JP2006037078A - Flame-retardant magnetic sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flame-retardant magnetic sheet which gives uniform stable flame retardance. <P>SOLUTION: This magnetic sheet having excellent flame retardancy and corrosion resistance is characterized in that a flat soft magnetic metal and, if necessary, a flame retardant are included in an organic binder having an oxygen index of ≥24 and an oxygen permeation coefficient of ≤3×10<SP>-17</SP>m<SP>4</SP>(N×s)(25°C) in a dispersed state. The flat soft magnetic metal includes Fe-Cr-based alloys such as Fe-Ni-Cr-based alloy, Fe-Si-Cr-based alloy, and Fe-Ni-Si-Cr-based alloy. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic sheet excellent in flame retardancy and corrosion resistance suitable for a noise suppressing sheet that suppresses noise by an electromagnetic wave shielding effect, a sheet that requires magnetic properties such as a magnetic shield sheet, and the like.

  Conventionally, a noise suppression sheet has a large amount of flat soft magnetic metal added to impart magnetism. At that time, the most frequently used soft magnetic metal was Sendust (Fe-Si-Al alloy). For example, Patent Document 1 describes an electromagnetic wave interference suppressor using a flat and / or needle-like Fe—Al—Si alloy powder.

  This sendust has high magnetic properties, but has the property of being easily oxidized. Also, oxidation occurs during flat processing or due to the effect of increasing the surface area resulting from the processing. The fact that it is easily oxidized means that it burns at the atomic level, and the metal fine particles may become highly flammable which is classified as a dangerous substance. In other words, it is necessary to pay sufficient attention to handling even in the powder state. If this cannot be controlled, it may cause fire or explosion. Therefore, explosion-proof measures are an essential item in the manufacturing process of this alloy.

  Since the noise suppression sheet to which such sendust is added in a large amount also has high flammability, flame retardant measures are required. As one countermeasure for this, there is a method of forming an oxide film. Thereby, corrosion resistance improves and it is supposed that an excessive oxidation reaction is suppressed. However, as described in Documents 2 to 4, the possibility that the oxide film itself contributes to combustion has been pointed out, and its effectiveness has been questioned.

  On the other hand, Patent Document 2 describes Fe-Si-Cr-based or Fe-Al-Cr-based flat Fe-based alloy powders for magnetic shields, and particularly describes the effect of improving corrosion resistance due to alloying of Cr. ing. However, the flame retardancy of the sheet containing the Fe-based alloy powder is not described.

  Patent Documents 3 to 5 describe flame retardant materials for electromagnetic wave shielding using Fe-Cr alloys. That is, the flame retardant materials described in Patent Documents 3 and 4 are obtained by adding a Fe-Cr flat soft magnetic metal to a flame retardant grade chlorinated polyethylene or the like. The electromagnetic wave absorber described in Patent Document 5 is obtained by mixing a flame retardant into an electromagnetic wave absorber in which soft magnetic metal powders such as Fe-Cr are bonded with a polymer.

  However, it is difficult to obtain stable flame retardancy only by using a flame retardant polymer or a flame retardant. Further, the magnetic sheet is required to have corrosion resistance. This is because, for example, no rust is generated in the salt spray test, but the mechanism is that the internal soft magnetic metal powder is oxidized (rusted) by contact with oxygen. Conventionally, these measures have been taken to increase the corrosion resistance by providing an oxide film on the surface of the flat soft magnetic metal, or when the flat soft magnetic metal powder is highly filled, the binder cannot be filled and voids are formed inside. For this reason, the main focus is on increasing the adhesion between the metal and the binder by using a coupling agent or the like. However, there was nothing that focused on the oxygen gas permeability of the binder.

Japanese Patent No. 3401650 JP 2000-87193 A JP-A-11-144931 Japanese Unexamined Patent Publication No. 2000-1000061 JP 2000-151183 A

In general, a noise suppression sheet is installed in the vicinity of a noise source or receiver to reduce radiation noise generated in the electronic device casing or to protect electronic devices from unwanted electromagnetic waves entering from outside the electronic device. It is a thin sheet. This sheet is designed to reduce energetically without causing electromagnetic noise to escape to the ground, and a sheet that is not a good conductor (that is, no electrical coupling occurs) is used. As the sheet base material, an organic binder, generally a polymer material is used. In order to reduce electromagnetic wave energy, it is necessary to increase the complex relative permeability (μ ′ and μ ″) of the sheet to enhance the heat conversion function of the electromagnetic wave. It is necessary to blend a large amount of magnetic metal.
Since a thin sheet contains a large amount of highly conductive metal, it is in a so-called combustible state, and the amount of the compounding material is close to the limit, so flame retardants and flame retardant aids Therefore, it is necessary to develop an effective flame retardant composition in a small amount.
In addition, Fe-based metals having excellent magnetic properties are materials that are very susceptible to oxidation. This has a risk that oxidation may occur even after sheet processing from the stage of raw materials before sheet processing. This is seen as an occurrence of rust as an evaluation item of the sheet, particularly in an accelerated test such as a salt spray test.
An object of the present invention is to solve the problems in the conventional techniques as described above, and to provide a magnetic sheet excellent in flame retardancy capable of obtaining uniform and stable flame retardancy and at the same time excellent in corrosion resistance.

