JP6274076B2 - Copper powder and copper paste, conductive paint, conductive sheet using the same - Google Patents

Description

  The present invention relates to copper powder used as a material for conductive paste and the like, and more specifically, copper powder having a novel shape capable of improving conductivity, copper paste using the same, and conductive paint The present invention relates to a conductive sheet.

  For the formation of wiring layers, electrodes, and the like in electronic devices, many pastes using metal fillers such as silver powder and copper powder, such as resin paste and fired paste, are used. A metal filler paste of silver or copper is applied or printed on various substrates of an electronic device, and is subjected to heat curing or heat baking treatment to form a conductive film that becomes 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 cured by heating 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 less, it is often used for a substrate using a heat-sensitive material such as a printed wiring board.

  On the other hand, the firing-type conductive paste is made of a metal filler, glass, a 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 printed wiring boards that use resin materials. However, since metal fillers are connected by sintering, they have low resistance. Is easy to obtain. Such a fired conductive paste is used, for example, 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 evaluating particles from the size in the three directions of length, width, and thickness, a flat plate shape with a small thickness contributes to a reduction in the thickness of the wiring material due to a decrease in thickness, and a certain thickness. There is an advantage that a larger area where the grains come into contact with each other than a certain cubic or spherical particle 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.

  Further, for example, Patent Document 2 discloses a technique relating to a copper powder for conductive paste, more specifically, a disk-shaped copper powder capable of obtaining 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 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, for example, Patent Document 3 discloses a method for obtaining electrolytic copper powder that can be molded with high strength, with improved formability than conventional electrolytic copper powder, without unnecessarily developing the branches of electrolytic copper powder. Yes. 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 size 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, and it has been 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.

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

  The present invention has been proposed in view of the above-described circumstances, and is preferably used as an application such as a conductive paste or an electromagnetic wave shield while ensuring excellent conductivity by increasing the number of contacts between copper powders. It aims at providing the copper powder which can do.

  The inventors of the present invention have made extensive studies for solving the above-described problems. As a result, it is a copper powder composed of flat 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 having a cross-sectional average thickness in a specific range. In addition, the average particle diameter (D50) of the copper powder is in a specific range, so that excellent conductivity can be ensured and, for example, it can be uniformly mixed with a resin, which is suitable for applications such as a conductive paste. The present invention has been completed by finding that it can be used. That is, the present invention provides the following.

  (1) A first invention according to the present invention is a copper powder in which 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, wherein the main trunk of the copper particles and The branch is a copper powder having a cross-sectional average thickness of 0.02 μm to 0.3 μm and an average particle diameter (D50) of the copper powder of 1.0 μm to 30 μm.

  (2) According to a second aspect of the present invention, in the first aspect, the surface of the copper particles has fine convex portions, and the average height of the convex portions is 0.01 μm to 0.3 μm. It is the copper powder characterized by this.

(3) In the third invention according to the present invention, in the first or second invention, a ratio obtained by dividing the cross-sectional thickness of the tabular copper particles by the average particle diameter (D50) of the copper powder is 8. 0 in the range of × ¹⁰ -4 ~1.5 × ^{10 -1,} and the copper bulk density of the copper powder is characterized in that in the range of 0.5g ^/ cm ³ ~5.0g ^/ cm 3 It is powder.

  (4) According to a fourth aspect of the present invention, in any one of the first to third aspects, the crystallite diameter at the Miller index of the (111) plane by X-ray diffraction belongs to a range of 800 to 2000 mm. It is a featured copper powder.

  (5) A fifth invention according to the present invention is a metal filler characterized by containing the copper powder of any one of the first to fourth inventions in a proportion of 20% by mass or more of the whole. .

  (6) A sixth invention according to the present invention is a copper paste obtained by mixing a metal filler according to the fifth invention with a resin.

  (7) A seventh invention according to the present invention is a conductive paint for electromagnetic wave shielding, characterized in that the metal filler according to the fifth invention is used.

  (8) An eighth invention according to the present invention is an electromagnetic wave shielding conductive sheet characterized by using the metal filler according to the fifth invention.

  According to the copper powder according to the present invention, it is possible to secure a large number of contacts and a large contact area, to ensure excellent conductivity, and to prevent aggregation, such as conductive paste and electromagnetic wave shield. It can utilize suitably for a use.

