JPS63173394A - Electromagnetic wave absorbing material and its composite unit - 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 an electromagnetic wave absorbing material that selectively absorbs electromagnetic waves of a specific frequency and a composite reinforced with the same.

(Prior technology) Electromagnetic waves play an important role in transmitting information through the means of spatial propagation, and measurements regarding antennas that play the main role in transmission and reception are performed in infinite space without the influence of surrounding topography or features. is ideal.

However, it is extremely difficult to fully satisfy the above conditions, as the antenna itself is quite large (and requires an even taller tower).

Therefore, when conducting model experiments such as antenna characteristic tests, propagation path reflection, diffraction, and absorbing materials, a laboratory that can be isometrically regarded as free space, such as an anechoic chamber or a radio acoustic chamber, is required. Materials that have good transmission of a range of electromagnetic waves are required.

This material requires a wall material that not only shields external electromagnetic waves but also effectively transmits radio waves emitted inside the laboratory. If you are simply shielding electromagnetic waves, you can seal it with a metal plate or metal mesh, but when plane waves propagate at right angles to these materials, most of the electromagnetic waves are reflected at the conductor surface. . Therefore, although the above-mentioned materials can be used for outer walls, they are not preferred as inner wall materials.

Since the material and structure are the main factors for electromagnetic wave absorbing materials for inner walls, various materials have been studied in the past.

For example, (1) a face-down resistor made by putting a mixture of spherical expanded polystyrene and graphite into a mold and then performing secondary foaming and compression molding; (2) a face-off resistor made by impregnating glass wool or animal hair with an appropriate amount of graphite and neoprene; (3) Absorbing materials in which graphite powder is mixed into magnetic materials such as ferrite have been developed. All of these electromagnetic wave absorbing materials have extremely low strength and are not suitable as structural materials, and in order to achieve even better electromagnetic wave absorbing properties, it is necessary to laminate multiple sheets of materials with varying graphite mixing ratios. was there.

(Objective of the Invention) The object of the present invention is to have high strength and elastic modulus, and to obtain 500 MII
An object of the present invention is to provide an electromagnetic wave absorbing material that selectively absorbs microwaves in the range of z to 300001+2, and a composite reinforced therewith.

(Summary of the Invention) According to the present invention, 30-62% by weight of silicon, 24-6% by weight of carbon
Amorphous inorganic fibers and/or β-SiC with a particle size of 500 Å or less, consisting essentially of 1% by weight and 2-30% by weight of oxygen
It is composed of inorganic fibers consisting of an aggregate of crystalline ultrafine particles, crystalline carbon and amorphous SiO2,
Has a resistivity of Ω・cmO, 500 MHz to 3000
An electromagnetic wave absorbing material is provided that is characterized by selectively absorbing microwaves in the GHz range.

According to the present invention, a composite reinforced with the electromagnetic wave absorbing material described above is provided.

(Detailed Description of the Invention) The electromagnetic wave absorbing material of the present invention comprises: (i) an amorphous substance consisting essentially of Si, C and 0; (ii) consisting essentially of β-SiC with a particle size of 500 Å or less Crystalline ultrafine particles, crystalline carbon and amorphous SiO
(iii) a mixed system of the amorphous material of (i) above and the aggregate of (11) above; Composed of M fibers.

The proportion of each element in inorganic fiber is Si; 30-62% by weight C; 24-61ffi amount% 0; 2-30% by weight It is.

The electromagnetic wave absorbing material of the present invention can be manufactured, for example, by the following method.

