WO2017212997A1 - フェライト粒子、樹脂組成物及び電磁波シールド材料 - Google Patents
フェライト粒子、樹脂組成物及び電磁波シールド材料 Download PDFInfo
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- WO2017212997A1 WO2017212997A1 PCT/JP2017/020229 JP2017020229W WO2017212997A1 WO 2017212997 A1 WO2017212997 A1 WO 2017212997A1 JP 2017020229 W JP2017020229 W JP 2017020229W WO 2017212997 A1 WO2017212997 A1 WO 2017212997A1
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Definitions
- the present invention relates to ferrite particles, a resin composition containing the ferrite particles, and an electromagnetic wave shielding material comprising the resin composition.
- an electromagnetic wave shielding material using ferrite particles a resin composition containing ferrite particles formed into a sheet shape can be considered.
- a sheet-shaped electromagnetic shielding material By attaching a sheet-shaped electromagnetic shielding material to digital electronic devices such as personal computers and mobile phones that require shielding of electromagnetic waves, leakage of electromagnetic waves to the outside of electronic devices can be prevented, or between electronic circuits. It becomes possible to prevent mutual interference of electromagnetic waves and to prevent malfunction of electronic devices due to external electromagnetic waves.
- Patent Document 1 does not show any specific numerical values regarding electromagnetic wave shielding performance.
- Patent Document 2 discloses ferrite particles which are single crystals having an average particle diameter of 0.3 ⁇ m to 1 ⁇ m and whose particle shape is an octahedral structure, and show ferrite particles containing Fe, Mn and Zn. Yes.
- the ferrite particles disclosed in Patent Document 2 exhibit a magnetic permeability of 1000 or more at a frequency of 1 MHz when the magnetic permeability is measured using a pressure-molded body made of a mixture mixed with alkali borosilicate glass powder and polyvinyl alcohol.
- Patent Document 2 does not show any electromagnetic wave shielding performance in a frequency band exceeding 1 MHz.
- Patent Document 3 discloses ferrite particles which are single crystals having an average particle diameter of 0.1 ⁇ m to 30 ⁇ m and have a spherical particle shape (including polyhedrons close to true spheres), and Fe, Mn and Zn are contained. Ferrite particles containing and ferrite particles containing Fe, Ni and Zn are shown. The ferrite particles containing Fe, Mn, and Zn disclosed in Patent Document 3 have a relative permeability ⁇ ′ (hereinafter referred to as “complex permeability real” using a pressure-molded body obtained by adding 10% by weight of water.
- the real part ⁇ ′ of the complex permeability is 32 to 60, but the real part ⁇ ′ is 0 in the frequency band of 550 MHz to 1 GHz. .
- the electromagnetic wave shielding material is configured using the ferrite particles described in Patent Document 3, there is a problem that the electromagnetic wave shielding material cannot shield electromagnetic waves in a frequency band of 550 MHz to 1 GHz.
- the ferrite particles according to the present invention are ferrite particles having a single crystal with an average particle diameter of 1 to 2000 nm and having a true spherical particle shape, and the ferrite particles substantially do not contain Zn, and contain Mn.
- the real part ⁇ ′ of the complex magnetic permeability measured by a molded body comprising 3 to 25% by weight and Fe of 43 to 65% by weight and comprising the ferrite particles and the binder resin has a maximum value in the frequency band of 100 MHz to 1 GHz. It is characterized by having.
- the ferrite particles according to the present invention preferably further contain 0 to 3.5% by weight of Mg.
- the ferrite particles according to the present invention preferably further contain 0 to 1.5% by weight of Sr.
- the resin composition according to the present invention is characterized by containing the ferrite particles as a filler.
- the electromagnetic wave shielding material according to the present invention is characterized by comprising the above resin composition.
- the ferrite particles according to the present invention have not only the frequency band of 1 MHz to 100 MHz but also the maximum value because the real part ⁇ ′ of the complex permeability measured by the molded body has a maximum value in the frequency band of 100 MHz to 1 GHz. Even in a frequency band higher than the frequency indicating the value and close to 1 GHz, the real part ⁇ ′ exceeds 0. Thereby, according to the ferrite particles of the present invention, a high magnetic permeability can be obtained in the frequency band of 1 MHz to 1 GHz.
- the ferrite particles according to the present invention can be contained as a filler in the resin composition.
- the resin composition containing the ferrite particles as a filler can be used as an electromagnetic wave shielding material.
- the electromagnetic wave shielding material can shield electromagnetic waves in a frequency band of 1 MHz to 1 GHz by using the ferrite particles.
- FIG. 1 is a transmission electron micrograph (magnification of 100,000 times) of the ferrite particles of Example 1.
- FIG. 2 is a transmission electron micrograph (magnification 500,000 times) of the ferrite particles of Example 1.
- FIG. 3 is a graph showing the frequency dependence of the real part ⁇ ′ of the complex permeability in the ferrite particles of Examples 1 to 4 and Comparative Examples 1 and 2.
- the ferrite particles according to the present invention are ferrite particles having a single crystal having an average particle diameter of 1 to 2000 nm and a true spherical particle shape.
- the ferrite particles can obtain high magnetic permeability in the frequency band of 1 MHz to 1 GHz.
- the magnetic permeability can be expressed by the real part ⁇ ′ of the complex magnetic permeability.
- the true spherical shape means a shape having an average spherical ratio of 1 to 1.2, preferably 1 to 1.1, and more preferably close to 1.
- the average sphericity exceeds 1.2, the sphericity of the ferrite particles is impaired.
