JP2009212189A - Radiowave absorber using fine carbon fiber-containing resistance coating having capacitive susceptance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiowave absorber, using a resistance coating having a capacitive susceptance, which is thinner than a conventional radiowave absorber using a resistance film and can be easily designed and manufactured. <P>SOLUTION: The radiowave absorber can be manufactured by coating a base material such as paper and a resin plate with a fine carbon fiber-dispersed resin solution, includes the resistance coating having the capacitive susceptance, and can absorb frequencies in a GHz-band region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a radio wave absorber for GHz band using a resistive film having a capacitive susceptance using fine carbon fibers, and particularly to a radio wave absorber useful in the millimeter wave band region.

In recent years, high-speed processing of electronic devices is accelerating, and the operating frequency of ICs such as LSIs and microprocessors is rapidly increasing, and radio waves that affect other electronic devices are likely to be emitted. . On the other hand, with the spread of high-speed and large-capacity communication, electronic devices are susceptible to malfunctions due to the influence of these communication radio waves or their reflected waves.

In the communication field, multimedia mobile communication using 1.5 GHz and 2.0 GHz radio waves, indoor wireless LAN communication using 2.4 GHz and 5.2 to 5.8 GHz radio waves, 22 GHz, 26 GHz or 38 GHz radio waves The use of FWA wireless LAN communication, high-speed communication networks using optical fibers, etc. is expected to be rapidly spread or spread.

In the ITS (Intelligent Transport System) field, an ETC system (electric toll collection, automatic toll collection system) using 5.8 GHz radio waves was introduced, and in the future AHS (driving support road system) using 60 GHz and 76 GHz radio waves. Is expected to be introduced in earnest.

In this way, the use of radio waves in the GHz band region has progressed in various fields, and in the future, an environment in which radio waves in the millimeter wave band region are particularly actively used is assumed. Therefore, EMC (Electro- Magnetic compatibility (electromagnetic compatibility), that is, individual devices do not emit radio waves that affect others (emission issues), and electronic devices operate normally without being affected by external radio waves (immunity issues) There is a strong demand for an electromagnetic environment.

In order to construct an electromagnetic environment suitable for EMC, the existence of a material (radio wave absorber) that can absorb unnecessary radio waves and reduce reflected waves as much as possible is essential. It has been actively conducted and reported.

A radio wave absorber refers to a material that converts most of the energy of an incident radio wave into heat energy inside the radio wave absorber. The types of radio wave absorbers are roughly classified into magnetic radio wave absorbers, dielectric radio wave absorbers, and radio wave absorbers using resistance films, depending on the absorbing material used.

A typical absorbing material used for the magnetic wave absorber is ferrite. A material having magnetism such as ferrite is the same as a state in which an electric current flows through a small coil because the internal electrons are spinning and the electrons have electric charges. When a current flows through the coil, it corresponds to the presence of an electromagnet, so that a lot of micromagnets exist in the absorbing material. When an AC magnetic field is applied to the material in such a state from the outside, the state is the same as a state in which another large electromagnet is placed outside. Therefore, the micromagnet inside the magnetic material changes direction in the direction of the added external magnet. In this case, in the low frequency external magnetic field, the magnetic moment of the micro magnet inside the magnetic material also changes its direction in the direction of the applied magnetic field, so it does not resist the change of the external magnetic field. Does not occur. However, as the frequency is gradually increased, a time delay occurs in the change of the minute magnet, and the direction of the magnetic moment of the minute magnet does not change in the same direction as the direction of the external magnet. These appear as electrical resistance equivalently, and the magnetic wave absorber absorbs radio waves. This is the radio wave absorption principle of the magnetic radio wave absorber. As the frequency is further increased, the micro magnet no longer follows the direction of the external magnetic field, and in this state, no electrical resistance appears. For this reason, a radio wave absorber using a magnetic material as an absorbing material has a drawback in that there is a limit to the applicable frequency range because of its large frequency characteristics.

For example, when a magnetic wave absorber is used as a wave absorber in the GHz band region, an electrically insulating organic substance and a loss material such as a spinel crystal structure soft magnetic metal material or carbon material are combined with rubber or resin. Sheets are being considered. However, the relative permeability of the soft magnetic metal oxide material having a spinel crystal structure rapidly decreases in the GHz band according to Snake's limit law. Therefore, the limit frequency as a radio wave absorber is several GHz. For soft magnetic metal materials, the radio wave absorption characteristics can be extended up to about 10 GHz by the effect of suppressing eddy current and the effect of shape magnetic anisotropy by making the particle thickness flattened below the skin depth. However, it cannot be applied to a higher frequency GHz band region, particularly a millimeter wave band region. In addition, radio wave absorbers using these magnetic materials use materials with a large specific gravity as the absorbing material, making it difficult to produce lightweight radio wave absorbers. It cannot meet the demand for weight reduction.

Dielectric wave absorption in which carbon-based materials such as graphite, carbon black, carbon fiber, and carbon nanocoil are dispersed in electrically insulating organic materials such as rubber and resin There is a body.

A dielectric wave absorber is a dielectric material in which a resistive material is dispersed in a lossless dielectric. A dielectric wave absorber can be designed using transmission line theory by representing a dielectric material with an electrical equivalent circuit. In transmission line theory, a dielectric material in which a resistive material is dispersed in a lossless dielectric is considered as a circuit in which the resistance of the resistive material itself and the capacitance between the resistive materials are combined in a complex manner. When an electric field is applied to this material, current does not flow at low frequencies, so there is almost no heat generation due to resistance. However, as the frequency increases, the impedance of the capacitor decreases in inverse proportion to the frequency, so that a current also flows through the resistor, and heat is generated inside the dielectric material. This phenomenon is the principle of radio wave absorption in the dielectric radio wave absorber, and as a result, radio wave energy is converted into heat energy, so that radio wave absorption is possible. However, when a carbon material such as graphite powder, carbon black, carbon fiber, or coiled carbon fiber (carbon nanocoil) is used as the resistive material, the absorption material has a small aspect ratio and is required to have low conductivity. In order to develop dielectric properties, a large amount of absorbing material and a certain amount of thickness are required. However, it is still not sufficient as a radio wave absorbing performance in the GHz band region, particularly in the millimeter wave band region.

A wave absorber using a resistive film is 376.7Ω (367.6Ω in vacuum and in air), which is a plane wave wave impedance at a position away from a metal plate by λ / 4 (λ is the wavelength in the spacer). It is a radio wave absorber in which a resistive film is disposed, and is called a λ / 4 type radio wave absorber (see, for example, Patent Document 1).

The reason why the surface resistivity of the resistive film used for the λ / 4 type wave absorber is 376.7Ω (367.6Ω in vacuum and in air) and the thickness of the spacer is limited to λ / 4 is shown below. . In other words, the λ / 4 type wave absorber is a wave absorber in which a resistive film is disposed on the front surface of a metal plate through an ε · γ spacer at an interval of d = λ / 4. This is a transmission line wave theory. In this case, the input impedance Z · L ′ in which the metal plate is expected from the slightly metal plate side of the resistance film is Z · L ′ = Z0 · tanh (j · (2πd / λ) · (ε · γμ · γ) 1 / 2). Therefore, the input impedance Z · L estimated from the front surface of the absorber in consideration of the resistance film is a parallel circuit of Z · L ′ and the surface resistance value R of the resistance film, so that Z · L = Z · L ′. R / (Z · L ′ + R). Therefore, the reflection coefficient R · can be calculated as Γ · = (Z · L−Z0) / (Z · L + Z0) using this Z · L. Therefore, by solving for d and R introduced from Γ · = 0, that is, Z · L = Z0, a λ / 4 type wave absorber can be designed using the dielectric constant ε · γ of the spacer as a parameter. This is because when the spacer is air, this solution is R≈367.6Ω and d = λ / 4.

