JP2007095829A - Electromagnetic wave absorbing sheet and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorbing sheet capable of raising radiation property by enhancing thermal conductivity, and reducing the number of manufacturing processes and the thickness of the whole sheet. <P>SOLUTION: The sheet includes a matrix resin 2 having light curing property and thermal curing property; and magnetic fillers 3 having a density distribution to be changed along a thickness direction, where the density of the magnetic fillers 3 is higher at one surface side 4 being vertical relative to the thickness direction, and is lower on the other surface side 5 compared with the one surface side 4. When the electromagnetic wave absorbing sheet 1 is made to adhere on a heat source 6 such as a semiconductor element, the other surface side 5 is made to contact with the heat source 6. Then the matrix resin 2 follows the recessed/projected shape of the surface of the heat source 6, so as to raise adhesion between the heat source 6 and the electromagnetic wave absorbing sheet 1. Consequently, thermal resistance is reduced in a part near a boundary between the heat source 6 and the sheet 1, so that the thermal conductivity is raised and the radiation property is raised. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electromagnetic wave absorbing sheet containing a matrix resin and a magnetic filler, and a method for producing the electromagnetic wave absorbing sheet.

  Electronic devices such as mobile phones, PDAs (Personal Digital Assistance), and personal computers (PCs) will function due to the effects of natural phenomena such as radiated electromagnetic waves from other nearby devices, lightning, and solar activity unless measures are taken. May be affected by degradation, malfunction, stoppage, loss of records, etc. In addition, electromagnetic waves emitted by the electronic device itself may adversely affect the operation of other devices.

  In particular, as electronic devices become more highly integrated, smaller, lighter, and more advanced, the adverse effects of electromagnetic interference increase, so it is essential to take some measures against the electronic devices.

The electromagnetic wave absorbing sheet is a CPU (central processing unit), a high-speed IC (
Electromagnetic interference is suppressed by absorbing electromagnetic waves coming from outside by being attached to a semiconductor element such as an integrated circuit) and electromagnetic waves emitted by the semiconductor element itself.

  Moreover, since the electromagnetic wave absorbing sheet is affixed to the semiconductor element, it is desirable to have thermal conductivity in order to cool the generated semiconductor element. Furthermore, the electromagnetic wave absorbing sheet is a mixture of soft magnetic powder and matrix resin, which is molded into a sheet body, and absorbs electromagnetic waves by converting the energy of electromagnetic waves into thermal energy and dissipating it. Conductivity is as important as electromagnetic wave absorption characteristics.

  The electromagnetic interference suppressor described in Patent Document 1 is perpendicular to the thickness direction of a composite magnetic layer formed by forming a mixture of soft magnetic powder and a binder into a sheet having a thickness of 3 mm or less. Productivity, handleability, heat resistance, thermal conductivity, and the like are improved by disposing a polymer material film having a thickness of 0.5 mm or less on at least one of these surfaces.

JP 2004-127986 A

  A conventional electromagnetic wave absorbing sheet is disposed between a semiconductor element and a heat sink, suppresses electromagnetic interference, and transmits heat generated in the semiconductor element to the heat sink. At this time, like the electromagnetic interference suppressor described in Patent Document 1, the thermal resistance is lowered by increasing the adhesion between the semiconductor element, which is a heat source, and the electromagnetic wave absorbing sheet by the polymer material film.

  As described above, in the conventional electromagnetic wave absorbing sheet, a member for increasing the adhesion to the semiconductor element is necessary, and thus a manufacturing process for bonding the members becomes indispensable, and further, the entire electromagnetic wave absorbing sheet including the member It is difficult to reduce the thickness. In addition, since thermal resistance is generated between the member for improving the adhesion and the magnetic layer, there is a limit to the reduction in thermal resistance as long as the member for improving the adhesion is used.

  An object of the present invention is to provide an electromagnetic wave absorbing sheet capable of improving heat dissipation by increasing thermal conductivity, and further reducing the number of manufacturing steps and reducing the thickness of the entire sheet. It is.

The present invention is an electromagnetic wave absorbing sheet comprising a matrix resin and a magnetic filler,
The matrix resin is an electromagnetic wave absorbing sheet, wherein the matrix resin has photocurability and thermosetting, and the magnetic filler has a concentration distribution that varies along a thickness direction.