- the sphericity can be determined as follows. First, ferrite particles are photographed at a magnification of 200,000 times using an FE-SEM (SU-8020, Hitachi High-Technologies Corporation) as a scanning electron microscope. At this time, the ferrite particles are photographed in a visual field capable of counting 100 particles or more. The photographed SEM image is subjected to image analysis using image analysis software (Image-Pro PLUS, Media Cybernetics). The circumscribed circle diameter and the inscribed circle diameter for each particle are obtained by manual measurement, and the ratio (circumscribed circle diameter / inscribed circle diameter) is defined as the spherical ratio. If the two diameters are the same, that is, a true sphere, this ratio is 1. In this embodiment, the average value of the sphericity in 100 ferrite particles is defined as the average sphericity.
- the average particle size of the ferrite particles according to the present invention is 1 to 2000 nm.
- the average particle size is less than 1 nm, the particles are aggregated even if the surface treatment is performed, and excellent dispersibility in the resin, solvent or resin composition cannot be obtained.
- the average particle diameter exceeds 2000 nm, the maximum value of the complex magnetic permeability ⁇ ′ does not exist in the frequency band of 100 MHz to 1 GHz but exists in the frequency band of less than 100 MHz.
- the said dispersibility can be ensured, when the molded object containing a ferrite particle is comprised, an unevenness
- the average particle diameter of the ferrite particles is preferably 1 to 800 nm, more preferably 1 to 500 nm, still more preferably 1 to 350 nm, and most preferably 1 to 130 nm.
- the average particle diameter of the ferrite particles can be obtained by, for example, measuring the horizontal ferret diameter by manual measurement for an image photographed at a magnification of 200,000, similarly to the average sphericity, and setting the average value as the average particle diameter.
- the ferrite particles according to the present invention are single crystals.
- fine pores are generated in the crystal grain boundaries in the fine structure in one particle during the process of crystal growth by firing.
- the resin composition or the like tends to enter the pores, so that it takes a long time until the ferrite particles and the resin composition are uniformly dispersed. It may take time.
- an unnecessarily large amount of resin, solvent or resin composition is required, which is disadvantageous in terms of cost.
- the ferrite particles according to the present invention can obtain a high magnetic permeability by being a single crystal.
- the real part ⁇ ′ of the complex permeability represents a normal permeability component, and the imaginary part ⁇ ′′ Represents a loss. Therefore, in order to shield an electromagnetic wave having a specific frequency, it is necessary that the real part ⁇ ′ of the complex permeability at that frequency is a numerical value greater than a certain value exceeding 0.
- the real part ⁇ ′ of the complex permeability has a maximum value in the frequency band of 100 MHz to 1 GHz, preferably in the frequency band of 100 MHz to 300 MHz. For this reason, not only in the frequency band of 1 MHz to 100 MHz, but also in the frequency band higher than the frequency showing the maximum value and close to 1 GHz, the real part ⁇ ′ becomes a value exceeding 0. Thereby, according to the ferrite particles of the present invention, a high magnetic permeability can be obtained in the frequency band of 1 MHz to 1 GHz. Therefore, when an electromagnetic wave shielding material is configured using the ferrite particles, the electromagnetic wave shielding material can shield electromagnetic waves in a frequency band of 1 MHz to 1 GHz.
- the maximum value of the real part ⁇ ′ of the complex permeability exists in the frequency band of 100 MHz to 300 MHz, and the maximum value is in the range of 7 to 9.
- the real part ⁇ ′ shows a range of 6 to 8 smaller than the maximum value.
- the real part ⁇ ′ is smaller than the maximum value and shows a range of 3 to 7, but never reaches 0.
- the real part ⁇ ′ of the complex permeability in the frequency band of 100 MHz to 1 GHz is in the range of 3 to 9, and always exceeds 0 in the frequency band of 100 MHz to 1 GHz. Magnetic susceptibility can be obtained.
- the electromagnetic wave shielding material using the ferrite particles has a frequency band in which the real part ⁇ ′ is 0. Can not shield the electromagnetic wave.
- the ferrite particle according to the present invention is a single crystal, a high magnetic permeability can be obtained at a relatively high frequency.
- the domain wall moves a plurality of grains when a magnetic field is applied. At this time, when the crystal orientation of each grain is different, a force that hinders the movement of the domain wall acts. Therefore, in the ferrite particles that are polycrystalline, the rise of magnetic permeability is poor.
- a force that hinders the movement of the domain wall due to such grains does not work, so that high magnetic permeability can be obtained.
- the measurement of the real part ⁇ ′ of the complex magnetic permeability is performed by using a molded body obtained by pressure-molding a mixture of 90 parts by weight of ferrite particles and 10 parts by weight of a powder binder resin as a measurement sample, and using Agilent Technologies. E4991A type RF impedance / material analyzer manufactured by 16454A magnetic material measurement electrode.
- the ferrite particles according to the present invention comprise a metal oxide containing 3 to 25% by weight of Mn and 43 to 65% by weight of Fe. However, the ferrite particles according to the present invention do not substantially contain Zn.
- the ferrite particles of the present invention are both soft magnetic permeability and low remanent magnetization by being a soft ferrite made of a metal oxide substantially free of Zn and containing Mn and Fe in the above range. Obtainable.
- the ferrite particles of the present invention may further contain 0 to 3.5% by weight of Mg in addition to Mn and Fe. Addition of Mg in the above range is more preferable because an effect of widening the width (peak width) of the maximum value of the real part ⁇ ′ of the complex permeability can be obtained.