The combustion mechanism of organic materials is generally (1) combustion generation in the combustion field, (2) radiation from the combustion field to the surface of the organic material, (3) heat conduction in the organic material, (4) decomposition in the organic material. (5) Diffusion of decomposed volatiles in the organic material, (6) Vapor phase diffusion of volatiles from the surface of the organic material, and arrival at the combustion field. Interrupting any part of this combustion cycle will lead to stopping the combustion. In addition, the combustion here refers to so-called fire spread, that is, burnout from a combustion source.
The purpose of blending flame retardants is to form a carbonized coating on organic materials to improve heat insulation and improve thermal stability, or release water during combustion to lower the combustion temperature, and further decompose to form radicals during combustion In addition, examples include those that trap active H radicals and OH radicals in the gas phase, and those that combine these, but all are designed to exert a flame-retardant effect only during combustion. That is, the countermeasures (2) and (6) of the combustion mechanism are the main.
The combustion mechanism includes a portion involving an organic material in addition to the gas phase. The present inventors paid particular attention to the relationship between the oxygen index of organic materials and the internal diffusivity of volatiles in organic materials. In the present invention, the internal diffusibility of volatile substances in the organic material is evaluated by gas barrier properties, particularly by oxygen permeability coefficient. In order to suppress the internal diffusivity of the generated volatiles, it is said that thickening by reactive cross-linking or physical entanglement of the binder is effective. As a measure of this diffusivity, a gas with higher mobility is used. This is because it has been determined that the numerical value of transmittance can be used as a scale. By suppressing this oxygen permeability coefficient, resistance to combustion and resistance to the oxidation reaction of the encapsulated flat soft magnetic metal can be obtained at the same time, improving the flame retardancy and corrosion resistance of the processed sheet, and further reducing the amount of outgas generated The present invention has been found to be able to suppress this. In other words, not only the flame retardant is added to the binder to increase the flame retardancy, but also the choice of a binder that gives corrosion resistance and outgas resistance in addition to flame retardancy and the effect of this binder is maximized. The present invention is the result of devising a processing method for obtaining an encapsulated state in a dispersed state of a flat soft magnetic metal that can be exhibited in the present invention.

The present invention has been completed as a result of the above studies. In other words, the flame-retardant magnetic sheet of the present invention has a flat soft magnetic property applied to an organic binder having an oxygen index of 24 or more and an oxygen permeability coefficient of 3 × 10 ⁻¹⁷ m ⁴ / (N · s) or less. The metal is included in a dispersed state. In addition, the numerical value of the oxygen permeability coefficient in this invention is a measurement result in 25 degreeC.

Furthermore, in the present invention, not only flame retardancy against fire spread but also self-ignition properties are taken into account, and measures against ignition are added as a sheet after sheet processing from the manufacturing process for handling soft magnetic metals.
First, the shape effect of soft magnetic metal on the combustibility is examined. In general, in order to suppress the combustibility of metal fine particles, it is preferable to use particles having a large particle size without using fine powder (average particle size of 10 μm or less) having high combustibility. The aspect ratio may be 5 or more because of the flat shape, but the average particle diameter is 30 μm or more, more preferably 50 μm or more, and the effect of combustion resistance is excellent. Here, the average particle diameter means the average major axis when the shape of the soft magnetic metal is elongated. In the present invention, the average particle diameter and the average major axis are values obtained by measurement with a particle size distribution measuring apparatus. By making the soft magnetic metal also have such a size, it is possible to avoid recognition of dangerous goods. And the resistance with respect to the combustibility of the sheet | seat using this will also increase.
Next, the composition of the flat soft magnetic metal is examined. When the flat soft magnetic metal is made of an Fe-Cr alloy, the alloy component Cr has excellent corrosion resistance and is difficult to oxidize, so that the alloy is combined with the flame retardant and the organic binder. When combined, flame retardancy can be easily obtained. The Fe-Cr alloy may be at least one alloy selected from Fe-Ni-Cr, Fe-Si-Cr, and Fe-Ni-Si-Cr. Among them, the Fe—Ni—Si—Cr system is most effective as an electromagnetic wave suppressing effect. More preferably, the Fe—Cr alloy is coated with a material having an insulating property (in the present invention, this means a non-defective conductor). These metals show only representative composition metals, and other components may be contained in a trace amount in addition to these compositions.
Even as a soft magnetic metal powder, by adding Cr to the composition, it is possible to suppress the degree of easy oxidization of the soft magnetic metal and not to be a dangerous substance. With the above shape effect and composition effect, self-ignitability can be remarkably suppressed in each process of metal storage, metal flattening, filling and kneading, and thin sheet production. Since the flammability of the metal is lowered even during combustion, the flammability of the entire sheet is also suppressed.
It is important to improve the corrosion resistance of the metal and reduce the chance of contact between the metal and oxygen throughout the sheet formation. For this purpose, it is necessary to devise a processing method for reducing the oxygen permeation coefficient of the binder and to make a structure (morphology) in which the metal powder is dispersed and included with a small amount of the binder.

