JP6328450B2 - Electromagnetic wave absorbing coating agent, sheet coated with coating agent, and method for producing coating agent - Google Patents

Description

  The present invention relates to an electromagnetic wave absorbing coating agent, a sheet coated with the coating agent, and a method for producing the coating agent.

  The inventor of the present invention mixed a microcoiled carbon fiber having a length of 0.5 mm or more and less than 3.0 mm in a sheet of dielectric loss material, and the amount of the mixed microcoiled carbon fiber was 100 weight of dielectric loss material. An electromagnetic wave absorbing sheet characterized by 1.0 to 1.5 parts by weight with respect to the part and a sheet thickness of 1.7 to 2.0 mm is disclosed (Patent Document 1). .

  In this invention, a microcoiled carbon fiber is mixed in a dielectric loss material such as silicone rubber, and this is molded into a sheet shape, whereby an electromagnetic wave absorption sheet having an electromagnetic wave absorption amount in the 60 GHz band of 15 to 22 dB. This is an excellent invention in that it can be obtained.

  However, the electromagnetic wave absorption characteristics of the invention have a problem that although the electromagnetic wave absorption amount is large, the electromagnetic wave absorption area is very narrow and the band has a sharp attenuation characteristic in a narrow band.

  The inventor discloses a magnetic material-supported coiled carbon fiber in which a magnetic oxide or a dielectric oxide is supported on the surface of the coiled carbon fiber by a coprecipitation method (Patent Document 2). The coiled carbon fiber carrying the magnetic oxide functions as an ultra-wideband wave absorber.

  However, since the magnetic material-supported coiled carbon fiber has a higher specific gravity than the coiled carbon fiber and has high cohesiveness, it is difficult to uniformly disperse in a solution state as a coating agent. It was also difficult to maintain a dispersed state.

JP 2001-77583 A JP 2012-12736 A

  SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a coating agent using a magnetic material-supported coiled carbon fiber capable of absorbing radio waves in a wide band and further providing a coating agent having broadband radio wave absorption performance.

  In order to achieve the above-mentioned object, the present invention employs the following means.

The electromagnetic wave absorbing coating agent according to the present invention is
water and,
An aqueous emulsion or thickener with silicone, acrylic or urethane;
Magnetic material-supported coiled carbon fiber;
It was supposed to contain.

  By dispersing the magnetic material-supported coiled carbon fiber in an emulsified state or by dispersing the magnetic material-carrying carbon fiber in a state of increasing the viscosity with a thickener, the dispersed state can be easily maintained.

  The aqueous emulsion may be characterized in that one or more resins selected from silicon, acrylic, urethane, epoxy, polyethylene, polypropylene, and bioplastic are dispersed.

In the electromagnetic wave absorbing coating agent according to the present invention, the magnetic material-supported coiled carbon fiber is supported by a magnetic oxide of Ni _x Zn _1-X Fe ₂ O ₄ (X is greater than 0 and less than 1). It may be characterized by being.

  Furthermore, the electromagnetic wave absorbing coating agent according to the present invention may be characterized by containing ferrite.

  Furthermore, the electromagnetic wave absorbing coating agent according to the present invention may include a thickener.

  Moreover, the fabric characterized by the coating of the electromagnetic wave absorbing coating agent described above may be used.

  In addition, the method for producing an electromagnetic wave absorbing coating agent according to the present invention comprises mixing the magnetic material-supported coiled carbon fiber in an aqueous emulsion dispersion system of silicon, acrylic or urethane, and ultrasonically dispersing the magnetic material-supported coiled carbon fiber. Is distributed.

  Furthermore, in the method for producing an electromagnetic wave absorbing coating agent according to the present invention, a foaming agent may be mixed.

FIG. 1 is a schematic diagram illustrating an electromagnetic wave absorption measurement method for return loss in an embodiment. FIG. 2 shows the results of electromagnetic wave absorption measurement in Example 1. FIG. 3 shows the electromagnetic wave absorption measurement results in Example 2. FIG. 4 shows the results of electromagnetic wave absorption measurement in Example 3. FIG. 5 is a schematic diagram illustrating an electromagnetic wave absorption measurement method for transmission attenuation in the example. FIG. 6 shows the results of electromagnetic wave absorption measurement in Example 4.

