JP2001308583A - Halogen-free electromagnetic wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a highly heat resistant halogen-free electromagnetic wave absorber generating no dioxins through incineration by dispersing powder of a soft magnetic metal into a matrix of rubber in which flame retardance is achieved as required. SOLUTION: Acryl rubber is employed as a matrix rubber. In a mode requiring flame retardance, one or two kind of aluminum hydroxide and magnesium hydroxide is added by 50-500 phr (total quantity in case of two kinds) as a flame retardant. In order to attain a higher flame retardance (V1 standard), red phosphorus is added by 1-30 phr, as an auxiliary flame retardant, in addition to aluminum hydroxide and (or) magnesium hydroxide. In order to attain a highest flame retardance (V0 standard), one or two kind of carbon powder and ethylene-vinyl acetate copolymer is added by 1-30 phr (total quantity in case of two kinds), as an auxiliary flame retardant, along with red phosphorus by 1-30 phr in addition to aluminum hydroxide and (or) magnesium hydroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave absorber which is halogen-free and does not generate dioxin when incinerated. The present invention also relates to an electromagnetic wave absorber which is halogen-free and optionally has low to high flame retardancy.

[0002]

2. Description of the Related Art In various electronic devices, various electromagnetic wave shields are used because it is necessary to prevent interference of noise electromagnetic waves coming from the outside and to suppress radiation of electromagnetic waves to the outside. Among them, a simple and universal means that is preferred is a composite material in which soft magnetic metal powder is dispersed in a rubber or plastic matrix, formed into a sheet or any other shape. Is to use an electromagnetic wave absorber. Atomized powders such as Sendust, Permalloy, and Fe-Cr-Al alloys are used as the soft magnetic metal powder, and chlorinated polyethylene rubber is used as the matrix material. Gender is bought and used favorably.

[0003] However, products made from chlorinated polyethylene, when incinerated when they become waste, cause harmful dioxins. With emphasis on environmental impact, this type of halogen-containing organic material will not be allowed to be used in the near future, or at least will be considerably restricted in its use.

Therefore, a matrix containing no halogen must be used for the electromagnetic wave absorber.
As a rubber-like material containing no halogen, there is silicone rubber, but the moldability when mixed with metal powder is low, so that a large amount of powder cannot be filled into silicone rubber, so that it has desired characteristics. It is difficult to obtain an electromagnetic wave absorber.

[0005] Other rubbers containing no halogen include ethylene-propylene copolymer rubber (EPDM).
And acrylonitrile-butadiene rubber (NBR). When these materials are to be made flame-retardant, a halogen compound must be used as a flame retardant. It is difficult to make it flame-retardant.

Another requirement for this kind of electromagnetic wave absorber is heat resistance. With the recent increase in the degree of integration of electronic circuits, the amount of heat generated by electronic devices tends to increase, and the temperature tends to increase. Therefore, efforts have been made to improve the heat resistance of the electromagnetic wave absorber. It is expected that technologies utilizing electromagnetic waves such as ITS will be applied to automobiles, and considering the spread of electric vehicles, the environment in which the electromagnetic wave absorber is used will inevitably become even higher in the future. EPDM and NBR cannot meet the heat resistance requirements.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to meet the demands for electromagnetic wave absorbers which are present and are expected to increase in the near future, and are halogen-free and have no problem in incineration treatment. An object of the present invention is to provide a product having high heat resistance and achieving flame retardancy as required.

[0008]

According to the present invention, there is provided an electromagnetic wave absorber which is halogen-free and has improved heat resistance, wherein the soft magnetic metal powder is dispersed in a rubber matrix. An acrylic rubber is used as the rubber.

The electromagnetic wave absorber of the present invention, which is halogen-free, has improved heat resistance, and has achieved predetermined flame retardancy,
In an electromagnetic wave absorber obtained by dispersing a soft magnetic metal powder in a rubber matrix, an acrylic rubber is used as the matrix rubber, and 50 to 500 phr of aluminum hydroxide and / or magnesium hydroxide is used as a flame retardant. It is characterized by being added.

