JPH04308001A - Production of electrically conductive particles - Google Patents

Abstract

PURPOSE:To produce electrically conductive particles useful as an electrically conductive filler for an electromagnetic wave shielding material, electrically conductive paste, etc. CONSTITUTION:Fine metal particles of 0.01-10mum average particle size obtd. by processing an aq. dispersion of metal particles with a cavitation type dispersion grinder and carrying out freeze drying are added to core particles of 1-200mum average particle size, other fine particles are further added as required and they are dry-mixed under mechanical strain stress. By this mixing, metal layers are formed on the surfaces of the core particles and electrically conductive particles are produced.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing conductive particles useful as conductive fillers for electromagnetic shielding materials, conductive paste materials, and the like.

0002

BACKGROUND OF THE INVENTION Conventionally, conductive powders have mainly been metal powders such as silver and copper, and these have been produced by electrolytic methods, reduction methods, atomization methods, mechanical pulverization methods, and the like. but,
As far as these metal powders are used as conductive particles, only the surfaces of expensive metal particles are used. Also, some metals have sizes that are difficult to manufacture.
Manufacturing costs may be high in some cases. Furthermore, since the specific gravity of these conductive particles is 7 to 10, which is significantly higher than that of resin, it is difficult to disperse them and it is difficult to obtain stable conductive performance.

[0003] In order to solve this drawback, conductive fillers with low specific gravity have recently been developed, such as carbon black, carbon fiber, and organic polymer particles in which a film of conductive material is formed by electroless plating. There is. However, carbon black and carbon fibers have inferior conductivity compared to metals, and in order to form a conductive film on organic polymer particles, uniform and good conductivity cannot be achieved unless a large amount of chemicals are used. However, there are problems in that there is a lot of wastage of chemicals and the cost of waste liquid treatment increases.

[0004] First, in order to solve the problems in the prior art, the present inventors prepared core particles (A) with an average particle size of 1 to 200 μm and metal fine particles (B) with an average particle size of 0.01 to 10 μm. ) and, if necessary, other fine particles (C), in a dry process with mechanical strain to form a metal layer on the surface of the core particles (A).
(Japanese Patent Application No. 2-162204), the present invention provides conductive particles having low specific gravity, low cost, and uniform conductivity, and a method for producing the same. However, there was a drawback that the metal particles (B) tended to aggregate and good conductivity was not necessarily obtained.

[0005]

[Problems to be Solved by the Invention] The present invention provides metal particles (
In order to prevent the re-agglomeration of B) and obtain conductive particles with good conductivity, the problem was solved by treating an aqueous dispersion of metal particles with a cavitation-type dispersion/pulverizer and freeze-drying. .

[0006]

[Means for Solving the Problems] The present invention has an average particle size of 1 to 1.
After processing the 200 μm core particles (A) and the water dispersion of metal particles with a cavitation type dispersion/pulverizer,
Metal fine particles (B) having an average particle diameter of 0.01 to 10 μm and other fine particles (C) obtained by freeze-drying are mixed into fine particles (B).
) are primary particles, by dry mixing with mechanical strain to cover 0.2 to 10 layers of core particles (A) and utilizing the spreadability of fine particles (B). , 30 to 100% of the surface of the core particle (A), preferably 90%
This is a method for producing conductive particles in which % or more of the conductive particles are coated with fine particles (B), and the coating of the fine particles (B) is in close contact with the surface of the core particle (A). The film thickness is adjusted to about 0.1 to 3 μm by changing the particle size and usage amount of the fine particles (B). If the film thickness is less than 0.1 μm, the unevenness of the surface of the core particle (A) will be affected, and the effect of forming the film will be insufficient.
The conductivity decreases, and if the thickness exceeds 3 μm, it is uneconomical.

Core particles (A) used in the present invention
For example, powders of various plastics such as polyethylene, nylon, polystyrene, and epoxy resins, silica, glass, etc. may be used. Further, powders of iron or its oxides may be used, or conductive metals may also be used. These core particles (
A) can be freely selected depending on required properties such as heat resistance and dispersibility.

[0008] The fine particles (B) have a particle size similar to that of the core particle (
Various metals, alloys, etc. having conductivity of 1/10 or less, preferably 1/20 or less of A) can be used. For example, copper, silver, gold, platinum, palladium, nickel, cobalt, aluminum, tin, zinc, etc. can be used. These can be used alone or in a multilayer structure. Average particle size 2
Fine particles (B) having a diameter of μm or more are uneconomical because the film thickness on the surface of the core particle (A) becomes too thick.

