JP6438687B2 - 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

  In recent years, an automobile in which an in-vehicle radar for detecting a front obstacle and following a front vehicle is provided on a front bumper has been put into practical use. The number of vehicles equipped with such on-vehicle radars is expected to increase in the future from the viewpoint of safety and convenience.

  By the way, evaluation of in-vehicle radars requires high-precision tests. When actually running a car equipped with in-vehicle radars, it is superior in surrounding structures to prevent irregular reflection of radio waves from in-vehicle radars. It is necessary to install a radio wave absorber that exhibits radio wave absorption performance.

  Usually, in-vehicle radars often use millimeter waves, particularly W-band (75 to 110 GHz) radio waves, and examples of radio wave absorbers that exhibit excellent radio wave absorption performance for such W-band radio waves include anechoic chambers. The pyramid type electromagnetic wave absorber used for the above is mentioned. However, since pyramid-type wave absorbers are used indoors in the first place, they are difficult to use outdoors, and they need to be installed outdoors every time they are tested, so there is no chipping or cracking. It is necessary to pay attention to handling. In addition, although the radio wave absorbers disclosed in Patent Documents 1 and 2 are suitable for outdoor use, it cannot be said that the radio wave absorption performance is sufficient for W-band radio waves.

  The present invention is to provide a radio wave absorber that is suitable for outdoor use and that exhibits excellent radio wave absorption performance with respect to radio waves in the W band.

The present invention includes a surface layer composed of fibers having a monofilament fineness of 3300 to 11000 dtex and a back surface layer composed of fibers having a monofilament fineness of 17 to 170 dtex. An electromagnetic wave absorber in which the constituent fibers are bonded to each other through an adhesive coating to form a nonwoven mat , and the surface of the fibers constituting the nonwoven mat is covered with a conductive coating, The surface is an uncompressed surface.

The present invention, on the back layer forming step of forming a fiber layer by spraying fibers having a monofilament fineness of 17 to 170 dtex for constituting the back layer, on the fiber layer formed in the back layer forming step, A surface layer forming step of spreading and laminating fibers having a monofilament fineness of 3300 to 11000 dtex for constituting the surface layer; and a fiber layer formed by laminating in the back layer forming step and the surface layer forming step. An adhesive step is applied to form a nonwoven fabric mat by bonding the fibers constituting the fiber layer through an adhesive coating, and a conductive paint is sprayed from the nonwoven fabric mat formed in the adhesion step. by spraying to dry, and a conductivity-imparting step of coating the surface of the fibers constituting the nonwoven mat with a conductive coating A method for producing a radio wave absorber, a is not conducted compression process which applies the surface of the surface layer at the flat surface.

  According to the present invention, since the fibers constituting the front surface layer and the back surface layer are bonded to each other through an adhesive coating and formed into a non-woven mat, it is easy to handle and suitable for outdoor use. Can be used. Further, since the surface of the surface layer composed of fibers having a monofilament fineness of 3300 to 11000 dtex is an uncompressed surface, the surface layer has a sparse fiber density and a surface having irregularities with raised fibers. Therefore, an incident wave in the W band having a short wavelength easily enters the inside of the radio wave absorber, and the incident wave that enters the inside of the radio wave absorber is repeatedly reflected and attenuated. Radio wave absorption performance can be obtained.

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. (A)-(e) is 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 a radio wave absorption performance measuring apparatus.

  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. It is.

  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, monofilaments are point-contacted or line-bonded in each layer of the front surface layer 11, the back surface layer 12, and the intermediate layer 13, and bonded and integrated by an adhesive film. 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 monofilament of the fiber constituting the surface layer 11 is 3300 to 11000 dtex, and the fineness of the monofilament of the fiber constituting the back surface layer 12 is 17 to 170 dtex. The fineness of the monofilament of the fiber constituting the intermediate layer 13 is intermediate between the fineness of the monofilament of the fiber constituting the front surface layer 11 and the fineness of the monofilament of the fiber constituting the back surface layer 12. 13 and the surface density of the surface layer 11 are decreasing in order. In the radio wave absorber 10 according to the embodiment, the surface 11a of the surface layer 11 is an uncompressed surface. 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.