A radio wave absorber using a resistance film was put into practical use in the 1940s, and the original resistance film was made of paper into which oil black was injected. Since then, many wave absorbers have been put into practical use, such as the development of resistance fabrics woven with conductive fibers and polyester yarns, and carbon fiber resistors. In recent years, along with the development of display elements such as transparent touch panels and electroluminescence elements, transparent conductive films having both transparency and conductivity have been developed, so that technology has been applied to radio wave absorbers, and transparent radio wave absorbers are practical. (For example, refer to Patent Document 2).

As an absorbing material used in a λ / 4 type wave absorber using a transparent resistance film, indium oxide (hereinafter referred to as ITO) is the most efficient absorbing material. In this λ / 4 type wave absorber, polyethylene terephthalate (hereinafter referred to as PET) is used as a base material, and an ITO film is formed on a PET sheet by vacuum deposition, sputtering, ion plating, or the like.

However, the electrical properties of the resistive film are resistive films that do not have inductive or capacitive susceptance. Therefore, the surface resistivity of the resistance film is 367.6 Ω / □, and the thickness of the spacer is λ / 4, so there is no design freedom. In addition, ITO, which is an absorbing material, is insecure due to material depletion, and the manufacturing method is also a vacuum deposition method, so that it becomes an expensive radio wave absorber. Further, the electromagnetic wave absorption performance in the millimeter wave band region is not sufficient.

Therefore, the use of fine carbon fibers with low specific gravity, high aspect ratio, and high conductivity as an absorbing material for producing radio wave absorbers having good absorption characteristics in the GHz band region, particularly the millimeter wave band region, has been devised. In addition, studies on radio wave absorbers using this fine carbon fiber as an absorbing material have been actively conducted.

Although fine carbon fiber is a material that is difficult to be uniformly dispersed and mixed by mixing with a resin or the like, it has been reported as a dielectric wave absorber by controlling the dispersion state (for example, patent document) 3-6).

The example of the electromagnetic wave absorber which used the fine carbon fiber as an absorption material is shown. In Patent Document 3, a resin composite containing 1 to 10 parts by weight of carbon nanotubes having a diameter of 1 to 100 nm and a length of 50 μm or less is used as a radio wave absorber, and 37 dB (9.5 GHz, thickness 1 mm), 27 dB (2.7 GHz). , Thickness 0.8 mm), and a return loss of 30 dB (2.1 GHz, thickness 0.8 mm) has been reported. Patent Document 4 discloses a radio wave absorber containing a three-dimensional network-like fine fiber structure, and depending on the amount added, 22.2 dB (7.7 GHz, thickness 11.4 mm), 23 dB (5.1 GHz, thickness 3). 0.5 mm), 29.7 dB (5 GHz, thickness 3.7 mm), and 23.7 dB (6.4 GHz, thickness 3.5 mm) are reported to have been obtained. Patent Document 5 discloses a radio wave absorber containing a three-dimensional network-like fine carbon fiber structure. Depending on the amount of addition, 21 dB (2 GHz, thickness 4.8 mm), 24 dB (8 GHz, thickness 4.8 mm), 38 dB. It has been reported that return loss of (10 GHz, thickness 4.8 mm), 36 dB (15 GHz, thickness 4.8 mm), and 55 dB (20 GHz, thickness 4.8 mm) was obtained. Patent Document 6 uses, as a radio wave absorber, a resin composite such as polyester containing 20 parts by weight of carbon nanotubes or iron-encapsulated carbon nanotubes encapsulating or encapsulating alkali, alkaline earth metal, rare earth, or group VIII metal, It has been reported that the return loss of 28 dB (16 GHz, thickness 1 mm), 34 dB (10 GHz, thickness 1.5 mm), and 27 dB (7 GHz, thickness 2 mm) was obtained.

The dielectric wave absorber described in Patent Document 3 uses carbon nanotubes having a diameter of 1 to 100 nm and a length of 50 μm or less, but the thickness of the absorber is also 1 mm, and the limit frequency is 10 GHz. It is not a radio wave absorber using a resistive film having capacitive susceptance.

The dielectric wave absorbers described in Patent Documents 4 and 5 use a three-dimensional network-like fine carbon fiber structure having high absorption characteristics, and exhibit high absorption characteristics when added in a small amount. However, its limit frequency is 20 GHz. It is not a radio wave absorber using a resistive film having capacitive susceptance.

The supporting technique used for the radio wave absorber described in Patent Document 6 is extremely difficult, and the detached supporting material and the carbon nanotubes are aggregated, and the radio wave absorption performance is deteriorated. In particular, metals are very small and thus are easily oxidized, and the radio wave absorption performance is reduced accordingly. These desorption and oxidation can be solved by encapsulating the support material in carbon nanotubes, but the yield is extremely low.

As a report of a radio wave absorber using fine carbon fibers, a report of a radio wave absorber using a resistance film containing fine carbon fibers has also been made (see, for example, Patent Document 7).

Patent Document 7, which describes a radio wave absorber using a resistance film containing fine carbon fibers, describes an electromagnetic wave absorbing coating composition containing carbon nanotubes, a resin and a solvent as a PET sheet which is an insulating layer (spacer). Λ / 4 type wave absorber prepared by applying to one or both sides of aramid paper, alumina-added acrylic resin sheet or barium titanate-added acrylic resin sheet, 8 dB (42 GHz, resistance film thickness 40 μm, spacer Resistive film is formed on both sides, spacer type: PET sheet, spacer thickness 0.075 mm), 8.2 dB (48 GHz, resistive film thickness 40 μm, resistive film is formed on both sides of spacer, spacer type: aramid Paper, spacer thickness 0.05 mm), 27.5 dB (10 GHz, resistance film thickness 4 μm, resistance film is formed on one side of spacer, spacer type: Alumina-added acrylic resin sheet, spacer thickness 0.5 mm, no reflection layer, 23 dB (17 GHz, resistance film thickness 40 μm, resistance film on both sides of spacer , Spacer type Alumina-added acrylic resin sheet, spacer thickness 0.5 mm), 36 dB (20 GHz, resistance film thickness 15 μm, resistance film formed on one side of spacer, spacer type: barium titanate 30% by volume Addition acrylic resin sheet, spacer thickness 0.5 mm, reflective layer copper foil), 21 dB (42 GHz, resistance film thickness 10 μm, forming a resistance film on both sides of the spacer, type of spacer: alumina-added acrylic resin sheet, spacer Has been reported that a return loss of 0.5 mm was obtained. . However, this radio wave absorber does not show high radio wave absorption characteristics when a PET sheet or aramid paper, which is a general spacer, is used. When an acrylic resin sheet containing inorganic components such as alumina and barium titanate is used for the spacer, radio wave absorption characteristics are obtained by forming a resistive film on one or both sides, but an inorganic component with a large specific gravity. Since the sheet | seat which contains is used, a lightweight electromagnetic wave absorber cannot be obtained. Moreover, when forming a resistive film on both surfaces, manufacturing difficulty is required. Furthermore, since this wave absorber is a λ / 4 type and is not a resistive film having a capacitive susceptance, the surface resistivity of the resistive film must be 376.7Ω / □, and the thickness of the wave absorber is also λ. Limited to / 4.

