Manufacturing method of surface-coated copper filler

Abstract

To provide a method of producing a surface-coated copper filler that is less in agglomerated copper particles and has a well oxidation resistance equivalent to the conventional one.SOLUTION: A method of producing a surface-coated copper filler includes the steps of: (A) immersing a copper particle in a solution containing 0.01-30 pts.mass of metal halide or ammonium halide derivative with respect to 100 pts.mass of a predetermined amine compound; and (B) immersing the copper particle subjected to the step (A) in a solution containing aliphatic monocarboxylic acid with a carbon number of 8-24.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a surface-coated copper filler, the surface-coated copper filler obtained by the production method, and a conductive composition containing the same. [Background technology]

[0002] BACKGROUND ART In the field of electronic materials, conductive compositions have conventionally been used for applications such as internal electrodes for MLCCs (multi-layer ceramic capacitors), through-hole bonding materials for printed circuit boards, and lead wiring forming materials for touch panels.

[0003] The conductive composition referred to here is a fluid compound, such as a silver paste. This conductive composition can be used to draw a pattern by screen printing, inkjet printing (hereinafter referred to as IJ printing), or the like, and then a conductive cured product can be formed by applying light or heat. Silver is often used as the conductive metal for conductive compositions because of its excellent oxidation resistance and low volume resistivity. However, silver has issues such as its high price and tendency to migrate. Therefore, in recent years, the use of copper in conductive compositions has been considered, as it has the second lowest volume resistivity after silver, is inexpensive, and has excellent migration resistance.

[0004] Generally, commercially available conductive copper particles with a particle size of 100 nm to 20 μm used in conductive compositions are coated on the surface with a fatty acid to improve the dispersibility and oxidation resistance of the copper particle powder. However, the oxidation resistance is not sufficient when coated with a fatty acid alone, and the conductive copper particles oxidize due to the high oxidizability of copper, resulting in copper oxide being present on part of the surface.

[0005] Patent Document 1 discloses a method for producing a surface-coated copper filler, in which copper particles are pretreated by washing them with an organic solvent or acid to prevent oxidation of the copper particle surface, and then a first coating layer of a specific amine compound and a second coating layer of a specific aliphatic monocarboxylic acid are formed. Patent Document 2 also discloses a method for removing impurities and oxides from the surface of copper particles using a stainless steel reaction vessel commonly used in the production of chemical products, in which copper particles are added to a solution containing a specific ammonium halide derivative, which is less corrosive than the acid, such as hydrochloric acid, used in the pretreatment of Patent Document 1, to adhere copper chloride to the copper particle surface, and then these copper chloride-adhered copper particles are added to a solution containing a specific amine compound to remove the copper chloride and form a coating layer of the specific amine compound on the copper particle surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2016 / 199811 [Patent Document 2] Japanese Patent Application Publication No. 2018-165382 Summary of the Invention [Problem to be solved by the invention]

[0007] The present inventors believed that the effects of both methods could be obtained by combining the methods described in Patent Documents 1 and 2, and investigated forming a coating layer of a specific amine compound on the surface of copper particles according to the method disclosed in Patent Document 2, and then forming a coating layer of a specific aliphatic monocarboxylic acid on that coating layer as disclosed in Patent Document 1. However, it was found that although the surface-coated copper filler obtained in this manner has superior oxidation resistance compared to that obtained by the method described in Patent Document 1, some of the copper particles may aggregate when the coating layer of the amine compound is formed.

[0008] When copper particles aggregate in this way, the aggregated copper particles have a lower bulk density and occupy a larger volume in the solution. Therefore, for example, when the copper particles are allowed to settle, the supernatant liquid is removed by decantation, and then a new treatment liquid is added to replace the treatment liquid, the replacement rate of the treatment liquid decreases, making it necessary to replace the treatment liquid more frequently, which may reduce production efficiency.

[0009] Furthermore, surface-coated copper fillers may be applied to, for example, conductive compositions. Generally, such conductive compositions are often used to form wiring patterns by screen printing. Therefore, when a conductive composition using a surface-coated copper filler containing agglomerated copper particles is used, the agglomerates often clog the mesh of the screen printing plate, causing defects in the printed wiring. This has been a factor that has hindered the use of conductive compositions using surface-coated copper fillers in forming wiring patterns.

[0010] Therefore, an object of the present invention is to provide a method for producing a surface-coated copper filler which has fewer agglomerated copper particles and has good oxidation resistance equivalent to that of conventional fillers. [Means for solving the problem]

[0011] The present inventors have conducted extensive research in view of the above-mentioned problems. As a result, they have found that, unlike Patent Documents 1 and 2, when forming a first coating layer of the specific amine compound on the surface of copper particles, by immersing the copper particles in a mixed solution in which the specific amine compound and the specific compound coexist in a predetermined mixing ratio, it is possible to produce a surface-coated copper filler with little aggregation of copper particles and good oxidation resistance, and have completed the present invention. That is, the gist of the present invention is as follows.

[0012] [1] (A) a step of immersing copper particles in a solution containing 0.01 to 30 parts by mass of a metal halide or an ammonium halide derivative per 100 parts by mass of an amine compound represented by formula (1);

[0013] [ka]

[0014] [In formula (1), m is an integer of 0 to 3, n is an integer of 0 to 2, and when n=0, m is any of 0 to 3, and when n=1 or n=2, m is any of 1 to 3.]

[0015] (B) a step of immersing the copper particles that have been subjected to the step (A) in a solution containing an aliphatic monocarboxylic acid having 8 to 24 carbon atoms; A method for producing a surface-coated copper filler, comprising:

[0016] [2] The method for producing a surface-coated copper filler according to the above item [1], wherein the halogen atoms contained in the metal halide and the ammonium halide derivative are chlorine atoms. [3] The method for producing a surface-coated copper filler according to the above item [1] or [2], wherein the ammonium halide derivative is selected from ammonium halide derivatives represented by formula (2):

[0017] [ka]

[0018] [In formula (2), a is an integer of 0 to 3, b is an integer of 0 to 3, and a+b=3.]

[0019] [4] A surface-coated copper filler obtained by the above-mentioned manufacturing method. [5] A conductive composition containing 10 to 95 mass % of the surface-coated copper filler. [Effects of the Invention]

[0020] The method for producing a surface-coated copper filler of the present invention can provide a method for producing a surface-coated copper filler with fewer agglomerated copper particles and with good oxidation resistance equivalent to that of conventional fillers. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described in detail.

