JP6909181B2 - Insulation coated metal particles - Google Patents

Description

The present invention relates to insulating coated metal particles having an electromagnetic wave shielding ability.

With the recent miniaturization and high-speed processing of electronic devices, the importance of measures against electromagnetic noise is increasing. Conventionally, as a noise countermeasure, a method of attaching an electromagnetic wave shielding sheet containing an electromagnetic wave shielding material to a noise source has been adopted. As the electromagnetic wave shielding material, soft magnetic metal particles are used because of their high electromagnetic wave absorption characteristics. In addition, from the viewpoint of preventing deterioration of the quality of electrical signals transmitted through the circuit and preventing an increase in reflectance due to eddy current loss, the soft magnetic metal particles are coated with an insulating property, and the insulating layer is high. Characteristics such as electrical resistance, high adhesion, and thinness are required.

Although the method using this electromagnetic wave shielding sheet can be expected to have a certain effect on noise reduction, it is necessary to install the sheet directly on the circuit board on which the element is mounted. The use was often restricted by the design of electronic devices.

On the other hand, a technology of using a resin mixed with an electromagnetic wave shielding material, that is, applying a resin mixed with an electromagnetic wave shielding material to the inner surface of an electronic device housing, and sealing the element itself with a resin mixed with an electromagnetic wave shielding material has been proposed. Has been done. For example, in the technique described in Patent Document 1, it has been proposed to use composite magnetic particles in which a plurality of magnetic metal particles are surrounded by ceramics by dispersing them in a resin as an electromagnetic wave absorber. Since this method does not directly impart insulation to individual magnetic metal particles, it is necessary to include a large amount of ceramics in order to sufficiently secure the insulation of the composite magnetic particles, resulting in insulation and electromagnetic wave shielding. It is difficult to achieve both characteristics at a high level. Further, as the shape of the obtained composite magnetic particles becomes complicated, there is a concern that the fluidity of the resin mixture may decrease.

As a policy of achieving both electromagnetic wave shielding ability, insulating property, and filling property in resin at a high level, it is conceivable to use electromagnetic wave shielding material particles having a high sphericity to impart insulating property to each particle. The filling property in the present specification means a property that high fluidity can be maintained even when the filling rate of the electromagnetic wave shielding material particles in the resin mixture is high, and the high filling property means the resin mixture. Means the high liquidity of. The low fluidity of the resin mixture is disadvantageous for molding into complex or fine shapes. As a method of imparting insulation to each particle, for example, in Patent Document 2, a method of forming a phosphate film on the surface of a soft magnetic metal powder, and in Patent Document 3, insulation containing an alkali halogen compound on the surface of an iron-based powder. Methods of providing the layer and the lubricating wax coating layer are disclosed respectively. However, in these methods, ionic components such as phosphoric acid and alkali metal remain in the insulating film, and the outflow of the ionic components may corrode the wiring and elements of the substrate. In addition, the resistance of the insulating film was also insufficient depending on the application. Patent Document 4 proposes to cover the surface of metal particles with a dielectric by using a spray pyrolysis method, but there is a risk of peeling at the interface between the metal particles and the dielectric. As described above, in the prior art, it has been difficult to obtain electromagnetic wave shielding material particles having a low risk of ionic component outflow, sufficient resistance, and a low possibility of film peeling.

Japanese Unexamined Patent Publication No. 2001-358493 JP-A-2002-305395 Japanese Unexamined Patent Publication No. 2014-141744 Japanese Unexamined Patent Publication No. 2001-338813

An object of the present invention is to provide an insulating layer that is hard to peel off from soft magnetic metal particles having an electromagnetic wave shielding ability and a high circularity, thereby providing an insulating coating that achieves both insulating properties and filling properties in a resin at a high level. It is to obtain metal particles.

