JP6479643B2 - Radio wave absorber and manufacturing method thereof - Google Patents

Description

  The present invention relates to a radio wave absorber and a manufacturing method thereof.

  It is known to use a radio wave absorber for countermeasures against communication failure and noise. As such a radio wave absorber, for example, in Patent Documents 1 and 2, a polyvinylidene chloride fiber coated with a conductive film containing carbon is entangled and formed into a mat shape, and thick fibers are arranged on the front side, while the back side There is disclosed a radio wave absorber in which fine fibers are arranged on the side and thereby the fiber density is changed in the thickness direction.

Japanese Patent Publication No. 6-32417 Japanese Patent Publication No. 7-105610

  An object of the present invention is to provide a radio wave absorber capable of obtaining excellent radio wave absorption performance even in a microwave of a frequency range of 1 to 18 GHz in addition to a W band radio wave of a frequency range of 75 to 110 GHz.

  Each of the radio wave absorbers of the present invention includes a surface layer and a back layer made of fibers and an intermediate layer provided therebetween, and the fibers constituting the surface layer, the back layer, and the intermediate layer are A radio wave absorber that is bonded to an adhesive film to form a non-woven mat and the surface of the surface layer is an uncompressed surface, and constitutes the surface layer, the back layer, and the intermediate layer When the fineness of the monofilament of the fiber is A (dtex), B (dtex), and C (dtex), the following formula (1) is satisfied.

  The method for producing a radio wave absorber according to the present invention includes a back surface layer forming step of forming a fiber layer by spraying fibers for constituting the back surface layer, and an intermediate layer on the fiber layer formed in the back surface layer forming step. An intermediate layer forming step of dispersing and laminating fibers for constituting a layer, and a fiber for constituting a surface layer being spread on the fiber layer formed in the back surface layer forming step and the intermediate layer forming step The fibers constituting the fiber layer are dispersed by spreading an adhesive from above the fiber layer formed by laminating in the surface layer forming step, the back layer forming step, the intermediate layer forming step, and the surface layer forming step. And a bonding step of forming a non-woven mat by bonding through an adhesive film, and compression processing for pressing the surface of the surface layer with a flat surface is not performed.

  According to the present invention, the fineness of the monofilaments of the fibers including the front surface layer, the back surface layer, and the intermediate layer, the surface of the surface layer being an uncompressed surface, and the fibers constituting the surface layer, the back surface layer, and the intermediate layer. By satisfying the above equation (1) when A (dtex), B (dtex), and C (dtex), respectively, in addition to the W-band radio wave in the frequency range 75 to 110 GHz, the micro in the frequency range 1 to 18 GHz Excellent wave absorption performance can be obtained even in waves.

It is a perspective view of the electromagnetic wave absorber which concerns on embodiment. It is sectional drawing of the electromagnetic wave absorber which concerns on embodiment. It is 1st explanatory drawing which shows the manufacturing method of the electromagnetic wave absorber which concerns on embodiment. It is 2nd explanatory drawing which shows the manufacturing method of the electromagnetic wave absorber which concerns on embodiment. It is 3rd explanatory drawing which shows the manufacturing method of the electromagnetic wave absorber which concerns on embodiment. It is a 4th explanatory view showing a manufacturing method of a wave absorber concerning an embodiment. It is 5th explanatory drawing which shows the manufacturing method of the electromagnetic wave absorber which concerns on embodiment. It is a figure which shows the structure of the electromagnetic wave absorption performance measuring apparatus for measuring the electromagnetic wave absorption performance in the electromagnetic wave of W band. It is a side view which shows the structure of the electromagnetic wave absorption performance measuring apparatus for measuring the electromagnetic wave absorption performance in a microwave. It is a top view which shows the structure of the electromagnetic wave absorption performance measuring apparatus for measuring the electromagnetic wave absorption performance in a microwave. It is a graph which shows the electromagnetic wave absorption performance in the microwave of an Example.

  Hereinafter, embodiments will be described in detail.

