JPH0351831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for applying a uniform electroplated coating to bundled carbon fibers.

In recent years, attempts have been made to coat carbon fibers used in fiber-reinforced alloys, fiber-reinforced sintered materials, conductive fillers for electromagnetic shielding, etc. with metals in order to improve their leakage with metals, synthetic resins, etc. I'm starting to be able to do it.

Possible methods for applying metal coating to carbon fibers include electroplating, electroless plating, vapor deposition, and high-temperature chemical coating, but carbon fibers are usually coated with a large number of filaments (for example, about 12,000). It forms a bundle of aggregates, and therefore, when viewed in this state, it has the following characteristics: it has a very large comparative area, it is a continuous fiber, and it has electrical conductivity. Considering these points, it can be said that the electroplating method is economically the most superior method for coating carbon fibers with metal.

By the way, to date, there have been almost no reports related to electroplating of carbon fibers, and there are only a few reports on carbon fibers electroplated with nickel or copper. The main focus was on the subsequent reaction between carbon fiber and metal, and was not concerned with research on the electroplating method itself. The electroplated carbon fiber shown therein was simply a small amount of carbon fiber coated with metal in a discontinuous manner.

As mentioned above, carbon fibers are usually made up of several thousand to 10,000 filaments with a diameter of about 8 μm, which are very thin, and are bundled together. Therefore, in this state, the surface area is smaller than the cross-sectional area. On the other hand, compared to metals, the electrical resistance is 2.7×10 ^-3 Ω・cm for the high-strength type and 1.8× for the high-elastic type.
10 ^-3 Ω・cm (for PAN carbon fiber), which is high, so it is not difficult to electroplat a small amount of carbon fiber discontinuously, but it is difficult to electroplat a large amount and continuously. It is extremely difficult to do so. That is, it is extremely difficult to continuously electroplat a carbon fiber bundle consisting of more than 10,000 filaments.

It tends to cause non-uniformity in cathode current density,
This is because there is a difference in coating thickness between the outside and inside of the fiber bundle, and a more important problem is that the filaments are crosslinked with each other due to the deposited metal.

From the above-mentioned viewpoint, the present inventors aimed to continuously coat each filament of a carbon fiber bundle with a uniform thickness of electrodeposited metal while leaving the carbon fiber bundle as it is. After conducting various tests and research, they discovered that these things become possible when the following conditions are met. That is, the bundle of carbon fibers loosens and spreads in the plating solution, and adjacent filaments do not come into contact with each other.

The plating current must sufficiently reach the inside of the carbon fiber bundle.

The plating liquid inside the carbon fiber bundle moves quickly and there is no difference in ion concentration between the inside of the carbon fiber bundle and the rest of the plating tank.

Carbon fibers must not be surface-treated.

Therefore, in order to perform uniform electroplating on individual bundles of carbon fibers on an industrial scale, the present inventors have conducted further research on a plating means that satisfies each of the above conditions. Oriented perpendicularly to the carbon fiber bundle that passes continuously through the plating liquid bath,
And when a plating liquid flow ejected from a plurality of arc-shaped slits provided at predetermined intervals along the length direction is made to collide with the carbon fiber bundle under the condition that the flow velocity at the ejection port is 0.1 m/min or more, The carbon fiber bundle loosens and spreads in the plating solution, making it possible to create a state in which adjacent carbon fiber filaments do not come into contact with each other. Therefore, the plating liquid inside the carbon fiber bundle is easily replaced with other plating liquid in the tank, eliminating the ion concentration gradient.
Since the cathode current density inside and outside of the carbon fiber bundle can be made uniform, each carbon fiber can be coated with a uniform metal, and adjacent filaments do not come into contact with each other, making it possible for individual filaments to They came to the knowledge that the bridging phenomenon of the filament caused by the deposited metal is prevented because of the vibration.

By the way, although carbon fiber conducts electricity as mentioned above, its volume resistivity is 2×10 ^-3 to 3×
Its electrical resistance is approximately 10 ^-3 Ω・cm, which is 10 ² to 10 ³ times higher than that of metals.

