JP2016098398A - Metal surface treatment method, and silver clad copper and composite metal body treated by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal surface treatment method for performing surface treatment with metal silver being interposed on the surface of metal copper or its alloy and making them composite to cause bonding between metal coppers (copper alloys) by fusion at a relatively low temperature.SOLUTION: An amine complex of an alkylamine and a silver compound capable of generating metal silver by being decomposed by heating is heated on a metal surface comprising metal copper or a copper alloy in the presence of an alkylamine to deposit silver on the metal surface.SELECTED DRAWING: None

Description

  In the present invention, an amine complex of a silver compound capable of being decomposed by heating to form metallic silver and an alkylamine is heated in the presence of an alkylamine on at least a part of the surface of a metal substrate such as copper, and the metal surface The present invention relates to a method for treating a metal surface on which silver is deposited, silver-coated copper treated by the method, and a composite metal body obtained by sintering this.

Metallic copper has been the most commonly used material for wiring since it has good electrical conductivity and is relatively inexpensive. In recent years, it has also been used for LSI internal wiring by taking advantage of the high electromigration resistance of metallic copper. On the other hand, joining of copper metal is generally difficult, and conventionally, joining via dissimilar metals represented by brazing such as soldering has been performed. Furthermore, in order to facilitate the joining by preventing the formation of oxides on the surface of the metallic copper to be joined, a technique for previously combining different metals suitable for joining on the copper surface is widely known. For example, Patent Document 1 discloses a technique for easily performing subsequent diffusion bonding by plating a copper surface with a noble metal.
On the other hand, in recent years, conductive ink and paste containing fine metal particles have been attracting attention as a wiring material in printed electronics (PE), which is the next generation process technology for producing electronic devices through simple printing and coating processes. ing. In particular, in PE, it is desired to use various resins as a substrate for the purpose of providing flexibility to the substrate on which the electronic device is mounted. In order to realize these demands, conductive ink and paste containing fine metal particles, which are wiring materials, can be easily sintered at about 120 ° C. or less, which is a heat resistant temperature of a relatively inexpensive resin. It is required to show conductivity.

As metal fine particles used for wiring materials that satisfy the above requirements, metal silver fine particles have attracted particular attention so far. In addition to having high electrical conductivity and oxidation resistance stability, metallic silver is known to be capable of forming a metallic silver coating by sintering at a relatively low temperature by making fine particles. It is considered to be the most practical material for wiring in Japan.
The silver fine particles can be produced by various methods. From the viewpoint of adding characteristics such as prevention of aggregation of the produced silver fine particles and improved dispersibility in a solvent, various kinds of silver fine particles are produced on the particle surface simultaneously with the production of the silver fine particles. A method of manufacturing as coated silver fine particles in which a protective film is formed is common. As a method for producing such coated fine silver particles, a silver atom is generated by reducing a silver compound using a reducing agent in an environment where a compound containing silver (silver compound) and an organic molecule serving as a protective film coexist. In general, silver fine particles are produced by the aggregation of silver atoms, and at the same time, a protective film is produced by organic molecules or the like coexisting on the surface of the silver fine particles. For example, Patent Document 2 describes a technique for producing coated silver fine particles by dropping a silver nitrate / amine complex onto ascorbic acid or the like as a reducing agent to reduce silver nitrate. Patent Document 3 describes a technique for producing silver fine particles coated with an organic protective agent by heating and reducing a silver salt such as silver nitrate in the presence of an organic protective agent and a reducing auxiliary agent. .
According to the above conventional method for producing silver fine particles, an oxidation-reduction reaction between the silver compound and the reducing agent is essential to produce silver atoms constituting the silver fine particles. Uniform mixing is not always easy, and it is inevitable that partial fluctuations in concentration occur in the system. For this reason, it is difficult to produce a uniform oxidation-reduction reaction in the system in the conventional method for producing silver fine particles, and as a result, it is inevitable that the particle diameters of the produced silver fine particles vary. Had.

  As a method for efficiently producing coated silver fine particles without causing such problems, the present inventors formed a complex compound by depositing alkylamine on a silver compound such as silver oxalate, Development of technology to obtain coated silver fine particles by heating and thermal decomposition of the complex compound produced (hereinafter also referred to as “amine complex thermal decomposition method” or in some cases “amine complex decomposition method”) (for example, And Patent Documents 4 to 7). According to the amine complex thermal decomposition method, the reaction when the silver complex is generated uses a reaction in which an amine complex, which is a single component, is thermally decomposed into multiple components. Therefore, silver fine particles having uniform characteristics are easily obtained, and generally no organic solvent is required, and silver fine particles can be obtained without a solvent. Furthermore, the formation of a complex compound with an alkylamine makes the silver compound chemically unstable, resulting in thermal decomposition at a temperature lower than the original thermal decomposition temperature, typically about 100 ° C., or Silver fine particles can be produced under relatively mild conditions below that, and are particularly suitable for the production of coated silver fine particles that easily cause low-temperature sintering.

  On the other hand, since metallic silver is expensive compared to metallic copper and inferior to metallic copper in terms of electromigration resistance, the use of copper fine particles as a wiring material in next-generation printed electronics has been widely studied. Various methods for producing copper fine particles have been proposed. However, even when fine particles are used, the sintering temperature (fusion temperature) of metallic copper is higher than that of metallic silver, so that the copper fine particles still have sinterability that allows wiring to be formed on the resin substrate. Has not been found. In addition, in copper fine particles, oxidation in manufacturing and use processes becomes a big problem due to an increase in specific surface area, and generally a special sintering environment such as manufacturing in an inert gas atmosphere, a reducing atmosphere or light irradiation is required. Such a problem is rather expensive as compared with silver fine particles.

As a means for solving the problems in the copper fine particles, the use of fine particles in which a noble metal such as silver is combined on the surface of copper has been studied, as in the case of relatively macro bonding as described in Patent Document 1 and the like. ing. Patent Document 8 discloses a composite fine particle (silver core silver copper alloy shell nanoparticle) in which a silver fine particle produced by an amine complex thermal decomposition method is used as a core and a shell is formed on the surface by copper atoms generated in an alkylamine. Is described. The composite fine particles are described as being electrically conductive by sintering at a low temperature of about 80 ° C. in a reducing atmosphere, and the shell portion of the composite fine particles contains a silver-copper alloy phase that does not exist in an equilibrium state. In addition, it is described that even a portion mainly made of copper is composed of a phase containing quasi-equilibrium copper such that the lattice constant thereof is the same as that of the silver phase. In addition, it has been confirmed that the composite fine particles do not substantially oxidize even when heated to about 120 ° C. in the atmosphere, and there is a possibility of improving the oxidation resistance of copper by combining with silver. Is shown.
Patent Document 9 describes metal nanoparticles in which a thin film layer is formed with copper as a core and a noble metal alkanoate (especially fatty acid silver) around the core, and the copper core is coated with a silver thin film layer. In nanoparticles, it is described that the oxidation of the copper core was prevented up to 131 ° C. due to the presence of the silver thin film layer, but the sinterability has not been evaluated.

  In Patent Document 10, a solution containing a first metal precursor and an organic solvent is heated to reduce the first metal precursor, and is composed of a first metal component derived from the first metal precursor. A step of generating one metal core, a second metal precursor is added to a solution containing the first metal core, and the solution is heated to reduce the second metal precursor, resulting from the second metal precursor Forming a second metal shell composed of a second metal component around the first metal core, and a method for producing metal nanoparticles, specifically covering a silver core with a copper shell It is described that fine particles were produced.

JP-A-6-262375 JP 2009-144197 A JP 2007-39718 A JP 2010-265543 A JP 2012-162767 A JP 2014-31542 A JP 2014-40630 A JP 2011-68936 A JP 2007-224420 A JP 2008-248298 A

Yamamoto M. et al., Langmuir, 2006, Vol.22, pp.8581-8586

As mentioned above, while there is a wide demand for using metal copper having a lower material price than metal silver as a material for wiring and the like and excellent in electromigration resistance, it has a fusion property between metal copper. Due to the low temperature, a technique for easily fusing metal copper at a low temperature has not been clarified. In particular, the fine particles containing copper that can be sintered in the heat-resistant temperature range of the flexible substrate and the production method thereof have not yet been clarified. In addition, the technology that sinters copper fine particles by mixing silver fine particles and the fine particles in which silver is combined with copper by surface treatment such as precipitation of silver on the surface of copper by various methods are not necessarily good. Has not yet shown good sinterability.
Therefore, the present invention particularly utilizes the low-temperature fusibility (sinterability) possessed by metallic silver, and composites the metallic copper and its alloy by interposing metallic silver on the surface to form a composite. It is an object of the present invention to provide a surface treatment method for metallic copper that causes bonding by fusion between (alloys) at a relatively low temperature. It is another object of the present invention to provide a surface treatment method for obtaining copper (alloy) fine particles suitable for forming metal wiring by a printing method, particularly by treating the surface of fine particles containing copper. Furthermore, it makes it a subject to provide the copper silver composite obtained by processing metal copper (alloy) by the said method.

  The present inventors diligently studied to solve the above-mentioned problems. As a result, an amine complex, which is a complex compound formed by mixing a silver compound capable of being decomposed by heating to form metallic silver and an alkylamine, In the presence of alkylamine, by heating on a metal surface containing metallic copper to deposit metallic silver, it is possible to efficiently form a silver coating on the metallic surface and to impart a certain environmental oxidation resistance, Moreover, it discovered that a metal surface could be joined through the low temperature melt | fusion of the silver coating formed by the said method, and completed this invention.

  That is, the method for treating a metal surface according to the first aspect of the present invention includes an amine complex of a silver compound that can be decomposed by heating to form metallic silver and an alkylamine, and metal copper or a copper alloy in the presence of the alkylamine. It heats on the metal surface containing and deposits silver on the said metal surface, It is characterized by the above-mentioned. In a different aspect of the present invention, there is provided a silver-coated copper coated with an alkylamine obtained by the above surface treatment method, and this silver-coated copper is at least a part of the surface of metal copper or a copper alloy, An amine complex of a silver compound capable of being decomposed by heating to form metallic silver and an alkylamine is heated in the presence of alkylamine to deposit metallic silver on the copper surface.

In still another aspect of the present invention, there is provided a composite metal body obtained by sintering the silver-coated copper, the composite metal body including a copper dispersed phase in a silver matrix, 3.0 It exhibits a volume resistivity of × 10 ⁻³ Ω · cm or less.

  According to the method for treating a metal surface of the present invention, metal silver can be efficiently deposited on a part of or the entire surface of the substrate without requiring special conditions such as complicated equipment and an inert gas atmosphere. . When metallic copper is used as the substrate, an atomic layer of silver is deposited in a metastable state on the surface of metallic copper, so that the treated copper surfaces can be joined by fusion at a low temperature. For example, the adhesion of the surfaces can be improved by depositing a silver atomic layer on the surface of a copper plate or the like by the treatment method according to the present invention. In particular, by applying a silver atomic layer to the copper fine powder by the processing method according to the present invention, the copper fine powder is easily fused to each other and sintered at a low temperature to form a wiring or the like. It becomes possible. In addition, by dispersing the silver-coated copper fine powder obtained by surface treatment according to the present invention in a dispersion medium, it is possible to obtain a dispersion such as an ink or paste for forming wiring or the like by a printing method. In addition, it is possible to obtain a composite metal body having good conductivity by fusing the silver-coated copper fine powder to each other.

