JP2004119855A - Electromagnetic wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electromagnetic wave absorber that has a fundamental performance as a building material and can be easily used for construction since a conventional paint and a board that have the electromagnetic wave absorbency effective in high frequency ranges have had such many problems or the like as it needs a special construction method, a combination with other boards and besides it is expensive, whereby they have been untreatable as a common construction material. <P>SOLUTION: The electromagnetic wave absorber is obtained with high efficiency and absorbency in the special high-frequency band of 1 GHz or more, the electromagnetic wave absorbency and a performance as an inexpensive construction material by combining the layers consisting mainly of graphite, microballoon and binder to form a multiple layer. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electromagnetic wave absorber for preventing electromagnetic interference due to a mobile phone, a PHS, a wireless network of a computer, a malfunction of an ETC and the like.
[0002]
[Prior art]
2. Description of the Related Art In recent years, high-capacity high-speed data communication such as a wireless LAN, a mobile phone, and an ITS (Intelligent Transport System) in a computer network has become widespread.
[0003]
However, the deterioration of the radio wave transmission environment due to the crosstalk of radio waves is inevitable, and the communication speed is reduced. Furthermore, ITS is being promoted. For example, a non-stop automatic toll collection system (ETC) that can be settled without stopping at a tollgate on an expressway has already been put into practical use. The two-way wireless communication between the two uses a high frequency band of 5.8 GHz, and there is a concern that a large trouble caused by malfunction due to irregular reflection of metal or the like may occur. It has been proposed as an effective means to provide an electromagnetic wave absorbing material for the purpose of improving them.
[0004]
However, systems such as mobile phones, PHSs, computer wireless networks, and ITS are required to process a large amount of bidirectional information in a short period of time, so that a high frequency band (1 GHz to 20 GHz) is used. However, the response in the equipment and environment in the high frequency band has not yet caught up.
[0005]
For example, most of the electromagnetic wave absorbers mainly use magnetic oxide powder such as ferrite, but have a half or less absorption performance in a band of 1 GHz or more, and paint using other conductive powders or electromagnetic wave loss materials. Plates and plates are effective in some high frequency bands, but they were not easily handled as general building materials.
[0006]
As an electromagnetic wave absorbing material effective in a high-frequency region, there is disclosed a material in which an insulating layer is formed on a conductive layer, and a resist layer is formed by spraying a paint mixed with a conductive powder (for example, Patent Document 1). 1).
Further, particularly as a building board, a gypsum board or a calcium silicate board containing an electromagnetic wave loss material is disclosed (for example, see Patent Document 2).
[0007]
[Patent Document 1]
JP 2001-320191 A
[Patent Document 2]
JP-A-6-209180
[0008]
[Problems to be solved by the invention]
Conventional paints and plates with effective electromagnetic wave absorption in the high-frequency range have many problems, such as those that are applied by a special construction method, that they need to be combined with other plates, and that they are more expensive. An object of the present invention is to obtain an electromagnetic wave absorber that has basic performance as a building material and can be easily constructed because the material cannot be treated as a typical building material.
[0009]
[Means for Solving the Problems]
In the present invention, by combining layers consisting mainly of graphite, microballoons, and binders to form a multilayer, high efficiency in a specific high-frequency band of 1 GHz or higher, electromagnetic wave absorption, and inexpensive building materials To obtain an electromagnetic wave absorber having the performance as described above.
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electromagnetic wave absorber for preventing electromagnetic interference due to a mobile phone, a PHS, a wireless network of a computer, a malfunction of an ETC and the like.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The graphite used in the present invention is in the form of powder or granules having a shape having an average particle diameter of 4 μm to an average particle diameter of 37 μm.
[0011]
The microballoon is a hollow body, there is a balloon made of an organic material typified by a copolymer such as vinylidene chloride or acrylic, a balloon made of an inorganic material typified by shirasu balloon and pearlite, but the density of the finished, The selection may be made in consideration of the physical performance, the manufacturing method, the type of the binder, and the like.