  Further, the invention is characterized in that the magnetic filler is distributed at a high concentration on one surface side perpendicular to the thickness direction, and is distributed at a lower concentration on the other surface side than on the one surface side.

In the invention, it is preferable that the magnetic filler is a soft magnetic powder.
Moreover, this invention is characterized by further including a heat conductive filler.

  Further, the present invention provides a light irradiation treatment in which light irradiation is performed in a state where a centrifugal force is applied to a reactive composition including a reactive vehicle having a photoreactivity and a thermal reactivity and a magnetic filler, and the reactive composition The manufacturing method of the electromagnetic wave absorption sheet | seat characterized by including the heat processing which heats with respect to a thing.

  According to this invention, it is an electromagnetic wave absorption sheet containing matrix resin and a magnetic filler. The matrix resin has photocurability and thermosetting. The magnetic filler has a concentration distribution that varies along the thickness direction.

  When the concentration distribution of the magnetic filler is, for example, distributed at a high concentration on one surface side perpendicular to the thickness direction and distributed at a lower concentration on the other surface side than the one surface side, a heat source, an electromagnetic wave absorbing sheet, Increased adhesion. Thereby, the thermal resistance in the vicinity of the boundary between the heat source and the electromagnetic wave absorbing sheet decreases, the thermal conductivity increases, and the heat dissipation improves.

  Furthermore, since a member that enhances adhesion to a heat source such as a polymer material film is not required as in the prior art, the manufacturing process for bonding the members can be omitted, and the thickness of the entire electromagnetic wave absorbing sheet can be reduced. . In addition, since no thermal resistance is generated between the member for improving the adhesion and the magnetic layer, the thermal resistance can be further reduced as compared with the prior art.

  According to the invention, the magnetic filler is preferably a soft magnetic powder from the viewpoint of electromagnetic wave absorption characteristics.

  Moreover, according to this invention, a heat conductive filler is further included. By including a heat conductive filler, the thermal resistance of the whole electromagnetic wave absorption sheet can be reduced, and heat dissipation is further improved.

  Moreover, according to this invention, an electromagnetic wave absorption sheet is manufactured by hardening the reactive composition containing the reactive vehicle which has photoreactivity and thermal reactivity, and a magnetic filler.

  When the reactive composition is cured, a light irradiation treatment for performing light irradiation in a state where a centrifugal force is applied to the reactive composition and a heat treatment for heating the reactive composition are performed.

Since the outer shape can be maintained by curing the surface layer portion by the light irradiation reaction, it can be quickly taken out from the reactor and subjected to other treatment such as heat treatment in the next step.
Thereby, productivity of an electromagnetic wave absorption sheet can be improved significantly.

  The present invention is an electromagnetic wave absorbing sheet including a matrix resin and a magnetic filler, wherein the matrix resin has photocuring and thermosetting properties, and the magnetic filler has a gradient having a concentration distribution that varies along the thickness direction. It is characterized by being a functional material.

  FIG. 1 is a cross-sectional view showing the configuration of the electromagnetic wave absorbing sheet 1. Since the magnetic filler 3 has a concentration distribution along the thickness direction inside the matrix resin 2, the magnetic filler 3 is distributed at a high concentration on the one surface side 4 perpendicular to the thickness direction, and on the other surface side 5. 3 is distributed at a lower density than the one side 4. For example, the concentration difference of the magnetic filler is 50 vol% or more, preferably 60 vol% or more, more preferably 70 vol% or more, on the one surface side and the other surface side.

  When affixing such an electromagnetic wave absorbing sheet 1 to a heat source 6 such as a semiconductor element, the other surface side 5 where the magnetic filler 3 is distributed at a low concentration is brought into contact with the heat source 6, so that the matrix resin 2 becomes the surface of the heat source 6. This improves the adhesion between the heat source 6 and the electromagnetic wave absorbing sheet 1. Thereby, the thermal resistance in the vicinity of the boundary between the heat source 6 and the electromagnetic wave absorbing sheet 1 is lowered, the thermal conductivity is increased, and the heat dissipation is improved.

  Since the member which improves adhesiveness with heat sources, such as the film of a polymeric material conventionally, is not required, the manufacturing process for bonding a member can be abbreviate | omitted, and the thickness of the electromagnetic wave absorption sheet whole can be made thin. In addition, since no thermal resistance is generated between the member for enhancing the adhesion and the magnetic layer, the thermal resistance can be further reduced.