2 is a scanning electron microscope image of the surface of a copper plate subjected to surface treatment in Example 1. FIG. It is a photograph of what fuse | melted the copper plates which surface-treated in Example 1 and Comparative Example 1. FIG. 3 is a scanning electron microscope image of copper fine particles synthesized in Example 2. FIG. 3 is a particle size distribution histogram obtained from a micrograph of copper fine particles synthesized in Example 2. FIG. 4 is a powder X-ray diffraction pattern of copper fine particles synthesized in Example 2. FIG. It is a thermogravimetric analysis result in the inert atmosphere of the copper fine particle synthesize | combined in Example 2. FIG. It is a thermogravimetric analysis result of the copper fine particles synthesized in Example 2 under atmospheric pressure. 2 is a powder X-ray diffraction pattern of metal fine particles obtained by performing surface treatment in Example 2, Example 4 and Comparative Example 2. FIG. 3 is a scanning electron microscope image of metal fine particles obtained by performing surface treatment in Example 2. FIG. 3 is a scanning electron microscope image of metal fine particles obtained by performing surface treatment in Example 3. FIG. 4 is a scanning electron microscope image of metal fine particles obtained by performing surface treatment in Example 4. FIG. It is a scanning transmission electron microscope image and elemental analysis mapping of the metal fine particle obtained by performing the surface treatment in Example 2. 3 is a scanning electron microscope image of metal fine particles obtained by performing surface treatment in Comparative Example 2. FIG. 3 is an X-ray diffraction pattern of a fired film of metal fine particles surface-treated in Example 2, Example 4, and Comparative Example 2. FIG. It is an ultraviolet-visible diffuse reflection spectrum of the fired film | membrane of the metal fine particle surface-treated in Example 2, Example 3, and Comparative Example 2. FIG. 3 is a scanning electron microscope image of the surface of a fired film of metal fine particles surface-treated in Example 2. FIG. 6 is a scanning electron microscope image of the surface of a fired film of metal fine particles surface-treated in Example 4. FIG. 4 is a scanning electron microscope image of the surface of a fired film of metal fine particles surface-treated in Comparative Example 2.

  Hereinafter, a surface treatment method for performing surface treatment involving the intervention of metallic silver on the surface of metallic copper according to the present invention, and silver-coated copper in which metallic silver is deposited on the surface of metallic copper obtained by using the method Will be described. In particular, a copper fine powder coated with metallic silver, a dispersion in which the copper fine powder is dispersed in a dispersion medium, and a composite metal body formed by joining the copper fine powder will be described. The copper metal to be treated by the method according to the present invention may be pure copper containing only inevitable impurities, or may be a copper alloy containing copper as a main component and an appropriate alloy element. Hereinafter, what is described as “metallic copper” or simply “copper” in the present specification includes a copper alloy containing copper as a main component in addition to pure copper.

  Among the surface treatments of metallic copper for improving the fusion property between metallic coppers, the present inventor made various studies on the surface treatment method in which metallic silver is intervened. By applying silver atoms generated in the amine complex pyrolysis method that has been developed for the production of silver fine particles to the surface of metallic copper, fusion between the surfaces after treatment is easy even at low temperatures. The present invention has been found out. It has also been found that, particularly by applying silver to a copper fine particle by an amine complex pyrolysis method, bonding due to fusion between the fine particles occurs even near room temperature and a good conductor can be formed. Although it is not clear why the silver atoms generated by the amine complex pyrolysis method adhere to the surface of metallic copper, the fusion between the surfaces easily occurs even at a low temperature. The fusion property of the metal copper shown is remarkable even when compared with ordinary metal silver or a silver coating provided on the copper surface by a conventionally known method, and the metal silver deposited by the method according to the present invention is It is presumed that a good metallic bond was formed with the underlying metallic copper and the deposited metallic silver coating layer was in an active state.

  The amine complex thermal decomposition methods described in Patent Documents 4 to 7 are characterized in that a complex compound of a silver compound serving as a silver atom supply source and various alkylamines is generated in advance. In the complex compound, it is considered that the amino group contained in the alkylamine has a coordinate bond to the silver atom contained in the silver compound, which makes the structure of the silver compound unstable, which is higher than the original decomposition temperature. It has been found that decomposition of silver compounds occurs at lower temperatures. Then, by heating the complex compound (hereinafter sometimes referred to as “amine complex”), the silver compound is decomposed at a relatively low temperature, and a silver atom having an alkylamine deposited thereon is generated. Therefore, it is considered that the generated silver atom has a low potential and the mobility is limited by the deposited alkylamine. As a result, in the production of silver fine particles using the amine complex thermal decomposition method, the silver fine particles produced under the condition that the density of silver atoms is very high without the presence of an organic solvent which is substantially a reaction medium. Is not coarsened and a fine and uniform particle size distribution is considered to be obtained (Patent Documents 4 to 7).

  In the study according to the present invention, when the complex compound of the silver compound and the alkylamine is thermally decomposed in a state where the surface of the metallic copper exists in the system, silver is preferentially deposited on the surface of the metallic copper. It was found to form a coating consisting of an atomic layer of silver. Due to the difference in lattice constant, etc., metallic copper and metallic silver do not produce an alloy phase in an equilibrium state and have low affinity. For example, as shown in Comparative Example 3 below, the copper fine particles are described in Patent Documents 4 to 7 It is difficult to satisfactorily join metallic copper and metallic silver, for example, when the sintered body obtained by this method is mixed and sintered, and the sintered body obtained has low conductivity. It is generally known. Nevertheless, according to the present invention, a coating composed of an atomic layer of silver is formed on the surface of metallic copper, and the mechanism in which metallic copper has a high fusing property by having the coating of silver is based on the amine complex thermal decomposition method. It is inferred to be related to the state of the silver atoms generated in In other words, the chemical potential of silver atoms generated in the amine complex pyrolysis method is low compared to the case where silver atoms are generated by reducing a compound containing silver, which is generally known, by the driving force of a reducing agent. As a result, formation of a stable phase accompanied by nucleation or the like becomes difficult, and as a result, a silver atomic layer is considered to be metastable bonded and deposited on the surface of copper. The silver atomic layer functions as a binder while maintaining a good bond with the copper surface, so that it is considered that bonding between the treated surfaces easily occurs even at low temperatures. At the same time as the deposition of silver, a coating of alkylamine is formed on the surface of the deposited silver and does not contain impurities such as silver ions on the surface, so that the surface of the deposited silver can be kept clean at low temperatures. It is thought that it contributes to fusion. On the other hand, in the method for producing silver fine particles protected with long-chain fatty acid ions described in Non-Patent Document 1, since the long-chain fatty acid ions compensate for the charge of silver, the silver fine particle surface contains silver ions as impurities. Conceivable. For this reason, as shown in Comparative Example 2, when the surface treatment of metallic copper is performed by such a method, silver ions act as impurities, and the silver atomic layer deposited on the copper surface is not necessarily metallic copper. It is presumed that no good bond is formed between the two.

There is no particular limitation on the form of metallic copper to be treated by the treatment method according to the present invention, and a silver atomic layer is covered with silver atoms generated by an amine complex thermal decomposition method on the surface of the metallic copper to be provided with fusibility. High fusing property can be imparted by attaching. For example, by attaching a silver atomic layer to the surface of a copper plate or the like by the treatment method according to the present invention, it is possible to improve the bondability by fusing the surfaces together. In particular, by applying a silver atomic layer to the copper fine particles by the processing method according to the present invention, a copper fine powder that is easy to fuse with each other and can be sintered at a low temperature to form a wiring or the like. Is possible.
Hereinafter, embodiments of the present invention will be specifically described.

(Substrate to be surface treated)
The substrate treated by the surface treatment according to the present invention will be described in detail below with reference to pure copper containing only inevitable impurities and metallic copper containing copper alloy containing copper as a main component and an appropriate alloy element. However, the substrate to be treated by the surface treatment according to the present invention is not limited to this, and any material can be used as long as it is a material in which silver atoms generated by the amine complex thermal decomposition method are deposited to form an atomic layer. Processing can be performed by surface treatment. That is, for example, the present invention can be applied to the surface of inorganic compounds and resins such as iron, steel, stainless steel, nickel-base alloys, copper, aluminum, and alloys thereof, and ceramics that are not conductive. It is.

The form and size of the metallic copper to be treated by the surface treatment according to the present invention are not particularly limited, and a degreasing process in which an appropriate form such as a plate shape, a foil shape, a wire shape (wire), or a powder shape is generally used. Alternatively, it can be used after being cleaned by performing an appropriate pretreatment such as acid cleaning or alkali cleaning. In addition, regarding the surface on which the silver atomic layer is deposited by the surface treatment according to the present invention, it is desirable that the metal phase is exposed without the presence of an oxide layer or the like, but the copper oxide formed on the surface of the metal copper Since it is dissolved and removed in the alkylamine bath used in the surface treatment according to the present invention, the surface treatment according to the present invention can be performed even if copper oxide is present on the surface of the metal copper to be treated. However, it goes without saying that in order to maintain the cleanliness of the alkylamine bath, it is desirable to remove the surface copper oxide before the start of the treatment.
Moreover, when performing the surface treatment which concerns on this invention with respect to copper fine powder for the purpose of using for wiring formation etc., the copper which was previously provided with various attributes for having a desirable characteristic when used in the form of copper paste etc. It is preferable to use a fine powder. Examples of such copper fine powder include copper fine powder produced by using a wet reduction method disclosed in JP-A-2005-314755, and water atomization disclosed in JP-A-2005-222737. Examples thereof include fine copper powder obtained by the method.

On the other hand, in one preferable embodiment of the present invention, a copper fine powder produced by reducing a compound containing copper in an alkylamine bath is used as the copper fine powder for performing the surface treatment according to the present invention. Can be mentioned. In these copper fine powders, since the surface of the copper fine powder is previously coated with an alkylamine as a protective film, the copper fine powder can be used easily and easily dispersed in the alkylamine bath for performing the surface treatment according to the present invention. . In particular, in the copper fine powder produced by the method described in JP2012-072418A and JP2014-148732A, the oxygen potential in the reaction system can be substantially ignored (deoxygenated). The surface treatment according to the present invention is performed for the purpose of wiring formation and the like because the surface of the fine powder is substantially free from an oxide layer because it is coated in a good condition with alkylamine. By this, it is possible to give further better sinterability. Further, in the copper fine powder described in the above publication, it is presumed that the density of oxygen atoms present in a solid solution in the copper fine powder is also low, so that the surface treatment according to the present invention will be described below. It can be preferably used also from the point of being considered to have high resistance to the formation of an oxide layer when sintering the copper fine powder after the sinter.
In the production of copper fine particles described in the above publication, copper fine particles coated with an alkylamine are produced using a copper-containing compound formed by bonding copper and other atoms (or atomic groups) as a supply source of copper atoms. To do. As a copper-containing compound to be used, any compound that can form a complex compound such as a complex with a reducing compound described later can be used as a metal source of copper fine particles.

  Examples of such copper-containing compounds include copper oxalate, copper formate, copper acetate, copper propionate, copper butyrate, copper isobutyrate, copper valerate, copper isovalerate, copper pivalate, copper malonate, and succinate. Examples include organic acid salts and inorganic acid salts of copper such as copper oxide, copper maleate, copper benzoate, copper citrate, copper tartrate, copper nitrate, copper nitrite, copper sulfite, copper sulfate, and copper phosphate. In addition, complex compounds represented by acetylacetonato copper coordinated with acetylacetone are exemplified.

  In the method for producing copper fine particles, first, a reducing compound having a reducing action is mixed with the copper-containing compound to produce a composite compound of a metal compound and a reducing compound. In such a composite compound, since the reducing compound becomes an electron donor to the copper ion in the copper-containing compound and easily causes reduction of the copper ion, the copper atom is spontaneously decomposed compared with the copper-containing compound used. Is likely to occur. For this reason, by using such a composite compound as a direct raw material for supplying copper atoms, it is not limited by the supply of substances involved in the reaction, and the composite compound can be set by setting conditions such as temperature and pressure. By causing a spontaneous decomposition reaction, copper atoms are supplied, and copper fine particles can be produced.

