JP2004031578A - Magnetic sheet - Google Patents

Abstract

An object of the present invention is to provide a magnetic sheet which is less likely to be bent, wrinkled, torn, or torn even when it is made thinner, and which is excellent in workability in sticking work.
A magnetic sheet is a sheet material having a three-layer structure in which a support, a magnetic layer, and an adhesive layer are laminated. The support 11 is a PET film having a thickness of 16 μm. The magnetic layer 12 is formed by dispersing Ni—Zn soft ferrite powder as a magnetic powder in an acrylic resin, and has a thickness of 60 μm. The adhesive layer 13 is an acrylic adhesive having a thickness of 20 μm.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic sheet.
[0002]
[Prior art]
BACKGROUND ART Conventionally, as a magnetic sheet for electromagnetic wave countermeasures, a sheet obtained by processing a magnetic composite material obtained by dispersing a magnetic material powder in a resin material into a sheet shape is known.
This type of magnetic sheet is attached to a place where electromagnetic waves are to be blocked, such as the inner surface of the housing of an electronic device or the outer surface of various electronic components, thereby preventing external electromagnetic waves from penetrating into the electronic device, Electromagnetic waves could be prevented from leaking from inside the device to the outside.
[0003]
By the way, in recent years, as electronic devices have become smaller and thinner, there is only a small space inside the electronic device, and even the magnetic sheet as described above can be easily manufactured without reducing the thickness. It is becoming impossible to arrange.
In addition, when electromagnetic wave countermeasures are applied to an FPC (Flexible Printed Circuit) cable, if a relatively thick magnetic sheet is adhered, the flexibility of the FPC cable is impaired, so that a very thin magnetic material is used. There is a request to use a seat.
[0004]
[Problems to be solved by the invention]
However, the thinner the magnetic sheet as described above, the thinner the sheet, the more likely it is to be a sheet without tension, and it is likely to bend or wrinkle during the sticking operation of the magnetic sheet. Further, since the magnetic composite material as described above has a relatively high content of the magnetic substance powder and a high brittleness, the thinner the material, the more likely it is torn or torn.
[0005]
Therefore, when a magnetic sheet made of a conventional magnetic composite material is simply reduced in thickness, in order to prevent bending, wrinkling, tearing, and tearing as described above, it is necessary to work with great care when attaching the magnetic sheet. Therefore, there is a problem that the working efficiency becomes very poor.
[0006]
The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a magnetic material which is less likely to bend, wrinkle, break, and tear even when it is made thinner, and has excellent workability at the time of sticking work. To provide a seat.
[0007]
Means for Solving the Problems and Effects of the Invention
The magnetic sheet of the present invention configured to achieve the above object is a magnetic sheet that is stuck to a sticking target portion and blocks electromagnetic waves at the sticking target portion, and a support made of a synthetic resin film. A magnetic layer formed of a magnetic composite material obtained by dispersing a magnetic material powder in a synthetic resin material is laminated thereon.
[0008]
In this magnetic sheet, examples of the magnetic powder contained in the magnetic composite material forming the magnetic layer include Ni-based ferrite magnetic powder, Mg-based ferrite magnetic powder, Mn-based ferrite magnetic powder, and Ba-based ferrite magnetic powder. Powder, Sr-based ferrite magnetic powder, Fe-Si alloy powder, Fe-Ni alloy powder, Fe-Co alloy powder, Fe-Si-Al alloy powder, Fe-Si-Cr alloy powder, iron powder, Fe-based amorphous , Co-based amorphous, Fe-based nanocrystal, or the like may be used.
One of these magnetic powders may be used alone, or a mixture of two or more thereof may be used.
