (111) plane and 30 nm to 58 nm in the Cu (111) plane.   Thickness is 0.35 micrometer or more and 0.70 micrometer or less, The silver covering flaky copper powder of Claim 1 characterized by the above-mentioned.   The product of the circularity coefficient and the aspect ratio measured by a scanning electron microscope image of the silver-coated flaky copper powder particles is 7.5 or more and 15.5 or less. Silver-coated flaky copper powder.   The aspect ratio (maximum long axis length / average thickness) of the long axis and the average thickness by measurement of a scanning electron microscope image of the silver-coated flaky copper powder particles is 17 or more and 34 or less. The silver-coated flaky copper powder according to any one of claims 1 to 3. 5. The silver-coated flaky copper powder according to claim 1, wherein the BET specific surface area is 0.45 m ² / g or more and 0.65 m ² / g or less. 6. The silver-coated flaky copper powder according to claim 1, wherein the tap density is 3.5 g / cm ³ or less and 2.0 g / cm ³ or more. A flattening treatment step for obtaining a flaky electrolytic copper powder by performing a flattening treatment using an attritor in the presence of water and / or an organic solvent on the electrolytic copper powder having a dendritic shape;
A silver coating step of coating silver on the surface of the flaky electrolytic copper powder obtained by the flattening treatment,
In the flattening treatment, the flattening treatment is performed by setting the value of [amount of electrolytic copper powder (kg) / attritor processing scale (L)] to 0.3 kg / L or more. Manufacturing method.   The method for producing a silver-coated flaky copper powder according to claim 7, wherein, in the flattening treatment step, the flaky electrolytic copper powder obtained after the flattening treatment is passed through a sieve having an opening of 25 µm.   9. The silver-coated flaky copper powder according to claim 7 or 8, wherein in the silver coating step, a wet cake containing water and silver-coated flaky copper powder obtained after the silver coating reaction is vacuum-dried. Manufacturing method. A conductive paste comprising the silver-coated flaky copper powder according to claim 1.