JP2018197379A - Method for producing copper powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of accurately producing a copper powder capable of ensuring high conductivity when used as a metal filler such as a conductive paste or an electromagnetic wave shield by an easy and rapid method. The present invention is a method for producing a copper powder having a dendritic shape, which comprises a step of producing copper powder by an electrolytic method, a reflectance of copper powder measured by a spectrophotometer, and a predetermined reflectance standard. And a step of inspecting the quality of the copper powder based on the above. For example, in the step of inspecting the quality of copper powder, the reflectance standard at a measurement wavelength of 400 nm is set to 9% or more. [Selection diagram] Figure 1

Description

  The present invention relates to a method for producing copper powder, and more particularly to a method for producing copper powder having a shape in which flat particles that can be used as a material such as a conductive paste and can improve conductivity are aggregated.

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

  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 heat-cured at 100 ° C. to 200 ° C. to form a conductive film. And forming electrodes. In the resin-type conductive paste, since the thermosetting resin is cured and contracted by heat, the metal fillers are pressed and contacted with each other so that the metal fillers overlap each other, and as a result, an electrically connected current path is formed. Since this resin-type conductive paste is processed at a curing temperature of 200 ° C. or lower, it is used for a substrate using a heat-sensitive material such as a printed wiring board.

  On the other hand, the fired 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 a conductive film. Form. The fired conductive paste is processed at a high temperature to sinter the metal fillers to ensure conductivity. Since this fired conductive paste is processed at such a high firing temperature, it cannot be used for a printed wiring board using a resin material, but the metal filler is sintered by high temperature processing. Low resistance can be realized. Therefore, the fired conductive paste is used for an external electrode of a multilayer ceramic capacitor.

  As a metal filler used in these resin-type conductive pastes and fired-type conductive pastes, silver powder has been conventionally used in many cases. However, in recent years, the price of precious metals has risen, and the use of copper powder that is cheaper than silver powder has been favored for cost reduction.

  Here, as powders, such as copper used as a metal filler, since particle | grains are connected and electrically conductive as mentioned above, shapes, such as a granular form, a dendritic shape, and flat form, have been used a lot. In particular, when the particles are evaluated from the size in the three directions of length, width, and thickness, the thin plate shape contributes to reducing the thickness of the wiring material by reducing the thickness. Compared to cubic or spherical particles having a certain thickness, there is an advantage that an area where the particles are in contact with each other can be ensured, and that low resistance, that is, high conductivity can be achieved. For this reason, tabular copper powder is particularly suitable for conductive paints and conductive pastes for which electrical conductivity is desired to be maintained. In addition, when using a thin conductive paste, it is preferable to consider the influence of impurities contained in the copper powder.

  In order to produce such a flat copper powder, for example, Patent Document 1 discloses a method for obtaining a flaky copper powder suitable for a metal filler of a conductive paste. Specifically, a spherical copper powder having an average particle size of 0.5 to 10 μm is used as a raw material, and mechanically 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.

  Patent Document 2 discloses a technique relating to a copper powder for conductive paste, more specifically, a disk-shaped copper powder having high performance as a copper paste for through-holes and external electrodes, and a method for producing the same. Specifically, the granular atomized copper powder is put into a medium agitating mill, and a steel ball having a diameter of 1/8 to 1/4 inch is used as a grinding medium. 1% is added and processed into a flat plate shape by grinding in air or in an inert atmosphere.

  Furthermore, Patent Document 3 discloses a method for obtaining electrolytic copper powder that can be molded with high strength, with improved formability compared to conventional electrolytic copper powder, without developing the electrolytic copper powder more than necessary. . Specifically, in order to increase the strength of the electrolytic copper powder itself and precipitate the electrolytic copper powder that can be molded to a high strength, the electrolytic solution is used for the purpose of reducing the size of the crystallites constituting the electrolytic copper powder. One or two or more selected from tungstate, molybdate, and sulfur-containing organic compounds are added to a certain aqueous copper sulfate solution to deposit electrolytic copper powder.

  In any of the methods disclosed in these patent documents, the obtained granular copper powder is mechanically deformed (processed) using a medium such as a ball to form a flat plate. As for the size of the copper powder, the average particle diameter is 1 to 30 μm in the technique of Patent Document 1, and the average particle diameter is 7 to 12 μm in the technique of Patent Document 3.

  On the other hand, electrolytic copper powder deposited in a dendritic shape called dendritic shape is known, and since the shape is dendritic, it has a large surface area, excellent formability and sinterability, and is used for powder metallurgy applications Used as a raw material for oil-impregnated bearings and machine parts. In particular, oil-impregnated bearings and the like have been reduced in size, and accordingly, have become porous, thin, and have complicated shapes.

  In order to satisfy these requirements, for example, Patent Document 4 discloses a copper powder for metal powder injection molding having a complicated three-dimensional shape and high dimensional accuracy, and a method for manufacturing an injection molded product using the same. Specifically, it has been shown that by further developing the dendritic shape, the dendrites of the electrolytic copper powder adjacent to each other at the time of compression molding are intertwined and firmly connected to each other, so that it can be molded with high strength. Furthermore, when it is used as a conductive paste or a metal filler for electromagnetic wave shielding, since it has a dendritic shape, it can be used that it can have more contacts than a spherical shape.

  However, when the dendritic copper powder as described above is used as a metal filler such as a conductive paste or a resin for electromagnetic wave shielding, the dendritic copper powder has a shape in which the metal filler in the resin has developed into a dendritic shape. They are entangled with each other and agglomerate occurs, which causes a problem that they are not uniformly dispersed in the resin, and the viscosity of the paste increases due to agglomeration, resulting in problems in wiring formation by printing. Such a problem is pointed out in Patent Document 3, for example.

  As described above, it is not easy to use dendritic copper powder as a metal filler such as a conductive paste, which is a cause of difficulty in improving the conductivity of the paste. In addition, in order to ensure electroconductivity, a dendritic shape is easy to ensure a contact rather than granular, and can ensure high electroconductivity as a conductive paste or an electromagnetic wave shield.

  In order to solve these problems, Patent Document 5 forms a dendritic shape in which tabular grains are aggregated, and the grains have a main trunk in which the grains grow linearly and a plurality of branches separated from the main trunk. Dendritic copper powder is disclosed. It is said that this dendritic copper powder is easy to ensure electrical contact between copper powders, and high conductivity is obtained when used as a conductive paste or electromagnetic wave seal.

Japanese Patent Laid-Open No. 2005-200734 JP 2002-15622 A JP 2011-58027 A Japanese Patent Laid-Open No. 9-3510 Japanese Patent No. 5907302

  The dendritic copper powder disclosed in Patent Document 5 is produced by precipitation by an electrolytic method from an acidic copper electrolyte containing an additive having a phenazine structure and the like, a nonionic surfactant, and chloride ions. The Indexes representing the shape of the cross-sectional average thickness of the tabular particles constituting the dendritic copper powder and the average particle diameter of the dendritic copper powder are additives, nonionic surfactants, chloride ions, copper in the electrolyte solution It is affected by each concentration of ions. Each concentration in these electrolytes changes every moment due to wear during electrolysis and adhesion at the time of taking out the dendritic copper powder, so when depositing the dendritic copper powder, these concentrations are managed within an appropriate range. However, the shape of the dendritic copper powder was not always in a controlled state. Therefore, even when these dendritic copper powders are used as a conductive paste or a metal filler for an electromagnetic wave shield, desired conductivity may not be obtained.

  The present invention has been proposed in view of such circumstances, and copper powder capable of ensuring high conductivity when used as a metal filler such as conductive paste and electromagnetic wave shield is easily and quickly obtained. It is an object to provide a method that can be manufactured.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has a correlation between the shape of the dendritic copper powder having a surface that easily reflects light and the reflectance, and the dendritic copper It has been found that there is a correlation between the shape of the powder and the conductivity when it is used as a metal filler. And even in the manufacturing process of dendritic copper powder, by using the reflectance as an index, the quality of the dendritic copper powder can be inspected easily and quickly, and when used as a metal filler such as conductive paste and electromagnetic wave shield The present inventors have found that a dendritic copper powder capable of ensuring high electrical conductivity can be obtained, and have completed the present invention. That is, the present invention provides the following.