  In order to increase the oxygen index, it is often necessary to add a flame retardant to the organic binder, but the layer with a high oxygen index does not need to cover the entire organic binder, and the organic material that receives radiant heat You may be unevenly distributed in the surface layer part. As this uneven distribution, in other words, a material that partially or completely coats the surface, a material (epoxy resin, polyvinyl alcohol resin, ethylene vinyl alcohol resin, etc.) excellent in oxygen gas barrier properties that contains a flame retardant can be used.

The flame retardant magnetic sheet of the present invention uses an organic binder having a high oxygen index and a small oxygen permeability coefficient to suppress oxygen from entering the inside. Uniform and stable flame retardant by improving the gas barrier property of the sheet in order to prevent the soft magnetic metal being oxidized from coming into contact with oxygen and to delay the dispersal of volatiles from the inside. Sex is obtained.
When the soft magnetic metal contained in the organic binder is an Fe—Cr alloy, the soft magnetic metal itself has oxidation resistance (corrosion resistance), and therefore self-ignition property can be suppressed. Coupled with the low oxygen permeability of the system binder, the oxidation reaction of the entire sheet can be suppressed, and a more uniform and stable flame retardancy can be obtained.

  Further, when the organic binder contains a flame retardant together with the soft magnetic metal, the flame retardancy is further improved.

  The flame-retardant magnetic sheet of the present invention is an organic binder containing a flat soft magnetic metal and encapsulating it. Examples of the flat soft magnetic metal include magnetic stainless steel (Fe—Cr—Al—Si alloy), sendust (Fe—Si—Al alloy), permalloy (Fe—Ni alloy), silicon copper (Fe—Cu—Si alloy), Fe-Si alloy, Fe-Si-B (-Cu-Nb) alloy, Fe-Ni-Cr-Si alloy, Fe-Si-Cr alloy, Fe-Si-Al-Ni-Cr alloy and the like can be mentioned. Pure iron particles may also be used. Examples of the pure iron particles include carbonyl iron powder. All are metals with high thermal conductivity and are Fe-based alloys that are easily oxidized.

  In the present invention, it is particularly preferable to use an Fe—Cr alloy, and specifically, at least one alloy selected from Fe—Ni—Cr, Fe—Si—Cr, and Fe—Ni—Si—Cr. It is good to use. Since these Fe—Cr alloys are alloyed with Cr, which is effective in corrosion resistance, they are not dangerous materials and greatly reduce flammability. For example, in an Fe—Ni—Cr alloy, magnetism is exhibited by Fe and Ni to control magnetic characteristics, and corrosion resistance is imparted by Cr. These magnetic materials may be used alone or in combination. The average particle diameter of the soft magnetic metal is 30 μm or more, preferably 50 to 100 μm. The aspect ratio of the flat soft magnetic metal is 5 to 500, preferably 10 to 100.

