Radio wave absorber

Abstract

To provide a radio wave absorber with high heat resistance and power resistance performance.SOLUTION: A radio wave absorber includes a board 11 in which a glass wool base material is impregnated with a conductive paint, the conductive paint contains carbon powder with silicone resin as a binder, and the board 11 is formed in a hollow pyramidal shape or a wedge shape.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a radio wave absorber.

Background Art

[0002] Conventionally, various radio wave absorbers have been developed. In particular, a pyramidal radio wave absorber in which a base material such as foamed polyurethane is impregnated with a conductive paint and dried and cured is old in history and widely used in large quantities. Although continuous bubbles exist in the foamed polyurethane, since the bubble size is small, there is almost no air flow, and in addition, the thermal conductivity is small. As a result, when a strong radio wave irradiates the radio wave absorber and the power density increases, the temperature inside the radio wave absorber becomes high. Since most of the radio wave absorbers made of foamed polyurethane are organic substances, a large amount of decomposition gas containing combustible gas is generated.

[0003] In addition, a radio wave absorber has also been developed in which a flat base material mainly composed of glass fibers is impregnated with a conductive paint containing carbon powder and dried and cured. Since this is mainly composed of inorganic substances, the amount of decomposition gas containing combustible gas generated is relatively small. However, due to its flat shape, it has a narrow-band characteristic in which absorption performance is exhibited only in a specific frequency band, and it is not suitable for use in an anechoic chamber.

[0004] In addition, among the currently popular radio wave absorbers, there is also a non-combustible high-power radio wave absorber that combines inorganic substances and carbon fibers. While it is completely non-combustible and has extremely excellent high-power resistance, it has a problem of large bulk specific gravity. Furthermore, a radio wave absorber in which a pyramidal structure having a honeycomb structure made of an organic material as a skeleton is impregnated with a conductive paint containing carbon powder is also used for high-power applications, but ignition (explosion) accidents due to thermal decomposition gas of the organic material have been reported. Under such circumstances, for example, Patent Document 1 discloses an invention of a "radio wave absorbing material" in which carbon is attached to ceramic fibers formed in a pyramidal shape to improve fire resistance.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the case of a conventional radio wave absorber including the invention disclosed in the above Patent Document 1, when irradiated with high-power radio waves, the conductive paint may burn, or when exposed to high temperatures, there is a concern about ignition (explosion) accidents due to the generation of pyrolysis gas containing a large amount of combustible gas. Further, although four mats of glass fiber material in the shape of an isosceles triangle having a predetermined thickness are assembled in a pyramidal shape to exhibit stable radio wave absorption performance in a wide band, when irradiated with high-power radio waves, the temperature rises sharply and the power resistance performance cannot be improved.

[0007] Therefore, in view of the various problems described above, an object of the present invention is to provide a radio wave absorber having high heat resistance and power resistance performance.

Means for Solving the Problems

[0008] (1) A board in which a glass wool base material is impregnated and dried with a conductive paint, the conductive paint contains carbon powder with a silicone resin as a binder, and the board is formed in a hollow pyramidal shape or wedge shape, characterized in that it is a radio wave absorber.

[0009] (2) The radio wave absorber according to (1) above, wherein the board is integrally formed and V-grooves are formed inside the corners in the pyramidal shape or the wedge shape.

[0010] (3) The radio wave absorber according to (1) or (2) above, wherein the board has ventilation holes penetrating the board formed on the surface in the pyramidal shape or the wedge shape.

[0011] (4) The ventilation holes are the electromagnetic wave absorber according to the above (3), which are formed at the bottom and / or near the bottom of the surface part in the pyramidal shape or the wedge shape.

[0012] (5) The electromagnetic wave absorber according to any one of the above (1) to (4), wherein the content of the silicone resin in the conductive paint is 2% by weight or less.

Advantages of the Invention

[0013] According to the invention according to the above (1), since a board is formed by impregnating and drying a glass wool base material having nonflammability with a conductive paint containing carbon powder using a silicone resin as a binder, the content of organic substances can also be reduced, and an electromagnetic wave absorber having extremely high heat resistance and power resistance performance can be obtained. Furthermore, by forming the above board in a hollow pyramidal shape or wedge shape, it is lightweight and broadband characteristics can be obtained, and it can be suitably used in an anechoic chamber or the like.

