Ferrite powder

Abstract

To obtain a highly absorbent ferrite powder, the ferrite powder of the present invention is represented by the following chemical formula (1): AxFe(12-y)AlyO19. In formula (1): A represents at least one element selected from the group consisting of Ba, Sr, and Ca; x is greater than or equal to 0.9 and less than or equal to 1.3; and y is greater than 0 and less than or equal to 2.0. The crystal distortion of said powder is less than or equal to 2.5 X 10-4.

Description

ferrite powder

[0001] The present invention relates to a ferrite powder, and more particularly to a ferrite powder capable of absorbing electromagnetic waves.

[0002] In recent years, research into ADAS (Advanced Driver-Assistance Systems) and AD (Autonomous Driving) has been progressing with regard to automobile driving. ADAS is a system that assists human driving operations in a vehicle, and AD is a technology that enables vehicles to travel automatically. Hereinafter, these technologies will be collectively referred to as "AD / ADAS." AD / ADAS is expected to reduce traffic accidents and congestion.

[0003] To realize AD / ADAS, it is necessary to acquire information such as the positions and relative distances of surrounding objects. Sensors are used to acquire this information, but because automobiles are used in a variety of environments, radar sensors (hereinafter simply referred to as "radar") that use electromagnetic waves are more suitable than optical sensors such as cameras. Among such radars, millimeter-wave radars that use electromagnetic waves called millimeter waves, which have wavelengths on the order of millimeters, have attracted particular attention.

[0004] Such radar is required to have EMC (Electromagnetic Compatibility), that is, not to be a source of electromagnetic interference, not to be affected by electromagnetic interference, or to operate normally even if affected.

[0005] However, in order to obtain information from all directions around the vehicle, it is possible that many millimeter-wave radars will be installed on a single vehicle, such as at the four corners and on the sides. As the number of millimeter-wave radars increases, interference between devices and self-poisoning (noise generated from circuits inside the radar housing can interfere with other circuits, reducing communication performance) become more likely to occur.

[0006] In order to solve or reduce such problems, an electromagnetic wave absorber has been proposed that includes a resin and powder (also called particles or filler) of a magnetic material or carbon dispersed in the resin.

[0007] For example, Patent Document 1 discloses a filler for a radio wave absorber, AFe （１２－ｘ） Al ｘ O １９ In the above publication, magnetoplumbite-type hexagonal ferrite particles are disclosed, which are represented by the formula: wherein A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.0≦x≦2.2.

[0008] Japanese Patent Application Laid-Open No. 2007-250823

[0009] In order to effectively suppress electromagnetic noise, higher absorption of electromagnetic waves at frequencies that cause noise is required. An object of the present invention is to realize a ferrite powder with higher absorption.

[0010] In order to solve the above problems, the present invention provides the following technology: [1] A compound represented by the following chemical formula (1): ｘ Fe （１２－ｙ） Al ｙ O １９ (1) A: at least one element selected from the group consisting of Ba, Sr, and Ca; x: 0.9 or more and 1.3 or less; y: more than 0 and 2.0 or less; and the crystal distortion is 2.5×10 －４ Below is the ferrite powder.

[0011] [2] 1 t / cm ２ The density obtained by compressing at a pressure of 3.0 g / cm ３ The ferrite powder according to [1] above.

[0012] In the ferrite powder of the present invention, the crystal distortion within the above range indicates that the aluminum element is uniformly dispersed, and uniform dispersion of the aluminum element means that the composition is uniform. Since the frequency at which ferrite can absorb electromagnetic waves shifts depending on the composition, ferrite powder with a uniform composition can exhibit excellent electromagnetic wave absorption properties in a specific frequency band. In other words, since the ferrite powder contains many particles that can absorb electromagnetic waves of the same frequency, high absorption of those electromagnetic waves is achieved.

[0013] <Ferrite Powder> The ferrite powder in this embodiment is represented by the following chemical formula (1): ｘ Fe （１２－ｙ） Al ｙ O １９ (1) A: at least one element selected from the group consisting of Ba, Sr, and Ca; x: 0.9 or more and 1.3 or less; y: more than 0 and 2.0 or less. In other words, the ferrite powder is a magnetoplumbite type. The crystal distortion of the ferrite powder is 2.5 × 10 －４ The crystal distortion of the ferrite powder is 1.5 × 10 －４ It is preferable that:

[0014] Magnetoplumbite ferrite can be designed to absorb at a desired frequency by adjusting the composition of the ferrite powder. The crystal distortion within the above range indicates that aluminum (Al) elements are uniformly dispersed, and uniform dispersion of aluminum elements means that the composition is uniform. In other words, since the ferrite powder contains many particles that can absorb electromagnetic waves of the same frequency, this ferrite powder exhibits high absorption at that frequency.

