JP2018145448A - Nickel-coated copper powder, method for producing same, and conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine and highly-crystallized nickel-coated copper powder having high sinterability and oxidation resistance, suitably used as a material such as a conductive paste, a method for producing the same, and a conductive paste.SOLUTION: The nickel-coated copper powder has a surface coated with nickel or a nickel alloy and contains 60% or more of a quasi-octahedral structure having a ratio (R/L) of diagonal length (L) to copper crystallite diameter (R) ranging from 0.2 to 0.5 as observed by a scanning electron microscope. The method for producing the nickel-coated copper powder by a wet method includes: a step (A) of preparing a slurry in which a copper hydroxide and a copper complex ion are coexisted by setting the pH of a copper salt with an alkali at pH of 12-14 and further adding a complexing agent; a step (B) of adding a reducing agent to the slurry to precipitate cuprous oxide (CuO); a step (C) of reducing the cuprous oxide to copper powder by adding a reducing agent; and a step (D) of coating the copper powder with nickel or a nickel alloy.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a copper powder (nickel-coated copper powder) coated with nickel (Ni) or a nickel alloy on its surface, a method for producing the same, and a conductive paste. More specifically, the present invention is suitably used as a material for a conductive paste or the like. The present invention relates to a fine and highly crystalline nickel-coated copper powder having both sinterability and oxidation resistance, a method for producing the same, and a conductive paste.

  In order to form wiring layers, electrodes, and the like in electronic devices, conductive pastes using metal fillers such as silver powder and copper powder, such as resin pastes and fired pastes, are frequently used. A paste using a metal filler such as silver powder or copper powder is applied or printed on various substrates, and is subjected to heat curing or heat baking treatment to form a conductive film to be a wiring layer, an electrode, or the like.

  The resin-type conductive paste is made of a metal filler, a resin, a curing agent, a solvent, etc., printed on a conductor circuit pattern or terminal, and cured by heating at 100 ° C. to 200 ° C. to form a conductive film. Form. In the resin-type conductive paste, since the thermosetting resin is cured and contracted by heat, the metal fillers are pressed and brought into contact with each other, so that the metal fillers overlap each other, and as a result, an electrically connected current path is formed. . Furthermore, since the metal powder generally has a higher sinterability as the particle size becomes finer, the use of a metal filler having a smaller particle size also increases the sintering effect and lowers the resistance. Since this resin-type conductive paste is processed at a curing temperature of 200 ° C. or lower, it is used for a substrate using a heat-sensitive material such as a printed wiring board.

  The firing type conductive paste is made of a metal filler, glass, solvent, etc., printed on a conductor circuit pattern or terminal, and heated and fired at a high temperature of 600 ° C. to 800 ° C. to form a conductive film. An electrode is formed. In the firing type conductive paste, it is processed at a high temperature, and the metal filler is sintered to ensure conductivity. Firing-type conductive paste is processed at such a high firing temperature, so it cannot be used for printed circuit boards that use resin materials, but low resistance is achieved because the metal filler is sintered by high-temperature processing. it can. Therefore, the fired conductive paste is used for an external electrode of a multilayer ceramic capacitor.

  When copper powder as a metal powder material used as a metal filler of such conductive paste is used, it is oxidized and the surface is covered with copper oxide, which adversely affects sinterability, corrosion resistance, weather resistance or conductivity. Sometimes. For this reason, in order to prevent oxidation of the copper powder, the surface of the copper particles is coated with a noble metal such as platinum, palladium, silver, gold, etc., coated with a silica-based oxide, or coated with nickel to resist oxidation. Those with improved chemical properties are known. However, if a noble metal is coated on the surface of the copper powder, these are expensive, resulting in an increase in cost. Among them, the copper powder coated with silver can be kept at a relatively low price, but silver has a problem that migration is likely to occur. Moreover, although the copper powder coated with an oxide can ensure oxidation resistance, it has problems such as poor sinterability. In view of this, attention has been paid to a method of coating nickel on copper powder as ensuring low oxidation resistance and relatively good weather resistance and sinterability while ensuring oxidation resistance and the like. For example, Patent Document 1 discloses a nickel-coated copper powder having a copper powder surface coated with nickel.

Patent Document 1 describes that the core material is copper particles, and a plating catalyst is fixed to the surface of the copper particles by a reduction reaction, and electroless nickel plating is applied to the outermost surface. And it is supposed that a catalyst forming material containing a catalytic element for plating such as palladium at a maximum of 1 × 10 ⁻¹ mol per 1 mol of Cu is added to the copper powder slurry. However, when a large amount of palladium is added in this way, the cost of nickel-coated copper powder increases because palladium is expensive.

  By the way, as a method for producing copper powder as a raw material, an electrolytic method in which an electrolytic solution containing copper ions is electrolyzed to deposit copper powder on the cathode, or a copper raw material is melted and the molten metal is made into droplets. An atomizing method for producing copper powder by rapid cooling and solidification, a wet method for producing a copper powder by adding a reducing agent in a solution, and the like are known. These production methods are employed as industrial production methods because of their high productivity and low production costs.

  Although the copper powder obtained by the electrolytic method has a feature that it becomes highly pure, most of the electrolytic copper powder is precipitated in a dendritic shape, and moreover, the particle size tends to be as coarse as 10 μm or more. Furthermore, it is not suitable for wiring applications requiring a low resistance with a conductive paste having a wide particle size distribution.

  In addition, the atomization method is a method in which a jet fluid is blown into a flow of a molten metal obtained by melting a metal at a high temperature, for example, as shown in Patent Document 2, but impurities are contained when the metal is melted. There is a problem that it is easy to oxidize and is easily oxidized when sprayed, and copper fine particles of 1 μm or less cannot be produced. As described above, the copper powder obtained by the atomizing method and the electrolytic method has a particle size of 2 μm or more and poor sinterability, so it is difficult to be low resistance, and it is polycrystalline and has grain boundaries, so it has poor oxidation resistance. The field of use as a conductive paste is limited.

  On the other hand, the wet method is a method of reducing and precipitating copper ions or the like in a solution with a reducing agent. Specifically, for example, as shown in Patent Document 3, an alkaline agent is added to a solution containing a copper salt to cause reaction to precipitate copper hydroxide, and then a reducing agent such as glucose is added to sub-oxidize. It reduces to copper, Furthermore, a secondary reducing agent like hydrazine is added and it reduces to metal copper, and obtains copper powder. Such a wet method has the advantage that a very fine spherical copper fine powder of submicron can be produced. However, as in Patent Document 2, since it is polycrystalline and has grain boundaries, its oxidation resistance is inferior. As a field of use is limited.

  On the other hand, Patent Documents 4 and 5 propose a method of obtaining single crystal copper powder having a fixed crystal orientation, but the main particle size is about 2 to 5 μm and the resin mold has a curing temperature of 100 to 200 ° C. The conductive paste does not satisfy the low resistance. Further, if the curing temperature is 200 ° C. or higher in order to reduce the resistance, the oxidation resistance becomes insufficient.

In Patent Document 4, in order to produce a copper powder having a regular octagonal pyramidal single crystal, it is reduced to a solution containing tartaric acid and alkali hydroxide in a molar ratio of 1 to 5 times the copper salt and copper. It is described that formaldehyde is added within 1 minute as an agent.
In addition, since the manufacturing method of Patent Document 5 requires a chelating agent such as tartrate at a molar ratio of 1 to 5 times that of copper, the cost of the chemical solution is increased, and at the same time, the cost of waste liquid treatment is also increased. There is also a problem that the cost becomes high. Furthermore, there is a condition that formaldehyde as a reducing agent is added within 1 minute for reduction, which is unsuitable for industrial mass production. On the other hand, although the copper powder obtained by patent document 5 is a high crystal | crystallization, it is plate shape, a specific surface area becomes high and it is easy to oxidize, and since a wiring edge becomes uneven, it is unsuitable for the use of an electrically conductive film.

  In general, when a conductive paste is used for an IC substrate, a printed circuit board, or the like, in order to form a fine pattern, for example, an acid resistance of 1% by mass or less at an oxidation increase of 200 ° C. in the atmosphere by thermogravimetric (TG) analysis. There is a demand for metal fillers that are excellent in chemical properties, fine, and have good dispersibility. In addition, due to the substrate heat resistance, etc., the contact resistance when the resin is cured and shrunk at a low temperature is reduced, and when the filler is fired in the air, for example, the powder resistivity baked in the air is as low as 500 μΩ · cm. It is required to become resistance. However, in the case of metal powders, particularly copper powders, there is a tendency to oxidize more easily as the particle size becomes finer. Therefore, a method for obtaining copper powders that are fine and excellent in oxidation resistance is desired. It has been.