[0022] <Copper particles as raw material> First, copper particles that are the raw material for the manufacturing method according to the embodiment of the present invention will be described. Hereinafter, when referring to copper particles, unless otherwise specified, it refers to raw copper particles.

[0023] Examples of copper particles include known copper particles commonly used in copper pastes and copper inks. The copper particles may be spherical, plate-like, dendritic, rod-like, or fibrous, or may be amorphous, such as hollow or porous. Furthermore, the copper particles may have a core-shell shape, in which the shell is copper and the core is made of a material other than copper.

[0024] The average particle size of the copper particles is not particularly limited. However, when used for a conductive composition, for example, the average particle size of the copper particles is controlled so that the conductive composition can be printed using various printing methods such as inkjet printing and screen printing. Specifically, the average particle size is preferably 5 nm to 20 μm. To suppress particle self-aggregation, suppress oxidation by increasing the surface area, or to print fine wiring of 100 μm or less, the average particle size is preferably 10 nm to 10 μm. When used for a conductive composition for screen printing with excellent continuous printability, the average particle size is preferably 100 nm to 10 μm. Furthermore, the copper particles may be of one type, or a mixture of copper particles with different shapes and average particle sizes may be used. In other words, a single type of powder of a homogeneous group having a certain particle size distribution may be used, or multiple types of such powders may be used in combination. Examples of combinations of different groups of powders include a combination of groups of copper particles with different shapes, or a combination of groups of copper particles with particle size distributions having different average particle sizes.

[0025] The average particle size of copper particles means the value obtained by arithmetically averaging the feret diameters of 100 particles randomly selected in a microscopic image obtained by observation with a transmission electron microscope or a scanning electron microscope.

[0026] <Surface-coated copper filler> The surface-coated copper filler according to an embodiment of the present invention comprises copper particles, a first coating layer of an amine compound represented by formula (1) (hereinafter sometimes simply referred to as "amine compound") that is chemically and / or physically bonded to copper atoms on the surface of the copper particles, and a second coating layer on the first coating layer of an aliphatic monocarboxylic acid having 8 to 24 carbon atoms that is chemically bonded to the amine compound.

[0027] [ka]

[0028] [In formula (1), m is an integer of 0 to 3, n is an integer of 0 to 2, and when n=0, m is any of 0 to 3, and when n=1 or n=2, m is any of 1 to 3.]

[0029] The first coating layer is a layer of an amine compound that is chemically and / or physically bonded to and adsorbed to copper atoms on the copper particle surface. From the viewpoint of oxidation resistance, it is ideal for the copper particle surface to be uniformly coated with the amine compound in the form of a monomolecular film. However, since it is difficult to achieve such an ideal state in practice, there may be some areas on the copper surface where the amine compound is not adsorbed, or there may be areas where two or more molecules are adsorbed in layers.

[0030] Therefore, the first coating layer includes not only a layer in which the amine compound uniformly coats the copper particle surface, but also a coating layer in which there is a portion of the copper particle surface to which the amine compound is not adsorbed.

[0031] The fact that the amine compound is adsorbed onto the copper particle surface to form the first coating layer can be confirmed by measuring the infrared absorption (IR) spectrum of the copper particle surface as described below (hereinafter sometimes referred to as "IR measurement").

[0032] Here, "chemically bonded and adsorbed" means that the amine compound forms a bond with the copper atoms on the copper particle surface through electrostatic interaction and is adsorbed to the copper particle surface. Here, electrostatic interaction refers to hydrogen bonding, ionic interaction (ionic bonding), etc. Furthermore, "physically bonded and adsorbed" means that the amine compound is adsorbed to the copper surface through physical adsorption due to van der Waals forces. In particular, the amino group contained in the amine compound has high electron donating properties, and it is thought that the amino group forms a bond by coordinating with copper. Therefore, it is thought that the amine compound is mainly adsorbed to the copper particle surface through chemical bonding due to electrostatic interaction, forming the first coating layer. However, some adsorption through physical bonding may also occur.

[0033] Furthermore, there may be a portion where two or more amine compound molecules are bonded to each other by, for example, hydrogen bonding, etc., and stacked.

[0034] The second coating layer is a layer laminated on the first coating layer, and is a layer of an aliphatic monocarboxylic acid having 8 to 24 carbon atoms (hereinafter, may be simply referred to as "aliphatic monocarboxylic acid") chemically bonded to the amine compound of the first coating layer. It is preferable that the first coating layer is a monomolecular film of the aliphatic monocarboxylic acid uniformly coated thereon.

[0035] Here, chemical bonding means that the carboxyl group of the aliphatic monocarboxylic acid and the amino group of the amine compound are bonded via electrostatic interaction. Here, electrostatic interaction refers to hydrogen bonding, ionic interaction (ionic bonding), etc. Therefore, the second coating layer can also be said to be a layer of aliphatic monocarboxylic acid that is bonded to the amine compound of the first coating layer via electrostatic interaction. Ideally, the amine compound of the first coating layer and the aliphatic monocarboxylic acid react in a 1:1 ratio to form the second coating layer, but in practice, such an ideal state is difficult to achieve. Therefore, some of the amine compound of the first coating layer may not be bonded to the aliphatic monocarboxylic acid, and the second coating layer may include portions where two or more molecules of the aliphatic monocarboxylic acid are stacked and adsorbed by physical adsorption or the like.

[0036] Therefore, the second coating layer, like the first coating layer, includes not only a layer in which the aliphatic monocarboxylic acid uniformly coats the first coating layer, but also a coating layer formed so that there are some portions where the aliphatic monocarboxylic acid is not bonded to the amine compound.

[0037] The fact that the aliphatic monocarboxylic acid is adsorbed to form the second coating layer is confirmed by IR measurement of the copper particle surface, as described below, in the same manner as the first coating layer.

[0038] Furthermore, when there is a portion of the copper particle surface to which the amine compound is not bonded, there may be a portion on the copper particle surface where the aliphatic monocarboxylic acid is directly adsorbed, and such surface-coated copper fillers are also within the scope of the present invention.

