JP2008227175A - Electromagnetic shielding material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic shielding material which shields electromagnetic waves with sure at a low cost. <P>SOLUTION: The material comprises a microcapsule 2 consisting of shells 20 and 21 and a connotation 22 sealed up in the shell, and a matrix including the microcapsule 2. The connotation 22 contains magnetic powder 24 and a dispersion medium 23, and the magnetic powder 24 is movable in the dispersion medium 23. The electromagnetic wave is absorbed by the energy loss that occurs when the magnetic powder 24 moves in the dispersion medium 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electromagnetic wave shielding material that shields electromagnetic waves radiated from electric devices and the like.

  In recent automobile fields, it is considered promising to use an electric motor as a drive source in order to reduce or prevent harmful exhaust gas, and hybrid vehicles, fuel cell vehicles, etc. using an internal combustion engine and an electric motor as drive sources Has been developed. In recent years, electronic control by a CPU is the mainstream of vehicle control.

  Electromagnetic waves are radiated from electric devices such as secondary batteries and motors or electronic components such as CPUs. This electromagnetic wave has problems such as electromagnetic noise causing malfunction of peripheral devices, information leakage, and adverse effects on the human body. Therefore, various electromagnetic wave shielding measures are taken.

  The electromagnetic wave shielding means that the space is separated into two regions by a conductive material and electromagnetically isolated. The electromagnetic wave can be shielded by attenuating the energy of the electromagnetic wave by combining reflection / absorption / multiple reflection of the electromagnetic wave by the conductive material.

  For example, it is effective to enclose the electromagnetic wave generation source with a casing made of a conductive plate or a net. However, such an electromagnetic wave shielding material is generally a metal and has a large weight, so that when used in an automobile, fuel consumption is deteriorated. Moreover, although it is necessary to surround an electromagnetic wave generation source without gaps with a housing | casing, there exists a problem that the process of opening parts, such as a junction part and a door, is very difficult.

  Therefore, a method of forming a conductive thin film on the housing is known, but there is a problem that the manufacturing process is complicated and the cost is high. Further, although an electromagnetic shielding material in which conductive powder, conductive fiber and the like are mixed in a resin is known, it is difficult to achieve both physical properties such as strength and an electromagnetic shielding effect.

  Japanese Patent Laid-Open No. 2000-031688 proposes an electromagnetic wave shielding material in which a coiled carbide fiber made of carbon, silicon carbide, titanium carbide or the like is enclosed in a microcapsule together with a dispersion medium. According to this electromagnetic wave shielding material, an induced current is generated in the coiled carbide fiber by the electromagnetic wave, thereby absorbing the electromagnetic wave.

However, the coiled carbide fiber has a drawback that it is expensive due to its complicated manufacturing technique. Further, although the absorption effect is highest when the electromagnetic wave passes through the inside of the coil, it is difficult to orient all the coiled carbide fibers in the capsule in the direction of the electromagnetic wave, and therefore the electromagnetic wave absorption effect is not necessarily high. Absent.
JP 2000-031688

  This invention is made | formed in view of the said situation, and makes it the subject which should be solved to set it as the electromagnetic wave shielding material which can shield electromagnetic waves reliably cheaply.

A feature of the electromagnetic shielding material of the present invention that solves the above problems is an electromagnetic shielding material comprising a microcapsule comprising a shell and an inclusion body enclosed in the shell, and a matrix containing the microcapsule,
The inclusion includes a magnetic powder and a dispersion medium in which the magnetic powder is dispersed, and the magnetic powder is movable in the dispersion medium.

  According to the electromagnetic wave shielding material of the present invention, the magnetic powder is magnetized by the electromagnetic wave, and is oriented in the direction of the electromagnetic wave, or repulsion or adsorption due to mutual magnetic force occurs, whereby the magnetic powder moves in the dispersion medium. Electromagnetic waves can be absorbed and attenuated by energy loss due to this kinetic energy.

  Since magnetic powder is inexpensive and can absorb electromagnetic waves of a specific frequency by controlling the particle size or adjusting the viscosity of the dispersion medium, it is extremely useful as an electromagnetic shielding material.

  The electromagnetic wave shielding material of the present invention comprises microcapsules in a matrix. The matrix stably holds the microcapsules, and a resin, an organic binder, or the like is used, and a matrix that can transmit electromagnetic waves is used. For example, an electromagnetic wave shield can be performed by forming a housing from a resin mixed with microcapsules and surrounding an electromagnetic wave generation source. Moreover, an electromagnetic wave shielding material can also be formed by preparing a coating material containing an organic binder and microcapsules and solidifying it after application to a woven fabric, a nonwoven fabric, a net-like body or the like.

