JPH0974297A - Radio wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a radio wave absorber which is light in weight, easily controlled in production factors such as film thickness, and excellent in electromagnetic wave absorbing properties to radio waves of wide frequency bandwidth by a method wherein at least two or more of thin films each composed of a non-magnetic support and a magnetic layer deposited on either or both sides of the support are laminated to serve as a radio wave absorber. SOLUTION: Two of thin films each composed of a non-magnetic support 1 and a magnetic layer 3 deposited on either side of the support 1 are laminated for the formation of a radio wave absorber 5. The number of laminated thin films is determined depending on conditions such as frequency bandwidth of radio waves to absorb and required absorption capacity of an absorber. As mentioned above, thin films each composed of the non-magnetic support 1 and the magnetic layer 3 deposited on the support 1 are laminated for the formation of the radio wave absorber 5 excellent in radio wave absorbing properties, and the radio wave absorber 5 can be lessened in weight because it is less in magnetic material content than a conventional one. A radio wave absorber of this constitution is more easily controlled in film thickness than a radio wave absorbing sheet formed of a mixture of rubber or synthetic resin and magnetic material and capable of absorbing radio waves of wider frequency bandwidth.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a radio wave absorber. More specifically, the present invention relates to a radio wave absorber formed by laminating a plurality of thin films each having a magnetic layer provided on one side or both sides of a non-magnetic layer.

[0002]

2. Description of the Related Art The use of radio waves has been rapidly increasing in recent years, especially in the field of mobile communications such as mobile phones, in keeping with the progress of the advanced information society. P has been put into practical use
If the use of HS (Personal Handyphone System) and wireless LAN becomes even more serious, this trend is expected to accelerate. On the other hand, consumer electronic devices equipped with personal computers and microcomputers have already become widespread, and in addition to the electromagnetic waves radiated by these devices, the future radio environment will become diversified, complicated, and even in the high frequency band. It is expected to continue.

Therefore, malfunctions of other electronic devices, electronic components, computers, machine tools, etc. due to electromagnetic wave interference and / or radio frequency interference generated from the above devices,
Information leakage, and so-called electromagnetic wave interference and / or radio frequency interference such as noise from television and radio are increasing year by year, and there is a concern that they will increase further in the future.

In particular, when the exterior of an electronic device, an electronic component or the like is made of plastic, there is no protection against disturbance electromagnetic waves and / or radio frequency interference. Therefore, measures against disturbance electromagnetic waves and / or radio frequency interference have been taken in such devices or parts.

As a countermeasure against such electromagnetic interference, an electromagnetic shield or an electromagnetic absorber is usually used. The electromagnetic wave shield prevents the electromagnetic wave from entering the inside and radiating to the outside by reflection, and is coated with metal or coated with a conductive paint. However, the trapped electromagnetic waves are likely to cause interference inside the device, and the effect is reduced with a small gap, so that there is a drawback that leakage from a joint or a joint portion greatly affects the effect. Therefore, a radio wave absorber having an effect of reducing a reflected wave and a transmitted wave with absorption has been attracting attention.

The radio wave absorber can convert incident radio waves into heat energy and greatly reduce the intensity of the transmitted or reflected radio waves. Ferrite and carbon are often used as the radio wave absorbing material, and sintered ferrite is effective for a relatively low frequency such as the VHF band, while carbon is effective for a relatively high frequency. It can also be used in the form of a mixture of ferrite and carbon dispersed in an organic substance such as rubber or plastic. In this case, the electromagnetic wave absorption characteristics can be controlled by the content rate of the electromagnetic wave absorption material or the use of multiple electromagnetic wave absorption materials. can do.

Since the ferrite sintered body which is widely used at present is heavy, there is a problem in workability and workability, and the electromagnetic wave absorption characteristic is remarkably deteriorated in the microwave band, so that its use range is limited. On the other hand, a type of electromagnetic wave absorber that disperses the electromagnetic wave absorbing material in synthetic resin or rubber can be made thin, but it is difficult to control the film thickness, which has a large effect on the electromagnetic wave absorption characteristics, and strict production control is required. is there.

