JP2011003582A - Composite sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite sheet containing soft magnetic metal at a high composition rate, having an improved electromagnetic wave absorption amount and having a significantly large difference in surface resistance values between both surfaces of the sheet.SOLUTION: The composite sheet containing a soft magnetic metal powder and a resin contains 50-95 pts.wt. of the soft magnetic metal power for 100 pts.wt. of the composite sheet, wherein the surface resistance value of one surface of the composite sheet is ≥10Ω and the surface resistance value of the other surface thereof is 10-10Ω.

Description

  The present invention relates to a composite sheet containing a soft magnetic metal powder and a resin.

  “Composite sheet”, which is a sheet containing soft magnetic metal powder and resin, is also referred to as an electromagnetic wave absorbing sheet or noise suppressing sheet. Electromagnetic noise generated mainly on circuit boards in information communication equipment such as personal computers and mobile phones. Absorbing the effect of preventing malfunction of the circuit and suppressing electromagnetic waves radiated to the outside of the device are exhibited.

  As the soft magnetic metal powder, for example, an iron-silicon-aluminum alloy (Fe-Si-Al) is suitable for the above-mentioned use because of its high initial magnetic permeability. A composite sheet obtained by blending the metal powder with a high composition ratio with respect to the resin and processing it into a thin sheet using such characteristics is disclosed (for example, Patent Document 1).

JP 2001-119189 A

  Soft magnetic metals such as the iron-silicon-aluminum alloy described above have electrical conductivity, but when combined with a resin, they have insulating properties, and even if used in the vicinity of a circuit board, the level is sufficient. Demonstrate electrical resistance. Even so, with the recent miniaturization of information and communication equipment, the need to attach a sheet closer to the circuit is increasing, and thus there is an increasing need for a sheet having a larger electric resistance (surface resistance). Examples of a method for producing such a sheet include a method in which an insulating film is bonded to the sheet surface, and a method in which a coating material is applied to the sheet surface to form an insulating film. However, by any of these methods, when trying to produce a composite sheet with improved electromagnetic wave absorption and a significantly large difference in surface resistance on both sides of the sheet, an increase in film thickness is inevitable and not practically suitable. There is a problem that only a sheet can be obtained and the number of processing steps is increased and complicated.

  Accordingly, an object of the present invention is to provide a composite sheet containing a soft magnetic metal at a high composition ratio, improving electromagnetic wave absorption, and having a significantly large difference in surface resistance between both surfaces of the sheet.

  In order to solve the above problems, the present inventors have intensively studied a composite sheet containing the soft magnetic metal powder and a resin. As a result, there is a significant difference in the surface resistance value on both sides of the sheet, and the surface with the smaller surface resistance value (hereinafter also referred to as “tackifying surface”) is in contact with the pressure-sensitive adhesive layer. It has been found that the insulation reliability of the circuit can be improved, and the present invention has been completed.

That is, the present invention is a composite sheet containing a soft magnetic metal powder and a resin, and contains 50 to 95 parts by weight of the soft magnetic metal powder with respect to 100 parts by weight of the composite sheet. The composite sheet has a surface resistance value of 10 ¹⁰ Ω or more on the surface and a surface resistance value of 10 ⁵ to 10 ⁹ Ω on the other surface.

  According to the present invention, it is possible to obtain a composite sheet containing a soft magnetic metal at a high composition ratio, improving electromagnetic wave absorption, and having a significantly large difference in surface resistance values on both sides of the sheet.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not restrict | limited to the following embodiment, In the range of the summary, various deformation | transformation can be implemented.

The present embodiment is a composite sheet containing a soft magnetic metal powder and a resin, containing 50 to 95 parts by weight of the soft magnetic metal powder with respect to 100 parts by weight of the composite sheet, and one of the composite sheets The composite sheet has a surface resistance value of 10 ¹⁰ Ω or more on the surface and a surface resistance value of 10 ⁵ to 10 ⁹ Ω on the other surface.

