JPS6134997A - Method of producing radio wave absorber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a radio wave absorber capable of absorbing microwave band radio waves and suppressing their reflection.

(Prior art and its problems) Traditionally, magnetic plates, resistor plates, etc. have been placed on the reflector for the purpose of suppressing reflected radio waves from radio wave reflectors such as ships, aircraft, vehicles, buildings, or steel towers. A radio wave absorbing material made by dispersing magnetic powder such as ferrite or conductive powder such as carbon black in a resin or resin solution is applied to the surface of a structure by means such as applying or adhering to a specified thickness. Attempts have been made to achieve this goal.

In order to obtain a predetermined radio wave absorption performance, the composition of the radio wave absorbing material and the thickness of the radio wave absorbing material are controlled to a specified value as described in Japanese Patent Application Laid-open No. 1"'55-36987 J and Patent Application "56-109686 J. It is necessary to.

For example, in the two-layer radio wave absorber described in Patent Application No. 56-109686 J, the change in film thickness must be suppressed to within 10 inches.

Figure 1 shows a laminated film thickness of 4.5cm, 8-13GH2 -20
As shown in FIG. 2, the absorption ability in the frequency band of 11.2 to 13σh is reduced by increasing the thickness of the material showing an absorption ability of dB or more by 5 cm.

Similarly, by reducing the thickness of the laminated film by 15 inches, the absorption capacity in the frequency band of 8 to 9.7 GHz is reduced, as shown in FIG.

In particular, paint-like radio wave absorbing materials have the advantage of being able to be applied directly to radio wave reflectors to exhibit radio wave absorption performance, but on the other hand, it is difficult to control the film thickness during on-site construction, and when the coated surface is not horizontal. However, there were problems such as the coating film flowing and changing the film thickness, and the radio wave absorption performance could not be fully demonstrated.

(Objective of the invention) The present invention facilitates the management of film thickness when applying a paint-like radio wave absorbing material, eliminates variations in film thickness due to paint flow, and achieves a specified radio wave absorption performance even during on-site construction. The purpose of the present invention is to provide a method for constructing a radio wave absorber that makes it possible to do this.

(Structure of the Invention) According to the present invention, a planar spacer is used to control the coating film thickness. It is a planar spacer, a fibrous material woven into a lattice shape, or a net-like material having an equivalent shape.

The thickness of the planar spacer is the thickness of the radio wave absorbing material coating film, and the radio wave absorbing coating film is formed by filling the openings with radio wave absorbing properties. In this case, since the thickness of the electromagnetic wave absorbing coating film is equal to the thickness of the planar spacer, the thickness of the stain wave absorbing coating film can be controlled by controlling the thickness of the planar spacer. It is easy to control the thickness of the planar spacer within the allowable range of the radio wave absorbing coating thickness. Of course, it is also possible to stack two or more planar spacers to obtain a predetermined thickness. In this case, if the material constituting the planar spacer has conductivity, it will reflect electromagnetic waves and will not form a radio wave absorbing coating, so a planar spacer made of a non-conductive material must be used.

According to the above method, even when applied to a vertical reflector, the flow of the paint is suppressed by the lattice of planar spacers, and variations in the thickness of the radio wave absorbing coating can be avoided.

(Detailed explanation of the structure) The planar spacer and the construction method using the same will be described in detail.

If the material of the planar spacer is conductive, it will reflect electromagnetic waves, and even if its opening is filled with a radio wave absorbing paint, it will not exhibit radio wave absorbing performance. Therefore, the material of the planar spacer is required to have poor conductivity. Commercially available spacer materials include synthetic resin laths, nets, knits, and glass fiber telop strand mats.
There are filament mats, roving cloths, glass cloths, etc., which are easily available and easy to use from an economical point of view. As for the glass fibers, any weaving methods such as plain weave, twill weave, satin weave, imitation weave, and leno weave can be used. Furthermore, the surfaces of these spacers may be subjected to surface treatment for the purpose of improving compatibility with the electromagnetic wave absorbing paint.