[0014] In addition, according to the invention according to the above (2), since the above board is integrally formed and a V-groove is provided inside the corner part in the pyramidal shape or the wedge shape, it is possible to fold at the corner part so that the cross-sections of the boards are joined in the V-groove, and it is possible to prevent the end surface of the board from being exposed on the surface of the electromagnetic wave absorber. Thereby, it is possible to effectively suppress delamination that is likely to occur particularly in a board made of glass wool and obtain a durable electromagnetic wave absorber.

[0015] In addition, according to the invention according to the above (3), since ventilation holes penetrating the board are provided on the surface part in the pyramidal shape or the wedge shape, it is possible to promote natural air cooling, reduce the temperature rise, and further improve the power resistance performance of the electromagnetic wave absorber.

[0016] In addition, according to the invention according to (4) above, ventilation holes are provided at the bottom and / or near the bottom of the surface portion in a pyramidal shape or a wedge shape, so that it is possible to reduce the temperature near the bottom of the radio wave absorber where the temperature is particularly likely to rise, and the electric power resistance performance of the radio wave absorber can be further improved.

[0017] In addition, according to the invention according to (5) above, in the conductive paint, the content of the silicone resin which is an organic substance is 2% by weight or less, so that the content of the organic substance is significantly reduced as compared with the conventional case, and it is possible to suppress the generation amount of decomposition gas containing combustible gas and significantly reduce the risk of fire and explosion.

Brief Description of the Drawings

[0018]

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Mode for Carrying Out the Invention

[0019] Hereinafter, embodiments of the radio wave absorber of the present invention will be described with reference to the drawings.

[0020] (First Embodiment) As shown in FIG. 1, the radio wave absorber 1 of the present embodiment is a board made of glass wool composed of glass fibers and molded into a pyramidal shape or a wedge shape (wedge shape). The board of the glass wool base material is impregnated with and dried with a conductive paint using a silicone resin as a binder to fix the carbon powder contained in the conductive paint.

[0021] Fig. 2(a) shows the component ratio of the conductive paint using the silicone binder used in this embodiment. The silicone binder has an inorganic main skeleton and a silicone resin with a heat-resistant temperature of 180°C (equivalent to heat-resistant class 180(H) of JISC4003:2010). Compared with other general resins used as binders, it not only has high heat resistance but also has a low organic content and is a resin that is difficult to burn even alone. And by using this silicone resin as a binder and impregnating it into a glass mat, which is a non-combustible material, the flame retardant that is usually essential for conductive paints becomes unnecessary. Therefore, the binder resin as a paste for the flame retardant is also unnecessary, and together these can significantly reduce the coating film adhesion amount of the conductive paint, that is, the organic content of the entire coating film. Therefore, the generation of decomposition gas containing combustible gas can be significantly suppressed. As a result, an extremely difficult-to-burn radio wave absorber 1 can be obtained.

[0022] Fig. 2(b) shows the component ratio of the conductive paint using the conventional chloroprene impregnated in a glass wool substrate as a comparison target, and Fig. 2(c) shows the component ratio of the conductive paint using the chloroprene impregnated in the conventional urethane foam substrate, respectively.

[0023] When impregnating a glass wool substrate of a predetermined size (for example, thickness 1.0 cm, width 66.6 cm, length 66.6 cm, weight about 212.6 g) with the conductive paint using the silicone binder of this embodiment, about 2000 g of the conductive paint will be impregnated, and about 12.4% by weight of the total weight of the radio wave absorber will be organic matter composed of silicone resin, etc. On the other hand, when impregnating with the conductive paint using the chloroprene binder, about 2150 g of the conductive paint will be impregnated, and about 32% by weight of the total weight of the radio wave absorber will be organic matter composed of chloroprene, etc.

[0024] Furthermore, when impregnating a urethane foam substrate (for example, having a thickness of 1.0 cm, a width of 74.5 cm, a length of 15 m, and a weight of approximately 2.523 kg) used in a general radio wave absorber with a conductive paint using a chloroprene binder, it is necessary to impregnate approximately 10.726 kg of the conductive paint, and approximately 96% by weight of the total weight of the radio wave absorber becomes an organic substance composed of urethane foam and chloroprene, etc. Therefore, by impregnating a glass wool substrate with the conductive paint using a silicone binder as in this embodiment, it becomes possible to significantly suppress the content of the organic substance contained in the radio wave absorber 1, and even when high-power radio waves are irradiated and the temperature becomes high, the generation of pyrolysis gas can be suppressed, and a radio wave absorber 1 having high heat resistance and high electric power resistance performance can be obtained.