- substantially free of Zn means that the ferrite particles do not contain positively added Zn and may contain inevitable Zn as an unavoidable impurity. It is described to make it. Therefore, when ferrite particles are analyzed, Zn is at a level that can be confirmed to a trace level.
- the Mn content is less than 3% by weight, a desired magnetic permeability may not be obtained. Further, the residual magnetization of the ferrite particles is increased and the ferrite particles are easily aggregated. In this case, it is difficult to uniformly disperse the ferrite particles in the resin, the solvent, or the resin composition. On the other hand, when the Mn content is more than 25% by weight, a desired magnetic permeability may not be obtained or a desired saturation magnetization necessary as ferrite particles may not be obtained.
- the Fe content is less than 43% by weight, the desired permeability may not be obtained in the ferrite particles.
- the Fe content exceeds 65% by weight, the residual magnetization of the ferrite particles increases, and the ferrite particles may easily aggregate. In that case, it becomes difficult to uniformly disperse the ferrite particles in the resin, solvent or resin composition.
- the ferrite particles of the present invention may contain Sr in addition to the above composition.
- Sr not only contributes to the adjustment of the uniformity during firing, but by containing it, the frequency characteristics of the ferrite particles can be easily finely adjusted.
- the content of Sr is preferably 0 to 1.5% by weight. When the content of Sr exceeds 1.5% by weight, the influence as hard ferrite starts to appear and there is a risk of lowering the magnetic permeability.
- the ferrite particles according to the present invention preferably have a BET specific surface area of 1 to 30 m 2 / g.
- the BET specific surface area is less than 1 m 2 / g, when a resin composition containing ferrite particles is formed, the affinity between the particle surface and the resin composition becomes insufficient, and the resin composition present on the particle surface is locally localized. May be exciting. For this reason, when a molded body is formed using this resin composition, irregularities may occur on the surface of the molded body, which is not preferable.
- ferrite particles composed of Fe, Mn, Mg and Sr often produce particles having a smooth surface state, and the BET specific surface area does not exceed 30 m 2 / g. More preferably, the BET specific surface area of the ferrite particles is 5 to 20 m 2 / g.
- the ferrite particles according to the present invention have a saturation magnetization of 45 to 95 Am 2 / kg measured when the ferrite particles are filled in a predetermined cell and a magnetic field of 5K ⁇ 1000 / 4 ⁇ ⁇ A / m is applied by a magnetometer. Preferably there is.
- the saturation magnetization in which the ferrite particles are filled in a predetermined cell and a magnetic field of 5K ⁇ 1000 / 4 ⁇ ⁇ A / m is applied by a magnetometer is hereinafter referred to as “saturation magnetization”.
- Ferrite particles having a saturation magnetization in the above range are suitable as a magnetic core material.
- the saturation magnetization is less than 45 Am 2 / kg, the performance is insufficient as a magnetic core material.
- ferrite particles composed of Fe, Mn, Mg and Sr it is difficult to realize saturation magnetization exceeding 95 Am 2 / kg.
- the ferrite particles according to the present invention preferably have a residual magnetization of 0 to 12 Am 2 / kg.
- the residual magnetization By setting the residual magnetization within the above range, it is possible to more reliably obtain dispersibility in the resin, the solvent, or the resin composition. If the remanent magnetization exceeds 12 Am 2 / kg, the ferrite particles may easily aggregate together, and in that case, it may be difficult to uniformly disperse the ferrite particles in the resin, solvent, or resin composition. .
- the ferrite particles can be produced by spraying a granulated material made of a ferrite raw material in the air to form a ferrite, followed by rapid solidification and then collecting only particles having a particle size within a predetermined range.
- the method for preparing the ferrite raw material is not particularly limited, and a conventionally known method can be adopted. A dry method or a wet method may be used.
- An example of a method for preparing a ferrite raw material is as follows: an Fe raw material, an Mn raw material, and, if necessary, an Mg raw material and an Sr raw material are weighed so as to have a desired ferrite composition, and then water is added. In addition, pulverize to prepare a slurry. The prepared slurry is granulated with a spray dryer and classified to prepare a granulated product having a predetermined particle size.
- the particle size of the granulated product is preferably about 500 to 10,000 nm in consideration of the particle size of the obtained ferrite particles.
- a ferrite raw material having a composition prepared is mixed, dry pulverized, each raw material is pulverized and dispersed, the mixture is granulated with a granulator, classified, and granulated with a predetermined particle size.
- a ferrite raw material having a composition prepared is mixed, dry pulverized, each raw material is pulverized and dispersed, the mixture is granulated with a granulator, classified, and granulated with a predetermined particle size.
- the granulated material thus prepared is sprayed in the atmosphere to be ferritized.
- a mixed gas of combustion gas and oxygen can be used as a combustible gas combustion flame, and the volume ratio of the combustion gas and oxygen is 1: 3.5 to 6.0.
- the proportion of oxygen in the combustible gas combustion flame is less than 3.5 with respect to the combustion gas, melting may be insufficient, and when the proportion of oxygen exceeds 6.0 with respect to the combustion gas, ferritization may occur. It becomes difficult.
- it can be used in a proportion of oxygen 35 ⁇ 60Nm 3 / hr against the combustion gases 10 Nm 3 / hr.
- propane gas, propylene gas, acetylene gas or the like can be used, and propane gas can be particularly preferably used.
- propane gas can be particularly preferably used.
- nitrogen, oxygen, or air can be used as a granulated material conveyance gas.
