JP6776973B2 - Method for manufacturing surface-coated copper filler intermediate - Google Patents

Description

The present invention relates to a method for producing an intermediate that contributes to the production of a surface-coated copper filler used in a conductive composition.

Conventionally, in the field of electronic materials, conductive compositions have been used for applications such as internal electrodes for MLCCs (Multi-layer ceramic Capacitors), through-hole bonding materials for printed circuit boards, and lead-out wiring forming materials for touch panels. in use.
The conductive composition referred to here is a fluid compound typified by silver paste, and a pattern is drawn by screen printing, inkjet printing (hereinafter referred to as IJ printing), or the like to generate light or heat. By adding, it is cured to form a conductive cured product. As the conductive metal used in the conductive composition, silver is often used because it has excellent oxidation resistance and low volume specific resistance. However, silver has a problem that it is expensive and prone to migration. Therefore, in recent years, it has been studied to use copper as a conductive composition, which has the second lowest volume specific resistance after silver, is inexpensive, and has excellent migration resistance.

The surface of conductive copper particles having a particle size of 100 nm to 20 μm, which is generally commercially available and used in conductive compositions, is coated with a fatty acid in order to improve the dispersibility and oxidation resistance of the copper particle powder. There is. However, imparting oxidation resistance by coating with only fatty acids is not sufficient, and the conductive copper particles are oxidized due to the high oxidative property of copper and contain copper oxide on a part of the surface.
Patent Document 1 describes a surface coating in which a first coating layer of an amine compound and a second coating layer of an aliphatic monocarboxylic acid are formed after surface treatment of copper particles with hydrochloric acid in order to prevent oxidation of the surface of the copper particles. Disclosure of copper filler.

International Publication 2016/199811

In Patent Document 1, since copper particles may have impurities such as copper salts, dispersants, and copper oxide derived from the production adhered to the surface, these impurities are removed by hydrochloric acid before surface coating is performed. It discloses that it is preferable to do so.
However, since hydrochloric acid has high corrosiveness to metals, there is a problem that the material of the reaction vessel is limited. If the scale is 10 L or less, it is possible to deal with the corrosiveness of hydrochloric acid by using a glass reaction tank, but if the scale is 10 L or more, it is difficult for the glass reaction tank to withstand the load of the tank filling. Therefore, it is necessary to use a glass-lined SUS reaction tank having both load resistance and corrosion resistance, or a reaction tank made of a material having high corrosion resistance such as Hastelloy. However, the installation of such a reaction tank is not preferable because it leads to an increase in industrial cost.

Therefore, the subject of the present invention is a surface coating having excellent oxidation resistance, which can remove impurities on the surface of copper particles, particularly copper oxide, by using a reaction tank made of SUS which is generally used for the production of chemical products. It is an object of the present invention to provide a method for producing an intermediate for enabling the production of a copper filler at low cost and efficiently.

As a result of diligent studies in view of the above problems, the present inventors have made the copper oxide highly compatible without corroding the SUS by using a specific treatment agent as an alternative to hydrochloric acid in removing copper oxide on the surface of copper particles. We have found that it can be removed, and have completed the present invention.
That is, according to the present invention, the following methods for producing the surface-coated copper filler intermediates [1] and [2] are provided.

［式（１）中、ａは１〜３の整数、ｂは０〜２の整数であり、ａ＋ｂ＝３である。］

［式（２）中、ｍは０〜３の整数、ｎは０〜２の整数であり、ｎ＝０のとき、ｍは０〜３のいずれか、ｎ＝１またはｎ＝２のとき、ｍは１〜３のいずれかである。］ [1]
Copper particles are added to a solution containing the compound represented by the formula (1) to prepare a mixed solution, and copper (I) oxide on the surface of the copper particles is reacted with the compound to prepare copper (I) chloride. And (B) the step of obtaining copper chloride-adhered copper particles having copper (I) chloride adhered to the surface, and (B) the amine represented by the formula (2) by separating the copper chloride-attached copper particles from the mixed solution. The surface of copper particles after cleaning, which is added to an amine compound solution containing a compound to remove copper (I) chloride adhering to the copper chloride-attached copper particles by reaction with the amine compound and from which copper (I) chloride has been removed. A method for producing a surface-coated copper filler intermediate, which comprises a step of forming a coating layer of the amine compound.

[In the equation (1), a is an integer of 1 to 3, b is an integer of 0 to 2, and a + b = 3. ]

[In equation (2), 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 one of 1 to 3. ]

[2]
The method for producing a surface-coated copper filler intermediate according to [1], wherein a carboxylic acid having 1 to 4 carbon atoms is further added to the mixed solution of the step (A).

Since the method for producing a surface-coated copper filler intermediate of the present invention uses the compound represented by the formula (1) for removing copper oxide adhering to the surface of copper particles, a general-purpose SUS reaction tank is used for the removal. Can be used. Thereby, a surface-coated copper filler having excellent oxidation resistance can be produced with high efficiency and low cost via the intermediate obtained by the production method of the present invention, and the surface-coated copper filler is a conductive composition. Can be suitably used for.

It is a figure which shows the spectrum obtained by XPS analysis of the copper chloride attached copper particle after the step (A) of Example 1-1.