[0015] Furthermore, the absorption amount can be controlled by adjusting the content of ferrite powder in the electromagnetic wave absorber. Therefore, the high electromagnetic wave absorption property of ferrite powder increases the degree of freedom in designing the thickness of the electromagnetic wave absorber.

[0016] The range of frequencies allocated to millimeter-wave radar for automotive applications is 76 GHz to 81 GHz, with the narrow band of 76 GHz to 77 GHz being the most widely used. The absorption frequency band of ferrite powder for automotive applications preferably includes this range. The frequency band can be adjusted by the aluminum element content. Note that the higher the aluminum element content, the more the frequency band tends to shift to the higher frequency side.

[0017] In the composition of the ferrite powder, x may be 0.95 or more and 1.0 or less, and y may be 0.6 or more.

[0018] The composition of the ferrite powder, that is, the elements contained therein and their contents, can be confirmed by a fluorescent X-ray spectrometer or the like.

[0019] When an electromagnetic wave absorber is used in an automobile, it needs to be environmentally resistant. The inside of a vehicle is a harsh environment, with high temperatures and the like, so in order for the electromagnetic wave absorber to maintain stable electromagnetic wave absorbing performance even in such an environment, it is preferable that the electromagnetic wave absorber has mechanical strength that prevents cracking or chipping.

[0020] From this viewpoint, the ferrite powder is 1 t / cm ２ The density obtained by compressing the material at a pressure of 3.0 g / cm ３ It is preferable that the above is the case. The reason why high compressed density provides strength is thought to be as follows: A high compressed density means that small particles can enter the spaces between relatively large particles. In other words, it can be said that the particle size distribution tends to be relatively large. Powders with such properties can be dispersed uniformly in resin, and a reinforcing effect by the powder can be expected.

[0021] Electromagnetic wave absorbers are often installed in narrow vehicle interiors where many parts and devices are arranged, or in inconspicuous locations on the vehicle body. Therefore, it is preferable that the resin composition containing ferrite powder has high moldability so that the molded product can be molded into a complex shape according to the installation location.

[0022] The higher the compressed density of the ferrite powder, the higher the fluidity of the mixture of molten resin and ferrite powder. When molding by injection or extrusion, the higher the fluidity of the mixture, the easier it is to process it into complex molded products. This also improves production efficiency during molding.

[0023] Furthermore, the high density can reduce the viscosity of a resin composition containing the ferrite powder when melted. In addition to the resin and filler, the electromagnetic wave absorber may contain additives as described below, and since the low viscosity when melted as described above allows the additives, which have a large effect on mechanical strength, to be micro-dispersed in the resin composition, it can be expected that the mechanical strength of the molded electromagnetic wave absorber will be improved.

[0024] <Electromagnetic Wave Absorber> The ferrite powder can be used in an electromagnetic wave absorber, which is, for example, a molded body containing a resin and ferrite powder as a filler dispersed in the resin.

[0025] The resin may be a thermoplastic resin, such as PPS or polyamide.

[0026] The electromagnetic wave absorber may further contain additives, such as a silane coupling agent and a titanium coupling agent.

[0027] The shape of the electromagnetic wave absorber is not particularly limited, and can be changed depending on the location where it is placed, the purpose of use, and the like.

[0028] The filler content in the electromagnetic wave absorber can be set depending on the desired absorption capacity, etc., and is, for example, preferably 35% by mass or more or 50% by mass or more, and 94% by mass or less or 89% by mass or less.

[0029] The absorption frequency band and absorption peak of the electromagnetic wave absorber are the same as those of the ferrite powder.

[0030] <Method of Manufacturing Ferrite Powder> The method of manufacturing ferrite powder comprises: (a) iron oxide containing aluminum (Fe ２ O ３ (b) weighing raw materials according to the desired composition, i.e., aluminum-containing Fe ２ O ３ (c) mixing the obtained raw material mixed powder with a flux; and (d) firing the mixture in air.

[0031] Step (a) may be carried out by either (i) a reaction in a solution or (ii) mixing of raw material powders.

