WO2021029246A1

WO2021029246A1 - Radio wave absorbing composition and radio wave absorbent

Info

Publication number: WO2021029246A1
Application number: PCT/JP2020/029623
Authority: WO
Inventors: 中井　義博; 橋本　浩一
Original assignee: 富士フイルム株式会社
Priority date: 2019-08-09
Filing date: 2020-08-03
Publication date: 2021-02-18
Also published as: JPWO2021029246A1; JP7427005B2

Abstract

This radio wave absorbing composition includes a magnetic powder and a binder. This radio wave absorbent includes a magnetic powder and a binder. The magnetic powder is a substituted hexagonal ferrite powder, the surface of which is treated with a surface treatment agent, and the surface treatment agent is a silicon-based compound. In addition, the binder is at least one resin selected from the group consisting of polyester and polycarbonate.

Description

Radio wave absorbing composition and radio wave absorber

The present invention relates to a radio wave absorbing composition and a radio wave absorber.

As a radio wave absorber, a material containing magnetic powder is known as a radio wave absorbing material. Further, examples of the radio wave absorber containing the magnetic powder include a radio wave absorber in which the magnetic powder and the binder are mixed (see Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 4-80274 Japanese Unexamined Patent Publication No. 2012-9977

In recent years, as an electronic device that uses radio waves, radar for recognizing an object by transmitting and receiving radio waves has attracted attention. For example, an in-vehicle radar transmits radio waves and recognizes the existence of the object, the distance to the object, etc. by receiving the radio waves reflected by the object (pedestrian, vehicle, etc.). be able to. In order to prevent collision with the object, the automatic driving control system of the car automatically applies the brakes to stop the car or to stop the car based on the result of the radar recognizing the object, if necessary. The speed can be controlled automatically to keep the distance.

In order to improve the reliability of the system that performs various controls based on the results recognized by the radar as described above, it is desirable to improve the performance of the radar. Therefore, in recent years, it has begun to be studied to install a radio wave absorber on the front side (the incident side of the radio wave incident from the outside) of the radio wave transmission / reception unit of the radar to improve the recognition accuracy. In order to improve the recognition accuracy, the radio wave absorber is required to have excellent radio wave absorption performance.

Furthermore, the radio wave absorber with excellent vibration resistance and chemical resistance is less likely to get tired even if it receives vibration during use, and is less likely to deteriorate even if chemicals adhere to it, so it can improve radar recognition accuracy for a long period of time. You can continue to contribute. Therefore, it is desirable that the radio wave absorber has excellent vibration fatigue resistance and chemical resistance.

In view of the above, one aspect of the present invention is to provide a radio wave absorber having excellent radio wave absorption performance, vibration fatigue resistance and chemical resistance.

As a result of diligent studies to achieve the above object, the present inventors have made a combination of a magnetic powder and a binder, that is, a substituted hexagonal ferrite powder surface-treated with a silicon-based compound, and polyester and polycarbonate. It has been newly found that a radio wave absorber having excellent radio wave absorption performance, vibration fatigue resistance and chemical resistance can be obtained by using in combination with one or more kinds of resins selected from the group consisting of It was.

That is, one aspect of the present invention is
A radio wave absorbing composition containing a magnetic powder and a binder.
The magnetic powder is a substituted hexagonal ferrite powder surface-treated with a surface treatment agent.
The radio wave absorbing composition, wherein the surface treatment agent is a silicon-based compound, and the binder is one or more resins selected from the group consisting of polyester and polycarbonate.
Regarding.

Moreover, one aspect of the present invention is
A radio wave absorber containing magnetic powder and a binder,
The magnetic powder is a substituted hexagonal ferrite powder surface-treated with a surface treatment agent.
The surface treatment agent is a silicon-based compound, and the binder is a radio wave absorber, which is one or more resins selected from the group consisting of polyester and polycarbonate.
Regarding.

In one form, the radio wave absorber can be a molded product obtained by molding the radio wave absorbing composition.

In one form, the substituted hexagonal ferrite can have a composition represented by the following general formula 1.
General formula 1: AFe _(12-x) Al _x O ₁₉
In the general formula 1, A represents one or more kinds of atoms selected from the group consisting of Sr, Ba, Ca and Pb, and x satisfies 1.50 or more ≦ x ≦ 8.00.

In one form, the substituted hexagonal ferrite can be a substituted hexagonal strontium ferrite.

In one form, the surface treatment agent can be a silicon-based compound represented by the following general formula 2.
General formula 2: (XL) _m- Si-Z _4-m
In general formula 2,
X is a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, an alicyclic group, a heterocyclic group, a hydroxy group, an acrylamide group, a sulfanyl group, an isocyanate group, a thiocyanate group, a ureido group, a cyano group, an acid anhydride group and an azide. Represents a group, carboxy group, acyl group, thiocarbamoyl group, phosphate group, phosphanyl group, sulfonic acid group or sulfamoyl group.
L is selected from the group consisting of a single bond, an alkylene group, an alkenylene group, an alkynylene group, an arylene group, -O-, -S-, -NR ^a- , an ester bond, a thioester bond, an amide bond, a thioamide bond and a sulfonyl group. Represents one type of divalent group or bond, or a combination of two or more of these divalent groups or bonds.
^Ra represents a hydrogen atom or a substituent and represents
Z represents a hydroxy group, an alkoxy group or an alkyl group.
m is an integer in the range of 1 to 3.