- the flow rate of the granulated material to be conveyed is preferably 20 to 60 m / sec.
- the thermal spraying is preferably performed at a temperature of 1000 to 3500 ° C., more preferably 2000 to 3500 ° C.
- the ferrite particles ferritized by thermal spraying are rapidly cooled and solidified by being carried in an air stream by air supply, and then ferrite particles having an average particle diameter of 1 to 2000 nm are collected and recovered. . Ferrite particles that are single crystals can be obtained by rapidly solidifying the ferritic ferrite particles.
- the above-described collection is carried by carrying rapidly cooled solidified ferrite particles in an air flow by air supply, and particles having a large particle size fall during the air flow conveyance, while other particles are conveyed downstream.
- ferrite particles having an average particle diameter in the above range can be collected by a filter provided on the downstream side of the airflow.
- the flow velocity at the time of the air flow By setting the flow velocity at the time of the air flow to 20 to 60 m / sec, particles having a large particle size are dropped in the middle of the air flow, and ferrite particles having an average particle size in the above range are efficiently recovered downstream of the air flow. be able to. If the flow velocity is less than 20 m / sec, even particles having a small particle diameter fall in the middle of airflow conveyance, so the average particle diameter of ferrite particles recovered downstream of the airflow is less than 1 nm, or In some cases, the absolute amount of ferrite particles recovered downstream is low and the productivity is low. On the other hand, if the flow rate exceeds 60 m / sec, even particles having a large particle diameter are conveyed to the downstream, so the average particle diameter of the ferrite particles recovered downstream of the airflow may exceed 2000 nm.
- the collected ferrite particles are classified as necessary, and the particle size is adjusted to a desired particle size.
- a classification method an existing air classification, mesh filtration method, sedimentation method, or the like can be used.
- ferrite particles having a particle size exceeding 2000 nm may be removed by classification.
- the obtained ferrite particles can be subject to a surface treatment with a coupling agent.
- the surface treatment with the coupling agent can further improve the dispersibility of the ferrite particles in the resin, solvent or resin composition.
- the coupling agent various silane coupling agents, titanate coupling agents, and aluminate coupling agents can be used, and decyltrimethyoxysilane and n-octyltriethoxysilane can be used more preferably.
- the surface treatment amount depends on the BET specific surface area of the ferrite particles, it is preferably 0.05 to 4% by weight, more preferably 0.05 to 2% by weight with respect to the ferrite particles in terms of silane coupling agent. Is more preferable.
- the ferrite particles according to the present invention can be used, for example, as an electromagnetic shielding material.
- ferrite particles are added to a resin composition containing a resin and an aqueous or solvent solvent, and the ferrite particles are dispersed in the resin composition by stirring and mixing.
- the ferrite particles are substantially free of Zn and are made of a metal oxide containing 3 to 25% by weight of Mn and 43 to 65% by weight of Fe, the residual magnetization is small. Aggregation can be prevented.
- an electromagnetic wave shielding material can be produced by applying the resin composition containing the obtained filler onto a substrate, volatilizing the solvent and curing the resin.
- the electromagnetic wave shielding material can shield electromagnetic waves in the frequency band of 1 MHz to 1 GHz by including the ferrite particles having the real value ⁇ ′ of the complex permeability having a maximum value in the frequency band of 100 MHz to 1 GHz. Moreover, since the said electromagnetic shielding material suppresses aggregation of the ferrite particle in a resin composition, while being able to obtain electromagnetic shielding performance uniformly over the whole electromagnetic shielding material, it can obtain a smooth surface. .
- the ferrite particles according to the present invention are not limited to the electromagnetic shielding material, and can be used for various applications.
- Ferrite particles may be used as magnetic core materials and fillers, particularly as magnetic fillers, and may be used as raw materials for molded bodies. When ferrite particles are used as a molding raw material, molding, granulation, coating, etc. can be performed, and firing may be performed.
- Example 1 Iron oxide (Fe 2 O 3 ) and manganese oxide (MnO) were weighed and mixed at a molar ratio of 80:20. Water was added to the obtained mixture and pulverized to prepare a slurry having a solid content of 50% by weight. The produced slurry was granulated with a spray dryer and classified to produce a granulated product having an average particle diameter of 5000 nm.
- propane obtained granules: oxygen 10 Nm 3 / hr: Sprayed ferritization by performing under conditions of 35 Nm 3 / hr of combustible gas flow rate in the combustion flame of about 40 m / sec, followed by It was rapidly cooled in the atmosphere by being carried in an air stream by air supply. At this time, since the granulated material was sprayed while continuously flowing, the particles after spraying and quenching were independent without being bound to each other. Subsequently, the cooled particles were collected by a filter provided on the downstream side of the airflow. At this time, the particles having a large particle size were not collected by the filter because they dropped in the middle of the air flow. Next, about the collected particles, coarse powder having a particle size exceeding 2000 nm was removed by classification to obtain ferrite particles. Therefore, among the obtained ferrite particles, the particle size of the largest particle size was 2000 nm or less.
- Example 2 In this example, ferrite particles were produced in the same manner as in Example 1 except that the molar ratio of iron oxide and manganese oxide was 50:50.
- Example 3 In this example, ferrite particles were produced in the same manner as in Example 1 except that the molar ratio of iron oxide and manganese oxide was 90:10.
- Example 4 In this example, iron oxide (Fe 2 O 3 ), manganese oxide (MnO), magnesium oxide (MgO), and strontium oxide (SrO) were mixed at a molar ratio of 50: 40: 10: 1.25. Except for the above, ferrite particles were obtained in the same manner as in Example 1.