  1 and 2 show a radio wave absorber 10 according to an embodiment. The radio wave absorber 10 according to the embodiment is installed in a surrounding structure for the purpose of preventing irregular reflection of radio waves from the in-vehicle radar, for example, when performing a running test of an automobile equipped with the in-vehicle radar outdoors, In addition, it is provided for absorbing radio waves in ETC using radio waves with a frequency of 5.8 GHz, or indoors, for absorbing radio waves in indoor wireless LANs using radio waves with a frequency of 2.4 GHz.

  The radio wave absorber 10 according to the embodiment includes a surface layer 11 and a back surface layer 12 made of fibers having different monofilament finenesses, and an intermediate layer 13 provided between the surface layer 11 and the back surface layer 12. The fibers constituting the surface layer 11, the back surface layer 12, and the intermediate layer 13 are bonded to each other through an adhesive film to form a nonwoven mat. Specifically, the monofilaments are in point contact or line contact within each layer of the front surface layer 11, the back surface layer 12, and the intermediate layer 13, and are bonded and integrated by an adhesive coating at those contact portions. Moreover, the surface of the fiber which comprises the surface layer 11, the back surface layer 12, and the intermediate | middle layer 13 is coat | covered with the electrically conductive film.

  In the radio wave absorber 10 according to the embodiment, the fineness of the monofilaments of the fibers constituting the front surface layer 11, the back surface layer 12, and the intermediate layer 13 is A (dtex), B (dtex), and C (dtex), respectively. The following formula (1) is satisfied.

  The fineness C (dtex) of the monofilament of the fiber constituting the intermediate layer 13 is determined by the fineness A (dtex) of the monofilament of the fiber constituting the surface layer 11 and the fineness B (dtex) of the monofilament of the fiber constituting the back surface layer 12. Therefore, the fiber density is lower in the order of the back layer 12, the intermediate layer 13, and the surface layer 11. Further, the interlayer between the surface layer 11 and the intermediate layer 13 is not necessarily clear, and a layer in which fibers constituting the surface layer 11 and fibers constituting the intermediate layer 13 are mixed may be formed. Similarly, the interlayer between the back surface layer 12 and the intermediate layer 13 may not necessarily be clear, and a layer in which fibers forming the back surface layer 12 and fibers forming the intermediate layer 13 are mixed may be formed. . Furthermore, the layers of the surface layer 11, the intermediate layer 13, and the back surface layer 12 are not necessarily clear, and the radio wave absorber 10 as a whole has a fiber so that the fineness gradually decreases from the surface side in the thickness direction toward the back surface side. It may be a configuration in which is distributed.

  In the radio wave absorber 10 according to the embodiment, the surface 11a of the surface layer 11 is an uncompressed surface. That is, the surface layer 11 is not subjected to compression processing that presses the surface with a flat surface.

  According to the radio wave absorber 10 according to such an embodiment, since the surface 11a of the surface layer 11 composed of fibers having a monofilament fineness A (dtex) of 3300 to 11000 dtex is an uncompressed surface, the surface layer 11 has a sparse fiber density, and is formed on an uneven surface with raised fibers. Therefore, a W-band radio wave having a short wavelength range of 75 to 110 GHz easily enters the radio wave absorber 10. Since the radio waves entering the absorber 10 are repeatedly reflected and attenuated, excellent radio wave absorption performance can be obtained particularly in W-band radio waves.

  In addition, the surface layer 11, the back surface layer 12, and the intermediate layer 13 are included, the surface of the surface layer 11 is an uncompressed surface, and the fibers constituting the surface layer 11, the back surface layer 12, and the intermediate layer 13 When the fineness of the monofilament satisfies the above formula (1), excellent radio wave absorption performance can be obtained not only in W band radio waves but also in microwaves in the frequency range of 1 to 18 GHz. Therefore, it is not necessary to use different radio wave absorbers for each of the application using the W-band radio wave and the microwave using the frequency range of 1 to 18 GHz, and the radio wave absorber 10 according to the single embodiment is used for both applications. It can correspond to.