  As described above, the present inventors have a significant difference in the surface resistance value of both surfaces of the composite sheet containing the soft magnetic metal powder and the resin, and the surface having the smaller surface resistance value (tackifying surface). It was found that the insulation reliability with respect to the electric circuit can be improved by contacting the adhesive layer with the adhesive layer. Here, the “tackifying surface” in the present specification is a surface having a smaller surface resistance value and is in contact with the adhesive layer, and the adhesive material constituting the adhesive layer is limited to the following. Although not, acrylic, silicone, rubber, etc. can be used.

  [Soft magnetic metal powder]

  The soft magnetic metal powder is a soft magnetic metal powder. The soft magnetic metal is a metal that can quickly respond to an external magnetic field signal and obtain a high magnetic flux density with almost no loss, and is also referred to as a high magnetic permeability material.

  Examples of the soft magnetic metal include, but are not limited to, pure iron, carbonyl iron, Fe-Si alloy, Fe-Al alloy, Fe-Cr-Ni alloy, Fe-Si-Al alloy, Fe-Ni alloy, And Fe-Co alloys. Among these, pure iron, carbonyl iron, Fe—Si—Al alloy, Fe—Cr—Ni alloy, and Fe—Ni alloy are preferable from the viewpoint of higher magnetic permeability. In addition, the measured value by the method implemented in the Example mentioned later is employ | adopted for "magnetic permeability" in this specification.

  Here, the measurement of magnetic permeability leads to the evaluation of the amount of radio wave absorption. The higher the magnetic permeability, the greater the amount of radio wave absorption. Even with the same blending amount, the permeability of the Fe-Si-Al alloy tends to be higher than that of the Fe-Cr-Ni alloy.

  From the viewpoint of obtaining a high electromagnetic wave absorption effect, the Fe—Si—Al alloy is preferably one having 8 to 12 parts by weight of Si and 5 to 8 parts by weight of Al in terms of atomic weight. Among them, those having 9.6 parts by weight of Si and 5.7 parts by weight of Al are particularly preferable, and an alloy having this composition is represented as “Fe-9.6Si-5.7Al” below. The carbonyl iron is a general name for a pure iron particle whose surface is covered with iron phosphate. The Fe—Ni alloy is generally called permalloy, and the composition of the Ni component with respect to 100 parts by weight of the alloy is usually 20 to 90 parts by weight.

As the Fe-Cr-Ni alloy, from the viewpoint of obtaining a high electromagnetic wave absorption amount,
In terms of atomic weight, it is preferable that Cr is 1.48 to 1.68 parts by weight and Ni is 0.50 to 0.70 parts by weight.

  The content of the soft magnetic metal powder is 50 to 95 parts by weight with respect to 100 parts by weight of the composite sheet. In the case of 50 parts by weight or more, the electromagnetic wave absorption amount of the resin composition as a raw material for sheet molding is excellent, and in the case of 95 parts by weight or less, the moldability of the resin composition and the flexibility of the sheet are excellent. Moreover, from a viewpoint of the coating property improvement with respect to the base material of a varnish, Preferably it is 60-90 weight part, More preferably, it is 70-90 weight part. Thus, the composite sheet according to the present embodiment contains the soft magnetic metal at a high composition ratio. Here, a method of calculating “electromagnetic wave absorption amount” in this specification will be described.

  <Calculation of electromagnetic wave absorption>

  The intensity of electromagnetic waves radiated from a micro split line having a width of 1 mm was observed with an electromagnetic wave visualization device. The radiated electromagnetic wave intensity at an arbitrary position on the line is measured, and the value is P1. A composite sheet is pasted at the same position, and the radiation electromagnetic wave intensity at that position is P2.

  The electromagnetic wave absorption amount (unit: dB) is obtained by the following formula.

  Electromagnetic absorption = 20 × log (P1 / P2)

  The composite sheet is a square of 1 cm square, and the measured value of the radiated electromagnetic wave is 500 MHz.

