JP2017066444A - Ni-COATED COPPER POWDER, AND CONDUCTIVE PASTE, CONDUCTIVE PAINT AND CONDUCTIVE SHEET USING THE SAME, AND METHOD FOR PRODUCING Ni-COATED COPPER POWDER - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dendritic Ni-coated copper powder capable of preventing agglomeration, thereby being suitably used for conductive pastes, electromagnetic shields or the like, while increasing the number of contact points when Ni- or Ni alloy-coated dendritic copper powders contact with one another to ensure excellent conductivity.SOLUTION: An Ni-coated copper powder according to the present invention is formed by agglomerating copper particles 1 having: a trunk 2 dendritically grown; and a plurality of branches 3 diverged from the trunk 2, wherein the copper powder has a surface coated with Ni or Ni alloy. The trunk 2 and the branches 3 of the copper particles 1 are in a plate shape having an average cross-sectional thickness of 0.02 to 0.5 μm. An average particle diameter (D50) of the Ni-coated copper powder is 1.0 to 30 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a copper powder (nickel-coated copper powder) coated with nickel (Ni) or Ni alloy on the surface, and more specifically, to improve conductivity by using it as a material such as a conductive paste. The present invention relates to a new dendritic nickel-coated copper powder.

  For the formation of wiring layers and electrodes in electronic devices, pastes and paints using metal fillers such as copper powder and silver powder, such as resin pastes, fired pastes, and electromagnetic wave shielding paints, are often used. Metal filler pastes such as copper powder and silver powder are applied or printed on various base materials, and are subjected to heat curing or heat baking treatment to form a conductive film to be a wiring layer or an electrode.

  For example, a resin-type conductive paste is made of a metal filler, a resin, a curing agent, a solvent, etc., printed on a conductor circuit pattern or terminal, and cured by heating at 100 ° C. to 200 ° C. An electrode is formed. In the resin-type conductive paste, since the thermosetting resin is cured and contracted by heat, when the metal filler is pressed and brought into contact, the metal filler overlaps and an electrically connected current path is formed. Since this resin-type conductive paste is processed at a curing temperature of 200 ° C. or less, it is used for a substrate using a heat-sensitive material such as a printed wiring board.

  Firing-type conductive paste is made of a metal filler, glass, solvent, etc., printed on a conductor circuit pattern or terminal, and heated and fired at 600 ° C. to 800 ° C. to form wiring and electrodes as a conductive film. To do. The fired conductive paste is processed at a high temperature to sinter the metal filler and ensure conductivity. Although this firing-type conductive paste has a high firing temperature, it cannot be used for printed wiring boards that use resin materials, but it can realize low resistance because the metal filler is sintered by high-temperature treatment. Become. Therefore, the fired conductive paste is used for an external electrode of a multilayer ceramic capacitor.

  On the other hand, electromagnetic wave shields are used to prevent the generation of electromagnetic noise from electronic equipment. Especially in recent years, personal computers and mobile phone cases have been made of resin, so that the case is made conductive. In order to secure the properties, there are a method of forming a thin metal film by a vapor deposition method or a sputtering method, a method of applying a conductive paint, a method of attaching a conductive sheet to a necessary place and shielding an electromagnetic wave, etc. Proposed. Among them, special methods are required in the processing process for the method of applying the metal filler dispersed in the resin and the method of dispersing the metal filler in the resin and processing it into a sheet and attaching it to the housing. It has excellent flexibility and is widely used.

  However, in the case where such a metal filler is dispersed in a resin and applied or processed into a sheet shape, the dispersion state of the metal filler in the resin is not uniform. A method such as increasing the filling rate of the metal filler is required. However, in such a case, the addition of a large amount of metal filler causes problems such as an increase in sheet weight and a loss of flexibility of the resin sheet. Therefore, for example, in Patent Document 1, a method of using a flat metal filler has been proposed in order to solve these problems, and as a result, a thin sheet having excellent electromagnetic shielding effect and good flexibility. Can be formed.

Copper powder as a metal powder material used as a metal filler for such conductive paste and electromagnetic wave shielding material is covered with copper oxide when oxidized, causing adverse effects on sinterability, corrosion resistance, or conductivity Become. For this reason, in order to prevent oxidation of the copper powder, the surface of the copper particles is coated with a noble metal such as Pt, Pd, Ag, Au, etc., coated with a SiO ₂ oxide, or coated with Ni. Those with improved oxidation resistance are known. For example, Patent Document 2 discloses a nickel-coated copper powder having a copper powder surface coated with nickel (Ni).

  On the other hand, the shape of the copper powder used as the metal filler is spherical, flat, dendritic, etc., and in particular, the flat copper powder is a contact point between fillers compared to granular or dendritic copper powder. Since a large area can be secured, it is widely used as a low-resistance conductive paste. As a method for producing such a flat copper powder, Patent Document 3 discloses a method of obtaining a flaky copper powder by mechanically processing a spherical copper powder into a flat shape. Specifically, a spherical copper powder having an average particle size of 0.5 μm to 10 μm is used as a raw material, and is processed into a flat plate shape by a mechanical energy of a medium loaded in the mill using a ball mill or a vibration mill. is there.

  Further, for example, Patent Document 4 discloses a technique relating to a copper powder for conductive paste, more specifically, a disk-shaped copper powder that provides high performance as a copper paste for through holes and external electrodes, and a method for manufacturing the same. Specifically, the granular atomized copper powder is put into a medium stirring mill, a steel ball having a diameter of 1/8 inch to 1/4 inch is used as a grinding medium, and the fatty acid is added to the copper powder by 0.5 by weight. % To 1%, and processed into a flat plate shape by pulverization in air or in an inert atmosphere.

Here, silver powder is used as the metal filler used for these conductive pastes and electromagnetic wave shields, and as described above, the surface of the copper particles is coated with a noble metal such as Pt, Pd, Ag, or Au. Thus, those having sufficient oxidation resistance are used. However, since these are expensive, the cost increases. Among them, a copper powder coated with Ag can be kept at a relatively low price, but there is a problem that migration tends to occur with Ag. Also, when the surface of the copper powder is coated with a SiO ₂ -based oxide, oxidation resistance can be secured, but there are problems such as poor sinterability.

  A method for coating copper powder with nickel is mentioned as a low cost and relatively good sinterability while ensuring oxidation resistance and the like.

  As a method for coating the surface of the copper powder with nickel, a method by electroless nickel plating may be mentioned. The coating method by electroless nickel plating is to perform nickel coating on the copper powder surface by reducing nickel ions in the plating solution with a reducing agent. The types of reducing agents are hypophosphites and borohydrides. And hydrazine compounds. Specifically, in nickel coating treatment using hypophosphite as a reducing agent, a Ni—P alloy coating is formed because phosphorus is contained in the coating during the reduction reaction. Further, in the nickel coating treatment using a borohydride compound as the reducing agent, since the boron is contained in the coating during the reduction reaction, a Ni-B alloy coating is formed. Further, in the nickel coating process using a hydrazine compound as a reducing agent, a high-purity Ni coating with few impurities is formed.

  As the copper powder, electrolytic copper powder deposited in a dendritic shape called a dendritic shape is known. Since the shape is a dendritic shape, it is characterized by a large surface area. Due to the dendritic shape as described above, when this is used for a conductive film or the like, the dendritic branches are overlapped with each other, conduction is easy, and the number of contact points between particles is larger than that of spherical particles. Therefore, there is an advantage that the amount of conductive filler such as conductive paste can be reduced. For example, Patent Document 5 discloses a technique for ensuring oxidation resistance by forming an Ni alloy layer on a copper surface and performing Ag coating thereon, and the copper powder used here is a dendritic electrolytic copper powder. Is preferable from the viewpoint of entanglement between particles.

  On the other hand, when developing a branch of electrolytic copper powder, when used in conductive paste, etc., the electrolytic copper powder is entangled more than necessary and agglomeration occurs, so that it does not disperse uniformly in the resin, and the fluidity is It is pointed out in Patent Document 6 that it decreases and becomes very difficult to handle, causing problems in wiring formation by printing or the like and reducing productivity. In addition, in patent document 6, in order to raise the intensity | strength of electrolytic copper powder itself, the intensity | strength of electrolytic copper powder itself is improved by adding tungstate in the copper sulfate aqueous solution of the electrolyte solution for depositing electrolytic copper powder. It is said that it is difficult to break the branches and can be molded with high strength.

  As described above, it is not easy to use dendritic copper powder as a metal filler such as a conductive paste, and it has been a cause of difficulty in improving the conductivity of the paste.

  In order to ensure conductivity, a dendritic shape having a three-dimensional shape is easier to secure a contact than a granular one, and high conductivity can be expected as a conductive paste or electromagnetic wave shield. . However, the conventional nickel-coated copper powder having a dendrite-like shape is a dendrite characterized by a long branch branched from the main shaft, and has a long and narrow branch-like shape. The structure is simple, and it is not an ideal shape for effectively securing a contact using less nickel-coated copper powder.

JP 2003-258490 A JP-A-5-342908 Japanese Patent Laid-Open No. 2005-200734 JP 2002-15622 A JP 2002-075057 A JP 2011-58027 A

  The present invention has been proposed in view of such circumstances, and prevents aggregation while increasing the number of contacts when the dendritic copper powders coated with nickel are in contact with each other to ensure excellent conductivity. An object of the present invention is to provide a dendritic nickel-coated copper powder that can be suitably used for applications such as conductive pastes and electromagnetic wave shields.

  This inventor repeated earnest examination for solving the subject mentioned above. As a result, flat copper particles having a shape having a main trunk that grows in a dendritic shape and a plurality of branches separated from the main trunk, and whose cross-sectional average thickness is in a specific range, are gathered on the surface. Ni coated copper powder coated with Ni or Ni alloy, and the average particle diameter of the Ni coated copper powder is within a specific range (D50), thereby preventing aggregation while ensuring excellent conductivity Thus, the present invention has been completed by finding out that it can be suitably used for applications such as conductive paste and electromagnetic wave shielding. That is, the present invention provides the following.