Iron-based alloy particles containing at least one of Si and Al and Fe, which have an insulating layer on the surface, and the insulating layer contains at least one of Si oxide and Al oxide and Fe oxide, and each concentration thereof. The insulating coated particles have a ratio of 1 or more, an average particle diameter of 5 to 50 μm, an average circularity of 0.90 or more, and a thickness of the insulating layer of 20 to 200 nm. ..
(Formula 1)
(Al oxide concentration + Si oxide concentration) / (Fe oxide concentration)
The Al oxide concentration, Si oxide concentration, and Fe oxide concentration in the formula are obtained when the sum of Al oxide, Si oxide, and Fe oxide obtained by X-ray photoelectron spectroscopy is 100 atom%. Each concentration (unit: atom%).

According to the present invention, it is possible to obtain insulating coated metal particles having an electromagnetic wave shielding ability, which can achieve both insulating properties and filling properties in a resin at a high level.

FIG. 1 is a photograph of the cross section of the insulating coated metal particles obtained in Example 1 observed using a scanning electron microscope. FIG. 2 is a photograph of the cross section of the insulating coated metal particles obtained in Example 1 observed using a scanning electron microscope, and has a higher magnification than that of FIG.

The insulating coated metal particles of the present invention have an iron-based alloy having soft magnetic properties and an insulating layer containing elements constituting the alloy on the surface thereof. By oxidizing a part of the elements contained in the iron-based alloy to form an oxide, and giving the oxide a form of an insulating layer covering the surface of the iron-based alloy particles, an insulating substance can be obtained from the outside. A uniform insulating layer can be provided as compared with the method of forming an insulating layer by adhering. Examples of iron-based alloys having soft magnetic properties include Fe-Ni-Si alloys, Fe-Al alloys, Fe-Si alloys, Fe-Si-Al alloys, Fe-Si-Cr alloys, and Fe-Si-B alloys. Can be used. All of these iron-based alloys are useful as soft magnetic metal materials because they have high saturation magnetic flux density and magnetic permeability and low coercive force. Al and Si contained in these alloys are oxidized on the surface to become oxides, and form an insulating layer having higher insulating properties than iron oxides. In particular, an Fe-Si-Al alloy is preferable, and it is more preferable that Si: 4 to 13% by mass and Al: 4 to 7% by mass, which have high magnetic permeability, and the balance is composed of Fe and unavoidable impurities. For example, when a Fe-Si-Al alloy is heat-treated in air, an insulating layer containing a large amount of Al oxide is formed on the surface.

The thickness of the insulating layer provided on the surface of the insulating coated metal particles of the present invention is 20 to 200 nm. If the insulating layer is too thin, sufficient insulating properties cannot be ensured, and if the insulating layer is made excessively thick, the risk of peeling of the insulating layer and impairing the insulating properties increases. More preferably, it is 30 to 150 nm.

As a method for forming the insulating layer, heat treatment in an oxidizing atmosphere is preferable. Exposure of the material to high temperatures in an oxidizing atmosphere promotes oxide formation on the surface and the accompanying intraparticle diffusion of oxide constituents and oxygen lost from the surface. In addition, the magnetic distortion can be released by exposing to a high temperature, and the magnetic characteristics can be further enhanced. Examples of the device used for heat treatment include an electric furnace, a rotary kiln, a roller herskilln, and a pusher furnace. Suitable heat treatment conditions differ depending on the material, but in the case of, for example, a Fe—Si—Al alloy, the heating temperature is preferably 600 to 900 ° C. and the heating time is preferably 15 to 300 minutes. If the temperature is low, the insulating layer on the surface does not grow sufficiently, and the insulating property of the particles becomes insufficient. When the temperature is high, the insulating layer is likely to be peeled off, and in addition, the unevenness of the particle surface becomes remarkable, and the fluidity of the resin mixture is lowered. Further, even if the time is short, the insulating film does not grow sufficiently, and if it is long, the risk that the insulating layer grows excessively and peeling occurs increases, and at the same time, the unevenness of the particle surface becomes remarkable. In addition, taking a long heating time causes a decrease in productivity.