Further, the dispersion type electromagnetic wave absorber has a narrower band than that of the ferrite sintered body and is not suitable for applications requiring a wide band. Therefore, a composite of several kinds of electromagnetic wave absorbing materials, or an electromagnetic wave absorber in which a sheet coated with a paint in which a high dielectric material is dispersed in a binder is laminated on paper or the like as disclosed in JP-A-6-140786, Japanese Patent Laid-Open No. Sho 63-63. -2339
Proposals have also been made for multilayering such as a radio wave absorber in which a synthetic resin layer containing graphite powder is laminated on a fiber substrate as shown in No. 7.

Regarding the one using a magnetic tape, as disclosed in JP-A-6-198649 and JP-A-6-314428, a waste magnetic tape is curled, and then a binder is added and pressure molding is proposed. Has been done. In order to use this molded body as a radio wave absorber, a radio wave absorbing material such as ferrite or carbon black must be added at the time of manufacturing.

[0010]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a radio wave absorber which is light in weight, easy in production control such as film thickness control, and has excellent electromagnetic wave absorption characteristics in a wide band. .

[0011]

The above problems can be solved by a radio wave absorber characterized by laminating at least two layers of thin films each having a magnetic layer on one or both sides of a non-magnetic support.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Since the radio wave absorber of the present invention has a laminated structure, reflection occurs at the boundary of each layer, and radio waves transmitted without being absorbed by a certain magnetic layer are incident on another magnetic layer again. Be absorbed. Therefore, the radio wave absorber of the present invention has a higher efficiency of absorbing a radio wave than a single layer structure, and can absorb a once-incident radio wave without reflecting it again to the outside. In addition, a wide band can be realized by laminating thin films of different types. On the other hand, since the thin film used in the present invention has a thin magnetic layer, it is relatively easy to control the thin film. Therefore, the thin film of the electromagnetic wave absorber can be easily controlled.

FIG. 1 is a schematic sectional view showing the structure of the radio wave absorber of the present invention. (A) is a cross-sectional view of a structure of a radio wave absorber 5 in which two thin films each having a magnetic layer 3 provided on one surface of a non-magnetic support 1 are laminated, and (b) is both surfaces of the non-magnetic support 1. FIG. 3 is a cross-sectional view of a structure of a radio wave absorber 5 in which two thin films each having a magnetic layer 3 provided therein are laminated, and FIG.
2D is a cross-sectional view of a structure of a radio wave absorber 5 in which two layers of thin films each having a magnetic layer 3 provided on one side thereof are laminated with the magnetic layer side as an adhesive surface, and FIG. 3 is a cross-sectional view of a structure of a radio wave absorber 5 in which two thin films provided with No. 3 are laminated with the support side as an adhesive surface, and (e) shows a magnetic layer 3 provided on one side or both sides of the non-magnetic support 1. FIG. 3 is a cross-sectional view of a configuration of a radio wave absorber 5 in which four layers of thin films are laminated with an arbitrary surface as an adhesive surface.

The radio wave absorber of the present invention is formed by laminating at least two thin films each comprising a support and a magnetic layer.
The number of layers can be changed according to the conditions of use such as the band of radio waves to be absorbed and the required amount of absorption.

In the electromagnetic wave absorber of the present invention, the types of thin films to be laminated do not have to be the same, and various thin films of different types can be appropriately mixed and laminated. The adhesive surface at the time of laminating may be any mode such as a support and a magnetic layer, a magnetic layer and a magnetic layer, a support and a support, and the thin film to be laminated has only a magnetic layer provided on both sides of the support and one side only. There is no problem even if the provided ones are mixed and used.