  As the reducing compound used in this case, those having an amino group are preferable. The reducing agent having an amino group easily forms a coordinate bond with a copper atom or the like in the copper-containing compound, and easily forms a composite compound with the copper-containing compound while maintaining the structure of the copper-containing compound. This is because a reduction reaction of copper occurs. As such a reducing compound, in particular, as long as it forms a composite compound that causes reduction / release of a copper atom by a spontaneous decomposition reaction in a temperature range in which evaporation or decomposition of the alkylamine as a reaction medium does not occur. Although not limited, typically, a compound selected from the group consisting of hydrazine, hydroxylamine, and derivatives thereof is particularly preferable. In these compounds, a nitrogen atom constituting the skeleton is bonded to a copper atom in the copper-containing compound by a coordination bond to form a composite compound. In addition, since the reducing power is generally stronger than that of alkylamine, the resulting composite compound undergoes spontaneous decomposition under relatively mild conditions to reduce and release copper atoms, and copper fine particles coated with alkylamine Can be generated.

  Here, the hydrazine derivative means one obtained by substituting 1-3 of hydrogen contained in hydrazine with a predetermined alkyl group or the like. Further, the hydroxylamine derivative means one obtained by substituting one of hydrogen contained in hydroxylamine with a predetermined alkyl group or the like. It is possible to adjust the reactivity with the copper-containing compound by appropriately selecting and using its derivatives instead of hydrazine and hydroxylamine, and spontaneously under appropriate conditions depending on the copper-containing compound used. Complex compounds that produce degradation can be produced. In particular, when using a copper-containing compound that easily causes a reduction reaction without generating a composite compound when mixed with hydrazine, it is effective to promote the formation of the composite compound by using an appropriately selected hydrazine derivative.

  Next, the composite compound produced above is heated in the presence of a sufficient amount of alkylamine, and copper atoms are formed and aggregated by the spontaneous decomposition reaction of the composite compound, thereby protecting the alkylamine used. Copper fine particles coated with a film can be obtained.

As described above, by performing the surface treatment according to the present invention, the silver atomic layer formed on the surface of the metallic copper functions as a binder at the time of fusion (sintering), and the surfaces of the metallic copper are bonded to each other. Compared with the fusion, the fusion temperature can be remarkably lowered, which is also useful from the viewpoint of preventing the oxidation of metallic copper. In addition, since the silver atomic layer suppresses the intrusion of oxygen into the metallic copper, the oxidation resistance due to oxygen from the sintering atmosphere can be improved particularly in the copper fine particles subjected to the surface treatment according to the present invention. Due to such a synergistic effect on oxidation resistance, the present invention is particularly effective for copper fine particles in which oxidation during sintering is a problem.
That is, the particle diameter of the copper fine particles to be surface-treated according to the present invention is not particularly limited, but a reducing atmosphere is particularly necessary during sintering even when fine copper fine particles having an average particle diameter of 50 nm or less are used. However, a good conductor can be formed by suppressing generation of an oxidized phase in a non-oxidizing atmosphere such as an inert gas atmosphere. In addition, when copper fine particles having an average particle diameter of 50 nm or more, and further 100 nm or more are used, before the oxidation phase is substantially generated even when sintering is performed in an air atmosphere by performing the surface treatment according to the present invention. It is possible to obtain a good conductor by completing the sintering. The reason why the fine particles of metal copper, which is a problem of oxidation, can be easily sintered in the atmosphere, is that in addition to the above-described effect of reducing the sintering temperature according to the present invention and the effect of suppressing the entry of oxygen into the copper fine particles, copper It is considered that the specific surface area of the copper fine particles decreases as the particle size of the fine particles increases, and the amount of oxygen permeation per unit volume can be reduced. On the other hand, from the viewpoint of forming fine printed wiring, it is desirable that the average particle diameter of the copper fine particles is 10 μm or less, preferably 1000 nm or less, more preferably 500 nm or less, and still more preferably 300 nm or less, depending on the application.

(Amine complex for supplying silver atoms in surface treatment)
In the surface treatment method according to the present invention, when a predetermined amine complex composed of a silver-containing compound and an alkylamine is heated and thermally decomposed, metallic copper is interposed, so that silver generated by decomposition of the amine complex on the surface Atom is deposited to form an atomic layer of silver. As the said amine complex used in this invention, the amine complex used in order to produce | generate silver fine particles in patent documents 4-7 is used, for example.

  A method of generating and supplying silver atoms by decomposing an amine complex is that a compound containing silver and an alkylamine form a complex compound, which makes the structure of the compound containing silver unstable and generally lowers the thermal decomposition temperature. Is to use that. In other words, via an amine complex, a compound containing silver is thermally decomposed at a relatively low temperature without using a reducing agent that is essential in a normal wet reduction reaction. It is possible to supply silver atoms having a relatively low potential, which is less likely to cause nonuniform reaction due to fluctuations in composition in the system. In addition, the alkylamine that formed the complex compound is considered to be attached to the silver atom even after the silver-containing compound is thermally decomposed. When the silver atom aggregates while suppressing the mobility of the silver atom In order to form the surface protective film, it is considered that the silver atom functions to prevent coarse aggregation of silver atoms.

(Silver compounds used in amine complexes)
As a silver compound used to form an amine complex to form silver atoms, it can form complexes with various alkylamines and easily decomposes by heating to produce atomic silver A silver compound is preferably used. Typical examples of such silver compounds include silver carboxylates in which silver atoms are combined with carboxylic acids such as formic acid, acetic acid, oxalic acid, malonic acid, benzoic acid, and phthalic acid, as well as silver chloride, silver nitrate, and silver carbonate. These can be used, and one or two or more of them can be mixed and used. Moreover, as a silver compound, the thing which does not produce the component which remains as an impurity in a reaction system after thermal decomposition is especially preferable. For example, when a fatty acid, which is a carboxylic acid having a long-chain or medium-chain alkyl group, is used, a compound containing an alkyl chain generated by thermal decomposition is incorporated into the protective film, thereby reducing the detachability of the protective film. The tendency to do is seen. From this point of view, silver oxalate is preferably used in which no by-product remains substantially in the reaction system after thermal decomposition. Silver oxalate has a high silver content and is usually easily decomposed at a low temperature of about 200 ° C. In addition, since oxalate ions are removed as carbon dioxide during decomposition, metal silver is obtained, so that impurities hardly remain. Is advantageous. As the silver oxalate used in the method of the present invention, for example, commercially available silver oxalate can be used. Moreover, you may use the silver compound which substituted the oxalate ion of silver oxalate by 1 or more types of 20 mol% or less of carbonate ion, nitrate ion, and oxide ion. In particular, silver oxalate in which 20 mol% or less of the oxalate ions are substituted with carbonate ions has improved thermal stability. However, when the substitution amount exceeds 20 mol%, the complex compound formed using the oxalate ions is thermally decomposed. It may be difficult. In addition, two or more kinds of silver compounds can be mixed and used as necessary.

(Alkylamine used for amine complex)
In the present invention, alkyl monoamines, alkyl diamines and the like in which an amino group is bonded to a part of the alkyl group are desirably used as the alkyl amine. In this specification, an alkylamine includes an alkyl monoamine in which one amino group is bonded to an alkyl group, and an alkyl diamine in which two amino groups are bonded to an alkyl group. Moreover, when distinguishing both, it describes as alkyl monoamine and alkyldiamine, respectively.
In the present invention, alkyl monoamines are mainly used as alkyl amines, but alkyl diamines can be appropriately mixed and used according to the purpose of surface treatment.

The alkylamine that can be used in the present invention is capable of forming a coordination bond via an amino group to the surface of a silver atom, so that the amino group contained in the amine moiety is a primary amino group. a is preferably an alkyl amine ^R 1 ^R 2 NH ₂ or secondary amino group. In the present specification, R, R ¹ and R ² each independently represent a hydrocarbon group, and these hydrocarbon groups contain a hetero atom such as an oxygen atom, a nitrogen atom, a sulfur atom or a silicon atom. May be. By including a primary or secondary amino group, a complex bond between the amine moiety and the metal compound can be formed by generating a coordinate bond to the metal atom by the unshared electron pair of the nitrogen atom in the amino group, As a result, an alkylamine film can be formed on the surface of silver atoms.

  As described above, in the present invention, an alkylamine facilitates thermal decomposition of a compound containing silver and functions as a surface protective film for silver atomic layers and silver fine particles generated by thermal decomposition. For this reason, an alkylamine that is stably present in the reaction system during thermal decomposition of a compound containing silver and that exhibits desirable characteristics when deposited on a silver atomic layer produced as a protective coating is appropriately selected. It is desirable to use it. In alkylamines and the like, generally, as the molecular weight of an alkyl group increases and becomes a long chain, the vapor pressure tends to decrease and the boiling point tends to increase. On the other hand, when the alkyl group has a small molecular weight and a short chain, the vapor pressure is high and the polarity tends to be strong. In addition, alkyldiamines having two amino groups in one molecule tend to be more polar than alkylmonoamines having one amino group in one molecule. According to the present invention, these arbitrary alkylamines can be used, and those alkyl groups containing 2 to 5 carbon atoms are short chain, those having 6 to 12 carbon atoms are medium chain, carbon Those having a number of 13 or more are defined as long chains, and their characteristics will be described below.

  Long- and medium-chain alkyl monoamines generally have low vapor pressures and are unlikely to evaporate, and because they have a high affinity with organic solvents, these alkyl monoamines and amine mixtures containing them can be used. A film containing a long-chain / medium-chain alkyl monoamine at a predetermined ratio on the surface of the silver atomic layer generated by the surface treatment will be generated, and the storage stability will be improved and the coating into a nonpolar organic solvent will be achieved. Dispersibility can be improved. In this regard, for example, when the copper fine powder surface-treated according to the present invention is dispersed in an appropriate organic solvent and used as an ink or the like, the alkylamine used includes a long-chain / medium-chain alkyl monoamine. It is desirable.

  Examples of such long and medium chain alkyl monoamines include dipropylamine (107 ° C), dibutylamine (159 ° C), hexylamine (131 ° C), cyclohexylamine (134 ° C), heptylamine (155 ° C). ), 3-butoxypropylamine (170 ° C), octylamine (176 ° C), nonylamine (201 ° C), decylamine (217 ° C), 3-aminopropyltriethoxysilane (217 ° C), dodecylamine (248 ° C), Alkylmonoamines such as hexadecylamine (330 ° C), oleylamine (349 ° C), octadecylamine (232 ° C (at 32 mmHg)) are practical in terms of easy availability, but are not limited thereto. For other long and medium chain alkyl monoamines having 6 or more carbon atoms, It can be used depending on.

  On the other hand, generally, as the alkyl chain of the alkyl monoamine becomes longer, the tendency of forming a complex compound with the silver compound decreases. Generally, long- and medium-chain alkyl monoamines are simply mixed with the silver compound. In some cases, it is difficult to form a complex compound.