  Therefore, Patent Document 6 proposes a method for obtaining a single crystal copper fine powder by a gas phase reaction. However, when the obtained copper powder is observed using a scanning electron microscope (SEM), it is a chamfered polyhedron. Since it is a single crystal and the powder particles are a single crystal, it has a smooth surface, no defects, and excellent oxidation resistance. However, in the production of copper powder by gas phase reaction, cuprous chloride is reacted with a reducing gas at a high temperature of 700 ° C. or higher to obtain single crystal copper powder, which complicates the mechanism of the apparatus and increases production costs. Further, there is a problem that the yield is poor, for example, the obtained copper powder is remelted and connected.

  As described above, as the metal filler used in the baked conductive paste, a copper powder nickel-plated is known, but as the core copper powder, the ones described in Patent Documents 2 to 6 were used. Therefore, even if the surface is coated with nickel, it does not have both sinterability and oxidation resistance, and the weather resistance is insufficient. There is a need for a method that can produce nickel-coated copper powder having these characteristics industrially at low cost.

JP 2006-28630 A Japanese Patent No. 4342746 Japanese Patent No. 4406738 Japanese Patent Publication No.7-111592 JP 2014-58713 A Japanese Patent Publication No. 6-76609

  In view of the above-mentioned problems of the prior art, the object of the present invention is a fine and highly crystalline material that can be suitably used as a material such as a conductive paste, has both sinterability and oxidation resistance, and also has high weather resistance. The object is to provide a nickel-coated copper powder, a method for producing the same, and a conductive paste.

  As a result of intensive studies to solve the above-described problems, the present inventor has a pseudo-octahedral structure, the diagonal length (L) is 0.1 μm to 2 μm, and the diagonal length (L) Copper powder containing 60% or more of the total ratio (R / L) with the crystallite diameter (R) of copper determined by the Scherrer method is in a specific pH range, with copper ions and copper hydroxide. In the coexistence, the first stage of reduction is made into cuprous oxide, and then in the second stage of reduction, cuprous oxide is reduced to copper with a specific amount of reducing agent to obtain fine and highly crystalline copper powder. It was found that by coating the surface of the obtained copper powder with nickel or a nickel alloy, a silver-coated copper powder with higher weather resistance can be obtained at a relatively low cost, and the present invention has been completed. It was.

  That is, according to the first aspect of the present invention, the copper powder surface is coated with nickel or a nickel alloy, and is observed to have a pseudo-octahedral structure by a scanning electron microscope (SEM), and the diagonal length ( L) is 0.1 μm to 2 μm, and the ratio (R / L) of the diagonal length (L) to the crystallite diameter (R) of copper determined by the Scherrer method is in the range of 0.2 to 0.5. There is provided a nickel-coated copper powder containing 60% or more of the total.

  According to a second aspect of the present invention, there is provided the nickel-coated copper powder according to the first aspect, wherein the number of copper crystal grains constituting the pseudo-octahedral structure is 5 to 130. Provided.

  According to a third invention of the present invention, in the first or second invention, the nickel or nickel alloy coating amount is 1 to 33% by mass of the entire nickel-coated copper powder. Copper powder is provided.

  According to a fourth invention of the present invention, in the third invention, the nickel alloy is at least one selected from cobalt, zinc, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron. A nickel-coated copper powder containing an element and having an element content of 0.1 to 20% by mass with respect to the nickel alloy is provided.

Further, according to the fifth aspect of the present invention, the step of preparing an aqueous solution of copper salt in an alkali range of pH 12 to 14 and further adding a complexing agent to coexist with copper hydroxide and copper complex ions ( in a), but the reducing agent 1-2 by adding an equivalent amount to the slurry, and step (B) for precipitating cuprous oxide _(Cu 2 O), to a slurry said cuprous oxide _(Cu 2 O) was deposited 1 A step (C) of adding a reducing agent equal to or more than an equivalent amount to reduce cuprous oxide to copper powder, and a step (D) of covering the obtained copper powder with nickel or a nickel alloy. A method for producing a nickel-coated copper powder is provided.

  According to a sixth invention of the present invention, in the fifth invention, the complexing agent is a synthetic resin having an average molecular weight of 500 to 50,000 selected from PEI, PVA, and PVP. A method for producing nickel-coated copper powder is provided.

  According to a seventh aspect of the present invention, in the fifth aspect, the complexing agent is added in an amount of 0.5 mass% to 50 mass% with respect to copper in the copper salt. A method for producing nickel-coated copper powder is provided.

  According to an eighth aspect of the present invention, in the fifth aspect, the amount of the reducing agent is 3 equivalents or more as the total amount of the step (B) and the step (C). A method for producing nickel-coated copper powder is provided.

  According to a ninth aspect of the present invention, there is provided the method for producing a nickel-coated copper powder according to any one of the fifth to eighth aspects, wherein the reducing agent forms a complex with copper. The

  According to a tenth aspect of the present invention, in any of the fifth to ninth aspects, the nickel powder obtained in the step (C) is coated with nickel or a nickel alloy by electroless plating after washing. A method for producing a nickel-coated copper powder is provided.

  Furthermore, according to the eleventh invention of the present invention, in any one of the fifth to tenth inventions, the nickel-coated copper powder has a pseudo-octahedron structure and a diagonal length (L) of 0.1 μm to Nickel-coated copper powder characterized in that the ratio (R / L) of the diagonal length (L) and the crystallite diameter (R) of copper is 2 μm and is in the range of 0.2 to 0.5 A manufacturing method is provided.

  On the other hand, according to the twelfth aspect of the present invention, there is provided a conductive paste including the nickel-coated copper powder of any one of the first to fourth aspects, a resin and a solvent.

  The nickel-coated copper powder according to the present invention has a pseudo-octahedron structure, is fine and has good sinterability, high crystallinity and good oxidation resistance, and is coated with nickel or a nickel alloy on the surface to provide weather resistance. Therefore, it can be suitably used as a metal filler such as a conductive paste such as a wiring material. In addition, the nickel-coated copper powder according to the present invention is not industrially low because a relatively inexpensive raw material and a simple process are employed in the copper powder production, regardless of the gas phase reaction that increases the production cost. Can be manufactured at cost.

It is a schematic diagram of the nickel coat copper powder of the pseudo octahedral structure which concerns on this invention. (A) is an octahedron shape, (b) shows a nickel-coated copper powder having a chamfered part of its apex, and (c) is a pseudo-octahedral shape of (a). The cross section of nickel coat copper powder is shown. It is a flowchart which shows the process of manufacturing nickel coat copper powder by this invention.

  Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the object of the present invention.

1. Nickel-coated copper powder The nickel-coated copper powder according to the present invention is obtained by coating the surface of a copper powder having a specific structure with nickel or a nickel alloy.

(Copper powder)
In the present invention, the copper powder whose surface is coated with nickel has a pseudo-octahedron structure, the diagonal length (L) is 0.1 μm to 2 μm, and the copper crystallite diameter (R) and the diagonal length. The ratio (R / L) to the thickness (L) is in the range of 0.2 to 0.5.

  As shown in FIG. 1, the pseudo-octahedron structure refers to a shape of an octahedron or a shape in which a part of its apex is chamfered. The copper powder having these shapes has a smooth surface. When the copper powder according to the present invention is observed with a scanning electron microscope (SEM), the copper powder having the pseudo-octahedron structure occupies 60% or more of the total copper powder number in the visual field. preferable. This number occupies 70% or more, and more preferably 80% or more. If 60% or more of the total copper powder number is a copper powder having a pseudo-octahedron structure, high sinterability and high oxidation resistance can be sufficiently exhibited as described later. Although the upper limit of the number of all copper powders is not limited, 95% or less is preferable, for example.

  The particle size of the copper powder according to the present invention is such that the copper powder has a pseudo-octahedron shape, and the diagonal length (L) that is the length between the apexes of the quadrangular pyramids as shown in FIG. . In addition, when the vertex of a quadrangular pyramid is chamfered like FIG.1 (b), let the length to the surface formed by chamfering be diagonal length (L).

The diagonal length (L) is 0.1 μm to 2 μm, preferably 0.2 μm to 1.5 μm, and more preferably 0.2 μm to 1 μm. When the diagonal length (L) is less than 0.1 μm, the specific surface area increases abruptly, and it is difficult to prevent oxidation even if the crystallinity is enhanced by coating nickel or a nickel alloy. On the other hand, when the thickness is larger than 2 μm, the sinterability is deteriorated and the resistance is not easily lowered, and it may be difficult to form a highly accurate wiring with a narrow wiring width. The diagonal length (L) can be obtained by observing with an SEM and processing the observed image.
The copper powder according to the present invention is not a single crystal but a polycrystalline body composed of several to several tens of crystal grains. However, since the number of crystal grains is small, grain boundary oxidation and corrosion are unlikely to occur, and the surface is smooth with a pseudo-octahedron structure, so the oxidation resistance of the copper powder itself is high, and the surface is coated with nickel or a nickel alloy. Therefore, the weather resistance is also excellent.

