JP6708067B2 - Method for producing copper-coated powder - Google Patents

Description

The present invention relates to a method for producing a copper-coated powder, and more specifically, it is suitable as a conductive filler mainly used for a conductive material, and evenly adheres copper to the surface of a non-conductive inorganic powder with good adhesion. The present invention relates to a method for producing the copper-coated powder.

In recent years, metal powder, particularly fine powder of silver or copper, has been mainly used as a conductive filler to be blended with a conductive paste or a conductive coating material for electromagnetic wave shielding. In particular, silver is often used despite its high price because of its excellent electrical conductivity and environmental resistance.

In addition, with the progress of miniaturization and high functionality of electronic devices, anisotropic conductive materials have been adopted for the connection between a large number of opposing electrodes and wirings. Examples of the anisotropic conductive material include an anisotropic conductive paste, an anisotropic conductive film, and an anisotropic conductive sheet. These anisotropic conductive materials are materials in which conductive fine particles are mixed with a binder resin or the like, and in order to exhibit anisotropy at the time of connection, conductive fine particles having a constant shape are required.

With commonly used metal particles, it is difficult to produce particles in the desired shape.Therefore, a method of coating a metal on the surface of an inorganic or organic powder that can be produced by controlling the shape to a certain extent is used. There is. For example, Patent Document 1 proposes conductive fine particles in which a powder of an inorganic or organic material (resin or the like) having an average particle diameter of 0.5 to 2.5 μm is coated with a noble metal by an electroless plating method. ..

Conventionally, as a method for coating the surface of a powder made of an inorganic material or an organic material with a metal, a method of coating by electroless plating has been often used. Specifically, the electroless plating method involves activating the powder surface by immersing the powder in a stannous chloride and palladium chloride solution or a colloidal solution of tin and palladium (activating treatment). ), a metal complex, a metal complexing agent, a pH adjusting agent, a reducing agent, etc., is immersed in the electroless plating bath to form a desired metal film.

There are various types of metal coatings formed by this method, depending on the type of metal salt, and examples of metals that can be used as conductive materials and electromagnetic wave shielding materials include nickel, copper, silver, and palladium. Although the types of metal salts, metal complexing agents, pH adjusters, and reducing agents in the electroless plating bath differ depending on the type of metal, the formation of a metal coating on the surface of a powder by electroless plating is usually performed using powder. After activating the body, it is immersed in an electroless plating bath from which the reducing agent or reducing agent and the metal salt have been removed, and the powder is sufficiently dispersed by stirring, and then the reducing agent or the reducing agent and the metal salt. And are gradually added to slowly form a metal film.

However, when the metal coating is formed on the powder surface by the above-mentioned method, in the step of activating the powder surface, uneven distribution of tin or palladium may occur due to a difference in adsorptivity or the like. During electroless plating, if unevenness in the distribution of tin or palladium causes areas where a metal film is likely to be formed and areas where it is difficult to form a metal film, the progress of film formation causes the metal film to be formed only on the areas where it is easy to form. As a result, unprecipitated portions are formed in the extreme portions, and the powder itself may be exposed on the surface.

In the electroless plating method, the reducing agent contained in the electroless plating solution is used because the palladium adsorbed on the powder surface in the activation step or the metal coating previously formed by electroless plating serves as a catalyst. Is oxidized, and electrons emitted at that time reduce the metal in the electroless plating solution to form a metal film. The reducing power of the reducing agent is represented by the redox potential, but since the redox potential changes depending on the type, concentration, temperature, pH, etc. of the reducing agent, in order to obtain a metal film with uniform and good adhesion. Needs that control.

For example, Patent Document 2 discloses a method in which powder after activation treatment is dispersed in a solution containing a reducing agent, the temperature and pH are controlled, and then the powder is added to an electroless plating solution containing no reducing agent. Proposed. However, as described above, the electroless plating method requires a great number of steps, and there is a problem that complicated management is required in order to produce a uniform metal film having good adhesion. Further, in the electroless plating method, the treatment cost of the waste liquid generated in the electroless plating also becomes a problem.

