Noise suppression sheet and laminate

Abstract

To provide a noise suppression sheet having a high suppression ability to a low frequency noise of 1 MHz or less and having a good followability to a complex unevenness shape of an adherend, and provide a laminate having a noise suppression layer.SOLUTION: A noise suppression sheet comprises: a n-layer magnetic layer having a magnetic layer (A1) and a magnetic layer (An); and a noise suppression layer having at least a conductive layer of a (n-1) layer. The magnetic layer and the conductive layer are alternately laminated. In each magnetic layer, Xi expressed by a formula (1) is 1 or more. The total of Xi of each magnetic layer is 4 or more and 15 or less. In all of the conductive layers, a proportional constant obtained when performing a linear approximation of a shield property of 0.2 to 1 MHz in a magnetic field shield property measurement by a KEC method is 4 or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sheet used for suppressing noise of 1 MHz or less, and a laminate having a noise suppression layer formed by the sheet.

Background Art

[0002] In recent years, there has been a strong demand for countermeasures against low-frequency noise generated from power control units mounted on electric vehicles and the like, and wireless communication devices such as AF / FM radios. As one of the noise countermeasures, there is a method of covering a noise source or a region, component, etc. to be protected with an electromagnetic wave shielding material. Conventionally, the influence of low-frequency noise has been suppressed by using a metal casing. Patent Document 1 discloses a mechanism for suppressing leaking noise, particularly noise in the low-frequency region, by a laminate of a layer containing carbon fiber and a layer containing a magnetic material. Patent Document 2 discloses a mechanism for suppressing noise in the kHz band by a laminate of a sheet of a ferromagnetic material and a sheet of a conductive material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, due to reasons such as improving the fuel efficiency of automobiles, the weight reduction of vehicle bodies has been promoted, and the replacement from conventional metal casings to resin molded products has been considered. In order to add the noise suppression function of the metal casing to the resin molded product, attempts have been made to bond a noise suppression sheet to its surface. However, there have been problems in achieving both the followability of the noise suppression sheet to the resin molded product having a complex uneven shape and the low-frequency noise suppression performance. For example, in the noise suppression sheet disclosed in Patent Document 1, the shielding effect at 500 MHz is described, but the noise suppression ability is insufficient in a lower frequency range such as 1 MHz or less. In the noise suppression sheet disclosed in Patent Document 2, a 1 mm thick metal layer is required, and there is a problem of insufficient flexibility to follow the unevenness of the molded product.

Means for Solving the Problems

[0005] As a result of intensive studies by the present inventors, it has been found that the problems of the present invention can be solved in the following aspects, and the present invention has been completed. That is, the present invention is a noise suppression sheet used for suppressing noise of 1 MHz or less, having an n-layer magnetic layer having a magnetic layer (A 1 ) and a magnetic layer (A n ), and a noise suppression layer having at least (n - 1) conductive layers, wherein the magnetic layer and the conductive layer are alternately laminated, each of the magnetic layers satisfies that X i represented by the following formula (1) is 1 or more, the sum of X i of each magnetic layer is 4 or more and 15 or less, and each of the conductive layers is characterized in that the proportionality constant obtained when linearly approximating the shielding property at 0.2 to 1 MHz in the magnetic field shielding property measurement by the KEC method is 4 or more. The present invention relates to a noise suppression sheet. X i =√μ´ i ×√t i ···Formula (1) Here, n is an integer of 2 or more, and i is an integer of 1 or more and n or less. μ´ i is the relative permeability at 1 MHz of the magnetic layer (A i ), and t i is the film thickness [mm] of the magnetic layer (A i ). That is.

[0006] The present invention also relates to a laminate having a noise suppression layer formed from the noise suppression sheet on a substrate.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a noise suppression sheet having high suppression ability against low-frequency noise of 1 MHz or less and excellent followability to the complex uneven shape of the substrate, and a laminate having a noise suppression layer.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an example of an embodiment to which the present invention is applied will be described. Note that the numerical values specified in this specification are values obtained by the methods disclosed in the embodiments or examples. Also, the numerical value "A to B" specified in this specification refers to a range that satisfies a value greater than numerical value A and a value less than numerical value B. Further, the "sheet" in this specification includes not only the "sheet" defined in JIS but also the "film". For clarity of explanation, the following description and drawings are simplified as appropriate. Also, the same element members are denoted by the same reference numerals in different embodiments. Each of the various components appearing in this specification may be used alone or in combination of two or more without particular annotation.

[0010] (Noise suppression sheet) The noise suppression sheet of the present invention is used to suppress noise of 1 MHz or less, magnetic layer (A 1 ) and an n-layer magnetic layer having a magnetic layer (A n ), and a noise suppression layer having at least (n - 1) conductive layers, the magnetic layer and the conductive layer are alternately laminated, each of the magnetic layers has X represented by the following formula (1) i of 1 or more, the total of X of each magnetic layer i is 4 or more and 15 or less, each of the conductive layers has a proportionality constant of 4 or more when the shielding property at 0.2 to 1 MHz is linearly approximated in the magnetic field shielding property measurement by the KEC method. X i = √μ' i × √t i ··· Formula (1) Note that n is an integer of 2 or more, i is an integer of 1 or more and n or less, μ' i is the relative permeability at 1 MHz of the magnetic layer (A i ), t i is the film thickness [mm] of the magnetic layer (A i ), is.

[0011] By being such a noise suppression sheet, it is possible to suppress low-frequency noise of 1 MHz or less in particular.

[0012] In addition to the noise suppression layer, the noise suppression sheet can further include other layers. Examples of the other layers include layers having hard coatability, thermal conductivity, heat insulation, water vapor barrier, oxygen barrier, low dielectric constant, high dielectric constant, low dielectric tangent, high dielectric tangent, heat resistance, etc. Further, as long as the magnetic layer and the conductive layer are alternately laminated in the noise suppression layer, the functional layer may be provided between the layers without affecting the effect. Further, when the magnetic layer is a magnetic metal layer or the conductive layer is a conductive metal layer, an adhesive layer may be used to bond to other layers.

[0013] The noise suppression sheet of the present invention can be used for all parts that require noise suppression of 1 MHz or less. Noise of 1 MHz or less has, for example, a wireless communication device mounted on an automobile as a source, and examples include AM / FM radio noise (522 kHz to 1.7 MHz), electronic tags and RFID for vehicle body management (135 kHz), smart keys (134 kHz), etc.

[0014] (Noise suppression layer) The noise suppression layer of the present invention is a laminate having the ability to suppress low-frequency noise of 1 MHz or less in particular, and has an n-layer magnetic layer having magnetic layers (A 1 ) and magnetic layers (A n ), and a noise suppression layer having at least (n - 1) conductive layers, and the magnetic layer and the conductive layer are alternately laminated.