  (1) In the first invention of the present invention, copper particles having a shape having a main trunk grown in a dendritic shape and a plurality of branches separated from the main trunk are aggregated, and the surface is coated with Ni or a Ni alloy. It is Ni coat copper powder, Comprising: The cross-sectional average thickness of the main trunk and branch of the said copper particle is 0.02 micrometer-0.5 micrometer flat shape, and the average particle diameter (D50) of the said Ni coat copper powder is 1.0 micrometer. A dendritic Ni-coated copper powder characterized by having a thickness of ˜30 μm.

  (2) According to a second aspect of the present invention, in the first aspect, there are fine convex portions on the surface of the copper particles, and the average height of the convex portions is 0.01 μm to 0.4 μm. Ni-coated copper powder.

  (3) According to a third aspect of the present invention, in the first or second aspect, the content of Ni coated as Ni or Ni alloy is 100% by mass of the entire dendritic Ni-coated copper powder. The dendritic Ni-coated copper powder is 1% by mass to 50% by mass.

  (4) According to a fourth aspect of the present invention, in any one of the first to third aspects, the surface of the copper particles is coated with a Ni alloy, and cobalt, zinc, tungsten, molybdenum, palladium, platinum, Coated with a Ni alloy containing at least one selected from the group consisting of tin, phosphorus, and boron at a content of 0.1% by mass to 20% by mass with respect to 100% by mass of the Ni alloy. Dendritic Ni-coated copper powder.

(5) Fifth invention of the present invention, in any one of the first to fourth, the bulk density is in the range of ^{0.5g / cm 3 ~5.0g / cm 3} , dendritic Ni coated copper It is powder.

(6) Sixth aspect of the present invention, in any one of the first to 5, BET specific surface area of 0.2m ² /g~5.0m ² / g, dendritic Ni-coated copper powder It is.

  (7) The seventh invention of the present invention is characterized by containing the dendritic Ni-coated copper powder according to any one of the first to sixth inventions in a proportion of 20% by mass or more of the whole. It is a metal filler.

  (8) The eighth invention of the present invention is a conductive paste characterized by mixing a metal filler according to the seventh invention with a resin.

  (9) A ninth invention of the present invention is a conductive paint for electromagnetic wave shielding, characterized by using the metal filler according to the seventh invention.

  (10) A tenth invention of the present invention is an electromagnetic wave shielding conductive sheet characterized by using the metal filler according to the seventh invention.

(11) An eleventh aspect of the present invention is a method for producing a Ni-coated copper powder according to any one of the first to sixth aspects, wherein the copper powder is deposited on the cathode from the electrolytic solution by an electrolytic method. And a step of coating the copper powder with nickel (Ni) or a Ni alloy, and the electrolytic solution includes a copper ion and a phenazine structure and an azobenzene structure represented by the following formula (1): It is a manufacturing method of Ni coat | court copper powder characterized by performing electrolysis by containing 1 type, or 2 or more types selected from the compound which has.
[In the formula (1), R ₁ , R ₂ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ are each independently hydrogen, Selected from the group consisting of halogen, amino, OH, ═O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, and C1-C8 alkyl It is a group. R ₃ is hydrogen, halogen, amino, OH, ═O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, lower alkyl, And a group selected from the group consisting of aryl. A ⁻ is a halide anion. ]

  According to the Ni-coated copper powder according to the present invention, it is possible to sufficiently ensure a contact point when the copper powders are in contact with each other while ensuring excellent conductivity, and to prevent agglomeration and uniformly with the resin or the like. It can be mixed and can be used suitably for uses, such as an electrically conductive paste and an electromagnetic wave shield.

It is the figure which showed typically the specific shape of the copper particle with which the nickel or nickel alloy which comprises dendritic nickel coat copper powder was coat | covered. It is a photograph figure which shows an observation image when the dendritic copper powder before coat | covering nickel or a nickel alloy is observed with a scanning electron microscope at a magnification of 10,000 times. It is a photograph figure which shows an observation image when dendritic nickel coat copper powder is observed with a scanning electron microscope at a magnification of 5,000 times. It is a photograph figure which shows an observation image when the dendritic nickel coat copper powder of another location is observed by 10,000 times magnification with the scanning electron microscope. It is a photograph figure which shows an observation image when the dendritic nickel coat copper powder of another location is observed with 1000-times multiplication factor with the scanning electron microscope. It is a photograph figure which shows an observation image when the copper powder obtained in the comparative example 1 is observed by 1000-times multiplication factor with a scanning electron microscope.

  Hereinafter, specific embodiments of the present invention (hereinafter referred to as “present embodiments”) will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments, and Various modifications can be made without departing from the scope of the invention. In this specification, “X to Y” (X and Y are arbitrary numerical values) means “X or more and Y or less”.

<< 1. Dendritic Ni-coated copper powder >>
The nickel-coated copper powder according to the present embodiment is a collection of copper particles having a shape having a main trunk grown in a dendritic shape and a plurality of branches separated from the main trunk, and the surface is coated with Ni or a Ni alloy. Copper powder with nickel coated on the surface. In this specification, nickel-coated copper powder is referred to as “Ni-coated copper powder”. Further, nickel or nickel alloy to be coated is expressed as “Ni” and “Ni alloy”, respectively, and when Ni is coated on the surface of copper powder or Ni alloy is coated on the surface of copper powder, “Ni coating” is generally used. ".

  FIG. 1 is a schematic diagram showing a specific shape of copper particles coated with Ni or Ni alloy, which constitute Ni-coated copper powder according to the present embodiment. As shown in the schematic diagram of FIG. 1, copper particles 1 coated with Ni or Ni alloy (hereinafter simply referred to as “copper particles 1”) have a dendritic shape that is a two-dimensional or three-dimensional form. ing.

  More specifically, the copper particle 1 coated with Ni or Ni alloy has a shape having a main trunk 2 grown in a dendritic shape and a plurality of branches 3 separated from the main trunk 2. The plate has a cross-sectional average thickness of 0.02 μm to 0.5 μm. Note that the branch 3 in the copper particle 1 means both a branch 3a branched from the main trunk 2 and a branch 3b further branched from the branch 3a.

  The Ni-coated copper powder according to the present embodiment is a dendritic copper powder (dendritic copper powder) having a main trunk and a plurality of branches, which is configured by aggregating such flat copper particles 1. Ni-coated copper powder (hereinafter also referred to as “dendritic Ni-coated copper powder”) having Ni or Ni alloy coated on the surface (see SEM images of Ni-coated copper powder in FIGS. 3 to 5). The average particle diameter (D50) of the dendritic Ni-coated copper powder composed of the copper particles 1 is 1.0 μm to 30 μm.

  As will be described later, the content of Ni coated as Ni or Ni alloy of the dendritic Ni-coated copper powder according to the present embodiment is the mass of the entire Ni-coated copper powder coated with Ni or Ni alloy. The thickness (coating thickness) of Ni or Ni alloy is an extremely thin film of about 0.1 μm or less. Therefore, this dendritic Ni-coated copper powder has a shape that retains the shape of the dendritic copper powder before coating with Ni or Ni alloy. Therefore, the shape of the dendritic copper powder before coating with Ni or Ni alloy and the shape of the dendritic Ni-coated copper powder after coating Ni or Ni alloy on the copper powder are both two-dimensional or three-dimensional. It is a dendritic shape that is a form of

  The dendritic Ni-coated copper powder according to the present embodiment will be described in detail later. For example, the anode and the cathode are immersed in a sulfuric acid electrolytic solution containing copper ions, and a direct current is passed to cause electrolysis. It can be produced by depositing dendritic copper powder on the surface and coating the surface of the obtained dendritic copper powder with Ni or a Ni alloy by an electroless plating method or the like.

  FIG. 2 is a photograph showing an example of an observation image when the dendritic copper powder before being coated with Ni or Ni alloy is observed with a scanning electron microscope (SEM). In addition, FIG. 2 observes the dendritic copper powder at a magnification of 10,000 times. Moreover, FIG. 3 is a photograph figure which shows an example of the observation image when it observes by SEM about the dendritic Ni coat copper powder which coat | covered the dendritic copper powder of FIG. 2 with Ni or Ni alloy. Moreover, FIG.4 and FIG.5 is a photograph figure which shows an example of an observation image when it observes by SEM about another location of the dendritic Ni coat | covered copper powder which coat | covered Ni or Ni alloy similarly to dendritic copper powder. is there. 3 shows the dendritic Ni-coated copper powder observed at a magnification of 5,000 times, FIG. 4 shows the dendritic Ni-coated copper powder observed at a magnification of 10,000 times, and FIG. 5 shows the dendritic Ni-coated copper powder. The Ni-coated copper powder is observed at a magnification of 1,000 times.

  As shown in the observation images of FIGS. 2 to 5, the Ni-coated copper powder according to the present embodiment has a two-dimensional or three-dimensional dendritic precipitation state having a main trunk and a branch branched from the main trunk. Presents. In addition, the main trunk and the branch are flat and have a dendritic shape, and the surface thereof is constituted by a collection of copper particles 1 coated with Ni or Ni alloy. Have fine protrusions.

  Here, the tabular copper particles 1 constituting the dendritic Ni-coated copper powder and coated with Ni or Ni alloy having the main trunk 2 and the branches 3 have an average cross-sectional thickness of 0.02 μm to 0.5 μm. is there. As the cross-sectional average thickness of the tabular copper particles 1 coated with Ni or Ni alloy is thinner, the effect as a flat plate is exhibited. That is, the main parts and branches of the dendritic copper powder are constituted by the flat copper particles 1 having a cross-sectional average thickness of 0.5 μm or less, whereby the copper particles 1 and the dendritic Ni-coated copper constituted thereby. A large area where the powders come into contact with each other can be secured. And since the contact area becomes large, low resistance, that is, high conductivity can be realized. Thereby, it is more excellent in electroconductivity, can maintain the electroconductivity favorably, and can be used suitably for the use of an electroconductive coating material or an electroconductive paste. Further, since the dendritic Ni-coated copper powder is composed of the flat copper particles 1, it can also contribute to thinning of the wiring material and the like.

