阅读说明：本技术 磁铅石型六方晶铁氧体的粒子及其制造方法以及电波吸收体 (Magnetite-type hexagonal ferrite particle, method for producing same, and radio wave absorber ) 是由 细谷阳一 白田雅史 见上龙雄 于 2018-12-25 设计创作，主要内容包括：本发明涉及一种由下述式(1)表示且晶相为单相的磁铅石型六方晶铁氧体的粒子及其应用。式(1)中,A表示选自包括Sr、Ba、Ca及Pb的组中的至少1种金属元素,x满足1.5≤x≤8.0。AFe<Sub>(12-x)</Sub>Al<Sub>x</Sub>O<Sub>19</Sub>……式(1)。(The present invention relates to particles of magnetoplumbite-type hexagonal ferrite represented by the following formula (1) and having a single-phase crystal phase, and use thereof. In the formula (1), A represents at least 1 metal element selected from the group consisting of Sr, Ba, Ca and Pb, and x satisfies 1.5. ltoreq. x.ltoreq.8.0. AFe (12‑x) Al x O 19 … … formula (1).)

1. A magnetoplumbite-type hexagonal ferrite particle represented by the following formula (1) having a single crystal phase,

AFe_(12-x)Al_xO₁₉formula (1)

In the formula (1), A represents at least 1 metal element selected from the group consisting of Sr, Ba, Ca and Pb, and x satisfies 1.5. ltoreq. x.ltoreq.8.0.

2. The particle of magnetoplumbite-type hexagonal ferrite according to claim 1, wherein,

x in the formula (1) satisfies 1.5-6.0.

3. The particles of magnetoplumbite-type hexagonal ferrite according to claim 1 or 2, which are used for an electric wave absorber.

4. The method for producing particles of magnetoplumbite-type hexagonal ferrite according to any one of claims 1 to 3, comprising:

a step (A) of obtaining a precipitate containing Fe, Al, and at least 1 metal element selected from the group consisting of Sr, Ba, Ca, and Pb by a liquid phase method; and

and a step B of calcining the precipitate obtained in the step A.

5. The method for producing magnetoplumbite-type hexagonal ferrite particles according to claim 4, wherein,

the step A includes: and a step of mixing an aqueous solution containing a salt of Fe, a salt of Al and the at least 1 metal element with an alkaline aqueous solution to obtain a reaction product.

6. An electric wave absorber comprising the magnetoplumbite-type hexagonal ferrite particles according to any one of claims 1 to 3 and a binder, and having a planar shape.

7. An electric wave absorber comprising the magnetoplumbite-type hexagonal ferrite particles according to any one of claims 1 to 3 and a binder, and having a three-dimensional shape.

Technical Field

The present invention relates to particles of magnetoplumbite-type hexagonal ferrite, a method for producing the same, and a radio wave absorber.

Background

In recent years, with diversification of use forms of radio waves in high frequency bands such as Electronic Toll Collection Systems (ETC), Automatic Highway Systems (AHS), and satellite broadcasting, malfunction and failure of Electronic devices due to radio wave interference have become a problem. In order to reduce the influence of such radio wave interference on the electronic device, a process of preventing reflection of radio waves by absorbing unnecessary radio waves by a radio wave absorber is performed.

As the radio wave absorber, a radio wave absorber using a magnetic material is generally used. An electric wave incident on an electric wave absorber containing a magnetic material generates a magnetic field in the magnetic material. When the generated magnetic field is reduced to energy of the electric wave, a part of the energy is lost and absorbed. Therefore, in the radio wave absorber containing a magnetic material, the frequency band in which the effect is exerted differs depending on the type of the magnetic material used.

For example, patent document 1 describes a magnetic powder for a radio wave absorber having a composition formula of Fe_(12-x)Al_xO₁₉(wherein A is at least 1 of Sr, Ba, Ca and Pb, and x is 1.0-2.2), the peak particle size of the laser diffraction scattering particle size distribution is at least 10 μm. The magnetic powder for a radio wave absorber disclosed in patent No. 4674380 exhibits excellent radio wave absorption performance in the vicinity of 76 GHz.

Disclosure of Invention

Technical problem to be solved by the invention

With the rapid development of information communication technology in recent years, it is considered that the use forms of radio waves in high frequency bands will be increasingly diversified in the future. Therefore, from the viewpoint of coping with radio waves of various frequencies, development of a radio wave absorber capable of exhibiting excellent radio wave absorption performance in a higher frequency band has been desired.

As a result of intensive studies on a magnetic material suitable for a radio wave absorber, the present inventors have found that a radio wave of a higher frequency band can be absorbed by increasing the ratio of aluminum atoms to iron atoms in particles of magnetoplumbite-type hexagonal ferrite in which iron is partially replaced with aluminum. However, as a result of further studies, the present inventors have found that, in the above-mentioned particles of magnetoplumbite-type hexagonal ferrite, when the proportion of aluminum atoms is increased, the radio wave absorption performance tends to be lowered although the radio wave that can be absorbed is shifted to a higher frequency band.