  Since the magnetic filler is distributed at a high concentration on one side of the electromagnetic wave absorbing sheet, the electromagnetic wave absorbing characteristics can be improved.

  The higher the magnetic filler concentration is, the higher the magnetic permeability μ ′ and μ ″ tends to increase, and therefore the electromagnetic wave absorption characteristics of the electromagnetic wave absorbing sheet are improved.

  When the magnetic filler has a concentration distribution that does not change along the thickness direction, that is, when the magnetic filler is uniformly distributed throughout the electromagnetic wave absorbing sheet, when the magnetic filler concentration exceeds a predetermined concentration, the ratio of the matrix resin contained in the entire sheet is It becomes difficult to form the sheet itself. On the other hand, in the present invention, since the concentration of the magnetic filler is increased on one side of the electromagnetic wave absorbing sheet, the molding becomes difficult when the local concentration on one side is uniformly distributed. Molding is possible even when the concentration is higher than the concentration.

  The electromagnetic wave absorbing sheet may include a thermally conductive filler. By including a heat conductive filler, the thermal resistance of the whole electromagnetic wave absorption sheet can be reduced, and heat dissipation is further improved.

  The electromagnetic wave absorbing sheet as described above is in a state where centrifugal force is applied by rotating a cylindrical reactor or the like to a reactive composition containing a reactive vehicle having a photoreactivity and a thermal reactivity and a magnetic filler. It is obtained by irradiating light and curing at least a part of the reactive composition. The whole may be cured by light irradiation, or the whole may be cured by heating.

  Light irradiation and heating may be performed at the same time, or only light irradiation may be performed first, and then only heating may be performed. First, only light irradiation is performed, and light irradiation and heating are performed, and only heating is performed. It may be. What is necessary is just to set the timing of light irradiation and a heating according to the characteristic of the composition of a reactive composition and an electromagnetic wave absorption sheet.

(Matrix resin)
As the matrix resin, various organic polymer materials can be used, and examples thereof include polymer materials such as rubber, thermoplastic elastomer, and various plastics.

  Examples of rubber include natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, ethylene-propylene rubber, ethylene-vinyl acetate rubber, butyl rubber, chloroprene rubber, nitrile rubber, acrylic rubber, ethylene acrylic rubber, epi Synthetic rubbers such as chlorohydrin rubber, fluorine rubber, urethane rubber, silicone rubber, chlorinated polyethylene rubber, hydrogenated nitrile rubber (HNBR) and their derivatives, or those modified by various modification treatments can be used. In particular, silicone rubber is preferable.

  These rubbers can be used alone or in combination. In addition to vulcanizing agents, rubbers may be appropriately mixed with vulcanization accelerators, anti-aging agents, softeners, plasticizers, fillers, coloring agents, and the like that have been conventionally used as rubber compounding agents. it can. In addition to these, arbitrary additives can be used. For example, a predetermined amount of dielectric (carbon black, graphite, titanium oxide, etc.) is used to control the dielectric constant and conductivity according to impedance matching to unnecessary electromagnetic waves generated in the electronic equipment used and the temperature environment. Material design can be added. Further, processing aids (lubricants, dispersants) may be appropriately selected and added.

  As thermoplastic elastomer, for example, chlorinated polyethylene such as chlorinated polyethylene, ethylene-based copolymer, acrylic, ethylene-acrylic copolymer, urethane, ester, silicone, styrene, amide, etc. Elastomers and their derivatives can be used.

  In addition, various plastics include, for example, polyethylene, polypropylene, AS resin (acrylonitrile styrene copolymer), ABS resin (acrylonitrile butadiene styrene copolymer), polystyrene-based resins such as polystyrene, polyvinyl chloride, and polyvinylidene chloride, and polyacetic acid. Thermoplastic resins such as vinyl, ethylene-vinyl acetate copolymer, fluororesin, silicone resin, acrylic resin, nylon, polycarbonate, polyethylene terephthalate, alkyd resin, unsaturated polyester, polysulfone, urethane resin, epoxy resin and the like Derivatives. As these binders, low molecular weight oligomer types and liquid types can be used. Any material can be selected as long as it becomes a sheet after molding by heat, pressure, ultraviolet rays, a curing agent, or the like.

