JPH10251527A - Production of radio wave absorber and radio wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a radio wave absorber capable of exhibiting stable absorbing characteristics, without the need of any complicated process control by mixing chip-like foam, electroconductive powder and liquid adhesive base with one another followed by injecting the resultant mixture with a curing agent under compression. SOLUTION: This radio wave absorber is obtained by mutually mixing (A) pref. 70-95 pts.wt. of chip-like resin foam (pref. flexible resin foam pref. 14-120kg/m<3> in apparent density). (B) pref. 5-40 pts.wt. of electroconductive powder (e.g. carbon black) and (C) pref. 5-30 pts.wt. of a liquid adhesive base (pref. urethane prepolymer) followed by compressing the resultant mixture in a mold and then injecting, while maintaining the mixture generally in this state, the inside of the mold with (D) a gaseous or liquid curing agent reactive to the component C (pref. steam) to effect curing the component C. Thus, the objective radio wave absorber useful in e.g. radio wave darkrooms can be easily afforded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a radio wave absorber and a radio wave absorber.

[0002]

2. Description of the Related Art Conventionally, a radio wave absorber in which a conductive powder such as carbon black is dispersed and contained in a resin foam such as a foamed polystyrene resin, a foamed polyurethane resin or a foamed polyethylene resin has been used to measure various characteristics of an antenna. It is widely used in electromagnetic wave anechoic chambers for testing electromagnetic field strength measuring instruments, for measuring interference wave radiation, and for countermeasures against radio interference from various devices.

[0003] In the case of the above-mentioned radio wave absorber, for example, in the case of a foamed flexible polyurethane, a liquid containing a conductive powder such as carbon black and an adhesive is prepared in advance, and the above liquid is added to this liquid. It has been manufactured by immersing a resin foam, squeezing it appropriately, and then drying.

However, the conventional manufacturing method as described above requires a large amount of equipment for manufacturing the radio wave absorber, and it takes a long time to dry the resin foam after being immersed in a liquid containing a conductive powder and an adhesive. And it was troublesome.

In addition, the conventional manufacturing method has a drawback that it is difficult to control a process for obtaining a radio wave absorber having stable absorption characteristics.

An object of the present invention is to solve the above-mentioned disadvantages of the prior art, and to provide a method capable of easily producing a radio wave absorber having stable absorption characteristics without requiring difficult process control. It was done for the main purpose.

[0007]

Means for Solving the Problems In order to achieve the above-mentioned object, the construction of the method of manufacturing a radio wave absorber adopted by the present invention is to mix a chip-like resin foam, a conductive powder and a liquid adhesive base. By compressing the mixture in a mold, and while substantially maintaining the state, by injecting a gaseous or liquid curing agent that reacts with the liquid adhesive base into the mold, the liquid adhesive base It is characterized by being cured.

At the same time, according to the present invention, after mixing the chip-shaped resin foam, the conductive powder, and the liquid adhesive base, the mixture is compressed in a mold, and while substantially maintaining the state, the mixture is placed in the mold. A radio wave absorber obtained by injecting a gaseous or liquid curing agent that reacts with a liquid adhesive base and curing the liquid adhesive base.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The chip-like resin foam used in the present invention may be, for example, an open-cell urethane resin foam, but is not limited thereto. What is called a resin foam or a hard resin foam can be used, and among them, a soft resin foam which has elastic repulsion when compressed and is hardly embrittled is preferable.

The above-mentioned chip-like resin foam has an apparent density of 14 to 120 kg / m ³ , preferably 18 to ³ kg / m ³ .
It is desirable to be in the range of 0 kg / m ³ .

In the present invention, as described above, a chip-shaped resin foam, that is, a small piece-shaped resin foam is used. In the present invention, the term "chip-shaped" refers to an average particle diameter of about 2 to 50 mm, preferably about 3 to 10 mm, particle size range up to about 70 mm and minimum about 1
mm.

When the average particle size of the chip-shaped resin foam used in the present invention is less than 2 mm, not only the chips become powdery and it becomes difficult to handle, but also the bulk density of the resin foam after molding described later becomes high. Conversely, if the average particle size exceeds 50 mm, the dispersion of the chip-shaped resin foam and the conductive powder becomes poor, and the performance of a radio wave absorber deteriorates.

In addition, as the chip-shaped resin foam, if the remaining material obtained by cutting a desired shape from the urethane resin foam is pulverized into chips, the remaining material is effectively used. be able to.

Examples of the conductive powder used in the present invention include carbon black, metal powder such as copper powder and iron powder, but are not limited thereto.
In short, what is necessary is just to be excellent in conductivity.

Further, the adhesive used in the present invention includes:
A two-component curing type composed of a liquid adhesive base and a gaseous or liquid curing agent can be used. For example, an adhesive composed of a urethane prepolymer (adhesive base) and water (curing agent), Examples of the adhesive include an epoxy resin base (adhesive base) and an amine-based curing agent.

The urethane polymer is an isocyanate compound such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) or dicyclohexylmethane diisocyanate (HDI).
By reacting with a polyol such as polypropylene glycol, the residual amount of isocyanate (NCO%) is about 1 to 10%, preferably 2 to 5 with a solvent such as methylene chloride.
%.

In the production method of the present invention, first, the above-mentioned chip-shaped resin foam, conductive powder and liquid adhesive base are mixed. In this mixing step, these components can be mixed. Appropriate methods and equipment can be used.