It is the figure which showed typically the specific shape of the copper particle which comprises dendritic copper powder. It is a photograph figure which shows an observation image when dendritic copper powder is observed at a magnification of 5,000 times with a scanning electron microscope. It is a photograph figure which shows an observation image when dendritic copper powder is observed by 1000-times multiplication factor with a scanning electron microscope. It is a photograph figure which shows an observation image when the copper particle which comprises dendritic copper powder is observed by 10,000 times magnification with the scanning electron microscope. It is a photograph figure which shows an observation image when the copper particle which comprises dendritic copper powder is observed by the scanning electron microscope with a magnification of 30,000 times. It is a photograph figure which shows an observation image when the copper powder obtained in the comparative example 1 is observed by 250 times of magnification with a scanning electron microscope.

  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.

<< 1. Dendritic copper powder >>
FIG. 1 is a schematic diagram showing a specific shape of copper particles constituting the copper powder according to the present embodiment. As shown in the schematic diagram of FIG. 1, the copper particles 1 have a dendritic shape that is a two-dimensional or three-dimensional form. More specifically, the copper particles 1 have a shape having a main trunk 2 grown in a dendritic shape and a plurality of branches 3 separated from the main trunk 2, and an average cross-sectional thickness of 0.02 μm to 0.3 μm. It is a flat plate shape. The copper powder according to the present embodiment is a dendritic copper powder (hereinafter referred to as “dendritic copper powder”) having a main trunk and a plurality of branches, which are configured by aggregating such flat copper particles 1. (Refer to SEM images of the copper powder in FIGS. 2 and 3), and the average particle diameter (D50) of the dendritic copper powder composed of the tabular copper particles 1 is 1.0 μm to 30 μm. is there.

  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.

  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 obtained by precipitation.

  FIG. 2 and FIG. 3 are photographic views showing an example of an observation image when the dendritic copper powder according to the present embodiment is observed by a scanning electron microscope (SEM). 2 shows the dendritic copper powder observed at a magnification of 5,000 times, and FIG. 3 shows the dendritic copper powder observed at a magnification of 1,000 times. FIG. 4 and FIG. 5 are photographic views showing an example of an observation image when the copper particles constituting the dendritic copper powder according to the present embodiment are observed with an SEM. 4 shows the copper particles observed at a magnification of 10,000 times, and FIG. 5 shows the copper particles observed at a magnification of 30,000 times.

  2 and 3, the dendritic 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. Moreover, in the dendritic copper powder which concerns on this Embodiment, the main trunk and the branch are flat shape, and the copper particle which has a dendritic shape aggregates and is comprised. Specifically, as shown in the observation images of the copper particles in FIGS. 4 and 5, the copper particles constituting the dendritic copper powder according to the present embodiment were separated from the main trunk grown in a dendritic shape and the main trunk. It is a resin having a plurality of branches and is a flat plate having a predetermined cross-sectional thickness.

  Here, the flat copper particles 1 constituting the dendritic copper powder according to the present embodiment and having the main trunk 2 and the branches 3 have an average cross-sectional thickness of 0.02 μm to 0.3 μm. The thinner the cross-sectional average thickness of the flat copper particles 1, the more effective the flat plate will be. That is, the main trunk and branches of the dendritic copper powder are constituted by the flat copper particles 1 having a cross-sectional average thickness of 0.3 μm or less, whereby the copper particles 1 and the dendritic copper powder constituted thereby are formed. It is possible to secure a large area for contact with each other. 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 copper powder is composed of the flat copper particles 1, it can contribute to thinning of the wiring material and the like.

  In addition, as a minimum of the cross-sectional average thickness of the flat copper particle 1, although not specifically limited, the method of making it deposit on a cathode by electrolyzing from the sulfuric acid electrolyte solution containing the copper ion mentioned later Then, the dendritic copper powder which the flat copper particle 1 which has a cross-sectional average thickness of 0.02 micrometer or more gathered can be obtained.

  Moreover, the flat copper particle 1 which comprises the dendritic 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. Specifically, it can be seen from the observation images of the copper particles shown in FIGS. 4 and 5 described above that fine convex portions exist on the surface of the flat copper particles. 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-0.3 micrometer.