[0039] The amine compound forming the first coating layer is an amine compound represented by formula (1). The amine compound has the effect of removing oxides from the copper particle surface and inhibiting oxidation due to the reducing amino group. The amine compound represented by formula (1) is not particularly limited and can be used. Specific examples include hydrazine, methylenediamine, ethylenediamine, 1,3-propanediamine, dimethylenetriamine, trimethylenetetramine, diethylenetriamine, triethylenetetramine, dipropylenetriamine, and tripropylenetetramine. The first coating layer may be formed using one or more of these amine compounds.

[0040] If the value of m in formula (1) is 4 or greater, the number of amino groups per unit area on the copper particle surface that contribute to chemical bonding and reduction decreases, which may result in insufficient desired oxidation resistance and increased surface oxidation of copper. Furthermore, if n in formula (1) is 3 or greater, the molecular chain becomes too long, which creates steric hindrance with adjacent amine compounds during coating, preventing sufficient coating of the copper particle surface. This, in turn, may result in insufficient desired oxidation resistance and increased surface oxidation of copper.

[0041] Examples of the aliphatic monocarboxylic acid having 8 to 24 carbon atoms that forms the second coating layer include linear saturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms, linear unsaturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms, branched saturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms, and branched unsaturated saturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms. Specific examples of linear saturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms include caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid, and arachidic acid. Examples of linear unsaturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms include myristoleic acid, palmitoleic acid, petroselinic acid, and oleic acid. Examples of branched saturated aliphatic monocarboxylic acids having 8 to 24 carbon atoms include 2-ethylhexanoic acid. The aliphatic monocarboxylic acids may be used alone or in combination of two or more.

[0042] If the carbon number is 7 or less, the alkyl chain length is short, which may result in poor dispersibility of the surface-coated copper filler. On the other hand, if the carbon number is 25 or more, the hydrophobicity of the aliphatic monocarboxylic acid increases, which increases compatibility with the binder, and when a conductive composition is formed, the aliphatic monocarboxylic acid is likely to be released from the second coating layer and leach into the binder.

[0043] From the viewpoint of further improving the dispersibility of the surface-coated copper filler in the conductive composition and reducing the amount of free aliphatic monocarboxylic acid in the conductive composition, an aliphatic monocarboxylic acid having 10 to 18 carbon atoms is preferred. Furthermore, a straight-chain saturated aliphatic monocarboxylic acid is more likely to have a close-packed structure than a branched-chain or unsaturated aliphatic monocarboxylic acid, resulting in a coating with fewer voids, so it is more preferable to use a straight-chain saturated aliphatic monocarboxylic acid having 10 to 18 carbon atoms for the coating.

[0044] As described above, the surface-coated copper filler comprises copper particles, a first coating layer of an amine compound that coats the surface of the copper particles, and a second coating layer of an aliphatic monocarboxylic acid that is formed on the first coating layer.

[0045] Furthermore, the amine compound contained in the first coating layer has a higher coordination ability with copper atoms than aliphatic monocarboxylic acids due to the effect of the lone electron pair of the nitrogen in the amino group, and is therefore more strongly bonded to the copper particle surface than aliphatic monocarboxylic acids, resulting in a higher surface coverage than aliphatic monocarboxylic acids. Furthermore, the amine compound is likely to form bonds with aliphatic monocarboxylic acids through electrostatic interactions. Here, electrostatic interactions refer to hydrogen bonds and ionic interactions, as described above. Therefore, by coating the copper particle surface with an amine compound with a high surface coverage and then further coating the outer surface with aliphatic monocarboxylic acids, the aliphatic monocarboxylic acids can be coated on the copper particles at a higher surface coverage than by directly coating the copper particles with the aliphatic monocarboxylic acids. Therefore, the surface-coated copper filler has higher oxidation resistance than copper fillers coated only with aliphatic monocarboxylic acids, due to the oxidation-inhibiting effect of the amine compound and the high coverage of the aliphatic monocarboxylic acids.

[0046] Furthermore, as described above, it is believed that the carboxyl group of the aliphatic monocarboxylic acid bonds to the amino group of the amine compound through electrostatic interaction. That is, it is believed that the hydrophilic carboxyl group faces the first coating layer of the amine compound, and the hydrophobic saturated or unsaturated aliphatic hydrocarbon group faces outward to form a second coating layer. Therefore, a surface-coated copper filler having a second coating layer of an aliphatic monocarboxylic acid can suppress copper filler aggregation and detachment of the amine compound more effectively than a copper filler in which copper particles are coated only with an amine compound.

[0047] As mentioned above, it is possible to confirm that a surface-coated copper filler has a first coating layer of an amine compound and a second coating layer of an aliphatic monocarboxylic acid by measuring the IR spectrum of the surface-coated copper filler. As an example, the results of measuring the IR spectrum of a surface-coated copper filler having a first coating layer of diethylenetriamine and a second coating layer of lauric acid are as follows.

[0048] When diethylenetriamine is measured alone, the NH bending vibration peak is 1598 cm-1 The peak of the NH bending vibration observed in the surface-coated copper filler appears at 1576 cm -1 This indicates that diethylenetriamine is coordinated to the surface of the copper particles. Also, the peak of the C=O stretching vibration of lauric acid shifted to 1700 cm -1 The carboxylate anion (-COO - ) peak at 1417 cm -1 This indicates that lauric acid exists in a state bound to the amine compound through electrostatic interaction.

[0049] <Method for manufacturing surface-coated copper filler> A method for producing a surface-coated copper filler according to an embodiment of the present invention will now be described. The production method can include, for example, the following steps (A) to (C).

[0050] (1) Process (A) Step (A) involves immersing copper particles in a solution containing 100 parts by mass of the amine compound represented by formula (1) and 0.01 to 10 parts by mass of a metal halide or ammonium halide derivative (hereinafter, both may be referred to as "halogen compound"). In this step, impurities on the copper particle surface can be removed and the copper particle surface can be coated with the amine compound while the copper particles are dispersed. Unlike the case of Patent Document 2, the coexistence of an amine compound and a halogen compound at a predetermined mass ratio and mixing them with the copper particles can suppress the occurrence of copper particle aggregation. Note that "impurities on the copper particle surface" refers to components attached to the surface of the copper particles, such as copper salts, dispersants, and copper oxide, which are derived from the production process.

