JPS6091699A - Electromagnetic shielding material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to electromagnetic shielding materials, particularly in the low frequency region (10
The present invention relates to an electromagnetic shielding material that effectively shields radio waves of up to 1000 MHz.

(Background technology) In fields such as Ichiko's 9 machines, telecommunications, and automatic control, with the shift to digitalization and IC, there is mutual interference within the circuit due to radiated noise generated by the electronic circuit. The impact on equipment has become a major problem (,%).Furthermore, 411
In order to meet the demand for plastic containers, development of electromagnetic shielding materials using composite materials has begun.

Most of them are made of composite materials in which conductive materials are mixed and dispersed in resin, and materials with properties similar to metals are being studied in various fields. In the case of conductive materials, although some of the electromagnetic waves are absorbed due to ohmic loss, most of the electromagnetic waves are reflected, thereby preventing the electromagnetic waves from passing through. Therefore, unnecessary electromagnetic waves are trapped inside the device, and their intensity increases. This not only increases the likelihood of interference between circuits within the device, but also leads to noise leakage from connectors and cables that are not sufficiently shielded.

To address these problems with conventional electromagnetic shielding materials, it is desirable to have an electromagnetic shielding material that can attenuate reflected waves by absorbing electromagnetic waves, rather than simply preventing the transmission of electromagnetic waves by reflecting them. It is rare.

To achieve this, it is best to use the magnetic loss of magnetic materials, and electromagnetic shielding materials of a composite type with ferrite powder and resin are being researched. Magnetic loss occurs as - due to the presence of the complex ratio permeability +g r -jL'r -g7r at high frequencies, and near the natural resonance frequency of the magnetic moment, rgr
Or has maximum 11th 1. Therefore, the natural resonant frequency is within the 1 to 4 wave number range (10 to IQOOMI) of electromagnetic shielding material.
-12) is desirable. However, ordinary ferrite powder has a natural resonance frequency of IG)12 or higher, so it does not have an IJ effect. Such continuous ferrite powder is produced by an aqueous solution method or a solid reaction-pulverization method. Here, regarding these manufacturing methods, 3zFe u-
In the case of X=O in X04, that is, magnetite (Fe
3O3) will be briefly explained using 119 as an example.

(I) Oh! The black pigment magnetite is produced using this method. FeC1 at a ratio of 1 molecule: 2 molecules
When NaOH aqueous solution is added to the aqueous solution of 7 and FeCl3,
Fe34 is obtained as a precipitate.

The reaction formula is as follows.

FeC17+2FeCI3+8NaOH+Na(O
H)2 + Fe(OH)3 +8NaCIFe(OH
)7 +2Fe(OH)3-+ Fe04 + 482
To obtain MzFe3-x03, MC12 (
For example, NHCl2) (b) Solid reaction-pulverization method The powder of α-Fe203 (Begara), which is a raw material, is reacted in a nitrogen atmosphere at a temperature of 1400°C for a firing time of 3 hours.
E! Get 3Q4. The reaction formula is as follows.

3Fea03+ 2Fe3Q4 + -02MIFe3
When obtaining -c03, a predetermined amount of MO (for example, N10) is mixed with a-Fe2Q3 and reacted. The ferrite thus obtained is ground into particles with an average particle size of 0.5 to 1 (lpm) using a grinding device such as a ball mill to obtain a target object.

However, conventional electromagnetic shielding materials using ferrite particles manufactured by such a manufacturing method have the following problems. That is, since the ferrite particles obtained by the method (a) above do not exceed Q,5p,m in average particle diameter and have a single magnetic domain structure, it is not possible to lower the rotational resonance frequency of the axis. In the frequency range (10 to 100,100 O) required for shielding, sufficient power cannot be obtained.

In addition, since the method (mentioned) involves sintering and further pulverization, it is not possible to lower the rotational resonance frequency of the shaft, which is in the frequency range required for shielding (10-10100O,!
), it is not possible to obtain an upward shift.

In addition, since the method (2) involves sintering, the crushing step 1
By selecting
The diameter is isotropically crushed particles, and the aspect ratio is small. Therefore, compared to method (a), although the natural resonance frequency can be shifted to a lower frequency region, it is not a major change.

(Objective of the Invention) The first object of the present invention is to solve such conventional problems,
Our objective is to provide an electromagnetic shielding material that can effectively shield radio waves in the frequency range required for shielding and that requires a lower blending ratio of ferrite than conventional ones. It is an electromagnetic shielding material made by mixing and dispersing plate-shaped ferrite particles in a volume percent.

Hereinafter, five aspects of the present invention will be explained with reference to the drawings.