- Comparative Example 1 In this comparative example, after obtaining a granulated product in the same manner as in Example 1, the granulated product was placed in a mortar and fired in an electric furnace at 1200 ° C. for 4 hours in a nitrogen atmosphere with an oxygen concentration of 0% by volume. Then, a fermented product obtained as a lump according to the shape of the mortar was obtained. The obtained fired product was rapidly cooled in the atmosphere, and the cooled fired product was pulverized by grinding with a mortar to obtain ferrite particles.
- Comparative Example 2 In this comparative example, ferrite particles were prepared in the same manner as in Example 1 except that the molar ratio of iron oxide and manganese oxide was 100: 0.
- the average sphericity was measured by the method described above. When the average sphericity was 1.2 or less, it was determined to be “true sphere”.
- the volume average particle size was measured using a Microtrac particle size analyzer (Model 9320-X100, Nikkiso Co., Ltd.). First, 10 g of the obtained ferrite particles were placed in a beaker together with 80 ml of water as a dispersion medium, and 2 to 3 drops of sodium hexametaphosphate as a dispersant were added. Next, the obtained solution was oscillated with an ultrasonic homogenizer (UH-150, SMT Co., Ltd.) for 20 seconds at an output level of 4 to disperse ferrite particles in the solution. Next, after removing bubbles generated on the beaker surface, solid-liquid separation was performed to collect ferrite particles. The volume average particle diameter of the recovered ferrite particles was measured.
- the BET specific surface area was measured using a specific surface area measuring device (Macsorb HM model-1208, Mountec Co., Ltd.). First, about 10 g of the obtained ferrite particles are placed on a medicine wrapping paper, deaerated with a vacuum dryer, and after confirming that the degree of vacuum is ⁇ 0.1 MPa or less, the ferrite particles are heated at 200 ° C. for 2 hours. The water adhering to the surface of was removed. Subsequently, about 0.5 to 4 g of ferrite particles from which moisture was removed were placed in a standard sample cell dedicated to the apparatus and accurately weighed with a precision balance. Subsequently, the weighed ferrite particles were set in the measurement port of the apparatus and measured. The measurement was performed by a one-point method. The measurement atmosphere was a temperature of 10 to 30 ° C. and a relative humidity of 20 to 80% (no condensation).
- the magnetic characteristics were measured using a vibration sample type magnetometer (VSM-C7-10A, Toei Industry Co., Ltd.). First, the obtained ferrite particles were filled in a cell having an inner diameter of 5 mm and a height of 2 mm, and set in the apparatus. In the above-mentioned apparatus, a magnetic field was applied and swept to 5K ⁇ 1000 / 4 ⁇ ⁇ A / m. Next, the applied magnetic field was decreased to create a hysteresis curve on the recording paper.
- VSM-C7-10A vibration sample type magnetometer
- the magnetization when the applied magnetic field is 5K ⁇ 1000 / 4 ⁇ ⁇ A / m is the saturation magnetization
- the magnetization when the applied magnetic field is 0K ⁇ 1000 / 4 ⁇ ⁇ A / m is the residual magnetization.
- the magnetic permeability was measured using an E4991A type RF impedance / material analyzer 16454A magnetic material measuring electrode manufactured by Agilent Technologies.
- 9 g of ferrite particles and 1 g of a binder resin (Kynar 301F: polyvinylidene fluoride) were placed in a 100 cc polyethylene container and mixed by stirring for 30 minutes with a 100 rpm ball mill.
- about 0.6 g of the obtained mixture is filled in a die having an inner diameter of 4.5 mm and an outer diameter of 13 mm, and is pressed with a press at a pressure of 40 MPa for 1 minute, so that the height is about 1.8 mm.
- a molded body was obtained.
- the obtained molded body was dried at a temperature of 140 ° C. for 2 hours with a hot air dryer to obtain a measurement sample.
- the measurement sample was set in the measurement device, and the outer diameter, inner diameter, and height of the measurement sample measured in advance were input to the measurement device.
- the amplitude was 100 mV
- the frequency range of 1 MHz to 1 GHz was swept on a logarithmic scale
- the real part ⁇ ′ of the complex permeability was measured. The obtained graph is shown in FIG.
- the ferrite particles of Examples 1 to 3 contain Fe and Mn, but do not substantially contain Mg, Sr, and Zn. Further, the ferrite particles of Example 4 contain Fe, Mn, Mg, and Sr but do not substantially contain Zn.
- the ferrite particles of Examples 1 to 4 had an average particle size in the range of 1 to 2000 nm and a BET specific surface area in the range of 1 to 30 m 2 / g.
- the ferrite particles of Example 1 were spherical. Further, as can be seen from the transmission image obtained by the TEM in FIG. 2, the state in which the crystal planes are oriented in the same direction inside one particle is observed in a striped manner, so that the ferrite particles of Example 1 are single. It is clear that it is a crystal. Similar results were obtained for the ferrite particles of Examples 2 to 4.
- the ferrite particles of Comparative Example 1 contain Fe and Mn as in Examples 1 to 3, but do not substantially contain Mg, Sr, or Zn.
- the ferrite particles of Comparative Example 1 were polycrystalline with an average particle size exceeding 2000 nm, the particle shape was not spherical but irregular, and the BET specific surface area was less than 1 m 2 / g.
