Copper-based metal powder

Abstract

This invention provides a copper-based metal powder suitable for use in conductive materials. Conductive pastes containing this copper-based metal powder are less prone to particle agglomeration or whitening during coating, exhibiting excellent coatability. Furthermore, if fired at low temperatures, a fired coating film displaying excellent conductivity can be produced. The average particle size of the copper-based metal powder is less than 10 μm, and the Torr value is greater than 90%.

Description

Copper-based metal powder The present invention relates to a copper-based metal powder. More specifically, it relates to a copper-based metal powder that can be applied to conductive materials, and the conductive paste containing this copper-based metal powder is not prone to agglomeration or bleeding of the copper-based metal powder, has excellent coatability, and even when fired at a low temperature, forms a fired coating film with excellent conductivity. Copper is widely known as a metal that exhibits excellent electrical conductivity and thermal conductivity second only to silver. It is much cheaper than silver and also has no migration problem. Therefore, it is widely used as a conductive material represented by conductive paste in the electronic parts and equipment industries. The powder of copper-based metal for conductive paste mainly uses flake powder obtained by mechanically processing spherical or granular raw material powder produced by atomization method or chemical reduction method. This is because by processing into a flake shape, the packing property is improved and the contact area between powder particles increases, so the electrical conductivity is improved compared to spherical or granular raw material powder. In the application of conductive paste, conductivity represented by the volume resistivity after firing is the most important property. However, when used in mass production equipment as a conductive paste, coatability that can be evenly coated on the substrate without agglomeration or bleeding of powder particles is also an important property. If there is agglomeration or bleeding of powder particles during coating, problems such as defects in the conductive film after firing or unstable resistance will occur. In addition, if there is agglomeration or bleeding, it is treated as a defect in the appearance during the paste coating process. Therefore, it is desired to develop a copper-based metal powder that can manufacture a conductive paste that is not prone to agglomeration or bleeding of powder particles during coating, can be fired at a low temperature, and has excellent conductivity of the fired coating film. Prior art documents Patent documents Patent Document 1: Japanese Patent Application Laid-Open No. 2005-200734 Patent Document 2: Japanese Patent Application Laid-Open No. 2017-25393 Problems to be solved by the invention Patent Document 1 describes a flaky copper powder that is suitable as a filler for a conductive paste with parameters obtained by combining the diameters of 10%, 50%, and 90% in the particle size distribution with the average thickness and standard deviation of 100 particles measured by a scanning electron microscope (SEM) within a specific range. Although the copper powder described in Patent Document 1 has better viscosity, printability, and conductivity than before, only the SEM observation of the surface and cross-section of the external electrode after firing was evaluated in Patent Document 1, and the conductivity was not evaluated. Therefore, it is not clear whether the conductivity is excellent. In addition, although parameters such as the aspect ratio are defined by properties such as the shape retention and surface smoothness of the external appearance, which are considered to be included in the coatability, since the coatability has not been evaluated, it is not clear whether the coatability is excellent. Patent Document 2 describes a copper powder containing various flaky particles having different aspect ratios. When the specific range of the aspect ratio is divided into 30 intervals and the number frequency of each interval is made into a line graph, the shape has a predetermined characteristic. In the invention described in Patent Document 2, it is described that the volume resistivity is measured as the conductivity of the conductor after firing, and the conductivity is higher in the examples than in the comparative examples. In addition, similar to Patent Document 1, the surface of the conductor is observed by SEM to evaluate the presence or absence of defects. However, since there is no evaluation when coated on a substrate, it is not clear whether the coatability is excellent. The inventors of the present invention made a large number of trial productions and evaluations repeatedly with the technical problem of solving the above-mentioned various problems, and as a result, obtained the following amazing insights and solved the above-mentioned technical problems: If the average particle diameter is 10 μm or less and the Latora value is 90% or more for a copper-based metal powder, then the conductive paste containing the copper-based metal powder is a conductive paste with excellent coatability that is not likely to cause aggregation or splashing during coating, and becomes a fired coating film showing high conductivity when fired at a low temperature. Therefore, it can be applied to conductive materials. Technical solutions for solving the problems The above-mentioned technical problems can be solved by the present invention as follows. The present invention is a copper-based metal powder having an average particle diameter of 10 μm or less and a Latora value of 90% or more. In addition, the present invention is a conductive material containing the copper-based metal powder. In addition, the present invention is a conductive paste