JPH032393A - Production of copper-coated iron powder - Google Patents

Abstract

PURPOSE:To form a uniform copper plating layer on the surface of iron powder in appropriate thickness without causing flocculation of powder and its deposition on a cathode by rotating an inclined cylindrical vessel on its axis and electroplating the Ni-coated iron powder in a copper plating soln. CONSTITUTION:A copper plating soln. of copper phosphate and the Ni-coated iron powder having 10mum to 1mm grain diameter are charged to the cylindrical vessel 1 provided with a cathode plate 2 at its bottom. The inclination of the center axis of the vessel 1 and the turning rate of the vessel 1 are appropriately adjusted so that the aggregate of iron powder descending due to the sp.gr. difference forms an appropriate fluidized region 10 in the lower part of the bath, and collison of the iron powder with the total area of the cathode plate 2 is repeated by the mixing effect of the rotation of the vessel 1 and a baffle 9 in the fluidized region 10. The iron powder is not floated up into the upper region 11, hence a nonfluidized region of the turning flow of only the soln. is formed at the upper part of the bath, an anode 3 is arranged in the upper soln. 11, a current is applied, and the powder is electroplated to produce copper- coated iron powder.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for producing a composite powder in which iron powder is coated with copper. This invention relates to a method for forming a copper plating layer of uniform and appropriate thickness.

[Conventional technology and problems]

Plating on powder can be done by electroless plating or electrolytic plating (for example, JP-A No. 6
1-258868)) 0 For example, "Practical Surface Technology, September 1980 Issue 8-12
The page explains electroless plating on inorganic materials. However, with electroless plating, the reaction tends to be unstable and it is difficult to control the plating thickness.

The life of the plating solution is short, a large amount of waste solution is generated, and the cost of processing the waste solution to prevent pollution has a large impact on costs. Moreover, it is difficult to uniformly coat each grain of powder.

In the case of a method in which copper is precipitated by displacement from a copper chloride solution using its ionization tendency (for example, JP-A-61-79706 and JP-A-61-79707), the bath composition changes significantly after one precipitation. Not only is it extremely difficult to control the desired plating thickness, but the amount of waste liquid generated as the bath deteriorates is also enormous.

For parts with a relatively small diameter of a few millimeters or more, such as machine screws and small washers, electroplating is carried out using an external anode type horizontal barrel, but for parts smaller than a few millimeters. For example, the powder would fall through the gap in the barrel, and although reducing the gap could prevent the powder from falling to some extent, it would not be possible to plate the powder with this conventional technique. This deteriorates the plating solution composition and makes it impossible to perform good plating. Even internally anode tilted barrels with several cathodes placed on the bottom of the barrel cannot plate powder efficiently, ie.

If left as is, not only will the plating speed be slow and the efficiency will be extremely poor, but the plating film thickness will be uneven, the powder will adhere to the cathode and form a lump, and the powder will simply slide along the inner wall and not flow properly. There are also structural issues.

In particular, Publication No. 61-40319 discloses a method of electroplating while stirring powder with an impeller.
Problems such as powder agglomeration and deposition on the cathode are common.

JP-A-63-18096 discloses a method of coating fine powder with a particle size of 100 angstroms to 1 μm with metal in a suspended state, but this method is not suitable for powders with a particle size of 10 AIm or more.

[Purpose of the invention]

The object of the present invention is to solve the above-mentioned problems.

To provide an inexpensive method for producing copper-coated iron powder that can evenly coat each grain of iron powder with copper to a predetermined thickness.

[Structure of the invention]

The method for producing copper-coated iron powder according to the present invention involves placing a copper plating solution in which bilorin is dissolved in a cylindrical container having a cathode plate on the bottom and a baffle plate on the inner peripheral wall, and a particle size ranging from 10 μm to 1-1 μm. This cylindrical container is rotated around the axis with its central axis tilted, and this rotation spreads the iron powder in the plating bath over substantially the entire area of the cathode plate. A fluid state of repeated collisions is formed above the bath, and a non-flow region is formed above the bath where the flow of iron powder does not substantially reach. An anode is disposed in this non-flow region and electricity is applied between the anode and the cathode plate. It is characterized by At that time, use a cathode plate large enough to occupy the entire area or most of the bottom area of the cylindrical container, and adjust the rotational speed of the cylindrical container so that the one circumferential speed is 2 to 30 m+/sin. Moreover, it is preferable to form a nickel thin film on the surface of the iron powder to be subjected to the copper coating treatment according to the present invention by electroless nickel plating treatment.