- the ferrite particles of Comparative Example 2 are single crystals having an average particle size of less than 2000 nm, a spherical shape, and a BET specific surface area of 1 to 30 m 2 / g, as in Examples 1 to 4. It was within the range.
- the maximum value of the real part ⁇ ′ of the complex permeability exists in the frequency band of 100 MHz to 300 MHz, and the maximum value of the real part ⁇ ′ is 7 to The range was 9. Further, in the frequency band of 1 MHz to 50 MHz, the real part ⁇ ′ is in the range of 6 to 8 smaller than the maximum value, and in the frequency band of 400 MHz to 1 GHz, the real part ⁇ ′ is in the range of 3 to 7 smaller than the maximum value. Although it did not reach 0.
- the maximum value of the real part ⁇ ′ of the complex magnetic permeability was present at a frequency of about 20 MHz, and the maximum value was about 7. Further, the real part ⁇ ′ was in the range of 5 to 6.5 in the frequency band of 1 MHz to 10 MHz. In the ferrite particles of Comparative Example 2, the maximum value of the real part ⁇ ′ of the complex magnetic permeability was in the frequency band of 350 MHz to 500 MHz, and the maximum value was about 6.2. Further, the real part ⁇ 'was in the range of 4 to 5.5 in the frequency band of 1 MHz to 100 MHz.
- the ferrite particles of Examples 1 to 4 have a larger real part ⁇ ′ of the complex permeability than the ferrite particles of Comparative Examples 1 and 2 over the entire frequency band of 1 MHz to 500 MHz. Further, although the ferrite particles of Examples 1 to 4 have a smaller real part ⁇ ′ than the ferrite particles of Comparative Examples 1 to 3 in the frequency band of 700 MHz to 1 GHz, they are not significantly different from Comparative Examples 1 to 2. Therefore, it is clear that the ferrite particles of Examples 1 to 4 exhibit excellent magnetic permeability in the frequency band of 1 MHz to 1 GHz as compared with the ferrite particles of Comparative Examples 1 and 2.
- the ferrite particles according to the present invention can stably shield electromagnetic waves in a wide frequency band that needs to be shielded regardless of frequency when used as an electromagnetic shielding material for electronic equipment.
- the ferrite particles have excellent dispersibility with respect to a resin, a solvent, or a resin composition
- a sheet-like electromagnetic shielding material is constituted by a resin composition containing the ferrite particles as a filler, an electromagnetic shielding material
- the ferrite particles can be prevented from agglomerating on the surface, and a smooth surface can be obtained, and the electromagnetic shielding performance can be obtained uniformly over the entire electromagnetic shielding material.
- the ferrite particles according to the present invention can also be suitably used as a magnetic filler or a molded body raw material.
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Abstract
Description
