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

Abstract

To provide surface-modified copper nanoparticles with high dispersibility and reduced carbon residue concentration after firing, and a method for producing the same. [Solution] 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 area, 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.

Description

[Technical Field]

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

[0002] In the joining and wiring formation of various electronic components, 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). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 7219842 [Overview of the Initiative] [Problems that the invention aims to solve]

[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. [Means for solving the problem]

[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 Surface-modified copper nanoparticles having more than 0.3 particles but less than 2.0 particles per unit area, wherein the average median diameter measured using a diffraction 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 [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 size 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 by reacting the silane coupling agent with the surface of the copper nanoparticles, the surface area of ​​the copper nanoparticles is reduced to 1 nm. 2 A method for producing surface-modified copper nanoparticles, wherein surface groups derived from the silane coupling agent are formed on surface-modified copper nanoparticles 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 portion of their surface. [6] A method for producing surface-modified copper nanoparticles according to [4] or [5], wherein the heat generated by dispersing the mixture under high pressure causes the silane coupling agent to react with the surface of the copper nanoparticles. [7] A 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]. [Effects of the Invention]

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

Brief Description of the Drawings

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

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the embodiments described below, and various modifications are possible without departing from the gist of the present invention.

[0010] The meanings and definitions of the terms in this specification are as follows. The numerical range represented by “~” means a numerical range having the numerical values before and after ~ as the lower limit value and the upper limit value. That the surface of the copper nanoparticles is modified with a silane coupling agent means that at least one of the following occurs: a dehydration condensation reaction occurs between the hydroxyl groups present on the surface of the particles and the silane coupling agent, and silanol is bonded to the surface; even when there are no hydroxyl groups, the silanol groups formed by hydrolysis of the silane coupling agent due to electrostatic interaction are adsorbed on the particle surface, and a film is formed on the surface by subsequent dehydration condensation between the 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 the copper nanoparticles is modified with a silane coupling agent.

[0012] [Copper Nanoparticles] It is preferable that copper nanoparticles 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 represented by the chemical formula Cu2O and is sometimes called cuprous oxide.

[0014] By having the above-mentioned 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 to confirm 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"). This can be confirmed by the presence or absence of peaks attributed to CuO and Cu2O in the obtained spectrum.

[0015] The average particle size of the copper nanoparticles is preferably, for example, 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 value is above the lower limit of the above range, the increase in surface energy associated with the increase in the specific surface area of ​​copper nanoparticles is suppressed, resulting in good dispersion of copper nanoparticles and uniform adhesion of the silane coupling agent to the surface of the copper nanoparticles. If the value 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 attached to the surface of the copper nanoparticles is fully exerted, improving dispersibility.

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

[0017]

number

[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] [Surface cardinality] In this embodiment, the surface of the surface-modified copper nanoparticles contains surface groups (atomic groups) derived from the silane coupling agent. The number of these surface groups corresponds to the surface area of ​​the surface-modified copper nanoparticles per 1 nm. 2 The number of winning tickets is preferably greater than 0.3 and less than 2.0, more preferably between 0.4 and 1.8, and even more preferably between 0.5 and 1.5. When the value exceeds the lower limit of the above range or is above the lower limit, the steric hindrance effect of the silane coupling agent is fully exerted, and the dispersibility is further improved. If the value is below or below the upper limit of the above range, the carbon component (which, if remaining in the sintered film, contributes to electrical resistance) can be 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]

number

[0022] The silicon concentration due to the silane coupling agent can be measured by dissolving surface-modified copper nanoparticles in nitric acid, hydrochloric acid, or a mixture of nitric acid and hydrochloric acid, diluting the solution, and measuring it using an inductively coupled plasma atomic emission spectrometer (for example, Shimadzu Corporation's "ICPS-8100"). More precisely, it is calculated from the difference between the silicon concentration of the copper nanoparticles used as raw material and the silicon concentration of the surface-modified copper nanoparticles after 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 Since it is O3Si and contains one silicon atom in the molecule, the molar mass of silicon atoms contained in n-octyltrimethoxysilane is 28.0855 (approximately 28) g / mol.

[0024] [Median diameter] In this embodiment, when the surface-modified copper nanoparticles are dispersed in ethanol, the average median diameter measured three or more times using a laser diffraction particle size analyzer is preferably 0.2 μm or less. This median diameter is an indicator of dispersibility; a smaller diameter indicates fewer aggregated particles. However, in principle, the median diameter cannot be smaller than the average particle diameter of the copper nanoparticles.

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

[0026] [Carbon residue concentration after firing] In this embodiment, the carbon concentration (post-firing carbon residue concentration) in the calcined product remaining after firing a sample of surface-modified copper nanoparticles in an inert gas atmosphere at 700°C 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 calcined product. Generally, the fewer impurities contained in the calcined product (sintered copper nanoparticles), the lower the electrical resistance of the calcined 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 chemically bond to the surface of copper nanoparticles by a silane coupling reaction and improves dispersibility in the solvent. Examples of such silane coupling agents include those having alkyl groups, amino groups, epoxy groups, methacrylic groups, or acrylic groups as functional groups. Examples of silane coupling agents containing alkyl groups include isobutyryltrimethylalkylsilane, hexyltrimethylalkylsilane, octyltrimethylalkylsilane, decyltrimethylalkylsilane, dodecyltrimethylalkylsilane, and octadecyltrimethylalkylsilane. Examples of silane coupling agents containing an amino group include 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane. Examples of silane coupling agents containing epoxy groups include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Examples of silane coupling agents containing a methacrylic group include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 8-methacryloxyoctyltrimethoxysilane. Examples of silane coupling agents containing an acrylic group include 3-acryloxypropyltrimethoxysilane.