In one form, in General Formula 2, m is 1 and X can represent an alkenyl group or a heterocyclic group, or m is 2 or 3, and a plurality of Xs are contained in General Formula 2. However, each can independently represent an alkenyl group or a heterocyclic group.

In one form, in General Formula 2, m is 1 and X represents an acyl group, an acrylamide group or a heterocyclic group, or m is 2 or 3, and a plurality of Xs are contained in General Formula 2. However, they can independently represent an acyl group, an acrylamide group, or a heterocyclic group. The acyl group can be a (meth) acryloyl group and the heterocyclic group can be an epoxy group.

In one form, in General Formula 2, X can represent an epoxy group.

In one form, L can contain an alkylene group having 4 to 12 carbon atoms in the general formula 2.

In one form, the resin is selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polytrimethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polylactic acid, polybutylene succinate, polyarylate, polycarbonate and polyester elastomer. It can be one or more kinds of resins.

In one form, the resin may be one or more resins selected from the group consisting of polyethylene naphthalate, polytrimethylene terephthalate, polybutylene naphthalate, polylactic acid, polybutylene succinate, polyarylate and polyester elastomer. it can.

According to one aspect of the present invention, it is possible to provide a radio wave absorber having excellent radio wave absorbing performance, vibration fatigue resistance and chemical resistance, and a radio wave absorbing composition that can be used for producing the radio wave absorber. ..

[Radio-absorbing composition, radio wave absorber]
One aspect of the present invention relates to a radio wave absorbing composition containing a magnetic powder and a binder. In the radio wave absorbing composition, the magnetic powder is a powder of a substituted hexagonal ferrite surface-treated with a surface treatment agent, the surface treatment agent is a silicon-based compound, and the binder is One or more resins selected from the group consisting of polyester and polycarbonate.

Further, one aspect of the present invention relates to a radio wave absorber containing a magnetic powder and a binder. In the radio wave absorber, the magnetic powder is a powder of a substituted hexagonal ferrite surface-treated with a surface treatment agent, the surface treatment agent is a silicon-based compound, and the binder is polyester and the binder. One or more resins selected from the group consisting of polycarbonate.

In the present invention and the present specification, "radio wave" means an electromagnetic wave having a frequency of 3 terahertz (THz) or less. The radio wave absorber and the composition used in the production of the radio wave absorber have radio wave absorbing properties. The radio wave absorption can be evaluated by, for example, the transmission attenuation and / or the reflection attenuation, and the higher the transmission attenuation value, the higher the reflection attenuation value, or the transmission attenuation value and the reflection attenuation. It can be said that the higher the amount value, the better the radio wave absorption.

In the present invention and the present specification, "powder" means an aggregate of a plurality of particles. The “aggregation” is not limited to the mode in which the particles constituting the set are in direct contact with each other, and also includes a mode in which a binder or the like is interposed between the particles.

Hereinafter, the radio wave absorbing composition and the radio wave absorber will be described in more detail.

<Magnetic powder>
The radio wave absorbing composition and the radio wave absorber include, as magnetic powder, a powder of a substituted hexagonal ferrite surface-treated with a surface treatment agent. The substituted hexagonal ferrite powder surface-treated with the surface treatment agent can also be said to be the substituted hexagonal ferrite powder coated with the surface treatment agent. In the substituted hexagonal ferrite powder surface-treated with a surface treatment agent, at least a part of the surface of at least a part of the particles constituting the powder is coated with the surface treatment agent. For example, it can be confirmed that the radio wave absorber contains the magnetic powder surface-treated with the surface treatment agent by analyzing the section sample cut out from the radio wave absorber by a known method. Alternatively, the magnetic powder is collected from the radio wave absorber or the radio wave absorbing composition by a known method, and the collected magnetic powder is analyzed by a known method such as mass spectrometry or gas chromatography for confirmation. Can be done.