[0012]
The binder may be either organic or inorganic, and may be determined in consideration of compatibility with graphite and microballoons, and if the surface material is to be integrated, in consideration of the compatibility with the surface material.
[0013]
The way of combining the layers is such that the graphite layer (density) of the reflection side layer is higher (higher) than the incident side layer, and the incident side layer is set thicker than the reflection side layer. More efficient. In addition, although it expresses here as a plurality of layers, it may be what is laminated by a wet method, or what is composed by laminating plate materials.
[0014]
Various settings are possible for the density of the electromagnetic wave absorber, but in consideration of the performance required as a building material, generally, the specific gravity is preferably 0.1 to 2.0.
[0015]
In addition, the electromagnetic wave absorber can be integrated with various surface materials, but the surface material on the incident side is plywood, decorative board, gypsum board, cloth, resin plate, etc., and the surface material on the reflection side is Materials used for construction and construction, such as metal plates, metal foils, and metallized films.
[0016]
(Example)
Graphite has a small aspect ratio, a grade having an average particle diameter of 8 μm and a maximum particle diameter of 44 μm, and Matsumoto Microsphere (registered trademark) F-50E is used as a microballoon. The microballoon is an unexpanded particle and has a relatively low temperature. The binder used is phenol.
[0017]
First adjust the viscosity by adding water to phenol, then mix and disperse the graphite thoroughly and stir, then add the catalyst and stir, immediately mix with the microballoons and mix well, then put in the mold However, at this time, it was spread in a mold so as to be as uniform as possible, pressed to a predetermined thickness with the upper mold, and heated at about 100 ° C. to accelerate the curing. Next, the sample is taken out of the mold and dried to remove residual moisture, thereby obtaining a further sample.
When preparing a two-layer sample, do not remove one sample from the mold, put the same mixture of phenol, water, graphite and microballoon on it, place the upper mold in the two-layer position, and heat did. Next, it was removed from the mold and dried to remove residual moisture.
One layer was similarly added over the two layers to make a three layer sample.
[0018]
When observing the cross section of the sample obtained in the above example, the microballoon is inflated, but this is not spherical like unexpanded before heating, but it is deformed so as to close the void of the binder as much as possible, One that matches the shape of the mold is obtained. This is because the heating at the time of preparing the sample not only hardened the binder but also softened the shell wall of the microballoon, which improves various performances of the electromagnetic wave absorber of the present invention.
[0019]
Although the microballoon used in the above example uses an acrylic copolymer, the smooth shell wall is excellent in the wetting characteristics of the phenol as a binder, and the amount of the binder can be reduced as much as possible, so that the microballoon is used as an electromagnetic wave absorber. Selection of reducing the influence of the material of the binder, increasing the characteristics of the binder, and the like becomes easy, and a more flexible absorber can be obtained.
[0020]
That is, by selecting a microballoon having a smooth surface, expanding at a specific temperature, and softening the shell wall, various designs can be made.
[0021]
However, electromagnetic wave absorbers manufactured using microballoons with a high shell wall softening point, that is, performance as an electromagnetic wave absorber even if the shape of the microballoons remain spherical, require, for example, especially fireproof performance. This is effective in cases such as
[0022]
With respect to the above samples, the amount of electromagnetic wave absorption, frequency, and the like were measured at an incident angle of 0 °. FIG. 1 is a graph showing the relationship between the amount of electromagnetic waves absorbed (actually measured values) and the total carbon density in each sample. The total carbon density is the carbon density of the entire sample (electromagnetic wave absorber).
[0023]
In FIG. 1, the sample indicated as “10/4” has a thickness of the reflection-side layer of 20 mm, a thickness of the intermediate layer of 10 mm, a thickness of the incident-side layer of 10 mm, and a carbon of the incident-side layer. The density is 0.04 g / cm ³ , “10/5” is 20 mm, 10 mm, 10 mm, 0.05 g / cm ³ , “20/4” is 10 mm, 10 mm, 20 mm, 0.04 g / cm ³ , “ “20/5” is 10 mm, 10 mm, 20 mm, and 0.05 g / cm ³ .
