JP7176714B2 - Electromagnetic wave absorbing powder, electromagnetic wave absorbing composition, electromagnetic wave absorber and paint - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act Released on June 18, 2017 in the abstract of the 28th Rare Earth Research Conference

Application of Article 30, Paragraph 2 of the Patent Law Presented at the 28th Rare Earth Research Conference held from June 18 to 22, 2017

Article 30, Paragraph 2 of the Patent Act applies.

Article 30, Paragraph 2 of the Patent Act applies.

Article 30, Paragraph 2 of the Patent Act applies Published on September 26, 2017 in Resources, Materials & EARTH Conference Program/Abstracts

Article 30, Paragraph 2 of the Patent Act applied Presented at Resources, Materials & EARTH 2017 held from September 26th to 28th, 2017

TECHNICAL FIELD The present invention relates to an electromagnetic wave absorbing powder, an electromagnetic wave absorbing composition, an electromagnetic wave absorber and a paint.

Conventionally, electromagnetic wave absorbing powders exhibiting electromagnetic wave absorbing properties are known (see, for example, Patent Document 1).

JP 2012-84577 A

An object of the present invention is to provide a novel electromagnetic wave absorbing powder.
A further object of the present invention is to provide an electromagnetic wave absorbing composition, an electromagnetic wave absorber and a paint using the electromagnetic wave absorbing powder.

As a result of intensive studies, the inventors of the present invention have found that the above object can be achieved by adopting the following configuration.

That is, the present invention provides the following [1] to [12].
[1] An electromagnetic wave absorbing powder containing a rare earth element, a sulfur element and an oxygen element, and having an X-ray diffraction spectrum showing a rare earth sulfide peak.
[2] The electromagnetic wave absorbing powder according to [1] above, wherein the rare earth element is a light rare earth element.
[3] The electromagnetic wave absorbing powder according to [1] or [2] above, wherein the rare earth element is at least one selected from the group consisting of lanthanum, cerium and praseodymium.
[4] The electromagnetic wave absorbing powder according to any one of [1] to [3], which has electromagnetic wave absorbing properties in at least a frequency band of 0.05 to 20 GHz.
[5] The electromagnetic wave absorbing powder according to any one of [1] to [4], wherein the content of the oxygen element is 0.10 to 2.00% by mass.
[6] The electromagnetic wave absorbing powder according to any one of [1] to [5] above, which has an average particle size of 0.1 to 10 μm.
[7] Any of the above [1] to [6], wherein the imaginary part of the complex permittivity has a relative dielectric constant of 3.0 or more and a dielectric loss tangent of 0.4 or more in at least a frequency band of 0.05 to 20 GHz. The electromagnetic wave absorbing powder according to claim 1.
[8] An electromagnetic wave absorbing composition containing the electromagnetic wave absorbing powder according to any one of [1] to [7] above and a binder resin.
[9] The electromagnetic wave absorbing composition according to [8] above, which further contains iron powder.
[10] The electromagnetic wave absorbing composition according to [9], wherein the content of the iron powder is 10 to 80 parts by mass with respect to 100 parts by mass of the electromagnetic wave absorbing powder.
[11] An electromagnetic wave absorber formed using the electromagnetic wave absorbing composition according to any one of [8] to [10] above.
[12] A paint containing the electromagnetic wave absorbing powder according to any one of [1] to [7] above.

According to the present invention, a novel electromagnetic wave absorbing powder can be provided.
Furthermore, according to the present invention, it is possible to provide an electromagnetic wave absorbing composition, an electromagnetic wave absorber and a paint using the electromagnetic wave absorbing powder.

4 is the XRD spectrum of Test Example I. FIG. 4 is a graph showing the amount of electromagnetic wave absorption (reflection) of Test Example I. FIG. 4 is a graph showing the electromagnetic wave absorption (transmission) of Test Example I. FIG. It is the XRD spectrum of Test Example II. It is a graph which shows the electromagnetic wave absorption amount (reflection) of Test Example II. It is a graph which shows the electromagnetic wave absorption amount (permeation|transmission) of Experiment II. 1 is a periodic table three-dimensionally showing lanthanoids contained in rare earth elements.