These flat soft magnetic metals, particularly Fe—Cr alloys, are preferably coated on the surface with a material having oxygen gas barrier properties. By directly coating the soft magnetic metal, the corrosion resistance of the metal can be improved. Moreover, since the affinity with the binding material is improved by the coating treatment, the flat soft magnetic metal can be filled with high density. As the material for coating the surface of flat soft magnetic metal, organic polymer materials (rubber, thermoplastic elastomer, various plastics) that are the same as the binder used or have excellent affinity with the binder used, and others Materials (inorganic materials, ceramics, water glass treatment, etc.) can be used. The coating amount of the resin is preferably about 0.5 to 10% by weight based on the content of the coated flat soft magnetic metal. The coating agent preferably has an insulating property. This is because when a high amount of soft magnetic metal is filled, the resistance of the conduction effect due to contact between the metals becomes a resistance. The material to be coated may be flammable. Further, the material to be coated may have an oxygen index containing a flame retardant of 24 or more and / or an oxygen permeability coefficient of 3 × 10 ⁻¹⁷ m ⁴ / (N · s) or less. That is, because the coating itself functions as an oxidation resistant coating (oxygen gas barrier layer), it provides resistance against fire as well as rust prevention.
For the organic binder of the present invention, various organic polymer materials having a polymer oxygen index of 24 or more can be used. Polymers are generally easy to burn because they are inferior in heat resistance compared to materials such as metals and ceramics. There is an oxygen index (OI) as a scale representing the flammability of the polymer. This represents the necessary minimum combustion amount of the polymer, and it can be said that the higher the value, the more resistant to combustion. In other words, those having a high number are considered to be flame retardant, but adding a flame retardant to the polymer and increasing the flame retardant leads to an increase in the oxygen index number.
From Table 1, when flame retarding treatment and blending are not performed, the natural rubber (NR), ethylene propylene rubber (EPR), and nitrile rubber (NBR) often have an oxygen index of 22 or less. It is insufficient. However, chloroprene rubber (CR), silicone rubber (Q), and fluororubber (FK) exceed 25, and it can be said that they still have flame retardancy.
The oxygen index (OI) of the resin material is 17-18 for polyethylene, polypropylene, polystyrene, and methacrylic resin, 29 for polyamide, 45 for polyvinyl chloride, and 95 for polytetrafluoroethylene. The oxygen index is a measure for evaluating the continuity of combustion according to ASTM D 2863. If it is 21 or more, it does not burn continuously, and if it is 25 to 27 or more, it is said that continuous combustion is not performed unless it is an extreme condition.

The organic binder in the present invention has an oxygen permeability coefficient of 3 × 10 ⁻¹⁷ m ⁴ / (N · s) or less. As such an organic binder, various organic polymer materials having an oxygen permeability coefficient of 3 × 10 ⁻¹⁷ m ⁴ / (N · s) or less can be used, such as rubber, thermoplastic elastomer, Examples include polymer materials such as plastic. Table 2 shows the oxygen permeability coefficient of various rubbers. From Table 2, nitrile rubber (NBR) (including HNBR), chloroprene rubber (CR), butyl rubber (IIR), and urethane rubber (U) are generally used as organic binders in the present invention. The resulting silicone rubber has a high oxygen permeability, oxygen gas easily passes even if the oxygen index is high, and the internal soft magnetic metal is susceptible to oxidation. Therefore, it turns out that it is unsuitable as an organic type binder in the present invention.

  Further, the resin material generally has a significantly lower oxygen permeability than the rubber material, and therefore functions as a gas barrier layer even if a resin material having an oxygen permeability coefficient within the above range is used as a thin layer. Therefore, the resin material is suitable as an organic binder containing a flat soft magnetic metal. This reason is due to the difference in elastic modulus between the resin material and the rubber material. A resin having a high elastic modulus and high molecular cohesiveness is difficult to pass gas. However, although gas is difficult to pass through, high filling with metal powder or the like is difficult, and the processing method needs to be devised. Examples of such a resin material include various thermoplastic elastomers and various plastics. Therefore, a sheet body containing a soft magnetic metal may be coated with a thin layer of the resin material.

  In the present invention, a flat soft magnetic metal and a flame retardant are encapsulated by an organic binder having an oxygen permeability coefficient in the above range. For example, the binder contains a soft magnetic metal and is formed into a sheet shape. In addition, the case where the binding material covers the surface of the sheet body containing the flat soft magnetic metal and the flame retardant is also included. Furthermore, the case where the above binder containing the flame retardant and covering the surface of the soft magnetic metal is dispersed in the sheet body is also included.

  In order to encapsulate the flat soft magnetic metal powder with a binder, and to disperse the powder in an orientation and alignment manner, it is necessary to uniformly coat the whole with a minimum amount of the binder. In this case, there is a need for a molding method that allows the binder to flow sufficiently to reach the surface and internal details so that the highly filled soft magnetic metal powder is not directly exposed to the outside air. In particular, a material having a low oxygen permeability coefficient has high rigidity centering on the resin, and thus requires heating and pressurization. As a molding method, a solvent is used, and after mixing and stirring the binder and the flat soft magnetic powder, coating, volatilizing the solvent, heating and pressurizing so as to eliminate voids, and flowing the binder And the method in which crosslinking is performed in that state is the best. This is because, even if the oxygen permeability of the binder is low, the oxidation reaction of the soft magnetic metal cannot be suppressed if there is a lack of flow and there are voids (in other words, air passages).