[0009] In order to produce particles with good conductivity, preliminary treatment is necessary before treatment. As a preliminary treatment, an aqueous dispersion of metal particles is processed using a cavitation-type dispersion/pulverizer, and then freeze-dried. As a cavitation type dispersion/pulverizer, homogenizer (AVP GOU
LIN Inc.) etc. In this dispersion/pulverizer, the processing liquid pressurized by a pump is forced into the gap between the seat and the valve. The opening degree of the gap can be set arbitrarily, and the back pressure corresponding to the opening degree is displayed on the pressure gauge. After the processing liquid is compressed under high pressure, it is released into the atmosphere through the minute gap between the seat and the valve as a high-speed flow in the supersonic range. This pressure change occurs instantaneously, over a few microseconds, and the processing liquid locally becomes vaporized, causing a so-called cavitation phenomenon, where high energy is applied to dispersed particles and droplets.
It becomes possible to make particles finer.

[0010] Furthermore, when pre-treating the metal particles,
Dispersion aids can also be used. As the dispersion aid, PMMA (polymethyl methacrylate), polyvinylidene fluoride, silica, alumina, etc. with an average particle size of 0.3 μm or less are used. This makes it easier for the fine particles (B) to adhere to the core particles (A) during premixing, and is advantageous for stabilizing the subsequent mixing and coating. The amount of the fine particles (C) is preferably such that the surface of the core particles (A) is coated with about 0.2 to 1 layer.

In the present invention, the conditions for coating the core particles (A) with the fine particles (B) using mechanical strain force are such that the strain force is so large that the core particles (A) may be finely pulverized. Industrially, the specific method to meet these conditions is to adjust the operating conditions of dispersion machines such as ball mills and sand mills, throughput, dispersion medium, etc. to achieve the above objectives. You can change it like this.

However, since ball mills and sand mills require a long time, industrially, the powder is in a fluidized bed state, and mixers that move the powder at high speed with airflow, or blades or hammers that give impact are installed. An example of such a mixer is the SI Mill (manufactured by Toyo Ink Mfg. Co., Ltd., the outline of which is published in the Japanese Patent Publication No. 57-1983).
43051), atomizer, free crusher (Nara Kikai Seisakusho Co., Ltd.), KTM-1 type crusher (manufactured by Kawasaki Heavy Industries, Ltd.), hybridizer (Nara Kikai Seisakusho Co., Ltd.), etc. These devices can be used as they are or modified as appropriate to meet the purpose of the present invention. Preferably, it is a circulation type and closed system device, such as a hybridizer.

[0013] The core particles (A), fine particles (B), and other fine particles (C) as needed may be mixed under weaker stirring conditions than the above-mentioned mixing treatment, such as a multi-blender mill (Nippon Seiki Co., Ltd.). It is preferable to pre-mix the mixture using a premix (manufactured by Seisakusho). If the fine particles (B) are physically attached to the core particles (A) through such premixing, the mixing process can be performed smoothly. The reason why a film of fine particles (B) is formed on the surface of core particles (A) by such a mixing process is that the fine particles (B) are coated with the core particles (A) by utilizing the ductility of metal.
) because it can be spread on the surface. Note that this mixing process may cause the system to reach a high temperature, and it may be necessary to cool the system using an external jacket or the like.

[0014]

[Effects of the Invention] As understood from the above explanation, the conductive composite particles of the present invention utilize the conductivity of the metal film present on the particle surface, so they can provide effective conductivity with a small amount of metal. can. Furthermore, since it is a dry method for producing conductive composite particles, it has superior workability compared to electroless plating, and can produce a wide variety of composite particles at low cost. Furthermore, since spherical particles with low specific gravity can be selected as core particles, they have excellent kneading workability and dispersion stability, and compared to conventional fillers, it is possible to fill the resin at a higher level, resulting in stable conductive performance and shielding effects. I can do it.

[0015]

EXAMPLES Examples will be shown below to explain the present invention more specifically, but the present invention is not limited to these examples. In the examples, parts and % indicate parts by weight, and particle diameters were measured by electron microscopy (SEM).

[0016] Example 1 Polyethylene true spherical fine particles with an average particle size of 5.2 μm (manufactured by Seitetsu Kagaku Kogyo Co., Ltd., trade name: Flow Beads LE-1)
080) 4 parts, water dispersion type silver (manufactured by Fukuda Metal Foil & Powder Industries Co., Ltd., trade name AgC-H) in a homogenizer (A
(manufactured by VP GOULIN) and pressure (500~6
00 KGF/cm2) 10 times, and then freeze-dried the silver particles 14 with an average particle size of 0.1 μm.
．． 0 parts were premixed in a multi-blender mill (manufactured by Nippon Seiki Seisakusho Co., Ltd., model BL-1) to obtain a mixture (A1). 13 g of the above mixture (A1) was added to a hybridizer NHS.
-0 type at 16,200 rpm for 5 minutes to obtain conductive composite particles with an average particle size of 5.8 μm. The composite particles were placed in a cylindrical Teflon cell and lightly pressed together, with a cross-sectional area of 2 cm.
The electrical resistance value was measured using a digital multimeter TR-4101 (manufactured by Advantest Co., Ltd.) using a gold-plated electrode of 1.5 x 10 -4 Ω·cm.