[Electromagnetic wave absorbing powder]
The electromagnetic wave absorbing powder of the present invention (hereinafter also simply referred to as "powder of the present invention") contains a rare earth element, a sulfur element and an oxygen element, and an X-ray diffraction (XRD) spectrum shows a rare earth sulfide peak. (See Figures 1 and 4).
Such a powder of the present invention has electromagnetic wave absorption properties at least in the frequency band of 0.05 to 20 GHz, as shown in FIGS. 2 to 3 and 5 to 6, for example.

FIG. 7 shows the periodic table. Among the elements belonging to Group 3 of the periodic table, the rare earth elements are scandium (Sc) and yttrium (Y), plus 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu). It is a general term for 17 elements.
Rare earth elements have a closed-shell structure in which the outermost electron configuration of +3 valence ions is s ² p ⁶ , and their properties are very similar to each other. Lanthanoids are treated as a group on the periodic table, as shown in FIG. 7, because each element has similar properties.

The rare earth element contained in the powder of the present invention is preferably a light rare earth element. Light rare earth elements are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), and europium (Eu). Among these, at least one selected from the group consisting of lanthanum (La), cerium (Ce) and praseodymium (Pr) is preferred, and at least one selected from the group consisting of lanthanum (La) and cerium (Ce) is more preferred. preferable.

In the powder of the present invention, the rare earth sulfide phase shown in the XRD spectrum is preferably β phase, γ phase, or a mixed phase of β phase and γ phase.

The fact that the powder of the present invention contains a rare earth element and a sulfur element can be confirmed by the fact that the XRD spectrum shows a rare earth sulfide peak.
The fact that the powder of the present invention contains elemental oxygen can be confirmed by the fact that the XRD spectrum shows a rare earth oxysulfide peak.

The measurement conditions for the X-ray diffraction (XRD) spectrum are as follows.
・X-ray: CuKα
・Tube voltage: 40 kV
・Tube current: 20mA

The content of oxygen element in the powder of the present invention is preferably 0.10 to 2.00% by mass, more preferably 0.15 to 1.80% by mass.
The oxygen element content is measured using an oxygen/nitrogen/hydrogen analyzer EMGA-930 manufactured by HORIBA.
It can also be confirmed by such measurements that the powder of the present invention contains elemental oxygen.

The average particle size of the powder of the present invention is preferably 0.1-10 μm, more preferably 0.2-10 μm.
The average particle size is measured using a laser diffraction particle size distribution analyzer SALD-2300 manufactured by SHIMADZU.

In the powder of the present invention, individual particles constituting the powder of the present invention may be coated with a fluorine-based coating.
Fluorine coatings include, for example, polyvinyl fluoride (PVF) coatings, polytetrafluoroethylene (PTFE) coatings, ethylene-tetrafluoroethylene copolymer (ETFE) coatings, and the like.
The method of applying fluorine-based coating to individual particles is not particularly limited, and conventionally known methods can be employed as appropriate.

The powder of the present invention preferably has a relative dielectric constant of the imaginary part of the complex dielectric constant of 3.0 or more and a dielectric loss tangent of 0.4 or more at least in the frequency band of 0.05 to 20 GHz.

[Method for producing electromagnetic wave absorbing powder]
The method for producing the electromagnetic wave-absorbing powder of the present invention (hereinafter also referred to as "the production method of the present invention" for convenience) includes, for example, the following methods 1 to 3. However, the manufacturing method of the present invention is not limited to the following method.

<Method 1: Pulse CVI method>
A pulse CVI (Chemical Vapor Infiltration) method will be described schematically. A reaction gas (for example, argon-hydrogen gas) containing a small amount of oxygen as an impurity is introduced into the reaction tube while the starting material powder is placed and heated. By applying a voltage between the two electrodes installed in the reaction tube, oxygen is ionized and doped into the powder of the starting raw material. When γ-Ce ₂ S ₃ is used as a starting material, at least part of it undergoes phase transformation to β-Ce ₂ S ₃ .
Decompression (vacuum drawing) in the reaction tube, gas introduction into the reaction tube, and holding after the gas introduction are set as one pulse, and by repeating this, new gas with good reactivity is introduced as needed. By changing the number of pulses, the phase ratio of the γ phase and β phase of the product (powder) can be changed.
The heating temperature is, for example, 1073-1473K.
The voltage applied between the two electrodes is, for example, 2-8 kV.
The pressure reduction time per pulse is, for example, 1 to 10 seconds.
The introduction time of the reactive gas for each pulse is, for example, 1 to 10 seconds.
The retention time for each pulse is, for example, 1 to 10 seconds.