  According to the radio wave absorber 10 according to such an embodiment, the fibers constituting the front 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. Since it is a structure, it is easy to handle and can be suitably used for outdoor use.

  Moreover, since the surface 11a of the surface layer 11 composed of fibers having a monofilament fineness of 3300 to 11000 dtex is an uncompressed surface, the fiber density of the surface layer 11 is sparse, and the fibers are raised and uneven. Since the incident wave in the W band (75 to 110 GHz) having a short wavelength easily enters the inside of the radio wave absorber 10, and the incident wave that enters the radio wave absorber 10 is repeatedly reflected and attenuated. In particular, it is possible to obtain excellent radio wave absorption performance with respect to radio waves in the W band.

  Furthermore, although the difference of the thickness of the fiber which comprises the surface layer 11 and the back surface layer 12 is large, it was comprised by the fiber of the middle thickness of the fiber which comprises them between the surface layer 11 and the back surface layer 12. By providing the intermediate layer 13, the fiber density gradient in the thickness direction in the plane can be made uniform.

  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 of the monofilament of the fibers constituting the surface layer 11 is preferably 4000 dtex or more, and preferably 4500 dtex or less, from the viewpoint of improving the radio wave absorption performance for W-band radio waves. 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 of the monofilament of the fibers constituting the back layer 12 is preferably 33 dtex or more, and preferably 130 dtex or less. The fineness of the monofilament of the fiber constituting the back surface layer 12 is preferably 20 times or more, more preferably from the viewpoint of improving the radio wave absorption performance for the W-band radio wave. It is 50 times or more, preferably 650 times or less, more preferably 70 times or less, and further preferably 60 times 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 of the monofilament of the fibers constituting the intermediate layer 13 is preferably 170 dtex or more, and preferably 1200 dtex or less. The fineness of the monofilaments of the fibers constituting the surface layer 11 is preferably 4 times or more, more preferably 6 times or more, and preferably 70 times or less of the fineness of the monofilaments of the fibers constituting the intermediate layer 13. More preferably, it is 10 times or less. The fineness of the monofilament of the fibers constituting the intermediate layer 13 is preferably 5 times or more, more preferably 8 times or more, and preferably 10 times or less of the fineness of the monofilaments of the fibers constituting the back layer 12. More preferably, it is 9 times or less. The fineness of the monofilament of the fiber constituting the intermediate layer 13 is preferably closer to the fineness of the monofilament of the fiber constituting the surface layer 11 than the fineness of the monofilament of the fiber 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 (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 fibers constituting the surface layer 11 in the entire fiber is preferably 60% by mass or more, more preferably 65% by mass, from the viewpoint of improving the radio wave absorption performance for W band radio waves. % 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 for W-band radio waves, specifically, the reaction force when a 65 mm square test piece is compressed by 30 mm at a speed of 100 mm / min is preferably 400 N or less, More preferably, 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 configuration preferably has a return loss amount in the W band of 30 dB or more.

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

First, as shown in FIG. 3 (a), on a flat base B, the fineness of the monofilament for forming the back layer 12 is sprayed randomly fibers _{f 1} is 17～170Dtex. 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).

Next, as shown in FIG. 3B, the fineness of the monofilament for constituting the intermediate layer 13 on the fiber layer F formed in the back surface layer forming step is the same as that of the monofilament of the fiber constituting the surface layer 11. fiber f ₂ which is an intermediate of the fineness of the monofilament of the fibers constituting the fineness and the back layer 12 is sprayed randomly. 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. 3 (c), a fiber having a fineness of monofilament for forming the surface layer 11 on the fiber layer F laminated in the back surface layer forming step and the intermediate layer forming step is 3300 to 11000 dtex. the f ₃ is sprayed 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 in FIG.3 (d), 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. 3 (e), the conductive paint P is sprayed and sprayed on the non-woven mat M formed in the bonding step and dried. 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 the two-layer structure of the front surface layer 11 and the back surface layer 12 is used. In addition, between the surface layer 11 and the intermediate layer 13 and / or between the intermediate layer 13 and the back surface layer 12, a single layer or a plurality of layers composed of fibers having different fineness of the adjacent layer and the filament. The structure in which the layer was provided may be sufficient.