[0015] An example of the noise suppression layer according to this embodiment will be described with reference to FIGS. 1 to 2. However, it is not limited thereto. For example, taking FIG. 1 as an example, a two-layer magnetic layer having A1; magnetic layer (A 1 ) and A2; magnetic layer (A 2 ), and one layer of B1; conductive layer (B 1It is a noise suppression layer provided with a noise suppression layer having

[0016] Also, as shown in FIG. 2, it may be at least a four-layer laminate further having a conductive layer (B2). The laminate shown in FIG. 2 has a configuration in which a conductive layer is further laminated on the magnetic layer of the three-layer noise suppression layer illustrated in FIG. 1. Such a four-layer noise suppression layer has an effect of enhancing noise suppression due to an increase in the number of different-layer interfaces, and is more preferable.

[0017] Also, as shown in FIG. 3, A1; magnetic layer (A 1 )、A2; magnetic layer (A 2 )、and A3; magnetic layer (A 3 ) having a three-layer magnetic layer, and two layers of B1; conductive layer (B 1 )、and B2; conductive layer (B 2 ) having a noise suppression layer, and a noise suppression layer having a five-layer laminate in which the magnetic layer and the conductive layer are alternately laminated, etc. may be mentioned.

[0018] The noise suppression layer may or may not be subjected to a heat and pressure treatment, but when using a conductive resin layer and a magnetic resin layer, it is preferable to perform a heat and pressure treatment because the noise suppression effect can be further enhanced.

[0019] The thickness of the noise suppression layer can be appropriately designed according to the application, but about 50 μm to 900 μm is preferable, and about 100 μm to 600 μm is more preferable. When it is 50 μm or more, good noise suppression ability can be obtained, and when it is 900 μm or less, the followability is more excellent.

[0020] The noise suppression layer of the present invention is a laminate having magnetic layers and conductive layers alternately, and for each layer of the magnetic layers of the noise suppression layer, √μ´×√t is 1 or more, and the sum thereof is 4 or more and 15 or less. In addition, for the conductive layer adjacent to these magnetic layers, in the magnetic field shielding property measurement by the KEC method, the proportionality constant obtained when linearly approximating the measurement results of the shielding property in the range of 0.2 to 1 MHz is 4 or more. As a result, it has been found that a noise suppression sheet having a high suppression ability against low-frequency noise of 1 MHz or less and excellent followability to the complex uneven shape of the adherend can be obtained.

[0021] Therefore, each magnetic layer all has X represented by the formula (1) i of 1 or more, and the sum of X i of each magnetic layer is 4 or more and 15 or less.

[0022] That is, in the case of the three-layer noise suppression layer shown in FIG. 1 or the four-layer noise suppression layer shown in FIG. 2, for the two magnetic layers A1; magnetic layer (A1) and A2; magnetic layer (A 2 ), each X 1 and X 2 are both 1 or more, and the sum of X 1 and X 2 is 4 or more and 15 or less.

[0023] In the case of the five-layer noise suppression layer shown in FIG. 3, for the three magnetic layers A1; magnetic layer (A 1 ), A2; magnetic layer (A 2 ), and A3; magnetic layer (A 3 ), each X 1 , X 2 and X 3 are both 1 or more, and the sum of X 1 and X 2 and X 3 is 4 or more and 15 or less.

[0024] In the magnetic field shielding property measurement by the KEC method, each conductive layer has a proportionality constant of 4 or more when the shielding property in the range of 0.2 to 1 MHz is linearly approximated. The proportionality constant of the conductive layer is preferably 4.5 or more, and more preferably 5 or more. Also, the larger the proportionality constant, the more preferable it is, and although infinity is particularly preferable, it is technically difficult. From this perspective, the upper limit is preferably 10 or less.

[0025] For each magnetic layer, if each value of Xi represented by the formula (1) is 1 or more, and further the sum of Xi of each magnetic layer is 4 or more and 15 or less, it may be formed using the same material or different materials.

[0026] In the case of a three-layer structure as shown in FIG. 1, for example, the following combinations can be given. Magnetic metal layer / Conductive layer / Magnetic resin layer (a), Magnetic metal layer / Conductive layer / Magnetic metal layer (i), Magnetic resin layer / Conductive layer / Magnetic resin layer (u). From the viewpoint of improving followability and low-frequency shielding property, the combination of (a) is preferable.

[0027] In the case of a four-layer structure as shown in FIG. 2, for example, the following combinations can be given. Magnetic layer / Conductive metal layer / Magnetic layer / Conductive resin layer (shi), Magnetic layer / Conductive metal layer / Magnetic layer / Conductive metal layer (su), Magnetic layer / Conductive resin layer / Magnetic layer / Conductive resin layer (se). From the viewpoint of improving followability and low-frequency shielding property, the combination of (se) is preferable.

[0028] In the case of a five-layer structure as shown in FIG. 3, for example, the following combinations can be given. Magnetic metal layer / Conductive layer / Magnetic resin layer / Conductive layer / Magnetic resin layer (e), Magnetic resin layer / Conductive layer / Magnetic metal layer / Conductive layer / Magnetic resin layer (o), Magnetic metal layer / Conductive layer / Magnetic metal layer / Conductive layer / Magnetic resin layer (ka), Magnetic metal layer / Conductive layer / Magnetic resin layer / Conductive layer / Magnetic metal layer (ki), Magnetic metal layer / Conductive layer / Magnetic metal layer / Conductive layer / Magnetic metal layer (ku), Magnetic resin layer / Conductive layer / Magnetic resin layer / Conductive layer / Magnetic resin layer (ke). From the viewpoint of improving followability and low-frequency shielding property, the combinations of (e) and (o) are preferable.

[0029] Similarly, when there are a plurality of conductive layers, each conductive layer may be formed using the same material or different materials as long as the proportionality constant obtained when linearly approximating the shielding property up to 0.2 to 1 MHz in the magnetic field shielding property measurement by the KEC method is 4 or more. For example, the following combinations can be mentioned. Magnetic layer / Conductive metal layer / Magnetic layer / Conductive metal layer / Magnetic layer (c), Magnetic layer / Conductive resin layer / Magnetic layer / Conductive metal layer / Magnetic layer (s), Magnetic layer / Conductive resin layer / Magnetic layer / Conductive resin layer / Magnetic layer (sh). From the viewpoint of improving followability and low-frequency shielding property, the combination of (sh) is preferable.

[0030] ≪Magnetic layer≫ The magnetic layer will be described. The noise suppression layer of the present invention has an n-layer magnetic layer having a magnetic layer (A 1 ) and a magnetic layer (A n ). Here, n is an integer of 2 or more, which is the number of magnetic layers. X i is the value of √μ' i ×√t i in the magnetic layer (A i ). Each magnetic layer satisfies X i represented by the following formula (1) is 1 or more, more preferably 2 or more, and even more preferably 3 or more. X i being 1 or more enables high low-frequency shielding property to be obtained. By controlling the relative permeability μ' and the film thickness t, Xi of each magnetic layer can be made 1 or more.

[0031] Furthermore, the sum of X i of each magnetic layer is 4 or more and 15 or less, preferably 4.5 or more and 14.5 or less, and more preferably 5 or more and 14 or less. Being 4 or more improves the low-frequency shielding property, and being 15 or less improves the followability.

[0032] X i =√μ' i ×√t i ···Equation (1) Note that i is an integer from 1 to n, μ' i is the relative permeability at 1 MHz of the magnetic layer (A i ), and t i is the film thickness [mm] of the magnetic layer (A i ). That is.

