TWI891601B - Manganese-magnesium ferrite powder, resin composition, electromagnetic wave shielding material, electronic material and electronic component - Google Patents

Abstract

The present invention provides a manganese-magnesium ferrite powder characterized by comprising a plurality of ferrite particles having a volume average particle size of 0.6 μm to 10 μm, and a cumulative distribution (below sieve) of 1.5% to 98% by volume on a volume basis of 2.106 μm.

Description

Manganese-magnesium ferrite powder, resin composition, electromagnetic wave shielding material, electronic material and electronic component

The present invention relates to manganese-magnesium ferrite powder, resin composition, electromagnetic wave shielding material, electronic material and electronic component.

It is known that ferrite powder is used in electromagnetic wave shielding materials (see, for example, Patent Documents 1, 2, and 3).

Electromagnetic shielding materials using ferrite powder can be formed into sheets from a resin composition containing ferrite powder. By attaching these sheets to digital electronic devices such as computers and mobile phones that require electromagnetic shielding, they can prevent electromagnetic waves from leaking outside the device, preventing electromagnetic waves from interfering with internal circuits, and preventing malfunctions caused by external electromagnetic waves.

Ferrite powder is used as an electromagnetic shield for electronic devices, with the goal of shielding electromagnetic waves across a wide frequency range. In recent years, there has been a particular demand for superior electromagnetic shielding in the high-frequency range. However, existing electromagnetic shielding materials have not been able to provide sufficient electromagnetic shielding in the high-frequency range (e.g., frequencies above 1 GHz and below 12 GHz).

Ferrite particles with specific sizes and crystal structures are also known, but even when using such ferrite particles, satisfactory results have not been achieved. [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Application Publication No. 2006-286729 Patent Document 2: Japanese Patent Application Publication No. 2016-060682 Patent Document 3: Japanese Patent Application Publication No. 2002-25816

[Identify the problem to be solved]

The present invention aims to provide a manganese-magnesium ferrite powder having excellent shielding properties against electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz, and excellent shielding properties against electromagnetic waves in the low-frequency range below 1 GHz; to provide an electromagnetic shielding material, electronic material, and electronic component having excellent shielding properties against electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz, and excellent shielding properties against electromagnetic waves in the low-frequency range below 1 GHz; and to provide a resin composition that can be preferably used to manufacture the electromagnetic shielding material, electronic material, and electronic component. [Means for Solving the Problem]

Such an object can be achieved by the present invention described below.

[1] A manganese-magnesium ferrite powder characterized by: comprising a plurality of ferrite particles; having a volume average particle size of not less than 0.6 μm and not more than 10 μm; having a cumulative distribution (below sieve) on a volume basis of 2.106 μm of not less than 1.5 volume % and not more than 98 volume %.

[2] The manganese-magnesium ferrite powder according to [1], wherein the BET specific surface area is not less than 0.7 m ² /g and not more than 9 m ² /g.

[3] The manganese-magnesium ferrite powder according to [1] or [2], wherein the ferrite particles have a true spherical shape or a polygonal shape having a cross section of at least hexagonal.

[4] The manganese-magnesium ferrite powder according to any one of [1] to [3], wherein the Mn content is at least 13 mass % and at most 25 mass %, the Mg content is at least 1 mass % and at most 3.5 mass %, and the Fe content is at least 43 mass % and at most 57 mass %.

[5] The manganese-magnesium ferrite powder according to any one of [1] to [4], wherein the powder contains Sr at a content of 1.5 mass % or less.

[6] A resin composition comprising the manganese-magnesium ferrite powder as described in any one of [1] to [5], and a resin material.

[7] An electromagnetic wave shielding material, characterized in that it is composed of a material comprising the manganese-magnesium ferrite powder described in any one of [1] to [5] and a resin material.

[8] An electronic material characterized in that it is composed of a material comprising the manganese-magnesium ferrite powder described in any one of [1] to [5].

[9] An electronic component characterized in that it is composed of a material comprising the manganese-magnesium ferrite powder described in any one of [1] to [5]. [Effect of the Invention]

According to the present invention, a manganese-magnesium ferrite powder can be provided that has excellent shielding properties against electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz, and has excellent shielding properties against electromagnetic waves in the low-frequency range below 1 GHz. This invention also provides an electromagnetic shielding material, an electronic material, and an electronic component that have excellent shielding properties against electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz, and has excellent shielding properties against electromagnetic waves in the low-frequency range below 1 GHz. Furthermore, a resin composition that can be preferably used to manufacture the electromagnetic shielding material, the electronic material, and the electronic component is provided.

The following describes in detail the preferred embodiments of the present invention. <<Mn-Mg-Based Ferrite Powder>> First, the manganese-magnesium-based ferrite powder of the present invention will be described.

However, although electromagnetic shielding materials containing ferrite powder have been widely used, previous electromagnetic shielding materials have not been able to fully meet the demand for electromagnetic shielding in the high-frequency range in recent years.

Therefore, the present inventors have diligently conducted research with the goal of solving the above-mentioned problems and have completed the present invention.

Specifically, the manganese-magnesium ferrite powder of the present invention (hereinafter referred to simply as "ferrite powder") is characterized by comprising a plurality of ferrite particles having a volume average particle size of not less than 0.6 μm and not more than 10 μm, and a cumulative distribution (after screening) of not less than 1.5 volume % and not more than 98 volume % on a volume basis of 2.106 μm.

This shifts the frequency point where μ' falls below 1 toward higher frequencies at frequencies above 1 GHz. This results in a ferrite powder with excellent shielding properties against electromagnetic waves in the high-frequency range above 1 GHz. The ferrite powder of the present invention also exhibits excellent shielding properties against electromagnetic waves in the low-frequency range below 1 GHz.

