TWI553661B - Silver powder and its use of conductive paste, conductive paint, conductive film - Google Patents

Description

Silver-coated copper powder and conductive paste, conductive paint, and conductive sheet using the same

The present invention relates to a copper powder (silver-coated copper powder) coated with silver on the surface, and more particularly to a novel dendritic silver-coated copper which can improve conductivity by using a material such as a conductive paste. Powder and copper paste, conductive paint, and conductive sheet using the same.

In the formation of a wiring layer or an electrode of an electronic device, a paste or a coating of a metal filler such as a silver paste or a silver-coated copper powder such as a resin paste or a fired paste or an electromagnetic wave shield paint is often used. The metal filler paste of silver powder or silver-coated copper is applied or printed on various substrates, and subjected to heat curing or heat baking to form a conductive film which is a wiring layer or an electrode.

For example, the resin-based conductive paste is composed of a metal filler, a resin, a curing agent, a solvent, or the like, and is printed on a conductor circuit pattern or a terminal, and is heat-hardened at 100 ° C to 200 ° C to form a wiring or an electrode in the form of a conductive film. . In the resin-based conductive paste, since the thermosetting resin is hardened and shrunk by heat, the metal filler is pressed and brought into contact, thereby overlapping the metal filler to form a current path for electrical connection. Since the resin-type conductive paste is treated at a curing temperature of 200 ° C or lower, it can be used for a substrate using a heat-resistant material such as a printed wiring board.

On the other hand, the fire-molded conductive paste is composed of a metal filler, glass, a solvent, etc., and is printed on a conductor circuit pattern or a terminal, and is heated and baked to 600 ° C to 800 ° C to be guided. Electrical film to form wiring or electrodes. The fire-molded conductive paste is obtained by sintering the metal fillers by treatment with a relatively high temperature to ensure conductivity. Since the baked conductive paste is treated at a high firing temperature as described above, there is a case where the printed wiring board cannot be used for a resin material. However, since the metal filler is sintered by high-temperature treatment, Achieve low resistance. Therefore, the fired conductive paste is used for an external electrode or the like of a laminated ceramic capacitor.

On the other hand, in order to prevent the generation of electromagnetic noise from an electronic device, the electromagnetic wave shielding is made of a resin, and in particular, in recent years, the casing of a personal computer or a mobile phone is made of resin. Therefore, in order to ensure electrical conductivity to the casing, the following is proposed. Method: a method of forming a thin metal film by a vapor deposition method or a sputtering method, a method of applying a conductive coating material, a method of attaching a conductive sheet to a desired portion, and shielding an electromagnetic wave. Among them, a method in which a metal filler is dispersed in a resin for coating, or a method in which a metal filler is dispersed in a resin and processed into a sheet shape and attached to a casing is excellent in degree of freedom in a processing step without special equipment. , thus being used frequently.

However, in the case where the metal filler is dispersed in the resin and coated, or processed into a sheet shape, the dispersion state of the metal filler in the resin is not uniform, so it is necessary to increase the metal filler in order to obtain the efficiency of electromagnetic wave shielding. Method such as filling rate. However, in this case, the weight of the sheet is increased due to the addition of a large amount of the metal filler, and the problem of flexibility of the resin sheet is impaired. For example, in Patent Document 1, in order to solve such problems, a method of using a flat metal filler has been proposed, whereby a thin sheet having excellent electromagnetic wave shielding effect and good flexibility can be formed.

Here, in order to produce a flat copper powder, for example, Patent Document 2 discloses a method of obtaining a flake shape copper powder suitable for a filler of a conductive paste. Specifically, a spherical copper powder having an average particle diameter of 0.5 μm to 10 μm is used as a raw material, and a ball mill or a vibrating machine is used. It is mechanically processed into a flat shape by the mechanical energy of the medium loaded in the grinder.

Further, for example, Patent Document 3 discloses a copper powder for conductive paste, and a disk-shaped copper powder which is high-performance as a copper paste for a via hole and an external electrode, and a method for producing the same. Specifically, the granular atomized copper powder is put into a medium agitating mill, and a steel ball having a diameter of 1/8 inch to 1/4 inch is used as a grinding medium, and 0.5% to 1% by weight is added to the copper powder. The fatty acid is pulverized in the air or in an inert gas atmosphere, thereby being processed into a flat shape.

On the other hand, as the metal filler used for the conductive paste or electromagnetic wave shielding, silver powder is often used, but the tendency to reduce the cost is to use silver coated on the surface of the copper powder which is cheaper than silver powder. The tendency to reduce the amount of silver used in silver-coated copper powder.

As a method of coating silver on the surface of the copper powder, there is a method of coating silver on the copper surface by a substitution reaction, and a method of coating silver in an electroless plating solution containing a reducing agent.

The method of coating silver by the substitution reaction forms a silver film on the copper surface by reducing silver ions by electrons generated when copper is eluted in the solution. For example, Patent Document 4 discloses a production method in which a copper film is formed by applying a copper powder to a solution in which silver ions are present, and a silver film is formed by a substitution reaction between copper and silver ions. However, in the method using the displacement reaction, if a silver film is formed on the surface of copper, the dissolution of copper to the above extent is not performed, and there is a problem that the amount of silver coating cannot be controlled.

In order to solve such a problem, there is a method of coating silver with an electroless plating solution containing a reducing agent. For example, Patent Document 5 proposes a method of producing a copper powder coated with silver by a reaction between copper powder and silver nitrate in a solution in which a reducing agent is dissolved.

In addition, as a copper powder, it is known that it is precipitated into a dendrite. Dendritic electrolytic copper powder is characterized by a large surface area due to its dendritic shape. By using a dendritic shape as described above, when it is used for a conductive film or the like, the branches of the dendrites overlap and are easily turned on, and the number of contacts between the particles is more than that of the spherical particles. Therefore, there is an advantage that the amount of the conductive filler in the conductive paste or the like can be reduced. For example, in Patent Documents 6 and 7, a silver-coated copper powder coated with silver on the surface of a dendritic copper powder is proposed.

Specifically, in Patent Documents 6 and 7, as a dendritic shape, a dendrite characterized by a long branch of an autonomous axis is disclosed, and the silver-coated copper powder has a more contact with each other due to particles. It is known that the dendrites are used to improve the conductivity, and when used for a conductive paste or the like, the conductivity can be improved even if the amount of the conductive powder is reduced.

On the other hand, it is pointed out in Patent Document 8 that when the branch of the electrolytic copper powder is developed, when used for a conductive paste or the like, the electrolytic copper powder is entangled with each other to a desired degree or more, and thus it becomes easy to occur. Aggregation, in turn, decreases in fluidity and becomes very difficult to operate, thereby reducing productivity. Further, in Patent Document 8, in order to increase the strength of the electrolytic copper powder itself, the strength of the electrolytic copper powder itself is increased by adding tungstate to the copper sulfate aqueous solution for causing the electrolytic copper powder to be deposited. It becomes difficult to break and can be formed into a higher strength.

Further, for example, in the case where the dendritic copper powder is used as a metal filler such as a conductive paste or a resin for electromagnetic wave shielding, if the metal filler has a shape which has developed into a dendritic shape, There is a problem that the dendritic copper powder is entangled with each other to cause aggregation, and is not uniformly dispersed in the resin, or the viscosity of the paste rises due to aggregation, thereby causing a problem in forming wiring by printing.

As described above, it is not easy to use the dendritic copper powder as a metal filler such as a conductive paste, and it has been difficult to advance the improvement of the conductivity of the paste.

In order to ensure conductivity, a dendritic shape having a three-dimensional shape is more likely to secure a contact than a granular one, and it is expected to ensure high conductivity as a conductive paste or electromagnetic wave shield. However, the conventional silver-coated copper powder having a dendritic shape is a dendrite characterized by a long branch of an autonomous axis branch, and has a slender dendritic shape, so that the structure is ensured from the viewpoint of securing the joint. The silver-coated copper powder, which is known to have a dendritic shape, is not a desirable shape because it is relatively simple and is used to effectively ensure the shape of the joint by using less silver-coated copper powder.