An object of one embodiment of the present invention is to provide particles of magnetoplumbite-type hexagonal ferrite having excellent magnetic properties and exhibiting excellent radio wave absorption performance even in a high frequency band.

Another object of another embodiment of the present invention is to provide a method for producing magnetoplumbite-type hexagonal ferrite particles having excellent magnetic properties and exhibiting excellent radio wave absorption performance even in a high frequency band.

Another object of the present invention is to provide a radio wave absorber that exhibits excellent radio wave absorption performance even in a high frequency band.

Means for solving the technical problem

The means for solving the above problems include the following means.

< 1 > particles of a magnetoplumbite-type hexagonal ferrite represented by the following formula (1) having a single phase as a crystal phase.

[ chemical formula 1]

AFe_(12-x)Al_xO₁₉… … type (1)

In the formula (1), A represents at least 1 metal element selected from the group consisting of Sr, Ba, Ca and Pb, and x satisfies 1.5. ltoreq. x.ltoreq.8.0.

< 2 > the magnetoplumbite-type hexagonal ferrite particles according to < 1 > wherein,

x in the formula (1) satisfies 1.5. ltoreq. x.ltoreq.6.0.

< 3 > the particles of magnetoplumbite-type hexagonal ferrite according to < 1 > or < 2 > for use in an electric wave absorber.

< 4 > a method for producing magnetoplumbite-type hexagonal ferrite particles, which is any one of < 1 > to < 3 >, comprising:

a step (A) of obtaining a precipitate containing Fe, Al, and at least 1 metal element selected from the group consisting of Sr, Ba, Ca, and Pb by a liquid phase method; and

and a step B of calcining the precipitate obtained in the step A.

< 5 > the method for producing magnetoplumbite-type hexagonal ferrite particles < 4 >, wherein,

the step a includes a step of mixing an aqueous solution containing a Fe salt, an Al salt, and a salt of the at least 1 metal element with an alkaline aqueous solution to obtain a reaction product.

< 6 > an electric wave absorber containing the particles of magnetoplumbite-type hexagonal ferrite described in any one of < 1 > to < 3 > and a binder and having a planar shape.

< 7 > an electric wave absorber containing particles of the magnetoplumbite-type hexagonal ferrite of any one of < 1 > to < 3 > and a binder and having a three-dimensional shape.

Effects of the invention

According to one embodiment of the present invention, there is provided particles of magnetoplumbite-type hexagonal ferrite having excellent magnetic properties and exhibiting excellent radio wave absorption performance even in a high frequency band.

Further, according to another embodiment of the present invention, there is provided a method for producing magnetoplumbite-type hexagonal ferrite particles having excellent magnetic properties and capable of exhibiting excellent radio wave absorption performance even in a high frequency band.

Further, according to another embodiment of the present invention, there is provided a radio wave absorber capable of exhibiting excellent radio wave absorption performance even in a high frequency band.

Drawings

Fig. 1 is a perspective view of a radio wave absorber according to example 6B.

Fig. 2 is a plan view of the radio wave absorber of example 6B.

Fig. 3 is a schematic cross-sectional view of the radio wave absorber of example 6B.

Fig. 4 is an optical photograph of the radio wave absorber as an embodiment of the present invention, viewed from the normal direction.

Detailed Description

Hereinafter, an example of an embodiment to which the magnetoplumbite-type hexagonal ferrite particles of the present invention are applied will be described. However, the present invention is not limited to the following embodiments, and can be implemented by being appropriately modified within the scope of the object of the present invention.

In the present invention, the numerical range represented by the term "to" represents a range including the numerical values before and after the term "to" as the minimum value and the maximum value, respectively.

In the numerical ranges recited in the present invention, the upper limit or the lower limit recited in a certain numerical range may be replaced with the upper limit or the lower limit recited in another numerical range recited in a stepwise manner. In addition, in the numerical ranges described in the present invention, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the values shown in the examples.

In the present invention, a combination of 2 or more preferred embodiments is a more preferred embodiment.

In the present invention, when there are a plurality of substances corresponding to each component, the amount of each component represents the total amount of the plurality of substances unless otherwise specified.

In the present invention, the term "step" includes not only an independent step, but also a step that can achieve the intended purpose of the step even when the step is not clearly distinguished from other steps.

[ particles of magnetoplumbite-type hexagonal ferrite ]

Particles of magnetoplumbite-type hexagonal ferrite of the present invention (hereinafter, also referred to as "magnetoplumbite-type hexagonal ferrite particles") are particles of magnetoplumbite-type hexagonal ferrite represented by the following formula (1) and having a single phase of crystal phase.

[ chemical formula 2]

AFe_(12-x)Al_xO₁₉… … type (1)

In the formula (1), A represents at least 1 metal element selected from the group consisting of Sr, Ba, Ca and Pb, and x satisfies 1.5. ltoreq. x.ltoreq.8.0.