A mixture of a polysilane having at least one alkyl group in the side chain and a polycyclic aromatic compound in a pinch is heated in the presence or absence of a catalyst or A mixture of preheated polysilane and a pinch of polycyclic aromatic compound,
A first step of producing polycyclic aromatic polycarbosilane by heating in the presence or absence of a catalyst, and a second step of preparing and spinning a spinning dope of the polycyclic aromatic polycarbosilane. a third step of making the spun fibers infusible under tension or no tension; and a fourth step of firing the infusible spun fibers at a temperature in the range of 800 to 1500°C in vacuum or in an inert gas atmosphere. An electromagnetic wave absorbing material consisting essentially of Si, C, and 0 can be manufactured from the above. 1st
The amount of polysilane used in the process is preferably 1 to 40 times the weight of the polycyclic aromatic compound. The specific resistance of the obtained electromagnetic wave absorbing material decreases as the firing temperature is increased within the firing temperature range of the fourth step.

The electromagnetic wave absorbing material of the present invention can be used as a composite having a plastic or ceramic matrix, if necessary.

Examples of plastic matrices include epoxy resin, modified epoxy resin, polyester resin, polyimide resin, phenol resin, polyurethane resin, polyamide resin, polycarbonate resin, silicone resin, phenoxy resin, polyphenylene sulfide resin, fluorine resin,
Hydrocarbon resin, halogen-containing resin, acrylic acid resin, A
Examples include BS resin, ultra-high molecular weight polyethylene, modified polyphenylene oxide, and polystyrene.

Examples of ceramic matrices include carbide ceramics such as silicon carbide, titanium carbide, zirconium carbide, niobium carbide, tantalum carbide, boron carbide, chromium carbide, tungsten carbide, molybdenum carbide; silicon nitride, titanium nitride, zirconium nitride, vanadium nitride. , niobium nitride, tantalum nitride, boron nitride, silicon aluminum nitride,
Nitride ceramics such as hafnium nitride; alumina,
Examples include oxide ceramics such as magnesia, mullite, and cordierite.

Plastic or ceramic composites can be manufactured according to methods known per se. The proportion of the electromagnetic wave absorbing material in the composite is preferably 10 to 70% by weight in terms of the strength and electromagnetic wave absorption characteristics of the composite.

The electromagnetic wave shielding effect of the electromagnetic wave absorbing material and composite body provided by the present invention can be determined from the total loss (db) expressed by the following formula.

f: Frequency (MHz) μg: Magnetic permeability σr of shielding conductor
:Specific conductivity S of the shielding conductor:Thickness of the shielding conductor) (Example) Examples are shown below.

Reference Example 1 2.51 g of anhydrous xylene and 400 g of sodium were placed in a 51-sized three flask and heated to the boiling point of xylene under a nitrogen gas stream, and 11 dimethyldichlorosilane was added dropwise over 1 hour. After the addition was completed, the mixture was heated under reflux for 10 hours to form a precipitate. The precipitate was filtered and washed with methanol and then water to obtain 420 g of white powder polydimethylsilane.

400 g of this polydimethylsilane was charged into a Mitsuro flask equipped with a gas inlet tube, a stirrer, a cooler, and a distillation tube, and heated at 420°C under a nitrogen gas stream while stirring, and 350 g was placed in a distillation receiver. A colorless and transparent slightly viscous liquid was obtained. The number average molecular weight of this liquid was 470 when vapor pressure permeability was measured. As a result of IR spectroscopy, this material has a total number of (Si CH2) bond units versus (S
i-3i) It was found to be an organosilicon polymer in which the ratio of the total number of bonding units was approximately 1:3.

Example 1 300 g of the organosilicon polymer obtained in Reference Example 1 was treated with ethanol to remove low molecular weight substances, resulting in a number average molecular weight of 12
00 polymer was obtained. As a result of IR spectroscopy, this material was found to have a total number of (Si-CH2) bond units versus (S
i-3i) It was found to be an organosilicon polymer in which the ratio of the total number of bonding units was approximately 1:2.