  (1) 1st invention of this invention is a manufacturing method of the copper powder which exhibits dendritic shape, Comprising: The reflectance of the said copper powder measured with the process which manufactures copper powder by the electrolysis method, and the spectrophotometer And a step of inspecting the quality of the copper powder based on a predetermined reflectance standard.

  (2) 2nd invention of this invention is a manufacturing method of copper powder which makes the measurement wavelength of the said reflectance 300nm-500nm in the process which test | inspects the quality of the said copper powder in 1st invention.

  (3) According to a third aspect of the present invention, in the second aspect of the invention, in the step of inspecting the quality of the copper powder, the reflectance standard at a measurement wavelength of 400 nm is 9% or more. It is.

(4) 4th invention of this invention has a phenazine structure represented by a copper ion and following formula (1) in the process of manufacturing the said copper powder in any one of 1st thru | or 3rd invention. Selected from the group consisting of compounds, the group consisting of compounds having an azobenzene structure represented by the following formula (2), and the group consisting of compounds having a phenazine structure and an azobenzene structure represented by the following formula (3). One or more, or two or more selected from different groups,
It is a manufacturing method of copper powder which manufactures copper powder by electrolysis using the electrolyte solution containing 1 or more types of nonionic surfactant.
[In Formula (1), R ₁ , R ₂ , R ₃ , R ₄ , R ₆ , R ₇ , R ₈ , R ₉ are each independently 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, R ₅ is hydrogen, halogen , selected amino, OH, -O, CN, SCN , SH, COOH, COO salt, COO _ester, SO 3 H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, from the group consisting of lower alkyl, and aryl And A ⁻ is a halide anion. ]
[In the formula (2), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ are each independently hydrogen, halogen, amino, OH, = O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, a group selected from the group consisting of benzenesulfonic acid, lower alkyl, and aryl. ]
[In the formula (3), 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 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, A group selected from the group consisting of lower alkyl and aryl, and A ⁻ is a halide anion. ]

  (5) According to the present invention, a fifth invention is the method for producing copper powder according to the fourth invention, wherein the electrolytic solution contains chloride ions.

  (6) In the sixth invention of the present invention, in any one of the first to fifth inventions, the step of inspecting the quality of the copper powder is a slurry of the copper powder obtained in the step of producing the copper powder. A step of transferring the slurry to a measurement cell to settle the copper powder, and a step of loading the measurement cell into a spectrophotometer and measuring the reflectance of the precipitated copper powder. It is a manufacturing method.

  (7) According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the copper powder has a dendritic shape having a main trunk that grows linearly and a plurality of branches that are separated from the main trunk. The main trunk and the branch are formed of flat copper particles having a cross-sectional average thickness of 0.02 μm to 5.0 μm determined by observation with a scanning electron microscope (SEM). The average particle diameter (D50) of the copper particles is 1.0 μm to 100 μm, and the maximum height in the direction perpendicular to the flat surface of the copper particles is the maximum length in the horizontal direction of the flat surface. On the other hand, it is the manufacturing method of copper powder which is 1/10 or less.

  (8) The eighth invention of the present invention is a step of mixing the copper powder obtained by the production method according to any one of the first to seventh inventions at a ratio of 20% by mass or more based on the total mass. Is a method for producing a metal filler.

  (9) A ninth invention of the present invention is a method for producing a conductive paste, comprising a step of kneading a metal filler obtained by the production method according to the eighth invention with a binder resin and a solvent.

  According to the copper powder manufacturing method of the present invention, it is possible to accurately obtain a copper powder that can ensure high conductivity when used as a metal filler such as a conductive paste or an electromagnetic wave shield by an easy and rapid method. .

It is the figure which showed typically the specific shape of dendritic copper powder. It is the figure which showed typically the specific shape of dendritic copper powder. It is a photograph figure which shows an observation image when the dendritic copper powder of Example 2 is observed by 5000 times of magnification with a scanning electron microscope (SEM). It is a photograph figure which shows an observation image when the dendritic copper powder of Example 4 is observed by 5000 time magnification by SEM. It is a figure which shows the correlation of the reflectance of the copper powder of Examples 1-5, and the specific resistance value of a film.

  Hereinafter, a specific embodiment of the copper powder according to the present invention (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, A various change is possible in the range which does not change the summary of this invention. Further, in this specification, the expression “X to Y” (X and Y are arbitrary numerical values) means “X or more and Y or less”.

<< 1. Dendritic copper powder >>
When observed using a scanning electron microscope (SEM), the copper powder according to the present embodiment has a dendritic shape having a main trunk that grows linearly and a plurality of branches that are separated from the main trunk (hereinafter referred to as the main trunk). The copper powder according to the present embodiment is also referred to as “dendritic copper powder”), and the main trunk and branches are copper powder composed of flat copper particles having a specific cross-sectional average thickness. .

  Specifically, in the dendritic copper powder according to the present embodiment, the main trunk and branches are assembled from flat copper particles having a cross-sectional average thickness of 0.02 μm to 5.0 μm determined by SEM observation. It is comprised and the average particle diameter (D50) of the said dendritic copper powder is 1.0 micrometer-100 micrometers. And in this dendritic copper powder, the height in the vertical direction with respect to the flat surface of the flat copper particles is 1/10 or less with respect to the maximum length in the horizontal direction, It has a smooth surface that suppresses growth in the vertical direction.

  Although the dendritic 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 applied to cause electrolysis to occur on the cathode. It can be produced by precipitation.

  FIG.1 and FIG.2 is the figure which showed typically the specific shape of the dendritic copper powder which concerns on this Embodiment. As shown in FIG. 1, the dendritic copper powder 1 has a dendritic shape having a main trunk 2 grown linearly and a plurality of branches 3 separated from the main trunk 2. The branch 3 in the dendritic copper powder 1 means not only the branches 3a and 3b branched from the main trunk 2, but also both branches further branched from the branches 3a and 3b.

  As described above, the main trunk 2 and the branch 3 are configured by aggregating tabular copper particles having an average cross-sectional thickness of 0.02 μm to 5.0 μm determined by SEM observation. The formation of such flat copper particles is caused by the fact that specific additives added to the electrolytic solution when electrolytically depositing copper powder are adsorbed on the surface of the copper particles, as will be described later. As a result, it is thought that it grows flat.

  However, for example, when copper powder grows in a direction perpendicular to the flat surface shown in FIG. 2 (the Z direction in FIG. 2), the copper particles of the grown branches themselves become flat, but the vertical Copper powder in which copper particles grow like protrusions is also formed in the direction. Note that FIG. 2 is a diagram showing a horizontal direction (flat plate direction) to the flat plate surface and a direction perpendicular to the flat plate surface. The flat plate direction indicates the XY direction, and the vertical direction. Indicates the Z direction.

  When the copper particles grow in the vertical direction, for example, when the copper powder is used for applications such as conductive pastes and conductive paints, the copper powder grows in bulk due to the growth of the copper particles in the vertical direction. There is a problem in that it cannot be obtained and sufficient conductivity cannot be secured.

  On the other hand, the dendritic copper powder 1 according to the present embodiment is a copper powder having a substantially smooth surface by suppressing the growth in a direction perpendicular to the flat surface. Specifically, as shown in FIG. 2, the dendritic copper powder 1 has a maximum height in the vertical direction (reference numeral “5” in FIG. 2) with respect to the flat plate surface, and the horizontal surface of the flat plate surface. It becomes 1/10 or less with respect to the maximum length (symbol “4” in FIG. 2) that is long in the direction. Note that the maximum height 5 in the direction perpendicular to the flat surface is not the thickness of the flat surface, but, for example, when the protrusion is formed on the flat surface, the height of the protrusion. Yes, it means the “height” in the direction opposite to the thickness direction with respect to the flat “surface”. Further, the maximum length 4 in the horizontal direction with respect to the flat surface means the major axis length of the flat surface.

  Here, FIG. 3 is a photographic view of the dendritic copper powder obtained in Example 2 described later when observed with an SEM (magnification 5000 times). As shown in this photograph, it can be seen that growth in the vertical direction with respect to the flat surface is suppressed, resulting in a dendritic and flat copper powder having a substantially smooth surface.