[Effect]

According to the present invention, rotation of the inclined cylindrical container around its axis creates a fluid state in which the iron powder in the bath collides with the cathode plate at the bottom of the bath in a high density and evenly. While the reduction and precipitation of copper ions in the plating solution is prevented, each iron powder particle that collides 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 is electroplated on the iron powder surface. In addition, since we are targeting iron powder with a relatively large particle size in the range of 10AI- to l+em, each iron powder has the effect of descending into the plating solution due to its own weight, and the rotation of the cylindrical container By setting the speed appropriately, a non-flowing region containing only the plating solution is formed above the flowing region of the iron powder, where the iron powder does not fly up. By immersing the anode in the upper zone containing only the plating solution, it is possible to avoid the iron powder from coming into contact with the anode, and as a result, the phenomenon of dissolving the iron powder and copper coating is also prevented, and the iron powder is completely absorbed. Copper plating is applied evenly to the surface of each grain. In addition, the thickness of the copper film to be plated can be arbitrarily and precisely controlled by the amount of current applied and the processing time, and the proper flow state of the iron powder that collides with the cathode plate can be controlled by setting it on the inner peripheral surface of the cylindrical container. The layer is well assisted by the baffle plate. moreover,
By configuring the device to be able to arbitrarily adjust the inclination angle and rotation speed of the cylindrical container, the flow state can be controlled more appropriately and easily.

When the iron powder used for this copper electroplating is subjected to electroless nickel plating as a pretreatment, it is possible to effectively prevent copper ions in the plating solution from being reduced by the iron powder. In other words, when iron powder is introduced into a plating solution in which 9w4 ions coexist, a displacement precipitation reaction occurs in which the iron powder dissolves in the solution and copper is precipitated due to the difference in ionization tendency. By forming it on the surface, it is possible to prevent the iron powder from dissolving. Even if electroless copper plating is performed instead of electroless nickel plating, the substitution reaction of iron elution from the powder and accompanying copper precipitation cannot be prevented, resulting in a porous film and failure to achieve good electroplating. , electroplating becomes possible by coating a large amount of copper with electroless copper plating, but because a large amount of waste liquid is generated from electroless plating,
The benefits of electroplating will be lost.

As a plating bath for electroplating, a copper pyrophosphate bath is recommended.A 6g acid copper bath or a copper borofluoride bath may dissolve even the pretreated iron powder, so good plating cannot be achieved. As mentioned above, iron powder plated with electroless nickel 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 birophosphate is dissolved is forcibly formed in an inclined rotating container, and this powder suspension flow is applied to the anode. The plating bath is cyclically collided with substantially the entire area of the cathode plate at the bottom of the container at a predetermined velocity component without substantially contacting the plating bath. By loading this cylindrical container with powder and tilting its center axis and rotating it around the axis, a fluid state is formed above the bath in which the powder in the plating bath repeatedly collides with the cathode plate, and the flow of the powder is A non-flowing region is formed above the bath, which is virtually unreachable, and an anode is disposed in this non-flowing region to perform copper electroplating on the surface of the iron powder. At that time! The suspension concentration in the flow region of the powder formed in the lower part of the plating solution is 30vol. % to 55vol. %
It is desirable that the flow area be within the range of 200 to 3000, and it is also necessary to form this flow region so that it does not come into contact with the anode plate. It is recommended that the powder suspension flow in this flow region collides with the cathode plate at a flow velocity of 2 areas/inch to 30 m/sin, which increases the circumferential speed of the container by 2 seconds per revolution.
/sin to 3 (Is/■In). This allows iron powder to be coated uniformly and with a high yield on each grain of iron powder, substantially regardless of the concentration of copper ions in the electroplating solution. Copper can be electroplated at a high yield of 90% or more.