[0025] Figure 3 shows a graph representing the relationship between the passage of time and temperature when a thermocouple is attached to a radio wave absorber impregnated and dried with a conductive paint using a chloroprene binder on a glass wool substrate and a radio wave absorber 1 impregnated and dried with a conductive paint using the silicone binder of this embodiment on a glass wool substrate, respectively, and radio waves are irradiated. The temperature rise of the radio wave absorber usually rises smoothly exponentially with the passage of the radio wave irradiation time. However, in the case of the conductive paint using a chloroprene binder, it deviates from the smooth exponential function at 190 °C and shows a rapid temperature rise.

[0026] On the other hand, the radio wave absorber 1 impregnated and dried with the conductive paint using the silicone binder of this embodiment does not show a rapid temperature rise deviating from the smooth exponential function even when it reaches 250 °C, indicating that it has high heat resistance. From this test result, it can be seen that the radio wave absorber 1 impregnated and dried with the conductive paint using a silicone binder on a glass wool substrate has a heat resistance temperature at least 1.3 times (approximately 250 °C / 190 °C) or more higher than that of the radio wave absorber impregnated and dried with the conductive paint using a chloroprene binder.

[0027] Figure 4 also shows the temperature data during the power withstand test of the radio wave absorber 1 of the present embodiment in a graph. More specifically, as shown in the cross-sectional view of FIG. 1, thermocouples TC1 to TC6 are installed at various locations of the radio wave absorber 1 (note that TC5 and TC6 are installed in the space of the hollow part), and 500 mW / cm 2 of radio waves output from a large horn antenna and 600 mW / cm 2 of radio waves output were irradiated, and the temperature changes over time at the installation positions of the respective thermocouples TC1 to TC6 were measured.

[0028] Figure 4(a) shows the temperature change when radio waves with an output of 500 mW / cm 2 were irradiated for 40 minutes, and Figure 4(b) shows the temperature change when radio waves with an output of 600 mW / cm 2 were irradiated for 30 minutes. Also, Figure 4(c) shows the temperature change when radio waves with an output of 460 mW / cm 2 were irradiated on a radio wave absorber obtained by impregnating and drying a radio wave absorber using a chloroplane binder.

[0029] From the measurement results, the radio wave absorber 1 of the present embodiment in which the conductive paint using a silicone binder was impregnated and dried on the glass wool base material did not rise above 204°C even at the bottom (TC4) where the temperature was the highest when irradiated with radio waves of 500 mW / cm 2 for 40 minutes, and no phenomena such as smoke generation were observed. Also, when irradiated with radio waves of 600 mW / cm 2 , a smell like burnt rubber was generated from around when the temperature exceeded 220°C at the bottom (TC4), and the temperature rose to 250°C at the time of 30 minutes of irradiation. On the other hand, the radio wave absorber impregnated and dried with the conductive paint using a chloroplane binder exceeded 300°C at each measurement location in just 10 minutes when irradiated with radio waves with an output of 460 mW / cm 2 . From such results, it can be seen that the radio wave absorber 1 of the present embodiment has high heat resistance and power withstand performance.

[0030] Next, a method for forming the radio wave absorber 1 of the present embodiment will be described. The radio wave absorber 1 of the present embodiment is formed into a pyramidal shape or a wedge shape by impregnating a board made of glass wool with the conductive paint using the silicone binder described above, drying it, and then forming it into a mold as shown in the development view of Fig. 5(a). Therefore, at the stage of creating the plate-like radio wave absorber (board 11) by impregnating the glass wool board with the conductive paint and further drying it, the attenuation amount (transmission loss) of the radio wave passing through the board 11 can be measured. Thus, an intermediate inspection of the electrical performance can be carried out, and it becomes possible to easily readjust in case of insufficient performance. As a result, after the completion of the pyramidal or wedge-shaped radio wave absorber 1, the yield of good products can be significantly improved.

[0031] Fig. 5(a) shows a development view of the board 11 constituting the radio wave absorber 1 of the present embodiment, which is composed of an integrally formed glass wool base material. In the illustrated example, the radio wave absorber 1 has a pyramidal shape. At each corner 12, as shown in the cross-section A - A of Fig. 5(b) and the cross-section B - B of Fig. 6, a V-groove is provided inside the corner 12 of the radio wave absorber 1 without cutting the board 11. Also, as shown in the figure, this V-groove extends to the top forming the tip of the radio wave absorber 1. As shown in the cross-sectional view near the top of Fig. 6, as the V-grooves approach the top, the respective V-grooves interfere with each other and the board 11 gradually becomes thinner.