In general, a radio wave absorber exhibits radio wave absorption performance by utilizing any of magnetic, dielectric, and resistive properties of the absorber. However, it may not be possible to become a radio wave absorber that satisfies recent needs by only using any of the characteristics of the absorbing material. Therefore, in recent years, studies have been made on improvement of a radio wave absorber using a resistance film, and a radio wave absorber having a dielectric film (capacitive or inductive) added to the resistance film has been developed and reported (for example, Patent Document 8, (See 9, 10)

That is, in a radio wave absorber using a resistive film, the thickness of the radio wave absorber can be made thicker or thinner than λ / 4 by controlling the complex amount (real part and imaginary part) of the surface resistance value of the resistive film. . In other words, by setting the real part and imaginary part of the sheet resistance value to positive values, it is possible to obtain a radio wave absorber using an inductive resistance film, and a radio wave absorber that is thicker than a λ / 4 type radio wave absorber. I can do it. In addition, by setting the real part of the sheet resistance value to a positive value and the imaginary part to a negative value, it becomes a radio wave absorber using a resistive resistive film, and is thinner than the λ / 4 type radio wave absorber. I can do it.

In Patent Document 8, a radio wave absorption in which ferrite is arranged in a pattern inside an exterior material, and an impedance adjustment member is disposed between the exterior material and the ferrite so as to have a capacitance in a low frequency region and an inductivity in a high frequency region. There is a report of the body (radiation absorbing wall). However, although ferrite is used as an absorbing material, it is described that it has a capacitive property in the low frequency region and an inductive property in the high frequency region, but the weight is reduced because it uses a ferrite with a large specific gravity. I can't do that. In addition, because it is a radio wave absorption wall with sufficient radio wave absorption performance in the VHF band (90 to 222 MHz) and UHF band (470 to 770 MHz) used for TV radio waves, it absorbs radio waves in the GHz band region. It is not a radio wave absorber.

The radio wave absorber described in Patent Document 9 is a radio wave absorber using a resistance film having a capacitive susceptance using flake graphite and earthy graphite as an absorbing material, and has a frequency of 5.8 GHz only as a resistance component. It has been reported that a return loss of 29 dB (surface resistance value of 405 Ω / □) was obtained at a thickness of 4.3 mm which is 45% thinner than a resistive film having a thickness of 4.3 mm. The radio wave absorber described in Patent Document 8 is made of flake graphite and earthy graphite having a small specific gravity as an absorbing material, and can be reduced in weight. Since graphite is mixed and used, it is difficult to uniformly disperse, and manufacturing is difficult. The reported maximum absorption frequency is 5.8 GHz, and no absorption characteristics in the millimeter wave region are obtained. These maximum absorption frequencies largely depend on the characteristics of the absorbing material. In the case of a resistive electromagnetic wave absorber having a capacitive susceptance using flake graphite and earthy graphite as the absorbing material, a high frequency GHz band region, particularly a millimeter wave is used. It is difficult to absorb the wave region.

The radio wave absorber described in Patent Document 10 is a radio wave absorber using a resistive film having a capacitive susceptance using flaky conductive powder having a small specific gravity as an absorbing material, and has a thickness of 25 dB (7.8 GHz, resistance film). 12 μm, surface resistivity 275 Ω / □), 28 dB (9.4 GHz, resistance film thickness 12 μm, surface resistivity 275 Ω / □), 12 dB (11.4 GHz, resistance film thickness 33 μm, surface resistivity 60 Ω / □), It has been reported that a return loss of 13.3 dB (14.8 GHz, resistance film thickness 65 μm, surface resistivity 380 Ω / □) was obtained. However, since the flaky conductive powder having a small specific gravity is used as the absorbing material, it is possible to reduce the weight, but the frequency having a good absorption characteristic is about 10 GHz. It does not have satisfactory performance. Therefore, it is difficult for a radio wave absorber using a resistance film having a capacitive susceptance reported to absorb radio waves in a high-frequency GHz band region, particularly a millimeter wave region.

The maximum absorption frequency of radio wave absorbers depends largely on the characteristics of the absorbing material. Carbon materials such as graphite powder, carbon black, carbon fiber, coiled carbon fiber (carbon nanocoil) flake graphite and earth graphite It is difficult to absorb radio waves in the GHz band region, particularly in the millimeter wave region, with a radio wave absorber using a resistive film having a capacitive susceptance that uses as a absorbing material.

As described above, various studies have been made on a radio wave absorber using a resistive film having an inductive or capacitive susceptance, but a resistive film having a capacitive susceptance using fine carbon fibers was used. There are no reports of radio wave absorbers, and examples of radio wave absorbers that can absorb radio waves in the GHz band region, high-frequency GHz band region, particularly the millimeter wave region using a resistive film having capacitive susceptance Absent.

Japanese Patent Laid-Open No. 11-54981 JP-A-5-335832 JP 2003-158395 A JP 2007-335680 A JP 2007-115854 A JP 2003-124011 JP 2006-114877 A JP 2000-345637 JP 2005-12031 A JP 2001-320191 A

Therefore, in view of the problems in the prior art as described above, the present invention uses a fine carbon fiber having a small specific gravity as an absorbing material and produces a radio wave absorber using a resistive film having a capacitive susceptance. It is an object of the present invention to provide a radio wave absorber that can be made thinner than a / 4 type radio wave absorber and that has good absorption characteristics in the GHz band region, particularly in the millimeter wave region.

As a result of intensive research in order to solve the above problems, the present inventor obtained a wave absorber using a resistive film having a capacitive susceptance coated with a radio wave absorbing coating composition on a base material. The thickness of the absorber can be made thinner than that of the type 4 wave absorber, and a wave absorber having good absorption characteristics in the GHz band region, particularly in the millimeter wave region has been found, and the present invention has been completed. That is, the present invention has the following contents.

An electromagnetic wave absorber using a resistive film made of fine carbon fiber and a resin material and having a capacitive susceptance.

An electromagnetic wave absorber formed by applying an electromagnetic wave absorbing coating composition containing fine carbon fibers, a resin material, and a solvent.

The electromagnetic wave absorber whose fine carbon fiber content rate in the said resistance film is the range of 1-15 mass%.

A radio wave absorber in which a surface resistivity of a resistance film obtained by applying a radio wave absorbing coating composition on a substrate is 950 to 3000 Ω / □.

A radio wave absorber in which the film thickness of a resistance film obtained by applying a radio wave absorbing coating composition to a substrate is 0.001 to 0.2 mm.

An electromagnetic wave absorber formed by applying an electromagnetic wave absorbing coating composition containing fine carbon fibers, a resin material, a solvent, and a dispersant.

