JPH11112192A - Electromagnetic wave shielding member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave shielding member, which is suitable for a complex shape like a plastic molded member, and shows excellent electromagnetic shielding effect in a low frequency band whose frequency is especially lower than or equal to 510 MHz. SOLUTION: An conductive metal layer 3 is formed on the surface of a substratum 2 of a plastic molded member or the like, using vacuum vapor deposition or the like of aluminum. A carbon sheet 5 formed by previously compression-bonding and pinching fine powder 5a of charcoal like binchou with the upper and the lower nonwoven fabrics 5b, 5c is laminated on the surface of the conductive metal layer 3, and built integrally via an insulating adhesive agent layer 4, and a shielding member 1 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave shielding material for shielding electromagnetic waves generated from various electronic devices such as mobile phones and personal computers.

[0002]

2. Description of the Related Art It has been known that electromagnetic waves emitted from various electronic devices such as mobile phones adversely affect the human body and also cause radio interference to various precision electronic devices. Various electromagnetic wave shielding materials have been proposed. I have.

[0003] Among them, it is known to use carbon fiber as a part of an electromagnetic wave shielding material. For example, in Japanese Patent Application Laid-Open No. 2-3869, a composite sheet is formed by laminating a sheet-like molded body made of carbon fiber on a plastic sheet via an ethylene-based adhesive layer, and molding this into a housing of an electronic device. It has been proposed to be used.

However, this known electromagnetic wave shielding material is not only relatively expensive since carbon fibers are used, but also has a limited use because it is necessary to form the composite sheet into a housing. I have.

As disclosed in Japanese Patent Application Laid-Open No. 8-293694, carbon fine powder obtained by shredding carbon fibers and crushing them with a crusher is used for shielding such carbon fibers. There has been proposed an electromagnetic wave shielding material which is adhered to the surface of a base member to be used in a coating form.

The base member used in the present invention is formed in a plate shape from metal or synthetic resin, and the noise shielding effect is to be obtained by carbon fine powder attached to the substrate. It functions as a carrier. However, the noise shielding effect of the carbon fine powder itself made of carbon fiber powder is not so large, and cannot provide a sufficient effect as an electromagnetic wave shielding material.

The inventor of the present invention has focused on the use of fine charcoal powder as an electromagnetic wave shielding material, and has conducted intensive experiments. As shown in Utility Model Registration No. 3038327, powder or fine particles of white charcoal are formed into a sheet. An electromagnetic wave shielding material having an excellent electromagnetic shielding effect is provided by pasting together a woven cloth using a white charcoal sheet obtained by compression processing and a yarn spun with a fiber containing at least copper and / or nickel.

[0008]

However, the above-mentioned electromagnetic wave shielding material has an excellent electromagnetic wave shielding effect at a frequency higher than 510 MHz, which is a relatively high frequency band, but still has a sufficient effect in a lower frequency band. Could not be done. Therefore, the present inventor further repeated experiments, and laminated a layer of carbon powder such as white charcoal sheet on a conductive sheet material such as aluminum or copper. Although it is almost the same as the electromagnetic wave shielding effect of the sheet material alone,
It has been found that when these are laminated via an insulating layer, an electromagnetic wave shielding effect which is remarkably superior to the case of these simple substances is exerted.

When the carbon powder is bonded to the conductive sheet via a thin adhesive layer, when the carbon powder is coated on the adhesive layer and pressed, a part of the carbon powder becomes conductive. In this case, the electromagnetic shielding effect is reduced as in the case where the carbon powder layer is brought into direct contact with the conductive sheet. In this case, it is necessary to interpose an insulating sheet between the two. is there. On the other hand, when the carbon powder is formed by pressurizing the carbon powder in a sheet shape in advance, the problem of the direct contact as described above occurs even if the layer of the carbon powder is bonded to the conductive sheet via the insulating adhesive. Does not occur, a desired electromagnetic shielding effect can be achieved.

