KR20220028925A - Shielding compounds with highly electro conduntive carbon fiber using cobalt based reducing agent - Google Patents

Abstract

The present invention relates to a shielding compound which can be used for shielding electromagnetic waves of cables and includes highly conductive carbon fibers using a cobalt-based reducing agent. The shielding compound according to the present invention is a compound material including carbon fibers having a nickel plating layer formed on the surfaces thereof, and a polymer material mixed with the carbon fibers, wherein the carbon fibers are dipped in a plating solution containing a nickel salt, a complexing agent, a stabilizer and a cobalt-based reducing agent so that the same may be plated with a nickel plating layer on the surfaces thereof, and the compound material has a specific resistance of 2 x 10^-4 Ωcm or less. Since the shielding compound according to the present invention uses a cobalt-based reducing agent, it is possible to realize high conductivity by preventing an increase in specific resistance caused by a phosphorus (P) ingredient. It is also possible to carry out nickel plating at a high content, even when the plating is performed at a lower temperature for a shorter time as compared to the plating using a conventional reducing agent, thereby providing increased plating efficiency.

Description

Shielding compound with high conductivity carbon fiber using cobalt-based reducing agent {SHIELDING COMPOUNDS WITH HIGHLY ELECTRO CONDUNTIVE CARBON FIBER USING COBALT BASED REDUCING AGENT}

The present invention relates to a shielding compound, and more particularly, to a shielding compound to which a high-conductive carbon fiber using a cobalt-based reducing agent that can be used for electromagnetic wave shielding of a cable is applied.

Recently, almost all devices are equipped with electrical and electronic devices for generating, transmitting, and storing information, and improving their effectiveness as the latest devices. However, as the use of these electrical and electronic equipment increases, the electromagnetic interference between the devices increases, and eventually causes a great social problem of electromagnetic interference, and even the serious harm to the human body has been verified and aroused high interest. .

Electromagnetic waves are a form of energy generated by the use of electricity, and are called by various names depending on the size of energy ranging from radio waves, microwaves, infrared rays, ultraviolet rays, X-rays, and gamma rays. In particular, almost all modern devices are equipped with electrical and electronic equipment/parts for information processing generation, transmission, storage, etc., and as electrical and electronic equipment becomes more complex and redundant, signal quality deteriorates due to mutual electromagnetic interference or noise And concerns about device malfunction are increasing.

In general, a large number of antennas are included in a vehicle, and more antennas are required for a connected car or autonomous vehicle, and higher-spec shielding is required when Ethernet for high-speed communication is introduced into a vehicle. In other words, it is observed that the possibility of EMI shielding shortage due to the trend of electrification of automobiles is high, and therefore the importance of electromagnetic wave shielding is gradually increasing.

In addition, in recent years, as intelligent safety systems such as high-output electrical components and driving assistance systems (ADAS) are applied to improve the fuel efficiency of vehicles as well as to increase driver safety and convenience, the existing 12V electric system has reached its limit and is not applied to the 48V electric system. There is a growing need for this, and the increase in the amount of electromagnetic wave emitted due to the increase in power consumption also includes risks such as malfunction of electrical equipment, so the importance of electromagnetic wave shielding in automobiles is increasing.

The main factors affecting the electromagnetic wave shielding performance are complex factors such as frequency, material length, and cross-sectional area. In order to expect a sufficient shielding effect, it is related to low volume resistivity, that is, high electrical conductivity of the material.

Conventionally, as a high-conductivity carbon fiber manufacturing technology, carbon fiber nickel electroless plating was mainly used to attach a nickel-phosphorus (P) alloy in a metal plating solution to the carbon fiber surface. However, as the phosphorus (P) content in the alloy increases, the specific resistance On the contrary, there was a problem that the conductivity was increased as a factor of reduction.

On the other hand, highly conductive carbon fibers have excellent properties such as heat resistance, chemical stability, electrical conductivity, electromagnetic wave shielding flexibility, and the like.