(Nickel coated copper powder)
In the nickel-coated copper powder according to this embodiment, a thin film of nickel or a nickel alloy is formed on the copper powder. Although nickel alloy is not limited by a component, What contains at least 1 or more types of elements chosen from zinc, cobalt, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron is preferable. For example, when the diagonal length (L) is 1 μm, the thickness of the coating (coating thickness) is 0.05 μm or less, preferably 0.03 μm or less. From this, the nickel-coated copper powder retains the pseudo-octahedral structure which is the shape of the copper powder before coating with nickel or a nickel alloy.

  That is, the nickel-coated copper powder also has a pseudo-octahedron structure, the diagonal length (L) is 0.1 μm to 2 μm, and the ratio of the copper crystallite diameter (R) to the diagonal length (L) (R / L) is in the range of 0.2 to 0.5.

  FIG. 1C is a cross section of the nickel-coated copper powder in the present invention having the pseudo-octahedron shape of FIG. 1A, and a nickel or nickel alloy coating 2 covering the surface and a plurality of copper crystal grains 1. The polycrystal which consists of is shown. The relationship between the diagonal length (L) and the crystallite diameter (R), which is an index of the size of each copper crystal grain, is as shown in FIG. 1 (c), and the copper content in one pseudo-octahedral particle is as follows. The number of crystal grains can be calculated as follows from the numerical values of the crystallite diameter (R) of copper and the diagonal length (L) of the pseudo octahedron. The number of copper crystal grains is obtained by dividing the pseudo octahedral particle volume by the copper crystallite size particle volume, and is determined by the relationship of (L / R), that is, the inverse power of (R / L) to the third power.

Specifically, for example, when (R / L) = 0.2, the number of copper crystal grains is 125, and when (R / L) = 0.5, the number of copper crystal grains is eight. . Accordingly, in the present invention, the number of copper crystal grains is preferably 5 to 130, and more preferably 5 to 100.
Thus, the ratio (R / L) is an index representing the number of copper crystal grains constituting the nickel-coated copper powder, and when R / L is less than 0.2, that is, when the crystallite diameter of copper is relatively small. Further, the number of crystal grains of copper increases, and grain boundary oxidation / corrosion due to polycrystallization tends to proceed, so that the oxidation resistance deteriorates. In addition, if R / L is larger than 0.5, it means that it approaches a single crystal (R / L is 1 for a single crystal), and oxidation resistance is good but sinterability deteriorates. It is difficult to form a current path connected to, and it is difficult to reduce resistance. Increasing the firing temperature to increase the current path due to sintering, for example, if the firing temperature is 200 ° C. or higher, the effect of oxidation begins to appear even though the oxidation resistance is high. .

  Here, the crystallite diameter of copper can be obtained by a Scherrer method or the like using an X-ray diffraction measurement apparatus (XRD). In the present invention, the number of copper crystal grains in the pseudo-octahedral particles is preferably 10 to 30, which is R / L = 0.3 to 0.5.

  The nickel-coated copper powder according to the present embodiment is not limited by the coating amount of nickel or a nickel alloy, but nickel or a nickel alloy at a ratio of 1% by mass to 33% by mass with respect to the entire nickel-coated copper powder on the surface of the copper powder. Those coated with are preferred.

  The coating amount of nickel or nickel alloy is preferably as small as possible from the viewpoint of cost, but if it is too small, a uniform nickel or nickel alloy coating cannot be secured on the surface of the copper powder, and improvement in weather resistance cannot be expected. Therefore, the coating amount of nickel or nickel alloy is preferably 1% by mass or more, more preferably 2% by mass or more, and more preferably 5% by mass or more with respect to the entire nickel-coated copper powder. preferable.

  On the other hand, an increase in the coating amount of nickel or nickel alloy is not preferable from the viewpoint of cost. Therefore, the coating amount of nickel or nickel alloy is preferably 33% by mass or less, more preferably 20% by mass or less, and more preferably 15% by mass or less with respect to the entire nickel-coated copper powder. Is more preferable. Further, as described later, in the nickel-coated copper powder, the nickel covered with the copper powder may be a nickel alloy. The element added as the nickel alloy is preferably at least one selected from zinc, cobalt, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron.

  The content of the elements constituting these nickel alloys is preferably 0.1% by mass to 20% by mass and preferably 1% by mass to 15% by mass with respect to the nickel alloy from the viewpoint of conductivity and dispersibility. More preferably, the content is 2% by mass to 10% by mass. In addition, also about the Ni-P alloy and Ni-B alloy which are each formed with the kind of reducing agent mentioned above, the content of the phosphorus and boron is 0.1 mass% with respect to 100 mass of nickel alloy film similarly. It is preferably ˜20% by mass, more preferably 1% by mass to 15% by mass, and further preferably 2% by mass to 10% by mass.

  If the content of an element other than nickel is too large when a nickel alloy is used, it is preferable to set the content to 20% by mass or less because it causes a decrease in conductivity. On the other hand, if the content is less than 0.1% by mass, the effect of improving the heat resistance and corrosion resistance cannot be sufficiently obtained even when nickel is contained by adding these elements together with nickel.

  In addition, content of the element in a nickel alloy can be measured by converting content of each element which comprises nickel coat | court copper powder, for example with a high frequency inductively coupled plasma (ICP) emission spectroscopy analysis method. In addition, each element in the nickel alloy film can be quantitatively analyzed from the cross section of the nickel-coated copper powder by an energy dispersive X-ray spectroscopy (EDX) method or an Auger electron spectroscopy (AES) method.

2. Method for producing nickel-coated copper powder by wet method The nickel-coated copper powder according to the present invention is produced by a wet method. In this method, an alkali is added to a solution containing a copper salt (copper ions) to obtain a pH range of 12 to 14, and a complexing agent is further added to coexist copper hydroxide and copper complex ions to form a slurry ( A) A step (B) of adding 1 to 2 equivalents of a reducing agent to this slurry to produce cuprous oxide (Cu ₂ O), and adding 1 equivalent or more of a reducing agent to convert the cuprous oxide into copper powder. A step (C) of reducing, and a step (D) of coating the surface of the obtained copper powder with nickel or a nickel alloy by an electroless plating method are included.

  Hereinafter, as shown in FIG. 2, a specific method of each step (A to D) will be described below.

(1) Step (A)
In the step (A), an alkali is added to a solution containing a copper salt (copper ions) to make the pH within a range of 12 to 14, and a complexing agent is further added so that copper hydroxide and copper complex ions coexist in the solution. The resulting slurry.

  As a copper salt, any salt may be used as long as it dissolves as an aqueous solution, such as copper sulfate, copper chloride, copper carbonate, copper acetate, and copper phosphate, and one kind may be used alone or a plurality may be used. Preferably, copper sulfate, copper chloride, and copper carbonate are suitable from the viewpoint that the anionic element is not mixed in the copper powder, the impurities are small, and the cost is low including the wastewater treatment cost. Furthermore, copper sulfate and copper carbonate are more preferable in consideration of the reliability of electronic components using conductive paste. These copper salts are dissolved to form a solution, but the solvent used is more preferably pure water in order to prevent contamination of impurities.

  The copper concentration in the solution is not particularly limited as long as the pH of the solution once dissolved is so high that it becomes a homogeneous solution and does not become supersaturated. However, the copper concentration is preferably in the range of 5 g / L to 250 g / L from the viewpoint of industrially high productivity and stable production.

In the present invention, an alkali is added to a solution containing a copper salt to adjust the pH to 12 to 14, but the type of alkali used is not particularly limited. For example, LiOH, KOH, NaOH, Ca (OH) ₂ and The salt of the weak acid can be used. Further preferred are KOH, NaOH and LiOH, which do not require separation of the precipitated salt resulting from neutralization after reduction.
By making pH into the range of 12-14, most copper can be made to exist with the form (slurry) of copper hydroxide. When the pH is less than 12, the abundance ratio of copper hydroxide becomes low, and the shape of the copper powder after reduction becomes difficult to have a highly crystalline pseudo-octahedral structure.

  In the present invention, copper is present in a form in which copper complex ions and copper hydroxide coexist in the slurry after pH adjustment with alkali. Complexing agents can also be added to adjust the ionic form of copper concentration. Preferable examples include compounds having one or more N, S atoms having a hydroxyl group, a carboxyl group, an unshared electron pair in the same molecule, and representative examples include ammonia, thiols, carboxylic acids, tartaric acid, amino acids, There are ethylenediamine and EDTA (ethylenediaminetetraacetate), and water-soluble organic synthetic resins such as PVA (polyvinyl alcohol) resin, PEI (polyethyleneimine) resin, and PVP (polyvinylpyrrolidone) resin can be used.

When an organic synthetic resin is used, the average molecular weight is preferably 500 to 50,000. It is 1,000 to 40,000 for PVA resin, 500 to 20,000 for PEI resin, and 2,000 to 50,000 for PVP resin.
If the average molecular weight is too small, it is difficult to obtain a dispersion effect. In addition, the adhesive force is too strong to cover the surface of the pseudo octahedron and increase the electrical resistance. Furthermore, it is easy to decompose | disassemble, and the filtrate after reaction becomes difficult to carry out wastewater treatment, and becomes high-cost. On the other hand, if the average molecular weight is too high, the solubility in water will be low, and even if it is dissolved, it is difficult to obtain a dispersion effect due to the structure in which molecules are condensed in water. Further, the viscosity of the aqueous solution is increased, and it becomes difficult to filter and filter the deposited pseudooctahedral particles, resulting in a decrease in productivity.

