JP4683189B2 - Carbonyl iron powder, electromagnetic interference suppressing sheet containing the carbonyl iron powder, and method for producing the electromagnetic interference suppressing sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carbonyl iron powder to be blended in an electromagnetic interference suppression sheet for suppressing interference of unnecessary electromagnetic waves generated from a digital electronic device, an electromagnetic interference suppression sheet containing the carbonyl iron powder, and a method for producing the electromagnetic interference suppression sheet. .

In recent years, digital electronic devices have made remarkable progress. Especially in mobile electronic devices such as mobile phones, digital cameras, and notebook computers, there are significant demands for higher frequency operation signals and smaller and lighter operating signals. High density mounting of electronic components and wiring boards is one of the biggest technical issues.

Due to the high-density mounting of electronic components and wiring boards for electronic devices and the increase in operating signal frequency, the distance between components that generate noise and other components can no longer be obtained. Microprocessors and LSIs for electronic devices Electromagnetic interference suppression sheets are used for suppressing unwanted radiation emitted from liquid crystal panels. The absorption and reflection phenomenon of electromagnetic waves in the near electromagnetic field as in this application is difficult to analyze using the transmission line theory as in the far-field electromagnetic field (when the electromagnetic wave is a plane wave) that has been conventionally known (Hashimoto). Osamu, “Trends in radio wave absorber”, Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 86 No. 10 pp. 800-803, October 2003), the design of the electromagnetic interference suppression sheet largely depends on experience. Recently, an electromagnetic interference suppression sheet of a type in which a flat metal magnetic powder is blended with a resin as a soft magnetic powder for absorbing electromagnetic waves in a near electromagnetic field, as in Patent Document 1 and Patent Document 2, has been used.

In Patent Document 1, as a soft magnetic powder, a flat Fe—Al—Si alloy powder having an average particle diameter of 10 μm is 90% by weight (for compositions 1 and 3, the alloy powder density is 6.9 kg / l, the resin content density Is calculated as 1.1 kg / l, an electromagnetic interference suppressor containing 58.9 vol%) is disclosed. The thickness of the electromagnetic wave interference suppressing body is 1.2 mm.

In Patent Document 2, “a magnetic coating material in which a flat metal magnetic powder is dispersed in a resin and a solvent is applied onto a substrate having a release layer and dried. A method for producing a magnetic sheet characterized in that a sheet is obtained is disclosed. Magnetic sheet with a dry film thickness of 120 μm and a sendust powder filling rate of up to 80% by weight (calculated assuming a sendust powder density of 6.9 kg / l and a resin content density of 1.1 kg / l, 56.0 vol%) The shield sheet is in the example, and it is shown that a thinner magnetic sheet can be realized as compared with Patent Document 1. A thin magnetic sheet is considered suitable for high-density mounting of electronic components and wiring boards.

Japanese Patent Laid-Open No. 7-212079 JP 2000-244171 A

Due to the progress of miniaturization and weight reduction of digital electronic devices, higher density mounting of electronic components and wiring boards is required, and even thinner, excellent electromagnetic wave absorption performance in the nearby electromagnetic field, for electromagnetic wave interference suppression with less electromagnetic wave reflection There is a strong demand for seats. In general, if the electromagnetic interference suppression sheet is made thinner, the electromagnetic wave absorption performance is lowered. Therefore, in order to make the sheet even thinner, it is necessary to increase the content of the magnetic powder and ensure the practical flexibility and strength of the sheet. There is. In addition, due to the high integration of heat-generating components in electronic equipment, the temperature inside the equipment has increased, and the electromagnetic interference suppression sheet has little change in electromagnetic wave absorption characteristics even when exposed to high temperatures of 80 ° C. Is strongly demanded.

Carbonyl iron powder of the present invention has an average particle diameter _{D 50} of the particle surface of the carbonyl iron powder 1~7μm is surface treated with 0.1-0.5% of phosphoric acid to the carbonyl iron powder, further 0. A carbonyl iron powder characterized by being surface-treated with 1-1 wt% of a silane coupling agent (Invention 1).