Furthermore, when the particle size conditions described above are met, the fluidity and ease of handling of ferrite powder, resin compositions containing the ferrite powder, and the like can be improved. As a result, for example, the productivity of electromagnetic shielding materials (including electronic materials, electronic components, and the like, hereinafter referred to as "electromagnetic shielding materials") containing ferrite powder can be improved. Furthermore, unintended compositional unevenness can be effectively prevented from occurring in various parts of the electromagnetic shielding material. Furthermore, while ensuring excellent formability, the filling rate (content ratio) of the ferrite powder in the electromagnetic shielding material can be increased. Consequently, the material can be advantageously used to manufacture electromagnetic shielding materials with excellent shielding properties against high-frequency electromagnetic waves exceeding 1 GHz and below 12 GHz.

Furthermore, the above-described composition achieves both high permeability and low coercivity at a high level. In contrast, satisfactory properties cannot be achieved if these conditions are not met.

For example, if the volume average particle size of the ferrite powder (specifically, the volume average particle size of all particles comprising the ferrite powder, the same shall apply hereinafter) is less than the aforementioned lower limit, the fluidity of the ferrite powder and the fluidity of the resin composition containing the ferrite powder will be reduced. Furthermore, particle aggregation will be more likely to occur, and the reliability of electromagnetic shielding materials, etc. manufactured using the ferrite powder (including shielding properties against high-frequency electromagnetic waves exceeding 1 GHz and below 12 GHz) will not be sufficiently excellent.

Furthermore, if the volume average particle size of the ferrite powder exceeds the upper limit, the spaces between the ferrite particles will become larger, resulting in insufficient ferrite particles filling the spaces and residual spaces, making it difficult to increase the magnetic permeability.

Furthermore, if the volume average particle size is not greater than 0.6 μm and less than 10 μm, the magnetic permeability cannot be increased in the 1 MHz to 1 GHz frequency range.

Furthermore, if the cumulative distribution of ferrite powder on a volume basis of 2.106μm falls below the lower limit, the ferrite powder's magnetic permeability will not be sufficiently high, and electromagnetic shielding properties in the low-frequency range below 1GHz will not be sufficiently good. Furthermore, electromagnetic shielding materials manufactured using ferrite powder are prone to developing unintended surface irregularities.

Furthermore, if the cumulative distribution of ferrite powder on a volume basis of 2.106 μm exceeds the upper limit, the fluidity of the ferrite powder and the resin composition containing it will be reduced, and particle aggregation will be more likely to occur. This will prevent the reliability of electromagnetic shielding materials manufactured using ferrite powder (including shielding properties against high-frequency electromagnetic waves exceeding 1 GHz and below 12 GHz) from being sufficiently good.

Furthermore, if the ferrite powder does not have a manganese-magnesium composition, the particles are easily oxidized during firing (spraying), making it difficult to obtain the desired magnetic properties.

The particle size distribution described in this specification refers to volume particle size distribution. The volume average particle size and particle size distribution (volume particle size distribution) are obtained by the following measurement. First, 10g of ferrite powder (sample) and 80ml of water are placed in a 100ml beaker, and two drops of dispersant (sodium hexametaphosphate) are added. Next, the mixture is dispersed using an ultrasonic homogenizer (UH-150, manufactured by SMT Co., Ltd.). The output level of the ultrasonic homogenizer (UH-150, manufactured by SMT Co., Ltd.) is set to 4, and dispersion is performed for 20 seconds. After removing bubbles from the beaker surface, the sample was placed in a laser diffraction particle size distribution analyzer (SALD-7500nano, manufactured by Shimadzu Corporation) and measured under the conditions of a refractive index of 1.70-0.50i and an absorbance of 0.04-0.12. Using the included software, automatic analysis was performed using a particle size cutoff of 101CH. The volume average particle size, particle size distribution (volume particle size distribution), and cumulative distribution based on a volume standard of 2.106μm (screened) were determined.

The magnetic permeability (real part μ' and imaginary part μ") of the complex permeability in the frequency range above 1 GHz and below 12 GHz is calculated as follows. Specifically, 70 parts by mass of ferrite powder are mixed with 30 parts by mass of epoxy resin. The mixture is then poured into a cylindrical metal mold with an inner diameter of 1.8 mm and a length of 100 mm and heated to cure. After the mold is returned to room temperature, a round rod-shaped sample is removed from the mold and used as a sample for magnetic permeability measurement. The sample is then placed in a resonator and the magnetic permeability is measured using a cavity resonator (e.g., S-band and C-band models manufactured by Kanto Electronics Application Development Co., Ltd.) and a network analyzer (e.g., E5071C manufactured by KEYSIGHT TECHNOLOGIES). The resulting value is used as the magnetic permeability value of the ferrite powder.

The volume average particle size of the ferrite powder can be from 0.6 μm to 10 μm, preferably from 0.6 μm to 8 μm, more preferably from 0.6 μm to 7 μm, and even more preferably from 0.8 μm to 7 μm. This allows for a more pronounced effect as described above.

The cumulative distribution of ferrite powder on a volume basis of 2.106μm (screened) should be at least 1.5 volume% and no more than 98 volume%, preferably at least 1.8 volume% and no more than 97 volume%, and even more preferably at least 1.8 volume% and no more than 96 volume%. This allows for a more pronounced effect.

The particle size of the ferrite particles constituting the ferrite powder is preferably between 1 nm and 2106 nm. Ferrite particles are typically single crystal particles (single crystal ferrite particles), but may also contain polycrystalline particles (polycrystalline ferrite particles). Single crystals can be confirmed by capturing a selected area electron diffraction image using a TEM, with only a plurality of particles of the aforementioned particle size present. In the resulting image, the dot-like pattern and the ring-like pattern are identified as being equally or more distinct. (Images were taken using a Hitachi HITECHNOLOGIES HF-2100 Cold-FE-TEM at Vacc: 200 kV and 100,000x magnification.)

The ferrite powder of the present invention preferably has a Mn content of 13% to 25% by mass, a Mg content of 1% to 3.5% by mass, and an Fe content of 43% to 57% by mass.

This makes it possible to easily adjust the magnetic properties during firing (spraying).