(Radio wave absorber)
<Example 1>
To form an intermediate layer on a fiber layer formed by randomly dispersing polyvinylidene chloride fibers (fiber length: 150 mm) having a monofilament fineness of 78 dtex on a flat base to form a back layer. Polyvinylidene chloride fiber (fiber length 150 mm) having a monofilament fineness of 670 dtex and a polyvinylidene chloride fiber (fiber length 150 mm) having a monofilament fineness of 4440 dtex for forming the surface layer are randomly scattered and laminated in order. After forming a non-woven mat by spraying and drying an adhesive of polyvinylidene chloride rubber latex on the obtained fiber layer, the polyvinylidene chloride rubber latex is further applied on the non-woven mat. Spray conductive paint with carbon dispersed in adhesive Is 燥, the wave absorber was prepared surface of the surface layer without compression process which applies a flat surface and the first embodiment.

  In the radio wave absorber of Example 1, the fineness of the monofilament of the fiber constituting the surface layer is 57 times the fineness of the monofilament of the fiber constituting the back surface layer, and the fineness of the monofilament of the fiber constituting the intermediate layer The fineness of the monofilament of the fiber constituting the surface layer is 6.6 times, and the fineness of the monofilament of the fiber constituting the back layer is 8.6 times the fineness of the monofilament of the fiber constituting the back surface layer.

  The radio wave absorber of Example 1 has a fiber content of 70% by mass constituting the surface layer in the entire fiber, a fiber content of 15% by mass constituting the intermediate layer in the entire fiber, and a back layer in the entire fiber. The content of the constituent fibers is 15% by mass.

<Example 2>
To form a surface layer on a fiber layer formed by randomly dispersing polyvinylidene chloride fibers (fiber length: 150 mm) having a monofilament fineness of 78 dtex for forming a back layer on a flat base. Polyvinylidene chloride fibers (fiber length 150 mm) having a monofilament fineness of 4440 dtex are randomly scattered in order and laminated, and an adhesive of polyvinylidene chloride rubber latex is sprayed and sprayed on the obtained fiber layer and dried. After forming a non-woven mat, the surface of the surface layer is flattened by spraying and spraying a conductive paint in which carbon is dispersed in an adhesive of polyvinylidene chloride rubber latex on the non-woven mat. A radio wave absorber manufactured without performing compression processing by pressing on the surface was taken as Example 2.

  In the radio wave absorber of Example 2, the fineness of the monofilament of the fibers constituting the surface layer is 57 times the fineness of the monofilament of the fibers constituting the back surface layer.

  In the radio wave absorber of Example 2, 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>
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.

(Test evaluation method)
<Radio wave absorption performance>
FIG. 4 shows the radio wave absorption performance measuring apparatus 20.

  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 1 and 2 and the comparative example, the above-described radio wave absorption characteristic measuring apparatus 20 was used, and “dielectric lens antenna method−” of item 9 in JIS R1679 “Radio wave absorption characteristic measurement method in millimeter wave band” The radio wave absorption performance was measured according to the “focused beam method”. Specifically, a square test piece S of 150 mm square is arranged in front of the horn antenna 21, and a radio wave is emitted from the horn antenna 21 to the test piece S at an incident angle of 0 ° (perpendicular incidence). 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 W band (75 to 110 GHz).

  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.