This means that carbon fibers can only carry a much smaller current than metals. In the measurements made by the inventors, in the atmosphere,
The allowable limit current value for the PAN type high-strength type (bundle of 6000 filaments) is only 1.5A, and the safe current value is 1A, and if a current exceeding 1.5A is passed, the carbon fiber may burn. It's coming. The greatest advantage of continuous electroplating is that it is highly productive and economical, but the fact that only 1A of current can be passed through 6K carbon fiber means that
If the effective electrolysis length is 30cm, the current density is
At 0.22 A/dm ² , for example, 11 minutes of plating is required to obtain a plating thickness of 0.5 μm, which may completely negate the economy, which is the greatest advantage of continuous plating. .

However, these problems can be solved by the following measures:
The problem can be satisfactorily solved by adopting (a) to (c).

(a) At the beginning of plating, plating is performed with a constant voltage, and after the specified current is reached, plating is performed with a constant current.

(b) Install multiple electroplating tanks and perform multi-stage electroplating.

(c) Connect electrical contacts to the inlet and outlet sides of the carbon fiber.
That is, they are provided on both sides of the plating tank.

Therefore, when implementing the continuous electroplating method for carbon fibers of the present invention, it is strongly recommended to also adopt the means shown in the above sections (a) to (c), especially the above section (a). It is.

Hereinafter, the effects obtained by the means shown in sections (a) to (c) above will be individually explained in detail.

Effects of the means in item (a) above: Since the carbon fiber before plating is not coated with metal, only a current of 1A can be passed in, for example, a 6K high-strength type. The carbon fibers are wetted with water to facilitate this. For this reason, although it is possible to flow a current slightly higher than 1A, it is still not possible to flow an unnecessarily large amount of current.

The allowable current value for unplated carbon fibers varies depending on the feeding speed of the carbon fibers, but is determined once various conditions are determined. Therefore, if constant voltage electrolysis is performed at a voltage corresponding to the allowable current value at this time, combustion due to heat generation of carbon fibers will be prevented,
Alternatively, even if combustion does not occur, the water adhering to the carbon fibers evaporates, and the impurities contained in the water solidify the carbon fibers, preventing them from spreading in the subsequent electroplating solution. It can be prevented.

As electrodeposition progresses, the resistance of the carbon fibers gradually decreases and the allowable current value increases, but with constant voltage electrolysis, a corresponding current flows.

In this way, constant voltage electrolysis is continued, and after reaching a predetermined current value, constant current electrolysis is performed.
This is because there is an appropriate current value suitable for controlling the plating thickness, the size of the plating tank, and the feed speed.

Effects of means (b) above: With one-stage electroplating, it is difficult to take advantage of the economy and productivity of continuous plating.

However, when continuous electroplating is performed in multiple stages,
Productivity will improve dramatically. for example,
If 3A of current can be passed through the 1st stage electric nickel metal, then 9A can be passed through the 2nd stage electric nickel, and an additional 15A can be passed through the 3rd stage electric nickel. be.

Effects of means (c) above: The electrical resistance of the carbon fibers is different between the inlet and outlet sides of the plating tank, and metal precipitation occurs on the carbon fibers on the outlet side, so the electrical resistance is lower on the outlet side. small.

Therefore, if electrical contacts are made from both the inlet and outlet sides of the plating tank, more than twice as much current can flow as compared to the case where electrical contacts are made only from the inlet side.

This invention was made based on the above knowledge, and includes a plating liquid jetting nozzle that is oriented perpendicularly to the carbon fiber bundle that continuously passes through the plating liquid bath.
and colliding a plating liquid flow ejected from a plurality of arcuate slits provided at predetermined intervals along the length with the carbon fiber bundle at a flow velocity of 0.1 m/min or more at the ejection port, After loosening this, electroplating is performed at a constant voltage at the beginning of electroplating, and at a constant current after reaching a predetermined current value.
This method is characterized by a method of forming a uniform electrodeposited metal coating on individual carbon fibers with high efficiency.