<Method 2: CS ₂ gas sulfidation method>
_The CS2 gas _sulfiding method is a method of using a rare earth oxide ₍ eg, CeO2, La2O3, _{PrO2 ,} etc.) as a starting material and _sulfiding it with CS2. This produces a rare earth sulfide (eg, β-phase) powder containing oxygen.
The sulfurization temperature is, for example, 923-1373K.
The sulfurization time is, for example, 3.6-28.8ks.

<Method 3: Method using a rotary furnace>
The starting material is oxidized by heating it in an Ar gas containing a trace amount of oxygen as an impurity using a rotary furnace. For example, γ-Ce ₂ S ₃ is used as a starting material. In this case, the phase ratio of the γ phase and β phase of the product (powder) can be changed by changing the heating conditions for phase transformation to β-Ce ₂ S ₃ by oxidation.

Regarding the production method of the present invention, the following additional remarks are made regarding Ce ₂ S ₃ , La ₂ S ₃ and Pr ₂ S ₃ .

Ce ₂ S ₃ undergoes phase transformation from orthorhombic α-Ce ₂ S ₃ to tetragonal β-Ce ₂ S ₃ from room temperature to high temperature, and further to Th ₃ P ₄ type cubic γ-Ce ₂ . It undergoes a phase transformation to _S3 . These phase transformations are reversible transformations. The phase transformation from β-Ce ₂ S ₃ to γ-Ce ₂ S ₃ has a transformation temperature of 1573 ± 100 K, but if an element such as Ti or Ca that deprives oxygen is added, the transformation temperature rises, and on the contrary, it provides oxygen. and the transformation temperature decreases. This suggests the possibility of phase transformation to β-Ce ₂ S ₃ when γ-Ce ₂ S ₃ is maintained at a temperature at which β-Ce ₂ S ₃ is stable and oxygen is supplied.

La ₂ S ₃ undergoes a phase transformation from orthorhombic α-La ₂ S ₃ to tetragonal β-La ₂ S ₃ at 923±50 K, and further transforms to cubic Th ₃ P ₄ type γ- at 1573±100 K. It undergoes a phase transformation to La ₂ S ₃ . The phase transformation temperature from β-La ₂ S ₃ to γ-La ₂ S ₃ shifts to the high temperature side depending on the oxygen concentration.

Pr ₂ S ₃ undergoes phase transformation from orthorhombic α-Pr ₂ S ₃ to tetragonal β-Pr ₂ S ₃ at 1198±75 K, and further transforms to cubic Th ₃ P ₄ type γ- at 1573±200 K. It undergoes a phase transformation to Pr ₂ S ₃ . The phase transformation temperature from β-Pr ₂ S ₃ to γ-Pr ₂ S ₃ shifts to the high temperature side depending on the oxygen concentration.

[Electromagnetic wave absorbing composition]
The electromagnetic wave absorbing composition of the present invention (hereinafter also simply referred to as "the composition of the present invention") contains the powder of the present invention described above and a binder resin.

The binder resin is not particularly limited, and examples thereof include PMMA (polymethyl methacrylate resin) and epoxy resin. Epoxy resin before curing is also included in the binder resin.
The content of the binder resin in the composition of the present invention is preferably 20 to 150 parts by mass, more preferably 30 to 120 parts by mass, per 100 parts by mass of the powder of the present invention.

The composition of the present invention preferably further contains iron powder for the reason that it has better electromagnetic wave absorption properties. The content of the iron powder in the composition of the present invention is preferably 10 to 80 parts by mass, more preferably 20 to 60 parts by mass, per 100 parts by mass of the powder of the present invention.

[Electromagnetic wave absorber]
The electromagnetic wave absorber of the present invention is an electromagnetic wave absorber formed using the composition of the present invention described above.
The method for producing the electromagnetic wave absorber of the present invention is not particularly limited, and is appropriately selected according to the binder resin and the like contained in the composition of the present invention.
When PMMA is used as the binder resin, for example, the electromagnetic wave absorber of the present invention can be obtained by mixing the composition of the present invention and compressing the resulting mixture using a hot press.
When an epoxy resin is used as the binder resin, there is a method of obtaining the electromagnetic wave absorber of the present invention by mixing the composition of the present invention containing the powder and the epoxy resin before curing, and heating and curing the resulting mixture. mentioned.