[0010]

In the present invention, the following flame retardant aids are added in addition to the hydroxide flame retardants according to the degree of flame retardancy required of the electromagnetic wave absorber. 1) Red phosphorus: 1 to 30 phr 2) Red phosphorus: 1 to 30 phr, and carbon powder: 1
1 to 30 phr and one or two of ethylene-vinyl acetate copolymer (in the case of two kinds, the total amount): 1 to 30 phr
r

The flame-retardant action of aluminum and magnesium hydroxides is due to the heat absorption caused by the dehydration reaction when heated and decomposed, resulting in cooling.
Therefore, in order to ensure the flame-retardant effect, a relatively large amount of addition is required. Therefore, a sufficient amount of soft magnetic metal powder to exhibit the desired electromagnetic wave absorbing ability is filled, and then the hydroxide is added. Is preferably added in a large amount within a possible range.

[0012] The action of red phosphorus as a flame retardant aid promotes carbonization and vitrification of the polymer material and prevents the surrounding oxygen from entering the burning material by forming a dense layer on the surface. It is in. It is considered that the effect of the flame retardant aid of the carbon powder and the ethylene-vinyl acetate copolymer is to assist the carbonization and vitrification promoting action of the above-mentioned red phosphorus.

[0013] The halogen-free electromagnetic wave absorber of the present invention comprises:
The intention is not to contain halogen,
If necessary, other additives, such as the flame-retardant plasticizers described in Examples below, can be optionally added as long as it does not become negative for achieving the desired flame retardancy.

[0014]

EXAMPLES [Examples 1 and 2] Fe-7Cr-9Al
The molten alloy was sprayed with water to obtain a powder having an average particle diameter of 20 μm (this is referred to as “spherical powder”). A part of the spherical powder was treated with an attritor to obtain a flaky powder having a thickness of 1 to 2 μm and a particle size of 10 to 30 μm (this is referred to as “flat powder”). These soft magnetic metal powders and acrylic rubber ("Nipol" manufactured by Zeon Corporation) were blended together with a vulcanizing agent and the like in the formulation (parts by weight) shown in Table 1. The mixture was kneaded using a roll, and the kneaded material was formed into a sheet by a hot press (170 ° C. × 20 minutes) and crosslinked to produce an electromagnetic wave absorbing sheet having a thickness of 1.0 mm.

Table 1 Working Materials Example 1 Example 2 Soft Magnetic Metal Powder Fe-7Cr-9Al Alloy Flat Powder 800 Spherical Powder 436 Compounding Ratio (Volume%) About 55% About 40% Matrix Acrylic Rubber 100 100 Vulcanization Sulfur 0.3 0.3 Vulcanization accelerator Na stearic acid Na 3 3 Stearic acid K 0.5 0.5 Lubricant Stearic acid 11 These electromagnetic wave absorbing sheets have a good return loss of about 10 dB near 1 GHz. The electromagnetic wave absorption performance was shown. However, there was no flame retardancy.

[Comparative Example] The above-mentioned soft magnetic metal flat powder was blended with silicone rubber so as to occupy 55% by volume, and an attempt was made to manufacture a sheet. It could not be processed into a sheet.

[Examples 3 to 5] Aluminum hydroxide ("Heidilite" manufactured by Showa Denko) and magnesium hydroxide ("Kisuma 5" manufactured by Kyowa Chemical Industry) were used as flame retardants and the formulations shown in Table 2 were used. Each component was blended and an electromagnetic wave absorbing sheet having a thickness of 1.0 mm was manufactured in the same manner as in Example 1.
Each sheet was subjected to a vertical combustion test specified in UL Standard 94 to examine flame retardancy. Table 2 shows the results.
Listed in

Table 2 Working materials Example 3 Example 4 Example 5 Soft magnetic metal powder Fe-7Cr-9Al alloy Flat powder 1324 Flat powder 1334 Spherical powder 327 Mixing ratio (% by volume) Approx. 55% Approx. 55% Approx. 20% matrix Acrylic rubber 100 100 100 Vulcanizing agent Sulfur 0.3 0.3 0.3 Vulcanization accelerator Na 33 3 stearate K 0.5 0.5 0.5 Lubricant Stearic acid 1 1 1 Flame retardant Hydroxide Al 150 230 Mg hydroxide -150- Flame retardant V1 equivalent V1 equivalent V0 equivalent

These electromagnetic wave absorbing sheets exhibited a good electromagnetic wave absorbing performance with a return loss near 1 GHz of about 10 dB.