  In addition, as the cross-sectional average thickness of the flat copper particles 1 coated with Ni or Ni alloy decreases, the number of contacts when the dendritic Ni-coated copper powders 1 come into contact with each other decreases. If the cross-sectional average thickness of the copper particles 1 is 0.02 μm or more, a sufficient number of contacts can be ensured, more preferably 0.2 μm or more, thereby effectively increasing the number of contacts. .

  Moreover, in the dendritic Ni coat copper powder which concerns on this Embodiment, the average particle diameter (D50) is 1.0 micrometer-30 micrometers. The average particle diameter can be controlled by changing the electrolysis conditions described later. Further, if necessary, it can be further adjusted to a desired size by adding mechanical pulverization such as a jet mill, a sample mill, a cyclone mill, and a bead mill. In addition, an average particle diameter (D50) can be measured by the laser diffraction scattering type particle size distribution measuring method, for example.

  Here, as pointed out in, for example, Patent Document 1, as a problem of dendritic Ni-coated copper powder, when used as a metal filler such as a conductive paste or a resin for electromagnetic wave shielding, the metal in the resin It is mentioned that when the filler has a dendritic shape, the dendritic copper powders are entangled with each other and agglomerate occurs and is not uniformly dispersed in the resin. In addition, the agglomeration increases the viscosity of the paste and causes problems in wiring formation by printing. This occurs because the dendritic Ni-coated copper powder has a large shape (particle diameter). In order to solve this problem while effectively utilizing the dendritic shape, the dendritic Ni-coated copper powder is used. It is necessary to reduce the shape of the. However, if the particle diameter of the dendritic Ni-coated copper powder is too small, the dendritic shape cannot be secured. Therefore, the effect of being in a dendritic shape, that is, a three-dimensional shape, has a large surface area and excellent moldability and sinterability, and can be molded with high strength by being firmly connected via a branch-like portion. In order to secure the effect, it is necessary that the dendritic Ni-coated copper powder has a size larger than a predetermined size.

  In this respect, in the dendritic Ni-coated copper powder according to the present embodiment, the average particle diameter is 1.0 μm to 30 μm, thereby increasing the surface area and ensuring good moldability and sinterability. it can. And in this dendritic Ni coat copper powder, in addition to having a dendritic shape, the dendritic shape having the main trunk 2 and the branches 3 and the copper particles 1 having a flat plate shape are assembled and configured. More contact points between the copper powders can be secured by the three-dimensional effect of being dendritic and the effect that the copper particles 1 constituting the dendritic shape are flat.

  Moreover, the flat copper particle 1 which comprises the dendritic Ni coat | court copper powder which concerns on this Embodiment, and has the main trunk 2 and the branch 3 has a fine convex part on the surface. And in the copper particle 1, it is preferable that the average height of the convex part which it has on the surface is 0.01 micrometer-0.4 micrometer.

  Here, as described in Patent Document 3 and Patent Document 4, when spherical copper powder is flattened by a mechanical method, for example, it is necessary to prevent copper oxidation during mechanical processing. It is processed into a flat plate shape by adding a fatty acid and pulverizing it in air or in an inert atmosphere. However, it cannot be completely prevented from oxidation, and the fatty acid added at the time of processing may affect the dispersibility when it is made into a paste. The fatty acid may firmly adhere to the copper surface due to the pressure during machining, which causes a problem that it cannot be completely removed. Further, since the surface is flattened by mechanical processing, the surface becomes smooth, and the flat copper powder formed for flattening by mechanical pressure is not a horizontal surface but a warped shape. Therefore, when using as a metal filler such as conductive paste and resin for electromagnetic wave shielding, when trying to secure the contact between the metal fillers, the mechanically flattened copper powder has a smooth and warped surface. Therefore, it becomes difficult to secure the contacts, and when used, the contacts between the metal fillers must be secured by a method of mixing not only the flat copper powder but also the granular copper powder.

  On the other hand, the flat copper particles 1 constituting the dendritic Ni-coated copper powder according to the present embodiment have fine convex portions on the surface, and the average height of the convex portions is preferably 0. 0.01 μm to 0.4 μm. The dendritic Ni-coated copper powder formed by aggregating such copper particles 1 has a feature that a contact between metal fillers can be easily ensured as compared with a flat copper powder obtained by mechanical processing. ing. That is, since the dendritic Ni-coated copper powder according to the present embodiment has fine convex portions on the surface of the flat copper particles 1 constituting the dendritic Ni-coated copper powder, a metal filler such as a conductive paste or a resin for electromagnetic wave shielding When using as, a contact can be easily ensured by the convex part of the surface of the tabular copper particle 1. Furthermore, this dendritic Ni-coated copper powder is produced by depositing tabular copper particles by direct electrolysis and growing them in the shape of dendritic copper powder without performing mechanical processing, which is a problem in machining. Occurrence of oxidation and removal of fatty acids are not necessary, and the electrical conductivity characteristics can be made extremely good.

  As described above, the average height of the fine protrusions on the surface of the flat copper particles 1 is preferably 0.01 μm to 0.4 μm. When the average height is less than 0.01 μm, a sufficient effect cannot be obtained as a shape for securing the contacts. On the other hand, when the average height exceeds 0.4 μm, it is used for a conductive paste or the like. In some cases, the filling rate of the metal filler in the paste does not increase, and a satisfactory resistance value may not be obtained.

≪2. Ni coating amount >>
As described above, the dendritic Ni-coated copper powder according to this embodiment is a flat plate having a cross-sectional average thickness of 0.02 μm to 0.5 μm, and the surface is coated with Ni or Ni alloy. 1 is a dendritic structure. Below, the coating | cover of Ni or Ni alloy with respect to the surface of Ni coat copper powder is demonstrated.

  The dendritic Ni-coated copper powder according to the present embodiment is preferably a dendritic copper powder before being coated with Ni or a Ni alloy, preferably with a Ni content of 100% by mass of the entire Ni-coated copper powder. Ni or Ni alloy is coated at a ratio of mass% to 50 mass%, and the thickness of Ni or Ni alloy (coating thickness) is 0.1 μm or less, preferably 0.02 μm or less. It is. From this, the dendritic Ni-coated copper powder has a shape that retains the shape of the dendritic copper powder before being coated with Ni or Ni alloy.

  The content of Ni coated as Ni or Ni alloy in the dendritic Ni-coated copper powder according to the present embodiment, as described above, is 1% by mass to 50% with respect to 100% by mass of the entire Ni-coated copper powder. It is preferably in the range of mass%. The content of Ni coated as Ni or Ni alloy is preferably as low as possible because the conductivity of Ni itself is lower than that of copper, but if it is too small, a uniform Ni or Ni alloy film can be secured on the copper surface. In other words, copper is oxidized to cause a decrease in conductivity. Therefore, the content of Ni coated as Ni or Ni alloy is preferably 1% by mass or more and more preferably 5% by mass or more with respect to 100% by mass of the entire Ni-coated copper powder. More preferably, it is 10 mass% or more.

  On the other hand, when the content of Ni coated as Ni or Ni alloy increases, it is not preferable from the viewpoint of decreasing the electrical conductivity, and as the content of Ni coated as Ni or Ni alloy, the Ni coated copper powder as a whole It is preferably 50% by mass or less, more preferably 30% by mass or less, and still more preferably 20% by mass or less with respect to 100% by mass.

  In the dendritic Ni-coated copper powder according to the present embodiment, the average thickness of Ni or Ni alloy coated on the surface of the copper particles is about 0.0003 μm to 0.1 μm, and 0.005 μm to 0.02 μm. It is preferable that When the Ni or Ni alloy coating thickness is less than 0.0003 μm on average, a uniform Ni or Ni alloy coating cannot be secured on the surface of the copper powder, and copper oxidation cannot be suppressed, resulting in a decrease in conductivity. Cause. On the other hand, if the coating thickness of Ni or Ni alloy exceeds 0.1 μm on average, it is not preferable from the viewpoint of decreasing the electrical conductivity.

  Thus, the average thickness of the Ni or Ni alloy coated on the surface of the dendritic Ni-coated copper powder is about 0.0003 μm to 0.1 μm, and constitutes the dendritic copper powder before coating the Ni or Ni alloy. This is smaller than the average cross-sectional thickness (0.02 μm to 0.5 μm) of the dendritic copper particles 1 to be used. Therefore, before and after coating the surface of the dendritic copper powder with Ni or Ni alloy, the form of the dendritic copper powder does not substantially change.

  Further, as will be described later, in the dendritic Ni-coated copper powder, Ni coated with the dendritic copper powder may be a Ni alloy. The element added as the Ni alloy is preferably an element from Group 6 to Group 14 of the periodic table, and particularly preferably at least one selected from zinc, cobalt, tungsten, molybdenum, palladium, platinum, and tin. In addition, as will be described later, when using electroless plating in the step of coating Ni on the dendritic copper powder, and further using hypophosphite and borohydride as the reducing agent, the resulting Ni coating is They are Ni-P alloy and Ni-B alloy, respectively.

Further, the dendritic Ni-coated copper powder according to the present embodiment is not particularly limited, it is preferable the value of the BET specific surface area of 0.2m ² /g~5.0m ² / g. When the value of the BET specific surface area is less than 0.2 m ² / g, the copper particles 1 coated with Ni or Ni alloy may not have the desired shape as described above, and high conductivity is obtained. There may not be. On the other hand, if the value of the BET specific surface area exceeds 5.0 m ² / g, the Ni or Ni alloy coating on the surface of the dendritic Ni-coated copper powder becomes non-uniform and high conductivity may not be obtained. In addition, the copper particles 1 constituting the dendritic Ni-coated copper powder become too fine, and the dendritic Ni-coated copper powder becomes a fine whisker-like state, and the conductivity may be lowered. The BET specific surface area can be measured in accordance with JIS Z8830: 2013.