[paint]
The paint of the present invention contains the powder of the present invention described above. As a result, the paint (and its coating film) of the present invention exhibits electromagnetic wave absorption properties.
The paint of the present invention may further contain a binder resin. The binder resin is not particularly limited, and the same binder resin as that contained in the composition of the present invention can be used.
The paint of the present invention is preferably a water-soluble or oil-based paint. At this time, it is preferable that the surfaces of individual particles constituting the powder of the present invention contained in the paint of the present invention are amphipathic. The method for making the surface of the particles amphipathic is not particularly limited, and conventionally known methods can be appropriately employed.

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these.

[Test Example I: Pulse CVI Method (Ce)]
<Preparation of electromagnetic wave absorbing powder>
Using a commercially available γ-Ce ₂ S ₃ powder (average particle size: 7 μm) as a starting material, an electromagnetic wave absorbing powder (hereinafter also simply referred to as “powder”) was produced by the pulse CVI method.
More specifically, a stainless steel cathode and an anode are provided at both ends of the reaction tube, a porous alumina cage containing γ-Ce ₂ S ₃ powder is placed in front of the cathode, and a voltage ( 4.5 kV) was applied while the reaction tube was heated to 1473 K. Then, pressure reduction in the reaction tube (10 seconds), introduction of Ar-7% H ₂ gas containing O ₂ as an impurity (2 seconds), and subsequent holding (10 seconds) were defined as one pulse. A powder was obtained by performing the number of times shown in 1 (number of pulses).

<XRD spectrum>
An XRD spectrum was measured for the obtained powder. The measurement results are shown in FIG. The phases shown in the XRD spectra are also listed in Table 1 below.

<Oxygen content and average particle size>
The content of oxygen element (oxygen content) and the average particle size of the obtained powder were measured. The measurement results are shown in Table 1 below. When not measured, "-" is indicated in Table 1 below (the same shall apply hereinafter).

<Electromagnetic wave absorption characteristics>
First, using the obtained powder and binder resin, a doughnut-shaped sample (electromagnetic wave absorber) having an inner diameter of 3 mm and an outer diameter of 7 mm was produced.
PMMA (polymethyl methacrylate resin) or epoxy resin was used as the binder resin.
As PMMA, Poly (methyl methacrylate) Model No. 4457461-500G (average particle size: 7 μm) manufactured by ALDRICH was used (hereinafter the same).
As the epoxy resin, TAAB EPON 812 kit (TAAB EPON 812, DDSA, MNA, DMP-30) was used (same below).

When PMMA was used, PMMA and powder were first mixed at a mass ratio of PMMA:powder=3:7. Then, the resulting mixture was molded by hot pressing (temperature: 443 K, pressure: 3 MPa, holding time: 600 s) using a hot press. A sample was produced by processing the obtained molded article. In some cases, iron powder was also mixed. In that case, a sample was prepared in the same manner as described above, except that the mass ratio was PMMA:powder:iron powder=3:5:2.

When an epoxy resin was used, powder was first mixed in the epoxy resin before curing at a mass ratio of epoxy resin:powder=5:5. The resulting mixture was cured by heating in an electric furnace (temperature: 338K, holding time: 43.2ks). A sample was prepared by processing the obtained cured product.

Using the prepared samples, the electromagnetic wave absorption (unit: dB) in the frequency band of 0.05 to 20 GHz was measured by the coaxial tube method. The results are shown in FIGS. 2-3.
In the coaxial tube method, when a high frequency signal is applied to the center conductor of the coaxial tube, an electric field and a magnetic field are generated in the internal space. The amount of reflection and transmission is measured by changes in the electric and magnetic fields when the sample is placed in the center of the coaxial tube. The difference between the amount of incidence and the amount of reflection represents the amount of radio wave absorption (reflection), and the difference between the amount of reflection and the amount of transmission represents the amount of radio wave absorption (transmission).

Example 18 is Example 1 with iron powder added. Thus, the powder of Example 18 is the same as the powder of Example 1.