JP 2000-30526 A JP-A-8-253870

Chemistry Dictionary 1 p1050, Kyoritsu Publishing Co., Ltd., published March 30, 1959

The present invention has been made in view of the above-mentioned problems of the conventional technique, a copper-coated powder obtained by uniformly adhering copper to the surface of a non-conductive inorganic powder with good adhesion, by a simple method, It is an object of the present invention to provide a method that can be manufactured more efficiently in terms of cost.

The present inventors have conducted extensive studies to achieve the above object. As a result, in the production of the copper-coated powder, the non-conductive inorganic powder and the copper oxide powder are further mixed with a specific copper salt, and the mixture is subjected to a reduction treatment while being fluidized, so that the temperature is relatively low. It was found that a copper-coated powder having good adhesion can be efficiently produced at the reduction temperature of. That is, the present invention is as follows.

(1) A first aspect of the present invention is to mix non-conductive inorganic powder with copper oxide powder and a copper salt having a melting point of 700° C. or lower, and heat the mixture in a reducing atmosphere at 350° C. or higher. It is a method for producing a copper-coated powder, in which copper is attached to the surface of the non-conductive inorganic powder by heating and reducing it while flowing at a temperature of 800° C. or lower.

(2) The second invention of the present invention is the same as the first invention, wherein, when the non-conductive inorganic powder, the copper oxide powder and the copper salt are mixed, the copper oxide powder is mixed with the non-conductive powder. The method is a method for producing a copper-coated powder, which comprises adding 5 mass% or more and 60 mass% or less in terms of the amount of metallic copper to a powder of a hydrophilic inorganic material.

(3) The third invention of the present invention is, in the first or second invention, in mixing the non-conductive inorganic powder, the copper oxide powder and the copper salt, the copper salt is It is a method for producing a copper-coated powder, which is added to copper oxide powder at a rate of 0.01% by mass or more and 10% by mass or less in terms of metallic copper.

(4) A fourth invention of the present invention is the method for producing a copper-coated powder according to any one of the first to third inventions, wherein the copper salt is copper chloride.

(5) A fifth invention of the present invention is the method for producing a copper-coated powder according to any one of the first to fourth inventions, wherein the non-conductive inorganic powder is a metal oxide powder. Is.

(6) A sixth invention of the copper-coated powder according to any one of the first to fifth inventions, wherein the non-conductive inorganic powder has an average particle size of 1 μm or more and 500 μm or less. It is a manufacturing method.

(7) A seventh invention of the present invention is the invention of any of the first to sixth inventions, wherein the copper oxide powder has an average particle diameter of 20 μm or less and a specific surface area of 0.5 m ² /g or more. It is a method for producing a copper-coated powder.

(8) An eighth invention of the present invention is the method for producing a copper-coated powder according to any one of the first to seventh inventions, wherein the reducing atmosphere is a mixed gas atmosphere of an inert gas and a reducing gas. Is.

According to the present invention, it is possible to efficiently produce a copper-coated powder in which copper is uniformly and adherently adhered to the surface of a non-conductive inorganic powder by a simple method and in terms of cost. it can.

3 is an SEM image of the zirconia powder having an average particle diameter of 300 μm (before being coated with copper) used in Example 1, taken at a magnification of 250 times. 6 is an SEM image of the zirconia powder having an average particle diameter of 15 μm (before being coated with copper) used in Example 5, taken at 1000 times. 3 is an SEM image of the copper-coated powder produced in Example 1 taken at 250×. 3 is an SEM image of the copper-coated powder produced in Example 1 taken at 1000 times. 7 is a SEM image of the copper-coated powder produced in Example 5 taken at 1000 times.

Hereinafter, specific embodiments of the present invention (hereinafter, referred to as “this embodiment”) will be described in detail. The present invention is not limited to the following embodiments, but can be modified as appropriate without departing from the scope of the invention. Further, in the present specification, the notation “x to y” (x and y are arbitrary numerical values) means “not less than x and not more than y” unless otherwise specified.

<<1. Manufacturing method of copper-coated powder >>
The method for producing a copper-coated powder according to the present embodiment is a method for producing a copper-coated powder by coating copper on the surface of a non-conductive inorganic powder, and a non-conductive inorganic powder. A copper-coated powder is obtained by a dry manufacturing method in which copper oxide powder is mixed and heated and reduced in a reducing atmosphere.

