Surface-modified copper nanoparticles and method for producing surface-modified copper nanoparticles

Abstract

The purpose of the present invention is to provide surface-modified copper nanoparticles which have high dispersibility and which have a reduced residual carbon concentration after being fired and a method which is for producing the surface-modified copper nanoparticles. Provided are surface-modified copper nanoparticles in which the surfaces of copper nanoparticles are modified with a silane coupling agent, wherein: each copper nanoparticle has, on at least a part of the surface thereof, a coating that contains a copper oxide; the number of surface groups that are on the surface of each surface-modified copper nanoparticle and that are derived from the silane coupling agent is more than 0.3 but less than 2.0 per square nanometer of the surface area of the surface-modified copper nanoparticle; and an average median diameter is not more than 0.2 μm as measured using a particle size distribution analyzer after the surface-modified copper nanoparticles are dispersed in ethanol.<sp / >

Description

Surface-modified copper nanoparticles, and method for producing surface-modified copper nanoparticles

[0001] The present invention relates to surface-modified copper nanoparticles and a method for producing surface-modified copper nanoparticles.

[0002] In applications such as joining various electronic components and forming wiring, inks or pastes primarily composed of copper nanoparticles are sometimes used. However, because copper nanoparticles have a particle size on the nanoscale, they are difficult to disperse and prone to the formation of aggregated particles. Therefore, a method has been disclosed in which the surface of copper nanoparticles is modified with a silane coupling agent to improve the dispersibility of copper nanoparticles (for example, Patent Document 1).

[0003] Patent No. 7219842

[0004] However, conventional technology has the challenge of difficulty in controlling the amount of silane coupling agent coating on the surface of copper nanoparticles. If the coating amount is too high, the amount of carbon remaining after firing increases, leading to a problem of increased impurities (carbon components) in the joints and wiring made of copper nanoparticles. Conversely, if the coating amount is too low, the intended dispersibility is reduced.

[0005] This invention has been made in view of the above circumstances, and provides surface-modified copper nanoparticles with high dispersibility and reduced carbon residual concentration after firing, and a method for producing the same.

[0006] The present invention includes the following embodiments: [1] Surface-modified copper nanoparticles in which the surface of copper nanoparticles is modified with a silane coupling agent, wherein the copper nanoparticles have a coating containing copper oxide on at least a portion of their surface, and the number of surface groups derived from the silane coupling agent on the surface of the surface-modified copper nanoparticles is equal to the surface area of ​​the surface-modified copper nanoparticles per 1 nm. ２[1] Surface-modified copper nanoparticles having more than 0.3 particles but less than 2.0 particles per unit, wherein the average median diameter measured using a particle size analyzer after dispersing the surface-modified copper nanoparticles in ethanol is 0.2 μm or less. [2] Surface-modified copper nanoparticles according to [1], wherein the amount of carbon contained in the calcined product remaining after calcining a sample of the surface-modified copper nanoparticles in an inert gas atmosphere to 700°C is 0.010% by mass or less relative to the mass of the sample. [3] Surface-modified copper nanoparticles according to [1] or [2], wherein the average particle diameter of the copper nanoparticles is 180 nm or less. [4] A mixture is obtained by mixing copper nanoparticles with an adhering water content of more than 1300 ppm and less than 6500 ppm, a silane coupling agent, and an organic solvent, and the silane coupling agent is reacted on the surface of the copper nanoparticles, thereby reducing the surface area of ​​the copper nanoparticles to 1 nm. ２ A method for producing surface-modified copper nanoparticles, wherein the surface groups derived from the silane coupling agent are formed in a quantity of more than 0.3 and less than 2.0 per nanoparticle. [5] The method for producing surface-modified copper nanoparticles according to [4], wherein the copper nanoparticles have a coating containing copper oxide on at least a part of their surface. [6] The method for producing surface-modified copper nanoparticles according to [4] or [5], wherein the heat generated by dispersing the mixture under high pressure reacts the silane coupling agent on the surface of the copper nanoparticles. [7] The method for producing surface-modified copper nanoparticles according to any one of [4] to [6], wherein the surface-modified copper nanoparticles are surface-modified copper nanoparticles according to any one of [1] to [3].

[0007] According to the present invention, it is possible to provide surface-modified copper nanoparticles with high dispersibility and reduced carbon residual concentration after firing, as well as a method for producing the same.

