Resin composition containing soft magnetic powder having electromagnetic wave shielding properties and molded article

Abstract

Provided is a soft-magnetic-powder-containing resin composition which has excellent shielding properties against electromagnetic waves having low frequencies not higher than 1 MHz and which can be melt-molded with heating.　The present invention provides a soft-magnetic-powder-containing resin composition comprising a thermoplastic resin and a soft-magnetic powder, wherein a sheet having a thickness of 2.0 mm obtained by molding the soft-magnetic-powder-containing resin composition exhibits a magnetic-field component attenuation rate of 10 dB or greater at frequencies of 0.3 MHz and 1 MHz according to measurement performed by a KEC method.

Description

[[TECHNICAL FIELD]]

[0001] The present invention relates to a soft magnetic powder-containing resin composition blended with soft magnetic powder having electromagnetic wave shielding performance in the low-frequency region, which suppresses electromagnetic noise by shielding or absorbing electromagnetic waves with a frequency of 1 MHz or less (hereinafter, this is often referred to as low-frequency region electromagnetic waves) generated inside various electronic devices, particularly from power conversion equipment and data processing devices mounted on electric vehicles, and also relates to molded articles such as sheets and hoses. [[BACKGROUND ART]]

[0002] Unwanted electromagnetic waves generated from various electronic devices affect other electronic devices and cause malfunctions. In order to suppress the harmful effects of such unwanted electromagnetic waves, electromagnetic wave shielding molded products obtained by further processing a resin composition in which magnetic powder is mixed and dispersed in rubber, synthetic resin, or the like into various molded bodies such as sheets, sheet laminates, hoses, and shield cases are widely used.

[0003] As such an electromagnetic wave shielding material, it has been proposed to add soft magnetic powders such as silicon steel, ferrite, permalloy, sendust, and permendur, and it is generally known that permalloys exhibit excellent shielding properties against electromagnetic waves with frequencies from several hundred MHz to several GHz.

[0004] Said sendust is a Fe-Si-Al alloy soft magnetic material discovered in 1937. In addition, Fe-Si alloys and Fe-Si-Cr alloys are also known soft magnetic materials. There are known examples in which the shielding properties of a composition obtained by kneading these known soft magnetic materials and a polymer together with an organic solvent and then drying the composition were evaluated against electromagnetic waves with a frequency of 300 MHz to 3 GHz. However, the shielding properties against low-frequency region electromagnetic waves of a melt-moldable composition obtained by heating, melting, and kneading the soft magnetic powder into a thermoplastic resin within a specific content range have not been sufficiently studied.

[0005] On the other hand, there are very few studies on shielding materials for low-frequency electromagnetic waves with frequencies of 1 MHz or less. For example, Patent Document 1 proposes a laminate in which a magnetic layer is formed between two or more carbon fiber reinforced resin layers using a magnetic shielding paint in which soft magnetic powder is dispersed in an organic solvent, and Patent Document 2 proposes an electromagnetic field shielding sheet in which soft magnetic powder is impregnated and fixed by applying a soft magnetic paint to a mesh-like structure and drying it. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6625435 [Patent Document 2] Japanese Patent Publication No. 2018-85391 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Until now, effective shielding of low-frequency electromagnetic waves below 1 MHz has been achieved by thickening and laminating existing soft magnetic materials, or by enclosing them in a case. However, these methods have the drawback of making the shielding portion excessively heavy. In order to achieve the miniaturization and weight reduction of various electronic devices and electric vehicles, there has been a demand for thermoplastic resin compositions that can be melt-molded to accommodate thin walls and complex part shapes.

[0008] In other words, the present invention provides a soft magnetic powder-containing resin composition that is mixed in a predetermined amount with a thermoplastic resin and has excellent shielding properties against low-frequency electromagnetic waves of 1 MHz or less, and is processable by heat melt molding, and also aims to provide a molded article of the composition. [Means for solving the problem]

[0009] According to the present invention, a soft magnetic powder-containing resin composition is provided, which contains a thermoplastic resin and soft magnetic powder, wherein a 2.0 mm thick sheet obtained by molding the soft magnetic powder-containing resin composition is measured by the KEC method and the attenuation rates of the magnetic field components at frequencies of 0.3 MHz and 1 MHz are both 10 dB or more.