  By using the flat dendritic copper powder 1 in which the growth in the vertical direction is suppressed, a large contact area between the copper powders can be secured. And since the contact area becomes large, low resistance, that is, high conductivity can be realized. Thereby, it is further 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. Moreover, when the dendritic copper powder 1 is configured by aggregating flat copper particles, the dendritic copper powder 1 can also contribute to thinning of the wiring material and the like.

  As described above, the flat copper particles constituting the main trunk 2 and the branches 3 in the dendritic copper powder 1 have a cross-sectional average thickness of 0.02 μm to 5.0 μm. The thinner the cross-sectional average thickness of the flat copper particles, the more the flat plate effect is exhibited. That is, the main trunk 2 and the branch 3 are constituted by flat copper particles having a cross-sectional average thickness of 5.0 μm or less, so that the copper particles and the dendritic copper powder 1 constituted thereby come into contact with each other. A large area can be secured.

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

  Moreover, in the dendritic copper powder 1 which concerns on this Embodiment, the average particle diameter (D50) is 1.0 micrometer-100 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 crushing or crushing such as a jet mill, a sample mill, a cyclone mill, or 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 Patent Document 3, for example, as a problem of the dendritic copper powder, when used as a metal filler such as a conductive paste or a resin for electromagnetic wave shielding, the metal filler in the resin is Due to the shape developed in a dendritic shape, the dendritic copper powders are entangled with each other to cause aggregation and are 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 shape (particle diameter) of the dendritic copper powder is large, and in order to solve this problem while effectively utilizing the dendritic shape, the shape of the dendritic copper powder is reduced. It is necessary to do. However, if the particle diameter of the dendritic 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 copper powder is larger than a predetermined size.

  In this respect, in the dendritic copper powder 1 according to the present embodiment, the average particle diameter is 1.0 μm to 100 μm, thereby increasing the surface area and ensuring good moldability and sinterability. it can. And in this dendritic copper powder 1, in addition to having a dendritic shape, the main trunk 2 and the branch 3 are constituted by an aggregate of flat copper particles, so that the three-dimensional shape of the dendritic copper powder 1 The contact between the copper powders can be ensured more due to the effect of the mechanical effect and the effect that the copper particles constituting the dendritic shape are flat.

  As a method for producing a flat copper powder, as described in Patent Document 1 and Patent Document 2, a method of forming a flat plate by a mechanical method is shown. In this mechanical method, for example, when spherical copper powder is formed into a flat plate shape, it is necessary to prevent copper oxidation during mechanical processing. Therefore, fatty acid is added and pulverized in air or in an inert atmosphere. This is processed into a flat plate shape. However, it cannot be completely prevented from oxidation, and the fatty acid added during processing may affect dispersibility when it is made into a paste, so it is necessary to remove it after the end of processing, Occasionally, the fatty acid may be firmly fixed to the copper surface due to the pressure during machining, which causes a problem that it cannot be completely removed, and an oxide film when used as a metal filler such as a conductive paste or resin for electromagnetic wave shielding. And the adhesion of fatty acids increases the resistance.

  On the other hand, the dendritic copper powder 1 according to the present embodiment can be grown directly by electrolysis into a flat plate shape without performing mechanical processing. Oxidation problems and problems due to residual fatty acids do not occur, and the copper powder has a good surface state, and can be in a very good state for electrical conductivity. For conductive paste and electromagnetic shielding When used as a metal filler such as resin, low resistance can be realized. In addition, the manufacturing method of this dendritic copper powder 1 is explained in full detail later.

  Further, in order to realize further low resistance, the filling rate of the metal filler becomes a problem. In order to further increase the filling rate, the flatness of the tabular dendritic copper powder is required. That is, the form of the dendritic copper powder 1 according to the present embodiment is such that the maximum height in the direction perpendicular to the flat surface is the maximum length in the direction horizontal to the flat surface. 1/10 or less, the smoothness is high and the filling rate is increased, and the number of contacts on the surface of the copper powders is increased, so that further low resistance can be realized.

The bulk density of the dendritic copper powder 1 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 copper powders 1 cannot be secured. On the other hand, when the bulk density exceeds 5.0 g / cm ³ , the average particle diameter of the dendritic copper powder 1 is also increased, and the surface area is decreased and the moldability and sinterability may be deteriorated.

Further, the dendritic copper powder 1 is not particularly limited, it is preferred that the BET specific surface area of 0.2m ² /g~5.0m ² / g. If the BET specific surface area is less than 0.2 m ² / g, the copper particles constituting the dendritic copper powder 1 may not have the desired shape as described above, and high conductivity may not be obtained. . On the other hand, when the BET specific surface area exceeds 5.0 m ² / g, the copper particles constituting the dendritic copper powder 1 become too fine, and the copper particles become finely whisker-like, resulting in a decrease in conductivity. There are things to do. The BET specific surface area can be measured in accordance with JIS Z8830: 2013.

  Moreover, although the dendritic copper powder 1 is not specifically limited, It is preferable that the crystallite diameter belongs to the range of 80 nm-300 nm. If the crystallite diameter is less than 80 nm, the copper particles constituting the main trunk and branches tend to be a shape close to a sphere rather than a flat shape, and it becomes difficult to ensure a sufficiently large contact area, and the conductivity is low. May be reduced. On the other hand, if the crystallite diameter exceeds 300 nm, moldability and sinterability may be deteriorated.

The crystallite diameter here is obtained from a diffraction pattern obtained by an X-ray diffractometer, based on Scherrer's formula expressed by the following formula, and in the Miller index of the (111) plane by X-ray diffraction. The crystallite size.
D = 0.9λ / βcos θ
(D: crystallite diameter (Å), β: diffraction peak spread (rad) depending on crystallite size, λ: X-ray wavelength [CuKα] (Å), θ: diffraction angle (°). .)

  In addition, when the dendritic copper powder 1 having the shape as described above is occupied at a predetermined ratio in the obtained copper powder when observed with an electron microscope, copper powder having other shapes is mixed. Even if it is, the effect similar to the copper powder which consists only of the dendritic copper powder 1 can be acquired. Specifically, when observed with an electron microscope (for example, 500 to 20,000 times), the dendritic copper powder 1 having the above-described shape is 80% by number or more, preferably 90% by number or more of the total copper powder. As long as it occupies the ratio, copper powder of other shapes may be included.

≪2. Method for producing dendritic copper powder >>
Next, the manufacturing method of the dendritic copper powder 1 which concerns on this Embodiment is demonstrated. Below, it demonstrates in order of the process of manufacturing the dendritic copper powder, and the process of test | inspecting the quality of copper powder by the reflectance of the dendritic copper powder 1 measured with the spectrophotometer, and a predetermined | prescribed reference | standard reflectance.

<2-1. Process for producing dendritic copper powder>
The dendritic copper powder 1 according to the present embodiment 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 fine dendritic copper powder can be deposited (electrodeposited) on the cathode with energization. In particular, in this embodiment, by adding a specific additive, a nonionic surfactant, and a chloride ion to a sulfuric acid acidic electrolyte solution containing a water-soluble copper salt serving as a copper ion source, A plate-like dendritic copper powder composed of copper particles can be deposited.

  In addition, in the manufacturing method according to the present embodiment, as described later, after copper powder is manufactured, the copper powder is subjected to a quality inspection process and the quality is controlled. It may be a dendritic copper powder deposited from a sulfuric acid electrolyte that does not contain any or all of the agent, nonionic surfactant and chloride ion.

(1) Copper ions 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 and copper nitrate, but are not particularly limited. Alternatively, copper oxide may be dissolved in a sulfuric acid solution to make a sulfuric acid acidic solution. 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.

(2) Sulfuric acid 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.

(3) Additive The additive is a compound selected from the group consisting of a compound having a phenazine structure, a group consisting of a compound having an azobenzene structure, and a group consisting of a compound having a phenazine structure and an azobenzene structure. At least one kind is used. Of course, two or more compounds selected from different groups and having different molecular structures may be used in combination. In the present embodiment, such an additive is added to the electrolyte together with a nonionic surfactant described later, thereby suppressing copper powder that suppresses growth in a direction perpendicular to the flat surface, that is, smooth. Copper powder having a surface can be produced.