  From the viewpoint of improving radio wave absorption performance in W-band radio waves and microwaves, it is preferable to satisfy the following formula (2).

  The above formula (2) indicates that the fineness C (dtex) of the monofilament of the fiber constituting the intermediate layer 13 is the fineness A (dtex) of the monofilament of the fiber constituting the surface layer 11 and the monofilament of the fiber constituting the back surface layer 12. Meaning that it is not less than the geometric mean of the fineness B (dtex) and not more than a value obtained by multiplying the geometric mean by 1.2, and this means that the diameter of the monofilament of the fibers constituting the intermediate layer 13 is the surface It also means that it is not less than the intermediate value between the diameter of the monofilament of the fiber constituting the layer 11 and the diameter of the monofilament of the fiber constituting the back layer 12 and not more than a value obtained by multiplying the intermediate value by 1.2. Ideally, the diameter of the monofilament of the fiber constituting the intermediate layer 13 is preferably an intermediate value between the diameter of the monofilament of the fiber constituting the surface layer 11 and the diameter of the monofilament of the fiber constituting the back layer 12. However, if the diameter of the monofilament of the fibers constituting the intermediate layer 13 is 1.2 times or less of the intermediate value, it is possible to obtain better radio wave absorption performance in microwaves in the frequency range of 1 to 18 GHz. The upper limit value is preferably 1.14 times or less of the intermediate value.

  Moreover, according to the electromagnetic wave absorber 10 which concerns on embodiment, although the difference of the thickness of the fiber which comprises the surface layer 11 and the back surface layer 12 is large, they are comprised between the surface layer 11 and the back surface layer 12. By providing the intermediate layer 13 made of fibers having an intermediate thickness, the fiber density gradient in the thickness direction in the plane can be made uniform.

  Furthermore, since the fibers constituting the surface layer 11, the back surface layer 12, and the intermediate layer 13 are bonded to each other through an adhesive film and formed into a non-woven mat, it is easy to handle and used outdoors. Can be suitably used.

  Here, as a fiber which comprises the surface layer 11, the back surface layer 12, and the intermediate | middle layer 13, a polyvinylidene chloride fiber, a nylon fiber, a polyester fiber, an acrylic fiber etc. are mentioned, for example. Of these, polyvinylidene chloride fibers are preferred from the viewpoint of excellent weather resistance. The fibers constituting the surface layer 11, the back layer 12, and the intermediate layer 13 are preferably of the same type. The fibers constituting the surface layer 11, the back layer 12, and the intermediate layer 13 are staples that are curled into a spring shape from the viewpoint of enhancing radio wave absorption performance by making each layer bulky and making radio waves easily incident. A fiber is preferred.

  The fineness A (dtex) of the monofilament of the fibers constituting the surface layer 11 is 3300 to 11000 dtex, and is preferably 4000 dtex or more from the viewpoint of improving the radio wave absorption performance in W-band radio waves and microwaves. Is 4500 dtex or less. The diameter of the monofilament of the fibers constituting the surface layer 11 is, for example, 0.50 to 0.70 mm. The fiber length (cut length) of the monofilament of the fibers constituting the surface layer 11 is preferably 100 mm or more, more preferably 125 mm or more, and preferably 200 mm or less, more preferably 175 mm or less.

  The fineness B (dtex) of the monofilament of the fibers constituting the back surface layer 12 is 17 to 170 dtex, and is preferably 33 dtex or more from the viewpoint of enhancing the radio wave absorption performance in W-band radio waves and microwaves. Is 130 dtex or less. The ratio (A / B) of the fineness A (dtex) of the monofilaments of the fibers constituting the surface layer 11 to the fineness B (dtex) of the monofilaments of the fibers constituting the back surface layer 12 is the radio wave absorption in W-band radio waves and microwaves. From the viewpoint of enhancing the performance, it is preferably 20 or more, more preferably 50 or more, preferably 650 or less, more preferably 70 or less, and still more preferably 60 or less.