(Structure and operation of the invention) First, plate-shaped ferrite particles will be explained. A plate-shaped ferrite particle is literally a ferrite particle formed into a plate shape. Figures 1 and 2 show plate-like ferrite 1. +L (-(Ni
O: ZnO: Fe 3 = 22.5: 22.
5:49.0), and the magnifications are 1550 times and 390θ times, respectively. As seen from these electron micrographs, ferrite particles are plate-shaped (
#1 piece shape).

Figure 3 shows the ferrite particles used in the conventional electromagnetic shield described above and the plate-shaped ferrite particles used in the present invention.
The relationship between the frequency of particles and the complex relative magnetic permeability μr (=p−'r − r) is shown. In the figure, curves A, A'
are p/r and gr, respectively, of the ferrite particles used in the conventional electromagnetic shield, and curves B and B' are gr and vr, respectively, of the plate-shaped ferrite particles used in the present invention. As can be seen from the figure, the natural resonance frequency of normal ferrite particles is approximately 2 to 3 GHz, the natural resonance frequency of plate-shaped ferrite particles is approximately 500 MH2, and IL:'r is considerably higher than that of conventional ones. Takes a large value.

Therefore, the frequency range (10 to 10
It can be seen that plate-shaped ferrite is extremely effective at 00100O. In each case of 21% in FIG. 3, 40% by volume of ferrite powder was mixed with 60% by volume of epoxy resin.

Here, a method for manufacturing plate-shaped ferrite particles will be explained. The plate-shaped ferrite particles are made from natural or synthetic plate-shaped hematite (11), and a method called the flux method is used. What is the flux method?・F e 203 and MO (M = Ni, Go,
In this method, ferrite is obtained by mixing powders of Mn, Cu, Mg, Zn, etc.) with fluxes such as sulfates, nitrides, halides, etc., and reacting them at a temperature of (C). Using platy hematite in this way,
A plate-shaped ferrite is obtained.

An example of the plate-like ferrite obtained in this way is as follows: Mixing ratio: 4 Fe2O3; 49 ll1 old, Ni
O; 25.5 mo1%.

ZnC1; 25.5 mo1% Flux: Li2SO4-Na25O* Heat treatment conditions: 800°C for 1 hour Electron micrographs: Figures 1 and 2, diameter 1-4 m,
Approximately 0.5 gm thick, 20 such plate-shaped ferrite particles are placed in the matrix.
Mix and disperse at ~65% by volume. Here, the ratio of the average diameter to the thickness of the plate-shaped ferrite particles is preferably such that the average diameter is 3 or more times the average thickness. Specifically, it is about 0.5 to 500 #i, m. This is because, as shown in Figure 3, the larger the ratio of the diameter to the thickness of the plate-shaped ferrite, the higher the effective magnetic permeability, and accordingly the natural resonance frequency shifts to a lower frequency, which is the applicable frequency of the electromagnetic shielding material. lO
The reason is that it is possible to increase the effect of magnetic loss by having a peak of . Furthermore, when a domain wall is generated in a particle, not only rotational resonance of the magnetic domain but also resonance due to movement of the domain wall occurs, which is more effective, but this is because a domain wall does not occur at Q, 5 gm or less. In addition, 20 plate-shaped ferrite particles are included in the matrix.
(1) Two-layer type (two-layer type consisting of a magnetic layer and a conductive layer) (2) Multi-component single-layer type (middle layer type with ferrite and conductive filler dispersed in resin) Mixed and dispersed at ~65% by volume (3) Middle component Middle layer type First, the two-layer type will be explained. The magnetic layer is made by mixing and dispersing plate-shaped turite particles at 2θ to 65% by volume in a 7-tooth (base material) made of a combination of one or more of various resins such as epoxy resins and silicone resins, or various rubbers. It is something.

The thickness is 1 to 5 IoO+. The conductive layer has a sheet resistance of 10Ω/or less in the case of a film, and 0.0Ω in the case of a thick layer.
It is necessary to have a volume resistivity of 10Ω-C1ll or less at a thickness of 3 to 2 fflIB.

The single layer type is composed of plate-shaped ferrite powder and conductive ferrite powder.
j11 filler in combination with a sexual substance in the matrix
It is used to combine and disperse. In this case, the plate-shaped ferrite powder and the conductive material are 20 to 60% by volume and 1% by volume, respectively.
It is preferable that the amount is 20% to 20%. The conductive substance is preferably a highly conductive substance such as metal or carbon, and is preferably granular, scaly, or short and fibrous in shape.