[0010] The resin composition having shielding properties for low-frequency electromagnetic waves, obtained by blending the soft magnetic powder according to the present invention with a thermoplastic resin, can be obtained by melt-kneading the thermoplastic resin at an appropriate temperature range set using a known sealed mixer or extruder. Furthermore, by using appropriate dies or molds, the melt-kneaded material can be molded into sheets, hoses, or other shapes.

[0011] The following are examples of various embodiments of the present invention. The embodiments shown below can be combined with each other. Preferably, the soft magnetic powder is a soft magnetic powder-containing resin composition mainly composed of Fe-Si-Al alloy powder. Preferably, a soft magnetic powder-containing resin composition containing 20 to 80 volume percent of the Fe-Si-Al alloy powder. Preferably, the thermoplastic resin is a soft magnetic powder-containing resin composition comprising at least one of the following: polyethylene, polypropylene, polystyrene, ABS resin, polyvinyl chloride, polyvinylidene chloride, ethylene-vinyl acetate resin, polyurethane, acrylic resin, polycarbonate, polyamide, polyimide, polyphenylene sulfide, polyvinylidene fluoride, polytetrafluoroethylene, and polybutylene terephthalate. From another aspect of the present invention, a molded article is provided which is obtained by heat-melt molding the above-mentioned soft magnetic powder-containing resin composition. [Effects of the Invention]

[0012] According to the present invention, by blending soft magnetic powder with a thermoplastic resin, it is possible to obtain a moldable composition that has excellent electromagnetic shielding properties against electromagnetic waves in the low-frequency range, and to provide molded articles such as sheets and hoses made from this composition. [Modes for carrying out the invention]

[0013] The embodiments for carrying out the present invention will be described in detail below. The embodiments described below are merely examples of typical embodiments of the present invention, and this should not be interpreted as narrowing the scope of the invention.

[0014] A soft magnetic powder-containing resin composition according to one embodiment of the present invention contains soft magnetic powder and thermoplastic resin, and a 2.0 mm thick sheet obtained by molding the composition has a magnetic field component attenuation rate of 10 dB or more at frequencies of 0.3 MHz and 1 MHz, as measured by the KEC method (using a 2.0 mm thick sheet, which is a molded product of the composition, the magnetic field component attenuation rate of electromagnetic waves measured by the KEC method for electromagnetic waves of frequencies of 0.3 MHz and 1 MHz). The composition has excellent shielding properties against electromagnetic waves in the low frequency range of 1 MHz or less.

[0015] The attenuation rate of the magnetic field component at a frequency of 0.3 MHz, measured by the KEC method on a 2.0 mm thick sheet obtained by molding the composition, is 10 dB or more, preferably 13 dB or more, more preferably 15 dB or more, and even more preferably 20 dB or more.

[0016] The attenuation rate of the magnetic field component at a frequency of 1 MHz, measured by the KEC method on a 2.0 mm thick sheet obtained by molding the composition, is 10 dB or more, preferably 14 dB or more, more preferably 15 dB or more, and even more preferably 20 dB or more.

[0017] The soft magnetic powder is not limited as long as it is a powder that has soft magnetism and can achieve the above-mentioned attenuation rate, but examples include powders of various alloys that have soft magnetism.

[0018] Examples of various alloys having soft magnetism include Fe-Si based alloys, Fe-Si-Cr based alloys, and Fe-Si-Al alloys. From the viewpoint of characteristics in the attenuatable frequency region, the soft magnetic powder preferably contains Fe-Si-Al alloy powder, and more preferably contains Fe-Si-Al alloy powder as a main component. When the soft magnetic powder contains Fe-Si-Al alloy powder as a main component, preferably 50% by mass or more of the soft magnetic powder is Fe-Si-Al alloy powder, more preferably the soft magnetic powder substantially consists only of Fe-Si-Al alloy powder, and particularly preferably the soft magnetic powder is Fe-Si-Al alloy powder.