[0008] Figure 1 is a graph showing the relationship between the number of surface units in surface-modified copper nanoparticles and the median diameter of the particle size distribution. Figure 2 is a graph showing the relationship between the number of surface units in surface-modified copper nanoparticles and the residual carbon concentration after firing.

[0009] The embodiments of the present invention will be described in detail below, but the present invention is not limited to the embodiments described later, and various modifications are possible as long as they do not depart from the spirit of the invention.

[0010] The meanings and definitions of terms used herein are as follows: A numerical range indicated by "~" means a numerical range where the numbers before and after "~" are the lower and upper limits, respectively. The surface of copper nanoparticles being modified with a silane coupling agent means at least one of the following: a dehydration condensation reaction occurs between hydroxyl groups present on the particle surface and the silane coupling agent, resulting in the bonding of silanols to the surface; or, even in the absence of hydroxyl groups, silanol groups formed by hydrolysis of the silane coupling agent due to electrostatic interaction are adsorbed onto the particle surface, and a film is formed on the surface by subsequent dehydration condensation between silane coupling agents.

[0011] <Surface-Modified Copper Nanoparticles> The first aspect of the present invention is surface-modified copper nanoparticles in which the surface of copper nanoparticles is modified with a silane coupling agent.

[0012] [Copper Nanoparticles] Copper nanoparticles preferably have a coating containing copper oxide on at least a portion of their surface. Examples of such copper nanoparticles include those produced by a dry process using a reducing flame. Copper nanoparticles produced by the dry process exhibit little thermal shrinkage even when sintered at temperatures above 300°C. In contrast, copper nanoparticles synthesized by the wet process exhibit significant thermal shrinkage.

[0013] Examples of copper oxide include copper(I) oxide, copper(II) oxide, and mixtures thereof. When the copper oxide is a mixture of copper(I) oxide and copper(II) oxide, the ratio of these amounts is not particularly limited. Copper(I) oxide is Cu ２ It is represented by the chemical formula O and is sometimes called cuprous oxide.

[0014] By having the above coating on the surface of copper nanoparticles, hydroxyl groups are generated on the particle surface, allowing the silane coupling agent to chemically adhere. One method for confirming the presence of copper oxide on the surface of copper nanoparticles is to use an X-ray photoelectron spectroscopy (XPS) analyzer (for example, ULVAC-PHI's "Quantera SXM"). CuO, Cu in the obtained spectrum ２ This can be confirmed by checking for the presence or absence of a peak attributed to O.

[0015] The average particle size of the copper nanoparticles is preferably 10 to 200 nm, more preferably 50 to 180 nm, even more preferably 60 to 160 nm, and particularly preferably 80 to 130 nm. If the particle size is above the lower limit of the above range, the increase in surface energy associated with an increase in the specific surface area of ​​the copper nanoparticles is suppressed, resulting in good dispersion of the copper nanoparticles and allowing the silane coupling agent to adhere uniformly to the surface of the copper nanoparticles. If the particle size is below the upper limit of the above range, the increase in weight per particle is suppressed, and the steric hindrance caused by the silane coupling agent adhering to the surface of the copper nanoparticles can be fully exerted, thereby improving dispersibility.

[0016] The average particle size of copper nanoparticles is calculated using the following formula (A).

[0017]

[0018] The specific surface area of ​​copper nanoparticles can be measured using the BET method, and can be measured using a commercially available BET adsorption device (for example, "MACSORB HM-1201" manufactured by Mountec Co., Ltd.). The density of copper is 8.96 g / cm³. ３ That is the case.

[0019] [Number of surface groups] Surface groups (atomic groups) originating from the silane coupling agent are present on the surface of the surface-modified copper nanoparticles in this embodiment. The number of surface groups is equal to the surface area of ​​the surface-modified copper nanoparticles per 1 nm. ２ Preferably, the number of particles per unit is greater than 0.3 and less than 2.0, more preferably 0.4 to 1.8, and even more preferably 0.5 to 1.5. If the number of particles per unit is greater than or equal to the lower limit of the above range, the steric hindrance effect of the silane coupling agent is fully exerted, and the dispersibility is further improved. If the number of particles per unit is less than or equal to the upper limit of the above range, the carbon component (which becomes electrical resistance if it remains in the sintered film) is easily removed by firing, and the residual carbon concentration after firing can be further reduced.

[0020] The number of surface groups in surface-modified copper nanoparticles is calculated using the following formula (B).