The particle size of the insulating coated metal particles of the present invention is 5 to 50 μm. When the particle size is less than 5 μm and exceeds 50 μm, the fluidity when mixed with the resin is lowered. More preferably, it is 7 to 20 μm.

The shape of the insulating coated metal particles of the present invention is spherical, and the sphericity thereof is 0.90 or more, more preferably 0.95 or more. When the sphericity is less than 0.90, the fluidity is lowered due to the increase in rolling resistance when mixed with the resin, and the moldability becomes difficult.

The soft magnetic metal particles used as a raw material for the insulating coated metal particles of the present invention can be produced by an atomizing method. Since the particles obtained by the atomizing method have a high average circularity, the fluidity of the resin mixture is not easily impaired even when the filling amount in the resin is increased, and good moldability is exhibited. In particular, the particles obtained by the gas atomization method using an inert gas such as argon have a high average circularity and are therefore suitable for this application. Further, the insulating coated metal particles can improve the filling property into the resin by adjusting the particle size distribution.

The insulating coated metal particles of the present invention can be further enhanced in filling property by subjecting the surface treatment. As the surface treatment agent, a silane coupling agent is generally used, but a titanate coupling agent and an aluminate-based coupling agent can also be used.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the Examples.

[Example 1]
(Preparation of insulating coated metal particles)
Gas atomized Fe-Si-Al alloy powder with an average particle size of 17 μm (manufactured by Sanyo Special Steel Co., Ltd., alloy name PST-S, particle size −32 μm) is passed through a 440 mesh sieve to remove coarse particles, and then 10 cm square and depth. 250 g was weighed in a 5 cm alumina container, heated at 800 ° C. for 90 minutes in an electric furnace, cooled, and then crushed in a Menou mortar to obtain insulating coated metal particles.

The characteristics of the insulating coated metal particles produced in Examples and Comparative Examples were evaluated by the following methods.
[Calculation of (Al oxide concentration + Si oxide concentration) / (Fe oxide concentration)]
The sample is filled in a sample holder for powder measurement manufactured by Thermo Fisher Scientific Co., Ltd. so that the sample surface is flat, and an X-ray photoelectron spectroscopic analyzer (Cermo Fisher Scientific Co., Ltd., K-Alpha type) is used. ). The measurement conditions are Al-Kα beam with a monochrome meter as the X-ray source, and a coaxial irradiation type dual beam of low-speed electrons and low-speed ions is used for charge neutralization, the detection angle is 90 °, the output is 36 W, and the measurement area is about 400 μm. × 200 μm, path energy is 50 eV, data is taken in at 0.1 eV / step, 50 msec, integration number is 5 times, measurement range is Al oxide: 65-85 eV, Si oxide: 95-110 eV, Fe oxide: It was set to 700 to 740 eV.
The correction coefficient (relative sensitivity coefficient, transmission) is the peak area (signal strength) derived from the binding components of Al—O, Si—O, and Fe—O calculated by subtracting the background from the peak obtained in the above measurement range. (Function, kinetic energy correction) was divided and calculated so that the total area after correction was 100, and each concentration (unit: atom%) of Al oxide, Si oxide, and Fe oxide was calculated. The correction coefficient (relative sensitivity coefficient, transmission function, kinetic energy correction) generally depends on the element to be measured and the measuring device. This time, the above operations and calculations were performed with the analysis software "Thermo Advantage" attached to the "K-Alpha type" manufactured by Thermo Fisher Scientific. Using the obtained values, (Al oxide concentration + Si oxide concentration) / (Fe oxide concentration) was calculated based on Equation 1. As a result, the ratio of the sum of the concentrations of Si oxide and Al oxide shown in Equation 1 to the Fe oxide concentration was 14.

