JP6332058B2 - Copper powder, and copper paste, conductive paint, and conductive sheet using the same - Google Patents

Description

  The present invention relates to a copper powder used as a material for a conductive paste or the like, and more specifically, a copper powder having a novel shape capable of improving the conductivity, a copper paste using the copper powder, and a conductive property The present invention relates to a paint and 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 made of silver powder, copper powder, or the like is applied or printed on various substrates of an electronic device, and is subjected to heat curing or heat baking 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. An electrode is formed. In the resin-type conductive paste, since the thermosetting resin is cured and contracted by heat, when the metal filler is pressed and brought into contact, the metal filler overlaps and an electrically connected current path is formed. Since this resin-type conductive paste is processed at a curing temperature of 200 ° C. or less, it is used for a substrate using a heat-sensitive material such as a printed wiring board.

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

  On the other hand, the electromagnetic wave shield is used to prevent generation of electromagnetic noise from the electronic device. In recent years, since the housing of personal computers and mobile phones has been made of resin, in order to ensure conductivity in the housing, a method of forming a thin metal film by vapor deposition or sputtering, or applying conductive paint Or a method of shielding an electromagnetic wave by attaching a conductive sheet to a necessary portion. And among them, the method of applying the metal filler dispersed in the resin and the method of shielding the electromagnetic wave by dispersing the metal filler in the resin and processing it into a sheet and attaching it to the housing It does not require special equipment in the process and is frequently used as a method with excellent flexibility.

  However, when such a metal filler is dispersed and applied in a resin or processed into a sheet shape, the dispersion state of the metal filler in the resin is not uniform. Therefore, in order to obtain the efficiency of the electromagnetic wave shield, a method of increasing the filling rate of the metal filler and eliminating it is necessary. However, in such a case, the addition of a large amount of metal filler increases the sheet weight and causes problems such as impairing the flexibility of the resin sheet. In order to solve these problems, for example, in Patent Document 1, it is said that by using a flat metal filler, it is possible to form a thin sheet having excellent electromagnetic wave shielding effect and good flexibility. .

  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 the powder of copper or silver used as the metal filler, particles, dendrites, flat plates, and the like have been used in many cases because the particles are connected to conduct electricity. In particular, when the particles are evaluated from the size in the three directions of length, width, and thickness, the flat plate shape with a small thickness contributes to the thinning of the wiring material due to the decrease in the thickness and has a certain thickness. There is an advantage that an area in which the grains are in contact with each other can be secured larger than that of certain cubic or spherical grains, and that low resistance, that is, high conductivity can be achieved. For this reason, the powder containing tabular copper particles is particularly suitable for use in conductive paints and conductive pastes for which electrical conductivity is desired to be maintained. When the conductive paste is applied thinly, the influence of impurities contained in the copper powder cannot be ignored.

  In order to produce such a flat copper powder, for example, Patent Document 2 discloses a method for obtaining a flaky copper powder suitable for a 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 is processed into a flat plate shape by a mechanical energy of a medium loaded in the mill using a ball mill or a vibration mill. is there.

  Further, for example, Patent Document 3 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 producing the same. Specifically, the granular atomized copper powder is put into a medium stirring mill, a steel ball having a diameter of 1/8 to 1/4 inch is used as a grinding medium, and the fatty acid is 0.5 to 1 by weight with respect to the copper powder. %, And processed into a flat plate by grinding in air or in an inert atmosphere.

  Furthermore, for example, Patent Document 4 discloses a method of 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, it is an electrolytic solution for the purpose of refining the size of the crystallites constituting the electrolytic copper powder in order to precipitate the electrolytic copper powder that can be molded to a high strength by increasing the strength of the electrolytic copper powder itself. One or more selected from tungstate, molybdate, and sulfur-containing organic compounds are added to an 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. For example, in the technique of Patent Document 2, the average particle diameter is 1 μm to 30 μm, and in the technique of Patent Document 4, the average particle diameter is 7 μm to 12 μm.

  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 5 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 4, for example.