[0051] Specifically, copper particles are added to a solution containing both an amine compound and a halogen compound in a predetermined ratio to form a mixture a, and the mixture a is stirred to suppress the aggregation of the copper particles while simultaneously removing impurities from the copper particle surface and forming a first coating layer of the amine compound on the copper particle surface. The stirring method is not particularly limited, and any stirring method can be used, as long as the copper particles are stirred sufficiently to bring the amine compound and halogen compound into contact with each other. For copper particles with a small average particle size (approximately 5 to 10 μm), a method of suppressing aggregation can be selected in which the copper particles are mixed with an amine compound solution that does not contain a halogen compound, stirred for a certain period of time, the copper particles are thoroughly dispersed in the solution, and then the halogen compound is added.

[0052] Ideally, it is desirable to form a first coating layer in which the amine compound uniformly coats the copper particle surface in the form of a monomolecular film, and it is preferable to form a good first coating layer that is as close to ideal as possible. Therefore, the mixing ratio of the copper particles and the amine compound in step (A) is preferably a ratio suitable for forming this good first coating layer.

[0053] Specifically, although it depends on the particle size of the copper particles, the amount of the amine compound is preferably 1 to 500 parts by mass per 100 parts by mass of copper particles, more preferably 10 to 350 parts by mass, even more preferably 30 to 250 parts by mass, and particularly preferably 50 to 150 parts by mass, in order to prevent free amine compound from remaining in the surface-coated copper filler. Since the smaller the particle size of the copper particles, the larger the surface area per unit mass, it is preferable to increase the amount of the amine compound mixed with smaller particle sizes.

[0054] The mixing ratio of the halogen compound also depends on the particle size of the copper particles, but is generally 0.01 to 30 parts by mass, preferably 0.01 to 25 parts by mass, more preferably 0.02 to 10 parts by mass, and even more preferably 0.05 to 5 parts by mass, of the halogen compound per 100 parts by mass of the amine compound. If the halogen compound is more than 30 parts by mass, the halogen compound may remain in the surface-coated copper filler and affect the composition as an impurity. If the halogen compound is less than 0.01 part by mass, the amount is too small to achieve sufficient impurity removal and oxidation resistance.

[0055] The halogen compound used is a metal halide or an ammonium halide derivative. These are preferred because they inhibit the aggregation of copper particles in the presence of an amine compound and are less corrosive to SUS reactors from the viewpoint of industrial usefulness. Furthermore, the halogen atom contained in the halogen compound may be any of bromine, fluorine, and iodine atoms, but chlorine atoms are particularly preferred from the viewpoint of oxidation resistance and availability. Furthermore, from the viewpoint of industrial availability, the metal halide is preferably at least one selected from copper chloride, iron chloride, potassium chloride, calcium chloride, sodium chloride, zinc chloride, magnesium chloride, and lithium chloride, and the ammonium halide derivative is preferably at least one selected from ammonium halide derivatives represented by formula (2) (hereinafter sometimes simply referred to as "ammonium halide derivatives").

[0056] [ka]

[0057] [In formula (2), a is an integer of 0 to 3, b is an integer of 0 to 3, and a+b=3.]

[0058] Specific examples of the ammonium halide derivatives represented by formula (2) include ammonium chloride (a:3, b:0), methylammonium chloride (a:2, b:1), dimethylammonium chloride (a:1, b:2), and trimethylammonium chloride (a:0, b:3).

[0059] Among the above halogen compounds, when the copper particle surface has a large amount of oxides or fatty acids or other deposits, ammonium halide derivatives are more preferred, and among these, ammonium chloride is particularly preferred from the standpoint of its impurity removal effect and availability.

[0060] The solvent for dissolving the amine compound and halogen compound is not particularly limited as long as it dissolves the amine compound, has good wettability with copper particles, and does not react with the amine compound and aliphatic monocarboxylic acid. Preferably, the solvent contains one or more selected from alcohols, ketones, ethers, nitriles, sulfoxides, pyrrolidones, and water. Specific examples of alcohols include methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, 1-pentanol, tert-amyl alcohol, ethylene glycol, butoxyethanol, methoxyethanol, ethoxyethanol, propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether. Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of ethers include diethyl ether and dibutyl ether. Examples of nitriles include acetonitrile, propionitrile, butyronitrile, and isobutyronitrile. Examples of sulfoxides include dimethyl sulfoxide, etc. Examples of pyrrolidones include 1-methyl-2-pyrrolidone, etc.

[0061] The treatment temperature for forming the first coating layer should be a temperature at which the coating of the amine compound proceeds without solidifying the solution, and should be a temperature at which oxidation of copper is minimized. Specifically, the treatment is preferably carried out at a temperature in the range of -10 to 120°C. From the viewpoint of further increasing the coating rate and further suppressing oxidation, the treatment is more preferably carried out at a temperature in the range of 30 to 100°C.

[0062] Although the treatment time is not particularly limited, 5 minutes to 10 hours is preferable because it allows sufficient coating of the amine compound and prevents the salt of the amine compound and carbon dioxide formed by the incorporation of carbon dioxide from the atmosphere from remaining as an impurity in the surface-coated copper filler. Furthermore, 5 minutes to 3 hours is more preferable from the viewpoint of production costs.

[0063] Furthermore, in order to prevent the formation of a salt between the amine compound and carbon dioxide in the air and the oxidation of copper, it is preferable to perform step (A) in an inert gas atmosphere, for example, by bubbling an inert gas. Specific examples of inert gases include nitrogen, argon, and helium. The bubbling may also serve as stirring; that is, if sufficient contact between the copper particles and the amine compound can be achieved by bubbling the inert gas alone, stirring may not be necessary.

[0064] (2) Process (A-2) Step (A-2) is a step of removing the solution containing free amine compounds and halogen compounds not used in forming the first coating layer from the mixture a to obtain intermediate 1 containing first-coated copper particles. Specifically, this step removes excess solution containing amine compounds and halogen compounds. Complete removal of the excess amine compounds and halogen compounds is not necessary; intermediate 1 can be obtained by natural sedimentation, centrifugation, or filtration. Small amounts of free amine compounds, halogen compounds, and solvent are contained in intermediate 1, and although they may be directly transferred to the next step (B), removal is preferred. When removing the small amounts of free amine compounds, halogen compounds, and solvent in intermediate 1, a preferred method, from the viewpoint of ease of operation, involves allowing the copper particles on which the first coating layer has been formed to settle by natural sedimentation, followed by decantation or aspirator suction to remove the supernatant solution containing the amine compounds and halogen compounds. The resulting intermediate 1 exhibits reduced aggregation of copper particles, which, compared to the method described in Patent Document 2, suppresses an increase in bulk density due to the lack of aggregation of copper particles. Therefore, for example, the efficiency of liquid replacement by decantation can be improved compared to conventional methods.