  The diameter of the monofilament of the fibers constituting the back layer 12 is, for example, 0.04 to 0.11 mm. The fiber length (cut length) of the monofilament of the fibers constituting the back layer 12 is preferably 30 mm or more, more preferably 50 mm or more, and preferably 150 mm or less, more preferably 100 mm or less. The fiber length (cut length) of the monofilament of the fiber constituting the back surface layer 12 is preferably shorter than the fiber length (cut length) of the monofilament of the fiber constituting the surface layer 11.

  The fineness C (dtex) of the monofilament of the fibers constituting the intermediate layer 13 is 170 to 1200 dtex, and is preferably 370 dtex or more from the viewpoint of enhancing the radio wave absorption performance in the W-band radio wave and microwave. Is 760 dtex or less. The ratio (A / C) of the fineness A (dtex) of the monofilament of the fiber constituting the surface layer 11 to the fineness C (dtex) of the monofilament of the fiber constituting the intermediate layer 13 is the radio wave absorption in W-band radio waves and microwaves. From the viewpoint of enhancing the performance, it is preferably 4 or more, more preferably 6 or more, and preferably 70 or less, more preferably 10 or less. The ratio (C / B) of the fineness C (dtex) of the monofilaments of the fibers constituting the intermediate layer 13 to the fineness B (dtex) of the monofilaments of the fibers constituting the back surface layer 12 is the radio wave absorption in W-band radio waves and microwaves. From the viewpoint of enhancing the performance, it is preferably 5 or more, more preferably 8 or more, and preferably 10 or less, more preferably 9 or less. The ratio (A / C) of the fineness A (dtex) of the monofilament of the fiber constituting the surface layer 11 to the fineness C (dtex) of the monofilament of the fiber constituting the intermediate layer 13 is the radio wave absorption in W-band radio waves and microwaves. From the viewpoint of enhancing the performance, it is preferably smaller than the ratio (C / B) of the fineness C (dtex) of the monofilaments of the fibers constituting the intermediate layer 13 to the fineness B (dtex) of the monofilaments of the fibers constituting the back surface layer 12. .

  The diameter of the monofilament of the fibers constituting the intermediate layer 13 is, for example, 0.10 to 0.30 mm. The fiber length (cut length) of the monofilament of the fibers constituting the intermediate layer 13 is preferably 30 mm or more, more preferably 50 mm or more, and preferably 150 mm or less, more preferably 100 mm or less. The fiber length (cut length) of the monofilament of the fiber constituting the intermediate layer 13 is greater than the fiber length (cut length) of the monofilament of the fiber constituting the back surface layer 12 (the fiber length of the monofilament of the fiber constituting the surface layer 11 ( It is preferable to be close to the cut length. The fiber length (cut length) of the monofilament of the fibers constituting the intermediate layer 13 may be the same as the fiber length (cut length) of the monofilament of the fibers constituting the surface layer 11.

  In the radio wave absorber 10 according to the embodiment, the content of the fiber constituting the surface layer 11 in the entire fiber is preferably 60% by mass or more, more preferably from the viewpoint of improving the radio wave absorption performance in the W-band radio wave and microwave. Is 65% by mass or more, preferably 80% by mass or less, more preferably 75% by mass or less. The content of the fiber constituting the back layer 12 in the entire fiber is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less. . The content of the fibers constituting the intermediate layer 13 in the entire fibers is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less. . The fiber content constituting the back layer 12 in the entire fiber and the fiber content constituting the intermediate layer 13 in the entire fiber may be the same.