[0032] In the method (i), the step (a) includes, for example, (1) mixing a solution of a salt containing iron and a solution of a salt containing aluminum with an alkaline solution, (2) heating the mixed solution obtained in the step (1) while passing air through it, (3) adjusting the pH of the solution after the step (2) to neutral, (4) recovering the reaction product generated in the step (3) by filtration or the like, and (5) calcining the reaction product. Specifically, the iron-containing salt is ferrous sulfate (FeSO ４ ), and aluminum-containing salts include aluminum sulfate (Al ２ (SO ４ ) ３ ), and the alkaline solution may be an aqueous solution of sodium hydroxide. ２ O ３ The material is crushed and used in the next step. The temperature during heating is about 90°C.

[0033] In the method (i), step (a) may include: (1') reacting a solution of a salt containing iron with an alkaline solution; (2') mixing a solution of a salt containing aluminum with the solution obtained in (1'); (3') adjusting the pH of the mixed solution after (2') to neutral; (4') recovering the reaction product produced in (3') by filtration or the like; and (5') calcining the reaction product. According to method (i), the aluminum element is incorporated into the structure of the iron oxide.

[0034] In the above method (ii), in step (a), an aluminum compound can also be wet-mixed with aluminum-free iron oxide powder. In this case, highly reactive fine powders are used as the raw iron oxide powder and aluminum compound powder, and the intensity of the wet mixing is increased to ensure that the aluminum compound powder is sufficiently dispersed in the iron oxide powder. That is, in the "aluminum-containing iron oxide" obtained in step (a), aluminum element may be doped into the structure of the iron oxide, an aluminum compound may be present on the surface of the iron oxide particles, or a fine powder of iron oxide and a fine powder of an aluminum compound may be mixed. Thus, step (a) produces iron oxide containing microscopically dispersed aluminum or a mixture of a finely dispersed aluminum compound and iron oxide, so that the composition of the ferrite powder finally obtained in step (d) is uniform.

[0035] In step (b), wet mixing is preferred, and filtration and drying are preferably carried out.

[0036] In the step (c), a known flux can be used, such as BaCl ２ ・2H ２ O, SrCl ２ ・6H ２ O, CaCl ２ ・2H ２ O, etc. are preferred, and multiple compounds may be used. In particular, a compound containing an element corresponding to A in formula (1) is preferably used. The amount of flux added is preferably 0.1 to 10.0 mass %, more preferably 0.1 to 8.0 mass %, based on the raw material mixture obtained above. The obtained mixture may be formed into granules by a molding method such as extrusion molding.

[0037] The firing temperature in step (d) is preferably 1200° C. or higher.

[0038] By firing at 1200°C or higher in step (d), the ferrite reaction can be sufficiently promoted, and as a result, a high saturation magnetization σ ｓ can be extracted.

[0039] After step (d), a step of pulverizing the fired product may be carried out.

[0040] Furthermore, after step (d) or any fine pulverization step, an annealing treatment may be carried out under known conditions, for example, at 500°C to 1000°C.

[0041] The obtained ferrite powder can be used to produce an electromagnetic wave absorber, which can be produced, for example, by melting a resin, adding ferrite powder and, if necessary, additives to the melted resin, mixing the mixture, and molding the mixture.

[0042] In this specification, the terms "mass," "parts by mass," and "mass %" are interchangeable with the terms "weight," "parts by weight," and "weight %."

[0043] <Production of Ferrite Powder> [Example 1] Approximately 90 L of an alkaline solution containing 293 mol of sodium hydroxide was charged into a reaction vessel, and the liquid temperature was heated to 90°C. Next, approximately 60 L of a metal salt solution containing 107 mol of ferrous sulfate and 8.7 mol of aluminum sulfate was charged into the reaction vessel, and the reaction was carried out at 90°C, with the stirrer rotating at 580 rpm and 150 L of air per minute being passed through. After completion of the reaction, the pH of the reaction solution was adjusted to 7, and the reaction solution was filtered, washed with water, and dried. The obtained powder was calcined at 750°C and then pulverized to obtain Al-containing Fe. ２ O ３ A powder was obtained.

[0044] Various powder raw materials (Al-containing Fe, ２ O ３ , SrCO ３ ) were mixed in a wet attritor for 15 minutes, filtered, and dried. 3.6 wt % of flux was added to the resulting raw material powder mixture and mixed thoroughly, and the mixture was then extrusion-molded. The resulting granules were fired in air at 1,280°C. The fired product was crushed in a hammer mill, then coarsely pulverized in a wet attritor, washed with water, filtered, and dried. The coarsely pulverized product was then finely pulverized in a vibration mill. The finely pulverized product was annealed in air at 900°C. The manufacturing conditions are shown in Table 1, and the properties of the resulting ferrite powder are shown in Table 2.