[0065] Furthermore, the precipitate or the residue after separation may be washed with a solvent capable of dissolving both the amine compound and the aliphatic monocarboxylic acid having 8 to 24 carbon atoms to obtain intermediate 1. This washing is preferable because it can reduce the amount of free amine compound mixed in.

[0066] Intermediate 1 may be dried to reduce the amount of solvent contained therein (the solvent of the solution containing the amine compound and the halogen compound). However, drying at this stage may oxidize the copper surface, so it is preferable not to dry, especially by heating.

[0067] If a large amount of free amine compound remains in Intermediate 1, the amine compound forms a salt with carbon dioxide in the atmosphere or an aliphatic monocarboxylic acid, which produces impurities that adversely affect the conductivity of the conductive composition, which is undesirable.

[0068] Therefore, the amount of the amine compound in intermediate 1, as the total amount of the amine compound forming the first coating layer and the free amine compound, is preferably 10% by mass or less of the amount of copper particles. It is more preferable to set it to 1.0% by mass or less so as not to affect the formation of the second coating layer of aliphatic monocarboxylic acid. The amount of the amine compound in intermediate 1 can be determined by measuring the amount of the amine compound in the supernatant, etc., and calculating the difference between this amount and the amount of the amine compound used in step (A).

[0069] Furthermore, the amount of halogen compounds in intermediate 1 is preferably 1% by mass or less of the amount of copper particles, and more preferably 0.01% or less. If a large amount of halogen compounds remain, they may react with the copper oxide remaining on the copper surface to form copper halides, which may interfere with subsequent processing.

[0070] (3) Process (B) Step (B) is a step of immersing the copper particles that have been subjected to step (A) in a solution containing an aliphatic monocarboxylic acid having 8 to 24 carbon atoms. In this embodiment, copper particles that have been subjected to step (A-2) are used. In step (B), a second coating layer of an aliphatic monocarboxylic acid having 8 to 24 carbon atoms can be formed on the first coating layer formed on the surface of the copper particles.

[0071] Specifically, an aliphatic monocarboxylic acid solution containing an aliphatic monocarboxylic acid having 8 to 24 carbon atoms is added to the intermediate 1 to prepare mixture b, and the mixture b is stirred to form a second coating layer of the aliphatic monocarboxylic acid on the first coating layer. Alternatively, the intermediate 1 may be added to the aliphatic monocarboxylic acid solution to prepare mixture b. The stirring method is not particularly limited, and may be any ordinary stirring method using a known stirrer such as a paddle stirrer or line mixer, as long as the copper particles on which the first coating layer has been formed are stirred sufficiently to bring the aliphatic monocarboxylic acid into contact with each other.

[0072] Ideally, the amine compound and the aliphatic monocarboxylic acid in the first coating layer bond to form a second coating layer in which the aliphatic monocarboxylic acid uniformly coats the first coating layer in the form of a monomolecular film, and it is preferable to form a good second coating layer that is as close to ideal as possible. Therefore, the mixing ratio of the copper particles and the aliphatic monocarboxylic acid in step (B) is preferably a ratio suitable for forming this good second coating layer.

[0073] Specifically, although it depends on the particle size of the copper particles, the amount of aliphatic monocarboxylic acid is preferably 0.1 to 50 parts by mass per 100 parts by mass of copper particles. 0.5 to 20 parts by mass is more preferable in terms of suppressing free aliphatic monocarboxylic acid from remaining in the surface-coated copper filler. Since the smaller the particle size of copper particles, the larger the surface area per unit mass, it is preferable to increase the amount of aliphatic monocarboxylic acid mixed with copper particles having a smaller particle size.

[0074] The solvent used to prepare the solution of aliphatic monocarboxylic acid having 8 to 24 carbon atoms is not particularly limited as long as it dissolves the aliphatic monocarboxylic acid, has good wettability with the copper particles and the copper particles on which the first coating layer is formed, and does not react with the amine compound and the aliphatic monocarboxylic acid. A solvent that can be easily dried and removed in the drying step of step (C) described below is preferred.

[0075] Preferred solvents include one or more selected from alcohols, ketones, ethers, nitriles, sulfoxides, and pyrrolidones. Specific examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, tert-amyl alcohol, ethylene glycol, butoxyethanol, methoxyethanol, ethoxyethanol, propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol monomethyl ether. Ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone. Ethers include diethyl ether and dibutyl ether. Nitriles include acetonitrile, propionitrile, butyronitrile, and isobutyronitrile. Sulfoxides include dimethyl sulfoxide. Pyrrolidones include 1-methyl-2-pyrrolidone.

[0076] The treatment temperature for forming the second coating layer may be any temperature at which the coating of the aliphatic monocarboxylic acid proceeds without solidifying the solution, and specifically, is preferably in the range of −10 to 80° C. From the viewpoints of further increasing the coating rate and suppressing the elimination of the aliphatic monocarboxylic acid that has formed the second coating layer, it is more preferable to perform the treatment at a temperature in the range of 10 to 60° C.

[0077] The treatment time is not particularly limited, but is preferably 5 minutes to 10 hours, since it allows the aliphatic monocarboxylic acid to be sufficiently coated and the components released as the copper-amine compound-aliphatic monocarboxylic acid complex are less likely to remain in the surface-coated copper filler. Furthermore, from the viewpoint of production costs, 5 minutes to 3 hours is more preferable.

[0078] Furthermore, it is preferable to carry out step (B) in an inert gas atmosphere, for example, by bubbling an inert gas, in order to prevent the amine compound of the first coating layer or a small amount of free amine compound from forming a salt with carbon dioxide in the atmosphere and to prevent oxidation of the copper. Specific examples of inert gases include nitrogen, argon, and helium. The bubbling may also serve as stirring; that is, as long as the inert gas bubbling alone is sufficient to bring the copper particles on which the first coating layer has been formed into contact with the aliphatic monocarboxylic acid, stirring may not be necessary.