  The electromagnetic wave absorbing coating agent according to the present invention will be described. The electromagnetic wave absorbing coating agent according to the embodiment mainly includes a water-based emulsion in which water as a solvent and silicon, acrylic, urethane, epoxy, polyethylene, polypropylene, bioplastic, and the like that finally function as a binder are dispersed. It contains a viscous agent and a magnetic material-supported coiled carbon fiber dispersed in water.

  The magnetic material-supported coiled carbon fiber is obtained by supporting a magnetic oxide or derivative oxide as a magnetic material on the surface of the coiled carbon fiber. As the coiled carbon fiber, a single wound coiled carbon fiber has a wire diameter of 1 nm to 1 μm, a coil diameter of 1 nm to 100 μm, a coil helical pitch of 1 nm to 100 μm, and a coil length of 1 μm to 10 mm, for example. Will be used. From the viewpoint of ease of manufacture and the like, the diameter of the coil is preferably 1 nm to 10 μm, and the helical pitch is preferably 10 nm to 10 μm. Further, the length of the coil is preferably 150 μm or less in order to ensure dispersibility in the aqueous emulsion. The coiled carbon fiber includes a structure in which the carbon fiber is only twisted in addition to a structure in which the carbon fiber is spirally wound. In addition, the winding direction of the coiled carbon fiber wound spirally may be either clockwise (right-handed) or counterclockwise (left-handed) around the axis of the coil. In addition, the twisted direction of the coiled carbon fiber having a twisted structure may be either clockwise (right-handed) or counterclockwise (left-handed) about the axis. As the coiled carbon fiber, a single coiled carbon fiber, a double coiled carbon fiber, a superelastic coil, or a mixture thereof is used. The single-winding coiled carbon fiber is formed such that a coil of carbon fiber having a constant wire diameter extends in a spiral manner with a single winding at a constant pitch (interval). The double-wound coiled carbon fiber extends in a spiral shape with two coils alternately in close contact with each other, has a substantially cylindrical shape as a whole, and has a cavity formed at the center. A superelastic coil refers to a coil having a large coil diameter and a small wire diameter, and having a higher elasticity.

  The method for producing the above-described coiled carbon fiber is not particularly limited. For example, a raw material gas such as acetylene is thermally decomposed in the presence of a catalyst such as nickel by a vapor deposition method (CVD method), whereby a coiled carbon fiber is produced from the raw material gas.

  In order to carry a magnetic oxide or derivative oxide on the surface of such a coiled carbon fiber, for example, the coiled carbon fiber is added to an aqueous solution of a metal salt, mixed and stirred, and sodium hydroxide is added to the stirred aqueous solution. By adding an aqueous solution and setting the pH to 12 or more, the metal hydroxide and the coiled carbon fiber can be co-precipitated. By holding the coprecipitate at 50 ° C. or higher, the crystal structure of the magnetic oxide or derivative oxide can be grown as a crystal structure on the surface of the coiled carbon fiber (for details, see Japanese Patent Application Laid-Open No. 2012-12736). No.).

  The metal used as a raw material of the magnetic oxide or dielectric oxide that can be supported (adsorbed) by the coiled carbon fiber by this manufacturing method is Fe, Ni, Mn, Zn, Co, Ba, Ti, Zr, Sr. , Ca, Mg, Y, Cu. The first feature common to these metals is that they are dissolved in water or an aqueous solution of hydrochloric acid, nitric acid, or sulfuric acid in the state of any compound of oxide, chloride, sulfate, and nitrate. . The second feature is that it coprecipitates with the coiled carbon fiber as a hydroxide under strong alkali conditions.