Electroless plating is the most used method for manufacturing high-conductivity carbon fibers. In the case of electroless plating, it not only has an excellent shielding effect, but also has the advantage of forming a plating layer of a certain thickness on the fiber surface.

However, in the conventional electroless plating method (Korean Patent No. 10-0486962), the carbon fiber is nickel-plated by chemical reduction with a metal plating solution in which a metal salt, a reducing agent, and a complexing agent coexist, so that the nano-sized nickel- It was a method of improving the conductivity of carbon fibers by forming a film of a certain thickness by introducing a phosphorus alloy. However, as the phosphorus content in the alloy increased, the specific resistance increased, resulting in a decrease in the conductivity of the carbon fibers.

Therefore, in order to realize the electromagnetic wave shielding performance of a suitable level of shielding cable for automobiles to which carbon fiber is applied, a high-conductivity carbon fiber manufacturing technology is required to further lower the carbon fiber specific resistance of about 1×10 ^-3 (Ω cm) level. Do.

In addition, conventional shielding cables for automobiles have been manufactured by braiding or taping processes using metal wires or metal tapes, which have a problem in that flexibility is poor and heavy due to the use of high-density metal. In fact, recently, in the automobile industry, flexible cable materials are required to shorten the manufacturing process time of automobiles and improve worker convenience along with the development of low-cost cables to reduce manufacturing costs. In addition, the weight reduction of the cable, which accounts for about 10 to 15% of the total weight, is a key development.

In addition, as HV/HEV development is active in line with the global trend of degassing, in the case of internal combustion engines, the use of cables, which used to be about 5% (20kg) of the vehicle weight, is about 10~15% ( 40~45kg), which is used more than twice as often. Since this is directly related to fuel efficiency improvement as well as concerns about increased electromagnetic wave interference due to the increase in cable usage, it is essential to develop a lightweight shielded cable in addition to the existing metal shielded cable.

Republic of Korea Patent Publication No. 10-2018-0118948 (filed on October 5, 2018)

In order to solve the above problems, the present invention has been successfully completed by providing a high-conductivity carbon fiber using a cobalt-based reducing agent that does not contain phosphorus. After all, it is an object of the present invention to provide a shielding compound to which a high-conductivity carbon fiber using a cobalt-based reducing agent is applied.

In order to solve the above problems, the present invention is a compound material comprising a carbon fiber having a nickel layer formed on the surface and a polymer material mixed with the carbon fiber, wherein the carbon fiber is a nickel salt, a complexing agent, a stabilizer and a cobalt-based The nickel plating layer is plated on the surface by being immersed in a plating solution containing a reducing agent, and the specific resistance of the compound material may be 2 X 10 -4 Ωcm or less.

The shielding compound to which the high-conductivity carbon fiber according to the present invention is applied can have high conductivity by using a cobalt-based reducing agent to prevent an increase in specific resistance due to the phosphorus (P) component, and is shorter than using a conventional reducing agent. Even when plating at a low temperature and time, a high content of nickel can be plated, increasing the plating efficiency.

1 is a view showing the structure of a conventional automobile harness cable.
2 is a view showing the structure of a cable to which a high-conductivity shielding compound using a cobalt-based reducing agent according to the present invention is applied.
3 is a view for explaining the shielding principle of the high-conductive carbon fiber applied shielding cable according to the present invention.
4 is a view showing a manufacturing process of a shielding cable to which a high-conductivity shielding compound according to the present invention is applied.
5 is a view showing a shielding cable manufacturing process using a shielding compound according to the present invention.
6 is a diagram illustrating an induced voltage of a core wire generated by an impedance of a shielding material.
7 is a diagram illustrating an induced voltage generated in an inner core of a cable.
8 is a view showing the surface transfer impedance by the shielding material.

Advantages and features of the present invention, and a method for achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms.

Hereinafter, the technical features of the present invention will be described in detail with reference to the accompanying drawings.

The present invention provides a high-conductivity shielding compound using a cobalt-based reducing agent.