50 cc of xylene was added to a mixture of 40 g of this polymer and 10 g of the polycyclic aromatic compound (xylenated melt) in a pinch to form a mixed solution consisting of a homogeneous phase, and the mixture was reacted under reflux with stirring in a nitrogen gas atmosphere for 1 hour. Ta. After this, the temperature was further increased to distill out the solvent xylene, and the temperature was increased to 400°C.
C for 5 hours to obtain a polycyclic aromatic organosilicon polymer. In this reaction, 5i present in the organosilicon polymer
-H bonds decreased by about 7%, and new generation of Si-Q bonds was observed.

A polycyclic aromatic organosilicon polymer is melt-spun and spun in air.
Infusibility treatment was performed at 90°C, followed by firing at 1300°C in a nitrogen gas atmosphere, resulting in a fiber diameter of 12.5μ and a tensile strength of 2.
An inorganic fiber mainly consisting of silicon, carbon and oxygen was obtained, having a weight of 80 kg/112 and a tensile modulus of 1/05.8 t/*w2. The specific resistance of this fiber is 2.3Ω・
cm, and well absorbed microwaves of 4 to 50 G) Iz.

Comparative Example 1 3 g of polyporodiphenylsiloxane was added to 100 g of the organosilicon polymer obtained in Reference Example 1, and the mixture was thermally condensed at 350°C in a nitrogen gas atmosphere to form carbosilane units of formula (S i -CH2). A polycarbosilane having a main main chain skeleton and a hydrogen atom and a methyl group in the silicon atom of the carbosilane unit was obtained. This polymer was melt-spun, treated to make it infusible at 190°C in air, and then fired at 1600°C in an argon gas atmosphere, resulting in a fiber diameter of 12.3 μm.
m, tensile strength 30kg/++m2, tensile modulus 4t/1
Recommendation 2, silicon carbide fibers mainly consisting of silicon, carbon and oxygen, was obtained.

Although this fiber has a specific resistance of 4.6Ω・Cm and exhibits good microwave absorption performance, it is brittle and cannot be used as a reinforcing fiber for composites. Example 2 Example The inorganic fibers obtained in step 1 were uniaxially aligned without surface treatment, and impregnated with a commercially available bisphenol A type epoxy resin to give a preliminary effect, to obtain a prepreg sheet with a thickness of 0.15 mm. After laminating these sheets, 1
An inorganic fiber-reinforced epoxy composite mainly consisting of silicon, titanium, carbon and oxygen with a thickness of 2 NTa was produced by hot pressing at 70 °C and 7 kg/cM for 4 hours. The fiber content of this composite was 60% by volume.

The resulting composite had a tensile strength of 150 kg/mm2, a tensile modulus of 13t/1A1A2, and a bending strength of 203 k.
g/ml 2, flexural modulus is 12.6 t/**2
It showed even better microwave absorption performance.

Claims (3)

[Claims] (1) Amorphous inorganic fibers and/or ultrafine crystals of β-SiC with a particle size of 500 Å or less, consisting essentially of 30 to 62% by weight of silicon, 24 to 61% by weight of carbon, and 2 to 30% by weight of oxygen; It is composed of inorganic fibers consisting of an aggregate of crystalline carbon and amorphous SiO_2, and has a resistance of 10^-^2 to 10^2 Ω・c
An electromagnetic wave absorbing material having a specific resistance of m and selectively absorbing microwaves in the range of 500 MHz to 3000 GHz. (2) Amorphous inorganic fibers and/or ultrafine crystals of β-SiC with a particle size of 500 Å or less, consisting essentially of 30 to 62% by weight of silicon, 24 to 61% by weight of carbon, and 2 to 30% by weight of oxygen; It is composed of inorganic fibers consisting of an aggregate of crystalline carbon and amorphous SiO_2, and has a resistance of 10^-^2 to 10^2 Ω・c
A composite body characterized in that the matrix is reinforced with an electromagnetic wave absorbing material having a specific resistance of m and selectively absorbing microwaves in the range of 500 MHz to 3000 GHz. (3) The composite according to claim 2, wherein the matrix is plastic or ceramic.