JPH1160974A - High frequency wave electroconductive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject electroconductive material having a light weight, also capable of dealing with a complex shape, excellent in electroconductivity in a high frequency wave region and in addition, low in electroconductivity in the region of the direct current and a low frequency wave by forming an electroconductive composition obtained by filling an electroconductive filler into s matrix material having an electric resistance of a prescribed value or higher. SOLUTION: This high frequency wave electroconductive material is composed of a formed material of an electroconductive composition material obtained by filling an electroconductive filter (suitably a short fiber filler having <=50 μm mean fiber diameter or a carbon black having <=500 nm primary particle diameter) to a matrix material having >=1×10<10> Ωcm electric resistance value (suitably, a thermoplastic resin such as a polytetrafluoroethylene), and has a frequency range in which electroconductivity thereof increases along with the elevation of the frequency. It is preferable to fill 3-150 pt.vol. electroconductive filler to 100 pts.vol. matrix material. It is possible to blend an additive such as an inorganic fibrous reinforcing material, an inorganic filler, a solid lubricant and a plasticizer as necessary to the objective electroconductive material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductor which exhibits low conductivity at direct current and low frequency and efficiently propagates high frequency signals. This is a car radio,
It can be used as a transceiver, an antenna of a transmitter / receiver that handles high-frequency signals such as mobile phones and satellite broadcasts, transmission cables, contact members, and transmission cables and connectors for high-frequency circuits such as personal computers.

[0002]

2. Description of the Related Art In recent years, the frequency band handled in the field of information equipment has been increasingly shifted to higher frequencies, and the processing speed of various information processing apparatuses has also become extremely high. Metal materials or alloy materials such as copper, titanium, and nickel are usually used for antennas, cables, and contact members that transmit these high-frequency signals. As the frequency increases, the high frequency current flowing through these conductors becomes more localized near the surface of the conductor as the frequency increases. As a result, the resistance increases due to the decrease in the effective area of the path, and the transmission efficiency decreases.

On the other hand, as a means for transferring a large amount of information such as video between independent devices, a method of connecting with a small number of signal lines using a high frequency by various modulation methods, for example, 14
A 4 MHz LAN or the like is used. A signal line such as a LAN may be connected between rooms or between buildings, and a potential difference of several hundred volts occurs between these independent devices when the grounding process is incomplete. In these devices, for safety, the power supply and the signal are separated from each other in terms of direct current, but sometimes the power supply is poorly insulated due to lightning surge or the like.
For example, in a railway vehicle, a holding bracket made of a strap is used for an antenna. In such a case, it is necessary for safety that the antenna and the power line are particularly reliably separated.

[0004] In an electric shock accident when the human body comes into contact with a conductor, if the frequency is low, current flows to an organ such as the heart, which is likely to be a fatal disaster. Because it flows, it is hard to be fatal. As described above, since the conductivity of the metal material increases as the frequency decreases, it is not a desirable material for safety.

[0005]

Conventionally, in order to solve this problem, transmission efficiency has been improved by using a cable in which a plurality of fine wires are bundled to increase the total surface area. However, this method not only increases the cost, but also has a limit in reducing the diameter of the thin wire, which is inadequate against the recent remarkable increase in the frequency.

[0006] Furthermore, miniaturization and densification of electric circuits have progressed, and miniaturization of not only cables but also signal transmission parts constituting signal transmission paths and transmission paths or antennas and the like and connection parts between signal generation parts or amplification members. Also, weight reduction is required.
However, at present, such connecting parts, such as antenna holders for mobile phones, use cut parts made of zinc die-casting, so that manufacturing costs are high and miniaturization is difficult. Problem.

[0007]

As a result of repeated studies to solve the above-mentioned problems, the present inventor can cope with a lightweight and complicated shape by using a material other than metal, and has excellent conductivity at high frequencies. On the other hand, it has been found that a high-frequency conductor having low conductivity in the direct current and low frequency regions is realized, and the present invention has been achieved.

