TW201634601A - Copper powder and copper paste using the same, conductive paint and conductive sheet - Google Patents

Abstract

The present invention provides a copper powder which can increase the number of mutual contacts of copper powders to ensure excellent electrical conductivity, and can be preferably used as a conductive paste or an electromagnetic wave shield or the like. The copper powder of this invention is formed into a trunk having a linearly growing trunk and a plurality of branches branched from the trunk, and the trunk and branches are formed of a flat plate-like copper particle 1 having an average cross-sectional thickness of 1.0 micrometer or more and 5.0 micrometers or less. Also, the flat plate-like copper powder, which is composed of a single layer or a laminated structure formed by stacking multiple layers, has an average particle diameter (D50) of 1.0 micrometer to 100 micrometers.

Description

Copper powder and copper paste, conductive paint, and conductive sheet using the same

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

In the formation of a wiring layer or an electrode of an electronic device, a paste obtained by using a metal filler such as silver powder or copper powder like a resin paste or a fired paste is often used. A metal filler paste formed of silver powder, copper powder or the like is applied or printed on various substrates of an electronic device, and subjected to heat curing or heat baking to form a conductive film which is a wiring layer or an electrode.

For example, the resin-type conductive paste is formed of a metal filler, a resin, a curing agent, a solvent, or the like, and is printed on a conductor circuit pattern or a terminal, and is heat-hardened at 100 ° C to 200 ° C in the form of a conductive film. Form wiring or electrodes. In the resin-type conductive paste, since the thermosetting resin is hardened and shrunk by heat, the metal filler is pressure-contacted and contacted, whereby the metal fillers are superposed to form a current path for electrical connection. Since the resin-type conductive paste is treated at a curing temperature of 200 ° C or lower, it is used for a substrate using a material having poor heat resistance such as a printed wiring board.

Further, the fired conductive paste is formed of a metal filler, glass, a solvent, or the like. This is printed on a conductor circuit pattern or a terminal, and is fired at 600 ° C to 800 ° C to form a wiring or an electrode in the form of a conductive film. The fired conductive paste is sintered by using a higher temperature to sinter the metal filler to ensure conductivity. Since the calcination conductive paste has a high firing temperature, it cannot be used for a printed wiring board using a resin material. However, since the metal filler is sintered by high-temperature treatment, low electrical resistance can be achieved. Therefore, the fired conductive paste can be used for an external electrode or the like of a laminated ceramic capacitor.

In addition, as a metal filler used for the resin-type conductive paste or the fire-conductive conductive paste, a powder of silver has been used in many cases. However, in recent years, the price of precious metals has risen, and in order to reduce costs, the use of copper powder having a lower price than silver powder has been gradually favored.

Here, as the powder of copper or the like used as the metal filler, as described above, in order to electrically connect the particles to each other, a shape such as a granular shape, a dendritic shape, or a flat shape is used. In particular, when the particles are evaluated in terms of the dimensions in the three directions of the longitudinal direction, the transverse direction, and the thickness direction, the thin plate-shaped shape has the following advantages: the thickness of the wiring material is reduced by the thickness reduction, and the particles are ensured to each other. The area of contact is larger than a cube-shaped or spherical particle having a certain thickness, and a low electrical resistance, that is, a high electrical conductivity can be achieved accordingly. Therefore, the flat-shaped copper powder is particularly suitable for the use of a conductive paint or a conductive paste for maintaining conductivity. Further, in the case where the conductive paste is applied in a thin manner, 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 of obtaining a flake shape copper powder suitable for a metal filler of a conductive paste. Specifically, spherical copper powder having an average particle diameter of 0.5 μm to 10 μm is used as a raw material, and is mechanically processed into a flat shape by a mechanical energy of a medium loaded in a mill using a ball mill or a vibrating mill.

Further, for example, Patent Document 2 discloses copper powder for conductive paste, In particular, it is a technique for obtaining a high-performance disk-shaped copper powder as a through-hole copper paste for external electrodes and a method for producing the same. Specifically, the granular atomized copper powder is put into a medium agitating mill, and a steel ball having a diameter of 1/8 inch to 1/4 inch is used as a grinding medium, and the copper powder is added by 0.5% to 1 by weight. % of fatty acid, which is pulverized in air or in an inactive environment, thereby being processed into a flat shape.

Further, for example, Patent Document 3 discloses a method of obtaining an electrolytic copper powder which can be formed at a higher strength than a known electrolytic copper powder without increasing the amount of branches of the electrolytic copper powder. Specifically, in order to increase the strength of the electrolytic copper powder itself, electrolytic copper powder which is formed at a high strength can be precipitated, and the size of the crystallites constituting the electrolytic copper powder can be made fine, and the copper sulfate aqueous solution as an electrolytic solution can be used. The electrolytic copper powder is precipitated by adding one or more selected from the group consisting of a tungstate, a molybdate, and a sulfur-containing organic compound.

The methods disclosed in the above patent documents are all formed into a flat shape by mechanically deforming (processing) the obtained granular copper powder using a medium such as a ball. Therefore, the size of the flat copper powder produced by the processing is, for example, an average particle diameter of 1 μm to 30 μm in the technique of Patent Document 1, and an average particle diameter of 7 μm to 12 μm in the technique of Patent Document 3.