[0010] Based on the above knowledge, the inventors of the present invention disclosed a prior application in Japanese Patent Application No. 9-191238, in which a carbon powder layer was laminated on a conductive metal sheet via an insulating sheet material. An integrated electromagnetic shielding material and an electromagnetic shielding material obtained by laminating and integrating a carbon sheet in which carbon powder is formed in a sheet shape in advance with a metal sheet via an insulating layer are provided.

The electromagnetic shielding material according to the prior application exhibits an electromagnetic shielding effect that is significantly superior to the sum of the electromagnetic shielding characteristics of the carbon powder and the metal sheet, and is particularly problematic in many electronic devices. An excellent shielding effect is exhibited in a frequency band of 510 MHz or less.

However, since the electromagnetic wave shielding material according to the prior application is formed in a sheet shape using a metal sheet, there is a problem that it is difficult to attach the material to a molded article having a relatively complicated shape. Was.

Therefore, an object of the present invention is to cope with the shape of various objects such as a molded article having a complicated shape without using a metal sheet.
An object of the present invention is to provide an electromagnetic shielding material capable of exhibiting an effect equivalent to an electromagnetic shielding effect obtained by a combination of a metal sheet and carbon powder.

[0014]

Means for Solving the Problems To achieve the above object, the electromagnetic wave shielding material of the present invention provides a conductive metal layer on the surface of a non-metallic substrate by plating, vapor deposition, powder bonding, powder coating and the like. And a carbon powder layer is laminated and integrated on the conductive metal layer via an insulating layer.

Further, another electromagnetic wave shielding material of the present invention is formed by coating a conductive metal layer on the surface of a non-metallic base material by coating a non-sheet material such as plating, vapor deposition, powder bonding, and powder coating. A carbon sheet formed by forming a carbon powder in a sheet shape on the conductive metal layer in advance is laminated and integrated via an insulating layer.

As a result, the electromagnetic wave shielding material according to the present invention has an electromagnetic shielding effect that is significantly better than the sum of the electromagnetic shielding characteristics of the carbon powder and the metal sheet.
Moreover, it can correspond to the shape of various objects such as a molded article having a complicated shape.

Preferably, aluminum or copper is used for the conductive metal layer, and charcoal powder is used as the carbon powder, and white charcoal such as Bincho charcoal is more preferably used.

In order to form the carbon powder into a sheet, for example, a slurry obtained by kneading charcoal powder with a binder is coated on a first non-woven fabric to a predetermined thickness, and a second non-woven fabric is coated thereon. It is to integrate through a pressure roller while coating.

As described above, the electromagnetic wave shielding material of the present invention comprises an electrically conductive metal layer and a carbon powder layer or a carbon sheet on the surface of a non-metallic device such as a molded plastic body for housing various electronic devices that generate electromagnetic waves. This electromagnetic wave shielding effect can be easily obtained through the above-mentioned Japanese Patent Application No. 9-1.
It is as excellent as those described in the specification of JP-A-91238.

As is well known, charcoal has a deodorizing property that absorbs odors, a moisture conditioning property that absorbs excess moisture in the air to keep humidity constant, and a negative ion that is considered to be good for health. Since it has the characteristic of releasing, when charcoal powder is used as the carbon powder, it can have the above-mentioned excellent characteristics in addition to the effect as an electromagnetic wave shielding material.

Among the charcoals, white charcoal such as Bincho charcoal may have other carbon by being laminated and integrated with the metal sheet via an insulating layer, probably because the pores are fine and dense and have excellent conductivity. It has an electromagnetic wave shielding effect that is even better than powder.

[0022]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows an electromagnetic wave shielding member 1 according to a preferred embodiment of the present invention. In this electromagnetic wave shielding material 1, an aluminum vapor-deposited layer 3 is integrally formed on the inner surface of a concave container part 2 molded of plastic by vacuum vapor deposition. Further, a carbon layer 5 is bonded to the inner surface of the aluminum vapor deposition layer 3 via an insulating adhesive layer 4.

As the carbon layer 5, as shown in the enlarged view of FIG. 1, a carbon sheet 5 in which fine charcoal powder 5a made of Bincho charcoal is previously sandwiched between upper and lower nonwoven fabrics 5b and 5c is used. I have. Further, in this case, as the insulating adhesive layer 4, it is preferable to use a heat-fusible insulating film applied and formed on the surface of the aluminum vapor-deposited layer 3 in advance.