The carbonyl iron powder according to the present invention is the carbonyl iron powder according to the first invention, wherein the carbonyl iron powder is a reduced carbonyl iron powder (Invention 2).

The carbonyl iron powder of the present invention is a carbonyl iron powder obtained by mixing two or more kinds of carbonyl iron powders, and at least one of the carbonyl iron powders to be mixed is a reduced carbonyl iron powder, and the carbonyl iron powder to be mixed Among them, at least one kind is a carbonyl iron powder according to any one of the present inventions 1 and 2 (Invention 3).

The carbonyl iron powder according to the present invention is the carbonyl iron powder according to the ^third invention, wherein the tap density of the carbonyl iron powder is 4.6 to 4.8 g / cm ³ (the present invention 4).

The electromagnetic interference suppression sheet of the present invention is a resin composition containing 60 vol% or more of the carbonyl iron powder described in any one of the present inventions 1 to 4, and has a thickness of 10 to 100 μm. It is a sheet | seat for electromagnetic wave interference suppression to perform (this invention 5).

The electromagnetic interference suppression sheet of the present invention contains 60-80 vol% carbonyl iron powder, 20-35 vol% resin, 1-5 vol% flame retardant, and 0.5-3 vol% antioxidant. The electromagnetic interference suppression sheet according to the fifth aspect of the present invention (Invention 6).

The electromagnetic interference suppression sheet of the present invention is a sheet having a thickness of 50 μm, the microstrip line measurement is performed, and the absorption amount is 10% or more at 500 MHz, 20% or more at 1 GHz, and 30% or more at 3 GHz. In addition, the present invention is a resin composition having a reflection amount in the range of 500 MHz to 3 GHz of −10 dB or less and a decrease in absorption loss after elapse of 200 hours in an air atmosphere at 80 ° C. of 10% or less. 5. The electromagnetic interference suppression sheet according to 5 and 6 (Invention 7).

The method for producing a sheet for suppressing electromagnetic interference according to the present invention is characterized in that the thickness after drying is adjusted by applying a paint in which carbonyl iron powder is dispersed, and then hot pressing is performed. To the electromagnetic interference suppressing sheet according to any one of the present invention 7 (Invention 8).

According to the present invention, it is possible to obtain a carbonyl iron powder having a higher filling and heat resistance than before, and by using the carbonyl iron powder, the electromagnetic wave absorption in the near electromagnetic field is excellent and the reflection is suppressed. Can be obtained. According to the manufacturing method of the present invention in which a magnetic paint using the carbonyl iron powder is applied so as to have a dry thickness of 10 to 100 μm and then subjected to heat and pressure molding, the electromagnetic wave absorption in the near electromagnetic field is excellent, and reflection is performed. An electromagnetic interference suppression sheet having high heat resistance and suitable for high-density mounting can be obtained.

The average particle diameter (D ₅₀ ) of the carbonyl iron powder of the present invention is preferably 1 to 7 μm. When the average particle size is less than 1 μm, it becomes difficult to maintain the oxidation stability and the cohesiveness becomes strong, so that it is difficult to improve the filling property of the carbonyl iron powder. When the average particle size exceeds 7 μm, the surface smoothness of the electromagnetic interference suppression sheet is deteriorated, so that the adhesion of the sheet to the electromagnetic wave generation source is deteriorated, and the electromagnetic wave absorbing performance is deteriorated. Preferably it is 1.2-6.5 micrometers.

The true density of the carbonyl iron powder of the present invention is preferably 7.5 to 7.8 g / cm ³ .