The average particle diameter (d ₅₀ ) of the soft magnetic metal powder is preferably 1 to 100 μm. When the thickness is 1 μm or more, the handleability of the powder is good, and when it is 100 μm or less, the sheet moldability of the resin composition is improved and the electromagnetic wave absorption is also improved. Moreover, from a viewpoint of powder handleability, More preferably, it is 2-60 micrometers, More preferably, it is 10-50 micrometers. In addition, the measuring method of the average particle diameter in this specification is a BET method.

  When a soft magnetic metal powder having a large particle size and a small particle size are mixed and used, the powder space (distance between powder particles) can be significantly reduced when kneaded with a resin. Therefore, the filling rate of the soft magnetic metal powder into the resin can be further increased, and the electromagnetic wave absorption amount of the composite sheet can be improved.

The specific surface area of the soft magnetic metal powder is preferably 0.3 to ² m ² / g. When 0.3 m ² / g or more, the sheet has excellent flexibility when kneaded with a resin to form a sheet, and when it is 2 m ² / g or less, the soft magnetic metal powder has a high concentration relative to the resin. Since it can mix | blend by (high composition ratio), the electromagnetic wave absorption amount of a sheet | seat can be improved. In addition, the measuring method of the specific surface area in this specification is BET method.

  The form of the soft magnetic metal powder is not limited to the following, and examples thereof include a spherical shape and a flat shape. Of these, a flat shape is preferred. In the case of a flat shape, the soft magnetic metal powder is easily oriented horizontally with respect to the sheet plane at the stage of kneading with the resin to form a sheet. And it can be said that the flat shape is preferable from the viewpoint that the electromagnetic wave absorption amount of the composite sheet is improved and the composite sheet can be significantly thinned by being horizontally oriented in this way. In particular, Fe-Si-Al alloy, Fe-Cr-Ni alloy, and Fe-Ni alloy powders processed into a flat shape are more preferable because of extremely high magnetic permeability.

  When the soft magnetic metal powder particles are flat, the thickness of the flat “plate” is preferably 0.05 to 5 μm. In the case of 0.05 μm or more, the shape can be maintained at the time of kneading with the resin, so that it is easy to form a composite sheet having a desired shape, and in the case of 5 μm or less, the composite sheet can be made thinner. More preferably, the thickness is 0.1 to 1 μm.

  The soft magnetic metal powder may be subjected to a coupling treatment on the particle surface of the powder for the purpose of further improving the adhesion with the resin. Although it does not restrict | limit to the following as said coupling process, For example, a silane coupling process is mentioned.

  The silane coupling agent used for the silane coupling treatment is not limited to the following, but, for example, an epoxy functional such as 3-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, etc. Amino-functional silanes such as 3-aminopropyltrimethoxysilane, N-2- (aminoethyl) 3-aminopropyltrimethoxysilane, N-2- (aminoethyl) 3-aminopropylmethyldimethoxysilane; vinyl Olefin-functional silanes such as trimethoxysilane, vinylphenyltrimethoxysilane, vinyltris (2-methoxyethoxy) silane; acrylic-functional silanes such as 3-acryloxypropyltrimethoxysilane; 3-methacryloxypropyltrimethoxysilane METAKU Le functional silanes; and, a mercapto-functional silane such as 3-mercaptopropyltrimethoxysilane. These silane coupling agents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  Examples of conditions for the silane coupling process will be described. First, as a composition of the treatment liquid, the above coupling agent may be dissolved in a solvent such as water at a concentration of 0.1 to 15 g / L. Moreover, the temperature of a process liquid should just be room temperature-50 degreeC. The immersion time of the soft magnetic metal powder in the treatment liquid is not particularly limited.

  After the silane coupling treatment, although not limited to the following, a stable bond is formed between the coupling agent and the soft magnetic metal powder by heating or ultraviolet irradiation, and the coupling agent is adsorbed on the soft magnetic metal powder. be able to. Note that conventionally known conditions may be used for the heating and ultraviolet irradiation conditions.

  [resin]

  The resin in the present embodiment may be either a thermoplastic resin or a thermosetting resin.

  As the thermoplastic resin, for example, a polymer or copolymer of a monomer having an unsaturated group such as a double bond or a triple bond can be used.