Some prior art uses gelatin. However, this is a unique reducing agent, complexing agent, and dispersing agent, and due to its characteristics as a biopolymer, it has an average molecular weight of about 100,000, has a large charge, is soluble and becomes a protective colloid, Is different from the organic synthetic resin of the present invention. It has a repetitive structure like PVA and has a function different from that of a synthetic resin that is not an electric charge but has a large dielectric constant and is soluble in water. A protective colloid is a carrier for dispersing fine particles and functions as a dispersant as a PVA, but in terms of molecular weight and charge, it has a polypeptide in which amino acids are polymerized, that is, has an amino group and a carboxyl group in the same molecule. So most of it is ionized in water. Since copper is ion-bonded and has a high adsorptive power and is difficult to clean, electrical resistance increases when firing at about 200 ° C.
On the other hand, the PVA of the present invention is only hydrated and formed into a dielectric material, and hardly contributes to the reduction reaction (velocity). However, it has an advantage in that it affects the growth reaction and can be removed by washing with water after the growth, and hardly affects the electrical resistance.

In the present invention, in order to obtain a copper powder having a highly crystalline pseudo-octahedral structure, the abundance ratio of copper hydroxide and copper complex ions in the step (A) is within an appropriate range together with the amount of the reducing agent described later. To do.
The abundance ratio of the copper hydroxide and the copper complex ion is preferably such that the addition amount of the complexing agent is 0.5% by mass to 50% by mass with respect to copper in the copper salt. The content is more preferably 0.5% by mass to 30% by mass, and further preferably 1% by mass to 10% by mass. If the addition amount of the complexing agent is less than 0.5% by mass or more than 50% by mass with respect to the copper in the copper salt, it becomes difficult to produce copper powder having a highly crystalline pseudo-octahedral structure, and spherical Copper powder may be mainly produced. The necessary amount of the complexing agent is 0.5% by mass to 50% by mass with respect to the copper in the copper salt, and the influence on the production cost is small.

(2) Process (B)
Step (B) is a step in which 1-2 equivalents of a reducing agent is added to the slurry prepared in step (A) to produce cuprous oxide (Cu ₂ O).

  The reducing agent used in the step (B) may be at least one selected from hydrazine and its derivatives such as hydrazine, hydrazine sulfate and hydrazine phosphate, ascorbic acid and its acid derivatives, formalin, glucose and polysaccharides. These reducing agents have a reducing power to reduce copper complex ions and hydroxides to cuprous oxide in the pH range of 12 to 14, and obtain cuprous oxide having a fine powdery crystalline pseudo-octahedral structure. Can do.

  Moreover, it is preferable that the addition amount of a reducing agent shall be 1-2 equivalent. Less than 1 equivalent is very impractical because the reduction is very slow, and adding more than 2 equivalents of a reducing agent rapidly reduces cuprous oxide and copper powder, so it is easy to oxidize ultra fine powder of 0.1 μm or less. Generate. Furthermore, even if a reducing agent is added in the step (C), it cannot be grown to the target particle size. In addition, 1 equivalent means the quantity required in order to reduce | restor all the copper in a copper salt stoichiometrically.

  As the reducing conditions in the step (B), the temperature, the stirring speed, and the suppression of foaming can be appropriately determined, but the liquid temperature is preferably 20 to 80 ° C. and the stirring speed is 100 rpm to 500 rpm. Further, by adding a surfactant such as a foam inhibitor as necessary, reduction with excellent productivity and reproducibility is performed.

  In the neutralization reaction in step (A) described above, copper becomes a hydroxide. At this stage, what is amorphous (fine) is reduced in the step (B) to form an oxide, thereby forming a pseudo-octahedral structure. The reason why copper oxide forms a crystalline quasi-octahedral structure is considered to be that organic synthetic resin such as PVA exists as a dispersant and that the hydroxide is slowly reduced to become copper oxide. . By stabilizing Cu ions with a reducing agent having a complexing action and coexisting with the hydroxide, it is considered that the reduction rate from the reduced amount of hydroxide to the oxide decreases. If the reduction rate becomes slow, the copper oxide becomes crystalline and approaches an octahedral structure.

(3) Process (C)
Step (C) is a step of generating copper by adding a reducing agent to the slurry reduced to cuprous oxide in step (B). The reducing agent that can be used in the step (C) is the same as in the step (B), and is selected from hydrazine and its derivatives such as hydrazine, hydrazine sulfate, hydrazine phosphate, ascorbic acid, ascorbic acid derivatives, formalin, glucose, and polysaccharides. It may be more than types.

  The addition amount is preferably 1 equivalent or more. Moreover, if the total addition amount of the reducing agent in the step (B) and the step (C) is 3 equivalents or more, more preferably 4 equivalents or more, the reduction time is shortened, the reduction rate (recovery rate of copper powder from cuprous oxide) ) Can be improved. The upper limit of the total amount of the reducing agent added in the step (B) and the step (C) is not particularly limited. However, even if it exceeds 7 equivalents, there is no effect of further reducing the reduction time, and the chemical cost increases, which is not preferable.

  The reason why copper hydroxide becomes cuprous oxide having a pseudo-octahedral structure in step (B) and high crystallization in step (C) is not clear, but these reducing agents also act as complexing agents. It is thought that the copper powder derived from the octahedral structure of the complex is formed by some complex formation between the agent and the reducing agent and copper. In the step (C), when the copper oxide having a pseudo-octahedral structure is dissolved by the complexing action of the reducing agent to form complex ions and is reduced to Cu, the rate of dissolution and reduction is locally controlled. For this purpose, the structure and reducing power of the reducing agent are important, and if the reducing agent is selected, it will be possible to take over the original structure.

  Moreover, temperature, stirring speed, and suppression of foaming can be suitably changed as reducing conditions in the step (C), and the liquid temperature is set to 20 to 80 ° C. and the stirring speed is set to 100 rpm to 500 rpm as in the step (B). preferable. Furthermore, reduction | restoration which was excellent in productivity and reproducibility stability is performed by adding surfactant, such as a foaming inhibitor, as needed.

  The copper powder generated in the step (C) is subjected to filtration, washing, and drying treatment, and the water adhering to the surface is removed. For the cleaning, a known method may be used. For example, pure water, alcohols such as ethanol, or a mixture thereof may be used as the cleaning liquid. The washing temperature is not particularly limited, but is preferably 5 to 50 ° C, more preferably 10 to 40 ° C. Washing is repeated until, for example, the impurity concentration falls within a desired range, and finally filtered to obtain copper powder. The drying method is not particularly limited, and a known method such as an oven, a spray dryer, or vacuum drying may be used.

  The wet copper powder obtained in this way is fine and has a relatively narrow particle size distribution, but because it is a highly crystalline particle, it has a smooth appearance, no defects, good crystallinity and stability (surface stability) ) Is high and has excellent oxidation resistance, but it is still not necessarily sufficient for a metal filler for a baked conductive paste.

(4) Process (D)
Therefore, the copper powder produced by the operations of the above steps (A) to (C) is coated with nickel or a nickel alloy using, for example, a reduction electroless plating method or a substitutional electroless plating method.

  The copper powder may be nickel-plated as it is, but is preferably washed before that. A uniform coating can be performed by dispersing the copper powder in the cleaning liquid and performing the cleaning while stirring. This washing treatment is preferably performed in an acidic solution, and after washing, filtration and separation of copper powder and washing with water are repeated as appropriate to obtain a water slurry in which copper powder is dispersed in water. In addition, what is necessary is just to use a well-known method about filtration, isolation | separation, and water washing.

  When applying Ni coating by electroless plating, add electroless Ni plating solution to copper slurry obtained after washing dendritic copper powder, or add copper slurry into electroless Ni plating solution and stir uniformly By doing so, the surface of the copper powder can be more uniformly coated with Ni or Ni alloy.

  The electroless nickel plating solution is not particularly limited. The electroless nickel plating solution is a coating of nickel by reducing nickel ions obtained from the nickel source in the plating solution with a reducing agent. The types of reducing agents are hypophosphite and borohydride. Compounds, and hydrazine compounds.

Specifically, examples of hypophosphites include hypophosphites such as potassium hypophosphite and sodium hypophosphite, and phosphites such as potassium phosphite and sodium phosphite. Can be mentioned.
Examples of the borohydride compound include dimethylhexaborane, dimethylamineborane (DMAB), diethylamineborane, morpholineborane, pyridineamineborane, piperidineborane, ethylenediamineborane, ethylenediaminebisborane, t-butylamineborane, imidazoleborane, methoxy Examples include ethylamine borane and sodium borohydride.