Specifically, the present invention can provide a high-conductivity carbon fiber shielding compound for plating nickel on carbon fibers by immersing the carbon fiber compound in a plating solution containing a nickel salt, a complexing agent, a stabilizer and a cobalt-based reducing agent.

In the present invention, as the nickel salt, which is a main component of the electroless nickel plating solution, NiSO ₄ ·6H ₂ O is preferable. This is because NiSO ₄ ·6H ₂ O has the effect of a fast plating rate at a low temperature. The reducing agent is preferably a cobalt (Co)-based reducing agent to which phosphorus is not added. This is because, unlike conventional reducing agents, the cobalt-based reducing agent does not contain phosphorus (P), and thus has an effect of preventing an increase in specific resistance due to the phosphorus component. Specifically, as the cobalt-based reducing agent, CoSO ₄ ·7H ₂ O or cobalt-ethylenediamine complex compound may be used. As the complexing agent, NaC ₆ H ₅ O7 may be used. When NaC ₆ HO ₇ is used as a complexing agent, a fast reduction rate of the salt can be suppressed. In addition, Pb(NO ₃ ) ₂ may be used as a stabilizer. When Pb(NO ₃ ) ₂ is used as a stabilizer, there are effects of preventing decomposition of the bath, preventing coarse nickel precipitation, and preventing precipitation of the plating bath.

In addition, the temperature of the plating solution is preferably 30 ~ 90 ℃. If the temperature is less than 30 ℃, the chemical reduction reaction is difficult to occur, and if it exceeds 90 ℃, the fiber surface may be damaged and the fiber itself may be burned.

In addition, in the present invention, the carbon fiber is preferably immersed in the plating solution for 1 to 30 minutes. Less than 1 minute is undesirable because the amount of nickel film formed on the fiber surface is small due to the autocatalytic reaction time being too short.

As described above, it is possible to control the thickness of the nickel plating film and the amount of nickel plating by controlling the plating solution temperature and the plating solution immersion time.

Before the carbon fiber compound is immersed in the plating solution, it may be activated with tin chloride (SnCl ₂ ) or palladium chloride (PdCl ₂ ).

By this process, tin or palladium nuclei are formed on the carbon surface, and these nuclei serve to catalyze metal precipitation.

In the present invention, the thickness of the nickel film plated on the surface of the carbon fiber compound is preferably 0.08 ~ 6.0㎛. If the thickness is less than 0.08㎛, it is difficult to measure electrical conductivity because the metal film is too thin, and there may be a problem in that it is difficult to protect the surface of the carbon fiber compound during plating. And if it exceeds 6.0㎛, the metal film is excessively thick, and not only loses the excellent properties of the carbon fiber compound, but also deteriorates workability, so it is not suitable.

In addition, the nickel content is preferably 5 to 60% by weight. If the content of nickel is less than 5% by weight, there may be a problem in that it is difficult to obtain even conductivity of the carbon fiber compound, and if it exceeds 60% by weight, there may be a problem of losing the properties of the fiber.

In addition, the specific resistance of the electroless-plated high-conductive carbon fiber compound is preferably 2 × 10 ^-4 Ωcm or less. If it exceeds 2 × 10 ^-4 Ωcm, it is difficult to use as a filler because the conductivity is too low.

Hereinafter, the present invention will be described in more detail through examples.

As the high-conductivity carbon fiber shielding compound of the present invention is applied, the structure of the cable made of a double of the existing copper or tin-plated annealed copper wire braided shield layer (Shield) and PVC jacket (Jacket) is a polymer and a shielding filler ( Conductive filler) can be replaced with a single structure of a mixed high-conductive carbon fiber shielding compound.

Figure 2 shows the structure of a shielding cable manufactured by the shielding compound to which the high-conductivity carbon fiber of the present invention is applied.

As shown in Figure 2, the cable has an insulator (Insulation, 20) formed on the outer surface of the conductor (Power Conductor, 10), and a shield comprising a carbon fiber compound on the outside of the insulator and a protection made of a jacket (Jacket) It has a structure of layer 30 .