(Substitution type hexagonal ferrite powder)
The magnetic powder is a substituted hexagonal ferrite powder surface-treated with a surface treatment agent. In the present invention and the present specification, the "hexagonal ferrite powder" refers to a magnetic powder in which a hexagonal ferrite type crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to a structure to which the highest intensity diffraction peak belongs in the X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, when the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs to the hexagonal ferrite type crystal structure, it is determined that the hexagonal ferrite type crystal structure is detected as the main phase. It shall be. When only a single structure is detected by X-ray diffraction analysis, this detected structure is used as the main phase. The hexagonal ferrite type crystal structure contains at least iron atoms, divalent metal atoms and oxygen atoms as constituent atoms. In the unsubstituted hexagonal ferrite, the only atoms constituting the crystal structure of the hexagonal ferrite are iron atom, divalent metal atom and oxygen atom. On the other hand, the substituted hexagonal ferrite contains one or more other atoms together with an iron atom, a divalent metal atom and an oxygen atom as atoms constituting the crystal structure of the hexagonal ferrite. This one or more other atoms are usually atoms that replace a part of iron in the crystal structure of hexagonal ferrite. The divalent metal atom is a metal atom that can be a divalent cation as an ion, and examples thereof include an alkaline earth metal atom such as a strontium atom, a barium atom, and a calcium atom, and a lead atom. In the present invention and the present specification, the "powder of hexagonal strontium ferrite" means that the main divalent metal atom contained in the crystal structure of hexagonal ferrite is a strontium atom. The main divalent metal atom refers to the divalent metal atom that occupies the largest amount on an atomic% basis among the divalent metal atoms contained in the crystal structure of hexagonal ferrite. However, rare earth atoms are not included in the above divalent metal atoms. The "rare earth atom" in the present invention and the present specification is selected from the group consisting of a scandium atom (Sc), a yttrium atom (Y), and a lanthanoid atom. The lanthanoid atoms are lanthanum atom (La), cerium atom (Ce), placeodium atom (Pr), neodymium atom (Nd), promethium atom (Pm), samarium atom (Sm), uropyum atom (Eu), gadolinium atom (Gd) ), Terbium atom (Tb), dysprosium atom (Dy), formium atom (Ho), elbium atom (Er), thulium atom (Tm), ytterbium atom (Yb), and lutetium atom (Lu). To.

Substitution type hexagonal ferrite contains one or more other atoms as well as iron atom, divalent metal atom and oxygen atom as atoms constituting the crystal structure of hexagonal ferrite. Examples of such atoms include one or more trivalent metal atoms selected from the group consisting of Al, Ga and In, and combinations of divalent and tetravalent metal atoms such as Mn and Ti, Co and Ti, Zn and Ti. be able to. The substituted hexagonal ferrite can preferably be a substituted hexagonal strontium ferrite.

In one form, the magnetic powder can be a magnetoplumbite-type (generally referred to as "M-type") substituted hexagonal ferrite powder surface-treated with a surface treatment agent. The magnetoplumbite-type hexagonal ferrite has a composition represented by the composition formula: AFe ₁₂ O ₁₉ when it does not contain an atom that replaces iron. Here, A can represent at least one atom selected from the group consisting of Sr, Ba, Ca and Pb, and includes an embodiment in which two or more of these atoms are contained in an arbitrary ratio.

As a preferable hexagonal ferrite from the viewpoint of radio wave absorption performance, a substituted magnetoplumbite-type hexagonal ferrite in which a part of iron atoms of the magnetoplumbite-type hexagonal ferrite is replaced with an aluminum atom can be mentioned. As one aspect of such hexagonal ferrite, a substituted hexagonal ferrite having a composition represented by the following general formula 1 can be mentioned.

General formula 1: AFe _(12-x) Al _x O ₁₉

In the general formula 1, A represents one or more kinds of atoms (hereinafter, also referred to as “A atom”) selected from the group consisting of Sr, Ba, Ca and Pb, and may be only one kind. Two or more kinds may be contained in an arbitrary ratio, and it is preferable that only one kind is contained from the viewpoint of improving the uniformity of the composition between the particles constituting the powder.
From the viewpoint of radio wave absorption performance in the high frequency band, A in the formula 1 is preferably one or more atoms selected from the group consisting of Sr, Ba and Ca, and more preferably Sr.

In Equation 1, x satisfies 1.50 ≦ x ≦ 8.00. From the viewpoint of radio wave absorption performance in the high frequency band, x is 1.50 or more, more preferably 1.50 or more, further preferably 2.00 or more, and more than 2.00. Is more preferable. Further, from the viewpoint of magnetic characteristics, x is 8.00 or less, preferably less than 8.00, more preferably 6.00 or less, and more preferably less than 6.00.

Specific examples of the magnetoplumbite-type substituted hexagonal ferrite represented by the formula 1 include SrFe _(9.58) Al _(2.42) O ₁₉ , SrFe _(9.37) Al _(2.63) O. ₁₉ , SrFe _(9.27) Al _(2.73) O ₁₉ , SrFe _(9.85) Al _(2.15) O ₁₉ , SrFe _(10.00) Al _(2.00) O ₁₉ , SrFe _{(9) .74)} Al _(2.26) O ₁₉ , SrFe _(10.44) Al _(1.56) O ₁₉ , SrFe _(9.79) Al _(2.21) O ₁₉ , SrFe _(9.33) Al _{( 2.67)} O ₁₉ , SrFe _(7.88) Al _(4.12) O ₁₉ , SrFe _(7.04) Al _(4.96) O ₁₉ , SrFe _(7.37) Al _(4.63) O ₁₉ , SrFe _(6.25) Al _(5.75) O ₁₉ , SrFe _(7.71) Al _(4.29) O ₁₉ , Sr _(0.80) Ba _(0.10) Ca _(0.10) Fe _(9.83) Al _(2.17) O ₁₉ , BaFe _(9.50) Al _(2.50) O ₁₉ , CaFe _(10.00) Al _(2.00) O ₁₉ , PbFe _{(9.00) )} Al _(3.00) O _{19 and the} like. Further, as a specific example, a substituted hexagonal strontium ferrite having the composition shown in Table 1 described later can also be mentioned. The composition of hexagonal ferrite can be confirmed by high frequency inductively coupled plasma emission spectroscopy. Specific examples of the confirmation method include the methods described in Examples described later. Alternatively, after exposing the cross section by cutting the radio wave absorber or the like, the composition of the magnetic powder contained in the radio wave absorber can be confirmed by performing, for example, energy dispersive X-ray analysis on the exposed cross section. You can also.

