JP5481613B2 - Resonant type electromagnetic wave absorber and manufacturing method thereof - Google Patents

Description

  The present invention relates to a resonance type electromagnetic wave absorber having stable absorption performance and improved durability, and a method for manufacturing the same.

  Resonant type electromagnetic wave absorbers are often used to improve the performance of parabolic antennas and ship masts. Because of their excellent durability, magnetic loss agents such as ferrite powder and carbonyl iron powder are dispersed in silicone resin. Is used.

  When the resonance type wave absorber is composed of one layer, the thickness becomes thick. However, if the back surface of the radio wave irradiation surface is made of a conductor such as a metal, the wave absorber can be formed into a thin sheet. When it is known and is not used by attaching to a conductor such as a metal surface, a metal plate or a conductive sheet is used as a conductive layer on the back surface.

  However, the radio wave absorption characteristic of the resonance type radio wave absorber is determined by adjusting the complex relative permittivity and thickness of the material, that is, the distance from the surface irradiated with the radio wave to the conductive layer.

  Because of this principle of operation, when a radio wave absorber that does not have a conductive layer on the back side is pasted on a metal surface, the tension applied when a silicone resin radio wave absorber with adhesive thickness or elastomer properties is pasted. The distance from the radio wave irradiation surface to the conductor, that is, the thickness may change due to a difference, and the radio wave absorption performance as designed may not be obtained. There is a risk that it will make no sense. This tendency is particularly noticeable for a short-wavelength wave absorber such as the millimeter wave region, which has recently been used frequently.

  When using a non-conductor conductor such as metal, it is necessary to paste a conductive layer such as a metal sheet on the back of the wave absorber in advance. If formed, the radio wave absorption performance checked in the product inspection process can be ensured even during actual use.

  However, silicone resin generally has poor adhesiveness and cannot be bonded unless it is a silicone-based adhesive. In addition, the adhesive mechanism of silicone adhesive is said to be due to a chemical reaction with the interface of the adherend, and if the silicone adhesive is diluted too much with a solvent or the like, the adhesiveness is significantly reduced. When adhering to a crab, a silicone-based adhesive must be used with a high viscosity.

  For this reason, even when a conductive layer is applied at the time of manufacturing a radio wave absorber, the thickness error of the adhesive layer when the silicone resin part is applied to the conductive layer is so thick that the influence on the radio wave absorption performance cannot be ignored. The absorption peak shifts to the low frequency side, or the resin is stretched while applying tension to the resin at the time of bonding, so it becomes thinner than the thickness at the time of molding, so it is higher than the design frequency In addition to shifting the absorption peak, the radio wave absorption performance itself is degraded.

  These trends are related to ITS in recent years, such as radio wave absorbers used in the millimeter-wave band, which has been increasingly used in recent years, such as 76.5 GHz used for automobile collision-preventing radar. In particular, there are problems such as a decrease in radio wave absorption performance, difficulty in securing performance confirmed in the product inspection process, and deterioration in manufacturing yield.

In addition, since the adhesive for bonding silicone resin reacts with moisture in the air, when the metal or metal deposition sheet is attached, the adhesive is cut off from the air, so the adhesive is cured. It takes a considerable number of days to do.
Japanese Patent Laid-Open No. 2001-036280

  The problem to be solved is to secure the radio wave absorption performance of the resonance type wave absorber made of silicone resin, which has high weather resistance but is difficult to adhere, as it is in the product inspection process. It exists in the technique of improving the stability of the thickness at the time of adhesion | attachment, ensuring radio wave absorption performance as desired, and raising a yield.

  In order to ensure the radio wave absorption performance as checked in the product inspection process when it is actually used, it is bonded to a conductive layer such as a metal sheet, a metal vapor-deposited sheet, or a metal plate in advance before the product inspection process, that is, in the molding process. It is desirable to keep it.

Therefore, first apply a moisture-curing silicone resin adhesive to the metal foil, metal vapor-deposited sheet, metal plate, etc. to be attached to the back of the radio wave absorber to form a cured silicone resin film that adheres firmly to the metal surface. Let

Radio wave loss agent and curing agent such as ferrite powder, carbonyl iron powder, or conductive carbon powder on metal foil, metal vapor-deposited sheet, metal plate, etc. with a silicone film formed on the surface in this way, on condensation type silicone resin After flowing a mixture of the above, a spacer with a desired thickness is sandwiched and a release sheet made of polypropylene or the like is placed on the sheet, and pressure forming is performed, or a roller whose gap is adjusted to obtain a desired thickness Formed into a sheet by passing through.

When the condensation-type silicone resin molded in this step is cured, the silicone resin cured film that has been formed on the metal surface in advance by reacting with moisture in the air reacts and adheres, resulting in a metal layer on the back surface. A silicone resin radio wave absorber having a thickness adjusted to absorb the target radio wave is obtained.

Here, if an addition type silicone resin is used instead of a condensation type silicone resin, the portion that touched the moisture curable silicone film formed on the conductor surface will inhibit the curing, and the conductor surface and the silicone resin sheet cannot be bonded. It is necessary to use condensation type silicone.