The radio wave absorber, wherein the dispersant is an organic compound having a hydroxyl group or a mixture of organic compounds having a hydroxyl group.

The fine carbon fiber is a three-dimensional network-like fine carbon fiber structure composed of fine carbon fibers having an outer diameter of 15 to 100 nm, and the fine carbon fiber structure includes a plurality of the fine carbon fibers extending. In an aspect, the radio wave absorber has a granular portion for bonding the fine carbon fibers to each other, and the granular material is formed during the growth process of the fine carbon fibers.

The fine carbon fiber is an electromagnetic wave absorber whose ID / IG measured by Raman spectroscopy is 0.2 or less.

A radio wave absorber, wherein the resin material used in the radio wave absorbing coating composition is a thermoplastic resin.

The radio wave absorber, wherein the thermoplastic resin is at least one selected from a styrene copolymer, a thermoplastic polyurethane resin, a chlorinated polypropylene, a vinyl acetate resin, or a cyclic polyolefin resin.

A radio wave absorber, wherein the resin material used in the radio wave absorbing coating composition is a thermosetting resin.

A radio wave absorber in which the thermosetting resin is a thermosetting polyurethane resin or an epoxy resin.

The electromagnetic wave absorber whose solvent used for the said electromagnetic wave absorption coating composition is any one or more of methanol, ethanol, 2-propanol, 2-butanone, toluene, or xylene.

The radio wave absorber, wherein the base material to which the radio wave absorbing coating composition is applied is paper, a resin sheet or a resin plate.

An electromagnetic wave absorber comprising a reflective layer provided on the back surface of a base material coated with a resistive film having capacitive susceptance.

A radio wave absorber in which the radio wave absorbing coating composition is applied to a substrate, and a reflective layer provided on the back surface thereof is an aluminum foil, a copper foil, or a stainless steel foil.

The wave absorber using the fine carbon fiber-containing resistive film having capacitive susceptance according to the present invention can be made thinner than the λ / 4 type wave absorber, and the GHz band, particularly the millimeter wave band region. Therefore, it can be suitably used as a radio wave absorber for computers, communication equipment, electromagnetic wave equipment, ETS, AHS, and building applications.

The radio wave absorber of the present invention is a radio wave absorber in which a resistive film having a capacitive susceptance is formed by applying a fine carbon fiber-containing radio wave absorbing coating composition on the surface of a substrate having a reflective layer provided on the back surface. It is lightweight because it uses fine carbon fiber as an absorbing material, and the thickness of the absorber can be made thinner than the λ / 4 type wave absorber, and the GHz band region, the high frequency GHz band region, particularly the millimeter wave region. It is characterized by being able to exhibit high absorption characteristics with respect to radio waves.

Hereinafter, the present invention will be described in detail based on embodiments.

The fine carbon fibers used for the absorbing material of the radio wave absorber of the present invention are single-layer, double-layer, and multilayer fine carbon fibers, which can be used according to the purpose. In the present invention, more preferably, multi-layered fine carbon fibers are used. The method for producing the fine carbon fiber is not particularly limited, and any conventionally known method such as a vapor phase growth method using a catalyst, an arc discharge method, a laser evaporation method, and a HiPco method (High-pressure carbon monoxide process). A manufacturing method may be used.

For example, a method for producing a single-layer fine carbon fiber by laser vapor deposition is shown below. As a raw material, graphite powder and a mixed lot of nickel and cobalt fine powder were prepared. This mixed lot is heated to 1250 ° C. in an electric furnace under an argon atmosphere of 665 hPa (500 Torr), and irradiated with a second harmonic pulse of 350 mJ / Pulse Nd: YAG laser to evaporate carbon and metal fine particles. Thus, a fine carbon fiber having a single layer can be produced.

The above manufacturing method is merely a typical example, and the metal type, gas type, electric furnace temperature, laser wavelength, and the like may be changed. In addition, other than laser deposition methods, for example, HiPco method, vapor phase growth method, arc discharge method, carbon monoxide thermal decomposition method, template method in which organic molecules are inserted into fine pores, thermal decomposition, fullerene -You may use the single layer fine carbon fiber produced by other methods, such as a metal co-evaporation method.

For example, a method for producing a two-layer fine carbon fiber by a constant temperature arc discharge method is shown below. The substrate was a surface-treated Si substrate, and the treatment method was a solution obtained by immersing alumina powder in a solution in which the catalyst metal and the catalyst auxiliary metal were dissolved for 30 minutes, and then dispersing by ultrasonic treatment for 3 hours. Was applied to a Si substrate and dried in air at 120 ° C. for maintenance. A substrate was installed in the reaction chamber of the fine carbon fiber production apparatus, a mixed gas of hydrogen and methane was used as a reaction gas, the supply amount of gas was 500 sccm for hydrogen, 10 sccm for methane, and the pressure in the reaction chamber was 70 Torr. As the cathode part, a rod-like discharge part made of Ta was used. Next, a DC voltage was applied between the anode part and the cathode part, and between the anode part and the substrate, and the discharge voltage was controlled so that the discharge current was constant at 2.5A. When the temperature of the cathode part is 2300 ° C. due to discharge, the normal glow discharge state is changed to an abnormal glow discharge state, and the discharge current is 2.5 A, the discharge voltage is 700 V, and the reaction gas temperature is 3000 ° C. for 10 minutes. Single-layer and double-layer fine carbon fibers can be produced on the entire substrate.

The above manufacturing method is merely an example, and various conditions such as the type of metal and the type of gas may be changed. Moreover, you may use the single layer fine carbon fiber produced by production methods other than the arc discharge method.

For example, a method for producing a multi-layered fine carbon fiber having a three-dimensional structure by a vapor deposition method is shown below. Basically, an organic compound such as a hydrocarbon is chemically pyrolyzed by CVD using transition metal ultrafine particles as a catalyst to obtain a fiber structure (hereinafter referred to as an intermediate), which is further subjected to high-temperature heat treatment to produce multilayer fine particles. Carbon fibers can be made.

As the raw material organic compound, hydrocarbons such as benzene, toluene and xylene, and alcohols such as carbon monoxide and ethanol are used, but it is preferable to use at least two or more carbon compounds having different decomposition temperatures as the carbon source. . Note that at least two or more carbon compounds do not necessarily use two or more types of raw material organic compounds, and even when one type of raw material organic compound is used, the fiber structure In the body synthesis process, for example, a reaction such as hydrogen dealkylation of toluene or xylene occurs, and in the subsequent thermal decomposition reaction system, it becomes two or more carbon compounds having different decomposition temperatures. Including embodiments. The atmosphere gas is an inert gas such as argon, helium, xenon or hydrogen, and the catalyst is a transition metal such as iron, cobalt or molybdenum, or a transition metal compound such as ferrocene or metal acetate, and sulfur or thiophene or iron sulfide. Use a mixture of sulfur compounds such as

The synthesis of the intermediate is carried out by using a CVD method such as hydrocarbon, which is usually performed, by evaporating the mixture of hydrocarbon and catalyst as raw materials, introducing hydrogen gas or the like into the reaction furnace as a carrier gas, Pyrolysis at a temperature of 1300 ° C. As a result, several centimeters in which a plurality of fine carbon fiber structures (intermediates) having a sparse three-dimensional structure in which fibers having an outer diameter of 15 to 100 nm are bonded together by granular materials grown using the catalyst particles as nuclei are collected. To synthesize an aggregate of several tens of centimeters.