In one form, the substituted hexagonal ferrite powder can have a single phase crystal phase and can include a plurality of crystal phases, preferably the crystal phase is a single phase, and the crystal phase is It is more preferable that the powder is a single-phase magnetoplumbite-type substituted hexagonal ferrite powder.
The case where "the crystal phase is a single phase" means that only one type of diffraction pattern showing an arbitrary crystal structure is observed in the X-ray diffraction analysis. The X-ray diffraction analysis can be performed, for example, by the method described in Examples described later. When a plurality of crystal phases are included, two or more types of diffraction patterns showing an arbitrary crystal structure are observed in the X-ray diffraction analysis. For the attribution of the diffraction pattern, for example, a database of the International Center for Diffraction Data (ICDD) can be referred to. For example, for the diffraction pattern of a magnetoplumbite-type hexagonal ferrite containing Sr, refer to "00-033-1340" of the International Center for Diffraction Data (ICDD). However, if a part of the iron atom is substituted with a substituted atom such as an aluminum atom, the peak position shifts from the peak position when the substituted atom is not included.

(Method for producing powder of substituted hexagonal ferrite)
Examples of the method for producing the powder of the substituted hexagonal ferrite include a solid phase method and a liquid phase method. The solid-phase method is a method for producing hexagonal ferrite powder by calcining a mixture obtained by mixing a plurality of solid raw materials in a dry manner. On the other hand, the liquid phase method includes a step of using a solution. Hereinafter, one form of a method for producing a powder of substituted hexagonal ferrite by the liquid phase method will be described. However, the production method described below is an example, and the production method of the magnetic powder contained in the radio wave absorbing composition and the radio wave absorber is not limited to the following examples.

One aspect of the liquid phase method is
Step 1 of obtaining a precipitate from a solution containing an iron atom, at least one atom selected from the group consisting of Sr, Ba, Ca and Pb, and one or more substitution atoms that replace the iron atom.
Step 2 to obtain a calcined body by calcining the precipitate obtained in step 1 and
Can be included. Hereinafter, each step will be described in detail.

Process 1
In step 1, a precursor of hexagonal ferrite can be obtained as a precipitate. For example, in order to obtain a hexagonal ferrite powder containing an aluminum atom as a substitution atom that replaces a part of an iron atom, an iron atom, an A atom and an aluminum atom can be mixed in a solution. In this case, it is presumed that the precipitate obtained in step 1 is iron hydroxide, aluminum hydroxide, a composite hydroxide of an iron atom, an aluminum atom, and an A atom, and the like.

The solution for obtaining the precipitate in step 1 is preferably a solution containing at least water, and more preferably an aqueous solution. For example, a precipitate can be produced by mixing an aqueous solution containing various atoms (hereinafter, also referred to as “raw material aqueous solution”) and an alkaline aqueous solution. In addition, step 1 can include a step of solid-liquid separation of the precipitate.

The raw material aqueous solution can be, for example, an aqueous solution containing an Fe salt, an Al salt and a salt of an A atom. These salts can be, for example, water-soluble inorganic acid salts such as nitrates, sulfates and chlorides.
Specific examples of the Fe salts, iron (III) chloride hexahydrate [FeCl ₃ · 6H ₂ O], iron (III) nitrate nonahydrate _{_{[Fe (NO 3) 3 · 9H}} 2 O ] and the like can be mentioned Be done.
Specific examples of the Al salt, aluminum hexahydrate [AlCl ₃ · 6H ₂ O] chloride, aluminum nitrate nonahydrate _{_{[Al (NO 3) 3 · 9H}} 2 O ] and the like.
The salt of the A atom can be one or more selected from the group consisting of Sr salt, Ba salt, Ca salt and Pb salt.
Specific examples of the Sr salt, strontium chloride hexahydrate [SrCl _₂ · 6H ₂ O], strontium nitrate [Sr _(NO _{3) 2],} strontium acetate hemihydrate _[Sr (CH 3 _{COO) 2} -0.5H ₂ O] and the like.
Specific examples of the Ba salt, barium chloride dihydrate [BaCl _₂ · 2H ₂ O], barium nitrate [Ba _(NO _{3) 2],} barium acetate _[(CH 3 _COO) 2 Ba] and the like.
Specific examples of the Ca salt is calcium chloride dihydrate [CaCl _₂ · 2H ₂ O], calcium nitrate tetrahydrate _{_{[Ca (NO 3) 2 · 4H}} 2 O ], calcium acetate monohydrate [( CH ₃ COO) ₂ Ca · H ₂ O] and the like.
Specific examples of the Pb salt include lead (II) chloride [PbCl ₂ ], lead (II) nitrate [Pb (NO ₃ ) ₂ ] and the like.
However, the above is an example, and other salts can be used. The mixing ratio of various salts for preparing the raw material aqueous solution may be determined according to the desired hexagonal ferrite composition.