[0032] By forming the board 11 as described above, when the board 11 is bent at the corner 12 to form a three-dimensional shape as shown in the cross-sectional view of Fig. 7, the cross-sections of the boards can be joined to each other in the V-groove as shown in the figure. Therefore, it becomes possible to make the tip of the radio wave absorber 1 sharp, and it also becomes possible to prevent the end face of the board 11 from being exposed on the surface of the radio wave absorber 1, and in particular, it is possible to effectively suppress the delamination that easily occurs in the glass wool base material.

[0033] (Second Embodiment) In order to further improve the heat resistance and power resistance performance of the radio wave absorber 1 of the first embodiment described above, as shown in FIGS. 8 and 9, a plurality of ventilation holes 13 penetrating the board 11 constituting the radio wave absorber 1 are provided in the board 11.

[0034] In this embodiment, as shown in FIG. 8, one ventilation hole 13 with a diameter of 1 cm and three ventilation holes 13 with a diameter of 2 cm are provided at one location on the top side with respect to the surface of the radio wave absorber 1, and these are formed on the four surfaces of the radio wave absorber 1. Further, in the embodiment shown in FIG. 9, one ventilation hole 13 with a diameter of 1 cm and two ventilation holes 13 with a diameter of 2 cm are provided from the top side of the radio wave absorber 1, and these are formed on the four surfaces of the radio wave absorber 1.

[0035] Also, FIG. 10 shows, in a graph, the temperature data during the power resistance test of the radio wave absorber 1 of this embodiment. More specifically, as shown in FIGS. 8 and 9, thermocouples TC1 to 6 are installed at various locations of the radio wave absorber 1 (note that TC5 and TC6 are installed in the space of the hollow part), and radio waves with an output of 500 mW / cm 2 from the horn antenna are irradiated for 35 minutes, and the temperature change over time at each installation position is measured.

[0036] FIG. 10(a) shows the temperature change of the radio wave absorber without the ventilation hole 13 as a comparison target, FIG. 10(b) shows the temperature change of the radio wave absorber shown in FIG. 8, and FIG. 10(c) shows the temperature change of the radio wave absorber shown in FIG. 9. And FIG. 11 shows the temperature of the base part 14 (refer to TC4 in FIG. 10) 35 minutes after the radio wave irradiation, the temperature of the hollow part near the bottom of the radio wave absorber (refer to TC6 in FIG. 10), and the ambient temperature corresponding to the room temperature (refer to TC7 in FIG. 10).

[0037] As shown in the figure, by providing the ventilation holes 13, it is possible to suppress the temperature rise in the base portion 14 to about 23 to 44 °C, and further suppress the temperature rise of about 76 to 81 °C in the hollow portion near the bottom of the radio wave absorber. Therefore, by providing the ventilation holes 13 in the board 11 constituting the radio wave absorber 1, it is possible to promote natural air cooling, reduce the temperature rise, and further improve the withstand power performance of the radio wave absorber 1. In particular, it can be said that providing the ventilation holes 13 in the base portion 14 (bottom) and / or the board 11 near the bottom of the radio wave absorber 1 where the temperature is likely to rise contributes to the improvement of the withstand power performance.

[0038] Furthermore, as a further modification, in addition to forming the ventilation holes 13 in the four side faces of the radio wave absorber 1 described above, it is also possible to form the ventilation holes 13 on the bottom surface of the radio wave absorber 1. For example, by providing the ventilation holes 13 in the base portion 14 that communicate with the hollow portion of the radio wave absorber 1 and arranging punching metal or the like on the back side thereof to fix the radio wave absorber 1, ventilation of the hollow portion can be achieved.

[0039] Also, as another modification, as shown in Fig. 12(a), ventilation holes 13 may be provided below the vicinity of the top of the radio wave absorber 1, and further, mounting surface side ventilation holes communicating with the hollow portion may be provided above the mounting surface of the radio wave absorber 1. That is, the warm air in the hollow portion is discharged to the back side of the mounting surface, thereby generating an air flow in the hollow portion. Then, cold air (outside air) is taken into the hollow portion through the ventilation holes 13 near the top. With such a configuration, it is possible to effectively suppress the temperature rise of the radio wave absorber 1 and improve the withstand power performance. At that time, as shown in Fig. 12(b), by mounting the radio wave absorber 1 so that the corner portion 12 of the radio wave absorber 1 is located upward and providing the mounting surface side ventilation holes, it is possible to efficiently collect and discharge the warm air in the hollow portion. It should be noted that the modification shown in Fig. 12 has a relatively high temperature reduction effect compared to the modification shown in Fig. 13 described later because the warm air exhausted from the hollow portion does not contact the adjacent radio wave absorber 1.

