JPH0750837B2 - Method for forming radio wave absorber film and radio wave absorber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a method for forming a thin film type electromagnetic wave absorber film used for preventing reflection of radio waves, and particularly for preventing reflection in a high frequency region of 9 to 10 GHz, and its use. The present invention relates to a radio wave absorber composition.

(Prior Art) A radio wave absorber is provided on the surface of a structure such as a bridge over the surface of the sea, a surface of a lake, or a river, so that a ship radar (mainly a radio wave of 9.4 GHz is used. ) Against the radio wave reflection from this structure is used to prevent navigational obstacles such as phantom radar.

Conventionally, as such a high-frequency wave absorber, for example, there is one using ferrite and carbon black as seen in JP-A-55-36987, but this wave absorber can be a thin film, but still It requires a thickness of about 2.5 mm, and there is a demand for a thin film type that is even smaller in terms of weight per unit area that affects the dead load of structures such as bridges.

Further, as seen in JP-A-62-109866 and JP-A-62-111499, there are some which use a graphite as a radio wave absorber, but these can be formed as a thin film. Grain size used is 100-600
Electromagnetic wave absorption that can be used for prevention of reflection interference by structures such as bridges (20 dB or more is required) because it is made of mesh (particles with an opening diameter smaller than 149 μm) and the electromagnetic reflection loss rate is as low as 7 dB. It cannot be a body.

(Problems to be Solved by the Invention) In the present invention, the problem of the above-described prior art is to reduce the thickness of the electromagnetic wave absorber film (0.9 to 1.1 mm), and especially for the thin film.
The object of the present invention is to provide a method for forming a radio wave absorber film capable of highly absorbing radio waves having a frequency of up to 10 GHz and a radio wave absorber composition used for the method.

(Means for Solving the Problems) As a result of intensive studies on thinning of the electromagnetic wave absorber film, the present inventors have found that the fixed carbon content is large, the graph has a specific large particle size and a specific aspect ratio. It has been found that the desired electromagnetic wave absorption performance can be obtained even in a thin film by utilizing the electromagnetic wave absorption performance due to the action of high conductivity of the iron, and the present invention has been completed based on this finding.

Thus, according to the present invention, in the method of forming a thin film type electromagnetic wave absorber film on the structure surface using the electromagnetic wave absorber composition, the electromagnetic wave absorber composition has a fixed carbon content of 80% or more and a particle size of 200%. Characterized by using a radio wave absorber composition containing, as an essential component, scaly graphite having a ratio (aspect ratio) L / D of the average major axis L of particles to the average thickness D of up to 800 μm. A method for forming a thin film type wave absorber coating is provided.

Further, according to the present invention, as a novel material suitably used in the above method, 5 to 60 parts by weight of scaly graphite, synthetic resin 95 to 40 parts by weight, the scaly graphite has a fixed carbon content. 80% or more, particle size 200 to 800 μm, and ratio of average major axis L of particle size to average thickness D (aspect ratio)
Provided is a thin-film type electromagnetic wave absorber composition having an L / D of 50 or more.

The graphite used in the present invention is selected from those having a high fixed carbon content and scale-like among graphites such as natural products or artificial products, and the particle size is appropriate to have good conductivity and adapt to the wavelength of radio waves. It is preferable that it has a large aspect ratio and a large aspect ratio. That is, a fixed carbon content of 80% or more, preferably 85% or more is used. Further, the particle size is 200 μm or more and 800 μm or less, more preferably 300 μm.
Those having a thickness of at least m and not more than 500 μm are used. The scale-like graphite pieces should have a thickness of 0.1 to 10 μm.
It is more preferably 0.5 to 1 μm. Therefore, the scale-like graphite has an aspect ratio of 50.
The above is preferable, and 200 to 800 are preferably used.

However, if the fixed carbon content of the graphite is less than 80%, or if the particle size of the graphite is less than 200 μm or more than 800 μm, the electromagnetic wave absorption performance in the thin film becomes low. Also, if the aspect ratio is less than 50, it is also inconvenient because the radio wave absorption performance cannot be obtained.