[0019] An Fe-Si-Al alloy is an alloy containing Fe, Si, and Al. The composition of the Fe-Si-Al alloy is preferably 3 to 12 atomic% of Si, 4 to 12 atomic% of Al, and the balance being Fe. One example of a typical composition of an Fe-Si-Al alloy is Fe 85 Si 10 Al5, and Fe 84.7 Si 9.5 Al 5.8 and the like. Specifically, the Si content in the Fe-Si-Al alloy is, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 atomic%, and may be within a range between any two of the values exemplified herein. Further, specifically, the Al content in the Fe-Si-Al alloy is, for example, 4, 5, 6, 7, 8, 9, 10, 11, or 12 atomic%, and may be within a range between any two of the values exemplified herein.

[0020] The shape of the soft magnetic powder may be any of spherical, flattened, or amorphous, and a similar shielding effect can be exhibited. The maximum diameter of the soft magnetic powder is 500 µm, preferably 100 µm, and the soft magnetic powder can be obtained by a known sieving operation. Note that the maximum diameter of the powder refers to the maximum diameter of each particle in the case of amorphous or flattened powder. When the maximum diameter of the powder exceeds 500 µm and becomes larger, the electromagnetic shielding property becomes inhomogeneous in the molded product, and there is a concern that the molded product may have defective sites, which is not preferable.

[0021] The soft magnetic powder-containing resin composition preferably contains 20 vol% to 80 vol% of the soft magnetic powder, more preferably 30 vol% to 70 vol%. If the content of the soft magnetic powder is less than 20 vol%, sufficiently satisfactory electromagnetic wave shielding properties cannot be exhibited, and if it exceeds 80 vol%, fluidity during kneading or molding may be insufficient, making it impossible to mold into a predetermined shape, and the kneaded product becomes brittle, which is not preferable. In addition, a small amount of Fe-Si based alloy powder, Fe-Si-Cr based alloy powder, or other soft magnetic powders may be added as long as the effects of the present invention are not impaired. Specifically, the content of the soft magnetic powder in the soft magnetic powder-containing resin composition is, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80 vol%, and may be within a range between any two of the numerical values exemplified herein.

[0022] The thermoplastic resin is at least one selected from the group consisting of polyethylene (PE), polypropylene (PP), polystyrene (PS), ABS resin, polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), ethylene-vinyl acetate resin (EVA), polyurethane (PU), acrylic resin (PMMA), polycarbonate (PC), polyamide (PA), polyimide (PI), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polybutylene terephthalate (PBT), and the like. From the viewpoints that the soft magnetic powder is easily dispersed and uniform electromagnetic wave shielding properties are easily obtained, ABS resin, polyvinyl chloride, ethylene-vinyl acetate resin, and the like may be preferable in some cases.

[0023] Further, molding processing aids and various compounding agents other than those described above may be added as long as the electromagnetic wave shielding properties in the low frequency region according to the present invention are not significantly impaired. When a processing aid is added, the content of the processing aid is preferably 0.1 mass% to 1 mass%, more preferably 0.3 mass% to 0.5 mass%, relative to the total of the thermoplastic resin and the soft magnetic powder. Examples of the processing aid include polyethylene glycol fatty acid esters and the like.

[0024] For the mixing method, a known melt mixer such as a closed mixer or extruder can be used. The mixing temperature and mixing time are selected from known appropriate conditions that allow mixing and molding for each thermoplastic resin. To improve the dispersibility of the soft magnetic powder, high-speed rotation and high-shear conditions are preferable, within a range where degradation of the thermoplastic resin and crushing of the soft magnetic powder do not clearly occur. Furthermore, the mixing order of the soft magnetic powder may be to add it all at once at the same time as the thermoplastic resin, or to add it after heating and melting the thermoplastic resin or during heating and melting (post-addition), and this is selected as appropriate from the viewpoint of improving dispersibility and suppressing resin degradation.

[0025] The resulting thermoplastic resin composition (molding raw material) containing the soft magnetic powder is molded into the desired shape using a hot press or melt extruder, and appropriate dies or molds. Possible shapes include sheets, hoses, and cases, and various shapes can be formed by selecting the appropriate mold. Furthermore, laminated sheets using multiple extrusion machines, and multi-layered laminate sheets using adhesives, can be produced.