  Examples of the monomer include, but are not limited to, ethylene, propylene, butadiene, isoprene, styrene, α-methylstyrene, methacrylic acid, acrylic acid, methacrylic ester, acrylic ester, vinyl chloride, vinylidene chloride, and fluorinated ethylene. , Acrylonitrile, maleic anhydride, and vinyl acetate.

  Further, the thermoplastic resin other than the polymer or copolymer of the above monomer is not limited to the following, but for example, polyphenylene ether, polyamide, polyimide, polyamideimide, polycarbonate, polyester, polyacetal, polyphenylene sulfide, polyethylene glycol, poly Examples include ether imide, polyketone, polyether ether ketone, polyether sulfone, and polyarylate.

  Examples of the thermosetting resin include, but are not limited to, phenol resin, epoxy resin, cyanate ester resin, polyimide, polyurethane, bismaleimide resin, alkyd resin, unsaturated polyester, silicone resin, and benzocyclobutene resin. It is done.

  The thermoplastic resin and the thermosetting resin may be modified with a compound having a functional group. Such functional groups are not limited to the following, but are selected from the group consisting of vinyl groups, allyl groups, carboxyl groups, acid anhydride groups, ester groups, hydroxyl groups, amino groups, amide groups, imide groups, epoxy groups, and halogens. There can be one or more.

  The above resin components may be used alone or in combination of two or more.

  Among the thermoplastic resins and thermosetting resins described above, from the viewpoints of solubility in solvents, adhesion to soft magnetic metal powders, and coating properties of varnishes kneaded with solvents and soft magnetic metal powders. A thermoplastic silicone resin or chlorinated polyethylene is preferred, and a thermoplastic silicone resin is more preferred. The thermoplastic silicone resin is mainly composed of repeating units of dimethylsiloxane, but those containing a segment having an interaction such as a hydrogen bond in the repeating unit forms a pseudo-crosslinking point via the hydrogen bond. And viscoelastic behavior as an elastomer. Therefore, it can be said that the thermoplastic silicone resin is preferable in terms of characteristics such as tensile strength and flexibility of the composite sheet according to the present embodiment. Although it does not restrict | limit as a segment which has said interaction as follows, From a viewpoint of the strength of interaction, Preferably it is an ester bond or a urea bond.

  The content of the resin is 1 to 50 parts by weight with respect to 100 parts by weight of the composite sheet. When the amount is 1 part by weight or more, the coating film formability is excellent, and when the amount is 50 parts by weight or less, the composite sheet has excellent magnetic properties and flame retardancy. Moreover, from a viewpoint of the ease of peeling with the base material at the time of coating, Preferably it is 5-20 weight part.

  [Composite sheet]

  The composite sheet according to the present embodiment is used such that there is a significant difference in the surface resistance value on both sides of the sheet, and the surface (tackifying surface) with the smaller surface resistance value is in contact with the adhesive layer. is there. More specifically, the surface resistance value of the one surface is significantly larger than the surface resistance value of the other surface, and the surface resistance value of the one surface is large as an absolute value. Due to such characteristics, the composite sheet can improve insulation reliability with respect to an electric circuit.

  The composite sheet according to the present embodiment may contain a flame retardant, an ultraviolet absorber, a plasticizer, a crosslinking agent, and the like depending on the purpose, in addition to the soft magnetic metal powder and the resin.

The composite sheet according to the present embodiment has a surface resistance value at 1 V of one surface of both surfaces of 10 ¹⁰ Ω or more from the viewpoint of insulation from the electric circuit. Further, from the viewpoint of higher insulation, it is preferably 10 ¹¹ Ω or more, more preferably 10 ¹² Ω or more.