  In order to ensure conductivity, a dendritic shape having a three-dimensional shape is easier to secure a contact than a granular one, and high conductivity can be expected as a conductive paste or electromagnetic wave shield. . However, as described above, it is not easy to use a dendritic copper powder as a metal filler such as a conductive paste, and this is also a cause of difficulty in improving the conductivity of the paste.

  In Patent Document 6, in the development of Ag powder as a metal filler for use as a conductive paste, in order to improve the contact rate between the metal fillers, the protrusions are radially extended, and the protrusions are We are proposing silver powders in the form of needles, hooks, and petals. With such a shape, the contact rate between metal fillers is improved, the filler weight contained in the silver paste can be reduced, and the cost can be greatly reduced.

JP 2003-258490 A 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. 4059486

  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, a plurality of pieces of copper particles are aggregated to form an agglomerated copper powder, and the pieces of copper particles are flat and have a specific range of dimensions. The present invention finds that the copper powder, which is an aggregate in which a plurality of copper particles are aggregated, is in a specific range, ensures excellent conductivity, and can be suitably used for applications such as conductive pastes. Was completed. That is, the present invention provides the following.

  (1) The first invention of the present invention is a copper powder in which a plurality of piece-like copper particles are aggregated to have an aggregate form, and the copper particles are obtained by observation with a scanning electron microscope (SEM). The average major axis diameter is 0.5 μm to 5 μm, the average cross-sectional thickness is 0.02 μm to 0.5 μm, and the average particle diameter (D50) determined by the laser diffraction scattering particle size distribution measurement method is It is a copper powder characterized by being 1.0 micrometer-30 micrometers.

(2) the second invention of the present invention, in the first aspect, a copper powder, wherein the tap density in the range of ^{0.5g / cm 3 ~5.0g / cm 3} .

(3) A third invention of the present invention, in the first or second invention, is a copper powder which is characterized in that the BET specific surface area value of 0.5m ² /g~3.0m ² / g .

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

  (5) The fifth invention of the present invention is a conductive paste characterized by mixing a metal filler according to the fourth invention with a resin.

  (6) A sixth invention of the present invention is a conductive paint for electromagnetic wave shielding, characterized in that the metal filler according to the fourth invention is dispersed in a resin.

  (7) A seventh invention of the present invention is a conductive sheet for electromagnetic wave shielding, characterized in that the metal filler according to the fourth invention is dispersed in a resin.

  The copper powder according to the present invention is a copper powder having a form of agglomerates by aggregating a plurality of copper particles which are in the form of individual pieces and have a plate shape having a specific range of dimensions. From this, it is possible to secure a large number of contacts and a large contact area, thereby ensuring excellent electrical conductivity and suitably using for applications such as conductive pastes and electromagnetic wave shields. Can do.

It is the schematic diagram which showed an example of the specific shape of copper powder (flat copper particle aggregation powder). It is a photograph figure which shows an observation image when tabular copper particle aggregated powder is observed by 10,000 times of magnification with a scanning electron microscope. It is a photograph figure which shows an observation image when a flat copper particle aggregated powder is observed with a scanning electron microscope at 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 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. Copper powder (flat copper particle agglomerated powder) >>
FIG. 1 is a schematic diagram showing a specific shape of the copper powder according to the present embodiment. As shown in the schematic diagram of FIG. 1, the copper powder 1 according to the present embodiment has a copper powder (hereinafter, referred to as a copper powder having a form in which the separated flat copper particles 2 are two-dimensionally or three-dimensionally aggregated. This copper powder is also referred to as “flat copper particle aggregated powder 1”).

  More specifically, the tabular copper particle aggregated powder 1 is in the form of an aggregated copper powder in which a plurality of tabular copper particles 2 are aggregated to form an aggregate, and the major axis diameter d of the tabular copper particle 2 is The average (average major axis diameter) is 0.5 μm to 5 μm, and the cross-sectional average thickness is 0.02 μm to 0.5 μm. And the magnitude | size of the said tabular copper particle aggregated powder 1 in which the tabular copper particle 2 aggregated and became the aggregate is 1.0 micrometer-30 micrometers in an average particle diameter (D50).

  The tabular copper particle aggregated powder 1 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 deposit on the cathode. Can be obtained.