In addition, by maintaining the state in which the entire area of the cathode plate is continuously exposed to the flow of powder, the cathode is exposed to the C in the liquid.
By preventing U ions from being electrolytically deposited and maintaining a state in which the flow region of the powder does not contact the anode,
The iron powder and the copper electrodeposited on its surface are also prevented from dissolving.

Note that the iron powder targeted in the present invention has a particle size of 10 μm or more. This is because if the particles are finer than this, they may fly up into the plating bath and float, causing problems such as not being plated or melting on contact with the anode. Although it will stop flying if you slow down the rotation,
This time, problems such as aggregation and precipitation on the cathode arise. Further, in order to maintain a dense collision state over the entire area of the cathode, the particle size does not need to be too large, so particles with a particle size of 1 mm or less are suitable for the method of the present invention. The circumferential speed when rotating the container should be 2 to 30 for the reasons mentioned above.
m/sin is appropriate, but on the other hand, if the speed is too high, the powder may be pressed against the inner wall of the container by centrifugal force and uniform stirring may not be possible, or the powder may fly up and come into contact with the anode and dissolve. If it is slower than this, problems such as precipitation on the agglomerates and cathode will occur due to insufficient stirring, so a circumferential speed within this range is appropriate. Note that if the particle size of the iron powder to be treated is small within the above range or the specific gravity is light, reduce the peripheral speed.

If the particle size of the iron powder is large or the specific gravity is heavy, it is better to increase the peripheral speed.In any case, the peripheral speed and inclination angle can be controlled depending on the characteristics of the iron powder to ensure stable flow around the cathode base at the bottom of the container. It is important to form layers.

FIG. 1 shows the main parts of an apparatus for carrying out the electroplating method of the present invention, including a cylindrical container L for containing treated iron powder and a plating solution.

A cathode plate 2 disposed at the bottom of the cylindrical container 1 in a direction perpendicular to the container axis, an anode 3 disposed near the surface of the plating solution in the cylindrical container 1, and a connection between the cathode plate 2 and the anode 3. and a power supply device 4 that applies a predetermined potential between the cylindrical container 1 and the cylindrical container 1. It is installed so that it can rotate around it. That is, the bottom of the container 1 is supported from the outside by a rotating shaft 5 at its center, thereby making the container 1 rotatable around the central axis, and a motor 6 that applies rotational power to the rotating shaft 5 is fixed to a base 7. do. By making the inclination of the base 7 adjustable with respect to the horizontal, the inclination angle of the container 1 is adjusted. Also, container 1
An idling roller 8 that rotates in contact with the outer periphery of the container 1 is provided to receive the load when the container 1 is tilted, and the load point of this idling roller 8 is also integrally connected to the base 7. The motor 6 is a variable speed motor, and can freely adjust the rotational speed of the container 1 around its axis. On the other hand, a baffle plate 9 is provided on the inner peripheral surface of the container 1 to promote the flow of the treated powder. This baffle plate 9 is shown in the example shown in FIG.

A plate protruding slightly inward in the radial direction from the inner wall of the container 1 is attached to the inner wall with its longitudinal direction along the axial direction of the container, as shown in FIG.
'Four pieces are installed at intervals.

By putting copper plating solution and iron powder into the electroplating apparatus configured in this way, and appropriately adjusting the inclination angle of the container 1 and the rotational speed of the motor 6 according to the loading amount and quantity ratio, the specific gravity difference can be reduced. Accordingly, the powder aggregate descending in the plating solution can be controlled to form an appropriate flow region 10 below the plating solution. That is, the powder flow area 1
0 constantly repeats collisions so as to cover the entire area of the cathode plate 2 while swirling and flowing due to the rotation of the container 1 and the stirring effect of the baffle plate 2, and no powder flies up into the upper region 11 of the plating solution. A steady state in which a swirling flow of only liquid is formed can be maintained. Once this steady state has been formed, the upper liquid 1 of the plating liquid where a swirling flow of liquid only is formed.
The anode 3 is placed on the plate 1, 1 electricity is started, electroplating is performed for a predetermined period of time, 9 the electricity is stopped, and the plated product is recovered. This recovery can be accomplished by rotating the base 7 to further tilt the container l and transferring the contents to another container.

