JPH0534435B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for electroplating powder and granular materials and an apparatus for electroplating. Electroplating is generally considered as a method for applying metal coating to electrically conductive powder, but in practice there are many very difficult problems. For example, small parts such as screws and nuts used in precision parts can be plated by using a small barrel, by using the netting method, or by using centrifugal force to bring the object to be plated into close contact with the inner wall of the plating tank. Electroplating can be carried out in various ways, such as by employing a method of. However, when attempting to uniformly plate a large number of articles, these methods are uneconomical because the equipment becomes large and an unnecessarily large amount of plating solution must be used. In addition, when electroplating powder or granular material, especially powder or granular material with a particle size of 500μ or less,
It is difficult to employ these methods, and it is especially difficult to employ the electroplating method for powder particles of about 0.5 to 50 μm. Furthermore, if a plating object, lead material, etc. dissolves into the plating solution, such impurities will be incorporated into the plating solution. Therefore, there is a method in which the powder is fluidized in an electroplating liquid under stirring action, the powder and the electroplating liquid form a slurry, and this slurry is brought into contact with the cathode to perform electroplating. Although this method has been proposed, since the plating liquid is not sent in a uniform laminar flow, there are problems with the uniformity of plating and the use of an unnecessary large amount of plating liquid. For this reason, the scientific plating method has conventionally been mainly used as a metal coating method for powder and granules.
This method has problems in terms of cost, and depending on the purpose of use, it may not always show satisfactory performance in terms of film strength, adhesion, quality safety, etc. In particular, we are trying to obtain conductive materials that can be added to paints, inks, adhesives, plastics, etc. as conductive powders to replace metal powders, and can be used for various purposes with performance comparable to that of metal powders. In this case, it is necessary to coat the base material powder with a metal plating film having a required thickness, uniformity, and good adhesion, and the manufacturing cost is also required to be low. When a scientific plating method is employed, it takes a considerable amount of time to form a thick plating film, and the plating solution itself is relatively expensive, resulting in high manufacturing costs. In view of the above circumstances, the present inventors have conducted intensive studies on a method and apparatus for uniformly and efficiently electroplating powder and granular materials. The stored powder and granules are electroplated in a fluidized state by the upward flow of the plating solution, and the velocity of the upward flow rising in the cathode chamber is reduced at the upper part of the cathode chamber to form an upward flow. A method for electroplating powder and granules, characterized in that accompanying powder and granules are prevented from flowing out to the outside with upward flow, and electroplating comprising a cylindrical anode and a cathode chamber having a powder and granule storage tank. The device has a plating liquid inlet at the bottom of the powder storage tank, and a fluidized particle dispersion prevention tower is installed at the top of the cathode chamber, the cross-sectional area of which gradually increases toward the top. It has been found that the above object can be achieved by an electroplating apparatus for powder and granular material, which is characterized in that an outlet for plating liquid is provided on the upper wall of the tower. That is, the inventors first used an open-type inclined barrel, used the barrel body itself as a cathode, put the powder inside, and inserted an anode through the open opening of the barrel body to control the rotation of the barrel. Electroplating was performed at various speeds in the range of 1 to 10 rpm, but uniform electroplating was not achieved, especially when using powder particles of 10 μm or less, even when the barrel rotation was made slow. The electrolyte was dispersed to a considerable extent in the plating solution, and the uniformity of the electrodeposit was very poor. In addition, a vibrating barrel was used instead of this type of rotating barrel to electroplate the powder and granules under vibration, but similarly good electroplating was not achieved. Powder was deposited on top, and the powder was electroplated while being stirred using ultrasonic waves, but in this case as well, only non-uniform electrodeposit was obtained. All of these are because the plating liquid does not form a uniform laminar flow, and the powder and granules are not fluidized. Therefore, as a result of further investigation, it was discovered that uniform and highly efficient electroplating can be obtained by electroplating in a fluidized state of the accumulated powder particles to be plated. That is, in the present invention, since the plating liquid has a laminar flow, the powder particles stick together and separate from each other in the plating liquid, forming a so-called porous state, and the inside of this porous state is plated. The liquid passes through. Therefore, when electroplating is performed, the entire porous state acts as a cathode, and the cathode surface area becomes extremely large, allowing efficient plating. In addition, the inlet side of the porous plating liquid has a higher concentration of the plating liquid than the outflow side and is plated thickly, but is stirred up by the water flow of the plating liquid. In this case, if the granules are too small, they will separate due to thermal vibrations in the plating solution, making it difficult to function as a cathode. The preferred range of the particle size of the powder and granules varies depending on the material, specific gravity, etc. of the powder and granules, and even relatively large particles can be used for those with low specific gravity such as carbonaceous powders. . The average particle diameter of the powder or granule is preferably 1 μm or more, and the powder or granule has a diameter of 10 μm or more.