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

  As shown in the observation image of FIG. 2, the tabular copper particle aggregated powder 1 has a form in which tabular copper particles 2 are aggregated. Further, as shown in the observation image in FIG. 3, the flat copper particles 2 are singulated and have a flat shape having a flat surface or a curved surface.

  Here, as shown in the schematic diagram of FIG. 1, the flat copper particles 2 have a flat surface having a smooth periphery, such as a substantially oval shape, an oval shape, or a so-called corn flake shape, which will be described later. The shape has a cross-sectional average thickness within a specific range. Of course, the surface having a substantially elliptical shape or the like may have protrusions and attached particles having a height of about twice or less the average cross-sectional thickness.

  As described above, the average major axis diameter d of these tabular copper particles 2 is 0.5 μm to 5 μm, more preferably 0.7 μm to 4 μm. Moreover, the cross-sectional average thickness of the copper particle 2 is 0.02 micrometer-0.5 micrometer, More preferably, it is 0.05 micrometer-0.4 micrometer. Here, the average major axis diameter d of the tabular copper particles 2 indicates the maximum width of a tabular surface having a shape such as an ellipse, as shown in FIG. Moreover, the average major axis diameter d and the cross-sectional average thickness can be obtained by observation using an SEM.

  When the average major axis diameter d of the tabular copper particles 2 is less than 0.5 μm or the cross-sectional average thickness exceeds 0.5 μm, the aggregated powders that are aggregated to form an aggregate contact each other. Therefore, it may not be possible to secure a large area, and the conductivity may decrease. On the other hand, the upper limit value of the average major axis diameter d of the tabular copper particles 2 is not particularly limited, but in the method of depositing on the cathode by electrolysis described later, the upper limit is about 5 μm. Moreover, although the lower limit of the cross-sectional average thickness of the flat copper particles 2 is not particularly limited, the lower limit is about 0.02 μm in the same method of depositing on the cathode by electrolysis.

  The size of the tabular copper particle aggregated powder 1 obtained by aggregating the tabular copper particles 2 into an aggregate is 1.0 μm to 30 μm in terms of an average particle diameter (D50). In addition, the average particle diameter (D50) of the tabular copper particle aggregated powder 1 can be measured by a laser diffraction scattering type particle size distribution measuring method.

  Thus, the flat copper particles 2 having an average cross-sectional thickness of 0.02 μm to 0.5 μm are aggregated to form the copper powder 1, whereby the copper powder having the above-described size is obtained. It is possible to ensure a large area where the agglomerated powders 1 and the copper particles 2 on the flat plate contact each other. And since the contact area becomes large, low resistance, that is, high conductivity can be realized. By this, it is more excellent in electroconductivity and can be used suitably for the use of a conductive paint and a conductive paste.

  Here, as pointed out in Patent Document 1, for example, when used as a metal filler such as a conductive paste or a resin for electromagnetic wave shielding, the metal filler in the resin has a dendritic shape, Dendritic copper powders are entangled with each other and agglomeration occurs, which may not be uniformly dispersed in the resin. In addition, the agglomeration increases the viscosity of the paste and causes problems in wiring formation by printing. This is because the shape of the dendritic copper powder grows in a needle shape, and when trying to prevent agglomeration, the shape of the dendritic copper powder is reduced. It becomes impossible to obtain the effect of securing the contact by eliminating.

  In addition, in the case where the plate is formed by the mechanical method of Patent Document 1 or Patent Document 2, it is necessary to prevent copper oxidation during mechanical processing. For example, after adding a fatty acid, in the air or inactive It is crushed in an atmosphere and processed into a flat plate shape. However, oxidation cannot be completely prevented, and the fatty acid added at the time of processing needs to be removed after processing to affect dispersibility when it is made into a paste. There is a problem that the fatty acid cannot be completely removed because it may firmly adhere to the copper surface. In addition, since it is flattened by mechanical processing, the surface is smooth, and because it is flattened by mechanical pressure, it is difficult to make the flat copper powder made flat and warped. . Since copper powder with a smooth and warped surface is difficult to secure contacts, when using it as a metal filler, the metal filler should be mixed with not only flat copper powder but also granular copper powder. It is necessary to secure contact points between each other.