[0033] The magnetic layer is preferably a magnetic metal layer or a magnetic resin layer composed of a magnetic filler and a binder resin. From the viewpoint of increasing the relative permeability, a magnetic metal layer is preferable, and from the viewpoint of improving the followability, a magnetic resin layer is preferable.

[0034] <Relative permeability> The relative permeability in the present invention is the ratio of the permeability μ of the object to the permeability μ 0 in vacuum, and refers to the real part of the relative permeability. From the viewpoints of obtaining followability to the complex uneven shape of the adherend and having a noise suppression sheet with low-frequency noise suppression ability, μ' of each magnetic layer is preferably 10 or more, more preferably 30 or more, and still more preferably 40 or more. When the relative permeability μ' is less than 10, the film thickness t satisfying the above range is large, and the flexibility may decrease.

[0035] <Film thickness> From the viewpoint of obtaining followability to the complex uneven shape of the adherend, t of each layer is preferably 10 μm to 500 μm, and more preferably 12 μm to 400 μm. The film thickness t of each magnetic layer is obtained by magnifying a cross-sectional image cut perpendicularly from the thickness direction of the layer 1000 to 2000 times with a laser microscope (manufactured by Keyence Corporation, VK-X100), observing the image, measuring at three locations based on the observed image, and calculating the average value.

[0036] <Magnetic metal layer> The magnetic layer is preferably a magnetic metal layer formed of a metal-based soft magnetic material that is at least one of a crystalline metal magnetic material and an amorphous metal magnetic material. The crystalline metal magnetic material includes a nanocrystalline metal magnetic material and the like. Examples of the crystalline metal material include Fe, Co, Ni, FeSi alloy, FeNi alloy, FeSiAl alloy, and FeSiCr alloy. By using the magnetic metal layer, a desired relative permeability μ' can be imparted to each magnetic layer. The thickness of the magnetic metal layer is preferably 10 μm to 30 μm. By setting it to 10 μm or more, μ' can be improved, and by setting it to 30 μm or less, the followability can be enhanced.

[0037] <Magnetic resin layer> When the magnetic layer is a magnetic resin layer, it is composed of a magnetic filler and a binder resin. [Magnetic filler] In the present invention, the magnetic filler imparts a desired relative permeability μ' to each magnetic layer. Examples of the magnetic filler include metal-based soft magnetic materials such as crystalline metal magnetic materials or amorphous metal magnetic materials, and ferrite-based substances. It preferably includes a metal-based soft magnetic material that is at least one of a crystalline metal magnetic material and an amorphous metal magnetic material. The crystalline metal magnetic material also includes a nanocrystalline metal magnetic material and the like. Examples of the crystalline metal magnetic material include Fe, Co, Ni, FeSi alloy, FeNi alloy, FeSiAl alloy, FeSiCr alloy. Examples of the ferrite-based substances include MnZn ferrite, MgZn ferrite, MnMg ferrite, CuZn ferrite, MgMnSr ferrite, and NiZn ferrite, which can be used. The magnetic fillers can be used alone or in combination of two or more. Among these, from the viewpoint of obtaining a higher relative permeability μ' 1 a metal-based soft magnetic material is more preferable, and a crystalline metal magnetic material is more preferable.

[0038] The content of the magnetic filler is preferably 20 to 90% by weight, more preferably 40 to 90% by weight, and particularly preferably 65 to 85% by weight in 100% by weight of the solid content of the first magnetic layer. By setting it within the above range, a desired relative permeability μ' can be obtained, and the shielding property at low frequencies is particularly excellent.

[0039] The shape of the magnetic filler is preferably flaky to obtain a high relative permeability μ´, and the average particle diameter D 50 is preferably 20 to 70 μm, more preferably 25 to 65 μm. By setting D 50 to 20 μm or more, μ´ 1 can be improved, and by setting it to 70 μm or less, it becomes easier to form a sheet.

[0040] The average particle diameter D of the magnetic filler 50 can be measured by the laser diffraction / scattering method. Specifically, for example, using a laser diffraction / scattering particle size distribution measuring device LS 13 320 (manufactured by Beckman Coulter), it is a numerical value obtained by measuring each conductive fine particle with a Turndoer dry powder sample module, and is the average particle diameter of the particle size at which the integrated value of the particles is 50%. The refractive index is set to 1.6 for measurement.

[0041] The tap density of the magnetic filler is preferably 0.2 to 4.0 g / cm from the viewpoint of obtaining a high volume occupancy ratio in the sheet and improving the relative permeability 3 is preferably 0.25 to 3.0 g / cm 3 is more preferably.

[0042] The average thickness of the magnetic filler is preferably 0.5 to 5 μm, more preferably 1 to 3 μm. By setting the average thickness of the magnetic filler within the above range, the orientation in the plane direction can be suppressed and the relative permeability can be improved.

[0043] The thickness of the flaky magnetic filler is obtained by measuring about 10 to 20 different particles based on an image magnified 1000 to 2000 times with a laser microscope (manufactured by Keyence, VK-X100) of a cross-sectional image obtained by vertically cutting the noise suppression sheet from the thickness direction, and is obtained from the average value.

[0044] [Binder resin] The binder resin used in the present invention is preferably a thermosetting resin or a thermoplastic resin, and a thermoplastic resin and a thermosetting resin may be used in combination.

[0045] A thermosetting resin is a resin having a plurality of crosslinkable reactive functional groups. Examples of the reactive functional groups include a hydroxyl group, a phenolic hydroxyl group, a carboxyl group, an amino group, an epoxy group, an oxetanyl group, an oxazoline group, an oxazine group, an aziridine group, a thiol group, an isocyanate group, a blocked isocyanate group, a silanol group, and the like. Among these, it is preferable to have a carboxyl group. Examples of the thermosetting resin having a reactive functional group include an acrylic resin, a maleic acid resin, a polybutadiene-based resin, a polyester resin, a condensation-type polyester resin, an addition-type polyester resin, a melamine resin, a polyurethane resin, a polyurethane urea resin, an epoxy resin, an oxetane resin, a phenoxy resin, a polyimide resin, a polyamide resin, a phenolic resin, an alkyd resin, an amino resin, a polylactic acid resin, an oxazoline resin, a benzoxazine resin, a silicone resin, a fluororesin, and the like. Among these, from the viewpoints of followability and volume resistivity, a polyurethane resin, a polyurethane urea resin, an epoxy resin, an addition-type polyester resin, a polyimide resin, a polyamide resin, and a polyamideimide resin are preferable. The thermosetting resins can be used alone or in combination of two or more.

[0046] Thermoplastic resins include polyolefin-based resins, vinyl-based resins, styrene-acrylic resins, diene-based resins, terpene resins, petroleum resins, cellulose-based resins, polyamide resins, polyurethane resins, polyester resins, polycarbonate resins, polyimide-based resins, fluororesins, etc., which do not have the curable functional groups.

