JPH0571199B2 - - Google Patents

Description

[Detailed description of the invention] B Industrial application field The present invention relates to an electromagnetic shielding material.

B. Prior art In recent years, with the spread of electrical and electronic devices, plastics have come to be used frequently to make these devices lighter and cheaper.
Electromagnetic interference due to electromagnetic waves leaking from electronic devices is becoming a major problem. Precision electrical and electronic devices such as computers and precision measuring instruments often malfunction or produce errors in measured values when exposed to external electromagnetic waves. For this reason, electromagnetic wave regulations have been enacted in the United States and West Germany, and it is planned that an electromagnetic wave regulation system will soon be established in Japan as well.

However, although various methods have been studied to shield electromagnetic waves, none of them are sufficient.

For example, methods for covering the surface of a plastic casing of electrical or electronic equipment with a shielding material include painting with conductive paint, zinc spraying, plating, vapor deposition, and sputtering. In these methods,
Shielding the electric field component is quite effective, but
It has little effect on magnetic field components in the low frequency range,
Furthermore, there is also the problem of peeling, which may cause trouble, and it cannot be said to be a sufficient countermeasure.

In addition, as a method of shielding electric and electronic equipment by mixing metal fillers into the plastic mentioned above, stainless steel fibers, etc. are used, considering the shielding of magnetic field components, but this also has a sufficient shielding effect. isn't it. That is, in order to have a sufficient shielding effect, it is necessary to add a considerable amount of the above-mentioned metal filler, which results in a decrease in the strength of the plastic, and also because the metal filler appears on the surface and requires further painting. The cost will be high.

Furthermore, iron foil is also being considered as a shielding material with consideration given to shielding the magnetic field component, but it has low magnetic permeability for magnetic field components in the low frequency range and cannot provide a sufficient shielding effect. Compared to copper, aluminum, etc., it has a higher electrical resistance with respect to electric field components, and its shielding properties are not sufficient.

C. Purpose of the Invention The present invention has been made in view of the above circumstances, and aims to improve the effects of electromagnetic waves over a wide frequency range, including magnetic field components in the low frequency range and electric field components in the high frequency range. The purpose of this invention is to provide an electromagnetic shielding material that is flexible and easy to handle.

D. Structure of the Invention The present invention comprises at least one amorphous alloy layer and at least one layer of a reticular conductive metal sheet, and the one layer of the amorphous alloy layer and the reticular conductive metal sheet. The amorphous alloy layer has a thickness of 5 to 100 μm and an aspect ratio (however, the aspect ratio is the ratio of the maximum length to the maximum thickness). ratio.) 10~
The present invention relates to an electromagnetic shielding material having a structure in which 15,000 scale-like or flake-like soft magnetic amorphous alloy pieces are laminated with a weight per unit area of 100 to 500 g/m ² .

E. Effects of the Invention Amorphous alloys have attracted attention as various functional materials because they exhibit unique chemical and mechanical properties that are not found in ordinary crystalline alloys. Among them, amorphous alloys such as iron-based and cobalt-based alloys do not exhibit crystal anisotropy, so they exhibit extremely good soft magnetic properties such as extremely low coercive force and high magnetic permeability.
It is hoped that this property will be utilized for practical application.

However, amorphous alloys are usually several tens of micrometers thick and wide.
It is supplied in a ribbon shape of about 100 mm, and it is extremely difficult to handle it because there are problems with damage when cutting it and adhesion when stacking it to make it into plates of the specified size. Furthermore, in order to obtain a predetermined thickness, it is necessary to laminate many layers, which requires a large number of man-hours and is problematic in terms of productivity.

As a result of intensive research, the present inventor has found that by making a magnetic amorphous alloy into scales and laminating them, the above-mentioned excellent properties of the magnetic amorphous alloy can be retained, and productivity can be improved. It was also discovered that an excellent magnetic shielding material can be obtained. The present invention has been made based on the above findings.