[0021]

[0022] The measurement of the "silicon concentration caused by the silane coupling agent" can be carried out by dissolving the surface-modified copper nanoparticles in nitric acid, hydrochloric acid, or a mixed acid of nitric acid and hydrochloric acid, diluting the resulting solution, and then measuring it using an inductively coupled plasma optical emission spectrometer (for example, "ICPS-8100" manufactured by Shimadzu Corporation). Specifically, it is calculated from the difference between the silicon concentration of the copper nanoparticles used as raw materials and the silicon concentration of the surface-modified copper nanoparticles after the silane coupling treatment.

[0023] The "molar mass of silicon atoms contained in the silane coupling agent" is calculated from the molecular formula of the silane coupling agent used for surface modification. For example, the molecular formula of n-octyltrimethoxysilane is C １１ H ２６ O ３ Si. Since it has one silicon atom in the molecule, the molar mass of the silicon atoms contained in n-octyltrimethoxysilane is 28.0855 (about 28) g / mol.

[0024] [Median diameter] The average of the median diameters measured three or more times using a particle size distribution meter, preferably a diffraction-type particle size distribution meter, more preferably a laser diffraction-type particle size distribution meter, after dispersing the surface-modified copper nanoparticles of the present embodiment in ethanol, is preferably 0.2 μm or less. This median diameter is an index of dispersibility, and the smaller it is, the fewer aggregated particles are indicated. However, in principle, the median diameter will not be smaller than the average particle diameter of the copper nanoparticles.

[0025] The particle size distribution of the surface-modified copper nanoparticles in ethanol can be measured using a laser diffraction-type wet particle size distribution meter (for example, "SALD-7100" manufactured by Shimadzu Corporation). A dispersion obtained by mixing the surface-modified copper nanoparticles with ethanol and dispersing them using an ultrasonic homogenizer is used as a measurement sample. The content of the surface-modified copper nanoparticles in the dispersion is preferably 0.1 to 1.0 g with respect to 100 mL of the volume of ethanol.

[0026] [Carbon Residual Concentration After Firing] The carbon concentration (carbon residual concentration after firing) in the fired product remaining after firing a sample of surface-modified copper nanoparticles according to this embodiment at a temperature of 700°C in an inert gas atmosphere is preferably 0.010% by mass or less relative to the mass of the sample. This carbon concentration is an indicator of the low amount of impurities remaining in the fired product. Generally, the fewer impurities contained in the fired product (sintered copper nanoparticles), the lower the electrical resistance of the fired product, which is preferable.

[0027] The residual carbon concentration after firing can be measured using a carbon-sulfur analyzer (for example, the "EMIA-920V" manufactured by Horiba, Ltd.).

[0028] <Silane Coupling Agent>The silane coupling agent is not particularly limited as long as it can be chemically bonded to the surface of copper nanoparticles by a silane coupling reaction and improves the dispersibility in a solvent. Examples of such silane coupling agents include those having an alkyl group, an amino group, an epoxy group, a methacryl group, or an acrylic group as a functional group. Examples of the silane coupling agent having an alkyl group include isobutyryltrimethylalkylsilane, hexyltrimethylalkylsilane, octyltrimethylalkylsilane, decyltrimethylalkylsilane, dodecyltrimethylalkylsilane, octadecyltrimethylalkylsilane, and the like. Examples of the silane coupling agent having an amino group include 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, and the like. Examples of the silane coupling agent having an epoxy group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and the like. Examples of the silane coupling agent having a methacryl group include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 8-methacryloxyoctyltrimethoxysilane, and the like. Examples of the silane coupling agent having an acrylic group include 3-acryloxypropyltrimethoxysilane, and the like.

[0029] Among the above-described silane coupling agents, those used for modifying the surface of copper nanoparticles preferably include silane coupling agents having an alkyl group. By using this, the carbon content of the surface-modified copper nanoparticles can be reduced without impairing the dispersibility of the surface-modified copper nanoparticles in an organic solvent.

[0030] The alkyl chain of the silane coupling agent preferably has 3 or more carbon atoms, more preferably 6 or more carbon atoms, and even more preferably 8 or more carbon atoms. If the alkyl chain has 3 or more carbon atoms, the alkyl chain can fully exhibit steric effects. On the other hand, if the alkyl chain is too long, it will cause an increase in carbon residues when sintering the surface-modified copper nanoparticles for electrode applications. Therefore, the alkyl chain of the silane coupling agent preferably has 10 or fewer carbon atoms. Considering the above, specifically, n-octyltrimethoxysilane is preferred.