In the carbonyl iron powder of the present invention, the particle surface is surface-treated with 0.1 to 0.5 wt% phosphoric acid based on phosphoric acid with respect to the carbonyl iron powder, and further 0.1% with respect to the carbonyl iron powder. It is surface-treated with ˜1.0 wt% silane coupling agent. When the amount of phosphoric acid is less than 0.1 wt%, the oxidation stability is lowered, the impedance is lowered, and the reflection is increased. When the amount of phosphoric acid exceeds 0.5 wt%, the impedance increases and the absorption decreases. Preferably it is 0.1-0.4 wt% . It is considered that phosphoric acid forms iron phosphate on the surface of carbonyl iron powder particles. If the treatment amount of the silane coupling agent is less than 0.1 wt%, the affinity for the resin cannot be sufficiently increased, so that the oxidation stability cannot be sufficiently maintained. If it exceeds 1.0 wt%, the impedance increases and the electromagnetic wave absorption amount decreases. Preferably it is 0.1-0.5 wt% . Silane coupling agents include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2- (3,4 epoxy cyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyltrimethyl, which are suitable as elastomer coupling agents. Methoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxy Silane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, N-2 (Ami Ethyl) 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis (triethoxysilylpropyl) tetra Silane coupling agents such as sulfides can be used.

The carbonyl iron powder of the present invention is preferably reduced carbonyl iron powder. The reduced carbonyl iron powder is not a standard grade but a carbonyl iron powder classified into a reduced grade, and is characterized by a lower carbon and nitrogen content than the standard grade. For example, in the case of products of International Specialty Products (hereinafter referred to as ISP), the standard grade carbon content is 0.7 to 0.76 wt%, while the reduced grade is 0.03 to 0.07 wt%. %. Similarly, the nitrogen content of the standard grade is 0.65 to 0.80 wt%, and the reduced grade is 0.01 to 0.02 wt%. The reason why reduced carbonyl iron powder is preferable as carbonyl iron powder is that the complex relative permeability and complex ratio are higher than the standard grade carbonyl iron powder (hereinafter referred to as non-reduced carbonyl iron powder) in the vicinity of the frequency range of 0.5 GHz to 3 GHz. This is because the dielectric constant is high.

In the carbonyl iron powder obtained by mixing two or more carbonyl iron powders of the present invention, the ratio of the carbonyl iron powder treated with the phosphoric acid-silane coupling agent to the total carbonyl iron powder needs to be 10 vol% or more. More preferably, it is 20 vol% or more. When it is less than 10 vol%, the electromagnetic wave reflection suppressing effect of the electromagnetic wave interference suppressing sheet is lowered. The ratio of the reduced carbonyl iron powder to be mixed to the entire carbonyl iron powder needs to be 50 vol% or more. More desirably, it is 55 vol% or more. When it is less than 50 vol%, the electromagnetic wave absorption amount of the electromagnetic interference suppression sheet is insufficient.

The tap density of the carbonyl iron powder of the present invention is preferably 4.6 to 4.8 g / cm ³ . When it is less than 4.6 g / cm ³ , high filling is difficult. When it exceeds 4.8 g / cm ³ , uniform dispersion in the powdered resin becomes difficult.

The carbonyl iron powder of the present invention is desirably used by mixing at least two kinds of carbonyl iron powder so that the ratio of the maximum average particle diameter to the minimum average particle diameter is 1.25-7. When the maximum average particle size ratio is less than 1.25, high filling is not possible. When the maximum average particle size ratio exceeds 7, the size of particles having a large average particle size becomes too large, the smoothness of the sheet decreases and the mechanical strength of the sheet also decreases, or the size of particles having a small average particle size. Becomes too small, mixing becomes worse and high filling is difficult. More preferably, the maximum average particle size ratio is 3-5.

  Next, the electromagnetic interference suppression sheet according to the present invention will be described.

The electromagnetic interference suppression sheet of the present invention preferably contains 60 vol% or more of the carbonyl iron powder of the present invention, and the thickness of the sheet is preferably 10 to 100 μm. If it is less than 60 vol%, the electromagnetic wave absorption is low. When the content of carbonyl iron powder exceeds 80 vol%, the reflection of electromagnetic waves increases, and the strength and flexibility of the sheet decrease, so the upper limit is 80 vol%. The thickness of the sheet is adjusted according to the state of use, but if it is less than 10 μm, the sheet tends to have insufficient strength. A thickness exceeding 100 μm is too thick for a high-density mounted electronic circuit.

