JP2000268630A - Copper powder for conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain conductive paste lowered in viscosity by smoothing a particle surface without changing a particle diameter, particle size distribution and specific surface area so much by mechanically colliding copper powder with one another for copper powder obtained by a wet reduction method. SOLUTION: Copper hydroxide is taken primary reduction to cuprous oxide by adding reducing agent to suspension suspended in water. By adding reducing agent in aqueous suspension of this cuprous oxide, the cuprous oxide is taken secondary reduction to metal copper. This copper powder is suitable as one for conductive paste in particle diameter and particle shape and has an average particle diameter of about 0.1 to 10 μm, but particle surfaces are in rugged states and hinder lowering of viscosity of conductive paste. This copper powder is charged into a cylindrical type high speed agitator fluidizing the particles, momentum is imparted to each particle, particles with one another are collided and angular parts on particle surfaces are smoothed. Also when a plane smoothing processing is performed for copper powder obtained by a wet reduction method after copper powder is coated with inorganic or organic materials, copper powder for conductive paste of low viscosity can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper powder capable of obtaining a low-viscosity conductive paste even at a high filling rate.

[0002]

2. Description of the Related Art Conventionally, when a thick film circuit board is manufactured by screen-printing a conductive paste on an insulating substrate, a silver-based paste has been mainly used as the conductive paste, but a copper paste is also used. Tend to be. This is because copper paste has the following advantages over silver-based paste.

(1) It is difficult to cause a short circuit because migration hardly occurs. (2) Since the conductor resistance and high-frequency loss are small, the circuit can be miniaturized. (3) High reliability due to excellent solder resistance. (4) Cost reduction is possible.

[0004] A copper paste having such advantages can be obtained by dispersing copper powder having a particle size of about 0.1 to 10 µm in a vehicle (resin).

As a method for producing copper powder, there are known a mechanical pulverizing method, an atomizing method in which molten copper is sprayed, an electrolytic deposition method on a cathode, an evaporation deposition method, a wet reduction method, and the like. Although each of these has its advantages and disadvantages, the wet reduction method is a main stream in the production of copper powder for conductive paste, since fine powder having a particle size suitable for paste can be obtained relatively easily. JP-A-4-116109, JP-A-2-197
No. 012 and Japanese Unexamined Patent Publication No. 62-99406 describe a method for producing copper powder by a wet reduction method.

[0006] The method of producing copper powder by the wet reduction method is based on the concept that copper hydroxide precipitated in water is primarily reduced to cuprous oxide, and then this cuprous oxide is secondarily reduced to metallic copper. In addition, glucose is used as a primary reducing agent, and hydrazine hydrate is used as a secondary reducing agent. At this time, the particle size and particle shape of the obtained copper powder can be controlled by setting the conditions of the copper hydroxide precipitation step, the primary reduction step, and the secondary reduction step. There is an advantage that it can be manufactured stably. The present inventors have previously described Japanese Patent Application No.
No. 323866 proposes a method of performing an oxidation treatment by blowing oxygen-containing gas between the primary reduction step and the secondary reduction step. By this oxidation treatment, a copper powder having a uniform particle size can be obtained, and the control of the particle size and the control of the particle shape can be further refined.

[0007]

Although the wet reduction method can produce copper powder having a particle size suitable for a conductive paste, the copper powder has a problem in obtaining a conductive paste having an appropriate viscosity. was there. The viscosity of the conductive paste depends on the viscosity of the resin used, the filling rate (filler value) of the copper powder, the particle size distribution of the copper powder, and the like. There is. In other words, it was found that there is a limit in reducing the viscosity of the conductive paste by the wet reduction method even if the particle size can be properly controlled.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve such a problem and to obtain a copper powder capable of securing a viscosity required for a conductive paste even when a copper powder obtained by a wet reduction method is used.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems. As a result, the copper powder obtained by the wet reduction method is mechanically collided with the copper powder. It has been found that the viscosity of the conductive paste can be significantly reduced by smoothing the particle surface without changing the particle size, particle size distribution and specific surface area so much. In other words, the irregularities and angular portions existing on the particle surface are smoothed by the collision of the particles without substantially changing the particle size or the particle size distribution. This process involves mechanically fluidizing the particles. It can be performed using a device capable of performing the above.