The compounds used as raw materials for the magnetic oxide or dielectric oxide used in the present invention are listed. As the chloride, one of FeCl ₃ , FeCl ₂ , NiCl ₂ , MnCl ₂ , ZnCl ₂ , CoCl ₂ , BaCl ₂ , TiCl ₄ , ZrCl ₄ , SrCl ₂ , CaCl ₂ , MgCl ₂ , YCl ₃ , CuCl ₂ is used. be able to. For sulfate, Fe ₂ (SO ₄ ) ₃ , FeSO ₄ , NiSO ₄ , MnSO ₄ , CoSO ₄ , ZnSO ₄ , BaSO ₄ , TiOSO ₄ , Ti (SO ₄ ) ₂ , ZrOSO ₄ , SrSO ₄ , CaSO ₄ , MgSO ₄ , Y (SO ₄ ) ₃ , or Cu (SO ₄ ) ₂ can be used. In nitrates, Fe (NO ₃ ) ₃ , Fe (NO ₃ ) ₂ , Ni (NO ₃ ) ₂ , Mn (NO ₃ ) ₂ , Mn (NO ₃ ) ₃ , Zn (NO ₃ ) ₂ , Co (NO ₃ ) ₂ , Co (NO ₃ ) ₃ , Ba (NO ₃ ) ₂ , Sr (NO ₃ ) ₂ , Ca (NO ₃ ) ₂ , Ti (NO ₃ ) ₄ , ZrO (NO ₃ ) ₂ , Mg (NO ₃ ) ₂ , Y (NO ₃ ) ₃ , or Cu (NO ₃ ) ₂ can be used. In addition, any of oxides of Fe, Ni, Mn, Co, Zn, Ba, Ti, Sr, Ca, Zr, Mg, Y, and Cu can be used.

  The coprecipitated metal hydroxide and the coiled carbon fiber are kept at a strong alkalinity of pH 12 or more for a predetermined time, so that the surface of the coiled carbon fiber has a magnetic oxide or dielectric oxide. Crystals are formed. The formed crystal structure is one of spinel type, perovskite type, garnet type, and hexagonal type.

  In order to grow a crystal structure under strongly alkaline conditions, it is necessary to hold a mixture of magnetic oxide or dielectric hydroxide and coiled carbon fiber for a predetermined time. In the case of holding at 50 ° C., a holding period of about one week is required. In the case of holding at 100 ° C. to 200 ° C., it is necessary to hold for several minutes or more. Thus, a magnetic material-supported coiled carbon fiber having a magnetic oxide or derivative oxide supported on the surface can be produced.

Specific examples of the support of the magnetic material-supported coiled carbon fiber include Ni _x Zn _1-X Fe ₂ O ₄ (X is greater than 0 and less than 1). Examples of the magnetic material-supported coiled carbon fibers include those in which a magnetic oxide of Ni _0.8 Zn _0.2 Fe ₂ O ₄ is supported.

  The content of the magnetic material-supported coiled carbon fiber in the electromagnetic wave absorbing coating agent varies depending on the type and amount of the magnetic material to be supported. The weight ratio of only the coiled carbon fiber contained in the magnetic material-supported coiled carbon fiber is 1% by weight with respect to the weight of the aqueous emulsion or thickener such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene and bioplastic. The content is preferably 40% by weight or less. More preferably, they are 1 weight% or more and 20 weight% or less. When the content of coiled carbon fiber is less than 1% by weight, the proportion of coiled carbon fiber in water-based emulsions or thickeners such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene and bioplastic is small, and electromagnetic wave absorption The rate drops. When the content of the coiled carbon fiber exceeds 40% by weight, the coiled carbon fibers in the water-based emulsion or thickener such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene and bioplastic are in contact with each other, and almost all There is a possibility that the coiled carbon fiber is not electrically independent of other coiled carbon fibers. When coiled carbon fibers in water-based emulsions or thickeners such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene and bioplastics are not electrically independent of each other, electromagnetic waves are generated due to increased conductivity. Reflects but does not absorb electromagnetic waves because individual coiled carbon fibers do not function as solenoids. On the other hand, when the content of the coiled carbon fiber is 40% by weight or less, at least a part of the coiled carbon fiber is electrically independent from other coiled carbon fibers. When coiled carbon fibers in water-based emulsions or thickeners such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene and bioplastics are electrically independent from each other, the coiled carbon fibers function as a solenoid. Absorbs electromagnetic waves. In addition, coiled carbon fibers function as reactance in water-based emulsions or thickeners such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene, and bioplastics, and silicon, acrylic, urethane, epoxy, polyethylene, polypropylene, and bio A water-based emulsion such as plastic or a thickener functions as a capacitance. Therefore, water-based emulsions or thickeners such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene, and bioplastic function as capacitance. Therefore, a structure in which a large number of LC circuits are electrostatically bonded to each other in a water-based emulsion or thickener such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene, and bioplastic can be constructed. As a result, water-based emulsions or thickeners such as silicon, acrylic, urethane, epoxy, polyethylene, polypropylene, and bioplastic strongly absorb electromagnetic waves at the resonance frequency of the LC circuit.