If the thickness of the soft magnetic amorphous alloy flake (hereinafter simply referred to as amorphous alloy flake) is less than 5 μm, it is difficult to manufacture an amorphous alloy flake, and if it becomes thicker than 100 μm, it will become amorphous. This thickness is set to 5 to 100 μm since it becomes difficult to form a thin film. Particularly preferred thickness is 20~
It is 60μm.

If the aspect ratio of the amorphous alloy flakes is less than 10, the magnetic permeability of the amorphous alloy flakes decreases, the magnetic properties of the amorphous alloy flakes change, and lamination becomes difficult, resulting in deterioration of magnetic shielding properties. It becomes like this. On the other hand, if the aspect ratio exceeds 15,000, handling of the amorphous alloy pieces becomes troublesome and productivity decreases. A particularly preferred range of aspect ratio is 50~
It is 10000.

The weight of the above amorphous alloy piece per unit area is
The amorphous alloy layer is made by laminating them at a density of 100 to 500 g/ ^m2 , but the amount of amorphous alloy pieces is
If it is less than 100 g/m ² , it becomes difficult to stack the amorphous alloy pieces and contact (conduct) between them, resulting in deterioration of magnetic shielding properties. If this exceeds 500g/ ^m2 , it becomes difficult to stack and adhere the amorphous alloy flakes, creating voids in the amorphous alloy layer, which increases the amount of amorphous alloy flakes per unit area. Despite this, the magnetic shielding properties deteriorate. A particularly preferable range of the above amount of amorphous alloy flakes is 200~
It is 350g/ ^m2 .

The amorphous alloy layer with the above structure is made of amorphous alloy pieces that exhibit good soft magnetic properties, so it is effective in shielding magnetic field components in the low frequency range, but it is effective in shielding magnetic field components in the high frequency range. Since the electric field component is the main component for electromagnetic waves, the electrical resistance is higher (100 to 150 μΩ cm) compared to conductive materials with low electrical resistance such as copper or aluminum, so the thickness must be increased. It is disadvantageous.

On the other hand, conductive materials with low electrical resistance are used for electromagnetic shielding materials used in high frequency regions, but since these are non-magnetic materials or magnetic materials with low magnetic permeability, they are susceptible to magnetic field components in low frequency regions. Against them, they are almost powerless.

Therefore, in the present invention, a layer made of laminated amorphous alloy flakes is used as a layer effective in shielding magnetic field components in a low frequency region, and a shield is effective in shielding electric field components in a high frequency region. Layers of conductive materials are laminated to effectively shield electromagnetic waves in a wide frequency range.

If the structure is such that the amorphous alloy layer and the conductive material layer are directly adhered to each other, the two layers will interfere with each other and the properties cannot be expected, and lamination using adhesive is industrially advantageous. , a space is provided between the two layers using an insulating material such as plastic film. If this distance, that is, the thickness of the insulating layer, is less than 5 μm, it is difficult to make close contact between the amorphous alloy layer and the insulating layer, and if it exceeds 500 μm, the shielding material becomes thick and difficult to handle, making it difficult to handle industrially. It is also disadvantageous. Therefore, the above distance (thickness of the insulating layer) is preferably within the range of 5 to 500 μm.

Further, when a plurality of amorphous alloy layers and a plurality of conductive material layers are provided, it is desirable that the two layers be arranged alternately at intervals (with an insulating layer in between).

As the conductive material, metals such as copper, aluminum, nickel, and iron can be used. Particularly in the present invention, in order to impart flexibility to the electromagnetic shielding material, the layer of the conductive material is a net-like conductive metal sheet. As the net-like metal sheet, an expanded metal sheet and a mesh sheet can be used. If the mesh is coarser than 5 meshes, there will be more spaces and the shielding performance in the high frequency range will deteriorate, and if the mesh is finer than 250 meshes, the wire diameter will become smaller and the weight of the sheet will decrease, resulting in poor shielding performance in the high frequency range. It's also expensive. Therefore, the roughness is preferably within the range of 5 to 250 mesh. A particularly preferred range is 10 to 100 meshes.