The thermal cracking reaction of the hydrocarbon as a raw material mainly occurs on the surface of the granular particles grown using the catalyst particles or the core, and the recrystallization of carbon generated by the decomposition proceeds in a certain direction from the catalytic particles or granular materials. Grows in a fibrous form. However, by intentionally changing the balance between the thermal decomposition rate and the growth rate, for example, by using at least two or more carbon compounds having different decomposition temperatures as a carbon source as described above, the carbon material is only in a one-dimensional direction. The carbon material is grown three-dimensionally around the granular material without growing the material. Of course, the growth of such three-dimensional fine carbon fibers does not depend only on the balance between the thermal decomposition rate and the growth rate, but the crystal face selectivity of the catalyst particles, the residence time in the reactor, Although it is affected by the temperature distribution, etc., in general, when the growth rate is faster than the thermal decomposition rate as described above, the carbon material grows in a fibrous form, while the thermal decomposition rate is higher than the growth rate. When fast, the carbon material grows in the circumferential direction of the catalyst particles. Therefore, by intentionally changing the balance between the pyrolysis rate and the growth rate, the growth of the carbon material as described above can be formed in a certain direction, and a three-dimensional structure can be formed in the other direction under control. Is something you can do. In the intermediate to be produced, the composition of the catalyst, the residence time in the reaction furnace, the reaction temperature, and the gas temperature are used to easily form the three-dimensional structure as described above in which the fibers are bonded together by the granular material. Etc. are preferably optimized.

An intermediate obtained by heating and generating a mixed gas of catalyst and hydrocarbon at a constant temperature in the range of 800 to 1300 ° C. has a structure in which patch-like sheet pieces made of carbon atoms are bonded together, and Raman When spectroscopic analysis is performed, the D band is very large and there are many defects. Moreover, the produced | generated intermediate body contains the unreacted raw material, non-fibrous carbon material, a tar content, and a catalyst metal.

Therefore, in order to remove these residues from such an intermediate and obtain the desired fine carbon fiber structure with few defects, high-temperature heat treatment at 2400 to 3000 ° C. is performed by an appropriate method.

That is, for example, the intermediate is heated at 800 to 1200 ° C. to remove volatile components such as unreacted raw materials and tars, and then annealed at a high temperature of 2400 to 3000 ° C. to prepare the desired structure. At the same time, the catalyst metal contained in the fiber is removed by evaporation. At this time, in order to protect the substance structure, a reducing gas or a small amount of carbon monoxide gas may be added to the inert gas atmosphere.

When the intermediate is annealed at a temperature in the range of 2400 to 3000 ° C., the patch-like sheet pieces made of carbon atoms are bonded to each other to form a plurality of graphene sheet-like layers.

Further, before or after such high-temperature heat treatment, the step of crushing the equivalent circle average diameter of the fine carbon fiber structure to several centimeters, and the equivalent circle average diameter of the fine carbon fiber structure subjected to the crush treatment The fine carbon fiber which has a desired circle equivalent average diameter is produced through the process of grind | pulverizing to 50-100 micrometers.

The above manufacturing method is merely an example, and various conditions such as the type of metal and the type of gas may be changed. Moreover, you may use the multilayer fine carbon fiber produced by production methods other than a vapor phase growth method.

About the addition amount of the fine carbon fiber of this invention, it is the range of 1-15 mass% with respect to 100 mass% of resin materials, Preferably it is 2-13 mass%, More preferably, it is 3-12 mass%. Thus, when there are few fine carbon fibers than 1 mass%, desired electroconductivity cannot be obtained. Moreover, when the fine carbon fiber is 15% by mass or more, the fine carbon fiber is bulky, so that a good resin film cannot be produced.

The thermoplastic resin of the present invention is not particularly limited. For example, chlorine such as chlorinated polyethylene resin, chlorinated polypropylene resin, chlorinated ethylene-propylene copolymer, chlorinated ethylene-vinyl acetate copolymer, etc. Polyolefin resin, polystyrene resin, styrene-acrylic copolymer, styrene-acetonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, styrene-maleimide copolymer, ASA resin, AES resin, Styrene resin such as ACS resin, PC-ABS alloy, PC-AES alloy, polyethylene terephthalate resin, polyester resin, vinyl acetate resin, cyclic polyolefin copolymer, polyamideimide resin, polyetherimide resin, polyvinyl formal resin, polyvinyl butyler Resins, polyphenylene ether resins, acrylic resins, thermoplastic polyurethane resins, silicone resins, cellulose acetate, and the like cellulose nitrate and these were modified resin. Also, ethylene-propylene-terpolymer rubber (EPT), chloroprene rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber, natural rubber, polyisoprene rubber, chlorosulfonated polyethylene rubber, chlorinated polyethylene rubber, ethylene-α-olefin rubber, Examples include various elastomers such as ethylene-propylene rubber, silicone rubber, acrylic rubber, and fluorine rubber.

Examples of the thermosetting resin of the present invention include epoxy resins, acrylic resins, urethane resins, phenol resins, polyester resins, urea resins, melamine resins, silicon resins, polyimide resins, and the like. Examples thereof include modified resins.

Although the organic solvent used by this invention is mentioned below, it is not specifically limited to these. For example, water, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, butyl alcohol, cyclohexanol), glycols (ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, polypropylene glycol, diethylene glycol monoethyl ether, polypropylene glycol monoethyl ether) , Polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, ethyl cellosolve, butyl cellosolve, carbitol, butyl carbitol, methoxybutanol) and ester ethers (cellosolve acetate, butyl cellosolve acetate, carbitol acetate, methoxybutyl acetate), ethers (tetrahydrofuran) , Dioxane), fat Hydrocarbons (mineral spirits), alicyclic hydrocarbons (turpentine oil), mixed hydrocarbons (HAWS, sorbet 100, sorbet 150), aromatic hydrocarbons (toluene, xylene, ethylbenzene), ketones (acetone, methyl ethyl ketone, Methyl isobutyl ketone, cyclohexanone, isophone), esters (ethyl acetate, butyl acetate, isobutyl acetate, amyl acetate), silicone oils (polydimethylsiloxane, partially octyl-substituted polydimethylsiloxane, partially phenyl-substituted polydimethylsiloxane), halogenated Examples include hydrocarbons (chlorobenzene, dichlorobenzene, chloroform, bromobenzene), fluorinated compounds, and the like. Two or more of these may be mixed. Furthermore, the amount of the solvent may be selected so that the viscosity when used as a paint is in an appropriate range that can be applied.

Specific examples of the dispersant for dispersing the fine carbon fibers of the present invention are shown in the following table, but are not limited thereto.

The average degree of polymerization of the dispersant for fine carbon fibers of the present invention is in the range of 200 to 8000, preferably 300 to 5000, and particularly preferably 400 to 3000. Thus, when the average degree of polymerization of the dispersant for fine carbon fibers is less than 200, the desired performance cannot be obtained, and when the average degree of polymerization of the dispersant for fine carbon fibers is 8000 or more, it is used. Since the compatibility with the resin is lowered, the characteristics may be lowered.