  In the present invention, since it is cured by light irradiation treatment and heat treatment, the reactive vehicle contained in the reactive composition is the matrix resin after the curing reaction, and is a photocurable monomer, photocurable Examples include oligomers or photocurable prepolymers, light / thermosetting monomers, light / thermosetting oligomers, or light / thermosetting prepolymers.

  Acrylic monomers or oligomers, epoxy monomers or oligomers, imide monomers or oligomers can be used. As the acrylic monomer or oligomer, epoxy acrylate, polyester acrylate, isobornial acrylate and the like are preferable. Further, monomers and oligomers having calixarene may be used.

(Magnetic filler)
As the magnetic filler, it is preferable to use soft magnetic powder. Examples of the soft magnetic powder 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, etc. are mentioned. Further, ferrite or pure iron particles may be used. Examples of the ferrite include soft ferrite such as Mn—Zn ferrite, Ni—Zn ferrite, Mn—Mg ferrite, Mn ferrite, Cu—Zn ferrite, and Cu—Mg—Zn ferrite, or hard ferrite that is a permanent magnet material. . Examples of the pure iron particles include carbonyl iron powder.

  The shape (spherical, flat, fibrous, etc.) of the soft magnetic powder is not particularly limited, but it is preferable to use a spherical or substantially spherical shape because the electromagnetic wave absorbing sheet can be filled with a high filling rate. These magnetic powders may be used alone or in combination. The average particle diameter of the magnetic powder or the long diameter of the flat soft magnetic powder is 0.1 to 500 μm, preferably 1 to 200 μm. The aspect ratio of the flat soft magnetic powder is 2 to 500, preferably 10 to 100. In addition, since the above-mentioned soft magnetic powder (magnetic metal or ceramics) also has thermal conductivity, it can also serve as a thermally conductive filler.

(Thermal conductive filler)
Various known materials can be used as the heat conductive filler. In particular, when a thermally conductive filler is used in combination with a soft magnetic powder that is a magnetic filler, boron nitride, aluminum nitride, silicon nitride, aluminum oxide, zinc oxide, silicon oxide, magnesium oxide and It is preferably at least one selected from ferrite.

(Other additives)
Other additives include polymerization initiators, viscosity reducing agents, polymerization inhibitors, thixotropic agents, antifoaming agents, silane coupling agents, plasticizers, solvents, non-reactive polymers, and colorants (pigments and dyes). Etc. can be used.

  The polymerization initiator is selected according to the vehicle used. The photocuring reaction includes an acrylic radical polymerization reaction and an epoxy cationic polymerization reaction, and a cationic polymerization initiator or a radical polymerization initiator is added by a vehicle.

  In addition, it is preferable that the reactive composition of this invention is a non-volatile composition which does not contain solvents, such as an organic solvent and water. By making it non-volatile, the time required for removing the transpiration of the solvent becomes unnecessary.

The substance constituting the reactive composition will be illustrated more specifically.
Examples of lipophilic acrylic monomers include dicyclopentanyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, benzyl tribromo (meth) acrylate, and phenoxyethyl tribromo (meth) acrylate. Biphenylethoxy (meth) acrylate, biphenyl epoxy (meth) acrylate, naphthylethoxy (meth) acrylate, fluorene epoxy (meth) acrylate, bisphenol A di (meth) acrylate, bisphenol A tetrabromodi (meth) acrylate , Ethoxy modified di (meth) acrylate bisphenol A, tetrabromoethoxy modified di (meth) acrylate bisphenol A, di (meth) acrylate bisphenol A epoxy, ethoxy modified di (meth) acrylate bisphenol A epoxy, Tetoraburomoji (meth) acrylate bisphenol A epoxy, such as tetra-bromoethoxy-modified di (meth) acrylate of bisphenol A epoxy and the like.

  Examples of hydrophilic acrylic monomers include 2-hydroxyethyl (meth) acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-methacryloyloxyethyl-2-hydroxypropyl acrylate, N, N-dimethylacrylamide, N, N-diethylacrylamide, acryloylmorpholine, N, N-dimethylaminopropylacrylamide, isopropylacrylamide, dimethylaminoethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meta ) Glycerin (meth) such as ethylene glycol-based (meth) acrylate such as acrylate, trimethylolpropane tri (meth) acrylate Chestnut rates esters, (meth) acrylic acid ester of hexanediol di (meth) diols such as acrylate, and Neopenchiruji (meth) acrylate.