  The electromagnetic wave absorption characteristic of the coiled carbon fiber carrying the magnetic material as the electromagnetic wave absorbing material is improved by the synergistic action of the coiled carbon fiber and the magnetic material. By supporting a magnetic material on the coiled carbon fiber, the inductance of the coil can be tuned. Thereby, the frequency band of the electromagnetic wave which a magnetic body can absorb is expanded.

Furthermore, optionally, as a second electromagnetic wave absorber, a conductor such as nickel or a ferrite (magnetic material) such as magnetite (Fe ₃ O ₄ ), manganese zinc ferrite, nickel zinc ferrite, or copper zinc ferrite may be mixed. Good. The content of the second electromagnetic wave absorbing material is preferably 10 times or less that of the coiled carbon fiber in weight ratio. By containing a magnetic material such as ferrite as the second electromagnetic wave absorbing material, the electromagnetic wave absorption band is different from that of the magnetic material-supported coiled carbon fiber, and therefore the frequency band of the electromagnetic wave that can be absorbed is expanded.

  The electromagnetic wave absorption characteristics of the electromagnetic wave absorbing coating agent containing a conductor as an electromagnetic wave absorbing material in addition to the coiled carbon fiber is improved by the synergistic action of the coiled carbon fiber and the conductor. In the electromagnetic wave absorbing coating agent, the coiled carbon fiber functions as reactance, the conductor functions as resistance, and the base material functions as capacitance. Therefore, an LC circuit, a CR circuit, and an LCR circuit are built in the electromagnetic wave absorbing coating agent. As a result, the electromagnetic wave absorbing coating agent strongly absorbs electromagnetic waves having resonance frequencies of these LC circuit, CR circuit and LCR circuit.

  The electromagnetic wave absorption characteristics of the electromagnetic wave absorbing coating agent containing a magnetic material as an electromagnetic wave absorbing material in addition to the magnetic material-supported coiled carbon fiber is improved by the synergistic action of the magnetic material-supported coiled carbon fiber and the magnetic material. In the electromagnetic wave absorbing coating agent, the coiled carbon fiber functions as reactance, and the base material functions as capacitance. Therefore, an LC circuit is built in the electromagnetic wave absorbing coating agent. When an induced current is generated in the reactance in the LC circuit located in the vicinity of the magnetic material, the magnetic resistance of the magnetic material is increased by an induced magnetic field based on the induced current. The increase in the magnetic resistance enhances the electromagnetic wave absorbing ability of the magnetic material and expands the frequency band of the electromagnetic wave that can be absorbed by the magnetic material.

  Furthermore, when producing the electromagnetic wave absorbing coating agent, it may be produced by mixing a foaming agent. Through various experiments, the present inventor has found that the multi-frequency absorption characteristics are detected by including the magnetic material-supported coiled carbon fiber in the porous resin, and has an electromagnetic wave absorption performance in a wide band. From this point of view, the foamable coating agent having a plurality of pores in the electromagnetic wave absorbing coating agent can be obtained by mixing the foaming agent when preparing the electromagnetic wave absorbing coating agent mixed with the magnetic material-supported coiled carbon fiber. . Thereby, the frequency band of electromagnetic waves that can be absorbed by the electromagnetic wave absorbing coating agent is expanded.