On the other hand, it is known that electrolytic copper powder which is dendritic in the form of dendrites has a large surface area and is excellent in formability and sinterability, and is used as a powder metallurgical application because of its dendritic shape. Used as a raw material for oil-impregnated bearings or mechanical parts. In particular, in oil-impregnated bearings and the like, it is becoming more and more miniaturized, and it is required to be porous or thinned, and complicated in shape. In order to satisfy such a request, for example, Patent Document 4 discloses a copper powder for metal powder injection molding which is a complicated three-dimensional shape and has high dimensional accuracy, and a method for producing an injection molded article using the same. Specifically, it is revealed that the shape of the dendron is more developed and is formed by pressure molding. When the adjacent branches of the electrolytic copper powder are entangled and firmly joined, they can be formed with higher strength. Further, in the case of being used as a conductive paste or a metal filler for electromagnetic wave shielding, it is possible to use a shape of a dendritic shape, so that the number of contacts can be increased as compared with 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, if the metal filler in the resin has developed into a dendritic shape, the dendritic copper powders are mutually Agglomeration occurs when they are entangled to cause uneven dispersion in the resin, or the viscosity of the paste rises due to aggregation, which causes problems in the formation of wiring by printing. Such a problem is also pointed out, for example, in Patent Document 3.

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 that the improvement in conductivity of the paste is hard to progress. Further, for the purpose of ensuring conductivity, the dendritic copper powder is easier to ensure contact than the granular copper powder, and can be used as a conductive paste or electromagnetic wave shield to ensure high conductivity.

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2005-200734

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2002-15622

[Patent Document 3] Japanese Laid-Open Patent Publication No. 2011-58027

[Patent Document 4] Japanese Patent Laid-Open Publication No. 9-3510

The present invention has been made in view of the above circumstances, and it is an object of the invention to provide a copper powder which can increase the contact of copper powder with each other to ensure excellent electrical conductivity, and can be preferably used as a conductive paste. Or electromagnetic wave shielding and other purposes.

The present inventors have repeatedly conducted intensive studies in order to solve the above problems. As a result, it was found that the copper powder is a trunk having a linear growth and a plurality of branched dendritic shapes which are separated from the trunk, and the stem and the branches are covered by a specific range of the average thickness of the plate-shaped copper particles. The average particle diameter (D50) of the copper powder is in a specific range, and excellent electrical conductivity can be ensured, and can be uniformly mixed with, for example, a resin, and can be preferably used for a conductive paste or the like to complete The invention has been made. That is, the present invention provides the following.

(1) A copper powder according to the first aspect of the present invention, characterized in that it is formed into a trunk having a linear growth and a branch shape of a plurality of branches branched from the trunk, and the trunk and the above-mentioned branches The branch is composed of flat copper particles having a cross-sectional average thickness of more than 1.0 μm and a thickness of 5.0 μm or less, and the copper powder is a flat plate having a laminated structure in which one layer or a plurality of layers are stacked, and the average particle diameter (D50) is 1.0. Mm~100μm.

(2) A copper powder according to the first aspect of the invention, wherein the ratio of the cross-sectional thickness of the tabular copper particles to the average particle diameter (D50) of the copper powder is more than 0.01 and in the range of 5.0 or less, and the bulk density of the copper powder is in the range of 0.5 g/cm ³ to 5 g/cm ³ .

(3) a third line of one kind of copper powder of the present invention, wherein: in the first invention, a BET specific surface area is 0.2m ² /g~3.0m ² / g.

(4) A copper powder according to the first aspect of the invention, characterized in that, in the first invention, the Miller index of the (111) plane obtained by X-ray diffraction of the flat copper particles is obtained. The microcrystalline diameter is in the range of 800 Å to 3,000 Å.

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

(6) A copper paste according to a sixth aspect of the invention is characterized in that the metal filler of the fifth invention is mixed with a resin.

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

(8) A conductive sheet for electromagnetic wave shielding according to the present invention, characterized in that the metal filler of the fifth invention is used.

According to the copper powder of the present invention, a large number of contacts can be secured and a large contact area can be obtained, and excellent electrical conductivity can be ensured, and aggregation can be prevented, and it is preferably used for applications such as conductive paste or electromagnetic wave shielding.

1‧‧‧ copper particles

2‧‧‧ (copper particles) trunk

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

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

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

Fig. 3 is a photographic view showing an observation image when a dendritic copper powder is observed at a magnification of 5,000 times by a scanning electron microscope.

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

Fig. 5 is a photographic view showing an observation image when a dendritic copper powder is observed at a magnification of 10,000 times by a scanning electron microscope.

Figure 6 is a view showing the comparison in Comparative Example 1 by a scanning electron microscope at a magnification of 10,000 times. A photo of the observation image when the copper powder is obtained.

Fig. 7 is a photographic view showing an observation image when the copper powder obtained in Comparative Example 2 was observed at a magnification of 10,000 times by a scanning electron microscope.

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

"1. Dendritic copper powder"

In the present embodiment, the copper powder is formed into a trunk having a linear growth and a plurality of branched dendrites separated from the trunk, and the trunk and the branch are formed by a flat plate having a specific average thickness of the section. Made up of copper particles.