  Epoxy resins include aromatic epoxy resins, alicyclic epoxy resins, and aliphatic epoxy resins, and polyglycidyl ethers of polyhydric phenols having at least one aromatic nucleus or their alkylene oxide adducts as aromatic epoxy resins. For example, glycidyl ether and epoxy novolac resin produced by the reaction of bisphenol A, bisphenol F or its alkylene oxide adduct and epichlorohydrin can be mentioned. In addition, as the alicyclic epoxy resin, a polyglycidyl ether of a polyhydric alcohol having at least one alicyclic ring, or a cyclohexene or cyclopentene ring-containing compound is mixed with an appropriate oxidizing agent such as hydrogen peroxide or peracid. Examples thereof include cyclohexene oxide or cyclopentene oxide-containing compound obtained by epoxidation.

  Examples of alicyclic epoxy resin monomers include hydrogenated bisphenol A diglycidyl ether, 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate, 2- (3,4-epoxycyclohexyl-5, 5-spiro-3,4-epoxy) cyclohexane-meta-dioxane, bis (3,4-epoxycyclohexylmethyl) adipate, vinylcyclohexene dioxide, 4-vinylepoxycyclohexane, bis (3,4-epoxy-6-methyl) Cyclohexyl-3,4-epoxy-6-methylcyclohexane) carboxylate, methylenebis (3,4-epoxycyclohexane), dicyclopentadiene diepoxide, ethylene glycol di (3,4-epoxycyclohexylmethyl) Ether, ethylenebis (3,4-epoxycyclohexane carboxylate), epoxy hexahydrophthalic acid dioctyl and epoxy hexahydrophthalic acid di-2-ethylhexyl and the like.

  Examples of aliphatic epoxy resin monomers include polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, polyglycidyl esters of aliphatic long-chain polybasic acids, homopolymers and copolymers of glycidyl acrylate and glycidyl methacrylate, and the like. Typical examples are 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, polyethylene glycol diglycol. One or more alkylene oxides for aliphatic polyhydric alcohols such as glycidyl ether, diglycidyl ether of polypropylene glycol, ethylene glycol, propylene glycol and glycerin Polyglycidyl ethers of polyether polyols obtained by adding include diglycidyl esters of aliphatic long-chain dibasic acids. Furthermore, monoglycidyl ether of higher aliphatic alcohol, phenol, cresol, butylphenol or polyether alcohol monoglycidyl ether obtained by adding alkylene oxide to these, glycidyl ester of higher fatty acid, epoxidized soybean oil, epoxy butyl stearate Octyl epoxy stearate, epoxidized linseed oil, epoxidized polybutadiene sugar and the like.

  Further, examples of the cationic polymerization reactive substance other than the epoxy resin include oxetane compounds such as trimethylene oxide, 3,3-dimethyloxetane, and 3,3-dichloromethyloxetane; tetrahydrofuran, 2,3-dimethyltetrahydrofuran and the like. Oxolane compounds; cyclic acetal compounds such as trioxane, 1,3-dioxolane, 1,3,6-trioxane cyclooctane; cyclic lactone compounds such as β-propiolactone and ε-caprolactone; ethylene sulfide, thioepichloro Thiirane compounds such as hydrin; 1,3-propyne sulfide, thietane compounds such as 3,3-dimethylthietane; ethylene glycol divinyl ether, alkyl vinyl ether, 3,4-dihydropyran-2-methyl (3,3) 4- Dihydropyran-2-carboxylate), vinyl ether compounds such as triethylene glycol divinyl ether; spiro orthoester compounds obtained by reaction of epoxy compounds with lactones; ethylenically unsaturated compounds such as vinylcyclohexane, isobutylene, polybutadiene and And derivatives of the above compounds.

Examples of cationic polymerization initiators include diazonium salts, iodonium salts, sulfonium salts, selenium salts, pyridinium salts, ferrocenium salts, phosphonium salts, and thiopyrinium salts, but aromatics that are relatively thermally stable. Onium salt polymerization initiators such as iodonium salts and aromatic sulfonium salts are preferred. In order to activate the onium salt polymerization initiator, irradiation with ultraviolet rays and visible light is preferable. When onium salt polymerization initiators such as aromatic iodonium salts and aromatic sulfonium salts are used, the anions include BF ₄ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , PF ₆ ⁻ , B (C ₆ F ₅ ) ₄ ^{− and the} like. Is mentioned.