  According to the method of the present invention, the thickness of the adhesive layer is controlled with respect to a conductive layer such as a metal sheet, a metal vapor-deposited sheet, and a metal plate in a silicone resin resonance type radio wave absorber that has high weather resistance but is hardly adhesive. And can be bonded. For this reason, since the change of the radio wave absorption characteristics due to the thickness error of the adhesive layer is unlikely to occur, a stable radio wave absorption performance can be obtained, and the product yield is significantly improved as compared with the method of bonding the conductive layer later. In addition, even if it adheres to a non-conductor during use, or even when it adheres to a conductor such as a metal plate, the absorption characteristics after bonding do not change, ensuring absorption performance during product inspection even during actual use. I can do it.

  Moreover, since the radio wave absorber itself is a silicone resin, the back side itself of the radio wave irradiation surface is a resin such as a metal or polyester, so that there is an advantage that the adhesive used is not limited to the silicone resin.

  A thin silicone adhesive TSE388 made by Toshiba Silicone Co., Ltd., which is a moisture curable silicone adhesive, is thinly applied to a 0.2 mm thick aluminum sheet, allowed to stand for 24 hours, cured by moisture in the air, and the surface of the aluminum sheet is silicone. A film was formed.

  With this method, ten aluminum sheets having a silicone film formed thereon were prepared, and a resonance type electromagnetic wave absorber for 76.5 GHz was obtained. On the other hand, a mixture of BASF carbonyl iron powder: 300 g and curing agent CE61: 1 g is poured, a polyethylene release sheet is placed on top, and the gap is adjusted so that the thickness of the wave absorber is 1.12 mm. After passing between the two rollers, it was allowed to stand in an oven at 80 ° C. for 12 hours to be cured.

  After 12 hours, when the resin was cured, the release sheet was peeled off, and the thickness of the sheet-shaped radio wave absorber was measured with a micrometer. All 10 sheets including the conductive layer were 1.15 ± 0.01 mm. As shown in FIG. 1, the return loss by the arch method was also within the range of 20 ± 2 dB.

  On the release sheet made of polyethylene, a mixture of carbonyl iron powder made by BASF: 300 g and curing agent CE61: 1 g was poured on a condensation silicone resin TSE352: 100 g made by Toshiba Silicone. For the purpose of obtaining a 76.5 GHz resonant electromagnetic wave absorber by placing a release sheet, after passing between two rollers whose gap was adjusted so that the thickness of the electromagnetic wave absorber was 1.12 mm, 80 Cured for 24 hours in a dryer at 0C.

  Twenty-four hours later, when the resin was cured, the release sheet was peeled off to apply the sheet-shaped radio wave absorber with a silicone-based adhesive TSE388 manufactured by Toshiba Silicone, and an aluminum sheet having a thickness of 0.2 mm was bonded, After curing for 24 hours, the thickness was measured with a micrometer and found to vary in the range of 1.19 ± 0.04 mm. The variation in resonance frequency as shown in FIG. 2 was recognized, and only one sheet was about 15 dB. The return loss was.

    As in Example 1, a silicone adhesive TSE388 manufactured by Toshiba Silicone Co., Ltd., which is a moisture-curing silicone adhesive, is thinly applied to an aluminum sheet having a thickness of 0.2 mm, left to stand for 24 hours, and cured by moisture in the air. To form a silicone film on the surface of the aluminum sheet.

  By this method, ten aluminum sheets having a silicone film formed thereon are formed, and each of them is added to the silicone resin TSE3455T (A): 100 g manufactured by Toshiba Silicone Co., 300 g of carbonyl iron powder manufactured by BASF, cured. Agent TSE3455T (B): Pour 10 g of the mixture, put a polyethylene release sheet on top, and pass between two rollers with the gap adjusted so that the thickness of the wave absorber is 1.12 mm. And then cured for 24 hours in an oven at 80 ° C.

  After 24 hours, when the resin was cured, the release sheet was peeled off, but the portion of the aluminum sheet that was in contact with the silicone film was inhibited from curing and was not adhered in a sticky state.

  Although it is a silicone resin radio wave absorber that has high weather resistance but can only be bonded with a silicone adhesive that takes a long time to bond and cure, it has a resin layer such as metal or polyester on the back side of the radio wave irradiation surface in advance. In addition to being able to easily adhere with the adhesives of the products, the radio wave absorption performance confirmed at the time of manufacture can be secured even during actual use, and the thickness of the adhesive layer can be easily controlled to stabilize the radio wave absorption performance. As in the wave band, the yield of products with strict thickness control can be improved.

The absorption characteristic figure of the electromagnetic wave absorber for 76.5 GHz manufactured by the method of the said patent. Example 1 The absorption characteristic figure of the electromagnetic wave absorber for 76.5 GHz manufactured by the method of adhere | attaching an aluminum sheet after sheet manufacture. (Example 2)

Claims (1)

  When a dielectric loss agent or magnetic loss agent or both powders are mixed with silicone resin to produce a resonant wave absorber having a conductive layer on the opposite side of the radio wave irradiation surface, it becomes a wave reflector. Metal foil or polyester, vinyl chloride, polystyrene, polyethylene terephthalate, etc., on the surface of the conductor of a sheet in which a metal that is a radio wave reflector such as aluminum, copper, nickel, silver is deposited on a resin film on which metal can be deposited, Apply a thin silicone adhesive in advance, and after the adhesive has hardened, place the pre-cure condensation-type silicone resin mixed with dielectric loss agent or magnetic loss agent powder, and adjust the thickness before molding. Resonance-type radio wave characterized by stable control of radio wave absorption performance by fusing the pre-cured condensation-type silicone resin and the pre-cured adhesive layer Method of manufacturing the absorbent body.

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