[0031] <<Method for Producing Surface-Modified Copper Nanoparticles>> The second aspect of the present invention is a method for producing surface-modified copper nanoparticles in which the surface of copper nanoparticles is modified with a silane coupling agent. By the production method of this aspect, the surface-modified copper nanoparticles of the first aspect can be easily produced. That is, according to the production method of this aspect, surface-modified copper nanoparticles in which more than 0.3 and less than 2.0 surface groups derived from the silane coupling agent are formed per 1 nm ２ of the surface area of the copper nanoparticles can be easily obtained.

[0032] The production method of this aspect preferably includes at least the humidification step and the mixing / dispersion step among the following preparation step, humidification step, mixing / dispersion step, reaction step, washing step, and drying step.

[0033] <Preparation Step> First, prepare copper nanoparticles having a film containing copper oxide on at least a part of the surface. Such copper nanoparticles can be produced by known wet methods or dry methods. Examples of the wet method include a method of dissolving a copper compound in a liquid, reducing a copper salt, and recovering the nanoparticles. Examples of the dry method include a chemical vapor deposition method using a reducing flame and a physical vapor deposition method using plasma or the like. Also, if commercially available copper nanoparticles are available, they may be used.

[0034] <Humidification Process> It is preferable to humidify the copper nanoparticles obtained in the preparation process to attach an appropriate amount of moisture. By performing the humidification process, the silane coupling agent can be efficiently attached to the copper nanoparticles even when only a small amount of the silane coupling agent is added.

[0035] For humidification, a preferred method is to allow moisture to adhere to the copper nanoparticles by bringing them into contact with a humidifying gas whose water vapor pressure and temperature have been adjusted for a specified period of time. One method for bringing the copper nanoparticles into contact with the humidifying gas is to place the copper nanoparticles in a sealed container and supply the humidifying gas. In this case, the copper nanoparticles in the sealed container may be left undisturbed or mixed. If mixing is used, a commercially available mixer that can mix the powder while supplying the humidifying gas into the container (for example, a rocking mixer manufactured by Aichi Electric Co., Ltd.) may be used.

[0036] The humidifying gas contains a carrier gas and water vapor. The carrier gas is not particularly limited and may be an inert gas or air. The water vapor pressure of the humidifying gas is, for example, 0.8 kPa to 3.5 kPa, and preferably 1.0 kPa to 3.0 kPa. If it is 1.0 kPa or higher, the amount of moisture contained will be sufficient, shortening the time required to achieve an appropriate amount of adhesion and increasing efficiency. If it is 3.0 kPa or lower, condensation is less likely to occur when the temperature is room temperature (around 25°C), making it easier to uniformly adhere moisture to the copper nanoparticles.

[0037] The humidification time can be adjusted as appropriate while observing the amount of water adhering to the copper nanoparticles (adhered water amount). The adhering water amount is preferably more than 1300 ppm and less than 6500 ppm, and more preferably between 2000 ppm and 6000 ppm. If the amount is above or below the lower limit of the above range, hydrolysis of the silane coupling agent adhering to the copper nanoparticles is more likely to occur, making it easier to control the number of surface groups and increasing the dispersibility of the resulting surface-modified copper nanoparticles. If the amount is below or below the upper limit of the above range, the reaction between silane coupling agents and the localization of the silane coupling agent due to excessive adhering water can be suppressed, allowing the silane coupling agent to adhere uniformly to the copper nanoparticles and increasing the dispersibility of the resulting surface-modified copper nanoparticles.

[0038] The amount of adhering water is determined by weighing the copper nanoparticles with water adhering to them in a dry room, measuring the mass of water adhering to the copper nanoparticles using the Karl Fischer method, and dividing by (mass of adhering water / mass of water-adhered copper nanoparticles). Examples of equipment and conditions for measurement using the Karl Fischer method include the following: • Equipment used: Metrohm Japan Coulometer Model 899 • Electrolyte used: Anode: HYDRANAL-Coulomat AG, Cathode: HYDRANAL-Coulomat CG • Carrier gas: Ar • Water vaporization temperature: 130℃

[0039] If the amount of water adhering to the measured copper nanoparticles is excessive, the amount of water can be reduced, for example, by bringing the copper nanoparticles into contact with a dry gas at room temperature. Examples of dry gases include air that has passed through a desiccant such as silica gel, or air dried in a refrigerated dryer. Through the above process, copper nanoparticles with a desired amount of water adhering to them can be obtained.