As described above, with the rapid development of information communication technology in recent years, a radio wave absorber capable of exhibiting excellent radio wave absorption performance in a higher frequency band is required from the viewpoint of coping with radio waves of various frequencies.

As a result of focusing attention on particles of magnetoplumbite-type hexagonal ferrite in which iron is partially replaced with aluminum as a magnetic material suitable for a radio wave absorber, the present inventors have found that radio waves in a higher frequency band can be absorbed by increasing the ratio of aluminum atoms to iron atoms. However, it is found that when the proportion of aluminum atoms is increased, the electric wave absorption performance tends to be lowered although the electric wave that can be absorbed is shifted to a higher frequency band. The present inventors have further studied and found that when the magnetoplumbite-type hexagonal ferrite has a single crystal phase, it has excellent magnetic properties and can exhibit excellent radio wave absorption performance even in a high frequency band.

That is, the magnetoplumbite-type hexagonal ferrite particles of the present invention are represented by formula (1) and have a single-phase crystal phase, and therefore have excellent magnetic properties and can exhibit excellent radio wave absorption performance even in a high-frequency band.

According to the magnetoplumbite-type hexagonal ferrite particles of the present invention, the absorption wavelength of the radio wave absorber can be designed by controlling the ratio of aluminum atoms, for example, and the absorption of the radio wave of a desired frequency can be efficiently improved.

The magnetoplumbite-type hexagonal ferrite particles of the present invention cannot exhibit excellent radio wave absorption performance even when the crystal phase is not single-phase (for example, the crystal phase is two-phase) compared to the magnetoplumbite-type hexagonal ferrite particles of the present invention even if the proportion of aluminum atoms is high (for example, refer to comparative example 1B and comparative example 2B described later).

Conventionally, particles of magnetoplumbite-type hexagonal ferrite are produced by a method (so-called solid phase method) in which particles are obtained from a plurality of solid raw materials by calcination. In this solid phase method, since aluminum atoms are less likely to enter the crystal after firing, when a large amount of aluminum raw material is used, the crystal phase is less likely to become a single phase (see, for example, comparative example 3A and comparative example 4A described later).

For example, a magnetoplumbite-type hexagonal ferrite powder described in patent publication No. 4674380 is produced by a solid-phase method. According to the findings of the present inventors, it was found that when the proportion of aluminum atoms in the magnetoplumbite-type hexagonal ferrite powder described in patent No. 4674380 is increased, the crystal phase becomes two-phase, and the radio wave absorption performance is lowered.

The magnetoplumbite-type hexagonal ferrite particles of the present invention can be obtained by a liquid phase method. According to the liquid phase method, unlike the conventional solid phase method, aluminum atoms are easily incorporated into the crystal, and it is considered that a single-phase crystal phase can be obtained even when a large amount of aluminum raw material is used.

The above presumption is not intended to be a limiting explanation of the magnetoplumbite-type hexagonal ferrite particles of the present invention, but is explained as an example.

The magnetoplumbite-type hexagonal ferrite particles of the present invention are particles of a compound represented by formula (1).

As long as a in formula (1) is at least 1 metal element selected from the group consisting of Sr, Ba, Ca and Pb, the kind and amount of the metal element are not particularly limited.

For example, a in formula (1) is preferably at least 1 metal element selected from the group consisting of Sr, Ba, and Ca from the viewpoint of handling and handling properties.

X in the formula (1) satisfies 1.5. ltoreq. x.ltoreq.8.0, preferably satisfies 1.5. ltoreq. x.ltoreq.6.0, and more preferably satisfies 2.0. ltoreq. x.ltoreq.6.0.

When x in the formula (1) is 1.5 or more, radio waves in a frequency band higher than 60GHz can be absorbed.

When x in formula (1) is 8.0 or less, the magnetoplumbite-type hexagonal ferrite particles have magnetism.

Specific examples of the magnetoplumbite-type hexagonal ferrite represented by formula (1) include SrFe_(9.58)Al_(2.42)O₁₉、SrFe_(9.37)Al_(2.63)O₁₉、SrFe_(9.27)Al_(2.73)O₁₉、SrFe_(9.85)Al_(2.15)O₁₉、SrFe_(10.00)Al_(2.00)O₁₉、SrFe_(9.74)Al_(2.26)O₁₉、SrFe_(10.44)Al_(1.56)O₁₉、SrFe_(9.79)Al_(2.21)O₁₉、SrFe_(9.33)Al_(2.67)O₁₉、SrFe_(7.88)Al_(4.12)O₁₉、SrFe_(7.04)Al_(4.96)O₁₉、SrFe_(7.37)Al_(4.63)O₁₉、SrFe_(6.25)Al_(5.75)O₁₉、SrFe_(7.71)Al_(4.29)O₁₉、Sr_(0.80)Ba_(0.10)Ca_(0.10)Fe_(9.83)Al_(2.17)O₁₉、BaFe_(9.50)Al_(2.50)O₁₉、CaFe_(10.00)Al_(2.00)O₁₉、PbFe_(9.00)Al_(3.00)O₁₉And the like.