[Average particle size]
The average particle size was determined using a laser diffraction / scattering type particle size distribution measuring device (MT3300EXII manufactured by Microtrac Bell). An appropriate amount of insulating coated metal particles are added to water in which 0.5% by weight of octylphenoxypolyethoxyethanol (Triton X-100, manufactured by Kanto Chemical Co., Inc.) is dissolved as a dispersant, and an ultrasonic irradiation device with a built-in circulator is stirred. The measurement was performed after irradiating 40 W ultrasonic waves for 3 minutes using the above. The particle size of 50% in the volume distribution was defined as the average particle size. As a result, the average particle size of the obtained insulating coated metal particles was 19 μm.

[Average circularity]
The measurement was performed using a powder image analyzer (PITA-1) manufactured by Seishin Enterprise Co., Ltd. The sample was dispersed in ethanol, this liquid was flowed into a planar stretch flow cell, and 200 insulating coated metal particles moving in the cell were recorded as an image with an objective lens, and averaged from this recorded image and Equation 2. The circularity was calculated. In Equation 2, S represents the area of the captured recorded image in the particle projection drawing, and L represents the perimeter of the particle projection drawing. The average value of 200 particles calculated in this way was taken as the average circularity of the insulating coated metal particles. As a result, the average circularity of the obtained insulating coated metal particles was 0.94.
(Formula 2)
Average circularity = 4πS / L ²

[Thickness of insulation layer]
The coated metal particle powder was embedded in epoxy resin, cut with an argon ion beam cross-section preparation device, and then the cut surface was observed with a scanning electron microscope (JSM-7001F, manufactured by JEOL Ltd.) to cut the coating. A cross-sectional photograph was obtained by searching for metal particles and setting the observation magnification to 100,000 times. A cross-sectional photograph actually obtained is shown in FIG. In the obtained photograph, the distance between the tangents drawn parallel to the contours of the outer surface and the inner surface of the insulating layer was randomly read at 5 points for each particle, and the total number of observed particles was 20 for a total of 100. The arithmetic mean value of the points was taken as the thickness of the insulating layer. The results are shown in Table 1. The thickness of the insulating layer of the obtained insulating coated metal particles was 122 nm.

[Insulation]
The insulating coated metal particles are allowed to stand in an environment of 25 ° C. and a humidity of 50 RH% for 24 hours, and 10 g is weighed and a powder resistivity measurement system (manufactured by Mitsubishi Chemical Analytech Co., Ltd., MCP-PD51 type and MCP-HT800 type) are combined. The volume resistivity was measured under the condition of a measurement voltage of 250 V while applying a pressure of 15.9 MPa using (Use). The measurement results are shown in Table 1. The volume resistivity of the obtained insulating coated metal particles was 4.2 × 10 ¹⁰ Ω · cm.

[Presence / absence of peeling of the insulating layer]
The insulating coated metal particles were embedded in epoxy resin, cut with an argon ion beam cross-section preparation device, and then the coated metal was cut by observing the cut surface with a scanning electron microscope (JSM-7001F, manufactured by JEOL Ltd.). The particles were searched for, and the number of particles in which the insulating layer was peeled off was counted from the 100 particles randomly observed at an observation magnification of 20000 times. The results are shown in Table 1. Of the 100 insulating coated metal particles obtained, 3 had peeling of the insulating layer.

[Viscosity of resin mixture]
The filling property of the insulating coated metal particles into the resin was evaluated by measuring the viscosity of the resin mixture. A resin mixture having a low viscosity has high fluidity and is advantageous for molding into a complicated shape or a fine shape when highly filled. After weighing 80 parts by mass of insulating coated metal particles and 20 parts by mass of bisphenol A type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER828), rotate using a planetary stirrer (manufactured by Shinky Co., Ltd., Awatori Rentaro AR-250). A resin composition was prepared by kneading at several 2000 rpm for 3 minutes. Using a rheometer (MCR300, manufactured by Sibel Hegner, Japan), the obtained resin composition was subjected to plate shape: circular flat plate 25 mmφ, sample thickness: 1 mm, temperature: 25 ± 1 ° C., shear rate: 0.1s ^-1 , The viscosity was measured under the conditions of. The results are shown in Table 1. The viscosity of the resin mixture of the obtained insulating coated metal particles was 241 Pa · s.