On the other hand, if the Mn content in the ferrite powder is less than the above lower limit, the coercive force increases due to its proximity to magnetite, making it more likely to adhere to magnetism during dispersion in resin, etc., thereby deteriorating the dispersibility of the ferrite powder and potentially increasing the viscosity of the resin paste in which the ferrite powder is dispersed.

Furthermore, if the Mn content in the ferrite powder exceeds the upper limit, the magnetic moment increases, but the frequency characteristics shift toward lower frequencies, making it difficult to achieve sufficiently good absorption of electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz.

Furthermore, if the Mg content in the ferrite powder is less than the aforementioned lower limit, it is difficult to achieve sufficiently excellent absorption of electromagnetic waves in the high-frequency range exceeding 1 GHz and not exceeding 12 GHz.

Furthermore, if the Mg content in the ferrite powder exceeds the upper limit, the magnetic moment of the ferrite decreases, making it difficult to achieve sufficiently good electromagnetic wave absorption (particularly absorption of electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz).

If the Fe content in the ferrite powder is less than the above lower limit, the magnetic moment of the ferrite becomes small, making it difficult to achieve sufficiently good electromagnetic wave absorption (particularly absorption of electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz).

If the Fe content in the ferrite powder exceeds the upper limit, the ferrite powder becomes closer to magnetite, the coercive force increases, and the powder may be easily aggregated.

The Mn content in the ferrite powder of the present invention is preferably 13% by mass or more and 25% by mass or less, more preferably 14% by mass or more and 24% by mass or less, further preferably 16% by mass or more and 23.5% by mass or less, and most preferably 18% by mass or more and 23% by mass or less. This significantly exhibits the aforementioned effects.

Furthermore, the ferrite powder of the present invention preferably has a Mg content of 1% by mass to 3.5% by mass, more preferably 1.1% by mass to 3.4% by mass, further preferably 1.3% by mass to 3.3% by mass, and most preferably 1.5% by mass to 3.2% by mass. This significantly enhances the aforementioned effects.

Furthermore, the Fe content in the ferrite powder of the present invention is preferably 43% by mass or more and 57% by mass or less, more preferably 43.3% by mass or more and 56.0% by mass or less, further preferably 43.6% by mass or more and 55.0% by mass or less, and most preferably 44.0% by mass or more and 54.0% by mass or less. This significantly exhibits the aforementioned effects.

The ferrite powder of the present invention may also contain Sr. This facilitates adjustment of sintering uniformity during ferrite powder production and also facilitates fine-tuning of the ferrite powder's frequency characteristics.

When the ferrite powder (manganese-magnesium-based ferrite powder) contains Sr, the Sr content in the ferrite powder is preferably 0.05 mass% to 1.5 mass%, more preferably 0.2 mass% to 1.3 mass%, and even more preferably 0.3 mass% to 1.0 mass%.

This can further enhance the effects of Sr inclusion, while also further enhancing the absorption of electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz.

The ferrite powder may contain elements other than Fe, O, Mn, Mg, and Sr. The content of elements other than Fe, O, Mn, Mg, and Sr in the ferrite powder (the sum of the contents of the elements when multiple elements are present) is preferably 2.0 mass% or less, more preferably 1.0 mass% or less, and even more preferably 0.5 mass% or less.

The content of each metal element constituting the ferrite powder was determined using an ICP analyzer. More specifically, 0.2 g of ferrite powder was weighed, and 20 mL of 1N hydrochloric acid and 20 mL of 1N nitric acid were added to 60 mL of pure water. The mixture was heated to prepare an aqueous solution in which the ferrite powder was completely dissolved. This aqueous solution was then analyzed using an ICP analyzer (ICPS-1000IV, manufactured by Shimadzu Corporation) to determine the content of each metal element.

The shape of the ferrite particles is not particularly limited, but preferably has a true spherical shape or a polygonal shape with a cross section of hexagon or greater.

This allows for a higher filling rate of ferrite powder in electromagnetic shielding materials made using ferrite powder, further enhancing the electromagnetic wave absorption properties of the electromagnetic shielding materials (particularly in the high-frequency range exceeding 1 GHz and below 12 GHz).

In this specification, the term "true spherical" refers to a true sphere or a shape sufficiently close to a true sphere. Specifically, it refers to a sphericity of at least 1 and no more than 1.2. The sphericity is calculated as follows.

First, ferrite particles were imaged using a scanning electron microscope (FE-SEM (SU-8020, manufactured by Hitachi HITECHNOLOGIES)) at magnifications of 1,000 to 200,000. The ferrite particles were then imaged using the SEM images to determine their circumscribed and inscribed diameters. The sphericity was calculated as the ratio (circumscribed diameter / inscribed diameter). If the two diameters are equal, the particle is a true sphere, and the ratio is 1.

Furthermore, when photographing particles with a Feret diameter (particle size) below 500nm, the best magnification is 100,000 to 200,000 times. When the Feret diameter (particle size) is above 500nm and below 3μm, the best magnification is 10,000 to 100,000 times. When photographing particles larger than 3μm, the best magnification is around 1,000 to 10,000 times.

Alternatively, the ferrite powder can be embedded in epoxy resin or the like, cured, and then a cross-section sample of the ferrite powder can be prepared using an ion milling device and photographed at the aforementioned magnification to calculate the sphericity.

Furthermore, the proportion of particles constituting the ferrite powder (ferrite particles) that are truly spherical is preferably 90% by number or greater, more preferably 91% by number or greater, and even more preferably 93% by number or greater. The above proportions are obtained using an image analyzer. Specifically, the particle shape measurement function of the E-MAX (EDX) is used in conjunction with an FE-SEM (SU-8020 manufactured by Hitachi HITECHNOLOGIES, Ltd.) and a Horiba, Ltd. instrument. This further enhances the aforementioned effect.