Then, in this manufacturing method, copper oxide powder and a copper salt having a melting point of 700° C. or lower are added to and mixed with the non-conductive inorganic powder, and the mixture is allowed to flow in a reducing atmosphere at 350° C. By heat-reducing at a temperature of 800° C., copper is attached to the surface of the non-conductive inorganic powder to obtain a copper-coated powder.

According to such a production method, even if the reduction temperature is low, the reduction and diffusion reactions of copper proceed efficiently and effectively, and evenly and well on the surface of the non-conductive inorganic powder. It is possible to form a copper film with adhesiveness. Further, according to this manufacturing method, since the copper coating can be formed by a dry method and at a relatively low reduction temperature, complicated process control, which has been a problem in the electroless plating method, becomes unnecessary, and a waste liquid is treated. Since there is no problem and less energy is required for heating, the copper-coated powder can be efficiently produced at low cost.

<<2. About each treatment in the manufacturing method of copper-coated powder >>
<Mixing of raw materials>
In the method for producing a copper-coated powder according to the present embodiment, copper oxide powder is mixed with non-conductive inorganic powder, and a specific copper salt is further added and mixed.

(1) Non-conductive inorganic powder The non-conductive inorganic powder is not particularly limited as long as it is a non-conductive inorganic powder, but is reduced by heating at a temperature of 350°C to 800°C in a reducing atmosphere. Therefore, a material that does not deteriorate even at that temperature is preferable, and a powder of a metal oxide having a melting point higher than the heating reduction temperature is more preferable.

Specifically, powders of ceramic-based inorganic materials such as alumina, titanium oxide, zirconia, silicon nitride, sialon, silicon carbide, mullite, and magnesia, borosilicate glass, soda lime glass, quartz glass, aluminosilicate glass, and potassium. Examples include powders of glass-based inorganic materials such as crystal glass, barium crystal glass, and titanium crystal glass.

As will be described later in detail, in the case of a metal oxide powder, when the copper salt melts during heating and reduction and is easily wet and spread when adhering to the powder surface, a more uniform and good adhesion copper coating is formed. Easy to do and preferred.

The average particle size of the non-conductive inorganic powder is not particularly limited, but if it is 1 μm to 500 μm (0.001 mm to 0.5 mm), it is evenly adhered to the non-conductive inorganic fluid surface by the method described above. A copper coating having good properties can be formed. As the base material of the anisotropic conductive material, it is preferable that the non-conductive inorganic powder has an average particle diameter of about 1 μm to 300 μm.

The average particle size of the non-conductive inorganic powder is 50% average particle size (D50, particle size at which 50% volume integration in a particle size distribution curve is achieved), and is measured by a laser diffraction/scattering particle size distribution measurement method. be able to.

(2) Copper oxide powder The copper oxide powder is not particularly limited, but is preferably a powder having an average particle diameter of 20 μm or less and a specific surface area of 0.5 m ² /g or more. Thus, by using a powder having a small particle size and a large specific surface area as the copper oxide powder to be used, it is efficiently mixed with the non-conductive inorganic powder, and the adhesion to the powder surface is improved. It can be increased.

The average particle size of the copper oxide powder is a 50% average particle size (D50, particle size at which 50% volume integration in a particle size distribution curve is obtained), and can be measured by a laser diffraction/scattering particle size distribution measuring method. The specific surface area of the copper oxide powder can be measured by the BET method according to JIS Z8830:2013.

Further, as the copper oxide powder, those produced by various methods can be used, among which, after copper oxide powder such as electrolytic copper powder and atomized powder is oxidized and roasted in an air atmosphere to form copper oxide. A method of pulverizing by a mechanical pulverizing method such as a ball mill is preferable because it can be manufactured at low cost.