Fig. 1 is a view showing the specific shape of copper particles constituting the copper powder of the present embodiment. As shown in the schematic view of Fig. 1, the copper particles 1 have a dendritic shape in a two-dimensional or three-dimensional form. More specifically, the copper particles 1 have a dendritic shape including a trunk 2 which grows linearly and a plurality of branches 3 which are branched from the trunk 2, and have a cross-sectional average thickness of more than 1.0 μm and less than 5.0 μm. Flat shape. Further, the branch 3 in the copper particles 1 means two kinds of branches 3a which are branched from the stem 2 and branches 3b which are branched from the branch 3a.

The copper powder of the present embodiment is a copper powder having a trunk shape and a plurality of branched dendritic shapes (hereinafter also referred to as "dendritic copper powder") composed of such flat copper particles 1 (see FIG. 2). The SEM image of the copper powder is composed of a laminated structure in which one layer or a plurality of layers are stacked. In the form of a flat plate (see the SEM image of the copper powder of FIG. 4 or FIG. 5), the average particle diameter (D50) of the dendritic copper powder composed of the copper particles 1 is 1.0 μm to 100 μm.

Further, as will be described in detail below, the dendritic copper powder of the present embodiment can be deposited on the cathode by, for example, immersing the anode and the cathode in a sulfuric acid acidic electrolyte containing copper ions and flowing a direct current for electrolysis. obtain.

2 to 5 are photographs showing an example of an observation image when the dendritic copper powder of the present embodiment is observed by a scanning electron microscope (SEM). Further, Fig. 2 is obtained by observing dendritic copper powder at a magnification of 1,000 times, Fig. 3 is obtained by observing dendritic copper powder at a magnification of 5,000 times, and Fig. 4 and Fig. 5 are observations of dendritic copper powder at a magnification of 10,000 times. .

As shown in the observation image of Fig. 2, the dendritic copper powder has a two-dimensional or three-dimensional dendritic precipitation state having a trunk and branches branched from the trunk. Further, as shown in the observation image of Fig. 3, the trunk and the branch constituting the dendritic copper powder are composed of a collection of copper particles 1 having a dendritic shape and a dendritic shape (see the schematic view of Fig. 1). Further, as shown in the observation images of FIGS. 4 and 5, the dendritic copper powder is formed into a multi-layered structure of a flat plate in FIG. 4 by the grown copper particles 1, and is formed into a flat plate in FIG. Single layer. As is apparent from the observation of the image by the SEM, the dendritic copper powder of the present embodiment is formed in a flat shape and has a laminated structure in which one layer or a plurality of layers are stacked, and is integrally formed to have a trunk and a branch from the trunk. Branched dendritic shape.

Here, the plate-shaped copper particles 1 constituting the dendritic copper powder of the present embodiment and having the trunk 2 and the branch 3 have an average thickness of a cross section of more than 1.0 μm and not more than 5.0 μm. By using the flat copper particles 1 having a cross-sectional average thickness of 5.0 μm or less to form the trunk and branches of the dendritic copper powder, it is possible to ensure that the copper particles 1 are in contact with each other or the dendritic copper powder composed thereof. Large area. Moreover, by increasing the contact area, low electrical resistance, that is, high electrical conductivity can be achieved. Thereby, the conductivity is more excellent, and the conductivity can be favorably maintained, and can be preferably used for the use of a conductive paint or a conductive paste. Further, by forming the dendritic copper powder from the flat copper particles 1, it is possible to contribute to the reduction in thickness of the wiring material or the like.

In addition, the lower limit of the average thickness of the cross-section of the tabular copper particles 1 is not particularly limited, and a method of depositing the cathode on the cathode by electrolysis from a sulfuric acid-containing acidic electrolyte containing copper ions can be used. A dendritic copper powder having a combination of flat copper particles 1 having a cross-sectional average thickness of more than 1.0 μm.

Further, the dendritic copper powder of the present embodiment has an average particle diameter (D50) of 1.0 μm to 100 μm. The average particle size can be controlled by changing the electrolysis conditions described below. Further, mechanical pulverization such as a jet mill, a sample mill, a cyclone mill, or a bead mill may be added as needed, and further adjusted to a desired size. Further, the average particle diameter (D50) can be measured by, for example, a laser diffraction scattering type particle size distribution measurement method.

Here, as described in, for example, Patent Document 1, the problem of the dendritic copper powder is as follows: when it 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 When the dendritic shape is developed, the dendritic copper powder is entangled with each other to agglomerate, so that it is not uniformly dispersed in the resin. Moreover, the viscosity of the paste rises due to the aggregation, which causes a problem in the formation of wiring by printing. The reason for this is that since the dendritic copper powder grows in the form of a needle-like shape, the dendritic copper powder is entangled with each other to be aggregated into a larger block.

In this respect, the dendritic copper powder of the present embodiment can be formed by the formation of tabular copper particles having a cross-sectional average thickness of more than 1.0 μm and 5.0 μm or less, thereby preventing aggregation due to the entanglement of the copper powders. That is, copper can be made by growing flat copper particles. The powders are brought into surface contact with each other to prevent aggregation due to the mutual entanglement of the copper powders, so that they are uniformly dispersed in the resin. Further, by growing the flat shape in such a manner that the copper powders are in surface contact with each other, the contact resistance can be suppressed to be low by contact with a wide area.