[0040] Furthermore, as another modification, as shown in FIG. 13, a ventilation hole 13 may be provided below the vicinity of the top of the radio wave absorber 1, and a ventilation hole near the bottom communicating with the hollow portion may be provided above the vicinity of the bottom of the radio wave absorber 1. That is, the warm air in the hollow portion is discharged from the ventilation hole near the bottom, thereby generating an air flow in the hollow portion. Then, cold air (outside air) is taken into the hollow portion from the ventilation hole 13 near the top. With such a configuration, it is possible to effectively suppress the temperature rise of the radio wave absorber 1 and improve the withstand power performance. At that time, the radio wave absorber 1 is attached so that the corner portion 12 of the radio wave absorber 1 is positioned upward, and by providing the ventilation hole near the bottom described above on the surface of the corner portion 12 of the radio wave absorber 1 or its vicinity, it becomes possible to efficiently collect and discharge the warm air in the hollow portion.

[0041] In each of the above-described modifications shown in FIGS. 12 and 13, by utilizing the phenomenon that warm air rises while drawing in cold air, the so-called "chimney effect", it is possible to efficiently generate an air flow in the hollow portion even with a small opening area, and obtain the temperature reduction effect of the radio wave absorber 1. Furthermore, since the above temperature reduction effect can be obtained even with a small opening area, it is not necessary to increase the opening area. Therefore, it is possible to suppress the intrusion of dust and insects into the radio wave absorber 1, and it is also possible to effectively suppress the reduction in the strength of the radio wave absorber 1 itself due to the provision of the opening.

[0042] Also, each of the above-described modifications shown in FIGS. 12 and 13 shows the installation mode of the radio wave absorber 1 on the wall surface. However, when the radio wave absorber 1 is installed downward on the ceiling surface, particularly in the case of the modification shown in FIG. 13, the discharged warm air may float near the ceiling, which may impair the temperature reduction effect of the radio wave absorber 1 group. In contrast, by applying a highly breathable member such as perforated metal to the mounting surface of the radio wave absorber 1 on the ceiling portion, it is possible to take in cold air (outside air) from the ventilation hole 13 near the top of the radio wave absorber 1 and efficiently discharge the warm air in the hollow portion through the perforated metal or the like.

[0043] Also, the warm air exhausted to the back side of the mounting surface of the radio wave absorber 1 as described above can be forced to discharge the warm air and / or inflow cold air (outside air) by adding a separate device or the like, and furthermore, it is also possible to improve the temperature reduction effect on the radio wave absorber 1.

[0044] As described above, the radio wave absorber of the present invention has been described based on each embodiment with reference to the drawings and the like. However, the specific configuration is not limited to these embodiments. The scope of the present invention is shown by the claims rather than the description of the above embodiments, and further includes all modifications within the meaning and scope equivalent to the claims. Also, the specific materials, dimensional shapes, etc. described in the above embodiments can be changed within the scope of solving the problems of the present invention.

Description of Reference Numerals

[0045] 1 Radio wave absorber 11 Board 12 Corner 13 Vent hole 14 Base part

Claims

1. A board in which a glass mat made of glass wool as a base material is impregnated with and dried with an electrically conductive paint, wherein the electrically conductive paint contains carbon powder using a silicone resin as a binder, and the board is formed in a hollow pyramidal shape or wedge shape characterizing the radio wave absorber.

2. The board is integrally formed, and a V-groove is formed inside the corner of the pyramidal shape or the wedge shape. The radio wave absorber according to Claim 1.

3. Ventilation holes penetrating the board are formed in the surface of the board in the pyramidal shape or the wedge shape. The radio wave absorber according to Claim 1 or 2.

4. The ventilation holes are formed at the bottom and / or near the bottom of the surface of the board in the pyramidal shape or the wedge shape. The radio wave absorber according to Claim 3.

5. The content of the silicone resin in the electrically conductive paint is 2% by weight or less. The radio wave absorber according to any one of Claims 1 to 4.

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