Composition and method for producing composition

Abstract

A composition comprising carbon-coated metal particles mixed in N-methyl-2-pyrrolidone or alcohol having 1 to 4 carbon atoms at a concentration of 0.01-2.0 g / mL, wherein each of the carbon-coated metal particles has a metal particle and a coating layer that covers at least a part of a surface of the metal particle and contains carbon, the metal particle consists of (1) tin, copper, or silver, and unavoidable impurities, or (2) a tin, copper, or silver alloy having a tin, copper, or silver content of 50 mass% or more, and unavoidable impurities, and the average particle diameter calculated from a BET specific surface area of the carbon-coated metal particles is 150 nm or less.

Description

Composition and method for producing the composition

[0001] This specification describes a composition and a method for producing the composition.

[0002] Metal powders consisting of a specified pure metal or alloy may be mixed with a liquid containing organic substances such as an organic binder or organic solvent to form a paste. Such pastes can be used, for example, as conductive pastes for forming wiring by printing, filling holes or joining, or as pastes for electronic equipment or energy devices, or as solder pastes used for soldering. In some fields, depending on the compatibility with the substrate to which the paste is applied, water, alcohol, or polar organic solvents may be used as solvents to form the paste.

[0003] As a technology related to carbon-coated metal particles, for example, Patent Document 1 proposes a carbon-coated metal powder suitable for additive manufacturing, under the objective of "providing a carbon-coated metal powder that has excellent fluidity and is capable of efficient absorption of energy rays." The carbon-coated metal powder is a carbon-coated metal powder having a carbon coating on the surface of metal particles with an average particle diameter of 1 μm or more and 100 μm or less, which is chemically coated with carbon derived from an organic compound, and the amount of carbon coating in the carbon-coated metal powder is 0.001% by mass or more and 2.0% by mass or less.

[0004] Japanese Patent Publication No. 2018-199862

[0005] As mentioned above, carbon-coated metal particles are sometimes used dispersed in polar solvents. However, due to the properties of carbon-coated metal particles, it can be difficult to disperse them well in polar solvents. Poor dispersion of carbon-coated metal particles in polar solvents can lead to a decrease in the quality of the manufactured material. Commonly used polar solvents for carbon-coated metal particles include N-methyl-2-pyrrolidone (NMP) or alcohols with 1 to 4 carbon atoms.

[0006] In view of these problems, embodiments of the present invention provide a composition in which carbon-coated metal particles can be well dispersed in a polar solvent such as N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms, and a method for producing the composition.

[0007] Embodiments of the present invention that solve the above problems are defined below. 1. A composition comprising carbon-coated metal particles having metal particles and a coating layer containing carbon covering at least a portion of the surface of the metal particles, mixed in N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms at a concentration of 0.01 to 2.0 g / mL, wherein the metal particles consist of (1) tin, copper or silver and unavoidable impurities, or (2) an alloy of tin, copper or silver with a tin, copper or silver content of 50% by mass or more and unavoidable impurities, and the average particle size calculated from the BET specific surface area of ​​the carbon-coated metal particles is 150 nm or less. 2. The composition according to 1, wherein the carbon content of the carbon-coated metal particles is 0.5 to 3.0% by mass. 3. The composition according to 1 or 2, wherein the hydrogen content of the carbon-coated metal particles is 0.01 to 0.25% by mass. 4. 1. The composition according to any one of 1 to 3, wherein the carbon-containing coating layer of the carbon-coated metal particles is composed of a mixture of graphite-based carbon and hydrocarbons. 5. The composition according to any one of 1 to 4, wherein the oxygen content of the carbon-coated metal particles is 3.0% by mass or less. 6. A method for producing a composition comprising the step of producing a composition containing carbon-coated metal particles by dispersing the carbon-coated metal particles in N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms by ultrasonic treatment, wherein the carbon-coated metal particles comprise metal particles and a coating layer containing carbon that covers at least a part of the surface of the metal particles, and the metal particles consist of (1) tin, copper or silver and unavoidable impurities, or (2) an alloy of tin, copper or silver with a tin, copper or silver content of 50% by mass or more and unavoidable impurities.