The average sphericity of the particles comprising the ferrite powder (ferrite particles) is preferably 1 or greater and 1.14 or less, and more preferably 1 or greater and 1.10 or less. This allows for a more pronounced effect.

The average sphericity is the average value of the sphericities of 100 particles (ferrite particles) randomly sampled from the ferrite powder.

The ferrite particles preferably have a polygonal cross-section with a hexagon or greater shape. The cross-sectional shape of the ferrite was determined by embedding the ferrite powder in a resin, processing the cross-section using an ion milling device, and measuring it using a FE-SEM (SU-8020 manufactured by Hitachi HITECHNOLOGIES).

The BET specific surface area of the ferrite powder (specifically, the BET specific surface area of all particles constituting the ferrite powder, the same shall apply hereinafter) is preferably 0.7 m ² /g to 9 m ² /g, more preferably 1 m ² /g to 8 m ² /g, and even more preferably 3 m ² /g to 8 m ² /g.

This improves electromagnetic shielding properties (particularly shielding properties against high-frequency electromagnetic waves exceeding 1 GHz and below 12 GHz). Furthermore, the adhesion between the ferrite powder and the resin material in electromagnetic shielding materials made using ferrite powder can be improved, resulting in particularly excellent durability of the electromagnetic shielding material.

In contrast, if the BET specific surface area of the particles constituting the ferrite powder is less than the above lower limit, it may be difficult to achieve good adhesion between the ferrite powder and the resin material in, for example, an electromagnetic shielding material manufactured using the ferrite powder, thereby reducing the durability of the electromagnetic shielding material.

If the BET specific surface area of the particles constituting the ferrite powder exceeds the upper limit, the electromagnetic shielding properties (particularly the electromagnetic shielding properties in the high-frequency range exceeding 1 GHz and not exceeding 12 GHz) may be reduced.

The BET specific surface area was measured using a specific surface area measuring apparatus (model: Macsorb HM model-1208 (manufactured by MOUNTECH)).

The tapped density of the ferrite powder is preferably 0.5 g/cm ³ or more and 3.5 g/cm ³ or less, and more preferably 0.5 g/cm ³ or more and 2.8 g/cm ³ or less.

This allows small particles to be mixed well with relatively large particles, allowing the small particles to penetrate well into the gaps between the large particles, making it easier to increase the filling amount of ferrite powder in electromagnetic wave shielding materials, etc.

In this specification, the term "tap density" refers to the density determined by measurement in accordance with JIS Z 2512-2012. The tap density measurement device used is a USP tap density measuring device (Hosokawa Micron Powder Tester PT-X, etc.).

The saturation magnetization of ferrite powder is preferably between 45 emu/g and 95 emu/g. Ferrite powder meeting these requirements has a high magnetic moment per unit volume, making it suitable for use as a filler in materials such as electromagnetic shielding materials.

The residual magnetization of the ferrite powder is preferably 0.5 emu/g or higher and 12 emu/g or lower. This ensures more reliable and excellent dispersibility of the ferrite powder in the resin composition. The coercive force of the ferrite powder is preferably 250e or higher and 800e or lower.

The saturated magnetization, residual magnetization, and coercive force values described above were obtained using a vibrating sample magnetometer (Model: VSM-C7-10A, manufactured by Toei Industry Co., Ltd.). Specifically, the sample was first placed in a sample container with an inner diameter of 5 mm and a height of 2 mm. The container was then placed in the vibrating sample magnetometer. A magnetic field was then applied and scanned to 5 K·1000/4π·A/m. The applied magnetic field was then reduced, and a hysteresis curve was created on a recording paper. The saturated magnetization, residual magnetization, and coercive force values at an applied magnetic field of 5 K·1000/4π·A/m were then determined from this curve data.

The resistivity (also called "volume resistance") of ferrite powder at 25°C is preferably 1×10 ⁶ to 1×10 ¹² Ω·cm, and more preferably 1×10 ⁷ to 1×10 ¹¹ Ω·cm. The volume resistance value is calculated as follows. First, ferrite powder is placed into a Teflon cylinder with an inner diameter of 22.5 mm and an electrode at the bottom, with the height reaching 4 mm. An electrode of the same size as the inner diameter is inserted from the top. Furthermore, with a load of 1 kg applied from above, the bottom and top electrodes are connected to a measuring device (Keithley Model 6517A) to measure the resistance. The volume resistance is calculated using the resistance value obtained from this measurement, the inner diameter, and the thickness.

For example, when ferrite particles are dispersed in a resin to produce an electromagnetic shielding material (resin molded body), the volume resistance of the electromagnetic shielding material can be maintained high, and leakage current is less likely to occur even when used near a voltage application point.

The ferrite powder may or may not contain particles other than ferrite particles.

Ferrite particles can be coated (surface treated) on their surfaces. This can, for example, enhance the insulation properties of the ferrite particles (ferrite powder). Furthermore, for example, it can improve the dispersibility of the ferrite powder in the resin.

For example, ferrite particles can be surface-treated with a coupling agent. This can improve the dispersibility of the ferrite powder in the resin, for example.

As the coupling agent, for example, various silane coupling agents, titanium salt-based coupling agents, aluminum salt-based coupling agents, etc. can be used.

In particular, when ferrite particles are treated with a silane coupling agent, the resulting ferrite powder can more reliably meet the desired resistivity requirements under favorable conditions. Furthermore, this effectively prevents aggregation of the ferrite particles, resulting in exceptionally improved fluidity and ease of handling for the ferrite powder and the resin composition containing it. Furthermore, due to the affinity between the silane coupling agent and the ferrite, the surface treatment with the silane coupling agent can be performed more uniformly across the ferrite particles serving as the mother particles.

As the silane coupling agent, for example, a silane compound having a silyl group and an alkyl group can be used, and particularly preferably, among the above-mentioned alkyl groups, one having a carbon number of 8 or more and 10 or less is preferred.