[0009]
Examples of the synthetic resin material in the magnetic composite material forming the magnetic layer include polyethylene, polypropylene, polyolefin derivatives, polystyrene, polyvinyl chloride, polyvinylidene chloride, fluororesin, polymethyl methacrylate, polyacrylonitrile, and polyacrylamide. , Alkyd resin, unsaturated polyester resin, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyphenylene oxide, polyimide, polyamide, polyphenylene sulfide, polysulfone, silicone resin, phenol resin, urea resin, melamine resin, polyurethane, epoxy resin, polyacetal, poly It is preferable to use an ether resin or the like.
[0010]
The amount of the magnetic substance powder can be arbitrarily adjusted within a range in which the form as the magnetic layer can be maintained after the sticking operation, assuming the force acting on the magnetic layer after the sticking operation. In the case of, at least during the attaching operation, the support mainly receives the force acting on the magnetic sheet, so that the magnetic layer itself becomes more brittle than when the magnetic sheet is formed by the magnetic layer alone. Regardless, the amount of the magnetic powder can be increased accordingly. The specific numerical range of the compounding amount of the magnetic powder may vary depending on the type of the magnetic powder, the particle size, the physical properties of the synthetic resin material serving as the matrix, and the like. It is preferable that about 40 to 50% by volume of a magnetic substance powder is blended.
[0011]
The support is made of a film material having a lower brittleness than the magnetic layer and capable of giving a proper tension to the magnetic sheet. Bending, wrinkling, tearing, tearing and the like of the magnetic sheet during the wearing operation are suppressed. As the resin material for forming the support, for example, polyethylene, polypropylene, polyethylene terephthalate, polyimide, and the like may be used, but polyethylene terephthalate is particularly preferable because it can maintain a tight state even when it is relatively thin. .
[0012]
In addition to the magnetic layer and the support, in addition to the above-described main component materials, various additives such as a plasticizer for adjusting flexibility, a coloring agent such as a pigment and a dye, a stabilizer, and a deterioration inhibitor are also used. May be included. The content of these additives is appropriately adjusted within a range that does not impair the functions of the magnetic layer and the support.
[0013]
According to the magnetic sheet configured as described above, the magnetic layer is laminated on the support, so that the support is formed by a synthetic resin film having a necessary mechanical strength and tension. As compared with a magnetic sheet composed of only a magnetic layer, a magnetic sheet having a high tension can be easily formed. Therefore, even when the magnetic sheet is made thinner, bending, wrinkling, tearing, tearing, etc. are less likely to occur during the sticking work of the magnetic sheet, and the sticking work does not need to be performed while paying excessive attention, thereby improving work efficiency. Is done.
[0014]
As a method of providing the magnetic sheet with tension, for example, by reducing the amount of the magnetic powder in the magnetic composite material or changing the type of the synthetic resin material serving as the matrix, the magnetic layer itself is formed. It is also conceivable to make it taut. However, in order to obtain the expected electromagnetic wave shielding performance, it is difficult to greatly change the content of the magnetic substance powder, and it is suitable for dispersing the magnetic substance powder, and when it is formed into a sheet. It is not easy to select a synthetic resin material that simultaneously satisfies the two conditions of obtaining the desired strength and tension.
[0015]
In this regard, if a structure in which the magnetic layer and the support are laminated as in the present invention is adopted, the magnetic layer is considered only to obtain the expected electromagnetic wave shielding performance without considering the sheet tension. On the other hand, for the support, the material can be selected only by giving the desired tension to the sheet material without considering the dispersibility of the magnetic powder, etc. The material used to form each layer can be easily selected as compared with a case where only the sheet material is used to improve both the electromagnetic wave shielding performance and the tension of the sheet material.
[0016]
By the way, in the present invention, it is desirable to further have the following configuration.
First, it is preferable that the support is peeled off from the magnetic layer after sticking to the sticking target portion while the magnetic layer is left at the sticking target portion.
[0017]
According to this magnetic sheet, since the support is present at the time of the sticking operation, the function and effect as described above are obtained, and bending and wrinkling hardly occur during the sticking operation of the magnetic sheet. After the attaching operation, the support can be peeled off while leaving only the magnetic layer, so that what is finally left at the portion to be adhered can be made thinner by the amount of the support than that which cannot be peeled off. Therefore, it is useful when the magnetic layer is used in a situation where an external force is less likely to act on the magnetic layer after the sticking operation than during the sticking operation.
