JP2006156783A - Rubber composition for radio absorptive material and radio absorbing sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin radio absorbing sheet displaying an excellent radio absorptive performance and having even a superior flexibility. <P>SOLUTION: In a rubber composition for a radio absorptive material, carbonyl iron of 300 to 1,500 pts.wt., preferably 500 to 1,000 pts.wt. is compounded with a rubber component of 100 pts.wt. such as a natural rubber. The remarkably excellent radio absorptive performance can be obtained by compounding a specified quantity of carbonyl iron to the rubber component. Accordingly, the thickness of the radio absorbing sheet can be thinned for obtaining the required quantity of a radio absorption. Since the rubber composition in which carbonyl iron is compounded with the rubber component has a low hardness and is remarkably superior even in the flexibility, a workability is improved, and the rubber composition is difficult to break and has even an excellent durability. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rubber composition for a radio wave absorber and a radio wave absorber sheet, and in particular, a rubber composition for a radio wave absorber that can provide a radio wave absorber sheet that is thin and exhibits excellent radio wave absorption performance and is also excellent in flexibility. And a radio wave absorber sheet formed by molding the rubber composition for radio wave absorbers into a sheet shape.

  In recent years, with the widespread use of ETC (Electronic Toll Collection System), OA equipment, communication equipment, etc., electromagnetic waves generated from these equipment have become a problem. That is, there are concerns about the influence of electromagnetic waves on the human body, and malfunctions of precision equipment due to electromagnetic waves are problematic.

  Therefore, various radio wave absorbing materials have been developed for various electronic devices in order to prevent the emission of electromagnetic waves to the outside, absorb the electromagnetic waves from the outside, and prevent mutual interference. Many of them are obtained by dispersing a powder of a magnetic material such as ferrite, permalloy, or sendust in a rubber or synthetic resin matrix and molding the powder into an appropriate shape. The shape is generally a sheet that is convenient for use. In such a radio wave absorbing sheet, it is desired that a thinner sheet exhibits better radio wave absorbing ability. In addition, it can be easily applied to devices having complicated shapes and large-sized devices, and is desired to be excellent in flexibility in order to be hard to break and have high durability.

  The ability to absorb radio waves is usually expressed using radio wave absorption. In order to increase the amount of radio wave absorption, it is basically necessary to increase the amount of magnetic material present in the radio wave path. However, the presence of more magnetic material in the thin sheet, that is, the high filling of the magnetic material powder into the molding material of the sheet results in a great loss of flexibility of the sheet. On the other hand, when the magnetic material is low blended, it is necessary to increase the thickness of the sheet in order to obtain the desired radio wave absorption performance.

  For this reason, in the past, there has been no actual wave absorbing sheet that can satisfy both high wave absorbing performance and flexibility with a thin wall.

  The present invention has been made in view of the above-mentioned conventional situation, and is a rubber composition for a radio wave absorber capable of providing a radio wave absorbing sheet that is thin and exhibits excellent radio wave absorption performance and is also excellent in flexibility, An object of the present invention is to provide a thin-walled electromagnetic wave absorbing sheet excellent in flexibility and electromagnetic wave absorbing performance, which is formed by molding the rubber composition for an electromagnetic wave absorber into a sheet shape.

  The rubber composition for a radio wave absorber according to the present invention (invention 1) is characterized by blending 300 to 1500 parts by weight of carbonyl iron with 100 parts by weight of a rubber component.

  The rubber composition for a radio wave absorber according to claim 2 is characterized in that, in claim 1, the rubber component is natural rubber.

  The rubber composition for a radio wave absorber according to claim 3 is characterized in that in claim 1 or 2, 500 to 1000 parts by weight of carbonyl iron is blended with 100 parts by weight of the rubber component.

  The rubber composition for a radio wave absorber according to claim 4 is characterized in that, in any one of claims 1 to 3, the carbonyl iron has an average particle diameter of 1 to 10 μm.