In addition, in the method of this invention, the flow velocity at the spout of the plating liquid flow jetted from the nozzle is set to 0.1.
The reason why the flow rate is set to be more than 0.1 m/min is that if the flow rate is less than 0.1 m/min, the carbon fiber bundle may not spread completely and adjacent filaments may cause cross-linking due to the deposited metal. This is because metal precipitation tends to hardly occur inside the carbon fiber bundle, and a flow rate of 0.5 m/min or more is desirable.

Furthermore, when carrying out the method of the present invention, it is recommended that the plating liquid bath be irradiated with ultrasonic waves to impart microscopic vibrations to the carbon fibers passing through the bath. By taking such measures, air bubbles that adhere to the carbon fibers and are brought into the plating bath are removed from the core carbon fiber surface, and the wettability of the carbon fibers is improved, plating defects are reduced, and more uniform plating is achieved. Metsuki becomes possible. Moreover, the carbon fibers vibrate violently in a microscopic manner, and the bridging phenomenon of the filament due to the deposited metal is suppressed more completely.

FIG. 1 is a schematic diagram showing the main parts of a continuous electroplating device for carbon fibers according to the present invention. The carbon fiber bundle 4 shown in FIG. In addition, what is shown with the code|symbol 5,5 is a dipping roll.

Moreover, FIG. 2 is a schematic front sectional view of the main part showing an example of a plating liquid jetting nozzle that spouts a plating liquid flow in a fan shape, which is used in the apparatus shown in FIG. 1, and FIG. It is a diagram. As shown in the figure, the plating liquid flow flows into the plating liquid jetting nozzle 2.
The carbon fibers are ejected from a plurality of arcuate slits that are oriented perpendicularly to the carbon fiber bundle 4 that passes continuously through the plating liquid bath and are provided at predetermined intervals along the length. The arrows from the plating liquid jetting nozzles shown in FIGS. 1 to 3 indicate the direction in which the plating liquid is jetted.

Now, in FIG. 1, the continuously fed carbon fiber bundle 4 is immersed in a plating liquid bath 3 by dipping rolls 5, 5, and electroplated while continuously passing through the bath. At that time, when a fan-shaped plating liquid stream is made to collide with the carbon fiber bundle 4 passing through the plating liquid bath 3 from the plating liquid jet nozzle 2, the carbon fiber bundle 4 is formed as shown in FIG. and as shown in FIG. 4 (FIG. 4 is a schematic diagram showing the part of the carbon fiber bundle immersed in the bath shown in FIG. The liquid flow loosens and expands the filaments, breaking the contact between adjacent filaments, and since the nozzle 2 is continuously provided with circular arc-shaped slits at regular intervals, the individual filaments experience macroscopic vibrations (oscillations). I will wake up. Therefore, at this point,
A uniform metal coating can be continuously applied by the plating current, and the bridging phenomenon of the filament due to the deposited metal can be effectively prevented.

Furthermore, in carrying out the method of the present invention, a plating tank 1 is used, for example as shown in FIG. It is preferable to do so.

This is because, in the absence of a current shielding plate, due to the high electrical resistance of carbon fibers, the carbon fiber bundles are not spread out in the areas near the inlet and outlet sides of the carbon fibers (in these areas, the carbon fiber bundles have not yet spread). ), preferential electrodeposition occurs, and there is a risk that carbon fibers will aggregate due to the crosslinking phenomenon caused by the deposited metal.
By providing a current shielding plate, the crosslinking phenomenon is completely eliminated, and the carbon fibers are fully expanded by the action of the liquid flow or both the liquid flow and the ultrasonic irradiation, and each filament is completely coated. This is because a uniform metal coating can be obtained. Note that the carbon fibers that have aggregated due to the crosslinking phenomenon will not loosen and spread even if they are subsequently exposed to a jetted liquid flow or irradiated with ultrasonic waves.

It goes without saying that when the plating liquid spout is located at the bottom of the plating tank, the anodes are preferably placed above and below the carbon fibers.