The aperture ratio of the spacer (the volume ratio of the area occupied by the spacer material to the area not occupied) will absorb radio waves as long as the spacer is made using the same material as the radio wave absorbing coating. Since it has no properties, it is desirable that it be as large as possible. Generally, 5 to 99.5% can be used, preferably 80 to 99%. In addition, the lattice shape of the spacer is efficiently used as a film thickness standard, so for example, in the case of a square spacer, it is 0.5 cm
5Crn or 5α×5 (about m is desirable. Q, 5
When cInX Q is 5cWL or less, the spacer lattice must be made extremely thin in order to increase the porosity, and there is a drawback that sufficient strength as a film thickness standard cannot be obtained. On the other hand, if it is 5cIrL×5α or more, the efficiency of use as a film thickness standard decreases, making it impossible to obtain uniform film thickness accuracy. Furthermore, if the porosity of the spacer is 5 or less, most of the surface of the object to be coated will be covered with the spacer, which is undesirable from the viewpoint of radio wave absorption ability.

(Example) Next, we will discuss the construction method in detail.

When adhering the spacer to the surface of the object to be coated, since the radio wave absorbing paint used in the present invention itself has adhesive properties, the paint is applied thinly to the surface of the object to be coated by brushing, etc., and then the spacer is attached on top of that. 11 is a preferred means of the present invention.

Of course, conventionally known adhesives can also be used,
It is also possible to bond the spacer by placing it on the surface of the object to be coated and directly applying roller coating thereon without using an adhesive.

Although the spacer used during painting may be removed, it is usually preferable to leave it as is in the coating film to improve the strength of the coating film itself, such as in the case of glass fiber reinforced plastics.

Further, as a coating method for the paint used in the present invention, both roller coating and spray coating are possible.

Several embodiments of two-layer radio wave absorbers will be shown below, but the present invention can of course be applied to, for example, single-layer radio wave absorbers.

The basic formulation and comparative formulation of the coating for the absorption layer are according to Tables 1 and 2, base materials A1 and A4, curing agents A2, A3,
A5 and A6 were created. That is, after mixing the resin, by-product ferrite, or nickel powder, the mixture was dispersed in a three-roll mill to obtain the absorbent layer coating material A1 or A4. Next, the hardening agent resin and the crushed copper powder were mixed and kneaded using a niegu to obtain a hardening agent A2 for an absorbent layer. Absorbent layer curing agents A3 and 86 were obtained in the same manner. Next, the basic composition of the paint for the modified layer is mixed according to the composition shown in Table 3 and Table 4.
By-product ferrite was dispersed using this roll mill to obtain base materials M1 and M3 of paints for modified layers.

(Hereafter, the remainder μ) ゛・ ゝ′−−1 Table 1. Basic composition of paint for absorbing layer (Examples 1 and 2) Table Z Comparison of comparative paint for absorbing layer (Comparative Examples 1 and 2) 1 By-product ferrite: Average particles obtained from wastewater treatment by the Wright method Diameter 0.25Jll11 7a
jite powder.

*2 Pulverized copper powder: Flaky powder with an average particle size of 80ml/5h obtained by grinding with an electric steel tube stamp mill.

Hata 3 11tJN lead powder: A teardrop-shaped powder with an average particle size of 100m5sb obtained by spraying electrolytic zinc in an inert gas.

*4 Nickel powder; Higenji? A flaky powder with an average particle size of 325B@@h obtained by crushing tar with a stamp mill.

*5' Brass fiber 2 Quality 3 Cuttings of brass with a diameter of about 60 μm.

Table 3 Basic formulation of paint for modified layer (Example 1) Table 4. Basic formulation of paint for modified layer (Example 2) *1 By-product 7-ite
: centre! 78 tweet powder with an average particle size of Oj5IIIm that can be obtained by wastewater treatment using the F, T method.