[0047] The polyolefin-based resin is preferably a homopolymer or copolymer of ethylene, propylene, an α-olefin compound, etc. Specifically, for example, polyethylene propylene rubber, an olefin-based thermoplastic elastomer, an α-olefin polymer, etc. can be mentioned. Vinyl resins are preferably polymers obtained by polymerization of vinyl esters such as vinyl acetate and copolymers of vinyl esters and olefin compounds such as ethylene. Specifically, for example, ethylene-vinyl acetate copolymers, partially saponified polyvinyl alcohol, etc. may be mentioned. Styrene-acrylic resins are preferably homopolymers or copolymers composed of styrene, (meth)acrylonitrile, acrylamides, (meth)acrylic acid esters, maleimides, etc. Specifically, for example, syndiotactic polystyrene, polyacrylonitrile, acrylic copolymers, ethylene-methyl methacrylate copolymers, etc. may be mentioned. Diene resins are preferably homopolymers or copolymers of conjugated diene compounds such as butadiene and isoprene and their hydrogenated products. Specifically, for example, styrene-butadiene rubber, styrene-isoprene block copolymer, etc. may be mentioned. Terpene resins are preferably polymers composed of terpenes or their hydrogenated products. Specifically, for example, aromatic-modified terpene resins, terpene phenol resins, hydrogenated terpene resins may be mentioned. Petroleum resins are preferably dicyclopentadiene-type petroleum resins and hydrogenated petroleum resins. Cellulose resins are preferably cellulose acetate butyrate resins. Polycarbonate resins are preferably bisphenol A polycarbonates. Polyimide resins are preferably thermoplastic polyimides, polyamideimide resins, and polyamic acid-type polyimide resins. Thermosetting resins can be used alone or in combination of two or more.

[0048] The weight average molecular weight of the binder resin to be used is preferably 20,000 to 200,000, more preferably 25,000 to 180,000. When the weight average molecular weight is 20,000 to 200,000, the desired volume resistivity, relative permeability μ´, and elongation can be achieved simultaneously. The measurement of the weight average molecular weight (Mw) can be determined using GPC (gel permeation chromatography) ("HPC-8020" manufactured by Tosoh Corporation).

[0049] Alternatively, a curing agent may be added. The curing agent has a plurality of functional groups capable of reacting with reactive functional groups in the thermosetting resin. Preferred curing agents include epoxy compounds, acid anhydride group-containing compounds, isocyanate compounds, aziridine compounds, dicyandiamide; amine compounds such as aromatic diamines; and phenol compounds such as phenol novolac resins. The curing agent can be used alone or in combination of two or more.

[0050] The composition constituting the magnetic resin layer may further contain a dispersant, a colorant, a flame retardant, an inorganic additive, a lubricant, an antiblocking agent, a silane coupling agent, etc.

[0051] Examples of the dispersant include phosphate ester surfactants, long-chain alkyl fatty acids, etc. Examples of the colorant include organic pigments, carbon black, ultramarine, bengara, zinc white, titanium oxide, graphite, etc. Among these, the print visibility is improved when printing on the sheet by including a black colorant. Examples of the flame retardant include halogen-containing flame retardants, phosphorus-containing flame retardants, nitrogen-containing flame retardants, inorganic flame retardants, etc. Examples of the inorganic additive include glass fiber, silica, talc, ceramic, etc. Examples of the lubricant include fatty acid esters, hydrocarbon resins, paraffin, higher fatty acids, fatty acid amides, aliphatic alcohols, metal soaps, modified silicones, etc. Examples of the antiblocking agent include calcium carbonate, silica, polymethylsilsesquioxane, aluminum silicate salts, etc.

[0052] The thickness of the magnetic resin layer is preferably 50 μm to 500 μm. By setting it to 50 μm or more, μ´1 can be improved, and by setting it to 500 μm or less, the followability can be enhanced.

[0053] The magnetic resin layer is obtained by coating a magnetic resin composition obtained by mixing and stirring a binder resin and a magnetic filler on a substrate such as a release film.

[0054] Stirring can be carried out using a known stirring device, and a dispermat or a homogenizer is preferred. For coating, known coating methods such as gravure coating method, kiss coating method, die coating method, lip coating method, comma coating method, blade coating method, roll coating method, knife coating method, spray coating method, bar coating method, spin coating method, dip coating method, etc. can be used. During coating, a drying process may be provided as necessary. For the drying, known drying devices such as a hot air dryer and an infrared heater can be used.

[0055] As the release film, a base material such as paper or plastic can be used, and it may be a sheet having a known release treatment on one surface of the base material, or a film having an adhesive layer with a slightly adhesive force formed instead of the release treatment.

[0056] It is preferable to perform a pressure treatment on the magnetic resin layer after coating and drying. The pressure treatment can be carried out, for example, by a flat press or a roll press, and it is preferably carried out while heating. The heating temperature is preferably 23 to 200 °C, more preferably 50 to 170 °C. If it exceeds 200 °C, the sheet may be damaged. The pressure is preferably 1 to 10 MPa, more preferably 2 to 8 MPa. By setting the heating temperature and the pressure within the above ranges, the relative permeability can be improved.

[0057] ≪Conductive layer≫ The conductive layer has at least (n - 1) layers in the noise suppression layer, and each conductive layer is characterized in that the proportionality constant obtained when linearly approximating the shielding property up to 0.2 to 1 MHz in the magnetic field shielding property measurement by the KEC method is 4 or more. The lower limit of the above proportionality constant is preferably 4, more preferably 4.5, and even more preferably 5. Also, the larger the above proportionality constant, the more preferable it is, and although infinity is preferable, it is technically difficult, so from this perspective, the upper limit is preferably 10 or less. By setting the proportionality constant to 4 or more, the low-frequency shielding property is significantly improved.

[0058] <Regarding the proportionality constant obtained by linear approximation of shielding property> In the present invention, the proportionality constant will be described. FIG. 4 is an example of the magnetic field shielding property of the conductive layer by the KEC method. As shown in FIG. 4, since the range from 0.1 MHz to less than 0.2 MHz is close to the lower limit of the measurement frequency and the numerical reliability is poor, the measurement results (dB) of the shielding property for 0.2 to 1 MHz are linearly approximated to calculate the proportionality constant (FIG. 5). By laminating a conductive layer having such a proportionality constant of 4 or more alternately with a magnetic layer to form a noise suppression layer, a remarkable effect on low-frequency noise suppression can be obtained. Thus, when the proportionality constant of the conductive layer adjacent to the magnetic layer is 4 or more, it can be made excellent in the low-frequency noise suppression effect. In addition, in the case of a laminate having at least four layers of magnetic layer / conductive layer / magnetic layer / conductive layer, or in the case of a laminate having at least five layers laminated in the order of magnetic layer / conductive layer / magnetic layer / conductive layer / magnetic layer, when there are a plurality of conductive layers, the proportionality constant of each conductive layer is 4 or more.

[0059] The conductive layer is preferably a conductive metal layer or a conductive resin layer composed of a conductive filler and a binder resin. From the viewpoint of enhancing the low-frequency shielding property, a conductive metal layer is preferable, and from the viewpoint of enhancing the followability, a conductive resin layer is preferable.