[0018]
For the specific structure for allowing the support to be peelable from the magnetic layer, various structures can be considered.For example, when the magnetic layer and the support are peeled from the magnetic layer, It is preferable that the magnetic layer is bonded to the magnetic layer together with the support by an adhesive layer peeled off from the magnetic layer. Such a structure may be formed, for example, by coating an adhesive on a support to form an adhesive layer, coating a release agent thereon to form a release layer, and coating the magnetic composite material thereon. It is obtained by forming a magnetic layer. The adhesive used to form the adhesive layer can be arbitrarily adopted as long as it exhibits the required adhesiveness to the support and the magnetic layer, for example, a rubber adhesive, an acrylic adhesive, and a silicone. A system adhesive or the like can be used.
[0019]
According to the magnetic sheet having such a structure, the magnetic layer and the support are adhered to each other via the adhesive layer laminated therebetween, so that the magnetic layer itself and the support itself are both one with respect to the other. The material does not have to be adhesive. Therefore, compared to a case where either the magnetic layer itself or the support itself is selected from a material having adhesiveness to the other and the magnetic layer and the support are bonded, the degree of freedom in selecting a material is high. Thus, the materials used for forming each layer of the magnetic layer and the support can be easily selected.
[0020]
When such an adhesive layer is provided, it is preferable that the adhesive layer be a foamable adhesive layer in which the adhesive force at the interface with the magnetic layer is reduced or lost by foaming with heating.
Such a foamable adhesive layer can be formed by adding a foaming agent to an adhesive.
[0021]
As a foaming agent that foams with heating, for example, a decomposition-type inorganic foaming agent such as ammonium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, and azides may be used. Further, an organic foaming agent such as an azo compound may be used. More specifically, fluorinated alkanes such as trichloromonofluoromethane and dichloromonofluoromethane, azo compounds such as azobisisobutyronitrile and azodicarbonamide, barium azodicarboxylate, paratoluenesulfonylhydrazide and diphenylsulfone Hydrazine compounds such as -3,3'-disulfonylhydrazide, 4,4'-oxybis (benzenesulfonylhydrazide) and allylbis (sulfonylhydrazide), ρ-toluylenesulfonyl semicarbazide and 4,4'-oxybis (benzenesulfonyl semicarbazide) ), Triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole, N, N'-dinitrosopentamethylenetetramine and N, N'-dimethyl-N, N'- Such as dinitrosoterephthalamide N- nitroso compounds, and other low-boiling compounds. Further, as another foaming agent, for example, a suitable substance that easily gasifies and exhibits thermal expansion property such as isobutane, propane, and pentane is encapsulated in a shell-forming substance by a coacervation method, an interfacial polymerization method, or the like. Functional fine particles can also be used. Examples of the shell-forming substance forming the heat-expandable fine particles include, for example, vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, and polysulfone. Any substance may be used as long as it is a substance that is destroyed by thermal expansion.
[0022]
The content of the foaming agent in the adhesive layer or the expansion ratio of the adhesive layer may be appropriately determined in consideration of a change in adhesive strength before and after foaming.
Further, it is considered that it is preferable that the adhesive layer, if not excessively reducing the adhesiveness with the support side, sufficiently reduce the adhesiveness with the magnetic layer side, because the adhesive layer is easily peeled off together with the support. For this purpose, it is preferable that the foaming agent is unevenly distributed on the magnetic layer side. As a method of distributing the foaming agent to the magnetic layer side, the adhesive layer itself may be a two-layered adhesive layer including a foamable adhesive layer containing a foaming agent and a non-foamable adhesive layer containing no foaming agent. .