This allows ferrite powder to more reliably meet specific resistivity requirements under favorable conditions. Furthermore, it effectively prevents aggregation of ferrite particles, resulting in exceptionally improved fluidity and ease of handling of the ferrite powder and resin compositions containing it. Furthermore, due to the affinity between the silane coupling agent and the ferrite, the surface treatment of the ferrite particles serving as the mother particles with the silane coupling agent can be performed more uniformly across all areas.

The surface treatment amount of the silane coupling agent, calculated as the silane coupling agent, is preferably not less than 0.05 mass % and not more than 2 mass % relative to the ferrite particles (mother particles).

Furthermore, the ferrite particles can be surface-treated with an aluminum compound. This reduces contact between ferrite particles in molded articles (e.g., electromagnetic shielding materials) using ferrite powder, thereby improving electrical resistance.

Examples of Al compounds include aluminum sulfate and sodium aluminate.

The surface treatment amount of the Al compound, calculated as Al, is preferably not less than 0.2 mass % and not more than 1 mass % relative to the ferrite particles (mother particles).

In addition, other surface treatment agents that can be used for surface treatment of ferrite particles include, for example, phosphoric acid compounds, carboxylic acids, and fluorine compounds.

Examples of the phosphoric acid compound include lauryl phosphate, lauryl-2 phosphate, steareth-2 phosphate, and phosphate ester of 2-(perfluorohexyl)ethylphosphonic acid.

Examples of carboxylic acids include compounds having an alkyl group and a carboxyl group (fatty acids). Specific examples of such compounds include decanoic acid, tetradecanoic acid, octadecanoic acid, and cis-9-octadecenoic acid.

Examples of the fluorine-based compounds include compounds having a structure in which at least a portion of the hydrogen atoms in the above-mentioned silane coupling agents, phosphoric acid compounds, and carboxylic acids are substituted with fluorine atoms (fluorine-based silane compounds, fluorine-based phosphoric acid compounds, fluorine-substituted fatty acids).

<<Method for Producing Ferrite Powder>> Next, the method for producing the ferrite powder of the present invention will be described. The ferrite powder of the present invention can be produced by any method, but can be preferably produced by the method described below, for example.

The ferrite powder of the present invention can be efficiently produced, for example, by flame spraying a ferrite raw material prepared to a predetermined composition in the atmosphere, followed by rapid solidification. This method allows the granulated material to be effectively used as the ferrite raw material.

The method for preparing the ferrite raw material is not particularly limited. For example, a dry method or a wet method may be used.

An example of a method for preparing ferrite raw materials (granules) is shown below. Specifically, multiple raw materials containing metal elements are weighed and mixed to correspond to the composition of the ferrite powder to be produced. Water is then added and the mixture is pulverized to create a slurry. The pulverized slurry is granulated in a spray dryer and graded to produce granules of a desired particle size.

Another example of a method for preparing ferrite raw materials (granules) is listed below. Specifically, multiple raw materials containing metal elements are weighed and mixed to match the composition of the ferrite powder to be produced. Dry milling is then performed to pulverize and disperse the raw materials. The mixture is then granulated using a granulator, and the granules are then graded to produce a powder of a predetermined particle size.

The granulated material prepared as described above is sprayed in the atmosphere to form a ferritized product. For spraying, a mixture of a combustion gas and oxygen can be used as the combustible gas flame.

The volume ratio of combustion gas to oxygen is preferably 1:3.5 or higher and 1:6.0 or lower. This allows for the efficient reprecipitation of volatile materials, resulting in the formation of relatively small ferrite particles. Furthermore, the shape of the resulting ferrite particles (e.g., BET specific surface area) can be precisely controlled. Furthermore, subsequent processing steps such as classification can be omitted or simplified, resulting in improved ferrite powder productivity. Furthermore, the proportion of particles removed during subsequent classification can be reduced, resulting in even better ferrite powder yield.

For example, for a combustion gas flow rate of 10 Nm ³ hr, oxygen can be used at a ratio of 35 Nm ³ hr or more and 60 Nm ³ hr or less.

The combustion gas used for melt spraying can be propane gas, propylene gas, acetylene gas, etc. Among them, propane gas can be used preferably.

Furthermore, in order to transport the granules in a combustible gas, nitrogen, oxygen, air, or the like can be used as the granule transporting gas.

The flow rate of the transported granules is preferably 20 m/s to 60 m/s. Furthermore, the spraying is preferably performed at a temperature of 1000°C to 3500°C, and more preferably 2000°C to 3500°C.

By satisfying the above conditions, the reprecipitation of volatile materials can be effectively performed to form relatively small ferrite particles. Furthermore, the shape of the resulting ferrite particles (e.g., BET specific surface area) can be more appropriately adjusted. Furthermore, subsequent processing steps such as classification can be omitted or simplified, resulting in improved ferrite powder productivity. Furthermore, the proportion of particles removed by subsequent classification can be reduced, resulting in even better ferrite powder yields.

The ferrite particles that have been ferritized by the spraying are rapidly cooled and solidified in water or the atmosphere and are collected by a filter.

Afterwards, the ferrite particles are collected and recovered by the filter and then classified as needed. Classification methods include conventional wind classification, screen filtration, and sedimentation to adjust the particle size to the desired size. Alternatively, cyclone separation can be used to recover larger particles.

The above-described method efficiently produces ferrite powder meeting the aforementioned particle size requirements. Furthermore, unlike wet granulation methods using acids, alkalis, and the like, this method effectively prevents the final ferrite powder from retaining impurities derived from the acids, alkalis, and the like. This improves the durability and reliability of the ferrite powder, resin compositions, and molded articles (e.g., electromagnetic shielding materials) produced using the ferrite powder.

Furthermore, the ferrite powder of the present invention may be prepared by mixing multiple types of powders produced by different methods (for example, a single crystal ferrite powder comprising a plurality of single crystal ferrite particles having a particle size of 1 nm or more and 2000 nm or less, and a polycrystalline ferrite powder comprising a plurality of polycrystalline ferrite particles having a particle size greater than 2000 nm).