[0079] (4) Process (B-2) Step (B-2) is a step of removing from the mixture b an aliphatic monocarboxylic acid solution (which may contain an amine compound or halogen compound derived from step A-2) containing free aliphatic monocarboxylic acid not used in forming the second coating layer, thereby obtaining intermediate 2 containing copper particles on which first and second coating layers have been formed. At this time, it is not necessary to completely remove the free aliphatic monocarboxylic acid; a small amount may remain (the same applies to the amine compound or halogen compound derived from step A-2, if present). Specifically, intermediate 2 can be obtained by filtration. Known filtration methods can be used, and examples include natural filtration, reduced pressure filtration, and pressure filtration.

[0080] (5) Process (C) Step (C) is a step of drying the intermediate 2 to obtain a surface-coated copper filler.

[0081] The method for drying intermediate 2 is not particularly limited, but examples include vacuum drying and freeze drying. Vacuum drying is preferred from the standpoint of production costs, and the drying temperature is preferably 20 to 120°C from the standpoints of drying efficiency and suppressing the acid value of copper. The degree of vacuum, drying temperature, and drying time may be determined appropriately depending on the combination of each condition and the type of solvent used, and are preferably conditions that allow drying to the extent that the amount of solvent in the surface-coated copper filler after drying is 1% by mass or less.

[0082] In this manner, a particulate surface-coated copper filler can be produced. Furthermore, the surface-coated copper filler obtained in this manner contains few agglomerated copper particles, and the copper particles have a first coating layer of an amine compound and a second coating layer of an aliphatic monocarboxylic acid, and have oxidation resistance and dispersibility equivalent to those of conventional copper fillers. Therefore, such surface-coated copper fillers are suitable, for example, as components of the conductive compositions described below.

[0083] <Conductive composition> The conductive composition according to an embodiment of the present invention will be described.

[0084] The conductive composition contains 10 to 95 mass % of the above-mentioned surface-coated copper filler in the conductive composition. The surface-coated copper filler can be any of those described above, and can be appropriately selected and used depending on the application of the conductive composition. When the surface-coated copper filler is a nanoparticle conductive composition, the copper particles used in producing the surface-coated copper filler preferably have an average particle size of 5 to 100 nm. This average particle size is suitable when the conductive composition is in the form of an ink, as described below.

[0085] In addition to the surface-coated copper filler, the conductive composition may contain various components commonly used in the art, such as a binder and a solvent.

[0086] Binders that can be used in the conductive composition may be any known binders that are used in, for example, metal pastes, and examples thereof include thermosetting resins that harden when heat is applied, photocurable resins that harden when light is applied, and thermoplastic resins.

[0087] Examples of thermosetting resins include epoxy resins, melamine resins, phenolic resins, silicone resins, oxazine resins, urea resins, polyurethane resins, unsaturated polyester resins, vinyl ester resins, xylene resins, acrylic resins, oxetane resins, diallyl phthalate resins, oligoester acrylate resins, bismaleimide triazine resins, furan resins, etc. Examples of photocurable resins include silicone resins, acrylic resins, imide resins, urethane resins, oxetane resins, etc.

[0088] Examples of thermoplastic resins include polyvinyl chloride, polyethylene, polypropylene, polystyrene, acrylonitrile-butadiene-styrene copolymer resin, acrylonitrile-styrene copolymer resin, polymethyl methacrylate, polyvinyl alcohol, polyvinylidene chloride, polyethylene terephthalate, polyamide, polyacetal, polycarbonate, polyphenylene ether, polybutylene terephthalate, polyvinylidene fluoride, polysulfone resin, polyethersulfone resin, polyphenylene sulfide resin, polyarylate, apolyamideimide, polyetherimide, polyetheretherketone, polyamide, polyimide, liquid crystal polymer, and polytetrafluoroethylene.

[0089] These binders may be used alone or in combination of two or more.

[0090] Solvents that can be used in the conductive composition are not particularly limited as long as they have good wettability with the surface-coated copper filler. Examples include alcohols, ethers, ketones, nitriles, aromatic compounds, and water. Examples of alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, tert-amyl alcohol, 1-hexanol, 1-octanol, 2-ethyl-1-hexanol, ethylene glycol, butoxyethanol, methoxyethanol, ethoxyethanol, ethyl carbitol, ethyl carbitol acetate, butyl carbitol, butyl carbitol acetate, propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, and terpineol. Examples of ethers include acetoxymethoxypropane, phenyl glycidyl ether, and ethylene glycol glycidyl. Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and γ-butyrolactone. Examples of nitriles include acetonitrile, propionitrile, butyronitrile, and isobutyronitrile. Examples of aromatic solvents include benzene, toluene, and xylene. Any one of these solvents may be used alone, or two or more may be mixed and used.

[0091] Specific examples of the form of the conductive composition include a paste in which the surface-coated copper filler is dispersed in a binder, an ink in which the surface-coated copper filler is dispersed in a solvent, etc. The contents of the binder and solvent can be selected depending on the form of the conductive composition.

[0092] When the conductive composition is in the form of a paste, the content of the binder in the conductive composition is preferably 10 to 400 parts by mass per 100 parts by mass of the surface-coated copper filler. When the conductive composition in the form of a paste is used to form fine wiring, it is necessary to make the cured product of the conductive composition have a lower volume resistivity. To achieve a low volume resistivity, it is necessary to increase the content of the surface-coated copper filler in the conductive composition and make it easier for the particles of the surface-coated copper filler to approach each other, so the amount of binder is more preferably 20 to 100 parts by mass.

[0093] When the conductive composition is in the form of ink, the content of the solvent in the conductive composition is preferably 10 to 600 parts by mass per 100 parts by mass of the surface-coated copper filler. This content ratio is suitable for nanoparticle ink in which the surface-coated copper filler is nanoparticles.

[0094] The conductive composition may contain various known additives, such as an oxide film remover, an antioxidant, a leveling agent, a viscosity modifier, a dispersant, etc. If the conductive composition is in the form of a paste, it may contain a solvent as a diluent within a range that exhibits paste properties, and if the conductive composition is in the form of an ink, it may contain a binder within a range that exhibits ink properties.