3 is a view showing the shielding principle of a shielding cable made of a shielding compound to which a high-conductivity carbon fiber is applied.

As shown in FIG. 3 , an electromagnetic wave generated from an electromagnetic resource is reflected and absorbed by an EMI material, and a conductive filler contained in a polymer ), the shielding action can be effectively achieved.

4 is a view showing the conventional braiding process and the extrusion process of the shielding compound to which the high-conductivity carbon fiber according to the present invention is applied.

Here, instead of the metal annealed wire braiding process, which is the most severe bottleneck process (process speed 1 to 5 m/min) in the cable manufacturing process, when changing to the extrusion process (process speed 40 m/min) applying a high-conductivity carbon fiber shielding compound, the process line Productivity can be improved by increasing the ship speed.

5 is a view showing a shielding cable manufacturing process using a shielding compound according to the present invention.

According to FIG. 5 , a cable may be manufactured through a wire drawing process, a bunching process, an extrusion process, an irradiation crosslinking process, a taping process, and a sheath process.

The following table shows the types of shielding materials for cables.

division metal shield braid metal shielding tape high conductivity carbon fiber
shield high conductivity carbon fiber
shielding compound Shielding performance height lowness very high height material cost fluctuations fluid stable stable stable durability lowness lowness very high height weight very heavy lightness lightness very light productivity middle speed middle very fast

On the other hand, electromagnetic waves (or electromagnetic waves) generate electric and magnetic fields around them when electricity flows, and refer to waves that occur as the strength changes periodically. Disturbances may occur as a result.

Electromagnetic interference may occur naturally or artificially, and signal distortion occurs due to electromagnetic interference.

There are grounding technique, filtering technique, shielding technique, and electromagnetic wave absorption technique as countermeasures against electromagnetic interference, and the grounding technique or shielding technique is mainly used for power cables.

Shielding of EV/HEV cables means that the central conductor through which power flows is surrounded by another conductive material to reduce electromagnetic wave emission and increase immunity to electromagnetic waves.

6 is a diagram illustrating an induced voltage of a core wire generated by an impedance of a shielding material. Referring to FIG. 6 , in the cable shielding effect (SE), an induced voltage is generated in the inner core wire according to the value of the impedance of the shielding material.

7 is a diagram illustrating an induced voltage generated in an inner core of a cable. When the shielding effect is induced by applying the shielding material to the cable harness according to the principle as described above, since the shielding material of the cable is not completely shielded, the induced voltage is induced as shown in FIG. 7 .

Since this induced voltage applies an external electromagnetic wave with severe curvature to the inner conductor according to a change in the surface current, the surface impedance of the shield layer is a very important value. The shielding effect of the cable harness can be calculated using the surface transfer impedance value.

8 is a view showing the surface transfer impedance by the shielding material. As shown in FIG. 8, assuming that a current I flows through the shielding surface ΔX, since the shielding is not a complete shielding, an induced voltage ΔV is induced in the core wire. Using the above two variables, the surface transfer impedance Zt can be obtained as follows.

[Equation 1]

Next, R. Martin's surface transfer impedance equation is used to derive the relation between the surface transfer impedance Z _t and the shielding effect SE.

[Equation 2]

where K is Z _g /Z ₀₁ , Z ₀₁ is the characteristic impedance of transmission line #1, Z ₀₂ is the characteristic impedance of transmission line #2, Z _g is the impedance of the signal power source, l is the length of the cable, and is is the reflection coefficient, p ₁₁ is the reflection coefficient at the portion close to transmission line #1, p ₁₂ is the reflection coefficient at the portion far from transmission line #1, p ₂₁ is the reflection coefficient at the portion close to transmission line #2, p ₂₁ is the reflection coefficient at the far part of transmission line #2, ε is the relative permittivity around the cable conductor, d is the cable diameter, and h is the cable height above the ground.

The definition of cable shielding effectiveness is as follows.

[Equation 3]

,

,

The surface transfer impedance can be expressed as

[Equation 4]

,

,

로 나타낼 수 있다.or

can be expressed as

Converting the algebraic expression to the above formula, it becomes as follows.