As a commercial product of a cationic polymerization initiator, for example, Cyracure UVI-6974 (mixture of bis [4- (diphenylsulfonio) phenyl] sulfide bishexafluoroantimonate and diphenyl-4-thiophenoxyphenylsulfonium hexafluoroantimonate) Syracure UVI-6990 (hexafluorophosphate of UVI-6974) (manufactured by Union Carbide), Adekaoptomer SP-151, Adekaoptomer SP-170 (Bis [4- (di (4- (2-hydroxy Ethyl) phenyl) sulfonio) phenyl] sulfide), Adekaoptomer SP-150 (hexafluorophosphate of Adekaoptomer SP-170), Adekaoptomer SP-171 (above, manufactured by Asahi Denka), and DTS-10 DTS-103, NAT-103, NDS-103 ((4-hydroxynaphthyl) -dimethylsulfonium hexafluoroantimonate), TPS-102 (triphenylsulfonium hexafluorophosphate), TPS-103 (triphenylphosphonium hexafluoroantimony) Nate), MDS-103 (4-methoxyphenyl-diphenylsulfonium hexafluoroantimonate), MPI-103 (4-methoxyphenyliodonium hexafluoroantimonate), BBI-101 (bis (4-t-butylphenyl) iodonium hexa) Fluorophosphate), BBI-103 (bis (4-t-butylphenyl) iodonium hexafluoroantimonate) (hereinafter referred to as Midori Kagaku) and Irgacure 2 1 (eta ^{5-2,4-cyclopentadiene-1-yl)} [(1,2,3,4,5,6-η) - (1- methylethyl) benzene] - iron (1+) hexafluorophosphate ( 1-)) (manufactured by Ciba Geigy), CD-1010, CD-1011, CD-1012 (4- (2-hydroxytetradecanyloxy) diphenyliodonium hexafluoroantimonate) (above, manufactured by Sartomer), CI- 2481, CI-2624, CI-2639, CI-2064 (manufactured by Nippon Soda), Dekacure K126 (bis [4- (diphenylsulfonio) phenyl] sulfide bishexafluorophosphate) (manufactured by Tegusa), RHODOLSIL PHOTOINITIATOR 2074 ((Tricumyl) iodonium tetrakis (pen Tafluorophenyl) borate) (manufactured by Rhodia) and the like.

  Examples of radical polymerization initiators include thioxanthones such as benzophenone, thioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, and 2,4-dichlorothioxanthone, and benzoins such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether. Ethers, benzyldimethyl ketals such as 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) ) -2-hydroxy-2-methylpropan-1-one, α-hydroxyalkylphenones such as 1-hydroxycyclohexyl phenyl ketone, and α-dicarbonyl compounds such as camphorquinone. The radical polymerization initiator is preferably used in an amount of 0.1 to 20 parts by mass with respect to 100 parts by mass of the photocurable composition.

  The reactive vehicle, magnetic filler and polymerization initiator as described above are dispersed and mixed using an appropriate method such as a high-speed impact mill or a high-speed impeller to obtain a reactive composition. Specifically, first, the vehicle and the polymerization initiator are mixed under red light, and the magnetic filler is added while sufficiently applying a shearing force using a high-speed mill or the like.

[Cylindrical reactor]
In order to apply a centrifugal force to the reactive composition, a cylindrical reactor is rotated at a predetermined rotational speed. There are two types of cylindrical reactors: drum type (vertical type, horizontal type) and basket type. In the drum system, the reactive composition is charged while rotating the container part that rotates the reactor, and in the basket system, the container part into which the reactive composition has been previously charged is rotated.

Further, the centrifugal force F which load is represented by F = mrω ^2. Here, m is the mass of the reactive composition, r is the position from the center of the container to the reactive composition, and ω is the angular velocity of the container. From the above formula, the centrifugal force to be applied increases as the specific gravity of the reactive composition increases, the container radius increases, and the container angular velocity increases. Since the angular velocity of the container is proportional to the number of rotations of the container, the centrifugal force is increased by rotating the container at a high speed.

  The cylindrical reactor is equipped with a lamp for heat-curing the reactive composition. As the lamp, a metal halide lamp, a xenon lamp, a mercury lamp, or the like can be used. According to the composition of the reactive composition, a lamp having an optimum wavelength and output may be selected. The lamp may be configured so that it can be taken in and out from inside the container as necessary.