[0010] Accordingly, the present invention provides a copper powder for a conductive paste obtained by subjecting a copper powder produced by a wet reduction method to a surface smoothing treatment for causing particles to mechanically collide with each other. The copper powder of the present invention has an average particle size of 0.1 to 10 μm, and has an epoxy equivalent of glycidyl esterified dimer acid of 446 and an epoxy resin having a viscosity of 730 cps at 25 ° C. of 8% by weight. 92% by weight of copper powder was kneaded, and the viscosity of the kneaded material was measured at 10 rpm using an E-type viscometer.
It shows a viscosity of 300 Pa · sec or less when measured in m.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, a reducing agent is added to a suspension of copper hydroxide in water to perform primary reduction to cuprous oxide, and the cuprous oxide is suspended in water. The copper powder produced by the so-called wet reduction method in which a reducing agent is added to the suspension to perform secondary reduction to metallic copper has a particle size and a particle shape suitable for a conductive paste. For example, when the average particle size is 0.1 to 1
0 μm, preferably 3 to 10 μm, more preferably 4 to 8 μm
m, the specific surface area (measured by the BET method) is 0.1 to 10
m ² / g preferably those of 0.1~1.0m ² / g can be stably obtained. However, even if the particles have a shape close to a sphere, they actually have a polyhedral shape with flat crystal faces exposed polyhedrally. As a whole, the particle surface is in an uneven state. Such a squared surface state is fundamentally different from a melt-processed surface such as atomized powder.

It has been found that the presence of such squareness (unevenness) hinders the lowering of the viscosity of the conductive paste. That is, the copper powder obtained by the wet reduction method is
This is why the viscosity of the conductive paste cannot be reduced. The present inventors have found that the viscosity of the conductive paste can be significantly reduced by making the squared portion a smooth curved surface without changing the particle size or specific surface area of the copper powder. That is, before dispersing in the resin,
A pretreatment is performed to mechanically collide the particles,
It was found that the viscosity can be significantly reduced when the particles are dispersed in resin after reducing the squared portions to form particles with smooth curved surfaces, compared to those before treatment.

This treatment can be carried out by fluidizing the powder, and the fluidization is conveniently carried out by a device for mechanically fluidizing the powder, for example, a cylindrical high-speed stirrer (fluid mixer). In other words, according to the method of imparting momentum to each particle and causing the moving particles to collide with each other to smooth the angular portion of the particle surface, the particle size and specific surface area are hardly changed. , The surface of each particle can be smoothed. The cylindrical high-speed stirrer can apply centrifugal force and buoyancy to the powder by rotating blades provided below the inside of a cylindrical closed container (a cylindrical container whose axis is perpendicular to the axis). As the powder flows, the surface is smoothed during this flow.

In the final stage of the wet reduction method, fine metallic copper powder generated in the liquid is separated from the liquid, and water is removed from the separated solid content. Therefore, it is necessary to disintegrate the particles with a disintegrator and separate the particles from each other. In the disintegrator, the attached particles are impacted to dissociate from each other, but the dissociated particles are almost restored to the final reduced particle shape. In this disintegration process, the irregularities on the particle surface are removed. It cannot be expected that the surface will be smooth. For this reason, the copper powder obtained by crushing the copper powder cake has a high viscosity when dispersed in a resin. For example, as shown in the examples below, the glycidyl esterified dimer acid has an epoxy equivalent of 446 g /
The crushed copper powder (92% by weight) was kneaded with 8% by weight of an epoxy resin having a viscosity of 730 cps at 25 ° C.
When the viscosity of this kneaded material is measured at 10 rpm using a mold viscometer, the kneaded product usually shows a viscosity of 400 Pa · sec or more, and a low viscosity of 300 Pa · sec or less, and in some cases, 200 Pa · sec or less. I can not hope at all.

On the other hand, in the case of copper powder which has been subjected to surface smoothing treatment by mechanically colliding particles with each other as described above, even if it is obtained by the same wet reduction method, Similarly, 92% by weight of this surface-smoothed copper powder was kneaded with 8% by weight of epoxy resin having an epoxy equivalent of 446 g / eq and a viscosity of 730 cps at 25 ° C. obtained by dimer acid glycidyl esterification. When the viscosity of the kneaded material is measured at 10 rpm using
Sec or less, more preferably 250 Pa · sec or less, and in some cases even 200 Pa · sec or less.