[0095] The conductive composition contains the above-mentioned surface-coated copper filler. As described above, the surface-coated copper filler has few aggregates, so that, for example, when a pattern is drawn by screen printing or inkjet printing, clogging of the screen or inkjet ink is suppressed, resulting in excellent printability. In addition, the surface-coated copper filler has good oxidation resistance and dispersibility, and its cured product has a volume resistivity equivalent to that of conventional fillers.

[0096] The conductive composition can be produced by known methods according to its form. Further, a cured product can be obtained by curing the conductive composition by a known method. This cured product is obtained by applying, for example, light or heat to the conductive composition. At this time, shrinkage occurs due to the volatilization of the solvent and the curing of the binder, and the copper particles approach each other due to this shrinkage, thereby exhibiting conductivity. Also, conductivity is exhibited by sintering some of the copper particles.

Examples

[0097] Hereinafter, embodiments of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0098] The measurement methods and evaluation methods used in each Example and Comparative Example are shown below.

[0099] <Volume ratio of copper particles in the treatment liquid> In Examples 1-1 to 1-13 and Comparative Examples 1-2 to 1-5, the copper particles and the solution were filtered using a filter with respect to 20 g of the dispersion liquid after Step [A]. Subsequently, 5 g of the filtered copper particles and 8 g of the filtered solution were weighed into a 10 mL vial, the lid was closed, and after sufficiently stirring, the mixture was allowed to stand for 30 minutes. When sedimentation of the copper particles was confirmed by standing, the height of the liquid surface including the sediment and the height of the sediment were measured. The value obtained by multiplying 100 by the value obtained by dividing the height of the sediment by the height of the liquid surface including the sediment was taken as the volume ratio of the copper particles in the treatment liquid.

[0100] It is assumed that the smaller the above volume ratio, the better the decantation property. The evaluation criteria were that those with 25% or less were qualified "○" and those greater than 25% were unqualified "×".

[0101] <IR spectrum analysis> Measuring instrument model: FT / IR-6100 manufactured by JASCO Corporation Measurement method: ATR method, resolution; 2 cm -1 , Number of integrations; 80 times,

[0102] <Blocking ratio of the screen plate after printing> (Evaluation method) Using a screen printing machine (MT-320, manufactured by Micro-Tech Co., Ltd.), a screen plate (SUS 200 mesh) with a 1 cm square solid film pattern was used to print the conductive compositions obtained in the Examples and Comparative Examples 10 times at 50 mm / sec onto a polyethylene terephthalate (PET) substrate. After printing, the proportion of the conductive composition remaining in the 1 cm square mesh portion of the solid film pattern in the screen plate was evaluated using a micromicroscope.

[0103] (Evaluation of blockage rate) After printing as described above, the 1 cm square peta film pattern on the screen was observed at 100x magnification using a micro microscope (Dino-Lite AM4113), and the percentage of all mesh grids in the field of view that were filled with paste was visually counted and calculated. The observation was repeated four times at different locations, and the average was calculated.

[0104] <Volume resistivity evaluation> (Sample preparation) The conductive compositions obtained in the Examples and Comparative Examples were applied to alkali-free glass using a metal mask to form a pattern measuring 1 cm wide x 3 cm long x 30 μm thick. The patterned glass was heated at 150°C for 15 minutes to produce a cured product. The volume resistivity of the resulting cured product was measured using the following method.

[0105] (Measurement method) The volume resistivity was measured and evaluated in accordance with JIS K 7194. Measuring instrument model: Resistivity meter MCP-T610 (manufactured by Mitsubishi Chemical Corporation), measurement conditions: 4-probe method, Probe: ASP, Sample size: 50mm x 50mm, Film thickness: 1 to 30μm, Number of measurements: 5,

[0106] <1. Manufacturing of surface-coated copper filler> Surface-coated copper fillers were produced using the components shown in Tables 1 to 4 and under the copper particle treatment conditions shown in Tables 5A and 5B, except that Comparative Example 1-1 is raw copper particles that were not surface-treated.

[0107] (Example 1-1) [Process (A)] 75 g of water, 300 g of ethylenediamine, and 0.2 g of ammonium chloride were placed in a flask and stirred at 25°C while bubbling with nitrogen for 30 minutes. Then, 100 g of copper particles (1400YP, manufactured by Mitsui Mining & Smelting, average particle size: 6 μm) were added, and the temperature was raised to 60°C. Stirring was continued at this temperature for 60 minutes. Stirring was carried out using a mechanical stirrer at a rotation speed of 150 rpm. Stirring in subsequent steps was also carried out using the same stirring device at the same rotation speed. After stirring for 60 minutes, 20 g of the dispersion was sampled, and the volume ratio of copper particles in the treatment solution was measured. The results are shown in Table 5A.

[0108] [Process (A-2)]

[0109] After stopping the stirring and leaving it to stand for 15 minutes, approximately 325 g of the supernatant was removed. Next, 150 g of ethanol was added to the precipitate as a washing solvent, and the mixture was stirred at 30°C for 3 minutes. After stopping the stirring and leaving it to stand for 15 minutes, approximately 150 g of the supernatant was removed, and intermediate 1 was obtained.

[0110] [Process (B)]

[0111] 150 g of a 10% by mass solution of capric acid in ethanol was added to Intermediate 1, and the mixture was stirred at 30° C. for 30 minutes. [Process (B-2)]

[0112] After stirring was stopped, the ethanol solution of capric acid was removed by filtration under reduced pressure to obtain intermediate 2. The filtration under reduced pressure was carried out by applying a pressure of 5C filter paper to a Kiriyama funnel using a diaphragm pump. [Process (C)]

[0113] A surface-coated copper filler was obtained by drying Intermediate 2 under reduced pressure for 6 hours at 25° C. The drying under reduced pressure was carried out by placing Intermediate 2 in a vacuum oven and reducing the pressure in the oven with an oil pump.

[0114] The IR spectrum of the surface of the obtained surface-coated copper filler was measured under the conditions described above, with the results shown below. When ethylenediamine used for coating was measured alone, the peak of the NH bending vibration was 1590 cm -1 The peak of the NH bending vibration observed in the surface-coated copper filler appears at 1562 cm -1 This indicates that ethylenediamine is coordinated to the surface of the copper particles. Also, the peak of the C=O stretching vibration of capric acid shifted to 1700 cm -1 The carboxylate anion (-COO - ) peak at 1413 cm -1 This indicates that capric acid exists in a state of binding with the amine compound through electrostatic interaction.