As the bulk density of the dendritic Ni-coated copper powder according to the present embodiment is not particularly ^limited, is preferably in the range of ^{0.5g / cm 3 ~5.0g / cm 3} . If the bulk density is less than 0.5 g / cm ³ , there is a possibility that sufficient contact between the dendritic Ni-coated copper powders cannot be ensured. On the other hand, if the bulk density exceeds 5.0 g / cm ³ , the average particle diameter of the dendritic Ni-coated copper powder also increases, and the surface area may decrease, and the formability and sinterability may deteriorate. .

  If the dendritic Ni-coated copper powder having the above-mentioned shape is occupied at a predetermined ratio in the obtained Ni-coated copper powder when observed with an electron microscope, Ni of other shapes Even if the coated copper powder is mixed, the same effect as that of the copper powder composed only of the dendritic Ni-coated copper powder can be obtained. Specifically, when observed with an electron microscope (for example, 500 to 20,000 times), the dendritic Ni-coated copper powder having the shape described above is 80% by number or more, preferably 90% of the total Ni-coated copper powder. As long as it occupies a ratio of several percent or more, Ni-coated copper powder of other shapes may be included.

≪3. Method for producing dendritic Ni-coated copper powder >>
Next, the manufacturing method of the dendritic Ni coat | court copper powder 1 which has the above characteristics is demonstrated. Below, the manufacturing method of the dendritic copper powder which comprises the dendritic Ni coat copper powder 1 is demonstrated first, Then, Ni or Ni alloy is coat | covered with respect to the dendritic copper powder, Dendritic Ni coat copper A method for obtaining the powder 1 will be described.

<3-1. Method for producing dendritic copper powder>
The dendritic copper powder before coating with Ni or Ni alloy can be produced, for example, by a predetermined electrolytic method using a sulfuric acid acidic solution containing copper ions as an electrolytic solution.

  In electrolysis, for example, the above-described sulfuric acid-containing electrolytic solution containing copper ions is accommodated in an electrolytic cell in which metallic copper is used as an anode (anode) and a stainless steel plate or a titanium plate is used as a cathode (cathode). The electrolytic solution is subjected to electrolytic treatment by applying a direct current at a predetermined current density. Thereby, a dendritic copper powder can be deposited (electrodeposition) on a cathode with electricity supply. In particular, in this embodiment, the fine copper particles in the form of a plate are gathered only by the electrolysis without mechanically deforming the granular copper powder obtained by electrolysis using a medium such as a ball. Thus, the dendritic copper powder having a dendritic shape can be deposited on the cathode surface.

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

  The water-soluble copper salt is a copper ion source that supplies copper ions, and examples thereof include copper sulfate such as copper sulfate pentahydrate, copper chloride, and copper nitrate, but are not particularly limited. The copper ion concentration in the electrolytic solution can be about 1 g / L to 20 g / L, preferably about 5 g / L to 10 g / L.

  Sulfuric acid is for making a sulfuric acid electrolyte. The sulfuric acid concentration in the electrolytic solution can be about 20 g / L to 300 g / L, preferably about 50 g / L to 150 g / L, as the free sulfuric acid concentration. Since the sulfuric acid concentration affects the conductivity of the electrolyte, it 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 contributes to shape control of the copper powder to be deposited together with chloride ions to be described later, and the copper powder to be deposited on the cathode surface is composed of flat copper particles having a predetermined cross-sectional thickness; A dendritic copper powder having branches branched from the main trunk can be obtained.

  As an amine compound, you may add individually by 1 type and may add it in combination of 2 or more types. Moreover, it is preferable to set it as the quantity from which the density | concentration in electrolyte solution becomes the range of about 0.1 mg / L-500 mg / L as addition amount of amine compounds.

  Specifically, the amine compound is not particularly limited, and a compound having a phenazine structure and an azobenzene structure, which can be represented by the following formula (1), can be used. More preferably, for example, Janus Green B (C30H31N6Cl, CAS number: 2869-83-2) can be used.

Here, in formula (1), R ₁ , R ₂ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ are each separately , Hydrogen, halogen, amino, OH, ═O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, and C1-C8 alkyl Is a group selected from R ₃ is hydrogen, halogen, amino, OH, ═O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, lower alkyl, And a group selected from the group consisting of aryl. A ⁻ is a halide anion.

  As a chloride ion, it can be made to contain by adding the compound (chloride ion source) which supplies chloride ions, such as hydrochloric acid and sodium chloride, in electrolyte solution. By containing chloride ions in the electrolytic solution, the shape of the deposited copper powder can be controlled more effectively. The chloride ion concentration in the electrolytic solution can be about 30 mg / L to 1000 mg / L, preferably about 50 mg / L to 800 mg / L, more preferably about 200 mg / L to 500 mg / L.

In the method for producing the dendritic copper powder according to the present embodiment, for example, the dendritic copper powder is produced by depositing on the cathode by electrolysis using the electrolytic solution having the composition described above. As the electrolysis method, a known method can be used. For example, the current density is preferably in the range of 5 A / dm ^{2 to} 30 A / dm ² when electrolyzing using a sulfuric acid electrolytic solution, and the electrolyte is energized while stirring. Moreover, as a liquid temperature (bath temperature) of electrolyte solution, it can be set as about 20 to 60 degreeC, for example.

<3-2. Ni or Ni alloy coating method (production of Ni-coated copper powder)>
The dendritic Ni-coated copper powder according to the present embodiment is produced by coating the surface of the dendritic copper powder prepared by the above-described electrolytic method with Ni or Ni alloy using, for example, an electroless plating method. Can do.

  In order to coat Ni or Ni alloy with a uniform thickness on the surface of the dendritic copper powder, it is preferable to wash before Ni plating, and the dendritic copper powder is dispersed in a cleaning solution and washed while stirring. It can be carried out. This washing treatment is preferably carried out in an acidic solution, and after washing, filtration, separation and washing of the dendritic copper powder are repeated as appropriate to obtain a water slurry in which the dendritic copper powder is dispersed in water. In addition, what is necessary is just to use a well-known method about filtration, isolation | separation, and water washing.

  Specifically, when Ni coating is performed by the electroless plating method, the electroless Ni plating solution is added to the copper slurry obtained after washing the dendritic copper powder, or the copper slurry is added to the electroless Ni plating solution. By uniformly stirring, the surface of the dendritic copper powder can be coated more uniformly with Ni or Ni alloy.

  The electroless Ni plating solution is not particularly limited. The electroless Ni plating solution performs Ni coating by reducing Ni ions in the plating solution with a reducing agent. Examples of the reducing agent include hypophosphites, borohydrides, and hydrazine compounds. It is done.

  Specifically, examples of hypophosphites include hypophosphites such as potassium hypophosphite and sodium hypophosphite, and phosphites such as potassium phosphite and sodium phosphite. Can be mentioned.

  Examples of the borohydride compound include dimethylhexaborane, dimethylamineborane (DMAB), diethylamineborane, morpholineborane, pyridineamineborane, piperidineborane, ethylenediamineborane, ethylenediaminebisborane, t-butylamineborane, imidazoleborane, methoxy Examples include ethylamine borane and sodium borohydride.

  As the hydrazine compound, hydrazine and hydrates thereof, hydrazine salts such as hydrazine sulfate and hydrazine hydrochloride, hydrazine derivatives such as pyrazoles, triazoles, and hydrazides can be used. Among these hydrazine derivatives, pyrazoles such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone can be used as pyrazoles in addition to pyrazole. As triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole, and the like can be used. As hydrazides, adipic hydrazide, maleic hydrazide, carbohydrazide, and the like can be used. As hydrazines, hydrazine sulfate, hydrazine hydrochloride, adipic hydrazide, maleic hydrazide, carbohydrazide, and the like can be used.

  Examples of the nickel source include nickel salts such as nickel sulfate, nickel chloride, nickel acetate, and nickel sulfamate.

  Further, the plating solution can contain a complexing agent, a pH buffering agent, and a pH adjusting agent.

  Specifically, a known complexing agent can be used as the complexing agent. For example, amino acids such as glycine, citrates such as sodium citrate and ammonium citrate, lactic acid, oxalic acid, malonic acid, malic acid, tartaric acid, aspartic acid, glutamic acid, gluconic acid, sodium salts or ammonium salts, ammonia, etc. Is mentioned.

  A known complexing agent can be used as the pH buffering agent. For example, ammonium chloride, ammonium sulfate, boric acid, sodium acetate and the like can be mentioned.

  A known complexing agent can be used as the pH adjuster. For example, an acid or alkali compound can be used, and examples thereof include alkali metal hydroxides such as ammonia and sodium hydroxide, nickel carbonate, sulfuric acid, and hydrochloric acid. In addition, when using ammonia, it can supply as ammonia water.

  Moreover, you may use an antifoamer and a dispersing agent as needed.

  Furthermore, in order to improve the permeability of the plating solution, a surfactant can be contained. As the surfactant, any of nonionic, cationic, anionic and amphoteric surfactants can be used, and one kind can be used alone, or two or more kinds can be used in combination.

  Here, in Ni coating by electroless plating, the Ni coating deposited differs depending on the hypophosphorous acid bath salt, the borohydride compound, and the hydrazine compound which are reducing agents in the electroless Ni plating solution. Specifically, when hypophosphorous acid bath salt is used as the reducing agent, since the phosphorus is contained in the coating during the reduction reaction, a Ni-P alloy coating is formed. Further, when a borohydride compound is used as the reducing agent, since a boron is contained in the coating during the reduction reaction, a Ni-B alloy coating is formed. Further, when a hydrazine compound is used as the reducing agent, a high-purity Ni film with few impurities is formed.

  Furthermore, by making the Ni film to be formed contain other elements, that is, by forming a Ni alloy film on the surface of the copper powder, using the Ni-coated copper powder, heat resistance and corrosion resistance In addition, an excellent conductive paste or the like can be realized.