Example 1 1443 parts by weight of coating material A for absorbing layer and 299 parts by weight of curing agent A
The weight parts were mixed and brushed onto a 400x400x32++w sandblasted copper plate, and Nitto Keisha's Chisetsubu Strand Mat MC900G was pressed down with a sponge roller to obtain an absorption layer coating with a specified thickness of 1.1 m.

After leaving it for another 24 hours, hardening agent M! 50 full view area and brushed on top of absorption layer coating, Nitto Keisha product glass cloth WS3
Three sheets of 50D were layered, pressed down with a sponge roller, and left to dry and harden at room temperature for 2 days to obtain a composite coating for radio wave absorbers. FIG. 4 shows the results of evaluating the electromagnetic wave absorption ability of the prepared coated steel plate in the range of 8 to 13 GHz.

Example 2゜Paint base material for absorption layer A 1443 parts by weight and curing agent A4
Mix 379 parts by weight, 400X 400x 3.2 parts
Paint with a brush on a degreased polished aluminum plate, and apply while impregnating it with Nitto Keisha's glass fiber roving cloth WR860B e plastic pressing roller.1.
An absorbent layer coating having a specified thickness of 1.5 mm was obtained.

After leaving it for another 24 hours, paint base material for modified layer Ms227.
Mixing 9.4 parts by weight of hardening agent Ma with 6 parts by weight,
The absorbent layer coating was applied with a brush, three sheets of glass cloth WS350D manufactured by Nitto Keisha were layered, and the coating was applied while impregnated with a plastic pressure roller to obtain a modified layer coating with a specified thickness of 3.51111. .

Further, the mixture was left at room temperature for two days to dry and harden to obtain a composite coating film for radio wave absorbing material. Figure 5 shows the results of measuring the radio wave absorption ability of the painted aluminum plate prepared.

Comparative Example 1 Mix 4,593 parts by weight of paint base material A for the absorption layer and 450 parts by weight of curing agent A, apply the mixture with a brush on a 400 x 400 x 3.2 m sandblasted copper plate, and apply glass fiber roving cloth WR860B manufactured by Nitto Seisha with a plastic press. Paint while impregnating with a roller, 1.111
Absorbent layer coatings with a thickness of 11 were prepared. Furthermore, after standing for 24 hours, based on 197 parts by weight of the modified layer coating base Mt,
Mix 250 parts by weight of hardening agent M, apply it with a brush on the absorption layer coating, and apply 3 parts of Nitto Keisha's glass cloth WS350D.
The layers were stacked one on top of the other, pressed down with a punch roller, and left to stand at room temperature for two days to dry and harden to obtain a composite coating for radio wave absorbers. Figure 6 shows the results of measuring the radio wave absorption ability of the prepared painted steel plate.

Comparative Example 2 Absorbent layer paint base Ar443 heavy background part and hardening agent A6150
The weight parts were mixed and brushed onto a 400 x 400 x 3.2 + m 2 sandblasted steel plate, and Nitto Keisha's Chop Strand Mat MC900G was pressed down with a sponge roller to obtain an absorbent layer coating with a thickness of 7, -1,11111. Furthermore, after leaving it for 24 hours, the paint base material for modified layer M1
Mixing 250 parts by weight of curing agent M with 197 parts by weight,
Brush paint on top of the absorption layer coating, layer 3 sheets of Nitto Keisha product glass cloth W8850D, apply pressure with a sponge roller, and leave at room temperature for 2 days to dry and harden to form a composite coating for radio wave absorbers. Obtained. Figure 3 shows the results of measuring the radio wave absorption ability of the prepared painted steel plate.

(Effects of the Invention) As is clear from FIGS. 3, 4, 5, and 6 showing the radio wave absorption characteristics of each of the above examples, in FIG. 3, the electric field component of the electromagnetic wave incident on the sample surface It has been shown that there is a difference in radio wave absorption ability when the sample is located in two different directions within the sample plane.