The electromagnetic interference suppression sheet of the present invention preferably contains 20 to 35 vol% of resin. If it is less than 20 vol%, the flexibility of the sheet is poor. When it exceeds 35 vol%, the electromagnetic wave absorption amount decreases. As the resin, styrene elastomer, olefin elastomer, polyester elastomer, polyamide elastomer, urethane elastomer, silicone elastomer and the like can be used. Styrenic elastomers include SEBS (styrene ethylene butylene styrene block copolymer). An elastomer can be used by mixing an acrylic resin, an epoxy resin, a polyolefin resin, or the like.

The electromagnetic interference suppression sheet of the present invention preferably contains 1 to 5 vol% of a flame retardant. If it is less than 1 vol%, the flame-retardant effect is insufficient. If it exceeds 5 vol%, the amount of absorption decreases, which is not preferable. It is preferable to use melamine polyphosphate as the flame retardant.

The electromagnetic interference suppression sheet of the present invention preferably contains 0.5 to 3% by volume of an antioxidant. If it is less than 0.5 vol%, the oxidation resistance is low, which is not preferable. Exceeding 3 vol% is not preferable because the amount of absorption decreases. Antioxidants include 2 ', 3-bis [[3- [3,5-di-tert-butyl-4-hydroxyphenyl] propionyl]] propionohydrazide (Ciba Specialty Chemicals, IRGANOX MD1024) and the like. It is preferred to use. When surface-treating carbonyl iron powder, it is preferable to mix an oxidation stabilizer after treating the silane coupling agent.

The electromagnetic interference suppression sheet of the present invention has a complex relative permeability μ _r ′ at 100 MHz of 8 or more, μ _r ″ of 1.0 or more, and a complex relative permittivity ∈ _r ′ of 20 to 40, It is preferable to comprise a resin composition having ε _r ″ of 1.0 or more. When this condition is satisfied, a suitable electromagnetic interference suppression sheet that is excellent in electromagnetic wave absorption in a wide frequency range of 0.5 GHz to 3 GHz and in which reflection is sufficiently suppressed can be obtained.

  The electromagnetic interference suppression sheet of the present invention is preferably a sheet having a thickness of 50 μm, and the electromagnetic wave absorption is preferably 10% or more at 0.5 GHz, 20% or more at 1 GHz, and 30% or more at 3 GHz. Below that, the amount of electromagnetic wave absorption is insufficient.

  The electromagnetic interference suppression sheet of the present invention is preferably a sheet having a thickness of 50 μm, and the electromagnetic wave reflection amount is −10 dB or less in a frequency range of 0.5 to 3 GHz. Above that, the electromagnetic wave reflection amount is too large, which is not desirable.

The method for producing a sheet for suppressing electromagnetic interference according to the present invention includes applying a magnetic coating material in which the carbonyl iron powder according to the present invention is dispersed to adjust the thickness of the magnetic sheet after drying, followed by hot pressing. Is preferred. A magnetic coating material is preferable because it can achieve high filling and uniform dispersion.

The measuring method of each measured value shown in an Example is described.

[True powder density]
The true powder density was measured as follows. Using a densitometer, a multi-borium density meter 1305 manufactured by Micromeritex Corporation, 28 g (W) of powder was weighed and put into a cell, and the sample volume (V) was determined from the helium gas pressure to determine the true density.
True density = W / V (g / cm ³ )

[Tap density]
The measurement of the tap density of the powder was performed as follows. For the measurement, a tap tester KRS-406 manufactured by Kuramotsu Scientific Instruments Ltd. is used. 10 g of sample is weighed and put into a 25 ml graduated cylinder, attached to a tap tester, tapped at 120 taps / minute, amplitude 2 cm, 5 minutes. After completion, the volume V (ml) of the graduated cylinder is read, The tap density is calculated by the following formula.
Tap density (g / ml) = 10 / V

[Measurement of complex relative permeability and complex relative permittivity]
[Preparation of specimen]
The prepared 50 μm sheet was cut out into a doughnut-shaped test piece by an cutter with an outer diameter of 7 mm, an inner diameter of 3 mm, and 30 sheets were laminated. Make a doughnut-shaped test piece of 5 ± 0.3 mm.