The composition of the magnetoplumbite-type hexagonal ferrite particles was confirmed by high-frequency Inductively Coupled Plasma (ICP: Inductively Coupled Plasma) emission spectrometry.

Specifically, a pressure-resistant container containing 12mg of sample particles and 4mol/L (liter; hereinafter, the same) of a hydrochloric acid aqueous solution 10mL was held in an oven at a set temperature of 120 ℃ for 12 hours to obtain a solution. Then, 30mL of pure water was added to the obtained solution, followed by filtration through a 0.1 μm membrane filter. Elemental analysis of the filtrate thus obtained was performed using a high-frequency Inductively Coupled Plasma (ICP) emission spectroscopic analyzer. From the obtained elemental analysis results, the content of each metal atom to 100 atomic% of iron atom was determined. The composition was confirmed from the obtained content.

As the measuring apparatus, for example, a high frequency Inductively Coupled Plasma (ICP) emission spectrometer (model: ICPS-8100) of Shimadzu Corporation can be suitably used. However, the measuring apparatus is not limited thereto.

The magnetoplumbite-type hexagonal ferrite particles of the present invention are particles of magnetoplumbite-type hexagonal ferrite having a single phase of crystal phase.

In the present invention, the case where the "crystal phase is a single phase" refers to a case where only 1 kind of Diffraction pattern showing the crystal structure of magnetoplumbite-type hexagonal ferrite of an arbitrary composition is observed in powder X-Ray Diffraction (XRD: X-Ray Diffraction) measurement. In other words, it means that a plurality of magnetoplumbite-type hexagonal ferrites of arbitrary compositions are mixed and no diffraction pattern of 2 or more or no crystal other than the magnetoplumbite-type hexagonal ferrite is observed. For the distribution of the diffraction patterns, for example, a database of International Centre for Diffraction Data (ICDD) can be referred to. For example, the diffraction pattern of a magnetoplumbite-type hexagonal ferrite containing Sr can be referred to as "00-033-. However, since a part of iron is replaced with aluminum, the peak position is shifted.

Confirmation that the crystal phase of the magnetoplumbite-type hexagonal ferrite is a single phase can be performed by, for example, an X-ray diffraction (XRD) method.

Specifically, a method of measuring under the following conditions using a powder X-ray diffraction apparatus is exemplified.

As the measuring apparatus, for example, an X' Pert Pro diffractometer manufactured by PANALYTICAL CORPORATION can be suitably used. However, the measuring apparatus is not limited thereto.

-conditions-

An X-ray source: CuK alpha line

[ wavelength:(0.154nm), output: 40mA, 45 kV)

Scanning range: 20 DEG < 2 theta < 70 DEG

Scanning interval: 0.05 degree

Scanning speed: 0.75 degree/min

The shape of the magnetoplumbite-type hexagonal ferrite particles of the present invention is not particularly limited, and examples thereof include a plate shape and an irregular shape.

The number average particle diameter D50 of the magnetoplumbite-type hexagonal ferrite of the present invention is not particularly limited, and is, for example, 2 μm or more and 100 μm or less.

The number average particle diameter D50 can be measured, for example, using a particle size distribution analyzer.

As the measurement device, for example, a laser diffraction/scattering type particle size distribution measurement device LA-960 (model) of HORIBA, ltd. However, the measuring apparatus is not limited thereto.

The coercive force (Hc) of the magnetoplumbite-type hexagonal ferrite particles of the present invention is preferably 400kA/m or more, more preferably 500kA/m or more, and still more preferably 600kA/m or more.

When the coercive force (Hc) of the magnetoplumbite-type hexagonal ferrite particles of the present invention is 400kA/m or more, radio wave absorption performance tends to be exhibited even in a high frequency band.

The upper limit of the coercive force (Hc) of the magnetoplumbite-type hexagonal ferrite particles of the present invention is not particularly limited, and is preferably 1500kA/m or less, for example.

The saturation magnetization(s) per unit mass of the magnetoplumbite-type hexagonal ferrite particles of the present invention is preferably 10Am²/kg or more, more preferably 20Am²/kg or more, more preferably 30Am²More than kg.

When the saturation magnetization(s) per unit mass of the magnetoplumbite-type hexagonal ferrite particles of the present invention is 10Am²At a concentration of more than kg, the radio wave absorption performance tends to be more excellent.

The upper limit of the saturation magnetization(s) per unit mass of the magnetoplumbite-type hexagonal ferrite particles of the present invention is not particularly limited, and is preferably 60Am, for example²Is less than/kg.

The coercive force (Hc) and saturation magnetization(s) per unit mass of the magnetoplumbite-type hexagonal ferrite particles were measured using a vibrating sample magnetometer under conditions of a maximum applied magnetic field 3589kA/m and a magnetic field scanning speed 1.994kA/m/s in an environment of an ambient air temperature of 23 ℃.

