Copper metal powder

Abstract

The present invention provides a copper-based metal powder that is suitable for use in a conductive material, and a conductive paste containing the copper-based metal powder has excellent applicability because the copper-based metal powder particles are less likely to aggregate or become blurred when applied, and can produce a fired coating film that exhibits excellent conductivity when fired at a low temperature. [Solution] A copper-based metal powder having an average particle size of 10 μm or less and a rattler value of 90% or more.

Description

[Technical field]

[0001] The present invention relates to a copper-based metal powder. More specifically, the present invention relates to a copper-based metal powder that can be suitably used for conductive materials, since a conductive paste containing the copper-based metal powder is less likely to cause aggregation or blurring of the copper-based metal powder, has excellent applicability, and forms a fired coating film with excellent conductivity even when fired at a low temperature. [Background technology]

[0002] Copper is known as a metal that exhibits excellent electrical and thermal conductivity second only to silver. It is much cheaper than silver and does not have migration issues, so it is widely used in the electronic parts and equipment industries as a conductive material, such as in conductive pastes.

[0003] The copper-based metal powder used in conductive pastes is primarily in the form of flake powder, which is mechanically processed from spherical or granular raw powder produced by atomization or chemical reduction.

[0004] Processing the powder into a flake shape improves packing properties and increases the contact area between powder particles, resulting in improved conductivity compared to spherical or granular raw powder.

[0005] In conductive paste applications, the most important characteristic is electrical conductivity, as represented by the volume resistivity after firing. However, when used as a conductive paste in mass production equipment, coatability, which allows the powder particles to be applied uniformly to a substrate without agglomeration or blurring, is also an important characteristic.

[0006] If the powder particles aggregate or become blurred during application, problems such as defects in the conductive film after firing or unstable electrical resistance can occur.

[0007] Furthermore, if there is any aggregation or smearing, this is treated as a defective appearance in the paste application process.

[0008] Therefore, there is a need for the development of a copper-based metal powder that is capable of producing a conductive paste in which the powder particles are less likely to aggregate or become blurred when applied, can be fired at a low temperature, and the fired coating film has excellent conductivity. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent Publication 2005-200734 [Patent Document 2] Patent Publication No. 2017-25393 Summary of the Invention [Problem to be solved by the invention]

[0010] Patent Document 1 describes a flake copper powder suitable as a filler for conductive paste, which has a specific range of parameters that combine the 10%, 50%, and 90% diameters in the particle size distribution, the average thickness of 100 particles measured with a scanning electron microscope (SEM), and its standard deviation.

[0011] The copper powder in Patent Document 1 is described as having better viscosity, printability, and conductivity than conventional powders. However, Patent Document 1 only evaluates the surface and cross section of the external electrode after firing using SEM observations, and does not evaluate the conductivity. Therefore, it is unclear whether the conductivity is superior.

[0012] Also, it is described that parameters such as aspect ratio are specified based on characteristics that are thought to be included in coatability, such as retention of external shape and surface smoothness, but since coatability has not been evaluated, it is unclear whether it has excellent coatability or not.

[0013] Patent Document 2 describes a copper powder that contains multiple types of flake particles with different aspect ratios, and when a specific range of the aspect ratios is divided into 30 intervals and the frequency of the particles in each interval is plotted as a line graph, the shape has predetermined characteristics.

[0014] In the invention described in Patent Document 2, the volume resistivity is measured as the conductivity of the conductor after firing, and it is described that the conductivity of the examples is higher than that of the comparative examples.

[0015] Furthermore, as in Patent Document 1, the surface of the conductor is observed with an SEM to evaluate the occurrence of defects, but since there is no evaluation when it is applied to a substrate, it is unclear whether the coating properties are excellent.

[0016] The inventors set out to solve the above-mentioned problems as a technical task, and as a result of numerous prototypes and evaluations, they made the remarkable discovery that if a copper-based metal powder has an average particle size of 10 μm or less and a Rattle value of 90% or more, a conductive paste containing the copper-based metal powder is a conductive paste with excellent application properties that are less likely to cause aggregation or smearing when applied, and is fired at a low temperature to form a fired coating film that exhibits high conductivity, so that it can be suitably used as a conductive material, thereby solving the above-mentioned technical tasks. [Means for solving the problem]

[0017] The above technical problems can be solved by the present invention as follows.

[0018] The present invention is a copper-based metal powder having an average particle size of 10 μm or less and a rattler value of 90% or more.

[0019] The present invention also relates to a conductive material containing the copper-based metal powder.

[0020] The present invention also provides a conductive paste containing 60% by weight or more and 80% by weight or less of the copper-based metal powder.