  Here, as described in Patent Document 1 and Patent Document 2, for example, when spherical copper powder is formed into a flat plate shape by a mechanical method, 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 during processing may affect dispersibility when it is made into a paste, so it is necessary to remove it after the end of processing, 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 since the surface is flattened by mechanical pressure, the formed flat copper powder has a warped shape rather than a horizontal surface. 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 copper powder according to the present embodiment have fine convex portions on the surface, and the average height of the convex portions is preferably 0.01 μm. ~ 0.3 μm. The dendritic copper powder in which the copper particles 1 are aggregated has a feature that a contact between metal fillers can be easily ensured as compared with a flat copper powder obtained by mechanical processing. . That is, the dendritic copper powder according to the present embodiment has fine convex portions on the surface of the flat copper particles 1 constituting the dendritic copper powder, and is therefore used as a metal filler such as a conductive paste or a resin for electromagnetic wave shielding. In this case, the contact can be easily secured by the convex portions on the surface of the flat copper particles 1. Furthermore, since this dendritic copper powder is produced by directly growing into the shape of dendritic copper powder without mechanical processing, generation of oxidation and removal of fatty acids, which are problematic in mechanical processing, are not necessary. The conductive 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 0.3 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 0.3 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.

  Moreover, in the dendritic copper powder which concerns on this Embodiment, the average particle diameter (D50) (average particle diameter of dendritic copper powder) is 1.0 micrometer-30 micrometers. In addition, an average particle diameter (D50) can be measured by the laser diffraction scattering type particle size distribution measuring method, for example.

  For example, as pointed out in Patent Document 1, when the dendritic copper powder is used as a metal filler such as a conductive paste or a resin for electromagnetic wave shielding, the metal filler in the resin is dendritic. When the shape is developed, the dendritic copper powders are entangled with each other to cause agglomeration 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 according to the present embodiment, the average particle diameter is 1.0 μm to 30 μm, so that the surface area is increased and good moldability and sinterability can be ensured. . In addition to the dendritic shape, this dendritic copper powder is constituted by a collection of copper particles 1 having a main plate 2 and branches 3 and having a flat plate shape. More contact points between the copper powders can be ensured by the three-dimensional effect of being in the shape of a plate and the effect of the copper particles 1 constituting the dendritic shape being flat.

Moreover, although the dendritic copper powder which concerns on this Embodiment is not specifically limited, The ratio which remove | divided the cross-sectional average thickness of the flat copper particle 1 mentioned above by the average particle diameter (D50) of the said dendritic copper powder. (Cross section average thickness / average particle diameter) is preferably in the range of 8.0 × 10 ^{−4 to} 1.5 × 10 ⁻¹ . The ratio (aspect ratio) represented by “average cross-sectional thickness / average particle diameter” is, for example, the degree of aggregation and dispersibility when processed as a conductive copper paste, and the retention of appearance when coating copper paste It becomes an indicator such as. If this aspect ratio is less than 8.0 × 10 ⁻⁴ , it approximates to copper powder made of spherical copper particles, and aggregation tends to occur, making it difficult to uniformly disperse in the resin during paste formation. It becomes. On the other hand, when the aspect ratio exceeds 1.5 × 10 ⁻¹ , the viscosity increases during paste formation, and the external shape retainability and surface smoothness during application of the copper paste may deteriorate.

As the bulk density of the dendritic 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 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 copper powder also increases, and the surface area may decrease to deteriorate the moldability and sinterability.

  Moreover, although the dendritic copper powder which concerns on this Embodiment is not specifically limited, It is preferable that the crystallite diameter belongs to the range of 800 to (angstrom)-2000 to. When the crystallite diameter is less than 800 mm, the copper particles 1 constituting the main trunk and branches tend to be in a shape close to a spherical shape instead of a flat shape, and it becomes difficult to ensure a sufficiently large contact area. May be reduced. On the other hand, when the crystallite diameter exceeds 2000 mm, the average particle diameter of the dendritic copper powder is also increased, and the surface area is decreased and the moldability and the sinterability may be deteriorated.

Here, the crystallite diameter is obtained from a diffraction pattern obtained by an X-ray diffraction measurement device based on Scherrer's calculation formula shown below, and is a (111) plane mirror by X-ray diffraction. It is the crystallite diameter in the index.
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 (°). .)