  On the other hand, in the tabular copper particle aggregated powder 1 according to the present embodiment, the tabular copper particles 2 have a shape in which the tabular copper particles 2 are aggregated, so that each tabular copper particle 2 has a three-dimensional shape. In this state, the two-dimensional contact effect and the three-dimensional contact effect are simultaneously satisfied. Furthermore, when the tabular copper particle aggregated powder 1 has an average particle diameter (D50) of 1.0 μm to 30 μm, the surface area is increased, and good moldability and sinterability are ensured. it can.

  In addition, this demonstrates the same effect that the contact rate of metal fillers improves by using the silver powder of the shape described in patent document 6, and the flat copper particle aggregation copper powder 1 is Since it is a three-dimensional concavo-convex structure, the contact rate between the metal fillers can be improved, the filler weight contained in the paste can be reduced, and the cost can be greatly reduced.

Then, the tap density of the tabular copper particles agglomerated powder 1 according to the present embodiment is not particularly limited, is preferably in the range of ^{0.5g / cm 3 ~5.0g / cm 3} . When the tap 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, when the tap density exceeds 5.0 g / cm ³ , the average particle diameter of the copper powder increases, the surface area decreases, and the moldability and sinterability may deteriorate.

As the BET specific surface area of the tabular copper particles agglomerated powder 1 is not particularly ^limited, it is preferably in the range of 0.5m ² /g~3.0m 2 / g. When the BET specific surface area exceeds 3.0 m ² / g, there is a possibility that sufficient contact between the copper powders cannot be ensured. On the other hand, when the BET specific surface area is less than 0.5 m ² / g, the average particle diameter of the copper powder also increases, the surface area decreases, and the moldability and sinterability may deteriorate. The BET specific surface area can be measured in accordance with JIS Z8830: 2013.

≪2. Method for producing flat copper particle agglomerated powder >>
The tabular copper particle aggregated powder 1 according to the present embodiment can be manufactured by a predetermined electrolytic method using, for example, a sulfuric acid acidic solution containing copper ions as an electrolytic solution.

  In the electrolysis (electrolysis), for example, the above-described sulfuric acid-containing electrolytic solution containing copper ions 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). And electrolytic treatment is performed by applying a direct current to the electrolytic solution at a predetermined current density. Thereby, the tabular copper particle aggregation copper powder 1 can be deposited (electrodeposited) on the cathode with energization.

  In particular, in the present embodiment, for example, the granular copper powder obtained by electrolysis is not deformed mechanically using a medium such as a ball, and the like, and the flat fine copper particles are obtained only by electrolysis. Aggregated tabular copper particle aggregated powder 1 can be deposited on the cathode surface.

  More specifically, in the manufacturing method in the present embodiment, the electrolytic solution contains, for example, a water-soluble copper salt, sulfuric acid, an additive such as an amine compound or a nonionic surfactant, 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. 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 is preferably about 1 g / L to 20 g / L, and more preferably about 5 g / L to 10 g / L. If the copper ion concentration is too high, it becomes difficult to deposit the copper powder having the above-mentioned shape on the cathode during electrolysis, but if it is 20 g / L or less, the tabular copper particle aggregated powder 1 is deposited without any problem. be able to. On the other hand, the lower limit of the copper ion concentration is not particularly limited, but it is preferably 1 g / L or more in consideration of efficiently depositing copper powder on the cathode during electrolysis.

  Sulfuric acid is for making a sulfuric acid electrolyte. The concentration of sulfuric acid in the electrolytic solution is preferably about 20 g / L to 300 g / L, more preferably about 50 g / L to 150 g / L in terms of 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 or a nonionic surfactant can be used. Thus, the amine compound added as an additive contributes to the shape control of the copper powder deposited together with the chloride ion and nonionic surfactant described later, and the copper powder deposited on the cathode has a predetermined cross-sectional average thickness. It can be set as the flat copper particle aggregation powder 1 comprised from the flat copper particle 2. FIG.