Specifically, for example, copper sulfate pentahydrate (CuSO ₄ .5H ₂ O) has a copper concentration of 5 g/L to 50 g/L and a free sulfuric acid concentration of 50 g/L to 250 g/L. Electrolysis is carried out for 5 hours at a current density of 5 A/dm ^{2 to} 30 A/dm ² and a bath temperature of 20° C. to 60° C. using the electrolytic solution of 1 to deposit powdered electrolytic copper powder on the cathode. Next, the obtained electrolytic copper powder is heated in an atmosphere containing oxygen such as air or pure oxygen under a temperature condition of 400° C. to 900° C. for a predetermined time to be oxidized and roasted to form copper oxide. .. Then, the obtained copper oxide is pulverized by, for example, a mechanical pulverization method so that the average particle diameter becomes about 20 μm or less, whereby the copper oxide powder can be manufactured.

The mixing ratio of the copper oxide powder is not particularly limited, but is preferably 5% by mass to 60% by mass in terms of the amount of metallic copper with respect to the mass of the nonconductive inorganic powder, and 10% by mass to 50% by mass. More preferably, it is mass %. When the mixing ratio of the copper oxide powder is less than 5% by mass with respect to the mass of the non-conductive inorganic powder, copper is insufficient and it becomes difficult to completely coat the surface of the non-conductive inorganic powder with copper. there is a possibility. On the other hand, when the content of the non-conductive inorganic powder exceeds 60% by mass, copper is unnecessarily attached to the surface of the non-conductive inorganic powder and easily peels off and is easily released. , Not preferable.

(3) Regarding Copper Salt In the method for producing the copper-coated powder according to the present embodiment, as described above, the non-conductive inorganic powder and the copper oxide powder are mixed, and further a specific copper salt is added. It is characterized by adding and mixing.

Specifically, a copper salt having a melting point of 700° C. or lower is used. For example, copper (I) chloride, copper (II) chloride, copper nitrate, copper carbonate, etc. can be mentioned. Among these, copper chloride (I) or copper chloride (II) is preferable. The reason is that the melting point of copper(I) chloride is as low as 422° C. and the melting point of copper(II) chloride is as low as 498° C., as shown in Non-Patent Document 1 (Kagaku University Dictionary 1 p1050, Kyoritsu Publishing Co.). is there.

In this way, by mixing a copper salt such as copper chloride having a low melting point of 700° C. or lower with the non-conductive inorganic powder and the copper oxide powder, the copper salt at the stage of the heat reduction treatment for the mixture is When melted and wetted to the surface of the non-conductive inorganic powder, the copper oxide acts to facilitate uniform attachment to the surface of the non-conductive inorganic powder. Then, by reducing the uniformly deposited copper oxide, it becomes possible to obtain a copper-coated powder in which a copper coating is uniformly formed on the surface of the non-conductive inorganic powder.

The added copper salt such as copper chloride undergoes a reduction reaction gradually after melting to form a copper film. For the purpose of simply lowering the melting point of copper, alloying with a low melting point metal such as zinc (Zn) or tin (Sn) is considered, but these are finally contained as impurities in the copper-coated powder. It is not the best method because it will be done. On the other hand, components other than copper in the above-mentioned various copper salts such as chlorine chloride of copper chloride and nitric acid component of copper nitrate are decomposed and volatilized during heat reduction, and therefore, in the copper of the non-conductive inorganic powder surface. The amount of remaining impurities is extremely small. Since the amount of impurities contained in the copper on the powder surface is a major factor in reducing the conductivity of the copper-coated powder, it is effective to use the copper salt also in this respect.

The mixing ratio of the copper salt is not particularly limited, but is preferably 0.01% by mass to 10% by mass, and 0.05% by mass to 5% by mass, in terms of the amount of metallic copper, based on the copper oxide powder used. % Is more preferable. When the mixing ratio of the copper salt is less than 0.01 mass% with respect to the mass of the copper oxide powder, it becomes difficult to sufficiently obtain the effect of wetting the surface of the non-conductive inorganic powder. On the other hand, if it exceeds 10 mass% with respect to the mass of the copper oxide powder, the effect itself such as wettability is not affected, but the addition amount increases, which causes a cost increase.

<About heat reduction treatment>
As described above, in the method for producing the copper-coated powder, the mixture obtained by adding and mixing the non-conductive inorganic powder, the copper oxide powder, and the copper salt having a melting point of 700° C. or less. On the other hand, heat treatment is performed in a reducing atmosphere. By this reduction heat treatment, copper derived from the copper oxide powder is reduced and diffused on the surface of the non-conductive inorganic powder to form a copper coating.