[0021] The present invention also relates to a method for producing the copper-based metal powder, which is produced from copper-based metal powder produced by a liquid atomization method in which a cooling liquid is sprayed onto a descending molten metal flow to produce metal powder. Effect of the Invention

[0022] The copper-based metal powder of the present invention has an average particle size of 10 μm or less and a rattler value of 90% or more, so that a conductive paste containing the copper-based metal powder of the present invention is less susceptible to aggregation or blurring of the copper-based metal powder particles and has excellent coatability, and when fired at low temperatures, it forms a fired coating film that exhibits excellent conductivity.

[0023] Furthermore, if the conductive paste contains 60% to 80% by weight of the copper-based metal powder of the present invention, the conductive paste will have even better coatability and conductivity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The Rattler value is a value used in the powder metallurgy industry to evaluate the compactibility of powders.

[0025] The method for measuring the rattler value is stipulated in the Japan Powder Metallurgy Association standard JPMA P11-1992. More specifically, five cylindrical samples made by powder compaction are prepared, placed in a wire mesh basket, and rotated at a constant speed to measure the weight loss rate of the compacted powder.

[0026] A powder with a low rattle value is less likely to chip or break in the green compact, so a powder with a low rattle value is preferred in the field of powder metallurgy. However, the rattle value in the present invention is a high value of 90% or more, making it difficult to use in the field of powder metallurgy.

[0027] It is thought that the powder characteristic that has the greatest effect on the Rattler value is the powder shape; however, since it is also influenced by other factors besides shape, such as the surface condition of the powder, including the presence or absence of a surface treatment layer, and the hardness of the powder particle matrix, it can be said to be a composite characteristic value of various powder characteristics.

[0028] In addition, if the powder compact can be molded using a press, the rattle value can be measured, making this a simple measurement method.

[0029] The Rattler value of the copper-based metal powder of the present invention is 90% or more, and more preferably 95% or more.

[0030] If the rattler value is less than 90%, the electrical conductivity decreases.

[0031] In addition, due to the shape of the copper-based metal powder, the particle coverage is low, so that a conductive paste containing copper-based metal powder with a rattler value of less than 90% is prone to smearing and pinholes when applied.

[0032] The copper-based metal powder in the present invention has an average particle size of 10 μm or less.

[0033] This is because a conductive paste containing copper-based metal powder with an average particle size of more than 10 μm may cause smearing due to aggregation of coarse particles when applied.

[0034] If the average particle size is more than 30 μm, it becomes difficult to apply the powder uniformly.

[0035] The average particle size in the present invention is the D50 value in the volume-based particle size distribution determined by a laser diffraction scattering method.

[0036] Generally, copper-based metal powder produced by atomization is spherical or irregular in shape, and the rattler value is less than 90%, so it is sufficient to grind the particles into flakes to increase the rattler value to 90% or more.

[0037] The pulverizing method is not particularly limited, but examples thereof include a general ball mill, an attritor, a jet mill, a vibration mill, a stamper, and a combination thereof.

[0038] In order to suppress particle aggregation and oxidation during the pulverization process, fatty acids and rust inhibitors may be added.

[0039] The fatty acid is not particularly limited, but stearic acid is an example.

[0040] The rust inhibitor is not particularly limited as long as it is suitable for use with copper-based metal powder, but an example of the rust inhibitor is benzotriazole.

[0041] The raw powder to be pulverized is preferably a spherical, monodispersed powder having a narrow particle size distribution and little aggregation or satellites.

[0042] This is because if the raw material powder is a spherical, monodispersed powder with a narrow particle size distribution and few agglomerates or satellites, a stable rattle value can be obtained even if the powder is pulverized under various pulverization conditions.

[0043] When the rattler value is stable, the copper-based metal powder has stable electrical conductivity.

[0044] An example of a spherical, monodispersed raw powder with few agglomerates or satellites is a fine powder of copper-based metal powder produced by a water atomization method.

[0045] In order to obtain a raw material powder having a narrow particle size distribution, the particle size may be made uniform by removing the coarse powder and the fine powder using a classification method suitable for fine powder, such as air classification.

[0046] This is because it contributes to obtaining a copper-based metal powder having a stable rattler value.

[0047] The rattler value of the raw material powder is preferably 10% or more.

[0048] The raw material powder is not particularly limited as long as it contains copper, and examples thereof include 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, and Cu-Ti.

[0049] The conductive paste containing the copper-based metal powder of the present invention is less likely to cause aggregation or smearing of the copper-based metal powder when applied.

[0050] The content of the copper-based metal powder in the conductive paste is preferably 60% to 80% by weight, and more preferably 65% ​​to 75% by weight.

[0051] If the content is less than 60% by weight, the electrical conductivity is poor, whereas if the content is more than 80% by weight, there is a risk of aggregation or smearing during application.

[0052] The method for producing the conductive paste is not particularly limited.