[Measurement of magnetic and dielectric properties]
The magnetic properties and dielectric properties were measured by the coaxial tube S-parameter method by mounting the above-mentioned donut-shaped test piece on a network analyzer 8720D manufactured by Hewlett-Packard Company.

[Measurement of electromagnetic wave absorption and reflection]
It is measured with a substrate on which a microstrip line adjusted to a length of 100 mm, a width of 2.3 mm, a thickness of 35 μm, and an impedance of 50Ω is applied. The produced sheet is cut into a width of 40 mm and a length of 50 mm to obtain a test piece.

The microstrip line is connected to a network analyzer 8720D manufactured by Hewlett-Packard Co., and the S parameter of the microstrip line is measured. Align the length direction of the sheet with the length direction of the microstrip line and install so that the centers of each match. The S-parameters are measured in a state where a 10 mm thick foamed polystyrene sheet having the same expansion ratio 20 to 30 times as that of the sheet is placed on the sheet and a load of 300 g is placed thereon. The absorption amount (%) and the reflection amount (dB) are calculated from the obtained S parameter.
Absorption amount = (1- | S ₁₁ | ² − | S ₂₁ | ² ) / 1 × 100 (%)
Reflection amount = 20 log | S ₁₁ | (dB)

[Average particle diameter (D ₅₀ )]
The average particle diameter (D ₅₀ ) was measured as follows. The average particle size was measured by a wet method using a laser diffraction particle size distribution device (manufactured by SYMPATEC, HELOS & RODOS) under the following conditions. The particle diameter is based on volume, and the average particle diameter is 50%.
Measurement range: 0.1-100 μm
Shape factor: 1
Measurement time: 10 seconds Sample concentration: Transmittance 80-90%
Stirring time: 5 minutes Density: 5 g / cm ³

[Example 1]
Reducing the carbonyl iron powder amount (average particle size 5.5 [mu] m, a true density of 7.8 g / cm ^3, a tap density of 4.5g / ^cm 3, ISP Corp. R-1470) 10 kg to phosphoric acid 20g and 100 g (phosphoric acid 5 times the amount of isopropyl alcohol) and mixing for 30 minutes with a universal stirrer with a stirring tank temperature of 30 to 40 ° C., the stirring tank temperature is raised to 80 ° C. and stirring is performed for 60 minutes. Thereafter, the temperature of the stirring tank is raised to 120 ° C., and stirring is further performed for 60 minutes. Then cool to 40 ° C. The same amount of isopropyl alcohol as 30 g of 3-aminopropyltriethoxysilane (Nihon Unicar Co., Ltd. silane coupling agent, A-1100) was added to the phosphoric acid-treated powder, and the stirring tank temperature was 30 to 40 as described above. After treating at 30 ° C. for 30 minutes, at 80 ° C. for 60 minutes, and at 120 ° C. for 60 minutes, it was cooled to 40 ° C. to obtain surface-treated reduced carbonyl iron powder. When the contents of P and Si were measured by a quantitative line method using a fluorescent X-ray apparatus, almost all of the added phosphoric acid and silane coupling agent remained. This surface-treated reduced carbonyl iron powder is designated as magnetic powder 1 (summarized in Table 1 together with other magnetic powders used in the examples).

