JP2673829B2 - Manufacturing method of copper-coated iron powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a composite powder in which iron powder is coated with copper. The iron powder surface is formed by electroplating copper on the iron powder in a rotary container. And a method for forming a copper plating layer having a uniform and appropriate thickness.

[Conventional technology and problems]

Plating on powder, electroless plating (for example, Japanese Patent Laid-Open No. 61-25
8868 gazette). For example, "Practical Surface Technology", September 1980, pages 8-12, describes electroless plating on inorganic materials. However, in electroless plating, the reaction tends to be unstable, it is difficult to control the plating thickness, the life of the plating solution is short, a large amount of waste liquid is generated, and the cost of waste liquid treatment to prevent pollution greatly affects the cost. However, it is difficult to uniformly coat each powder.

A method of substituting and depositing copper from a copper chloride solution by utilizing the ionization tendency (for example, JP-A-61-79706 and JP-A-61).
In the case of Japanese Patent Publication No. 79707) as well, since the bath composition changes remarkably due to precipitation, not only is it extremely difficult to control the target plating thickness, but the amount of waste liquid that accompanies deterioration of the bath is enormous. Will be things.

For parts with a relatively small diameter of several millimeters or more, such as machine screws and small washers, electroplating is performed using an external anode horizontal barrel, but less than a few millimeters. This prior art could not be plated for the powders of. For example, the powder falls from the gap of the barrel, and if the gap is made small, the fall of the powder can be prevented to some extent, but the circulation of the plating solution deteriorates and the composition of the plating solution collapses, which makes good plating impossible. Even an internal anode tilted barrel with several cathodes on the bottom of the barrel cannot efficiently plate powder. That is, as it is, not only the plating speed is slow and the efficiency is not so bad, but also the unevenness of the plating film thickness becomes large, and the powder adheres to the cathode to form a bump or the powder slides along the inner wall and flows well. There is also a structural problem such as not doing it.

Japanese Examined Patent Publication No. 61-40319 discloses a method of electroplating powder while stirring with an impeller, but there are problems such as agglomeration of powder and deposition on the cathode.

Japanese Unexamined Patent Publication (Kokai) No. 63-18096 discloses a method of coating a fine powder having a particle size of 100 Å to 1 μm with a metal in a suspended state, but it is not suitable for powder having a particle size of 10 μm or more.

[Object of the invention]

An object of the present invention is to solve the above-mentioned problems and provide an inexpensive copper-coated iron powder manufacturing method capable of uniformly coating each iron powder with a predetermined thickness of copper. is there.

[Configuration of the invention]

The method for producing copper-coated iron powder according to the present invention includes a copper plating solution in which copper pyrophosphate is dissolved and a particle size of 10 μm to 1 mm in a cylindrical container having a cathode plate on the bottom surface and a baffle plate on the inner peripheral wall. The iron powder in the plating bath is repeatedly loaded on the substantially entire area of the cathode plate by loading the iron powder in the range of ## EQU1 ## and rotating the cylindrical container around its axis with the central axis inclined. While forming a colliding flow state below the bath and forming a non-fluid region above the bath where iron powder flow does not substantially reach,
It is characterized in that an anode is arranged in this non-flowing region and electricity is conducted between the anode and the cathode plate. At that time, use a cathode plate of such a size that it occupies the entire area or most of the bottom surface of the cylindrical container, and the rotational speed of the cylindrical container is set so that the peripheral speed is 2 to 30 m / min. The iron powder to be subjected to the copper coating treatment according to the present invention preferably has a nickel thin film formed on its surface by electroless nickel plating treatment.