[0040] <Mixing and Dispersion Process> Copper nanoparticles, which have been humidified to a predetermined amount of attached water, are mixed with a reaction solvent and a silane coupling agent. The mixture is then subjected to a dispersion process to obtain a dispersion of copper nanoparticles. The mixing and dispersion of each material may be performed individually or simultaneously. The mixing of each material can be performed using, for example, a motor-driven stirrer. Methods for dispersing copper nanoparticles in the mixture include, for example, pressurized dispersion by sending the mixture into a narrow channel and causing collisions or shear forces to be applied, dispersion using a bead mill, and dispersion using blades or rolls.

[0041] Examples of commercially available high-pressure wet dispersers capable of performing pressurized dispersion treatment include the "NanoVeta B-ED" manufactured by Yoshida Machinery Industry Co., Ltd. and the "Starburst HJP-25005V2" manufactured by Sugino Machine Co., Ltd.

[0042] The set value for the dispersion pressure of the high-pressure wet disperser is preferably 50 MPa to 200 MPa, and more preferably 50 MPa to 150 MPa. If the pressure is 50 MPa or higher, copper nanoparticles that are weakly aggregated in the atmosphere can be sufficiently broken down and dispersed, and if the pressure is 200 MPa or lower, the risk of flattening or deterioration of the copper nanoparticle surface due to excessive shear stress can be sufficiently reduced.

[0043] In a high-pressure wet disperser, the dispersion time can be expressed by the number of times the mixture passes through a predetermined point in the apparatus (number of passes). In the commercially available apparatus described above, the number of passes can be set to, for example, 1 to 20 times, with 2 to 20 times being preferred. By setting the number of passes to 2 or more, the entire copper nanoparticle can be uniformly broken down and dispersed. By setting the number of passes to 20 or less, the risk of flattening of the copper nanoparticles due to excessive shear stress can be sufficiently reduced.

[0044] The reaction solvent can be any organic solvent capable of dissolving the silane coupling agent. By utilizing the water adhering to copper nanoparticles as the water required for the hydrolysis reaction of the silane coupling agent, non-polar solvents that do not contain water can also be selected. Examples of polar organic solvents include alcohols (methanol, ethanol, 1-propanol, 2-propanol, butanol, terpineol, etc.), ketones (acetone, methyl ethyl ketone, etc.), and polyols (ethylene glycol, dimethyl glycol, triethylene glycol, etc.). Examples of non-polar organic solvents include aromatic organic solvents such as benzene, toluene, xylene, and ethylbenzene, and aliphatic hydrocarbon organic solvents such as pentane, hexane, heptane, octane, cyclohexane, methylcyclohexane, and decahydronaphthalene. A solution obtained by mixing the above solvents in any proportion can also be used as the reaction solvent.

[0045] The amount of silane coupling agent mixed into the aforementioned mixture is appropriately adjusted according to the amount of water adhering to the copper nanoparticles. It is preferable to determine the amount of silane coupling agent that yields the desired number of surface groups in advance through preliminary experiments. Within the aforementioned preferred range of adhering water, a correlation between the amount of silane coupling agent and the number of surface groups is easily obtained.

[0046] The heat generated by dispersing the aforementioned mixture under high pressure can also be used to react a silane coupling agent with the surface of copper nanoparticles.

[0047] <Reaction Step> If necessary, the dispersion of the copper nanoparticle mixture obtained in the previous step may be further heated and stirred to chemically bond the silane coupling agent to the surface of the copper nanoparticles. The temperature of the dispersion suitable for the silane coupling reaction depends on the type of silane coupling agent, but for example, 40°C or higher is preferred, and 80°C or higher is more preferred. If the temperature of the heated dispersion exceeds the boiling point of the reaction solvent, it is preferable to use a pressure-resistant container, a magnetic stirrer, and a stirring bar to prevent the reaction solvent from volatilizing.

[0048] If the temperature of the dispersion rises sufficiently during the preceding mixing and dispersion step due to the heat generated by friction, crushing, and dispersion of copper nanoparticles, and the silane coupling reaction proceeds adequately, the reaction step may be omitted.