[0029] Among the silane coupling agents mentioned above, silane coupling agents having an alkyl group are preferred for use in modifying the surface of copper nanoparticles. 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 organic solvents.

[0030] The alkyl chain in the silane coupling agent is preferably an alkyl chain having 3 or more carbon atoms, more preferably an alkyl chain having 6 or more carbon atoms, and even more preferably an alkyl chain having 8 or more carbon atoms. If the alkyl chain has 3 or more carbon atoms, the alkyl chain can fully exert its steric effects. On the other hand, if the alkyl chain is longer than necessary, it can lead to an increase in carbon residue when surface-modified copper nanoparticles are sintered and applied to electrodes. Therefore, it is preferable that the alkyl chain of the silane coupling agent has 10 or fewer carbon atoms. Taking the above into consideration, specifically, n-octyltrimethoxysilane is preferred.

[0031] ≪Method for producing surface-modified copper nanoparticles≫ A 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. The production method of this aspect allows for the easy production of surface-modified copper nanoparticles as described in the first aspect. Specifically, according to the production method of this aspect, the surface area of ​​the copper nanoparticles is 1 nm. 2 Surface-modified copper nanoparticles can be easily obtained in which surface groups derived from the silane coupling agent are formed in quantities of more than 0.3 and less than 2.0 per nanoparticle.

[0032] The manufacturing method according to this embodiment preferably includes at least the humidification step and the mixing / dispersion step from the following preparation step, humidification step, mixing / dispersion step, reaction step, washing step, and drying step.

[0033] <Preparation process> First, prepare copper nanoparticles having a coating containing copper oxide on at least a portion of their surface. Such copper nanoparticles can be manufactured by known wet or dry methods. Wet methods include dissolving a copper compound in a liquid and reducing the copper salt to recover the nanoparticles. Dry methods include chemical vapor deposition using a reducing flame and physical vapor deposition using plasma, etc. If commercially available copper nanoparticles are available, they may also be used.

[0034] <Humidification process> It is preferable to humidify the copper nanoparticles obtained in the preparation step to attach an appropriate amount of moisture to them. By humidifying, 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] As a humidification process, a preferred method is to contact copper nanoparticles with a humidifying gas whose water vapor pressure and temperature have been adjusted for a specified period of time, thereby causing moisture to adhere to the copper nanoparticles. One method for bringing copper nanoparticles into contact with a 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 can be, for example, 0.8 kPa to 3.5 kPa, with 1.0 kPa to 3.0 kPa being preferred. If it is 1.0 kPa or higher, the amount of moisture contained will be sufficient, shortening the time required to achieve the 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 should be adjusted as appropriate while observing the amount of water adhering to the copper nanoparticles (adhered water amount). The adhered water amount is preferably more than 1300 ppm and less than 6500 ppm, and more preferably between 2000 ppm and 6000 ppm. If the value exceeds the lower limit of the above range or is above the lower limit, hydrolysis of the silane coupling agent attached to the copper nanoparticles is more likely to occur, making it easier to control the number of surface groups and improving the dispersibility of the resulting surface-modified copper nanoparticles. If the amount of water is below or below the upper limit of the above range, it is possible to suppress the reaction between silane coupling agents and the localization of silane coupling agents due to excessive amount of adhering water, allowing the silane coupling agent to adhere uniformly to the copper nanoparticles, and improving the dispersibility of the resulting surface-modified copper nanoparticles.

[0038] The amount of attached water is determined by weighing the copper nanoparticles with water attached in a dry room, measuring the mass of water attached to the copper nanoparticles using the Karl Fischer method, and dividing it by (mass of attached water / mass of copper nanoparticles with water attached). Examples of the equipment and conditions used for measurement in 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 • Moisture 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 any amount of attached water can be obtained.

[0040] <Mixing / 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. This mixture is then subjected to a dispersion treatment 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 done using, for example, a motor-driven agitator. Methods for dispersing copper nanoparticles in a mixture include, for example, a method of pressurizing the mixture and sending it into a narrow channel, causing collisions between the mixture particles or applying shear force to perform a pressurized dispersion treatment; a method of dispersion using a bead mill; and a method of 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 preferred dispersion pressure setting for a high-pressure wet disperser is 50 MPa to 200 MPa, and more preferably 50 MPa to 150 MPa. A pressure of 50 MPa or higher is sufficient to adequately break down and disperse copper nanoparticles that are weakly aggregated in the atmosphere, while a pressure of 200 MPa or lower is sufficient to adequately reduce the risk of flattening or deterioration of the copper nanoparticle surface due to excessive shear stress.