  In the radio wave absorber 10 according to the embodiment, since the surface 11a of the surface layer 11 is a non-compressed processed surface having irregularities, the thickness is not uniform, but the maximum thickness at the most protruding portion of the surface layer 11 is, for example, 35. ~ 55 mm. Further, in the radio wave absorber 10 according to the embodiment, since the surface 11a of the surface layer 11 is a non-compressed processed surface having irregularities, the reaction force against compressive deformation is compared with the case where the surface is made flat by compression processing. However, from the viewpoint of improving the radio wave absorption performance in W-band radio waves and microwaves, specifically, the reaction force when a 65 mm square test piece is compressed by 30 mm at a speed of 100 mm / min is 400 N or less. Is preferable, and it is more preferable that it is 300 N or less. In the case of the radio wave absorber 10 whose surface is flattened by compression processing, the reaction force exceeds 500N.

  The adhesive coating is composed of, for example, a solidified rubber latex adhesive. Examples of such rubber latex adhesives include polyvinylidene chloride rubber latex adhesives. The thickness of the adhesive coating is, for example, 5 to 50 μm.

  The conductive film is made of, for example, a solidified conductive paint containing a conductive material. An example of such a conductive paint is one in which carbon is dispersed in an adhesive of polyvinylidene chloride rubber latex. The thickness of the conductive film is, for example, 5 to 50 μm.

  The radio wave absorber 10 according to the embodiment having the above-described configuration preferably has a return loss that is radio wave absorption performance in the frequency range of 75 to 110 GHz of W-band radio waves, preferably 30 dB or more, and has a micro frequency range of 1 to 18 GHz. The return loss in the wave is preferably 20 dB or more. The return loss amount in the W-band radio wave is measured based on “Dielectric lens antenna method—focused beam method” in item 9 in JIS R1679 “Method for measuring radio wave absorption characteristics of radio wave absorber in millimeter wave band”. The return loss in the microwave is measured by causing linearly polarized waves (TE waves) to be perpendicularly incident (incident angle 0 °) on the surface 11a of the surface layer 11 of the radio wave absorber 10 based on the reflected power method. .

  Next, a method for manufacturing the radio wave absorber 10 according to the embodiment will be described.

First, as shown in FIG. 3A, fibers f ₁ for constituting the back layer 12 are randomly scattered on the flat base B. In this case, the fiber layer F of the fiber f ₁ for constituting the back layer 12 is formed on the base B (back surface layer forming step).

Then, as shown in FIG. 3B, on the fiber layer F formed in the back surface layer forming step, spraying a fiber f ₂ for constituting the intermediate layer 13 at random. At this time, the fibers f ₂ for forming the intermediate layer 13 are laminated on the fiber layer F (intermediate layer forming step).

Subsequently, as shown in FIG. 3C, on the fiber layer F laminated on the back layer formation step and the intermediate layer forming step, spraying a fiber f ₃ for constituting the surface layer 11 at random. At this time, the fibers f ₃ for forming the surface layer 11 are laminated on the fiber layer F (surface layer forming step).

  And as shown to FIG. 3D, the adhesive agent A is spray-sprayed and dried on the fiber layer F formed by laminating | stacking at a back surface layer formation step, an intermediate | middle layer formation step, and a surface layer formation step. At this time, the fibers constituting the fiber layer F are bonded through an adhesive film to form a non-woven mat M (adhesion step).

  Finally, as shown in FIG. 3E, the conductive coating P is sprayed and dried on the non-woven mat M formed in the bonding step. At this time, the surface of the fiber which comprises the nonwoven fabric-like mat M is coat | covered with a conductive film (conductivity provision step).

In the manufacturing method of the radio wave absorber 10 according to the embodiment, the radio wave absorber 10 is completed as described above, and the surface 11a of the surface layer 11 is compressed by a hot platen and heat set, or between hot platens having a predetermined gap. without compression process which applies a flat surface of the surface 11a of the surface layer 11 such that heat set through the surface 11a of the surface layer 11, a state left as it is when the sprayed fibers f _3.

  In the above-described embodiment, the three-layer structure of the front surface layer 11, the back surface layer 12, and the intermediate layer 13 is used. However, the present invention is not particularly limited to this, and between the surface layer 11 and the intermediate layer 13, and / or Alternatively, a structure in which a single layer or a plurality of layers made of fibers having different fineness of the adjacent layer and the filament is provided between the intermediate layer 13 and the back surface layer 12 may be used.