  The concentration of the additive selected from the group consisting of a compound having a phenazine structure, a compound having an azobenzene structure, and a compound having a phenazine structure and an azobenzene structure in the electrolyte solution is 1 mg / L to 1000 mg in total. / L is preferable.

(Compound having phenazine structure)
A compound having a phenazine structure can be represented by the following formula (1). In the present embodiment, one or more compounds having a phenazine structure represented by the following formula (1) can be contained as an additive.
Here, in Formula (1), R ₁ , R ₂ , R ₃ , R ₄ , R ₆ , R ₇ , R ₈ , R ₉ are each independently hydrogen, halogen, amino, OH, ═O, CN, SCN, a group SH, COOH, COO salt, COO _ester, SO 3 H, SO ₃ salt, is selected SO ₃ ester, benzenesulfonic acid, and from the group consisting of C1~C8 alkyl. R ₅ 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.

  Specifically, examples of the compound having a phenazine structure include 5-methylphenazine-5-ium, eruginosine B, aeruginosine A, 5-ethylphenazine-5-ium, 3,7-diamino-5-phenylphenazine-5. -Ium, 5-ethylphenazine-5-ium, 5-methylphenazine-5-ium, 3-amino-5-phenyl-7- (diethylamino) phenazine-5-ium, 2,8-dimethyl-3,7- Diamino-5-phenylphenazine-5-ium, 1-methoxy-5-methylphenazine-5-ium, 3-amino-7- (dimethylamino) -1,2-dimethyl-5- (3-sulfonatophenyl) Phenazine-5-ium, 1,3-diamino-5-methylphenazine-5-ium, 1,3-diamino-5-phenylphen Din-5-ium, 3-amino-7- (diethylamino) -2-methyl-5-phenylphenazine-5-ium, 3,7-bis (diethylamino) -5-phenylphenazine-5-ium, 2,8 -Dimethyl-3,7-diamino-5- (4-methylphenyl) phenazine-5-ium, 3- (methylamino) -5-methylphenazine-5-ium, 3-hydroxy-7- (diethylamino) -5 -Phenylphenazine-5-ium, 5-azoniaphenazine, 1-hydroxy-5-methylphenazine-5-ium, 4H, 6H-5-phenyl-3,7-dioxophenazine-5-ium, anilinoap Safranin, phenosafranine, neutral red and the like can be mentioned.

(Compound having azobenzene structure)
The compound having an azobenzene structure can be represented by the following formula (2). In the present embodiment, one or more compounds having an azobenzene structure represented by the following formula (2) can be contained as an additive.

Here, in formula (2), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ are each independently hydrogen, halogen, amino A group selected from the group consisting of OH, ═O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, lower alkyl, and aryl. is there.

  Specifically, examples of the compound having an azobenzene structure include azobenzene, 4-aminoazobenzene-4'-sulfonic acid, 4- (dimethylamino) -4 '-(trifluoromethyl) azobenzene, C.I. I. Acid Red 13, Mercury Orange, 2 ′, 4′-Diamino-5′-methylazobenzene-4-sulfonic acid sodium salt, methyl red, methyl yellow, methyl orange, azobenzene-2,4-diamine, alizarin yellow GG, 4- Dimethylaminoazobenzene, orange I, salazosulfapyridine, 4- (diethylamino) azobenzene, orange OT, 3-methoxy-4-aminoazobenzene, 4-aminoazobenzene, N, N, 2-trimethylazobenzene-4-amine, 4 -Hydroxyazobenzene, Sudan I, 4-amino-3,5-dimethylazobenzene, N, N-dimethyl-4-[(quinolin-6-yl) azo] benzenamine, o-aminoazotoluene, Alizarin Yellow R, 4 '-(Aminosulfonyl) 4-hydroxy-azobenzene-3-carboxylic acid, Congo red, vital red, Metanil Yellow, Orange II, Disperse Orange 3, C. I. Direct orange 39, 2,2'-dihydroxyazobenzene, azobenzene-4,4'-diol, naphthyl red, 5-phenylazobenzene-2-ol, 2,2'-dimethylazobenzene, C.I. I. Examples include Mordant Yellow 12, Mordant Yellow 10, Acid Yellow, Disperse Blue, New Yellow RMF, Vistramine Brown G, and the like.

(Compound having phenazine structure and azobenzene structure)
A compound having a phenazine structure and an azobenzene structure can be represented by the following formula (3). In the present embodiment, one or more compounds having a phenazine structure and an azobenzene structure represented by the following formula (3) can be contained as an additive.

Here, in Formula (3), 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.

  Specifically, examples of the compound having a phenazine structure and an azobenzene structure include 3- (diethylamino) -7-[(4-hydroxyphenyl) azo] -2,8-dimethyl-5-phenylphenazine-5-ium. , 3-[[4- (Dimethylamino) phenyl] azo] -7- (diethylamino) -5-phenylphenazine-5-ium, Janus Green B, 3-amino-7-[(2,4-diaminophenyl) Azo] -2,8-dimethyl-5-phenylphenazine-5-ium, 2,8-dimethyl-3-amino-5-phenyl-7- (2-hydroxy-1-naphthylazo) phenazine-5-ium, 3 -[[4- (Dimethylamino) phenyl] azo] -7- (dimethylamino) -5-phenylphenazine-5-ium, 3-amino-7-[[4 (Dimethylamino) phenyl] azo] -5-phenylphenazine-5-ium, 2- (diethylamino) -7- [4- (methylpropargylamino) phenylazo] -9-phenyl-9-azonia-10-azaanthracene, 2- (Diethylamino) -7- [4- (methyl 4-pentynylamino) phenylazo] -9-phenyl-9-azonia-10-azaanthracene, 2- (diethylamino) -7- [4- (methyl 2, 3-dihydroxypropylamino) phenylazo] -9-phenyl-9-azonia-10-azaanthracene and the like.

(4) Surfactant A nonionic surfactant is contained as the surfactant. In this embodiment, a nonionic surfactant is added to the electrolytic solution together with the above-described additives, thereby suppressing the growth in the direction perpendicular to the flat surface, that is, having a smooth surface. Copper powder can be produced.

  As the nonionic surfactant, one kind can be used alone, or two or more kinds can be used in combination, and the concentration in the electrolytic solution can be about 1 mg / L to 10,000 mg / L in total.

Although it does not specifically limit as a number average molecular weight of a nonionic surfactant, It is preferable that it is 100-200000, It is more preferable that it is 200-15000, It is further more preferable that it is 1000-10000. When the surfactant has a number average molecular weight of less than 100, fine electrolytic copper powder that does not exhibit a dendritic shape may be deposited. On the other hand, if the surfactant has a number average molecular weight of more than 200,000, electrolytic copper powder having a large average particle diameter may be precipitated, and only a dendritic copper powder having a specific surface area of less than 0.2 m ² / g may be obtained. There is sex. In the present embodiment, the number average molecular weight is a molecular weight in terms of polystyrene determined by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

  The type of nonionic surfactant is not particularly limited, but is preferably a surfactant having an ether group, for example, polyethylene glycol, polypropylene glycol, polyethyleneimine, pluronic surfactant, tetronic surfactant. , Polyoxyethylene glycol / glycerin ether, polyoxyethylene glycol / dialkyl ether, polyoxyethylene polyoxypropylene glycol / alkyl ether, aromatic alcohol alkoxylate, polymer compound represented by the following formula (x), and the like. These nonionic surfactants can be used alone or in combination of two or more.

More specifically, as polyethylene glycol, what is represented, for example by following formula (i) can be used.
(In formula (i), n1 represents an integer of 1 to 120.)

Moreover, as polypropylene glycol, what is represented, for example by following formula (ii) can be used.
(In formula (ii), n1 represents an integer of 1 to 90.)

Moreover, as polyethyleneimine, what is represented, for example by following formula (iii) can be used.
(In formula (iii), n1 represents an integer of 1 to 120.)

Moreover, as a pluronic-type surfactant, what is represented, for example by following formula (iv) can be used.
(In formula (iv), n2 and l2 represent an integer of 1 to 30, and m2 represents an integer of 10 to 100.)