  Specifically, the amine compound is not particularly limited, and for example, Janus Green (Janus Green, C30H31N6Cl, CAS number: 2869-83-2) 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 used as the addition amount of an amine compound in the range about 0.1 mg / L-500 mg / L in the density | concentration in electrolyte solution.

  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. Chloride ions contribute to shape control of the deposited copper powder together with the above-described amine compound and nonionic surfactant additives. The chloride ion concentration in the electrolytic solution is not particularly limited, but is preferably about 200 mg / L to 1000 mg / L, and more preferably about 250 mg / L to 800 mg / L.

  Although it does not specifically limit as a nonionic surfactant, What has an ether group is preferable. Specific examples include polyethylene glycol, polypropylene glycol, polyethyleneimine, pluronic surfactant, tetronic surfactant, polyoxyethylene glycol / glyceryl ether, polyoxyethylene glycol / dialkyl ether, polyoxyethylene polyoxypropylene glycol. -Alkyl ether, aromatic alcohol alkoxylate, the compound represented by following formula (x), etc. are mentioned.

(However, in formula (x), R ₁ has a higher alcohol residue having 5 to 30 carbon atoms, an alkylphenol residue having an alkyl group having 1 to 30 carbon atoms, and an alkyl group having 1 to 30 carbon atoms. A residue of an alkyl naphthol, a residue of a fatty acid amide having 3 to 25 carbon atoms, a residue or a hydroxyl group of an alkyl amine having 2 to 5 carbon atoms, R ₂ and R ₃ represent a hydrogen atom or a methyl group, m And n represents an integer of 1 to 100.)

  The number average molecular weight of the nonionic surfactant is not particularly limited, but is preferably 100 to 200,000, more preferably 200 to 15,000, and further preferably 1,000 to 10,000. preferable. 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.

  These nonionic surfactants may be added singly or in combination of two or more. The amount of the nonionic surfactant added is not particularly limited, but is preferably about 200 mg / L to 5000 mg / L, more preferably about 500 mg / L to 2000 mg / L in terms of concentration in the electrolytic solution. preferable.

In the manufacturing method of the flat copper particle aggregation copper powder 1 which concerns on this Embodiment, it electrolyzes using the electrolyte solution of a composition as mentioned above, for example, deposits copper powder on a cathode, and manufactures it. . 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} 40 A / dm ² in electrolysis 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 tabular copper particle aggregated powder 1 according to the present embodiment is in the form of aggregated copper powder in which a plurality of tabular copper particles 2 are aggregated to form an aggregate. The tabular copper particles 2 have an average major axis diameter of 0.5 μm to 5 μm, an average cross-sectional thickness of 0.02 to 0.5 μm, and a plurality of tabular copper particles 2 are assembled. The size of the aggregated copper powder 1 that has become an aggregate is 1.0 μm to 30 μm in terms of average particle diameter (D50).

  The flat copper particle agglomerated powder 1 according to the present embodiment has such a characteristic structure, so that a large number of contacts can be ensured and a large contact area can be ensured, resulting in excellent conductivity. To demonstrate. Moreover, according to the flat copper particle aggregated powder 1 having such a predetermined structure, even when it is a copper paste or the like, aggregation can be suppressed and the resin can be uniformly dispersed in the resin. In addition, it is possible to suppress the occurrence of poor printability due to an increase in the viscosity of the paste. Therefore, the flat copper particle aggregated powder 1 can be suitably used for applications such as conductive paste and conductive paint.

  Here, in using the tabular copper particle aggregated powder 1 according to the present embodiment as a metal filler, the amount of the tabular copper particle aggregated powder 1 is 20% by mass or more based on the whole in the metal filler. Configure to be included as a percentage. Thus, by setting the ratio of the tabular copper particle aggregated powder 1 to 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. It is possible to effectively prevent the viscosity from increasing excessively and causing poor printability. In addition, since the tabular copper particle aggregated powder 1 composed of an aggregate of tabular copper particles 2 is contained in the metal filler at a ratio of 20% by mass or more, the conductive property is more excellent as a conductive paste. The ability to show off. In addition, the flat copper particle aggregated powder 1 should just be contained in the metal filler in the ratio of 20 mass% or more, for example, you may mix spherical copper powder etc., for example of about 1 micrometer-10 micrometers.