If it exceeds mm, the required flow rate of the plating liquid will increase, making the device large, which is not preferable. In addition, in a fluidized state, the plating liquid flows inside the powder and the entire powder needs to act as a cathode, so the volume of the porous state during plating is the same as the original plating. volume of accumulated material
1.1 to 1.5 times is good for workability. Furthermore, in the apparatus of the present invention, the plating liquid outflow side is opened outward and the velocity of the plating liquid is weakened, so that the powder and granules do not flow out together with the plating liquid. In the powder storage tank, a fluid state is maintained due to uniform laminar flow, allowing uniform electroplating without impurities. Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of the electroplating apparatus according to the present invention, and FIG. 2 is a -
FIG. The electrolytic cell body 1 consists of a cylindrical body with an open upper surface and an outward flange 2 connected to the upper end, and a downward plating liquid inlet 3 is provided in the center of the lower surface of the body 1. An anode supporting cylinder 4 is installed near the lower end of the inner wall of the main body 1.
A donut-shaped anode lower frame 7 in which a lattice-shaped support piece 6 is installed is mounted via the ring 5 . A porous cylindrical anode 8 is erected on the upper edge of the anode lower frame 7 by welding or the like. As the material of the anode, graphite, stainless steel, platinum, titanium coated with a noble metal oxide, ferrite, etc. can be used. The lower end of a short cylindrical anode upper frame 10 with an outwardly bent part 9 connected to the upper end is connected to the upper end of the anode 8 by welding or the like, and the outer end of the outwardly bent part 9 is , a gasket 11 is interposed between the outward bent portion 9 and the outward flange 2 and aligned with the outer end of the outward flange 2 . On the inner surface of the anode 8 and the anode upper frame 10 and on the lattice-like support piece 6, there are a large number of particles of about 0.1μ to 100μ made of a non-conductive organic compound or a non-conductive inorganic compound such as nylon, polyethylene, polypropylene, etc. A bag-shaped diaphragm 12 having pores is housed in the anode upper frame 10 , and the upper end of the diaphragm 12 is bent outward and held between a pair of gaskets 13 and 14 so as to face outward of the anode upper frame 10 . It is placed on the bending part 9. A recess 15 is provided on the central upper surface of the inner lower part of the bag-shaped diaphragm 12 at the portion that contacts the anode lower frame 7 via the diaphragm 12, and a vertical communication hole 1 is provided in the upper center surface.
A solution dispersion plate 17 made of vinyl chloride resin or the like with holes 6 is placed thereon. This dispersion plate 17 may be omitted. A gasket 14 is placed on the upper end of the bag-shaped diaphragm 12.
An outward facing flange 19 at the lower end of the fluidized particle diffusion prevention tower 18 is mounted through the flange 19 and fastened with bolts 20 . The fluidized particle diffusion prevention tower 18 includes, in order from the bottom, the lower end outward flange 19, the small diameter part 2
1. Consists of a tapered part 22, a large diameter part 23, and an upper end outward flange 24, and the outward flange 2
A disk-shaped lid 25 is fastened onto the top of the housing 4 with bolts 26. A cathode current collector 27 is vertically disposed on the lower center surface of the lid 25, and the lower end reaches near the recess 15. Part 29
and a hollow cylindrical main body 30, the main body 30
Wing bodies 31 are radially arranged on the outer periphery of the blade body 31 to increase the contact area with the granular material. Bag-like septum 12
The inside of the particle size is about 1μ to 10mm, preferably 0.05mm.