[Action]

According to the present invention, the rotation of the inclined cylindrical container about the axis forms a flow state in which the iron powder in the bath collides with the cathode plate at the bottom of the container in high density and uniformly. While the phenomenon that copper ions in the plating solution are reduced and precipitated is prevented, each iron powder particle colliding with the cathode plate is negatively charged by being discharged from the cathode plate, and as a result, the copper ions in the plating solution are Electroplated on iron powder surface. In addition, since iron powder with a relatively large particle size in the range of 10 μm to 1 mm is targeted, each iron powder has a function of descending into the plating solution due to its own weight, and the rotation speed of the cylindrical container By appropriately adjusting the above, a non-fluid region of only the plating solution in which the iron powder does not rise is formed above the iron powder flowing region. By immersing the anode in the zone containing only the plating solution above this,
The iron powder is prevented from coming into contact with the anode, and as a result, the phenomenon that the iron powder and the copper coating are dissolved is prevented, and the surface of each iron powder is evenly plated with copper. In addition, the thickness of the plated copper can be controlled arbitrarily and accurately by adjusting the amount of electricity and the processing time, and the proper flow state of the iron powder that collides with the cathode plate is provided on the inner peripheral surface of the cylindrical container. It is further supported by the baffle. Further, by configuring the device capable of arbitrarily adjusting the inclination angle and the rotation speed of the cylindrical container, the flow state can be controlled more appropriately and easily.

The iron powder used for this copper electroplating was
By using electroless nickel plating, it is possible to prevent copper ions in the plating solution from being reduced by iron powder. That is, when iron powder is added to a plating solution in which copper ions coexist, a substitution precipitation reaction occurs in which the iron powder dissolves in the solution and copper is deposited due to the difference in ionization tendency. If it is formed on the surface of, the dissolution of this iron powder can be prevented. Even if electroless copper plating is performed instead of electroless nickel plating, the substitution reaction of elution of iron from the powder and the accompanying precipitation of copper cannot be prevented, so the film becomes porous and good electroplating cannot be performed. If a large amount of copper is coated by electroless copper plating, electroplating can be performed, but since a large amount of electroless plating waste liquid is generated,
The benefits of electroplating are gone.

A copper pyrophosphate bath is a good plating bath for electroplating. In a copper sulfate bath or a copper borofluoride bath, even pretreated iron powder may dissolve, so good plating cannot be performed. In the copper pyrophosphate bath, the electroless nickel-plated iron powder as described above does not dissolve.

[Specific disclosure of the invention]

In the present invention, a powder suspension flow in which iron powder is suspended at a predetermined suspension concentration in a copper plating solution in which copper pyrophosphate is dissolved is forcibly formed in an inclined rotary container, and this powder suspension flow is used as an anode. Does not come into contact with each other, but circulates and collides with substantially the entire area of the cathode plate at the bottom of the container with a predetermined velocity component. Specifically, the plating bath is placed in a cylindrical container having a cathode plate on the bottom surface. Then, the cylindrical container is tilted about its central axis and rotated about its axis to form a flow state in which the powder in the plating bath repeatedly collides with the cathode plate under the bath and the powder flows. A non-fluid zone that does not substantially reach is formed above the bath, and an anode is placed in this non-fluid zone to electroplate copper on the iron powder surface. At that time, it is desirable that the suspension concentration of the powder formed below in the electroplating solution is in the range of 30 vol.% To 55 vol.%. It is necessary to form so as not to contact. The powder suspension flow in this flow region is 2m / min with respect to the cathode plate.
It is better to collide with a flow velocity of ~ 30m / min,
This can be controlled so that the peripheral speed of the rotating container is in the range of 2 m / min to 30 m / min. As a result, copper can be electroplated uniformly and with high yield (high yield of 90% or more) on each iron powder particle, substantially independently of the concentration of copper ions in the electroplating solution. Also, by keeping the whole area of the cathode plate continuously receiving the flow of powder, it is possible to prevent Cu ions in the liquid from being electrodeposited on the cathode and Maintaining the state of not contacting the anode also prevents the iron powder and the copper deposited on the surface thereof from melting.