Hereinafter, embodiments of the present invention will be described in detail.
First, copper particles used as a raw material for a surface-coated copper filler intermediate produced by the production method of the present invention will be described. Hereinafter, the term copper particles shall refer to raw copper particles unless otherwise specified.
Examples of the copper particles include known copper particles generally used for copper paste and copper ink. The shape may be spherical, plate-shaped, dendritic-shaped, rod-shaped, fibrous, or irregular, such as hollow or porous. Further, it may have a core-shell shape in which the shell is copper and the core is a substance other than copper.
The average particle size of the copper particles is not particularly limited, but when used for a conductive composition, the particle size of the copper particles is adjusted so that the conductive composition can be printed by various printing methods such as IJ printing and screen printing. Control. Specifically, 5 nm to 20 μm is preferable. When suppressing self-aggregation of particles, suppressing oxidation by increasing the surface area, or drawing fine wiring of 100 μm or less, a particle size of 10 nm to 10 μm is preferable. It is preferably 100 nm to 10 μm for use in a conductive composition for screen printing having excellent continuous printability.
Moreover, although one kind of copper particles may be used, copper particles having different shapes and average particle diameters may be mixed and used.
The average particle size of copper particles is a value obtained by additively averaging the feret diameters of 100 randomly selected particles in a microscope image obtained by observing with a transmission electron microscope or a scanning electron microscope. Shall mean.

The method for producing the surface-coated copper filler intermediate of the present invention is a production method including carrying out each of the treatments shown in the following steps (A) and (B) on the copper particles.
Due to its production, copper particles may have an organic dispersant such as a higher fatty acid attached to the surface as one of the impurities. The impurities can be removed by a treatment step using the compound represented by the formula (1) in the step (A), but in order to effectively carry out the desired treatment of the copper particle surface in the step (A), the step ( Prior to A), the following pretreatment for removing the organic dispersant may be carried out. Since the main function of the compound of the formula (1) of the step (A) is the removal of copper oxide, it is preferable to carry out the pretreatment when the adhesion of the organic dispersant is clear.

[Preprocessing]
The method is not particularly limited as long as the organic dispersant can be removed from the surface of the copper particles, and for example, there is a cleaning method using an organic solvent. The type of organic solvent is not particularly limited, but a solvent that has good wettability to the surface of copper particles and is easily removed after a cleaning treatment is preferable, and can be used alone or in combination. Specific examples thereof include alcohols, ketones, hydrocarbons, ethers, nitriles, isobutyronitrile, water, 1-methyl-2-pyrrolidone and the like.

［式（１）中、ａは１〜３の整数、ｂは０〜２の整数であり、ａ＋ｂ＝３である。］ [Step (A)]
In the step (A), copper particles are added to a solution containing the compound represented by the formula (1), a mixed solution in which the copper particles are immersed in the solution is prepared, and oxidation existing on the surface of the copper particles is prepared. This is a step of converting copper (I) into copper (I) chloride by reaction with a compound represented by the formula (1). By this reaction, copper chloride-attached copper particles in which copper (I) chloride is attached to the surface instead of copper (I) oxide are obtained. Hereinafter, the compound represented by the formula (1) will be referred to as a compound (1).

[In the equation (1), a is an integer of 1 to 3, b is an integer of 0 to 2, and a + b = 3. ]

銅粒子表面上の酸化銅（Ｉ）と化合物（１）が反応し、酸化銅（Ｉ）が塩化銅（Ｉ）に変化する。塩化銅（Ｉ）は、非水溶性のため極性溶剤への溶解性が低いので、銅粒子表面上に付着した状態の塩化銅（Ｉ）層が形成される。この塩化銅（Ｉ）層が酸素と銅粒子表面の反応を阻害するため、銅粒子表面の再酸化が抑制される。なお、塩化銅（Ｉ）は、工程（Ｂ）において、式（２）で表されるアミン化合物を含むアミン化合物溶液に溶解して銅粒子表面から除去される。従って、工程（Ｂ）においてアミン化合物の被覆を阻害することはない。
銅粒子表面上に付着する塩化銅（Ｉ）層の存在は、例えばＸＰＳ（Ｘ線光電分光法）により確認することができる。ＸＰＳによる分析には、例えばＪＰＳ-９２００（日本電子株式会社製）を使用することができる。 Most of the copper oxide present on the surface of copper particles is copper (I) oxide, and the mechanism by which this copper (I) oxide reacts with the compound (1) to produce copper (I) chloride is as follows. It is considered that this is due to the reaction shown in 3).

Copper (I) oxide on the surface of copper particles reacts with compound (1), and copper (I) oxide is changed to copper (I) chloride. Since copper (I) chloride is water-insoluble, its solubility in a polar solvent is low, so that a copper (I) chloride layer adhered to the surface of copper particles is formed. Since this copper (I) chloride layer inhibits the reaction between oxygen and the surface of the copper particles, reoxidation of the surface of the copper particles is suppressed. In the step (B), copper (I) chloride is dissolved in an amine compound solution containing the amine compound represented by the formula (2) and removed from the surface of the copper particles. Therefore, the coating of the amine compound is not inhibited in the step (B).
The presence of the copper (I) chloride layer adhering to the surface of the copper particles can be confirmed by, for example, XPS (X-ray photoelectron spectroscopy). For analysis by XPS, for example, JPS-9200 (manufactured by JEOL Ltd.) can be used.

Further, copper (II) oxide present in a trace amount on the surface of copper particles is changed to copper (II) chloride by reacting with compound (1). Copper (II) chloride has high solubility in a polar solvent and is dissolved in a solvent used as a solvent in a solution containing the compound (1), so that it is removed from the surface of copper particles.
Hereinafter, unless otherwise specified, both copper (I) and (II) are referred to as copper oxide, and both copper (I) and (II) are referred to as copper chloride. It shall point.