  As the resin used as the matrix, various thermoplastic resins such as polyolefin, polystyrene, polyamide, and ABS are suitable, but in some cases, a thermosetting resin such as epoxy resin and polyurethane can also be used. In addition, the mixing amount of the microcapsules in the matrix can be variously selected according to the use, the kind of the matrix, and the like.

  The microcapsule that characterizes the present invention includes a shell and an inclusion body enclosed in the shell. The shell is not particularly limited as long as it transmits electromagnetic waves, and conventionally used microcapsule shells such as acrylic resin, polyurethane, polyamide, epoxy resin, natural resin, melamine resin, urea resin, and gelatin are used. be able to. The thickness is not particularly limited.

  The inclusion body includes a magnetic powder and a dispersion medium in which the magnetic powder is dispersed. As the magnetic powder, powders such as paramagnetic substances and ferromagnetic substances can be used, but magnetic powders such as ferrite, iron oxide, and a high permeability Ni alloy (trade name: Permalloy) are preferable.

  The shape of the magnetic powder is not particularly limited, but is preferably a shape that is easy to move in the dispersion medium, such as granular or acicular. The particle size of the magnetic powder is preferably in the range of 0.1 to 10 μm. If the particle size is smaller than 0.1 μm, the energy loss during movement is reduced and the electromagnetic shielding effect is lowered, and if it is larger than 10 μm, it becomes difficult to form microcapsules.

  The frequency of electromagnetic waves that can be absorbed varies depending on the particle size of the magnetic powder. Therefore, by controlling the particle size of the magnetic powder, it is possible to absorb electromagnetic waves having a desired frequency according to the application. Further, if a plurality of kinds of magnetic powders having different particle diameters are mixed in one microcapsule, an electromagnetic wave shielding effect can be obtained in a wide frequency band.

  The dispersion medium is one that disperses and holds the magnetic powder in a movable manner, and liquid or gas is used. As the liquid dispersion medium, those having a low viscosity at room temperature are generally preferred, and various organic materials having a relatively low molecular weight such as aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, aliphatic esters, aromatic esters, alcohols and the like. A solvent, water, or the like can be used. Further, the moving speed of the magnetic powder can be defined by the viscosity of the dispersion medium, and the frequency of electromagnetic waves that can be absorbed can be adjusted. Depending on the frequency of the electromagnetic wave to be absorbed, or depending on the temperature of the environment in which it is used, high-molecular-weight hydrocarbons, liquids in which polymers are dissolved in various solvents, etc. It is also possible to use a liquid that becomes liquid. The gas dispersion medium is not particularly limited, such as air or nitrogen gas.

  The content of the magnetic powder in the inclusion body has an electromagnetic wave shielding effect as long as it is contained, but it is preferable to contain 10% by volume or more. The upper limit is desirably 50% by volume. If the magnetic powder exceeds 50% by volume, it becomes difficult to move in the dispersion medium, so that the loss energy is reduced and the electromagnetic shielding effect is reduced. A range of 10 to 30% by volume is particularly preferable.

  The inclusion body can also contain a dispersant, a surfactant, and the like for improving the dispersibility of the magnetic powder. Moreover, you may use the magnetic body powder previously processed with the coupling agent. By doing so, precipitation and solidification of the magnetic powder can be prevented.

  Further, a magnetic fluid in which magnetic fine particles are suspended in a high concentration in a fluid medium can be used as it is as an inclusion body or in a state of being dispersed or dissolved in another dispersion medium. In the magnetic fluid, the magnetic powder is stably dispersed by the surfactant, so that precipitation and solidification of the magnetic powder can be reliably prevented.

  In order to prepare a microcapsule encapsulating an inclusion body containing magnetic powder and a dispersion medium, a phase separation method in which a concentrated polymer phase is separated around the inclusion body dispersed in the polymer solution, and the dispersion is dispersed in the polymer solution. In-situ polymerization method in which the polymer is cured around the inclusion body, and a monomer or a polymerization catalyst is supplied from one of the inner phase or the outer phase of the emulsion in which the inclusion body is dispersed, and the periphery of the inclusion body is covered with the polymer. Further, an interfacial polymerization method in which a monomer is supplied from both the inner phase and the outer phase of an emulsion in which an inclusion body is dispersed can be used.

  Hereinafter, the present invention will be described specifically by way of examples.

Example 1
FIG. 1 shows an electromagnetic wave shielding material according to an embodiment of the present invention. This electromagnetic wave shielding material is composed of a resin plate 1 made of epoxy resin as a matrix and microcapsules 2 uniformly dispersed and held in the resin plate 1. The thickness of the resin plate 1 is about 2 mm, and the microcapsule 2 is contained by 50% by volume.