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-258490

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2005-200734

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2002-15622

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2000-248303

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2006-161081

[Patent Document 6] Japanese Patent Laid-Open Publication No. 2013-89576

[Patent Document 7] Japanese Laid-Open Patent Publication No. 2013-100592

[Patent Document 8] Japanese Patent No. 4976643

[Patent Document 9] Japanese Patent Laid-Open Publication No. 2011-58027

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an increase in the contact point when the dendritic copper powder coated with silver is brought into contact with each other, thereby ensuring excellent conductivity and preventing aggregation, and is preferably used for conducting electricity. Dendritic silver-coated copper powder for use in adhesive or electromagnetic wave shielding.

The present inventors have repeatedly conducted intensive studies to solve the above problems. Result There is a silver-coated copper powder which is composed of flat copper particles and is coated with silver on the surface of the copper particles. The flat copper particles grow into a dendritic shape having a trunk and a plurality of branches from the trunk branch. The dendritic shape and the average thickness of the cross section are in a specific range. By setting the average particle diameter (D50) of the copper powder to a specific range, excellent electrical conductivity can be ensured, and it can be preferably uniformly mixed with, for example, a resin. The present invention is used for applications such as conductive pastes, thereby completing the present invention. That is, the present invention provides the following.

(1) The silver-coated copper powder of the present invention is a silver-coated copper powder obtained by collecting dendritic copper particles and coating the surface with silver, and the dendritic copper particles have a linear growth trunk. And a dendritic shape of a plurality of branches from the main branch; the silver-coated copper powder characterized in that the copper particles have a trunk and a branch having an average thickness of more than 1.0 μm and a thickness of 5.0 μm or less and a flat shape. The silver-coated copper powder is a flat plate composed of a laminated structure in which one layer or a plurality of layers are stacked, and the average particle diameter (D50) is from 1.0 μm to 100 μm.

(2) The silver-coated copper powder according to the first aspect of the invention, wherein the average thickness of the cross-section of the copper-coated copper particles is divided by the average particle diameter (D50) of the silver-coated copper powder. The ratio is in the range of more than 0.01 and in the range of 5.0 or less.

(3) The silver-coated copper powder according to the first aspect of the invention, wherein the silver coating amount is from 1% by mass to 50% by mass based on 100% by mass of the silver-coated copper-coated copper powder.

(4) The silver-coated copper powder according to the first aspect of the invention is characterized in that the bulk density is in the range of 0.5 g/cm ³ to 5.0 g/cm ³ .

(5) A fifth invention of the present invention based silver coated copper powder as a first invention, BET specific surface area is 0.2m ² /g~3.0m ² / g.

(6) A metal filler according to the present invention is characterized in that the silver-coated copper powder according to any one of the first to fifth inventions is contained in a ratio of 20% by mass or more of the whole.

(7) A conductive paste according to a seventh aspect of the invention is characterized in that the metal filler of the sixth invention is mixed with a resin.

(8) The conductive paint for electromagnetic wave shielding according to the invention of the present invention is characterized in that the metal filler of the sixth invention is used.

(9) A conductive sheet for electromagnetic wave shielding according to the invention of the present invention is characterized in that the metal filler according to the sixth aspect of the invention is used.

According to the silver-coated copper powder of the present invention, excellent electrical conductivity can be ensured, and the contact points when the copper powders are in contact with each other can be sufficiently ensured, and aggregation can be prevented to be uniformly mixed with a resin or the like, and can be preferably used for conductivity. Use for paste or electromagnetic wave shielding.

1‧‧‧ copper particles

2‧‧‧ (copper particles) trunk

3, 3a, 3b‧‧‧ (copper particles) branches

Fig. 1 is a view schematically showing a specific shape of silver-coated copper particles constituting a dendritic silver-coated copper powder.

Fig. 2 is a photographic view showing an observation image when a dendritic copper powder before silver coating is observed at a magnification of 1,000 times by a scanning electron microscope.

Fig. 3 is a photographic view showing an observation image when a dendritic copper powder before silver coating is observed at a magnification of 10,000 times by a scanning electron microscope.

Fig. 4 is a photographic view showing an observation image when a dendritic copper powder before silver coating is observed at a magnification of 10,000 times by a scanning electron microscope.

Figure 5 is a view showing the dendritic silver-coated copper powder at a magnification of 1,000 times by a scanning electron microscope. A photo of the observed image.

Fig. 6 is a photographic view showing an observation image when a dendritic silver-coated copper powder is observed at a magnification of 10,000 times by a scanning electron microscope.

Fig. 7 is a photographic view showing an observation image when the copper powder obtained in Comparative Example 1 was observed at a magnification of 5,000 times by a scanning electron microscope.

Fig. 8 is a photographic view showing an observation image when the copper powder obtained in Comparative Example 2 was observed at a magnification of 5,000 times by a scanning electron microscope.

In the following, a specific embodiment of the copper powder of the present invention (hereinafter referred to as "this embodiment") will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments and may not be changed. Various modifications are possible within the scope of the gist of the invention. In addition, in the present specification, the expression "X~Y" (where X and Y are arbitrary values) means "X or more and Y or less".

"1. Dendritic silver-coated copper powder"

The silver-coated copper powder of the present embodiment is formed by collecting copper particles and coating the surface of the copper particles with silver, and the copper particles are formed into a dendritic shape having a trunk and a plurality of branches from the trunk branch.

Fig. 1 is a schematic view showing a specific shape of silver-coated copper particles constituting the silver-coated copper powder of the present embodiment. As shown in the schematic view of Fig. 1, the silver-coated copper particles 1 (hereinafter, simply referred to as "copper particles 1") have a dendritic shape in a two-dimensional or three-dimensional form. More specifically, the copper particles 1 have a shape of a trunk 2 and a plurality of branches 3 having branches from the trunk 2 Further, the copper particles 1 have a cross-sectional average thickness of more than 1.0 μm and a thickness of 5.0 μm or less and are flat. Further, the branch 3 of the copper particles 1 means both the branch 3a of the autonomous dry branch and the branch 3b which is further branched from the branch 3a.

The silver-coated copper powder of the present embodiment is composed of such flat copper particles 1 and is coated with silver on the surface of a copper powder (dendritic copper powder) having a trunk shape and a plurality of branches. Also known as "dendritic silver-coated copper powder", it is in the form of a flat layer composed of a laminated structure in which one layer or a plurality of layers are stacked (see the SEM image of the copper powder of FIG. 3 or FIG. 4). Further, the average particle diameter (D50) of the dendritic silver-coated copper powder composed of the tabular copper particles 1 is 1.0 μm to 100 μm.

Further, as shown below, the silver coating amount of the dendritic silver-coated copper powder of the present embodiment is 100% by mass based on the total mass of the silver-coated copper powder coated with silver, and is 1% by mass to 50% by mass, but is silver. The thickness (coating thickness) is an extremely thin film of about 0.15 μm or less. Therefore, the dendritic silver-coated copper powder has a shape that remains in the shape of the dendritic copper powder before the silver coating. Therefore, both the shape of the dendritic copper powder coated with silver and the shape of the dendritic silver-coated copper powder after the copper powder is coated with silver have a dendritic shape in a two-dimensional or three-dimensional form, and The layer or the multi-layered multilayer structure is formed into a flat plate shape.

Further, as will be described in detail later, the dendritic silver-coated copper powder of the present embodiment can be obtained, for example, by coating silver on the surface of the dendritic copper powder by reduction electroless plating or displacement electroless plating. The dendritic copper powder is obtained by impregnating an anode and a cathode with an electrolyte of a copper ion-containing acidic acid and electrolyzing it with a direct current to precipitate it on the cathode.

2 to 4 are photographs showing an example of an observation image when a dendritic copper powder before silver coating is observed by a scanning electron microscope (SEM). Furthermore, Figure 2 is based on The 3,000-fold magnification was observed for the dendritic copper powder. Figures 3 and 4 show that the dendritic copper powder was observed at a magnification of 10,000 times. Moreover, FIG. 5 is a photographic view showing an example of an observation image when the dendritic silver-coated copper powder in which the dendritic copper powder of FIG. 2 is coated with silver is observed by SEM. Moreover, FIG. 6 is a photographic view showing an example of an observation image when the other side of the dendritic silver-coated copper powder in which the dendritic copper powder is coated with silver is observed by SEM in the same manner. Further, Fig. 5 shows that the dendritic silver-coated copper powder was observed at a magnification of 1,000 times, and Fig. 6 was obtained by observing the dendritic silver-coated copper powder at a magnification of 10,000 times.