[Equation 5]

Since the cable is used on the ground, the characteristic impedance Z _O1 of transmission line #1 is as follows.

[Equation 6]

When the periphery of the cable is filled with air, ε becomes 1, Z _O1 is about 50 Ω, and Z _O2 is about 30 Ω depending on the cable structure. Substituting this into the above equation,

[Equation 7]

It can be seen that the shielding effect SE and the surface transfer impedance Zt are inversely proportional to each other, and as the length l increases, the shielding effect gradually decreases.

As a material for shielding cables, materials with high conductivity and economical efficiency such as copper or aluminum are currently used.

The shielded cable of the cable is mainly used where a lot of electromagnetic waves are generated in a narrow space such as automobiles, aircraft, and ships, and in this special use case, high flexibility and light weight are required.

In the case of copper or aluminum, which are currently mainly used as shielding materials, problems occur due to low flexibility and heavy weight compared to high conductivity as a metal.

On the other hand, carbon fiber has high tensile strength and electrical conductivity because it is basically composed of more than 95% of carbon, and is a material with low weight due to low density and high flexibility due to low diameter.

The electrical conductivity of carbon fiber depends the most on the carbon content in the fiber when manufacturing carbon fiber. The more heteroatoms such as oxygen, nitrogen and sulfur in the carbon fiber, the more the electrical conductivity of carbon decreases. The electrical conductivity is reduced, and structurally, it is reported that anisotropic carbon fibers have higher electrical conductivity than isotropic carbon fibers.

Although carbon fiber itself has electrical conductivity, higher electrical conductivity is required depending on the purpose, which is sometimes given characteristics by using electrolytic and electroless plating methods.

Carbon fiber has been widely used as an adsorbent or a filling material to improve the properties of polymer materials due to its high strength and conductivity. Various methods for modifying the surface of carbon fibers have been proposed because the bonding strength with carbon fibers is increased, so that the physical properties of the composite material are improved or the adsorption properties are improved.

The conventional invention is a technology that can significantly improve conductivity by significantly lowering the specific resistance of carbon fibers through nickel electroless plating surface treatment. Existing reducing agents including phosphorus (P) such as sodium hypophosphite and monohydrate (NaH ₂ PO ₂ ·H ₂ O) have been mainly used, but as nickel is coated, phosphorus remains and increases the resistivity. Accordingly, by replacing the reducing agent with a cobalt-based reducing agent such as CoSO ₄ ·7H ₂ O or Tris(etheylenediamine) cobalt(III) chloride complex, it is possible to reduce the increase in specific resistance and manufacture high-conductivity carbon fibers. In addition, it is possible to introduce a high content of nickel in a shorter time and a lower temperature condition than using a conventional reducing agent, thereby improving the efficiency of metal plating.

The table below shows the improvement of nickel introduction efficiency and reduction of specific resistance according to the use of a cobalt-based reducing agent.

No. reducing agent hours (minutes) temperature( ^o C) Nickel content (%) Specific resistance (Ω cm) One Cobalt-ethylenediamine complex One 30 5 9.18×10 ^-5 2 10 60 35 3.37×10 ^-5 3 20 30 40 2.20×10 ^-5 4 25 40 45 1.83×10 ^-6 5 30 40 50 1.82×10 ^-6 6 10 90 40 2.81×10 ^-5 7 NaH ₂ PO ₂ 30 50 3 0.81×10 ^-3 8 30 80 4 0.92×10 ^-3

As can be seen in the above table, when a cobalt-based reducing agent is used, it can be seen that the nickel content is increased even when plated at a lower temperature and a shorter time than carbon fibers plated with nickel using a reducing agent including phosphorus. In addition, when comparing conditions No. 1 and No. 8, similar nickel content ratios are shown, but the specific resistance of the nickel-plated carbon fiber prepared in Condition No. 1 using the cobalt-based reducing agent is lower than that of Condition No. 8. indicates

In order to improve the electrical conductivity of carbon fibers by metal coating, high conductivity carbon fibers can be manufactured without using other metals and other expensive chemicals, thereby securing economic feasibility. In addition, since a special process is not added or changed in the coating process, it is easy to manufacture, so that it can be quickly introduced into the market when the technology is commercialized.