The form in which soft magnetic metal is encapsulated in a dispersed state with a binder having a high oxygen index and a low oxygen permeability coefficient is close to the method of forming a char layer, which is one of flame retardant measures, on the outer periphery of the sheet To do. The method of making flame-retardant using a char layer (char) is to form a char layer on the surface of the organic material at the time of combustion, so that the char layer acts as a heat insulation layer and suppresses radiation to the organic material. Combustion is suppressed by suppressing vapor phase diffusion of decomposition volatiles from In order to utilize the effect of this carbonized layer, it is said that the polymer structure is composed of a benzene ring, a heterocyclic ring, S, N or the like. This is because the bond energy is higher than that of the aliphatic C—C bond. Inclusion of soft magnetic metal with a binder having a high oxygen index and a low oxygen permeability coefficient reduces the thermal conductivity due to the compounding of the metal, which gives the heat insulation effect of the char layer. It will be. Specifically, in order to encapsulate the soft magnetic metal, the soft magnetic metal may be uniformly dispersed inside the binder.
The oxygen permeability coefficient can be measured by the method B (isobaric method) of JIS K 7126.

  Examples of the thermoplastic elastomer include various thermoplastic elastomers such as polyvinyl chloride such as chlorinated polyethylene, polystyrene, polyolefin, polyurethane, polyester, and polyamide.

  Further, as various plastics, for example, polyethylene, polypropylene, AS resin, ABS resin, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymer, fluorine resin, acrylic resin, nylon, polycarbonate And thermoplastic resins such as polyethylene terephthalate, alkyd resin, unsaturated polyester, polysulfone, polyurethane, phenol resin, urea resin, and epoxy resin, or thermosetting resins. As these binder materials, appropriate materials are selected based on the oxygen permeability coefficient and the oxygen index.

Organic binder with an oxygen permeability coefficient at 25 ° C. of 3 × 10 ⁻¹⁷ m ⁴ / (N · s) or less and flame retardancy (a material having an oxygen index of 24 or more without flame retardant treatment) When is used, flame retardancy can be imparted without adding a flame retardant. Examples of such an organic binder include fluororubber and fluororesin. As a coating method in the case of a fluororesin, a surface coating of an organic material or an inorganic material can be performed using a thermal spraying technique or the like.

  In addition to the vulcanizing agent, the rubber may be appropriately blended with those conventionally used as rubber compounding agents such as a vulcanization accelerator, an anti-aging agent, a softening agent, a plasticizer, a filler, and a coloring agent. Can do. In addition to these, arbitrary additives can be used. For example, a predetermined amount of dielectric (carbon black, graphite, titanium oxide, etc.) for controlling the dielectric constant, and a heat conductive material (boron nitride, aluminum hydroxide, aluminum nitride, alumina, oxidation) for imparting heat dissipation characteristics Magnesium, zinc oxide, etc.) can be added by designing the material according to impedance matching to the unnecessary electromagnetic wave generated in the electronic equipment used and the temperature environment. Further, processing aids (such as lubricants) may be appropriately selected and added.

  Additives such as plasticizers and anti-aging agents contained in rubber materials have the problem of outgassing when they are used in products, but they are a binder with excellent resin thin layer coating and gas barrier properties. Using is effective as a countermeasure for reducing outgas.

  In the present invention, it is preferable that the flame retardant is included in the organic binder together with the flat soft magnetic metal in order to further improve the flame retardancy. As the flame retardant, for example, at least one selected from phosphoric flame retardants, hydroxide flame retardants, bromine flame retardants, and metal compound flame retardants can be used. The flame retardant is included in the binder in an amount of 1 to 40% by volume, preferably 5 to 30% by volume.

  Examples of the phosphoric acid flame retardant include phosphoric acid ester, ammonium polyphosphate, and red phosphorus. Examples of the hydroxide flame retardant include magnesium hydroxide, aluminum hydroxide, zirconium hydroxide, calcium sulfate hydrate, zinc borate hydrate and the like. Examples of brominated flame retardants include decabromodiphenyl oxide, 2,2-bis (3,5-dibromo-4-hydroxyphenyl), 1,2,5,6,9,10-hexabromocyclododecane, hexabromo Examples thereof include benzene, tetrabromophthalic anhydride, pentabromotoluene and the like. Examples of the metal compound flame retardant include antimony trioxide, molybdenum oxide, manganese oxide, chromium oxide, and iron oxide.