[0049] <Washing Process> Surface-modified copper nanoparticles, whose surfaces have been modified by the silane coupling reaction, are separated from the mixture using a solid-liquid method to obtain wet surface-modified copper nanoparticles. The solid-liquid separation can be performed by filtration or supernatant removal. By adding a washing solvent to the wet surface-modified copper nanoparticles, stirring, and then performing solid-liquid separation again, excess silane coupling agent free in the washing solvent can be removed. Stirring can be performed using a stirrer, ultrasonic bath, or shaker.

[0050] The purpose of the washing step is to remove any unreacted silane coupling agent from the copper nanoparticle surface. If a sufficient amount of silane coupling agent is used in the mixing step relative to the surface area of ​​the copper nanoparticles, the amount of unreacted silane coupling agent will be extremely small, and therefore the washing step may be omitted.

[0051] (Washing Solvent) It is desirable that the washing solvent be composed of at least part or all of a polar organic solvent. Examples of such polar organic solvents include alcohols (methanol, ethanol, 1-propanol, 2-propanol, butanol, terpineol, etc.), ketones (acetone, methyl ethyl ketone, etc.), and polyols (ethylene glycol, dimethyl glycol, triethylene glycol, etc.). By including a polar organic solvent in at least part of the washing solvent, the unreacted silane coupling agent that is physically attached to the copper nanoparticle surface via hydrogen bonds can be cleaved without chemically bonding to the copper nanoparticle surface, thereby releasing the unreacted silane coupling agent into the washing solvent and removing it. A mixture of the above-mentioned washing solvents in any proportion may also be used as the washing solvent.

[0052] <Drying Process> Finally, the surface-modified copper nanoparticles obtained in the previous step are dried. Examples of drying methods include filtration drying, reduced-pressure drying, forced-air drying, and spray drying. These methods may be used individually or in combination of two or more.

[0053] The effects of the present invention will be described in detail below based on verification tests. The present invention is not limited to the contents of the following verification tests.

[0054] [Manufacturing Example 1] Manufacturing of Copper Nanoparticles The copper nanoparticles were manufactured by the manufacturing method described in Japanese Patent No. 6130616. The manufacturing conditions were as follows: • Powder raw material: Copper powder (manufactured by Nippon Atomize Processing Co., Ltd., average particle size 10 μm) • Fuel gas supplied to the burner: Liquefied natural gas • Combustion-supporting gas: Oxygen As a result of evaluating the manufactured copper nanoparticles, the specific surface area was found to be 5.82 m². ２ / g, average particle size: 115 nm, surface Cu ２ The oxygen concentration was 9.9 atomic%, and the silicon concentration was less than 0.005 ppm.

[0055] [Example 1] (Humidification Treatment) 1 liter of purified water was placed in a 2 liter gas washing bottle, and dry air was introduced through one of the two nozzles at the top, while humidified air was taken out through the other. The extracted humidified air was diluted with dry air as needed while monitoring the dew point with a dew point meter to obtain a humidified gas with a water vapor pressure of 3.0 kPa. 100 g of copper nanoparticles produced in Production Example 1 were placed in a sealed container equipped with a supply port and an outlet through which the humidifying gas could flow, and the above humidifying gas was passed through. After standing in this state for 0.16 hours, copper nanoparticles with an attached water content of 2000 ppm were obtained.

[0056] (Silane coupling treatment) Weigh 20 g of the copper nanoparticles with an adhering water content of 2000 ppm and 60 g of ethanol into a beaker, and use octyltrimethoxysisilane (OTMS) (manufactured by Tokyo Chemical Industry Co., Ltd.; T2875) as the silane coupling agent with a surface group count of 1.0 ions / nm ２An amount (amount X) was added and mixed using a motor-driven stirrer. These mixtures were then dispersed using Yoshida Machinery Industry's "NanoVeta B-ED". The dispersion pressure was 100 MPa and the number of dispersion passes was 20. The temperature of the dispersion during this process was 80°C. After 20 passes, the silicon concentration of the copper nanoparticles was measured and found to be 1.0 silicon atoms / nm. ２ Since the reaction had reached a certain point, the aforementioned reaction step was omitted. The obtained dispersion was separated into solid and liquid by filtration, 60 g of ethanol was weighed into another beaker, and the wet surface-modified copper nanoparticles deposited on the filter paper were added. The beaker was then immersed in an ultrasonic bath and stirred for 10 minutes. The obtained dispersion was filtered again to separate the solid and liquid, and the obtained wet surface-modified copper nanoparticles were transferred to a stainless steel tray and air-dried at 40°C for 16 hours to obtain silane-coupled surface-modified copper nanoparticles.