By forming the conductive metal layer into a net-like sheet layer, the electromagnetic shielding material is provided with excellent shielding properties and flexibility, making its handling convenient.

Example Examples of the present invention will be described below.

FIG. 1 is a plan view of an electromagnetic shielding material according to the present invention, and FIG. 2 is an enlarged sectional view schematically showing the structure.

In this example, an amorphous alloy layer 2 formed by laminating amorphous alloy pieces 2a and a layer 3 of a mesh sheet of conductive metal such as copper sandwich a polyester film 4, and further on the amorphous metal layer 2. This is an example in which the electromagnetic shielding material 1 has a four-layer laminated structure in which the same polyester film 4 is adhered to the two layers. However, in FIG. 1, the outermost polyester film is not shown.

As can be seen from FIG. 1, the amorphous alloy pieces 2a are uniformly dispersed and stacked in random directions, so that they are naturally non-directional. On the other hand, laminating amorphous alloy ribbons and crystalline alloy ribbons requires repeated cutting and gluing, and gluing in different cross directions and angles to achieve non-directionality.
The work is extremely troublesome. If directionality is required in the present invention, applying a slight magnetic field along a predetermined direction while uniformly dispersing the amorphous alloy pieces will align the amorphous alloy pieces in the longitudinal direction and change the direction. can be given gender.

If the composition of the amorphous alloy piece exhibits soft magnetism, it exhibits magnetic shielding properties.

Amorphous alloy flakes can be made by cutting from a ribbon or by a known melt extraction method, but from the viewpoint of productivity, it is preferable to make the periphery of the amorphous alloy flake thinner to make it flake-like. Therefore, the cavitation method (which has a surface layer with low wettability to the molten metal and which deposits the molten metal on the surface of a roll rotating at high speed) which the present applicant previously proposed in Japanese Patent Application Laid-open No. 58-6907. It is desirable to apply a method in which the molten metal is supplied, the molten metal is divided into fine molten metal droplets, and then the molten metal droplets are collided with a metal rotating body rotating at high speed to rapidly solidify.

Specific examples of the present invention will be described below.

Example 1 Co _69.8 Fe _4.2 by the cavitation method
An amorphous alloy piece of Si ₁₇ B ₉ (the number attached to the element symbol represents the atomic percent of the elemental component; the same applies hereinafter) was produced. The average thickness of this amorphous alloy piece is 30μm,
Aspect ratio is 400-600.

Using this amorphous alloy piece, an electromagnetic device having one layer each of an amorphous alloy layer 2 and an expanded metal layer 3 of copper corresponding to 13 to 20 meshes as shown in FIGS. 1 and 2 is used. It was used as shield material 1. That is,
Thickness above 3 sheets of copper expanded metal
A 25 μm thick polyester film 4 is placed on top of which the amorphous alloy pieces 2a are laminated at a thickness of 250 g/m ² , and then a 25 μm thick polyester film 4 is placed as the outermost layer, and these are bonded with an adhesive (not shown). ) to obtain electromagnetic shielding material 1.

The electromagnetic shielding properties of this electromagnetic shielding material 1 were measured using a spectrum analyzer TR-4172 manufactured by Advantest. Measurement instructions
The magnetic field component is schematically shown in FIG. 10, and the electric field component is schematically shown in FIG. 11. 200mm
10mm on one side from ×200mm electromagnetic shielding material 1
A magnetic wave transmitting loop antenna 5 with a diameter of 10 mm or a radio wave transmitting probe antenna 15 with a length of 10 mm is placed on the other side, and a magnetic wave receiving loop antenna 6 with a diameter of 10 mm or a radio wave with a length of 10 mm is placed on the other side at a distance of 10 mm. Receiving probe antennas 16 are respectively arranged and connected to a spectrum analyzer TR41727 with a tracking generator. Attenuation of the magnetic waves or radio waves from the transmitting antenna 5 or 15 by the electromagnetic shielding material 1 is detected by the receiving antenna 6 or 16, and the spectrum analyzer TR41727
Measure with.