  A particularly preferable flame retardant is a flame retardant added with decabromodiphenyl oxide and antimony trioxide, and a high flame retardant effect can be obtained in a small amount. In this case, a flame retardant product in which decabromodiphenyl oxide and antimony trioxide are mixed, for example, a trade name “Polysafe FCP-5” sold by Ajinomoto Fine Technology, Inc. may be used.

  In the case of producing a sheet using a flat soft magnetic metal and an organic binder as main components, the blending ratio is preferably 30 to 70% by volume of the flat soft magnetic metal and 30 to 70% by volume of the binder. It is more preferable that they are 40-60 volume% of magnetic metals and 40-60 volume% of binders. If the content of the flat soft magnetic metal is less than 30% by volume and the content of the binder exceeds 70% by volume, the desired electromagnetic interference suppression effect cannot be obtained. Conversely, when the content of the flat soft magnetic metal exceeds 70% by volume and the content of the binder is less than 30% by volume, it becomes difficult to encapsulate the flat soft magnetic metal, and the obtained electromagnetic interference suppressor Processing becomes difficult because it becomes brittle.

  Moreover, in order to improve the dispersibility of a flat soft magnetic metal, you may add 1 to 5 weight% of dispersing agents with respect to content of a flat soft magnetic metal. Examples of the dispersant include higher fatty acids or higher fatty acid salts. Examples of the higher fatty acid herein include stearic acid, lauric acid, maleic acid, behenic acid and the like. Examples of higher fatty acid salts include aluminum salts, sodium salts, potassium salts, lithium salts, barium salts, calcium salts, and magnesium salts of these higher fatty acids. These may be used alone or blended. When blended and used, the ratio of higher fatty acid / higher fatty acid salt is preferably 20/80 to 80/20 by weight.

  The magnetic sheet of the present invention has a thickness of about 1 μm to 1 mm, preferably about 10 μm to 0.5 mm.

The magnetic sheet having insulating properties according to the present invention includes a noise suppression sheet, a magnetic shield sheet, and a magnetic shield sheet for improving antenna communication when mounting an RFID function in a small information device, which requires high magnetic properties. Used in various electronic devices such as home electric appliances such as TVs, computers such as personal computers, mobile communication devices such as mobile phones, and medical devices. Unwanted electromagnetic waves emitted from these electronic devices are used in other electronic devices and electronic parts, It is possible to suppress the occurrence of malfunction by affecting the circuit board. Specifically, electromagnetic interference caused by interference of unnecessary electromagnetic waves is effectively suppressed by being disposed inside or around the electronic devices. For this reason, as a usage form of the electromagnetic interference suppressor of the present invention, for example, a sheet-like magnetic sheet is appropriately cut and pasted in the vicinity of the noise source of the apparatus, or applied as described above to the noise source of the apparatus or in the vicinity thereof. For example, an electromagnetic interference suppressor is formed.
Furthermore, it can also be used as a flame retardant compounding of low-frequency (10 MHz or less) compatible magnetic shield, GHz band wireless communication, wireless LAN, and ETC radio wave absorber.

  Hereinafter, although an electromagnetic interference suppression object of the present invention is explained in detail using an example and a comparative example, the present invention is not limited to the following examples.

50% by volume of flat soft magnetic metal powder (Fe—Si—Al-based metal, average particle size = 55 μm, average aspect ratio = about 20) is added to the fluororubber, and blended with a vulcanizing agent in a small kneader. The mixture was kneaded and a magnetic sheet was obtained with a calender roll. Triallyl isocyanurate and peroxide were used as the crosslinking agent, and the crosslinking conditions were 160 ° C. × 10 minutes. The oxygen permeability coefficient of fluororubber is 1 × 10 ⁻¹⁷ m ⁴ / (N · s) (25 ° C.), and the oxygen index is 68. This sheet did not contain any flame retardant. The flame retardancy of this magnetic sheet was evaluated according to the method described in UL94. The sheet thickness when the flame retardancy was evaluated was 100 μm. As a result, evaluation equivalent to UL94V0 showing good flame retardancy was obtained.