[0024]
From the graph of FIG. 1, it can be seen that a sample having a lower carbon density of the incident side layer has a higher absorption amount at a lower total carbon density than a sample having a higher carbon density, and a sample having a thickness of the incident side layer of 20 mm than 10 mm. Can be seen to tend to show a higher absorption at a lower total carbon density.
[0025]
The thickness of the two-layer sample was changed and measured. FIG. 2A shows the thickness on the horizontal axis and the maximum absorption wavelength on the vertical axis, and FIG. 2B shows the absorption amount on the vertical axis. ). The thickness is the thickness of the entire sample. The thickness of the layer on the incident side is fixed to 20 mm, and only the thickness of the layer on the reflection side is changed.
[0026]
Peaks 2, 3, and 4 in FIG. 2A are peaks of a curve composed of a frequency and an absorption amount in a sample having a constant thickness, and are the order of peaks appearing at 1 GHz or more. From FIG. 2A, it can be seen that the peak 3 covers around 5.8 GHz, which is the frequency used in ETC.
[0027]
FIG. 2 (B) shows the relationship between the thickness and the amount of absorption for peak 3, and the value between 34 and 40 mm satisfies the value of 20 dB or more, which is the performance standard value of the ETC electromagnetic wave absorbing panel. It can be seen that the maximum absorption amount is the thickness of 37.5 mm.
[0028]
Although not shown in the figure, the two-layered sample, like the three-layered sample, tends to show a higher absorption at a lower total carbon density than a sample with a lower carbon density in the incident side layer. It was confirmed that the sample having the incident side layer having a thickness of 20 mm was more likely to exhibit a higher absorption amount at a lower carbon density than the sample having a thickness of 10 mm.
[0029]
【The invention's effect】
According to the present invention, (1) a high-efficiency electromagnetic wave absorber can be easily set in a required specific frequency band by combining layers having different graphite densities and microballoon sizes and thicknesses. The use of micro-balloons makes it excellent in lightness and can be used as a building material. Further, by being integrated with the surface material, it is useful not only as an electromagnetic wave absorber but also as a building material. Since graphite is mixed into the binder and then mixed with the microballoons, a uniform distribution matrix can be easily obtained. (4) If microballoons with smooth shell walls are used, the amount of binder can be reduced as much as possible. (5) Heating makes it easy to select the effect of reducing the influence of the material of the binder on the absorber and increasing the characteristics of the binder. By adopting micro-balloons that expand, foam, and soften, the resulting micro-balloons of the electromagnetic wave absorber are not spherical, but have a shape that closes the gaps between the binders as much as possible. It becomes an electromagnetic wave absorber with excellent absorbability. (5) It can be made into a complex shape by using a mold or the like, and can be provided as a material that satisfies complicated shapes such as buildings. If a balloon is used, a flexible electromagnetic wave absorber can be obtained. (7) If an inorganic microballoon is used, an electromagnetic wave absorber excellent in fire resistance can be obtained. (8) It is extremely useful as an electromagnetic wave absorber. Features and effects such as inexpensiveness can be obtained.
[Brief description of the drawings]
FIG. 1 is a graph showing a relationship between an electromagnetic wave absorption amount and a total carbon density.
FIG. 2A is a graph showing the relationship between the maximum absorption wavelength and the thickness of the electromagnetic wave absorber, and FIG. 2B is a graph showing the relationship between the absorption amount and the thickness.

Claims (3)

An electromagnetic wave absorber comprising a combination of at least a plurality of layers formed of graphite, microballoons, and a binder. 2. The electromagnetic wave absorber according to claim 1, wherein a face material is integrated at least on one side. 3. The electromagnetic wave absorber according to claim 2, wherein the one side material is a metal or a material containing a metal.

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