[0026] The molded product may be a molded member used to shield electromagnetic waves in the low-frequency range of various devices, and as an example, it may be processed into a sheet as described above. It should be noted that the shielding effect may be amplified even if the sheet is composed of multiple layers, even if the thickness is the same. In one embodiment of the present invention, a high shielding effect can be expected when the sheet consists of multiple layers. On the other hand, in the present invention, a sufficient shielding effect can be obtained even in embodiments where the sheet is composed of a single layer.

[0027] As a method for evaluating the shielding (blocking) performance of electromagnetic noise, the KEC method developed by the Kansai Electronics Industry Promotion Center (KEC) is well known and has been introduced, for example, in Textile Product Consumer Science (Journal of Textile Products) vol.40, No.2 (1999) and at "https: / / www.kec.jp / testing-division / kec-method / ". The KEC method measures the shielding effect of electromagnetic waves generated in the near field by separating it into electric field and magnetic field components. Electromagnetic waves transmitted from a transmitting antenna (transmitting jig) are received by a receiving antenna (receiving jig) via a sheet-like measurement sample, and the attenuated electromagnetic waves are measured and quantified as the attenuation rate (measurement unit: dB). In this invention, under room temperature conditions, the attenuation rate of the magnetic field component was measured in the frequency range of 0.1 MHz to 1000 MHz using a sample of constant thickness (2.0 mm). Furthermore, the electromagnetic shielding performance (magnetic field component) at frequencies below 1 MHz, which is important in this invention, was determined by comparing the attenuation rate measurements at 0.3 MHz and 1 MHz. [Examples]

[0028] The effects of the present invention will be explained below with reference to examples and comparative examples of the present invention.

[0029] [Examples 1-7] Resin compositions containing soft magnetic powder were prepared according to the compositions shown in Table 1. Fe-Si-Al alloy powder with an average particle size of 40 μm (manufactured by Sanyo Special Steel, FME3D-AH, specific gravity 6.9) was used as the soft magnetic powder. EVA resin (manufactured by Tosoh Corporation, EVA resin U-636, specific gravity 0.94) was used as the thermoplastic resin. In Examples 5 to 7, polyethylene glycol fatty acid ester (manufactured by Kao Corporation, Emanone 1112) was added as a molding aid at a concentration of 0.3% by weight relative to the total weight of the EVA resin and Fe-Si-Al alloy powder. A Laboplast Mill (internal volume 60 mL) manufactured by Toyo Seiki was used as the mixing device, and the EVA resin and the soft magnetic powder according to the present invention were added simultaneously to the composition shown in Table 1. The mixture was kneaded at a rotation speed of 50 rpm and 130°C for 10 minutes to obtain a resin composition containing soft magnetic powder (hereinafter simply referred to as "composition"). This composition was melt-molded using a hot press set to 150°C and a 2mm thick sheet mold to produce a 2.0mm thick, square molded sheet with dimensions of 150mm x 150mm. The electromagnetic shielding properties (magnetic field component) of the 2.0mm molded sheet were measured at the KEC Kansai Electronics Industry Promotion Center (Seika-cho, Soraku-gun, Kyoto Prefecture). At the same center, the molded sheet was placed between a pair of magnetic field shielding effect evaluation cells (Figure 6) as described in "Textile Product Consumer Science (Journal of Textile Products) vol. 40, No. 2 (1999)," and the measurement was taken using the apparatus shown in Figure 7. The applied frequency in the measurement was continuously varied in the range of 0.1MHz to 1000MHz, but the attenuation rate (relative value) calculated from the transmit / receive intensity values ​​at 0.3MHz and 1MHz was adopted as a representative value of the magnetic field shielding effect in this invention. The results are shown in Table 1. Sheets of the composition according to the present invention all exhibit attenuation rates of 10 dB or more at frequencies of 0.3 MHz and 1 MHz, demonstrating good electromagnetic shielding properties. Furthermore, it can be seen that the attenuation rate improves as the amount of Fe-Si-Al powder added increases from 20 volume% to 80 volume%. In particular, at a blending rate of 40 volume% or more, the attenuation rate is approximately 15 dB or more, indicating that the resin composition has excellent electromagnetic (magnetic field component) shielding properties.