As shown in the observation images of FIG. 2 to FIG. 4, the dendritic copper powder constituting the silver-coated copper powder of the present embodiment has a state of being precipitated in a two-dimensional or three-dimensional dendritic shape having a trunk and a branch from the trunk branch. Further, the main particles and the copper particles 1 having a dendritic shape and a dendritic shape (see the schematic view of Fig. 1) are collectively formed, and further, the copper particles 1 have fine convex portions on the surface.

Here, the average thickness of the cross-sectional copper particles 1 constituting the dendritic copper powder and having the stem 2 and the stem 3 is more than 1.0 μm and not more than 5.0 μm. The thinner average thickness of the flat copper particles 1 can be exerted as a flat plate. In other words, by forming the stem and the branches of the dendritic copper powder with the tabular copper particles 1 having an average thickness of 5.0 μm or less, the copper particles 1 and the dendritic silver-coated copper powder composed of the copper particles 1 can be brought into contact with each other. The area is guaranteed to be large. Moreover, by making the contact area large, low electrical resistance, that is, high electrical conductivity can be achieved. Thereby, the conductivity is more excellent, and the conductivity can be favorably maintained, and it can be preferably used for the use of a conductive paint or a conductive paste. Moreover, by forming the dendritic copper powder with the flat copper particles 1, it is also possible to contribute to the reduction in thickness of the wiring material or the like.

In addition, the lower limit of the average thickness of the cross-section of the flat copper particles 1 is not particularly limited, and is hereinafter referred to as "by electrolysis of an electrolyte having a sulfuric acid containing copper ions. In the method of "upper", the tabular copper particles 1 having a cross-sectional average thickness of more than 1.0 μm can be obtained.

Further, the average particle diameter (D50) of the dendritic silver-coated copper powder of the present embodiment is from 1.0 μm to 100 μm. Further, the average particle diameter (D50) can be measured, for example, by a laser diffraction scattering type particle size distribution measurement method.

For example, as described in Patent Document 1, the problem of the dendritic silver-coated copper powder is as a metal filler in a resin such as a conductive paste or an electromagnetic wave shielding resin. The filler has developed into a dendritic shape, so that the dendritic copper powders are entangled with each other to agglomerate and are not uniformly dispersed in the resin. Moreover, the viscosity of the paste rises due to the aggregation, which causes a problem in that wiring is formed by printing. In this case, since the shape (particle diameter) of the dendritic silver-coated copper powder is large, in order to effectively utilize the shape of the dendritic shape and solve the problem, it is necessary to reduce the shape of the dendritic silver-coated copper powder. However, if the particle diameter of the dendritic silver-coated copper powder is too small, the dendritic shape cannot be ensured. Therefore, by the effect of a dendritic shape, that is, by having a three-dimensional shape, the surface area is large, and the formability and the sinterability are excellent, and the effect of forming at a high strength can be ensured in order to secure the connection through the branch-like portion. It is necessary to make the dendritic silver-coated copper powder to a specific size or more.

In this regard, in the dendritic silver-coated copper powder of the present embodiment, the average particle diameter is 1.0 μm to 100 μm, and the surface area is increased to ensure good formability or sinterability. Further, the dendritic silver-coated copper powder is composed of a collection of copper particles 1 having a dendritic shape having a trunk 2 and a branch 3 and having a flat plate shape, and thus may be dendritic. The three-dimensional effect and the effect of the copper particles 1 constituting the shape of the branches are flat, and the contact of the copper powders with each other is more ensured.

Here, as described in Patent Document 2 or Patent Document 3, when a spherical copper powder is formed into a flat shape by a mechanical method, it is necessary to prevent oxidation of copper during machining, and therefore, by adding The fatty acid is pulverized in the air or in an inert gas atmosphere to be processed into a flat shape. However, there is a case where oxidation cannot be completely prevented, or there is a case where dispersibility is affected when the fatty acid added during processing is gelatinized, and therefore it is necessary to remove it after the completion of the processing, but the fatty acid is firmly fixed by the force during machining. When it is fixed on the copper surface, there is a problem that it cannot be completely removed.

On the other hand, the tabular copper particles 1 constituting the dendritic silver-coated copper powder of the present embodiment are produced by directly growing into the shape of dendritic copper powder without mechanical processing, so that it is not necessary to prevent oxidation which is a problem in machining. The generation or removal of fatty acids makes the electrical conductivity characteristics extremely excellent.

Further, the dendritic silver-coated copper powder of the present embodiment is not particularly limited, and is preferably a ratio obtained by dividing the average thickness of the flat copper particles 1 by the average particle diameter (D50) of the silver-coated copper powder (profile). The average thickness/average particle diameter is in the range of more than 0.01 and not more than 5.0.

The ratio (aspect ratio) expressed by the "average cross-sectional average thickness / average particle diameter" is, for example, an index of the degree of aggregation or dispersibility when processed into a conductive copper paste, or the retention of the appearance shape at the time of application of a copper paste. . When the aspect ratio exceeds 5.0, the copper powder composed of spherical copper particles is obtained, and the effect by the surface contact disappears. On the other hand, when the aspect ratio is 0.01 or less, there is a case where the viscosity is high at the time of gelatinization, and the shape retainability or surface smoothness at the time of application of the copper paste is deteriorated.

Further, the bulk density of the dendritic silver-coated copper powder of the present embodiment is not particularly limited, but is preferably in the range of 0.5 g/cm ³ to 5.0 g/cm ³ . If the bulk density is less than 0.5 g/cm ³ , there is a possibility that the contact between the silver-coated copper powders cannot be sufficiently ensured. On the other hand, when the bulk density is more than 5.0 g/cm ³ , the average particle diameter of the silver-coated copper powder is also increased, so that the surface area is small and the formability or sinterability is deteriorated.

Further, when observed by an electron microscope, if the dendritic silver-coated copper powder having the shape as described above is occupied by the obtained silver-coated copper powder at a specific ratio, even if the dendritic silver-coated copper powder is mixed therein Copper powder of a shape other than the same can also obtain the same effect as the silver-coated copper powder composed only of the dendritic silver-coated copper powder. Specifically, when observed by an electron microscope (for example, 500 times to 20,000 times), the dendritic silver-coated copper powder having the above shape accounts for 80% or more, preferably 90% or more of the total silver-coated copper powder. The ratio may also include silver-coated copper powder of other shapes.

"2. Silver Coverage"

As described above, the dendritic silver-coated copper powder of the present embodiment is formed of a dendritic shape in which the copper particles 1 having a plate-like average thickness of more than 1.0 μm and a thickness of 5.0 μm or less and having silver coated on the surface thereof are formed into a dendritic shape. Hereinafter, the silver coating on the surface of the silver-coated copper powder will be described.

The dendritic silver-coated copper powder of the present embodiment is preferably a dendritic layer coated with silver at a ratio of 100% by mass to 50% by mass based on 100% by mass of the total silver-coated copper powder coated with silver. The copper powder is coated with silver, and the thickness of the silver (coating thickness) is an extremely thin film of 0.15 μm or less. According to this case, the dendritic silver-coated copper powder has a shape that remains in the shape of the dendritic copper powder before the silver coating.

As described above, the coating amount of silver in the dendritic silver-coated copper powder is preferably in the range of 1% by mass to 50% by mass based on 100% by mass of the entire silver-coated copper powder coated with silver. The amount of silver covered is preferably as small as possible from the viewpoint of cost, but if it is too small, it cannot be used in copper powder. The surface ensures a uniform silver film, which causes a decrease in conductivity. Therefore, the amount of silver coating is preferably 1% by mass or more, more preferably 5% by mass or more, and still more preferably 10% by mass or more based on 100% by mass of the silver-coated copper powder coated with silver.

On the other hand, if the amount of coating of silver is increased, it is not preferable from the viewpoint of cost, and the amount of silver coated is preferably 50% by mass based on 100% by mass of the silver-coated copper powder coated with silver. Hereinafter, it is more preferably 30% by mass or less, further preferably 20% by mass or less.