Moreover, as a tetronic type surfactant, what is represented, for example by following formula (v) can be used.
(In formula (v), n3 represents an integer of 1 to 200, and m3 represents an integer of 1 to 40.)

Moreover, as polyoxyethylene glycol glyceryl ether, what is represented, for example by a following formula (vi) can be used.
(In formula (vi), n4, m4, and l4 each represent an integer of 1 to 200.)

Moreover, as polyoxyethylene glycol dialkyl ether, what is represented, for example by a following formula (vii) can be used.
(In formula (vii), R ₁ and R ₂ represent a hydrogen atom or a lower alkyl group having 1 to 5 carbon atoms, and n5 represents an integer of 2 to 200.)

Moreover, as polyoxyethylene polyoxypropylene glycol alkyl ether, what is represented, for example by a following formula (viii) can be used.
(In the formula (viii), R ₃ represents a hydrogen atom or a lower alkyl group having 1 to 5 carbon atoms, and m6 or n6 represents an integer of 2 to 100.)

Moreover, as an aromatic alcohol alkoxylate, what is represented, for example by a following formula (ix) can be used.
(In formula (ix), m7 represents an integer of 1 to 5, and n7 represents an integer of 1 to 120.)

Also, a polymer compound represented by the following formula (x) can be used.
(In Formula (x), R ₁ is a residue of a higher alcohol having 5 to 30 carbon atoms, a residue of an alkylphenol having an alkyl group having 1 to 30 carbon atoms, or an alkyl naphthol having an alkyl group having 1 to 30 carbon atoms. A residue of a fatty acid amide having 3 to 25 carbon atoms, a residue of an alkylamine having 2 to 5 carbon atoms, or a hydroxyl group, and R ₂ and R _{3 each} represent a hydrogen atom or a methyl group. Moreover, m and n show the integer of 1-100.)

(5) Chloride ions As chloride ions, compounds that supply chloride ions such as hydrochloric acid and sodium chloride (chloride ion source) can be added to the electrolyte solution. Chloride ions contribute to the shape control of the precipitated copper powder together with the above-described additives and nonionic surfactants. Although it does not specifically limit as a chloride ion density | concentration in electrolyte solution, It can be set as about 1 mg / L-500 mg / L.

In the method for producing the dendritic copper powder 1, for example, the copper powder is produced by depositing on the cathode by electrolysis using the electrolytic solution having the composition as described above. As the electrolysis method, a known method can be used. For example, the current density is preferably in the range of 3 A / dm ^{2 to} 30 A / dm ² when electrolyzing using a sulfuric acid electrolyte, 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.

  As described above, in the present embodiment, the dendritic copper powder 1 has a copper ion, a group consisting of a compound having a phenazine structure, a group consisting of a compound having an azobenzene structure, and a phenazine structure and an azobenzene structure. A sulfuric acid acidic solution containing an additive which is at least one selected from each of the group consisting of compounds, or two or more selected from different groups, a nonionic surfactant, and components such as chloride ions The electrolytic solution is produced by being deposited on the cathode by an electrolytic method.

  Therefore, since copper ions in the electrolytic solution are consumed by precipitation due to electrolysis, the copper ion concentration decreases with the passage of time of electrolysis. In addition, organic compounds such as additives and nonionic surfactants may be decomposed or consumed directly by electrolysis or indirectly through reaction byproducts. Furthermore, when taking out the deposited copper powder from the electrolytic solution, each component in the electrolytic solution may adhere to the copper powder and be discharged out of the electrolytic cell. As described above, the concentration of each component in the electrolytic solution decreases due to various factors. Therefore, the management width is determined so that the copper powder has a desired dendritic shape, and each component is appropriately supplemented. Is generally done.

<2-2. Process for inspecting the quality of dendritic copper powder>
Here, there is a close relationship between the shape of the copper powder and the electrical resistance of a coating film or electromagnetic wave shield obtained from a conductive paste using this as a metal filler. Therefore, it is extremely important for quality assurance to appropriately manage the shape of the copper powder used for the metal filler. As explained above, in order to obtain excellent conductivity (low electrical resistance), it is necessary to bring the copper powders into contact with each other on the surface and to keep the contact resistance low by contact with a large area. The shape of the copper powder is particularly important for bringing the copper powders into contact with each other on the surface, and, like the dendritic copper powder 1 in the present embodiment, if the dendritic shape is a collection of flat copper particles, It is extremely advantageous for bringing copper powders into contact with each other on the surface.

  The shape of the copper powder depends on the balance of the concentration of each component in the electrolytic solution. Therefore, even when the concentration management width of each component is set and appropriately managed, the shape of the obtained copper powder is not necessarily in a managed state.

  Then, in the manufacturing method which concerns on this Embodiment, it has the process of test | inspecting the quality of copper powder after the process of manufacturing dendritic copper powder. The quality of copper powder typically includes the shape of the copper powder. Below, the process which test | inspects the quality (shape of copper powder) of copper powder is demonstrated in detail.

  Specifically, the step of inspecting the quality of the copper powder includes the step of slurrying the copper powder, the step of precipitating the copper powder in the slurry, and the reflectance of the precipitated copper powder using a spectrophotometer. And a step of determining the shape of the copper powder.

<2-2-1. Step of slurrying copper powder>
In the step of slurrying copper powder (hereinafter also referred to as “copper powder slurrying step”), the copper powder obtained by precipitation by the electrolytic method is dispersed in water to obtain a copper powder water slurry.

  Copper powder deposited on the cathode by the electrolysis method is scraped off from the cathode and collected. Since each component of the electrolytic solution adheres to the recovered copper powder and may affect the reflectance of the copper powder described later, a cleaning process may be performed. In addition, as a washing | cleaning process, copper powder can be disperse | distributed in a washing | cleaning liquid and it can wash | clean while stirring. As the washing liquid, an acidic solution or pure water may be used, and after washing, filtration and separation of copper powder and washing with water are repeated as appropriate. For example, by repeating the washing operation in this way, a water slurry in which copper powder is dispersed in water can be obtained. In addition, what is necessary is just to use a well-known method about filtration, isolation | separation, and water washing.

<2-2-2. Step of settling copper powder in slurry>
In the step of settling the copper powder in the slurry (hereinafter also referred to as “settling step”), the copper powder slurry is separated and transferred to a measurement cell that can be loaded into a spectrophotometer, and the copper powder in the slurry is settling ( Filling).

  The measurement cell may be appropriately selected according to the spectrophotometer, but with a cap when centrifugation is employed as a process in the step of fixing the copper powder filled in the measurement cell as described later. It is preferable to use a measurement cell, and it is more preferable to use a measurement cell with a screw cap. By using a measurement cell with a cap, the centrifugation operation can be facilitated.

  As an operation for sedimentation, a known method such as decantation may be used. As will be described later, in order to measure the reflectance of copper powder with a spectrophotometer, a predetermined sample amount corresponding to the apparatus is required. It is sufficient if the required amount can be ensured by one transfer, but if the required amount cannot be ensured by one transfer, the supernatant liquid as a solvent is discarded, and the slurry is further separated and added to the measurement cell. A series of operations for settling the copper powder after the transfer is repeated, and the height of the copper powder settling and filling the bottom of the measurement cell is set to an amount required for the measurement by the spectrophotometer.

  The copper powder settled (filled) at the bottom of the measurement cell is preferably fixed. By fixing the copper powder that has settled at the bottom of the measurement cell, it is possible to prevent the copper powder from being redispersed in the solvent due to vibrations etc. when the measurement cell is transported or loaded into the spectrophotometer. Further, since the filling state becomes uniform and the density increases by fixing, the measurement accuracy of the reflectance can be improved.

  As a method of immobilization, any method may be used as long as the copper powder is packed more densely, but it is preferable to load the centrifuge with a measurement cell and immobilize by centrifugation.

  The centrifugation conditions may be set as appropriate as long as the copper powder is not easily redispersed and is packed uniformly and densely. For example, the rotation speed is 500 rpm to 5000 ppm, and the rotation time is 10 seconds to 10 seconds. It can be set as a minute.

<2-2-3. Process of measuring reflectance of copper powder>
In the step of measuring the reflectance of copper powder (hereinafter also referred to as “reflectance measurement step”), a spectrophotometer is loaded with a measurement cell in which copper powder is immobilized, and the reflectance of copper powder at a specific wavelength is measured. To do.