[0045] Example 2 The same method as in Example 1 was used to prepare the powder, except that the time for fine pulverization in the vibration mill was increased.

[0046] Example 3 The same method as in Example 1 was used to prepare the powder, except that the fine pulverization using the vibration mill was omitted.

[0047] [Example 4] Al-containing Fe ２ O ３ The preparation was carried out in the same manner as in Example 1, except that the amount of sodium hydroxide was changed to 256 mol and the amount of aluminum sulfate was changed to 2.4 mol.

[0048] [Example 5] Approximately 90 L of an alkaline solution containing 357 mol of sodium hydroxide was added to a reaction vessel, and the liquid temperature was heated to 90 ° C. Next, approximately 60 L of a metal salt solution containing 165 mol of ferrous sulfate was added to the reaction vessel, and the reaction was carried out at 90 ° C., with the stirrer rotation speed at 580 rpm and 150 L of air per minute being passed through. Approximately 15 L of a metal salt solution containing 27.4 mol of aluminum sulfate was added to the solution, and the reaction solution was adjusted to pH 7 at approximately 60 ° C., filtered, washed with water, and dried. The resulting powder was calcined at 750 ° C. and then pulverized to obtain an Al-containing hematite powder.

[0049] Various powder raw materials (Al-containing Fe, ２ O ３ , SrCO ３ The procedure of Example 1 was repeated except that the amount of HCl was varied and the mixture was mixed for 1 minute in a wet attritor.

[0050] [Example 6] Various powder raw materials (Fe, ２ O ３ , Al ２ O ３ , SrCO ３ First, Al was weighed in a wet attritor. ２ O ３ After stirring for 5 minutes, the other raw materials were added and mixed for 1 minute, filtered, and dried.

[0051] [Example 7] Various powder raw materials (Fe, ２ O ３ , Al ２ O ３ , SrCO ３ First, Al was weighed in a wet attritor. ２ O ３ After stirring for 5 minutes, the other raw materials were added and mixed for 15 minutes, filtered, and dried. After that, the same procedure as in Example 1 was repeated.

[0052] [Example 8] Various powder raw materials (Fe, ２ O ３ , Al ２ O ３ , SrCO ３ ) were mixed in a wet attritor for 15 minutes, filtered, and dried.

[0053] Comparative Example 1 A powder was produced in the same manner as in Example 8, except that the powder raw materials were mixed for 1 minute.

[0054] <Analysis of Ferrite Powder> [Composition Analysis] With respect to the composition ratios x and y of the ferrite powder, the contents of aluminum element, strontium element, and iron element were determined by quantitative measurement using a fluorescent X-ray spectrometer "ZSX Primus II" (manufactured by Rigaku Corporation), and then the contents of aluminum element, strontium element, and iron element were calculated in molar terms.

[0055] [Crystal strain] To evaluate the crystal strain of the ferrite powder, measurements were performed using an XRD "D8 ADVANCE manufactured by Bruker Japan Co., Ltd." The measurement conditions were 2θ: 15° to 100°, measurement interval: 1 / 10 or less of the half-width of the main peak, and integration time: the time required for the peak intensity of the strongest line to reach 12,000 counts. The crystal strain was calculated from the obtained measurement data using the Williamson-Hall method using the analysis software TOPAS.

[0056] [Compressed density] The weighed ferrite powder was compressed to 1 t / cm using a hydraulic press. ２The volume after compression was measured, and the compressed density was calculated based on the measurement results.

[0057] [Bulk Density] Using a measuring instrument specified in JIS K5101:2014 (measurement of apparent density by static method), ferrite powder was placed in a 30 cm ３ The ferrite powder was dispersed and dropped into a cylindrical container until it was heaped, and the heaped portion was cut off with a spatula or the like. The mass of the ferrite powder in the cylindrical container was measured, and this mass was calculated based on the volume (30 cm ３ ) was used as the bulk density.

[0058] [Tap density] 10 g of ferrite powder passed through a sieve with an opening of 500 μm was weighed and ３ The measuring cylinder was tapped for 5 minutes (600 times, 2 mm height) using a tap tester KRS-406 manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd. The volume of the sample in the measuring cylinder was read to the 0.1 mm graduation, and the mass (10 g) was calculated based on the volume (25 cm ３ The value obtained by dividing by the above formula was used as the tap density.