  As the hydrazine compound, hydrazine and hydrates thereof, hydrazine salts such as hydrazine sulfate and hydrazine hydrochloride, hydrazine derivatives such as pyrazoles, triazoles, and hydrazides can be used. Among these hydrazine derivatives, pyrazoles such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone can be used as pyrazoles in addition to pyrazole. As triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole, and the like can be used. As hydrazides, adipic hydrazide, maleic hydrazide, carbohydrazide, and the like can be used. As hydrazines, hydrazine sulfate, hydrazine hydrochloride, adipic hydrazide, maleic hydrazide, carbohydrazide, and the like can be used.

  Examples of the nickel source include nickel salts such as nickel sulfate, nickel chloride, nickel acetate, and nickel sulfamate.

Further, the plating solution can contain a complexing agent, a pH buffering agent, and a pH adjusting agent.
Specifically, a known complexing agent can be used as the complexing agent. For example, amino acids such as glycine, citrates such as sodium citrate and ammonium citrate, lactic acid, oxalic acid, malonic acid, malic acid, tartaric acid, aspartic acid, glutamic acid, gluconic acid, sodium salts or ammonium salts, ammonia, etc. Is mentioned.

A known complexing agent can be used as the pH buffering agent. For example, ammonium chloride, ammonium sulfate, boric acid, sodium acetate and the like can be mentioned.
A known complexing agent can be used as the pH adjuster. For example, an acid or alkali compound can be used, and examples thereof include alkali metal hydroxides such as ammonia and sodium hydroxide, nickel carbonate, sulfuric acid, and hydrochloric acid. In addition, when using ammonia, it can supply as ammonia water.
Moreover, you may use an antifoamer and a dispersing agent as needed.

  Furthermore, in order to improve the permeability of the plating solution, a surfactant can be contained. As the surfactant, any of nonionic, cationic, anionic and amphoteric surfactants can be used, and one kind can be used alone, or two or more kinds can be used in combination.

  Here, in the nickel coating by electroless plating, the nickel coating deposited differs depending on the hypophosphorous acid bath salt, the borohydride compound, and the hydrazine compound which are reducing agents in the electroless nickel plating solution. Specifically, when hypophosphorous acid bath salt is used as the reducing agent, since the phosphorus (P) is contained in the coating during the reduction reaction, a Ni-P alloy coating is formed. Further, when a borohydride compound is used as the reducing agent, since the boron (B) is contained in the coating during the reduction reaction, a Ni—B alloy coating is formed. Moreover, when a hydrazine compound is used as the reducing agent, a high-purity nickel film with few impurities is formed.

  Furthermore, by making other elements contained in the nickel film to be formed, that is, by forming a nickel alloy film on the surface of the copper powder, the nickel-coated copper powder can be used for heat resistance and corrosion resistance. In addition, an excellent conductive paste or the like can be realized.

  Specifically, elements included in the nickel film, that is, elements other than nickel constituting the nickel alloy include elements of Group 6 to Group 14 of the periodic table, and among them, zinc, palladium, cobalt Rhodium, iron, platinum, iridium, tungsten, molybdenum, chromium, tin and the like. In particular, one or more elements selected from zinc, cobalt, tungsten, molybdenum, palladium, platinum, and tin are preferable, and a nickel alloy film having excellent conductivity is formed by using a nickel alloy containing these elements. be able to.

  The content of the elements constituting these nickel alloys is preferably 0.1% by mass to 20% by mass and preferably 1% by mass to 15% by mass with respect to the nickel alloy from the viewpoint of conductivity and dispersibility. More preferably, the content is 2% by mass to 10% by mass. In addition, also about the Ni-P alloy and Ni-B alloy which are each formed with the kind of reducing agent mentioned above, the content of the phosphorus and boron is 0.1 mass% with respect to 100 mass of nickel alloy film similarly. It is preferably ˜20% by mass, more preferably 1% by mass to 15% by mass, and further preferably 2% by mass to 10% by mass.

  As a method for forming a nickel alloy film, an ion such as cobalt, zinc, tungsten, molybdenum, palladium, platinum, and tin is added to the above-described electroless Ni plating solution, and electroless plating using the plating solution is performed. Can be formed. The ion source such as cobalt, zinc, tungsten, molybdenum, palladium, platinum, and tin is not particularly limited as long as it is a soluble metal salt.

  Specifically, the cobalt ion source is not particularly limited as long as it is soluble in the plating solution as a cobalt compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include cobalt sulfate, cobalt chloride, and cobalt sulfamate. These cobalt compounds can be used individually by 1 type or in mixture of 2 or more types.

  The zinc ion source is not particularly limited as long as it is soluble in the plating solution as a zinc compound and can obtain an aqueous solution having a predetermined concentration. For example, zinc chloride, zinc sulfamate, zinc sulfate, zinc acetate and the like can be mentioned. These zinc compounds can be used singly or in combination of two or more.

  The tungsten ion source is not particularly limited as long as it is soluble in a plating solution as a tungsten compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include sodium tungstate, potassium tungstate, and ammonium tungstate. These tungsten compounds can be used singly or in combination of two or more.

  The molybdenum ion source is not particularly limited as long as it is soluble in a plating solution as a molybdenum compound and can obtain an aqueous solution having a predetermined concentration. Examples thereof include molybdenum trioxide, sodium molybdate, diammonium molybdate, calcium molybdate, molybdic acid, phosphomolybdic acid, and molybdate gluconic acid complex. These molybdenum compounds can be used singly or in combination of two or more.

  The palladium ion source is not particularly limited as long as it is soluble in the plating solution as a palladium compound and can obtain an aqueous solution having a predetermined concentration. For example, water-soluble palladium compounds such as palladium sulfate, palladium chloride, palladium acetate, dichlorodiethine rediamine palladium, and tetraammine palladium dichloride can be used. Further, as the palladium compound, a so-called palladium solution in which palladium is made into a solution can also be used. As the palladium solution, for example, a dichlorodiethylenediamine palladium solution or a tetraammine palladium dichloride solution can be used. These palladium compounds can be used individually by 1 type or in mixture of 2 or more types.

  Patent Document 1 describes that, as described above, the core material is copper particles, and a plating catalyst is fixed to the surface of the copper particles by a reduction reaction, and electroless nickel plating is applied to the outermost surface. ing. In addition, a catalyst forming material containing a catalytic element such as palladium is added as a plating catalyst, but in this method, palladium does not form an alloy with nickel and has a two-layer structure, which is a single layer nickel as in the present invention. Not coated copper particles.

  The platinum ion source is not particularly limited as long as it is soluble in a plating solution as a platinum compound and can obtain an aqueous solution having a predetermined concentration. For example, platinum chloride, chloroplatinic acid, chloroplatinic acid salt, platinum hydroxide acid, platinum hydroxide salt, dinitrodiammine platinum complex salt, dinitrosulfitoplatinum complex salt, tetraammine platinum complex salt, hexaammine platinum complex salt can be mentioned. A platinum compound can be used individually by 1 type or in mixture of 2 or more types.

  The tin ion source is not particularly limited as long as it is a tin compound that is soluble in the plating solution and can obtain an aqueous solution having a predetermined concentration. For example, stannous chloride, stannous chloride, stannous sulfate, stannous sulfate, tin pyrophosphate and other inorganic acid salts of tin, stannous citrate, stannous citrate, stannous oxalate Of tin carboxylates such as stannic oxalate, tin methanesulfonate, tin 1-ethanesulfonate, tin 2-ethanesulfonate, tin 1-propanesulfonate, tin 3-propanesulfonate Alkane sulfonate, tin methanol sulfonate, tin hydroxyethane-1-sulfonate, tin 1-hydroxypropane-1-sulfonate, tin hydroxyethane-2-sulfonate, tin 1-hydroxypropane-3-sulfonate, etc. Alkanol sulfonates of the above, stannous hydroxides such as stannous hydroxide and stannic hydroxide, and metastannic acid.

  In addition, as a method of forming a nickel alloy film, it is not limited to the method by the electroless plating method mentioned above. For example, an element other than nickel constituting the nickel alloy is contained in the copper powder before being coated with nickel, and after a film made only of nickel (Ni film) is formed, it is previously contained in the copper powder. The nickel alloy film can also be formed by diffusing the element in the nickel film. More preferably, as a method for improving the resistivity of nickel and nickel alloy coat film, adhesion with copper powder and oxidation resistance, there is a treatment method of applying heat or mechanical energy, and the nickel coat copper powder is appropriately treated. can do.

  The wet copper powder obtained in this way is fine and has a relatively narrow particle size distribution, but because it is a highly crystalline particle, it has a smooth appearance, no defects, good crystallinity and stability (surface stability) ) And high oxidation resistance, and the copper powder is coated with nickel or a nickel alloy on the surface.

3. From this, when the nickel coat copper powder which concerns on this invention is used as a material (metal filler) of an electroconductive paste, the outstanding dispersibility which disperse | distributes uniformly without aggregating in resin is shown. Further, by having oxidation resistance, the conductive paste using the nickel-coated copper powder as a metal filler can be appropriately subjected to a baking treatment such as high-temperature baking even in an oxidizing atmosphere.