To further explain the single-component single-layer type, the plate-shaped ferrite particles described above had only magnetism, but better characteristics can be obtained if they also have conductivity. A typical plate-shaped ferrite having electrical conductivity is plate-shaped magnetite. Here, conductive ferrite is expressed as χFe5-xOt+ in the chemical formula (M = Ni, GO
, Kn, Cu, Zn, Mg; "l knee = 0
~0.5), the specific resistance is to-'-to-3Ω-cm
It is.

In another embodiment, the plate-shaped ferrite particles may be aligned in a certain direction. This is done by applying a magnetic field during molding,
Obtained by rolling. If the plate-shaped ferrite particles are aligned parallel to the plane on which the radio waves arrive, good shielding properties can be obtained.

Next, 1! according to the present invention described above! A preferred example of an electromagnetic shielding material using a magnetic shielding material will be described. Figure 4.5 shows measurement of frequency characteristics of transmission-1 and reflection ht of an electromagnetic shielding material using commonly used granular ferrite particles and an electromagnetic shielding material using plate-shaped ferrite particles J- according to the present invention. Show the results.

No. 41N is an example of a two-layer type, and the conventional example of the magnetic layer is a mixture of 60% by volume of granular ferrite in resin + knee ・1iJ'J grain size 2p, ta mixed and dispersed in a sorted shape with a thickness of 3 mm. The present invention is an electromagnetic shielding material made of wood 1.
nii Yumiko・IZ average diameter 4 wells, q7. Uniform thickness 0.5
These electromagnetic shielding materials are made by mixing and dispersing 60% by volume of plate-like ferrite grains of 50% by volume into a sorted shape with a thickness of 3mm. A sheet of 0.8 mm thick was prepared by mixing and dispersing % by volume of Chenpler (EC) and was formed on the back surface of the magnetic layer. The specific resistance of this conductive layer is 0.6 Ω-cm.

Figure 5 shows an example of a multi-component single layer type, and the conventional example is a resin containing 50% by volume of granular ferrite with -Ii average particle diameter of 21L, m and short copper fibers (diameter: 80mm, length: 3mm). This is a sample prepared by mixing and dispersing 8% by volume of ferrite particles into a sheet with a thickness of 3IIll, and in the present invention, plate-shaped ferrite particles with an average II'J diameter of 4ILm and an average thickness of 0.5pm are mixed and dispersed in a resin.
This is an electromagnetic shielding material made by mixing and dispersing 8% by volume of short fibers of zero body volume and negative phase (same as the conventional example) and forming it into a sheet with a thickness of 3IIll. In addition, in these figures,
The solid line shows the case where plate-shaped ferrite is used, and the broken line shows the case where granular ferrite is used.

As is clear from these figures, the present invention applies to the low frequency region (
100111 MHz) (7) It is extremely good as an electromagnetic shielding material that effectively shields radio waves.

(Effects of the Invention) As explained in [2], according to the present invention, it is possible to not only attenuate the amount of transmission but also the amount of reflection for radiation noise in the frequency range required for electromagnetic shielding materials. An electromagnetic shielding material is obtained.

[Brief explanation of the drawing]

Figures 1 and 2 have magnifications of 1550x and 38x, respectively.
Electron micrograph of plate-shaped ferrite at 00x, No. 3
The figure shows conventional granular ferrite and the plate-shaped ferrite of the present invention!・
Figure 4 is a diagram showing the frequency characteristics of the complex relative permeability of a sample in which 40% by volume of H2 is mixed and dispersed in a resin, Figure 4 is a diagram showing the relationship between transmission h1 and reflection amount with respect to frequency of a two-layer type electromagnetic shielding material, and Figure 5 The figure is a diagram showing the relationship between the amount of transmission and the amount of reflection with respect to frequency in a multi-component single layer type. A-11 End 'rA' when using granular ferrite
--- f when using granular ferrite. B --- p/rB when using a single plate ferrite
′---When using a single plate-like ferrite''r Patent applicant TDC Co., Ltd. 11+ t=+ Qiao #脣1 Patent attorney Tadashi Yamaki- Figure 4 Figure 5 Procedural amendment ( Method) % formula % 1, Incident display Showa 1-8 !I4j permission request No. 199206 2
, Name of the invention Electromagnetic shielding material 3, Relationship with the amended person's case Name of patent applicant (306) TDC Co., Ltd. (Other 1)
6. Column 7 for a brief explanation of drawings in the specification to be amended, "Fig. 1...Photograph" in page 12, line 16 to line 18 of the specification of the contents of the amendment has been changed to "Fig. In each figure, the magnification is 1.
"Electron micrographs of the grain structure of plate-shaped ferrite at 550x and 3900x". above names)

Claims (1)

[Claims] ゛11! 20 to 65% by volume of plate-shaped ferrite is mixed and dispersed in the matrix. , magnetic shielding material.