[0115] From the above IR spectrum, it can be determined that the surface-coated copper filler obtained in Example 1-1 has both the ethylenediamine in the first coating layer and the capric acid in the second coating layer chemically bonded to form each coating layer.

[0116] (Examples 1-2 to 1-13) Surface-coated copper fillers were obtained and subjected to IR measurement in the same manner as in Example 1-1, except that the copper particle treatment conditions shown in Table 5A were used. Furthermore, the volume fraction of copper particles in the treatment solution after step (A) was evaluated in the same manner as in Example 1-1. The results are shown in Table 5A. The IR measurement results for the surface-coated copper fillers obtained in Examples 1-2 to 1-13 confirmed that the amine compound in the first coating layer and the aliphatic monocarboxylic acid in the second coating layer were both chemically bonded to form respective coating layers.

[0117] (Comparative Example 1-2) [Pretreatment process] An aqueous ammonium chloride solution was prepared by dissolving 10 g of ammonium chloride in 200 g of water, and 100 g of copper particles (1400YP, manufactured by Mitsui Mining & Smelting, average particle size: 6 μm) was added to the aqueous ammonium chloride solution. The mixture was stirred at 30°C for 60 minutes under nitrogen bubbling, and the copper particles were then filtered off using a filter. As a result of this treatment, copper chloride adhered to the surfaces of the copper particles, as described in Patent Document 2.

[0118] [Process (A)~(C)] A surface-coated copper filler was obtained and subjected to IR measurement in the same manner as in Example 1-1, except that copper particles that had been pretreated as described above were used and the copper particle treatment conditions shown in Table 5B were used. Furthermore, the volume fraction of the copper particles in the treatment solution described above after step (A) was evaluated in the same manner as in Example 1-1. The results are shown in Table 5B. The IR measurement of the surface-coated copper filler obtained in Comparative Example 1-2 confirmed that the amine compound in the first coating layer and the aliphatic monocarboxylic acid in the second coating layer both formed coating layers bonded by chemical bonds.

[0119] (Comparative Examples 1-3 to 1-5) A surface-coated copper filler was obtained and subjected to IR measurement in the same manner as in Example 1-1, except that the copper particle treatment conditions shown in Table 5B were used. Furthermore, the volume fraction of the copper particles in the treatment solution after step (A) was evaluated in the same manner as in Example 1-1. The results of the IR measurement confirmed that the surface-coated copper filler obtained in Comparative Example 1-3 had the predetermined first and second coating layers, the surface-coated copper filler obtained in Comparative Example 1-4 had only a coating layer of an aliphatic monocarboxylic acid, and the surface-coated copper filler obtained in Comparative Example 1-5 had only a coating layer of an amine compound.

[0120] [Table 1]

[0121] [Table 2]

[0122] [Table 3]

[0123] [Table 4]

[0124] [Table 5A]

[0125] [Table 5B]

[0126] As shown in Tables 5A and 5B, the proportion of sediment in Examples 1-1 to 1-13 was around 20%, which was a passing grade of "○", whereas the sample pretreated in Comparative Example 1-2 had a bulky sediment proportion of 40%, which resulted in poor decantation properties.

[0127] Example 2-1 20 g of the surface-coated copper filler prepared in Example 1-1 was mixed with 5.7 g of a resol-type phenolic resin (PL-5208, manufactured by Gunei Chemical Industry Co., Ltd.) as a binder, 0.3 g of N,N'-bis(salicylidene)ethylenediamine as an additive (oxide film remover), and 1.0 g of terpineol as a diluent. The mixture was then mixed at room temperature for 30 seconds at 1500 rpm using a planetary mixer (ARV-310, manufactured by Thinky Corporation) for primary mixing. The mixture was then mixed five times at room temperature with a roll distance of 5 μm using a three-roll mill (EXAKT-M80S, manufactured by Nagase Screen Printing Research Institute Co., Ltd.) for secondary mixing to produce a conductive composition. The resulting conductive composition was used to evaluate the blockage rate and volume resistivity of the screen stencil after printing. The evaluation results are shown in Table 6A.

[0128] (Examples 2-2 to 2-13, Comparative Examples 2-1 to 2-5) A conductive composition was prepared in the same manner as in Example 2-1, except that the blending ratios shown in Tables 6A and 6B were used, and the blockage rate and volume resistivity of the screen stencil after printing were evaluated. The evaluation results are shown in Tables 6A and 6B.

[0129] [Table 6A]

[0130] [Table 6B]

[0131] Tables 6A and 6B reveal the following: The conductive compositions of Examples 2-1 to 2-13 all had a clogging rate of 5% or less, indicating that the conductive composition did not clog the screen stencil and had good printability. On the other hand, Comparative Examples 2-1 to 2-5, including the untreated ones, had a high clogging rate on the screen stencil, indicating that clogging occurred. Furthermore, the volume resistivities of Examples 2-1 to 2-13 were equivalent to those of Comparative Example 2-2, which contained the surface-coated copper filler of Comparative Example 1-2 obtained by a method corresponding to the method described in Patent Document 2, and it was confirmed that the copper particles had oxidation resistance. On the other hand, Comparative Examples 2-3 to 2-5 had high volume resistivities and poor oxidation resistance.

Claims

1. (A) a step of immersing copper particles in a solution containing 0.01 to 30 parts by mass of a metal halide or an ammonium halide derivative per 100 parts by mass of an amine compound represented by formula (1); 【Chemistry 1】 [In formula (1), m is an integer of 0 to 3, n is an integer of 0 to 2, and when n=0, m is any of 0 to 3, and when n=1 or n=2, m is any of 1 to 3.] (B) a step of immersing the copper particles that have been subjected to the step (A) in a solution containing an aliphatic monocarboxylic acid having 8 to 24 carbon atoms; A method for producing a surface-coated copper filler, comprising:

2. 2. The method for producing a surface-coated copper filler according to claim 1, wherein the halogen atom contained in the metal halide or the ammonium halide derivative is a chlorine atom.

3. The method for producing a surface-coated copper filler according to claim 1 or 2, wherein the ammonium halide derivative is selected from ammonium halide derivatives represented by formula (2): 【Chemistry 2】 [In formula (2), a is an integer of 0 to 3, b is an integer of 0 to 3, and a+b=3.]

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