The iron powder targeted by the present invention preferably has a particle size of 10 μm or more. This is because if it is fine, a phenomenon such that it floats up and floats in the plating bath occurs, and problems such as non-plating and contact with the anode and melting occur. If the rotation is slowed down, it will not rise, but this time there will be problems such as aggregation and deposition on the cathode.
Also, the particle size may not be too large to maintain a dense collision state over the entire area of the cathode. Therefore, those having a particle size of 1 mm or less are suitable for the method of the present invention. The peripheral speed when rotating the container is 2 to 30 for the reasons described above.
m / min is suitable, but for the other reason, if it is too fast, the powder will be pressed against the inner wall of the container by centrifugal force and uniform stirring will not be possible, or the powder will rise and come into contact with the anode to dissolve. If it is too slow or slower than this, problems such as agglomeration and deposition on the cathode may occur due to insufficient stirring, so the peripheral speed in this range is appropriate. In addition,
When the particle size of the iron powder to be treated is small or has a low specific gravity within the above range, the peripheral speed may be decreased, and when the particle size of the iron powder is large or the specific gravity is large, the peripheral speed may be increased. In any case, it is important to control the peripheral speed and the inclination angle to form a stable fluidized bed around the cathode plate on the bottom of the container, depending on the characteristics of iron powder.

FIG. 1 shows an essential part of an apparatus for carrying out the electroplating method of the present invention, which is a cylindrical container 1 for containing treated iron powder and a plating solution, and this cylindrical container 1 Cathode plate 2 arranged in the direction orthogonal to the vessel axis at the bottom of the
And the anode 3 placed near the surface of the plating solution in the cylindrical container 1.
And a power supply device 4 for applying a predetermined potential between the cathode plate 2 and the anode 3, and the central axis of the cylindrical container 1 is inclined with respect to the vertical (in the illustrated example, the vertical It is installed so that it can rotate around the central axis (with an inclination of 45 °). That is, the container 1 is supported from the outside by the rotating shaft 5 at the center of the bottom of the container 1, thereby enabling the container 1 to rotate about the central axis, and fixing the motor 6 for imparting rotational power to the rotating shaft 5 to the base 7. To do. The tilt angle of the container 1 is adjusted by making the tilt of the base 7 adjustable with respect to the horizontal. Further, in order to receive the load when the container 1 is tilted, an idler roller 8 is provided which rotates in contact with the outer periphery of the container 1. The load point of the idler roller 8 is also integrally connected to the base 7. Has been done. The motor 6 is a variable speed motor and can freely adjust the rotation speed of the container 1 about its axis. On the other hand, a baffle plate 9 for promoting the flow of the treated powder is provided on the inner peripheral surface of the container 1. In the illustrated example, the baffle plate 9 is a plate that slightly protrudes inward in the radial direction from the inner wall of the container 1, and is attached to the inner wall so that its longitudinal direction is along the axial direction of the container. As shown in Fig. 2, four pieces are attached at 90 ° intervals.

A copper plating solution and iron powder are put into the electroplating apparatus configured as described above, and the inclination angle of the container 1 and the rotation speed of the motor 6 are appropriately adjusted in accordance with the loading amount and the volume ratio, so that the specific gravity difference is increased. By this, it is possible to control so that the aggregate of powders descending in the plating solution forms an appropriate flow region 10 below the plating solution. That is, powder flow region 10
While rotating by the rotation of the container 1 and the stirrer effect by the baffle plate 2, the collision constantly repeats so as to cover the entire surface of the cathode plate 2 while swirling and flowing, and the powder does not rise in the upper area 11 of the plating solution. A steady state in which only a swirling flow is formed can be maintained. If this steady state is formed, the anode 3 is placed in the upper solution 11 of the plating solution in which a swirling flow of only the solution is formed, the energization is started, the electroplating process is performed for a predetermined time, and then the energization is performed. Stop and collect the plated product. This recovery may be performed by rotating the base 7 to further tilt the container 1 and transfer the contents to another container.

Typical examples of carrying out the method of the present invention using this apparatus will be given below.

[Example 1] Copper plating is performed using the iron powder of KIP300A manufactured by Kawasaki Steel Co., Ltd. shown in Table 1. First, as a pretreatment, 1 kg of the iron powder
Put it in the 2 tall beaker and make it by Tokyo Rika Kikai Co., Ltd.
Using a DC stirrer (DC-2RT type), add 60 ml of hydrochloric acid little by little while stirring with a Teflon propeller and perform pickling. Next, after washing with water three times, a DC stirrer (DC-2
RT type) and stirring at 560 rpm while performing electroless plating with the alkaline electroless nickel plating solution "TMP chemical nickel" manufactured by Okuno Chemical Industries Co., Ltd. Next, wash with water 3
Do it twice.