That is, the high-frequency conductor according to the present invention comprises:
Electric resistance of resin, ceramics, etc. is 1 × 10 ¹⁰ Ωcm
A high-frequency conductor made of a molded product of the conductive composition material in which the above-described matrix material is filled with a conductive filler, and having a frequency range in which the conductivity increases as the frequency increases.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in more detail. The high-frequency conductor according to the present invention not only has excellent conductivity for high-frequency current, but also decreases in conductivity as the frequency decreases. Furthermore, since the shape is excellent, a complicated shape can be obtained at low cost. In general, the conductivity of a composite obtained by dispersing a conductive filler in an insulating matrix such as a resin is inferior to a metal material at direct current and low frequency current, and is insufficient for practical use. However, it has excellent conductivity at high frequencies.

Although the mechanism is not yet clear,
The following reasons are considered. The high-frequency current flowing through the conductor of the present invention flows through a fine conductive path formed by the conductive filler. More precisely, it flows near the surface of the fine conductive path. The surface area of the conductive path is determined by the filling amount (volume fraction) of the conductive filler and the particle diameter or fiber diameter. The fine wire of the wire for winding used in the communication equipment is at least 60 μm at the minimum, whereas, for example, the fiber system of a general carbon fiber is about 7 to 12 μm, and the total surface area in the same volume is three times. Up to 8 times. Further, the current path formed by the structure of the conductive carbon black is 100 times or more.

A major reason why a conductor made of a composite material of an insulating material and a conductive filler cannot exhibit sufficient conductivity at a direct current or a low frequency is that the electrical contact between the conductive fillers is insufficient and the conductive path is poor. The separation may be caused by the insulating matrix. However, in the case of a high frequency, it is considered that electromagnetic induction occurs between the current paths physically separated inside the matrix, thereby electrically coupling the current paths, and as a result, high conductivity is exhibited.

The conductor of the present invention has excellent conductivity at high frequencies, but has reduced conductivity at DC or low frequencies for the above-described reasons. This means that the present conductor has frequency selectivity, and is also effective in improving safety and reducing low-frequency noise. The high-frequency conductor of the present invention can be manufactured at a low cost while effectively securing an electric circuit even in a complicated shape by using a molding method suitable for the insulating matrix.

[1] Matrix Material The matrix material used for the conductor of the present invention has a resistance value of 1 × 10 ¹⁰ Ωcm or more (preferably 1 × 10 ¹² Ω).
cm or more, more preferably 10 ¹⁴ Ωcm or more), but a resin material is preferable because it is lightweight and inexpensive. Examples of the resin material include a thermosetting resin and a thermoplastic resin, and a thermoplastic resin is more preferable in terms of excellent moldability. Examples of the thermosetting resin include an epoxy resin, a phenol resin, and a melamine resin.

Examples of the thermoplastic resin include polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), and polyvinylidene fluoride (PVD).
F) fluoropolymers such as polyethylene, polypropylene,
Aliphatic polyolefins and alicyclic polyolefins such as polybutene and polymethylpentene, aromatic polycarbonate, polybutylene terephthalate, polyphenylene sulfide, various polyamides (nylon 6, 66, nylon 610, nylon MXD6, etc.), polyetherimide, polysulfone, Non-olefin resins such as polyethersulfone, polyetheretherketone, acrylic resin, styrene resin, modified polyphenylene ether, liquid crystalline polyester, and vinyl chloride.

Further, the flexural modulus is 5000 kg / cm ^2.
The following elastomer materials may be used. Neoprene rubber, chloroprene rubber,
Crosslinked elastomers such as nitrile rubber and fluorine rubber, various thermoplastic elastomers (olefin, styrene, ester, urethane, amide, fluorine, soft vinyl chloride, ethylene-vinyl acetate copolymer)
Is mentioned. One of these matrix materials may be used, or a plurality of them may be used in combination.