The mixing ratio in the mixing step may be, for example, in the range of a chip-shaped resin foam 70 to 95, a conductive powder 5 to 40, and a liquid adhesive base 5 to 30 by weight.

In the present invention, the mixture obtained as described above is then compressed in a mold, and the size and shape of the mold are not particularly limited. What is necessary is just to perform to the extent that the adhesion of the powder is sufficiently obtained.

In the present invention, a gaseous or liquid curing agent that reacts with the liquid adhesive base is placed in the mold while maintaining the compressed state (of course, some fluctuations are allowed). For example, when the adhesive base is a urethane prepolymer, the liquid adhesive base is cured by injecting water, preferably water vapor, to obtain the radio wave absorber of the present invention.

From the viewpoint of diffusion of the curing agent into the mold and promotion of the reaction, it is more preferable to inject water as steam when the adhesive base is a urethane prepolymer.

The radio wave absorber of the present invention thus obtained is dispersed in a chip-like resin foam adhered by an adhesive in an appropriately compressed state and at least a bonding portion of the chip-like resin foam. Made of conductive powder,
By cutting the molded article as it is or by cutting it into an appropriate shape, a radio wave absorber having stable absorption characteristics can be obtained.

As long as the performance as a radio wave absorber is not deteriorated, a filler such as a flame retardant, a magnetic substance, a fungicide, or an antibacterial agent can be used in addition to the conductive powder.

[0025]

The present invention will be described in more detail with reference to the following examples.

Example 1 6 kg of a chip-like soft urethane resin foam having an average particle size of 30 mm (particle size range of about 20 to 35 mm) (average apparent density: 22 kg / m ³ ), 0.5 kg of carbon powder (product name: V
ALCAN XC-72; manufactured by Sumika Color Co., Ltd.
Same as in Examples]) and urethane prepolymer as an adhesive base (NCO% = 3.2%, product name: Hyprene NH-1000; manufactured by Mitsui Toatsu Chemicals, Inc.)
kg were mixed in a mixing vessel with a stirrer. Thereafter, the mixture was placed in a chip mold having a size of 600 mm × 600 mm × 1000 mm (height), compressed 50% in the height direction, and kept as it was at 150 ° C. and 4 atmospheres of steam for 10 minutes.
By injecting and spraying from the hole at the bottom of the chip mold and curing the adhesive base, 600 mm × 6
One example of a radio wave absorber having a size of 00 mm × 500 mm (height) was obtained, and this radio wave absorber was cut with a three-dimensional cutter.
A radio wave absorber having a pyramid shape was obtained.

Example 2 6 kg of a chip-shaped soft urethane resin foam having an average particle diameter of 5 mm (particle diameter range of about 2 to 7 mm) (average apparent density of 22 k)
g / m ³ ), except that 0.9 kg of carbon powder and 1.5 kg of urethane prepolymer were used as an adhesive base.
A radio wave absorber was obtained in the same manner as in Example 1.

Example 3 The procedure of Example 2 was repeated except that 2.0 kg of carbon powder and 2.0 kg of urethane prepolymer were used as an adhesive base.

The radio wave absorption rate of the radio wave absorber of the above embodiment was measured. Table 1 shows the results.

[Table 1]

The radio wave absorption in Table 1 is 3 GHz.
Was measured by the NRL arch test method.

The ferrite composite absorptivity in the above table is:
This refers to the radio absorptivity of a radio wave absorber in which a 20 mm thick ferrite plate (product name: grid type ferrite absorption plate; manufactured by Nisshinbo Tempest) is attached to the entire bottom side of the radio wave absorber with an adhesive (neoprene rubber).

[0032]

As described above, according to the present invention, a radio wave absorber of a stable quality can be manufactured in a short time without requiring a large amount of equipment unlike the conventional immersion and drying methods. .

Further, in the present invention, the manufacturing process itself is shortened, and in addition, the use of the cutting residual material of the urethane resin foam for the chip-like foam can greatly reduce the manufacturing cost. Also suitable for the production of small lots of various kinds.

Further, in the present invention, by changing the ratio of the conductive powder in the mixing step of the chip-shaped resin foam, the conductive powder and the liquid adhesive base, the electromagnetic wave absorbers having different conductive powder contents can be obtained. Can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a cone-shaped radio wave absorption band obtained by the present invention.

Claims (4)

[Claims] After mixing a chip-shaped resin foam, a conductive powder, and a liquid adhesive base, the mixture is compressed in a mold, and the liquid adhesive base is placed in the mold while maintaining the state substantially. A method for manufacturing a radio wave absorber, wherein the liquid adhesive base is cured by injecting a gaseous or liquid curing agent that reacts with the agent. 2. The method according to claim 1, wherein the liquid adhesive base is a urethane prepolymer, and the curing agent is water vapor. 3. After mixing the chip-shaped resin foam, the conductive powder, and the liquid adhesive base, the mixture is compressed in a mold, and the liquid adhesive base is kept in the mold while substantially maintaining the state. A radio wave absorber obtained by injecting a gaseous or liquid curing agent that reacts with an agent, and curing the liquid adhesive base. 4. A chip-shaped resin foam bonded by an adhesive in an appropriately compressed state, and a conductive powder dispersed at least in a bonding portion of the chip-shaped resin foam. Radio wave absorber.