[0023]
According to the magnetic sheet provided with such a foamable adhesive layer, the adhesive layer foams with heating, so that the adhesive force at the magnetic layer side interface is reduced or lost. The support can be easily peeled off only by heating the support, as compared with the one having the above. Further, since the support is not easily peeled off before heating, it is less likely to cause a trouble that the support is erroneously peeled off as compared with the case where the support is easily peeled off by simply sandwiching a release layer made of a release agent.
[0024]
Next, when the support has a structure capable of being peeled as described above, the magnetic layer further comprises a synthetic resin film and remains on the magnetic layer side when the support is peeled from the magnetic layer. May be provided with a surface protective layer for protecting the surface.
For example, the synthetic resin film serving as the surface protective layer is sufficient if it can prevent the magnetic powder from detaching from the magnetic layer or prevent a part of the magnetic layer from peeling off. It is not necessary to make the thickness so as to give the following, and it is sufficient to form the film with a film thinner than the support. As a resin material for forming the surface protective layer, for example, polyethylene, polypropylene, polyethylene terephthalate, and polyimide may be used. According to the magnetic sheet having such a surface protective layer, the support is separated from the magnetic layer. However, since the surface protective layer remains on the magnetic layer side to protect the surface of the magnetic layer, the remaining magnetic layer is less likely to be scratched as compared with the case without the surface protective layer.
[0025]
Next, when sticking the magnetic sheet to the sticking target place, after applying an adhesive or the like to the sticking target place, the magnetic sheet may be stuck, but the magnetic sheet itself, An adhesive layer used for sticking to the sticking target portion may be provided, which facilitates sticking work to the sticking target portion.
[0026]
Such an adhesive layer can be formed with the same adhesive as the above-mentioned adhesive layer.
Further, the adhesive layer may be formed of a heat-fusible composition that is heat-fused to a portion to be adhered with heating.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with some examples.
[Embodiment 1]
The magnetic sheet 1 described below is a sheet material having a three-layer structure in which a support 11, a magnetic layer 12, and an adhesive layer 13 are laminated as shown in FIG.
[0028]
The support 11 is a 16 μm-thick polyethylene terephthalate film (hereinafter referred to as a PET film).
The magnetic layer 12 is formed by dispersing Ni—Zn soft ferrite powder, which is a magnetic powder, in an acrylic resin, and has a thickness of 60 μm.
[0029]
The adhesive layer 13 is an acrylic adhesive having a thickness of 20 μm.
The magnetic sheet 1 is manufactured according to the following procedure.
First, 100 parts by weight of an acrylic resin and 700 parts by weight of a Ni-Zn soft ferrite powder as a magnetic powder are blended, and a small amount of additives such as a curing agent and a flame retardant are blended. The compounded material is in the form of a slurry and is stirred by a mixer. At this time, the inside of the mixer is depressurized at the same time by depressurizing to obtain a magnetic composite material for forming the magnetic layer 12. Can be.
[0030]
Then, the magnetic composite material is applied to the surface of a PET film serving as the support 11 using a coater, and dried to form the magnetic layer 12.
Furthermore, the acrylic pressure-sensitive adhesive sheet produced by the coater is bonded to the surface on the magnetic layer 12 side to form the pressure-sensitive adhesive layer 13, whereby the three-layer magnetic sheet 1 can be obtained.
[0031]
The obtained magnetic sheet 1 had such a tension that it did not wrinkle or bend unless it was intentionally bent. In addition, even when picked up with a fingertip and pulled, it was not easily torn or torn. Therefore, the magnetic layer was not bent, wrinkled, broken, or torn during the sticking operation, and the sticking operation could be easily performed.
[0032]
The magnetic sheet 1 is cut into a width of 5 mm and a length of 50 mm, and a flat rectangular wire (hereinafter, referred to as an electric wire) having a width of 1 mm and a length of 60 mm is arranged at the center of the cut magnetic sheet 1. Covered with sheet 1. At that time, portions each of which was not covered with the magnetic sheet 1 were formed at both ends of the electric wire by 5 mm.