  For example, as the conductive paste (copper paste), the tabular copper particle agglomerated powder 1 is contained as a metal filler, and kneaded with a binder resin, a solvent, and, if necessary, an additive such as an antioxidant or a coupling agent. Can be produced.

  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. The amount of the organic solvent added is not particularly limited, but the amount added in consideration of the particle size of the tabular copper particle agglomerated powder 1 so as to have a viscosity suitable for a conductive film forming method such as screen printing or dispenser. Can be adjusted.

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

  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% by mass to 15% by weight in consideration of the antioxidant effect, the viscosity of the paste, and the like.

  Next, even when the tabular copper particle aggregated powder 1 is used as a metal filler as an electromagnetic shielding material, it is not limited to use under particularly limited conditions, but a general method such as a metal filler is used. It can be used by mixing with resin.

  For example, when forming the electromagnetic wave shielding layer of the conductive sheet for electromagnetic wave shielding, the resin to be used is not particularly limited, and vinyl chloride resin, vinyl acetate resin, vinylidene chloride, which are conventionally used, are not limited. Resin, acrylic resin, polyurethane resin, polyester resin, olefin resin, chlorinated olefin resin, polyvinyl alcohol resin, alkyd resin, thermoplastic resin made of various polymers and copolymers, thermosetting resin, radiation A curable resin or the like can be used as appropriate.

  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 metal filler according to the present embodiment is used as the material for the conductive coating for electromagnetic wave shielding, it is not limited to use under particularly limited conditions, but a general method such as a metal filler Can be mixed with a resin and a solvent, and further mixed with an antioxidant, a thickener, an anti-settling agent, etc., if necessary, and kneaded to obtain a conductive paint.

  The binder resin and solvent used at this time are not particularly limited, and vinyl chloride resin, vinyl acetate resin, acrylic resin, polyester resin, fluororesin, silicon resin, and phenol resin as conventionally used are used. Etc. can be used. As for the solvent, alcohols such as isopropanol, aromatic hydrocarbons such as toluene, esters such as methyl acetate, ketones such as methyl ethyl ketone, and the like, which have been conventionally used, can be used. In addition, as an antioxidant as an additive, a fatty acid amide, a higher fatty acid amine, a phenylenediamine derivative, a titanate coupling agent, and the like that are conventionally used 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≫
About the copper powder obtained by the following Example and the comparative example, observation of a shape and measurement of the average particle diameter were performed with the following method.

(Observation of shape)
With a scanning electron microscope (manufactured by JEOL Ltd., JSM-7100F type), 20 fields of view were arbitrarily observed at a magnification of 1,000 times, and the copper powder contained in the field of view 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).

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

(Tap density)
The tap density was measured using a shaking specific gravity measuring device (manufactured by Kuramochi Scientific Instruments, tapping machine KRS-40).

(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 film was measured by SURFCO M130A), and the sheet resistance value was obtained by dividing by the film thickness.

(Electromagnetic wave shielding characteristics)
The electromagnetic shielding characteristics were evaluated by measuring the attenuation rate of the samples obtained in each example and comparative example using an electromagnetic wave having a frequency of 1 GHz. Specifically, in Comparative Example 3 which is a flat copper powder produced by mechanical flattening, the level in the case of a flat surface is set as “△”, and the case where it is worse than this level is “×”, which is better than this level The case was evaluated as “◯”, and the case where it was superior was evaluated as “◎”.

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

≪Example, comparative example≫
[Example 1]
An electrolytic cell having a capacity of 100 L is charged with an electrolytic solution in the electrolytic cell using a titanium electrode plate having an electrode area of 200 mm × 200 mm as a cathode and a copper plate having an electrode area of 200 mm × 200 mm as an anode. Then, a direct current was passed through this 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 was added to this electrolytic solution so that the concentration in the electrolytic solution was 125 mg / L, and polyethylene glycol having a molecular weight of 2000 (Wako Pure Chemical Industries, Ltd.) Was added so that the concentration in the electrolytic solution was 800 mg / L. Furthermore, 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 above concentration at a flow rate of 10 L / min using a pump, the temperature was maintained at 30 ° C. and the cathode current density was 25 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. .