In order to form the carbon sheet 5, as an example, a fine powder 5a obtained by pulverizing Bincho charcoal with a powder processing machine and kneading it with a volatile binder is used to form a slurry using a doctor blade or the like. A predetermined thickness is applied on the running first nonwoven fabric 5b, and then it is sandwiched between the second nonwoven fabrics 5c running from above, and these are passed between a pair of upper and lower pressure rollers so as to be tightly integrated. Then, these may be dried to volatilize the binder.

It is preferable that the fine particles of Bincho charcoal have a particle size of several microns to several tens of microns, and the carbon sheet 5 has a total thickness of several tens to several hundred microns. In the carbon sheet 5 thus formed, the fine powder of Bincho charcoal is sandwiched between the upper and lower nonwoven fabrics 5b and 5c, so that the fine powder 5a of Bincho charcoal does not peel off from the carbon sheet 5.

FIG. 2 shows Japanese Patent Application No. 9-1 according to the prior application of the present invention.
In the figure showing the electromagnetic shielding effect of the invention of No. 91238, A shows the electromagnetic shielding properties of the carbon sheet alone, B shows the electromagnetic shielding properties of the aluminum foil, and the C carbon sheet and the aluminum foil are interposed via an insulating layer. 3 shows the electromagnetic wave shielding characteristics of the electromagnetic wave shielding material bonded. Note that the above A and B
In the carbon sheet used in the above, the content of the fine powder of Bincho charcoal was 490 g per square meter. In addition, these characteristic diagrams show the characteristics when each electromagnetic wave shielding material is grounded in any case.

As is clear from this figure, the carbon sheet alone has almost no electromagnetic wave shielding effect, but when this is combined with the aluminum foil, the electromagnetic wave shielding effect is significantly larger than the sum of the two electromagnetic wave shielding effects. You can see it plays.

In the present invention, it can be said that the same electromagnetic shielding effect can be obtained. That is, in the present invention, instead of the aluminum foil, the aluminum vapor-deposited layer 3 is formed on the inner surface of the plastic container part 2, and the aluminum vapor-deposited layer 3 is equivalent to the aluminum foil. The electromagnetic wave shielding material of the present invention in which the carbon sheet 5 is attached to the inner surface via an insulating adhesive layer is similar to the electromagnetic wave shielding effect of the above-mentioned prior application or is smaller than the electromagnetic wave shielding effect of the previous application due to the presence of the plastic container 2. It can be said that excellent effects can be achieved.

The concave container 2 according to the present invention accommodates an electronic device that generates an electromagnetic wave therein.
In this example, it is molded from plastic, but other non-metallic base materials such as natural leather, synthetic leather, and rubber can be used. The aluminum vapor deposition 3 is formed on the inner surface of the plastic container 2 by vacuum vapor deposition of aluminum, but may be formed by electroless plating, aluminum powder bonding, powder coating, or the like in addition to vacuum vapor deposition. it can.

In the above embodiment, fine carbon powder (bincho charcoal) 5a is used as the carbon sheet 5 in the upper and lower two nonwoven fabrics.
Although a material sandwiched between b and 5c is used, a fundamentally important structure in the present invention is that a conductive metal layer 3 and a carbon powder layer 5 are integrally laminated and bonded via an insulating layer 4. It is to be. Therefore, in the present invention, instead of the carbon sheet 5, a conductive metal layer 3 such as an aluminum vapor-deposited layer is formed on the surface of a non-metallic substrate such as the plastic container portion 2 and the insulating layer 4 is further formed on the surface. The same effect as in the present invention can be obtained even if the carbon fine powder is coated via the carbon black. If the carbon fine powder is pressed from above and a part thereof contacts the conductive metal layer 3, the effect of the present invention cannot be obtained. It is preferable to apply and coat in advance on the surface of the layer.