[2] Conductive Filler As the conductive filler used in the conductor of the present invention, a filler having a conductive property such as a particle, a flake, or a short fiber can be used. Specifically, aluminum, silver, copper,
Metal fillers such as zinc, nickel, stainless steel, brass and titanium, various carbon blacks, graphite (artificial graphite,
Natural graphite), glassy carbon particles, pitch-based carbon fibers, PAN-based carbon fibers, carbon-based fillers such as graphite whiskers, and conductive fillers such as metal oxide-based fillers such as zinc oxide, tin oxide, and indium oxide. Can be

In the case of metal oxide-based fillers which exhibit conductivity by generating excess electrons due to the presence of lattice defects, those having increased conductivity by adding a dopant may be used. For example, aluminum is used as zinc oxide, antimony is used as tin oxide, tin is used as indium oxide, and tin is used as a dopant. In addition, a composite conductive filler in which conductive tin oxide is formed on the surface of a potassium titanate whisker by coating a metal on a carbon fiber or the like can also be used. Among the conductive fillers, short fibrous fillers or carbon black are desirable.

The short fibrous filler has an electric resistance of 1 × 10
^It is preferably ⁴ Ωcm or less, preferably 1 × 10 ² Ωcm or less (more preferably 1 × 10 ⁰ Ωcm or less, particularly preferably 1 × 10 ⁻¹ Ωcm or less). Further, those having an average fiber diameter of 50 μm or less (preferably 20 μm or less, more desirably 15 μm or less) are desirable in that high-frequency conductivity is obtained by increasing the surface area. If the fiber diameter is larger than this, not only the surface area, that is, the conductive path is reduced, but also the distance between the dispersed fillers is too large, so that the electromagnetic coupling becomes difficult to occur and the conductivity is impaired. Further, it is preferable that the aspect ratio (fiber length / fiber diameter) of the fibers dispersed in the conductor be 5 or more (preferably 10 or more) because the conductivity is improved.

As carbon black, acetylene
Rack, furnace black, channel black, etc.
But the primary particle diameter is 500 nm or less,
100 nm or less, specific surface area is 10 to 200 m^Two/
g, pH 6 to 11. 100Kg / cm
^Two1 × 10 under pressure⁶Ωcm or less, preferably 1 × 10
^FourΩcm or less, more preferably 1 × 10^TwoΩcm or less
Those are preferred. The conductive filler of the present invention, the above-mentioned
One of these may be used, or two or more may be used in combination.
May be used.

The filling amount of the conductive filler is 0.1 to 300 parts by volume, preferably 1 to 200 parts by volume, more preferably 3 to 15 parts by volume with respect to 100 parts by volume of the matrix.
0 parts by volume. If the filling amount is less than this, the conductivity is insufficient, while if it is too large, the moldability and the mechanical strength of the molded body are impaired.

[3] Additional Components Additional components can be added to the conductor of the present invention as needed. For example, glass fiber, silica fiber, silica
Inorganic fibrous reinforcement such as alumina fiber, potassium titanate fiber, aluminum borate fiber, etc., organic fibrous reinforcement such as aramid fiber, polyimide fiber, fluororesin fiber, talc, calcium carbonate, mica, glass beads, glass powder, glass Inorganic fillers such as balloons, solid lubricants such as fluororesin powder and molybdenum disulfide, magnetic powders such as iron oxide, plasticizers such as paraffin oil, antioxidants, heat stabilizers, light stabilizers, and ultraviolet absorbers And various additives such as a neutralizing agent, a lubricant, a compatibilizer, an anti-fogging agent, an anti-blocking agent, a slip agent, a dispersant, a coloring agent, a bactericide, and a fluorescent brightener.