  The microcapsule 2 has a spherical shape with a diameter of 700 μm to 800 μm as shown in FIG. 2 and has a melamine resin outer shell 20 and a gelatin inner shell 21 formed on the inner peripheral surface of the outer shell 20. And an inclusion body 22 that fills the inside of the inner shell 21. The outer shell 20 has a thickness of about 50 μm, and the inner shell 21 has a thickness of about 50 μm.

  The inclusion body 22 includes a kerosene 23 (dispersion medium) having a viscosity of 10 centipoise and a ferrite powder 24 (magnetic powder) dispersed in the kerosene 23. The ferrite powder 24 has a particle size of 0.3 μm ± 0.1 μm and is contained in the inclusion body 20 by 20% by volume. The ferrite powder 24 is uniformly dispersed in the kerosene 23.

  This microcapsule 2 was prepared as follows. First, solution A in which ferrite powder 24 is dispersed in kerosene at a predetermined concentration is mixed with solution B in which gelatin is dissolved in water, and dispersed using an homogenizer so that the diameter of the oil droplets is about 700 μm. A W dispersion was prepared. On the surface of the oil droplet, an inner shell 21 is formed by gelatin solidification.

  The obtained solidified body comprising the inner shell 21 was mixed with a melamine-formaldehyde resin aqueous solution, and then a 20% aqueous acetic acid solution was added dropwise to adjust the pH to 6. The liquid temperature was raised to 65 ° C. and a condensation reaction was carried out for 6 hours to form an outer shell 20 made of melamine resin on the surface of the inner shell 21.

  Next, a predetermined amount of the microcapsule 2 obtained by filtration and drying was mixed with a liquid epoxy resin and injection molded into a mold to obtain an electromagnetic wave shielding material shown in FIG.

  This electromagnetic wave shielding material was cut into test pieces, and an electromagnetic wave shielding test was conducted in the thickness direction by the KEC method. As a result, an electric field attenuation of about 5 dB was observed in the range of 1 MHz to 1 GHz, and it was confirmed that the electromagnetic wave was absorbed by the movement of the ferrite powder 24 in the microcapsule 2.

(Example 2)
FIG. 3 shows an electromagnetic shielding material according to a second embodiment of the present invention. This electromagnetic shielding material is an electromagnetic shielding apron, and includes an apron body 3 made of woven fabric and a shield layer 4 formed on the surface of the apron body 3. The shield layer 4 is composed of a matrix 40 made of polyvinyl pyrrolidone and microcapsules 5 uniformly dispersed in the matrix 40.

  The microcapsule 5 shown in FIG. 4 was the same as that in Example 1 except that the particle size of the ferrite powder 50 was different, and was formed in the same manner as in Example 1. The ferrite powder 50 has an average particle size of 0.3 μm, and the particle size distribution has a normal distribution in the range of 0.1 μm to 0.5 μm centering on the average particle size.

  This electromagnetic wave shielding material was formed by applying a coating material in which microcapsules 5 were mixed with a melamine resin aqueous solution to the surface of the apron body 3 and curing it by heating.

  Also in the electromagnetic wave shielding material of the present embodiment, electromagnetic waves in a wide frequency range can be absorbed by the loss energy due to the movement of the ferrite powder 50 in the microcapsule 5 by the electromagnetic waves, and the human body can be protected.

It is a principal part expanded sectional view of the electromagnetic wave shielding material which concerns on one Example of this invention. It is an expanded sectional view of the microcapsule used for the electromagnetic wave shielding material which concerns on one Example of this invention. It is a principal part expanded sectional view of the electromagnetic wave shielding material which concerns on the 2nd Example of this invention. It is an expanded sectional view of the microcapsule used for the electromagnetic wave shielding material which concerns on the 2nd Example of this invention.

Explanation of symbols

1: Resin plate (matrix) 2: Microcapsule
20: outer shell (shell) 21: inner shell (shell) 22: inclusion
23: Kerosene (dispersion medium) 24: Ferrite powder (magnetic powder)

Claims (2)

An electromagnetic shielding material comprising a microcapsule comprising a shell and an inclusion body enclosed in the shell, and a matrix containing the microcapsule,
The inclusion includes a magnetic powder and a dispersion medium for dispersing the magnetic powder,
An electromagnetic wave shielding material, wherein the magnetic powder is movable in the dispersion medium.   The electromagnetic shielding material according to claim 1, wherein the dispersion medium is liquid at normal temperature.

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