containing 60% by weight or more and 80% by weight or less of the copper-based metal powder. In addition, the present invention is a method for manufacturing the copper-based metal powder, in which the copper-based metal powder is manufactured from a copper-based metal powder manufactured by a liquid atomization method, and the liquid atomization method is a method for manufacturing metal powder by spraying a coolant onto a flowing molten metal stream. Effects of the invention The copper-based metal powder of the present invention has an average particle diameter of 10 μm or less and a Latora value of 90% or more. Therefore, the conductive paste containing the copper-based metal powder of the present invention is not likely to cause aggregation or splashing of the copper-based metal powder particles, has excellent coatability, and in addition, becomes a fired coating film showing excellent conductivity when fired at a low temperature. In addition, if the conductive paste contains 60% to 80% by weight of the copper-based metal powder of the present invention, it becomes a conductive paste with more excellent coatability and conductivity. The Latora value is a value used to evaluate the formability of powders in the powder metallurgy industry. The method for measuring the Latora value is specified by the Japan Powder Metallurgy Industry Association Standard JPMA P11-1992. Specifically, it is the value obtained by preparing five specimens in which the powder is formed into a cylindrical shape by powder pressing, and measuring the weight reduction rate of the powder compact when the specimen is put into a wire mesh cage and rotated for a certain period. Powders with a low Latora value are powders that are less likely to cause defects or breakage of the powder compact. Therefore, in the field of powder metallurgy, powders with a low Latora value are preferred. However, since the Latora value of the present invention is as high as 90% or more, it is difficult to be used in the field of powder metallurgy. It is considered that the powder property that has the greatest influence on the Latora value is the shape of the powder. However, since it is also affected by the surface state of the powder including the presence or absence of a surface treatment layer and the hardness of the matrix of the powder particles, it can be said that it is a characteristic value that is a composite of various powder properties. In addition, as long as a powder compact can be formed by a press, the Latora value can be measured, so the measurement method is simple. The Latora value of the copper-based metal powder of the present invention is 90% or more, more preferably 95% or more. This is because when the Latora value is less than 90%, the conductivity decreases. In addition, since the coating property of the particles is lowered due to the shape of the copper-based metal powder, the conductive paste containing the copper-based metal powder with a Latora value less than 90% is likely to cause white spots or pinholes during coating. The average particle diameter of the copper-based metal powder of the present invention is 10 μm or less. This is because when the conductive paste containing the copper-based metal powder with an average particle diameter greater than 10 μm is coated, there may be white spots caused by the aggregation of coarse particles. When the average particle diameter is 30 μm or more, it is difficult to coat evenly. The average particle diameter in the present invention is the value of D50 in the volume-based particle size distribution based on the laser diffraction scattering method. Generally, the copper-based metal powder produced by the atomization method is spherical or irregular in shape, and the Latora value is less than 90%. Therefore, the particle shape is made into a flaky shape by comminution processing so that the Latora value is 90% or more. The comminution processing method is not particularly limited, and examples include ordinary ball mills, grinders, jet mills, vibration mills, crushers, and combinations thereof. In order to suppress the aggregation or oxidation of particles in the comminution processing step, fatty acids or rust preventives can also be added. The fatty acid is not particularly limited, but stearic acid is exemplified. The rust preventive agent is not particularly limited as long as it can be applied to copper-based metal powders, and benzotriazole is exemplified. The raw material powder for comminution processing is preferably a spherical, monodispersed powder with a narrow particle size distribution and less aggregation or satelliting. This is because, if a spherical, monodispersed powder with a narrow particle size distribution and less aggregation or satelliting is used as the raw material powder, stable Latora values can be obtained even when comminution processing is carried out under various comminution processing conditions. When the Latora value is stable, it becomes a copper-based metal powder with stable conductivity. As a spherical, monodispersed raw material powder with less aggregation or satelliting, fine powders of copper-based metal powders produced by the water atomization method are exemplified. In order to obtain a raw material powder with a narrow particle size distribution, coarse powders and fine powders can also be cut by a classification method suitable for fine powders such as air classification to make the particle sizes uniform. This is because it helps to obtain a copper-based metal powder with a stable Latora value. The Latora value of the raw material powder is preferably 10% or more. The raw material powder is not particularly limited as long as it contains copper, and copper powder and alloy powders of Cu-Sn, Cu-Zn, Cu-Ni, Cu-Ni-Zn, Cu-Ni-Si, Cu-Sn-P, Cu-Ag, Cu-Cr, Cu-Zr, Cu-Ti can be exemplified. When the conductive paste containing the copper-based metal powder of the present