Further, the conductive filler and the additional component of the present invention have an affinity with a matrix material for the purpose of improving mechanical strength and preventing intrusion of moisture and other impurities into the interface between the matrix and the filler. Various surface treatments may be applied to enhance the surface treatment. For example, silane coupling agents, titanium coupling agents, higher fatty acids such as stearic acid and oleic acid, higher fatty acid glycerin esters, amides, higher fatty acid metal salts, higher alcohols, and various waxes can be used.

[4] Manufacturing Method of Conductor The manufacturing method of the conductor of the present invention is not particularly limited as long as it is a manufacturing method suitable for the selected matrix material. For example, when the matrix material is a thermoplastic resin, after previously mixing the thermoplastic resin and the conductive filler, a Banbury mixer, a roll, a Brabender,
A composite material can be produced by melt-kneading with a single-screw kneading extruder, a twin-screw kneading extruder, a kneader, or the like. Thereafter, the conductor can be obtained by molding using various melt molding methods. Specific examples include press molding, extrusion molding, vacuum molding, blow molding, and injection molding.

[0024]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. [Sample preparation method] Example 1 As a matrix material, a polybutylene terephthalate resin (PB manufactured by Mitsubishi Engineering-Plastics Corporation) was used.
T) Novadour 5010 (trade name) as a conductive filler, PAN-based carbon fiber (Vesfight HTA-C6-SR (trade name, manufactured by Toho Rayon Co., Ltd.): average fiber type 7)
[mu] m, cut length 6 mm, the resistance value 1.5 × 10 ^{over 3} [Omega] cm)
It was used. First, after mixing 65 parts by weight (45 parts by volume) of carbon fiber with 100 parts by weight of PBT resin, the mixture was melt-kneaded at 260 ° C. using a biaxial kneading extruder to obtain a pellet-shaped composition. Next, this was molded by an injection molding machine at a molding temperature of 270 ° C. and a mold temperature of 50 ° C.
A molded product of 0 mm × 100 mm × 2 mmt was obtained.

Example 2 Polyphenylene sulfide (PPS) resin (T4 (trade name) manufactured by Toprene Co., Ltd .: viscosity 2000 poise at 300 ° C.) 1
00 parts by weight, carbon fibers two Kkerukoto as the conductive filler (Toho Rayon Co., Besfite MC (trade name): Mean fiber system 7.8 .mu.m, cut length 6 mm, the resistance value 7.5 × 10 ^{over 5} [Omega] cm) 40 parts by weight (24 parts by volume)
A sample was prepared in the same manner as in Example 1 with the addition. The processing was performed at a kneading temperature of 280 ° C. and a molding temperature of 300 ° C.

Example 3 Polycarbonate (PC) resin (Iupilon H3000 (trade name) manufactured by Mitsubishi Engineering-Plastics Corporation)
100 parts by weight of carbon black (Denka Black (trade name) manufactured by Denki Kagaku Kogyo KK) 2 as a conductive filler
0 parts by weight (11.1 parts by volume) and 5 parts by weight (2.5 parts by volume) of graphite (CP / B (trade name) manufactured by Nippon Graphite Co., Ltd.) were added, and a sample was obtained in the same manner as in the example. . The processing was performed at a kneading temperature of 270 ° C. and a molding temperature of 290 ° C.

Example 4 Polyphenylene sulfide (PPS) resin (LD10 (trade name) manufactured by Topren Corporation: viscosity 10,000 poise at 300)
C) 100 parts by weight of nickel-coated carbon fiber as conductive filler (Vesfight M, manufactured by Toho Rayon Co., Ltd.)
C (trade name): average fiber type 7.8 μm, cut length 6 m
m, resistance value 7.5 × 10 ⁻⁵ Ωcm) to 40 parts by weight (24
(Volume part) and a sample was prepared in the same manner as in Example 1. Processing conditions are as follows: kneading temperature 280 ° C, molding temperature 300 ° C.
I went in.

Comparative Example 1 Aluminum was cut in the same dimensions as the following sample shape to obtain a sample for measurement.