The following operations can be exemplified as the embodiment of the step (A).
First, a solution containing compound (1) is prepared as follows.
The solvent used as the solvent for the solution is not particularly limited as long as the compound (1) dissolves and has good wettability with copper particles, but is a polar solvent in terms of its action on copper chloride.
Specifically, it is a solvent containing at least one selected from water, alcohols, sulfoxides, pyrrolidones, ionic liquids, ethylene carbonates, propylene carbonates, and nitriles. Specifically, the alcohols include methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, 1-pentanol, tert-amyl alcohol, ethylene glycol, butoxyethanol, methoxyethanol, ethoxyethanol, Examples thereof include propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether and dipropylene glycol monomethyl ether. Examples of the 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 and the like. Examples of pyrrolidones include 1-methyl-2-pyrrolidone.

Ideally, the treatment of step (A) should transform the copper oxide on the surface of the copper particles to copper chloride as completely as possible. Therefore, the mixing ratio of the copper particles and the compound (1) is preferably 0.1 to 100 parts by mass of the compound (1) with respect to 100 parts by mass of the copper particles. If the amount added is less than 0.1 parts by mass, the conversion to copper chloride may be insufficient, and if it is more than 100 parts by mass, the compound (1) is added in a post-process or surface coating. It may remain as an impurity in the copper filler intermediate. In that case, when the surface-coated copper filler is produced from the intermediate, its conductivity may decrease.

The amount of the solvent may be an amount that can disperse the copper particles to such an extent that the surface treatment of the copper particles is satisfactorily performed and can dissolve the compound (1). Specifically, 100 to 1000 parts by mass of the solvent is preferable with respect to 100 parts by mass of the copper particles. If it is less than 100 parts by mass, the dispersion of copper particles may be insufficient. Even if it is more than 1000 parts by mass, there is almost no change in the dispersion effect of the copper particles, and there is no advantage in terms of cost effectiveness.

The solution containing the compound (1) may be prepared and used so as to satisfy the range of the amounts of the compound (1) and the solvent described above with respect to the copper particles.

Copper particles are added to the solution containing the compound (1) prepared in this manner to prepare a mixed solution, and the mixture is stirred to treat the copper particles and change the copper oxide on the surface of the copper particles to copper chloride. The stirring method is not particularly limited, and the copper particles may be stirred so as to be in sufficient contact with the compound (1), and a general stirring method may be used using a known stirring machine such as a paddle stirrer, a line mixer, or a magnetic stirrer. Just do it.

The treatment temperature of the copper particles by the compound (1) [the temperature of the solution containing the compound (1)] is a temperature at which the solution does not solidify or higher and the reaction for changing from copper oxide to copper chloride proceeds sufficiently. Just do it. Specifically, it is preferably carried out in the range of −10 to 120 ° C. It is more preferable to carry out the reaction in the range of 0 to 60 ° C. in terms of the reaction rate and the suppression of side reactions.

The treatment time is not particularly limited, but is preferably 5 minutes to 10 hours, more preferably 5 minutes to 3 hours. If it is less than 5 minutes, the reaction of changing from copper oxide to copper chloride may be insufficient, and since the reaction is almost completed after 10 hours, there is no advantage of spending more time than that.

The main purpose of the step (A) is to change the copper oxide on the surface of the copper particles to copper chloride, but since copper is easily oxidized, copper is unexpectedly changed during the reaction in which copper oxide is changed to copper chloride. Copper on the particle surface may be oxidized. Therefore, the treatment in step (A) is preferably carried out in an atmosphere of an inert gas, and for example, bubbling of the inert gas is preferably performed. Specific examples of the inert gas include nitrogen, argon, and helium. Further, the bubbling may also be used for stirring, that is, if the copper particles and the compound (1) can be sufficiently contacted only by the bubbling of the inert gas, the stirring may not be particularly performed.

By the way, ammonia or amine is by-produced by the reaction of the above formula (3). This by-product may react with water and copper ions in the mixed solution of step (A) to produce copper hydroxide. Then, when the copper chloride-attached copper particles obtained in the step (A) are separated in the step (B) by, for example, filtration, the copper hydroxide may adversely affect the filterability.
Therefore, in order to prevent the problem, it is preferable to further add a carboxylic acid having 1 to 4 carbon atoms to the mixed solution. This is because the carboxylic acid reacts with ammonia or amine as a by-product to prevent the formation of copper hydroxide.
A carboxylic acid having 5 or more carbon atoms has a low solubility in the solution, so that the desired effect is reduced.

Specific examples of the carboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, and succinic acid. The amount of the carboxylic acid added is preferably 0.1 to 50 parts by mass with respect to 100 parts by mass of the compound (1) used in the step (A). If the amount added is less than 0.1 parts by mass, a sufficient effect of improving the filterability cannot be obtained, and if it is more than 50 parts by mass, the amount of carboxylic acid remaining as unreacted increases, and after filtration. It may adversely affect the solvent cleaning of the copper particles and the coating treatment of the copper particle surface after cleaning in the step (B).

［式（２）中、ｍは０〜３の整数、ｎは０〜２の整数であり、ｎ＝０のとき、ｍは０〜３のいずれか、ｎ＝１またはｎ＝２のとき、ｍは１〜３のいずれかである。］ [Step (B)]
In the step (B), the copper chloride-attached copper particles obtained in the step (A) are added to a solution containing an amine compound represented by the formula (2) to remove the copper (I) chloride and the amine compound. This is a step of performing surface coating.

[In equation (2), 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 one of 1 to 3. ]

First, after the operation of the step (A) is completed, the copper chloride-attached copper particles are separated from the mixed solution. The separation method is not particularly limited, but copper chloride-attached copper particles can be separated by, for example, filtration or decantation. As the filtration method, a known method can be applied, and natural filtration, vacuum filtration, pressure filtration and the like can be exemplified.
Since the separated product separated by the above method contains a small amount of the post-treatment solution in addition to the copper chloride-attached copper particles, it is preferable to wash the separated product with a solvent to remove the remaining post-treatment solution. .. As the cleaning solvent, it is preferable to use water, alcohol having 1 to 4 carbon atoms, or a mixed solvent thereof. Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, 1-propanol, 1-butanol, isopropanol and the like.