On the other hand, when an alkyl diamine or a short-chain alkyl monoamine having 5 or less carbon atoms is used, a complex compound with a silver compound can be formed relatively easily. For this reason, when producing | generating a silver atom by decomposition | disassembly of an amine complex, it is also effective to use such an alkyldiamine and a short-chain alkylmonoamine with 5 or less carbon atoms as an alkylamine. On the other hand, short-chain alkyl monoamines having 5 or less carbon atoms have a high vapor pressure. Therefore, evaporation when heating the amine complex to decompose the silver compound becomes a problem. Further, when a large amount of alkyldiamine is used, the protective film formed on the silver surface tends to be difficult to be detached during sintering. This is presumably because the structure of the protective coating is complicated due to the fact that the alkyldiamine contains two amino groups.
Considering the characteristics of various alkylamines as described above, the main components are long- and medium-chain alkyl monoamines, which are expected to be stable when silver atoms are formed and to form a good protective film. By using a short-chain alkyl monoamine having 5 or less carbon atoms in a predetermined ratio mainly as an auxiliary aid for the formation of the complex compound, the advantages of both can be utilized. That is, by using a mixture containing an alkylamine in which both are mixed at an appropriate ratio, a complex compound with a silver compound can be formed well, and a good surface treatment can be performed, and the metallic copper after the surface treatment can be obtained. It is possible to impart desirable fusing properties to the film.

  Examples of the short-chain alkyl monoamine include amylamine (boiling point 104 ° C.), 2-ethoxyethylamine (105 ° C.), 4-methoxybutylamine, diisopropylamine (84 ° C.), butylamine (78 ° C.), diethylamine (55 ° C.), Propylamine (48 ° C.), isopropylamine (34 ° C.), ethylamine (17 ° C.), dimethylamine (7 ° C.) and the like are commercially available and are desirably used.

  The alkyl diamine has a boiling point of 100 ° C. or higher if the thermal decomposition temperature of the complex compound is taken into consideration, and 250% if the fusion or sinterability of the metallic copper after the surface treatment is taken into consideration at a low temperature. It is considered that the boiling point is not higher than ° C. For example, ethylenediamine (118 ° C), N, N-dimethylethylenediamine (105 ° C), N, N'-dimethylethylenediamine (119 ° C), N, N-diethylethylenediamine (146 ° C), N, N'-diethylethylenediamine ( 153 ° C.), 1,3-propanediamine (140 ° C.), 2,2-dimethyl-1,3-propanediamine (153 ° C.), N, N-dimethyl-1,3-diaminopropane (136 ° C.), N , N′-dimethyl-1,3-diaminopropane (145 ° C.), N, N-diethyl-1,3-diaminopropane (171 ° C.), 1,4-diaminobutane (159 ° C.), 1,5-diamino 2-methylpentane (193 ° C.), 1,6-diaminohexane (204 ° C.), N, N′-dimethyl-1,6-diaminohexane (228 ° C.) , 1,7-diaminoheptane (224 ° C.), 1,8-but-diamino octane (225 ° C.), and the like, but is not limited thereto.

(Additional aid for other complex compounds)
As described above, the inclusion of a long-chain / medium-chain alkyl monoamine in a complex compound with a silver compound generally makes it possible to cause good thermal decomposition of the silver compound, and the atomic layer of silver produced thereby It is possible to form a good protective film on the surface. On the other hand, since it is difficult to form a complex compound with a silver compound only by a long chain / medium chain alkyl monoamine, alkyldiamine or a short chain having 5 or less carbon atoms as a complex compound formation aid as described above. It is effective to use an alkyl monoamine. In addition to such complex compound formation aids, when forming a complex compound of a silver compound and an alkylamine, an alcohol compound having a certain degree of polarity and / or carbon atoms and heteroatoms in the molecule. It has been clarified that the formation of a complex compound of a silver compound and an alkylamine is facilitated by interposing a compound containing multiple bonds or multiple bonds of heteroatoms. The specific action of such an additive component is not necessarily clear, but in a silver compound in a solid state, molecules or ions containing silver as the silver compound aggregate to form crystals and the like.・ Coordination to silver atoms by medium-chain alkylamines, etc. does not proceed well, but when the compound is mixed with alkylamines, coordination bonds to silver compounds by alkylamines, etc. It is considered that complex compounds are formed efficiently. Such an effect is considered to be due to the fact that the compound efficiently disintegrates crystals of the silver compound and the like, and the frequency with which the alkylamine or the like contacts the silver compound is increased. In order to further enhance such effects, the compound comprising the additive component is preferably a solvent having excellent compatibility with the alkylamine.

  The alcohol compound having a certain degree of polarity or more is typically an alcohol compound exhibiting solubility in water, and as a linear alkyl alcohol having one OH group, from methanol having 1 carbon atom to carbon The octanol of number 8 is mentioned. On the other hand, when the number of carbon atoms is 9 or more, it does not substantially dissolve in water, and even if such an alcohol compound is interposed during the formation of the complex compound, the formation promoting effect of the complex compound is not observed. In addition to alkyl alcohols, phenols or those obtained by substituting hydrogen atoms of appropriate hydrocarbons having an ether bond in the molecule with OH groups can be used.

In an alcohol compound, strong polarity develops as the number of OH groups contained in one molecule increases, and in the present invention, glycols containing two OH groups and glycerin containing three OH groups are also present. Pentaerythritol containing 4 OH groups is preferably used.
Examples of such alcohol compounds include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, allyl alcohol, benzyl alcohol, pinacol, propylene glycol, menthol, catechol, hydroquinone, salicyl alcohol, pentaerythritol, sucrose, Examples thereof include glucose, xylitol, methoxyethanol, triethylene glycol monomethyl ether, pentaerythritol, and the like, and polyethylene glycols including ethylene glycol, triethylene glycol, tetraethylene glycol, and pentaethylene glycol.

  The amount of the alcohol compound used when forming the complex compound is preferably about 5 mol% to 500 mol% with respect to the alkylamine used when generating the complex compound. When the amount of the alcohol compound used is 5 mol% or less with respect to the alkylamine, there is a tendency that the complex compound formation promoting action is not sufficient. On the other hand, when the amount of the alcohol compound used is 500 mol% or more with respect to the alkylamine, the activity of the alkylamine tends to be reduced and the formation of the complex compound tends to be inhibited.

  In particular, when the amount of the alcohol compound used is about 10 mol% to 300 mol% with respect to the alkylamine, the formation of the complex compound is favorably promoted and a good complex compound can be produced. . Further, when the proportion of the alcohol compound is increased within this range, the formation time of the complex compound is generally shortened, and the proportion of the alcohol compound contained in the complex compound is increased, so that the coated silver generated by the thermal decomposition of the complex compound. As the particle diameter of the fine particles increases, the dispersibility of the resulting coated silver fine particles in a polar solvent can be improved. On the other hand, by decreasing the proportion of the alcohol compound, the alcohol compound contained in the complex compound or the coating of the coated silver fine particles is decreased, and a tendency to obtain coated silver fine particles having a fine and dense coating is observed.

Most typically, the amount of the alcohol compound is preferably about 25 mol% to 100 mol% with respect to the alkylamine, but the type and proportion of the alcohol compound to be specifically used are the coated silver fine particles to be produced. It is preferable to adjust appropriately according to the characteristics required for the above.
In addition to alcohol compounds, auxiliary agents that promote the formation of complex compounds of silver compounds and alkylamines include compounds that contain multiple bonds of carbon atoms and heteroatoms in the molecule or multiple bonds of heteroatoms. . In such compounds, the distribution of electrons related to the bonds belonging to the heteroatoms that form multiple bonds is biased by the multiple bonds, and the unshared electron pairs of the heteroatoms tend to be exposed. It is known that activity for reactions involving electron pairs tends to improve. Although the specific reason why the formation of the complex compound is promoted by interposing the compound having the predetermined multiple bond in forming the complex compound of the silver compound and the alkylamine is not clear, the compound is as described above. It is presumed that the inclusion of a hetero atom having an active unshared electron pair is related to the promotion of the formation of a complex compound.

  More specifically, the compounds used for this purpose include carbonyl compounds and isocyanate compounds containing carbon and oxygen double bonds, oxime compounds containing multiple bonds of carbon and nitrogen, Schiff base compounds and nitriles. Examples include compounds, nitro compounds and nitroso compounds containing multiple bonds of oxygen and nitrogen, and azo compounds, diazo compounds and azides containing multiple bonds of nitrogen atoms. A complex compound of a silver compound and an alkylamine can also be promoted by a compound containing a multiple bond related to sulfur, phosphorus or the like as a hetero atom. However, for example, in the production of silver fine particles used to form conductive wiring, since the sulfur atoms and phosphorus atoms tend to be adversely affected, the use of the produced silver fine particles It is desirable to consider use accordingly.

  In addition, for compounds used for this purpose, the effect of promoting the formation of complex compounds decreases as the number of carbons contained in the compound and the number of carbons contained in each functional group in the compound increase. The tendency to do is observed. The effect of the number of carbons on the action of promoting the formation of complex compounds varies depending on the basic structure of the compound. For example, in a compound having one multiple bond, the number of carbons contained in the compound generally exceeds 14. There is a tendency for the effect of promoting the formation of complex compounds to decrease. On the other hand, when the number of carbon atoms contained in the compound is 7 or less, generally a remarkable effect of promoting the formation of complex compounds is observed.

  As an example of a carbonyl compound as a compound used in the formation of a complex compound of a silver compound and an alkylamine in the present invention, a ketone compound can be mentioned, and non-limiting examples thereof include acetone, methyl ethyl ketone. Acetylacetone, 2-butanone, 3-pentanone, 4-heptanone, 4-methyl-3-penten-2-one (mesityl oxide), 4-methyl-2-pentanone, diacetyl, pinacholine, 2,4-dimethylpenta Non, aliphatic such as 2,6-dimethyl-3-heptanone, isoamyl methyl ketone, 3-methyl-2-butanone, 5-methyl-heptanone, 4-methyl-2-pentanone, ethynyl isopropyl ketone, 2-octanone, etc. Ketone, cyclopentanone, cyclohexanone, 2-cyclohexenone, iso Ron, dicyclohexyl ketone, alicyclic ketones etc., as well as acetophenone, benzophenone, 4-phenyl-2-butanone, isobutyrophenone phenone, benzalacetone, aromatic ketones such as propiophenone.

Further, as ketone compounds, methyl acetoacetate, ethyl acetoacetate, dimethyl acetylsuccinate, α-acetyl-γ-butyrolactone, acetoacetate, methyl pyruvate, pyruvate, N, N-dimethylacetoacetamide, acetoacetanilide, Examples thereof include keto acid compounds containing an oxygen atom such as N-acetoacetylmorpholine.
In addition, as an example of the carbonyl compound used in the formation of the complex compound in the present invention, an aldehyde compound in which one hydrogen atom is bonded to the carbonyl carbon can be given, and non-limiting examples thereof include propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-pentylaldehyde, 2-methylbutyraldehyde, n-hexylaldehyde, 2-methylpentanal, n-heptylaldehyde, 2-hexenal, n-octylaldehyde, benzaldehyde, cuminaldehyde, anise Aldehyde, chlorobenzaldehyde, cinnamaldehyde, crotonaldehyde, isobutyraldehyde, butyraldehyde, pyrubinaldehyde, terephthalaldehyde, tolualdehyde, ethynyl phenyl ketone, furfural Among these, a particularly preferable aldehyde compound is an aliphatic or aromatic aldehyde having 3 to 14 carbon atoms, and more preferably 3 to 7 carbon atoms. Is an aliphatic aldehyde.

  In addition, ester compounds, amide compounds, carboxylic acid amide compounds, isocyanate compounds (R—N═C═O), oxime compounds (> C═N—OH), nitrile compounds, azo compounds, diazo compounds and azides A compound etc. can also be mentioned. These specific modes are described in JP 2014-31542 A or JP 2014-40630 A, and are incorporated herein by reference.