[0060] <Conductive metal layer> When the conductive layer is a conductive metal layer, by forming it from any one of gold, silver, copper, nickel, and aluminum or an alloy thereof, a desired proportionality constant can be imparted to each conductive layer. From the viewpoints of controlling the proportionality constant and cost, copper and aluminum are preferable. The lower limit of the thickness of the conductive metal layer is preferably 1 μm or more, more preferably 5 μm or more. On the other hand, the upper limit of the thickness of the metal foil is preferably 30 μm or less, more preferably 20 μm or less. By setting the range as above, a desired proportionality constant can be satisfied and the followability can be achieved at the same time.

[0061] <Conductive resin layer> When the conductive layer is a conductive resin layer, it is composed of a conductive filler and a binder resin. As the binder resin, the same binder resin as that described for the magnetic resin layer can be used.

[0062] [Conductive filler] In the present invention, as the conductive filler, metal powders such as gold, silver, copper, nickel, and aluminum, alloy powders such as solder, core-shell type particles such as silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, and gold-coated nickel powder can be used to impart a desired proportionality constant to the conductive resin layer. The conductive fillers can be used alone or in combination of two or more. From the viewpoint of obtaining excellent conductivity in terms of weight, a conductive filler containing gold, silver, or copper is preferable. From the viewpoints of controlling the proportionality constant and cost, silver-coated copper powder is preferable. The silver content in silver-coated copper is preferably 6 to 20% by weight, more preferably 8 to 17% by mass, and still more preferably 10 to 15% by weight based on 100% by weight in total of silver and copper. In the case of core-shell type particles, the coating rate of the coating layer with respect to the core part is preferably 60% by weight or more on average, more preferably 70% by weight or more, and still more preferably 80% by weight or more. The core part may be non-metallic, but from the viewpoint of conductivity, a conductive substance is preferable, and metal particles are more preferable. To obtain a desired proportionality constant, the volume resistivity should be 1.0×10 -4 Ω·m or less. For organic conductive materials different from the above materials, such as carbon-based conductive materials such as carbon black, carbon nanotubes, and graphite, and conductive polymers such as polyacetylene and polythiophene, it may be difficult to satisfy the range of the above proportionality constant of 4 or more.

[0063] As the shape of the conductive filler, flake-like particles, dendritic particles, plate-like particles, grape-like particles, and spherical particles can be used, but flake-like particles and dendritic particles are preferable, and flake-like particles are more preferable.

[0064] The average particle diameter D of the conductive filler 50 is preferably 4 to 20 μm. The flaky particles may be mixed with nano-sized conductive fillers. By mixing nano-sized particles, the phenomenon of melting point depression of nanoparticles is utilized to form an intermetallic bond during thermocompression bonding, which has the effect of improving the shielding property.

[0065] The average particle diameter D of the conductive filler 50 can be measured in the same manner as the magnetic filler.

[0066] The average thickness of the flaky conductive filler is preferably 0.01 to 1.5 μm, more preferably 0.05 to 1.0 μm. By setting the average thickness of the conductive filler within the above range, it can be appropriately oriented in the thickness direction within the noise suppression sheet and the volume resistance value can be reduced.

[0067] The thickness of the conductive filler can be determined in the same manner as the magnetic filler.

[0068] As the conductive filler, it is preferable to use flaky particles, but flaky particles and particles of other shapes may be used in combination. The shape of the particles used in combination is not particularly limited, but particles selected from the group consisting of dendritic particles, fibrous particles, acicular particles, and spherical particles are preferable. The particles used in combination are used alone or in combination. When used in combination, examples include a combination of flaky particles and dendritic particles, a combination of flaky particles, dendritic particles, and spherical particles, and a combination of flaky particles and spherical particles. Among these, from the viewpoint of enhancing the noise suppression ability and the elongation rate, it is more preferable to use flaky particles alone or a combination of flaky particles and dendritic particles.

[0069] The tap density of the conductive filler is preferably 0.2 to 4.0 g / cm to obtain a high volume occupancy rate within the sheet 3 and more preferably 0.25 to 3.0 g / cm 3 is more preferable.

[0070] The thickness of the conductive resin layer is preferably 25 μm to 400 μm. By setting it to 25 μm or more, the desired proportionality constant can be satisfied, and by setting it to 400 μm or less, the followability can be enhanced.

[0071] The conductive resin layer is obtained by coating a conductive resin composition obtained by mixing and stirring a binder resin and a conductive filler on a base material such as a release film.

[0072] Stirring and coating can be performed in the same manner as for the magnetic resin layer.

[0073] As the release film, the same one as the magnetic resin layer can be used.

[0074] The conductive resin layer is preferably subjected to a pressure treatment after coating and drying. The pressure treatment can be performed in the same manner as for the magnetic resin layer.

[0075] <Method for manufacturing noise suppression sheet> The noise suppression sheet of the present invention is formed by forming a noise suppression layer on a base material such as a release film, and is obtained by sequentially laminating a magnetic sheet having a magnetic layer formed on the base material and a conductive sheet having a conductive layer formed on the base material. As the release film, paper, plastic, etc. can be used, and it may be a sheet having a known release treatment on one surface of the base material, or a film having an adhesive layer with a slightly adhesive force formed instead of the release treatment. The noise suppression layer is obtained by alternately laminating a magnetic layer and a conductive layer. Lamination of the magnetic layer and the conductive layer can be carried out by a pressure treatment. Also, when the noise suppression layer has a conductive layer, it is obtained by laminating in the order of magnetic layer / conductive layer / magnetic layer / conductive layer, and when it further has a magnetic layer, it is obtained by laminating in the order of magnetic layer / conductive layer / magnetic layer / conductive layer / magnetic layer. Lamination of each layer can be carried out by a pressure treatment.

[0076] The pressing treatment can be carried out, for example, using a flat press or a roll press, and it is preferably carried out while heating. The heating temperature is preferably 23 to 200°C, more preferably 50 to 170°C. If it exceeds 200°C, destruction of each layer may occur. The pressing pressure is preferably 1 to 10 MPa, more preferably 2 to 8 MPa. By setting the heating temperature and the pressing pressure within the above ranges, lamination becomes possible.

[0077] When a magnetic metal layer is used as the magnetic layer and a conductive metal layer is used as the conductive layer, an adhesive layer for laminating the respective layers may be provided. As the adhesive layer, the binder resin described for the magnetic resin layer can be selected, and a curing agent can also be used in combination as necessary. When at least one conductive layer is a conductive metal layer and the magnetic layer (Ai) is a magnetic resin layer, the magnetic resin layer can also be formed by directly applying a magnetic resin composition to the conductive metal layer. Further, when the magnetic layer (Ai) is a magnetic metal layer and the conductive layer is a conductive resin layer, the conductive layer can be formed by directly applying a conductive resin composition to the magnetic metal layer which is the magnetic layer (Ai).

[0078] The coating methods of the above-described magnetic resin composition and conductive resin composition can be carried out in the same manner as the coating method of the magnetic resin layer. Further, the magnetic layer and the conductive resin layer formed by direct coating are preferably subjected to a pressing treatment. The pressing treatment method can be carried out in the same manner as the magnetic resin layer.