  The reflectance of the copper powder at a specific wavelength is obtained by adding the influence of the geometric shape to the intrinsic reflectance of the copper powder material. Specifically, if the copper powder has a smooth surface and a flat surface, the reflectance becomes high, and if the copper powder has a rough surface, the reflectance becomes low. Therefore, by providing the reflectance measurement step in this way, copper powder having a relatively large number of planes such as plate-like, scale-like, flake-like, and copper powder that is said to have a dendritic shape in which they are assembled Therefore, it is possible to effectively evaluate whether or not it has a desired shape.

  The wavelength (measurement wavelength) used for measuring the reflectance of the copper powder is preferably in the range from 300 nm to 500 nm from ultraviolet to visible light. In the following, the reflectance at a measurement wavelength of 300 nm to 500 nm is sometimes referred to as “ultraviolet visible reflectance”.

  For example, the reflectance of bulk copper is as high as about 80% or higher in the region where the wavelength is 600 nm or more, but decreases in the region where the wavelength is 500 nm or less, about 50% at the wavelength of 500 nm, and about 30% at the wavelength of 300 nm. Not expensive. In a bulk copper region where the reflectance is about 50% or less, it is easily affected by the geometric shape, and the tabular particles easily reflect incident light. As the shape develops, the reflectance tends to increase, which is suitable for inspecting the shape of the copper powder. On the other hand, in the wavelength region where the reflectivity is high for bulk copper, the reflectivity is high even if it is not a plate-like particle, and the difference in reflectivity with respect to the difference in the shape of the copper powder is small and the sensitivity is lowered. Not suitable for use in

  Therefore, the upper limit of the measurement wavelength is preferably 500 nm or less. The lower limit of the measurement wavelength is not particularly limited, but in view of the measurement wavelength specification of a widely used ultraviolet-visible spectrophotometer, the shape of the copper powder is effectively inspected as long as it is 300 nm or more. can do. Of course, it does not prevent the measurement wavelength from being set to 200 nm or 250 nm, for example, for measurement in the process of inspecting copper powder.

  As long as the spectrophotometer used for the measurement is a specification capable of measuring the range of the selected measurement wavelength as described above, a commercially available device may be appropriately selected. For example, an ultraviolet-visible spectrophotometer can be used. .

Here, the reflectance (%) is preferably a relative reflectance with respect to a standard white plate as a reference attached to the spectrophotometer, which is obtained by the following equation.
Reflectance (relative reflectance) (%)
= (Light quantity reflected by copper powder / light quantity reflected by standard white plate) × 100

<2-2-4. Step of determining the shape of the dendritic copper powder>
As described above, the reflectance becomes higher as the copper powder has a shape that can be easily reflected geometrically. Therefore, in the manufacturing method of the dendritic copper powder 1 according to the present embodiment, the copper powder has a desired shape based on the measured reflectance of the copper powder and a predetermined reference reflectance determined in advance. The quality of the copper powder is inspected and the quality is controlled. Hereinafter, the step of determining the shape of the copper powder is also referred to as a “shape determination step”.

  The copper powder deposited by the electrolytic method shows a reflectance of about 5% to 35% when the ultraviolet visible reflectance is measured at a measurement wavelength of 300 nm to 500 nm by the method described above. Therefore, in the shape determination step, for example, for the measurement wavelength of 400 nm, the reference reflectance is set to 9%, and it is determined whether or not the measured reflectance of the copper powder is 9% or more. Accordingly, it can be determined that the copper powder having a reflectance of 9% or more has a particle shape in which a plane surface is developed.

  The upper limit of the reflectance of the copper powder at the measurement wavelength of 400 nm is not particularly limited, and the reflectance of the bulk copper at the wavelength of 400 nm is about 40%, and the copper powder is substantially 30% or less. .

  Similarly, for the measurement wavelength of 300 nm, the reference reflectance is set to 7.5%, and it is determined whether or not the measured reflectance of the copper powder is 7.5% or more. Accordingly, it is possible to determine that the copper powder having a reflectance of 7.5% or more has a particle shape in which a plane surface is developed.

  The upper limit of the reflectance of the copper powder at the measurement wavelength of 300 nm is not particularly limited, and is substantially 25% or less for the copper powder.

  Similarly, for the measurement wavelength of 500 nm, the reference reflectance is set to 10%, and it is determined whether or not the measured reflectance of the copper powder is 10% or more. Thereby, it can be determined that the copper powder having a reflectance of 10% or more has a particle shape in which a plane surface is developed.

  The upper limit of the reflectance of the copper powder at the measurement wavelength of 500 nm is not particularly limited, and is substantially 35% or less for the copper powder.

  In addition, although the reference | standard based on a predetermined reflectance was illustrated as a quality reference | standard (quality determination reference | standard) of copper powder, it is not limited to this.

  As described above, there is a correlation between the shape of the dendritic copper powder and the reflectance. As is clear from the examples described later, the shape of the dendritic copper powder 1 and the conductivity when the copper powder is used in a conductive paste or the like have a correlation. That is, for example, among the copper powders having a dendritic shape in which flat copper particles are aggregated, the particles having developed flat surfaces, the specific resistance value (volume) of the coating made of the conductive paste using these as metal fillers (Resistivity) becomes low and conductivity becomes high. Therefore, by selecting the measurement wavelength and setting the reference reflectance, and determining whether or not the measured reflectance of the copper powder is greater than (or exceeds) the reference reflectance, the metal filler used for the conductive paste or the like It becomes possible to inspect whether the quality (conductivity) is satisfied.

  Thus, the quality of copper powder can be evaluated easily and rapidly by measuring copper powder with a spectrophotometer and using the measured reflectance as an index. Thus, the quality-controlled dendritic copper powder 1 can be provided by providing a step of inspecting the quality of the dendritic copper powder 1 when the dendritic copper powder 1 is produced. As a result, when the obtained dendritic copper powder 1 is used as a metal filler such as a conductive paste or an electromagnetic wave shield, the dendritic copper powder 1 capable of ensuring high conductivity can be accurately produced.

≪3. Use of conductive paste, conductive paint for electromagnetic wave shield, conductive sheet >>
As described above, the dendritic copper powder 1 according to the present embodiment is a dendritic copper powder having a main trunk 2 and a plurality of branches 3, and the main trunk 2 and the plurality of branches 3 branched from the main trunk 2. Is composed of flat copper particles having a cross-sectional average thickness of 0.02 μm to 5.0 μm. Moreover, the average particle diameter (D50) of the dendritic copper powder 1 is 1.0 μm to 100 μm. In such a dendritic copper powder 1, the dendritic shape increases the surface area, provides excellent formability and sinterability, and is dendritic and has a predetermined cross-sectional average thickness. By being composed of flat copper particles, a large number of contacts can be secured, and excellent conductivity is exhibited.

  Moreover, the dendritic copper powder 1 has a maximum height in the vertical direction with respect to the flat surface of the copper particles of 1/10 or less with respect to the maximum length in the horizontal direction of the flat surface. It is a copper powder having a smooth surface that suppresses growth in the vertical direction. According to such a dendritic copper powder 1, the contact points between the copper powders can be further increased, and the conductivity can be improved.

  Moreover, according to the dendritic copper powder 1 having such a predetermined structure, even when it is a copper paste or the like, it is possible to suppress agglomeration and to uniformly disperse 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, the dendritic copper powder 1 can be suitably used for applications such as a conductive paste.

  For example, as a conductive paste (copper paste), the dendritic copper powder 1 according to the present embodiment is included as a metal filler (copper powder), a binder resin, a solvent, and an antioxidant, a coupling agent, and the like as necessary. It can be produced by kneading with the additive.

  In the present embodiment, the dendritic copper powder 1 described above in the metal filler is 20% by mass or more, preferably 30% by mass or more, more preferably 50% by mass or more with respect to 100% by mass of the entire metal filler. Mix in proportions. If the ratio of the dendritic copper powder 1 in the metal filler is 20% by mass or more, for example, when the metal filler is used in the copper paste, it can be uniformly dispersed in the resin, and the paste has an excessive viscosity. It is possible to prevent the printability from being increased. Moreover, the electroconductivity excellent as an electrically conductive paste can be exhibited by being the dendritic copper powder 1 which consists of an aggregate | assembly of a tabular fine copper particle.