On the other hand, the surface resistance value of the other surface of the composite sheet is 10 ⁵ to 10 ⁹ Ω. When it is 10 ⁵ Ω or more, the insulation with the electric circuit is further improved, and when it is 10 ⁹ Ω or less, the electromagnetic wave absorption can be improved. In view of the above, it is preferably 10 ⁶ to 10 ⁹ Ω, more preferably 10 ⁶ to 10 ⁸ Ω. Here, the “surface resistance value” in the present specification employs the method implemented in the examples described later.
The composite sheet of the present invention can be obtained by casting or coating a varnish in which a soft magnetic alloy powder and a resin are uniformly dispersed in a solution on a base film, and then drying to remove the solvent. The range of the preferable liquid viscosity at 30 ° C. of the varnish is 1,000 mPa · s to 1,000,000 mPa · s, and from the viewpoint of controlling the thickness of the composite sheet as desired, more preferably 10,000 mPa · s to 50,000 mPa · s. If it is 1,000 mPa · s or more, the sedimentation rate of the soft magnetic metal powder in the coating film can be suppressed, and the surface resistivity of the composite sheet can be easily controlled within the range defined by the present invention. Since the soft magnetic metal powder settles at an appropriate speed even at 1,000,000 mPa · s or less, it is preferable from the viewpoint of controlling the surface resistivity of the composite sheet.
Solvents used in the varnish can be toluene, xylene, acetone, 2-butanone, tetrahydrofuran, methyl isobutyl ketone, and in order to further adjust the coating shape, high-boiling solvents such as diacetone alcohol and dimethylformamide are used. A small amount of 5% or less may be added.
The base film for applying the varnish only needs to be resistant to the solvent to be used, and a polyolefin film such as polyethylene and a polyester film such as PET are preferably used to facilitate peeling of the composite film from the base film. Alternatively, a film coated with fluorine or silicone can be used.

  In the composite sheet according to the present embodiment, from the viewpoint of insulation reliability with the electronic circuit, the surface with the lower surface resistance value, the surface with the higher surface resistance, or both surfaces are covered with an insulating layer. It is preferable. It is preferable that the surface having a lower surface resistance value is covered with an insulating layer because the insulation between the composite sheet and the electric circuit is further improved. Although it does not restrict | limit as a method of coat | covering with an insulating layer below, For example, lamination | stacking of a resin film and resin coating are mentioned. Covering both surfaces of the composite sheet with a film having an adhesive layer is preferable because the sheet can be easily attached to a desired location of an electronic device.

  Since the composite sheet can be remarkably thinned, the entire film thickness can be reduced even if a resin film is laminated or coated on the sheet surface. As a result, in the present embodiment, the above-described problems (problems) caused by resin film lamination and resin coating do not occur.

  Although the composite sheet which concerns on this Embodiment is not restrict | limited to the following, after coat | covering the varnish obtained by knead | mixing resin, a soft magnetic metal powder, and a solvent uniformly on a base material (a film, a sheet, etc.), it dries. It is obtained by removing the solvent. This coating method may be performed in the presence of a magnetic field or an electric field as necessary, or may be performed while irradiating ultrasonic waves, electromagnetic waves, or ultraviolet rays.

  Examples of the solvent include, but are not limited to, toluene, xylene, acetone, 2-butanone (MEK), tetrahydrofuran, methanol, ethanol, propanol, dimethylformamide, and dimethyl sulfoxide.

  In the composite sheet obtained by removing the solvent through the above process, the sheet can be made thinner by pressing in the direction perpendicular to the sheet surface. Heating at the same time as pressurization is preferable from the viewpoint of thinning effect.

  Hereinafter, the present embodiment will be described more specifically with reference to examples and comparative examples, but the present embodiment is not limited to only these examples.

  [Measurement of surface resistance]

  According to the standard of ASTM D257; 1993, the electrode size is 25 mm as the main electrode, the guard electrode is a donut shape with an inner diameter of 38 mm and an outer diameter of 50 mm, and the measured value when the applied voltage is 1 V is the surface resistance value. It was.

  [Measurement of permeability]

  Cut out a donut-shaped sample having an inner diameter of 17 mm and an outer diameter of 39 mm from the composite sheets obtained in Examples and Comparative Examples described later, and using the S-parameter reflection method with a coaxial tube using this sample, the imaginary permeability at 100 MHz Part values were determined. The value of the magnetic permeability imaginary part was evaluated as the magnetic permeability.