40% by volume of flat soft magnetic metal powder (Fe—Ni—Si—Cr-based metal, average particle size = 40 μm, average aspect ratio = about 20) was added to HNBR (hydrogenated acrylonitrile-butadiene rubber). To this mixture, 20% by volume of a flame retardant composed of decabromodiphenyl oxide and antimony trioxide (“Ajinomoto Fine Technology Co., Ltd.“ Polysafe FCP-5 ”) was added and kneaded in a solvent with a vulcanizing agent. After coating, the film was dried and cured, and then subjected to hot press molding at 180 ° C. for 4 minutes to obtain a magnetic sheet. HNBR has an oxygen permeability coefficient of 1.2 × 10 ⁻¹⁷ m ⁴ / (N · s) ml (25 ° C.) and an oxygen index of 27. The flame retardancy of this magnetic sheet was evaluated according to the method described in UL94. The sheet thickness when the flame retardancy was evaluated was 100 μm. As a result, evaluation equivalent to UL94V0 showing good flame retardancy was obtained. In addition, although the coating alone did not reach the state in which the binder contained the soft magnetic metal, the formation of a skin layer covering the soft magnetic metal powder on the surface layer portion was confirmed by the effect of press molding, and the soft magnetic metal powder was directly Can be prevented from being exposed to the outside air, and the soft magnetic metal can be prevented from being oxidized by a binder having a low oxygen permeability coefficient. When this sheet was subjected to a salt spray test (JIS Z2371 salt spray test method, hereinafter the same), no rust was found.

図２にその測定結果を示す。実施例３にて得られたシートの材料定数を図３に示す。

本実施例３での１００ＭＨｚにおける複素比透磁率（実数部）μ'は２８、複素比透磁率（虚数部）μ”は１６であり、また１ＧＨｚにおける複素比透磁率（実数部）μ'は１１、複素比透磁率（虚数部）μ”は１０である。ＵＬ９４規格のＶ０相当の難燃性を有しながら、伝送損失（１ＧＨｚ）は高く、電磁干渉抑制シート４として優れた特性を持つことがわかる。難燃性と高性能を同時に達成しているといえる。本実施例も、実施例２と同様に、撹拌及び塗工後、熱プレスにより、結合材の流動及び架橋を付与したため、配向、配列して分散した軟磁性金属粉を結合材で内包した状態の構造を固定化でき、結合材の酸素透過係数の低さを活かすことができた。このシートに塩水噴霧試験を施したところ、錆発生は見られなかった。また表面抵抗率は１．８×１０⁸Ω／□であった。
A magnetic paint was prepared with the composition shown in Table 3 (unit: parts by weight), and applied to a PET (peeling support) and dried by a doctor blade method to form a sheet. Next, the peeling support was peeled off, followed by press molding (surface pressure = 15 MPa, crosslinking conditions = 170 ° C. × 8 minutes) to obtain a 100 μm-thick electromagnetic interference suppression sheet. About the obtained electromagnetic interference suppression sheet | seat, 1 GHz transmission loss was measured. Further, a flame retardant test was performed based on the UL94 standard. The results are also shown in Table 3. Here, the flat soft magnetic powder (Fe—Ni—Si—Cr-based metal, average particle size = 40 μm, average aspect ratio = about 20) is 40% by volume, and the binder is 43% by volume. EVA resin (binding material) is EPDM having an oxygen permeability coefficient at 25 ° C. of 15 × 10 ⁻¹⁷ m ⁴ / (N · s) and an oxygen index of 22, but by adding a flame retardant, the oxygen index is 32 It became. As the cross-linking agent, a peroxide (dicumyl peroxide) is used.
A microstrip line with impedance Z = 50Ω was used for measurement of transmission loss. The microstrip line is a method for measuring transmission loss of nearby noise that is widely used due to its structure suitable for mounting surface-mounted components and ease of production. FIG. 1 is a schematic diagram of a transmission loss measuring apparatus using a microstrip line. In this embodiment, a linear conductor path 2 is provided on the surface of the insulator substrate 1, and an electromagnetic interference suppression sheet 4 is placed on the conductor path 2. Both ends of the conductor path 2 are connected to a network analyzer (not shown). Then, with respect to the incident wave indicated by the arrow A, the reflection amount (dB) (indicated by the arrow S11) and the transmission amount (dB) (indicated by the arrow S21) from the placement site of the electromagnetic wave absorbing material 4 are measured. The transmission loss (absorption amount) was calculated from the following equation.

FIG. 2 shows the measurement results. The material constants of the sheet obtained in Example 3 are shown in FIG.

In Example 3, the complex relative permeability (real part) μ ′ at 100 MHz is 28, the complex relative permeability (imaginary part) μ ″ is 16, and the complex relative permeability (real part) μ ′ at 1 GHz is 11. The complex relative permeability (imaginary part) μ ″ is 10. It can be seen that the transmission loss (1 GHz) is high and has excellent characteristics as the electromagnetic interference suppression sheet 4 while having flame resistance equivalent to V0 of the UL94 standard. It can be said that flame retardancy and high performance are achieved at the same time. In this example, as in Example 2, after the stirring and coating, the binder was flowed and crosslinked by hot pressing, so that the soft magnetic metal powder dispersed and aligned and aligned was encapsulated in the binder. Thus, the low oxygen permeability coefficient of the binder could be utilized. When this sheet was subjected to a salt spray test, no rust was observed. The surface resistivity was 1.8 × 10 ⁸ Ω / □.