As a method for laminating thin films formed by providing a magnetic layer on a non-magnetic support, for example, pressure molding is used, but the method is not limited to this. For example,
If necessary, an adhesive or the like may be used for lamination. The types of adhesives suitable for such purpose are well known to those skilled in the art. It is also possible to apply pressure while heating. The pressurizing condition during lamination depends on the type of thin film, the number of laminations, and the properties of the adhesive when it is used, but it is generally preferable to be in the range of 1 to 500 kg / cm ² . Moreover, when heating at the time of lamination, it is generally preferable that the heating condition is within a range of room temperature to 250 ° C.

The thickness of the radio wave absorber of the present invention formed by laminating two or more thin films is not particularly limited, but generally it is preferably in the range of 0.05 mm to 20 cm. If it is less than 0.05 mm, there arises such a disadvantage that the absorption characteristics are deteriorated. On the other hand, if it exceeds 20 cm, the productivity is poor.

Examples of the non-magnetic support used to form the radio wave absorber of the present invention include, but are not limited to, paper or paper laminated with polyolefins, plastic, cloth, non-woven fabric and the like. Other materials can be used as well. The thickness of these supports is not particularly limited, but if the thickness of the support increases, the film thickness when the laminated electromagnetic wave absorber is manufactured also increases. The thickness of the support is 1
mm or less.

The magnetic layer formed on the surface of the non-magnetic support has a thickness of 1 mm or less and is formed by coating the surface of the support with a magnetic coating material in which a magnetic powder such as ferrite is mixed with a binder and drying. Alternatively, it can be formed by using a vacuum thin film forming technique such as a vacuum deposition method, an ion plating method, and a sputtering method using a magnetic metal material. If the thickness of the magnetic layer is controlled to 1 mm or less, the warpage of the magnetic layer,
It is possible to prevent cracks on the surface layer. Further, the coating method is preferable as the method for forming the magnetic layer from the viewpoints of ease of production, cost, and the like.

The magnetic powder used when forming the magnetic layer by the coating method is, for example, Ni-Zn ferrite, Mn-Zn ferrite, MO.Fe ₂ O ₃ (where M is Mn, Co. , Ni, Cu, Zn, Ba, Mg, etc.), γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-γ-Fe.
Various ferrites such as ₂ O ₃ or α-Fe, CrO ₃
Examples of such magnetic recording materials include, but are not limited to, and magnetic powders are not a problem. Also, a material obtained by coating the magnetic powder with a metal such as Ni or Co by a method such as plating can be used. The particle size of these magnetic powders is not particularly limited, but is generally preferably 100 μm or less.
If the particle size of the magnetic powder is too large, the surface properties and physical properties of the magnetic layer after film formation are deteriorated, which is not preferable.

In the magnetic coating material for forming the magnetic layer,
In addition to the magnetic powder, auxiliary additives such as carbon, metal powder, conductive metal oxide, and high dielectric material may be added. The particle size of these auxiliary additives is preferably 100 μm or less from the viewpoint of surface properties and physical properties after film formation. If the content of these auxiliary additives in the magnetic layer exceeds 50 wt% with respect to the magnetic powder, the content of the magnetic powder in the magnetic layer will decrease, and the electromagnetic wave absorption characteristics may deteriorate. The compounding amount of the agent is 50 wt% with respect to the magnetic powder.
It is preferably less than.

Examples of the binder used for preparing the magnetic coating material include polyphenylene sulfide, rosin, shellac, chloroprene rubber, polyolefin resin, vinylidene chloride resin, polyamide resin, polyetherketone resin, vinyl chloride resin, polyester resin, Alkyd resin, phenol resin, epoxy resin, acrylic resin, urethane resin, silicon resin, cellulose resin,
Vinyl acetate resin or the like can be used. Further, if necessary, an auxiliary agent such as a solvent, a dispersant, a plasticizer, a cross-linking agent, an antioxidant and a vulcanization accelerator can be added.