[0057] The silicon concentration of the obtained surface-modified copper nanoparticles was measured, and the number of surface units was calculated from the results. Particle size distribution measurements were also performed to obtain the median diameter. Furthermore, the surface-modified copper nanoparticles were calcined at 700°C under a nitrogen atmosphere, and the carbon concentration was measured to obtain the residual carbon concentration after calcination. The results are shown in Table 1.

[0058] (Example 2) In Example 1, the silane coupling agent OTMS was given a surface group count of 0.5 groups / nm ２ The amount added (amount Y) was such that the result was obtained. The rest of the procedure was the same as in Example 1.

[0059] (Example 3) In Example 1, the silane coupling agent OTMS was given a surface group count of 1.5 groups / nm ２ The amount added (amount Z) was such that [result]. The rest of the procedure was the same as in Example 1.

[0060] (Example 4) In Example 1, copper nanoparticles with 6000 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was added with a surface group count of 0.5 units / nm ２ The amount added (the aforementioned amount Y) was used. The rest of the procedure was the same as in Example 1.

[0061] (Example 5) In Example 1, copper nanoparticles with 6000 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 1.5 units / nm. ２ The amount added (the aforementioned amount Z) was used. The rest of the procedure was the same as in Example 1.

[0062] (Comparative Example 1) In Example 1, copper nanoparticles with 800 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 1.5 units / nm ２ The amount added (the aforementioned amount Z) was used. The rest of the procedure was the same as in Example 1.

[0063] (Comparative Example 2) In Example 1, copper nanoparticles with 1300 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 1.5 units / nm. ２ The amount added (the aforementioned amount Z) was used. The rest of the procedure was the same as in Example 1.

[0064] (Comparative Example 3) In Example 1, copper nanoparticles with 2000 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 0.3 units / nm ２ The amount added was such that (0.2 times the amount Z mentioned above). The rest of the procedure was the same as in Example 1.

[0065] (Comparative Example 4) In Example 1, copper nanoparticles with 2000 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 2.0 units / nm ２ The amount added was twice the amount of the aforementioned addition X. The rest of the procedure was the same as in Example 1.

[0066] (Comparative Example 5) In Example 1, copper nanoparticles with 6000 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 0.3 units / nm ２ The amount added was such that (0.2 times the amount Z mentioned above). The rest of the procedure was the same as in Example 1.

[0067] (Comparative Example 6) In Example 1, copper nanoparticles with 6000 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 2.0 units / nm ２The amount added was twice the amount of the aforementioned addition X. The rest of the procedure was the same as in Example 1.

[0068] (Comparative Example 7) In Example 1, copper nanoparticles with 6500 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 0.3 units / nm ２ The amount added was such that (0.2 times the amount Z mentioned above). The rest of the procedure was the same as in Example 1.

[0069] (Comparative Example 8) In Example 1, copper nanoparticles with 6500 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 0.5 units / nm ２ The amount added (the aforementioned amount Y) was used. The rest of the procedure was the same as in Example 1.

[0070] (Comparative Example 9) In Example 1, copper nanoparticles with 6500 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 1.5 units / nm. ２ The amount added (the aforementioned amount Z) was used. The rest of the procedure was the same as in Example 1.

[0071] (Comparative Example 10) In Example 1, copper nanoparticles with 6500 ppm of adhering water were produced by humidification treatment, and the silane coupling agent OTMS was used with a surface group count of 2.0 units / nm ２ The amount added was twice the amount of the aforementioned addition X. The rest of the procedure was the same as in Example 1.

[0072] The results of the above tests are shown in Table 1.

[0073]

[0074] <Evaluation 1> Figure 1 is a graph showing the relationship between the number of surface units and the median diameter of the particle size distribution for Examples 1 to 5 and Comparative Examples 1 to 10. In Figure 1, the X-axis represents the 1 nm of the silane coupling agent adhering to the surface of the surface-modified copper nanoparticles. ２ The Y-axis represents the number of surface zones per unit area, and the Y-axis represents the median diameter (in μm) of surface-modified copper nanoparticles dispersed in ethanol.