(Radio wave absorber)
<Example>
On a flat base, an intermediate layer is formed on a fiber layer formed by randomly dispersing polyvinylidene chloride fibers (fiber length 150 mm) having a monofilament fineness B (dtex) of 78 dtex for constituting a back layer. Polyvinylidene chloride fiber (fiber length 150 mm) having a monofilament fineness C (dtex) of 670 dtex for constituting a surface layer, and polyvinylidene chloride fiber having a monofilament fineness A (dtex) 4440 dtex for constituting a surface layer ( After forming a nonwoven fabric mat by spraying and drying an adhesive of polyvinylidene chloride rubber latex from above the obtained fiber layer by spraying randomly and laminating the fiber length 150 mm) in order. Put the polyvinylidene chloride rubber latex adhesive on the non-woven mat The conductive coating material containing dispersed emissions dried by spraying spraying, the wave absorber was prepared surface of the surface layer without compression process which applies a flat surface and Example.

  In the radio wave absorber of the example, the geometric average of the fineness A (dtex) of the monofilament of the fiber constituting the surface layer and the fineness B (dtex) of the monofilament of the fiber constituting the back surface layer is 588 dtex, and constitutes the intermediate layer. When this is divided by the fineness C (dtex) of the monofilament of the fiber, it becomes 1.14, which is 1.2 or less. Further, the ratio (A / B) of the fineness A (dtex) of the monofilaments of the fibers constituting the surface layer to the fineness B (dtex) of the monofilaments of the fibers constituting the back surface layer is 57, and the monofilaments of the fibers constituting the intermediate layer The ratio (A / C) of the fineness A (dtex) of the monofilament of the fiber constituting the surface layer to the fineness C (dtex) is 6.6, and the intermediate layer relative to the fineness B (dtex) of the monofilament of the fiber constituting the back surface layer The ratio (C / B) of the fineness C (dtex) of the monofilament of the fibers constituting 8.6 is 8.6.

  In the radio wave absorber of the example, the content of the fiber constituting the surface layer in the whole fiber is 70% by mass, the content of the fiber constituting the intermediate layer in the whole fiber is 15% by mass, and the back layer in the whole fiber is constituted. The content of the fibers is 15% by mass.

<Comparative Example 1>
On a flat base, a surface layer is formed on a fiber layer formed by randomly dispersing polyvinylidene chloride fibers (fiber length 150 mm) having a monofilament fineness B (dtex) of 78 dtex on the flat base. Polyvinylidene chloride fibers (fiber length: 150 mm) having a monofilament fineness A (dtex) of 4440 dtex for forming the fiber are randomly scattered and laminated in order, and adhesion of the polyvinylidene chloride rubber latex is obtained from above the obtained fiber layer. After forming a non-woven mat by spraying and spraying the agent, spraying and spraying a conductive paint in which carbon is dispersed in the adhesive of polyvinylidene chloride rubber latex from the non-woven mat. A radio wave absorber produced without compressing the surface layer with a flat surface was used as Comparative Example 1.

  In the radio wave absorber of Comparative Example 1, the content of the fiber constituting the surface layer in the entire fiber is 70% by mass, and the content of the fiber constituting the back layer in the entire fiber is 30% by mass.

<Comparative example 2>
A radio wave absorber manufactured in the same manner as in Example 1 except that compression processing (heat setting) in which the surface of the surface layer was pressed with a flat surface was performed was used as a comparative example.