In the case of producing the magnetic paint, magnetic powder,
Components such as auxiliary additives, binders and auxiliaries can be dispersed and mixed by using an appropriate device such as a kneader, ball mill, sand mill, roll mill, jet mill or homogenizer. Other mixers, dispersers, grinders, crushers and the like can be appropriately selected and used according to the situation.

The magnetic layer can be formed by applying the magnetic coating material to the surface of the support with a conventional coating machine such as a roll coater, a bar coater, a gravure coater, a cast coater, and a spray coater. The magnetic layer can be provided on one side or both sides of the non-magnetic support. Although the thickness of the magnetic layer after drying is not particularly limited, it is generally 0.
It is preferably 1 μm or more. The thickness of the magnetic layer is 0.
If it is less than 1 μm, a uniform magnetic layer may not be formed. In addition to the magnetic layer, a lubricating layer, a protective layer, a back coat layer and the like may be provided without any problem. Therefore, the electromagnetic wave absorber of the present invention can be produced by using a commercially available coating type magnetic recording medium or a magnetic recording medium waste material generated at the time of production.

When the magnetic layer is formed by the vacuum thin film forming technique, Co, CoNi, CoNiP, CoCr, Fe
A ferromagnetic material such as is deposited on a non-magnetic support made of a long tape by a vacuum deposition method. In this case, it is preferable to use a plastic film as the non-magnetic support. Such vacuum deposition methods are well known to those skilled in the art.

[0026]

EXAMPLES The production and effects of the radio wave absorber of the present invention will be illustrated below with specific examples.

Example 1 The components of the following composition 1 were mixed by a ball mill and uniformly dispersed to prepare a magnetic coating material. This magnetic paint was applied onto a polyimide film (film thickness 50 μm) by a gravure roll so that the thickness of the dried magnetic layer would be 3 μm, and then a thin film 1 was prepared. Next, 500 thin films 1 were laminated and molded under heating and pressurization at 180 ° C. and 100 kg / cm ² for 60 minutes to produce a radio wave absorber 1 having a thickness of 1.5 cm. The electric wave absorption capacity of the electric wave absorber 1 is 100 to 110.
The measurement was performed in the frequency range of 0 MHz.

The measurement of the radio wave absorption characteristic was performed using a network analyzer. In this embodiment, 100 MHz
The return loss was measured and evaluated in the range of 1.1 GHz.
The obtained measurement result is shown in FIG.

(Composition 1) Vinyl chloride resin 25 parts by weight α-Fe ₂ O ₃ 60 parts by weight Carbon black 10 parts by weight Alumina 5 parts by weight Toluene 150 parts by weight

Example 2 The components of the following composition 2 were mixed by a ball mill and uniformly dispersed to prepare a magnetic coating material. This magnetic coating was gravure-rolled onto a polyethylene terephthalate film (film thickness 10 μm) to give a magnetic layer having a thickness of 1 μm after drying.
Then, the thin film 2 was prepared. Next, 1000 thin films 2 are laminated and 130 ° C., 70 kg / cm ²
Molded under heat and pressure for 100 minutes under conditions of 1cm thickness
The electromagnetic wave absorber 2 of was produced. The radio wave absorbing ability of the radio wave absorber 2 was measured by the same method as in Example 1. The obtained measurement result is shown in FIG.

(Composition 2) Urethane resin 25 parts by weight Cellulose resin 60 parts by weight Ni-Zn ferrite powder 10 parts by weight Alumina 5 parts by weight Toluene 150 parts by weight

Example 3 700 sheets of commercially available audio tapes (magnetic layer: γ-Fe ₂ O ₃ , magnetic layer thickness: 5 μm, polyethylene terephthalate film thickness: 10 μm) were laminated at 150 ° C. and 50 k.
A radio wave absorber 3 having a thickness of 5 mm was produced by molding under heat and pressure for 120 minutes under the condition of g / cm ² . The radio wave absorbing ability of the radio wave absorber 3 was measured by the same method as in Example 1. The obtained measurement result is shown in FIG.