<<Resin Composition>> The resin composition of the present invention comprises the ferrite powder described above and a resin material.

This provides a resin composition that can be advantageously used in the production of electromagnetic shielding materials, etc., that have excellent shielding properties against electromagnetic waves in the high-frequency range. Furthermore, for example, the resulting electromagnetic shielding materials, etc. (molded articles), as described below, exhibit excellent formability. Furthermore, the resulting resin composition can stably prevent unintended aggregation of ferrite powder over a long period of time. Furthermore, since the resin composition can prevent unintended aggregation of ferrite powder and unintended compositional nonuniformity within the resin composition, unintended compositional nonuniformity can be effectively prevented in electromagnetic shielding materials, etc. (molded articles) produced using the resin composition.

Resin materials constituting the resin composition include, for example, epoxy resins, urethane resins, acrylic resins, silicone resins, various modified silicone resins (acrylic modified, urethane modified, epoxy modified, fluorine), polyamide resins, polyimide resins, polyamideimide resins, fluorine, etc., and one or more of these resins can be selected and used in combination.

Furthermore, the resin composition may also contain components (other components) other than ferrite powder and resin materials.

Examples of such components include solvents, fillers (organic fillers, inorganic fillers), plasticizers, antioxidants, dispersants, colorants such as pigments, and thermally conductive particles (particles with high thermal conductivity).

In the resin composition, the ratio (content) of the ferrite powder relative to the total solid content is preferably 50 mass% or more and 95 mass% or less, and more preferably 80 mass% or more and 95 mass% or less.

This improves the dispersion stability of the ferrite powder in the resin composition, the storage stability of the resin composition, and the moldability of the resin composition. Furthermore, the mechanical strength and electromagnetic shielding properties of molded articles (e.g., electromagnetic shielding materials) made using the resin composition can be improved.

In the resin composition, the ratio (content) of the resin material relative to the total solids is preferably 5 mass% or more and 50 mass% or less, and more preferably 5 mass% or more and 20 mass% or less.

This improves the dispersion stability of the ferrite powder in the resin composition, the storage stability of the resin composition, and the moldability of the resin composition. Furthermore, the mechanical strength and electromagnetic shielding properties of molded articles (e.g., electromagnetic shielding materials) made using the resin composition can be improved.

<<Electromagnetic Wave Shielding Material>> The electromagnetic wave shielding material (molded article) of the present invention can be formed from a material comprising the ferrite powder of the present invention and a resin material.

This allows for the provision of an electromagnetic shielding material with excellent shielding properties against electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz. Furthermore, ferrite powder that meets these requirements can exert an excellent filler effect, resulting in exceptionally excellent mechanical strength and other properties of the electromagnetic shielding material (molded article).

The electromagnetic wave shielding material (molded article) of the present invention can be favorably produced using the resin composition of the present invention as described above.

Methods for forming the electromagnetic wave shielding material (molded article) include, for example, compression molding, extrusion molding, injection molding, blow molding, curtain molding, and various coating methods. Furthermore, the electromagnetic wave shielding material (molded article) can be formed by directly applying the resin composition to the component on which the electromagnetic wave shielding material (molded article) is to be formed, or it can be separately manufactured and then disposed on the target component (e.g., a printed circuit board, metal foil (e.g., copper foil), etc.).

Furthermore, the ferrite powder of the present invention can be used without the steps of mixing with a resin, dispersing, and calcining. For example, the ferrite particles can be formed into a desired shape through steps such as molding, granulation, and coating, and then calcined to produce a sintered compact (electromagnetic wave shielding material).

<<Electronic Materials and Electronic Components>> The electronic materials and electronic components of the present invention can be composed of a material comprising the ferrite powder of the present invention and a resin material.

This allows the provision of electronic materials and components with excellent shielding properties against electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz. Furthermore, ferrite powder that meets these requirements can exert an excellent filler effect, resulting in electronic materials and components with particularly excellent mechanical strength.

Examples of the electronic materials of the present invention include electronic substrates, LSI encapsulants, noise suppression pastes, noise suppression sheets, and casting pastes.

In addition, the electronic components of the present invention include, for example, inductors and reactors.

The electronic material and electronic device of the present invention can be preferably produced using the resin composition of the present invention as described above.

Methods for forming electronic materials and electronic components include, for example, compression molding, extrusion molding, injection molding, blow molding, curtain molding, and various coating methods. Furthermore, electronic materials and electronic components can be formed by directly applying a resin composition to a component on which they are to be formed, or they can be separately manufactured and then disposed on the target component.

Furthermore, the ferrite powder of the present invention can be used without the steps of mixing with a resin, dispersing, and sintering. For example, the ferrite particles can be formed into a desired shape through steps such as molding, granulation, and coating, and then sintered to produce electronic materials or electronic components as a sintered body.

The above describes the preferred embodiments of the present invention, but the present invention should not be limited thereto.

For example, in the method for producing ferrite powder of the present invention, other steps (pre-treatment step, intermediate step, post-treatment step) may be added to the above steps as needed.

Furthermore, the ferrite powder of the present invention is not limited to that produced by the above-mentioned method, and can be produced by any method.

Furthermore, in the above-described embodiments, the ferrite powder and resin composition of the present invention are used as a representative example for the manufacture of electromagnetic wave shielding materials, electronic materials, and electronic components. However, the ferrite powder and resin composition of the present invention can also be used for manufacture other than these. Examples

The present invention is described in detail below based on the following examples and comparative examples, but the present invention should not be limited thereto. In the following description, the treatments and measurements without particular reference to temperature conditions are performed at room temperature (25°C).

<<1>> Ferrite Powder Preparation The ferrite powder for each Example and Comparative Example was prepared as follows.

(Example 1) First, _Fe2O3 , _Mn3O4 , _Mg (OH) ₂ , and _SrCO3 as raw materials were mixed in a predetermined ratio using a Henschel mixer for 15 minutes. _The resulting pulverized product was granulated using a roller press and then calcined in a rotary kiln at 900°C for 5 hours in air.

