JP2005076058A - Method for manufacturing flaky metal powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently manufacturing a fine flaky metal powder which has a narrow width of a particle size distribution and is uniformly flattened. <P>SOLUTION: The manufacturing method for making a metal powder flaky with the use of a ball mill comprises a step of; when pulverizing the metal powder with steel balls in air or an inert atmosphere along with employing a starting material of the spherical or granular metal powder with a particle diameter of 5 μm or smaller and a grinding media of the steel balls with diameters of 2 to 5 mm, adding grinding auxiliaries to them, using a cylindrical rotation vessel with a shielding plate on the inner wall, and making the shielding plate lift and drop the metal powder and the steel balls along the wall surface during the rotation of the vessel. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a fine metal powder having a small particle size for use in conductive pastes, metallic paints, rust-proof paints, and the like. Specifically, narrow particle size distribution width that can provide excellent coating film conductive performance, narrow piece size copper powder, flaky nickel powder, flaky silver powder, narrow particle size distribution range that gives excellent metallic glossy coating film The present invention relates to a method for efficiently producing a flake metal powder such as a flake tin powder with a small amount of fine powder and a flake zinc powder having a large specific surface area that can provide excellent hiding power and antirust effect.

  Conventionally, a method for producing a flake metal powder has been to flake a relatively large metal powder or lump with a strong impact force and shear force using a crusher such as a stamp mill, an attritor, or a ball mill. Recently, however, it has been found that as a flake metal powder for conductive paste, a coating film having a narrow particle size distribution width, a uniform spread processing, and a finer particle size can provide better coating film conductive performance. Metallic powders that are uniformly spread and processed for metallic paints and that do not contain fine powder during pulverization have a glossy coating film. When a metal powder or lump with a large particle size is pulverized to produce a flaky metal powder with a small particle size, a lot of very fine powder is generated during pulverization, the particle size distribution width is wide, and the pulverization time is long. There were also problems of oxidation of the powder and exothermic combustion of the metal powder. For these reasons, it is better to use metal powder as fine as possible as the starting material.

  However, when metal powder with a fine starting material is strongly pulverized with a conventional pulverizer, the metal powders are pressed and agglomerated to form coarse flakes, and each particle cannot be spread and processed uniformly. As a solution to these problems, a method in which a starting material powder is dispersed in water to form a slurry and is flaked with a zirconia bead of 1 mm or less in a medium-type stirring mill (for example, see Patent Document 1), a slurry concentration of 5 to 60%. Has been proposed (see, for example, Patent Document 2), in which a piece is processed with a medium stirring mill using beads of 0.5 to 3 mm.

  However, since it is processed into a piece in a solvent, it is necessary to separate the solution and the powder after pulverization. In particular, separation becomes difficult when a fine piece of powder is formed. As a method of processing in a piece in air or in an inert atmosphere, a method of using a steel ball with a diameter of 1/8 to 1/4 inch and adding a fatty acid and manufacturing with a medium stirring mill has been proposed (for example, see Patent Document 3). However, it is suitable for the production of a disk-shaped powder having a short pulverization time, but it is difficult to produce a fine flaky metal powder having a starting material powder of 5 μm or less because of strong pulverization and shearing force.

When slab processing is performed with a ball mill whose grinding force is weaker than that of a medium agitation mill, if the starting material powder has a small particle size, the pulverized powder adheres to the wall surface or ball of the cylindrical rotary container. Hard metals and spherical powders that are very weak are difficult to machine and take a long time. A ball mill with a large ball diameter can provide impact force, but the number of contact points of the ball with each particle is reduced, and only flaky metal powder with a wide particle size distribution width, in which coarse flaky powder and granular powder are mixed, is manufactured. I could not.
JP 2000-80409 A Japanese Patent Laid-Open No. 4-56701 JP 2002-15622 A

  The present invention has found a method for efficiently producing the above-mentioned problems of the prior art by improving the ball mill grinding method, and provides a uniform finely processed flake metal powder having a narrow particle size distribution width. Is an issue.