About the composition ratio (X: Y: Z) of the dispersing agent for fine carbon fibers of this invention, the range of 65-90: 5-30: 0-10 is employable, Preferably it is 70-85: 10-25: 0. It is -8, Most preferably, it is 75-85: 15-20: 1-5. Thus, when the composition ratio of X is less than 65 in the dispersant for fine carbon fibers, the dispersion and defibration performance of the dispersant for fine carbon fibers cannot be obtained, and the composition ratio of X in the dispersant for fine carbon fibers is In the case of 90 or more, the compatibility with the resin being used is lowered, so that the characteristics may be lowered.

About the addition amount of the dispersing agent for fine carbon fibers of this invention, it is the range of 0.0005-500 mass% with respect to 100 mass% of fine carbon fibers, Preferably it is 0.015-250 mass%, Especially preferably. Is 0.025-100 mass%. Thus, when there are few dispersing agents for fine carbon fibers than 0.0005 mass%, desired performance cannot be obtained. Moreover, when the dispersing agent for fine carbon fibers is 500 mass% or more, the characteristic of resin currently used may be reduced.

Additives may be added to the radio wave absorbing coating composition used in the present invention according to other applications. For example, inorganic pigments, organic pigments, fillers, whiskers, thickeners, anti-settling agents, UV inhibitors, wetting agents, emulsifiers, anti-skinning agents, polymerization inhibitors, anti-sagging agents, antifoaming agents, color separation prevention Agent, leveling agent, drying agent, curing agent, curing accelerator, plasticizer, fireproofing / preventing agent, fungicide / algaeproofing agent, antibacterial agent, insecticide, marine antifouling agent, metal surface treatment agent, derusting agent, Examples include degreasing agents, film forming agents, bleaching agents, colorants, wood sealers, sealants, sanding sealers, sealers, cement fillers, and resin-containing cement pastes.

In the disperser for producing the radio wave absorbing coating composition used in the present invention, a general disperser is used. For example, planetary mill, ball mill, triple roll, kneader, Henschel mixer, open roll mixer, Banbury mixer, bead mill (Dyno Mill, Shinmaru Enterprise Co., Ltd.), TK Lab Disper, TK Philmix, TK Pipeline Mixer, TK Homo Mickline Mill, TK Homojetter, TK Unimixer, TK Homomic Line Flow, TK Aji Homo Dispers (Special Machine Industries Co., Ltd.), Homogenizer Polytron (Central Science Trade Co., Ltd.), Homogenizer Histron ( Nihon Medical Science Equipment Co., Ltd.), Biomixer (Nihon Seiki Seisakusho Co., Ltd.), Turbo-type stirrer (Kodaira Seisakusho Co., Ltd.), Ultra Disper (Asada Steel Co., Ltd.), Ebara Mileser (Ebara Seisakusho Co., Ltd.) Co.)), ultrasonic equipment or supersonic Washing machine (manufactured by AS ONE Corporation), and the like.

The method for coating the radio wave absorbing coating composition of the present invention on a substrate includes the following general coating methods, but is not particularly limited thereto. Examples thereof include air spray coating, airless spray coating, low-pressure atomizing spray coating, coating by a bar coder method, and coating using a spin coater. Although there is no restriction | limiting in particular also in the thickness of a coating film, it is preferable that a resistance film is 0.001-0.2 mm, More preferably, it is 0.002-0.1 mm, Most preferably, it is 0.003-0. .05 mm.

In the radio wave absorption coating composition of the present invention, when a thermoplastic resin is used as a resin material, the fine carbon fiber-containing resistance film obtained by coating the base material by the above method should be dried at room temperature. You can also. However, in order to sufficiently dry the coating film, the drying temperature is preferably heated to 10 to 200 ° C, more preferably 30 to 150 ° C, and particularly preferably 60 to 120 ° C. If the drying temperature is less than 10 ° C, the drying may not proceed sufficiently. If the drying temperature exceeds 200 ° C, the material may be deformed, the coating film may turn yellow, or the film properties may deteriorate. The drying time is considered depending on the type of the organic solvent-soluble resin, the solvent, and the base material.

In the radio wave absorbing coating composition of the present invention, when a thermosetting resin is used as the resin material, the fine carbon fiber-containing resistive film obtained by coating the base material by the above method is dried at room temperature. It can also be cured. However, in order to sufficiently dry and cure the coating film, the drying temperature is preferably heated to 10 to 400 ° C, more preferably 30 to 350 ° C, and particularly preferably 60 to 300 ° C. If the drying temperature is less than 10 ° C, the drying may not proceed sufficiently. If the drying temperature exceeds 400 ° C, the material may be deformed, the coating film may turn yellow, or the film properties may deteriorate. The drying and curing time is considered depending on the type of thermosetting resin, solvent, and substrate.

The substrate to which the radio wave absorbing coating composition of the present invention is applied is not particularly limited, and examples thereof include paper, glass, resin, nonwoven fabric, metal, etc., and the shape is also a film, sheet, plate. And various shapes such as a solid.

For the base material, for example, an ultraviolet absorber, an antioxidant, a release agent, an antistatic agent, a colorant, a flame retardant, a fiber reinforcing agent such as glass fiber, an inorganic filler, etc. 1 type, or 2 or more types can be contained.

The reflective layer is not particularly limited as long as it is a conductive thin film, for example, a metal foil such as an aluminum foil, a copper foil, or a stainless steel foil, a conductive cloth woven with a metal fiber or a metal-plated fiber, or Examples thereof include conductive non-woven fabric, plating such as vapor deposition plating and electroless plating, other conductive paints (metal-based or carbon-based paints or plating), and conductive sheets. By providing a reflective layer such as a metal foil on the back surface of the base material coated with a capacitive film in this way, the electromagnetic wave absorber is not only attached to the metal surface but also an exception. Even in the case, desired radio wave absorption characteristics can be exhibited.

In the λ / 4 type wave absorber, the surface resistivity of the resistance film formed on the base material is limited to 367.6 Ω / □, but the wave absorber using the resistive film having the capacitance described in this report. Is preferably in the range of 950 to 3000 Ω / □, more preferably 1000 to 2500 Ω / □, and particularly preferably 1200 to 2000 Ω / □. As described above, since a favorable radio wave absorption characteristic can be obtained at a surface resistivity where the surface resistivity of the resistance film is higher than that of the λ / 4 type wave absorber, it is possible to reduce the amount of the absorbing material added in the resistance film. . When the surface resistivity of the capacitive resistive film is less than 950Ω / □, the return loss of radio waves is difficult to achieve the desired value, and even when it is greater than 3000Ω / □, the return loss of radio waves is the desired value. It is hard to become. That is, the amount of radio wave reflection that satisfies the performance as a radio wave absorber may not reach 20 dB.

The thickness of the resistance film formed on the substrate is preferably as thin as possible, but is preferably 0.001 to 0.2 mm, preferably 0.002 mm to 0.1 mm, and more preferably 0.003 to 0.3 mm. 05 mm. Thus, if it is 0.001 mm or less, it is difficult to obtain a resistance film having a desired surface resistivity, and if it is 0.2 mm or more, it is difficult to produce using a radio wave absorbing paint composition.