Comparative Example 1 100 parts by weight of chloroprene rubber, 30 parts by weight of a compounding agent such as a plasticizer, an antioxidant and a vulcanization accelerator, and Co-γ-
Fe ₂ O ₃ was mixed in an amount of 50 parts by weight, mixed with a Banbury mixer, and rolled into a sheet to prepare a radio wave absorber 4 having a thickness of 5 mm. The radio wave absorbing ability of the radio wave absorber 4 was measured by the same method as in Example 1. The obtained measurement result is shown in FIG.

As apparent from FIGS. 2 to 4, the radio wave absorber of the present invention has a peak at a specific frequency and exhibits a return loss of 10 dB (90%) or more in a wide band. On the other hand, the electromagnetic wave absorber in which the magnetic powder of Comparative Example 1 shown in FIG. 5 was mixed with rubber exhibited an electromagnetic wave absorption characteristic without an absorption peak and a low reflection loss as a whole.

[0035]

As described above, according to the present invention,
By laminating a plurality of thin films each provided with a magnetic layer on a non-magnetic support, a radio wave absorber exhibiting excellent radio wave absorption characteristics can be manufactured. The radio wave absorber of the present invention has a lower content ratio of the magnetic material than the conventional product, and thus can be made lightweight. Further, since the radio wave absorber of the present invention has a laminated structure, it is easier to control the film thickness than the sheet-like radio wave absorber in which a magnetic material is mixed with rubber, synthetic resin, etc. be able to.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a radio wave absorber of the present invention, (a) is a radio wave absorber 5 in which two thin films each having a magnetic layer provided on one surface of a non-magnetic support are laminated. FIG. 1B is a cross-sectional view of a structure, FIG. 6B is a cross-sectional view of a radio wave absorber in which two thin films each having a magnetic layer provided on both surfaces of a non-magnetic support are stacked, and FIG. 1 is a cross-sectional view of a structure of a radio wave absorber 5 in which two thin films each having a magnetic layer 3 provided on one side thereof are laminated with the magnetic layer side as an adhesive surface. FIG. FIG. 3 is a cross-sectional view of a structure of a radio wave absorber 5 in which two thin films provided with a layer 3 are laminated with the support side as an adhesive surface, and (e) the magnetic layer 3 is provided on one or both sides of the non-magnetic support 1. The thin film is bonded to any surface 4
FIG. 3 is a cross-sectional view of the configuration of the radio wave absorber 5 in which layers are laminated.

FIG. 2 is a characteristic diagram showing the radio wave absorbing ability of the radio wave absorber obtained in Example 1.

FIG. 3 is a characteristic diagram showing the radio wave absorbing ability of the radio wave absorber obtained in Example 2.

FIG. 4 is a characteristic diagram showing the radio wave absorbing ability of the radio wave absorber obtained in Example 3.

5 is a characteristic diagram showing the radio wave absorbing ability of the radio wave absorber obtained in Comparative Example 1. FIG.

[Explanation of symbols]

 1 non-magnetic support 3 magnetic layer 5 radio wave absorber

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaru Chino 1-3-2 Hayashi, Yokosuka City, Kanagawa Prefecture (72) Inventor Shinichi Kitabata 1-188 Yuta, Ibaraki City, Osaka Prefecture Hitachi Maxell Co., Ltd.

Claims (3)

[Claims] 1. A radio wave absorber comprising at least two thin films each having a magnetic layer provided on one or both sides of a non-magnetic support. 2. The magnetic layer provided on the non-magnetic support is formed by applying a magnetic coating material containing at least a ferromagnetic material or a paramagnetic material on the surface of the support. Radio wave absorber. 3. The radio wave absorber according to claim 1, wherein the thickness of the magnetic layer provided on the non-magnetic support is 1 mm or less.