The copper chloride-attached copper particles separated in this manner are added to an amine compound solution containing an amine compound to form a mixture a, and the mixture a is stirred to temporarily place the copper chloride-attached copper particles on the surface of the copper particles in the step (A). The formed copper (I) chloride layer is removed. After cleaning, the copper (I) chloride layer is removed, and the amine compound is adsorbed on the surface of the copper particles to form a coating layer.
The stirring method is not particularly limited, and the stirring may be performed so that the copper chloride-attached copper particles and the amine compound are in sufficient contact with each other. Good.

Ideally, it is desirable to form a coating layer in which the surface of the copper particles is uniformly coated with the amine compound in the form of a monomolecular film after cleaning, and it is preferable that a good coating layer as close to the ideal as possible is formed. Therefore, the mixing ratio of the copper chloride-attached copper particles and the amine compound in the step (B) is preferably a ratio suitable for forming this good coating layer.
Specifically, although it depends on the particle size of the copper particles, 0.1 to 200 parts by mass is preferable with respect to 100 parts by mass of the copper chloride-attached copper particles. 1 to 100 parts by mass is more preferable in that the free amine compound is prevented from remaining in the surface-coated copper filler produced via the surface-coated copper filler intermediate. The smaller the particle size of the copper particles, the larger the surface area per unit mass. Therefore, it is preferable that the smaller the particle size, the larger the mixing amount of the amine compound.

Here, the solvent for dissolving the amine compound represented by the formula (2) is not particularly limited as long as it has good wettability with copper chloride-attached copper particles and does not react with the amine compound and the aliphatic monocarboxylic acid. .. A solvent containing at least one selected from alcohols, ketones, ethers, nitriles, sulfoxides, pyrrolidones, and water is preferable. Specifically, the alcohols include methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, 1-pentanol, tert-amyl alcohol, ethylene glycol, butoxyethanol, methoxyethanol, ethoxyethanol, Examples thereof include 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, isobutyronitrile and the like. Examples of sulfoxides include dimethyl sulfoxide and the like. Examples of pyrrolidones include 1-methyl-2-pyrrolidone.

The treatment temperature for forming the coating layer may be a temperature at which the coating of the amine compound proceeds and the solution does not solidify, and a temperature at which the oxidation promotion of copper is small is preferable. Specifically, it is preferably carried out in the range of −10 to 120 ° C. It is more preferable to carry out in the range of 30 to 100 ° C. in that the coating rate can be further increased and the promotion of oxidation can be further suppressed.
The processing time is not particularly limited, but is preferably 5 minutes to 10 hours. Further, in terms of manufacturing cost, 5 minutes to 3 hours are more preferable. If it is less than 5 minutes, the coating with the amine compound may be insufficient, and if it exceeds 10 hours, the amine compound forms a salt with carbon dioxide mixed from the atmosphere, and the surface-coated copper filler intermediate. It may remain as an impurity in it.

Further, the step (B) is preferably performed in an inert gas atmosphere because it is possible to form a salt of the amine compound and carbon dioxide in the atmosphere and suppress the oxidation of copper. For example, bubbling of the inert gas. Etc. are preferable. Specific examples of the inert gas include nitrogen, argon, and helium. Further, the bubbling may also be used for stirring, that is, if the copper particles and the amine compound can be sufficiently contacted only by the bubbling of the inert gas, the stirring may not be particularly performed.

In step (B), after cleaning, a coating layer of an amine compound that is chemically and / or physically bonded to and adsorbed to copper on the surface of copper particles is formed. Adsorption by chemical bond means that the amine compound forms a bond with copper on the surface of copper particles after cleaning and is adsorbed on the surface. The electrostatic interaction referred to here refers to a hydrogen bond, an ion-ion interaction (ionic bond), and the like. Further, the adsorption by physical bonding means that the surface is adsorbed by physical adsorption by Van der Waals force. In particular, since the amino group has a high electron donating property and it is considered that the amino group forms a bond by forming a coordination with copper, the amine compound is mainly formed by a chemical bond due to an electrostatic interaction. It is considered that the coating layer is formed by adsorbing to the coating layer. However, there may be some adsorption due to physical binding.

By applying the above steps (A) and (B) to the copper particles, a surface-coated copper filler intermediate on which a coating layer of the amine compound represented by the formula (2) is formed can be produced.
The surface-coated copper filler intermediate is easily oxidized in the atmosphere and is not practical as a surface-coated copper filler as it is. Therefore, it is necessary to form a second coating layer on the coating layer of the amine compound. For example, the surface coated copper filler intermediate is treated with a compound that binds to the amine compound by reaction to form a second coating layer.
As the compound that binds to the amine compound by reaction, a compound such that the two-layer coating layer formed by the amine compound and the compound that binds to the amine compound by reaction is stable in the atmosphere is selected.

An aliphatic monocarboxylic acid can be mentioned as an example of a compound that binds to an amine compound by a reaction. An embodiment of a production method for producing a surface-coated copper filler by forming a second coating layer with an aliphatic monocarboxylic acid is shown below.
For example, after the completion of the step (B), the following steps (C) to (F) are carried out to carry out a two-layer type surface having a first coating layer of an amine compound and a second coating layer of an aliphatic monocarboxylic acid. Use a coated copper filler.
Hereinafter, the coating layer of the amine compound will be referred to as a first coating layer.