[0008] According to embodiments of the present invention, it is possible to provide a composition in which carbon-coated metal particles can be well dispersed in a polar solvent such as N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms, and a method for producing the composition.

[0009] This is a schematic cross-sectional view of the surface-coated particles. This is a photograph of the appearance of a test tube showing the results of a dispersibility evaluation test in NMP for the compositions according to the examples. This is a graph showing the particle size distribution for Example 1 and Comparative Example 1. This is the Raman spectrum for Test Example 1. This is a graph showing the particle size distribution for Example 2.

[0010] Preferred embodiments of the present invention will be described below, but the present invention should not be construed as being limited thereto, and various modifications and improvements can be made based on the knowledge of those skilled in the art, without departing from the spirit of the invention. The multiple components disclosed in this embodiment can be combined in appropriate ways to form various inventions. For example, some components may be removed from all the components shown in this embodiment.

[0011] <Composition> The composition according to the embodiment of the present invention is a mixture of carbon-coated metal particles in N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms at a concentration of 0.01 to 2.0 g / mL. The carbon-coated metal particles consist of metal particles and a coating layer containing carbon that covers at least a portion of the surface of the metal particles. The metal particles consist of (1) tin, copper or silver and unavoidable impurities, or (2) an alloy of tin, copper or silver with a tin, copper or silver content of 50% by mass or more and unavoidable impurities.

[0012] The carbon-coated metal particles in the composition according to the embodiment of the present invention are particles including surface-coated particles 3, which are formed by covering metal particles 1 with a coating layer 2, as illustrated in Figure 1, and are composed mostly or almost entirely of surface-coated particles 3. In Figure 1, the entire surface of the metal particle 1 is covered with the coating layer 2, but it is sufficient if the coating layer 2 adheres to the surface of the metal particle 1 such that it covers at least a portion of the surface of the metal particle 1. In other words, a portion of the surface of the metal particle 1 may be exposed and not covered by the coating layer 2.

[0013] The metal particles contained in the carbon-coated metal particles according to the embodiment of the present invention consist of (1) tin, copper, or silver and unavoidable impurities, or (2) an alloy of tin, copper, or silver with a tin, copper, or silver content of 50% by mass or more and unavoidable impurities.

[0014] When the metal particles of the carbon-coated metal particles according to the embodiment of the present invention contain metal, the content of tin, copper, or silver in the metal portion of the carbon-coated metal particles may be, for example, 99.0% by mass or more, typically 99.9% by mass or more, and preferably 99.99% by mass or more.

[0015] When the metal particles of the carbon-coated metal particles according to the embodiment of the present invention include an alloy, the content of tin, copper, or silver in the carbon-coated metal particles is 50% by mass or more. More preferably, the content of tin, copper, or silver in the carbon-coated metal particles is 60% by mass or more. For tin, copper, or silver alloys, it is preferable to control the content of tin, copper, or silver in the carbon-coated metal particles according to the application, etc.

[0016] Examples of unavoidable impurities contained in the metal particles of the carbon-coated metal particles according to the embodiment of the present invention include Si, Cu, Ag, Fe, Na, Mg, etc. The content of unavoidable impurities contained in the metal particles of the carbon-coated metal particles is preferably 1.0% by mass or less, and more preferably 0.1% by mass or less. Note that the content of unavoidable impurities is the total content of multiple types of unavoidable impurities if they are present.

[0017] The tin, copper, or silver content in carbon-coated metal particles, as well as the content of alloying elements and impurities if the metal particles are alloys, can be measured by ICP-MS if the sample is a liquid, and by GD-MS if it is a solid. For example, carbon-coated metal particles can be solidified by placing them in a measuring container and applying pressure, and then measured by GD-MS. The impurity content can be analyzed, for example, by the total amount of tin, copper, and silver, or by their proportion (mass ppm) relative to the alloy.