Further, when a spherical copper powder is formed into a flat shape by a mechanical method as described in Patent Document 1 or Patent Document 2, since it is necessary to prevent oxidation of copper during mechanical processing, fatty acid is added. And pulverized in air or in an inactive environment, and processed into a flat shape. However, there is a problem that oxidation cannot be completely prevented, or since the fatty acid added during processing affects dispersibility when gelatinization occurs, it must be removed after the end of processing, but there is pressure due to machining. It is firmly fixed to the copper surface and cannot completely remove fatty acids. In the case of using a metal filler such as a conductive paste or a resin for electromagnetic wave shielding, if an oxide film or a fatty acid which inhibits electrical conductivity on the surface of the metal filler is present, the electrical impedance is increased, and the electrical resistance cannot be sufficiently Take advantage of the characteristics of metal fillers.

In this respect, the dendritic copper powder of the present embodiment is produced by directly growing into the shape of dendritic copper powder without mechanical processing, so that it does not cause oxidized coating or fatty acid which has been plagued to date. The copper powder in a state in which the surface state is good, which is caused by the residual state, can be made into an extremely excellent state as electrical conductivity. Further, a method for producing copper powder is described below.

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

The ratio (aspect ratio) indicated by the "average thickness of the section/average particle diameter" is the degree of aggregation or dispersibility when processed into, for example, a conductive copper paste, and the appearance shape at the time of coating of the copper paste. Indicators such as retention. When the aspect ratio is 0.01 or less, aggregation tends to occur easily, and it is difficult to uniformly disperse in the resin during gelatinization. On the other hand, when the aspect ratio exceeds 5.0, the copper powder composed of spherical copper particles is obtained, and the effect of the flat plate shape cannot be sufficiently exhibited.

Further, the bulk density of the dendritic copper powder is not particularly limited, but is preferably in the range of 0.5 g/cm ³ to 5.0 g/cm ³ . If the bulk density is less than 0.5 g/cm ³ , there is a possibility that the contact of the copper powders with each other cannot be sufficiently ensured. On the other hand, when the bulk density exceeds 5.0 g/cm ³ , the average particle diameter of the dendritic copper powder also increases, and as a result, the surface area becomes small, and the formability or the sinterability deteriorate.

Further, the dendritic copper is not particularly limited, preferred values for BET specific surface area of 0.2m ² /g~3.0m ² / g. When the BET specific surface area value is less than 0.2 m ² /g, the copper particles 1 constituting the dendritic copper powder do not have the desired flat shape as described above, and there is no possibility of obtaining high conductivity. Happening. On the other hand, when the BET specific surface area value exceeds 3.0 m ² /g, aggregation tends to occur, and it is difficult to uniformly disperse in the resin during gelatinization. Further, the BET specific surface area can be measured in accordance with JIS Z8830:2013.

Further, the dendritic copper powder is not particularly limited, and it is preferable that the crystallite diameter is in the range of 800 Å (Å) to 3,000 Å. When the crystallite diameter is less than 800 Å, the copper particles 1 constituting the trunk or the branch tend not to be flat, but tend to be close to a spherical shape, and it is difficult to ensure that the contact area is sufficiently large, and there is a possibility that the conductivity is lowered. . On the other hand, when the crystallite diameter exceeds 3,000 Å, moldability or sinterability may be deteriorated.

In addition, the microcrystal diameter here is a diffraction pattern obtained by the X-ray diffraction measuring apparatus, and is obtained based on the calculation formula of Scherrer represented by the following mathematical expression, and is obtained by X The microcrystalline diameter in the Miller index of the (111) plane obtained by diffraction.

D=0.9 λ/β cos θ

(Further, D: microcrystalline diameter (Å), β: diffraction peak (rad) caused by the size of crystallites, λ: wavelength of X-ray [CuK α] (Å), θ: diffraction angle ( °))

Further, when observed by an electron microscope, as long as the dendritic copper powder having the shape as described above occupies a specific ratio in the obtained copper powder, even if a copper powder having a shape other than the above is mixed, The same effect as the copper powder composed only of the dendritic copper powder was obtained. Specifically, when observed by an electron microscope (for example, 500 times to 20,000 times), the dendritic copper powder having the above shape accounts for 80% or more, preferably 90% or more of the total number of copper powders. It can also contain copper powder of other shapes.

"2. Method for manufacturing dendritic copper powder"

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

In the electrolysis, the sulfuric acid-containing acidic electrolyte containing the copper ions is contained in, for example, an electrolytic cell provided with a metal copper as an anode and a stainless steel plate or a titanium plate as a cathode. Electrolytic treatment is carried out by flowing a direct current at a specific current density in the electrolytic solution. Thereby, dendritic copper powder can be deposited (electrodeposited) on the cathode with energization. In particular, in the present embodiment, it is not necessary to mechanically deform a copper powder such as a granular material obtained by electrolysis using a medium such as a ball, and the flat copper particles can be formed only by the electrolysis. The dendritic copper powder which is formed into dendrites is deposited on the surface of the cathode.

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

The water-soluble copper salt is a copper ion source for supplying copper ions, and for example, copper sulfate five Copper sulfate, copper chloride, copper nitrate or the like such as hydrate is not particularly limited. Further, the concentration of copper ions in the electrolytic solution may be about 1 g/L to 20 g/L, and preferably about 2 g/L to 10 g/L.

Sulfuric acid is used to make a sulfuric acid acidic electrolyte. The concentration of sulfuric acid in the electrolytic solution can be set to about 20 g/L to 300 g/L, preferably about 50 g/L to 200 g/L, in terms of free sulfuric acid concentration. The concentration of sulfuric acid affects the conductivity of the electrolyte and therefore affects the homogeneity of the copper powder obtained on the cathode.