Representative examples in which the method of the present invention was carried out using this apparatus are listed below.

[Example 1] Copper plating is performed using IP300A iron powder made by Kawasaki Steel Corporation shown in Table 1.First, as a pretreatment, 1k of the iron powder is applied.
g into a 2Il tall beaker and using a Tokyo Rikakikai Seiku C stirrer (DC-2RT model).

While stirring with a Teflon propeller, add hydrochloric acid 60-1 little by little for pickling.Next, after washing with water three times,
560r using a DC stirrer (DC-2RT type)
While stirring at pm, electroless plating is performed using an alkaline electroless nickel plating solution R TMP Chemical Nickel manufactured by Okuno Pharmaceutical Co., Ltd. Next, washing with water is performed three times.

On the other hand, as a plating solution, a copper pyrophosphate bath 1.51 having the liquid composition shown below is prepared.

Plating solution composition Copper birophosphate (CutP got 3) (to
) 29g/j! Potassium birophosphate (K, PO?
) 254g/j! Potassium citrate (KH
tC1sOヮ) 23 g/l This plating bath and the above-mentioned pretreated iron powder were loaded into the illustrated container 1, and
The plating process was carried out by rotating the container 1 at a circumferential speed of 9.1 m/sin using a motor 6 (ring cone RXM-40-GSM type manufactured by Shinpo Kogyo ■) at an inclination angle of 45 degrees.

At this time, the anode 3 used was a copper plate for copper pyrophosphate plating bath (tlP-CM47/-do, manufactured by Sumitomo Metal Mining), and the cathode 2 was made of stainless steel (SUS304) with a diameter of 110 m. The inner diameter of the container is 120 mm in diameter. Each baffle plate 9 has a height of 5II11 and a length of 120-1, which are provided on the inner wall of the container 1 at 90° intervals. DC power supply 4 has ■
5ANREXDCAUTO15300 manufactured by Sansha Denki Seisakusho
Plating was performed using a mold with a zero current flow of 260AH.

After plating was completed, it was washed with water, filtered under reduced pressure using a Buchner funnel, washed with ethanol, and dried in a vacuum dryer at room temperature by continuously drawing a vacuum with a water ring pump equipped with an ejector all day and night. The powder after drying weighed 1302 g. When this powder was analyzed, it was found to be 23.2wt and XCu. The current efficiency showed a high value of 98%. When this powder was sieved, +80 mesh was found to be 0.373%. This was an increase of only 0.33% compared to the raw material iron powder, and therefore almost no agglomeration was observed.

FIG. 3 shows a cross-sectional photograph of the obtained milling powder.

[Example 2] After degreasing 300 g of iron powder with a particle size of 20 μm and applying electroless copper-nickel plating in the same manner as in Example 1, plating was performed as described above using Takasago Seisakusho TM01B-3 type as a DC power source. Copper plating was performed using a device at a circumferential speed of 2II/1 inch. 257AH plating was performed using oxygen-free copper as an anode and using the following copper plating solution.

Plating solution composition HCI IJ 7 acid $M (CLl, P, O, ・3
HtO) 80g/l BiOIJ 7 acid power IJum (K
, Pt0t) 255g/j! ammonia water
4ml/1 Potassium nitrate (KNOs) 12g/j! Hereinafter, as a result of processing in the same manner as in Example 1, the powder after drying was 60%
It was 1g. Analyzing this powder.

It was 50.1wt, XCu. The current efficiency was as high as 99%.

[Example 3] After pre-treating 300 g of iron powder with a particle size of 0.7 mm in the same manner as in Example 2, it was processed in the same manner as in Example 2 except that the circumferential speed was set to 30 s/win using the device described above. Copper plated.

Thereafter, the powder was treated in the same manner as in Example 1, and the amount of powder after drying was 316 g. Analyzing this powder.

It was 5.1wt, XCu. The current efficiency showed a high value of 99%.