  FIG. 2 is a schematic view showing an example of the cylindrical reactor 1. As can be seen from the figure, the cylindrical reactor 11 is a vertical drum system. The lamp 12 is disposed on a rotating shaft in the container 13, and one end thereof is connected to the sliding device 14. The sliding device 14 slides the lamp 12 with a predetermined stroke and linear velocity in the direction of the rotation axis around the central portion of the container 13. The container 13 includes a molding tray 15 detachably attached to an inner wall, and a bottom portion is connected to a rotation device 16 via a shaft. The rotation device 16 rotates the container 13 at a predetermined rotation number around a vertical rotation axis.

  The reactive composition is stored in the storage tank 17 and supplied to the molding tray 15 from the supply port of the supply pipe 19 by the supply pump 18 while the container 13 is rotating.

  The light irradiated from the lamp 12 is uniformly irradiated in almost all directions around the lamp 12, so that the surface of the composition in the molding tray 15 is uniformly irradiated by centrifugal force to be uniformly cured. Can do.

  As the cylindrical reactor, in addition to the vertical drum system shown in FIG. 2, a horizontal drum system can be used. The horizontal drum system is classified according to the driving system, and is a rotating shaft driving system in which a rotating shaft as shown in FIG. 3A is connected to a container to rotate the container, and a container as shown in FIG. 3B. A rotating roll contact driving system for rotating the container by rotating the rotating roller 20 that contacts the outer periphery of 13, the rotating roller 21 and the container 13 as shown in FIG. There is a belt rotation driving type in which the rotational driving force of the rotating roller 21 is transmitted to the container 13 by the belt 22 to rotate the container 13. In addition to the drum system, as shown in FIG. 4, the container 13 is swingably attached to both ends of a rotating body 31 extending in the vertical direction of the rotating shaft 30, and the rotating shaft is rotated by a rotating device 32. Thus, it is also possible to use a rotary pendulum type (basket type) reactor in which the container 13 is rotated in the horizontal plane direction and centrifugal force acts on the bottom surface of the container 13.

  In the case of the horizontal drum system, as in the case of the vertical drum system, the lamp 12 is configured to be able to be taken in and out from the inside of the container, and light irradiation can be performed while the container is rotating. In the case of the rotary pendulum method, as shown in FIG. 4, a lamp 33 is provided in the vicinity of the opening of the container 13 in a stationary state, and light is emitted from the opening to the inside of the container with the container 13 stationary.

  The molding tray 15 may be a detachable cylindrical tray inserted into the container 13, and a plurality of trays are detachably held on the inner peripheral surface of the container 13 (for example, 90 on the inner peripheral surface). (4 trays may be held at every angle), or a plurality of trays may be held on the inner peripheral surface of a removable cylinder inserted into the container 13. Good.

  In addition, the molding tray 15 is not necessarily required, and it may be configured such that the reactive composition is directly supplied into the container and the container is removed after being subjected to centrifugal load and light irradiation, and the entire container is heated.

  Photocuring is faster than thermal curing, and can be cured in a fluid state until the distribution of the vehicle and filler in the reaction product is stabilized by centrifugal force. Can be adjusted in detail.

  Moreover, although the reach | attainment depth of light becomes shallow depending on the magnetic filler to mix, since at least a surface layer part can be hardened | cured by light irradiation, the characteristic of a surface layer part can be adjusted. Further, since the outer shape can be maintained by curing the surface layer portion, it can be taken out from the cylindrical reactor and subjected to other treatment such as heat treatment in the next step. Since the centrifugal force does not act after taking out from the reactor, for example, an electromagnetic wave absorbing sheet comprising an inclined portion hardened by light irradiation under the action of centrifugal force and a uniform portion hardened by heating after taking out is used. It can also be generated.

  Depending on the characteristics desired for the electromagnetic wave absorbing sheet to be generated, it may be preferable to cure the outer surface layer portion in the radial direction or to inward from the outer surface layer portion in the radial direction when the centrifugal force is applied. In such a case, the container is made of a light transmissive member, and a plurality of lamps are arranged on the outside so as to surround the container.