After calcination, the calcined material was pulverized with water (wet pulverization) to obtain a slurry. The volume average particle size of the powdered calcined material (calcined powder) contained in the slurry was 1.3 μm.

The resulting slurry was then granulated using a spray dryer and classified to obtain granules with an average particle size of 5 μm.

The resulting granules were then sprayed in a combustible gas flame with a propane:oxygen ratio of 10 ^Nm³ /hr: ^{35 Nm³} /hr at a feed rate of 5 kg/hr. Since the granules were continuously flowed during spraying, the particles after spraying and rapid cooling were independent and not interconnected. The cooled particles were then collected by a filter (bag filter) located downstream of the gas flow, yielding ferrite powder (manganese-magnesium-based ferrite powder) with a predetermined volume average particle size and particle size distribution.

The volume average particle size and particle size distribution (volume particle size distribution) of the ferrite powder were determined as follows. First, 10g of the sample powder and 80ml of water were placed in a 100ml beaker, and two drops of a dispersant (sodium hexametaphosphate) were added. The mixture was then dispersed using an ultrasonic homogenizer (UH-150, manufactured by SMT Co., Ltd.). The output level of the ultrasonic homogenizer was set to 4, and dispersion was performed for 20 seconds. Afterwards, the surface of the beaker was de-bubbled and the particle size distribution was measured using a laser diffraction particle size analyzer (SALD-7500nano, manufactured by Shimadzu Corporation) within a refractive index range of 1.70-0.50i and an absorbance range of 0.04-0.12. The same procedure was followed for the Examples and Comparative Examples described below.

Furthermore, electron diffraction images of the ferrite powder were observed using a transmission electron microscope HF-2100 Cold-FE-TEM (manufactured by Hitachi HITECHNOLOGIES Co., Ltd.) at magnifications of 100,000x and 500,000x. The results confirmed the presence of single-crystal ferrite particles and polycrystalline ferrite particles.

The volume average particle size of the obtained ferrite powder was 0.814 μm, and the BET specific surface area was 6.59 ^{m 2} /g. Furthermore, the cumulative distribution (below the sieve) of the obtained ferrite powder on a volume basis of 2.106 μm was 95.9 volume %.

The BET specific surface area is determined using a specific surface area measuring device (Model: Macsorb HM model-1208 (manufactured by MOUNTECH)). More specifically, approximately 5 g of the sample to be measured is placed in a standard sample container dedicated to the specific surface area measuring device, accurately weighed using a precision balance, and the sample (ferrite powder) is set at the measuring port to begin the measurement. The measurement is performed using the single-point method. At the end of the measurement, the BET specific surface area is automatically calculated by inputting the sample weight. Furthermore, as a pretreatment before the measurement, approximately 20 g of the sample to be measured is aliquoted onto a weighing paper, which is then evacuated to -0.1 MPa in a vacuum dryer. After confirming that the vacuum level is below -0.1 MPa, the sample is heated at 200°C for 2 hours. The measurement environment is temperature: 10~30℃, humidity: 20~80% relative humidity, no condensation.

The tap density of the obtained ferrite powder was 0.75 g/cm ³ . The tap density was measured using a tapping device (USP tap density tester, Powder Tester PT-X manufactured by Hosokawa Micron Co., Ltd.) in accordance with JIS Z 2512-2012. Tapping was performed at 100 taps/min for 3 minutes.

Example 2 Also changing the spraying conditions, instead of using a bag filter for collection, a cyclone was used for recovery followed by classification. Ferrite powder was produced in the same manner as in Example 1.

(Example 3) The ferrite powder obtained in Comparative Example 1 described below was mixed with the ferrite powder obtained in Comparative Example 2 described below at a mass ratio of 5:95 to produce the ferrite powder of this example.

(Comparative Example 1) _Fe₂O₃ , _Mn₃O₄ , _Mg (OH) _₂ , and _SrCO₃ as raw materials were mixed in a predetermined ratio, water was added, and _the mixture was wet-milled for 6 hours to obtain a slurry. The resulting slurry was granulated and dried, then maintained at 1135°C in air for 6 hours and then pulverized to obtain ferrite powder (manganese-magnesium ferrite powder).

The obtained ferrite powder was spheroidized at a feed rate of 40 kg/hr in a flame supplied with 5 Nm ³ /hr of propane and 25 Nm ³ /hr of oxygen. The particle size distribution was then adjusted to obtain the target ferrite powder (manganese-magnesium-based ferrite powder) with a volume average particle size of 0.088 μm.

(Comparative Examples 2 and 3) Ferrite powder was produced in the same manner as in Example 1, except that the raw material ratios, calcination conditions, spray dryer granulation conditions, spray treatment conditions, and classification conditions were adjusted as shown in Table 1. The ferrite powder conditions were adjusted to those shown in Table 2.

The production conditions of the ferrite powders of the above-mentioned examples and comparative examples are summarized in Table 1, and the compositions of the ferrite powders of the above-mentioned examples and comparative examples are summarized in Table 2.

The content of each metal element constituting the ferrite powder was determined using an ICP analyzer. Specifically, 0.2 g of ferrite powder was weighed, and 20 mL of 1N hydrochloric acid and 20 mL of 1N nitric acid were added to 60 mL of pure water. The mixture was heated to prepare an aqueous solution in which the ferrite powder was completely dissolved. This aqueous solution was then analyzed using an ICP analyzer (ICPS-10001V, manufactured by Shimadzu Corporation) to determine the content of each metal element.

The iron ion (Fe ²⁺ ) concentration in the ferrite powder was measured by redox titration with potassium permanganate. The proportion of true spherical particles in the ferrite powder was determined as described above.

The true density was measured in accordance with JIS Z 8807:2012 using a fully automatic true density measuring device, Macpycno, manufactured by MOUNTECH.