  In addition, as a metal filler, as long as it mixes so that the dendritic copper powder 1 may become a ratio of the quantity of 20 mass% or more as mentioned above, others mix spherical copper powder etc. of about 1 micrometer-20 micrometers, etc., for example. You may combine them.

  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 is adjusted in consideration of the particle size of the dendritic copper powder 1 so as to have a viscosity suitable for a conductive film forming method such as screen printing or a dispenser. can do.

  Furthermore, other resin components can be added for viscosity adjustment. For example, a cellulose-based resin typified by ethyl cellulose can be used, which is 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 preferred. 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.

  Next, even when the dendritic copper powder 1 according to the present embodiment is used as a metal filler as an electromagnetic wave shielding material, it is not limited to use under particularly limited conditions, but a general method, For example, a metal filler can be used by mixing with a resin.

  For example, the resin used for forming the electromagnetic wave shielding layer of the electromagnetic wave shielding conductive sheet is not particularly limited, and conventionally used vinyl chloride resin, vinyl acetate resin, vinylidene chloride resin, Thermoplastic resin, thermosetting resin, radiation curable type made of various polymers and copolymers such as acrylic resin, polyurethane resin, polyester resin, olefin resin, chlorinated olefin resin, polyvinyl alcohol resin, alkyd resin, phenol resin, etc. Resin etc. can be used suitably.

  As a method for producing an electromagnetic shielding material, for example, the above-described metal filler and resin are dispersed or dissolved in a solvent to form a coating material, and the coating material is applied or printed on the substrate to form the electromagnetic shielding layer. It can be manufactured by forming and drying to such an extent that the surface solidifies. Moreover, a metal filler can also be utilized for the conductive adhesive layer of a conductive sheet.

  Further, even when the dendritic copper powder 1 according to the present embodiment is used as a metal filler to form a conductive paint for electromagnetic wave shielding, it is not limited to use under particularly limited conditions. It can be used as a conductive paint by mixing a method, for example, a metal filler with a resin and a solvent, and further mixing with an antioxidant, a thickener, an anti-settling agent and the like as necessary.

  The binder resin and solvent used at this time are not particularly limited, and conventionally used vinyl chloride resin, vinyl acetate resin, acrylic resin, polyester resin, fluorine resin, silicon resin, phenol resin, etc. are used. can do. 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. Well, as the antioxidant as an additive, conventionally used fatty acid amides, higher fatty acid amines, phenylenediamine derivatives, titanate coupling agents and the like can be used.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Evaluation method>
The copper powder obtained in the following examples was subjected to shape observation, average particle diameter measurement, specific surface area measurement, 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 copper powder contained in the visual field was observed.

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

(Specific resistance measurement)
About the specific resistance value (volume resistivity) of the film, the sheet resistance value was 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 film was measured by a thickness measuring instrument (SURFCOM130A, manufactured by Tokyo Seimitsu Co., Ltd.), and the sheet resistance value was divided by the film thickness.

[Example 1]
<Manufacture of dendritic copper powder>
In an electrolytic cell having a capacity of 100 L, a titanium electrode plate having an electrode area of 200 mm × 200 mm is used as a cathode, and a copper electrode plate having an electrode area of 200 mm × 200 mm is used as an anode, and an electrolytic solution is loaded in 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 5 g / L and a sulfuric acid concentration of 100 g / L was used. Further, a hydrochloric acid solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the electrolytic solution so that the chloride ion (chlorine ion) concentration in the electrolytic solution was 50 mg / L. In addition, safranin (manufactured by Kanto Chemical Co., Ltd.), which is a compound having a phenazine structure, is added as an additive to the electrolytic solution so that the concentration in the electrolytic solution is 50 mg / L, and a nonionic surfactant is further added. Polyethylene glycol (PEG) having a molecular weight of 1000 (manufactured by Wako Pure Chemical Industries, Ltd.) was added to a concentration of 20 mg / L in the electrolytic solution.

Then, while circulating the electrolytic solution adjusted to the concentration as described above at a flow rate of 15 L / min using a pump, the temperature is maintained at 25 ° C. and the current density of the cathode is 10 A / dm ^2. Then, copper powder was deposited 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. .

<Measurement of UV-visible reflectance>
A part of the copper powder scraped off to the bottom of the electrolytic cell was collected and used for the measurement of ultraviolet visible reflectance. The procedure up to the measurement is as follows.

  That is, the collected aqueous slurry of copper powder was pipetted, transferred to a cell with a screw cap as a measurement cell, decanted to precipitate the copper powder, and the supernatant was discarded. And the copper powder fractionated with the pipette was further added in the cell with a screw cap, decanted, the copper powder was settled, and the supernatant liquid was discarded. This operation is repeated until the height of the settled copper powder reaches the height required for the measurement with the spectrophotometer, and the copper in the measurement cell becomes copper until the height from the bottom of the cell with the screw cap reaches 2 cm. Filled with flour.

  Next, a cell with a screw cap (inner diameter: 10 mm) filled with copper powder at the bottom is loaded into a centrifuge, centrifuged at 3000 rpm for 1 minute, and the filling state is made uniform and more densely packed and fixed. Turned into.

Next, the cell with a screw cap was loaded into an ultraviolet-visible infrared spectrophotometer (V-770iRM manufactured by JASCO Corporation), and the reflectance of copper powder at a wavelength of 400 nm was measured. The reflectance is a relative reflectance based on a standard white board obtained by the following equation. The obtained reflectance was 10.2%.
Reflectance (%) = (light quantity reflected by copper powder / light quantity reflected by standard white plate) × 100

  As a result of observing this copper powder with a field of view at a magnification of 5,000 times by SEM, at least 90% by number or more of the copper powder is a collection of flat copper particles, and the dendritic copper powder has a dendritic shape. Met.

  Further, while observing the obtained dendritic copper powder by SEM, the cross-sectional average thickness of the flat copper particles, the maximum length and the flat plate grown in the direction perpendicular to the flat surface of the dendritic copper powder. The ratio of the long axis length in the horizontal direction with respect to the shape surface was measured. As a result, the copper particles constituting the obtained dendritic copper powder were in the form of a flat plate having a cross-sectional average thickness of 1.0 μm. Moreover, the average particle diameter (D50) of the dendritic copper powder was 17.8 μm. The ratio of the maximum length of the dendritic copper powder grown in the vertical direction from the flat surface to the maximum length in the direction horizontal to the flat surface (flat direction) (vertical length / flat length in the flat plate direction) Was an average of 0.067.

<Preparation of conductive paste>
15 parts by mass of phenol resin (manufactured by Gunei Chemical Co., Ltd., PL-2211) and 10 parts by mass of butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., deer special grade) are mixed with 55 parts by mass of the prepared dendritic copper powder, and a small kneader ( Using a non-bubbling kneader NBK-1 manufactured by Nippon Seiki Seisakusho, paste was made by repeating kneading at 1200 rpm for 3 minutes three times. The obtained conductive paste was printed on a glass with a metal squeegee and cured in an air atmosphere.

The specific resistance value of the film obtained by curing was 9.7 × 10 ⁻⁴ Ω · cm.

[Example 2]
In the production of dendritic copper powder, electrolytic copper powder was deposited on the cathode plate under the same conditions as in Example 1 except that the safranine concentration was 10 mg / L. A part of the water slurry after the copper powder was washed with pure water was sampled, and the ultraviolet visible reflectance was measured under the same conditions as in Example 1. The measurement result of the reflectance was 9.5%. In FIG. 3, the photograph figure which observed the obtained copper powder by SEM (5,000-times multiplication factor) is shown.

  This copper powder was observed by SEM, and it was confirmed that at least 80% by number or more of the copper powder was a dendritic copper powder in which flat copper particles gathered together to form a dendritic shape. The average cross-sectional thickness of the tabular copper particles is 1.2 μm, and the ratio of the maximum length grown in the direction perpendicular to the tabular surface to the major axis length in the horizontal direction relative to the tabular surface is 0.072. The average particle diameter (D50) of the dendritic copper powder was 20.1 μm.