≪2. Method for producing dendritic copper powder >>
The dendritic copper powder 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 the electrolysis, for example, the above-described sulfuric acid-containing electrolytic solution containing copper ions is contained in an electrolytic cell in which metallic copper is used as an anode (anode) and a stainless plate or 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. This amine compound, together with chloride ions described later, contributes to shape control of the deposited copper powder, and the copper powder deposited on the cathode surface has a dendritic shape and is a flat plate having a predetermined average cross-sectional thickness. A dendritic copper powder composed of copper particles and having a main trunk and a plurality of branches can be obtained.

The amine compounds, for example, Janus Green B _{(Janus Green, C 30 H 31} N 6 Cl, CAS Number: 2869-83-2), or the like can be used. In addition, 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 will be the range of about 0.1 mg / L-500 mg / L as addition amount of amine compounds.

  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. A chloride ion contributes to shape control of the copper powder to precipitate with additives, such as an amine compound mentioned above. Although it does not specifically limit as a chloride ion density | concentration in electrolyte solution, About 200 mg / L-1000 mg / L, Preferably it can be set as about 250 mg / L-800 mg / L.

In the method for producing a dendritic copper powder according to the present embodiment, for example, the copper powder is deposited and produced 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 5 A / dm ^{2 to} 30 A / dm ² when electrolyzing using a sulfuric acid electrolytic solution, and the electrolytic solution 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. Applications of conductive paste, conductive paint, etc. >>
As described above, the dendritic copper powder according to the present embodiment is a dendritic copper powder having a main trunk and a plurality of branches, and the dendritic copper powder is as shown in the schematic diagram of FIG. And a plate-like copper particle 1 having a main branch 2 and a plurality of branches 3 branched from the main trunk 2 and having a cross-sectional thickness of 0.02 μm to 0.3 μm. . And the average particle diameter (D50) of the said dendritic copper powder is 1.0 micrometer-30 micrometers. In such a dendritic copper powder, a dendritic shape has a large surface area, an excellent moldability and sinterability, and a dendritic flat plate having a predetermined cross-sectional average thickness. By being comprised from the shape-like copper particle 1, many contact points can be ensured and the outstanding electroconductivity is exhibited.

  In addition, according to the dendritic copper powder having such a predetermined structure, even when a copper paste or the like is used, aggregation can be suppressed, and the resin can be uniformly dispersed in the resin. Occurrence of poor printability due to an increase in paste viscosity can be suppressed. Therefore, the dendritic copper powder can be suitably used for applications such as conductive paste and conductive paint.

  In this Embodiment, it comprises so that the dendritic copper powder mentioned above may become a ratio of the quantity of 20 mass% or more, Preferably it is 30 mass% or more, More preferably, it is 50 mass% or more in a metal filler. If the ratio of the dendritic copper powder 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 viscosity of the paste excessively increases. As a result, it is possible to prevent printability defects. Moreover, the electroconductivity excellent as an electrically conductive paste can be exhibited by being dendritic copper powder which consists of an aggregate | assembly of the flat copper particle 1 of flat form. In addition, as a metal filler, what is necessary is just to contain so that dendritic copper powder may become the ratio of the quantity of 20 mass% or more as mentioned above, others mix spherical copper powder etc. about 1 micrometer-10 micrometers, etc., for example. Also good.

  For example, as a conductive paste (copper paste), the dendritic copper powder according to the present embodiment is contained as a metal filler, and kneaded with a binder resin, a solvent, and further an additive such as an antioxidant or a coupling agent as necessary. It can produce by doing.

  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 so that the viscosity is suitable for a conductive film forming method such as screen printing or a dispenser. be able to.

  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 preferable, and citric acid or malic acid having a high adsorptive power to copper is particularly preferable. The addition amount of the antioxidant can be, for example, about 1 to 15% by mass in consideration of the antioxidant effect and the viscosity of the paste.

  Next, even when the metal filler according to the present embodiment is used as an electromagnetic wave shielding material, it is not used under particularly limited conditions. For example, a metal filler is mixed with a resin. Can be used.

  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 wave shielding material, for example, a metal filler and a resin as described above are dispersed or dissolved in a solvent to form a paint, and an electromagnetic wave shielding layer is formed on the substrate by coating or printing. It can be produced by drying to such an extent that the surface solidifies. Moreover, the metal filler which concerns on this Embodiment can also be utilized for the conductive adhesive layer of a conductive sheet.

  Further, even when a conductive paint for electromagnetic wave shielding is used by using the metal filler according to the present embodiment, it is not used under particularly limited conditions, and a general method, for example, a metal filler is used as a resin and a solvent. And further mixed with an antioxidant, a thickener, an anti-settling agent, etc., if necessary, and kneaded, and can be used as a conductive paint.