  The conductive paste according to the present invention can be obtained by mixing at least the above nickel-coated copper powder, resin (binder resin) and solvent and kneading them. In addition to nickel-coated copper powder, resin, and solvent, the conductive paste contains additives such as antioxidants and coupling agents as necessary to improve the conductivity after curing. can do.

  Although the kind of resin is not specifically limited, An epoxy resin, a phenol resin, an ethyl cellulose resin, etc. can be used.

  Moreover, as a solvent, organic solvents, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerol, and terpineol, can be used. Further, the amount of the organic solvent is not particularly limited, but the addition amount can be adjusted in consideration of the average particle size of the copper powder so as to have a viscosity suitable for a conductive film forming method such as screen printing or a dispenser. it can.

  Moreover, the kind of antioxidant is not specifically limited, For example, hydroxycarboxylic acid etc. can be mentioned. More specifically, hydroxycarboxylic acids such as citric acid, malic acid, tartaric acid, and lactic acid are preferable, and citric acid or malic acid having a high adsorptive power to copper is particularly preferable. In addition, a coupling agent, a viscosity modifier, a dispersant, a flame retardant, an anti-settling agent, and the like can be used.

This conductive paste can be manufactured by a method similar to the conventional technique as long as the above-described constituent components can be uniformly dispersed. For example, the above-described constituent components can be uniformly kneaded by a three roll mill or the like.
The timing of adding the above-mentioned additives is not particularly limited, and the nickel-coated copper powder and the binder resin may be added and kneaded simultaneously with the solvent, or the nickel-coated copper powder and the binder resin may be mixed with the solvent. And kneaded, and may be added using a self-revolving mixer or the like.

  This conductive paste is printed on a conductor circuit pattern or terminal, and is heated and fired at a high temperature of 600 ° C. to 800 ° C. to form a conductive film, whereby wiring and electrodes are formed. In the firing type conductive paste, it is processed at a high temperature, and the metal filler is sintered to ensure conductivity.

  EXAMPLES Examples of the present invention will be described below in detail with reference to comparative examples, but the present invention is not limited to the following examples. In addition, the nickel coat copper powder obtained by the following Example and the comparative example measured the observation of the shape, the crystallite diameter of copper, oxidation resistance, and sintering resistance with the following method.

(Observation of shape)
The nickel-coated copper powder is observed with a scanning electron microscope (SEM) (manufactured by JEOL Ltd., JSM-7100F) at an arbitrary magnification (20 visual fields), and the appearance of the nickel-coated copper powder contained in the visual field is observed. Observed. The diagonal length (L) of the pseudooctahedron was measured by image analysis (analysis software MacViewer etc.). The number ratio of copper powder having a pseudo-octahedron structure in the total number of copper powders in the field of view observed by image analysis was also measured.

(Measurement of crystallinity and crystallite diameter)
Measured with an X-ray diffractometer (XRD) (manufactured by PAN artificial, trade name: X'Pert PRO) to confirm the formation of cuprous oxide and copper oxide, and further the crystallite diameter of copper of nickel-coated copper powder (R ) Was determined by the Scherrer method of X-ray diffraction. The crystallinity of single crystal or polycrystal is judged by the ratio (R / L) to the diagonal length (L).

(Oxidation resistance)
The oxidation resistance was obtained by drying nickel-coated copper powder obtained by drying into cylindrical pellets having a diameter of about 3 mm and a thickness of 2 mm using a tableting press, and by thermogravimetry (TG; manufactured by Rigaku) in the atmosphere at 200 ° C. The temperature was raised to 0 and the weight gain due to oxidation was measured.

(Sintering resistance)
The resistance value of the pellet after TG evaluation of oxidation resistance was measured by a four-terminal resistance measuring instrument (manufactured by Mitsubishi Chemical Analytical), and the resistivity (μΩ · cm) was calculated from the pellet shape.

(Weatherability)
Use the pellet after measuring the firing resistance, leave it under constant temperature and humidity, calculate the resistivity by measuring the resistivity for each fixed time using the above four-terminal resistance meter, and before measuring the constant temperature and humidity Based on the above, the change rate (%) of the resistivity was calculated. Specifically, as a typical example of constant temperature and humidity conditions, a temperature of 85 ° C. and a humidity of 85% R.D. H. The change rate of resistivity after 500 hours was calculated. The change rate of the resistivity is required to be 20% or less.

[Example 1]
Copper sulfate hydrate (manufactured by Sumitomo Metal Mining) was dissolved in pure water (ion exchange resin treatment) as a copper salt to obtain an aqueous solution having a copper concentration of 40 g / L. Polyethyleneimine (PEI resin, manufactured by Nippon Shokubai Co., Ltd.) having an average molecular weight of 1% by mass / copper mass is added to this blue Cu solution, and a 25% aqueous sodium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) as an alkali. Was added dropwise to adjust the pH to 12.5. As a result, the solution became dark blue due to the copper complex ions, and became a slurry state in which precipitation of white copper hydroxide coexists (step (A)).
When this solution was brought to 40 ° C., stirred at 300 rpm, and 2 equivalents of a reducing agent consisting of a single hydrazine hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added, bright orange cuprous oxide (from XRD analysis) Cu ₂ O was identified) (step (B)). Subsequently, when 2 equivalents of hydrazine hydrate reducing agent was further added, the bright orange color changed to light brown, and XRD measurement showed that cuprous oxide was reduced to copper powder (step (C)). The obtained copper powder was once filtered, filtered again after surface treatment by washing with water and addition of a stearic acid emulsion for preventing aggregation, and dried in a vacuum oven at 30 ° C. for 6 hours.
Next, using the copper powder produced by the method described above, the surface of the copper powder was coated with nickel by electroless nickel plating to produce a nickel-coated copper powder. In addition, since the electroless nickel plating liquid whose reducing agent is a hypophosphite was used, the obtained film | membrane becomes a Ni-P alloy.
Specifically, as an electroless nickel plating solution, nickel sulfate 20 g / L, sodium hypophosphite 25 g / L, sodium acetate 10 g / L, sodium citrate 10 g / L are added at each concentration, and sodium hydroxide is further added. 500 mL of a plating solution adjusted to pH 5.0 by adding the above was prepared.
In this electroless nickel plating solution, a slurry in which 100 g of copper powder prepared by the above-described method is dispersed in 100 mL of water is stirred and stirred at 25 ° C. for 10 minutes, and then the bath temperature is heated to 90 ° C. and stirred for 60 minutes. did. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol (step (D)).
The shape of the nickel-coated copper powder thus obtained was observed by the method using the SEM described above. The silver-coated copper powder has a pseudo-octahedron structure, and the number of nickel-coated copper powders having this pseudo-octahedron structure was 80% or more of the total number. Moreover, the average value of the diagonal length (L) of the polycrystalline pseudo-octahedron is 0.50 μm, the crystallite diameter (R) of copper by XRD is 0.15 μm, and the obtained nickel-coated copper powder is As shown in Table 1, it was confirmed that the surface of the fine and highly crystalline copper powder with R / L = 0.30 was coated with a nickel alloy. Moreover, when the coating amount of the nickel alloy was measured, the coating amount of the nickel alloy was 13.9% by mass with respect to the entire nickel-coated copper powder, and the phosphorus content contained in the nickel alloy was 8. It was 1% by mass. Furthermore, the 200 ° C. oxidation increase (TG measurement) was as small as 0.5% by mass, and the resistivity was as low as 122 μΩ · cm. The weather resistance was very good at 8.4%.

[Example 2]
In Example 1, instead of PEI resin, polyvinyl alcohol (PVA resin, manufactured by Kanto Chemical Co., Inc.) having an average molecular weight of 1% by mass / copper mass was added, and 25% sodium hydroxide aqueous solution (Wako Pure Chemical Industries) was used as an alkali. Yaku Kogyo Co., Ltd.) was added dropwise to adjust the pH to 13.5, and 2 equivalents of ascorbic acid reducing agent was added in step (C). The other conditions were the same. As in Example 1, the solution in step (A) is in a slurry state in which dark blue and white copper hydroxide precipitates due to copper complex ions coexist, and in step (B), bright orange cuprous oxide (XRD analysis) And identified as Cu ₂ O), and in step (C), the bright orange color changed to light brown and was reduced to copper powder from XRD measurement.
The obtained nickel-coated copper powder was observed by SEM as in Example 1. The nickel-coated copper powder has a pseudo-octahedral structure, and the number of nickel-coated copper powders having this pseudo-octahedral structure was 80% or more of the total number. Moreover, as shown in Table 1, the average value of the diagonal length (L) of the polycrystalline pseudo-octahedron was 0.70 μm, and the crystallite diameter (R) of copper by XRD was 0.30 μm. It was confirmed that the coated copper powder was coated with a nickel alloy on the surface of a fine and highly crystalline copper powder of R / L = 0.43. Further, when the coating amount of the nickel alloy was measured, the coating amount of the nickel alloy with respect to the entire nickel-coated copper powder was 13.0% by mass, and the content of phosphorus contained in the nickel alloy was 8. It was 0 mass%. Furthermore, the 200 ° C. oxidation increase (TG measurement) was as small as 0.4 mass%, and the resistivity was as low as 95 μΩ · cm. The weather resistance was very good at 10.0%.