[Method of measuring high-frequency signal transmission efficiency] 100 ×
From a 100 × 2 mmt sample, the cross section was 2 mm × 2 mm (± 0.1 mm) using a water-cooled diamond cutter.
mm) and a columnar sample having a length of 60 mm was cut out to obtain a measurement sample. At this time, the sample was cut so that the longitudinal direction of the sample coincided with the flow direction of the material during molding. next,
The sample was bridged between two electrodes fixed in parallel at 50 mm intervals, and the transmission efficiency of a high-frequency signal between the electrodes was measured. At this time, the sample was pressed so that the molding surface of the sample was sufficiently in contact with the electrode. Contact area between sample and electrode is 4
mm ² , the surface roughness of the contact portion between the electrode and the sample was 10 μm or less in ten-point average roughness (Rz). The pressing load on the electrode was 50 g per electrode, and the measurement was started one minute after the load was applied. 100 mV at various frequencies (100 kHz to 990 MHz) to the above one electrode
And the output from the other electrode was measured with a load of 50Ω. The measured value was obtained by converting the ratio between input and output to a dBV value. FIG. 1 shows measurement results in which the frequency (logarithmic scale) is plotted on the horizontal axis and the output is plotted on the vertical axis.

[0030]

As is clear from FIG. 1, the conductor of the present invention has excellent conductivity at high frequencies, and the conductivity decreases as the frequency decreases. This is completely opposite to the tendency of a general metal material to develop due to the skin effect. As described above, the cause is not clear, but the possible reasons are described below.

Although the conductive filler dispersed in the conductor forms a continuous conductive path to some extent, it is partially divided into an insulating matrix resin, and has an effect of preventing conductivity at low frequencies. In addition, of the contact part with the electrode,
A skin layer made of a resin formed on the conductor surface layer has the same effect. However, it is considered that as the frequency increases, the electromagnetic coupling occurs between the divided conductive paths, thereby improving the conductivity. Further, comparing Examples 2 and 4, when the same PPS is used for the matrix resin, the higher the melt viscosity of the resin, the greater the frequency dependence of the conductivity. This is thought to be because the higher the melt viscosity, the more likely the conductive filler is cut during kneading, and thus more electromagnetic coupling occurs between the separated conductive paths. This can be said to be excellent in safety since a communication system using a high-frequency signal between devices having a plurality of independent power sources can insulate them at a direct current or a low frequency.

It is generally said that a conductive path having a length of about 波長 wavelength of an electromagnetic wave is required for efficient electromagnetic coupling, and the frequency in the range of the embodiment is 4 to 400 cm.
Should be required. On the other hand, the path length formed inside the conductor of the present embodiment is considered to be at most about 2 cm, and it is easy to consider that electromagnetic induction is unlikely to occur. occured.

In this embodiment, only the measurement at a frequency of 1 GHz or less was performed. By analogy with this result, in the region of 1 GHz or more, conductivity superior to that of a metal material can be sufficiently expected. Further, it can be inferred that by adjusting the diameter and length of the conductive filler, the frequency characteristics of the conductivity can be controlled. Further, since the conductor of the present invention has not only the above-mentioned electrical characteristics but also excellent moldability as shown in the examples, it is possible to manufacture conductive parts having complicated shapes at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between frequency and conductivity of samples in Examples and Comparative Examples.

Claims (3)

[Claims] 1. A molded product of a conductive composition material in which a matrix material having an electric resistance value of 1 × 10 ¹⁰ Ωcm or more is filled with a conductive filler, and has a frequency range in which the conductivity increases as the frequency increases. High frequency conductor. 2. The high-frequency conductor according to claim 1, wherein the matrix material is a thermoplastic resin. 3. The high-frequency conductor according to claim 1, wherein the conductive filler is a short fibrous filler having a fiber diameter of 50 μm or less, or carbon black having a primary particle diameter of 500 nm or less.