Examples

[0079] Hereinafter, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited only to the following examples. In the following, "parts" are "parts by weight" and "%" are values based on "wt%". In addition, in order to align with the invention according to Claim 1, Example 4 described later shall be read as Reference Example 1, Example 14 as Reference Example 2, and Example 15 as Reference Example 3.

[0080] Note that the average particle diameter D of the conductive filler and the magnetic filler 50 The acid value of the thickness resin of the conductive filler and the magnetic filler, and the weight average molecular weight of the resin were measured by the following methods.

[0081] <Measurement of average particle diameter D 50 > The average particle diameter D 50 was measured using a laser diffraction / scattering particle size distribution analyzer LS13320 (manufactured by Beckman Coulter, Inc.) with a Turndo Dry Powder Sample Module for conductive fillers and magnetic fillers. The refractive index was set to 1.6.

[0082] <Measurement of filler thickness The thicknesses of the magnetic filler and the conductive filler were determined by measuring about 10 - 20 different particles based on an image magnified 1000 - 2000 times with a laser microscope (VK-X100, manufactured by Keyence Corporation) of a cross-sectional image obtained by vertically cutting a noise suppression sheet in the thickness direction, and calculating the average value.

[0083] <Measurement of acid value 1 g of the thermosetting resin was dissolved in 40 ml of methyl ethyl ketone, and an automatic titrator "AT-510" manufactured by Kyoto Electronics Industry Co., Ltd. with "APB-510-20B" manufactured by the same company connected as a burette was used. Potentiometric titration was performed using a 0.1 mol / L ethanolic KOH solution as the titrant, and the number of mg of KOH per 1 g of the resin was calculated.

[0084] <Weight-average molecular weight (Mw)> The weight-average molecular weight (Mw) was measured using GPC (gel permeation chromatography) ("HPC-8020" manufactured by Tosoh Corporation). GPC is a liquid chromatography that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on the difference in their molecular sizes. In the measurement of the present invention, two "LF-604" (manufactured by Showa Denko K.K.: GPC column for rapid analysis: 6 mm ID × 150 mm size) columns were connected in series and used, and the measurement was performed under the conditions of a flow rate of 0.6 ml / min and a column temperature of 40°C. The weight-average molecular weight (Mw) was determined in terms of polystyrene conversion.

[0085] <Synthesis of thermosetting resin [Synthesis Example 1] Into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube, 414 parts of a diol having a number average molecular weight (hereinafter referred to as "Mn") = 1006 obtained from adipic acid, terephthalic acid, and 3-methyl-1,5-pentanediol, 8 parts of dimethylolbutanoic acid, 145 parts of isophorone diisocyanate, and 40 parts of toluene were charged, and the mixture was reacted at 90 °C for 3 hours under a nitrogen atmosphere. To this, 300 parts of toluene was added to obtain a solution of a urethane prepolymer having isocyanate groups at the terminals. Next, 816 parts of the obtained solution of the urethane prepolymer was added to a mixture of 27 parts of isophorone diamine, 3 parts of di-n-butylamine, 342 parts of 2-propanol, and 576 parts of toluene, and the mixture was reacted at 70 °C for 3 hours to obtain a solution of a polyurethane-polyurea resin having a weight average molecular weight (hereinafter referred to as "Mw") = 54,000 and an acid value of 5 mg KOH / g. To this, 144 parts of toluene and 72 parts of 2-propanol were added to obtain a polyurethane-polyurea resin solution having a solid content of 50%.

[0086] The materials used in the examples are shown below. · Magnetic filler 1: Fe-Si-Al-based soft magnetic particles (average particle diameter D 50 : 45 μm, average thickness 1.3 μm) manufactured by Sanyo Special Steel Co., Ltd. · Conductive filler 1: Flaky silver particles (average particle diameter D 50 : 5.1 μm, average thickness 0.3 μm) manufactured by Fukuda Metal Co., Ltd. · Dispersant: Phosphate ester-based dispersant (trade name: Disparon (registered trademark) PW-36, manufactured by Nambon Kasei Co., Ltd.) · Silane coupling agent: 3-acryloxypropyltrimethoxysilane (trade name: KBM-5103, manufactured by Shin-Etsu Silicone Co., Ltd.) · Aziridine-based compound: "Chemite PZ-33" manufactured by Nippon Catalyst Co., Ltd.

[0087] <Manufacture of magnetic sheet> (Magnetic sheet (a-1)) 15.7 parts of a thermosetting resin, 80 parts of magnetic filler 1, 2 parts of a dispersant, 2 parts of a silane coupling agent, and 0.3 part of an aziridine compound were charged into a container (all in terms of solid content), and a mixed solvent of toluene:isopropyl alcohol (weight ratio 2:1) was added so that the non-volatile content concentration became 50% by weight, and the mixture was stirred with a disper for 10 minutes to obtain a magnetic resin composition. Next, the magnetic resin composition was coated onto a release film using a doctor blade so that the dry thickness became 150 μm, and then dried in an electric oven at 100 °C for 10 minutes to obtain a magnetic resin layer with a release film. Further, the magnetic resin layer with a release film was pressure-treated in a flat press machine at 90 °C, 2 MPa for 5 minutes to obtain a magnetic sheet (a-1) with a thickness of 100 μm.

[0088] (Magnetic sheets (a-2 to 8, ac-1)) Magnetic sheets (a-2 to 8, ac-1) were obtained in the same manner as the magnetic sheet (a-1), except that the types and blending amounts (parts by weight) of the raw materials of the magnetic sheet (a-1) were changed as shown in Table 1.

[0089] (Magnetic sheet (a-9)) Magnetic metal layer 1: Co-Fe-Mo-Nb-Si-B alloy (thickness 20 μm) manufactured by EMR Shielding Solutions was used as the magnetic sheet (a-9).

[0090]

Table 1

[0091] (Production of a conductive sheet) (Conductive sheet (b-1)) 15.7 parts of a thermosetting resin, 80 parts of a conductive filler 1, 2 parts of a dispersant, 2 parts of a silane coupling agent, and 0.3 part of an aziridine compound were charged into a container (all in terms of solid content), and a mixed solvent of toluene:isopropyl alcohol (weight ratio 2:1) was added so that the non-volatile content concentration became 50% by weight, and the mixture was stirred with a disper for 10 minutes to obtain a conductive resin composition. Next, the conductive resin composition was coated on a release film using a doctor blade so that the dry thickness became 110 μm, and further dried in an electric oven at 100 °C for 10 minutes to obtain a conductive resin layer with a release film. Further, the conductive resin layer with a release film was pressure-treated at 90 °C, 2 MPa, and for 5 minutes using a flat plate press to obtain a conductive sheet (b-1) with a thickness of 50 μm.

[0092] (Conductive sheets (b-2 to 6, bc-1)) Conductive sheets (b-2 to 6, bc-1) were obtained in the same manner as the conductive sheet (b-1), except that the types and blending amounts (parts by weight) of the raw materials of the conductive sheet (b-1) were changed as shown in Table 2.