[0018] The carbon-coated metal particles according to the embodiment of the present invention contain carbon because they include a coating layer containing carbon. The carbon content of the carbon-coated metal particles is preferably 0.5 to 3.0% by mass, more preferably 0.5 to 2.0% by mass. If the carbon content is too low, there is a concern that oxidation will not be adequately suppressed. On the other hand, if the carbon content is too high, the conductivity between particles may decrease, or the surface may become inert, hindering the fusion of particles during heating. In the carbon-coated metal particles according to the embodiment of the present invention, the carbon-containing coating layer may be composed of a mixture of graphite-based carbon and hydrocarbons. Here, graphite-based carbon is produced by superheating hydrocarbons in an inert atmosphere (e.g., a gas atmosphere such as nitrogen or argon) or in a sealed environment with air. The coating on the metal particles can be formed by spraying hydrocarbons such as methane onto the superheated metal particles. Graphite-based carbon has a Raman shift of 1350 cm⁻¹ by Raman analysis. -1 Nearby is the "D band," 1600 cm -1 Nearby is the "G band," at 2680 cm. -1 A peak in the "2D band" or "G' band" is detected in the vicinity. Thus, it is preferable that hydrocarbons are contained in the coating layer of the carbon-coated metal particles, and the hydrogen content is preferably 0.01 to 0.25% by mass, more preferably 0.01 to 0.1% by mass. Since the hydrogen contained in this coating layer is hydrogen from hydrocarbons such as methane, if the hydrogen content is too high, the carbon content will also increase, which may reduce the conductivity between particles or make the surface inert, hindering the fusion of particles during heating. The carbon content or hydrogen content of carbon-coated metal particles can be analyzed by non-dispersive infrared absorption spectroscopy and measured as a percentage (mass ppm) of the total mass of the carbon-coated metal particles.

[0019] In the embodiment of the present invention, the carbon-coated metal particles are covered with a carbon-containing coating layer, which suppresses oxidation of the metal particles, resulting in a material that contains little to no oxygen. The oxygen content of the carbon-coated metal particles may be, for example, 3.0% by mass or less, typically 2.5% by mass or less, and even 1.5% by mass or less. A low oxygen content is thought to make the metal more easily melted when heated. The oxygen content can be analyzed by non-dispersive infrared absorption spectroscopy and measured as a percentage (mass ppm) of the total mass of the carbon-coated metal particles.

[0020] The carbon-coated metal particles according to the embodiment of the present invention have a relatively small particle size. Specifically, the average particle size (so-called BET diameter) calculated from the BET specific surface area of ​​the carbon-coated metal particles is 150 nm or less, typically 100 nm or less, and more typically 50 to 80 nm. If the average particle size is too large, the dispersibility in polar solvents may decrease.

[0021] The BET specific surface area of ​​the carbon-coated metal particles according to the embodiment of the present invention can be measured in accordance with JIS Z8830:2013, for example, using a Macsorb / HM model-1208 manufactured by MOUNTEC Corporation, with helium as the carrier gas and nitrogen as the adsorbent gas (mixing concentration 30.1%, flow rate 25 ml / m). The average particle size d (μm) calculated from the BET specific surface area can be calculated from this BET specific surface area using the formula: d = 6 / (ρ × s). In this formula, ρ is the density (g / cm³) of tin, copper, or silver, which is determined according to the composition of the metal particles. 3 ) or the density (g / cm³) of an alloy of tin, copper, or silver 3 ) and s is the BET specific surface area (m 2 It is / g).

[0022] In the embodiment of the present invention, carbon-coated metal particles are mixed in N-methyl-2-pyrrolidone (NMP) or an alcohol having 1 to 4 carbon atoms at a concentration of 0.01 to 2.0 g / mL. In a composition with such a configuration, the carbon-coated metal particles can be well dispersed in NMP or an alcohol having 1 to 4 carbon atoms. The carbon-coated metal particles may be mixed in NMP or an alcohol having 1 to 4 carbon atoms at a concentration of 0.01 to 1.0 g / mL, 0.05 to 1.0 g / mL, 0.08 to 1.0 g / mL, 0.1 to 1.0 g / mL, or 0.1 to 0.2 g / mL. Examples of alcohols having 1 to 4 carbon atoms include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, and 2-methyl-2-propanol.

