JPS61193499A - Electromagnetic wave shielding sheet - 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 <Industrial Application Field> The present invention relates to an electromagnetic shielding sheet for preventing electromagnetic wave noise generated from electronic equipment from leaking to the outside of the equipment.

<Prior Art> When electronic devices such as microcomputers and word processors are used, the generation of electromagnetic noise is unavoidable.

If this electromagnetic wave noise leaks outside the device that is generating it, it may invade other electronic devices operating in the vicinity of the device and have an adverse effect.

Conventionally, as a shielding material for preventing such electromagnetic noise from leaking to the outside of the device, Japanese Patent Application Laid-Open No. 57-1380
There have been known devices in which an aluminum plate or a copper plate is pressed onto at least one side of a copper strip, as described in Japanese Patent Laid-Open No. 57-17199.

<Problems to be Solved by the Invention> However, with the above-mentioned conventional electromagnetic shielding materials, the initial magnetic permeability of the copper strip is only about 300 at most, regardless of the shielding performance in the high frequency range, and the magnetic field shielding performance in the low frequency range is still sufficient. However, improvements were desired.

Therefore, an object of the present invention is to provide a material that has excellent electric field and magnetic field shielding properties over a wide range from high frequency ranges to low frequency ranges.

<Means to Solve the Problem> As a result of intensive studies to develop a shielding material that also has excellent low frequency magnetic field shielding properties, the inventors of the present invention found that at least one of the high magnetic permeability layers whose initial magnetic permeability is a predetermined value or more It was discovered that this objective could be achieved by disposing a highly electrically conductive metal layer on one side, and this led to the completion of the present invention.

That is, the electromagnetic shielding sheet according to the present invention comprises a high magnetic permeability layer having an initial magnetic permeability of 1000 or more, and a highly electrically conductive metal layer disposed on at least one side of the high magnetic permeability layer. It is.

The high magnetic permeability layer in the present invention has an initial magnetic permeability layer of 1000
For example, an amorphous metal whose main component is an alloy of a transition metal such as Mn=, Fe%Co%Ni and a semimetal such as P, C, B, 8i, Ge, a transition metal and Zr, N.
b, Amorphous metal whose main component is an alloy with metal such as Ta, Sulpermalloy whose main component is Ni or Fe,
Ni-based permalloy containing Mo, Cr, Mn%Cu, etc., Fe-AA-Si-based permalloy, sheets made by mixing the above alloy particles or fibers, Mn-Zn-based ferrite, etc. with an organic binder, etc. can be used. This high magnetic permeability layer.

If the initial magnetic permeability is too small, the low frequency shielding effect will be small, so there will be no favorable fL<.

On the other hand, the highly electrically conductive metal layer is made of Ag, Cu, AJ
It can be configured by

Hereinafter, the present invention will be described in detail with reference to the drawings. In FIG. 1, reference numeral 1 denotes a high magnetic permeability material layer having an initial magnetic permeability of 1000 or more, and a highly electrically conductive metal layer 2 is integrally bonded to one side of the layer with an adhesive (not shown).

This electromagnetic shielding sheet can be attached to the wall surface of the box of electronic equipment or installed near the electronic circuit inside the box, and has a high magnetic permeability to prevent short circuits due to contact with electronic circuits. An insulating film 3 made of polyethylene, polyvinyl chloride, polyester, fluororesin, or the like can be formed on the body layer and/or the highly electrically conductive metal layer by adhesion or the like.

Here, the principle of electromagnetic shielding according to the present invention will be explained. As shown in Figure 2, due to the noise magnetic field 4 radiated from electronic equipment (coming from the left side as viewed in the figure),
An induced current 6 is generated in the electromagnetic shielding sheet 5, and a magnetic field 7 due to the induced current 6 has a phase opposite to that of the noise magnetic field 4 passing through the sheet 5, so that the noise magnetic field 4 is weakened. Since the induced current 6 is proportional to the magnitude of the time change in the magnetic flux passing through the sheet 5, the magnetic field shielding effect is reduced at low frequencies.

In order to increase the magnetic field shielding effect in the low frequency range, it is only necessary to increase the time change of the magnetic flux passing through the sheet 5, so it is desirable for the sheet 5 to be made of a material that has high electrical conductivity and high initial magnetic permeability. However, since such an ideal material does not exist in reality, the electromagnetic shielding sheet having a novel multilayer structure according to the present invention is designed to have effectively equivalent performance.

In the electromagnetic shielding sheet according to the present invention, when the noise magnetic field 4 arrives, a large magnetic flux is generated in the high magnetic permeability material layer, and a large induced current is generated in the highly electrically conductive metal layer due to its time change. However, it also exhibits an excellent shielding effect against low-frequency magnetic fields.

FIG. 3 shows another example, in which the superimposed high magnetic permeability layer 1 and high electrical conductivity metal layer 2 are entirely sealed with two insulating films 3.3. 8.8 is film 3. : This is the heat-sealed part at the edge of 3.