  The present invention has been made for the purpose of solving such conventional problems. The starting material is a spherical or granular metal powder having a particle size of 5 μm or less and a steel ball having a diameter of 2 to 5 mm as a grinding medium. When a small amount of grinding aid is added and the metal powder is pulverized by the steel balls in air or in an inert atmosphere, a cylindrical rotary container with a jammer plate on the inner wall is used to rotate the metal powder during the rotation. The metal powder and the steel ball are lifted along the wall surface by the jammer plate and dropped, and it is possible to obtain a fine piece-like metal powder with a narrow particle size distribution width in which each particle is uniformly spread.

  The effect of the present invention is that a ball mill pulverizer conventionally used can be used by improving the ball rolling of the ball mill pulverization method, and a sphere-shaped or fine powder flaky process does not use a solvent. It has become possible, and it has become possible to provide a large amount of fine metal flakes having various metal compositions with a narrow particle size distribution at a low cost.

  Hereafter, the manufacture which processes a metal powder in the shape of a piece with the ball mill of this invention is demonstrated in detail. The metal powder as the starting material of the present invention must be a spherical or granular powder having a particle size of 5 μm or less. When the particle size of the metal powder is 5 μm or more, it is difficult to uniformly flank the process according to the present invention, and it is not preferable because it takes a long time for the flaky process. As the particle size becomes finer, a uniform piece-like metal powder can be obtained. However, when the particle size is 0.5 μm or less, it is difficult to obtain a monodispersed spherical or granular metal powder. It is preferable to use in a dispersed manner.

As the metal powder that can be used in the present invention, any production method and metal composition can be used as long as the particle diameter is a spherical or granular powder having a particle size of 5 μm or less.
Specifically, in the atomization method, copper powder, copper alloy powder, silver powder, and tin powder. Copper powder in aqueous solution electrolysis. In the solution reduction method, copper powder and silver powder. Zinc powder in the distillation method. Examples of the carbonyl method include nickel powder. It is important that the cylindrical rotating container has a structure with a jammer plate that allows steel balls and metal powder to be lifted along the wall surface during rotation and dropped at a fixed position on the inner wall of the cylindrical rotating container. Mounted in the normal direction toward the center.

  The dimensions of the jammer plate are preferably 1 / 30D or more in the radial direction and 2 / 3L or more in the longitudinal direction when the cylindrical inner diameter (D) and the longitudinal (L) are taken. The size of the jammer plate may be efficient according to the metal powder composition to be processed into a piece and the application. When the size of the jammer plate is shorter than 1 / 30D, the stirring effect and impact force of the steel ball and the metal powder are weak, and when it is longer than 3 / 10D, the rolling of the steel ball becomes uneven and the efficiency is deteriorated. If the length is shorter than 2 / 3L, the effect of the jammer plate cannot be obtained, and it is preferably equivalent to the L of the cylinder.

  The jammer plate may be a plate or a perforated plate made of a material or a thickness that does not deform or wear during grinding such as stainless steel or iron. The number of jammers is preferably 2 to 6, and the number within this range may be attached to a uniform width. By attaching a jammer plate to the inner wall of the cylinder, a spherical or granular metal powder with a small particle size and a pulverized ball with a small diameter are always forcibly agitated, mixed, and separated, thereby preventing aggregation during the pulverization process.

  Also, by dropping the ball from a certain position, an impact force higher than that of a normal ball mill is applied, and even a small ball can be processed into a piece. In order to uniformly process the metal particles into pieces, it is necessary that the diameter of the steel ball of the grinding medium is 2 to 5 mm. If it is finer than that, it will take a long time for slab processing even with a jammer plate, and a large ball will reduce the number of points of contact with the metal powder, so that each particle cannot be uniformly slab processed.

  Although the pulverizing atmosphere is usually possible in the air, if there is a risk of oxidation or ignition of the metal powder, it may be pulverized in an inert atmosphere such as nitrogen filling. The grinding aid is necessary for dispersion of the metal powder and prevention of aggregation during the grinding process, and fatty acids such as stearic acid and palmitic acid are preferable, and the addition amount is the particle size of the metal powder to be ground, the metal composition, and the desired flake metal powder Depending on the particle size and application, it is preferable to add 0.1 to 2 wt% to the metal powder to be crushed.