[Electromagnetic wave shielding ability]
16 parts by mass of bisphenol F type liquid epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd., jER807), 4.7 parts by mass of 4,4'-diaminodiphenylmethane (manufactured by Tokyo Kasei Co., Ltd.) were mixed while being melted at 95 ° C. 79.3 parts by mass of the obtained coated metal particles were added, and the mixture was mixed using a planetary stirrer (Sinky Co., Ltd., Awatori Rentaro AR-250) at a rotation speed of 2000 rpm. The above mixture is poured into a preheated silicone 13 cm square, 2 mm deep mold, and allowed to stand at 70 ° C. for 30 minutes to flatten the liquid level, and then a vacuum heating press (manufactured by Imoto Seisakusho Co., Ltd.). , IMC-1674-A), heat-pressed at 80 ° C. and 0.5 MPa for 30 minutes, then heat-pressed at 80 ° C. and 1.0 MPa for 30 minutes, and then heat-pressed at 150 ° C. and 3 MPa for 1 hour. It was cured by doing. The cured sample was processed to a measurement sample size (120 mm × 120 mm × 2 mm) to obtain a cured resin product. Using the obtained cured resin, the measurement frequency is 0.1 to 1000 MHz, the distance between the transmitter and receiver is 10 mm, the temperature and humidity in the test room is 20 ° C, 50% RH, and the electromagnetic wave shielding ability is determined by the KEC method. evaluated. The results are shown in Table 2.

[Example 2]
Gas atomized Fe-Si-Al alloy powder (manufactured by Sanyo Special Steel Co., Ltd., PST-S, -106 μm) having an average particle diameter of 27 μm was used as a raw material, and the treatment was performed at the heating temperature and heating time shown in Table 1 as in Example 1. Insulating coated metal particles were obtained in the same manner. The evaluation results are shown in Tables 1 and 2.

[Example 3]
Insulating coated metal particles were obtained in the same manner as in Example 1 except that the treatment was performed at the heating temperature and heating time shown in Table 1. The evaluation results are shown in Tables 1 and 2.

[Example 4]
Water atomized Fe-Si-Al alloy powder (manufactured by Epson Atomix, SENDUST ALLOY T, PF-18F) with an average particle size of 9 μm is used as a swirling airflow classifier (manufactured by Nisshin Engineering Co., Ltd., Aerofine Classifier AC-20). ), And an insulating coated metal particle having an average particle size of 4 μm was obtained in the same manner as in Example 1 except that the obtained raw material having an average particle size of 3 μm was used. The obtained insulating coated metal particles were mixed with the insulating coated metal particles of Example 1 at a ratio of 2: 8 to obtain a mixed powder. The results of evaluating the mixed powder in the same manner as in Example 1 are shown in Tables 1 and 2. The viscosity of the resin mixture of the mixed powder was 215 Pa · s.

[Comparative Example 1]
Insulating coated metal particles were obtained in the same manner as in Example 1 except that the treatment was performed at the heating temperature and heating time shown in Table 1. The evaluation results are shown in Table 1. The volume resistivity of the resulting insulated coated metal particles was 9.3 × 10 ⁶ Ω · cm.

[Comparative Example 2]
Water atomized Fe-Si-Al alloy powder (manufactured by Epson Atmix, SENDUST ALLOY T, PF-18F) with an average particle size of 9 μm is used as a swirling airflow classifier (manufactured by Nisshin Engineering Co., Ltd., Aerofine Classifier AC-20). ) Was used to classify, and insulating coated metal particles were obtained in the same manner as in Example 1 except that the obtained raw material having an average particle diameter of 3 μm was used. The evaluation results are shown in Table 1. The average particle size of the obtained insulating coated metal particles was 4 μm, and the viscosity of the resin mixture was 661 Pa · s.