[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 nonpolar 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 solvents listed above 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 Process> If necessary, the dispersion of copper nanoparticles 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, or 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, allowing the silane coupling reaction to proceed adequately, the reaction step may be omitted.

[0049] <Washing process> Surface-modified copper nanoparticles, whose surfaces have been modified by a 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) The washing solvent is preferably 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 a portion of the washing solvent, the unreacted silane coupling agent, which is physically attached to the copper nanoparticle surface via hydrogen bonds without chemically bonding to the copper nanoparticle surface, can be released into the washing solvent and removed. A mixture of the above-mentioned washing solvents in any proportion may 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. [Examples]

[0053] Hereinafter, the effects of the present invention will be described in detail by verification tests. The present invention is not limited only to the contents of the following verification tests.

[0054] [Production Example 1] Production of Copper Nanoparticles The copper nanoparticles were produced by the production method described in Japanese Patent No. 6130616. The production conditions were as follows. · Powder raw material: Copper powder (manufactured by Nippon Atomizing K.K., average particle diameter 10 μm) · Fuel gas supplied to the burner: Liquefied natural gas · Support combustion gas: Oxygen As a result of evaluating the produced copper nanoparticles, the specific surface area was 5.82 m 2 / g, average particle diameter: 115 nm, surface Cu2O concentration: 9.9 atomic%, and silicon concentration: less than 0.005 ppm.

[0055] [Example 1] (Humidification treatment) 1 L of purified water was placed in a 2 L gas washing bottle, dry air was introduced from one of the two nozzles at the upper part, and humid air was taken out from the other. While monitoring the taken-out humid air with a dew point meter, it was appropriately diluted with dry air to obtain a humid gas with a water vapor pressure of 3.0 kPa. 100 g of the copper nanoparticles produced in Production Example 1 were left standing in a sealed container provided with a supply port and a discharge port through which the humidifying gas could flow, and the above humidifying gas was circulated. When left standing in this state for 0.16 hour, copper nanoparticles with an attached water amount of 2000 ppm were obtained.

[0056] (Silane coupling treatment) 20 g of the copper nanoparticles with an attached water amount of 2000 ppm and 60 g of ethanol were weighed into a beaker, and octyltrimethoxysilane (OTMS) (manufactured by Tokyo Chemical Industry Co., Ltd.; T2875) was used as a silane coupling agent with a surface density of 1.0 piece / nm 2 in an amount (addition amount X) to be added, and they were stirred and mixed with a motor-driven stirrer. These mixtures were 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 the number of surface groups was 1.0 / nm. 2 Since the reaction had reached this point, the aforementioned reaction step was omitted. The resulting 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 components, and the resulting 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 used with 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 used with a surface group count of 1.5 groups / nm. 2 The amount (amount added Z) was added to achieve the desired 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 groups / nm. 2The 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 added with a surface group count of 1.5 groups / nm. 2 The amount added was such that (the amount added Z). 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 added with a surface group count of 1.5 groups / nm. 2 The amount added was such that (the amount added Z). 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 added with a surface group count of 1.5 groups / nm. 2 The amount added was such that (the amount added Z). 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 added with a surface group count of 0.3 groups / nm. 2 The amount added was such that (0.2 times the amount of the above-mentioned addition Z). 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 added 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 added with a surface group count of 0.3 groups / nm. 2 The substance was added in an amount equivalent to the above-mentioned amount Z (0.2 times the amount added). 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 added with a surface group count of 2.0 groups / 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.

[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 added with a surface group count of 0.3 groups / nm. 2 The substance was added in an amount equivalent to the above-mentioned amount Z (0.2 times the amount added). 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 added with a surface group count of 0.5 groups / 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 added with a surface group count of 1.5 groups / nm. 2 The amount added was such that (the amount added Z). 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 added 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] [Table 1]

[0074] <Rating 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 1-5 and Comparative Examples 1-10. 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] <Rating 2> Figure 2 is a graph showing the relationship between the number of surface groups and the residual carbon concentration after firing for Examples 1-5 and Comparative Examples 1-10. 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 moisture was attached at 2000-6000 rpm during humidification, 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 small, so even when a sufficient amount of silane coupling agent was added to the reaction system, the reactivity with the copper nanoparticles was poor, resulting in 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 small, 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 large, resulting in inferior copper nanoparticles with a high residual carbon concentration after calcination. In comparative examples 7-10, the amount of water attached to the copper nanoparticles was high, resulting in copper nanoparticles with poor dispersibility.

[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, The copper nanoparticles have a coating containing copper oxide on at least a portion of their surface. 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 at 1 nm. ２ The probability of getting a winning combination is greater than 0.3 but less than 2.

0. Surface-modified copper nanoparticles, wherein the surface-modified copper nanoparticles are dispersed in ethanol and the average median diameter measured using a particle size analyzer 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 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. Surface area of ​​the copper nanoparticles 1 nm ２ To obtain surface-modified copper nanoparticles having more than 0.3 but less than 2.0 surface groups derived from the silane coupling agent per nanoparticle, A method for producing surface-modified copper nanoparticles.

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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