  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.

  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>
The copper powder obtained in the following Examples and Comparative Examples was subjected to shape observation, average particle diameter measurement, and crystallite diameter measurement 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 analyzer (manufactured by Nikkiso Co., Ltd., HRA9320 X-100).

(Measurement of crystallite diameter)
From a diffraction pattern obtained by an X-ray diffractometer (manufactured by PANanalytical, X'Pert PRO), calculation was performed using a known method generally known as Scherrer's equation.

(Aspect ratio measurement)
The obtained copper powder was embedded in an epoxy resin to prepare a measurement sample, the sample was cut and polished, and observed with a scanning electron microscope to observe the cross section of the copper powder. First, 20 copper powders were observed, and the average thickness (cross-sectional average thickness) of the copper powder was determined. Next, the aspect ratio (average thickness / D50) was determined from the ratio between the average thickness value and the average particle size (D50) determined with a laser diffraction / scattering particle size distribution analyzer.

(Specific resistance measurement)
The specific resistance value of the film was measured by measuring the sheet resistance value by a four-terminal method using a low resistivity meter (Loresta-GP MCP-T600, manufactured by Mitsubishi Chemical Corporation), and a surface roughness shape measuring instrument (Tokyo Seimitsu Co., Ltd.). The film thickness of the coating was measured by SURFCOM130A) and the sheet resistance value was divided 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 in the case of Comparative Example 3 not using the dendritic copper powder is set as “△”, and the level worse than the level of Comparative Example 3 is set as “X”. Was evaluated as “◯”, and when it was excellent, “◎”.

  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.

<Examples and comparative examples>
[Example 1]
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 10 g / L and a sulfuric acid concentration of 100 g / L was used. In addition, Janus Green (manufactured by Wako Pure Chemical Industries, Ltd.) as an additive is added to this electrolytic solution so that the concentration in the electrolytic solution is 125 mg / L, and further a hydrochloric acid solution (manufactured by Wako Pure Chemical Industries, Ltd.) Was added so that the chloride ion (chlorine ion) concentration in the electrolyte solution was 50 mg / L. Then, while circulating the electrolytic solution adjusted to the concentration as described above at a flow rate of 15 L / min using a metering pump, the temperature is maintained at 25 ° C. and the current density of the cathode is 15 A / dm ^2. 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 obtained electrolytic copper powder by the method using the scanning electron microscope (SEM) described above, the deposited copper powder is a two-dimensional or three-dimensional dendritic copper powder, And a plurality of branches branched from the main trunk, and a dendritic copper powder formed by agglomeration of copper particles having a dendritic shape having a branch further branched from the branch. Further, the dendritic copper particles having the main trunk and the branch were flat plate having a cross-sectional thickness (cross-sectional average thickness) of 0.03 μm, and had fine convex portions on the surface thereof. The height of the convex portions formed on the surface was 0.02 μm on average. Moreover, the average particle diameter (D50) of the dendritic copper powder was 26.7 μm. And the aspect ratio (cross-sectional average thickness / average particle diameter) calculated from the cross-sectional average thickness of the copper particles and the average particle diameter of the dendritic copper powder was 1.1 × 10 ⁻³ . Moreover, the bulk density of the obtained dendritic copper powder was 1.2 g / cm ³ . The crystallite diameter of the dendritic copper powder was 1826cm. In addition, it was confirmed that such dendritic copper powder exists in the ratio of at least 65% or more in the whole obtained copper powder. Table 1 summarizes these results.

[Example 2]
As an electrolytic solution, a composition having a copper ion concentration of 8 g / L and a sulfuric acid concentration of 100 g / L is used, and Janus Green is added to the electrolytic solution so that the concentration in the electrolytic solution is 150 mg / L. Further, a hydrochloric acid solution was added so that the chlorine ion concentration in the electrolytic solution was 125 mg / L. Then, while circulating the electrolytic solution adjusted to the concentration as described above at a flow rate of 20 L / min using a metering pump, the temperature is maintained at 30 ° C. and the current density of the cathode is 20 A / dm ^2. Energization was performed to deposit copper powder on the cathode plate. The electrolytic copper powder was prepared under the same conditions as in Example 1 except for these conditions.