[Example 3]
In Example 1, the production method of the copper powders in steps (A) to (C) is the same, and the electroless nickel plating solution in which the reducing agent is a borohydride compound is used in step (D). Then, a nickel film was formed on the surface. This is an example where the coating is a Ni-B alloy.
Specifically, as an electroless nickel plating solution, nickel sulfate 30 g / L, sodium succinate 50 g / L, boric acid 30 g / L, ammonium chloride 30 g / L, dimethylamine borane 4 g / L were added at each concentration, Further, 500 mL of a plating solution adjusted to pH 6.0 by adding sodium hydroxide was prepared.
In this electroless nickel plating solution, a slurry in which 100 g of the copper powder prepared by the above-described method is dispersed in 100 mL of water is placed in the nickel plating solution, stirred at 25 ° C. for 10 minutes, and then the bath temperature is heated to 60 ° C. And stirred for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol (step (D)).
The shape of the obtained nickel-coated copper powder was observed by the method using SEM as in Example 1. The nickel-coated copper powder has a pseudo-octahedral structure, and the number of nickel-coated copper powders having this pseudo-octahedral structure was 80% or more of the total number. Moreover, the average value of the diagonal length (L) of the polycrystalline pseudo-octahedron is 0.51 μm, the crystallite diameter (R) of copper by XRD is 0.15 μm, and the obtained nickel-coated copper powder is It was confirmed that the nickel alloy was coated on the surface of the fine and highly crystalline copper powder having R / L = 0.29. Moreover, when the coating amount of the nickel alloy was measured, the coating amount of the nickel alloy was 18.4% by mass with respect to the entire nickel-coated copper powder, and the boron content contained in the nickel alloy was 6. It was 3 mass%. Further, the 200 ° C. oxidation increase (TG measurement) was as small as 0.3% by mass, and the resistivity was as low as 350 μΩ · cm. The weather resistance was very good at 8.9%.

[Example 4]
In Example 1, the preparation method of the copper powder from step (A) to (C) is the same, and changed to use an electroless nickel plating solution whose reducing agent is a hydrazine compound in step (D). A nickel coating was formed on the surface. This is an example where the coating is nickel that has not been alloyed.
Specifically, nickel acetate was added to a slurry in which 100 g of the obtained copper powder was dispersed in 500 mL of water to a concentration of 12.4 g / L, and 6 g of a hydrazine monohydrate 80% by mass aqueous solution was added to the bath. The solution was added dropwise with stirring gradually over 60 minutes. At this time, the bath temperature was controlled to 60 ° C. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol (step (D)).
The shape of the obtained nickel-coated copper powder was observed by the method using SEM as in Example 1. The nickel-coated copper powder has a pseudo-octahedral structure, and the number of nickel-coated copper powders having this pseudo-octahedral structure was 80% or more of the total number. Moreover, the average value of the diagonal length (L) of the polycrystalline pseudo-octahedron is 0.50 μm, the crystallite diameter (R) of copper by XRD is 0.15 μm, and the obtained silver-coated copper powder is It was confirmed that nickel was coated on the surface of the fine and highly crystalline copper powder having R / L = 0.30. Moreover, when nickel coating amount was measured, nickel coating amount was 7.7 mass% with respect to the whole nickel coat copper powder. Furthermore, the 200 ° C. oxidation increase (TG measurement) was as small as 0.5% by mass, and the resistivity was as low as 185 μΩ · cm. The weather resistance was very good at 8.4%.

[Examples 5 to 11]
In Example 1, the preparation method of the copper powder from the steps (A) to (C) is the same, and changed to use various electroless nickel plating solutions in the step (D). Was formed.
As an electroless nickel plating solution for alloys, nickel acetate was added to a slurry in which 100 g of the obtained copper powder was dispersed in 500 mL of water to a concentration of 12.4 g / L, and 3.2 g of hydrazine was added to the bath. The solution was added dropwise with stirring gradually over 60 minutes. The bath temperature was controlled to 60 ° C.
At this time, each metal compound was added to a bath containing copper powder slurry and nickel acetate, and hydrazine was gradually added so that each desired Ni alloy film was formed. As a metal compound, in Example 5, 1.5 g of sodium tungstate was added to form a Ni—W alloy film. In Example 6, 2 g of cobalt sulfate was added to form a Ni—Co alloy film. In Example 7, 4 g each of zinc sulfate heptahydrate and sodium citrate were added to form a Ni—Zn alloy film. In Example 8, 2 g of palladium chloride was added to form a Ni—Pd alloy film. In Example 9, 2 g of potassium tetrachloroplatinate and 1 g of glycine were added to form a Ni—Pt alloy film. In Example 10, 1 g each of sodium molybdate and trisodium citrate was added to form a Ni—Mo alloy coating. In Example 11, 1 g of sodium stannate was added to form a Ni—Sn alloy film.
After completion of each reaction, the powder was filtered, washed with water and dried through ethanol (step (D)).
The shape of the obtained nickel-coated copper powder was observed by the method using SEM as in Example 1. The nickel-coated copper powder has a pseudo-octahedral structure, and the number of nickel-coated copper powders having this pseudo-octahedral structure was 80% or more of the total number. In addition, the diagonal length of the polycrystalline pseudo-octahedron (L), the crystallite diameter of copper by XRD (R), the coating amount of the nickel alloy over the entire nickel-coated copper powder, and the content of each element contained in the nickel alloy, Table 1 summarizes the results of 200 ° C. oxidation increase (TG measurement), resistivity, and weather resistance.

[Example 12]
In Example 1, the copper powder production method from step (A) to step (C) is performed under the same conditions, and step (D) is electroless nickel plating in which the reducing agent is hypophosphite and contains tungstate. Instead of using a liquid, a nickel film was formed on the surface. This is an example in which the coating is an Ni-P-W alloy.
Specifically, as an electroless nickel plating solution, a plating solution in which nickel sulfate 20 g / L, sodium hypophosphite 25 g / L, sodium acetate 10 g / L, and sodium citrate 10 g / L are added at each concentration, 500 g of a plating solution prepared by adding 1.5 g of sodium tungstate and adjusting the pH to 5.0 by adding sodium hydroxide was prepared. In this electroless Ni plating solution, a slurry in which 100 g of the dendritic copper powder prepared in Example 1 was dispersed in 100 mL of water was added and stirred at 25 ° C. for 10 minutes, and then the bath temperature was heated to 90 ° C. Stir for 60 minutes. After the reaction was completed, the powder was filtered, washed with water and dried through ethanol (step (D)).
The shape of the obtained nickel-coated copper powder was observed by the method using SEM as in Example 1. The nickel-coated copper powder has a pseudo-octahedral structure, and the number of nickel-coated copper powders having this pseudo-octahedral structure was 80% or more of the total number. Moreover, the average value of the diagonal length (L) of the polycrystalline pseudo-octahedron is 0.51 μm, the crystallite diameter (R) of copper by XRD is 0.15 μm, and the obtained nickel-coated copper powder is It was confirmed that the nickel alloy was coated on the surface of the fine and highly crystalline copper powder having R / L = 0.29. Moreover, when the coating amount of the nickel alloy was measured, the coating amount of the nickel alloy was 12.4% by mass with respect to the entire nickel-coated copper powder, and the content of phosphorus contained in the nickel alloy was 7. The content of tungsten contained in the nickel alloy as well as 4% by mass was 5.4% by mass relative to the nickel alloy. Furthermore, the 200 ° C. oxidation increase (TG measurement) was as small as 0.3% by mass, and the resistivity was as low as 210 μΩ · cm. The weather resistance was very good at 12.7%.

[Comparative Example 1]
In step (A) of Example 1, 25% aqueous sodium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise as an alkali to adjust the pH to 10.5. Otherwise, the same procedure as in Example 1 was performed.
The obtained nickel-coated copper powder was observed by SEM as in Example 1. The nickel-coated copper powder became an ultrafine powder having an irregular shape and an average particle size of 0.1 μm or less rather than a pseudo-octahedral structure. In addition, the crystallite diameter (R) of copper by XRD is 0.015 μm, and the obtained silver-coated copper powder has a low crystallinity copper powder with R / L ≦ 0.15 and is coated with a nickel alloy. Was confirmed. Therefore, the 200 ° C. oxidation increase (TG measurement) was as large as 2.0 mass%, and the resistivity was as high as 10000 μΩ · cm. Moreover, it was an ultrafine powder in which granular copper powder particles were aggregated, and it was difficult to obtain a paste. In addition, when the coating amount of the nickel alloy was measured, the coating amount of the nickel alloy was 13.1% by mass with respect to the entire nickel-coated copper powder, and the content of phosphorus contained in the nickel alloy was 8% with respect to the nickel alloy. It was 6 mass%. The weather resistance was 100% or more, and the resistivity could not be measured after 500 hours.