As the measuring apparatus, for example, a vibration test magnetometer (model: TM-TRVSM5050-SMSL) of TAMAKAWA CO. However, the measuring apparatus is not limited thereto.

Use of magnetoplumbite-type hexagonal ferrite particles

The magnetoplumbite-type hexagonal ferrite particles of the present invention are excellent in magnetic properties and exhibit excellent radio wave absorption performance even in a high frequency band, and therefore are suitable for use as a radio wave absorber.

In the magnetoplumbite-type hexagonal ferrite particles of the present invention, when the proportion of aluminum atoms is increased, the radio wave that can be absorbed is shifted to a higher frequency band and excellent radio wave absorption performance can be exhibited in the high frequency band. Therefore, when the magnetoplumbite-type hexagonal ferrite particles of the present invention are used as a radio wave absorber, the selection range of frequencies applicable in a high frequency band can be expanded.

[ method for producing magnetoplumbite-type hexagonal ferrite particles ]

The magnetoplumbite-type hexagonal ferrite particles of the present invention can be produced by a method including a step a of obtaining a precipitate containing Fe, Al, and at least 1 metal element selected from the group consisting of Sr, Ba, Ca, and Pb (hereinafter also referred to as "specific metal element") by a liquid phase method, and a step B of calcining the precipitate obtained in the step a.

The step A and the step B may be divided into 2 or more stages.

Hereinafter, each step will be described in detail.

< Process A >

The step a is a step of obtaining a precipitate containing Fe, Al, and at least 1 metal element (i.e., a specific metal element) selected from the group consisting of Sr, Ba, Ca, and Pb by a liquid phase method.

In step a, a precipitate of a reaction product serving as a precursor of the magnetoplumbite-type hexagonal ferrite particles can be obtained. The precipitate obtained in step a is assumed to be iron hydroxide, aluminum hydroxide, a composite hydroxide of iron, aluminum, and a specific metal element, or the like.

The step a preferably includes a step (hereinafter, also referred to as "step a 1") of mixing an aqueous solution containing an Fe salt, an Al salt, and a salt of a specific metal element (hereinafter, also referred to as "raw material aqueous solution") and an alkaline aqueous solution to obtain a reaction product.

In step a1, an aqueous solution (so-called precursor-containing aqueous solution) containing a reaction product that becomes a precursor of the magnetoplumbite-type hexagonal ferrite particles can be obtained.

Preferably, the step a includes a step of solid-liquid separating the reaction product obtained in the step a1 (hereinafter, also referred to as "step a 2").

In step a2, a precipitate of the reaction product that becomes a precursor of the magnetoplumbite-type hexagonal ferrite particles (i.e., the precipitate in step a) can be obtained.

(Process A1)

Step a1 is a step of mixing an aqueous solution (i.e., a raw material aqueous solution) containing a Fe salt, an Al salt, and a salt of a specific metal element with an alkaline aqueous solution to obtain a reaction product.

The salt of Fe, Al, or a salt of a specific metal element is not particularly limited, and for example, a water-soluble inorganic acid salt such as a nitrate, a sulfate, or a chloride is preferable from the viewpoint of availability and cost.

Specific examples of the Fe salt include iron (III) chloride hexahydrate [ FeCl ]₃·6H₂O, iron (III) nitrate nonahydrate [ Fe (NO)₃)₃·9H₂O, etc.

Specific examples of the Al salt include aluminum chloride hexahydrate [ AlCl ]₃·6H₂O, aluminum nitrate nonahydrate [ Al (NO)₃)₃·9H₂O, etc.

Specific examples of the Sr salt include strontium chloride hexahydrate [ SrCl ]₂·6H₂O ] and strontium nitrate [ Sr (NO)₃)₂Strontium acetate 0.5 hydrate [ Sr (CH) ]₃COO)₂·0.5H₂O, etc.

Specific examples of the Ba salt include barium chloride dihydrate [ BaCl ]₂·2H₂O ] and barium nitrate [ Ba (NO)₃)₂Barium acetate [ (CH ]₃COO)₂Ba, etc.

Specific examples of the Ca salt include calcium chloride dihydrate [ CaCl [ ]₂·2H₂O, calcium nitrate tetrahydrate [ Ca (NO)₃)₂·4H₂O ], calcium acetate monohydrate [ (CH)₃COO)₂Ca·H₂O, etc.

Specific examples of the Pb salt include lead (II) chloride [ PbCl ]₂Lead (II) nitrate [ Pb (NO)₃)₂And the like.

The alkaline aqueous solution is not particularly limited, and examples thereof include an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution.

The concentration of the alkaline aqueous solution is not particularly limited, and may be, for example, 0.1 to 10 mol/L.

The raw material aqueous solution and the alkaline aqueous solution may be simply mixed. The raw material aqueous solution and the alkaline aqueous solution may be mixed in a total amount at once, or the raw material aqueous solution and the alkaline aqueous solution may be mixed little by little. Further, the raw material aqueous solution and the alkaline aqueous solution may be mixed while adding one to the other one little by little.