Examples 6 and 7 In addition to the above flame retardants aluminum hydroxide and magnesium hydroxide, red phosphorus, carbon black and ethylene-vinyl acetate copolymer ("Ultracene" manufactured by Tosoh Corporation) were used as flame retardant aids. )It was used. In Example 6, a plasticizer triaryl phosphate ester (Ajinomoto “Rephos 65”) that imparts flame retardancy was used. Each component was blended according to the recipe shown in Table 3, and an electromagnetic wave absorbing sheet having a thickness of 1.0 mm was produced in the same manner as in Example 1. These sheets were also examined for flame retardancy. The results are shown in Table 3.

Table 3 Working Materials Example 6 Example 7 Soft Magnetic Powder Fe-7Cr-9Al Alloy Flat Powder 1328 Spherical Powder 748 Compounding Ratio (Volume%) About 55% About 40% Matrix Acrylic Rubber 100 100 Vulcanizing Agent Sulfur 0.3 0.3 Vulcanization accelerator Na stearic acid Na 3 3 Stearic acid K 0.5 0.5 Lubricant Stearic acid 11 11 Flame retardant Al hydroxide-Mg hydroxide 130 150 Flame retardant auxiliary Red phosphorus 11 DESCRIPTION OF SYMBOLS 10 Carbon black 55 Ethylene vinyl acetate copolymer 9- Flame retardant plasticizer Triaryl phosphate ester 11- Flame resistance V0 equivalent V0 equivalent

With respect to the electromagnetic wave absorbing sheet of Example 6, 1
FIG. 1 shows the return loss at a frequency of 0 GHz or less.

[0023]

According to the halogen-free electromagnetic wave absorber of the present invention, since an acrylic rubber containing no halogen is used for the matrix material, even if the used one is incinerated, no dioxin is generated.

Since the acrylic rubber has excellent heat resistance, the electromagnetic wave absorber of the present invention has a wide usable temperature range, and a continuous usable temperature of 140 to 160 ° C.
It is much more advantageous when compared to that of other rubbers which cannot be much higher than 100 ° C. For this reason, the electromagnetic wave absorber of the present invention can be tuned to the trend of miniaturization and high density of electronic devices, and can help this.

The electromagnetic wave absorber according to a preferred embodiment of the present invention, to which a flame retardant and, if necessary, a flame retardant auxiliary agent have been added, is obtained from V1 of the UL94 vertical combustion test method and further to V0
High flame retardancy that meets the specifications is compatible with electromagnetic wave absorption performance.

[Brief description of the drawings]

FIG. 1 shows that the return loss of a halogen-free electromagnetic wave absorbing sheet having high flame retardancy manufactured in Example 6 of the present invention was 1
4 is a graph shown in a frequency range of 0 GHz or less.

Claims (4)

[Claims] 1. A halogen-free electromagnetic wave absorber comprising a soft magnetic metal powder dispersed in a rubber matrix, wherein acrylic rubber is used as the matrix rubber. 2. An aluminum hydroxide and / or magnesium hydroxide is used as a flame retardant in an amount of 50 to 500 ph.
2. The electromagnetic wave absorber according to claim 1, wherein the addition of r gives flame retardancy. 3. In addition to aluminum hydroxide and / or magnesium hydroxide, red phosphorus is used as a flame retardant aid.
The electromagnetic wave absorber according to claim 2, wherein the flame retardancy is increased by adding up to 30 phr. 4. In addition to aluminum hydroxide and / or magnesium hydroxide and red phosphorus, 1 to 30 phr of carbon powder and / or 1 to 30 phr of ethylene-vinyl acetate copolymer are used as further flame retardant aids. 4. The electromagnetic wave absorber according to claim 3, wherein the flame retardancy is further enhanced by adding the same.