  The rubber composition for a radio wave absorber according to claim 5 is the rubber composition according to any one of claims 1 to 4, wherein the rubber component is added and kneaded with a compounding component other than carbonyl iron, and then the carbonyl iron is added two or more times. It is characterized by being obtained by adding and kneading it separately.

  The rubber composition for a radio wave absorber according to claim 6 is characterized in that, in claim 5, the amount of carbonyl iron added and kneaded at one time is 100 to 200 parts by weight with respect to 100 parts by weight of the rubber component. .

  The radio wave absorbing sheet of the present invention (invention 7) is characterized in that the rubber composition for an electromagnetic wave absorber according to any one of claims 1 to 6 is formed into a sheet shape.

  The radio wave absorption sheet according to claim 8 is the radio wave absorption sheet according to claim 7, wherein the hardness according to JIS K6253 (measured using type A as a durometer) is 80 degrees or less, and the 5.8 GHz radio wave absorption amount at a thickness of 3 mm or less is 15 dB or more. It is characterized by that.

  According to the present invention, by blending a predetermined amount of carbonyl iron with a rubber component such as natural rubber, a remarkably excellent radio wave absorption performance can be obtained. The thickness of the absorbent sheet can be reduced. In addition, a rubber component such as natural rubber blended with carbonyl iron has a low hardness and remarkably excellent flexibility, and therefore has good workability, hardly breaks, and is excellent in durability.

  According to the present invention, an electromagnetic wave shielding measure can be easily taken for locations of various shapes and areas by a thin and flexible high-performance electromagnetic wave absorbing sheet.

  In the present invention, natural rubber is preferred as the rubber component. In addition, by setting the blending amount with respect to 100 parts by weight of the rubber component to 500 to 1000 parts by weight of carbonyl iron, it is possible to more reliably achieve both radio wave absorption performance and flexibility. Carbonyl iron having an average particle diameter of 1 to 10 μm is preferable.

  In addition, in order to uniformly disperse carbonyl iron, the rubber composition for a radio wave absorber of the present invention is obtained by adding and kneading compounding components other than carbonyl iron to the rubber component, and then adding carbonyl iron to the rubber component two or more times. It is preferable to add and knead separately, and it is particularly preferable to add and knead so that the amount of carbonyl iron to be added and kneaded at one time is 100 to 200 parts by weight with respect to 100 parts by weight of the rubber component.

  The radio wave absorption sheet of the present invention formed by molding the rubber composition for a radio wave absorber of the present invention into a sheet shape has a hardness of 80 degrees or less according to JIS K6253 (type A) and a thickness of 3 mm or less. It is preferable that the 8 GHz radio wave absorption amount exhibits a radio wave absorption performance of 15 dB or more.

  Hereinafter, embodiments of the rubber composition for a radio wave absorber and the radio wave absorption sheet of the present invention will be described in detail.

  The rubber composition for a radio wave absorber of the present invention is obtained by blending a predetermined amount of carbonyl iron with a rubber component.

  The carbonyl iron powder used in the present invention is an almost granular fine powder having an average particle diameter of about 1 to 10 μm obtained by pyrolyzing iron carbonylated as an organometallic compound. It is an excellent radio wave absorptive material that absorbs electromagnetic waves as resistance loss due to its conductivity.

  In the present invention, if the amount of carbonyl iron added to the rubber component is small, sufficient radio wave absorption performance cannot be obtained, and if it is large, the flexibility tends to decrease. Accordingly, carbonyl iron is blended in an amount of 300 to 1500 parts by weight, preferably 500 to 1000 parts by weight, based on 100 parts by weight of the rubber component.

  The rubber composition for a radio wave absorber of the present invention includes various vulcanizing agents, vulcanizing aids, and other vulcanization accelerating aids, softening agents, anti-aging agents, plasticizers, release agents, as well as carbonyl iron. Various additives usually used in rubber compositions such as a mold, a curing agent, a foaming agent, and a colorant are blended and added as necessary.

  Examples of the vulcanizing agent include sulfur, organic sulfur-containing compounds, metal oxides (such as zinc white and magnesia), and organic peroxides (benzoyl peroxide), but are not limited thereto.