<Appearance>
Each of Examples 1 and 2 and the comparative example 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 Example 1 (thickness 40 mm) and commercially available radio wave absorber (FP-2, thickness 40 mm, manufactured by Mitsubishi Cable Industries, Ltd.), a 65 mm square test piece was compressed by 30 mm at a speed of 100 mm / min. The force was measured.

  The above-mentioned commercially available radio wave absorber has a surface layer of polyvinylidene chloride fiber (fiber length 150 mm) having a monofilament fineness of 1100 dtex, and an intermediate layer of polyvinylidene chloride fiber (fiber length 150 mm) having a monofilament fineness of 132 dtex. , And a polyvinylidene chloride fiber (fiber length: 150 mm) each having a monofilament fineness of 78 dtex, each comprising a back layer, the content of the fiber constituting the surface layer of the entire fiber being 70% by mass, and forming an intermediate layer in the entire fiber The fiber content is 15% by mass, and the fiber content of the back surface layer in the entire fiber is 15% by mass, and the surface layer is pressed by a flat surface (heat set). .

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

  According to Table 1, in Example 1, the radio wave absorption performance for W-band radio waves is excellent and the appearance is uniform. In Example 2, although the radio wave absorption performance for W-band radio waves is excellent, the external appearance is Is non-uniform. On the other hand, in the comparative example, although the appearance is uniform, the radio wave absorption performance with respect to the W-band radio wave is not sufficient. As a result, by obtaining a non-compressed processed surface that does not perform compression processing that compresses the surface layer with a flat surface, it is possible to obtain excellent radio wave absorption performance such that the return loss in the W band is 30 dB or more. You can see that In addition, a uniform appearance can be obtained by providing the intermediate layer, but it is understood that this does not particularly affect the radio wave absorption performance.

  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 a commercially available wave absorber, 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 for a radio wave absorber and a method for manufacturing the same.

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

Claims (5)

A fiber comprising a surface layer composed of fibers having a monofilament fineness of 3300 to 11000 dtex and a back layer composed of fibers having a monofilament fineness of 17 to 170 dtex, and constituting the surface layer and the back surface layer; A radio wave absorber that is bonded to an adhesive coating to form a nonwoven mat and the surface of the fibers constituting the nonwoven mat is covered with a conductive coating, and the surface of the surface layer is uncompressed. An electromagnetic wave absorber that is a processed surface. In the electromagnetic wave absorber according to claim 1,
The electromagnetic wave absorber whose fineness of the monofilament of the fiber which comprises the said surface layer is 20-650 times with respect to the fineness of the monofilament of the fiber which comprises the said back surface layer. In the radio wave absorber according to claim 1 or 2,
Between the surface layer and the back layer, the fineness of the monofilament is composed of fibers that are intermediate between the fineness of the monofilament of the fibers constituting the surface layer and the monofilament of the fibers constituting the back layer. further look-containing intermediate layer, the wave absorber surface of the fibers constituting the intermediate layer is also coated with a conductive coating. In the radio wave absorber according to claim 3,
The radio wave absorber in which the fineness of the monofilament of the fiber constituting the intermediate layer is closer to the fineness of the monofilament of the fiber constituting the surface layer than the fineness of the monofilament of the fiber constituting the back layer. A back layer forming step of forming a fiber layer by dispersing fibers having a monofilament fineness of 17 to 170 dtex for constituting the back layer;
On the fiber layer formed in the back surface layer forming step, a surface layer forming step of spreading and laminating fibers having a monofilament fineness of 3300 to 11000 dtex for constituting the surface layer;
An adhesive is sprayed on the fiber layer formed by laminating in the back surface layer forming step and the front surface layer forming step, and the fibers constituting the fiber layer are bonded through an adhesive film to form a non-woven mat. Bonding step,
Conductivity imparting step of coating the surface of fibers constituting the nonwoven fabric-like mat with a conductive coating by spraying and drying a conductive paint on the nonwoven fabric-like mat formed in the bonding step;
A method of manufacturing a radio wave absorber having
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.

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