  Specifically, as an element to be included in the Ni film, that is, as an element other than Ni constituting the Ni alloy, elements of Groups 6 to 14 of the periodic table can be mentioned, and among them, zinc, palladium, Examples include cobalt, rhodium, iron, platinum, iridium, tungsten, molybdenum, chromium, and tin. In particular, one or more elements selected from zinc, cobalt, tungsten, molybdenum, palladium, platinum, and tin are preferable, and a Ni alloy film having excellent conductivity is formed by using an Ni alloy containing these elements. be able to.

  The content of these elements constituting the Ni alloy is preferably 0.1% by mass to 20% by mass with respect to 100% by mass of the Ni alloy, from the viewpoint of conductivity and dispersibility, and preferably 1% by mass to 15%. More preferably, it is more preferably 2% by mass to 10% by mass. In addition, also about the Ni-P alloy and Ni-B alloy which are each formed with the kind of reducing agent mentioned above, the content of phosphorus or boron is 0.1 mass% with respect to 100 mass of Ni alloy film similarly. It is preferably ˜20% by mass, more preferably 1% by mass to 15% by mass, and further preferably 2% by mass to 10% by mass.

  When the Ni alloy is used, if the content of elements other than Ni is excessively increased, the conductivity is lowered, so that the content is preferably 20% by mass or less. On the other hand, if the content is less than 0.1% by mass, the effect of improving the heat resistance and corrosion resistance cannot be sufficiently obtained even if these elements are contained together with Ni to form a Ni alloy. In addition, content of the element in Ni alloy can be measured by converting content of each element which comprises Ni coat | court copper powder, for example by a high frequency inductively coupled plasma (ICP) emission spectroscopy analysis method. In addition, each element in the Ni alloy coating can be quantitatively analyzed from the cross section of the Ni-coated copper powder or the like by energy dispersive X-ray spectroscopy (EDX) method or Auger electron spectroscopy (AES) method.

  As a method for forming a Ni alloy coating, ions such as cobalt, zinc, tungsten, molybdenum, palladium, platinum, and tin are added to the above-described electroless Ni plating solution, and electroless plating using the plating solution is performed. Can be formed. The ion source such as cobalt, zinc, tungsten, molybdenum, palladium, platinum, and tin is not particularly limited as long as it is a soluble metal salt.

  Specifically, the cobalt ion source is not particularly limited as long as it is soluble in the plating solution as a cobalt compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include cobalt sulfate, cobalt chloride, and cobalt sulfamate. These cobalt compounds can be used individually by 1 type or in mixture of 2 or more types.

  The zinc ion source is not particularly limited as long as it is soluble in the plating solution as a zinc compound and can obtain an aqueous solution having a predetermined concentration. For example, zinc chloride, zinc sulfamate, zinc sulfate, zinc acetate and the like can be mentioned. These zinc compounds can be used singly or in combination of two or more.

  The tungsten ion source is not particularly limited as long as it is soluble in a plating solution as a tungsten compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include sodium tungstate, potassium tungstate, and ammonium tungstate. These tungsten compounds can be used singly or in combination of two or more.

  The molybdenum ion source is not particularly limited as long as it is soluble in a plating solution as a molybdenum compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include molybdenum trioxide, sodium molybdate, diammonium molybdate, calcium molybdate, molybdic acid, phosphomolybdic acid, and molybdate gluconic acid complex. These molybdenum compounds can be used singly or in combination of two or more.

  The palladium ion source is not particularly limited as long as it is soluble in the plating solution as a palladium compound and can obtain an aqueous solution having a predetermined concentration. For example, water-soluble palladium compounds such as palladium sulfate, palladium chloride, palladium acetate, dichlorodiethine rediamine palladium, and tetraammine palladium dichloride can be used. Further, as the palladium compound, a so-called palladium solution in which palladium is made into a solution can also be used. As the palladium solution, for example, a dichlorodiethylenediamine palladium solution or a tetraammine palladium dichloride solution can be used. These palladium compounds can be used individually by 1 type or in mixture of 2 or more types.

  The platinum ion source is not particularly limited as long as it is soluble in a plating solution as a platinum compound and can obtain an aqueous solution having a predetermined concentration. For example, platinum chloride, chloroplatinic acid, chloroplatinic acid salt, platinum hydroxide acid, platinum hydroxide salt, dinitrodiammine platinum complex salt, dinitrosulfitoplatinum complex salt, tetraammine platinum complex salt, hexaammine platinum complex salt can be mentioned. A platinum compound can be used individually by 1 type or in mixture of 2 or more types.

  The tin ion source is not particularly limited as long as it is soluble in the plating solution as a tin compound and can obtain an aqueous solution having a predetermined concentration. For example, stannous chloride, stannic chloride, stannous sulfate, stannic sulfate, stannous pyrophosphate, and other inorganic acid salts of tin, stannous citrate, stannous citrate, stannous oxalate Of tin carboxylates such as stannic oxalate, tin methanesulfonate, tin 1-ethanesulfonate, tin 2-ethanesulfonate, tin 1-propanesulfonate, tin 3-propanesulfonate Alkane sulfonate, tin methanol sulfonate, tin hydroxyethane-1-sulfonate, tin 1-hydroxypropane-1-sulfonate, tin tin hydroxyethane-2-sulfonate, tin 1-hydroxypropane-3-sulfonate, etc. Alkanol sulfonates, tin hydroxides such as stannous hydroxide and stannic hydroxide, and metastannic acid.

  The method for forming the Ni alloy film is not limited to the above-described electroless plating method. For example, an element other than Ni constituting the Ni alloy is included in the dendritic copper powder before coating with Ni, and after forming a film made only of Ni (Ni film), it is added to the copper powder in advance. A Ni alloy film can also be formed by diffusing the elements previously deposited into the Ni film.

<< 4. Use of conductive paste, conductive paint for electromagnetic wave shield, conductive sheet >>
As described above, the dendritic Ni-coated copper powder according to the present embodiment is a dendritic Ni-coated copper powder having a main trunk and a plurality of branches branched from the main trunk, as shown in the schematic diagram of FIG. Further, Ni or a Ni alloy having a main trunk 2 grown in a dendritic shape and a plurality of branches 3 separated from the main trunk 2 and having an average cross-sectional thickness of 0.02 μm to 0.5 μm is coated. The flat plate-like copper particles 1 are assembled. And the average particle diameter (D50) of the said dendritic Ni coat | cover copper powder is 1.0 micrometer-30 micrometers.

  Such a dendritic Ni-coated copper powder has a dendritic shape, which increases the surface area, has excellent formability and sinterability, and is a flat copper particle 1 having a predetermined average cross-sectional thickness. By gathering and being configured in a dendritic shape, a large number of contacts can be secured, and excellent conductivity is exhibited.

  Further, according to the dendritic Ni-coated copper powder having such a predetermined structure, even when it is a copper paste or the like, aggregation can be suppressed and it can be uniformly dispersed in the resin. In addition, it is possible to suppress the occurrence of poor printability due to an increase in the viscosity of the paste. Therefore, this dendritic Ni-coated copper powder can be suitably used for applications such as conductive pastes and conductive paints.

  For example, as the conductive paste (copper paste), the dendritic Ni-coated copper powder according to the present embodiment is included as a metal filler, a binder resin, a solvent, and further, if necessary, a curing agent, an antioxidant, a coupling agent, It can be produced by kneading with an additive such as a corrosion inhibitor.

  Specifically, the binder resin is not particularly limited, but an epoxy resin, a phenol resin, or the like can be used. Moreover, as a solvent, organic solvents, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerol, and terpineol, can be used. Further, the amount of the organic solvent added is not particularly limited, but the amount added in consideration of the particle size of the dendritic Ni-coated copper powder 1 so as to have a viscosity suitable for a conductive film forming method such as screen printing or dispenser. Can be adjusted.

  Furthermore, other resin components can be added for viscosity adjustment. For example, a cellulose-based resin typified by ethyl cellulose can be used, and it can be added as an organic vehicle dissolved in an organic solvent such as terpineol. In addition, it is necessary to suppress the addition amount of the resin component to an extent that does not impair the sinterability, and is preferably 5% by mass or less of the whole.

  Moreover, as an additive, in order to improve the electroconductivity after baking, antioxidant etc. can be added. Although it does not specifically limit as antioxidant, For example, a hydroxycarboxylic acid etc. can be mentioned. More specifically, hydroxycarboxylic acids such as citric acid, malic acid, tartaric acid, and lactic acid are preferable, and citric acid or malic acid that has high adsorptive power to copper coated with Ni or Ni alloy is particularly preferable. The addition amount of the antioxidant can be, for example, about 1% by mass to 15% by mass in consideration of the antioxidant effect, the viscosity of the paste, and the like.

  Moreover, conventionally used 2-ethyl 4-methylimidazole etc. can be used also about a hardening | curing agent. Furthermore, conventionally used benzothiazole, benzimidazole, and the like can also be used for the corrosion inhibitor.

  In addition, when the dendritic Ni-coated copper powder according to the present embodiment is used as a metal filler for conductive paste, other shapes of copper powder, Ni-coated copper powder, and conductivity such as nickel, silver, tin, etc. It can be used by mixing with a metal filler. At this time, the proportion of dendritic Ni-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 40% by mass or more. More preferably it is. Thus, when used as a metal filler, by mixing a metal filler such as copper powder of another shape together with the dendritic Ni-coated copper powder according to the present embodiment, the gap between the dendritic Ni-coated copper powder The copper powder of another shape comes to be filled, and this makes it possible to secure more contacts for ensuring conductivity. As a result, the total amount of dendritic Ni-coated copper powder and other shapes of copper powder can be reduced.

  If the dendritic Ni-coated copper powder is less than 20% by mass of the total amount of copper powder used as the metal filler, the contact points between the dendritic Ni-coated copper powders are reduced and mixed with copper powder of other shapes. Even if the increase of the contact by carrying out is taken into consideration, as a metal filler, electroconductivity will fall.