  This example was carried out using spherical copper powder by an atomizing method having an average particle diameter of 5 μm in which the starting metal powder was monodispersed. 2 kg of this spherical copper powder, 10 kg of a 3/16 inch diameter (4.76 mm) steel ball and 2 g of stearic acid as a grinding medium were charged into a cylindrical rotating container. It has an inner diameter of 20 cm, a length of 30 cm, and a total volume of 20 liters. Three jammer plates having a radial direction of 3 cm and a longitudinal direction of 28 cm are attached to the inner wall so as to divide the circumference into three. The pulverization process was performed in air at a ball mill rotational speed of 40 rpm for 8 hours. As a result, when observed with an electron microscope, it was possible to produce a flaky copper powder having a very narrow particle size distribution width of 7 to 8 μm on average and in which each particle was uniformly flaked.

  This example was carried out using spherical copper powder by an atomizing method having an average particle diameter of 3 μm in which the starting metal powder was monodispersed. 2 kg of this spherical copper powder, 10 kg of steel balls having a 1/8 inch diameter (3.17 mm) as a grinding medium, and 10 g of stearic acid were charged into a cylindrical rotating container. It has an inner diameter of 20 cm, a length of 30 cm, and a total volume of 20 liters, and three jammer plates having a radial direction of 3 cm and a longitudinal direction of 28 cm are attached to the inner wall so as to divide the circumference into three. The pulverization process was performed in air at a ball mill rotational speed of 40 rpm for 8 hours. As a result, when observed with an electron microscope, a flaky copper powder having an average particle diameter of 5 to 7 μm and a very narrow particle size distribution width in which each particle was uniformly flaked could be produced.

  This example is a copper powder obtained by reducing and depositing a starting material metal powder by an aqueous solution reduction method, and using a granular copper powder having a particle diameter of 0.3 μm, which is monodispersed by a jet mill. 1.5 kg of this granular copper powder, 10 kg of a 3/32 inch diameter (2.38 mm) steel ball and 15 g of stearic acid as a grinding medium were charged into a cylindrical rotating container. This has an inner diameter of 20 cm, a length of 30 cm, and a total volume of 20 liters. Six diametric plates are attached to the inner wall so as to divide the junk plate into a circumference of 0.7 cm and a longitudinal direction of 30 cm. The pulverization process was performed in a nitrogen atmosphere at a ball mill rotational speed of 20 rpm for 20 hours. As a result, when observed with an electron microscope, a flaky copper powder having an average particle diameter of 2 to 4 μm and a very narrow particle size distribution width in which each particle was uniformly flaked could be produced.

  This example was carried out using a granular silver powder having a particle size of 0.5 μm obtained by reducing and depositing a starting metal powder by an aqueous solution reduction method. 2 kg of this granular silver powder, 10 kg of a 3/32 inch diameter steel ball and 20 g of stearic acid as a grinding medium were put into a cylindrical rotary container. It has an inner diameter of 20 cm, a length of 30 cm, and a total volume of 20 liters. Three jammer plates having a radial direction of 3 cm and a longitudinal direction of 25 cm are attached to the inner wall so as to divide the circumference into three. The pulverization process was carried out in air at a ball mill rotational speed of 20 rpm for 20 hours. As a result, when observed with an electron microscope, a flaky silver powder having an average particle diameter of 3 to 6 μm and a very narrow particle size distribution width in which each particle was uniformly flaked could be produced.

  This example was carried out using spherical silver powder having an average particle diameter of 2 μm in which the starting metal powder was monodispersed by the atomization method. 3 kg of this spherical silver powder, 10 kg of a 1/8 inch diameter steel ball and 6 g of palmitic acid were added as a grinding medium to a cylindrical rotary container. It has an inner diameter of 20 cm, a length of 30 cm, and a total volume of 20 liters. Three jammer plates having a radial direction of 3 cm and a longitudinal direction of 25 cm are attached to the inner wall so as to divide the circumference into three. The pulverization process was performed in air at a ball mill rotational speed of 30 rpm for 8 hours. As a result, when observed with an electron microscope, a flaky silver powder having an average particle diameter of 5 to 6 μm and a very narrow particle size distribution width in which each particle was uniformly flaked could be produced.