[0093] (Conductive sheet (b-7)) Conductive metal layer 1: Aluminum foil, alloy number 8021, thickness 12 μm, manufactured by UACJ Foil Co., Ltd. was used as the conductive sheet (b-7).

[0094]

Table 2

[0095] [Example 1] Two magnetic sheets (a-1) and one conductive sheet (b-1) were prepared. The magnetic resin layer surface of the magnetic sheet (a-1) and the conductive resin layer surface of the conductive sheet (b-1) were pressure-treated at 120 °C and 5 MPa using a roll press and laminated. The release film on the conductive resin layer side of the obtained laminate was peeled off, and the conductive resin layer surface of the exposed conductive layer and the magnetic resin layer surface of the other magnetic sheet (a-1) were pressure-treated at 120 °C and 5 MPa using a roll press to obtain a noise suppression sheet having a three-layer laminate.

[0096] [Examples 2 - 8, Comparative Examples 1 - 5] Noise suppression sheets were obtained in the same manner as in Example 1, except that the types and amounts (parts by weight) of the raw materials in Example 1 were changed as shown in Tables 3 - 5. Note that in Comparative Examples 3 and 4, noise suppression sheets were obtained using only the magnetic sheet (a - 3) or the conductive sheet (b - 3), respectively.

[0097] [Example 9] Two magnetic sheets (a - 1) and one conductive sheet (b - 7), which is a 12 - μm aluminum foil, were prepared. The magnetic resin layer side of the magnetic sheet (a - 1) and the conductive sheet (b - 7) were pressure - treated at 120°C and 5 MPa using a roll press and laminated. The metal layer side of the obtained laminate and the magnetic resin layer side of another magnetic sheet (a - 1) were pressure - treated at 120°C and 5 MPa using a roll press to obtain a noise suppression sheet having a three - layer laminate.

[0098] [Example 10] One magnetic sheet (a - 1), one magnetic sheet (a - 9), and one conductive sheet (b - 2) were prepared. The conductive resin layer side of the conductive sheet (b - 2) and the 20 - μm magnetic metal layer of the magnetic sheet (a - 9) were pressure - treated at 120°C and 5 MPa using a roll press and laminated. The release film on the conductive layer side of the obtained laminate was peeled off, and the conductive resin layer side of the exposed conductive layer and the magnetic resin layer side of the magnetic sheet (a - 1) were pressure - treated at 120°C and 5 MPa using a roll press to obtain a noise suppression sheet having a three - layer laminate.

[0099] [Example 11] Three magnetic sheets (a - 1) and two conductive sheets (b - 1) were prepared. The magnetic resin layer side of the magnetic sheet (a - 1) and the conductive resin layer side of the conductive sheet (b - 1) were pressure - treated at 120°C and 5 MPa using a roll press to obtain laminate 1. Laminate 2 was obtained by laminating another conductive sheet (b - 1) and another magnetic sheet (a - 1) in the same manner. Next, the release film on the conductive layer side of the obtained laminate 1 was peeled off, and the conductive resin layer surface of the exposed conductive layer and the magnetic resin layer surface of the remaining magnetic sheet (a-1) were pressure-treated at 120 °C and 5 MPa using a roll press to obtain laminate 3. The release film on the magnetic resin layer side of laminate 3 was peeled off, and the magnetic resin layer surface of the exposed magnetic layer and the conductive resin layer surface of the conductive layer obtained by peeling off the release film on the conductive layer side of laminate 2 were pressure-treated at 120 °C and 5 MPa using a roll press to obtain a noise suppression sheet having a five-layer laminate.

[0100] [Example 12, Comparative Examples 6 and 7] A noise suppression sheet was obtained in the same manner as in Example 10, except that the types of sheets in Example 10 were changed as shown in Tables 3 to 5.

[0101] [Example 13] Three magnetic sheets (a-1) and two conductive sheets (b-7) were prepared. The magnetic resin layer surface of the magnetic sheet (a-1) and the conductive sheet (b-7), which is a 12-μm aluminum foil (conductive metal layer), were pressure-treated at 120 °C and 5 MPa using a roll press to obtain a laminate. The conductive metal layer side of the obtained laminate and the magnetic resin layer surface of the other magnetic sheet (a-1) were pressure-treated at 120 °C and 5 MPa using a roll press to obtain laminate 1. The release film on the magnetic sheet (a-1) side of laminate 1 was peeled off, and the exposed magnetic resin layer surface and the conductive metal layer were pressure-treated at 120 °C and 5 MPa using a roll press to obtain laminate 2. The conductive metal layer side of the obtained laminate 2 and the magnetic resin layer surface of the remaining magnetic sheet (a-1) were pressure-treated at 120 °C and 5 MPa using a roll press to obtain a noise suppression sheet.

[0102] [Examples 14 and 15] A noise suppression sheet was obtained in the same manner as in Example 13, except that the types of sheets in Example 13 were changed as shown in Table 4.

[0103] [Example 16] Two magnetic sheets (a-1) and two conductive sheets (b-1) were prepared. The magnetic resin layer surface of the magnetic sheet (a-1) and the conductive resin layer surface of the conductive sheet (b-1) were pressure-treated at 120 °C and 5 MPa using a roll press to obtain laminate 1. In the same manner, laminate 2 was obtained by laminating another conductive sheet (b-1) and another magnetic sheet (a-1). Next, the release film on the conductive layer side of the obtained laminate 1 was peeled off, and the conductive resin layer surface of the exposed conductive layer and the magnetic resin layer surface of the magnetic layer exposed by peeling off the release film on the magnetic resin layer side of laminate 2 were pressure-treated at 120 °C and 5 MPa using a roll press to obtain a noise suppression sheet having a four-layer laminate.

[0104] Regarding the above examples and comparative examples, physical property values were measured and evaluated according to the following measurement methods and evaluation criteria. The results are shown in Table 1.

[0105] <Film thickness t of the magnetic resin layer or the conductive resin layer> A magnetic sheet or a conductive sheet was prepared in a size of 50 mm in width and 50 mm in length. Next, a polyimide film (Kapton 300H, manufactured by Toray DuPont Co., Ltd.) with a thickness of 50 μm was pressure-bonded to the exposed magnetic resin layer or conductive resin layer surface at 90 °C, 2 MPa, and for 5 minutes. After pressure-bonding, 0.05 g of an epoxy resin (Petropoxy 154, manufactured by Maruto Co., Ltd.) was dropped onto a slide glass, and the sheet 1 from which the release film had been removed and the polyimide film were adhered to obtain a laminate having a structure of (slide glass / magnetic resin layer or conductive resin layer / polyimide film). The obtained laminate was cut by ion beam irradiation from the polyimide film side using a cross-section polisher (SM-09010, manufactured by JEOL Ltd.) to form a cross-section of the magnetic sheet or the conductive sheet. The exposed cross-section was observed at a magnification of 1000 to 2000 times using a laser microscope (VK-X100, manufactured by Keyence Corporation) to measure the film thickness t.