Next, in a solution of styrene elastomer (density 0.9 g / cm ³ ) 20% by weight dissolved in ethylcyclohexanone (TF-4200E manufactured by Hitachi Chemical Co., Ltd.), magnetic powder 1 and melamine polyphosphate (three MPP-A, density 1.77 g / cm ³ ), and 2 ′, 3-bis [[3- [3,5-di-tert-butyl-4-hydroxyphenyl] propionyl as an oxidation stabilizer. ]] Propionohydrazide (manufactured by Ciba Specialty Chemicals, IRGANOX MD1024, density 1.1 g / cm ³ ), the volume ratio after removing the solvent is 76 vol% for magnetic powder 1, 20 vol% for styrene elastomer, flame retardant Is 1.4 vol% and the oxidation stabilizer is 2.6 vol%, and they are mixed and mixed using a power homogenizer manufactured by SMT. 8000 was obtained 30 minutes stirring the slurry on a rotary. At that time, ethylcyclohexanone having the same volume as the elastomer solution was added to adjust the viscosity. The obtained slurry was subjected to vacuum defoaming treatment, and then applied to a carrier film using a doctor blade. After drying the organic solvent, a sheet having a sheet thickness of 65 μm was produced. Further, the obtained sheet was molded under the conditions of a temperature of 130 ° C., a pressure of 90 MPa, and a pressing time of 5 minutes to obtain a sheet having a thickness of 50 μm. The obtained sheet has a smooth surface and excellent bendability, and the complex relative permeability μ _r ′ of 100 MHz measured by the coaxial tube method is 15, μ _r ″ is 3.5, and the complex relative dielectric constant ε _r ′ is 35. , Ε _r ″ was 3.5. In addition, the S parameter was measured with a network analyzer using a microstrip line with a length of 100 mm, a width of 2.3 mm, a thickness of 35 μm, and an impedance of 50Ω, and as a result of calculating the amount of absorption and reflection, the amount of absorption was 20% at 500 MHz. The reflection amount is -13 dB, the absorption amount is 31% at 1 GHz, the reflection amount is -16 dB, the absorption amount is 55% at 3 GHz, the reflection amount is -20 dB, the absorption amount is high in a wide frequency range, and the reflection amount is low. The balance was excellent. When this sheet was subjected to a microstrip line measurement after a heat test at 80 ° C. for 200 hours, the characteristics thereof hardly changed, and the rate of change ((initial amount−after heat test) / initial amount) was 10% or less.

[Example 2]
In the blending amount in the sheet, the magnetic powder 1 is 25 vol%, the magnetic powder 2 without surface treatment (ISP R-1470) is 20 vol%, the non-reduced carbonyl iron powder (ISP S-3000, average particle size 1.5 μm) In the same manner as in Example 1, the true density 7.6 g / cm ³ ) was 15 vol% for the magnetic powder 4 subjected to the surface treatment with the surface treatment amount shown in Table 1, and 16 vol% for the magnetic powder 5 that was not surface-treated. The powder was mixed as follows. The tap density was as high as 4.8 g / cm ³ . The powder was used and evaluated in the same manner as in Example 1. Its characteristics are excellent in surface property and flexibility, and the complex relative permeability μ _r ′ of 16 MHz measured by the coaxial tube method is 16, μ _r ″ is 3.6, the complex relative dielectric constant is ε _r ′ is 37, ε _r '' Was 3.8. In S-parameter evaluation using a microstrip line, absorption is 24% at 500 MHz, reflection is -12 dB, absorption is 35% at 1 GHz, reflection is -14 dB, absorption is 58% at 3 GHz, and reflection is -18 dB. The absorption was high in the frequency range, the reflection was low, and the balance was excellent. When this sheet was subjected to a microstrip line measurement after a heat resistance test at 80 ° C. for 200 hours, the characteristics thereof hardly changed and the rate of change was 10% or less.