[Comparative Example 3]
Gas atomized Fe-Si-Al alloy powder (manufactured by Sanyo Special Steel Co., Ltd., PST-S, -106 μm) having an average particle size of 27 μm was passed through a sieve using a 440 mesh sieve, and the average particle size remaining on the sieve was 55 μm. Insulation-coated metal particles were obtained in the same manner as in Example 1 except that the raw material was used. The evaluation results are shown in Table 1. The average particle size of the obtained insulating coated metal particles was 57 μm, and the viscosity of the resin mixture was 434 Pa · s.

[Comparative Example 4]
Insulation coated metal particles were obtained in the same manner as in Example 1 except that water atomized Fe-Si-Al alloy powder (manufactured by Epson Atomix, SENDUST ALLOY T, PF-18F) having an average particle size of 9 μm was used as a raw material. .. The evaluation results are shown in Table 1. The average circularity of the obtained insulating coated metal particles was 0.85, and the viscosity of the resin mixture was 1375 Pa · s.

[Comparative Example 5]
Insulating coated metal particles were obtained in the same manner as in Example 1 except that the treatment was performed at the heating temperature and heating time shown in Table 1. The evaluation results are shown in Table 1. Of the 100 insulating coated metal particles obtained, 43 were observed to peel off the insulating layer, and the viscosity of the resin mixture was 1131 Pa · s.

[Comparative Example 6]
Gas atomized Fe-Si-Al alloy powder (Sanyo Special Steel Co., Ltd., PST-S, -106 μm) was passed through a 440 mesh sieve to remove coarse particles, and 400 g of powder and polyvinylidene fluoride powder (manufactured by Alchema Co., Ltd., Kynar 761). ) 50 g was put into a multipurpose mixer (manufactured by Nippon Coke Industries Co., Ltd., MP-5 type, using CP2 tank) and treated at 1500 rpm for 30 minutes to obtain insulating coated metal particles. The evaluation results are shown in Table 1. Of the 100 insulating coated metal particles obtained, 36 were observed to be peeled off from the insulating layer.

[Comparative Example 7]
Electromagnetic waves were obtained by the KEC method in the same manner as in Example 1 except that a cured resin product was obtained using a gas atomized Fe-Si-Al alloy powder (manufactured by Sanyo Special Steel Co., Ltd., PST-S, -106 μm) having an average particle size of 27 μm. The shielding ability was evaluated. The results are shown in Table 2.

The insulating coated metal particles of the present invention had a high volume resistivity, were provided without peeling the insulating layer, and had high fluidity even when mixed with a resin. Further, the electromagnetic wave shielding ability is not impaired by the insulation treatment in the present invention, but rather is enhanced by the heat treatment.

The insulating coated metal particles of the present invention have a high volume resistivity, the insulating layer is not peeled off, and the fluidity of the resin mixture is high. Therefore, a resin composite or a sealing material having electromagnetic wave shielding properties. Suitable for.

1 Inside of insulating coated metal particles 2 Insulating layer 3 Insulating coated metal particles 4 Inner surface of insulating layer 5 Outer surface of insulating layer 6 Embedding resin

Claims (2)

Iron-based alloy particles containing Si , Al and Fe, having an insulating layer on the surface, the insulating layer containing at least one of Si oxide and Al oxide and Fe oxide, and formula 1 from each concentration. The ratio shown in (1) is 2 or more , the average particle size is 7 to 29 μm, the average circularity is 0.94 or more , and the thickness of the insulating layer is 20 to 171 nm (excluding 43 nm or less). Insulation coated particles.
(Formula 1)
(Al oxide concentration + Si oxide concentration) / (Fe oxide concentration)
The Al oxide concentration, Si oxide concentration, and Fe oxide concentration in the formula are obtained when the sum of Al oxide, Si oxide, and Fe oxide obtained by X-ray photoelectron spectroscopy is 100 atom%. Each concentration (unit: atom%). The insulating coating particle according to claim 1, wherein the thickness of the insulating layer is 122 to 171 nm.

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