  The cylindrical reactor may be equipped with a heating device for heat-curing the reactive composition. The heating device covers the entire container and contains the reactive composition to uniformly heat the entire container.The heating device is in contact with the inner wall of the reactive composition with a heating wire or hot water pipe embedded in the peripheral wall of the container. For example, a heater device that heats a heated surface, hot air or hot water is jetted onto the reactive composition, and a hot air or hot water jet device that heats a portion in contact with the hot air or hot water can be used.

  Heat curing may be performed in a state in which the container is rotated and a centrifugal force is applied, or may be performed in a state in which the centrifugal force is not applied by stopping the rotation of the container after light irradiation or taking out from the container.

  By combining the light irradiation lamp and the heating device as described above, even when the reaction composition having the same composition is used, it is possible to obtain an electromagnetic wave absorbing sheet in which the distribution state of the magnetic filler and the local concentration of the reactive vehicle are different. . Here, the combination includes the timing of light irradiation and heating as described above, in addition to the arrangement of the lamp and the type of the heating device. There is a large difference in the curing reaction speed between photocuring and thermal curing, and by using this difference in speed, it is possible to absorb electromagnetic waves by appropriately selecting the light irradiation and heating start time, end time, irradiation and heating time. The sheet characteristics can be adjusted in more detail.

  Further, the first layer is formed by photocuring the surface, and a second layer is formed on the surface of the first layer by introducing a new reactive composition and performing light irradiation and heating. By repeating this, a laminate in which composite materials are laminated can be formed.

  A composite material can also be formed by placing, fixing, bonding, and embedding a plate, foil, cloth, or net-like material. For example, an expanded metal, which is a net-like material, is previously placed on a molding tray, and a laminate including the expanded metal can be formed by performing rotational molding as described above.

Examples of the present invention will be described below.
(Reactive composition)
Matrix resin: Silicone rubber (100 parts by weight)
Additive: Epoxy monomer (8 parts by weight), cationic polymerization initiator (0.20 parts by weight)
Magnetic filler: Example 1 Sendust (900 parts by weight)
Example 2 Permalloy (900 parts by weight)

(Reaction conditions)
The kneaded product of the silicone resin, magnetic filler and additive was placed in a horizontal drum type cylindrical reactor (inner diameter 200 mm), and light irradiation was performed with a centrifugal force applied.
Rotation speed and light irradiation time: 500 rpm, 7 minutes

(Heating conditions)
After the light irradiation, the molding tray was taken out and heated at 150 ° C. for 10 minutes.

  In the state after light irradiation, the surface portion was cured and the inside was green sheet-like and uncured in any of the examples. Since the surface portion was cured, the sheet shape was maintained even when the molding tray was removed from the reaction vessel, and the heating process, which was the next process, could be started quickly.

  Each Example was obtained as an electromagnetic wave absorbing sheet in which the magnetic filler was distributed in the thickness direction by centrifugal force.

1 is a cross-sectional view illustrating a configuration of an electromagnetic wave absorbing sheet 1. 1 is a schematic view showing an example of a cylindrical reactor 1. It is the schematic which shows the cylindrical reactor of a horizontal drum system. It is the schematic which shows the cylindrical reactor of a rotary pendulum system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electromagnetic wave absorption sheet 2 Matrix resin 3 Magnetic filler 11 Cylindrical reactor 12 Lamp 13 Container 14 Sliding device 15 Molding tray 16 Rotating device 17 Storage tank 18 Supply pump 19 Supply pipe

Claims (5)

An electromagnetic wave absorbing sheet containing a matrix resin and a magnetic filler,
The said matrix resin has photocurability and thermosetting, The said magnetic filler has density distribution which changes along the thickness direction, The electromagnetic wave absorption sheet | seat characterized by the above-mentioned.   2. The electromagnetic wave absorbing sheet according to claim 1, wherein the magnetic filler is distributed in a high concentration on one surface side perpendicular to the thickness direction, and is distributed in a lower concentration on the other surface side than on the one surface side. .   The electromagnetic wave absorbing sheet according to claim 1, wherein the magnetic filler is a soft magnetic powder.   The electromagnetic wave absorbing sheet according to claim 1, further comprising a thermally conductive filler.   A light irradiation treatment in which light is applied to the reactive composition containing a reactive vehicle having heat reactivity and a thermal reactivity and a magnetic filler under a centrifugal force, and the reactive composition is heated. The manufacturing method of the electromagnetic wave absorption sheet | seat characterized by including the heat processing which performs.

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