In order to adjust the absorption frequency of the electromagnetic wave absorber of the present invention, it is desirable to adjust the thickness of the substrate on which the radio wave absorbing coating composition is applied. In order to absorb low-frequency electromagnetic waves, it is desirable to make the substrate thicker. To absorb high frequencies, the substrate may be made thinner.

In other words, the thickness of the spacer for the radio wave absorber using the fine carbon fiber-containing resistive film having the capacitive susceptance of the present invention to absorb the GHz band region can be made thinner than the λ / 4 type radio wave absorber. For example, for a 1 GHz radio wave, it can be thinner than 75 mm, which is λ / 4, for a 2.4 GHz radio wave, it can be thinner than 31.45 mm, which is λ / 4, and for a 10 GHz radio wave, it is λ / 4. It can be made thinner than 7.5 mm, can be made thinner than 1.62 mm, which is λ / 4 at 38 GHz radio wave, can be made thinner than 1.25 mm, which is λ / 4 at 60 GHz, and can be made thinner than 1.25 mm at 60 GHz. It can be made thinner than 1.0 mm which is λ / 4, and it can be made thinner than 0.8 mm which is λ / 4 for a radio wave of 94 GHz.

In the complex amount of the surface resistance value of the resistance film of the present invention, the real part must be a positive value and the imaginary part must be a negative value. The absolute value of the real part value is preferably smaller than the absolute value of the imaginary part value.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

<Method for preparing radio wave absorbing coating composition>
[Operation number 1-12]
Acrylonitrile-styrene resin [Daicel Polymer Co., Ltd. Sebian N] 53 g was dissolved in a mixed solvent of 224 g of 2-butanone and 224 g of toluene to prepare 501 g of a 10.8% by mass resin solution. In this resin solution, 5.91 g of fine carbon fibers (manufactured by Nano Carbon Technologies, outer diameter of 40 to 90 nm, length of several tens of μm) and 0.591 g of compound 1 shown in Table 1 as a carbon fiber dispersant are added. The mixture was stirred for 1 hour to prepare a fine carbon fiber-containing resin solution.

The prepared fine carbon fiber-containing resin solution is dispersed in a bead mill grinder (made by Shinmaru Enterprise Co., Ltd., bead diameter 0.6 mm) to uniformly disperse and defibrate the fine carbon fibers. A composition was prepared.

<Preparation method of resistance film>
The prepared radio wave absorbing coating composition was applied onto a polypropylene resin substrate (160 × 160 × 3 mm) by a bar coater method, and allowed to dry at room temperature for 60 minutes to prepare a resistive film containing fine carbon fibers.

In order to reduce the concentration of the fine carbon fibers of the radio wave absorbing coating composition, dilution is performed by adding a 10.8% by mass acrylonitrile-styrene resin solution. The acrylonitrile-styrene resin solution for dilution was prepared by dissolving 53 g of acrylonitrile-styrene resin [Cebian N, Daicel Polymer Co., Ltd.] in a mixed solvent of 224 g of 2-butanone and 224 g of toluene, and 501 g of a 10.8% by mass resin solution. Prepared.

[Implementation number 13]
A radio wave absorbing coating composition in which a 10.8% by mass acrylonitrile-styrene resin solution is added to the radio wave absorbing coating composition prepared above, and the content of fine carbon fibers in the resistance film is 10% by mass with respect to the resin. The method was the same as in Example 1 except that the type of bar coater was changed.

[Operation numbers 14, 20, 21]
A radio wave absorbing coating composition in which a 10.8% by mass acrylonitrile-styrene resin solution is added to the radio wave absorbing coating composition prepared above, and the content of fine carbon fibers in the resistance film is 9.0% by mass with respect to the resin. Example 1 was followed except that the type of bar coater was changed.

[Operation numbers 15, 16]
A radio wave absorbing coating composition in which a 10.8% by mass acrylonitrile-styrene resin solution is added to the radio wave absorbing coating composition prepared above, and the content of fine carbon fibers in the resistance film is 10.5% by mass with respect to the resin. Example 1 was followed except that the type of bar coater was changed.

[No. 17, 22]
A radio wave absorbing coating composition in which a 10.8% by mass acrylonitrile-styrene resin solution is added to the radio wave absorbing coating composition prepared above, and the content of fine carbon fibers in the resistance film is 8.5% by mass with respect to the resin. Example 1 was followed except that the type of bar coater was changed.

[Operation numbers 18, 19]
A radio wave absorbing coating composition in which a 10.8% by mass acrylonitrile-styrene resin solution is added to the radio wave absorbing coating composition prepared above, and the content of fine carbon fibers in the resistance film is 8.0% by mass with respect to the resin. Example 1 was followed except that the type of bar coater was changed.

<Measurement of surface resistivity>
The resistance film produced on the polypropylene resin substrate was measured for the resistance (Ω) at nine places on the coating film surface using a four-end needle type resistivity meter (Loresta AP MCP-T400 manufactured by Mitsubishi Chemical Corporation). The surface resistivity (Ω / □) was converted with the same resistance meter, and the average value was calculated. The results are as shown in Table 2.

<Measurement of return loss and complex dielectric constant>
The measurement of the return loss and the complex relative dielectric constant is performed by using a vector network analyzer (E8364A), regarding the one-to-one lens antenna as a transmission path, and further using a dielectric lens to converge the radio wave. The lens method was used to measure the transmission coefficient and reflection coefficient. For the measurement of the return loss, the initial setting of the VNA was performed, and the transmission characteristics of the VNA were normalized by performing TRL calibration. Next, a time gate process was also performed so that only the time required for the measurement was measured. In the measurement of the return loss, it was calculated by introducing the reflection coefficient in a state where the metal plate was lined into the radio wave absorber sample with reference to the reflection coefficient of the metal plate. The complex dielectric constant was estimated from the amplitude and phase information using 85071 manufactured by Agilent Technologies. In addition, the measurement frequency area | region measured about the time of perpendicular incidence in a 34-54 GHz band area | region, and the result was shown in Table 2 and FIGS.

[Comparative Example 1]
With respect to the polypropylene resin (160 × 160 × 3 mm) as a spacer, the surface resistivity, complex relative permittivity, and radio wave absorption characteristics were measured according to the above method. The complex relative dielectric constant ε · γ of the polypropylene resin of the spacer was 2.29-j0 according to the complex relative dielectric constant measured by the lens method.

<Calculation of complex amount of surface resistance value in resistive film>
Using the surface resistivity of the resistive film and the results of radio wave absorption characteristics, the complex quantity of the surface resistance value of the resistive film was substituted into the following theoretical formula for calculating the absorbed quantity to estimate the complex quantity of the surface resistance value. In other words, the complex amount R · s of the surface resistance value in the resistive film, the thickness d of the spacer, and the reflection coefficient Γ · using the impedance Z · in2 with the inside viewed from the front of the absorber can be expressed by the following equation.
Γ · = (Z · in2−Z0) / (Z · in2 + Z0)
Z · in2 = (R · s · Z · in1) / (R · s + Z · in1)
Z · in1 = Z · c · tanh (γ · d)
Z · c = Z0 / (ε · γ) 1/2
γ · = 2π · (ε · γ) 1/2 / λ
Z0 = 376.7
Using this R ·, the radio wave absorption amount S [dB] can be obtained by the following equation. S = −20log | Γ · | Table 3 shows the results of estimating the complex quantity (real part, imaginary part) of any surface resistance value of the resistive film using the surface resistivity and radio wave absorption characteristics of the resistive film. FIG. 8 shows a distribution diagram of the complex amount of the surface resistance value of the resistance film. FIG. 9 shows the relationship between the complex amount of the sheet resistance value of the resistance film and the DC sheet resistance value. Assuming that the resistive film containing the fine carbon fiber of the example has capacitive susceptance, the radio wave absorption characteristics calculated by calculation are shown in FIGS.