[0017] Example 2 Polyethylene true spherical fine particles with an average particle size of 11.9 μm (manufactured by Seitetsu Kagaku Kogyo Co., Ltd., trade name: Flow Beads CL-2080)
) and water-dispersed type gold powder using a homogenizer, treated in the same manner as in Example 1, and freeze-dried to obtain gold powder with an average particle size of 0.5 μm (manufactured by Tokuriki Kagaku Kenkyujo Co., Ltd., product). Mix 10 parts of TA-2) with Multi Blender Mill (Co., Ltd.)
The mixture was premixed using a Nippon Seiki Seisakusho (model BL-1) to obtain a mixture (A2). 12 g of the above mixture (A2) was treated with a hybridizer NHS-0 model at 16,200 rpm for 5 minutes to obtain conductive composite particles having an average particle size of 12.8 μm. The electrical resistance value of the composite particles was measured in the same manner as in Example 1 and was found to be 4 x 10-3 Ω·cm.

Example 3 6 parts of glass fine particles with an average particle size of 4 μm (manufactured by Toshiba Ballotini Corporation, trade name MB-10) and 5 parts of silver fine particles with an average particle size of 0.1 μm treated in the same manner as in Example 1. 73 parts were mixed into a multi-blender mill (manufactured by Nippon Seiki Seisakusho Co., Ltd., BL-
1 type) to obtain a mixture (A3). 12g of the above mixture (A3) was mixed with a hybridizer NHS-0 type.
The average particle size was 4.3 μm after processing at 6200 rpm for 5 minutes.
Conductive composite particles were obtained. When the electrical resistance value of this composite particle was measured in the same manner as in Example 1, it was found to be 2 x 10-3
It was Ωcm.

Example 4 10 parts of nylon fine particles with an average particle size of 5 μm (manufactured by Toray Industries, Inc., trade name SP-500) and 16.47 parts of silver fine particles with an average particle size of 0.1 μm treated in the same manner as in Example 1. The mixture was premixed using a multi-blender mill (manufactured by Nippon Seiki Seisakusho Co., Ltd., Model BL-1) to obtain a mixture (A4). The above mixture (
A4) 13g with hybridizer NHS-0 type 162
Conductive composite particles having an average particle size of 5.3 μm were obtained by processing at 00 rpm for 5 minutes. The electrical resistance value of the composite particles was measured in the same manner as in Example 1 and was found to be 2×10-3Ω・
It was cm.

Example 5 Conductive particles were mixed and dispersed so that the volume concentration of the conductive particles obtained in Example 1 in the epoxy resin was 50%, followed by casting and heat curing for 24 hours. A sample of an epoxy dispersion with an electrode was prepared using the following steps. The electrical resistance value of this sample is
When measured with a digital multimeter TR-4101 (manufactured by Advantest Co., Ltd.), it was 1 x 10-3 Ω・cm
Met. Further, the amount of silver in 1 cm3 of this sample was determined to be 1.2 g.

Example 6 A coating film was prepared in the same manner as in Comparative Example 2, except that the conductive particles obtained in Example 1 were blended so that the volume concentration in the acrylic resin was 60%. A coated plate with a thickness of 48 μm was prepared. The electromagnetic shielding effect of this sample was evaluated using spectrum analyzer TR-4171 and evaluation device TR-173.
When measured with 01A (manufactured by Advantest Co., Ltd.),
It exhibited a good electromagnetic shielding effect, with an electric field attenuation rate of 47 db and an electric field attenuation rate of 40 db at a frequency of 500 MHz.

Example 7 In Example 5, the conductive particles obtained in Example 3 or 4 were used in place of the conductive particles in Example 1, and the epoxy dispersion was prepared in the same manner as in Example 5. When a sample was prepared, almost the same results as in Example 5 were obtained.

Claims (6)

[Claims] Claim 1: Core particles with an average particle diameter of 1 to 200 μm (
A) and an aqueous dispersion of metal particles are treated with a cavitation type dispersion/pulverizer, and then lyophilized to produce metal fine particles (B) with an average particle size of 0.01 to 10 μm, and if necessary, other fine particles ( A method for producing conductive particles, which comprises dry mixing C) with mechanical strain to form a metal layer on the surface of the core particles (A). 2. The method for producing conductive particles according to claim 1, characterized in that a multilayer metal layer is formed on the surface of the core particle (A) by sequentially using a plurality of conductive metal fine particles (B). . 3. The method for producing conductive particles according to claim 1, wherein the core particles (A) are made of silica or glass. 4. The method for producing conductive particles according to claim 1, wherein the core particles (A) are made of plastic. 5. The method for producing conductive particles according to claim 1, wherein the core particle (A) is a metal or a metal oxide. [Claim 6] Fine particles (C) have an average particle size of 0.3.
The method for producing conductive particles according to any one of claims 1 to 5, characterized in that one or more selected from polymethyl methacrylate and silica having a particle size of 10 μm or less are used. 0001