[0023] <Method for Manufacturing Carbon-Coated Metal Particles> In a method for manufacturing carbon-coated metal particles according to the embodiment of the present invention, preferably, first, large metal particles with a particle size of several micrometers to several tens of micrometers are prepared by gas atomization or the like, and then these metal particles can be miniaturized using RF plasma. In RF plasma, the metal on the surface of the metal particles evaporates, and the diameter of the metal particles decreases.

[0024] Then, while the metal particles are still at a high temperature after the RF plasma treatment, a hydrocarbon gas containing methane or the like can be blown onto them. At this time, the blowing of the hydrocarbon gas causes decomposition and carbonization reactions on the surface of the metal particles, forming a carbon-containing coating layer. By changing the amount of gas blown, the proportion of hydrocarbons in the carbon coating can be changed. If necessary, after the RF plasma treatment, gas flow classification or other classification is performed to remove coarse particles. In this way, carbon-coated metal particles are obtained, which have a predetermined small average particle size and include surface-coated particles in which at least a portion of the surface of the metal particles is covered with a coating layer.

[0025] <Method for Producing the Composition> The method for producing the composition according to the embodiment of the present invention includes the step of producing a composition containing carbon-coated metal particles by dispersing the carbon-coated metal particles in N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms by ultrasonic treatment, wherein the carbon-coated metal particles consist of metal particles and a coating layer containing carbon that covers at least a part of the surface of the metal particles, and the metal particles consist of (1) tin, copper or silver and unavoidable impurities, or (2) an alloy of tin, copper or silver with a tin, copper or silver content of 50% by mass or more and unavoidable impurities. As a method for producing the composition according to the embodiment of the present invention, first, an amount of carbon-coated metal particles in the form of 0.01 to 2.0 g / mL is added to NMP or an alcohol having 1 to 4 carbon atoms. At that time, the NMP or alcohol having 1 to 4 carbon atoms and the carbon-coated metal particles are added little by little while stirring so that they mix well. Ultrasound is applied to the paste thus produced using an ultrasonic cleaner (single frequency) MCS series manufactured by AS ONE Corporation to sufficiently disperse the carbon-coated metal particles. The frequency range for ultrasonic dispersion is 20 kHz to 200 kHz, and the output range is 50 W to several thousand W. The frequency and output are optimized as appropriate depending on the degree of aggregation. By performing ultrasonic treatment and stirring in this manner, a composition according to the embodiment of the present invention can be produced.

[0026] Next, we fabricated the carbon-coated metal particles described above and confirmed their effects, which are explained below. However, this explanation is for illustrative purposes only and is not intended to be limiting.

[0027] <Test Example 1> For Test Example 1, atomized powder (average particle size D50: 5.5 μm) manufactured by Nippon Atomize Processing Co., Ltd. was prepared as the raw material. The raw material for Test Example 1 was miniaturized by the output of an RF plasma, and then coated with carbon by spraying methane after the RF plasma treatment. In this way, a sample of carbon-coated metal particles related to Test Example 1 was prepared.

[0028] (BET diameter) For the sample of carbon-coated metal particles according to Test Example 1, the BET diameter (average particle diameter calculated from the BET specific surface area) was measured as follows. The BET specific surface area was measured by the BET method in accordance with JIS Z8830:2013 using a (Macsorb / HM model-1208) manufactured by Mountec Co., Ltd. The carrier gas was helium and the adsorption gas was nitrogen (mixed concentration 30.1%, flow rate 25 ml / m). The average particle diameter d calculated from the BET specific surface area was calculated from this BET specific surface area using the formula: d = 6 / (ρ×s). In this formula, ρ is the density of tin (g / cm 3 ) or the density of an alloy of tin (g / cm 3 ), and s is the BET specific surface area (m 2 / g). The obtained BET diameter (average particle diameter calculated from the BET specific surface area) was 80 nm.