The alcohol compound and the compound containing a predetermined multiple bond as described above can be appropriately selected and used according to the type of alkylamine used, the properties expected of the copper-silver composite to be produced, and the like. In addition, it is possible to use a combination of a plurality of types of compounds. In addition to the reaction time for complex formation, the combination of the types of alkylamines and the characteristics expected of silver copper and surface-treated metallic copper are considered. It is also possible.
In particular, compounds that assist in the formation of complex compounds are also included in the complex compounds that are produced and in the covering portion of the silver atomic layer that is produced by thermally decomposing them, so various compounds are appropriately selected in the present invention. By using these, various functions can be added to the metal copper to be surface-treated. For this reason, even when a short-chain alkylamine or alkyldiamine is present, the compound can be interposed as a means for imparting a predetermined characteristic to the metal copper to be surface-treated, together with the aid of the formation of the complex compound.

(Amine complex formation process)
In general, the amine complex is formed by mixing a predetermined amount of an alkylamine with a powdery silver compound. At this time, it is effective to promote the formation of the amine complex by interposing a predetermined compound for assisting the formation of the amine complex described above and a small amount of water as an auxiliary agent for the formation of the amine complex. As a method of interposing an amine complex formation aid in the reaction system, a silver compound may be added to a mixture of an alkylamine and an amine complex formation aid prepared in advance, and an amine complex formation aid is mainly used. An appropriate method can be used such as mixing with a silver compound and crushing the silver compound and then adding an alkylamine to form an amine complex.

  The formation process of the amine complex is, for example, by utilizing the fact that the crystal of the silver compound etc. is crushed and the generated complex compound generally exhibits a color corresponding to its constituent components, thereby completing the color change of the mixture by the reaction. Can be detected by an appropriate spectroscopic method or the like to detect the end point of the amine complex formation reaction. In addition, the complex compound formed by silver oxalate, which is mainly used in the following examples, is generally colorless (white), but even in this case, the formation of the complex compound is based on the change in form such as the viscosity of the mixed solution is changed. The state can be detected.

  In the present invention, it is not always necessary to complete the generation of the amine complex before heating for thermal decomposition of the amine complex, and the generation of the amine complex is promoted by appropriately heating in the process of forming the amine complex. be able to. The generation of the amine complex is preferably performed in a temperature range in which the generation of the decomposition reaction of the silver compound and the evaporation of the alkylamine and the amine complex generation auxiliary agent can be suppressed. Typically, the complex compound can be produced by stirring at around room temperature, but it is also possible to heat the complex compound in a range that does not cause the decomposition reaction of the silver compound in terms of promoting the formation of the complex compound. . Moreover, since the coordination reaction of the amine with respect to the silver compound is accompanied by heat generation, it is also preferable to carry out stirring while cooling to room temperature or lower as necessary in order to suppress the decomposition reaction of the silver compound.

  In the formation of a complex compound of a silver compound and an alkylamine, it is desirable that the total amount of alkylamine to be used is greater than or equal to the stoichiometric amount (equal mole) of silver atoms contained in the silver compound. If the total amount of alkylamine is less than the stoichiometric amount with the silver atom, a silver compound that does not become a complex compound is generated, so that enlargement or subsequent thermal decomposition does not occur during the formation of silver fine particles. This is not preferable because a silver compound remaining in the substrate is generated. Typically, silver fine particles having a uniform particle diameter can be stably obtained by mixing an alkylamine having a molar amount of 2 times or more of silver atoms when a complex compound is formed. Moreover, since the excess alkylamine which does not form a complex compound with a silver compound remains in a reaction system, it can be used as it is as a reaction medium when performing surface treatment of metallic copper in the next step. It is also possible to separate the produced complex compound from an excess of alkylamine and add another solvent as a reaction medium to perform the surface treatment of metallic copper.

  In one embodiment, when silver carboxylate such as silver oxalate or silver acetate is used as the silver compound, both the oxygen atom derived from the carboxylic acid and the nitrogen atom derived from the alkylamine are coordinated to the silver atom. It is preferable as a complex compound used in the present invention. The ratio of the number of oxygen atoms and the number of nitrogen atoms coordinated to silver atoms is not particularly limited, but a silver complex in which the number of oxygen atoms and nitrogen atoms is coordinated at a ratio of 2: 1 to silver atoms is particularly preferable. .

  Depending on the complex compound used, the reaction for generating silver atoms is different. For example, when silver oxalate is used as the silver compound, it is heated at about 100 ° C. or lower by heating in an alkylamine. Silver atoms are generated while generating carbon dioxide. This is because atomic silver is generated by thermal decomposition of the complex compound, and a reaction in which the oxalate ion is changed to carbon dioxide gas progresses. In the thermal decomposition of the complex compound, the reaction atmosphere is maintained inactive by the generated carbon dioxide gas. Therefore, even when the surface treatment of the metallic copper is performed by thermal decomposition of the complex compound in the air, the oxidation of the metallic copper is performed. Is effectively suppressed, and stable surface treatment of metallic copper is possible.

(Generation of silver atoms by thermal decomposition of amine complexes and deposition on metallic copper surfaces)
By heating the complex compound of the silver compound and amine mixture produced as described above, the silver compound contained in the complex compound is decomposed to liberate silver atoms, and these come into contact with the surface of metallic copper in the presence of alkylamine. As a result, a silver film is formed on the surface of the metallic copper. The binary phase diagram of metallic copper and metallic silver is a typical eutectic type, and it is known that there is no solid solution region where the other forms a solid solution in any phase particularly at 200 ° C. or lower. Further, as shown as Comparative Example 3 of the present invention, even when silver fine particles and copper fine particles produced by an amine complex decomposition method are mixed and sintered, mutual fusion hardly occurs, and a good conductor and For example, it is presumed that the affinity between copper and silver in the solid phase is low. Nevertheless, although the mechanism by which the silver film is formed in close contact with the surface of the metallic copper according to the present invention is not clear, the potential of the silver atom produced by thermal decomposition of the amine complex is responsible for the nucleation of metallic silver. Is not necessarily sufficient, and a mechanism such as a state change in which silver atoms precipitate in a metastable state on the surface of metallic copper existing in the reaction system may be considered. On the other hand, when silver fine particles and copper fine particles are mixed and sintered as described above, it is difficult to cause movement of atoms between copper and silver having low affinity and hardly cause fusion. Conceivable.
In addition, in the process of generating silver atoms by the amine complex thermal decomposition method used in the present invention, atomic silver is supplied by the thermal decomposition reaction of a single component (complex compound) generated in advance, so a reducing agent was used. Compared to the case of a chemical reaction between a plurality of components, it is presumed that unevenness of the reaction due to fluctuations in the concentration of each component is less likely to occur, and a uniform silver film can be formed on the coated metal surface. For this reason, the method of the present invention by the amine complex decomposition method is considered to be advantageous particularly in a large-scale industrial production process in which it is difficult to uniformly mix a plurality of components involved in the reaction.

  When a silver compound complexed by coordination of alkylamine is released by thermal decomposition etc. under appropriate conditions to release atomic silver, the alkylamine is released with respect to the released atomic silver. It is inferred that the molecule maintains a coordinate bond via the amino group. For this reason, when free atomic silver aggregates with each other to form an aggregate, an alkyl chain fixed by a coordinate bond of an amino group is present at a high density around the aggregate to form a film. As a result, the generated silver atoms are prevented from growing beyond a predetermined thickness or size.For example, when the silver amine complex is thermally decomposed on the surface of the copper fine particles, A silver shell is formed on the surface, and fine particles whose surface is coated with an alkylamine are formed.

  The step of precipitating silver atoms generated by the amine complex thermal decomposition method on the surface of the metallic copper is desirably performed by heating the amine complex generated as described above in a reaction medium containing an alkylamine. In other words, after forming an amine complex by mixing an amine complex formation auxiliary agent such as an excess of alkylamine or alcohol compound with respect to the silver compound, the metal copper to be subjected to surface treatment using the remaining alkylamine or the like as a reaction medium. It may be added and heated as it is, and if necessary, an appropriate alkylamine or the like may be further mixed to form a reaction medium. Also, after separating the amine complex from the mixture containing the produced amine complex by a method such as centrifugation, the mixture is heated in a state of being remixed with a reaction medium containing an appropriate alkylamine or the like and metal copper for surface treatment. It is also possible to perform surface treatment of metallic copper by substituting a part of alkylamine or the like forming an amine complex with another alkylamine. In addition, when the copper metal to be surface-treated does not cause an unintended reaction with each component forming the amine complex, the metal copper is put into the reaction system for forming the amine complex, It is also possible to carry out the surface treatment by heating as it is after forming.

  The temperature at which the amine complex is thermally decomposed to liberate atomic silver varies depending on the type of amine complex to be used, but in general, it should be performed in the temperature range immediately above the temperature at which the liberation of the atomic silver starts. preferable. On the other hand, when excessive heating is performed, the coordination bond of the alkylamine to the silver is easily released, so that the silver deposition process on the metal copper surface becomes unstable and coarse particles are easily generated. It is not preferable. In view of active evaporation of alkylamine or the like constituting the reaction medium, the temperature at which atomic silver is liberated from the amine complex is preferably as low as possible within the range in which atomic silver is liberated. Specifically, it is preferable to decompose the silver compound contained in the amine complex by heating to a temperature range of 70 to 150 ° C., more typically 80 to 120 ° C.

In the present invention, silver carboxylate is preferably used as the silver compound, and silver oxalate / silver acetate is particularly preferably used. Silver oxalate usually decomposes at about 200 ° C., and oxalate ions are removed as carbon dioxide, leaving metallic silver. On the other hand, by using an amine complex by the method according to the present invention, the thermal decomposition temperature of the silver oxalate portion is lowered, and thermal decomposition occurs at a temperature of about 100 ° C., thereby making it possible to liberate metallic silver. Similar to the above, this temperature is desirably set to a low temperature within a range in which thermal decomposition of oxalate ions occurs. However, since the rate of thermal decomposition increases as the temperature rises, it is good for the surface of metallic copper. The heating temperature can be appropriately increased within a range where a silver film can be obtained.
In the present invention, when surface treatment is performed by thermal decomposition of an amine complex, other components can be interposed without departing from the spirit of the present invention. For example, it is also effective to include a reducing substance or an adsorbing substance in the reaction system for converting into a substance that does not affect the surface treatment by reacting with a by-product generated by decomposition of the silver compound.

(Dispersion medium)
It is desirable to store the metallic copper surface-treated by the method according to the present invention under the condition that the protective film containing alkylamine formed on the outermost surface by the surface treatment is not detached. In particular, when the surface treatment of copper fine particles is performed, depending on the application used, the selection of the alkylamine used mainly, for example, polar solvents such as alcohol and ester solvents, nonpolar such as octane It can be used as a dispersion liquid dispersed at a high concentration in an appropriate organic solvent such as a solvent or a mixed solvent thereof. Moreover, it can be set as a paste-form composition. By using the copper fine particles subjected to the surface treatment by the method according to the present invention as a dispersion or paste, it can be preferably used as a material for forming wirings at a particularly low temperature.
The organic solvent used in the case of dispersing the copper fine particles that have been surface-treated by the method according to the present invention to form a dispersion is one that hardly causes desorption of alkylamine or the like contained in the protective film of the copper fine particles. Preferably used.