[0075] <Evaluation 2> Figure 2 is a graph showing the relationship between the number of surface groups and the residual carbon concentration after firing for Examples 1 to 5 and Comparative Examples 1 to 10. In Figure 2, the X-axis represents the 1 nm of the silane coupling agent attached to the surface of the surface-modified copper nanoparticles. ２ The Y-axis represents the number of surface zones per unit area, and the Y-axis represents the residual carbon concentration after firing relative to the total mass of surface-modified copper nanoparticles (unit: mass%), measured by the method described above.

[0076] As is clear from Figures 1-2, in Examples 1-5, which used copper nanoparticles to which 2000-6000 rpm of moisture had been attached by humidification treatment as raw materials, it was easy to adjust the surface number to the desired level. Furthermore, the surface-modified copper nanoparticles obtained in Examples 1-5 had a surface number of 0.5-1.5 particles / nm. ２ As a result, the median diameter was less than 0.2 μm in all cases, demonstrating excellent dispersibility. Furthermore, the surface-modified copper nanoparticles obtained in Examples 1 to 5 all had a low residual carbon concentration of less than 0.01% after firing.

[0077] In Comparative Examples 1 and 2, the amount of water attached to the copper nanoparticles was insufficient, resulting in poor reactivity with the copper nanoparticles even when a sufficient amount of silane coupling agent was incorporated into the reaction system. This led to a reduced number of surface groups and poorly dispersible copper nanoparticles. In Comparative Examples 3 and 5, the amount of silane coupling agent incorporated into the reaction system was insufficient, resulting in a reduced number of surface groups and poorly dispersible copper nanoparticles. In Comparative Examples 4 and 6, the amount of silane coupling agent incorporated into the reaction system was excessive, resulting in high residual carbon concentration after calcination and inferior copper nanoparticles. In Comparative Examples 7 to 10, the amount of water attached to the copper nanoparticles was excessive, resulting in poorly dispersible copper nanoparticles.

[0078] As described above, the surface-modified copper nanoparticles obtained by the manufacturing method according to the present invention can be dispersed with a median diameter of less than 0.2 μm, and the residual carbon concentration after sintering can be reduced to less than 0.01%. Therefore, if the surface-modified copper nanoparticles according to the present invention are used as the main component of conductive inks or conductive pastes, both sufficient dispersibility and a reduction in residual carbon after sintering can be achieved. Such excellent conductive inks and conductive pastes are suitable for forming electrodes and wiring in various electronic components.

Claims

1. Surface-modified copper nanoparticles in which the surface of copper nanoparticles is modified with a silane coupling agent, wherein the copper nanoparticles have a coating containing copper oxide on at least a portion of their surface, and the number of surface groups derived from the silane coupling agent on the surface of the surface-modified copper nanoparticles is equal to the surface area of ​​the surface-modified copper nanoparticles per 1 nm. ２ Surface-modified copper nanoparticles having more than 0.3 particles but less than 2.0 particles per unit, wherein the average median diameter measured using a particle size analyzer after dispersing the surface-modified copper nanoparticles in ethanol is 0.2 μm or less.

2. The surface-modified copper nanoparticles according to claim 1, wherein the amount of carbon contained in the calcined product remaining after calcining a sample of the surface-modified copper nanoparticles in an inert gas atmosphere at a temperature of 700°C is 0.010% by mass or less relative to the mass of the sample.

3. The surface-modified copper nanoparticles according to claim 2, wherein the average particle size of the copper nanoparticles is 180 nm or less.

4. A mixture is obtained by mixing copper nanoparticles with an attached water content of more than 1300 ppm and less than 6500 ppm, a silane coupling agent, and an organic solvent, and the silane coupling agent is reacted on the surface of the copper nanoparticles, thereby increasing the surface area of ​​the copper nanoparticles to 1 nm. ２ A method for producing surface-modified copper nanoparticles, wherein surface groups derived from the silane coupling agent are formed on each nanoparticle in an amount of more than 0.3 and less than 2.0 per nanoparticle.

5. The method for producing surface-modified copper nanoparticles according to claim 4, wherein the copper nanoparticles have a coating containing copper oxide on at least a portion of their surface.

6. A method for producing surface-modified copper nanoparticles according to claim 5, wherein the heat generated by dispersing the mixture under high pressure is used to react the silane coupling agent on the surface of the copper nanoparticles.

7. The method for producing surface-modified copper nanoparticles according to claim 4, wherein the surface-modified copper nanoparticles are the surface-modified copper nanoparticles described in any one of claims 1 to 3.

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