  [Example 1]

In a solution obtained by dissolving 15 g of a thermoplastic silicone resin (GENIOMER 140, manufactured by Asahi Kasei Wacker Co., Ltd .; 90 g / 10 min) of a melt flow index (180 ° C., load 21.6 Kg) in 20 g of 2-butanone, flat Fe A powder of -9.6Si-5.7Al alloy (specific surface area 0.57 m ² / g; d ₅₀ = 59 μm, d ₉₀ = 133 μm) was added and stirred and mixed (kneaded) sufficiently. With the alloy powder uniformly dispersed in the solution, the dispersion was cast on a PET film and dried with hot air at 100 ° C. As a result, a 0.2 mm thick film was obtained. This film was hot-pressed under conditions of 5 MPa and 200 ° C. for 3 minutes to produce a composite sheet having a thickness of 0.1 mm. As a result of measuring the surface resistance value of both surfaces of the obtained composite sheet, one surface was 1 × 10 ¹¹ Ω and the other surface was 1 × 10 ⁶ Ω. The value of the imaginary part of magnetic permeability at 100 MHz of this composite sheet was 25. An acrylic adhesive layer was coated on the surface of the composite sheet having a surface resistance value of 1 × 10 ⁶ Ω for the purpose of adhesion to an electronic device. As a result, when this composite sheet was affixed in an electronic device, insulation reliability could be imparted to the electric circuit.

  [Example 2]

The same thickness as in Example 1 except that the addition amount of the thermoplastic silicone resin was 25 g and the addition amount of the powder of the flat Fe-9.6Si-5.7Al alloy was 75 g. A composite sheet was produced. As a result of measuring the surface resistance value of both surfaces of the obtained composite sheet, one surface was 1 × 10 ¹² Ω and the other surface was 5 × 10 ⁸ Ω. The value of the imaginary part of the magnetic permeability at 100 MHz of this composite sheet was 22. An acrylic adhesive layer was coated on the surface of the composite sheet having a surface resistance of 5 × 10 ⁸ Ω for the purpose of adhesion to an electronic device. As a result, when this composite sheet was affixed in an electronic device, insulation reliability could be imparted to the electric circuit.

  [Example 3]

Chlorinated polyethylene (Elaslene 301A, manufactured by Showa Denko KK; Melt flow index (180 ° C., load 21.6 Kg) 1.6 g / min) 20 g, and 97Fe-2Cr-1Ni alloy powder (specific surface area 0.87 m) ² / g; d ₅₀ = 19 μm, d ₉₀ = 39 μm) 80 g was well dispersed in 20 g of toluene. Thereafter, the dispersion was cast on a PET film and dried with hot air at 100 ° C. As a result, a film having a thickness of 0.3 mm was obtained. This film was hot-pressed under conditions of 5 MPa and 200 ° C. for 3 minutes to produce a composite sheet having a thickness of 0.15 mm. As a result of measuring the surface resistance value of both surfaces of the obtained composite sheet, one surface was 1.2 × 10 ¹⁰ Ω and the other surface was 8 × 10 ⁸ Ω. The value of the imaginary part of the magnetic permeability at 100 MHz of this composite sheet was 13. An acrylic adhesive layer was applied to the surface of the composite sheet having a surface resistance value of 8 × 10 ⁸ Ω for the purpose of adhesion to an electronic device. As a result, when this composite sheet was affixed in an electronic device, insulation reliability could be imparted to the electric circuit.

  [Comparative Example 1]

25 g of thermoplastic silicone resin and 75 g of Fe-9.6Si-5.7Al alloy powder were kneaded at 150 ° C. using a small mixer to obtain a resin composition in which the alloy powder was uniformly dispersed. This resin composition was hot-pressed under conditions of 5 MPa and 200 ° C. for 3 minutes to produce a composite sheet having a thickness of 0.1 mm. The resin and alloy powder used are the same as those used in Example 1. As a result of measuring the surface resistance value of both surfaces of the obtained composite sheet, one surface was 1 × 10 ⁹ Ω and the other surface was 5.5 × 10 ⁸ Ω. The value of the imaginary part of magnetic permeability at 100 MHz of this composite sheet was 15. As a result, insulation reliability could not be imparted to the electric circuit by simply pasting the composite sheet in the electronic device. In order for this composite sheet to provide insulation reliability to an electric circuit, a PET film having a thickness of 38 μm is further attached to one surface for the purpose of increasing electrical resistance, and an electronic device is also applied to the other surface of the composite sheet. It was necessary to apply an acrylic adhesive layer for adhesion purposes.