In the present invention, it is possible to provide a high-conductivity shielding material for electromagnetic wave shielding using a cobalt-based reducing agent that satisfies the following conditions.

- Shield thickness ≤ 0.5 mm

- Electromagnetic shielding rate > 40 dB (@510kHz~3MHz) (ISO 14572 & IEC 62153-4-6 standard)

- Oil resistance: 50℃ ISO 6722 standard

- Flame retardant: Satisfies JASO D618 standard

On the other hand, by using the high-conductivity shielding compound according to the present invention, it is possible to manufacture a carbon fiber shielding cable for automobiles.

<Wire design table> nominal
cross-sectional area
㎟ 　　　　　　 body insulator
thickness
mm (ⓑ) Isolation
outside diameter
mm (ⓒ) conductor resistance
(20℃)
Ω/km composition
Minsu / So Seon-kyung
No./mm (ⓐ) calculate
cross-sectional area
㎟ outside diameter
(Approx.) mm 3 119/0.18 [TA] 3.0282 2.4 0.75 3.9 5.65

For the insulator applied in manufacturing the wire, XLPE (Cross-linked polyethylene) material for high voltage for automobiles (125℃) can be used, and PVC (polyvinyl chloride) material (95℃) for sheath can be used.

Carbon fiber 3K, 6K, and 12K were applied to braid the fabricated wire and compare the comparison before and after plating. MCF Metal Coated Carbon Fiber 3K & 6K & 12K was applied and braiding was carried out by applying 16 braiding machine.

In the case of general carbon fiber, the sizing material is reported as 1wt%, so MCF also used 1wt% sizing. During wet plating, damage to the fiber due to chemicals and breakage of the carbon fiber due to current during plating, so 1wt% of It is considered that the sizing material cannot reduce the occurrence of fluff. Therefore, in order to proceed with braiding for electric wires, it was determined that braiding was possible only when the sizing was 5 wt% or more, and this was carried out.

When braiding, the braid density was maintained at a level of 90% or more. In the case of high voltage cables for automobiles, it is stipulated that the density of the shielding should be maintained at 90% or more. This is because, when the shielding density is low, electromagnetic waves may be emitted or introduced to the outside through a hole in the braid to give an abnormal signal.

Calculation of shielding density was carried out based on the table and formula below.

D Insulation outer diameter [mm]

D' Braided strand core diameter [mm] D1 Braid (layer) outer diameter [mm] P braid pitch [mm] α Braid (angle between cable longitudinal axis and braid) [˚ ] W Fiber width [mm] C Number of carriers (or number of strokes)

Length of braid required per 1 pitch [mm] F filling factor
(Filling factor: the extent to which the surface of the electric wire is covered by the braided element in one direction) B optical braid density [%]

[Equation 8]

,

,

,

,

In this case, the width of the carbon fiber was determined by observing the width of the carbon fiber before braiding under a microscope.

As described above, a carbon fiber shielding wire can be manufactured.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Accordingly, the embodiments disclosed in the present invention are for explanation rather than limiting the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these embodiments.

Therefore, the protection scope of the present invention should be interpreted by the following claims rather than being limited by the above-described embodiments, and all technical ideas within the equivalent range should be interpreted as being included in the scope of the present invention.

10: conductor 20: insulator
30: protective layer

Claims (1)

As a compound material comprising a carbon fiber having a nickel layer formed on the surface and a polymer material mixed with the carbon fiber,
The carbon fiber is immersed in a plating solution containing a nickel salt, a complexing agent, a stabilizer and a cobalt-based reducing agent so that the nickel plating layer is plated on the surface,
The specific resistance of the compound material is a shielding compound to which high-conductivity carbon fiber is applied using a cobalt-based reducing agent, characterized in that less than 2 X 10 ^-4 Ωcm.

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