[0029] (XRD measurement) For the sample of carbon-coated metal particles according to Test Example 1, measurement was carried out using an XRD diffractometer SmartLab manufactured by Rigaku Corporation. As a result, it was found that the sample of carbon-coated metal particles according to Test Example 1 was pure tin.

[0030] (SEM observation) For the sample of carbon-coated metal particles according to Test Example 1, observation was carried out at an acceleration voltage of 15.0 kV and magnifications of 2000 times and 10000 times using a scanning electron microscope (SEM): JXA-8500F (5CH) manufactured by JEOL Ltd. As a result, it was confirmed that the carbon-coated metal particles according to Test Example 1 were particles of several tens of nm.

[0031] (Structural analysis of the carbon-containing coating layer) For the sample of carbon-coated metal particles according to Test Example 1, measurement was carried out using a microscopic Raman apparatus manufactured by Renishaw plc at a laser wavelength of 532 nm, a Raman shift range of 100 to 3500 cm -1 , and an integration number of 100 times, and structural analysis was performed by Raman spectrum. The results are shown in Fig. 4. For Test Example 1, there was a "D band" near a Raman shift of 1350 cm -1 , a "G band" near 1600 cm -1 , and 2680 cm -1A peak in the vicinity of the "2D band" or "G' band" was detected, confirming the presence of graphite-based carbon. Additionally, at 2931 cm⁻¹, a peak was detected. -1 and 3221cm -1 A peak due to CH bonds was obtained, confirming the presence of hydrocarbons. Thus, it was found that the carbon-coated metal particles in Test Example 1 are a mixture of graphite-based carbon and hydrocarbons.

[0032] For the carbon-coated metal particle samples related to Test Example 1, the carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and sulfur (S) content was analyzed using non-dispersive infrared absorption spectroscopy (LECO Japan LLC, model numbers: CS600(C,S), TC600(O,N), TCH600(H)), and measured as a percentage (mass ppm) of the total mass of the carbon-coated metal particles. Similarly, the total content of impurities excluding CHNOS was analyzed and measured as a percentage (mass ppm) of the total mass of the carbon-coated metal particles. The measurement results are shown in Table 1.

[0033]

[0034] <Example 1> 1.03 g / mL of carbon-coated metal particles from Test Example 1 were added to NMP. The particles were added gradually while stirring to ensure good mixing between the NMP and the carbon-coated metal particles. The resulting paste was then subjected to ultrasonic waves for 60 minutes using an AS ONE Corporation ultrasonic cleaner (single frequency) MCS series (model number: MCS-10) at an output of 200 W and an oscillation frequency of 40 kHz, to thoroughly disperse the carbon-coated metal particles. The composition was prepared by performing this ultrasonic treatment and stirring.

[0035] A small amount of the composition after ultrasonic stirring was put into NMP, and the appearance observation photo after standing for 30 seconds is shown in Fig. 2. As can be seen from Fig. 2, it was confirmed that the carbon-coated metal particles were uniformly mixed in NMP visually. Specifically, when 0.05 g of the carbon-coated metal powder sample was added, the powder spread well, and after 30 seconds from the addition, the powder did not precipitate and remained in NMP. Also, as a confirmation of uniform mixing, the particle size distribution measurement may be carried out as follows. That is, NMP was used as the dispersion medium of the carbon-coated metal powder sample, and only a stirrer was used for dispersion, and it was stirred for 90 minutes. For this particle size distribution measurement, MASTERSIZER 3000 of Malvern Panalytical Business Unit of Spectris Co., Ltd. was used. The particle size distribution of Example 1 using NMP as the dispersion medium is shown in Fig. 3. As shown in Fig. 3, by pre-pasting and performing ultrasonic treatment, it was well dispersed even with only the stirring of the stirrer, and the peak of aggregates as seen during the measurement of the powder disappeared. This shows that it is uniformly mixed.