Further, in the dendritic silver-coated copper powder of the present embodiment, the average thickness of the silver coated on the surface of the dendritic copper powder is about 0.0003 μm to 0.15 μm, preferably 0.005 μm to 0.05 μm. If the coating thickness of silver is less than 0.0003 μm on average, it is impossible to ensure uniform silver coating on the surface of the copper powder, and this causes a decrease in conductivity. On the other hand, if the coating thickness of silver exceeds 0.15 μm on average, it is not preferable from the viewpoint of cost.

The average thickness of silver coated on the surface of the dendritic copper powder as described above is about 0.0003 μm to 0.15 μm, which is smaller than the average cross-sectional thickness (0.5 μm to 5.0 μm) of the tabular copper particles 1 constituting the dendritic copper powder. Therefore, the average thickness of the cross-section of the tabular copper particles does not substantially change until the surface of the dendritic copper powder is coated with silver.

Moreover, silver coated copper on the dendritic shape of the present embodiment, the BET specific surface area value is preferably 0.2m ² /g~3.0m ² / g, but is not particularly limited. When the BET specific surface area value is less than 0.2 m ² /g, the copper particles 1 coated with silver may not have the desired shape as described above, and high conductivity may not be obtained. On the other hand, when the BET specific surface area value exceeds 3.0 m ² /g, the silver coating on the surface of the dendritic silver-coated copper powder may become uneven, and high conductivity may not be obtained. In addition, the copper particles 1 constituting the silver-coated copper powder are too fine, and the silver-coated copper powder is in a state of being finer, and the conductivity is lowered. Further, the BET specific surface area can be measured in accordance with JIS Z8830:2013.

"3. Method for manufacturing silver-coated copper powder"

Next, a method of producing the dendritic silver-coated copper powder of the present embodiment will be described. Hereinafter, a method for producing a dendritic copper powder constituting a dendritic silver-coated copper powder will be described. Next, a method of obtaining dendritic silver-coated copper powder by coating silver with the dendritic copper powder will be described.

<3-1. Method for producing dendritic copper powder>

The dendritic copper powder before the coating of silver can be produced, for example, by using an acidic solution of sulfuric acid containing copper ions as an electrolytic solution by a specific electrolytic method.

In the electrolysis, for example, an electrolytic solution containing copper ions and containing a copper ion is placed in an electrolytic cell in which a metal copper is an anode and a stainless steel plate or a titanium plate is provided as a cathode, to a specific current. The density is passed through a direct current to the electrolyte, whereby electrolytic treatment is performed. Thereby, dendritic copper powder can be deposited (electrodeposited) onto the cathode with energization. In particular, in the present embodiment, the copper powder such as the granular material obtained by electrolysis can be mechanically deformed without using a medium such as a ball, and the flat copper particles 1 can be collectively formed by the electrolysis to form a branch. The dendritic copper powder precipitates to the surface of the cathode.

More specifically, as the electrolytic solution, for example, an additive such as a water-soluble copper salt, sulfuric acid or an amine compound, or a chloride ion can be used.

The water-soluble copper salt is a copper ion source to which copper ions are supplied, and examples thereof include copper sulfate such as copper sulfate pentahydrate, copper chloride, copper nitrate, and the like, but are not particularly limited. Further, the concentration of copper ions in the electrolytic solution may be about 1 g/L to 20 g/L, and preferably about 2 g/L to 10 g/L.

Sulfuric acid is used to make an acid electrolyte of sulfuric acid. About sulfuric acid in the electrolyte The concentration can be set to about 20 g/L to 300 g/L as the free sulfuric acid concentration, and preferably about 50 g/L to 200 g/L. The concentration of sulfuric acid has an influence on the conductivity of the electrolyte, and thus affects the uniformity of the copper powder obtained on the cathode.

As the additive, for example, an amine compound can be used. The amine compound and the chloride ions described below all contribute to the shape control of the precipitated copper powder, and the copper powder deposited on the surface of the cathode can be made into a flat plate having a dendritic shape and having a specific average thickness of the section. The copper particles constitute a dendritic copper powder having a trunk and a plurality of branches.

As the amine compound, for example, Safranin O (3,7-diamino-2,8-dimethyl-5-phenyl-5-chloromorph) can be used. 鎓, C ₂₀ H ₁₉ N ₄ Cl, CAS number: 477-73-64), and the like. In addition, as the amine compound, one type may be added alone or two or more types may be used in combination. In addition, the amount of the amine compound to be added is preferably such that the concentration in the electrolytic solution exceeds 50 mg/L and is in the range of 500 mg/L or less, and more preferably ranges from 100 mg/L to 400 mg/L. the amount.

The chloride ion can be contained by adding a compound (chloride ion source) to which chloride ions are supplied, such as hydrochloric acid or sodium chloride, to the electrolytic solution. Additives such as chloride ions and the above amine compounds contribute to the shape control of the precipitated copper powder. The concentration of the chloride ion in the electrolytic solution is not particularly limited, and may be about 1 mg/L to 1000 mg/L, and preferably about 10 mg/L to 500 mg/L.

In the method for producing the dendritic copper powder, for example, electrolysis is carried out using an electrolytic solution having a composition as described above, and copper powder is precipitated and produced on the cathode. As the electrolysis method, a known method can be used. For example, when the electrolysis is performed using an electrolyte having a sulfuric acid acidity as the current density, it is preferably in the range of 5 A/dm ² to 30 A/dm ² and is energized while stirring the electrolytic solution. Further, the liquid temperature (bath temperature) of the electrolytic solution can be, for example, about 20 ° C to 60 ° C.

<3-2. Silver coating method (manufacturing of silver-coated copper powder)>

The dendritic silver-coated copper powder of the present embodiment can be produced by, for example, using a reduced electroless plating method or a replacement electroless plating method on the surface of the dendritic copper powder produced by the above electrolysis method. Covered with silver.

In order to coat the surface of the dendritic copper powder with a uniform thickness, it is preferable to wash it before silver plating, and to disperse the dendritic copper powder in the cleaning liquid and wash it while stirring. The washing treatment is preferably carried out in an acidic solution, and more preferably a polycarboxylic acid which can be used as a reducing agent as described below. After washing, the dendritic copper powder was appropriately filtered, separated, and washed with water to prepare a water slurry in which dendritic copper powder was dispersed in water. Further, filtration, separation, and water washing may be carried out by using a known method.

Specifically, when silver plating is performed by a reduced electroless plating method, a reducing agent and a silver ion solution may be added to the water slurry obtained by washing the dendritic copper powder, and the branches are applied to the branches. The surface of the copper powder is covered with silver. Here, by adding a reducing agent to the water slurry and dispersing it in advance, a silver ion solution is continuously added to the water slurry containing the reducing agent and the dendritic copper powder, so that the surface of the dendritic copper powder can be more uniformly Covered with silver.

As the reducing agent, various reducing agents can be used, and a reducing agent which is incapable of reducing the dislocation ion of copper and having a weak reducing power is preferable. As the reducing agent having a weak reducing power, a reducing organic compound can be used, and for example, a carbohydrate, a polyvalent carboxylic acid, a salt thereof, an aldehyde or the like can be used. More specifically, glucose, lactic acid, oxalic acid, tartaric acid, malic acid, malonic acid, glycolic acid, sodium potassium tartrate, and fumarin can be mentioned.

Preferably, after adding a reducing agent to the water slurry containing the dendritic copper powder, in order to fully The reducing agent is dispersed and stirred or the like. Further, in order to adjust the water slurry to a desired pH value, an acid or a base may be appropriately added. Further, dispersion of the reducing organic compound as a reducing agent can be promoted by adding a water-soluble organic solvent such as an alcohol.

As the silver ion solution to be continuously added, a known one can be used as the silver plating solution, but among them, a silver nitrate solution is preferably used. Further, in the case where the silver nitrate solution is easily misaligned, it is more preferably added in the form of an ammoniacal silver nitrate solution. Further, the ammonia used in the ammoniacal silver nitrate solution may be any one of the following methods, including: adding to the silver nitrate solution; adding to the aqueous slurry together with the reducing agent and dispersing; as the silver nitrate The ammonia solution in which the solution is separated is simultaneously added to the water slurry; or a combination of the above.