invention is applied, aggregation or streaking of the copper-based metal powder is not likely to occur. The content of the copper-based metal powder contained in the conductive paste is preferably 60% by weight to 80% by weight, more preferably 65% by weight to 75% by weight. If it is less than 60% by weight, the conductivity is poor, and if it is more than 80% by weight, aggregation or streaking may occur during application. The manufacturing method of the conductive paste is not particularly limited. For example, the conductive paste can be produced by kneading the copper-based metal powder, polyvinyl butyral resin, and diethylene glycol monobutyl ether acetate of the present invention using a planetary stirring device. The conductive paste of the present invention can be used to produce a fired coating film with excellent conductivity by firing in a low temperature range of 250 °C to 400 °C. [Examples] Examples of the present invention are shown below, but the present invention is not limited thereto. (Production of raw material powder) Copper powder is produced by the water atomization method using high-pressure water as the spraying medium. The particle size of the produced copper powder is adjusted using an air classifier so that D50 is 10 μm or less. The copper powder with adjusted particle size is used as the raw material powder and pulverized by a ball mill. As the balls, chromium steel balls with a diameter of φ1 / 16 inches are used, and 0.3 wt% of stearic acid is added as a lubricant. The ratio of the balls to the raw material powder is 10:1 by weight. The rotation speed is set in the range of 0 rpm to 30 rpm. The pulverization time is set in the range of 0 h to 20 h. Under the above conditions, the degree of pulverization is controlled to produce copper powders with different Latora values respectively. (Measurement of Latora value) The Latora value of the copper powder is measured in accordance with the Japan Powder Metallurgy Industry Association standard JPMA P11-1992. The forming pressure is set to 490 MPa. (Measurement of average particle size) The average particle size of the copper powder is measured using a laser diffraction particle size distribution measuring device MT3000II (manufactured by MicrotracBEL Co., Ltd.). The "average particle size" is the cumulative 50% particle size (D50) based on volume. (Evaluation of conductivity) The copper powder, polyvinyl butyral resin, and diethylene glycol monobutyl ether acetate are mixed at ratios of 72 wt%, 8 wt%, and 20 wt% respectively to produce a conductive paste. The produced conductive paste is applied on a glass slide and fired at 250 °C or 400 °C for 60 minutes in a nitrogen atmosphere to produce a fired coating film. The resistance value of the produced fired coating film is measured by the four-terminal method, and the film thickness is measured by a surface roughness meter. Then, the volume resistivity of the fired coating film is calculated. Regarding conductivity, if the volume resistivity is 1.0×10 -3 Ω·cm or less at any one of the temperatures of 250 °C and 400 °C in a nitrogen atmosphere, it is evaluated as "OK". If the volume resistivity exceeds 1.0×10 -3 Ω·cm at both temperatures, it is evaluated as "NG". (Evaluation of coatability) 72 wt% of copper powder, 8 wt% of polyvinyl butyral resin, and 20 wt% of diethylene glycol monobutyl ether acetate are added and mixed to produce a conductive paste. The produced conductive paste is manually applied onto a glass plate with a side length of 10 cm masked with masking tape using a spatula at a certain speed. Light is irradiated from the back of the coated glass, and the presence or absence of defects in the coating film is visually evaluated. The evaluation was carried out with 5 pieces for each level. If no agglomeration, splashing or pinholes occurred on all the coating surfaces of the 5 pieces, it was evaluated as "OK". If agglomeration, splashing or pinholes occurred on even 1 piece, it was evaluated as "NG". The pulverization conditions and the resulting powder characteristics are shown in Table 1, and the results are shown in Table 2. In addition, Comparative Example 1 represents the raw material powder. [Table 1] [Table 2] From the results of Examples 1 to 5 and Comparative Examples 1 to 4, it was confirmed that copper-based metal powders with an average particle diameter of 10 μm or less and a Latora value of 90% or more had good coatability without splashing or pinholes during coating. Also, when fired at a low temperature of 400°C or lower, a fired coating film with excellent conductivity was obtained. Industrial applicability The conductive paste containing the copper-based metal powder of the present invention is less likely to cause agglomeration or splashing of the copper-based metal powder during coating, and can be fired at a low temperature to produce a conductive coating film with excellent conductivity. Therefore, it is a copper-based metal powder applicable to conductive materials. Thus, the present invention is an invention with high industrial applicability. (None)

Claims

1. A thin, flake-like copper-based metal powder, wherein, The average particle size is below 10 μm, and the Latola value is above 90%; the average particle size is the D50 value in the particle size distribution based on the volume reference of laser diffraction scattering method.

2. A conductive material, wherein, Contains copper-based metal powder as described in claim 1.

3. A conductive paste, wherein, Contains 60% by weight or more and 80% by weight of the copper-based metal powder as described in claim 1.

4. A method for manufacturing copper-based metal powder as described in claim 1, wherein, The copper-based metal powder is manufactured from copper-based metal powder produced by a liquid atomization method, which is a method of manufacturing metal powder by spraying coolant onto a stream of molten metal.