Examples of the vulcanization accelerator include the following, but are not limited thereto.
[Aldehyde / Ammonia]
AC: Acetaldehyde ammonia Hexa: Hexamethylene tetramine [aldehyde amines]
K: Acetaldehyde / aniline 8: Butyraldehyde / aniline [guanidines]
D (DPG): Diphenyl guanidine DT (DOTG): Di-o-tolyl guanidine BG: o-tolyl biguanide [thiazoles]
M: 2-mercapto benzothiazole DM: dibenzothiazyl disulfide MZ: zinc salt of 2-mercapto benzothiazole CZ: N-cyclohexyl-2-benzothiazole sulfenamide NOBS: N-oxydiethylene-2- Benzothiazylsulfenamide [Thiurams]
TT: Tetramethyl, thiuram, di-sulfide TS: Tetramethyl-thiuram, mono-sulfide [dithio-carbamates]
P: Pipecoline / Methylpentamethylene / Di-thiocarbamate PZ: Dimethyl / dithiocarbamate EZ: Diethyl / dithiocarbamate BZ: Dibutyl / dithiocarbamate PX: Ethyl / phenyl dithiocarbamate SDC: Diethyl / dithiocarbamate TP: Sodium dibutyl dithiocarbamate

  In the rubber composition for a radio wave absorber of the present invention, usually, the vulcanizing agent is 0.1 to 10 parts by weight, particularly 1 to 5 parts by weight, and the vulcanization accelerator is a rubber component with respect to 100 parts by weight of the rubber component. It is preferable to mix | blend so that it may become 0.1-10 weight part with respect to 100 weight part, especially 1-5 weight part.

  In the rubber composition for a radio wave absorber of the present invention, natural rubber (NR) and various synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber, isoprene rubber, chloroprene rubber, butyl rubber ( IIR), halogenated butyl rubber, bromide (isobutylene-4-methylstyrene copolymer), ethylene-propylene rubber, acrylic rubber, chlorosulfonated polyethylene rubber, fluorine rubber latex, silicone rubber latex, urethane rubber latex, etc. Alternatively, two or more kinds of thermoplastic elastomers such as SBS (styrene-butadiene-styrene) and SEBS (styrene- (ethylene-butadiene) -styrene) can be used, and natural rubber is particularly preferable.

  In addition, the rubber composition for a radio wave absorber of the present invention may contain a magnetic material other than carbonyl iron, such as ferrite powder, but in this case, the radio wave absorber has excellent radio wave absorption performance. In obtaining, it is preferable that the other magnetic material is 1700% by weight or less, particularly 1200% by weight or less based on the total of carbonyl iron and the other magnetic material.

  In order to prepare such a rubber composition for a radio wave absorber of the present invention, the rubber component is blended in advance with a blending component other than carbonyl iron (in the case of using another magnetic material, a blending component other than carbonyl iron and the magnetic material). ) Is added and kneaded in two or more times, and the powdered carbonyl iron is uniformly dispersed in the rubber matrix, and the radio wave absorption performance is excellent in uniformity. It is preferable when obtaining the rubber composition for electromagnetic wave absorbers. In particular, it is preferable to add and knead the carbonyl iron added and kneaded at a time so as to be 100 to 200 parts by weight with respect to 100 parts by weight of the rubber component.

  The radio wave absorbing sheet of the present invention is obtained by vulcanizing and molding such a rubber composition for a radio wave absorber of the present invention into a sheet, and the radio wave absorbing sheet of the present invention is particularly JIS K6253 (type It is preferably designed such that the hardness according to A) is 80 degrees or less and the 5.8 GHz radio wave absorption at a thickness of 3 mm or less is 15 dB or more, especially the thickness is 2.0 mm or less and the hardness is 75 degrees or less, 5.8 GHz. It is preferable for various applications to be designed to have a radio wave absorption of 20 dB or more.

  Such a radio wave absorption sheet of the present invention may be used by being laminated with a radio wave absorption sheet of another configuration, and if necessary, an adhesive layer or an adhesive layer may be formed on the back side, or the front side For example, a design layer may be formed on the surface and used.

  Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples and Reference Examples.

  The basic rubber compounding employed in the following examples, comparative examples and reference examples is shown in Table 1 below.

Details of carbonyl iron and M-type ferrite used in Examples, Comparative Examples and Reference Examples are as follows.
Carbonyl iron: "S-1641" manufactured by ASP Japan Co., Ltd.
Average particle size 3-6μm
M-type ferrite: “EWA-1-V” manufactured by Nippon Valve Engineering Co., Ltd.
Average particle size of 2.9 μm

Examples 1 and 2, Comparative Examples 1 to 4, Reference Example 1
With respect to the rubber compounding shown in Table 1, carbonyl iron or M-type ferrite is added at the ratio shown in Table 2, and the number of additions shown in Table 2 (the amount added once is the amount obtained by dividing the compounding amount by the number of additions). Therefore, in Examples 1 and 2, the amount of carbonyl iron added to the compound obtained by adding and kneading components other than carbonyl iron to the carbonyl iron is 125% by weight with respect to 100 parts by weight of natural rubber. The rubber composition for a radio wave absorber was prepared by adding and mixing. By vulcanizing and molding this rubber composition for an electromagnetic wave absorber, an electromagnetic wave absorbing sheet having a thickness shown in Table 2 was obtained (however, in Reference Example 1, the sheet cannot be molded).

  About each rubber composition for radio wave absorbers, good dispersibility (◯), no (x) is visually evaluated, and the hardness is measured according to JIS K6253 (type A). 8 GHz radio wave absorption was measured by the reflected power method, and the results are shown in Table 2.

  From Table 2, the following is clear. That is, when M type ferrite is used, in Comparative Example 1 with a small amount of blending, the hardness is small, but the radio wave absorption performance is low, and the sheet thickness is also thick. In Comparative Examples 2 and 3, the sheet thickness was reduced because the amount of M-type ferrite was increased, but the hardness increased and the flexibility was impaired. Even if carbonyl iron is blended, in Comparative Example 4 with a small blending amount, the hardness is small and flexible, but the radio wave absorption performance is insufficient and the sheet thickness is thick.

  Reference Example 1 is an example in which the entire amount of carbonyl iron is added at once, but carbonyl iron is not uniformly dispersed in natural rubber, the dispersibility is poor, and a kneaded rubber sheet cannot be obtained.

  On the other hand, in Examples 1 and 2, in which 500 parts by weight or 1000 parts by weight of carbonyl iron is blended with respect to 100 parts by weight of natural rubber, the sheet thickness is 3 mm or less, the radio wave absorption performance is 15 dB or more, and the hardness is 80. Less flexibility and excellent flexibility.

Claims (8)

  A rubber composition for a radio wave absorber, comprising 100 to 100 parts by weight of a rubber component and 300 to 1500 parts by weight of carbonyl iron.   The rubber composition for a radio wave absorber according to claim 1, wherein the rubber component is natural rubber.   3. A rubber composition for a radio wave absorber according to claim 1, wherein 500 to 1000 parts by weight of carbonyl iron is blended with 100 parts by weight of the rubber component.   The rubber composition for a radio wave absorber according to any one of claims 1 to 3, wherein an average particle diameter of the carbonyl iron is 1 to 10 µm.   The rubber component according to any one of claims 1 to 4, wherein the rubber component is obtained by adding and kneading a compounding component other than carbonyl iron and then adding and kneading the carbonyl iron in two or more times. A rubber composition for a radio wave absorber.   6. The rubber composition for a radio wave absorber according to claim 5, wherein the amount of carbonyl iron added and kneaded at one time is 100 to 200 parts by weight with respect to 100 parts by weight of the rubber component.   A radio wave absorbing sheet, comprising the rubber composition for a radio wave absorber according to any one of claims 1 to 6 formed into a sheet shape.   8. The radio wave absorption sheet according to claim 7, wherein a hardness according to JIS K6253 (type A) is 80 degrees or less and a 5.8 GHz radio wave absorption amount at a thickness of 3 mm or less is 15 dB or more.