A large number of powder particles 32 of about 3.0 mm are deposited. The material of the powder may be any material as long as it has conductivity and can be electroplated, such as metal powder such as copper powder, iron powder, aluminum powder, new powder, carbon, etc. Conductive inorganic powder such as powder,
Examples include non-conductive inorganic powder such as Al ₂ O ₃ or SiO ₂ or resin powder made conductive using an appropriate conductive treatment method such as chemical plating or vacuum evaporation. When electroplating is performed using these powders, pretreatment can be carried out depending on the material, if necessary. For example, copper powder, iron powder, etc. are subjected to degreasing and pickling treatment, and aluminum powder, etc., is subjected to a known zinc substitution treatment, followed by copper bronze strike plating. , good electroplating can be performed. In addition, in the case of non-conductive powder, known chemical plating methods such as chemical nickel plating, chemical copper plating, etc. are suitable after applying a catalytic metal such as palladium. The non-conductive powder particles made conductive in this way can be electroplated in the same manner as metal powder particles. In the present invention, the type of electroplating solution is not limited, and known plating solutions such as copper, nickel, chromium, tin, zinc, silver, platinum, gold, rhodium, and palladium can be used. In this case, either an acidic solution or an alkaline solution can be suitably used as the plating solution, and multilayer plating can also be performed, such as nickel plating followed by silver plating. Furthermore, appropriate plating conditions are adopted depending on the type of electroplating solution. In the present invention, if necessary, a pump may be used to circulate the plating liquid, and plating can be performed while constantly replacing the plating liquid with a new one. 33 is an anode gas and anolyte outlet connected to the upper side of the electrolytic cell body 1; 34 is a catholyte outlet connected to the side of the large diameter part 23 of the fluidized particle diffusion prevention tower 18; 35; is a cathode gas outlet connected to the top surface of the lid 25. A plating solution is supplied from the solution inlet 3 to the electrolytic cell main body 1 having the above structure. The supplied solution is
Pores of bag-like diaphragm 12 and communication holes 1 of solution distribution plate 17
6 into the cathode chamber. In this case, the solution plays the role of maintaining the powder 32 in a suspended state and stirring it. Metal ions in the solution are powder particles 32
It is electrolytically reduced above, becomes metal atoms, and becomes powder particles 32.
At the same time, as a side reaction, water is electrolyzed and hydrogen is generated, and this hydrogen is passed through the cathode gas outlet 3.
5. A part of the plating solution flows into the anode chamber through the bag-like diaphragm 12, and water is electrolyzed on the anode 8 to generate oxygen, which is then discharged from the anode gas outlet 33 or the cathode gas outlet 35. It is taken out of the electrolytic cell. Further, the plating solution usually contains other ions such as cyan ions, and nitrogen, ammonia, etc. produced by the oxidation of these cyan ions are also extracted. The plating solution whose metal ion concentration has been reduced overflows from the solution outlet 34 and is taken out of the electrolytic cell. On the other hand, the powder 32 rises together with the plating liquid, but the flow rate decreases as it rises in the fluidized particle scattering prevention tower 18 whose cross-sectional area becomes larger toward the upper part, and the fluidized particles that have risen together with the plating liquid do not cause plating. Since the particles are separated from the liquid, there is no need to provide a filter or the like at the outlet of the pampering liquid provided in the fluidized particle diffusion prevention tower to separate the fluidized particles. In this electrolyzer, in order to efficiently impart a cathode potential to the powder in the fluidized bed and deposit uniformly on the cathode with high current efficiency and low electrolytic voltage, plating must be performed under the following electrolytic conditions. This is desirable. Cathode current density: 30A/ ^dm2 or less (preferably
10A/dm ² or less) Anode current density: 20A/dm ² or less (preferably
5A/dm2 or ^less ) Current concentration in fluidized bed: 30A/- fluidized bed or less (preferably 10A/- fluidized bed or less) Fluidized bed void ratio: 40 to 90% (preferably 60 to 75
%) Here, the cathode density exceeds 30A/ ^dm2 , and
When the anode current density exceeds 20 A/ ^dm2 , the voltage increases, and furthermore, when the current concentration in the fluidized bed exceeds 30 A/dm2, not only does the voltage increase, but plugging occurs, and the fluidized bed void ratio decreases to 90. If it exceeds 40%, the voltage will rise, and if it falls below 40%, plugging will occur near the plating liquid inlet, so it is best to keep it within the above range. In addition, if this electrolytic operation is performed continuously, the diameter of the cathode particles increases as the metal is deposited, so the fluidization conditions (fluidized bed height, fluidized bed void ratio, fluidized bed pressure loss) change, so this electrolysis The fluidized bed section of the tank is preferably designed as follows. In other words, the height of the fluidized bed is 1.2 of the initial fluidized bed.