  Moreover, various electrical circuits can be formed using the conductive paste produced using the metal filler described above. Even in this case, the circuit pattern forming method or the like conventionally used can be used without being limited to use under particularly limited conditions. For example, a conductive paste produced using the metal filler is applied or printed on a fired substrate or an unfired substrate, heated, and then pressed and cured as needed to cure and print. An electric circuit of an electronic component, an external electrode, or the like can be formed.

  Further, even when the above-described metal filler is used as an electromagnetic wave shielding material, it is not limited to use under particularly limited conditions, and a general method, for example, using the metal filler mixed with a resin can be used. it can.

  For example, in the case of using the above-described metal filler as a conductive coating for electromagnetic wave shielding, a general method, for example, mixing the metal filler with a resin and a solvent, and further adding an antioxidant, a thickener as necessary. A conductive paint can be obtained by mixing and kneading with an agent, an anti-settling agent and the like. The binder resin and solvent used at this time are not particularly limited, and those conventionally used can be used.

  Specifically, vinyl chloride resin, vinyl acetate resin, acrylic resin, polyester resin, fluorine resin, silicon resin, phenol resin, or the like can be used as the binder resin. As the solvent, conventionally used alcohols such as isopropanol, aromatic hydrocarbons such as toluene, esters such as methyl acetate, ketones such as methyl ethyl ketone, and the like can be used. As for the antioxidant, conventionally used fatty acid amides, higher fatty acid amines, phenylenediamine derivatives, titanate coupling agents and the like can be used.

  Further, even when a conductive sheet for electromagnetic wave shielding is made using a metal filler, the resin for forming the electromagnetic wave shielding layer of the conductive sheet for electromagnetic wave shielding is not particularly limited and conventionally used. You can use what you have. For example, various polymers and copolymers such as vinyl chloride resin, vinyl acetate resin, vinylidene chloride resin, acrylic resin, polyurethane resin, polyester resin, olefin resin, chlorinated olefin resin, polyvinyl alcohol resin, alkyd resin, phenol resin, etc. A thermoplastic resin, a thermosetting resin, a radiation curable resin, and the like can be appropriately used.

  The method for producing the electromagnetic shielding material is not particularly limited. For example, an electromagnetic shielding layer is formed by applying or printing a coating material in which a metal filler and a resin are dispersed or dissolved in a solvent on a substrate, and the surface is solidified. It can manufacture by drying to such an extent. In the conductive adhesive layer of the conductive sheet, a metal filler containing the dendritic Ni-coated copper powder 1 according to the present embodiment can also be used.

  Examples of the present invention will be described below in more detail with reference to comparative examples, but the present invention is not limited to the following examples.

≪Evaluation method≫
With respect to the Ni-coated copper powders obtained in the following examples and comparative examples, the shape was observed, the average particle diameter was measured, and the like by the following methods.

(Observation of shape)
With a scanning electron microscope (manufactured by JEOL Ltd., JSM-7100F type), 20 visual fields were arbitrarily observed with a predetermined magnification, and the appearance of the copper powder contained in the visual field was observed.

(Measurement of average particle size)
The average particle diameter (D50) of the obtained Ni-coated copper powder was measured using a laser diffraction / scattering particle size distribution measuring instrument (manufactured by Nikkiso Co., Ltd., HRA9320 X-100).

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

(Specific resistance measurement)
About the specific resistance value of a film, a sheet resistance value is measured by a four-terminal method using a low resistivity meter (manufactured by Mitsubishi Chemical Corporation, Loresta-GP MCP-T600). The film thickness of the coating film was measured by SURFCOM130A, manufactured by Tokyo Seimitsu Co., Ltd., and the sheet resistance value was determined by dividing the film thickness by the film thickness.

(Electromagnetic wave shielding characteristics)
The electromagnetic shielding characteristics were evaluated by measuring the attenuation rate of the samples obtained in the examples and comparative examples using an electromagnetic wave having a frequency of 1 GHz. Specifically, the level of Comparative Example 3 in which no dendritic Ni-coated copper powder is used is “△”, and the level worse than that of Comparative Example 3 is “×”. The case where it was better than the level was evaluated as “◯”, and the case where it was superior was evaluated as “◎”.

  Moreover, in order to evaluate also about the flexibility of an electromagnetic wave shield, the produced electromagnetic wave shield was bent and it was confirmed whether the electromagnetic wave shielding characteristic changed.

≪Example, comparative example≫
[Example 1]
<Preparation of electrolytic copper powder>
An electrolytic cell with a capacity of 100 L is used with a titanium electrode plate having an electrode area of 200 mm × 200 mm as a cathode and a copper electrode plate with an electrode area of 200 mm × 200 mm as an anode, and an electrolytic solution is charged into the electrolytic cell. Then, a direct current was applied thereto to deposit copper powder on the cathode plate.

  At this time, an electrolytic solution having a composition with a copper ion concentration of 10 g / L and a sulfuric acid concentration of 125 g / L was used. In addition, Janus Green B (manufactured by Kanto Chemical Co., Inc.) as an additive is added to the electrolytic solution so that the concentration in the electrolytic solution is 80 mg / L, and a hydrochloric acid solution (manufactured by Wako Pure Chemical Industries, Ltd.) is further added. It added so that it might become 30 mg / L as chloride ion (chlorine ion) density | concentration in electrolyte solution.

Then, while circulating the electrolytic solution whose concentration is adjusted as described above at a flow rate of 15 L / min using a pump, the current density of the cathode is 15 A / dm ² under the condition that the temperature is maintained at 25 ° C. Current was applied to deposit copper powder on the cathode plate.

  The electrolytic copper powder deposited on the cathode plate was recovered by mechanically scraping it off the bottom of the electrolytic cell using a scraper, and the recovered copper powder was washed with pure water and then put in a vacuum dryer and dried. .

  As a result of observing the shape of the copper powder thus obtained in the field of view with a magnification of 1,000 times by the method using the scanning electron microscope (SEM) described above, the deposited copper powder was a main chain that grew linearly and the main trunk. It was a dendritic copper powder exhibiting a two-dimensional or three-dimensional dendritic shape in which copper particles having a shape having a plurality of branches branched linearly from the branch and branches further branched from the branch were collected. .

<Preparation of dendritic Ni-coated copper powder (reducing agent: borohydride)>
Next, using the dendritic copper powder produced by the above-described method, Ni was coated on the surface of the copper powder by electroless Ni plating to produce Ni-coated copper powder. In addition, the electroless Ni plating solution whose reducing agent is a borohydride compound was used.

  Specifically, as an electroless Ni plating solution, nickel sulfate 30 g / L, sodium succinate 50 g / L, boric acid 30 g / L, ammonium chloride 30 g / L, dimethylamine borane 4 g / L were added at each concentration, Further, 500 mL of a plating solution adjusted to pH 6.0 by adding sodium hydroxide was prepared.

  In this electroless Ni plating solution, a slurry in which 100 g of the dendritic copper powder prepared by the above method is dispersed in 100 mL of water is stirred for 10 minutes at 25 ° C., and then the bath temperature is heated to 60 ° C. to 60 ° C. Stir for minutes.

  After the reaction was completed, the powder was filtered, washed with water, and dried through ethanol. As a result, Ni-coated copper powder in which Ni was coated on the surface of the dendritic copper powder was obtained. When the Ni-coated copper powder was recovered and the Ni content was measured, it was 18.6% by mass with respect to 100% by mass of the entire Ni-coated copper powder. Further, the content of boron (B) contained in the Ni alloy was 6.1% by mass with respect to 100% by mass of the Ni alloy.

  Further, as a result of observing the obtained Ni-coated copper powder with a field of view of 5,000 times by SEM, at least 90% by number or more of Ni-coated copper powder was found on the surface of the dendritic copper powder before coating the Ni alloy. A two-dimensional or three-dimensional dendritic shape uniformly coated with a Ni alloy, a main trunk that has grown into a dendritic shape, a plurality of branches branched from the main trunk, and a branch further branched from the branch The dendritic Ni-coated copper powder had a dendritic shape.

  Further, the copper particles constituting the main trunk and branches of the dendritic Ni-coated copper powder had a flat cross-sectional thickness of 0.09 μm on average, and had fine convex portions on the surface. In addition, the average height of the convex portions formed on the surface was 0.06 μm.

  The average particle diameter (D50) of the dendritic Ni-coated copper powder was 21.2 μm.

Furthermore, the bulk density of the obtained dendritic Ni-coated copper powder was 1.25 g / cm ³ . The BET specific surface area was 1.7 m ² / g.

[Example 2]
<Preparation of electrolytic copper powder>
An electrolytic solution having a copper ion concentration of 10 g / L and a sulfuric acid concentration of 125 g / L is used, and Janus Green B as an additive is added to the electrolytic solution to a concentration of 150 mg / L in the electrolytic solution. In addition, copper powder was deposited on the cathode plate under the same conditions as in Example 1 except that the hydrochloric acid solution was added so that the chlorine ion concentration in the electrolytic solution was 100 mg / L.

<Production of dendritic Ni-coated copper powder (reducing agent: hypophosphite)>
Next, using the dendritic copper powder produced by the above-described method, Ni was coated on the surface of the copper powder by electroless Ni plating to produce Ni-coated copper powder. In addition, an electroless Ni plating solution whose reducing agent is hypophosphite was used.

  Specifically, as an electroless Ni plating solution, nickel sulfate 20 g / L, sodium hypophosphite 25 g / L, sodium acetate 10 g / L, sodium citrate 10 g / L are added at each concentration, and sodium hydroxide is further added. 500 mL of a plating solution adjusted to pH 5.0 by adding the above was prepared.

  In this electroless Ni plating solution, a slurry in which 100 g of the dendritic copper powder prepared by the above method is dispersed in 100 mL of water is stirred for 10 minutes at 25 ° C., and then the bath temperature is heated to 90 ° C. to 60 ° C. Stir for minutes.