(Silver coated copper)
An example of the silver-coated copper surface-treated by the method of the present invention is shown in FIG. FIG. 1 shows a surface obtained by depositing silver on the surface of a commercially available copper plate by the method according to the present invention, in which silver fine particles mainly having a particle size of about several tens of nanometers adhere to the surface of the copper plate coated with metallic silver Is shown. By bringing the surfaces of the metal copper in such a state into close contact with each other under an air atmosphere, the surfaces of the metal copper can be fused and joined even at room temperature, as shown in FIG.
FIG. 7 shows the copper fine particles coated with silver by the method according to the present invention on the alkylamine-coated copper fine particles produced in Example 2 (2.1) and the like, and the surface is coated with metallic silver. And a mixture of fine silver particles is shown. For such silver-coated copper fine particles, the particle size of the silver-coated copper fine particles can be selected by selecting the particle size of the copper fine particles as the core according to the purpose of use. The particle size of the silver-coated copper fine particles is typically about 50 nm to 10 μm, preferably about 100 nm to 1 μm, more preferably about 100 nm to 500 nm. The surface of the particles is provided with a silver atomic layer having a thickness of about several nm to several tens of nm depending on the amount of silver produced, and silver fine particles having a particle diameter of 100 nm or less are present together. A copper-silver composite having a dense sintered structure can be obtained by fusing. Further, by covering these particle surfaces with a protective film containing an alkylamine having a thickness of about several nanometers, each silver-coated copper fine particle can exist independently and stably as shown in FIG. .

(Fusion treatment of silver-coated copper)
Joining by fusion between copper surfaces that have been surface-treated according to the present invention is performed by directly contacting metal silver with each other by removing a protective film containing alkylamine formed on the surface after the treatment. It can be carried out. For example, when fusing a surface-treated copper plate, by pressing the surfaces that have been surface-treated, alkylamine molecules attached to the surface are eliminated, causing contact between the metallic silver and the atmosphere. Even in an atmosphere, fusion can be caused at a temperature of about room temperature. In addition, it is also preferable to promote contact between metallic silver by washing and removing alkylamine molecules and the like attached to the surface to be fused in advance with an appropriate solvent. In the case of a copper fine particle or the like that has been subjected to surface treatment, fusion (sintering) can be started by applying a copper fine particle dispersed in an appropriate solvent and then evaporating and removing the solvent. In addition, by performing appropriate heating, evaporation of the solvent, alkylamine molecules, and the like is promoted and interdiffusion of silver atoms is promoted, so that the degree of fusion can be increased. The abundance ratio of copper and silver in the silver-coated copper fine particles is not particularly limited as long as at least a part of the surface of the metal copper is coated with metal silver, but is obtained by sintering the silver-coated copper fine particles. From the viewpoint of reducing the ratio of silver in the obtained copper-silver composite, the weight ratio of metal silver to metal copper may be ½ or less, preferably 1/5 or less, more preferably about 1/10. can do. By reducing the ratio of metallic silver to this level, it contributes to the reduction of manufacturing costs, and in particular, the resistance to electrolysis when a copper-silver composite obtained by sintering silver-coated copper fine particles is used as a wiring material. Migration can be improved.

  The surface treatment method according to the present invention is preferably applied particularly to the surface of metallic copper to be joined with the expectation of ensuring conductivity. For example, by using a copper plate surface-treated by the surface treatment method according to the present invention for a crimping element or the like, the connection resistance can be made lower than before. Moreover, it can replace with the conventional brazing (soldering) and can use the copper plate surface-treated by this invention. Further, the surface treatment according to the present invention can be applied to the contact pad used for wire bonding and the surface of the wire. In particular, the copper fine particles surface-treated according to the present invention are used in an appropriate form according to the characteristics and applications. For example, when silver-coated copper fine particles are applied in a predetermined shape by ink jet or the like to form a copper-silver composite film by low-temperature sintering, silver as a reaction medium is replaced with a desired organic solvent. It is desirable to store and use in a state in which the coating of the silver-coated copper fine particles is difficult to be removed by using an ink-like dispersion (dispersion) in which the copper-coated fine particles are dispersed in an organic solvent. Further, the silver-coated copper fine particles can be mixed and dispersed with an appropriate dispersion medium such as terpin oil and used as a paste. Further, in the case of silver-coated copper fine particles provided with a film mainly composed of a relatively long chain alkylamine, the silver-coated copper fine particles can be stored as a powdery product from which the amine as a reaction medium has been removed. .

(Composite metal body formed by sintering)
By using the silver-coated copper fine particles surface-treated according to the present invention, it is possible to obtain a composite metal body having sufficient conductivity with metallic copper as a main component even in the air and at room temperature without particularly adjusting the atmosphere. Can do. In the composite metal body obtained by fusing (sintering) the silver-coated copper fine particles surface-treated according to the present invention, the copper fine particles become a dispersed phase, and the copper fine particles are fused with the metallic silver on the surface as a binder. Alternatively, extremely good conductivity can be obtained by having a structure in which the copper fine particles are fused via the silver fine particles so that the silver matrix contains a copper dispersed phase. In particular, the density of the composite metal body can be increased by increasing the blending ratio of silver and increasing the temperature at the time of fusion, and high conductivity can be obtained. In the composite metal body according to the present invention, an ink or paste containing the silver-coated copper fine particles produced according to the present invention is applied to various substrates in a desired form and bonded by fusion between the silver-coated copper fine particles. Therefore, it is preferably used as a wiring constituting various electronic devices.

The fusion (firing) in obtaining the composite metal body according to the present invention is preferably performed at a temperature as high as possible within the allowable temperature range determined according to the purpose, and the conductivity and the processing time can be shortened. This is preferable. The upper limit of the fusing temperature is not particularly limited, but it is preferable to perform the treatment at 140 ° C. or lower because the oxidation of copper becomes remarkable in the temperature range of 140 ° C. or higher particularly in the treatment in the atmosphere. On the other hand, when performing fusion on the surface of a resin substrate having particularly low heat resistance, treatment at 120 ° C. or lower is preferable, and treatment at 100 ° C. or lower is particularly preferable. Further, as shown in the following examples, the composite metal body according to the present invention can exhibit good conductivity by causing fusion even at room temperature.
The atmosphere at the time of fusing the silver-coated copper fine particles according to the present invention to obtain a composite metal body is not particularly limited and can be treated in an air atmosphere, but in particular the reliability of the composite metal body as a wiring material From the viewpoint of improving the properties, it is also preferable to perform fusion in an inert gas atmosphere or a reducing gas atmosphere. Further, from the viewpoint of promoting fusion, fusion treatment in an atmosphere containing a large amount of water vapor is particularly preferable.
In the composite metal body according to the present invention, in the silver-coated copper fine particles to be used, in the range where the surface of the copper fine particles is coated with metallic silver, it is possible to reduce the ratio of silver to copper in terms of cost and electromigration resistance. Is desirable. Depending on the particle size of the copper fine particles used, for example, if the weight ratio of metal silver to metal copper when the copper fine particles are surface-treated to form silver-coated copper fine particles is about 1/2, copper Since the fine particles are covered with a sufficient amount of silver and fine silver fine particles are formed, particularly high fusing property can be obtained. Moreover, even if the weight ratio of metallic silver to metallic copper is about 1/5 or less, more preferably about 1/10, a composite metal body having good conductivity can be obtained.

The electrical conductivity of the composite metal body according to the present invention is determined according to its use and the like, but typically a composite metal body having a volume resistivity of 3.0 × 10 ⁻³ Ω · cm or less is easily obtained. be able to. In addition, a composite having a volume resistivity of about 1.0 × 10 ⁻³ Ω · cm to 1.0 × 10 ⁻⁴ Ω · cm or less is also obtained by the fusion treatment near room temperature, depending on the content of metallic silver. A metal body can be obtained. Furthermore, a composite metal body having a volume resistivity of about 2.0 × 10 ⁻⁵ Ω · cm or less can be obtained by performing a fusion treatment at about 100 ° C.

  On the other hand, in FIG. 12C in which the copper fine particles subjected to the surface treatment using the long-chain fatty acid silver described as Comparative Example 2 were sintered, it was observed that the silver fine particles remained on the copper surface. It was done. This is because the bond formation at the interface between copper and silver after surface treatment is insufficient, so silver does not function as a binder, and it is difficult to remove fatty acid ions that are protective molecules. It is considered that the fusion of the particles did not proceed and the electrical conductivity of the sintered composite metal body was not improved.

[Example 1] Surface treatment on the surface of a copper plate Surface treatment was performed on the copper plate by the surface treatment method according to the present invention by the method shown below, and the fusion property of the copper plate after the treatment was evaluated.
(1.1) Preparation of Amine Complex i) Alkylamine-Silver Oxalate Complex Compound An amine complex was prepared using silver oxalate as a silver compound for supplying silver atoms. Silver oxalate was synthesized by mixing silver nitrate (Kanto Chemical Co., Ltd., first grade) and oxalic acid dihydrate (Kanto Chemical, special grade). According to Patent Document 4, n-hexylamine (Tokyo Kasei Co., Ltd., special grade) 3.0 g (30 mmol), n-dodecylamine (Kanto Chemical, special grade) 0.25 g (1.3 mmol), N, N-dimethyl-1 , 3-Diaminopropane (Tokyo Kasei Co., Ltd., special grade) 0.75 g (7.3 mmol) mixed solution was added with 0.50 g (1.6 mmol) of silver oxalate and stirred at room temperature. An alkylamine-silver oxalate complex compound was formed in the alkylamine.

ii) Alkylamine-silver acetate complex compound The same as above except that 0.55 g (3.3 mmol) of silver acetate (Wako Pure Chemical Industries, Ltd.) was used instead of 0.50 g (1.6 mmol) of silver oxalate. The process produced alkylamine-silver acetate complex in excess of alkylamine. Silver oxalate contains 2 silver atoms per molecule, whereas silver acetate contains 1 silver atom per molecule, so the amount of silver atoms contained in the silver acetate used is Same as silver oxalate.

(1.2) Surface treatment of copper plate 1.0 g of a 0.3 mm-thick copper plate (HIKARI, HC0316) obtained by degreasing and washing each mixture of the alkylamine and amine complex produced above (15. as metallic copper). 9 mmol) was divided into 8 pieces, and each was added and heated and stirred at 80 ° C. Decomposition of the complex compound accompanied by generation of carbon dioxide was caused by heating. After heating and stirring for 2 hours, the surface-treated copper plate was taken out and washed with acetone and toluene.
In addition, for comparison, a known method (Non-patent Document 1) for synthesizing silver fine particles without using an amine complex is applied, and a copper plate is interposed when synthesizing silver fine particles by the method. Processing was performed (Comparative Example 1). In this document, silver myristate (C ₁₃ H ₂₇ COOAg), which is fatty acid silver, is reduced and decomposed by heating in triethylamine, which is a reducing agent, so that the surface of silver fine particles is protected by myristic acid ions. A method for producing myristic acid-protected silver fine particles is described. In Comparative Example 1, a thickness obtained by performing degreasing washing in the same manner as described above to a mixture obtained by adding 7.26 g (71.7 mmol) of triethylamine (Tokyo Kasei, special grade) and 1.19 g (3.55 mmol) of silver myristate. A 0.3 mm copper plate (1.0 g) was divided into 8 pieces, and the mixture was heated and stirred at 90 ° C. After heating and stirring for 3 hours, the copper plate was taken out and washed with acetone and toluene.

  1A to 1C show images of a field emission scanning electron microscope (FE-SEM, (JEOL Ltd., JFM-7600F)) of each copper plate subjected to surface treatment as described above. On the surface of the copper plate surface-treated with an amine complex containing silver oxalate (FIG. 1 (a)), a metallic silver coating is formed and silver particles of about several tens of nanometers are attached to the entire surface. Was observed. In addition, on the surface of the copper plate surface-treated with an amine complex containing silver acetate (FIG. 1 (b)), a coating of metallic silver is formed and slightly coarse silver particles are attached to the entire surface. The situation was observed. Further, it was observed that fine silver fine particles were uniformly deposited on the surface of the copper plate (FIG. 1 (c)) surface-treated by reductive decomposition of fatty acid silver. As described above, metallic silver could be deposited on the surface of metallic copper by placing a copper plate in a reaction system that causes thermal decomposition of an amine complex or in a system for reduction reaction of fatty acid silver.