For example, from the viewpoint of reproducibility of the radio wave absorption performance, it is preferable to gradually mix the raw material aqueous solution and the alkaline aqueous solution little by little.

The method of mixing the raw material aqueous solution and the alkaline aqueous solution is not particularly limited, and examples thereof include a method of mixing by stirring.

The stirring mechanism is not particularly limited, and a general stirrer or a stirring device can be used.

The stirring time is not particularly limited as long as the reaction of the components to be mixed is completed, and can be appropriately set according to the composition of the raw material aqueous solution, the kind of a stirrer, a stirring device, and the like.

For example, the temperature at the time of mixing the raw material aqueous solution and the alkaline aqueous solution is preferably 100 ℃ or lower from the viewpoint of preventing bumping, and is more preferably 95 ℃ or lower, and still more preferably 15 ℃ or higher and 92 ℃ or lower from the viewpoint of obtaining a good reaction product.

The mechanism for adjusting the temperature is not particularly limited, and a general heating device, cooling device, or the like can be used.

For example, the pH of the aqueous solution obtained by mixing the raw material aqueous solution and the alkaline aqueous solution at 25 ℃ is preferably 5 to 13, more preferably 6 to 12, from the viewpoint of easier availability of the precipitate.

(Process A2)

Step a2 is a step of solid-liquid separating the reaction product obtained in step a 1.

The method of solid-liquid separation is not particularly limited, and examples thereof include decantation, centrifugal separation, filtration (suction filtration, pressure filtration, etc.), and the like.

When the method of solid-liquid separation is centrifugal separation, conditions for centrifugal separation are not particularly limited, and for example, centrifugal separation is preferably performed at a rotation speed of 2000rpm (revolutions per minute); the same applies hereinafter) or more for 3 to 30 minutes. Also, the centrifugal separation may be performed a plurality of times.

< Process B >

The step B is a step of calcining the precipitate obtained in the step a.

In the step B, the precipitate obtained in the step a is calcined to obtain magnetoplumbite-type hexagonal ferrite particles of the present invention.

Calcination can be carried out using a heating device.

The heating device is not particularly limited as long as it can heat to a target temperature, and any known heating device can be used. As the heating device, for example, a calcining device independently manufactured in accordance with a production line can be used in addition to the electric furnace.

The calcination is preferably carried out in an atmospheric environment.

The calcination temperature is not particularly limited, and is, for example, preferably 900 ℃ or higher, more preferably 900 to 1400 ℃, and further preferably 1000 to 1200 ℃.

The calcination time is not particularly limited, and is, for example, preferably 1 hour to 10 hours, and more preferably 2 hours to 6 hours.

From the viewpoint of reproducibility of the radio wave absorption performance, the precipitate obtained in the step a is preferably dried, for example, before calcination.

The drying means is not particularly limited, and examples thereof include a dryer such as an oven.

The drying temperature is not particularly limited, and is, for example, preferably 50 to 200 ℃ and more preferably 70 to 150 ℃.

The drying time is not particularly limited, and is, for example, preferably 2 to 50 hours, and more preferably 5 to 30 hours.

[ electric wave absorber ]

The radio wave absorber of the present invention contains the magnetoplumbite-type hexagonal ferrite particles of the present invention (hereinafter, also referred to as "specific magnetoplumbite-type hexagonal ferrite particles") and a binder.

The radio wave absorber of the present invention contains the specific magnetoplumbite-type hexagonal ferrite particles, and therefore can exhibit excellent radio wave absorption performance even in a high frequency band.

In the radio wave absorber of the present invention, for example, by controlling the ratio of aluminum atoms to iron atoms in the specific magnetoplumbite-type hexagonal ferrite particles (i.e., the value of x in formula (1)), the absorption wavelength of the radio wave absorber can be designed, and the absorption of the radio wave of a desired frequency can be efficiently improved.

The radio wave absorber of the present invention may have a planar shape or a three-dimensional shape.

The planar shape is not particularly limited, and a sheet shape, a film shape, and the like can be given.

The three-dimensional shape is not particularly limited, and examples thereof include polygonal columnar shapes, cylindrical shapes, pyramidal shapes, conical shapes, honeycomb shapes, and the like having a triangular or more shape. As an example of the radio wave absorber having a three-dimensional shape, a linear radio wave absorber shown in fig. 4 may be mentioned.

The three-dimensional shape may be a combination of the planar shape and the three-dimensional shape. As an example, a shape in which a radio wave absorber having a planar shape of a sheet and a radio wave absorber having a three-dimensional shape of a cone are combined as shown in fig. 1 is given. The details of the radio wave absorber shown in fig. 1 will be described later.

In the radio wave absorber of the present invention, the radio wave absorption performance can be controlled depending on the shape of the radio wave absorber, in addition to specifying the content of the magnetoplumbite-type hexagonal ferrite particles.