[0059]

[0060]

[0061] <Evaluation of absorption properties> [Examples 9 to 16] The ferrite powders obtained in Examples 1 to 8 were mixed with EVA (ethylene vinyl acetate copolymer) resin, a polymer base material, in a quantitative ratio such that the ferrite powder content was 90 mass %. The resulting mixture was rolled to a thickness of 1 mm by hot pressing, to produce the electromagnetic wave absorbing sheets of Examples 9 to 16.

[0062] Comparative Example 2 The ferrite powder of Comparative Example 1 was used to prepare an electromagnetic wave absorbing sheet in the same manner as in Examples 9 to 16.

[0063] [Electromagnetic wave absorption characteristics] For the obtained electromagnetic wave absorbing sheet, the intensity of the transmitted electromagnetic wave was measured by the S21 parameter in the free space method using a free space measuring device "BD1-26.5A" (manufactured by Keycom Co., Ltd.) and a network analyzer "MS4647B" (manufactured by Anritsu Co., Ltd.). The electromagnetic wave absorption characteristics at this time are shown in Table 3.

[0064]

[0065] Examples 9 to 11 and 13 to 16 exhibited the same peak frequency and were able to attenuate electromagnetic waves more than Comparative Example 2. Furthermore, Example 12 exhibited good transmission attenuation in different frequency bands.

[0066] <Evaluation of Strength and Fluidity> [Examples 17 to 19] 4000 g of each of the ferrite powders obtained in Examples 1 to 3 was mixed in a Henschel mixer at 120° C. for 30 minutes until homogeneous, with an aminoalkyl silane coupling agent diluted with water and alcohol added in an amount of 0.5% by mass relative to the ferrite. Further, 11.53% by mass of 12-nylon resin relative to the ferrite was added at room temperature, and the mixture was mixed for an additional 10 minutes.

[0067] The mixture was fed in a fixed amount into a twin-screw kneader and kneaded at a temperature at which the 12-nylon melts. The kneaded mixture was formed into strands, removed, and cut into pellets measuring 3 mm diameter x 3 mm to obtain a resin composition.

[0068] The resulting resin composition was dried at 100° C. for 3 hours and then used to measure the molding density and MFR.

[0069] The dried resin composition was molded using a J50ADS30U injection molding machine manufactured by The Japan Steel Works, Ltd., and used to measure bending strength, tensile strength, elongation, and IZOD. Specifically, the resin composition was melted at 290-310°C and injection molded in a mold set at 80°C to prepare a sheet-like molded product having a total length of 175 mm, a width of 12.5 mm, and a thickness of 3.2 mm. The evaluation results of the obtained molded product are shown in Table 4.

[0070] [Molded Density] The resin composition was placed in a mold having a diameter of 25 mm and a height of 10.5 mm in a molten state and molded into a core, and the density was measured using an electronic specific gravity meter EW-300SG manufactured by Alpha Mirage Co., Ltd. to determine the molded density.

[0071] [Flexural Strength] Flexural strength was measured in accordance with ASTM D790 standard using a computerized precision universal testing machine AG-1 manufactured by Shimadzu Corporation.

[0072] [Tensile Strength and Elongation] Tensile strength and elongation were measured using a computerized precision universal testing machine AG-1 manufactured by Shimadzu Corporation in accordance with ASTM D638 standard.

[0073] [IZOD] Izod impact strength (IZOD) was measured in accordance with ASTM D256 standard using an Izod impact tester No. 158 manufactured by Yasuda Seiki Seisakusho Co., Ltd.

[0074] [MFR] The melt mass flow rate (MFR) of a resin composition was determined in accordance with JIS K7210 by melting the resin composition at 270°C and measuring the MFR under a load of 10 kg.

[0075]

[0076] Although the molding densities of the respective molded bodies were the same, Examples 17 and 18, which contained the powders of Examples 1 and 2, which had higher compressed densities than Example 19, had higher mechanical strengths (flexural strength, tensile strength, tensile elongation, IZOD). Furthermore, the resin compositions used for molding in Examples 17 and 18 also had high fluidity (MFR), and can be said to have excellent moldability.

Claims

1. Represented by the following chemical formula (1): A ｘ Fe （１２－ｙ） Al ｙ O １９ (1) A: at least one element selected from the group consisting of Ba, Sr, and Ca; x: 0.9 or more and 1.3 or less; y: more than 0 and 2.0 or less; and the crystal distortion is 2.5×10 －４ Below is the ferrite powder.

2. 1 ton / cm ２ The density obtained by compressing at a pressure of 3.0 g / cm ３ The ferrite powder according to claim 1 , wherein the above-mentioned

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