As a result of observing the shape of the obtained electrolytic copper powder by the method using the scanning electron microscope (SEM) described above, the deposited copper powder is a two-dimensional or three-dimensional dendritic copper powder, It was a dendritic copper powder formed by aggregating copper particles having a dendritic shape having a plurality of branches branched from and a branch further branched from the branches. In addition, the dendritic copper particles having the main trunk and the branches had a flat plate shape with a cross-sectional thickness (average cross-sectional thickness) of 0.08 μm, and had fine convex portions on the surface thereof. The height of the convex portions formed on the surface was 0.02 μm on average. Moreover, the average particle diameter (D50) of the dendritic copper powder was 14.3 μm. And the aspect ratio (cross-sectional average thickness / average particle diameter) calculated from the cross-sectional average thickness of the copper particle and the average particle diameter of the dendritic copper powder was 5.6 × 10 ⁻³ . Moreover, the bulk density of the obtained dendritic copper powder was 2.2 g / cm ³ . The crystallite diameter of the dendritic copper powder was 1568 mm. In addition, it was confirmed that such dendritic copper powder exists in the copper powder of the whole obtained copper powder in the ratio of at least 70% or more. Table 1 summarizes these results.

[Example 3]
An electrolytic solution having a copper ion concentration of 5 g / L and a sulfuric acid concentration of 125 g / L is used, and Janus Green is added to the electrolytic solution so that the concentration in the electrolytic solution is 200 mg / L. Further, a hydrochloric acid solution was added so that the chlorine ion concentration in the electrolytic solution was 150 mg / L. Then, while circulating the electrolyte adjusted to the concentration as described above at a flow rate of 25 L / min using a metering pump, the temperature is maintained at 35 ° C. and the current density of the cathode is 25 A / dm ^2. Current was applied to deposit copper powder on the cathode plate. The electrolytic copper powder was prepared under the same conditions as in Example 1 except for these conditions.

As a result of observing the shape of the obtained electrolytic copper powder by the method using the scanning electron microscope (SEM) described above, the deposited copper powder is a two-dimensional or three-dimensional dendritic copper powder, It was a dendritic copper powder formed by agglomerating copper particles having a dendritic shape having a plurality of branches branched linearly from and further branched from the branches. Moreover, the copper particle which has the main trunk and the branch was flat form whose cross-sectional thickness (cross-sectional average thickness) is 0.12 micrometer, and had the fine convex part on the surface. The height of the convex portions formed on the surface was 0.02 μm on average. Moreover, the average particle diameter (D50) of the dendritic copper powder was 7.8 μm. And the aspect-ratio (cross-sectional average thickness / average particle diameter) computed from the cross-sectional average thickness of the copper particle and the average particle diameter of dendritic copper powder was 1.5 * 10 ^<-2 >. Moreover, the bulk density of the obtained dendritic copper powder was 3.8 g / cm ³ . The crystallite diameter of the dendritic copper powder was 912 mm. In addition, it was confirmed that such dendritic copper powder exists in the copper powder of the whole obtained copper powder in the ratio of at least 75% or more. Table 1 summarizes these results.

[Example 4]
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 dendritic copper powder obtained in Example 1. Then, using a small 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 a glass with a metal squeegee and cured at 150 ° C. and 200 ° C. for 30 minutes in an air atmosphere.

The specific resistance values of the films obtained by curing were 7.8 × 10 ⁻⁵ Ω · cm (curing temperature 150 ° C.) and 2.2 × 10 ⁻⁵ Ω · cm (curing temperature 200 ° C.), respectively. . Table 1 summarizes these results.

[Example 5]
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 dendritic copper powder obtained in Example 2. Then, using a small 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 a glass with a metal squeegee and cured at 150 ° C. and 200 ° C. for 30 minutes in an air atmosphere.

The specific resistance values of the films obtained by curing were 8.1 × 10 ⁻⁵ Ω · cm (curing temperature 150 ° C.) and 2.6 × 10 ⁻⁵ Ω · cm (curing temperature 200 ° C.), respectively. . Table 1 summarizes these results.

[Example 6]
The dendritic copper powder prepared in Example 1 was dispersed in a resin to obtain an electromagnetic wave shielding material.