[0016] Further, when copper powder produced by the wet reduction method is coated with an inorganic or organic substance and then subjected to a surface smoothing treatment for causing particles to collide with each other mechanically, the copper powder also exhibits low viscosity. I understood. In the case of copper powder for conductive paste, the surface of the copper powder may be coated with a metal such as silver to further improve the electrical conductivity, or may be coated with an organic compound such as carboxylic acid such as stearic acid to prevent surface oxidation. Advantageously, such a coating treatment can be performed at the final stage in the case of the production of copper powder by the wet reduction method. And, for this coated copper powder,
When the surface is smoothed by mechanically colliding particles with each other in the same manner as described above, the surface can be smoothed without damaging the coated portion, and therefore, the characteristics due to the coating are provided. As a result, it was found that a low-viscosity conductive paste was obtained.

[0017]

EXAMPLE A copper sulfate aqueous solution and a caustic soda aqueous solution are mixed at an equivalent ratio of 1.25 mol of caustic soda to 1 mol of copper to obtain a suspension in which copper hydroxide is precipitated. A glucose solution is added to the suspension in an equivalent amount or more, and the temperature of the solution is increased to 70 in 30 minutes after the addition.
After the temperature was raised to ℃, the mixture was maintained for 15 minutes to primarily reduce copper hydroxide to cuprous oxide. All the processing operations so far are performed in a nitrogen atmosphere. After oxidizing by bubbling air into the solution, the solution was allowed to stand in a nitrogen atmosphere for 2 days, the supernatant was removed, almost all of the precipitate was collected, and pure water was added to the precipitate. Hydrazine hydrate is added to the suspension in an equivalent amount or more for secondary reduction to copper metal. After completion of the reaction, the suspension was subjected to solid-liquid separation, and the solid content was dried in a nitrogen atmosphere at 120 ° C.
Obtain a copper powder cake.

In the above-mentioned method for producing copper powder by the wet reduction method, only the time for the oxidation treatment of air bubbling is changed.
Three types of copper powder cakes A, B and C were obtained. Each of the obtained cakes was bisected, and one was charged into a crusher and crushed in a nitrogen atmosphere to obtain copper powders A1, B1 and C1. The other was charged into a cylindrical high-speed stirrer and fluidized in a nitrogen atmosphere to obtain copper powders A2, B2 and C2.

The crusher used in the crushing process is an impact crusher equipped with a swinging hammer, and crushes the coagulated and dried copper powder cake into fine particles obtained in the final step of the wet reduction method. Has almost no function of smoothing the particle surface. The cylindrical high-speed stirrer used in the fluidization treatment is a mixer having two rotating blades at the bottom of a cylindrical container with a vertical axis, and the powder given centrifugal force by the rotation of the blades moves upward. The particles flow and the particles repeatedly collide with each other during this flow, so that the irregularities on the particle surface are smoothed.

A copper powder A1 obtained by crushing a copper powder cake A;
Electron microscope SEM image of fluidized copper powder A2 (a is 2
000 times and b is 5000 times) are shown in FIG. 1 and FIG. FIGS. 3 to 4 show electron microscope SEM images (a is 2000 times, b is 5000 times) of copper powders B1 and C1 obtained by crushing copper powder cakes B and C, and copper powders B2 and C2 obtained by fluidization. This is shown in FIGS. In addition, these SEM
The average particle size of each copper powder was investigated from the images, and the specific surface area, bulk density, and TAP density were measured by the BET method, and the results are shown in Table 1.

Further, 8% by weight of each copper powder is mixed with an epoxy resin 92
The resulting paste was kneaded with a vibrating mixer to measure the viscosity of the obtained paste. As the epoxy resin, an epoxy resin obtained by dimer acid glycidyl esterification and having an epoxy equivalent of 446 g / eq and a viscosity of 730 cps at 25 ° C. was used. The kneading conditions were constant for each copper powder, and the viscosity of each paste was E-type viscosity. Using a meter at a rotation speed of 10 rpm
It was measured at 5 ° C. The results are also shown in Table 1.