As the additive, for example, an amine compound can be used. The amine compound can be controlled by the shape of the copper powder which is assisted by the following chloride ions, and the copper powder deposited on the surface of the cathode is made of flat copper particles having a dendritic shape and a specific average thickness of the section. A dendritic copper powder having a trunk and a plurality of branches.

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

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

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

"3. Uses of conductive paste, conductive paint, etc."

As described above, the dendritic copper powder of the present embodiment has a trunk and a plurality of branched dendritic copper powders, and the dendritic copper powder is composed of a collection of copper particles 1 as shown in the schematic view of FIG. The copper particles 1 are dendrites having a trunk 2 and a plurality of branches 3 branched from the trunk 2, and have a flat plate shape having an average cross-sectional thickness of more than 1.0 μm and a thickness of 5.0 μm or less. Further, the dendritic copper powder has an average particle diameter (D50) of from 1.0 μm to 100 μm. Such a dendritic copper powder has a dendritic shape and has a large surface area and is excellent in formability or sinterability. Further, the dendritic copper powder is composed of flat plate-shaped copper particles 1 which are dendritic and have a specific average thickness of the cross section, thereby ensuring a large number of contacts and exhibiting excellent electrical conductivity.

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

In the present embodiment, the metal filler has a ratio of the dendritic copper powder to 20% by mass or more, preferably 30% by mass or more, and more preferably 50% by mass or more. When the ratio of the dendritic copper powder in the metal filler is 20% by mass or more, for example, the gold is When the filler is used in the case of a copper paste, it can be uniformly dispersed in the resin, and the viscosity of the paste can be prevented from excessively rising to cause poor printability. In addition, the dendritic copper powder composed of the aggregate of the plate-shaped fine copper particles 1 can exhibit excellent conductivity as a conductive paste. In addition, as the metal filler, the dendritic copper powder may be contained in a ratio of 20% by mass or more as described above, and a spherical copper powder of, for example, about 1 μm to 20 μm may be mixed.

For example, the conductive paste (copper paste) can be produced by mixing the dendritic copper powder of the present embodiment as a metal filler with an adhesive resin, a solvent, and optionally an additive such as an antioxidant or a coupling agent.

Specifically, the binder resin is not particularly limited, and an epoxy resin, a phenol resin or the like can be used. Further, as the solvent, an organic solvent such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin or terpineol can be used. In addition, the amount of the organic solvent to be added is not particularly limited, and may be a form suitable for the viscosity of a conductive film forming method such as screen printing or dispenser printing, and the amount of addition may be adjusted in consideration of the particle size of the dendritic copper powder.

Further, other resin components may be added in order to adjust the viscosity. For example, a cellulose-based resin represented by ethyl cellulose is used, and it is added as an organic medium dissolved in an organic solvent such as terpineol. In addition, the amount of the resin component to be added must be suppressed to such an extent that the sinterability is not inhibited, and it is preferably 5% by mass or less of the whole.

Further, as an additive, an antioxidant or the like may be added in order to improve the conductivity after firing. The antioxidant is not particularly limited, and examples thereof include a hydroxycarboxylic acid and the like. More specifically, a hydroxycarboxylic acid such as citric acid, malic acid, tartaric acid or lactic acid is preferred, and citric acid or malic acid having a high adsorption power to copper is particularly preferred. As an antioxidant, the antioxidant effect or paste can be considered. The viscosity is, for example, about 1 to 15% by mass.

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

For example, the resin used to form the electromagnetic wave shielding layer of the conductive sheet for electromagnetic wave shielding is not particularly limited, and the previously used vinyl chloride resin, vinyl acetate resin, vinylidene chloride resin, acrylic resin, or polyurethane may be suitably used. Polyurethane resin, thermosetting resin, radiation curable resin composed of various polymers and copolymers such as a resin, a polyester resin, an olefin resin, a chlorinated olefin resin, a polyvinyl alcohol resin, an alkyd resin, and a phenol resin. Wait.

As a method of manufacturing an electromagnetic wave shielding material, for example, it can be produced by dispersing or dissolving a metal filler and a resin as described above in a solvent to form a coating, and coating or printing the coating on a substrate. An electromagnetic wave shielding layer is formed and dried to the extent that the surface is cured. Further, the metal filler of the present embodiment may be used for the conductive adhesive layer of the conductive sheet.

Further, when the conductive coating material for electromagnetic wave shielding is used in the case of using the metal filler of the present embodiment, it is not limited to use under particularly limited conditions, and the metal filler can be mixed with a resin and a solvent by a general method. It is mixed with an antioxidant, a tackifier, an anti-precipitant, etc., and kneaded as needed, and used as a conductive coating.

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

[Examples]

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

<Evaluation method>

The copper powder obtained in the following examples and comparative examples was observed for shape, measurement of average particle diameter, and measurement of crystallite diameter by the following methods.

(observation of shape)

The 20-view field was arbitrarily observed by a scanning electron microscope (manufactured by JEOL Ltd., JSM-7100F type) at a specific magnification, and the copper powder contained in the viewing zone was observed.