Examples of the alkaline aqueous solution include a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution. The concentration of the alkaline aqueous solution can be, for example, 0.1 mol / L to 10 mol / L. However, the type and concentration of the alkaline aqueous solution are not limited to the above examples as long as a precipitate can be produced.

The raw material aqueous solution and the alkaline aqueous solution may be simply mixed. The total amount of the raw material aqueous solution and the alkaline aqueous solution may be mixed at once, or the raw material aqueous solution and the alkaline aqueous solution may be gradually mixed. Further, it may be mixed while gradually adding the other to either the raw material aqueous solution or the alkaline aqueous solution. 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 means is not particularly limited, and general stirring means can be used. The stirring time may be set to a time during which a precipitate can be formed, and can be appropriately set according to the composition of the raw material aqueous solution, the type of stirring means used, and the like.
The temperature (liquid temperature) when the raw material aqueous solution and the alkaline aqueous solution are mixed is preferably 100 ° C. or lower from the viewpoint of preventing bumping, and 95 ° C. from the viewpoint of satisfactorily advancing the precipitation reaction. The temperature is more preferably 15 ° C. or higher and 92 ° C. or lower. As a means for adjusting the temperature, a general heating device, cooling device, or the like can be used. The pH of the aqueous solution obtained by mixing the raw material aqueous solution and the alkaline aqueous solution at a liquid temperature of 25 ° C. is preferably in the range of 5 to 13, preferably in the range of 6 to 12, from the viewpoint of making it easier to obtain a precipitate, for example. Is more preferable. The content of the substituted atom can be controlled by adjusting the pH.

When the obtained precipitate is solid-liquid separated after the precipitate is formed, the method is not particularly limited, and examples thereof include decantation, centrifugation, and filtration (suction filtration, pressure filtration, etc.). For example, when solid-liquid separation is performed by centrifugation, the conditions for centrifugation are not particularly limited, and for example, centrifugation can be performed for 3 to 30 minutes at a rotation speed of 2000 rpm (revolutions per minute) or higher. Further, the centrifugation may be performed a plurality of times.

Process 2
Step 2 is a step of calcining the precipitate obtained in Step 1.
In step 2, the precursor of hexagonal ferrite can be converted to hexagonal ferrite by calcining the precipitate obtained in step 1. Firing can be performed using a heating device. The heating device is not particularly limited, and a known heating device such as an electric furnace, a firing device manufactured according to a production line, or the like can be used. Firing can be performed, for example, in an atmospheric atmosphere. The firing temperature and firing time may be set within a range in which the precursor of hexagonal ferrite can be converted to hexagonal ferrite. The firing temperature is, for example, preferably 900 ° C. or higher, more preferably 900 ° C. to 1400 ° C., and even more preferably 1000 ° C. to 1200 ° C. The firing time is, for example, preferably in the range of 1 hour to 10 hours, and more preferably in the range of 2 hours to 6 hours. In addition, the precipitate obtained in step 1 can be dried before firing. The drying means is not particularly limited, and examples thereof include a dryer such as an oven. The drying temperature is, for example, preferably in the range of 50 ° C. to 200 ° C., and more preferably in the range of 70 ° C. to 150 ° C. The drying time is preferably in the range of, for example, 2 hours to 50 hours, and more preferably in the range of 5 hours to 30 hours. The above firing temperature and drying temperature can be the internal ambient temperature of the apparatus for firing or drying.

The fired body obtained in the above step 2 can be a massive fired body or a powder-shaped fired body in which the precursor of hexagonal ferrite is converted to show the crystal structure of hexagonal ferrite. Further, a step of crushing the fired body can also be carried out. The crushing can be performed by a known crushing means such as a mortar and pestle, a crusher (cutter mill, ball mill, bead mill, roller mill, jet mill, hammer mill, attritor, etc.). For example, in the case of pulverization using a medium, the particle size of the medium (so-called media diameter) is preferably in the range of 0.1 mm to 5.0 mm, and preferably in the range of 0.5 mm to 3.0 mm. More preferred. By "media diameter" is meant, in the case of spherical media, the arithmetic mean of the diameters of a plurality of randomly selected media (eg, beads). In the case of non-spherical media (for example, non-spherical beads), a plurality of randomly selected images obtained from observation images of a transmission electron microscope (TEM; Transmission Electron Microscope) or a scanning electron microscope (SEM). It means the arithmetic average of the circle equivalent diameter of the media. Examples of the material of the media include glass, alumina, steel, zirconia, and ceramics. When crushing with a cutter mill, the crushing conditions can be determined according to the amount of the fired body to be crushed, the scale of the cutter mill to be used, and the like. For example, in one form, the rotation speed of the cutter mill can be about 5000 to 25000 rpm.