[0030] [Table 1]

[0031] [Examples 8-14] Except for using Fe-Si-Al alloy flattened powder (POCO Holding Co., Ltd, average particle size 55 μm, flatness approximately 10) as the soft magnetic powder, a resin composition containing soft magnetic powder was prepared in the same manner as in Examples 1 to 7, and a molded sheet with a thickness of 2.0 mm was obtained. The electromagnetic shielding properties (magnetic field component) of this 2.0 mm molded sheet were measured in the same manner as in Example 1, and the results are shown in Table 2. All sheets of the composition according to the present invention showed attenuation rates of 10 dB or more at frequencies of 0.3 MHz and 1 MHz, indicating good electromagnetic shielding properties. Furthermore, it can be seen that the attenuation rate improved as the amount of Fe-Si-Al powder added increased from 20 volume% to 80 volume%. In particular, at an amount of 40 volume% or more, the attenuation rate was approximately 15 dB or more, indicating that the resin composition has excellent electromagnetic (magnetic field component) shielding properties.

[0032] [Table 2]

[0033] [Examples 15-17] A single-screw extruder with a barrel diameter of 30 mm and an L / D ratio of 16, equipped with a kneading function, was used. A T-die with a 2 mm slit and a width of 200 mm was attached to the tip. Under conditions of a barrel temperature of 80-150°C and a rotation speed of 40 rpm, a predetermined amount of EVA resin, a processing aid (polyethylene glycol fatty acid ester), and Fe-Si-Al alloy powder (manufactured by Sanyo Special Steel Co., Ltd.) with an average particle size of 40 μm was added as soft magnetic powder to obtain a sheet-like molded product of the resin composition containing the soft magnetic powder. Next, to fine-tune the thickness of this molded sheet, it was press-molded again using a hot press set to 150°C and a sheet mold with a thickness of 2 mm, finally obtaining a molded sheet with a thickness of 2.0 mm. The electromagnetic shielding properties (magnetic field components) of this 2.0 mm molded sheet were measured using the same method as in Example 1, and the results are shown in Table 3.

[0034] [Examples 18-20] Instead of using the methods described in Examples 15-17, a twin-screw extruder with a barrel diameter of 40 mm and an L / D ratio of 20, which has a powder feed port in the middle of the barrel, was used. A T-die with a 2 mm slit and a width of 200 mm was attached to the tip, and EVA resin and processing aids were introduced under conditions of a barrel temperature of 80-150°C and a rotation speed of 25 rpm. Soft magnetic powder was fed in from the middle of the barrel to the predetermined proportions (powder added midway), and the mixture was melt-kneaded to obtain a sheet-like molded product. Next, in order to fine-tune the thickness of the obtained molded sheet, it was molded again using a hot press set to 150°C and a sheet mold with a thickness of 2 mm, and finally a molded sheet with a thickness of 2.0 mm was obtained. The electromagnetic shielding properties (magnetic field components) of this 2.0 mm molded sheet were measured using the same method as in Example 1, and the results are shown in Table 3.

[0035] [Example 21] In Example 18, a hose-shaped extrusion die with an inner diameter of 8 mm and an outer diameter of 12 mm, and a cooling water bath were prepared at the tip of the extruder. EVA resin was introduced under conditions of a barrel temperature of 80-150°C and a rotation speed of 25 rpm. Soft magnetic powder was fed in from the middle of the barrel to the predetermined amount and melted and kneaded. After being extruded in a hose shape, it was immediately introduced into the water bath and cooled to obtain a hose molded product. A portion of the hose molded product obtained in this way was sampled, and a sheet with a final thickness of 2.0 mm was produced using a hot press and a sheet mold. The electromagnetic shielding properties (magnetic field components) of this sheet were measured using the same method as in Example 1, and the results are shown in Table 3.