[0053] For example, a conductive paste can be prepared by kneading the copper-based metal powder of the present invention with a polyvinyl butyral resin and diethylene glycol monobutyl ether acetate using a planetary stirrer.

[0054] The conductive paste of the present invention can be fired at a low temperature range of 250°C to 400°C to produce a fired coating film that exhibits excellent conductivity. EXAMPLES

[0055] Examples of the present invention are shown below, but the present invention is not limited to these.

[0056] (Preparation of raw powder) Copper powder was produced by the water atomization method using high-pressure water as the atomizing medium.

[0057] The particle size of the produced copper powder was adjusted using an air classifier so that D50 was 10 μm or less.

[0058] Copper powder with adjusted particle size was used as the raw material powder and was pulverized in a ball mill.

[0059] The balls used were chrome steel balls with a diameter of 1 / 16 inch, and 0.3% by weight of stearic acid was added as a lubricant.

[0060] The ratio of balls to raw powder was 10:1 by weight.

[0061] The rotation speed was in the range of 0 rpm to 30 rpm, and the grinding time was in the range of 0 h to 20 h.

[0062] The degree of grinding was controlled under the above conditions, and copper powders with different rattler values ​​were produced.

[0063] (Measurement of Rattler Value) The rattle value of the copper powder was measured in accordance with the Japan Powder Metallurgy Association standard JPMA P11-1992.

[0064] The molding pressure was set at 490 MPa.

[0065] (Measurement of average particle size) The average particle size of the copper powder was measured using a laser diffraction particle size distribution analyzer MT3000II (Microtrack Bell Corporation).

[0066] "Average particle size" is the cumulative 50% particle size (D50) on a volume basis.

[0067] (Evaluation of electrical conductivity) A conductive paste was prepared by mixing 72% by weight of copper powder, 8% by weight of polyvinyl butyral resin, and 20% by weight of diethylene glycol monobutyl ether acetate.

[0068] The prepared conductive paste was applied onto a slide glass and baked at 250°C or 400°C for 60 minutes in a nitrogen atmosphere to prepare a baked coating film.

[0069] The electrical resistance of the baked coating film thus produced was measured by a four-terminal method, the coating film thickness was measured with a surface roughness meter, and then the volume resistivity of the baked coating film was calculated.

[0070] The electrical conductivity is 1.0×10 volume resistivity at either 250℃ or 400℃ in a nitrogen atmosphere. -3 If the volume resistivity is less than 1.0×10 Ω·cm, it is considered "OK". -3 If it exceeded Ω·cm, it was rated as "NG".

[0071] (Evaluation of Coatability) A conductive paste was prepared by mixing 72% by weight of copper powder, 8% by weight of polyvinyl butyral resin, and 20% by weight of diethylene glycol monobutyl ether acetate.

[0072] The prepared conductive paste was manually applied at a constant speed using a spatula onto a glass plate masked with a 10 cm square area using masking tape.

[0073] A light was shone from behind the coated glass, and the presence or absence of defects in the coating was visually evaluated.

[0074] The evaluation was carried out on five sheets for each level, and if there was no aggregation, smearing, or pinholes on all five coated surfaces, it was rated as "OK", but if there was any on even one sheet, it was rated as "NG".

[0075] The grinding conditions and the properties of the resulting powder are shown in Table 1, and the results are shown in Table 2. Comparative Example 1 represents the raw material powder.

[0076] [Table 1]

[0077] [Table 2]

[0078] From the results of Examples 1 to 5 and Comparative Examples 1 to 4, it was confirmed that a copper-based metal powder having an average particle size of 10 μm or less and a rattler value of 90% or more has good coatability without causing smearing or pinholes when applied, and that a fired coating film exhibiting excellent conductivity can be obtained by firing at a low temperature of 400° C. or less. [Industrial Applicability]

[0079] The conductive paste containing the copper-based metal powder of the present invention is less likely to cause aggregation or smearing of the copper-based metal powder when applied, and can be fired at a low temperature to produce a conductive coating film that exhibits excellent conductivity, making it a copper-based metal powder that can be suitably used as a conductive material. Therefore, the present invention has high industrial applicability.

Claims

1. A flake-shaped copper-based metal powder having an average particle size, which is the D50 value in the volume-based particle size distribution measured by the laser diffraction scattering method, of 10 μm or less and a Rattra value of 90% or more.

2. A conductive material comprising the copper-based metal powder according to claim 1.

3. 2. A conductive paste containing 60% by weight or more and 80% by weight or less of the copper-based metal powder according to claim 1.

4. 2. The method for producing copper-based metal powder according to claim 1, wherein the copper-based metal powder is produced by a liquid atomization method in which a metal powder is produced by spraying a cooling liquid onto a falling molten metal stream.

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