(Surface treatment agent)
The substituted hexagonal ferrite powder is surface-treated with a surface treatment agent. Here, the surface treatment agent is a silicon-based compound. By using a powder of substituted hexagonal ferrite surface-treated with a silicon compound and a resin whose details will be described later, it is possible to improve the radio wave absorption performance, vibration fatigue resistance and chemical resistance of the radio wave absorber. This was newly discovered as a result of diligent studies by the present inventors.
Regarding vibration fatigue resistance, a radio wave absorber having excellent vibration fatigue resistance is preferable because it does not easily get tired even if it is vibrated during use, and can continue to contribute to improving radar recognition accuracy for a long period of time. By combining a substituted hexagonal ferrite powder surface-treated with a silicon-based compound as a magnetic powder and a resin described later as a binder, the compatibility and bonding strength between the particles constituting the magnetic powder and the binder can be determined. It is presumed that the amount can be increased and the occurrence of the destruction phenomenon that occurs at the interface between the particles and the binder can be suppressed. It is considered that this makes it possible to improve the vibration fatigue resistance.
Further, the interaction between the particles constituting the magnetic powder and the binder can contribute to the improvement of the chemical resistance of the radio wave absorber. Regarding this interaction, the combination of the above magnetic powder and the binder makes it possible to enhance the compatibility between the particles constituting the magnetic powder and the binder, so that a minute space (non-compliance) at the interface between the particles and the binder can be obtained. It is presumed that the occurrence of continuous sites) can be reduced. This is considered to contribute to suppressing the generation of cracks and the like due to the permeation of chemicals into the minute space at the interface. It is presumed that this makes it possible to improve chemical resistance.
However, the above is a speculation and does not limit the present invention.

The radio wave absorbing composition and the powder of the substituted hexagonal ferrite contained in the radio wave absorber are surface-treated with a silicon compound. In the present invention and the present specification, "system" means "including". The silicon-based compound can be an organic compound or an inorganic compound, and is preferably an organic compound from the viewpoint of further improving vibration fatigue resistance and chemical resistance.

At least a part of the groups contained in the silicon-based compound that can be used as the surface treatment agent described below may be a reactive group. A reactive group is a group that can react with another group or bond and has a structure different from that before the reaction after the reaction. In the surface treatment agent, the reactive group may be present in the post-reaction form in a state of being coated with the powder of the substituted hexagonal ferrite after the surface treatment, and such an embodiment is also included in the present invention. ..

Silicon-based compounds Examples of silicon-based compounds suitable as surface treatment agents include silicon-based compounds represented by the following general formula 2.

General formula 2: (XL) _m- Si-Z _4-m

In the general formula 2, X is a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, an alicyclic group, a heterocyclic group, a hydroxy group, an acrylamide group, a sulfanyl group, an isocyanate group, a thiocianate group, a ureido group, a cyano group and an acid. Represents an anhydride group, an azide group, a carboxy group, an acyl group, a thiocarbamoyl group, a phosphoric acid group, a phosphanyl group, a sulfonic acid group or a sulfamoyl group.
L is selected from the group consisting of a single bond, an alkylene group, an alkenylene group, an alkynylene group, an arylene group, -O-, -S-, -NR ^a- , an ester bond, a thioester bond, an amide bond, a thioamide bond and a sulfonyl group. Represents one type of divalent group or bond, or a combination of two or more of these divalent groups or bonds.
^Ra represents a hydrogen atom or a substituent.
Z represents a hydroxy group, an alkoxy group or an alkyl group.
m is an integer in the range of 1 to 3.

The group represented by X and the group and bond represented by L may have a substituent or may not have (that is, be unsubstituted). Examples of the substituent include a hydroxy group, a sulfanyl group, a thiocianate group, a ureido group, an acid anhydride group, a carboxy group, an acyl group, a carbamoyl group and the like. In the present invention and the present specification, with respect to a group having a substituent and a bond, the carbon number means the carbon number of a portion other than the substituent unless otherwise specified. In the structure represented by "XL-", if there is a part that can be understood as both a part contained in X and a part contained in L, such a part is interpreted as a part contained in X. It shall be.

When m is 2 or 3, the plurality of Xs contained in the general formula 2 can be the same in one form and can be different in the other form. This point is the same for L, and also for Z when "4-m" is 2 or 3.

The general formula 2 will be described in more detail below.

In the general formula 2, X is a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, an alicyclic group, a heterocyclic group, a hydroxy group, an acrylamide group, a sulfanyl group, an isocyanate group, a thiocianate group, a ureido group, a cyano group and an acid. Represents an anhydride group, an azide group, a carboxy group, an acyl group, a thiocarbamoyl group, a phosphoric acid group, a phosphanyl group, a sulfonic acid group or a sulfamoyl group.

The number of carbon atoms of the alkyl group, the alkenyl group, and the aryl group that can be taken as X is preferably in the range of 1 to 30, more preferably in the range of 1 to 25, and in the range of 1 to 20. It is more preferably in the range of 1 to 15. Unless otherwise specified in the present invention and the present specification, the "alkyl group" shall not include a cycloalkyl group. Alkyl groups include linear alkyl groups and branched alkyl groups.