The silver ion solution is preferably added at a relatively slow rate, for example, when added to a water slurry containing dendritic copper powder and a reducing agent, thereby forming a uniform thickness of silver on the surface of the dendritic copper powder. Membrane. Further, in order to increase the uniformity of the thickness of the film, it is more preferable to set the speed of the addition to be constant. Further, the reducing agent or the like previously added to the aqueous slurry may be adjusted by using another solution, and may be added in an additional form together with the silver ion solution.

In this manner, the aqueous slurry to which the silver ion solution or the like is added is filtered, separated, and washed with water, and then dried to obtain dendritic silver-coated copper powder. The processing means after the filtration is not particularly limited, and any known method can be used.

On the other hand, a method of performing silver coating by a substitution type electroless plating method utilizes a difference in ionization tendency between copper and silver, and causes electrons generated by dissolving copper in a solution to cause a solution in the solution. Silver ions are reduced and precipitated onto the copper surface. Therefore, the replacement electroless silver plating solution can be silver-plated as long as it is composed of a silver salt, a coupling agent, and a conductive salt as a silver ion source. However, in order to more uniformly perform silver coating, it is necessary to add an interface activity as needed. Agent, brightener, A crystal modifier, a pH adjuster, a precipitation inhibitor, a stabilizer, and the like. In the production of the silver-coated copper powder of the present embodiment, the plating solution is not particularly limited.

More specifically, as the silver salt, silver nitrate, silver iodide, silver sulfate, silver formate, silver acetate, silver lactate or the like can be used, and it can be reacted with dendritic copper powder dispersed in a water slurry. The silver ion concentration in the plating solution can be set to about 1 g/L to 10 g/L.

Further, the complexing agent is a complex compound with silver ions, and as a representative, citric acid, tartaric acid, ethylenediaminetetraacetic acid, nitrogen triacetic acid, or the like, or ethylenediamine, glycine, and acetylene can be used. An N-containing compound such as urea, pyrrolidone or butylimine, hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, mercaptopropionic acid, thioglycol, thiamine or the like. The concentration of the complexing agent in the plating solution can be set to about 10 g/L to 100 g/L.

Further, as the conductive salt, an inorganic acid such as nitric acid, boric acid or phosphoric acid, an organic acid such as citric acid, maleic acid, tartaric acid or phthalic acid, or a sodium, potassium or ammonium salt thereof may be used. The concentration of the conductive salt in the plating solution can be set to about 5 g/L to 50 g/L.

The control of the amount of coating when the surface of the dendritic copper powder is coated with silver can be controlled, for example, by changing the amount of silver input to the replacement electroless plating solution. Moreover, in order to improve the uniformity of the thickness of the film, it is preferable to set the speed of addition to be fixed.

Thus, the slurry after completion of the reaction can be filtered, separated, and washed with water, and then dried to obtain dendritic silver-coated copper powder. The processing means after the filtration is not particularly limited, and any known method can be used.

"4. Conductive paste, conductive paint for electromagnetic wave shielding, and use of conductive sheet"

As described above, the dendritic silver-coated copper powder of the present embodiment has a trunk and a plurality of dendritic silver-coated copper powders from the main branches, and is silver-coated as shown in the schematic view of Fig. 1 The flat copper particles are aggregated, and the silver-coated flat copper particles grow into a dendritic shape having a trunk 2 and a plurality of branches 3 from the trunk 2, and the average thickness of the cross section exceeds 1.0 μm and is 5.0 μm. the following. Further, the dendritic silver-coated copper powder has an average particle diameter (D50) of 1.0 μm to 100 μm. The dendritic silver-coated copper powder has a large surface area due to a dendritic shape, and is excellent in formability and sinterability, and is formed into a dendritic shape by a combination of flat copper particles having a specific average cross-sectional thickness. Multi-site ensures the number of joints and exerts excellent electrical conductivity.

Further, according to such a dendritic silver-coated copper powder having a specific structure, even when a copper paste or the like is formed, aggregation can be suppressed, and the resin can be uniformly dispersed in the resin, and the viscosity of the paste can be suppressed. The occurrence of poor printability caused by the rise or the like. Therefore, the dendritic silver-coated copper powder can be preferably used for applications such as conductive pastes and conductive coatings.

For example, the conductive paste (copper paste) is not limited to use under particularly limited conditions, and the dendritic silver-coated copper powder of the present embodiment can be used as a metal filler, and kneaded with a binder resin or a solvent. It is prepared by mixing with hardeners or additives such as antioxidants, coupling agents, and anti-corrosion agents.

Specifically, the binder resin is not particularly limited, and a prior user can be used. For example, an epoxy resin or a phenol resin, an unsaturated polyester resin, or the like can be used.

Further, as the solvent, an organic solvent such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, terpineol, ethyl carbitol, carbitol acetate, or butyl cellosolve may be used. . In addition, the amount of the organic solvent to be added is not particularly limited, and may be adjusted to the viscosity of the conductive film forming method such as screen printing or a dispenser, and the particle size of the dendritic silver-coated copper powder may be adjusted.

Further, in order to adjust the viscosity, other resin components may be added. For example, can be listed A cellulose-based resin typified by ethyl cellulose or the like can be added as an organic vehicle dissolved in an organic solvent such as terpineol. In addition, the amount of the resin component to be added needs to be suppressed so as not to inhibit the sinterability, and is preferably 5% by weight or less of the whole.

Moreover, as an additive, for example, in order to improve the electroconductivity after baking, an antioxidant etc. can be added. The antioxidant is not particularly limited, and examples thereof include a hydroxycarboxylic acid and the like. More specifically, a hydroxycarboxylic acid such as citric acid, malic acid, tartaric acid or lactic acid is preferred, and citric acid or malic acid having a high adsorption power to copper is particularly preferred. The amount of the antioxidant to be added is, for example, about 1% by weight to 15% by weight in consideration of the antioxidant effect, the viscosity of the paste, and the like.

Further, as the curing agent, 2-ethyl-4-methylimidazole or the like which has been used in the past can also be used. Further, as the corrosion inhibitor, benzothiazole, benzimidazole or the like which has been previously used may also be used.

Further, when the dendritic silver-coated copper powder of the present embodiment is used as a metal filler for a conductive paste, it is possible to mix copper powder or silver-coated copper powder of another shape, and further mix a conductive metal such as nickel or tin. Used as a filler. In this case, the ratio of the dendritic silver-coated copper powder in the total amount of the metal filler used as the conductive paste is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more. As described above, when used as a metal filler, a metal filler such as copper powder of another shape is mixed together with the dendritic silver-coated copper powder of the present embodiment, and the gap between the dendritic silver-coated copper powder is filled. Copper powder of other shapes, whereby the joint for ensuring electrical conductivity can be more ensured. Further, as a result, the total amount of the input of the dendritic silver-coated copper powder and the copper powder of other shapes can be reduced.

If the dendritic silver-coated copper powder in the total amount of the copper powder used as the metal filler is less than 20% by mass, the dendritic silver-coated copper powder is reduced in contact with each other even by means of copper with other shapes. The increase in the contact point achieved by the powder mixing also reduces the electrical conductivity as a metal filler.

Various circuits can be formed using the conductive paste made of the above metal filler. In this case, it is not limited to use under particularly limited conditions, and a circuit pattern forming method or the like which has been previously performed can be used. For example, a conductive paste prepared by using the metal filler is applied or printed on a fired substrate or an unfired substrate, and after heating, it is pressed, cured, and baked as necessary to form a printed wiring board or various electrons. The circuit of the part or the external electrode.

When the metal filler is used as the material for electromagnetic wave shielding, it is not limited to use under particularly limited conditions, and it can be used by, for example, mixing the metal filler with a resin by a usual method.

For example, when the above-mentioned metal filler is used as the conductive coating material for electromagnetic wave shielding, it can be mixed with a resin and a solvent by a usual method, for example, and an antioxidant, a tackifier, and a precipitation inhibitor as needed. It is mixed and kneaded to be used as a conductive paint.

The binder resin and the solvent used at this time are not particularly limited, and the prior user can be used. For example, as the binder resin, a vinyl chloride resin, a vinyl acetate resin, an acrylic resin, a polyester resin, a fluororesin, an anthracene resin, or a phenol resin can be used. Further, as the solvent, an alcohol such as isopropyl alcohol or an aromatic hydrocarbon such as toluene, an ester such as methyl acetate or a ketone such as methyl ethyl ketone may be used. Further, as the antioxidant, a fatty amide, a higher fatty acid amine, a phenylenediamine derivative, a titanate coupling agent or the like which has been used in the past may be used.