(Measurement of average particle size)

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

(Measurement of microcrystalline diameter)

The diffraction pattern obtained by an X-ray diffraction measuring apparatus (X'Pert PRO, manufactured by PAN Exploration Co., Ltd.) was calculated by a known method which is generally known as Scherrer's formula.

(measurement of aspect ratio)

The obtained copper powder is embedded in an epoxy resin to prepare a measurement sample, and the sample is cut. The cross section of the copper powder was observed by cutting, grinding, and observation using a scanning electron microscope. Specifically, first, 20 copper powders were observed, and the average thickness (sectional average thickness) of the copper powder was determined. Secondly, according to the value of the average thickness of the section and by laser diffraction. The ratio of the average particle diameter (D50) obtained by the scattering particle size distribution measuring device was determined, and the aspect ratio (sectional average thickness / D50) was determined.

(BET specific surface area)

The BET specific surface area is the specific surface area. The pore distribution measuring device (manufactured by Quantachrome, QUADRASORB SI) was measured.

(measured by specific resistance value)

The specific resistance value of the film was obtained by using a low resistivity meter (manufactured by Mitsubishi Chemical Corporation, Loresta-GP MCP-T600) and measuring the sheet resistance value by a four-terminal method by surface The roughness shape measuring instrument (SURFCOM 130A, manufactured by Tokyo Seimitsu Co., Ltd.) measures the film thickness of the film and divides the sheet resistance value by the film thickness.

(Electromagnetic wave shielding characteristics)

The electromagnetic wave shielding characteristics were evaluated by measuring the attenuation rate of the samples obtained in the respective examples and comparative examples using electromagnetic waves having a frequency of 1 GHz. Specifically, the level of the case of Comparative Example 4 in which no dendritic copper powder was used was evaluated as "△", and the case of the level difference of Comparative Example 4 was evaluated as "X", which was higher than that of Comparative Example 4. The good case was evaluated as "○", and the more excellent case was evaluated as "◎".

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

<Examples, 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 was used as a cathode, and a copper electrode plate having an electrode area of 200 mm × 200 mm was used as an anode, and an electrolytic solution was charged in the electrolytic cell. The direct current is passed therethrough to cause the copper powder to be deposited out of the cathode plate.

At this time, as the electrolytic solution, a composition having a copper ion concentration of 5 g/L and a sulfuric acid concentration of 150 g/L was used. Further, in the electrolytic solution, Safranin O (manufactured by Kanto Chemical Industry Co., Ltd.) as an additive is added so as to be 100 mg/L in terms of the concentration in the electrolytic solution, and further, the chloride ion in the electrolytic solution is added. A hydrochloric acid solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added to a concentration of 10 mg/L (chlorine ion). Then, the electrolytic solution adjusted to the concentration as described above was used while circulating at a flow rate of 15 L/min using a metering pump while maintaining the temperature at 25 ° C, and energizing the current density of the cathode to 25 A/dm ² . The copper powder is deposited on the cathode plate. The electrolytic copper powder deposited on the cathode plate was mechanically scraped off to the bottom of the electrolytic cell by a scraper and recovered, and the recovered copper powder was washed with pure water, and then placed in a vacuum dryer to be dried.

The shape of the obtained electrolytic copper powder was observed by the above-described scanning electron microscope (SEM) method, and it was found that at least 90% or more of the copper powder in the precipitated copper powder was a two-dimensional or three-dimensional dendritic shape. a copper powder, which is a dendritic copper powder obtained by assembling copper particles, the copper particles having a branch having a trunk and branches from the trunk, and branches branched from the branches and branches Shape. Further, the copper powder is a flat plate composed of a laminated structure in which one layer or a plurality of layers are stacked.

Further, the copper particles having a trunk shape and a branched dendritic shape have a plate-like average thickness of 3.4 μm. Further, the dendritic copper powder had an average particle diameter (D50) of 58.6 μm. Further, the aspect ratio (sectional average thickness/average particle diameter) calculated from the average thickness of the cross section of the copper particles and the average particle diameter of the dendritic copper powder was 0.06. Further, the dendritic copper powder obtained had a bulk density of 2.9 g/cm ³ . Moreover, the dendritic copper powder has a microcrystalline diameter of 2538 Å. Further, the BET specific surface area was 1.1 m ² /g.

[Embodiment 2]

As the electrolyte solution, a composition having a copper ion concentration of 7 g/L and a sulfuric acid concentration of 150 g/L is used, and as the additive, Safranin O is added as an additive so as to be 150 mg/L in terms of the concentration in the electrolytic solution. Further, a hydrochloric acid solution was added so as to be 25 mg/L in terms of the chloride ion concentration in the electrolytic solution. Then, the electrolytic solution adjusted to the concentration as described above was used while circulating at a flow rate of 20 L/min using a metering pump while maintaining the temperature at 30 ° C, and energizing the current density of the cathode to 20 A/dm ² . The copper powder is deposited on the cathode plate. An electrolytic copper powder was produced in the same manner as in Example 1 except for these conditions.

The shape of the obtained electrolytic copper powder was observed by the above-described scanning electron microscope (SEM) method, and it was found that at least 90% or more of the copper powder in the precipitated copper powder was a two-dimensional or three-dimensional dendritic shape. A copper powder, which is a dendritic copper powder in which copper particles are aggregated, and the copper particles have a dendritic shape having a plurality of branches which are autonomously branched and branched from the branches. Further, the copper powder is a flat plate composed of a laminated structure in which one layer or a plurality of layers are stacked.