The alicyclic group that can be taken as X may be any of a cycloalkyl group, a cycloalkenyl group and a cycloalkynyl group. The number of carbon atoms of the cycloalkyl group is preferably in the range of 3 to 20, more preferably in the range of 4 to 15, and even more preferably in the range of 5 to 10. The carbon number of each of the cycloalkenyl group and the cycloalkynyl group is preferably in the range of 6 to 20, more preferably in the range of 6 to 15, and further preferably in the range of 6 to 10. , 6 is more preferable.

The heterocycle constituting the heterocyclic group that can be taken as X may be a saturated or unsaturated aliphatic heterocycle or an aromatic heterocycle, and may be a monocyclic ring or a condensed ring. It may also be a bridge ring. Examples of the hetero atom contained in the heterocycle include an oxygen atom, a nitrogen atom and a sulfur atom. The number of heteroatoms contained in one heterocycle is not particularly limited, and is preferably 1 to 3, more preferably 1 or 2, for example. The number of carbon atoms in the heterocycle is preferably in the range of 2 to 10, and more preferably 4 or 5. The heterocycle is preferably a 3- to 7-membered ring, more preferably a 3- to 6-membered ring, and even more preferably a 3- to 5-membered ring. Specific examples of the heterocycle include an epoxy ring, a 3,4-epoxycyclohexane ring, a furan ring and a thiophene ring. In one form, the heterocyclic group represented by X can be an epoxy group. In the present invention and the present specification, the "epoxide group" includes an embodiment in which the heterocycle contained in this group is an epoxy ring (three-membered ring) and a ring having a structure in which an epoxy ring and a saturated hydrocarbon ring are fused. Aspects including groups shall be included. Examples of such a cyclic group include a 3,4-epoxycyclohexane ring.

As the acid anhydride group that can be taken as X, a monovalent group having a structure of a carboxylic acid anhydride is preferable, and for example, a maleic anhydride group such as 3,4-dihydro-2,5-frangionyl and a succinic anhydride group. , Glutaric anhydride group, adipic anhydride group and citraconic anhydride group.

The number of carbon atoms of the acyl group that can be taken as X is preferably in the range of 1 to 40, more preferably in the range of 1 to 30, further preferably in the range of 1 to 20, and in the range of 2 to 15. Is more preferable. In the present invention and the present specification, the "acyl group" includes a formyl group, a carbamoyl group, an alkylcarbonyl group, an alkenylcarbonyl group and an arylcarbonyl group. The alkenylcarbonyl group preferably includes a (meth) acryloyl group. In the present invention and the present specification, the "(meth) acryloyl group" includes an acryloyl group and a methacryloyl group.

The alkylene group that can be taken as L may be either a linear alkylene group or a branched alkylene group. The carbon number of the alkylene group is preferably in the range of 1 to 30, more preferably in the range of 2 to 25, further preferably in the range of 3 to 20, and in the range of 4 to 12. Is more preferable. Specific examples of the alkylene group include a methylene group, an ethylene group, an isopropylene group, a butylene group, a pentylene group, a cyclohexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group and an undecylene group.

The alkenylene group that can be taken as L may be either a linear alkenylene group or a branched alkenylene group. The carbon number of the alkenylene group is preferably in the range of 2 to 20, more preferably in the range of 2 to 15, further preferably in the range of 2 to 10, and in the range of 2 to 6. Is more preferable. Specific examples of the alkenylene group include an ethenylene group and a propenylene group.

The alkynylene group that can be taken as L may be either a linear alkynylene group or a branched alkynylene group. The carbon number of the alkynylene group is preferably in the range of 2 to 20, more preferably in the range of 2 to 15, further preferably in the range of 2 to 10, and in the range of 2 to 6. Is more preferable. Specific examples of the alkynylene group include an ethynylene group and a propynylene group.

The carbon number of the arylene group that can be taken as L is preferably in the range of 6 to 20, more preferably in the range of 6 to 15, further preferably in the range of 6 to 12, and in the range of 6 to 10. Is more preferable. Specific examples of the arylene group include a phenylene group and a naphthylene group.

-NR ^a, which may take as L - Examples of the substituent of ^{R a} of an alkyl group (preferably having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms), an alkenyl group (preferably 2 to 12 carbon atoms, more Preferably carbon number 2-8), alkynyl group (preferably carbon number 2-12, more preferably carbon number 2-8), aryl group (preferably carbon number 6-20, more preferably carbon number 6-10). And heterocyclic groups. Examples of the heterocycle constituting the heterocyclic group that can be adopted as ^Ra include the heterocycle shown above as the heterocycle constituting the heterocyclic group that can be adopted as X, and a preferable heterocyclic group can also be adopted as X. As described for the heterocyclic group. Examples of -NR ^a- include -NH-.