The cross-sectional area of the fluidized particle diffusion prevention tower should be at least 1.5 times the cross-sectional area of the electrolytic cell body.
At least twice that amount, preferably at least twice as much, to prevent the powder from escaping. In addition, since fluidized powder is used as the cathode, the surface area of the cathode is extremely large, allowing plating with a lower current density, and cathode particles suspended in a uniform laminar flow collide with each other. Since the electric double layer is made unstable, electrolysis can be carried out at low electrolytic voltage and high current efficiency, and uniform electroplating can be achieved. Furthermore, even if the plating solution contains impurity metals other than the precipitated metal, an electroplated film containing no impurities can be obtained by utilizing the potential difference between the two metals. The electroplated film-coated powder particles thus obtained can be suitably used as materials for conductive inks, catalysts, paints, adhesives, plastics, electromagnetic shielding materials, contacts, and the like. In particular, the silver-coated powder obtained by electrolytic silver plating has almost the same performance as silver powder, and can be produced at a lower cost than silver powder, so it can be used as a substitute for silver powder for pastes. It is extremely effective. FIG. 3 shows a second embodiment of the electroplating apparatus according to the present invention.
FIG. 3 is a longitudinal cross-sectional view showing an example. This electroplating apparatus is an improvement of the electroplating apparatus of the first embodiment, and the same members as those of the first embodiment are given the same reference numerals and explanations thereof will be omitted. The electrolytic cell body 1' consists of a dish-shaped lower frame 36 in which a plating liquid inlet 3 is connected, and a cylindrical anode 8', with both upper and lower ends of the anode 8' facing outward. It is bent. The porous diaphragm consists of a cylindrical upper diaphragm 12' and a flat lower diaphragm 12'', and both upper and lower ends of the upper diaphragm 12' are bent outward. Solution distribution plate 17' is approximately the same as the diameter of the lower diaphragm 12'',
A communication hole 16' is provided only in the center. The bent portion at the upper end of the upper diaphragm 12' is held between the outward flange 19 of the fluidized particle diffusion prevention tower 18 and the bent portion at the upper end of the anode 8' via gaskets 13 and 14, and is secured by bolts 20. It is fastened.
The peripheral edge of the solution distribution plate 17' is connected to the upper diaphragm 12' which is held between a pair of gaskets 37 and 38, respectively.
It is held between the bent portion at the lower end and the lower diaphragm 12'', and is fastened with bolts 39. When the plating solution is supplied to this electrolytic cell from the solution inlet 3, it is the same as in the case of the first embodiment. In the electrolytic cell of this example, the thickness of the anode chamber is apparently zero, but the diaphragm does not come into close contact with the anode, and the diaphragm and the diaphragm do not come into close contact. An anode chamber exists between the anode and the anode. Electrolytic gas generated on the surface of the anode reaches the cathode chamber through the diaphragm and is taken out together with the cathode gas from the cathode gas outlet 35. The electrolytic cell main body is composed of the anode, and the solution dispersion plate is connected to the electrolytic cell main body, so the number of parts is smaller than that of the electrolytic cell of the first embodiment, and the structure is compact.Also, the anode is not exposed to the atmosphere. Although it is exposed, there is no risk of electric shock because the applied voltage is small.In addition, in the present invention, in order to improve the uniformity of the plating thickness, mechanical stirring such as an impeller type stirrer is used in combination to inhibit the flow state. In addition, a spiral groove may be provided in the main body 30 of the cathode current collector 27 to generate a uniform laminar vortex flow to lengthen the flow path of the plating solution. When the object to be plated is lighter than the plating liquid, the apparatus of this embodiment is reversed.The present invention will be specifically explained below by referring to Examples, but the present invention is limited to the following Examples. Example 1 Copper particles (spherical particles with an average particle size of 100 μm) were plated with gold by the following method. First, 5 kg of copper particles were degreased, and then washed with water, pickled, and washed with water to remove copper. Dirt and oxide film on the surface of the particles were removed.Next, the pretreated copper particles were deposited using the apparatus shown in Figure 1, and then electroplated with gold under the following conditions. Plating conditions Plating liquid: Autoronex C (acidic cyan plating liquid manufactured by Nippon Electroplating Engineers Co., Ltd.) with 8 g of gold Impurities: Copper 40 ppm Plating liquid amount: 50 Current: 45 A Voltage: 4 V Plating temperature: 50℃ Plating time: 60 minutes Flow rate: 0.3 cm/sec The entire copper particle turned golden in about 10 minutes. After gold plating, remove the plating solution, wash thoroughly with water, filter, and dry. Particles (Au/Cu particles) were obtained in which copper particles were coated with a gold plating film of 0.1 μm. Regarding the Au/Cu particles obtained by the method described above,