[0106] <Specific magnetic permeability> A magnetic sheet was prepared with a size of 50 mm in length and 50 mm. Next, a polyimide film (Kapton 300H, manufactured by Toray DuPont Co., Ltd.) with a thickness of 50 μm was pressure-bonded to the exposed magnetic resin layer surface under the conditions of 90 °C, 2 MPa, and 5 minutes. After the pressure bonding, the release film was peeled off, and it was cut out to an outer shape of 18 mm and an inner diameter of 5 mm to obtain a measurement sample. The measurement was performed using an impedance analyzer (model number 4294A, manufactured by Agilent Technologies) and a test fixture 16454A (manufactured by Keysight Technologies). In the case of the magnetic metal layer, a magnetic metal layer with a thickness of 20 μm was prepared with a size of 50 mm in width and 50 mm in length, and it was cut out to an outer shape of 18 mm and an inner diameter of 5 mm to obtain a measurement sample.

[0107] <Proportional constant> A conductive sheet was prepared with a size of 70 mm in width and 70 mm in length. Next, a polyimide film (Kapton 300H, manufactured by Toray DuPont Co., Ltd.) with a thickness of 50 μm was pressure-bonded to the exposed conductive resin layer surface under the conditions of 90 °C, 2 MPa, and 5 minutes. After the pressure bonding, the shielding performance was measured by the KEC method using a magnetic field antenna. The proportional constant was obtained by linearly approximating the numerical values from 0.2 to 1 MHz of the obtained results and calculating a linear equation. In the case of the conductive metal layer, the conductive metal layer was prepared with a size of 70 mm in width and 70 mm in length, and the measurement was performed with a polyimide film (Kapton 300H, manufactured by Toray DuPont Co., Ltd.) with a thickness of 50 μm sandwiched so that the device and the sample were not in direct contact.

[0108] <Low-frequency shielding performance> The obtained noise suppression sheet was prepared with a size of 70 mm in width and 70 mm in length to obtain a measurement sample. The shielding performance was measured by the KEC method using a magnetic field antenna, and the shielding performance at 300 kHz was evaluated. The evaluation criteria are as follows. ○: 13 dB or more. It is a very good result. △: 10 dB or more and less than 13 dB. It is a good result. ×: Less than 10 dB. It is not practical.

[0109] <Followability> A description will be given with reference to Fig. 6(1). A polyimide film 13 with an adhesive having a thickness of 200 μm, a width of 20 mm, and a length of 30 mm, a stainless steel plate 15 having a thickness of 200 μm, a width of 50 mm, and a length of 50 mm, and the noise suppression layer 12 described in the embodiment sandwiched between release films 10 and 11 were prepared to a size of 40 mm in width and 40 mm in length as a sample. An adhesive was applied onto the stainless steel plate 14 and thermocompression bonded so that the polyimide film 14 was positioned substantially at the center. Next, the release film 10 was peeled off, and the noise suppression sheet 12 and the release film 11 were placed so that the noise suppression sheet 12 was in contact with the polyimide film 14. These were pressure-bonded under the conditions of 90°C, 2 MPa, and 5 min, and the release film 11 was peeled off to obtain a laminate 15 shown in Fig. 6(2). Then, the followability between the noise suppression layer and the stainless steel plate 14 was evaluated by observing a 50-fold magnified image of the stepped portion of the circular broken line 16 of the laminate 15 using the naked eye and a microscope. ◎: The noise suppression sheet follows the stepped portion without any gaps. Good result. ○: The noise suppression sheet follows the stepped portion with a slight gap. Practicable. ×: The noise suppression sheet does not follow the stepped portion and large gaps are observed. Not practicable

[0110]

Table 3

[0111]

Table 4

[0112]

Table 5

[0113] From Tables 3 to 5, the noise suppression sheet of the present invention has a magnetic layer (A 1 ) and a magnetic layer (A nAn n-layer magnetic layer having ) and a noise suppression layer having at least (n - 1) conductive layers, wherein the magnetic layer and the conductive layer are alternately laminated, and each of the magnetic layers is X represented by the following formula (1). i is 1 or more, and the sum of X i of each magnetic layer is 4 or more and 15 or less, and each of the conductive layers has a high suppression ability against low-frequency noise of 1 MHz or less because the proportionality constant obtained when approximating the shielding property of 0.2 to 1 MHz linearly in the magnetic field shielding property measurement by the KEC method is 4 or more. Furthermore, it was confirmed that the followability to the complicated uneven shape of the adherend is good.

Explanation of Symbols

[0114] 1 Noise suppression sheet 2 Magnetic layer (A 1 ) 3 Conductive layer (B 1 ) 4 Magnetic layer (A 2 ) 5 Noise suppression layer 6 Release film 7 Conductive layer (B 2 ) 8 Magnetic layer (A 3 ) 11 Release film 12 Noise suppression sheet 13 Polyimide film 14 Stainless steel plate 15 Laminate

Claims

1. A noise suppression sheet used to suppress noise of 1 MHz or less, comprising a magnetic layer (A １ ) and a magnetic layer (A ｎ ) and a noise suppression layer having at least (n−1) conductive layers, the magnetic layers and the conductive layers are alternately laminated, The magnetic layer is a magnetic metal layer or a magnetic resin layer containing a magnetic filler and a binder resin, the magnetic metal layer and the magnetic filler contain a crystalline metal magnetic material selected from the group consisting of an FeSiAl alloy and a Co—Fe—Mo—Nb—Si—B alloy; The average particle size D of the magnetic filler is 20 to 70 μm; The noise suppression layer has a thickness of 100 to 600 μm, In each of the magnetic layers, Xi represented by the following formula (1) is 1 or more, X of each of the magnetic layers ｉ The sum of is between 4 and 15, Each of the conductive layers is a conductive metal layer or a conductive resin layer composed of a conductive filler and a binder resin, however, The conductive metal layer is a metal sheet other than an iron-based metal selected from the group consisting of gold, silver, copper, and aluminum, or alloys thereof; The conductive filler is a powder other than an iron-based metal selected from the group consisting of metal powders, alloy powders, and core-shell particles, The metal powder is selected from the group consisting of gold, silver, copper, and aluminum; The alloy powder is an alloy of a metal selected from the group consisting of gold, silver, copper, and aluminum, and the core-shell particles are selected from the group consisting of silver-coated copper powder and gold-coated copper powder, A noise suppression sheet characterized in that each of the conductive layers has a proportional constant of 4 or more and 10 or less when the shielding property of 0.2 to 1 MHz is linearly approximated in a magnetic field shielding property measurement by the KEC method. Xi=√μ´ ｉ ×√t ｉ ・・・Formula (1) Here, n is an integer of 2 or more, and i is an integer of 1 or more and n or less, μ´ ｉ is the magnetic layer (A ｉ ) relative permeability at 1 MHz, t ｉ is the magnetic layer (A ｉ ) film thickness [mm], It is.

2. A noise suppression sheet as described in claim 1, wherein the conductive metal layer is copper or aluminum.

3. A noise suppression sheet as described in claim 1, wherein the conductive filler is silver-coated copper powder.

4. A laminate having a noise suppression layer formed from the noise suppression sheet according to any one of claims 1 to 3 on an adherend.

Images