[0033]
After attaching the magnetic sheet, the impedance values at both ends of the electric wire not covered with the magnetic sheet 1 were measured using a commercially available impedance material analyzer (HP-4291A). For comparison, the impedance value of the electric wire to which the magnetic sheet 1 was not attached was also measured by the same method. The result is shown in FIG.
[0034]
As is clear from the measurement results, the impedance value of the electric wire to which the magnetic sheet 1 is attached is larger. Therefore, it is considered that by attaching the magnetic sheet 1 to the electric wire, the conductive noise suppressing power flowing through the electric wire can be increased, and an effective electromagnetic wave countermeasure effect can be obtained.
[0035]
[Embodiment 2]
The magnetic sheet 2 described below is a sheet material having a four-layer structure in which a support 21, a foamable adhesive layer 22, a magnetic layer 23, and an adhesive layer 24 are laminated as shown in FIG.
The support 21 is a PET film having a thickness of 100 μm.
[0036]
The foamable adhesive layer 22 is formed by adding and mixing a base polymer composed of a copolymer of ethyl acrylate, butyl acrylate and 2-hydroxyethyl acrylate, a polyurethane-based crosslinking agent, and thermally expandable fine particles to toluene. A liquid composition (adhesive) is coated on the surface of the PET film and dried, and has a thickness of 50 μm.
[0037]
The magnetic layer 23 is formed by dispersing Ni-Zn soft ferrite powder, which is a magnetic powder, in an acrylic resin, and has a thickness of 60 μm.
The adhesive layer 24 is made of a synthetic rubber adhesive and has a thickness of 9 μm.
This magnetic sheet 2 is manufactured by the following procedure.
[0038]
100 parts by weight of a base polymer composed of a copolymer (weight average molecular weight: about 600,000) of 50 parts by weight of ethyl acrylate, 50 parts by weight of butyl acrylate, and 1 part by weight of 2-hydroxyethyl acrylate, and 5 parts by weight of a polyurethane crosslinking agent And a toluene solution to which 30 parts by weight of heat-expandable fine particles (average particle size: 15 μm, specific gravity: 1.01) were added and coated on the surface of a PET film serving as the support 21, and dried. Was formed. The support 21 and the foamable adhesive layer 22 can be formed by using a commercially available thermal release sheet. For example, a thermal release sheet manufactured by Nitto Denko Corporation (product number: No. 3195HS, PET base material thickness: 100 μm, adhesive layer thickness: 45 μm) and the like can be used.
[0039]
Subsequently, in the same manner as in the first embodiment, the magnetic composite material was overlaid, coated, and dried to form the magnetic layer 23.
Subsequently, an adhesive layer 24 was formed by applying a synthetic rubber-based heat sealing material on the surface of the magnetic layer 23 to obtain a magnetic sheet 2 having a four-layer structure. The adhesive layer 24 can also be formed by bonding a commercially available thermal adhesive tape. For example, a thermal adhesive tape (product number: M-5205, thickness: 9 μm) manufactured by Nitto Denko Corporation is thermally bonded. The adhesive layer 24 may be formed by pressing the magnetic layer 23 using the temporary adhesive force of the tape.
[0040]
The obtained magnetic sheet 2 had such a tension that it did not wrinkle or bend unless it was intentionally bent. In addition, even when picked up with a fingertip and pulled, it was not easily torn or torn. Therefore, the magnetic layer was not bent, wrinkled, broken, or torn during the sticking operation, and the sticking operation could be easily performed.
[0041]
The magnetic sheet 2 was used in a manufacturing process of an FPC cable to form an FPC cable with a magnetic layer.
In general, an FPC cable adheres the electric wire and the polyimide by covering the upper and lower surfaces of the electric wire with a polyimide sheet, pressurizing and heating them from above and below, and thermally fusing a heat adhesive layer provided on the polyimide sheet. Then, it is manufactured by a procedure of cutting into a required shape.