(1.3) Fusing test of copper plates subjected to surface treatment In order to examine the fusing property between the copper plates subjected to surface treatment as described above, the copper plates subjected to surface treatment as described above are pressure-bonded at room temperature in the atmosphere. A test was conducted. The crimping was performed by stacking the copper plates that had been surface-treated as described above and pressing them in the atmosphere at room temperature and a load of 2 kN (about 200 kgf / cm ² ) for 10 seconds (Shimadzu, hand press SSP10A).
FIGS. 2A to 2C show photographs of the copper plates that have been pressure-bonded under the above conditions. It turned out that the copper plate which surface-treated using the amine complex containing silver oxalate or silver acetate can be joined by press (FIG. 2 (a), (b)). On the other hand, the copper plate subjected to the surface treatment by reductive decomposition of the fatty acid only caused discoloration of the pressurized portion by the pressing under the above conditions, and could not be joined (FIG. 2 (c)). In addition, for reference, the copper plates are also subjected to pressing between the copper plates that are not subjected to surface treatment or between the copper plates that are not subjected to surface treatment by interposing silver fine particles having high fusibility generated according to Patent Document 4. There was no bonding between them.

  From the above, by the surface treatment method according to the present invention, silver is deposited on the surface of the metallic copper and an interfacial bond is formed between the copper-silver fine particles in advance, so that the silver coating or silver fine particles on the surface of the metallic copper is formed. It was shown that metallic copper can be easily joined as a binder. The mechanism in which the metallic copper treated by the surface treatment method according to the present invention is easily fused to form a bond is that a substantial bond exists between the metallic silver deposited by the surface treatment and the metallic copper, and This shows that the deposited silver metal is active. Despite the low wettability between metallic copper and metallic silver, the mechanism that causes substantial bonding between metallic silver and metallic copper deposited by surface treatment is the silver atom produced by the thermal decomposition of the amine complex. It is presumed that the generation of silver nuclei is not always easy because of the low potential, and precipitates by binding to the copper surface in a metastable state.

[Example 2]
By the method shown below, surface treatment was performed on the copper fine particles having an alkylamine coating by the surface treatment method according to the present invention, and the treated copper fine particles were evaluated.
(2.1) Synthesis of copper fine particles having alkylamine coating Copper fine particles having an alkylamine coating were synthesized by the method described in JP2012-072418A. 3- (2-ethylhexyloxy) propylamine (Tokyo Kasei, special grade) 10 g (53 mmol), 2-hydrazinoethanol (Tokyo Kasei, special grade) 3.0 g (39 mmol) and copper oxalate 0.5 hydrate (Synthesized from copper sulfate pentahydrate (Kanto Chemical, special grade) and oxalic acid dihydrate (Kanto chemical, special grade)) 3.00 g (18.7 mmol) was mixed and stirred at 0 ° C. for several minutes. Then, it changed from white to a pale yellow viscous mixture, and the complex compound which consists of copper oxalate, 2-hydrazinoethanol, etc. was produced | generated. Next, by heating to 170 ° C. and stirring for 2 hours, the complex compound decomposes in the presence of 3- (2-ethylhexyloxy) propylamine to form and aggregate copper atoms, and copper having an alkylamine coating It changed to a red suspension containing fine particles. Acetone (Wako Pure Chemical Industries, Ltd., 5 mL) is added to the reaction mixture, the precipitate obtained by centrifugation (4000 rpm, 1 minute) is separated, 5 mL of acetone is added again, and the precipitate is stirred. Then, copper fine particles having an alkylamine coating were obtained by centrifugation (1.10 g). As described in JP2012-0772418, the copper fine particles having an alkylamine coating synthesized by the above method are substantially free of an oxidation phase and have a relatively high mutual fusion property (sinterability). is there.

(2.2) Analysis of Copper Fine Particles Having Alkylamine Coating FIG. 3 (a) shows an FE-SEM image observed by attaching the copper fine particles obtained in (2.1) to a carbon horizontal sample stage. Indicated. From the particle size distribution shown in FIG. 3B, the average particle size of the copper fine particles was 224 ± 112 nm, indicating that crystalline copper fine particles surrounded by a smooth crystal plane were generated. FIG. 4 shows a powder X-ray diffraction pattern (Rigaku Corporation, SmartLab) of the copper fine particles obtained in (2.1). All the observed signals were derived from metallic copper, and no component of copper oxide was detected.

(2.3) Thermogravimetric analysis of copper fine particles having an alkylamine coating FIG. 5 (a) shows the thermogravimetric analysis (TA instruments, SDT Q600) in an inert atmosphere of the copper fine particles obtained in (2.1). The results of performing a heating rate of 10 ° C./min in a helium stream at 200 mL / min) are shown. A weight loss of 0.5% by weight resulting from the elimination of the protective molecule was observed. The weight reduction is accompanied by the elimination of the alkylamine forming the copper fine particle coating. The copper content in the obtained copper fine particles having an alkylamine coating is 99.5% by weight, and the yield of copper fine particles based on the copper oxalate used as a raw material is 90.7%.
FIG. 5 (b) shows the thermogravimetric analysis (Shimadzu, TGA-50, 40 mL / min synthetic air stream) held at 140 ° C. for 1 hour for the copper fine particles obtained in (2.1). Thereafter, the results are shown in FIG. Even when kept at 140 ° C. for 1 hour in synthetic air, the weight increase derived from copper oxidation (formation of copper oxide) is 0.5% or less, and the copper fine particles obtained in (2.1) Shows a predetermined oxidation resistance at 140 ° C. or lower. On the other hand, the copper fine particles obtained in (2.1) have a significant increase in weight due to air oxidation at 140 ° C. or higher.

(2.4) Surface treatment of copper fine particles 1.10 g of copper fine particles having an alkylamine coating synthesized in (2.1) (17.2 mmol as copper) are produced under the same conditions as in (1.1). A mixture of the alkylamine-silver oxalate complex compound and an excess amount of the alkylamine was added, and the complex compound was decomposed by heating and stirring at 80 ° C. for 2 hours to obtain a red-brown suspension. 5 mL of acetone is added to this, and the precipitate obtained by centrifugation is separated. Further, 5 mL of hexane (Kanto Chemical Co., Ltd.) is added, and the precipitate is stirred and centrifuged to obtain 1.40 g (to silver oxalate). In contrast, a precipitate having a silver yield (silver reference yield of about 82%) was separated.
The separated precipitate was subjected to thermogravimetry-mass analysis (TG-MS: gas generated from SDT Q600 by mass spectrometry using JEOL JMS-Q1050GC) in an inert atmosphere. As a result, 1.1 wt% A decrease in weight was observed, and alkylamine molecules (hexylamine and N, N-dimethyl-1,3-diaminopropane) were detected corresponding to this weight decrease, and the resulting precipitate was coated with alkylamine. It was confirmed that the metal fine particles had.

(2.5) Evaluation of surface-treated copper fine particles FIG. 6 shows a powder X-ray pattern of metal fine particles obtained by performing the surface treatment in (2.4) together with other results. . It was found that the metal fine particles obtained in (2.4) contained both a metal copper phase and a metal silver phase. FIG. 7A shows an FE-SEM image of the metal fine particles obtained in (2.4). It was shown that particles having a particle size of about submicron and particles having a particle size of about several tens of nanometers exist in the metal fine particles obtained in (2.4). In addition, it was found that fine irregularities are uniformly formed on a flat crystal surface in particles of about submicron. In FIG. 8, the metal fine particles obtained in (2.4) are dispersed in toluene and applied to a carbon support film for electron microscope (EM Japan, molybdenum 200 mesh). , JEM2100F) shows an image observed. From elemental mapping by energy dispersive X-ray fluorescence analysis (EDS), it was found that copper was distributed in the core portion of the submicron particles and silver was distributed around the core. From these results, it was considered that the submicron particles contained in the metal fine particles obtained in (2.4) had silver deposited on the surface of the copper fine particles subjected to the surface treatment. That is, the fine and uniform irregularities generated on the flat crystal surface of the submicron particles shown in FIG. 7A are due to silver atoms deposited on the surface of the copper crystal. It shows that interfacial bonding of fine particles is formed. Further, the particles of about several tens of nanometers are silver fine particles generated independently during the surface treatment.

[Example 3]
By the method shown below, surface treatment was performed on the copper fine particles having an alkylamine coating by the surface treatment method according to the present invention, and the treated copper fine particles were evaluated.
(3.1) Formation of Complex Compound Composed of Alkylamine and Silver Acetate A mixture of an alkylamine-silver acetate complex compound and an excess amount of alkylamine was formed under the same conditions as in (1.1). In addition, since silver oxalate contains two silver atoms per molecule, silver acetate contains one silver atom per molecule. Therefore, silver oxalate contains silver atoms contained in the silver acetate used in this example. The amount is the same as in Example 2.

(3.2) Surface treatment of copper fine particles The complex compound produced in (3.1) with respect to 1.10 g (17.2 mmol as copper) of the copper fine particles having an alkylamine coating synthesized in (2.1). And an excess amount of alkylamine were added, and the complex compound was decomposed by heating and stirring at 80 ° C. for 2 hours to obtain a red-brown suspension. To this, 5 mL of acetone is added, and the precipitate obtained by centrifugation is separated. Further, 5 mL of hexane is added, and the precipitate is stirred and centrifuged to obtain 1.38 g (yield based on silver is about 41%). The precipitate was separated.

(3.3) Evaluation of surface-treated copper fine particles FIG. 7B shows an FE-SEM image of the precipitate obtained in (3.2). Even when silver acetate is used as the silver compound contained in the complex compound used for the surface treatment, silver is precipitated on the surface of the copper fine particles as well as silver oxalate. It was done.

[Example 4]
By the method shown below, surface treatment was performed on the flaky copper fine particles produced by the atomizing method by the surface treatment method according to the present invention, and the treated copper fine particles were evaluated.
(4.1) Surface treatment of copper atomized fine particles 1.10 g (17.2 mmol as copper) of flaky copper fine particles produced by a commercially available atomizing method was produced under the same conditions as (1.1). A mixture of an alkylamine-silver oxalate complex compound and an excess amount of an alkylamine was added, and the complex compound was decomposed by heating and stirring at 80 ° C. for 2 hours to obtain a red-brown suspension. To this, 5 mL of acetone is added, and the precipitate obtained by centrifugation is separated. Further, 5 mL of hexane is added, and the precipitate is stirred and centrifuged to obtain 1.25 g (yield based on silver is about 76%). The precipitate was separated. As a result of thermogravimetric analysis of the separated precipitate in an inert atmosphere, the separated precipitate was subjected to thermogravimetric-mass spectrometry (TG-MS) in an inert atmosphere. Observed and alkylamine molecules (hexylamine and N, N-dimethyl-1,3-diaminopropane) were detected in response to this weight loss, the resulting precipitate was a metal with an alkylamine coating. Fine particles.

(4.2) Evaluation of surface-treated copper atomized fine particles FIG. 6 shows the result of the powder X-ray diffraction of the precipitate obtained by performing the surface treatment in this example compared with other examples. Indicated. It was found that the precipitate obtained by performing the surface treatment in this example contained both a metallic copper phase and a metallic silver phase. FIG. 7C shows an FE-SEM image of the precipitate obtained in (4.1). It was observed that silver was deposited on the surface of the copper atomized fine particles having a diameter of about 10 μm by the surface treatment. In addition, the number of silver fine particles generated independently is small compared to Example 2 (2.4) (FIG. 7A) and Example 3 (3.2) (FIG. 7B). I understood. In the surface treatment of copper atomized fine particles having a large specific surface area due to the flake shape, it is presumed that silver atoms generated by thermal decomposition of alkylamine-silver oxalate complex compound are preferentially deposited on the surface of metallic copper. Is done.