  Examples of the foaming agent include resin fine particles having a so-called core-shell structure in which an aliphatic hydrocarbon (foaming agent) is wrapped with an acrylic plastic resin. The outer shell resin begins to soften by heating, and at the same time, the vapor pressure of the encapsulated foaming agent rises to a pressure sufficient to deform the particles, and expands when the outer resin is stretched. Thereafter, when the heating is stopped, the outer shell resin is hardened to form a hollow plastic balloon. It may be foamed after coating, or may be foamed and placed in a coating agent. For example, a microsphere in which a foaming agent is included in an outer resin may be used. As the microsphere, for example, Matsumoto Microsphere (registered trademark) manufactured by Matsumoto Yushi Co., Ltd., Expancel (registered trademark) manufactured by Nippon Ferrite Co., Ltd. can be preferably used.

  The following method is mentioned as an example as a preparation example using a foaming agent. The foaming agent is dispersed in the resin of the emulsion, and the resin is subjected to secondary foaming by reheating at the same time as or after drying. Then, the volume is increased by expanding the gas in the resin, and the magnetic material-supported coiled carbon fiber can be efficiently dispersed in the resin. The microspheres and the magnetic material-supported coil are sufficiently agitated and sufficiently uniformly in the resin until the microspheres and the magnetic material-supported coiled carbon fiber are prevented from aggregating and non-uniformly dispersing. Magnetic material-supported coiled carbon fiber in a coating resin dried by coating on a coating agent, for example, raw cloth or nonwoven fabric, and drying by foaming Can be dispersed uniformly and have a bubble-like structure with a space inside.

  The electromagnetic wave absorbing coating agent produced as described above has an expanded frequency band of electromagnetic waves that can be absorbed. By coating various parts, fabrics, etc., various parts, fabrics, etc. can be made into electromagnetic wave absorbing members. Can do. For example, in a conventional electronic device, a noise countermeasure material having specifications (characteristics, shape, etc.) suitable for a noise frequency or an installation site is selected and properly installed to take EMC countermeasures. On the other hand, the electromagnetic wave absorbing coating agent according to the present invention can absorb broadband electromagnetic waves in both the near field and the far field, and can also be used to coat various sheets, equipment and other parts to provide electromagnetic wave absorbing performance to the parts. Can be granted. For this reason, if the sheet is coated on the exterior of an electronic device or an electromagnetic wave absorbing coating agent is coated on the sheet, it can be expected to cope with almost all noise countermeasures.

  In particular, the coating agent of the present invention is coated or impregnated on a fabric such as a nonwoven fabric, so that a space is formed between the fibers of the nonwoven fabric.

  The electromagnetic wave absorbing coating agent described above is produced by the following method. In addition, the following manufacturing methods illustrate some of the embodiments of the present invention, and are not used for the purpose of limiting to these methods, and may be modified as appropriate without departing from the scope of the present invention. be able to.

(Production Method 1)
A magnetic material-supported coiled carbon fiber is mixed in a mixed solution of water, an alcohol solvent, and a surfactant, and the magnetic material-supported coiled carbon fiber is uniformly dispersed in the solution by stirring or ultrasonic dispersion. . As the alcohol solvent, a solvent having high affinity to both inorganic and organic materials and finally easily evaporated is selected. For example, C _n of at least one of methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, ter-butyl alcohol, 1-pentanol, 2-pentanol and 3-pentanol Alcohols represented by the structural formula of H _{2n + 1} OH can be used. In addition, divalent glycols, trivalent glycerols, and other polyhydric alcohols can be used as appropriate.

  As a surfactant, a magnetic substance is retained, so that an activator of naphthalene sulfonic acid formalin condensate as a dispersant for inorganic particles and an anionic activator for improving surface wettability to inorganics Should be used. Of course, a nonionic surfactant may be used.