On the other hand, as the plating solution, prepare a copper pyrophosphate bath 1.5 having the following composition.

Plating solution composition Copper pyrophosphate (Cu ₂ P ₂ O ₇ / 3H ₂ O) 29g / Potassium pyrophosphate (K ₄ P ₂ O ₇ ) 254g / Potassium citrate (KH ₂ C ₆ H ₅ O ₇ ) 23g / This plating The bath and the above-mentioned pretreated iron powder were loaded into the container 1 shown above and the inclination angle of the container 1 was 45 °, and the motor 6 (Apple Corn RXM-40-G5M manufactured by Shinpo Industry Co., Ltd.) was used.
The container 1 was rotated at a peripheral speed of 9.1 m / min to perform plating treatment. At that time, a copper plate for copper pyrophosphate plating bath (UP-C copper anode manufactured by Sumitomo Metal Mining Co., Ltd.) was used for the anode 3, and stainless steel (SUS304) having a diameter of 110 mm was used for the cathode 2. The inner diameter of the container is 120 mm. Each baffle plate 9 is a plate having a height of 5 mm and a length of 120 mm provided on the inner wall of the container 1 at 90 ° intervals. The DC power supply 4 is manufactured by Sansha Electric Co., Ltd.
SANRXDC AUTO 1530D type was used. Plating was performed with the amount of electricity applied to 260 AH.

After the plating was completed, the plate was washed with water, filtered under reduced pressure with a Buchner funnel, washed with ethanol, and dried in a vacuum dryer at room temperature with a water-sealed pump equipped with an radiator for 24 hours. The powder after drying was 1302 g. The powder was analyzed and found to be 23.2 wt.% CU. The current efficiency was as high as 98%. When this powder was sieved, +80 mesh was 0.73%. This was an increase of only 0.33% compared to the raw iron plate, so almost no agglomeration was observed.

 Fig. 3 shows a cross-sectional photograph of the obtained plating powder.

Example 2 300 g of iron powder having a particle size of 20 μm was degreased, electroless copper nickel plating was applied in the same manner as in Example 1, and then a DC power supply of Takasago Seisakusho TMO18-3 type was used. Peripheral speed 2 with plating equipment
Copper was plated at m / min. Oxygen-free copper was used as the anode, and 257AH plating was performed using the following copper plating solution.

Plating solution composition Copper pyrophosphate (Cu ₂ P ₂ O ₇ / 3H ₂ O) 80 g / Potassium pyrophosphate (K ₄ P ₂ O ₇ ) 255 g / Ammonia water 4 ml / Potassium sulfate (KNO ₃ ) 12 g / Below, Example 1 As a result of the same treatment as above, the powder after drying was 601 g. The powder was analyzed and found to be 50.1 wt.% Cu. The current efficiency was as high as 99%.

[Example 3] 14 AH copper plating was performed in the same manner as in Example 2 except that 300 g of iron powder having a particle size of 0.7 mm was pretreated in the same manner as in Example 2 and then the peripheral speed was set to 30 m / min in the previously described apparatus. gave.

After that, the same treatment as in Example 1 was performed, and as a result, the amount of powder after drying was 316 g. The powder was analyzed and found to be 5.1 wt.% Cu. The current efficiency was as high as 99%.

[Comparative Example 1] Next, for comparison, the result of plating according to the method described in Japanese Patent Publication No. 61-40319 is shown. Example 1 was prepared by adding 500 g of the iron powder shown in Table 1 to a tall beaker.
After performing pickling and electroless nickel plating in the same manner as in, place in a plating tank having a cathode on the bottom of the plating tank, add a plating solution having the same composition as in Example 1, and make by Tokyo Rika Kikai Co., Ltd. Using a DC stirrer (DC-2RT type), while stirring the powder with a Teflon propeller, 128.6 AH plating was performed using Takasago Seisakusho TMO18-3 type as a DC power source. However, the powder adhered to and accumulated on the cathode on the bottom surface and gradually became thicker, and the deposited powder and the stirring propeller contacted each other, and there was a rattling noise. After plating, the powder was 445 g and the deposit on the cathode was 184 g. In other words, the yield of the whip is 71%, which is extremely poor, and the powder of plastic generated from the worn propeller is mixed in the powder.
It was not usable.