Such a difference proves that the method shown in FIG. 4, which is an embodiment of the present invention, is effective as a method with high precision in applied film thickness. Furthermore, in FIG. 6, which is a comparative example in which the method of the present invention was applied to mesh 11 and metal powder of 100 mesh or less was used, 7 Q w
Despite containing t% or more, the specified high frequency inductivity cannot be obtained, and the absorption performance and absorption frequency range are poor.

[Brief explanation of the drawing]

Figure 1 shows the radio wave absorption characteristics when the layer thickness is 45%, Figure 2 shows the radio wave absorption characteristics when the laminated film thickness changes by ±15%, and Figure 3 shows the electric field vector of the incident radio wave. Comparative Example 2) shows the radio wave absorption characteristics in two different directions within the sample plane, and FIG. 4 shows Example 1. FIG. 5 shows the radio wave absorption characteristics of Example 2 and FIG. 6 shows the radio wave absorption characteristics of Comparative Example 1. ＼-J,〉Noah 1-1 Figure 71-2 Figure FREQUENCY [MH2] E 3 Figure 4 FREQUENCY [:MH2] 71-5 Figure FREQUENCY [MH2] E 6 Figure FREQUENCY [MH2] Procedural amendment (method) 29 Name of the invention Construction method of radio wave absorber 3 Relationship with the amended case Applicant 5-33-1 Shiba, Minato-ku, Tokyo (423) Representative of NEC Corporation Tadahiro Sekimoto (lFl brother) 4. Agent: Sumitomo Sanda Building 5, 37-8 Shiba 5-chome, Minato-ku, Tokyo 108
, Date of amendment order July 30, 1985 (shipment date) 6. Column 7 for detailed explanation of the invention in the specification subject to amendment, Contents of amendment (1) Pages 9 onwards of the specification are attached. I'll replace it with something else. (No changes to the content other than those stated in the subject of amendment) Representative Patent Attorney Uchihara, Kyu +:, J', "'"j・,Mi' Table 1. Basic formulation of coating for absorption layer (Examples 1 and 2)
) Table 2. Formulation of comparative paint for absorption layer (Comparative Examples 1 and 2)
．． ) *1 By-product ferrite powder: Ferrite powder with an average particle size of 0.25 pm obtained by wastewater treatment using the ferrite method. *2 Pulverized copper powder: Flaky powder with an average particle size of 80 mesh obtained by grinding electrolytic copper with a stamp mill. *3 Sprayed zinc powder: A teardrop-shaped powder with an average particle size of 100 mesh obtained by spraying electrolytic zinc in an inert gas. *4 Nickel powder: Flaky powder with an average particle size of 325 mesh obtained by grinding reduced nickel with a stamp mill. *5 Brass fiber: serious chips with a length of 3 mm and a diameter of about 60 pm. Table 3. Basic formulation of paint for modified layer (Example 1) Table 4. Basic formulation of paint for modified layer (Example 2) Agent *1 By-product ferrite: Ferrite powder with an average particle size of 0.25 pm obtained by wastewater treatment by the ferrite method. Example 1 A mixture of 443 parts by weight of paint base material for absorbing layer A1 and 299 parts by weight of curing agent A was applied with a brush onto a 400 x 400 x 3.2 mm sandblasted copper plate, and Nitto Keisha's Chop Strand Mat MO900G was pressed down with a sponge roller. It was coated to obtain an absorbent layer coating with a specified thickness of 1.1 mm. After leaving it for another 24 hours, paint base material M1 for modified layer
Mix 197 parts by weight with 250 parts by weight of hardening agent M, apply it with a brush on top of the absorbent layer coating, layer 3 sheets of Nitto Keisha product glass cloth WS350D, apply pressure with a sponge roller, and leave at room temperature for 2 days. The mixture was dried and cured to obtain a composite coating film for radio wave absorbing material. FIG. 4 shows the results of evaluating the electromagnetic wave absorption ability of the prepared coated steel plate in the range of 8 to 13 GHz. Example 2: Absorbing layer paint base A1443 and curing agent Aa 379 parts by weight were mixed and applied with a brush onto a 400 x 400 x 3.2 mm degreased and polished aluminum plate, while impregnated with glass fiber roving cloth WR860B manufactured by Nitto Keisha with a plastic pressing roller. It was coated to obtain an absorbent layer coating with a specified thickness of 1.1 mm. After leaving for another 24 hours, hardening agent M49°4 was added to 227.6 parts by weight of paint base material Ma for modified layer.