  Next, a thickener is mixed into the uniformly dispersed solution to increase the viscosity of the solution and delay the aggregation of the dispersion. As the thickener used in this case, it is preferable to use an acrylic thickener that also functions as a binder. As for the thickener, for example, the viscosity of the emulsion is stably dispersed by thickening the emulsion using the thickener Visiser AP-2 (manufactured by Sanyo Chemical Industries), so that the coiled carbon fiber carrying the ferrite and the magnetic material is stably dispersed. It can be set as a coating agent and can give the optimal viscosity to a coating agent. Further, if necessary, a formalin condensate of sodium naphthalene sulfonate may be mixed to maintain dispersion. In addition, in order to maintain dispersion, not only formalin condensate of sodium naphthalene sulfonate but also cellulose, urethane, acrylic polyamide, or bentonite materials can be used for polymers that exhibit thixotropy or a crosslinked structure. The magnetic material-supported coiled carbon fiber can be dispersed and held.

Further, if necessary, magnetite _(Fe 3 _{O 4)} etc. of the ferrite (magnetic body) may be mixed.

  Thereafter, some or all of the alcohol in the solution is evaporated to complete the electromagnetic wave absorbing coating agent.

(Production method 2)
First, a monomer constituting silicon, acrylic, urethane, epoxy, polyethylene, polypropylene, bioplastic, and the like, water, and an appropriate surfactant as necessary are mixed to prepare an aqueous emulsion dispersion. The urethane may be a forced emulsification type emulsion using a surfactant as an emulsifier, or a self-emulsification type in which a hydrophilic group is introduced into a urethane resin. At this time, if necessary, an alcohol solvent may be mixed in order to improve dispersibility. As the alcohol solvent, a solvent having a high affinity for both inorganic and organic materials as described above and finally easily evaporated is selected. For example, C _n of at least one of methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, ter-butyl alcohol, 1-pentanol, 2-pentanol and 3-pentanol Alcohol represented by the structural formula of H _{2n + 1} OH can be used.

The magnetic substance-supported coiled carbon fiber described above is mixed into the prepared aqueous emulsion dispersion system, and stirred or ultrasonically dispersed to uniformly disperse the magnetic substance-supported coiled carbon fiber in the solution. As a result, the magnetic material-supported coiled carbon fibers are dispersed between the emulsions, and aggregation is prevented. Further, if necessary, a formalin condensate of sodium naphthalene sulfonate may be mixed to maintain dispersion. Further, if necessary, ferrite (magnetic material) such as magnetite (Fe ₃ O ₄ ) may be mixed.

  Thereafter, the alcohol in the solution is evaporated to obtain an electromagnetic wave absorbing coating agent.

  In addition, in the production method 1 and the production method 2 described above, a foaming agent may be mixed and foamed.

  An electromagnetic wave absorber can be obtained by applying the electromagnetic wave absorbing coating agent thus prepared to paper as a sheet. The substrate to be applied may be not only a sheet having a flexible fiber entangled but also a plate. It can be applied to a plate made of a synthetic resin such as acrylic or polyethylene, or to natural wood. It can also be applied to inorganic glass. Moreover, the resin sheet of an electromagnetic wave absorber can be obtained by using a fluororesin sheet or a water-repellent and oil-repellent sheet. Furthermore, the coating to the plate-like material can be performed by adjusting the coating amount using a flow coater or a knife coater using an electromagnetic wave absorbing coating agent.

(Example of production of magnetic material-supported coiled fiber)
As the magnetic material-supported coiled carbon fiber, a carbon microcoil having a length of 10 μm to 10 mm is prepared, and the coprecipitated nickel hydroxide, zinc hydroxide, iron hydroxide (III), and the prepared coiled carbon fiber, The solution was kept at 100 ° C. or higher for 16 hours while being precipitated in a strongly alkaline reaction solution. Thus, water molecules were removed from the state in which the above three metal hydroxides were polymerized by the crystallization step, and a stable spinel crystal structure was obtained. The composition ratio was Ni _x Zn _1-X Fe ₂ O _4. A magnetic material-supported coiled carbon fiber supporting a magnetic oxide (X = 0 and less than 1) was obtained. The weight ratio between the coiled carbon fiber and the magnetic oxide is 5: 7.