  That is, 100 g of vinyl chloride resin and 200 g of methyl ethyl ketone were mixed with 40 g of the dendritic copper powder obtained in Example 1, and kneading at 1200 rpm for 3 minutes was 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 on a base material made of a transparent polyethylene terephthalate sheet having a thickness of 100 μm using a Mayer bar 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 the results of the characteristic evaluation.

[Comparative Example 1]
Copper powder was deposited on the cathode plate under the same conditions as in Example 1 except that Janus Green as an additive and chlorine ions were not added to the electrolytic solution to produce electrolytic copper powder.

  As a result of observing the shape of the obtained electrolytic copper powder by the method using the scanning electron microscope (SEM) described above, the obtained copper powder had a dendritic shape, but granular copper particles were aggregated. Met. FIG. 6 is an SEM observation image (magnification: 250 times) of the copper powder obtained in Comparative Example 1. Moreover, it was confirmed that the obtained copper powder is a very large dendritic copper powder having an average particle diameter (D50) of 40 μm or more. Further, no minute convex portion was formed on the dendritic portion.

[Comparative Example 2]
In order to compare with the conventional flat copper powder, it was flattened mechanically to produce a flat copper powder. Specifically, the flat copper powder was prepared by adding 5 g of stearic acid to 500 g of granular atomized copper powder (manufactured by Mekin Metal Powders) having an average particle diameter of 5.4 μm, and performing a flattening treatment 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. As a result of measuring the flat copper powder thus produced with a laser diffraction / scattering particle size distribution measuring instrument, the average particle diameter was 12.6 μm, and the thickness was 0.5 μm as a result of observation with a scanning electron microscope. The surface was smooth and no minute protrusions were formed. And the aspect ratio (cross-sectional average thickness / average particle diameter) calculated from the cross-sectional average thickness and average particle diameter was 3.9 * 10 < ^-3 >.

  In the same manner as in Example 4, the obtained flat copper powder was added to 55 parts by mass of flat copper powder, 15 parts by mass of phenol resin (manufactured by Gunei Chemical Co., Ltd., PL-2211), and butyl cellosolve (manufactured by Kanto Chemical Co., Ltd.). , Deer special grade) 10 parts by mass were mixed, and paste was made by repeating kneading at 1200 rpm for 3 minutes three times using a small kneader (Nippon Seiki Seisakusho, non-bubbling kneader NBK-1). The obtained conductive paste was printed on a glass with a metal squeegee and cured at 150 ° C. and 200 ° C. for 30 minutes in an air atmosphere.

The specific resistance values of the films obtained by curing were 5.6 × 10 ⁻⁴ Ω · cm (curing temperature 150 ° C.) and 8.3 × 10 ⁻⁵ Ω · cm (curing temperature 200 ° C.), respectively. . Table 1 summarizes these results.

[Comparative Example 3]
The flat copper powder produced in Comparative Example 2 was dispersed in a resin to obtain an electromagnetic wave shielding material.

  That is, 100 g of vinyl chloride resin and 200 g of methyl ethyl ketone are mixed with 40 g of the flat copper powder obtained in Comparative Example 2, 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 the results of the characteristic evaluation.

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

Claims (8)

A copper powder in which copper particles in a shape having a main trunk grown in a dendritic shape and a plurality of branches separated from the main trunk are assembled,
The main trunks and branches of the copper particles have a flat plate shape with a cross-sectional average thickness of 0.02 μm to 0.3 μm,
The copper powder is characterized in that the average particle diameter (D50) of the copper powder is 1.0 μm to 30 μm.   The 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 0.3 μm. The ratio obtained by dividing the cross-sectional thickness of the flat copper particles by the average particle diameter (D50) of the copper powder is in the range of 8.0 × 10 ^{−4 to} 1.5 × 10 ⁻¹ , and the copper copper powder according to claim 1 or 2 the bulk density of the powder is characterized in that in the range of ^{0.5g / cm 3 ~5.0g / cm 3} .   The copper powder according to any one of claims 1 to 3, wherein a crystallite diameter in a Miller index of a (111) plane by X-ray diffraction belongs to a range of 800 to 2000 mm.   A metal filler containing the copper powder according to any one of claims 1 to 4 at a ratio of 20% by mass or more of the whole.   A copper paste obtained by mixing the metal filler according to claim 5 into a resin.   6. A conductive paint for electromagnetic wave shielding, wherein the metal filler according to claim 5 is used.   An electroconductive sheet for electromagnetic wave shielding, wherein the metal filler according to claim 5 is used.