[Step (C)]
The step (C) is a step of removing the amine compound solution containing the free amine compound that was not used for forming the first coating layer from the mixture a to obtain the intermediate 1 containing the surface-coated copper filler intermediate. is there. That is, it is a step of removing the excess amine compound solution. The copper chloride is also dissolved in the excess amine compound solution.
At this time, it is not necessary to completely remove the excess amine compound, and the above intermediate 1 can be obtained by natural sedimentation, separation by centrifugation, or filtration. That is, although a small amount of the free amine compound and the solvent are contained in the intermediate 1, the process may proceed to the next step (D) as it is. Since the operation is simple, the surface-coated copper filler intermediate (copper particles on which the first coating layer is formed) is settled by natural sedimentation, and then the supernatant amine compound solution is removed by decantation or suction by an aspirator. The method is preferable.
Further, the precipitate or the filtrate after the separation may be washed with a solvent capable of dissolving both the amine compound and the aliphatic monocarboxylic acid having 8 to 20 carbon atoms to obtain the intermediate 1. This cleaning is preferable because the amount of the free amine compound mixed can be reduced. However, if washing with water or the like is carried out for the purpose of completely removing the free amine compound, the amine compound forming the first coating layer may also be separated from the copper surface and removed, so washing with water is not preferable.
The intermediate 1 may be dried to reduce the amount of the contained solvent (solvent of the amine compound solution), but since the copper surface may be oxidized if the intermediate 1 is dried at this stage, drying, particularly heat drying, is carried out. It is preferable not to do so.

When a large amount of free amine compound remains in Intermediate 1, impurities generated by the amine compound forming a salt with carbon dioxide or an aliphatic monocarboxylic acid in the atmosphere adversely affect the conductivity of the conductive composition. Therefore, it is not preferable.
Therefore, the amount of the amine compound in the intermediate 1 is preferably 10% by mass or less of the amount of copper particles as the total amount of the amine compound and the free amine compound forming the first coating layer. It is more preferably 1.0% by mass or less because it does not affect the formation of the second coating layer of the aliphatic monocarboxylic acid. The amount of the amine compound in the intermediate 1 can be determined from the difference from the amount of the amine compound used in the step (B) by measuring the amount of the amine compound in the supernatant or the like.

[Step (D)]
The step (D) is a step of forming a second coating layer of an aliphatic monocarboxylic acid having 8 to 20 carbon atoms on the first coating layer.
Specifically, an aliphatic monocarboxylic acid solution containing an aliphatic monocarboxylic acid having 8 to 20 carbon atoms is added to the intermediate 1 to form a mixture b, and the mixture b is stirred to obtain the mixture on the first coating layer. To form a second coating layer of the aliphatic monocarboxylic acid. The intermediate 1 may be added to an aliphatic monocarboxylic acid solution containing an aliphatic monocarboxylic acid having 8 to 20 carbon atoms to obtain a mixture b. The stirring method is not particularly limited, and the copper particles on which the first coating layer is formed may be stirred so that the aliphatic monocarboxylic acid is in sufficient contact with each other, and a known stirring machine such as a paddle stirring machine or a line mixer may be used. A general stirring method may be used.

Ideally, the bond between the amine compound of the first coating layer and the aliphatic monocarboxylic acid forms a second coating layer in which the first coating layer is uniformly coated with the aliphatic monocarboxylic acid in the form of a monomolecular film. It is preferable that a good second coating layer as close to the ideal as possible is formed. Therefore, as the mixing ratio of the copper particles and the aliphatic monocarboxylic acid in the step (D), a ratio suitable for forming this good second coating layer is preferable.
Specifically, although it depends on the particle size of the copper particles, 0.1 to 50 parts by mass is preferable with respect to 100 parts by mass of the copper particles. 0.5 to 10 parts by mass is more preferable in that free aliphatic monocarboxylic acid is suppressed from remaining in the two-layer surface-coated copper filler. The smaller the particle size of the copper particles, the larger the surface area per unit mass. Therefore, it is preferable that the smaller the particle size, the larger the mixing amount of the aliphatic monocarboxylic acid.

The solvent used for preparing the aliphatic monocarboxylic acid solution having 8 to 20 carbon atoms is that the aliphatic monocarboxylic acid is dissolved and has good wettability with the copper particles on which the first coating layer is formed, and is an amine compound and an aliphatic monocarboxylic acid. It is not particularly limited as long as it does not react with the monocarboxylic acid. Any solvent that can be easily dried and removed in the drying step of step (F) described later is preferable.
A preferred solvent is a solvent containing one or more selected from alcohols, ketones, ethers, nitriles, sulfoxides, and pyrrolidones. Specifically, the alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, tert-amyl alcohol, ethylene glycol, butoxyethanol, methoxyethanol and ethoxyethanol. , Propylene glycol, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether and the like. Examples of the 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, isobutyronitrile and the like. Examples of sulfoxides include dimethyl sulfoxide and the like. Examples of pyrrolidones include 1-methyl-2-pyrrolidone.

The treatment temperature for forming the second coating layer may be a temperature at which the coating of the aliphatic monocarboxylic acid proceeds and the solution does not solidify, and specifically, it is carried out in the range of −10 to 80 ° C. Is preferable. It is more preferable to carry out the coating in the range of 10 to 60 ° C. in that the coating speed is further increased and the aliphatic monocarboxylic acid forming the second coating layer is suppressed from being desorbed.
The processing time is not particularly limited, but is preferably 5 minutes to 10 hours. Further, in terms of manufacturing cost, 5 minutes to 3 hours are more preferable. If it is less than 5 minutes, the coating with the aliphatic monocarboxylic acid may be insufficient, and if it exceeds 10 hours, the component desorbed as a complex of copper-amine compound-fatty acid is a two-layer surface-coated copper filler. It is not preferable because it may remain in the conductive composition and may adversely affect the conductivity of the conductive composition.