The measured value of the radio wave absorption characteristics of the wave absorber having the resistance film of the example and the radio wave absorption characteristics calculated on the assumption that the resistance film of the wave absorber having the resistance film has capacitive susceptance are in good agreement. Indicated. Therefore, it was shown that the radio wave absorber using the resistive film having the capacitive susceptance obtained in the example can be designed by performing the above calculation.

<Design of electromagnetic wave absorber>
FIG. 9 shows the relationship between the complex amount of the sheet resistance value and the DC sheet resistance value. As a result, when the sheet resistance value of the resistance film is 1590 Ω / □, Γ · = (Z · in2−Z0) / Since it is closest to the non-reflection curve derived using the equation (Z · in2 + Z0), the complex amount of the surface resistance value at this time is used, and the radio wave absorber for the FWA fixed wireless LAN that uses the radio wave of 38 GHz is used. Designed. FIG. 10 shows the thickness of the spacer that can absorb the maximum 38 GHz radio wave, and FIG. 11 shows the absorption peak. From FIG. 10, it is calculated that the thickness of the spacer is 0.73 mm, which can be 55% shorter than the spacer thickness (1.62 mm) of the λ / 4 type wave absorber.

According to Examples 1 to 5, it is clear that the resistive film using fine carbon fibers as the absorbent material has a capacitive susceptance. In addition, since a fine carbon fiber having a small specific gravity is used, a lightweight radio wave absorber can be manufactured.

According to Examples 1 to 5, a radio wave absorber using the fine carbon fiber of this report as an absorbent material and having a resistive film having a capacitive susceptance formed on a base material has radio wave absorption characteristics in the GHz band region, particularly in the millimeter wave region. In particular, when the surface resistivity of the resistive film is in the range of 950 to 3000 Ω / □, high radio wave absorption characteristics can be exhibited in the GHz band region, particularly in the millimeter wave region.

According to the sixth embodiment, by using a resistive film having a capacitive susceptance, the thickness of the absorber can be greatly reduced as compared with the λ / 4 type wave absorber.

The radio wave absorber using a resistive film having a capacitive property using the fine carbon fiber of the present invention as an absorbing material is lighter than a radio wave absorber using an inorganic material as the absorbing material, and is a λ / 4 type radio wave absorber. Since the thickness of the absorber can be made thinner, and it exhibits good radio wave absorption characteristics for radio waves in the GHz band, particularly in the millimeter wave band, it is used for computers, communication equipment, electromagnetic wave equipment, ETS, AHS, and architectural applications. It can be used as a radio wave absorber.

It is the actual measurement value and calculation value of the electromagnetic wave absorption characteristic in the implementation number 1. It is the actual measurement value and calculation value of the electromagnetic wave absorption characteristic in execution number 9. It is the actual measurement value and calculation value of the electromagnetic wave absorption characteristic in execution number 11. It is the actual measurement value and calculation value of the electromagnetic wave absorption characteristic in execution number 12. It is the actual measurement value and calculation value of the electromagnetic wave absorption characteristic in the implementation number 13. It is the actual measurement value and calculation value of the electromagnetic wave absorption characteristic in the implementation number 15. It is the actual measurement value and calculation value of the electromagnetic wave absorption characteristic in execution number 19. It is a distribution map of the complex quantity of the sheet resistance value of the resistance film in execution numbers 1-22. It is a correlation diagram of the complex quantity of the surface resistance value of the resistance film and the direct current surface resistance value in execution numbers 4, 5, 6, 12, 14, and 20. FIG. 5 is a correlation diagram between spacer film thickness and return loss in the case of designing a radio wave absorber for a 38 GHz FWA fixed wireless LAN. It is a radio wave absorption characteristic peak when a radio wave absorber for a 38 GHz FWA fixed wireless LAN is designed.

Claims (17)

An electromagnetic wave absorber comprising a resistive film made of fine carbon fiber and a resin material and having a capacitive susceptance. 2. The radio wave absorber according to claim 1, wherein a radio wave absorbing coating composition containing fine carbon fibers, a resin material and a solvent is applied. The radio wave absorber according to claim 1 or 2, wherein the content of fine carbon fibers in the resistance film is in the range of 1 to 15 mass%. 4. The radio wave absorber according to claim 1, wherein a surface resistivity of a resistance film obtained by applying the radio wave absorption coating composition to a substrate is 950 to 3000 Ω / □. 5. The radio wave absorber according to claim 1, wherein the film thickness of the resistance film obtained by applying the radio wave absorption coating composition to a substrate is 0.001 to 0.2 mm. The radio wave absorber according to claim 1, wherein a radio wave absorbing coating composition containing fine carbon fibers, a resin material, a solvent and a dispersant is applied. The radio wave absorber according to claim 6, wherein the dispersant is an organic compound having a hydroxyl group or a mixture of organic compounds having a hydroxyl group. The fine carbon fiber is a three-dimensional network-like fine carbon fiber structure composed of fine carbon fibers having an outer diameter of 15 to 100 nm, and the fine carbon fiber structure includes a plurality of the fine carbon fibers extending. The aspect according to claim 1, wherein the fine carbon fibers have a granular part for bonding the fine carbon fibers to each other, and the granular material is formed during the growth process of the fine carbon fibers. The electromagnetic wave absorber described. The electromagnetic wave absorber according to claim 1, wherein the fine carbon fiber has an I _D / I _G measured by Raman spectroscopy of 0.2 or less. The radio wave absorber according to claim 1, wherein the resin material used for the radio wave absorption coating composition is a thermoplastic resin. 11. The radio wave absorption according to claim 10, wherein the thermoplastic resin is at least one selected from a styrene copolymer, a thermoplastic polyurethane resin, a chlorinated polypropylene, a vinyl acetate resin, or a cyclic polyolefin resin. body. The radio wave absorber according to claim 1, wherein the resin material used for the radio wave absorbing coating composition is a thermosetting resin. The radio wave absorber according to claim 12, wherein the thermosetting resin is a thermosetting polyurethane resin or an epoxy resin. The electromagnetic wave absorber according to claim 1, wherein the solvent used in the electromagnetic wave absorbing coating composition is at least one of methanol, ethanol, 2-propanol 2-butanone, toluene, and xylene. . The radio wave absorber according to claim 1, wherein the base material to which the radio wave absorbing coating composition is applied is paper, a resin sheet, or a resin plate. The radio wave absorber according to claim 1, wherein a reflection layer is provided on a back surface of a base material coated with a resistive film having capacitive susceptance. The electromagnetic wave absorber according to any one of claims 1 to 16, wherein the electromagnetic wave absorbing coating composition is applied to a substrate, and the reflective layer provided on the back surface thereof is an aluminum foil, a copper foil, or a stainless steel foil.

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