Example 1
120 g of an acrylic emulsion and 10.24 g of the magnetic material-supported coiled carbon fiber obtained above (mass in which the magnetic material-supported coiled carbon fiber is 10 wt% with respect to the solid content of the emulsion) are stirred for 30 minutes. , Mixed and stirred to obtain an electromagnetic wave absorbing coating agent. 5.80 g of this electromagnetic wave absorbing coating agent was applied to one side of an acrylic plate of 150 mm (length) × 150 mm (width) × 1 mm (thickness), dried and solidified at 100 ° C. (Example 1).

  As Comparative Example 1, a 150 mm (vertical) × 150 mm (horizontal) × 1 mm (thickness) acrylic plate to which nothing was applied was prepared.

The reflection attenuation factors of the acrylic plates of Example 1 and Comparative Example 1 were measured. The method of measuring the return loss rate is as follows. As shown in FIG. 1, a metal reflector (aluminum plate) is placed behind the object to be measured (sheet), and the magnitude of the reflected wave (amplitude V ₁ ) is measured when a plane wave (amplitude V ₀ ) is irradiated. The ratio was expressed as decibel (dB) by the following formula.

Return loss = 20 × log 10 (V ₁ / V ₀ )

The measurement results are shown in FIG. From this measurement result, it can be seen that the peak of attenuation is not observed in Comparative Example 1, whereas in Example 1, the reflected wave is attenuated in almost the entire frequency range of 70 to 110 GHz. In particular, it can be seen that a peak of attenuation is observed at 95 GHz to 100 GHz.

(Example 2)
40 g of the acrylic emulsion and 8.0 g of the magnetic material-supported coiled carbon fiber obtained above (mass in which the magnetic material-supported coiled carbon fiber is 16 wt% with respect to the solid content of the emulsion) are mixed with a stirrer for 30 minutes. , Mixed and stirred to obtain an electromagnetic wave absorbing coating agent. 20 g of the electromagnetic wave absorbing coating agent was applied on both sides of the polyester nonwoven fabric, dried and solidified at 100 ° C. (Example 2-1). 45 g of an acrylic emulsion, 7.8 g of the magnetic material-supported coiled carbon fiber obtained above and 15.8 g of ferrite (ratio in which the weight ratio of the magnetic material-supported coiled carbon fiber and ferrite is 1: 2). Mixing and stirring were performed for 30 minutes with a stirrer to obtain an electromagnetic wave absorbing coating agent. 20 g of the electromagnetic wave absorbing coating agent was applied to both sides of the polyester nonwoven fabric, dried and solidified at 100 ° C. (Example 2-2). The measurement results are shown in FIG. From this measurement result, it can be seen that in Example 2-2 using the coating agent of Preparation Example 2 mixed with ferrite, attenuation peaks are observed at two locations near 20 GHz and near 95 GHz.

(Example 3)
350 g of acrylic emulsion and 30 g of the magnetic material-supported coiled carbon fiber obtained above (mass in which the magnetic material-supported coiled carbon fiber is 10 wt% with respect to the solid content of the emulsion) are mixed with a stirrer for 30 minutes. Then, it was diluted with water and poured into a thick (on one side) 250 mm × 250 mm × 5 mm quartz plate (thickness 3 mm) using a stirring bar. Then, it dried and solidified at 100 degreeC (Example 3). As Comparative Example 2, a quartz plate (thickness 3 mm) only was prepared. The measurement results are shown in FIG. From this measurement result, it can be seen that in Comparative Example 2, no attenuation peak is observed, whereas in Example 3, attenuation peaks are observed at two locations near 75 GHz and 100 GHz.