In particular, in the manufacturing method according to the present embodiment, since the copper salt having a melting point of 700° C. or less is added to and mixed with the non-conductive inorganic powder, the mixture is heated. By doing so, the copper salt in the mixture first melts and wets the surface of the non-conductive inorganic powder. Then, since the copper oxide powder is reduced and diffused on the surface of the powder wetted by the copper salt, the reduction and diffusion reaction of copper can be efficiently and effectively progressed, and the non-conductive inorganic powder Copper oxide will adhere evenly to the surface. Moreover, since the surface of the powder is wetted by the copper salt, the adhesion between the non-conductive inorganic powder and the copper coating can be improved.

When the non-conductive inorganic powder is a metal oxide powder, the oxide on the powder surface further promotes the wetting and spreading of the copper salt, and the copper oxide powder is a more non-conductive inorganic powder. The copper film easily diffuses and adheres to the body surface, and a uniform and good adhesion copper film is easily obtained.

In this heat reduction treatment, since the reduction and diffusion reaction of copper is efficiently and effectively progressed by treating a mixture containing a copper salt having a melting point of 700° C. or lower, the heating temperature is Can be relatively low temperature. Specifically, the treatment can be performed in a reducing atmosphere at a temperature of 350° C. or higher and 800° C. or lower. Thereby, the heat energy for heating can be suppressed, and the copper-coated powder can be manufactured more efficiently in terms of cost. Furthermore, since the reaction is performed at a relatively low temperature, it is possible to suppress sintering of the powder particles during the reduction.

When the heat treatment temperature is lower than 350° C. as the temperature condition in the heat reduction treatment, the reduction and diffusion of copper does not proceed sufficiently, the film formation is insufficient and becomes non-uniform, and the residual ratio of free copper powder that does not become a film is Increase. On the other hand, when the heat treatment temperature exceeds 800° C., the powder particles sinter with each other to cause agglomeration, which makes it difficult to handle and requires treatment such as pulverization after the heat treatment, which may cause peeling of the formed copper coating. Become. Furthermore, the thermal energy required for heating increases, which leads to an increase in cost and makes efficient manufacturing difficult.

The temperature condition of the heat reduction treatment is preferably higher than the melting point of the copper salt. Of course, even if the heat treatment temperature is in the range of 350° C. or higher and 800° C. or lower, the temperature should not exceed the melting point of the non-conductive inorganic powder, and preferably 50° C. from the melting point of the non-conductive inorganic powder. Keep the temperature below the low temperature.

The conditions of the reducing atmosphere in the heat reduction treatment are not particularly limited, but from the viewpoint of easy handling, it is preferable to supply a mixed gas of an inert gas and a reducing gas to form the reducing atmosphere. Specifically, it is preferable to use nitrogen or argon as the inert gas. Further, it is preferable to use hydrogen gas as the reducing gas, and by using hydrogen gas as the reducing gas in this way, an increase in the amount of impurities in the copper coating can be suppressed.

In addition, the reduction heat treatment is performed while flowing the mixture to be heated. This is because when the copper oxide powder is reduced and copper diffuses to cover the surface of the non-conductive inorganic powder, the individual inorganic powders may sinter and become agglomerated powder. By heating and reducing while flowing, agglomeration due to sintering can be prevented. Further, by heating and reducing while flowing, it is possible to further improve the uniformity of the copper coating and the adhesion between the non-conductive inorganic powder and the copper coating.

Specifically, this reduction heat treatment can be performed using a rolling kiln such as a rotary kiln or a fluidized bed reduction furnace. In addition, the method is not particularly limited as long as it can be heated while stirring and flowing the mixture.

As described above, according to the method for producing a copper-coated powder according to the present embodiment, the dry and relatively low heat treatment temperature is applied to the surface of the non-conductive inorganic powder with uniform and good adhesion. A copper coating can be formed. Furthermore, unlike the conventional electroless plating method, many complicated steps are not required, there is no problem with waste liquid treatment, and the energy required for heating is low, so that the copper-coated powder is low cost and efficient. Can be manufactured.

Examples of the present invention will be specifically described below together with comparative examples. However, the present invention is not limited to the following examples.