As a result of examining the gold distribution image using SEM photographs and an X-ray microanalyzer, it was found that gold was uniformly electrodeposited on the copper particles. In addition, copper as an impurity remained at 40 ppm even after plating. The Au/Cu particles obtained in this way could be used as a material for electrical contacts. Example 2 Using Al ₂ O ₃ particles 2 with an average particle diameter of 1 mm, plating was performed by the following method. First, the Al ₂ O ₃ particles were degreased, then washed with water, pickled, and washed with water, and then chemically plated with nickel according to the following steps. Sensitizing: Stannous chloride solution 2 ↓ Water washing ↓ Activation: Palladium chloride solution 2 ↓ Water washing ↓ Chemical nickel plating: Uemura Kogyo Co., Ltd. BEL Nickel 5 (reducing agent dimethylborazane) ↓ Water washing Next, the Al ₂ O ₂ particles were subjected to electroplating using an apparatus as shown in FIG. 3 under the following conditions according to Example 1. Platinum plating conditions Plating solution: 10 g of chloroplatinic acid/0.3N hydrochloric acid Amount of plating solution: 50 Current: 200 A Voltage: 20 V Plating temperature: 20°C Plating time: 60 minutes Flow rate: 0.2 cm/sec As described above All of the Pt/Ni/Al ₂ O ₃ particles obtained by this method have a uniform electroplated film, and the particles reliably contact the plating bath, which is the cathode, to ensure uniform electroplating. It has been found that an electrodeposited material can be obtained. In addition, if the particles are non-conductive, it is necessary to apply chemical plating to the electroplating side, but in the present invention, when chemical plating is applied to the particles, the film thickness must be at a level that allows electroplating. Compared to the case where highly conductive particles are obtained only by chemical plating, the film thickness can be made thinner, and the cost can be significantly reduced. As described above, the conductive material coated with the electroplated film obtained in Examples 1 and 2 has a stronger film and better adhesion than vapor-deposited or chemically plated products, and does not contain impurities and has a good quality. It is stable, inexpensive, and can be effectively used for various purposes.

[Brief explanation of the drawing]

FIG. 1 shows the first part of the electroplating apparatus according to the present invention.
FIG. 2 is a partially cutaway front view showing an embodiment, FIG. 2 is a cross-sectional view taken along the line -- in FIG. 1, and FIG. 3 is a partially cutaway front view showing a second embodiment of the electroplating apparatus according to the present invention. . 1, 1'... Electrolytic cell body, 3... Plating liquid inlet, 8, 8'... Anode, 27... Cathode current collector, 3
2... Powder, 18... Fluidized particle diffusion prevention tower, 2
2... Taper part.

Claims (1)

[Claims] 1. In a method of electroplating powder or granules in a cathode chamber of an electrolytic cell, the powder or granules are brought into a fluid state by an upward flow of a plating solution supplied from the bottom of the cathode chamber, and then electroplated by electroplating. At the same time, the flow velocity of the upward flow is reduced by a fluidized particle dispersion prevention tower provided at the upper part of the cathode chamber, the cross-sectional area of which gradually increases toward the upper part, and the powder accompanying the upward flow is separated from the upward flow. A method for electroplating powder and granular material, characterized by preventing the powder and granular material from flowing out. 2 The powder and granular material to be coated has an average particle size of 1ηm~
The method of electroplating a powder or granular material according to claim 1, wherein the powder is 10 mm. 3. The powder or granular material according to claim 1 or 2, wherein the height of the powder or granular material in a fluidized state is 1.1 to 1.5 times the height in a non-flowing state. Electroplating method. 4. In an electroplating device consisting of a cylindrical anode and a cathode chamber having a powder storage tank, a plating liquid inlet is provided at the bottom of the powder storage tank, and a cross-sectional area is provided at the top of the cathode chamber. An electroplating apparatus characterized in that a fluidized particle dispersion prevention tower is installed which increases gradually toward the top, and an outlet for plating liquid is provided on the upper wall of the fluidized particle dispersion prevention tower.