Next, the present invention will be specifically explained with reference to Examples.

Example 1 A PAN-based high-strength type 6K carbon fiber bundle that was not subjected to sizing treatment or acid treatment was prepared, and Ni plating was applied to it using a continuous electroplating device as shown in Fig. 6. .

First, details of the apparatus shown in FIG. 6 will be explained.

This continuous electroplating device is equipped with water-wet and energized tank 1.
1. Electrolytic degreasing liquid recovery tanks 12 and 14, Electrolytic degreasing tank 13, Washing tank (TW) 15, Pickling tank 16, Water washing energizing tank (DIW) 17, 20 and 23, Ni plating liquid recovery tank 18 and 22, Ni Plating tanks 19 and 2
1. Wetting/energizing tank 22, methanol substitution tank 24,
It is composed of an electrolytic degreasing liquid storage tank 25, a pickling liquid storage tank 26, a Ni plating liquid storage tank 27, a DIW storage tank 28, and an ethanol storage tank 29, and the carbon fiber bundle is unwound from the payout reel 30 and sent to the speed control motor 44. When the rotation of is transmitted through the transmission shaft, the feed/conductor rolls 32, 34, 36
and 38, and the rubber feed rolls 31, 33, 35, and 37 with high friction coefficients located above the rubber feed rolls press the feed roll surfaces to transfer the waste to each processing tank. . The feed rate can be adjusted by a speed control motor 44.

In the water-wet energizing tank 11, water is showered to facilitate handling of the carbon fibers.

Note that the feed rubber roll 31 is also showered with water in order to prevent broken carbon fibers from getting entangled with the feed rubber roll. Even so, some broken carbon fibers may become entangled with the feed rubber roll, so the feed rubber roll 31
A brush (not shown) is installed on top of the .

These methods are also adopted in the 17th section of the water washing energizing tank.

The water-showered carbon fiber bundle is placed in an electrolytic degreasing tank 1.
Degreased in step 3, two-stage Ni plating tank 19
After being plated in steps 21 and 21, it is washed with water, dried, and wound up with a take-up roll 39. In the electrolytic parts of the electrolytic degreasing tank 13 and the Ni plating tanks 19 and 21, plating liquid jetting pipes 45, 46 and 47 for spouting plating liquid from arc-shaped slits and ultrasonic vibrators 40, 41 and 42 are installed. has been
The carbon fiber bundle is expanded in the processing solution and subjected to microscopic vibrations. In addition, the code 43
The one shown is a dryer.

Further, the electrolytic degreasing liquid recovery tank 14, the washing tank 15, the pickling tank 16, the washing energizing tanks 17, 20 and 23, and the ethanol replacement tank 24 each use a shower system.

The process of applying Ni plating to 6K carbon fiber using the continuous electroplating device described above was summarized as follows.

Carbon fiber (6K) → water washing → electrolytic degreasing → water washing → neutralization → water washing → first stage Ni plating → water washing → alcohol substitution → drying.

The processing conditions were: carbon fiber feeding speed: 10 cm/min, electrolytic degreasing solution: an aqueous solution containing 30 g of NaOH at a temperature of 50°C, electrolytic degreasing current: 1 A (ampere), neutralizing solution: 1 %H ₂ SO ₄ aqueous solution, Ni plating liquid composition: Nickel sulfate...240g/, Nickel chloride...45g/, Boric acid...30g/, Ni plating PH: 4.0, Ni plating liquid bath temperature: 40℃, Current value: 1st The Ni plating tank in the first stage was 2A, and the Ni plating tank in the second stage was 2A.

In the Ni-coated carbon fibers produced under these conditions, each filament was completely and uniformly coated with Ni, and no crosslinking phenomenon due to electrodeposition was observed.

This Ni-coated carbon fiber had a Ni coating thickness of 0.5 μm and a specific volume resistivity of 4.2×10 ⁻⁵ Ω·cm.

Example 2 A carbon fiber bundle similar to that in Example 2 was prepared, and using part of the apparatus shown in FIG. 6, the carbon fiber bundle was subjected to NI plating treatment in the next step.