<<Production of copper-coated powder>>
[Example 1]
As the non-conductive inorganic powder, a zirconia powder having an average particle diameter of about 300 μm shown in FIG. 1 was used. 100 g of this zirconia powder had an average particle diameter of about 10 μm and a BET specific surface area of 0. 6 m ² /g of copper oxide powder was added and mixed in an amount of 20 mass% in terms of the amount of metallic copper.

Here, the copper oxide powder was manufactured as follows. That is, a cathode was added to an electrolytic solution having a bath composition prepared using copper sulfate pentahydrate (CuSO ₄ .5H ₂ O) having a copper concentration of 8 g/L and a free sulfuric acid (H ₂ SO ₄ ) concentration of 55 g/L. A titanium plate and a copper plate were placed on the anode, and a current was supplied at a bath temperature of 25° C. and a current density of 10 A/dm ² for 8 hours to scrape off the copper electrodeposited on the cathode to produce electrolytic copper powder. The obtained electrolytic copper powder was oxidized and roasted at 800° C. for 3 hours in an air atmosphere to form copper oxide, and then a small crusher (manufactured by Kyoritsu Riko Co., Ltd., trade name: Sample Mill SK-M10). ), and the copper oxide powder was manufactured.

Next, to a mixture of zirconia powder and copper oxide powder, copper(I) chloride (CuCl) was added at a ratio of 0.05 mass% in terms of the amount of metallic copper to the copper oxide powder and mixed uniformly. In order to do so, the mixture was stirred for 5 minutes with a small pulverizer.

Then, the mixture thus obtained was charged into a small rotary kiln which was self-made, and the rotary kiln was rotated at a rotation speed of 20 rpm in a reducing atmosphere consisting of a nitrogen-hydrogen mixed gas having a hydrogen concentration of 2% to form a mixture. While flowing, heat reduction was performed for 30 minutes at a temperature of 500° C. to produce a copper-coated powder.

[Examples 2 to 4]
Copper (I) chloride was added to a mixture of zirconia powder and copper oxide powder in an amount of 1% by mass (Example 2), 5% by mass (Example 3), and 10% by mass (Example), respectively. A copper-coated powder was produced in the same manner as in Example 1 except that the proportion was added in the proportion of Example 4).

[Example 5]
As the non-conductive inorganic powder, copper was used in the same manner as in Example 1 except that a zirconia powder having an average particle size of about 15 μm shown in FIG. A coated powder was produced.

[Example 6]
Copper-coated powder in the same manner as in Example 5 except that copper(I) chloride was added to the mixture of zirconia powder and copper oxide powder at a ratio of 5% by mass to copper oxide powder. Manufactured body.

[Example 7]
As the non-conductive inorganic powder, a copper-coated powder was used in the same manner as in Example 1 except that a soda-lime glass powder having an average particle diameter of about 30 μm was used and the temperature during heating and reduction was 400° C. Manufactured body.

[Examples 8 to 10]
Copper (I) chloride was added to a mixture of soda-lime glass powder and copper oxide powder in an amount of 1% by mass (Example 8), 5% by mass (Example 9), and 10% by mass with respect to the copper oxide powder. A copper-coated powder was produced in the same manner as in Example 7, except that the content was added in the proportion of (Example 10).

[Comparative Example 1]
A copper-coated powder was produced in the same manner as in Example 1 except that copper (I) chloride was not added.

[Comparative example 2]
A copper-coated powder was produced in the same manner as in Example 3, except that the rotation of the small rotary kiln was stopped, that is, the mixture was not allowed to flow.

[Comparative Examples 3 and 4]
A copper-coated powder was produced in the same manner as in Example 3, except that the temperatures at the time of heat reduction were 300° C. (Comparative Example 3) and 900° C. (Comparative Example 4), respectively.

<<Evaluation>>
With respect to the copper-coated powders of Examples 1 to 10 and Comparative Examples 1 to 4 obtained as described above, the uniformity and adhesion of the copper coating film were evaluated according to the criteria shown below. The results are shown in Table 1.