[0036] <Comparative Example 1> A small amount of the powder of the carbon-coated metal particles of Test Example 1 was put into NMP, and the appearance was observed after standing for 30 seconds. As a result, in the sample of Comparative Example 1, the powder of the carbon-coated metal particles floated on the surface of NMP or immediately precipitated, and almost no retention of the powder in NMP was observed. Next, the particle size distribution measurement was carried out using MASTERSIZER 3000 of Malvern Panalytical Business Unit of Spectris Co., Ltd. The particle size distribution of Comparative Example 1 using NMP as the dispersion medium is shown in Fig. 3. As shown in Fig. 3, it can be seen that Comparative Example 1, which was not pre-pasted and ultrasonically treated, is inferior in dispersibility to Example 1.

[0037] <Example 2> To NMP, carbon-coated metal particles from Test Example 1 were added in amounts of 0.1 g / mL, 0.2 g / mL, 1.0 g / mL, and 1.7 g / mL, respectively. At that time, the particles were added in small amounts while stirring to ensure that the NMP and carbon-coated metal particles were well mixed. The resulting paste was then subjected to ultrasonic waves for 60 minutes using an ultrasonic cleaner (single frequency) MCS series manufactured by AS ONE Corporation to thoroughly disperse the carbon-coated metal particles. The composition was manufactured by performing ultrasonic treatment and stirring in this manner. The particle size distribution of the composition was measured using a MASTER SIZER 3000 from Malvern Panalytical Division, Spectris Corporation. Figure 5 shows the particle size distribution of each sample in Example 2 using NMP as the dispersion medium. As shown in Figure 5, it was confirmed that all samples showed improvement over the particle size distribution of Comparative Example 1. Furthermore, since the particle size distribution improves as the concentration of carbon-coated metal particles decreases, it is expected that dispersibility will improve even when carbon-coated metal particles are mixed in NMP at concentrations lower than 0.1 g / mL, such as 0.01 g / mL, 0.05 g / mL, and 0.08 g / mL. In addition, while a distribution towards larger particle sizes is observed at higher concentrations of carbon-coated metal particles, this is due to aggregates, and it is expected that extending the ultrasonic treatment time will disperse these aggregates and improve the particle size distribution.

[0038] (Potential Contribution to SDGs) According to the embodiments described above, it is possible to provide a composition and a method for producing the composition in which carbon-coated metal particles can be well dispersed in a polar solvent such as N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms. For this reason, this embodiment has the potential to contribute to Goal 9 "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation" and Goal 12 "Ensure sustainable consumption and production patterns" of the United Nations-led Sustainable Development Goals (SDGs).

[0039] 1 Metal particles 2 Coating layer 3 Surface coating particles

Claims

1. A composition comprising carbon-coated metal particles having metal particles and a coating layer containing carbon covering at least a portion of the surface of the metal particles, mixed in N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms at a concentration of 0.01 to 2.0 g / mL, wherein the metal particles consist of (1) tin, copper, or silver and unavoidable impurities, or (2) an alloy of tin, copper, or silver with a tin, copper, or silver content of 50% by mass or more and unavoidable impurities, and the average particle size calculated from the BET specific surface area of ​​the carbon-coated metal particles is 150 nm or less.

2. The composition according to claim 1, wherein the carbon content of the carbon-coated metal particles is 0.5 to 3.0% by mass.

3. The composition according to claim 1, wherein the hydrogen content of the carbon-coated metal particles is 0.01 to 0.25% by mass.

4. The composition according to claim 1, wherein the carbon-containing coating layer of the carbon-coated metal particles is composed of a mixture of graphite-based carbon and hydrocarbons.

5. The composition according to claim 1, wherein the oxygen content of the carbon-coated metal particles is 3.0% by mass or less.

6. A method for producing a composition comprising the step of producing a composition containing carbon-coated metal particles by dispersing the carbon-coated metal particles in N-methyl-2-pyrrolidone or an alcohol having 1 to 4 carbon atoms by ultrasonic treatment, wherein the carbon-coated metal particles comprise metal particles and a coating layer containing carbon that covers at least a portion of the surface of the metal particles, and the metal particles consist of (1) tin, copper or silver and unavoidable impurities, or (2) an alloy of tin, copper or silver with a tin, copper or silver content of 50% by mass or more and unavoidable impurities.

Images