The radio wave absorber of the present invention may contain only 1 kind of specific magnetoplumbite-type hexagonal ferrite particles, or may contain 2 or more kinds of specific magnetoplumbite-type hexagonal ferrite particles.

The content of the specific magnetoplumbite-type hexagonal ferrite particles in the radio wave absorber of the present invention is not particularly limited, and is, for example, preferably 10 mass% or more, more preferably 30 mass% or more, and still more preferably 50 mass% or more with respect to the total solid content of the radio wave absorber, from the viewpoint of ensuring good radio wave absorption characteristics.

In addition, for example, from the viewpoint of production applicability and durability, the content of the specific magnetoplumbite-type hexagonal ferrite particles in the radio wave absorber of the present invention is preferably 98 mass% or less, more preferably 95 mass% or less, and even more preferably 92 mass% or less, with respect to the total solid content of the radio wave absorber.

The radio wave absorber of the present invention contains a binder.

In the present invention, the "binder" is a general term for a substance capable of forming a form of a radio wave absorber while maintaining a state in which specific magnetoplumbite-type hexagonal ferrite particles are dispersed.

The binder is not particularly limited, and examples thereof include a resin, a rubber, and a combination of a resin and a rubber.

The resin may be any of a thermoplastic resin and a thermosetting resin.

Specific examples of the thermoplastic resin include: acrylic resin; a polyacetal; a polyamide; polyethylene; polypropylene; polyethylene terephthalate; polybutylene terephthalate; a polycarbonate; polystyrene; polyphenylene sulfide; polyvinyl chloride; ABS (acrylonitrile butadiene styrene) resin obtained by copolymerizing acrylonitrile, butadiene and styrene; AS (acrylonitrile-styrene) resins obtained by copolymerizing acrylonitrile and styrene, and the like.

Specific examples of the thermosetting resin include phenol resin, epoxy resin, melamine resin, urea resin, unsaturated polyester, diallyl phthalate resin, polyurethane resin, and silicone resin.

As the binder contained in the radio wave absorber of the present invention, rubber is preferable.

The rubber is not particularly limited, and for example, from the viewpoint of being able to form a radio wave absorber having good mixing properties with the specific magnetoplumbite-type hexagonal ferrite particles and further excellent durability, weather resistance and impact resistance, it is preferable that: butadiene rubber; isoprene rubber; chloroprene rubber; halogenated butyl rubber; a fluororubber; a urethane rubber; acrylic rubber (ACM) obtained by copolymerizing acrylic esters (e.g., ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate) and other monomers; ethylene-propylene rubbers obtained by coordination polymerization of ethylene and propylene using a ziegler catalyst; butyl rubber (IIR) obtained by copolymerizing isobutylene and isoprene; styrene Butadiene Rubber (SBR) obtained by copolymerizing polybutadiene and styrene; acrylonitrile butadiene rubber (NBR) obtained by copolymerizing acrylonitrile and butadiene; synthetic rubbers such as silicone rubber.

Examples of the combination of the resin and the rubber include thermoplastic elastomers (TPEs).

Specific examples of the thermoplastic elastomer include olefinic thermoplastic elastomer (TPO), styrenic thermoplastic elastomer (TPS), amide thermoplastic elastomer (TPA), and polyester thermoplastic elastomer (TPC).

When the radio wave absorber of the present invention contains rubber as a binder, various additives such as a vulcanizing agent, a vulcanization aid, a softening agent, and a plasticizer may be contained in addition to the rubber.

Examples of the vulcanizing agent include sulfur, an organic sulfur compound, and a metal oxide.

The radio wave absorber of the present invention may contain only 1 kind of binder, or may contain 2 or more kinds of binders.

The content of the binder in the radio wave absorber of the present invention is not particularly limited, and for example, from the viewpoint of dispersibility of the specific magnetoplumbite-type hexagonal ferrite particles and from the viewpoint of production applicability and durability of the radio wave absorber, the content is preferably 2 mass% or more, more preferably 5 mass% or more, and still more preferably 8 mass% or more, relative to the total solid content of the radio wave absorber.

In addition, for example, from the viewpoint of ensuring good radio wave absorption characteristics, the content of the binder in the radio wave absorber of the present invention is preferably 90 mass% or less, more preferably 70 mass% or less, and still more preferably 50 mass% or less, with respect to the total solid content of the radio wave absorber.

The electric wave absorber of the present invention may contain various additives (so-called other additives) as necessary within a range not impairing the effects of the present embodiment, in addition to the specific magnetoplumbite-type hexagonal ferrite particles and the binder.

Examples of the other additives include a dispersant, a dispersing aid, a fungicide, an antistatic agent, and an antioxidant. The other additives may be additives in which 1 component has 2 or more functions.

The specific magnetoplumbite-type hexagonal ferrite particles contained in the radio wave absorber can be confirmed, for example, by the following method.