(Evaluation of uniformity of copper film)
The evaluation of the uniformity of the copper coating was observed using a scanning electron microscope (SEM), and when the copper coating was uniformly and uniformly attached to the surface of the non-conductive inorganic powder, "○", Even when a part of the non-conductive inorganic powder surface was exposed, it was evaluated as “x”. 3 and 4 show SEM observation images of the copper-coated powder produced in Example 1, and FIG. 5 shows SEM observation images of the copper-coated powder produced in Example 5.

(Evaluation of adhesion of copper film)
To evaluate the adhesion of the copper coating, 50 g of the copper-coated powder produced was placed in a stainless steel container together with 50 g of zirconia beads having a particle diameter of 1 mm, and a small ball mill (manufactured by Asahi Rika Seisakusho, product name: AV-1) was used. Type), it is rotated at a rotation speed of 300 rpm for 1 hour, and after sieving it, the peeled copper is recovered and the amount of copper is measured by chemical analysis. From the ratio of the amount of peeled copper to the added copper amount, It was evaluated by determining the peeling rate. In addition, when the average particle diameter of the non-conductive inorganic powder is 100 μm or less, sieving cannot be performed, so only the uniformity of the copper coating was evaluated.

As is clear from the results of Table 1 and FIGS. 3 to 5, in the copper-coated powders of Examples 1 to 10, in addition to the non-conductive inorganic powder and the copper oxide powder, copper chloride (I ) Was added and mixed, the mixture was heated and reduced in a reducing atmosphere to produce a uniform copper film. In addition, it was confirmed that in this copper-coated powder, a copper coating was formed on the surface of the powder with high adhesiveness (from the results of the peeling rates of Examples 1 to 4).

On the other hand, in the copper-coated powder of Comparative Example 1 produced without adding the copper salt, the copper coating was not formed uniformly, and the zirconia was partially exposed. Moreover, the peeling rate of the copper-coated powder of Comparative Example 1 was very high, and the copper coating was in a state of not being in close contact with the powder. Further, in the copper-coated powder of Comparative Example 2 produced by heating the mixture without flowing, zirconia was exposed on a part of the powder surface, and part of the powder was sintered and aggregated. It was in a state of being.

Further, in the copper-coated powder of Comparative Example 3 produced at a heating reduction temperature of 300° C., diffusion of the reduced copper did not proceed sufficiently, so the copper coating was non-uniform. On the other hand, in the copper-coated powder of Comparative Example 4 produced at a heating reduction temperature of 900° C., the heating reduction temperature was too high, so sintering progressed and the powder was agglomerated. Moreover, the peeling rate of the copper-coated powders of Comparative Examples 3 and 4 was higher than that of the copper-coated powders of Examples 1 to 4.

Claims (8)

Copper oxide powder and a copper salt having a melting point of 700° C. or lower are mixed with non-conductive inorganic powder, and the mixture is heated and reduced while flowing in a reducing atmosphere at a temperature of 350° C. or higher and 800° C. or lower. The method for producing a copper-coated powder, wherein copper is adhered to the surface of the non-conductive inorganic powder by doing so. When mixing the non-conductive inorganic powder, the copper oxide powder, and the copper salt,
The method for producing a copper-coated powder according to claim 1, wherein the copper oxide powder is added to the non-conductive inorganic powder at a ratio of 5% by mass or more and 60% by mass or less in terms of the amount of metallic copper. When mixing the non-conductive inorganic powder, the copper oxide powder, and the copper salt,
The method for producing a copper-coated powder according to claim 1 or 2, wherein the copper salt is added to the copper oxide powder in a proportion of 0.01% by mass or more and 10% by mass or less in terms of metallic copper. The method for producing a copper-coated powder according to claim 1, wherein the copper salt is copper chloride. The method for producing a copper-coated powder according to claim 1, wherein the non-conductive inorganic powder is a metal oxide powder. The method for producing a copper-coated powder according to claim 1, wherein the non-conductive inorganic powder has an average particle size of 1 μm or more and 500 μm or less. The method for producing a copper-coated powder according to claim 1, wherein the copper oxide powder has an average particle size of 20 μm or less and a specific surface area of 0.5 m ² /g or more. The method for producing a copper-coated powder according to claim 1, wherein the reducing atmosphere is a mixed gas atmosphere of an inert gas and a reducing gas.