[0022]

[Table 1]

From the results shown in Table 1, the fluidized copper powder A
2, B2 and C2 are copper powders A1, B which are not fluidized
It can be seen that the average particle size, specific surface area, bulk density and TAP density are not so different from those of Nos. 1 and C1, but the viscosity of the paste when kneaded with the resin is significantly reduced. The decrease in the viscosity of the paste although the particle size and specific surface area did not change so much was apparent from the comparison between FIGS. 1 and 2, FIGS. 3 and 4, and FIGS. Can be considered to be due to the fact that the squareness of the particle surface was removed to form a smooth curved surface.

[0024]

As described above, according to the present invention,
A copper powder that can be converted into a paste having a low viscosity even when kneaded with a resin at a high filling rate can be produced by a wet reduction method, and as a result, a high-quality copper paste can be stably obtained.

[Brief description of the drawings]

FIG. 1 is an electron microscopic SEM image of copper powder A1 obtained by crushing copper powder cake A. FIG.
(B) of FIG. 1 is 5000 times.

FIG. 2 is an electron microscope SEM image of copper powder A2 obtained by fluidizing copper powder cake A, and FIG.
2 (b) is 5000 times.

FIG. 3 is an electron microscope SEM image of copper powder B1 obtained by crushing copper powder cake B. FIG.
(B) of FIG. 3 is 5000 times.

FIG. 4 is an SEM image of copper powder B2 obtained by fluidizing copper powder cake B, and FIG.
4 (b) is 5000 times.

5 is a scanning electron microscope (SEM) image of copper powder C1 obtained by crushing copper powder cake C. FIG.
(B) of FIG. 5 is 5000 times.

6 is a scanning electron microscope (SEM) image of copper powder C2 obtained by fluidizing copper powder cake C. FIG.
6 (b) is 5000 times.

[Procedure amendment]

[Submission date] December 15, 1999 (1999.12.
15)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

Further, 92 % by weight of each copper powder is made of an epoxy resin.
The mixture was kneaded to 8 % by weight with a vibration mixer, and the viscosity of the obtained paste was measured. The epoxy equivalent of glycidyl ester of dimer acid is 446g / eq.
And an epoxy resin having a viscosity of 730 cps at 25 ° C., and the kneading conditions were fixed for each copper powder.
It was measured at 5 ° C. The results are also shown in Table 1.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01B 1/22 H01B 1/22 A 13/00 503 13/00 503C (72) Inventor Hiromasa Miyoshi Chiyoda, Tokyo 1-8-2, Marunouchi-ku F-term in Dowa Mining Co., Ltd. (Reference) 4K017 AA01 BA05 CA07 DA01 DA09 EA03 EA13 EH03 EH16 4K018 BA02 BB04 BC08 BC09 BC28 BC29 BD04 5G301 DA06 DA57 DD01 DE03

Claims (6)

[Claims] 1. A copper powder for a conductive paste obtained by subjecting a copper powder produced by a wet reduction method to a surface smoothing treatment for causing particles to mechanically collide with each other. 2. The copper powder for a conductive paste according to claim 1, having an average particle size of 0.1 to 10 μm. 3. In the wet reduction method, a reducing agent is added to a suspension in which copper hydroxide is suspended in water to perform primary reduction to cuprous oxide, and the suspension is prepared by suspending the cuprous oxide in water. The copper powder for a conductive paste according to claim 1 or 2, wherein the method is a method in which a reducing agent is added to the suspension to perform a secondary reduction to metallic copper. 4. The copper powder for a conductive paste according to claim 3, wherein an oxidation treatment is provided between the first reduction treatment and the second reduction treatment. 5. A copper powder for a conductive paste obtained by coating a copper powder produced by a wet reduction method with an inorganic or organic substance and subjecting the particles to mechanical collision with each other. 6. The glycidyl esterified dimer acid has an epoxy equivalent of 446 g / eq and a viscosity of 730 c at 25 ° C.
92% by weight of the target copper powder is kneaded with 8% by weight of a ps epoxy resin, and the viscosity of the kneaded material is measured at 10 r using an E-type viscometer.
Copper powder for conductive paste having a viscosity of 300 Pa · sec or less when measured in pm.