Example 4
40 g of the acrylic emulsion and 5.12 g of the magnetic material-supported coiled carbon fiber obtained above (mass in which the magnetic material-supported coiled carbon fiber is 10 wt% with respect to the solid content of the emulsion) are mixed with a stirrer for 30 minutes. , Mixed and stirred to obtain an electromagnetic wave absorbing coating agent. The electromagnetic wave absorbing coating agent was applied to an automobile fabric using the coating agent in an amount of 6.1 g and a film thickness of 81.1 μm, dried at 100 ° C., and solidified (Example 4). In order to see the effect of superposition of the sheets coated with the coating agent, the radio wave absorption characteristics (transmission) in the case where the automotive fabric on which the coating film of Example 4 is formed n times (n = 1 to 4) Attenuation) was measured. As Comparative Example 3, only a material for automobiles was also measured. As shown in FIG. 5, the measurement method was such that a plane wave (amplitude V ₀ ) was incident on the object sheet, and the transmission attenuation was determined from the transmitted wave (amplitude V ₂ ) by the following equation.

Transmission attenuation = 20 × log 10 (V ₂ / V ₀ )

The measurement results are shown in FIG.
From this measurement result, it can be seen that the radio wave absorption characteristics are superior when a plurality of sheets are stacked, and the attenuation change is particularly large at 70 GHz to 100 GHz when a plurality of sheets are stacked.

(Other examples)
40 g of the epoxy emulsion and 7.9 g of the magnetic material-supported coiled carbon fiber obtained above were mixed and stirred with a stirrer for 30 minutes to obtain an electromagnetic wave absorbing coating agent. 6.30 g of the electromagnetic wave absorbing coating agent was applied to a 250 mm × 300 mm × 1 mm (thickness) nonwoven fabric by a coater, and then dried and solidified at 110 ° C. Even in such an epoxy emulsion, a reflection attenuation amount and a transmission attenuation amount substantially similar to those in the above embodiment can be obtained.

  40 g of the polyethylene emulsion and 7.9 g of the magnetic material-supported coiled carbon fiber obtained above were mixed and stirred with a stirrer for 30 minutes, and an acrylic thickener was added to this to adjust the viscosity and electromagnetic waves. An absorbent coating was obtained. 6.60 g of the electromagnetic wave absorbing coating agent was applied to a non-woven fabric of 250 mm × 300 mm × 1 mm (thickness) with a coater, and then dried and solidified at 110 ° C. Even in such a polyethylene emulsion, almost the same amount of reflection attenuation and transmission attenuation can be obtained as in the above embodiment.

  40 g of the silicon emulsion and 7.9 g of the magnetic material-supported coiled carbon fiber obtained above were mixed and stirred with a stirrer for 30 minutes, and an acrylic thickener was added thereto to adjust the viscosity. An electromagnetic wave absorbing coating agent was obtained. 7.10 g of the electromagnetic wave absorbing coating agent was applied to a non-woven fabric of 250 mm × 300 mm × 1 mm (thickness) using a coater, and then dried and solidified at 110 ° C. Even in such a polyethylene emulsion, almost the same amount of reflection attenuation and transmission attenuation can be obtained as in the above embodiment.

  In addition, this invention is not limited to each embodiment mentioned above, and it cannot be overemphasized that it can implement with a various aspect, as long as it belongs to the technical scope of this invention.

As shown in the above-described embodiment, there is industrial applicability as an electromagnetic wave absorber.

Claims (4)

water and,
An aqueous emulsion in which an acrylic resin is dispersed ;
A magnetic material-supported coiled carbon fiber on which a magnetic oxide of NixZn _1-X Fe ₂ O ₄ (X is greater than 0 and less than 1) is supported ;
Containing electromagnetic wave absorbing coating agent.   The electromagnetic wave absorbing coating agent according to claim 1, further comprising ferrite.   The electromagnetic wave absorbing coating agent according to claim 1 or 2, further comprising a foaming agent. A sheet coated with the electromagnetic wave absorbing coating agent according to any one of claims 1 to 3.

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