[Examples 3 to 6]
In the same manner as in Examples 1 and 2, the magnetic powder of Table 1 was used, a sheet was prepared with the formulation of Table 2, and the results of Table 3 were obtained. In any of the formulations shown in Table 2, a good electromagnetic interference suppression sheet could be obtained, and the absorption was high in a wide frequency range, the reflection amount was low, and the balance was excellent. Moreover, the rate of change was 10% or less before and after the heat resistance test. Table 3 shows the ratio of the phosphoric acid-silane coupling agent surface-treated carbonyl iron powder to the whole carbonyl iron powder used as the surface-treated carbonyl iron powder ratio, and the ratio of the reduced carbonyl iron powder to the whole carbonyl iron powder used. The ratio of the reduced carbonyl iron powder, the tap density of the used carbonyl iron powder as a whole, and the volume ratio of the magnetic powder in the sheet are shown together.

[Comparative Examples 1-9]
Comparative Examples 1-9 used the magnetic powder of Table 1 like Example 1 and 2, created the sheet | seat with the mixing | blending of Table 4, and obtained the result of Table 5.

Comparative Examples 1 to 3 are examples using carbonyl iron powder as magnetic powder, but are examples using no reduced carbonyl iron powder. Comparative Example 3 is an example in which no phosphoric acid-silane coupling agent surface-treated carbonyl iron powder is used. As a result, only the electromagnetic wave interference suppression sheet having a low electromagnetic wave absorption amount was obtained in any combination.

  Comparative Examples 4 to 6 are examples using flat metal powder having an aspect ratio of 15 to 20 as magnetic powder. In Comparative Examples 4 and 6, only an electromagnetic interference suppression sheet having a low electromagnetic wave absorption amount was obtained. Moreover, the decreasing rate of the absorption amount before and after the heat resistance test was large and was 10% or more. Comparative Example 5 was an example in which the volume ratio of the magnetic powder in the sheet was increased to 60%, but the viscosity of the magnetic coating material was too high to be formed into a sheet. This is probably because a highly filled sheet is difficult to obtain because the particle shape of the magnetic powder is flat.

Comparative Examples 7 to 9 are examples using granular metal powder as magnetic powder. In Comparative Example 9, the surface-treated reduced carbonyl iron powder and non-reduced carbonyl iron powder are blended together, but the amount is insufficient. In any combination, only an electromagnetic interference suppression sheet having a low electromagnetic wave absorption amount was obtained.

Claims (6)

It is a carbonyl iron powder formed by mixing two or more types of carbonyl iron powder, at least one of the carbonyl iron powders to be mixed is a reduced carbonyl iron powder, and at least one of the carbonyl iron powders to be mixed is an average is a and particle surfaces carbonyl iron powder having a particle diameter _{D 50} 1 to 7 [mu] m surface treated with 0.1-0.5% of phosphoric acid with respect to the carbonyl iron powder, further 0.1 to 1 wt% of silane Carbonyl iron powder characterized by being carbonyl iron powder surface-treated with a coupling agent . The carbonyl iron powder according to claim 1 , wherein the tap density of the carbonyl iron powder is 4.6 to 4.8 g / cm ³ . An electromagnetic interference suppression sheet comprising a resin composition containing 60 vol% or more of the carbonyl iron powder described in claim 1 or 2 and having a thickness of 10 to 100 µm. 60～80Vol% carbonyl iron powder, the resin 20～35Vol%, electromagnetic noise suppression according to claim 3, characterized in that it comprises 0.5～3Vol% including the 1～5Vol% and an antioxidant flame retardant Sheet. Microstrip line measurement is performed on a sheet having a thickness of 50 μm, the electromagnetic wave absorption is 10% or more at 500 MHz, 20% or more at 1 GHz, 30% or more at 3 GHz, and the electromagnetic wave reflection amount in the range from 500 MHz to 3 GHz is −10 dB. 5. The electromagnetic interference suppression sheet according to claim 3 , wherein the electromagnetic interference suppression sheet comprises a resin composition having a decrease in electromagnetic wave absorption after 200 hours in an air atmosphere at 80 ° C. of 10% or less. . The electromagnetic interference suppression according to any one of claims 3 to 5 , wherein a coating thickness in which carbonyl iron powder is dispersed is applied to adjust a layer thickness after drying, followed by thermo-press molding. Sheet manufacturing method.