[0042]
In this manufacturing process, when the upper and lower surfaces of the electric wire are covered with the polyimide sheet, the upper and lower surfaces are further covered with the magnetic sheet 2, and the magnetic sheet 2 is temporarily fixed to the polyimide sheet. Then, when they are pressed and heated from above and below to thermally fuse the thermal adhesive layer provided on the polyimide sheet, the adhesive layer 24 simultaneously thermally fuses to the FPC cable and the foamable adhesive layer 22 foams. . After the foaming of the foamable adhesive layer 22, the PET film as the support 21 could be easily peeled off.
[0043]
After peeling off the PET film, the FPC sheet in which only the magnetic layer 23 and the adhesive layer 24 were left was punched to obtain an intended FPC cable with a magnetic layer. In this FPC cable with a magnetic layer, only the very thin magnetic layer 23 and the adhesive layer 24 are stuck on the surface layer, so the original flexibility of the FPC cable is not impaired, and the magnetic layer 23 and the adhesive layer 24 are not provided. It can be used in much the same way as an FPC cable.
[0044]
As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described specific embodiments, and can be implemented in various other modes.
For example, in the above-described first embodiment, the magnetic sheet having a three-layer structure is shown. However, when the magnetic sheet is applied after applying the adhesive to the application target area, the adhesive sheet 13 is provided. A magnetic sheet having a two-layer structure that is not provided may be used.
[0045]
In the second embodiment, the magnetic sheet having a four-layer structure is shown. However, a thin plastic film is further interposed between the foamable adhesive layer 22 and the magnetic layer 23 to form a five-layer structure. A surface protection layer for protecting the surface of the magnetic layer 23 may be formed. In this case, if there is no self-adhesion between the surface protective layer and the magnetic layer 23, an adhesive layer made of an adhesive may be further provided between the two. If the surface of the magnetic layer 23 is protected by providing such a surface protective layer, even if the support 21 is peeled off from the magnetic layer 23, the surface protective layer remains on the magnetic layer 23 side and the surface of the magnetic layer 23 is protected. Therefore, the remaining magnetic layer 23 is less likely to be scratched as compared with the case where the surface protective layer is not provided.
[Brief description of the drawings]
FIG. 1 is a structural diagram of a magnetic sheet according to a first embodiment.
FIG. 2 is a graph showing a difference in an impedance value of an electric wire depending on the presence or absence of a magnetic sheet.
FIG. 3 is a structural diagram of a magnetic sheet according to a second embodiment.
[Explanation of symbols]
1,2 ... magnetic sheet, 11,21 ... support, 12,23 ... magnetic layer, 13,24 ... adhesive layer.

Claims (6)

A magnetic sheet that is stuck to a sticking target portion and blocks electromagnetic waves at the sticking target portion,
A magnetic sheet having a structure in which a magnetic layer formed of a magnetic composite material obtained by dispersing a magnetic powder in a synthetic resin material is laminated on a support made of a synthetic resin film. The structure according to claim 1, wherein the support is detachable from the magnetic layer while the magnetic layer is left at the sticking target location after sticking to the sticking target spot. 3. Magnetic sheet. 3. The magnetic layer according to claim 2, wherein the magnetic layer and the support are bonded together with the support by an adhesive layer peeled off from the magnetic layer when the support is peeled off from the magnetic layer. Magnetic sheet. 4. The magnetic sheet according to claim 3, wherein the adhesive layer is a foamable adhesive layer in which the adhesive force at the interface with the magnetic layer is reduced or lost by foaming with heating. 5. A surface protection layer made of a synthetic resin film and remaining on the magnetic layer side when the support is peeled off from the magnetic layer to protect the surface of the magnetic layer. Item 6. A magnetic sheet according to any one of Items 4. The magnetic sheet according to claim 1, further comprising an adhesive layer used for sticking to the sticking target portion.

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