In the case of using the above-mentioned metal filler as the conductive sheet for electromagnetic wave shielding, the resin for forming the electromagnetic wave shielding layer for the conductive sheet for electromagnetic wave shielding is not particularly limited, and the prior art can be used. For example, a vinyl chloride resin, a vinyl acetate resin, a vinylidene chloride resin, an acrylic resin, a polyurethane resin, or the like may be suitably used. A thermoplastic resin, a thermosetting resin, a radiation curable resin, or the like which is composed of various polymers and copolymers such as a polyester resin, an olefin resin, a chlorinated olefin resin, a polyvinyl alcohol resin, an alkyd resin, and a phenol resin.

The method for producing the electromagnetic wave shielding material is not particularly limited, and can be produced, for example, by forming an electromagnetic wave shielding layer by coating or printing a coating material obtained by dispersing or dissolving a metal filler and a resin in a solvent on a substrate. Allow it to dry to the extent that the surface cures. Further, a metal filler containing the dendritic silver-coated copper powder of the present embodiment may be used in the conductive adhesive layer of the conductive sheet.

[Examples]

Hereinafter, the examples of the present invention will be specifically described together with the comparative examples, but the present invention is not limited to the following examples.

Evaluation Method

With respect to the silver-coated copper powder obtained in the following examples and comparative examples, the shape observation, the measurement of the average particle diameter, and the like were carried out by the following methods.

(observation of shape)

By scanning electron microscopy (manufactured by JEOL Ltd., model JSM-7100F), 20 fields of view were arbitrarily observed at a specific magnification, and the appearance of the copper powder contained in the field of view was observed.

(Measurement of average particle size)

The average particle diameter (D50) was measured using a laser diffraction-scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., HRA9320 X-100).

(measurement of aspect ratio)

The obtained silver-coated copper powder was embedded in an epoxy resin to prepare a measurement sample, and the sample was cut, polished, and observed by a scanning electron microscope to observe the cross section of the silver-coated copper powder. More specifically, 20 copper powders were observed, and the average thickness (sectional average thickness) of the copper powder was determined, and the average thickness of the cross-section and the average particle obtained by the laser diffraction-scattering particle size analyzer were determined. The aspect ratio (d50) is obtained by the ratio of the diameter (D50).

(BET specific surface area)

The BET specific surface area was measured using a specific surface area-pore distribution measuring apparatus (manufactured by Quantachrome, QUADRASORB SI).

(measured by specific resistance value)

The specific resistance value of the film was determined by measuring the sheet resistance value by a four-terminal method using a low-resistivity meter (Loresta-GP MCP-T600, manufactured by Mitsubishi Chemical Corporation), and measuring the surface roughness. The film thickness (manufactured by Tokyo Precision Co., Ltd., SURFCO M130A) was measured, and the sheet resistance was divided by the film thickness.

(Electromagnetic wave shielding characteristics)

The evaluation of the electromagnetic wave shielding characteristics was evaluated by measuring the attenuation rate of the electromagnetic wave having a frequency of 1 GHz using the sample obtained in each of the examples and the comparative examples. Specifically, the grade in the case of Comparative Example 4 in which the dendritic silver-coated copper powder was not used was evaluated as "△", and the case where the grade was inferior to the level of Comparative Example 4 was evaluated as "X", which would be compared with the comparative example. The case where the level of 4 is good is evaluated as "○", and the case of being excellent is evaluated as "◎".

Moreover, in order to evaluate the flexibility of the electromagnetic wave shield, the electromagnetic wave shield thus produced was bent to confirm whether or not the electromagnetic wave shielding characteristics were changed.

"Examples, Comparative Examples"

[Example 1]

<Manufacture of dendritic copper powder>

In an electrolytic cell having a capacity of 100 L, an electrode plate made of titanium having an electrode area of 200 mm × 200 mm was used as a cathode, and an electrode plate made of copper having an electrode area of 200 mm × 200 mm was used as an anode, and an electrolytic solution was charged into the electrolytic cell. A copper current (dendritic copper powder) is deposited on the cathode plate by applying a direct current thereto.

At this time, as the electrolytic solution, a composition having a copper ion concentration of 5 g/L and a sulfuric acid concentration of 150 g/L was used. In addition, as the additive, Safranin O (manufactured by Kanto Chemical Co., Ltd.) is added as an additive in a concentration of 100 mg/L in the electrolytic solution, and further, chloride ions (chloride ions) in the electrolyte solution are added. A hydrochloric acid solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added in such a manner that the concentration meter became 10 mg/L. Then, the copper powder was discharged to the cathode plate under the following conditions such that the current density of the cathode was 25 A/dm ² , which was a condition that the concentration of the electrolyte was adjusted to 15 L/min using a pump as described above. The flow was cycled and the temperature was maintained at 25 °C. The electrolytic copper powder deposited on the cathode plate is mechanically scraped off to the bottom of the electrolytic cell by a scraper, and the recovered copper powder is washed with pure water, and then placed in a vacuum dryer for drying. .

The shape of the copper powder obtained in this manner is observed by the scanning electron microscope (SEM) method described above, and as a result, at least 90% or more of the copper powder in the precipitated copper powder is a collection of copper particles as follows. The dendritic copper powder having a two-dimensional or three-dimensional dendritic shape, the copper particles having a trunk that grows linearly, a plurality of branches that are linearly branched from the stem, and a branch that branches further from the branch. Further, the copper powder is in the form of a flat plate composed of a laminated structure in which one layer or a plurality of layers are stacked.

<Manufacture of dendritic silver-coated copper powder by reduction method>

Next, silver-coated copper powder was produced using the dendritic copper powder produced by the above method.

Namely, 100 g of the obtained dendritic copper powder was stirred in a 3% aqueous solution of tartaric acid for about 1 hour, and then filtered, washed with water, and dispersed in 2 liters of ion-exchanged water. 5 g of tartaric acid, 5 g of glucose, 50 ml of ethanol, and 50 ml of 28% aqueous ammonia were added thereto, and the mixture was stirred. Thereafter, 60 g of silver nitrate was dissolved in an aqueous solution obtained by dissolving 60 g of silver nitrate in 4 liters of ion-exchanged water, and 25 g of glucose and 25 g of tartaric acid were added. 250 ml of ethanol was dissolved in 750 ml of ion-exchanged water and 250 ml of 28% ammonia water. Furthermore, the bath temperature at this time was 25 °C.

After the completion of the addition of each aqueous solution, the powder was filtered, washed with water, and ethanol was passed through and dried. As a result, the surface of the dendritic copper powder was coated with silver-like dendritic silver-coated copper powder. Further, the dendritic silver-coated copper powder has a flat shape composed of a laminated structure in which one layer or a plurality of layers are stacked. The dendritic silver-coated copper powder was collected, and the amount of the silver coating was measured. As a result, the mass of the silver-coated copper-coated copper powder was 100% by mass of 26.2% by mass. Further, the dendritic silver-coated copper powder obtained by observation of the SEM at a magnification of 5,000 times was found to be a dendritic silver-coated copper powder which was uniformly coated with silver on the surface of the dendritic copper powder before the coating of silver. , in the shape of a two-dimensional or three-dimensional dendritic shape, and having a dendritic shape having a trunk, a plurality of branches from the trunk branch, and further branches from the branch. Further, at least 90% or more of the obtained silver-coated copper powder is a dendritic silver-coated copper powder having the above shape.

Further, the main particles and the copper particles constituting the dendritic silver-coated copper powder have a flat plate shape having an average thickness of 3.4 μm, and the average particle diameter (D50) of the dendritic silver-coated copper powder is 58.9 μm. Further, the aspect ratio (sectional average thickness/average particle diameter) calculated from the average thickness of the cross section of the copper particles constituting the dendritic silver-coated copper powder and the average particle diameter of the dendritic silver-coated copper powder was 0.006. Further, the obtained copper powder had a bulk density of 3.0 g/cm ³ . Further, the BET specific surface area was 1.1 m ² /g.

<Conductive gelatinization>

Next, the dendritic silver-coated copper powder produced by the above method was pasted to prepare a conductive paste.