The synthetic resin used as the dispersion medium for the graphite in the present invention may be either an organic polymer or a polymerizable monomer. Examples of synthetic resins include thermosetting resins such as phenol resin, urea resin, epoxy resin, unsaturated polyester resin, silicone resin and polyurethane resin, and thermoplastic resins such as polyethylene, polypropylene, nylon, vinyl chloride and thermoplastic polyester. And acrylic acid esters, methacrylic acid esters, polymerizable monomers such as styrene and butadiene, or low polymers, and the like, and specifically selected from the above depending on the intended use of the radio wave absorber. However, considering the dispersion method, the method of implementation, etc., a resin that is liquid at room temperature and capable of polymerization or curing is preferable.

Among the above-mentioned synthetic resins, a resin composed of a combination of a liquid bisphenol type epoxy resin and a liquid polyamide curing agent is particularly preferable because excellent rust prevention performance is imparted.

The compounding ratio of the scale-like graphite and the synthetic resin in the radio wave absorber composition of the present invention is such that the former is 5 to 60 parts by weight (preferably
The latter is 95-40 parts by weight (preferably 20-50 parts by weight)
80 to 50 parts by weight) so that the total amount of both is 100 parts by weight. If the content of graphite is less than the above range, the desired radio wave absorption performance cannot be obtained, while if it is too large, that is, if the amount of the synthetic resin component is too small, it becomes difficult to form a film, and incompletely. The formed film also has poor durability.

The composition of the present invention can be dispersed by an ordinary disperser, and a solvent and other additives can be added if necessary.

The formation of a radio wave absorber film using the radio wave absorber composition of the present invention is carried out by directly applying the composition to a structure,
Alternatively, it is carried out by preparing the composition in the form of a sheet in advance and attaching it to the structure.

As a method of applying to the former structure, a method of uniformly applying a predetermined amount using a spatula or a brush, a method of uniformly applying with a spatula using a synthetic resin of constant thickness, glass fiber or metal laths, A method such as airless spray coating and adjusting the thickness using a wet film gauge, a method of evenly applying a predetermined amount on a release plate with a spatula, and affixing with an adhesive after curing are used. .

Also, the latter method of sticking in a sheet form is to mix the wave absorber composition with a stirrer, process this into a sheet of a constant thickness with an extruder, and apply this sheet to the structure with an adhesive. It is performed by using and pasting.

The structure to which the method of the present invention is applied is not particularly limited and includes not only structures on the sea (bridges etc.) but also onshore structures such as buildings.

(Function) The radio wave absorber composition according to the present invention can realize a specific gravity of about 1.5 or less, and the thickness when used is 1.1 m.
Since it can be realized in m or less, the dead load of the target structure to be constructed can be reduced, laying is easy, and a great advantage in practical use is brought about. Further, by using a graphite having a large fixed carbon content, an appropriately large particle size, and a large aspect ratio, it is possible to obtain a characteristic with a reflection loss of 20 dB or more.

EXAMPLES Hereinafter, the present invention will be described in more detail in comparison with its preferred examples and comparative examples.

Example 1 Scale-like graphite (fixed carbon content 90%, average particle size
500 μm, aspect ratio of 500) was mixed with the epoxy resin in the compounding parts number (parts by weight, the same hereinafter) shown in Table 1 and dispersed for 10 minutes with a paint mill to prepare a base. A polyamide resin curing agent was mixed with the obtained base at the ratio shown in Table 1, and was uniformly applied to a 220 × 220 × 3.2 mm sandblasted steel plate with a spatula to a thickness of 0.9 mm. The coated plate was left for 2 days at 20 ° C. and dried and cured to obtain a thin film type electromagnetic wave absorber film.
About the created test plate, its electromagnetic wave absorption performance is 8 ~ 13G
The result evaluated about Hz is shown in FIG. It shows a characteristic with a sharp absorption peak at 9.5 GHz, and the peak reflection loss of 40 dB at this time indicates that 99.9% or more of the radio wave energy was absorbed. The specific gravity of this composition is 1.37 and the weight per unit area is 1.23 kg / m ² . The weight per unit area of the electromagnetic wave absorber film shown in Comparative Example 1 was 4.85 kg / m ^2, and it was possible to reduce the weight by about 75%.