In this way, even if the high magnetic permeability layer 1 and the highly electrically conductive metal layer 2 are not bonded to each other, there will be no misalignment between the two.

FIG. 4 shows yet another example in which highly electrically conductive layers 2.2 are bonded and integrated on both sides of a high magnetic permeability layer 1, and an insulating film 3 is placed on one highly electrically conductive metal layer 2. is glued.

<Example> Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example I Amorphous metal sheet based on Co, Mn and 8i (thickness 30 ims initial permeability 10000)
A copper foil with a thickness of 50 #rz was adhered to one side of the sheet using an acrylic pressure-sensitive adhesive, and a polyvinyl chloride film with a thickness of 50 μm was adhered onto the amorphous metal sheet and the copper foil using an acrylic pressure-sensitive adhesive. An electromagnetic shielding sheet (sample A) was obtained.

Example 2 Butyl rubber and Mn-Zn ferrite in a weight ratio of 1:5
After uniformly mixing in the ratio of
Create.

Next, on one side of this sheet, a copper foil with a thickness of 5() μm was adhered using an acrylic pressure-sensitive adhesive, and on the other side, the same adhesive as above was applied to a polyvinyl chloride sheet with a thickness of 5071t7z. It was sealed with two films to obtain an electromagnetic shielding sheet (sample B).

Example 3 An electromagnetic shielding sheet (Sample C) was obtained in the same manner as in Example 1 except that the highly electrically conductive metal layer was formed of aluminum foil (30.1 m thick) instead of copper foil.

Example 4 An electromagnetic shielding sheet (sample D) was obtained in the same manner as in Example 2 except that the highly electrically conductive metal layer was formed of aluminum foil (1 height 30/Im) instead of copper foil.

Example 5 Copper foil with a thickness of 504 m was adhered to both sides of an amorphous metal sheet (thickness: 307 m, initial magnetic permeability: 10,000) mainly composed of Co%Mn and Si, and further on the copper foil. A polyvinyl chloride film having a thickness of 50 μm was adhered to each of the sheets using an acrylic pressure-sensitive adhesive to obtain an electromagnetic shielding sheet (sample E).

Example 6 Butyl rubber and Mn-Zn ferrite weight ratio l:5
A sheet of 900 pm thick (initial magnetic permeability 1500
).

Next, copper foil with a thickness of 50 μm was adhered to both sides of this sheet using an acrylic pressure-sensitive adhesive, and two polyvinyl chloride films with a thickness of 50 μm were coated on one side with the same adhesive as above. The low frequency shielding properties of the sealed sheet A%B were measured using TR-4172 manufactured by Takeda Riken Co., Ltd. The results obtained are shown in FIG.

In Figure 5, G and H%I are both comparative examples, G is copper foil with a thickness of 75) 1 m, H is a thickness of 25/+ m, and initial magnetic permeability is 3.
This sheet is made by adhering No. 00 iron foil and 50/1 m thick copper foil with an acrylic pressure-sensitive adhesive.

In addition, ■ is a sheet of 900 pm thick (initial magnetic permeability 9
00), adhered a 507 m thick copper foil to one side using an acrylic pressure-sensitive adhesive, and sealed the entire thing with two polyvinyl chloride films coated with an acrylic pressure-sensitive adhesive on one side. This is a sheet for electromagnetic shielding.

Next, the low frequency shield principle of electromagnetic shielding sheets C and D obtained in Examples 3 and 4 is shown in FIG.

In Figure 6, J, , and L are all comparative examples, J is 55μm thick aluminum foil, K is 25fims thick, iron foil with initial magnetic permeability 300 and aluminum foil with 30/Im thickness are acrylic. This is a sheet adhered with a pressure-sensitive adhesive. Further, L is a sheet obtained in the same manner as in the process except that aluminum foil with a thickness of 30) 1 m was used instead of copper foil.

Furthermore, the low frequency shielding properties of the electromagnetic shielding sheets obtained in Examples 5 and 6 were similarly measured and the results obtained are shown in FIG. For comparison, data for a copper foil (sample number M) with a thickness of 140/1 m is also shown.

<Effects of the Invention> The present invention provides magnetic permeability of the high magnetic permeability layer to be equal to or higher than a predetermined value,
Since this layer and a highly electrically conductive layer are combined to form a multilayer structure, as can be seen from the above examples and comparative examples, it is characterized by excellent shielding properties in the low frequency range.

[Brief explanation of the drawing]

1.3 and 4 are both side views showing examples of the electromagnetic shielding sheet according to the present invention, and FIG. 2 is an explanatory diagram showing the shielding principle by the shielding sheet according to the present invention.
5.6 and 7 are graphs showing the shielding effect of the shielding sheet according to the present invention. l...High magnetic permeability layer 2...High electrical conductivity metal layer 3...Insulating film

Claims (1)

[Claims] An electromagnetic shielding sheet comprising a high magnetic permeability layer having an initial magnetic permeability of 1000 or more and a highly electrically conductive metal layer disposed on at least one side of the high magnetic permeability layer.