本発明に係るフェライト粒子は、下記に示すように、平均粒径が1~2000nmの単結晶であり且つ真球状の粒子形状を備えるフェライト粒子である。当該フェライト粒子は、1MHz~1GHzの周波数帯域において高い透磁率を得ることができる。上記透磁率は、複素透磁率の実部μ’で表すことができる。
球状率は、次のようにして求めることができる。まず、走査型電子顕微鏡としてのFE-SEM(SU-8020、株式会社日立ハイテクノロジーズ)を用いて倍率20万倍でフェライト粒子を撮影する。このとき、フェライト粒子を100粒子以上カウント可能な視野において撮影する。撮影したSEM画像について、画像解析ソフト(Image-Pro PLUS、メディアサイバネティクス(MEDIA CYBERNETICS)社)を用いて画像解析を行う。マニュアル測定によって各粒子に対する外接円直径、内接円直径を求め、その比(外接円直径/内接円直径)を球状率とする。2つの直径が同一である、すなわち、真球であれば、この比が1となる。本実施形態では、フェライト粒子100粒子における球状率の平均値を平均球状率とした。
本発明に係るフェライト粒子の平均粒径は1~2000nmである。平均粒径が1nm未満では、表面処理を行ったとしても粒子が凝集してしまい、樹脂、溶媒又は樹脂組成物に対する優れた分散性を得ることができない。一方、平均粒径が2000nmを超えると、複素透磁率μ’の極大値が100MHz~1GHzの周波数帯域の範囲に存在せずに100MHz未満の周波数帯域に存在することとなる。また、上記分散性を確保できるものの、フェライト粒子を含有する成形体を構成したときに、フェライト粒子の存在によって成形体の表面に凹凸が生じることがある。フェライト粒子の平均粒径は、好ましくは1~800nmであり、より好ましくは1~500nmであり、さらに好ましくは1~350nmであり、最も好ましくは1~130nmである。
また、本発明に係るフェライト粒子は、その形態が単結晶である。多結晶であるフェライト粒子の場合には、焼成による結晶成長の過程で1粒子内の微細構造において結晶粒界内に微細な気孔が生じてしまう。その結果、フェライト粒子を樹脂、溶媒又は樹脂組成物に混合したときに、当該気孔に樹脂組成物等が侵入しようとするため、フェライト粒子と樹脂組成物等とが均一に分散されるまでに長時間を要することがある。また、条件によっては、必要以上の量の樹脂、溶媒又は樹脂組成物を必要とし、コスト的にも不利である。これに対し、単結晶であるフェライト粒子の場合には、このような不都合は解消される。さらに、後述するように、本発明に係るフェライト粒子は、単結晶であることにより高い透磁率を得ることができる。
フェライト粒子を用いて電磁シールドを構成し、特定の周波数の電磁波を遮蔽するためには、その周波数における透磁率μが大きいことが必要である。透磁率μは、一般的に複素透磁率μ=μ’-jμ”として表現される(jは虚数単位)。複素透磁率の実部μ’は通常の透磁率成分を表し、虚部μ”は損失を表している。よって、特定の周波数の電磁波を遮蔽するには、その周波数における複素透磁率の実部μ’が0を上回る一定以上の数値であることが必要である。
本発明に係るフェライト粒子は、Mnを3~25重量%、Feを43~65重量%を含有する金属酸化物からなる。ただし、本発明に係るフェライト粒子は、Znを実質的に含有していない。本発明のフェライト粒子は、Znを実質的に含有せず且つMnとFeとを上記範囲で含有する金属酸化物からなるソフトフェライトであることにより、高い透磁率と低い残留磁化とを両立して得ることができる。また、本発明のフェライト粒子は、Mn及びFeに加えて、さらにMgを0~3.5重量%含有してもよい。Mgを上記範囲で添加することにより複素透磁率の実部μ’の極大値の幅(ピーク幅)を広げる効果が得られるのでより好ましい。
本発明に係るフェライト粒子は、BET比表面積が1~30m2/gであることが好ましい。BET比表面積が1m2/g未満では、フェライト粒子を含有する樹脂組成物を構成したときに、粒子表面と樹脂組成物との親和性が不十分となり、粒子表面に存在する樹脂組成物が局所的に盛り上がることがある。そのため、この樹脂組成物を用いて成形体を構成したときに、成形体の表面に凹凸が生じることがあり好ましくない。一方、Fe,Mn,Mg及びSrから組成されるフェライト粒子は、表面状態が平滑な粒子が生成されることが多く、BET比表面積が30m2/gを超えることはない。フェライト粒子のBET比表面積は、5~20m2/gであることがさらに好ましい。
本発明に係るフェライト粒子は、当該フェライト粒子を所定のセルに充填し磁気測定装置で5K・1000/4π・A/mの磁場を印加したときに測定した飽和磁化が45~95Am2/kgであることが好ましい。なお、本明細書において、前記フェライト粒子を所定のセルに充填し磁気測定装置で5K・1000/4π・A/mの磁場を印加した飽和磁化を、以下、「飽和磁化」と称す。飽和磁化が上記範囲であるフェライト粒子は、磁芯材料として好適である。飽和磁化が45Am2/kg未満では、磁芯材料としては性能不足である。一方、Fe,Mn,Mg及びSrから組成されるフェライト粒子においては、95Am2/kgを超える飽和磁化を実現するのは困難である。
本発明に係るフェライト粒子は、残留磁化が0~12Am2/kgであることが好ましい。残留磁化を上記範囲とすることにより、樹脂、溶媒又は樹脂組成物に対する分散性をより確実に得ることができる。残留磁化が12Am2/kgを上回ると、フェライト粒子同士が凝集し易くなることがあり、その場合、樹脂、溶媒又は樹脂組成物に当該フェライト粒子を均一に分散させるのが困難になることがある。
次に、上記フェライト粒子の製造方法について説明する。
本発明に係るフェライト粒子は、例えば、電磁波シールド材料に用いることができる。まず、フェライト粒子を、樹脂と水系又は溶剤系の溶媒とを含む樹脂組成物に添加し、撹拌、混合することにより、樹脂組成物中にフェライト粒子を分散させる。当該フェライト粒子は、上述のとおり、Znを実質的に含有せず、Mn3~25重量%、Fe43~65重量%を含有する金属酸化物からなることにより残留磁化が小さいので、樹脂組成物中における凝集を防ぐことができる。続いて、得られたフィラーを含有する樹脂組成物を基材上に塗布し、溶媒を揮発させ樹脂を硬化させることにより、電磁波シールド材料を作製することができる。また、樹脂組成物をシート状に成形して電磁遮蔽を必要とするプリント配線基板や配線パターン上に貼付することにより、電磁波シールド材料を構成してもよい。
〔実施例1〕
酸化鉄(Fe2O3)及び酸化マンガン(MnO)をモル比で80:20の割合で計量し、混合した。得られた混合物に水を加えて粉砕し固形分50重量%のスラリーを作製した。作製されたスラリーをスプレードライヤーで造粒し、分級して平均粒径5000nmの造粒物を作製した。
本実施例では、酸化鉄及び酸化マンガンをモル比で50:50の割合とした以外は、実施例1と同様にしてフェライト粒子を作製した。