The measurement results are shown in FIGS. 4 and 5. In addition, in FIGS. 4 and 5, the shielding effect is expressed as an absolute value in dB. For comparison, FIGS. 4 and 5 show the same expanded copper sheet as above (Comparative Example 1) and an electromagnetic plate having the same amorphous alloy layer as in the above example but without a metal layer sheet. The results of similar measurements performed on the shielding material (Comparative Example 2) are also shown (only Comparative Example 1 is shown in FIG. 5).

Example 2 The average thickness of the amorphous alloy piece in Example 1 was
40 μm, aspect ratio 200 to 500, and the amount
300 g/m ² , the metal sheet was a copper mesh sheet with 80 meshes, and the amorphous alloy layer and the metal sheet were bonded together with a polypropylene film 50 μm thick sandwiched therebetween to form an electromagnetic shielding material. Other conditions were the same as in Example 1 above.

Regarding this electromagnetic shielding material, the same shielding effect measurement as in Example 1 was performed.

The measurement results are shown in FIGS. 6 and 7. For comparison, FIG. 5 and FIG. 7 show an electromagnetic shielding material having the same copper mesh sheet as above (Comparative Example 3) and the same amorphous alloy layer as in Example 2 but without a metal sheet. The results of similar measurements for (Comparative Example 4) are also shown (only Comparative Example 3 is shown in FIG. 7).

As seen in FIGS. 4 to 7, Example 1,
Both of these materials exhibit superior shielding properties over a wide frequency range from low frequencies to high frequencies, compared to comparative electromagnetic shielding materials.

Example 3 As shown in FIG. 3, two amorphous alloy layers 2 are made of the same amorphous alloy flakes 2a as in Example 1 at 250 g/m ² , and these layers 2, 2 are In between, sheets 3 of copper expanded metal similar to those in Example 1 and two polyester films 4, 4 are arranged alternately, and both surfaces are further sandwiched between the same polyester films 4, 4 to create a seven-layer structure. An electromagnetic shielding material 11 was produced. Regarding this electromagnetic shielding material 11, the same measurements as in Examples 1 and 2 were performed.

The measurement results are shown in FIGS. 8 and 9.

This example shows even better magnetic shielding properties than those of Examples 1 and 2, especially with respect to magnetic field components in the low frequency region.

Since the electromagnetic shielding materials of Examples 1 to 3 have a metal layer in the form of a mesh sheet, they all have flexibility and are convenient to handle.

[Brief explanation of the drawing]

Figure 1 is a plan view of the electromagnetic shielding material, Figures 2 and 3 are enlarged sectional views schematically showing the structure of the electromagnetic shielding material, Figures 4, 5, 6, and 7.
8 and 9 are graphs showing the relationship between frequency and shielding effect, respectively, and FIGS. 10 and 11 are schematic diagrams showing the procedure for measuring the shielding effect. In addition, in the symbols shown in the drawings, 1, 11
... Electromagnetic shielding material, 2 ... Amorphous alloy layer, 2a
...Soft magnetic amorphous alloy piece, 3... Layer of reticular conductive metal sheet, 4... Resin film, 5, 15...
Transmission antenna, 6, 16...reception antenna,
7... Measuring instrument (spectrum analyzer).

Claims (1)

[Claims] 1 comprising at least one amorphous alloy layer and at least one layer of a reticulated conductive metal sheet, one of the amorphous alloy layers and one of the reticulated conductive metal sheets; The amorphous alloy layers are stacked at intervals of 5 to 500 μm, and have a thickness of 5 to 500 μm.
100μm, aspect ratio (however, aspect ratio is the ratio of maximum length to maximum thickness) 10-15000
An electromagnetic shielding material having a structure in which scale-like or flake-like soft magnetic amorphous alloy pieces are laminated with a weight per unit area of 100 to 500 g/ ^m2 .