Carbon fiber (6K) → water treatment → first stage Ni plating → water washing → alcohol replacement → drying.

The processing conditions at this time were: Carbon fiber feeding speed: 30cm/min, Ni plating liquid: composition, pH and bath temperature were the same as in Example 1, current value: 1st stage Ni plating tank...4A, 2nd stage Ni plating tank 8A was.

The Ni-coated carbon fiber prepared under these conditions was
As shown in Figures a and 4b, each filament was completely and uniformly coated with Ni, and no crosslinking phenomenon due to electrodeposition was observed. Note that FIG. 7a is a 390x microscopic photograph of a cross section of the coated carbon fiber, and FIG. 7b is a 3900x microscopic photograph of the cross section of the coated carbon fiber.

This Ni-coated carbon fiber had a Ni coating thickness of 0.5 μm and a volume resistivity of 4.4×10 ⁻⁵ Ω·cm.

As described above, according to the present invention, it is possible to completely and uniformly coat the surface of each filament of a carbon fiber bundle with metal, and since no crosslinking phenomenon occurs due to electrodeposition, it is possible to coat the surface of each filament in a carbon fiber bundle continuously. , it is possible to mass-produce metal-coated carbon fibers of high quality at low cost, and the obtained metal-coated carbon fibers exhibit excellent properties as reinforcing fibers for composite materials or as conductive fillers for electromagnetic shielding. , industrially useful effects are brought about.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the main parts of a continuous electroplating device for carbon fibers according to the present invention, and Fig. 2 is a schematic front sectional view of the main parts showing an example of a plating liquid jet nozzle used in the method of the present invention. , FIG. 3 is a side view of the plating liquid jetting nozzle shown in FIG. 2, FIG. 4 is a schematic diagram showing the part of the carbon fiber bundle immersed in the bath shown in FIG. 1 viewed from above, and FIG. The figure is a schematic plan view of the main parts showing an example of a plating tank in which current shielding plates are installed on both sides of the anode, Figure 6 is a schematic diagram showing the continuous electroplating device for carbon fiber used in the example, and Figure 7 is FIG. 7a is a micrograph of a cross section of the Ni-coated carbon fiber obtained in the example.
Figure 7b is magnified 390 times, and Figure 7b is magnified 3900 times. In the drawings, 1... plating tank, 2... plating liquid jet nozzle, 3... plating liquid bath, 4... carbon fiber bundle, 5... dipping roll, 6... current shielding plate, 7
...Anode, 11...Water wet/energized tank, 12, 14...
... Electrolytic degreasing liquid recovery tank, 13... Electrolytic degreasing tank, 15
...Water washing tank (TW), 16...Pickling tank, 17,2
0,23...Washing energizing tank (DIW), 18,22
...Ni plating liquid recovery tank, 19, 21...Ni plating tank, 22...Wetting/energizing tank, 24...Ethanol replacement tank, 25...Electrolytic degreasing liquid storage tank, 26...Pickling liquid storage tank, 27... ...Ni plating liquid storage tank, 28...
DIW storage tank, 29... Ethanol storage tank, 30...
Payout reel, 31, 33, 35, 37...Feed rubber roll, 32, 34, 36, 38...Feed/
Conductor roll, 39... Winding roll, 4
0, 41, 42... Ultrasonic generator, 43... Dryer, 44... Speed control motor, 4
5, 46, 47...Metsuki liquid spout pipe.

Claims (1)

[Claims] 1 A plating liquid jetting nozzle has a plating liquid ejected from a plurality of arcuate slits that are oriented perpendicularly to the carbon fiber bundle that passes continuously through the plating liquid bath and are provided at predetermined intervals along the length direction. The liquid flow is made to collide with the carbon fiber bundle at a flow rate of 0.1 m/min or more at the spout to loosen it, and at the beginning of electroplating, a constant voltage is applied, and after reaching a predetermined current value, A continuous electroplating method for carbon fiber bundles characterized by electroplating with a constant current.