[Comparative Example 2]
Up to step (A), the same procedure as in Example 1 was carried out, and in step (B), 0.8 equivalent of a reducing agent consisting of a single hydrazine hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added. This caused a slight change in the color of the solution, and no cuprous oxide was produced. One more equivalent of hydrazine hydrate was added to the slurry. Only bright orange cuprous oxide (identified as Cu ₂ O from XRD analysis) was precipitated, and no copper powder was obtained.

[Comparative Example 3]
Up to step (A), the same procedure as in Example 1 was carried out, and in step (B), 3 equivalents of a reducing agent consisting of a single hydrazine hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added all at once. When a reducing agent was added, a bright brown precipitate was generated instead of a bright orange color, which was confirmed to be copper powder by XRD analysis. This copper powder was coated with a nickel alloy under the conditions of step (D) in the same manner as in Example 1 to produce a nickel-coated copper powder.
The shape of the nickel-coated copper powder thus obtained was observed by a method using SEM as in the examples. The nickel-coated copper powder became an ultrafine powder having an irregular shape and an average particle size of 0.1 μm or less rather than a pseudo-octahedral structure. In addition, the crystallite diameter (R) of copper by XRD is 0.01 μm, and the obtained nickel-coated copper powder has R / L ≦ 0.1 and a low-crystalline copper powder coated with a nickel alloy. Was confirmed. Therefore, the 200 ° C. oxidation increase (TG measurement) was 3% by mass or more and the resistivity was 10,000 μΩ · cm or more, resulting in high resistance. Moreover, it was an ultrafine powder in which granular copper powder particles were aggregated, and it was difficult to obtain a paste. In addition, when the coating amount of the nickel alloy was measured, the coating amount of the nickel alloy was 12.8% by mass with respect to the entire nickel-coated copper powder, and the content of phosphorus contained in the nickel alloy was 7% with respect to the nickel alloy. It was 9 mass%. The weather resistance had a high initial resistance, and an accurate value could not be obtained, but it deteriorated with a change rate of 20% or more.

[Comparative Example 4]
The procedure was the same as Example 1 except that polyethyleneimine (PEI resin) was not added in the step (A). As a result, the color of the solution was slightly blue, but a slurry state in which white copper hydroxide precipitates coexisted, and most of the copper salt was in the form of copper hydroxide.
When this solution was brought to 40 ° C. and stirred at 300 rpm and 2 equivalents of a reducing agent consisting of a single hydrazine hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added, bright orange cuprous oxide (from XRD analysis, Cu ₂ O and identification) was precipitated. When 2 equivalents of hydrazine hydrate reducing agent was further added, the bright orange color changed to light brown, and XRD measurement showed that cuprous oxide was reduced to copper powder. This copper powder was coated with nickel under the conditions of step (D) in the same manner as in Example 1 to produce a nickel-coated copper powder.
The shape of the nickel-coated copper powder thus obtained was observed by the method using SEM as in Example 1. The nickel-coated copper powder was not a pseudo-octahedral structure but spherical and had an average particle size of 1.5 μm. Moreover, the crystallite diameter (R) of copper by XRD is 0.05 μm, and the obtained nickel-coated copper powder is coated with a nickel alloy on copper powder having a very low crystallinity of R / L = 0.033. It was confirmed. Therefore, the 200 ° C. oxidation increase (TG measurement) was 3% by mass or more and the resistivity was 10000 μΩ · cm or more, resulting in high resistance. When the nickel alloy coating amount was measured, the nickel alloy coating amount was 13.9% by mass with respect to the entire nickel-coated copper powder, and the phosphorus content contained in the nickel alloy was 8. It was 2 mass%. The weather resistance had a high initial resistance, and an accurate value could not be obtained, but it deteriorated with a change rate of 20% or more.

"Evaluation"
From Table 1 that summarizes the results of Examples 1 to 12 and Comparative Examples 1 to 4, the following can be said. In Examples 1 to 12, the copper powder obtained by the wet method had a pseudo-octahedron structure, and the number of nickel-coated copper powders having this pseudo-octahedron structure was 80% or more of the total number. Moreover, the average value of the diagonal length (L) of the polycrystalline pseudo-octahedron is 0.1 to 2 μm, and the ratio to the crystallite diameter (R) of copper by XRD is R / L = 0.2 to 0.5. Therefore, it has both sinterability and oxidation resistance. By coating nickel on the surface of this fine and highly crystalline copper powder, the 200 ° C. oxidation increase (TG measurement) is as small as 0.2 to 0.5 mass%, and the resistivity is 95 to 350 μΩ · cm. The resistance change rate (weather resistance) was as good as 14.5% or less. Thus, because it has both excellent weather resistance, oxidation resistance and sintering / low resistance, the nickel-coated copper powder that satisfies the conditions of the present invention is a resin for forming wiring layers and electrodes in electronic devices. It is useful as a metal filler as a raw material for mold pastes and fired pastes.

  On the other hand, in Comparative Examples 1 and 3, although the wet method was used, the conditions did not satisfy the conditions of the present invention. Therefore, the obtained copper powder had an irregular shape and an average particle size of 0.1 μm or less. Comparative Example 2 Then, copper powder is not obtained. In Comparative Example 4, it was spherical and the average particle size was as large as 1.5 μm. For this reason, all of the nickel-coated copper powders of Comparative Examples 1, 3, and 4 have a 200 ° C. oxidation increase (TG measurement) of 2% by mass or more and a resistivity of 10000 μΩ · cm, and a resistance change rate (weather resistance). Also increased to over 20%. Such nickel-coated copper powder is difficult to use as a raw material filler for resin-type paste and fired-type paste.

  The nickel-coated copper powder of the present invention can be used as a metal filler as a raw material for resin-type pastes and low-temperature firing-type pastes in order to form wiring layers and electrodes in electronic devices.

Claims (12)

  The surface of the copper powder is coated with nickel or a nickel alloy, and observed to have a pseudo-octahedral structure with a scanning electron microscope (SEM), the diagonal length (L) is 0.1 μm to 2 μm, and the diagonal length The ratio (R / L) between the thickness (L) and the crystallite diameter (R) of copper determined by the Scherrer method is in the range of 0.2 to 0.5. Nickel-coated copper powder.   The nickel-coated copper powder according to claim 1, wherein the number of crystal grains of copper constituting the pseudo-octahedral structure is 5 to 130.   The nickel-coated copper powder according to claim 1 or 2, wherein the coating amount of nickel or a nickel alloy is 1 to 33 mass% of the entire nickel-coated copper powder.   The nickel alloy contains at least one element selected from cobalt, zinc, tungsten, molybdenum, palladium, platinum, tin, phosphorus, and boron, and the element content is 0.1 to the nickel alloy. The nickel-coated copper powder according to claim 3, which is ˜20 mass%. A step (A) in which an aqueous solution of a copper salt is made alkaline with a pH of 12 to 14 and a complexing agent is further added to form a slurry in which copper hydroxide and copper complex ions coexist;
The reducing agent 1-2 by adding an equivalent amount to the slurry, and step (B) for precipitating cuprous oxide (Cu 2 _O), the cuprous oxide (Cu 2 _O) reduction 1 or more equivalents of the slurry precipitated Adding an agent to reduce cuprous oxide to copper powder (C);
Furthermore, the step (D) of coating the copper powder with nickel or a nickel alloy;
The manufacturing method of the nickel coat copper powder characterized by including.   The method for producing nickel-coated copper powder according to claim 5, wherein the complexing agent is a synthetic resin having an average molecular weight of 500 to 50,000 selected from PEI, PVA, and PVP.   The said complexing agent is added 0.5 mass%-50 mass% with respect to the copper in copper salt, The manufacturing method of the nickel coat copper powder of Claim 5 characterized by the above-mentioned.   The method for producing a nickel-coated copper powder according to claim 5, wherein the amount of the reducing agent is 3 equivalents or more as a total amount of the step (B) and the step (C).   The said reducing agent forms a complex with copper, The manufacturing method of the nickel coat copper powder in any one of Claims 5-8 characterized by the above-mentioned.   The copper powder obtained in the step (C) is coated with nickel or a nickel alloy by an electroless plating method after washing, and manufacturing the nickel-coated copper powder according to any one of claims 5 to 9 Method.   The nickel-coated copper powder has a pseudo-octahedral structure, has a diagonal length (L) of 0.1 μm to 2 μm, and a ratio of the diagonal length (L) to the crystallite diameter (R) of copper ( R / L) is the range of 0.2-0.5, The manufacturing method of the nickel coat copper powder of any one of Claims 5-10 characterized by the above-mentioned.   The electroconductive paste containing the nickel coat copper powder in any one of Claims 1-4, resin, and a solvent.

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