Further, the copper particles having a trunk shape and a branched dendritic shape have a plate-like average thickness of 1.2 μm and a plate shape, and the dendritic copper powder has an average particle diameter (D50) of 44.3 μm. Further, the aspect ratio (sectional average thickness/average particle diameter) calculated from the average thickness of the cross section of the copper particles and the average particle diameter of the dendritic copper powder was 0.03. Further, the obtained dendritic copper powder had a bulk density of 1.5 g/cm ³ . Moreover, the dendritic copper powder has a microcrystalline diameter of 1861 Å. Further, the BET specific surface area was 1.7 m ² /g.

[Example 3]

As the electrolyte solution, a composition having a copper ion concentration of 5 g/L and a sulfuric acid concentration of 125 g/L is used, and as the additive, Safranin O is added as an additive so as to be 200 mg/L in terms of the concentration in the electrolytic solution. Further, a hydrochloric acid solution was added so as to be 25 mg/L in terms of the chloride ion concentration in the electrolytic solution. Then, the electrolytic solution adjusted to the concentration as described above was used while circulating at a flow rate of 25 L/min using a metering pump while maintaining the temperature at 35 ° C, and energizing the current density of the cathode to 25 A/dm ² . The copper powder is deposited on the cathode plate. An electrolytic copper powder was produced in the same manner as in Example 1 except for these conditions.

Observed by the above-described method using a scanning electron microscope (SEM) The shape of the copper powder was solved, and it was found that at least 90% of the copper powder in the precipitated copper powder was a two-dimensional or three-dimensional dendritic copper powder, and the copper powder was a dendritic copper powder. . The copper particles are in the form of a branch having a plurality of branches which are branched in a straight line and a branch which branches out from the branches. Further, the copper powder is a flat plate structure composed of a laminated structure in which one layer or a plurality of layers are stacked.

Further, the copper particles having the stem and the branch have a plate-like average thickness of 2.6 μm. Further, the dendritic copper powder had an average particle diameter (D50) of 37.4 μm. Further, the aspect ratio (sectional average thickness/average particle diameter) calculated from the average thickness of the cross section of the copper particles and the average particle diameter of the dendritic copper powder was 0.07. Further, the dendritic copper powder obtained had a bulk density of 1.4 g/cm ³ . Moreover, the dendritic copper powder has a microcrystalline diameter of 1630 Å. Further, the BET specific surface area was 1.6 m ² /g.

[Example 4]

To 60 parts by mass of the dendritic copper powder obtained in Example 1, the phenol resin was mixed (Group Rong Chemical Manufactured by the company, PL-2211) 20 parts by mass, butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., Rote grade), 10 parts by mass, and using a small kneading machine (manufactured by Nippon Seiki Co., Ltd., non-foaming kneader NBK-1) ), the 1500 rpm and 3 minutes of mixing were repeated four times to thereby gelatinize. The obtained conductive paste was printed on glass by a metal squeegee and hardened at 150 ° C and 200 ° C for 30 minutes in an atmospheric environment.

The specific resistance of the film obtained by hardening is 9.4×10 ^-5 Ω, respectively. Cm (hardening temperature 150 ° C), 2.5 × 10 ^-5 Ω. Cm (hardening temperature 200 ° C).

[Example 5]

To 60 parts by mass of the dendritic copper powder obtained in Example 2, 20 parts by mass of phenol resin (PL-2211, manufactured by Kyoei Chemical Co., Ltd.) and butyl cellosolve (manufactured by Kanto Chemical Co., Ltd., Rote grade) were mixed. 10 parts by mass, and using a small kneader (manufactured by Nippon Seiki Co., Ltd., non-foaming kneader NBK-1), the 1500 rpm and 3 minutes of kneading were repeated four times to thereby gelatinize. The obtained conductive paste was printed on glass by a metal squeegee and hardened at 150 ° C and 200 ° C for 30 minutes in an atmospheric environment.

The specific resistance of the film obtained by hardening is 9.7×10 ^-5 Ω. Cm (hardening temperature 150 ° C), 3.1 × 10 ^-5 Ω. Cm (hardening temperature 200 ° C).

[Embodiment 6]

The dendritic copper powder prepared in Example 1 was dispersed in a resin to prepare an electromagnetic wave shielding material.

Specifically, 100 g of the dendritic copper powder obtained in Example 1 was mixed with 100 g of a vinyl chloride resin and 200 g of methyl ethyl ketone, and kneaded by repeating mixing at 1500 rpm for 3 minutes using a small kneader. At the time of gelatinization, the copper powder does not aggregate and is uniformly dispersed in the resin. It was applied to a transparent polyethylene terephthalate having a thickness of 100 μm using a Meyer bar. The substrate composed of the diester sheet was dried and formed into an electromagnetic wave shielding layer having a thickness of 20 μm.

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

[Comparative Example 1]

The copper powder was deposited on a cathode plate under the same conditions as in Example 1 except that the conditions of the Safranin O and the chloride ion as additives were not added to the electrolytic solution to prepare electrolytic copper powder.

The shape of the obtained electrolytic copper powder was observed by the above-described scanning electron microscope (SEM) method. As a result, it was found that although the obtained copper powder had a dendritic shape, it was a collection of granular copper particles. In addition, FIG. 6 is an SEM observation image (magnification: 10,000 times) of the copper powder obtained in the comparative example 1. Further, it was confirmed that the obtained copper powder had an average particle diameter (D50) of 40 μm or more and was a very large dendritic copper powder.