Mix parts by weight and apply with a brush on the absorbent layer coating film,
3 layers of Nitto Keisha product glass cloth WS350D,
Paint while impregnating with a plastic pressure roller,
A modified layer coating with a specified thickness of 3.5 mm was obtained. 2 more
The mixture was left at room temperature for several days to dry and harden to obtain a composite coating film for radio wave absorbers. Figure 5 shows the results of measuring the radio wave absorption ability of the painted aluminum plate prepared. Comparative Example 1 A mixture of 4593 parts by weight of the paint base material for the absorption layer A4 and 450 parts by weight of the curing agent A was applied with a brush onto a 400 x 400 x 3.2 mm sandblasted copper plate, while impregnated with Nitto Keisha's glass fiber roving cloth WR860B using a plastic pressing roller. It was coated to create an absorption layer coating film with a thickness of 1.1 mm. Furthermore, after standing for 24 hours, hardening agent M2 was added to 197 parts by weight of the modified layer coating base material Mz.
Mix 50 parts by weight and apply with a brush on the absorption layer coating,
3 layers of Nitto Keisha product glass cloth WS350D,
It was applied with a sponge roller and left at room temperature for 2 days to dry and harden, thereby obtaining a composite coating film for absorbing radio waves. Figure 6 shows the results of measuring the radio wave absorption ability of the prepared painted steel plate. Comparative Example 2 Absorbent layer coating base material A1443 parts by weight and curing agent A6150
The weight parts were mixed and brushed onto a 400 x 400 x 3.2 mm sandblasted copper plate, and Nitto Keisha's Chopped Strand Mat M0900G was pressed down with a sponge roller to obtain an absorption layer coating film with a thickness of 1.1 mm. Furthermore, after standing for 24 hours, 250 parts by weight of hardening agent M was mixed with 1197 parts by weight of the paint base material for the modified layer M, and the mixture was applied with a brush onto the absorption layer coating.
Layer 3 sheets of 0D and apply with a sponge roller, 2
The mixture was left at room temperature for several days to dry and harden, thereby obtaining a composite coating film for absorbing radio waves. Figure 3 shows the results of measuring the radio wave absorption ability of the prepared painted steel plate. (Effects of the Invention) As is clear from FIGS. 3, 4, 5, and 6 showing the radio wave absorption characteristics of each of the above-mentioned Examples, in FIG. It has been shown that there is a difference in radio wave absorption ability when the sample is located in two different directions within the sample plane. Such a difference is not seen in the cases of FIGS. 4 and 5, which are examples of the present invention. This method has been proven to be effective as a method with good film thickness accuracy. Furthermore, in Figure 6, which is a comparative example using the method of the present invention and using metal powder of 100 mesh or less, the specified high frequency permittivity could not be obtained even though the metal powder was mixed at 70 wt% or more. Performance and absorption frequency range are poor. Brief description of the drawing

Claims (1)

[Claims] In the process of applying radio wave absorbing paint to a radio wave reflector, after adhering a planar spacer formed in a grid shape from a non-conductive material to the surface to be coated, at least the openings of the planar spacer are filled with radio wave absorbing paint. A method for constructing a radio wave absorber characterized by: