JPH0719995B2 - Electromagnetic shield material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to electronic devices that emit electromagnetic waves to cause so-called electromagnetic interference, such as TVs, typewriters, NC machine tools, passenger ticket vending machines, and personal computers. The present invention relates to an electromagnetic wave shield material that is attached to and reflects and absorbs electromagnetic wave energy, thereby preventing the propagation of energy and attenuating the propagation energy.

[Prior Art] The prevention of electromagnetic interference is basically carried out by the circuit design of an electronic device, but it is difficult to sufficiently prevent the emission of electromagnetic waves by itself. Therefore, it is necessary to shield the electromagnetic waves from the case of the electronic device so that the electromagnetic waves are not emitted to the outside.

However, most of current electronic device cases are plastic molded products, and since these plastic molded products are usually electrical insulators, they have no electromagnetic wave shielding function. Therefore, a shield material is attached to the plastic molded product.

Recently, electromagnetic waves have been shielded beforehand with conductive materials (conductive plastic, wire mesh, etc.). For example, the opening of computer room doors, building windows and exhaust holes, or the opening and closing of metal cases. There is a problem that electromagnetic waves leak from the gaps of the electromagnetic shield portion, even though the electromagnetic shield means is applied, and the electromagnetic shield material that fills the gaps is used as an auxiliary material (member) for electromagnetic shield. Although it is called, in such an electromagnetic wave shielding material, in addition to the original electromagnetic wave shielding function,
As an auxiliary material that can satisfy these conditions, (1) it has a sealing property to fill the gap, (2) it is a material with a large thickness, and (3) it has a compressive restoration property. The current situation is that there is no electromagnetic wave shielding material.

As the known electromagnetic wave shield material, it is said that most of materials having conductivity can be used, but the shield effect is greatly different as shown in Table 1.

The flexible graphite sheet shown in Table 1 above is obtained by treating natural graphite particles with an acid and expanding the graphite particles to at least 25 times the original volume,
It is a sheet formed by opening the superposed carbon layers without using adhesives and additives.
For this reason, in addition to maintaining the original properties of graphite as it is, it has a special property of flexibility that was not expected in conventional graphite.

Therefore, the electromagnetic wave shielding material made of a flexible graphite sheet is light and flexible, easy to cut and bend, and even if the electronic device case has irregularities, it can be attached along the irregularities. As you can see, it has a fairly good shielding effect. However, on the other hand, it has the following problems. That is, when bent or cut and processed, graphite easily peels off from the processed part and is inferior in handleability, and the shield effect is impaired, and a short circuit occurs. Furthermore, the ground cannot be soldered.

Therefore, as a result of research, the present inventor has found that if a paper or plastic film is adhered to a flexible graphite sheet, the flexibility peculiar to the flexible graphite sheet is not impaired, and the above problems can be solved. Found. It is based on the viewpoint of the present invention.

[Means for solving problems]

The electromagnetic wave shielding material according to the present invention made to solve the above-mentioned problems is expanded into at least 25 times the original volume to form a sheet-like graphite particle having an open carbon layer between the superposed carbon layers. It is formed by adhering a paper or plastic film to at least one surface of a molded flexible graphite sheet.

[Action]

According to the present invention having the above-described structure, as described above, the flexible graphite sheet retains the original properties of graphite as it is, and of course, has a unique performance of flexibility. Since the paper or plastic film that is adhered to reinforce the flexible graphite sheet also has flexibility, the electromagnetic wave shielding material itself has a sufficient thickness and is easy to cut and bend, but it is also lightweight. It is excellent in flexibility and can be easily attached along the unevenness of the electronic device case or the like. Also, since the paper or plastic film is bonded and reinforced, even if it is bent or cut and processed, the graphite does not peel off from the processed part, and it is possible to improve handleability, It is possible to stably maintain an excellent shield effect against electromagnetic waves.

〔Example〕

Hereinafter, a first embodiment of the present invention will be described with reference to FIG. The electromagnetic wave shielding material of this embodiment is a flexible graphite sheet 1 to which papers 2 are adhered on both sides. Paper 2
For example, Japanese paper is used and adhered to both sides of the flexible graphite sheet 1 via an adhesive (glue). The flexible graphite sheet 1 is a sheet-like product obtained by subjecting natural graphite particles to acid treatment and then expanding it to 25 times its original volume or more to open the overlapping carbon layers without using an adhesive or an additive. It is recommended that the thickness be 0.1 mm or more and 3 mm or less. That is, if it is less than 0.1 mm, the shielding effect is small, and if it exceeds 3 mm, the flexibility becomes poor. The thickness of the Japanese paper is preferably 0.05 mm or more and 0.3 mm or less. That is, if it is less than 0.05 mm, the strength, particularly the tensile strength, is small, and if it exceeds 0.3 mm, the flexibility is lowered and the handleability becomes poor.

In the first embodiment, the paper 2 is adhered to both sides of the flexible graphite sheet 1, but the paper (Japanese paper) 2 is adhered to only one side of the flexible graphite sheet 1 as shown in FIG. It may be configured.

Based on the embodiment shown in FIGS. 1 and 2, 0.38 mm
Thick flexible graphite sheet A with 0.1 mm thick Japanese paper adhered to both sides or one side and 0.25 mm thick flexible graphite sheet with both 0.1 mm thick Japanese paper adhered to both sides or B The relationship between the shield effect and frequency is shown in FIG. As is clear from this figure, it can be seen that an average shielding effect (see Table 1) is obtained in the low frequency region around 200 MHz, and an extremely excellent shielding effect can be secured in the high frequency region above 300 MHz.

The paper 2 is an electrically insulating material and therefore does not contribute to the shielding effect, but the flexible graphite sheet 1
Since the paper is reinforced by the paper 2, the graphite does not exfoliate and fall off in these processed portions even if the processing such as cutting or bending is performed, so that a predetermined shield effect can be maintained. Further, since it can be easily bent and attached along an uneven surface of an electronic device case or the like, the handling property is remarkably improved, and a short circuit can be prevented from the place where the graphite does not peel off as described above.

A 0.1 mm thick paper (Japanese paper) 2 was adhered to both sides of a 0.25 mm thick flexible graphite sheet alone and the product of the present invention shown in FIG. 1, that is, a 0.25 mm thick flexible graphite sheet 1. A dumbbell-shaped material with a width of 25 mm specified in JIS R3454 is prepared, each material is pulled at a speed of 200 mm / min by an Instron type tester, and the strength comparison when the load at cutting is the tensile strength The flexible graphite sheet alone and the product of the present invention
Create 150mm wide x 90mm long samples and add 90g to these samples.
Table 2 shows a comparison of flexibility in which bending is performed 90 ° to the left and right while applying tension of f, and the number of bends when cutting is flexible.
Shown in.

From Table 2 above, it can be seen that both the tensile strength and the flexibility of the product of the present invention are remarkably improved as compared with the flexible graphite sheet alone.

FIG. 4 shows another embodiment of the present invention. In addition to the product of the present invention shown in FIG. 1, a known wrinkle roll is used to form wrinkles 3 in the longitudinal direction at predetermined width intervals. It has a formed structure. By forming the wrinkles 3 in the vertical direction in this way, flexibility in the horizontal direction is improved, and although not shown, by forming wrinkles in the horizontal direction with a predetermined vertical interval,
Vertical flexibility is improved. Of course, if wrinkles are formed in the vertical and horizontal directions, flexibility in both directions can be improved, and bending or cutting of ordinary paper or cardboard can be performed, which facilitates handling.

FIG. 5 shows still another embodiment of the present invention. Paper (Japanese paper) 2 is adhered to one surface of the flexible sheet 1, and double-sided adhesive paper 2A with release paper is adhered to the other surface. is doing. Therefore,
At the time of use, by peeling off the release paper 2a on the outer surface,
It can be easily attached to walls. Further, as shown in FIG. 6, by forming a large number of holes 4 in the double-sided adhesive paper 2A with release paper, as shown in FIG. Even though the flexible graphite sheet 1 is in close contact with the metal case 5 through the holes 4, that is, the double-sided adhesive paper 2A with release paper on the metal case 5 side is an electrical insulating material. It is possible to obtain the state where the earth is secured.

In each of the above-described embodiments, Japanese paper is used as the paper 2. However, other types of paper may be used instead of Japanese paper, but the Japanese paper is stronger, Is also advantageous in terms of handleability. Furthermore, even if a plastic film is used instead of the paper 2, the same effect as that of each of the above-described embodiments can be obtained.

〔The invention's effect〕

As described above, according to the present invention, at least 25 of the original volume is used.
By using a flexible graphite sheet that is formed by forming graphite particles that have expanded between carbon layers that have been expanded by more than twice and that are open between carbon layers without using an adhesive, the graphite of the flexible graphite sheet originally has That is, the excellent shielding effect in a relatively wide frequency range can be maintained as it is, the peculiar performance of flexibility is not impaired, and the paper or plastic film adhered to it can be used. Since it has flexibility, it can be easily attached along the unevenness of the electronic device case, etc., and it has a sufficient thickness as the electromagnetic wave shielding material as a whole and is easy to cut and bend. However, it can be made light and highly flexible. Therefore, it is extremely useful as an electromagnetic wave shielding auxiliary material for filling the gap. Moreover, since the paper or plastic film is bonded and reinforced on at least one side of the flexible graphite sheet, the graphite does not peel off from the processed part even if it is bent or cut and processed. Therefore, it is possible to improve the handleability, it is possible to stably maintain an excellent shielding effect against electromagnetic waves, there is no fear that the exfoliated part of graphite will cause a short circuit, and it is also safe to use. It has an excellent effect.

[Brief description of drawings]

1 is a perspective view showing a first embodiment of the present invention, FIG. 2 is a perspective view showing a second embodiment of the present invention, and FIG.
FIG. 4 is a perspective view showing a third embodiment of the present invention, FIG. 5 is a cross-sectional view of the fourth embodiment, and FIG. 6 is a graph of FIG. FIG. 7 is a sectional view showing a modification, and FIG. 7 is a partially enlarged sectional view at the time of use. 1 ... Flexible graphite sheet 2 ... Paper or plastic film

Claims (1)

[Claims] 1. A flexible graphite sheet formed by expanding at least 25 times the original volume and overlapping between overlapping carbon layers to form a graphite particle in the shape of a sheet without using an adhesive, and paper or plastic on at least one side of the flexible graphite sheet. An electromagnetic wave shielding material made by bonding a film.