  [Comparative Example 2]

20 g of chlorinated polyethylene and 80 g of 97Fe-2Cr-1Ni alloy powder were kneaded at 120 ° C. using a small mixer to obtain a resin composition in which the alloy powder was uniformly dispersed. This resin composition was hot-pressed under conditions of 5 MPa and 120 ° C. for 3 minutes to produce a composite sheet having a thickness of 0.15 mm. The resin and alloy powder used are the same as those used in Example 3. As a result of measuring the surface resistance value of both surfaces of the obtained composite sheet, one surface was 1 × 10 ⁹ Ω and the other surface was 5.5 × 10 ⁹ Ω. The value of the imaginary part of the magnetic permeability at 100 MHz of this composite sheet was 13. As a result, insulation reliability could not be imparted to the electric circuit by simply pasting the composite sheet in the electronic device. In order for this composite sheet to provide insulation reliability to an electric circuit, a PET film having a thickness of 38 μm is further attached to one surface for the purpose of increasing electrical resistance, and an electronic device is also applied to the other surface of the composite sheet. It was necessary to apply an acrylic adhesive layer for adhesion purposes.

  [Comparative Example 3]

A composite sheet having a thickness of 0.3 mm was produced in the same manner as in Example 1 except that the addition amount of the thermoplastic silicone resin was 4 g and the addition amount of the Fe-9.6Si-5.7Al alloy powder was 96 g. did. As a result of measuring the surface resistance value of both surfaces of the obtained composite sheet, one surface was 7 × 10 ⁴ Ω and the other surface was 6 × 10 ⁴ Ω. An attempt was made to measure the magnetic permeability of this composite sheet. However, because the sheet was brittle, a predetermined donut-shaped sample for measurement could not be cut out and measured.
Moreover, although the application of the acrylic adhesion layer was tried with respect to each surface of this composite sheet, the said layer peeled from the composite sheet surface after coating.

  [Comparative Example 4]

A composite sheet having a thickness of 0.3 mm is manufactured in the same manner as in Example 1 except that the addition amount of the thermoplastic silicone resin is 55 g and the addition amount of the powder of the Fe-9.6Si-5.7Al alloy is 45 g. did. As a result of measuring the surface resistance value of both surfaces of the obtained composite sheet, one surface was 1 × 10 ¹³ Ω and the other surface was 1 × 10 ¹⁴ Ω. The value of the imaginary part of magnetic permeability at 100 MHz of this composite sheet was 3.

  The value of the imaginary part of the permeability is a parameter for converting the absorbed electromagnetic wave into heat, and the larger the value, the greater the effect of converting the electromagnetic wave into heat, that is, the amount of radio wave absorption.

The above results are summarized in Table 1 below.

  The composite sheet according to the present invention is affixed to members such as wiring boards, CPUs, LSIs, and wirings mounted in electronic devices such as mobile phones, personal computers and digital cameras, and information communication devices. It can be used for absorbing unnecessary electromagnetic noise that causes operation.

Claims (4)

A composite sheet containing soft magnetic metal powder and resin,
50 to 95 parts by weight of the soft magnetic metal powder is contained with respect to 100 parts by weight of the composite sheet, the surface resistance value of one surface of the composite sheet is 10 ¹⁰ Ω or more, and the surface resistance value of the other surface is A composite sheet of 10 ⁵ to 10 ⁹ Ω.   The composite sheet according to claim 1, wherein the soft magnetic metal powder is flat.   The composite sheet according to claim 1, wherein the resin is a thermoplastic silicone resin.   The composite sheet according to any one of claims 1 to 3, wherein a surface having a lower surface resistance value is coated with an insulating layer.