The dendritic copper powder was made into a conductive paste under the same conditions as in Example 1, and this conductive paste was printed on glass with a metal squeegee and cured in an air atmosphere to form a film. The specific resistance value of this film was 1.8 × 10 ⁻³ Ω · cm. These are summarized in Table 1.

[Example 3]
In the production of dendritic copper powder, electrolytic copper powder was deposited on the cathode plate under the same conditions as in Example 1 except that the polyethylene glycol concentration was 10 mg / L. A part of the water slurry after the copper powder was washed with pure water was sampled, and the ultraviolet visible reflectance was measured under the same conditions as in Example 1. The measurement result of the reflectance was 9.2%.

  This copper powder was observed by SEM, and it was confirmed that at least 80% by number or more of the copper powder was a dendritic copper powder in which flat copper particles gathered together to form a dendritic shape. The average cross-sectional thickness of the tabular copper particles is 1.5 μm, and the ratio between the maximum length grown in the direction perpendicular to the tabular surface and the major axis length in the horizontal direction relative to the tabular surface is It was 0.077. The average particle diameter (D50) of the dendritic copper powder was 22.0 μm.

The dendritic copper powder was made into a conductive paste under the same conditions as in Example 1, and this conductive paste was printed on glass with a metal squeegee and cured in an air atmosphere to form a film. The specific resistance value of this film was 2.3 × 10 ⁻³ Ω · cm. These are summarized in Table 1.

[Example 4]
In the production of dendritic copper powder, electrolytic copper powder was deposited on the cathode plate under the same conditions as in Example 1 except that the safranin concentration was 0.1 mg / L. A part of the water slurry after the copper powder was washed with pure water was sampled, and the ultraviolet visible reflectance was measured under the same conditions as in Example 1. The measurement result of the reflectance was 7.5%. In FIG. 4, the photograph figure which observed the obtained copper powder by SEM (5,000-times multiplication factor) is shown.

  This copper powder was observed by SEM, and it was confirmed that the dendritic copper powder in which the flat copper particles were densely formed to form a dendritic shape was at most 20% by number or less. The average particle diameter (D50) of the dendritic copper powder was 18.6 μm.

The dendritic copper powder was made into a conductive paste under the same conditions as in Example 1, and this conductive paste was printed on glass with a metal squeegee and cured in an air atmosphere to form a film. The specific resistance value of this film was 4.4 × 10 ⁻³ Ω · cm. These are summarized in Table 1.

[Example 5]
In the production of dendritic copper powder, electrolytic copper powder was deposited on the cathode plate under the same conditions as in Example 1 except that the polyethylene glycol concentration was 0.1 mg / L. A part of the water slurry after the copper powder was washed with pure water was sampled, and the ultraviolet visible reflectance was measured under the same conditions as in Example 1. The measurement result of the reflectance was 8.7%.

  As a result of observing this copper powder with SEM, it was confirmed that the dendritic copper powder in which the flat copper particles were densely formed to form a dendritic shape was at most 30% by number or less. The average particle size (D50) of the dendritic copper powder was 22.7 μm.

The dendritic copper powder was made into a conductive paste under the same conditions as in Example 1, and this conductive paste was printed on glass with a metal squeegee and cured in an air atmosphere to form a film. The specific resistance value of this film was 3.0 × 10 ⁻³ Ω · cm. These are summarized in Table 1.

  Moreover, in FIG. 5, the relationship between the reflectance of the copper powder measured in Examples 1-5 and the specific resistance value of the film produced with the electrically conductive paste which used this copper powder as a metal filler is shown. FIG. 5 shows that there is a negative correlation between the reflectance of the copper powder and the specific resistance value of the coating. That is, as described above, the higher the reflectance of the copper powder, the more the flat particles are developed and have a dendritic shape in which they are assembled, and the specific resistance value decreases. This is considered to be because as the flat copper particles develop, the number of contacts increases in the coating and the conductivity increases.

  Therefore, by measuring the ultraviolet-visible reflectance of the copper powder, the quality of the copper powder can be controlled in terms of shape, and the conductivity when the final product is a conductive paste can be predicted.

Also, if 9% or more reflectivity of the copper powder at a measurement wavelength of 400 nm, a specific resistance value of the coating becomes less 2.5 × 10 ^-3 Ω · cm, it is seen that more excellent conductivity. Therefore, if the inspection to measure the reflectance of the copper powder produced by the electrolytic method is performed and only the copper powder showing a reflectance of 9% or more at a wavelength of 400 nm is used as the metal filler, it is extremely effective for quality assurance. I understand that there is.

DESCRIPTION OF SYMBOLS 1 Dendritic copper powder 2 Main trunk 3,3a, 3b Branch 4 Maximum length to a horizontal direction (XY direction) with respect to a flat surface 5 Vertical direction with respect to a flat surface (XY plane) Maximum height to

Claims (9)

A method for producing a copper powder having a dendritic shape,
A process of producing copper powder by an electrolytic method;
Inspecting the quality of the copper powder based on the reflectance of the copper powder measured by a spectrophotometer and a predetermined reflectance standard;
A method for producing a copper powder. In the step of inspecting the quality of the copper powder,
The method for producing a copper powder according to claim 1, wherein a measurement wavelength of the reflectance is 300 nm to 500 nm. In the step of inspecting the quality of the copper powder,
The method for producing copper powder according to claim 2, wherein the reflectance reference at a measurement wavelength of 400 nm is 9% or more. In the process of producing the copper powder,
Copper ions,
A group consisting of a compound having a phenazine structure represented by the following formula (1), a group consisting of a compound having an azobenzene structure represented by the following formula (2), and a phenazine structure and azobenzene represented by the following formula (3) One or more types each selected from the group consisting of compounds having a structure, or two or more types selected from different groups,
One or more types of nonionic surfactants;
The manufacturing method of the copper powder in any one of Claims 1 thru | or 3 which manufactures copper powder by electrolysis using the electrolyte solution containing this.
[In Formula (1), R ₁ , R ₂ , R ₃ , R ₄ , R ₆ , R ₇ , R ₈ , R ₉ are each independently 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, R ₅ is hydrogen, halogen , selected amino, OH, -O, CN, SCN , SH, COOH, COO salt, COO _ester, SO 3 H, SO ₃ salt, SO ₃ ester, benzenesulfonic acid, from the group consisting of lower alkyl, and aryl And A ⁻ is a halide anion. ]
[In the formula (2), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ are each independently hydrogen, halogen, amino, OH, = O, CN, SCN, SH, COOH, COO salt, COO ester, SO ₃ H, SO ₃ salt, SO ₃ ester, a group selected from the group consisting of benzenesulfonic acid, lower alkyl, and aryl. ]
[In the formula (3), 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 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, A group selected from the group consisting of lower alkyl and aryl, and A ⁻ is a halide anion. ] The method for producing copper powder according to claim 4, wherein the electrolytic solution contains chloride ions. The step of inspecting the quality of the copper powder includes:
Slurrying the copper powder obtained in the step of producing the copper powder;
Transferring the slurry to a measurement cell and allowing copper powder to settle;
The method for producing a copper powder according to claim 1, further comprising: loading the measurement cell into a spectrophotometer and measuring the reflectance of the precipitated copper powder. The copper powder is
A dendritic shape having a main trunk that grows linearly and a plurality of branches separated from the main trunk,
The main trunk and the branch are constituted by a collection of tabular copper particles having an average cross-sectional thickness of 0.02 μm to 5.0 μm determined by scanning electron microscope (SEM) observation,
The average particle diameter (D50) of the copper powder is 1.0 μm to 100 μm,
The maximum height in the vertical direction with respect to the flat surface of the copper particles is 1/10 or less with respect to the maximum length in the horizontal direction of the flat surface.
The manufacturing method of the copper powder in any one of Claims 1 thru | or 6.   The manufacturing method of a metal filler including the process of mixing the copper powder obtained by the manufacturing method in any one of Claims 1 thru | or in the ratio of 20 mass% or more with respect to the whole mass.   The manufacturing method of an electrically conductive paste including the process of knead | mixing the metal filler obtained by the manufacturing method of Claim 8 with binder resin and a solvent.