[Comparative Example 2]

As the electrolytic solution, a composition having a copper ion concentration of 10 g/L and a sulfuric acid concentration of 150 g/L was used. Further, in the electrolytic solution, Safranin O (manufactured by Kanto Chemical Industry Co., Ltd.) as an additive is added so as to be 50 mg/L in terms of the concentration in the electrolytic solution, and further, the chloride ion in the electrolytic solution is added. A hydrochloric acid solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added to a concentration of 10 mg/L (chlorine ion). Then, the electrolytic solution adjusted to the concentration as described above was used while circulating at a flow rate of 15 L/min using a metering pump while maintaining the temperature at 45 ° C and energizing the current density of the cathode to 20 A/dm ² . The copper powder is deposited on the cathode plate. Further, conditions other than these were prepared in the same manner as in Example 1 to prepare electrolytic copper powder.

In Fig. 7, the results obtained by observing the shape of the electrolytic copper powder obtained by the SEM at a magnification of 10,000 times are shown. Two-dimensional or three-dimensional collection of precipitated copper powder granular copper particles Made of dendritic copper powder. The trunk and branches of the dendrites are curved, and are not formed into a flat shape composed of a laminated structure of one layer or a plurality of layers as the copper powder obtained in the embodiment.

[Comparative Example 3]

In order to compare with the conventional flat copper powder, it is mechanically flattened to produce a flat copper powder. Specifically, in the production of the flat copper powder, 5 g of stearic acid was added to 500 g of granular atomized copper powder (manufactured by Makin Metal Powders Co., Ltd.) having an average particle diameter of 5.4 μm, and flattened by a ball mill. 5 kg of 3 mm zirconia beads were placed in a ball mill and rotated at a rotation speed of 500 rpm for 90 minutes.

By laser diffraction. The flat copper powder thus produced was measured by a scattering particle size analyzer, and as a result, it was found that the average particle diameter was 12.6 μm, and observation by a scanning electron microscope revealed that the average thickness of the cross section was 0.5 μm. Further, the aspect ratio (sectional average thickness/average particle diameter) calculated from the average thickness of the cross section and the average particle diameter was 0.04.

In the same manner as in Example 4, 15 parts by mass of phenol resin (PL-2211, manufactured by Kyoei Chemical Co., Ltd.) and butyl cellosolve (Kantong Chemical Co., Ltd.) were mixed with 55 parts by mass of the flat copper powder. 10 parts by mass of the company, and a small kneading machine (manufactured by Nippon Seiki Co., Ltd., non-foaming kneader NBK-1), and repeated 1500 rpm and 3 minutes of kneading, thereby gelatinizing. The obtained conductive paste was printed on glass by a metal squeegee and hardened at 150 ° C and 200 ° C for 30 minutes in an atmospheric environment.

The specific resistance of the film obtained by hardening is 5.4×10 ^-4 Ω, respectively. Cm (hardening temperature 150 ° C), 8.2 × 10 ^-5 Ω. Cm (hardening temperature 200 ° C).

[Comparative Example 4]

The flat copper powder prepared in Comparative Example 3 was dispersed in a resin to prepare an electromagnetic wave shielding material.

In other words, 100 g of the polyvinyl chloride resin and 200 g of methyl ethyl ketone were mixed with 40 g of the flat copper powder obtained in Comparative Example 2, and the mixture was fused at 1500 rpm for 3 minutes using a small kneader. At the time of gelatinization, the copper powder does not aggregate and is uniformly dispersed in the resin. This was coated on a substrate composed of a transparent polyethylene terephthalate sheet having a thickness of 100 μm using a Meyer rod, and dried to form an electromagnetic wave shielding layer having a thickness of 25 μm.

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

1‧‧‧ copper particles

2‧‧‧ (copper particles) trunk

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

Claims (8)

a copper powder formed into a trunk having a linear growth and a plurality of branch dendrites separated from the trunk, wherein the trunk and the branch are formed by a flat plate having an average thickness of more than 1.0 μm and a thickness of 5.0 μm or less The copper powder is composed of a single layer or a laminated structure in which a plurality of layers are stacked, and the average particle diameter (D50) is 1.0 μm to 100 μm. The copper powder according to claim 1, wherein the ratio of the cross-sectional thickness of the flat copper particles divided by the average particle diameter (D50) of the copper powder is more than 0.01 and less than 5.0, and the ratio is The bulk density of the copper powder is in the range of 0.5 g/cm ³ to 5 g/cm ³ . The scope of the patent copper, Paragraph 1, BET specific surface area is 0.2m ² /g~3.0m ² / g. The copper powder according to claim 1, wherein the crystallite diameter of the (111) plane obtained by X-ray diffraction of the above-mentioned flat copper particles is 800 Å to 3000 Å in the Miller index. The scope. A metal filler containing the copper powder of any one of claims 1 to 4 in a ratio of 20% by mass or more of the whole. A copper paste obtained by mixing a metal filler of the fifth aspect of the patent application with a resin. A conductive coating for electromagnetic wave shielding, which uses the metal filler of claim 5 of the patent application. A conductive sheet for electromagnetic wave shielding, which uses the metal filler of the fifth aspect of the patent application.