Example 2 The scale-like graphite shown in Example 1 was mixed with liquid polybutadiene in the compounding number shown in Table 2 and dispersed by the method shown in Example 1 to prepare a base. An isocyanate curing agent was mixed with the obtained base at a ratio shown in Table 2, and a net made of synthetic resin having a constant thickness was spread on the same steel plate as in Example 1 and uniformly applied to a thickness of 1.1 using a spatula. did. It was dried and cured in the same manner as in Example 1 to obtain a radio wave absorber film. The result of evaluating the electromagnetic wave absorption performance of the prepared test plate in the same manner as in Example 1 is shown in FIG. It showed a characteristic with a sharp absorption peak at 9.6 GHz, and the peak reflection loss at this time was 40 dB.

The weight per unit area of this coating was 1.46 kg / m ² , and it was possible to reduce the weight by about 70% as compared with the case of the radio wave absorber coating shown in Comparative Example 1.

Example 3 The scale-like graphite shown in Example 1 was mixed with the unsaturated polyester resin in the compounding number shown in Table 3 and dispersed by the method shown in Example 1 to obtain a base. The obtained base was mixed with the curing agent in the proportion shown in Table 3, and uniformly coated on the release plate with a spatula to a thickness of 1.0 mm. Similarly to the method of Example 1, the dry and cured radio wave absorber film was removed from the release plate and attached to the same steel plate as in Example 1 using an epoxy resin adhesive. The result of evaluating the electromagnetic wave absorption performance of the prepared test plate in the same manner as in Example 1 is shown in FIG. 9.5G
It showed a characteristic with a sharp absorption peak at Hz, and the peak reflection loss at this time was 40 dB. The specific gravity of this composition is 1.40
And the weight per unit area when the thickness is 1.0 mm
It was 1.40 kg / m ² , which was approximately 71% lighter than the case of the electromagnetic wave absorber film shown in Comparative Example 1.

Example 4 Scale-like graphite (fixed carbon content 85%, average particle size
200 μm, aspect ratio 500) was mixed with the epoxy resin in the compounding number shown in Table 4 and dispersed by the method shown in Example 1 to obtain a base. A polyamide resin curing agent was mixed with the obtained base at a ratio shown in Table 4, airless spray coating was applied to the same steel plate as in Example 1, and the thickness was uniformly applied to 1.1 mm while measuring the thickness using a wet film gauge. Attached.
FIG. 4 shows the result of evaluation of radio wave absorption performance after drying and curing in the same manner as in Example 1. It showed a characteristic with a sharp absorption peak at 9.0 GHz, and the peak reflection loss at this time was 30 dB. The specific gravity of this composition is 1.27, and the weight per unit area when the thickness is 1.1 mm is 1.39 kg / m ^2, which is about 71% lighter than the case of the electromagnetic wave absorber film shown in Comparative Example 1. Was possible.

Example 5 Scale-like graphite (fixed carbon content 95%, average particle size
700 μm, aspect ratio 700) was mixed with the epoxy resin in the compounding number shown in Table 5 and dispersed by the method shown in Example 1 to obtain a base. A polyamide resin curing agent was mixed in the ratio shown in Table 5 to the obtained base, applied in a thickness of 1.1 mm in the same manner as in Example 1, dried and cured, and the result of evaluating the electromagnetic wave absorption performance is shown in FIG. It was It showed a characteristic with a sharp absorption peak at 10.0 GHz, and the peak reflection loss at this time was 30 dB. The specific gravity of this composition is 1.30, and the weight per unit area when the thickness is 1.1 mm is 1.43 kg / m ^2, which is about 71% lighter than the case of the electromagnetic wave absorber film shown in Comparative Example 1. Was possible.

Comparative Example 1 Epoxy resin was mixed with by-product ferrite and conductive carbon black in the compounding amounts shown in Table 6, and dispersed by the method shown in Example 1 to obtain a base. A polyamide resin curing agent was mixed with the obtained base in a ratio shown in Table 6, coated in a thickness of 2.5 mm in the same manner as in Example 1, dried and cured, and the result of evaluating the electromagnetic wave absorption performance is shown in FIG. Indicated. The specific gravity of this composition was 1.94, and the weight per unit area when the thickness was 2.5 mm was 4.85 kg / m ² .