<Commercial item>
A commercially available radio wave absorber (FP-2 manufactured by Mitsubishi Cable Industries, Ltd., thickness 40 mm) was prepared. This commercially available radio wave absorber is composed of a polyvinylidene chloride fiber (fiber length 150 mm) with a monofilament fineness of 1100 dtex, a surface layer, a polyvinylidene chloride fiber (fiber length 150 mm) with a monofilament fineness of 132 dtex, an intermediate layer, and a monofilament The back layer is composed of polyvinylidene chloride fibers (fiber length: 150 mm) each having a fineness of 78 dtex, the fiber content constituting the surface layer in the entire fiber is 70% by mass, and the fiber constituting the intermediate layer in the entire fiber. The content is 15% by mass, and the content of the fibers constituting the back layer in the entire fiber is 15% by mass, and compression processing (heat setting) is performed in which the surface of the surface layer is pressed with a flat surface.

(Test evaluation method)
<Radio wave absorption performance>
―W Band―
FIG. 4 shows a radio wave absorption performance measuring apparatus 20 for measuring the radio wave absorption performance of W-band radio waves.

  The radio wave absorption characteristic measuring apparatus 20 is composed of a horn antenna 21 with a dielectric lens and a network analyzer 22.

  For each of Examples and Comparative Examples 1 and 2, using the above-described radio wave absorption characteristic measuring apparatus 20, JIS R1679 “Radio wave absorption characteristic measurement method in millimeter wave band of radio wave absorber” in item 9 “Dielectric lens antenna method— The radio wave absorption performance was measured based on the “focused beam method”. Specifically, a test piece S having a square view of 150 mm square is arranged in front of the horn antenna 21, and radio waves are vertically incident on the test piece S from the horn antenna 21 (incident angle 0 °). The reflected wave with respect to the incident wave was received by the horn antenna 21 and the return loss was measured by the network analyzer 22. At this time, the measurement frequency range was set to 75 to 110 GHz in the W band.

  And the case where the reflection attenuation amount in W band was 30 dB or more was evaluated as OK, and the case where it was less than 30 dB was evaluated as NG.

―Microwave―
5A and 5B show a radio wave absorption performance measuring apparatus 30 for measuring the radio wave absorption performance in microwaves.

  The radio wave absorption characteristic measuring apparatus 30 is provided with a measuring table 31 having a horizontal sample mounting surface, a surface of the measuring table 31 as a reference position, and a position 1500 mm away from the center of the measuring table 31 so as to be movable in an arc shape. The transmission / reception antenna 32 and a network analyzer 33 connected to the transmission / reception antenna 32 are configured.

  For each of the Examples, Comparative Examples 1 and 2, and a commercial product, the radio wave absorption performance was measured based on the reflected power method using the radio wave absorption characteristic measuring device 30. Specifically, a square test piece S of 1000 mm × 1000 mm square in plan view is placed on the measurement table 31, and the linearly polarized wave (TE wave) is perpendicular to the test piece S that is 1500 mm away from the transmission / reception antenna 32. The incident light was incident at an incident angle of 0 °, and the reflected wave with respect to the incident wave was received by the transmission / reception antenna 32, and the return loss was measured by the network analyzer 33. At this time, the measurement frequency range was set to 1 to 18 GHz as a part of the microwave.

  And the case where the return loss amount in the microwave of the frequency range 1-18 GHz is 20 dB or more was evaluated as OK, and the case where it was less than 20 dB was evaluated as NG.

<Appearance>
Each of the examples and comparative examples 1 and 2 was visually evaluated for appearance.

  And, when there is no fiber density in the plane of the radio wave absorber, and therefore the variation in the fiber density gradient in the thickness direction is small and uniform, it is evaluated as A, and there is density due to the deviation of the fiber. A case where the variation in the fiber density gradient in the direction was large and non-uniform was evaluated as B.

<Compression characteristics>
For each of the example (thickness 40 mm) and the commercially available product, the reaction force when a 65 mm square test piece was compressed 30 mm at a speed of 100 mm / min was measured.

(Test evaluation results)
Table 1 shows the test evaluation results.

  According to Table 1, in the Example, it turns out that the radio wave absorption performance in the W band radio wave is excellent and the appearance is uniform. Moreover, as shown in FIG. 6, the reflection attenuation amount in the microwave of the frequency range 1 to 18 GHz is 20 dB or more, and the radio wave absorption performance in the microwave of the frequency range 1 to 18 GHz is excellent in addition to the W band radio wave. I understand.

  On the other hand, in Comparative Example 1, it can be seen that although the radio wave absorption performance in the W-band radio wave is excellent, the radio wave absorption performance in the microwave is inferior and the appearance is not uniform. In Comparative Example 2, it can be seen that although the radio wave absorption performance in the microwave is excellent and the appearance is uniform, the radio wave absorption performance in the W band radio wave is inferior. In addition, although it turns out that the electromagnetic wave absorption performance in a microwave is excellent in a commercial item, from the result of the comparative example 2 similarly heat set, it is anticipated that the electromagnetic wave absorption performance in the W band electromagnetic wave is inferior.

  Furthermore, in Example 1, the reaction force when a 65 mm square test piece was compressed by 30 mm at a speed of 100 mm / min was 300 N or less, whereas in the commercial product, it exceeded 500 N. From this, it can be seen that if the surface of the surface layer is a non-compressed surface, the reaction force against compressive deformation is lower than when the surface is made flat by compression.

  The present invention is useful in the technical field of a radio wave absorber and a manufacturing method thereof.

A Adhesive B Base F Fiber layer f _{1 to} f ₃ Fiber M Matt P Conductive paint S Test piece 10 Radio wave absorber 11 Surface layer 11a Surface 12 Back surface layer 13 Intermediate layer 20 Radio wave absorption characteristic measuring device 21 Horn antenna 22 Network analyzer 30 Radio wave absorption characteristic measuring device 31 Measuring table 32 Transmitting / receiving antenna 33 Network analyzer

Claims (5)

Each of which includes a surface layer and a back layer made of fibers and an intermediate layer provided therebetween, and the fibers constituting the surface layer, the back layer and the intermediate layer are bonded via an adhesive coating. A radio wave absorber that is formed on a non-woven mat and the surface of the surface layer is a non-compressed surface,
A radio wave absorber that satisfies the following formula (1) when the fineness of the monofilaments of the fibers constituting the surface layer, the back surface layer, and the intermediate layer is A (dtex), B (dtex), and C (dtex), respectively. .

In the electromagnetic wave absorber according to claim 1,
Furthermore, the electromagnetic wave absorber which satisfy | fills following formula (2).

In the radio wave absorber according to claim 1 or 2,
The ratio (A / C) of the fineness A (dtex) of the monofilament of the fiber constituting the surface layer to the fineness C (dtex) of the monofilament of the fiber constituting the intermediate layer is equal to the monofilament of the fiber constituting the back layer. A radio wave absorber smaller than a ratio (C / B) of a fineness C (dtex) of monofilaments of fibers constituting the intermediate layer to a fineness B (dtex). The radio wave absorber according to any one of claims 1 to 3,
A radio wave absorber having a radio wave absorption performance of 30 dB or more in a frequency range of 75 to 110 GHz obtained as a return loss based on the reflected power method, and a radio wave absorption performance of 20 dB or more in a frequency range of 1 to 18 GHz. In the manufacturing method of the electromagnetic wave absorber according to any one of claims 1 to 4,
A back surface layer forming step of forming a fiber layer by spreading fibers for constituting the back surface layer;
On the fiber layer formed in the back surface layer forming step, an intermediate layer forming step of dispersing and laminating fibers for constituting the intermediate layer;
On the fiber layer formed in the back surface layer forming step and the intermediate layer forming step, a surface layer forming step of spreading and laminating fibers for constituting the surface layer;
An adhesive is sprayed from above the fiber layer formed by laminating in the back surface layer forming step, the intermediate layer forming step, and the surface layer forming step, and the fibers constituting the fiber layer are bonded through an adhesive film. An adhesion step to form a non-woven mat;
Have
A method of manufacturing a radio wave absorber that does not perform compression processing that presses the surface of a surface layer with a flat surface.

Images