[0036] [Table 3]

[0037] Examples 15-21 show that the electromagnetic shielding properties (magnetic field component) of the composition sheets according to the present invention, obtained by kneading using an extruder, all exhibit attenuation rates of 10 dB or more at frequencies of 0.3 MHz and 1 MHz, demonstrating good electromagnetic shielding properties. In particular, at a blending amount of 40 volume% or more, the attenuation rate is 15 dB or more, clearly indicating excellent electromagnetic shielding properties (magnetic field component) as a resin composition. Furthermore, Example 21 shows that the soft magnetic powder-containing resin composition according to the present invention can be molded into a hose.

[0038] [Comparative Examples 1-5] Comparative Example 1 is the case where the Fe-Si-Al alloy powder according to the present invention is not incorporated. The attenuation rate is about 0.1 to 0.2 dB, showing almost no electromagnetic shielding properties. Comparative Example 2 shows an attenuation rate of 5 dB or less at 0.3 MHz and 1 MHz, indicating that the electromagnetic shielding properties are not sufficient. Comparative Example 3's molded product was very brittle and could not maintain a sheet state, making KEC method measurement impossible. Comparative Example 4 is the case where 50 volume% of ferrite powder (average particle size 6 μm) is added as a soft magnetic powder. Comparative Example 5 is the case where 50 volume% of permalloy C powder (average particle size 30 μm) with a Ni content of 78 wt% is added as a soft magnetic powder. In all cases, the attenuation rate at 0.3 MHz and 1 MHz is less than 3.0.

[0039] [Table 4] [Industrial applicability]

[0040] The thermoplastic resin composition containing the soft magnetic powder according to the present invention has excellent shielding performance against electromagnetic noise in the low-frequency range of 1 MHz or less, and is extremely useful in industry. Furthermore, it can be heat-melt-molded and is suitable as a molded component (molded product) for shielding low-frequency electromagnetic noise generated from various electronic devices and power conversion equipment and data processing equipment installed in electric vehicles.

Claims

1. A thermoplastic resin composition for heat-melt molding containing soft magnetic powder, comprising a thermoplastic resin and soft magnetic powder, A sheet with a thickness of 2.0 mm obtained by molding the aforementioned soft magnetic powder-containing thermoplastic resin composition for heat melt molding was measured by the KEC method and found that the attenuation rate of the magnetic field component at a frequency of 0.3 MHz was 13 dB or more, and the attenuation rate of the magnetic field component at 1 MHz was 14 dB or more. The soft magnetic powder mainly consists of Fe-Si-Al alloy powder. The thermoplastic resin comprises at least one of the following: ethylene vinyl acetate resin, acrylic resin, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, and polybutylene terephthalate. A thermoplastic resin composition for heat-melt molding containing soft magnetic powder, containing 50 to 80 volume percent of the Fe-Si-Al alloy powder (excluding those containing 50 volume percent of the Fe-Si-Al alloy powder, and soft magnetic resin compositions characterized by incorporating 25 to 65 volume percent of a soft magnetic metal flat powder with a bulk density / true density of Fe as the master alloy into the resin binder).

2. A thermoplastic resin composition for heat-melt molding containing a soft magnetic powder, comprising a thermoplastic resin and a soft magnetic powder, A sheet with a thickness of 2.0 mm obtained by molding the aforementioned soft magnetic powder-containing thermoplastic resin composition for heat melt molding was measured by the KEC method and found that the attenuation rate of the magnetic field component at a frequency of 0.3 MHz was 13 dB or more, and the attenuation rate of the magnetic field component at 1 MHz was 14 dB or more. The soft magnetic powder mainly consists of Fe-Si-Al alloy powder. The thermoplastic resin comprises at least one of the following: ethylene vinyl acetate resin, acrylic resin, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, and polybutylene terephthalate. A thermoplastic resin composition for heat-melt molding containing soft magnetic powder, comprising 65 to 80 volume percent of the Fe-Si-Al alloy powder (excluding those containing 65 volume percent of the Fe-Si-Al alloy powder).

3. The thermoplastic resin composition for heat melt molding containing soft magnetic powder according to claim 1 or claim 2, wherein the thermoplastic resin comprises at least one of ethylene vinyl acetate resin, polyimide, polyvinylidene fluoride, and polytetrafluoroethylene.

4. A molded article obtained by heat-melt molding a thermoplastic resin composition for heat-melt molding containing soft magnetic powder according to any one of claims 1 to 3.

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