  As a result of observing the shape of the obtained electrolytic copper powder by the method using the above-mentioned scanning electron microscope (SEM), the deposited copper powder is a copper powder having a shape in which flat copper particles are aggregated (flat copper). Particle agglomerated powder).

The tabular copper particles have a cross-sectional thickness (average cross-sectional thickness) of 0.2 μm and an average major axis diameter (diameter indicated by “d” in the schematic diagram of FIG. 1) of 2. It was 5 μm. The size of the agglomerated copper powder in which a plurality of tabular copper particles were aggregated into an aggregate was 7.3 μm in terms of average particle diameter (D50) measured with a laser diffraction / scattering particle size distribution analyzer. . Moreover, the tap density of the aggregated copper powder was 2.7 g / cm ³ and the BET specific surface area was 2.2 m ² / g. 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. Then, polyethylene glycol having a molecular weight of 2000 was added so that the concentration in the electrolyte was 800 mg / L. Further, a hydrochloric acid solution was added so that the chloride 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 pump, the temperature was maintained at 35 ° C. and the current density of the cathode was 30 A / dm ^2. Other than these, copper powder was deposited on the cathode plate in the same manner as in Example 1.

  As a result of observing the shape of the obtained electrolytic copper powder by the SEM method described above, the deposited copper powder was a copper powder (flat copper particle aggregated powder) having a shape in which flat copper particles were aggregated. It was.

The tabular copper particles had a cross-sectional thickness (average cross-sectional thickness) of 0.3 μm and an average major axis diameter of 3.4 μm. The size of the agglomerated copper powder in which a plurality of tabular copper particles aggregated into an aggregate was 12.4 μm in terms of average particle diameter (D50) measured with a laser diffraction / scattering particle size distribution analyzer. . Moreover, the tap density of the aggregated copper powder was 3.5 g / cm ³ and the BET specific surface area was 1.6 m ² / g. Table 1 summarizes these results.

[Example 3]
15 g of phenol resin (manufactured by Gunei Chemical Co., Ltd., PL-2211) and 10 g of butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., deer special grade) are mixed with 30 g of the tabular copper particle agglomerated powder obtained in Example 1. Using a kneader (Nippon Seiki Seisakusho, non-bubbling kneader NBK-1), kneading at 1200 rpm for 3 minutes was repeated three times to form a paste.

  The obtained conductive paste was printed on glass with a metal squeegee and cured at 150 ° C. and 200 ° C. for 30 minutes in an air atmosphere.

The specific resistance values of the films obtained by curing are 7.9 × 10 ⁻⁵ Ω · cm (curing temperature 150 ° C.) and 1.6 × 10 ⁻⁵ Ω · cm (curing temperature 200 ° C.), respectively. It was found that excellent conductivity was exhibited. Table 2 shows these results.

[Example 4]
15 g of phenol resin (manufactured by Gunei Chemical Co., Ltd., PL-2211) and 10 g of butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., deer special grade) are mixed with 30 g of the tabular copper particle agglomerated powder obtained in Example 2. Using a kneader (Nippon Seiki Seisakusho, non-bubbling kneader NBK-1), kneading at 1200 rpm for 3 minutes was repeated three times to form a paste.

  The obtained conductive paste was printed on glass with a metal squeegee and cured at 150 ° C. and 200 ° C. for 30 minutes in an air atmosphere.

The specific resistance values of the films obtained by curing are 8.8 × 10 ⁻⁵ Ω · cm (curing temperature 150 ° C.) and 2.3 × 10 ⁻⁵ Ω · cm (curing temperature 200 ° C.), respectively. It was found that excellent conductivity was exhibited. Table 2 shows these results.

[Example 5]
In Example 5, the tabular copper particle aggregated powder produced 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 30 g of the obtained tabular copper particle aggregated copper powder, respectively, and kneading at 1200 rpm for 3 minutes was repeated three times using a small kneader. Pasted. 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 2 shows these results.