  After the reaction was completed, the powder was filtered, washed with water, and dried through ethanol. As a result, Ni-coated copper powder in which Ni alloy containing phosphorus (P) was coated on the surface of dendritic copper powder was obtained. When the Ni-coated copper powder was recovered and the Ni content was measured, it was 13.1% by mass with respect to 100% by mass of the entire Ni-coated copper powder. Moreover, content of P contained in Ni alloy was 8.1 mass% with respect to 100 mass of Ni alloy.

  Further, as a result of observing the obtained Ni-coated copper powder with a field of view of 5,000 times by SEM, at least 90% by number or more of Ni-coated copper powder was found on the surface of the dendritic copper powder before coating the Ni alloy. A two-dimensional or three-dimensional dendritic shape uniformly coated with a Ni alloy, a main trunk that has grown into a dendritic shape, a plurality of branches branched from the main trunk, and a branch further branched from the branch The dendritic Ni-coated copper powder had a dendritic shape.

  Further, the copper particles constituting the main trunk and branches of the dendritic Ni-coated copper powder had a flat cross-sectional thickness of 0.11 μm on average, and had fine convex portions on the surface. The height of the convex portions formed on the surface was 0.23 μm on average.

  The average particle diameter (D50) of the dendritic Ni-coated copper powder was 8.3 μm.

Further, the bulk density of the resultant dendritic Ni-coated copper powder was 2.77 g / cm ^3. The BET specific surface area was 1.2 m ² / g.

[Example 3]
<Preparation of dendritic Ni-coated copper powder (reducing agent: hydrazine compound)>
Using 100 g of the dendritic copper powder obtained in Example 2, Ni was coated on the surface of the copper powder by electroless Ni plating to prepare a Ni-coated copper powder. Electroless Ni plating using a hydrazine compound as a reducing agent was performed.

  Specifically, nickel acetate was added to a slurry in which 100 g of the dendritic copper powder obtained in Example 2 was dispersed in 500 mL of water to a concentration of 12.4 g / L, and an 80% by mass aqueous solution of hydrazine monohydrate. 6 g was added dropwise into the bath with slow stirring over 60 minutes. At this time, the bath temperature was controlled to 60 ° C.

  After the reaction was completed, the powder was filtered, washed with water, and dried through ethanol. As a result, Ni-coated copper powder in which Ni was coated on the surface of the dendritic copper powder was obtained. When the Ni-coated copper powder was recovered and the Ni content was measured, it was 7.7% by mass with respect to 100% by mass of the entire Ni-coated copper powder.

  Further, as a result of observing the obtained Ni-coated copper powder with a field of view of 5,000 times by SEM, at least 90% by number or more of Ni-coated copper powder was found on the surface of the dendritic copper powder before coating the Ni alloy. A two-dimensional or three-dimensional dendritic shape uniformly coated with Ni, having a main trunk grown into a dendritic shape, a plurality of branches branched from the main trunk, and branches further branched from the branch The dendritic Ni-coated copper powder had a dendritic shape.

  Further, the copper particles constituting the main trunk and branches of the dendritic Ni-coated copper powder had a flat cross-sectional thickness of 0.15 μm and had fine convex portions on the surface. The height of the convex portions formed on the surface was 0.27 μm on average.

  The average particle diameter (D50) of the dendritic Ni-coated copper powder was 9.6 μm.

Furthermore, the bulk density of the obtained dendritic Ni-coated copper powder was 2.92 g / cm ³ . Further, the BET specific surface area was 1.6 m ² / g.

[Examples 4 to 10]
<Manufacture of dendritic Ni-coated copper powder (Ni alloy)>
Using 100 g of the dendritic copper powder obtained in Example 2, the surface of the copper powder was coated with a Ni alloy by electroless plating.

  As an electroless Ni plating solution for an alloy, nickel acetate was added to a slurry in which 100 g of the dendritic copper powder obtained in Example 2 was dispersed in 500 mL of water to a concentration of 12.4 g / L, and hydrazine 3. 2 g was added dropwise into the bath over 60 minutes with slow stirring. The bath temperature was controlled to 60 ° C.

  At this time, each metal compound was added to a bath containing copper powder slurry and nickel acetate, and hydrazine was gradually added so that each desired Ni alloy film was formed. As a metal compound, in Example 4, 1.5 g of sodium tungstate was added to form a Ni—W alloy film. In Example 5, 2 g of cobalt sulfate was added to form a Ni—Co alloy film. In Example 6, 4 g each of zinc sulfate heptahydrate and sodium citrate were added to form a Ni—Zn alloy film. In Example 7, 2 g of palladium chloride was added to form a Ni—Pd alloy film. In Example 8, 2 g of potassium tetrachloroplatinate and 1 g of glycine were added to form a Ni—Pt alloy film. In Example 9, 1 g of each of sodium molybdate and trisodium citrate was added to form a Ni-Mo alloy coating. In Example 10, 1 g of sodium stannate was added to form a Ni—Sn alloy film.

  After each reaction was completed, the powder was filtered, washed with water, and dried through ethanol. As a result, Ni-coated copper powder in which Ni was coated on the surface of the dendritic copper powder was obtained. The Ni-coated copper powder was recovered and the Ni alloy coating amount was measured. Table 1 shows the results of measuring the content of Ni with respect to 100% by mass of the entire Ni-coated copper powder and the content of elements that become Ni alloys with respect to 100% by mass of the Ni alloy.

  In addition, as a result of observing each of the obtained Ni-coated copper powder with a field of view of 5,000 times by SEM, at least 90% by number or more of the Ni-coated copper powder is dendritic before coating with the Ni alloy. A two-dimensional or three-dimensional dendritic Ni-coated copper powder in which the Ni powder is uniformly coated on the surface of the copper powder, and the main trunk that grows linearly and the main trunk that branches linearly The dendritic Ni-coated copper powder had a dendritic shape having a plurality of branches and a branch further branched from the branches.

  Moreover, about these dendritic Ni coat copper powder, the average particle diameter (D50), the bulk density, and the BET specific surface area were measured. Table 1 summarizes these measurement results.

[Example 11]
<Preparation of dendritic Ni-coated copper powder (hypophosphite + tungsten compound)>
In Example 11, 100 g of the dendritic copper powder produced in Example 1 was used, and the copper powder surface was coated with a Ni alloy by electroless plating.

  As the electroless Ni plating solution, a plating solution containing hypophosphite as the same reducing agent as in Example 1 was used, and a metal other than Ni was added to the plating solution to produce a Ni alloy.

  Specifically, as an electroless Ni plating solution, a plating solution in which nickel sulfate 20 g / L, sodium hypophosphite 25 g / L, sodium acetate 10 g / L, and sodium citrate 10 g / L are added at each concentration, 500 g of a plating solution prepared by adding 1.5 g of sodium tungstate and adjusting the pH to 5.0 by adding sodium hydroxide was prepared.

  In this electroless Ni plating solution, a slurry in which 100 g of the dendritic copper powder prepared in Example 1 was dispersed in 100 mL of water was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 90 ° C. Stir for 60 minutes.

  After the reaction was completed, the powder was filtered, washed with water, and dried through ethanol. As a result, Ni-coated copper powder coated with a Ni-WP alloy was obtained. When the Ni-coated copper powder was recovered and the Ni content was measured, it was 12.3% by mass relative to 100% by mass of the entire Ni-coated copper powder. The content of P contained in the Ni alloy was 7.1% by mass with respect to 100% by mass of the Ni alloy. Moreover, content of W contained in Ni alloy was 5.5 mass% with respect to 100 mass of Ni alloy.

  Further, as a result of observing the obtained Ni-coated copper powder with a field of view of 5,000 times by SEM, at least 90% by number or more of Ni-coated copper powder was found on the surface of the dendritic copper powder before coating the Ni alloy. A two-dimensional or three-dimensional dendritic shape uniformly coated with a Ni alloy, a main trunk that has grown into a dendritic shape, a plurality of branches branched from the main trunk, and a branch further branched from the branch The dendritic Ni-coated copper powder had a dendritic shape.

  Further, the copper particles constituting the main trunk and branches of the dendritic Ni-coated copper powder had a flat cross-sectional thickness of 0.09 μm on average, and had fine convex portions on the surface. In addition, the average height of the convex portions formed on the surface was 0.06 μm.

  The average particle diameter (D50) of the dendritic Ni-coated copper powder was 21.2 μm.

Furthermore, the bulk density of the obtained dendritic Ni-coated copper powder was 1.25 g / cm ³ . The BET specific surface area was 1.7 m ² / g.

[Example 12]
30 g of the dendritic Ni-coated copper powder obtained in Example 1 is mixed with 15 g of phenol resin (PL-2211, manufactured by Gunei Chemical Co., Ltd.) and 10 g of butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., deer special grade). Using a kneader (manufactured by Nippon Seiki Seisakusho, non-bubbling kneader NBK-1), it was made into a paste by repeating kneading at 1200 rpm for 3 minutes three times. The obtained conductive paste was printed on glass with a metal squeegee and cured at 200 ° C. for 30 minutes in an air atmosphere.

The specific resistance value of the film obtained by curing was 9.0 × 10 ⁻⁵ Ω · cm, and it was found that excellent conductivity was exhibited.

[Example 13]
30 g of the dendritic Ni-coated copper powder obtained in Example 2 is mixed with 20 g of a phenolic resin (manufactured by Gunei Chemical Co., Ltd., PL-2211) and 10 g of butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., deer special grade). Using a kneader (Nippon Seiki Seisakusho, non-bubbling kneader NBK-1), kneading at 1200 rpm for 3 minutes was repeated three times to form a paste. The obtained conductive paste was printed on glass with a metal squeegee and cured at 200 ° C. for 30 minutes in an air atmosphere.

The specific resistance value of the film obtained by curing was 9.2 × 10 ⁻⁵ Ω · cm, and it was found that excellent conductivity was exhibited.

[Example 14]
The dendritic Ni-coated copper powder prepared in Example 1 was dispersed in a resin to obtain an electromagnetic wave shielding material.