To EPDM having an oxygen permeability coefficient at 25 ° C. of 15 × 10 ⁻¹⁷ m ⁴ / (N · s) and an oxygen index of 17, the same amount of the same soft magnetic powder as in Example 1 was added, and the vulcanizing agent was added to the solvent. Kneading and stirring, coating with a control coater, drying and curing, followed by hot press molding at 180 ° C. for 4 minutes to obtain a magnetic sheet having a thickness of 100 μm. This is coated with a resin material (flame retardant vinyl chloride resin enamel) having an oxygen permeability coefficient at 25 ° C. of 1.5 × 10 ⁻¹⁷ m ⁴ / (N · s) and an oxygen index of 49 so as to enclose the sheet. did. Coating was performed by immersing a coating solution obtained by diluting a resin material with thinner on the sheet surface. Heat treatment (120 ° C. × 1 hour) was applied to remove the solvent and cure the coating layer. Since the thickness of the coating layer was 35 μm, the sheet thickness was 170 μm when flame retardancy was evaluated. At this time, when the same amount of the same flame retardant as in Example 1 was added to the coating layer and EPDM in the same amount as in Example 1, the flame retardance of UL94 was evaluated based on the evaluation of flame retardancy of UL94. Flame retardancy was obtained.

[Comparative Example 1]
The same amount of the same soft magnetic powder as in Example 2 was added to EPDM, and 10% by volume of the same flame retardant was added to obtain a magnetic sheet having the same thickness as in Example 1. The oxygen permeability coefficient of this EPDM is 15 × 10 ⁻¹⁷ m ⁴ / (N · s) (25 ° C.), and the oxygen index is 20. The flame retardancy of this sheet was evaluated according to the method described in UL94. As a result, it was an evaluation equivalent to UL94V2 on the flame retardance scale, and the flame retardancy was considerably inferior.

[Comparative Example 2]
50% by volume of flat sendust (Fe—Si—Al alloy, average particle size = 15 μm, average aspect ratio = about 20) powder was added to the HNBR rubber. 11 vol.% Of the same flame retardant (“Polysafe FCP-5”) as in Example 1 was added to this mixture, and a magnetic sheet was obtained in the same manner as in Example 1. The oxygen permeability coefficient of HNBR was 1.2 × 10 ⁻¹⁷ m ⁴ / (N · s) (25 ° C.), but the oxygen index was 22. The flame retardancy of this magnetic sheet was evaluated according to the method described in UL94. The sheet thickness when the flame retardancy was evaluated was the same as in Example 1. As a result, evaluation equivalent to UL94V1 showing good flame retardancy was obtained, but V0 was not achieved.

It is the schematic of the transmission loss measuring apparatus by the microstrip line used for the measurement of transmission loss. It is a measurement result of a transmission loss characteristic. It is a graph which shows the material constant of the obtained sheet | seat.

Explanation of symbols

  4: Electromagnetic interference suppression sheet, 11: Electromagnetic interference suppression body

Claims (7)

A flat soft magnetic metal is included in a dispersed state in an organic binder having an oxygen index of 24 or more and an oxygen permeability coefficient of 3 × 10 ^-17 m ⁴ / (N · s) or less. A flame retardant magnetic sheet.   2. The flame-retardant magnetic sheet according to claim 1, wherein the flat soft magnetic metal is an Fe—Cr alloy having an aspect ratio of 5 or more and an average particle diameter of the metal of 30 μm or more.   The flame-retardant magnetic sheet according to claim 2, wherein the Fe-Cr alloy is at least one alloy selected from Fe-Ni-Cr, Fe-Si-Cr, and Fe-Ni-Si-Cr.   The magnetic sheet according to claim 2 or 3, wherein the Fe-Cr alloy is coated with a material having an oxygen gas barrier property.   2. At least one flame retardant selected from a phosphoric flame retardant, a hydroxide flame retardant, a bromine flame retardant, and a metal compound flame retardant is encapsulated by an organic binder together with the flat soft magnetic metal. The magnetic sheet in any one of -4.   The magnetic sheet according to claim 1, wherein the organic binder contains the flat soft magnetic metal and is formed into a sheet shape. The magnetic sheet according to any one of claims 1 to 5, wherein the organic binder covers the surface of the sheet body containing the flat soft magnetic metal.

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