1 to 3 and the results shown in Table 1 above, the powder of Test Example I contains rare earth elements, sulfur elements and oxygen elements, the X-ray diffraction spectrum shows a rare earth sulfide peak, and at least 0 It was found to have electromagnetic wave absorption properties in the frequency band of .05 to 20 GHz.
As the number of pulses increased, the oxygen content tended to increase.

[Test Example II: CS ₂ gas sulfidation method (La)]
<Preparation of electromagnetic wave absorbing powder>
Using commercially available La ₂ O ₃ powder (average particle size: 1 μm) as a starting material, an electromagnetic wave absorbing powder (powder) was produced by the CS ₂ gas sulfidation method.
More specifically, the La ₂ O ₃ powder was previously heated in the atmosphere at 673 K and 3.6 ks in order to remove water of crystallization. After that, the La ₂ O ₃ powder was put on a quartz boat and inserted into an electric furnace, and while introducing the CS ₂ gas vaporized from the CS ₂ solution using an Ar carrier gas, the conditions shown in Table 2 below ( A powder was obtained by sulfidation at a sulfidation temperature and sulfidation time).

<XRD spectrum>
An XRD spectrum was measured for the obtained powder. The measurement results are shown in FIG. The phases shown in the XRD spectra are also listed in Table 2 below.

<Oxygen content and average particle size>
The content of oxygen element (oxygen content) and the average particle size of the obtained powder were measured. The measurement results are shown in Table 2 below.

<Electromagnetic wave absorption characteristics>
Using the obtained powder, a sample was prepared in the same manner as in Test Example I, and the electromagnetic wave absorption in the frequency band of 0.05 to 20 GHz was measured. The results are shown in FIGS. 5-6.

From the results shown in FIGS. 4 to 6 and Table 2 above, the powder of Test Example II contains rare earth elements, sulfur elements and oxygen elements, the X-ray diffraction spectrum shows a rare earth sulfide peak, and at least 0 It was found to have electromagnetic wave absorption properties in the frequency band of .05 to 20 GHz.
As the sulfurization temperature became lower and as the sulfurization time became shorter, the oxygen content tended to increase.

[Test Example III (Paint)]
A paint was prepared using the electromagnetic wave absorbing powder (powder) produced in Test Examples I and II.
Specifically, the paint was obtained by mixing the powder with the epoxy resin before curing at a mass ratio of powder:epoxy resin=1:4.
The resulting paint was applied onto a SUS430 plate using a spatula and heated in an electric furnace (temperature: 338K) to form a coating film.

Claims (11)

containing rare earth elements, sulfur elements and oxygen elements,
The X-ray diffraction spectrum shows rare earth sulfide peaks,
The electromagnetic wave absorbing powder, wherein the oxygen element content is 0.10% by mass or more and 0.61% by mass or less. 2. The electromagnetic wave absorbing powder according to claim 1, wherein said rare earth element is a light rare earth element. 3. The electromagnetic wave absorbing powder according to claim 1, wherein said rare earth element is at least one selected from the group consisting of lanthanum, cerium and praseodymium. The electromagnetic wave absorbing powder according to any one of claims 1 to 3, which has electromagnetic wave absorbing properties in at least a frequency band of 0.05 to 20 GHz. The electromagnetic wave absorbing powder according to any one of claims 1 to 4 , having an average particle size of 0.1 to 10 µm. The dielectric constant of the imaginary part of the complex dielectric constant is 3.0 or more and the dielectric loss tangent is 0.4 or more at least in the frequency band of 0.05 to 20 GHz, according to any one of claims 1 to 5 . Electromagnetic wave absorption powder. An electromagnetic wave absorbing composition containing the electromagnetic wave absorbing powder according to any one of claims 1 to 6 and a binder resin. 8. The electromagnetic wave absorbing composition according to claim 7 , further comprising iron powder. The electromagnetic wave absorbing composition according to claim 8 , wherein the content of said iron powder is 10 to 80 parts by mass with respect to 100 parts by mass of said electromagnetic wave absorbing powder. An electromagnetic wave absorber formed using the electromagnetic wave absorbing composition according to any one of claims 7 to 9 . A paint containing the electromagnetic wave absorbing powder according to any one of claims 1 to 6 .

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