[Comparative Example 2] Iron powder shown in Table 1 was pickled, and copper plating was performed using Takasago Seisakusho TMO18-3 type as a DC power supply in the same manner as in Example 1 without applying electroless nickel. As a result, the iron powder began to dissolve, the plating solution suddenly began to become cloudy, and it decomposed.

[Comparative Example 3] The iron powder shown in Table 1 was pickled in the same manner as in Example 1, and the high-speed electroless copper plating solution "OP" manufactured by Okuno Chemical Industries Co., Ltd.
After performing electroless plating with "C copper", when using a Takasago Seisakusho TMO18-3 type as a DC power source in the same manner as in Example 1, copper plating suddenly began to become cloudy. It has been disassembled.

[Comparative Example 4] Electroplating was carried out in the same manner as in Example 1 except that the iron powder shown in Table 1 was replaced with a copper sulfate bath. The electroplating could not be continued because the substitution reaction of the precipitation of was remarkable.

[Comparative Example 5] Electroplating was carried out in the same manner as in Example 1 except that the iron powder shown in Table 1 was changed to a copper borofluoride bath only in the plating bath. As a result, the substitution reaction of copper precipitation was significant, and electroplating could not be continued.

〔effect〕

According to the method of the present invention, there is no problem of deterioration of the plating bath as in the case of electroless plating or substitutional deposition, and since the bath life is long, the generation of waste liquid is remarkably small, and thus iron powder can be coated inexpensively. Furthermore, since current efficiency is good and stable plating is possible, the thickness of the plating and the plating amount can be easily controlled by the amount of electricity supplied. In addition, since a good and stable powder flow state can be maintained over the entire area of the cathode plate, there is no problem of powder agglomeration or deposition on the cathode, and there is no dissolution of iron powder. A copper film can be formed without using it.
Further, by arranging a circular cathode having a size considerably larger than the area of the bottom surface of the container, the powder is prevented from adhering to the cathode, and the copper coating is efficiently formed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a main part of an example of a plating apparatus of the present invention,
FIG. 2 is a sectional view taken along the line II-II ′ of FIG. 1, and FIG. 3 is a sectional photograph showing the metallographic structure of the copper-coated iron powder obtained in Example 1. 1 ... cylindrical container, 2 ... cathode, 3 ... anode, 4 ... power supply device, 5 ... rotating shaft, 6 ... motor, 7 ... base, 9 ... baffle plate, 10 ... powder Flow region.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshima Koki, 1 at 7 Shintachi, Takaya Shinmachi, Ichikawa City, Chiba, Nisshin Steel Co., Ltd. (56) Reference JP-A-1-247594 (JP, A) Actual Development Sho 59-133670 (JP, U) Japanese Patent Sho 61-40319 (JP, B2)

Claims (3)

(57) [Claims] 1. A copper container in which a cathode plate is arranged on the bottom surface and a baffle plate is arranged on the inner peripheral wall, and a copper plating solution in which copper pyrophosphate is dissolved and a nickel-coated iron having a particle size in the range of 10 μm to 1 mm. Powder state is loaded, and the cylindrical container is rotated about its axis with its central axis tilted, and this rotation causes the iron powder in the plating bath to repeatedly collide with substantially the entire area of the cathode plate. Is formed below the bath and a non-fluid region where the flow of iron powder does not substantially reach is formed above the bath, and an anode is arranged in this non-fluid region to conduct current between the cathode plate and the non-fluid region. Method for producing copper-coated iron powder. 2. The method for producing copper-coated iron powder according to claim 1, wherein the nickel-coated iron powder has a nickel thin film formed on its surface by electroless nickel plating. 3. The method for producing copper-coated iron powder according to claim 1, wherein the rotation of the cylindrical container is controlled so that the peripheral speed is 2 to 30 m / min.