In other words, 20 g of a phenol resin (PL-2211, manufactured by Kyoei Chemical Co., Ltd.) and 10 g of butyl cellulose (manufactured by Kanto Chemical Co., Ltd., Rotters grade) were mixed with 40 g of the obtained dendritic silver-coated copper powder. A small kneading machine (manufactured by Nippon Seiki Co., Ltd., non-foaming kneader NBK-1) was repeatedly kneaded by repeating four times of 1500 rpm and three minutes of kneading. When gelatinizing, the copper powder does not aggregate and is uniformly dispersed in the resin. The obtained conductive paste was printed on glass using a metal squeegee and hardened in an atmospheric environment at 150 ° C and 200 ° C for 30 minutes.

The specific resistance values of the film obtained by hardening were measured, and the results were 16 × 10 ^-6 Ω, respectively. Cm (hardening temperature is 150 ° C), 2.3 × 10 ^-6 Ω. Cm (hardening temperature is 200 ° C), and it is understood that excellent electrical conductivity is exhibited.

[Embodiment 2]

<Manufacture of dendritic copper powder>

As the electrolyte solution, a composition having a copper ion concentration of 7 g/L and a sulfuric acid concentration of 150 g/L is used, and the electrolyte is added as an additive of Safranin O in such a manner that the concentration in the electrolytic solution is 150 mg/L. The hydrochloric acid solution was added so as to be 25 mg/L in terms of the chloride ion concentration in the electrolytic solution. Then, the copper powder was deposited on the cathode plate under the following conditions such that the current density of the cathode was 20 A/dm ² , which was a condition that the concentration of the electrolyte was adjusted to 15 L/min using a pump as described above. The flow was cycled and the temperature was maintained at 25 °C. The electrolytic copper powder deposited on the cathode plate is mechanically scraped off to the bottom of the electrolytic cell by a scraper, and the recovered copper powder is washed with pure water, and then placed in a vacuum dryer for drying. .

<Production of dendritic silver-coated copper powder by replacement method>

100 g of the obtained dendritic copper powder was subjected to silver coating on the surface of the copper powder by a substitution type electroless plating solution.

As a replacement type electroless plating solution, a solution in which 20 g of silver nitrate, 20 g of citric acid, and 10 g of ethylenediamine were dissolved in 1 liter of ion-exchanged water was used, and 100 g of dendritic copper powder was placed in the solution, and the mixture was stirred for 60 minutes. Its reaction. The bath temperature at this time was 25 °C.

After the completion of the reaction, the powder was filtered, washed with water, and ethanol was passed through and dried. As a result, the surface of the dendritic copper powder was coated with silver-like dendritic silver-coated copper powder. Further, the dendritic silver-coated copper powder has a flat shape composed of a laminated structure in which one layer or a plurality of layers are stacked. The dendritic silver-coated copper powder was collected, and the amount of silver coating was measured. As a result, the mass of the silver-coated copper-coated copper powder covered with silver was 100% by weight of 10.6% by mass. Moreover, the dendritic silver-coated copper powder obtained by observing the SEM at a magnification of 5,000 times can be realized as a dendritic silver-coated copper in which the surface of the dendritic copper powder before the silver coating is uniformly coated with silver. The powder, and the silver-coated copper powder is a two-dimensional or three-dimensional dendritic shape having a trunk, a plurality of branches from the trunk branch, and further branches from the branch. Further, at least 90% or more of the obtained silver-coated copper powder is a dendritic silver-coated copper powder having the above shape.

Further, the main particles and the branched copper particles constituting the dendritic silver-coated copper powder have a flat plate shape having an average thickness of 1.2 μm, and have fine convex portions on the surface thereof. Further, the dendritic silver-coated copper powder had an average particle diameter (D50) of 44.6 μm. Further, the aspect ratio (sectional average thickness / average particle diameter) calculated from the average thickness of the cross section of the copper particles and the average particle diameter of the dendritic copper powder was 0.03. Further, the obtained copper powder had a bulk density of 1.6 g/cm ³ . Further, the BET specific surface area was 1.7 m ² /g.

<Electrically conductive gelatinization>

Next, the dendritic silver-coated copper powder produced by the above method was pasted to prepare a conductive paste.

In other words, 20 g of a phenol resin (PL-2211, manufactured by Kyoei Chemical Co., Ltd.) and 10 g of butyl cellulose (manufactured by Kanto Chemical Co., Ltd., Rotters grade) were mixed with 40 g of the obtained dendritic silver-coated copper powder. A small kneading machine (manufactured by Nippon Seiki Co., Ltd., non-foaming kneader NBK-1) was repeatedly kneaded by performing 1500 rpm and 3 minutes of kneading four times. When gelatinizing, the copper powder does not aggregate and is uniformly dispersed in the resin. The obtained conductive paste was printed on glass using a metal squeegee and hardened in an atmospheric environment at 150 ° C and 200 ° C for 30 minutes.

The specific resistance of the film obtained by hardening was measured, and the results were 28×10 ^-6 Ω, respectively. Cm (hardening temperature is 150 ° C), 3.9 × 10 ^-6 Ω. Cm (hardening temperature is 200 ° C), and it is understood that excellent electrical conductivity is exhibited.

[Example 3]

The dendritic silver-coated copper powder prepared in Example 1 was dispersed in a resin to prepare an electromagnetic wave shielding material. Further, the conditions for producing the dendritic copper powder of the dendritic silver-coated copper powder and the conditions for producing the dendritic silver-coated copper powder by coating the dendritic copper powder with silver are the same as in the first embodiment, and silver is used. The dendritic silver-coated copper powder having a coating amount of 26.2% by mass based on 100% by mass of the silver-coated silver-coated copper powder as a whole.

100 g of a vinyl chloride resin and 200 g of methyl ethyl ketone were mixed with 40 g of the dendritic silver-coated copper powder, and the gelatinization was carried out by kneading four times at 1500 rpm for three minutes using a small kneader. When gelatinizing, the copper powder does not aggregate and is uniformly dispersed in the resin. This was applied to a substrate made of a transparent polyethylene terephthalate sheet having a thickness of 100 μm using a Meyer bar and dried to form an electromagnetic wave shielding layer having a thickness of 25 μm.

The characteristics of electromagnetic wave shielding were evaluated by measuring the attenuation rate using an electromagnetic wave having a frequency of 1 GHz. The results are shown in Table 1.

[Comparative Example 1]

Copper powder was deposited on the cathode plate in the same manner as in Example 1 except that the conditions of adding Safranin O and the chloride ion as additives were not added to the electrolytic solution. Thereafter, silver powder was obtained by coating silver on the surface of the copper powder in the same manner as in Example 1 to obtain a copper-coated copper powder. The silver coating amount of the silver-coated copper powder was 26.1% by mass based on 100% of the mass of the silver-coated silver-coated copper powder.

In Fig. 7, the results of the shape of the silver-coated copper powder obtained by observation of the SEM at a magnification of 5,000 times are shown. As shown in the photograph of Fig. 7, the shape of the silver-coated copper powder obtained is a dendritic shape in which the particles of copper are collected, and the surface of the copper powder is covered with silver. The average particle diameter (D50) of the copper powder was 45.3 μm. Further, no minute convex portions are formed in the dendrites.

40 g of a silver-coated copper powder prepared by the above method, 20 g of a phenol resin (PL-2211, manufactured by Kyoei Chemical Co., Ltd.), and 10 g of butyl cellulose (manufactured by Kanto Chemical Co., Ltd., Rote grade) were used. A small kneading machine (manufactured by Nippon Seiki Co., Ltd., non-foaming kneader NBK-1) was repeatedly kneaded by repeating four times of 1500 rpm and three minutes of kneading. When gelatinizing, the viscosity rises every time it is re-mixed. The reason for this is considered to be that a part of the copper powder is agglomerated, so that it is difficult to uniformly disperse. The obtained conductive paste was printed on glass using a metal squeegee and hardened in an atmospheric environment at 150 ° C and 200 ° C for 30 minutes.

The specific resistance values of the film obtained by hardening were measured, and the results were 670 × 10 ^-6 Ω, respectively. Cm (hardening temperature is 150 ° C), 310 × 10 ^-6 Ω. Cm (hardening temperature: 200 ° C), compared with the conductive paste obtained in the examples, the specific resistance value was high and the conductivity was poor.