  This example was carried out using spherical tin powder having an average particle diameter of 2.5 μm, in which the starting metal powder was monodispersed by the atomization method. 3 kg of this spherical tin powder, 10 kg of a 3/16 inch diameter steel ball and 15 g of stearic acid as a grinding medium were put into a cylindrical rotary container. It has an inner diameter of 20 cm, a length of 30 cm, and a total volume of 20 liters. Three jammer plates having a radial direction of 3 cm and a longitudinal direction of 25 cm are attached to the inner wall so as to divide the circumference into three. The pulverization process was carried out in air at a ball mill rotational speed of 40 rpm for 30 hours. As a result, when observed with an electron microscope, it was possible to produce a flaky tin powder having an average particle diameter of 10 to 15 μm and having a very narrow particle size distribution width, each particle being uniformly thinly processed and having a silver metallic appearance.

This example was carried out using spherical zinc powder having an average particle size of 3 μm in which the starting metal powder was monodispersed by distillation. 2 kg of this spherical zinc powder, 10 kg of a 1/8 inch diameter steel ball and 20 g of stearic acid as a grinding medium were put into a cylindrical rotary container. It has an inner diameter of 20 cm, a length of 30 cm, and a total volume of 20 liters. Three jammer plates having a radial direction of 3 cm and a longitudinal direction of 25 cm are attached to the inner wall so as to divide the circumference into three. The pulverization process was performed in air at a ball mill rotational speed of 40 rpm for 20 hours, and then 20 g of stearic acid was added and the operation was continued for 30 hours. As a result, it is possible to produce a flaky zinc powder having a specific surface area value of 15000 cm ² / g, with an average particle diameter of 6 to 10 μm and a very narrow particle size distribution width, each particle being uniformly thinly processed into a flaky shape when observed with an electron microscope. It was.

  In this example, the starting metal powder was a granular nickel powder having a primary particle size of 4 μm by the carbonyl method. 2 kg of the granular nickel powder, 10 kg of a 1/8 inch diameter steel ball and 10 g of stearic acid as a grinding medium were put into a cylindrical rotary container. It has an inner diameter of 20 cm, a length of 30 cm, and a total volume of 20 liters. A jama plate (a perforated plate with a diameter of 2 cm) having a diameter of 6 cm and a length of 25 cm is attached to the inner wall so as to divide the circumference into two. Yes. The pulverization process was performed in air at a ball mill rotational speed of 40 rpm for 14 hours. As a result, when observed with an electron microscope, uniform flake nickel powder having an average particle diameter of 6 to 9 μm and a narrow particle size distribution width could be produced.

Comparative Example 1

  As a comparative example, a ball mill pulverization method for a conventional cylindrical rotating container without a jammer plate will be described. 2 kg of spherical copper powder by an atomizing method having an average particle diameter of 3 μm used in Example 2, 10 kg of 1/8 inch diameter steel balls and 10 g of stearic acid as a grinding medium were charged into a cylindrical rotating container. This has an inner diameter of 20 cm, a length of 30 cm and a total volume of 20 liters, and its inner wall is a structure free of obstacles. The pulverization process was performed in air at a ball mill rotational speed of 40 rpm for 8 hours. As a result, when observed with an electron microscope, powders of various shapes such as flakes, polyhedrons, and spheres were mixed. Thereafter, the powder was pulverized for 20 hours, but the flake powder was coarsened to 15 μm or more, and a small amount of fine spherical powder remained as it was, and a uniform flake copper powder could not be obtained.

The method for producing the flake metal powder of the present invention is the same as the conventional ball mill method, and the process is simple, and since a fine spherical or granular powder can be used as a starting material, the pulverization time is shortened and the particle size distribution width is narrow. Thus, it has become possible to provide uniform flake metal powder at a low cost. Such flake metal powder is extremely useful industrially as a material for functional materials such as conductive paste fillers, metallic pigments, flake powder for anticorrosion paints.

Claims (1)

In the manufacturing method in which metal powder is processed into a piece by a ball mill, a grinding aid is added to a spherical or granular metal powder having a particle size of 5 μm or less as a starting material and a steel ball having a diameter of 2 to 5 mm as a grinding medium. When the steel ball is pulverized with the steel ball in air or in an inert atmosphere, a cylindrical rotating container with a jama plate on the inner wall is used, and during the rotation, the metal powder and the steel ball are moved along the wall surface by the jama plate. A method for producing flake metal powder, characterized in that it is lifted and dropped.