[Table 1]

[Table 2]

<<2>> Viscosity Measurement 70 parts by mass of the ferrite powders from each of the Examples and Comparative Examples were mixed and dispersed with 30 parts by mass of a PVA aqueous solution (10% solids) in an auto-rotating stirrer for 3 minutes. The viscosity of the resulting mixture was then measured using a B-type viscometer. The viscosity was evaluated at the initial 1st and 10th revolutions.

<<3>> Magnetic Permeability of Ferrite Powder (1 Hz to GHz) The magnetic permeability of the ferrite powders used in the above Examples and Comparative Examples was measured as follows. The magnetic permeability was measured using an Agilent Technologies E4991A RF Impedance/Material Analyzer 16454A Magnetic Material Measurement Electrode. First, 4.5 g of ferrite powder and 0.5 g of fluorine-based powdered resin were placed in a 100 cc polyethylene container and stirred in a ball mill at 100 rpm for 30 minutes. After stirring, approximately 0.8 g of the resulting mixture was filled into a mold with an inner diameter of 4.5 mm and an outer diameter of 13 mm and pressed at 40 MPa for 1 minute using a press. The resulting molded body was cured in a hot air dryer at 140°C for 2 hours to obtain a measurement sample. The sample was then placed in a measuring device, and the previously measured outer diameter, inner diameter, and height of the sample were input into the device. The measurement was performed with an amplitude of 100 mV and a frequency range of 1 MHz to 3 GHz, scanning on a logarithmic scale to measure the magnetic permeability (μ', the real part of the complex permeability).

<<4>> Magnetic Permeability Measurement Above 1 GHz and Below 12 GHz 30 parts by mass of epoxy resin was mixed with 70 parts by mass of ferrite powder. The mixture was then poured into a cylindrical metal mold with an inner diameter of 1.8 mm and a length of 100 mm and heated to cure. After the mold returned to room temperature, the round rod-shaped sample was removed from the mold and used as the sample for magnetic permeability measurement. The resulting sample was placed in a resonator and measured using cavity resonators (S-band and C-band, both manufactured by Kanto Electronics Application Development Co., Ltd.) and a network analyzer (Keysight Technologies E5071C).

＜＜4-1＞＞ Frequency at which μ' falls below 1 Based on the above measurement results, determine the frequency at which μ' falls below 1 in the frequency range above 1 GHz and below 12 GHz.

＜＜5＞＞ Saturated Magnetization, Residual Magnetization, and Coercive Force For the ferrite powders of each of the above Examples and Comparative Examples, the saturated magnetization, residual magnetization, and coercive force were determined.

Saturated magnetization, residual magnetization, and coercive force were determined as follows. First, ferrite powder was placed in a sample container with an inner diameter of 5 mm and a height of 2 mm. The container was then placed in a vibrating sample magnetometer (VSM-C7-10A, manufactured by Toei Industry Co., Ltd.). A magnetic field was then applied and scanned to 5K·1000/4π·A/m. The applied magnetic field was then reduced to create a hysteresis curve. The saturated magnetization, residual magnetization, and coercive force were then determined from this curve data.

<<6>> Volume Resistance The volume resistance value was calculated as follows. First, the obtained ferrite powder was placed into a Teflon cylinder with an inner diameter of 22.5 mm and an electrode at the bottom, with the height of the cylinder at 4 mm. An electrode of the same size as the inner diameter was inserted from the top. Furthermore, with a 1 kg load applied from above, the bottom and top electrodes were connected to a measuring device (Keithley Model 6517A) to measure the resistance. The volume resistance was calculated using the resistance value obtained from this measurement, the inner diameter, and the thickness.

These results are summarized in Table 3.

[Table 3]

As can be seen from Table 3, while the present invention achieved excellent results, the comparative example did not achieve satisfactory results. [Industrial Profitability]

The manganese-magnesium ferrite powder of the present invention is characterized by comprising a plurality of ferrite particles having a volume-average particle size of 0.6 μm to 10 μm, and a cumulative distribution (screened) of 1.5% to 98% on a volume basis of 2.106 μm. This provides a ferrite powder that exhibits excellent shielding properties against electromagnetic waves in the high-frequency range exceeding 1 GHz and below 12 GHz, as well as excellent shielding properties against electromagnetic waves in the low-frequency range below 1 GHz. Therefore, the ferrite powder of the present invention has industrial applicability.

While the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. This invention is based on Japanese Patent Application No. 2018-023564, filed on February 13, 2018, the entire contents of which are incorporated herein by reference.

without.

without.

without.

Claims (8)

A manganese-magnesium ferrite powder is characterized by comprising a plurality of ferrite particles having a volume average particle size of 0.6 μm to 10 μm, a cumulative distribution (below sieve) of 1.5% to 98% on a volume basis at 2.106 μm, a BET surface area of 0.7 ^m² /g to 9 ^m² /g, and a tapped density of 0.5 g/ ^cm³ to 2.8 g/ ^cm³ . The ferrite particles of the manganese-magnesium ferrite powder described in Item 1 of the patent application have a true spherical shape or a polygonal shape with a cross section of hexagon or greater. The manganese-magnesium ferrite powder as described in item 1 or 2 of the patent application, wherein the Mn content is not less than 13 mass% and not more than 25 mass%, the Mg content is not less than 1 mass% and not more than 3.5 mass%, and the Fe content is not less than 43 mass% and not more than 57 mass%. The manganese-magnesium ferrite powder as described in item 1 or 2 of the patent application contains Sr at a content of 1.5% by mass or less. A resin composition characterized by comprising: a manganese-magnesium ferrite powder as described in any one of claims 1 to 4, and a resin material. An electromagnetic wave shielding material is characterized in that it is composed of a material comprising the manganese-magnesium ferrite powder as described in any one of claims 1 to 4 and a resin material. An electronic material characterized in that it is composed of a material containing the manganese-magnesium ferrite powder as described in any one of claims 1 to 4. An electronic component characterized in that it is composed of a material containing the manganese-magnesium ferrite powder as described in any one of claims 1 to 4.