[Comparative Example 1]
Copper powder was deposited on the cathode plate under the same conditions as in Example 1 except that Janus Green, polyethylene glycol, and chloride ions were not added to the electrolytic solution.

  As a result of observing the shape of the obtained electrolytic copper powder by the method by SEM described above, the obtained copper powder is a copper powder having a dendritic shape, like the copper powder obtained in the examples. The shape of the flat pieces was not agglomerated. FIG. 4 is an SEM observation image of the copper powder obtained in Comparative Example 1. Moreover, the average particle diameter (D50) measured with the laser diffraction and the scattering method particle size distribution measuring device of the obtained copper powder was 22.1 micrometers. Table 1 shows the results.

[Comparative Example 2]
In order to compare with the conventional flat copper powder, in Comparative Example 2, the flat copper powder produced by mechanical flattening was evaluated.

  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.

The average particle diameter (D50) measured by the laser diffraction / scattering particle size distribution analyzer of the flat copper powder thus prepared was 12.6 μm. Moreover, the thickness (cross-sectional average thickness) of the flat copper powder measured by SEM observation was 0.5 μm. Moreover, the tap density of the flat copper powder was 3.2 g / cm ³ and the BET specific surface area was 0.8 m ² / g. Table 1 summarizes these results.

[Comparative Example 3]
In Comparative Example 3, the flat copper powder produced in Comparative Example 2 was used to make a paste in the same manner as in Example 4.

  Specifically, 30 g of the obtained flat copper powder was mixed with 15 g of a phenol resin (PL-2211, manufactured by Gunei Chemical Co., Ltd.) and 10 g of butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., deer special grade), and a small kneader (Nippon Seiki Co., Ltd.). Using a non-bubbling kneader NBK-1) manufactured by Seisakusho, te, 1200 rpm, and kneading for 3 minutes were repeated three times to form a paste.

  The obtained conductive paste was printed on glass with a metal squeegee and cured at 150 ° C. and 200 ° C. for 30 minutes in a nitrogen atmosphere.

The specific resistance values of the coatings obtained by curing were 56 × 10 ⁻⁵ Ω · cm (curing temperature 150 ° C.) and 8.3 × 10 ⁻⁵ Ω · cm (curing temperature 200 ° C.), respectively. Table 2 shows these results.

[Comparative Example 4]
In Comparative Example 4, the flat copper powder prepared in Comparative Example 2 was dispersed in a resin to obtain an electromagnetic wave shielding material.

  That is, with respect to 40 g of the obtained flat copper powder, 100 g of vinyl chloride resin and 200 g of methyl ethyl ketone were mixed, and the mixture was made into a paste by repeating kneading at 1200 rpm for 3 minutes three times using a small kneader. . 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 2 shows these results.

1 Copper powder (flat copper particle agglomerated powder)
2 Flat copper particles d Major axis diameter of flat copper particles

Claims (7)

It is a copper powder having a form of agglomerates by aggregating a plurality of piece-like copper particles,
The copper particles are in the form of a flat plate having an average major axis diameter determined from observation with a scanning electron microscope (SEM) of 0.5 μm to 5 μm and a cross-sectional average thickness of 0.02 μm to 0.5 μm.
A copper powder having an average particle diameter (D50) determined by a laser diffraction / scattering particle size distribution measurement method of 1.0 μm to 30 μm. Copper powder according to claim 1, tap density, characterized in that in the range of ^{0.5g / cm 3 ~5.0g / cm 3} . Copper powder according to claim 1 or 2 BET specific surface area value is equal to or is 0.5m ² /g~3.0m ² / g.   A metal filler comprising the copper powder according to any one of claims 1 to 3 in a proportion of 20% by mass or more of the whole.   A conductive paste comprising the metal filler according to claim 4 mixed with a resin.   A conductive paint for electromagnetic wave shielding, comprising the metal filler according to claim 4 dispersed in a resin. An electroconductive sheet for electromagnetic wave shielding, wherein the metal filler according to claim 4 is dispersed in a resin.