本実施例では、酸化鉄及び酸化マンガンをモル比で90:10の割合とした以外は、実施例1と同様にしてフェライト粒子を作製した。
本実施例では、酸化鉄(Fe2O3)、酸化マンガン(MnO)、酸化マグネシウム(MgO)及び酸化ストロンチウム(SrO)をモル比で50:40:10:1.25の割合として混合物を得た以外は、実施例1と全く同様にしてフェライト粒子を得た。
本比較例では、実施例1と同様にして造粒物を得た後に、造粒物を匣鉢に収容し、電気炉で1200℃、4時間、酸素濃度0体積%の窒素雰囲気下で焼成してフェライト化することにより、匣鉢の形状に即した塊となった焼成物を得た。得られた焼成物を大気中で急冷し、冷却された焼成物を乳鉢で磨砕することによって粉砕し、フェライト粒子を得た。
本比較例では、酸化鉄及び酸化マンガンをモル比で100:0の割合とした以外は、実施例1と同様にしてフェライト粒子を作製した。
得られた実施例1~4及び比較例1~2のフェライト粒子について、化学分析を行うと共に、粉体特性・磁気特性(形状、結晶形態、平均粒径、BET比表面積、飽和磁化、残留磁化及び透磁率)を評価した。化学分析、BET比表面積、磁気特性、抵抗及び透磁率の測定方法は下記のとおりであり、その他の測定方法は上述のとおりである。結果を表1~2に示す。
フェライト粒子におけるFe,Mn,Mg及びSrの含有量を次のようにして測定した。まず、フェライト粒子0.2gを秤量し、純水60mlに1Nの塩酸20ml及び1Nの硝酸20mlを加えたものを加熱し、フェライト粒子を完全溶解させた水溶液を調製した。得られた水溶液をICP分析装置(ICPS-1000IV、株式会社島津製作所)にセットし、フェライト粒子における金属成分の含有量を測定した。なお、表1中の「<0.01」という記載は、測定誤差であるか又は不純物として存在することを意味している。
平均球状率は、上述の方法によって測定した。平均球状率が1.2以下である場合に「真球状」であると判定した。
実施例1のフェライト粒子を透過電子顕微鏡(TEM)によって倍率10万倍及び50万倍で観察した。得られた写真を図1及び図2に示す。
実施例1~3のフェライト粒子については、上述した水平フェレ径を平均粒径とし、比較例1~2のフェライト粒子については、下記の体積平均粒径を平均粒径とした。
体積平均粒径は、マイクロトラック粒度分析計(Model9320-X100、日機装株式会社)を用いて測定した。まず、得られたフェライト粒子10gを、分散媒としての水80mlと共にビーカーにいれ、分散剤としてのヘキサメタリン酸ナトリウムを2~3滴添加した。次いで、得られた溶液に対して、超音波ホモジナイザー(UH-150、株式会社エスエムテー)によって、出力レベル4で20秒間発振させることにより、溶液中にフェライト粒子を分散させた。次に、ビーカー表面に生じた泡を取り除いた後、固液分離し、フェライト粒子を回収した。回収したフェライト粒子について体積平均粒径を測定した。
BET比表面積の測定は、比表面積測定装置(Macsorb HM model-1208、株式会社マウンテック)を用いて行った。まず、得られたフェライト粒子約10gを薬包紙に載せ、真空乾燥機で脱気して真空度が-0.1MPa以下であることを確認した後に、200℃で2時間加熱することにより、フェライト粒子の表面に付着している水分を除去した。続いて、水分が除去されたフェライト粒子を当該装置専用の標準サンプルセルに約0.5~4g入れ、精密天秤で正確に秤量した。続いて、秤量したフェライト粒子を当該装置の測定ポートにセットして測定した。測定は1点法で行った。測定雰囲気は、温度10~30℃、相対湿度20~80%(結露なし)であった。
磁気特性の測定は、振動試料型磁気測定装置(VSM-C7-10A、東英工業株式会社)を用いて行った。まず、得られたフェライト粒子を内径5mm、高さ2mmのセルに充填し、上記装置にセットした。上記装置において、磁場を印加し、5K・1000/4π・A/mまで掃引した。次いで、印加磁場を減少させ、記録紙上にヒステリシスカーブを作成した。このカーブにおいて、印加磁場が5K・1000/4π・A/mであるときの磁化を飽和磁化とすると共に、印加磁場が0K・1000/4π・A/mであるときの磁化を残留磁化とした。
透磁率の測定は、アジレントテクノロジー社製E4991A型RFインピーダンス/マテリアル・アナライザ 16454A磁性材料測定電極を用いて行った。まず、フェライト粒子9gとバインダー樹脂(Kynar301F:ポリフッ化ビニリデン)1gとを100ccのポリエチレン製容器に収容し、100rpmのボールミルで30分間撹拌して混合した。撹拌終了後、得られた混合物0.6g程度を、内径4.5mm、外径13mm、のダイスに充填し、プレス機で40MPaの圧力で1分間加圧することにより、高さ1.8mm程度の成型体を得た。得られた成形体を熱風乾燥機によって温度140℃で2時間乾燥させることにより、測定用サンプルを得た。
Claims (5)
- 平均粒径が1~2000nmの単結晶であり且つ真球状の粒子形状を備えるフェライト粒子であって、
当該フェライト粒子は、Znを実質的に含有せず、Mnを3~25重量%、Feを43~65重量%を含有し、
当該フェライト粒子とバインダー樹脂とからなる成形体によって測定した複素透磁率の実部μ’が100MHz~1GHzの周波数帯域において極大値を有することを特徴とするフェライト粒子。 - Mgを0~3.5重量%含有する請求項1に記載のフェライト粒子。
- Srを0~1.5重量%含有する請求項1又は請求項2に記載のフェライト粒子。
- 請求項1~3のいずれか一項に記載のフェライト粒子をフィラーとして含有することを特徴とする樹脂組成物。
- 請求項4に記載の樹脂組成物からなることを特徴とする電磁波シールド材料。
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WO2021070871A1 (ja) | 2019-10-07 | 2021-04-15 | パウダーテック株式会社 | フェライト粉末、フェライト樹脂複合材料並びに電磁波シールド材、電子材料又は電子部品 |
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WO2022009960A1 (ja) | 2020-07-08 | 2022-01-13 | 株式会社ダイセル | 樹脂成形体及びその製造方法 |
WO2022209640A1 (ja) | 2021-03-31 | 2022-10-06 | パウダーテック株式会社 | フェライト粉末、フェライト樹脂複合材料並びに電磁波シールド材、電子材料又は電子部品 |
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