After the radio wave absorber is finely cut, the radio wave absorber is immersed in a solvent (e.g., acetone) for 1 to 2 days, and then dried. The structure can be confirmed by further finely grinding the dried radio wave absorber and performing powder X-ray diffraction (XRD) measurement. After the section of the radio wave absorber is cut out, the composition can be confirmed by using, for example, an energy dispersive X-ray analyzer.

The method for producing the radio wave absorber of the present invention is not particularly limited.

The radio wave absorber of the present invention can be produced by a known method using specific magnetoplumbite-type hexagonal ferrite particles, a binder and a solvent (if necessary, other components are used).

For example, a radio wave absorber having a planar shape can be produced by applying a radio wave absorber-forming composition containing specific magnetoplumbite-type hexagonal ferrite particles, a binder and a solvent (containing other components as necessary) onto a support and drying the composition.

Further, for example, a radio wave absorber having a three-dimensional shape can be produced by ejecting a radio wave absorber-forming composition containing specific magnetoplumbite-type hexagonal ferrite particles, a binder, and a solvent (containing other components as necessary) onto a support using a nozzle and drying the composition.

The solvent is not particularly limited, and examples thereof include water, an organic solvent, and a mixed solvent of water and an organic solvent.

The organic solvent is not particularly limited, and examples thereof include alcohols such as methanol, ethanol, n-propanol, isopropanol and methoxypropanol, ketones such as acetone, methyl ethyl ketone and cyclohexane, tetrahydrofuran, acetonitrile, ethyl acetate and toluene.

Among them, at least 1 kind selected from the group consisting of methyl ethyl ketone and cyclohexane is preferable as the solvent from the viewpoint of low boiling point and easy drying.

The content ratios of the specific magnetoplumbite-type hexagonal ferrite particles and the binder in the radio wave absorber-forming composition may be adjusted so that the content ratios of the specific magnetoplumbite-type hexagonal ferrite particles and the binder in the finally obtained radio wave absorber become the content ratios of the specific magnetoplumbite-type hexagonal ferrite particles and the binder in the radio wave absorber described above, respectively.

The content of the solvent in the composition for forming a radio wave absorber is not particularly limited, and may be appropriately selected depending on the kind, amount, and the like of the components blended in the composition for forming a radio wave absorber.

In the composition for forming a radio wave absorber, the specific magnetoplumbite-type hexagonal ferrite particles and the binder may be simply mixed.

The method of mixing the specific magnetoplumbite-type hexagonal ferrite particles with the binder is not particularly limited, and examples thereof include a method of mixing by stirring.

The stirring mechanism is not particularly limited, and a general stirring device can be used.

Examples of the stirring device include a paddle stirrer, an impeller stirrer, and the like.

The stirring time is not particularly limited, and may be appropriately set according to the type of the stirring device, the composition of the composition for forming a radio wave absorber, and the like.

The support is not particularly limited, and a known support can be used.

Examples of the material constituting the support include a metal plate (a metal plate such as aluminum, zinc, and copper), a plastic sheet [ polyester (polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and the like), polyethylene (linear low-density polyethylene, high-density polyethylene, and the like), polypropylene, polystyrene, polycarbonate, polyimide, polyamide, polyamideimide, polysulfone, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, polyetherimide, polyether sulfone, polyvinyl acetal, and a sheet such as acrylic resin ], and a plastic sheet in which the above-described metals are laminated or vapor-deposited.

The support can function to hold the form of the formed radio wave absorber. In the case where the form of the formed radio wave absorber itself can be maintained, the radio wave absorber may be removed from the support after the formation of the radio wave absorber by using a release film as the support.

The shape, structure, size, and the like of the support can be appropriately selected according to the purpose.

Examples of the shape of the support include a flat plate shape.

The structure of the support may be a single-layer structure or a laminated structure having 2 or more layers.

The size of the support can be appropriately selected according to the size of the radio wave absorber and the like.

The thickness of the support is not particularly limited, but is usually about 0.01mm to 10mm, and for example, from the viewpoint of handling properties, it is preferably 0.02mm to 3mm, and more preferably 0.05mm to 1 mm.

The method of applying the composition for forming a radio wave absorber on a support is not particularly limited, and examples thereof include a method using a film coater, a knife coater, an applicator, and the like.

The method of drying the composition for forming a radio wave absorber applied or ejected onto the support is not particularly limited, and examples thereof include a method using a heating device such as an oven.

The drying temperature and the drying time are not particularly limited as long as the solvent in the composition for forming a radio wave absorber can be volatilized. For example, it can be dried by heating at 30 to 150 ℃ for 0.01 to 2 hours.

For example, a composition for forming a radio wave absorber containing specific magnetoplumbite-type hexagonal ferrite particles and a binder (containing other components as needed) is mixed by a kneader while being heated, and after obtaining a mixture, the obtained mixture is molded (processed by extrusion molding, injection molding, in-mold molding, or the like) into a planar shape (for example, a sheet shape) or a three-dimensional shape, whereby a radio wave absorber having a desired shape can be produced.