[Comparative Example 1] Next, for comparison, the results of plating according to the method described in Japanese Patent Publication No. 61-40319 are shown.
Put 500g of iron powder shown in the table into 12 tall beakers,
After pickling and electroless nickel plating in the same manner as in Example 1, the plating tank was placed in a plating tank equipped with a cathode on the bottom, and a plating solution with the same composition as in Example 1 was added. While stirring the powder with a Teflon propeller using a DC stirrer (model DC-2RT) manufactured by
AI+plating was performed. However, powder adhered to the cathode on the bottom and gradually became thicker, and the stirring propeller came into contact with the accumulated powder, making a grinding noise. After plating is completed.

There were 445 g of powder and 184 g of deposits on the cathode. The yield was extremely poor at 71%, and the powder contained plastic powder generated from the worn propeller, making it unusable.

[Comparative Example 2] The iron powder shown in Table 1 was pickled, and without applying electroless nickel.
When I tried to plate copper using M018-3 type,
The iron powder began to dissolve, and the plating solution suddenly became cloudy and decomposed.

[Comparative Example 3] The iron powder shown in Table 1 was pickled in the same manner as in Example 1, and then treated with high-speed electroless copper plating solution ROPC manufactured by Okuno Pharmaceutical Co., Ltd.
After electroless plating with ``Copper'' 1 When I tried to plate copper in the same manner as in Example 1 using Takasago Seisakusho TM018-3 as a DC power supply, the plating solution started to become cloudy and decomposed. It happened.

(Comparative Example 4) When electroplating the iron powder shown in Table 1 in the same manner as in Example 1 except that the plating bath was changed to a copper sulfate bath, iron was eluted from the powder and copper The substitution reaction of precipitation was so severe that electroplating could not be continued.

[Comparative Example 5] When electroplating was performed using the iron powder shown in Table 1 in the same manner as in Example 1 except that the plating bath was changed to a copper boride bath, iron was eluted from the powder and The accompanying substitution reaction of copper precipitation was so severe that electroplating could not be continued.

[Effects] 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 displacement deposition, and the life of one bath is long.
The generation of waste liquid is extremely small, and copper can be coated on iron powder at low cost. Furthermore, since it has a good fluidity and enables stable plating, the thickness of the plating and the amount of plating can be easily controlled by changing the amount of current applied. In addition, since a good and stable powder fluidity state can be maintained over the entire area of the cathode plate, there is no struggle such as powder aggregation or deposition on the cathode, and there is no melting of iron powder, so each particle of powder is Copper coating can be formed evenly.

Furthermore, by arranging a circular cathode that is considerably large relative to the area of the bottom surface of the container, powder does not adhere to the cathode, and a copper coating can be efficiently formed.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic sectional view showing the main parts of an example of a plating apparatus of the present invention;
FIG. 2 is a sectional view taken along line nn' in FIG. 1. FIG. 3 is a cross-sectional photograph showing the metal structure of the copper-coated iron powder obtained in Example 1. 1. Cylindrical container 1 2. Cathode 3. Positive irradiation. 4. Power supply device, 5. Rotating shaft, 6. Motor. 7. Range of motion.・Base. baffle board. lO・・Powder flow

Claims (3)

[Claims] (1) In a cylindrical container with a cathode plate on the bottom and a baffle plate on the inner peripheral wall, add a copper plating solution in which copper pyrophosphate is dissolved and nickel-coated iron powder with a particle size in the range of 10 μm to 1 mm. The cylindrical container is rotated around the axis with its central axis tilted, and this rotation creates a fluid state in which the iron powder in the plating bath repeatedly collides with substantially the entire area of the cathode plate. A copper bath characterized in that a non-flowing region is formed at the bottom and above the bath where the flow of iron powder does not substantially reach, and an anode is disposed in this non-flowing region and current is passed between it and the cathode plate. Method for producing coated iron powder. (2) The method for producing copper-coated iron powder according to claim 1, wherein the nickel-coated iron powder has a thin nickel film formed on its surface by electroless nickel plating. (3) The method for producing copper-coated iron powder according to claim 1 or 2, wherein the rotation of the cylindrical container is controlled so that the circumferential speed is 2 to 30 m/min.