JPH0212898A - Manufacture of radio wave absorber - Google Patents

Abstract

PURPOSE:To obtain radio wave absorber having high mechanical strength, hardly loosing a material and having desirable radio wave absorbing properties by stacking sheets of non-woven cloth consisting of conductive high polymer fibers plated with a metal and non-conductive polymer fibers including thermosoftening fibers and thermally bonding the sheets together. CONSTITUTION:Sheets of non-woven cloth consisting of conductive high polymer fibers plated with a metal and non-conductive high polymer fibers including thermosoftening fibers are stacked and bonded with each other thermally. According to an embodiment, predetermined weights of conductive high polymer fibers plated with nickel, non-conductive thermosoftening polyester fibers and non-conductive flame retardant polymer fibers are weighed and set manually. The raw material is fed by a belt and a laminate of non-woven cloth sheets 1 is produced by means of an automatic machine capable of blending fibers, producing non-woven cloth and stacking sheets of non-woven cloth. The laminate is then heated so that the sheets are bonded together. The conductive polymer fibers are incorporated in the non-woven cloth at a proportion of 1%. The laminate of the non-woven cloth sheets has a thickness of 10cm and a weight per unit area of 2000gr/m<2>, The laminate is heated at 130 deg.C for 30 minutes.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a radio wave absorber for use in an anechoic chamber, for example, for preventing broadband radio interference.

(Prior Art) Conventionally, as a material for this kind of broadband radio wave absorber, one in which powdered carbon is dispersed in polyurethane foam is well known, and other materials are hardly known. Radio wave absorbers made of foamed polyurethane with powdered carbon dispersed therein include so-called pyramid-shaped, wedge-shaped, and multilayered radio wave absorbers. They are,
The thickness, shape, and content of powdered carbon contained therein are appropriately designed and used depending on the required frequency band or required absorption characteristics.

On the other hand, there are examples of conductive fibers being used in radio wave shielding materials in the form of thin sheets of textiles.

(Problems to be solved by the invention) A broadband radio wave absorber made by dispersing powdered carbon in polyurethane has weak mechanical strength, its shape changes after construction, the polyurethane chips often fall off, and carbon powder There were drawbacks such as the lack of performance.

(Means for Solving the Problems) The present invention laminates and heats non-woven fabrics made of conductive polymer fibers plated with metals such as nickel and copper and non-conductive polymer fibers including heat-softening fibers. By softening the heat-softening fibers, between the laminations or within the nonwoven sheet,
It is manufactured by forming a network of fibers with each other and joining them after cooling.

(Function) By using the manufacturing method described above, the radio wave absorber of the present invention has overwhelmingly stronger mechanical strength than that of conventional foamed polyurethane materials, and since only fibers are used, material removal is extremely difficult. Since the conductive polymer fibers having a small number of effective lengths are dispersed while being in contact with each other with a certain probability, the current loss is large and the radio wave absorption characteristics are also improved.

(Example) Conductive polymer fibers plated with nickel, non-conductive heat-softening polyester fibers, and flame-retardant polymer fibers were weighed and set manually, then conveyed with a belt and blended. A laminate of nonwoven fabric 1 was manufactured using a normal automatic machine capable of (a process of loosening the fibers), forming into a nonwoven fabric (a process of feeding out fibers little by little to form a sheet), and laminating. Next, the laminate was heated and bonded (FIG. 1). On the other hand, cut out a 60cm square from the laminate, take into account the thickness of the laminate, prepare another piece of nonwoven fabric with a larger mesh than the other 60cm square, place one on the top and bottom of the laminate, and cut out the edges. 2
was pressurized, heated, and crimped (Fig. 2).

In this example, the blending ratio of conductive polymer fibers was kept constant at 1%, the thickness of the nonwoven fabric laminate was 10 cm, and the weight of the laminate per unit area (referred to as basis weight) was 2.000 gr/m.
2, and the heating conditions were 130°C for 30 minutes. Then, samples shown in Table 1 were prepared by changing the content of heat-softening polyester fiber. Samples without edge treatment are indicated by sample symbol A, and samples with edge treatment are indicated by sample symbol B.

The nonwoven fabrics used on the top and bottom of the laminate for edge treatment had a basis weight of 80 gr 1 m 2 , a thickness of 4 mm, and the content of heat-softening polyester fibers was the same as that of the laminate. In addition, 1 cm square plates were attached to the surface of the nonwoven fabric and the vertical plane of these samples using epoxy resin, and the tensile strength was measured five times each. The same measurements were carried out on a conventional foamed polyurethane pyramid-shaped absorbent body. The measured values are shown in Table 1 with maximum and minimum values.

In addition, the radio wave absorption characteristics of these radio wave absorbers from 3 GHz to 18 GHz were measured for vertically incident waves using the normal arch method, and the average value was calculated. Sample code A-1 to A-
4 and B-1 to B-4, the reflection amount is -20±4d
A-5 was -15 dB, and B-5 was -14 dB.

Table 1 (Effects of the Invention) As explained above, the present invention has higher mechanical strength than the conventional pyramid type using foamed polyurethane, and does not suffer from chipping of the material, which was considered the biggest drawback in the past. , Nuki is a big improvement over falling. Moreover, it can be said that these phenomena do not occur at all in products that have undergone edge treatment.

Further, these absorbers of the present invention can be designed as required, such as when higher strength or flame retardance is required. Furthermore, the properties as an absorbent material can be adapted to various uses by designing the laminated structure, thickness, and shape of the nonwoven fabric laminate.

Finally, in the examples, only the cases where nickel plating was used for the conductive polymer fibers and polyester were used for the heat-softening polymer fibers were described, but due to the nature of the present invention, there is no limitation to this. It is clear that the same effect as the present invention can be obtained even if other materials that are more likely to have the same effect are used.

[Brief explanation of the drawing]

1 and 2 show structural diagrams of the present invention. In addition, in the figure, 1... nonwoven fabric, 2... end portion bonded by heat and pressure.

Claims (1)

[Claims] (1) A method for producing a radio wave absorber, which comprises laminating nonwoven fabrics made of conductive polymer fibers plated with metal and non-conductive polymer fibers containing heat-softening fibers and bonding them together by heating.