  That is, 30 g of dendritic Ni-coated copper powder obtained in Example 1 was mixed with 100 g of vinyl chloride resin and 200 g of methyl ethyl ketone, and kneaded at 1200 rpm for 3 minutes using a small kneader. The paste was made by repeating the process once. During pasting, the copper powder was uniformly dispersed in the resin without agglomeration. This was coated and dried using a Mayer bar on a substrate made of a transparent polyethylene terephthalate sheet having a thickness of 100 μm to form an electromagnetic wave shielding layer having a thickness of 25 μm.

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

[Comparative Example 1]
<Preparation of electrolytic copper powder>
Copper powder was deposited on the cathode plate in the same manner as in Example 1 except that Janus Green B as an additive and chlorine ions were not added to the electrolytic solution. The shape of the obtained Ni-coated copper powder was a dendritic shape in which particulate copper was aggregated, and no fine convex portions were formed.

<Production of Ni-coated copper powder (reducing agent: hypophosphite)>
Next, Ni coat copper powder was produced using the obtained copper powder.

  Specifically, as an electroless Ni plating solution, nickel sulfate 20 g / L, sodium hypophosphite 25 g / L, sodium acetate 10 g / L, sodium citrate 10 g / L are added at each concentration, and sodium hydroxide is further added. 500 mL of a plating solution adjusted to pH 5.0 by adding the above was prepared.

  In this electroless Ni plating solution, a slurry in which 100 g of the copper powder prepared by the above-described method is dispersed in 100 mL of water is stirred and stirred at 25 ° C. for 10 minutes, and then the bath temperature is heated to 90 ° C. and stirred for 60 minutes. did.

  After the reaction was completed, the powder was filtered, washed with water, and dried through ethanol. As a result, a Ni-coated copper powder in which the Ni alloy containing P was coated on the surface of the copper powder was obtained. Moreover, when the Ni-coated copper powder was recovered and the Ni content was measured, it was 13.6% by mass relative to 100% by mass of the entire Ni-coated copper powder. The content of P contained in the Ni alloy was 7.8% by mass with respect to 100% by mass of the Ni alloy.

  FIG. 6 shows the result of observing the shape of the obtained Ni-coated copper powder with a SEM field of view at a magnification of 1,000 times. As shown in the photograph of FIG. 6, the shape of the obtained Ni-coated copper powder is a dendritic shape in which particulate copper particles are aggregated, and the surface of the copper powder is coated with a Ni alloy. It was. Moreover, the average particle diameter (D50) of the Ni-coated copper powder was 22.5 μm. In addition, the fine convex part was not formed in the dendritic part.

<Evaluation of conductive paste>
Next, 20 g of phenol resin (manufactured by Gunei Chemical Co., Ltd., PL-2211) and 10 g of butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., deer special grade) are mixed with 40 g of Ni-coated copper powder produced by the above-described method. Then, using a small kneader (Nippon Seiki Seisakusho Co., Ltd., non-bubbling kneader NBK-1), it was made into a paste by repeating kneading at 1200 rpm for 3 minutes three times. During pasting, the viscosity increased every time kneading was repeated. This is considered to be caused by a part of the copper powder being aggregated, and uniform dispersion was difficult. The obtained conductive paste was printed on glass with a metal squeegee and cured at 200 ° C. for 30 minutes in the air atmosphere.

The specific resistance value of the film obtained by curing is 63.8 × 10 ⁻⁵ Ω · cm, which is higher in specific resistance value and inferior in conductivity than the conductive paste obtained in the examples. there were.

[Comparative Example 2]
<Production of mechanically flattened flat copper powder>
The characteristic of the conductive paste by Ni coat copper powder which coat | covered Ni with the conventional flat copper powder was evaluated, and it compared with the characteristic of the conductive paste produced using the dendritic Ni coat copper powder in an Example.

  The flat copper powder was prepared by mechanically flattening granular electrolytic copper powder. Specifically, 5 g of stearic acid was added to 500 g of granular atomized copper powder (manufactured by Mekin Metal Powders Co., Ltd.) having an average particle size of 5.4 μm, and flattened with a ball mill. The ball mill was charged with 5 kg of 3 mm zirconia beads and rotated for 90 minutes at a rotation speed of 500 rpm.

<Production of Ni-coated copper powder (reducing agent: borohydride)>
With respect to 100 g of the obtained flat copper powder, the surface of the copper powder was coated with Ni by electroless plating.

  Specifically, as an electroless Ni plating solution, nickel sulfate 30 g / L, sodium succinate 50 g / L, boric acid 30 g / L, ammonium chloride 30 g / L, dimethylamine borane 4 g / L were added at each concentration, Further, 500 mL of a plating solution adjusted to pH 6.0 by adding sodium hydroxide was prepared.

  In this electroless Ni plating solution, a slurry in which 100 g of copper powder on a flat plate prepared by the above method is dispersed in 100 mL of water is stirred for 10 minutes at 25 ° C., and then the bath temperature is heated to 60 ° C. to 60 ° C. Stir for minutes.

  After the reaction was completed, the powder was filtered, washed with water and dried through ethanol. As a result, a Ni-coated copper powder in which the surface of the flat copper powder was coated with a Ni alloy was obtained. When the Ni-coated copper powder was recovered and the Ni content was measured, it was 18.2% by mass with respect to 100% by mass of the entire Ni-coated copper powder. Moreover, content of B contained in Ni alloy was 6.7 mass% with respect to 100 mass of Ni alloy.

  The plate-like Ni-coated copper powder produced in this way was measured with a laser diffraction / scattering particle size distribution analyzer, and as a result, the average particle size (D50) was 21.8 μm. Moreover, the thickness (cross-sectional average thickness) of the plate-like Ni-coated copper powder measured by SEM observation was 0.40 μm. In the flat Ni-coated copper powder, no fine protrusions were observed on the surface.

<Evaluation of conductive paste>
Next, 20 g of phenol resin (manufactured by Gunei Chemical Co., Ltd., PL-2211) and 10 g of butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., deer special grade) are mixed with 40 g of Ni-coated copper powder produced by the above-described method. Then, using a small kneader (Nippon Seiki Seisakusho Co., Ltd., non-bubbling kneader NBK-1), it was made into a paste by repeating kneading at 1200 rpm for 3 minutes three times. During pasting, the viscosity increased every time kneading was repeated. This is considered to be caused by a part of the copper powder being aggregated, and uniform dispersion was difficult. The obtained conductive paste was printed on a glass with a metal squeegee and cured at 200 ° C. for 30 minutes in an air atmosphere.

The specific resistance value of the film obtained by curing is 26.5 × 10 ⁻⁵ Ω · cm, and the specific resistance value is extremely high and inferior in conductivity compared to the conductive paste obtained in the examples. Met.

[Comparative Example 3]
The tabular Ni-coated copper powder prepared in Comparative Example 2 was dispersed in a resin to obtain an electromagnetic wave shielding material.

  Specifically, 100 g of vinyl chloride resin and 200 g of methyl ethyl ketone are mixed with 40 g of the obtained tabular Ni-coated copper powder, and kneading at 1200 rpm for 3 minutes is repeated three times using a small kneader. To make a paste. During pasting, the copper powder was uniformly dispersed in the resin without agglomeration. This was coated and dried using a Mayer bar on a substrate made of a transparent polyethylene terephthalate sheet having a thickness of 100 μm to form an electromagnetic wave shielding layer having a thickness of 25 μm.

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

1 Copper particle 2 Main trunk (of copper particle) 3, 3a, 3b (copper particle) branch

Claims (11)

A copper particle having a shape having a main trunk that grows in a dendritic shape and a plurality of branches separated from the main trunk, and is a Ni-coated copper powder coated on the surface with Ni or Ni alloy,
The copper particles have a plate-like shape with a cross-sectional average thickness of main trunks and branches of 0.02 μm to 0.5 μm,
The average particle diameter (D50) of the said Ni coat copper powder is 1.0 micrometer-30 micrometers. Dendritic Ni coat copper powder characterized by the above-mentioned. The dendritic Ni-coated copper powder according to claim 1, wherein the surface of the copper particles has fine convex portions, and the average height of the convex portions is 0.01 μm to 0.4 μm. The dendritic Ni according to claim 1 or 2, wherein the content of Ni coated as Ni or Ni alloy is 1% by mass to 50% by mass with respect to 100% by mass of the entire dendritic Ni-coated copper powder. Coat copper powder. Ni alloy is coated on the surface of the copper particles,
At least one selected from the group consisting of cobalt, zinc, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron is 0.1% by mass to 20% by mass with respect to 100% by mass of the Ni alloy. The dendritic Ni-coated copper powder according to any one of claims 1 to 3, which is coated with a Ni alloy contained in a content. Dendritic Ni-coated copper powder according to any one of claims 1 to 4 bulk density is in the range of ^{0.5g / cm 3 ~5.0g / cm 3} . Dendritic Ni-coated copper powder according to any one of claims 1 to 5 BET specific surface area of 0.2m ² /g~5.0m ² / g.   A metal filler comprising the dendritic Ni-coated copper powder according to any one of claims 1 to 6 in a proportion of 20% by mass or more of the whole.   A conductive paste comprising the metal filler according to claim 7 mixed with a resin.   A conductive paint for electromagnetic wave shielding, comprising the metal filler according to claim 7.   An electroconductive sheet for electromagnetic wave shielding, comprising the metal filler according to claim 7. A method for producing the Ni-coated copper powder according to any one of claims 1 to 6,
A step of depositing copper powder on the cathode from the electrolyte by an electrolytic method;
Coating the copper powder with nickel (Ni) or Ni alloy,
In the electrolyte,
Copper ions,
One or more selected from compounds having a phenazine structure and an azobenzene structure represented by the following formula (1):
A method for producing a Ni-coated copper powder, characterized in that electrolysis is carried out by containing.
[In the formula (1), R ₁ , R ₂ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ are each independently hydrogen, Selected from the group consisting of halogen, amino, OH, ═O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, and C1-C8 alkyl It is a group. R ₃ is hydrogen, halogen, amino, OH, ═O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, lower alkyl, And a group selected from the group consisting of aryl. A ⁻ is a halide anion. ]