In addition, step (D) is also inert in that it is possible to form a salt of the amine compound of the first coating layer or the free amine compound mixed in a small amount with carbon dioxide in the atmosphere and suppress the oxidation of copper. It is preferable to carry out in a gas atmosphere, for example, bubbling of an inert gas or the like is preferable. Specific examples of the inert gas include nitrogen, argon, and helium. Further, the bubbling may also be used for stirring, that is, if the copper particles on which the first coating layer is formed and the aliphatic monocarboxylic acid can be sufficiently contacted only by bubbling the inert gas. In particular, stirring does not have to be carried out.

In step (D), a second coating layer of an aliphatic monocarboxylic acid having 8 to 20 carbon atoms, which is chemically bonded to the amine compound of the first coating layer, is formed. The chemical bond means that the carboxyl group of the aliphatic monocarboxylic acid and the amino group of the amine compound are bonded by an electrostatic interaction. The electrostatic interaction referred to here refers to a hydrogen bond, an ion-ion interaction (ionic bond), and the like.

[Step (E)]
In step (E), the aliphatic monocarboxylic acid solution containing the free aliphatic monocarboxylic acid that was not used for forming the second coating layer was removed from the mixture b, and the first and second coating layer-forming copper particles were removed. This is a step of obtaining an intermediate 2 containing the above. Specifically, Intermediate 2 can be obtained by filtration. As the filtration method, a known method can be applied, and natural filtration, vacuum filtration, pressure filtration and the like can be exemplified.
Also, in terms of removing as much free aliphatic monocarboxylic acid and free amine compound as possible, the filtrate was washed with a solvent for an aliphatic monocarboxylic acid solution having 8 to 20 carbon atoms to form the intermediate 2. [Step (Ea)]. By reducing the amount of free aliphatic monocarboxylic acid by washing, the adhesion of the composition to the conductive composition is improved.

[Step (F)]
The step (F) is a step of drying the intermediate 2 to obtain a two-layer surface-coated copper filler in the form of copper particles.
The drying method is not particularly limited, and examples thereof include vacuum drying and freeze drying. In terms of production cost, vacuum drying is preferable, and the drying temperature is preferably 20 to 120 ° C. Below 20 ° C., the drying time may be long, and at temperatures higher than 120 ° C., copper may be oxidized. The degree of reduced pressure, the drying temperature, and the drying time may be appropriately determined depending on the combination of each condition, the type of solvent used, and the like, and the amount of the solvent in the two-layer surface-coated copper filler after drying is 1% by mass or less. It is preferable if the conditions allow it to be dried to a certain extent.
By the above manufacturing method, a two-layer surface-coated copper filler in the form of copper particles can be manufactured.

Hereinafter, embodiments of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In this embodiment, an example in which a two-layer type surface-coated copper filler is continuously produced from the production of the surface-coated copper filler intermediate is shown as an example of the embodiment. The two-layer surface-coated copper filler is simply referred to as a surface-coated copper filler.
The evaluation methods used in each Example and Comparative Example are shown below.

<SUS corrosiveness>
The SUS corrosiveness in the production methods of each Example and Comparative Example is that the solution containing the compound (1) in step (A) or the solution corresponding to the solution is made of SUS304 (NAS304, manufactured by Nippon Jikin Kogyo Co., Ltd.). The sample piece was immersed and evaluated. The whole sample piece was not immersed in the solution, but a part of the sample piece was immersed so as to come out from the liquid surface into the atmosphere.
-Sample piece; 50 mm x 30 mm x 1.5 mm
-Immersion temperature and time; 25 ° C., 72 hours-Corrosiveness evaluation; The sample piece was taken out from the solution, the solution on the surface of the sample piece was wiped off, and then evaluated by visual observation according to the following criteria.
〇 No change on the surface of the sample piece △ Liquid marks on the liquid interface on the surface of the sample piece × The surface of the sample piece becomes cloudy

<Filtability of copper chloride-attached copper particles or treated copper particles>
The filterability of the copper chloride-attached copper particles after the step (A) or the post-treatment copper particles after the step corresponding to the step (A) was evaluated according to the following criteria.
◎ Filtration time is less than 90 seconds under reduced pressure filtration condition of -90 kPa ○ Filtration time is 90 seconds or more and 180 seconds or less under reduced pressure filtration condition of -90 kPa × Filtration time is more than 180 seconds under reduced pressure filtration condition of -90 kPa

<Volume resistivity>
A conductive composition was prepared using the surface-coated copper filler produced by the methods of each Example and Comparative Example, and the volume resistivity of the cured product of the conductive composition was measured in accordance with JIS K 7194. evaluated.
Measuring instrument model: resistivity meter MCP-T610 (manufactured by Mitsubishi Chemical Corporation), measuring conditions; 4 probe method Probe: ASP
Sample (cured product); A cured product obtained by applying a conductive composition to a pattern of width x length x thickness = 1 cm x 3 cm x 30 μm.
Number of measurements; 5 times