When the carbon powder is formed in a sheet shape in advance, the above-described embodiment has a three-layer structure.
This may have a two-layer structure. That is, when charcoal fine powder was mixed with a binder on a single nonwoven fabric and applied to a uniform thickness by a doctor blade, and then pressed with a roller to form a uniform thickness, the molded product was formed. The charcoal fine powder can be bonded to the conductive metal layer 3 via an insulating adhesive layer applied relatively thickly.
This is because the charcoal fine powder layer is already pressed
This is because even if the charcoal fine powder layer is bonded to the conductive metal layer 3 via the adhesive layer, it is possible to prevent the charcoal fine powder layer from directly contacting the conductive metal layer 3.

As the carbon powder, charcoal powder is preferable. Among them, white coal such as Bincho charcoal has a finer structure than black charcoal and has excellent electric conductivity because of its fine pores. Performance is excellent. And, as is well known, charcoal is a deodorant that absorbs odors, absorbs excess moisture in the air to keep humidity constant, and releases negative ions that are considered to be good for health Because of having the above-mentioned properties, the electromagnetic wave shielding material of the present invention using charcoal fine powder is not only excellent in electromagnetic wave shielding properties,
It is preferable that the present invention be applied to the inner surface of a container for housing electronic equipment because of its deodorizing property, humidity control property, negative ion releasing property and the like.

In the above embodiment of the present invention, aluminum is exemplified as the metal of the conductive metal layer 3. However, the present invention is not limited to this, and copper or the like can be used as a suitable material.

[0035]

As is apparent from the above description, the electromagnetic wave shielding material according to the present invention has a remarkably superior electromagnetic shielding effect than the sum of the electromagnetic shielding characteristics of the carbon powder and the metal sheet. It has an excellent shielding effect in a frequency band of 510 MHz or less, which is a problem in the electronic device.

Further, it is possible to provide an electromagnetic shielding material integrally adhered to the inner surface of a substrate having a complicated shape such as a plastic molded article.

When charcoal fine powder is used as the carbon powder, the present invention is preferably applied to the inner surface of a container for accommodating electronic equipment due to the deodorizing property, humidity control property and negative ion releasing property of charcoal. .

[Brief description of the drawings]

FIG. 1 is a partial sectional perspective view of an electromagnetic wave shielding material used in the present invention.

FIG. 2 is a diagram showing the electromagnetic wave shielding characteristics of an electromagnetic wave shielding material obtained by laminating an aluminum foil and a carbon sheet via an insulating layer, in comparison with the electromagnetic wave shielding characteristics of a member constituting the shielding material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electromagnetic wave shielding material 2 Plastic container part 3 Aluminum vapor deposition layer 4 Insulating adhesive layer 5 Carbon layer (carbon sheet) 5a Fine powder of charcoal 5b, 5c Nonwoven fabric

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuyoshi Masuda 2-3-5 Minakugahara, Ota-ku, Tokyo

Claims (6)

[Claims] 1. A conductive metal layer is formed on the surface of a non-metallic base material by plating, vapor deposition, powder bonding, powder coating or the like with a non-sheet material, and an insulating layer is formed on the conductive metal layer. An electromagnetic wave shielding material obtained by laminating and integrating a carbon powder layer through a layer. 2. A conductive metal layer is formed on the surface of a non-metallic base material by coating a non-sheet material such as plating, vapor deposition, powder bonding, and powder coating, and an insulating layer is formed on the conductive metal layer. An electromagnetic wave shielding material obtained by laminating and integrating a carbon sheet obtained by forming carbon powder in a sheet shape in advance. 3. The electromagnetic wave shielding material according to claim 1, wherein the carbon powder is charcoal powder. 4. The electromagnetic wave shielding material according to claim 1, wherein the conductive metal layer is formed from aluminum or copper. 5. The carbon sheet is formed by sandwiching and pressing charcoal powder between upper and lower nonwoven fabrics, and laminating and integrating the carbon sheet with the conductive metal layer via the insulating layer. The electromagnetic wave shielding material according to any one of claims 2 to 4. 6. The electromagnetic wave shielding material according to claim 3, wherein the charcoal powder is made of white charcoal powder such as Bincho charcoal.