[Comparative Example 2]
As a comparative example of the surface treatment method according to the present invention, the copper fine particles were surface-treated by the following method without using a complex compound of an alkylamine and a silver compound.
(5.1) Surface treatment of copper fine particles by decomposition of fatty acid silver In this Comparative Example 2, the surface treatment of copper fine particles was carried out by the same method as the surface treatment of copper plates by reductive decomposition of fatty acid silver in (1.2). went.
Specifically, 7.26 g (71.7 mmol) of triethylamine (Tokyo Kasei, special grade) with respect to 1.10 g of copper fine particles having an alkylamine coating synthesized in (2.1) (17.2 mmol as copper) A black suspension was obtained by heating and stirring the mixture to which 1.19 g (3.55 mmol) of silver myristate was added at 90 ° C. for 3 hours. Acetone 5 mL was added to this, the precipitate obtained by centrifugation was separated, acetone 5 mL was added once more, the precipitate was stirred, and 1.49 g of precipitate was separated by centrifugation. The separated precipitate was subjected to thermogravimetric-mass spectrometry (TG-MS) in an inert atmosphere. As a result, a 2.3% weight loss was observed, and myristic acid was detected corresponding to this weight reduction. Therefore, the obtained precipitate is metal fine particles having a myristic acid coating.

(5.2) Evaluation of copper fine particles subjected to surface treatment using fatty acid silver FIG. 6 shows the results of the powder X-ray diffraction of the precipitates obtained by performing the surface treatment in this comparative example and other examples. Shown in comparison. It was found that both the metallic copper phase and the metallic silver phase were also contained in this comparative example. FIG. 9 shows an FE-SEM image of the precipitate obtained in (5.1). It was observed that silver fine particles of several nanometers to several tens of nanometers were deposited on the surface of the copper fine particles by the surface treatment, and silver fine particles were also deposited around the copper fine particles and filled between the copper fine particles.

[Example 5] Evaluation of sinterability of copper fine particles subjected to surface treatment The sinterability of copper fine particles subjected to surface treatment in Examples 2 and 4 and Comparative Example 2 was evaluated by the following method.
(6.1) Preparation of dispersion / suspension of surface-treated copper fine particles and baking treatment The precipitates were 50% by weight with respect to the precipitates obtained in Examples 2 and 4 and Comparative Example 2. Toluene (Kanto Chemical Co., Ltd., special grade) was added to each to prepare a paste in which the precipitate was dispersed and suspended. Further, as Comparative Example 3, 1.10 g of copper fine particles having an alkylamine coating that was not subjected to surface treatment as synthesized in (2.1) (17.2 mmol as copper), and Patent Document 4 (Example 10) A paste was prepared by mixing 0.35 g (2.99 mmol as silver) of silver fine particles having an alkylamine coating synthesized by the method described in 1. and dispersing and suspending in 1.40 mL of toluene. The silver fine particles having an alkylamine coating used show a low resistance value of about 10 μΩ · cm or less when baked at 100 ° C. for 60 minutes, and have been confirmed to have high mutual fusion properties. Next, each prepared paste was applied to one side of a slide glass (Matsunami Glass Industrial Co., Ltd., S1127) using a bar coater, and allowed to stand until toluene was volatilized to obtain a coating film. The slide glass provided with the coating film was baked at 100 ° C. for 30 to 120 minutes in the atmosphere with a Yamato DK240S blower thermostat (Yamato DK240S).

(6.2) Evaluation of fired film (X-ray diffraction)
FIG. 10 shows X-ray diffraction patterns of films obtained by firing the copper fine particles surface-treated in Examples 2, 4 and Comparative Example 2. All diffraction patterns showed the presence of metallic copper and metallic silver, and no diffraction pattern due to copper oxide or the like was observed despite firing in the atmosphere. In general, since copper metal is easily oxidized to produce copper oxide, in the copper fine particles in which silver is deposited on the surface by performing surface treatment in Examples 2, 4 and Comparative Example 2, It is considered that the progress of oxidation is suppressed. Further, the signals of metallic silver in Examples 2 and 4 are sharper than those in Comparative Example 2, and in Examples 2 and 4, crystal growth due to the sintering of silver fine particles is more remarkable than in Comparative Example 2. I understand.

(6.3) Evaluation of fired film (X-ray fluorescence analysis)
Table 1 shows films obtained by firing the copper fine particles surface-treated in Examples 2 (2.4), 4 (4.1), and Comparative Example 2 (5.1), and Comparative Examples Table 1 shows the composition ratio (weight ratio) of silver and copper obtained by a desktop wavelength dispersion type fluorescent X-ray apparatus (Rigaku Primini) for the film obtained by firing the paste prepared in 3.

(7.4) Evaluation of fired film (electric resistance measurement)
Table 2 shows the copper fine particles surface-treated in Examples 2 (2.4), 4 (4.1), and Comparative Example 2 (5.1), and the paste according to Comparative Example 3 before and after firing. The electrical resistance was shown. The sheet resistance value was measured by the four probe method (Kyowa Riken K-705RS). The volume resistance value was converted by multiplying the surface resistance value by the film thickness measured with a stylus profilometer (Bruker, DektakXT). In Table 2, “applied film” was measured for a state in which toluene was volatilized after applying the paste, and “fired film” was measured for a film that was baked under the respective conditions (heating temperature, heating time). It is a result.

  As shown in Table 2, the copper fine particles surface-treated in Example 2 (2.4) and Example 4 (4.1) were compared with those in Comparative Example 2 (5.1) and Comparative Example 3. It showed very good conductivity. This indicates that the copper fine particles surface-treated in Examples 2 and 4 are fused to each other to form an electrical connection. On the other hand, in Comparative Examples 2 and 3, the bonding between the particles is not sufficient, and it is assumed that the conductive path is formed mainly by the bonding between the silver fine particles or the simple contact between the copper fine particles.

(7.5) Evaluation of fired film (observation 1 of fired film, UV-visible diffuse reflection spectrum)
In order to clarify the reason for the difference in the volume resistivity of the fired film of each paste, the surface state of the fired film was examined with an ultraviolet-visible diffuse reflectance spectrum (Shimadzu UV-3600) (FIG. 11). The copper fine particles of Example 2 (2.4) surface-treated with a complex compound containing silver oxalate and Example 3 (3.2) surface-treated with a complex compound containing silver acetate were used. In the fired film of Comparative Example 2 in which the surface treatment by reduction of fatty acid silver was performed on the fired fired film, a characteristic light absorption band on the longer wavelength side than 500 nm that was not seen in Examples 2 and 3 was observed. Visually, it was blue. This light absorption band longer than 500 nm is similar to the absorption by the surface plasmons of the unsintered silver nanoparticle powder. This is because, in the copper fine particles surface-treated in Comparative Example 2 (5.1), the silver covering the copper fine particle surface shown in the FE-SEM image of FIG. 9 even after heating at 100 ° C. for 120 minutes. It shows that there is almost no fusion of fine particles.

(7.6) Evaluation of fired film (Observation of fired film 2, FE-SEM image)
FIG. 12 shows Example 2 (2.4) (FIG. 12A), Example 4 (4.1) (FIG. 12B), and Comparative Example 2 (5.1) (FIG. 12 ( The FE-SEM image of the fired film | membrane of the copper fine particle surface-treated by c)) was shown. In Example 2 and Example 4, as compared with before firing (FIGS. 7A and 7C), the fusion of the silver fine particles to the surface of the copper fine particles clearly proceeds, and the silver fine particles are fused. It was observed that the copper fine particles coated with silver were joined together by the fused silver fine particles. On the other hand, in Comparative Example 2 (FIG. 12C), the silver fine particles maintain an independent shape as compared with that before firing (FIG. 9), and a flat surface that seems to be a crystal surface of metallic copper is exposed. It was observed that the fusion between the copper fine particles and the silver fine particles and the fusion between the silver fine particles did not occur remarkably.
As described above, from the results of the UV-visible diffuse reflection spectrum and the FE-SEM image, in the copper fine particles surface-treated in Comparative Example 2, although the silver fine particles are deposited on the surface of the copper fine particles, the stable coating with silver is not necessarily performed. It does not occur, and it can be seen that the fusion property is inferior to the example of the present invention. In Comparative Example 2, the generation mechanism of silver atoms during the surface treatment of copper fine particles is different, and fatty acid ions are attached to the surface of the generated silver fine particles. Due to such differences, the formation of a copper-silver bonding interface during surface treatment and the interfacial bonding between copper-silver fine particles and silver fine particles during firing are hindered. Presumed to be.

(Comparative Example 3)
In Comparative Example 3, instead of performing the surface treatment of the copper fine particles in Example 2, silver fine particles produced under the same conditions except that metal copper is not interposed are mixed and fired. Nevertheless, the reason why the volume resistivity after firing is larger than that in Example 2 is considered to be due to the presence or absence of a silver coating formed on the surface of the copper fine particles during the surface treatment in Example 2. That is, by the surface treatment method according to the present invention, by depositing an atomic layer of silver by decomposition of an amine complex on the crystal surface of metal copper, a copper-silver interface junction is favorably formed on the surface of metal copper. It is considered that the fusion of metallic copper is promoted using a silver atomic layer as a binder.

[Example 6]
(Environmental resistance test)
With respect to the fired film (Example 5 (6.1)) obtained by firing the coating film of copper fine particles obtained by surface treatment in Example 2 (2.4) at 100 ° C. in the atmosphere, the environment resistance A test was conducted. Specifically, the fired film was placed in an environmental tester (ESPEC, LHL-113) set at a temperature of 85 ° C. and a relative humidity of 85%. When the fired film was exposed to a temperature of 85 ° C. and a relative humidity of 85% for at least 2 weeks, no significant increase in volumetric efficiency was observed, indicating that the oxidation resistance of the copper particles was maintained.

Claims (14)

  A silver compound that can be decomposed by heating to produce metallic silver and an amine complex containing an alkylamine is heated on the surface of the metallic copper in the presence of the alkylamine to deposit silver on the metallic copper surface. Metal surface treatment method.   2. The method for treating a metal surface according to claim 1, wherein the amine complex is a complex compound in which both an oxygen atom and a nitrogen atom are coordinated with a silver atom.   The method for treating a metal surface according to claim 1 or 2, wherein the silver compound contains silver oxalate and / or silver acetate as a main component.   An amine complex containing a silver compound that can be decomposed by heating to form metallic silver and an alkylamine is heated in the presence of an alkylamine on at least a part of the surface of the metallic copper, and a metal is formed on at least a part of the metallic copper surface. Silver-coated copper characterized by depositing silver.   5. The silver-coated copper according to claim 4, wherein at least a part of the metallic silver deposited on the surface of the metallic copper is coated with an alkylamine.   The silver-coated copper according to claim 4 or 5, wherein the metallic copper is in the form of fine particles.   The silver-coated copper according to claim 6, wherein an average particle diameter of the fine metal copper is 50 nm to 10 µm.   A dispersion comprising the silver-coated copper according to claim 6 or 7 dispersed in a dispersion medium.   The dispersion according to claim 8, further comprising silver fine particles having an alkylamine coating.   The dispersion according to claim 8 or 9, wherein the weight ratio of silver to the content of metallic copper is ½ or less. A composite metal body having a structure in which metallic copper is used as a dispersed phase and the dispersed phase is bonded with silver, and exhibits a volume resistivity of 3.0 × 10 ⁻³ Ω · cm or less body.   The composite metal body according to claim 11, wherein at least a part of the surface of the metallic copper is covered with silver.   The composite metal body according to claim 11 or 12, wherein the weight ratio of silver to the content of metallic copper is ½ or less.   A device comprising the composite metal body according to claim 11.