[Comparative Example 2]

<Manufacture of dendritic copper powder>

As the electrolytic solution, a composition having a copper ion concentration of 10 g/L and a sulfuric acid concentration of 150 g/L was used. In addition, as the additive, Safranin O (manufactured by Kanto Chemical Industry Co., Ltd.) is added as the additive so as to be 50 mg/L in terms of the concentration in the electrolytic solution, and further, chloride ions (chloride ions) in the electrolyte solution are added. A hydrochloric acid solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added in such a manner that the concentration meter became 10 mg/L. Next, the electrolytic solution adjusted to the concentration as described above was circulated at a flow rate of 15 L/min using a metering pump, and the temperature was maintained at 45 ° C, and the current density of the cathode was 20 A/dm ² to conduct the copper powder. To the cathode plate.

In Fig. 8, the results of the shape of the silver-coated copper powder obtained by observation of the SEM at a magnification of 5,000 times are shown. As shown in the photograph of Fig. 8, the shape of the obtained electrolytic copper powder is a dendritic copper powder obtained by collecting granular copper particles. However, the dendritic trunk and the branching arc are not in the form of a flat layer composed of a laminated structure in which one layer or a plurality of layers are stacked as in the copper powder obtained in the examples.

<Manufacture of dendritic silver-coated copper powder by reduction method>

Next, silver-coated copper powder was produced in the same manner as in Example 1 using the obtained dendritic copper powder.

The amount of silver coating was measured by recovering the obtained dendritic silver-coated copper powder, and as a result, the mass of the silver-coated copper-coated copper powder covered with silver was 100% by mass of 26.5% by mass. Further, the dendritic silver-coated copper powder obtained by observation of the field of view at a magnification of 5,000 times by SEM was used as the branch before the silver coating. The surface of the copper powder is uniformly coated with a two-dimensional or three-dimensional dendritic shape of silver, and is not a flat plate composed of a laminated structure of one layer or a plurality of layers as a silver-coated copper powder obtained in the embodiment. .

<Electrically conductive gelatinization>

Next, the dendritic silver-coated copper powder produced by the above method was pasted to prepare a conductive paste.

In other words, 20 g of a phenol resin (PL-2211, manufactured by Kyoei Chemical Co., Ltd.) and 10 g of butyl cellulose (manufactured by Kanto Chemical Co., Ltd., Rotters grade) were mixed with 40 g of the obtained dendritic silver-coated copper powder. A small kneading machine (manufactured by Nippon Seiki Co., Ltd., non-foaming kneader NBK-1) was repeatedly kneaded by repeating four times of 1500 rpm and three minutes of kneading. When gelatinizing, the copper powder does not aggregate and is uniformly dispersed in the resin. The obtained conductive paste was printed on glass using a metal squeegee and hardened in an atmospheric environment at 150 ° C and 200 ° C for 30 minutes.

The specific resistance values of the film obtained by hardening were 530×10 ^-6 Ω, respectively. Cm (hardening temperature is 150 ° C), 360 × 10 ^-6 Ω. Cm (hardening temperature is 200 ° C).

[Comparative Example 3]

The characteristics of the conductive paste formed of silver-coated copper powder obtained by coating silver with a known flat copper powder were evaluated and compared with the conductive paste produced by using the dendritic silver-coated copper powder of the example.

The flat copper powder is produced by mechanically flattening the granular electrolytic copper powder. Specifically, 5 g of stearic acid was added to 500 g of granular atomized copper powder (manufactured by Makin Metal Powders Co., Ltd.) having an average particle diameter of 7.9 μm, and flattened by a ball mill. 5 kg of 3 mm zirconia beads were placed in a ball mill, and rotated at a rotation speed of 500 rpm for 60 minutes to carry out a flattening treatment.

The obtained flat copper powder was coated by the same method as in Example 1. silver. The silver coating amount of the flat silver-coated copper powder produced was 26.4% by mass based on 100% of the mass of the silver-coated silver-coated copper powder. The plate-shaped silver-coated copper powder prepared in this manner was measured by a laser diffraction-scattering particle size analyzer, and as a result, the average particle diameter (D50) was 24.1 μm, and observed by SEM, the thickness was 0.6 μm, and the surface was smooth. And no tiny convex portions were formed. Further, the aspect ratio (sectional average thickness/average particle diameter) calculated from the average thickness of the cross section and the average particle diameter was 0.02.

Next, 20 g of a phenol resin (PL-2211, manufactured by Kyoei Chemical Co., Ltd.) and 10 g of butyl cellulite (manufactured by Kanto Chemical Co., Ltd., Route grade) were mixed with 40 g of the plate-shaped silver-coated copper powder obtained. Using a small kneading machine (manufactured by Nippon Seiki Co., Ltd., non-foaming kneader NBK-1), the mixing was carried out four times at 1500 rpm for three minutes to carry out gelatinization. When gelatinizing, the copper powder does not aggregate and is uniformly dispersed in the resin. The obtained conductive paste was printed on glass using a metal squeegee and hardened in an atmospheric environment at 150 ° C and 200 ° C for 30 minutes.

The specific resistance values of the film obtained by hardening were measured, and the results were respectively 59 × 10 ^-6 Ω. Cm (hardening temperature is 150 ° C), 10 × 10 ^-6 Ω. The cm (hardening temperature was 200 ° C) was higher than the copper paste obtained in Examples 1 and 2, and the electrical conductivity was inferior.

[Comparative Example 4]

The silver-coated copper powder obtained by flattening the granular copper powder prepared by flattening the granular electrolytic copper powder in the same manner as the user of the comparative example 3 was prepared, and the silver-coated copper powder was evaluated. The characteristics of the electromagnetic wave shield were compared with the electromagnetic wave shield produced by using the dendritic silver-coated copper powder of the example to study the effect of the dendritic shape. Further, the flat silver-coated copper powder used was coated with silver by the same method as in the first embodiment. Silver coating of flat silver-coated copper powder produced The amount of the silver-coated copper powder coated with silver was 100% by mass of 26.1% by mass.

100 g of a vinyl chloride resin and 200 g of methyl ethyl ketone were mixed with 40 g of the flat silver-coated copper powder, and the gelatinization was carried out by kneading four times at 1500 rpm for three minutes using a small kneader. When gelatinizing, the copper powder does not aggregate and is uniformly dispersed in the resin. This was applied to a substrate made of a transparent polyethylene terephthalate sheet having a thickness of 100 μm using a Meyer rod and dried to form an electromagnetic wave shielding layer having a thickness of 25 μm.

The characteristics of electromagnetic wave shielding were evaluated by measuring the attenuation rate using an electromagnetic wave having a frequency of 1 GHz. The results are shown in Table 1.

1‧‧‧ copper particles

2‧‧‧ (copper particles) trunk

3, 3a, 3b‧‧‧ (copper particles) branches

Claims (6)

A silver-coated copper powder comprising a collection of dendritic copper particles and having a surface coated with silver, the dendritic copper particles having a linear growth trunk and a plurality of branches from the trunk branch The silver-coated copper powder is characterized in that the copper particles have a cross-sectional average thickness of more than 1.0 μm and a thickness of 5.0 μm or less, and are in the form of a flat plate; and the silver-coated copper powder is a laminated structure composed of one layer or a plurality of layers. a flat plate shape and an average particle diameter (D50) of 1.0μm ~ 100μm; bulk density 0.5g / cm ³ ~ 5.0g / cm ³ of the range; a BET specific surface area is 0.2m ² /g~3.0m ² / g; The amount of the silver coating is 100% by mass to 50% by mass based on 100% of the mass of the silver-coated copper powder coated with silver. The silver-coated copper powder according to claim 1, wherein the ratio of the average thickness of the copper-coated copper particles divided by the average particle diameter (D50) of the silver-coated copper powder is more than 0.01 and is 5.0. The following range. A metal filler comprising the silver-coated copper powder of claim 1 or 2 in a ratio of 20% by mass or more of the whole. A conductive paste obtained by mixing a metal filler of the third application of the patent application with a resin. A conductive coating for electromagnetic wave shielding, which is obtained by using a metal filler of the third item of the patent application. A conductive sheet for electromagnetic wave shielding, which is obtained by using a metal filler of the third item of the patent application.