(Example 1-1)
A surface-coated copper filler was produced via a surface-coated copper filler intermediate by the following production method.
[Step (A)]
As a solution (treatment solution) containing the compound (1), an aqueous ammonium chloride solution prepared by dissolving 5 g of ammonium chloride in 100 g of water was prepared.
50 g of copper particles [1400 YP; particle size (D50) 6.9 μm, specific surface area 0.26 m ² / g, manufactured by Mitsui Mining & Smelting Co., Ltd.] was added to the ammonium chloride aqueous solution, and under nitrogen bubbling, at 30 ° C. for 60 minutes. Stirred. The stirring was carried out using a mechanical stirrer at a rotation speed of 150 rpm. Hereinafter, stirring was performed at the same rotation speed using the same stirring device.
After the stirring was completed, the copper chloride-attached copper particles were filtered off by vacuum filtration using a Kiriyama funnel of 5C filter paper, and subsequently, the copper chloride-attached copper particles were washed twice with 150 g of water on the Kiriyama funnel. The filterability of the copper chloride-attached copper particles before washing with water was evaluated.
Table 1 shows the treatment conditions and the evaluation results of the filterability in the step (A).
[Step (B)]
The washed copper chloride-attached copper particles were added to 250 g of a 40 mass% diethylenetriamine aqueous solution, and the mixture was heated and stirred at 60 ° C. for 1 hour while carrying out nitrogen bubbling.
[Step (C)]
After stopping the stirring and letting it stand for 5 minutes, about 200 g of the supernatant liquid was withdrawn and removed. Subsequently, 200 g of isopropanol was added to the precipitate as a cleaning solvent, and the mixture was stirred at 30 ° C. for 3 minutes. After the stirring was stopped and the mixture was allowed to stand for 5 minutes, about 200 g of the supernatant was withdrawn and removed to obtain Intermediate 1.
[Step (D)]
After adding 250 g of a 2 mass% isopropanol solution of laurate to Intermediate 1, the mixture was stirred at 30 ° C. for 30 minutes.
[Step (E)]
After stopping stirring, the isopropanol solution laurate was removed by vacuum filtration to obtain Intermediate 2. Vacuum filtration was carried out by depressurizing the Kiriyama funnel of 5C filter paper with a diaphragm pump.
[Step (F)]
The intermediate 2 was dried under reduced pressure at 25 ° C. for 3 hours to obtain a surface-coated copper filler. The vacuum drying was carried out by placing the intermediate 2 in a vacuum oven and depressurizing the oven with an oil pump.

A small amount of the washed copper chloride-attached copper particles obtained in the step (A) was collected, dried, and subjected to XPS analysis under the following measurement conditions by JPS-9200. As a result, a peak due to binding chlorine, which was not observed on the surface of the raw material copper particles, was observed around 200-210 eV, and it was confirmed that copper chloride was attached to the surface of the copper particles. The spectrum observed by XPS analysis is shown in FIG.
[Measurement condition]
-Filament conditions: 10 kV, 10 mA
-Detector path energy; 30
・ Accumulation time: 300ms
・ Number of scans; 10 times

In parallel with the production of the surface-coated copper filler, the SUS corrosiveness of the ammonium chloride aqueous solution was evaluated. The results are shown in Table 1.

The IR spectrum of the surface of the obtained surface-coated copper filler was measured. As a result, the peak of the NH variable vibration of diethylenetriamine shifted from 1590 cm ^-1 (measured by diethylenetriamine alone) to 1562 cm ^-1 on the low wavenumber side, and diethylenetriamine was coordinated to the surface of the copper particles. It was confirmed that it was done. The peak of C = O stretching vibration of lauric acid is not observed in 1700 cm ^-1, a carboxylate anion (-COO ^-) peaks of was observed at 1400 cm ^-1, lauric acid amine compound and electrostatic mutual It was confirmed that they were combined and existed by the action.
From the IR spectrum, it can be determined that both the diethylenetriamine of the first coating layer and the lauric acid of the second coating layer are bonded by a chemical bond to form each coating layer. Similarly, in each of the Examples and Comparative Examples shown below, both diethylenetriamine in the first coating layer and lauric acid in the second coating layer are bonded by chemical bonds to form each coating layer from the IR spectrum. Can be judged.

(Example 1-2)
In step (A), the solution containing the compound (1) was changed to an ammonium chloride-acetic acid aqueous solution in which 5 g of ammonium chloride and 5 g of acetic acid were dissolved in 100 g of water, and the washing of copper chloride-attached copper particles was changed to isopropanol. Obtained a surface-coated copper filler in the same manner as in Example 1-1. In addition, the filterability and the SUS corrosiveness of the ammonium chloride-acetic acid aqueous solution were evaluated. Table 1 shows the processing conditions and the evaluation results. In the obtained surface-coated copper filler, peak shifts in the IR spectra of diethylenetriamine and lauric acid were observed, and it is judged that a coating layer of diethylenetriamine and lauric acid was formed.

(Example 1-3)
In the step (A), the solution containing the compound (1) was changed to an aqueous solution of methylammonium chloride-acetic acid in which 10 g of methylammonium chloride and 5 g of acetic acid were dissolved in 100 g of water, and the washing of copper chloride-attached copper particles was changed to ethanol. A surface-coated copper filler was obtained in the same manner as in Example 1-1 except for the above. In addition, the filterability and the SUS corrosiveness of the methylammonium chloride-acetic acid aqueous solution were evaluated. Table 1 shows the processing conditions and the evaluation results. In the obtained surface-coated copper filler, peak shifts in the IR spectra of diethylenetriamine and lauric acid were observed, and it is judged that the surface-coated copper filler formed a coating layer of diethylenetriamine and lauric acid.

(Example 1-4)
In the step (A), the solution containing the compound (1) was changed to an aqueous solution of ammonium chloride-formic acid in which 5 g of ammonium chloride and 10 g of formic acid were dissolved in 100 g of water, and the copper chloride-attached copper particles were washed with methanol and water. A surface-coated copper filler was obtained in the same manner as in Example 1-1 except that the mixed solvent was changed to a mixed solvent having a mass ratio of 80:20. In addition, the filterability and the SUS corrosiveness of the ammonium chloride-formic acid aqueous solution were evaluated. Table 1 shows the processing conditions and the evaluation results. In the obtained surface-coated copper filler, peak shifts in the IR spectra of diethylenetriamine and lauric acid were observed, and it is judged that the surface-coated copper filler formed a coating layer of diethylenetriamine and lauric acid.

(Comparative Example 1-1)
A surface-coated copper filler was obtained in the same manner as in Example 1-1 except that the step (A) was not carried out. The processing conditions are shown in Table 1. In the obtained surface-coated copper filler, peak shifts in the IR spectra of diethylenetriamine and lauric acid were observed, and it is judged that a coating layer of diethylenetriamine and lauric acid was formed.

(Comparative Example 1-2)
As a step corresponding to the step (A), the copper particles were treated in the same manner as in Example 1-1 except that 100 g of a 3.5 mass% sulfuric acid aqueous solution was used instead of the solution containing the compound (1). Steps (B) to (F) were carried out in the same manner as in Example 1-1 except that the copper particles after the treatment by the sulfuric acid treatment thus obtained were used to obtain a surface-coated copper filler. In addition, the filterability in the step corresponding to the step (A) and the SUS corrosiveness of the sulfuric acid aqueous solution were evaluated. Table 1 shows the processing conditions and the evaluation results. In the obtained surface-coated copper filler, peak shifts in the IR spectra of diethylenetriamine and lauric acid were observed, and it is judged that a coating layer of diethylenetriamine and lauric acid was formed.

(Comparative Example 1-3)
As a step corresponding to the step (A), the copper particles were treated in the same manner as in Example 1-1 except that 100 g of a 0.01 mass% hydrazine aqueous solution was used instead of the solution containing the compound (1). Steps (B) to (F) were carried out in the same manner as in Example 1-1 except that the copper particles after the treatment by the hydrazine treatment thus obtained were used to obtain a surface-coated copper filler. In addition, the filterability in the step corresponding to the step (A) and the SUS corrosiveness of the hydrazine aqueous solution were evaluated. Table 1 shows the processing conditions and the evaluation results. In the obtained surface-coated copper filler, peak shifts in the IR spectra of diethylenetriamine and lauric acid were observed, and it is judged that the surface-coated copper filler formed a coating layer of diethylenetriamine and lauric acid.

(Example 2-1)
20 g of surface-coated copper filler produced in Example 1-1, 5.4 g of resole-type phenol resin [PL-5208, manufactured by Gun Ei Chemical Industry Co., Ltd.] as a binder, and 1,4 as an additive (oxide remover). -0.3 g of phenylenediamine was mixed. Next, using a planetary mixer [ARV-310, manufactured by Shinky Co., Ltd.], the mixture was stirred at a rotation speed of 1500 rpm for 30 seconds at room temperature for primary kneading.
Next, secondary kneading was carried out by passing the three roll mills [EXAKT-M80S, manufactured by Nagase Screen Printing Laboratory Co., Ltd.] five times under the conditions of room temperature and a distance between rolls of 5 μm.
Next, 0.5 g of ethylcarbitol acetate as a solvent is added to the kneaded product obtained by the secondary kneading, and the mixture is stirred at room temperature and vacuum conditions at a rotation speed of 1000 rpm for 90 seconds using a planetary mixer to defoam and knead. As a result, a conductive composition was produced.
The obtained conductive composition was applied onto a non-alkali glass in a pattern of width × length × thickness = 1 cm × 3 cm × 30 μm using a metal mask. A cured product was produced by heating the patterned glass at 150 ° C. for 15 minutes. The volume resistivity of the obtained cured product was measured by the above method. Table 2 shows the measurement results of the blending amount (g) and volume resistivity of each component of the conductive composition.

(Examples 2-2 to 2-4 and Comparative Examples 2-1 to 2-3)
Using the surface-coated copper fillers produced in Examples 1-2 to 1-4 and Comparative Examples 1-1 to 1-3, each conductive composition and cured product were produced in the same manner as in Example 2-1. .. In addition, the volume resistivity of each of the obtained cured products was measured. Table 2 shows the measurement results of the blending amount (g) and volume resistivity of each component of each conductive composition.

In Examples 2-1 to 2-4, the volume resistivitys are all 30 μΩ · cm or less, and the conductivity is improved as compared with the composition using copper particles in which the step (A) of Comparative Example 2-1 is not performed. doing.
As a step corresponding to the step (A), Comparative Example 2-2 was treated with sulfuric acid, and Comparative Example 2-3 was treated with hydrazine. In the case of the treatment with these, unlike the treatment with the compound (1), the copper (I) chloride layer is not formed on the surface of the copper particles after the treatment, so that it is considered that the surface reoxidation has progressed after the treatment, and as a result, the amine The surface coating effect of the compound and the aliphatic monocarboxylic acid was inferior to that of the examples.

Claims (2)

Copper particles are added to a solution containing the compound represented by the formula (1) to prepare a mixed solution, and copper (I) oxide on the surface of the copper particles is reacted with the compound to prepare copper (I) chloride. And (B) the step of obtaining copper chloride-adhered copper particles having copper (I) chloride adhered to the surface, and (B) separating the copper chloride-attached copper particles from the mixed solution to form an amine represented by the formula (2). The surface of copper particles after cleaning, which is added to an amine compound solution containing a compound to remove copper (I) chloride adhering to the copper chloride-attached copper particles by reaction with the amine compound and from which copper (I) chloride has been removed. To have a step of forming a coating layer of the amine compound.
A method for producing a surface-coated copper filler intermediate.

[In the equation (1), a is an integer of 1 to 3, b is an integer of 0 to 2, and a + b = 3. ]

[In equation (2), 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 one of 1 to 3. ] A carboxylic acid having 1 to 4 carbon atoms is further added to the mixed solution of the step (A).
The method for producing a surface-coated copper filler intermediate according to claim 1.

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