Comparative Example 2 Scaly Graphite (fixed carbon content 60%, average particle size
500 μm, aspect ratio 500) was mixed with the epoxy resin in the compounding number shown in Table 7 and dispersed by the method shown in Example 1 to obtain a base. A polyamide resin curing agent was mixed in the ratio shown in Table 7 to the obtained base, applied in a thickness of 1.1 mm in the same manner as in Example 1, dried and cured, and the result of evaluating the electromagnetic wave absorption performance is shown in FIG. It was shown to. As a whole, there was no absorption peak, and the electromagnetic absorption characteristics with low reflection loss were exhibited.

Comparative Example 3 Scale-like graphite (fixed carbon content 99%, average particle size
100 μm, aspect ratio 100) was mixed with the epoxy resin in the compounding number shown in Table 8 and dispersed by the method shown in Example 1 to obtain a base. The obtained base was mixed with a polyamide resin curing agent in the proportions shown in Table 8, applied in a thickness of 1.1 mm in the same manner as in Example 1, dried and cured, and the result of evaluating the electromagnetic wave absorption performance is shown in FIG. It was shown to. As a whole, there was no absorption peak, and the electromagnetic absorption characteristics with low reflection loss were exhibited.

Comparative Example 4 Blocky Graphite (fixed carbon content 99%, average particle size 40
0 μm, aspect ratio 10) was mixed with the epoxy resin in the compounding parts shown in Table 9 and dispersed by the method shown in Example 1,
It was based. A polyamide resin curing agent was mixed in the ratio shown in Table 9 to the obtained base, applied in a thickness of 1.1 mm in the same manner as in Example 1, dried and cured, and the results of evaluating the electromagnetic wave absorption performance are shown in FIG. It was shown to. As a whole, there was no absorption peak, and the electromagnetic absorption characteristics with low reflection loss were exhibited.

Comparative Example 5 Mica powder (average particle size 500 μm, aspect ratio 500) is shown in Table 10.
The mixture was mixed with the epoxy resin in the compounding ratio shown in 1 and dispersed by the method shown in Example 1 to prepare a base. A polyamide resin curing agent was mixed in the ratio shown in Table 10 to the obtained base, applied in a thickness of 1.1 mm in the same manner as in Example 1, dried and cured, and the result of evaluating the electromagnetic wave absorption performance is shown in FIG. It was shown to. As a whole, there was no absorption peak, and the electromagnetic absorption characteristics with low reflection loss were exhibited.

(Effects of the Invention) The radio wave absorber coating formed according to the present invention can be realized as a thin film with a light weight (small specific gravity).
It is capable of highly absorbing radio waves of the frequency. When applying or pasting a large area on a bridge or the like to provide a radio wave absorber film, reduction of dead load,
Various advantages can be brought about, such as ease of installation, no risk of falling off, and low cost.

[Brief description of drawings]

1 to 5 are views showing reflection loss characteristics of the radio wave absorber coatings according to Examples 1 to 5 of the present invention, and FIGS. 6 to 10 are Comparative Examples 1 to 5 respectively. It is a figure which shows the reflection loss characteristic by.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akatsuki Akatsuki 1-4-4 Mita, Minato-ku, Tokyo NEC Environmental Engineering Co., Ltd. (72) Inventor Kenzo Shirai 4-17-1 Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd. (72) Inventor Toshikazu Nakaya 4-17-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd.

Claims (2)

[Claims] 1. A method of forming a thin film type electromagnetic wave absorber film on a structure surface using an electromagnetic wave absorber composition, wherein the electromagnetic wave absorber composition has a fixed carbon content of 80% or more and a particle size of 20.
A thin film characterized by using a radio wave absorber composition containing, as an essential component, a scaly graphite having an average major axis L of particles and an average thickness D (aspect ratio) L / D of 50 or more. Method of forming a type electromagnetic wave absorber film. 2. The scale-like graphite comprises 5 to 60 parts by weight and the synthetic resin 95 to 40 parts by weight. The scale-like graphite has a fixed carbon content of 80% or more, a particle size of 200 to 800 μm, and a particle size of 200 to 800 μm. Ratio of average major axis L and average thickness D (aspect ratio) L /
A thin film type electromagnetic wave absorber composition, characterized in that D is 50 or more.