L is selected from the group consisting of a single bond, an alkylene group, an alkenylene group, an alkynylene group, an arylene group, -O-, -S-, -NR ^a- , an ester bond, a thioester bond, an amide bond, a thioamide bond and a sulfonyl group. When representing a divalent group consisting of a combination of two or more of these groups (hereinafter, also referred to as "combined group that can be taken as L"), the above group constituting the combined group that can be taken as L. And the number of bonds is preferably in the range of 2-8, more preferably in the range of 2-6, and even more preferably in the range of 2-4.
The molecular weight of the combined group that can be taken as L is preferably in the range of 20 to 1000, more preferably in the range of 30 to 500, and even more preferably in the range of 40 to 200.
Examples of the combined group that can be taken as L include a urea bond, a thiourea bond, a carbamate group, a sulfonamide bond, an arylene group-alkylene group, an -O-alkylene group, an amide bond-alkylene group, and an -S-alkylene group. , Alkylene group-O-amide bond-alkylene group, alkylene group-amide bond-alkylene group, alkenylene group-amide bond-alkylene group, alkylene group-ester bond-alkylene group, arylene group-ester bond-alkylene group,-( Alkylene group-O)-, alkylene group-O- (alkylene group-O) -alkylene group ("(alkylene group-O)" is a repeating unit), arylene group-sulfonyl group-O-alkylene group and ester bond -The alkylene group can be mentioned.

Regarding the alkyl group constituting the alkoxy group that can be taken as Z, the "alkyl group" also includes a cycloalkyl group. The alkyl group constituting the alkoxy group that can be taken as Z may be any of a linear alkyl group, a branched alkyl group and a cycloalkyl group, and may have a combination of these forms. The alkyl group that can be taken as Z is preferably a linear alkyl group.

The number of carbon atoms of the alkyl group constituting the alkoxy group that can be taken as Z is preferably in the range of 1 to 15, more preferably 1 to 10, further preferably 1 to 5, and 1 or 2. Is more preferable. Specific examples of the alkyl group constituting the alkoxy group include a methyl group, an ethyl group, a propyl group, a t-butyl group, a pentyl group and a cyclohexyl group.

Examples of the alkyl group that can be taken as Z include an alkyl group that constitutes an alkoxy group that can be taken as Z, and the preferred alkyl group is as described for the alkyl group that constitutes an alkoxy group that can be taken as Z.

In the general formula 2, X or L and at least one of Z may be connected to each other to form a ring. The number of ring-constituting atoms in this ring is preferably in the range of 3 to 10, more preferably in the range of 4 to 8, and even more preferably in the range of 5 or 6.

In the general formula 2, it is preferable that X represents a hydrogen atom, an alicyclic group, a heterocyclic group, an acrylamide group, a hydroxy group, a sulfanyl group, a thiocianate group, an acid anhydride group, a carboxy group, an acyl group or a sulfonic acid group. .. Further, one type of L selected from the group consisting of an alkylene group, an alkenylene group, an alkynylene group, an arylene group, -O-, -S-, -NR ^a- , an ester bond, a thioester bond, an amide bond and a sulfonyl group. It is preferable to show a divalent group or bond, or a divalent group or bond formed by combining two or more of these.

In one form, in the general formula 2, m is 1 and X can represent an alkenyl group or a heterocyclic group. In the other form, m is 2 or 3, and a plurality of Xs contained in the general formula 2 can independently represent an alkenyl group or a heterocyclic group.

Further, in one form, in the general formula 2, m is 1 and X can represent a (meth) acryloyl group, an acrylamide group or an epoxy group. In another form, m is 2 or 3, and a plurality of Xs contained in the general formula 2 can independently represent a (meth) acryloyl group, an acrylamide group, or an epoxy group.

In one form, in General Formula 2, X preferably represents a (meth) acryloyl group, an acrylamide group or an epoxy group. Further, L is one divalent group or bond selected from the group consisting of an alkylene group, an alkenylene group, -O-, -NR ^a- , an ester bond and an amide bond, or a combination of two or more of these. It is more preferable to represent a divalent group or bond.

In one form, in General Formula 2, at least two of Z are preferably selected from the group consisting of an alkoxy group and a hydroxy group, and more preferably all Z is selected from the group consisting of an alkoxy group and a hydroxy group.

From the viewpoint of further improving vibration fatigue resistance, a silicon-based compound containing an epoxy group is preferable, an epoxysilane is more preferable, and an epoxysilane having a large number of carbon atoms is further preferable. It is presumed that this is because the flexibility at the interface between the surface of the magnetic powder particles and the resin described later is increased. From this point, in the general formula 2, it is preferable that X represents an epoxy group, X represents an epoxy group, and L contains an alkylene group having 4 to 12 carbon atoms.

Specific examples of the silicon-based compound that can be used as a surface treatment agent include various compounds used in Examples described later. Moreover, the following compound can be mentioned as a specific example of the silicon-based compound which can be used as a surface treatment agent. However, the present invention is not limited to these specific examples.
Methyltriacetoxysilane,
Ethyltriethoxysilane,
Methyltriethoxysilane,
Methyltrimethoxysilane,
n-propyltrimethoxysilane,
Isopropyltrimethoxysilane,
n-hexyltrimethoxysilane,
n-dodecyltriethoxysilane,
n-octyltriethoxysilane,
n-octadecyltriethoxysilane,
Pentyl triethoxysilane,
Diacetoxydimethylsilane,
Diethoxydimethylsilane,
Dimethoxydimethylsilane,
Dimethoxydiphenylsilane,
Dimethoxymethylphenylsilane,
Vinyl diethoxymethylsilane,
Vinyltris (2-methoxyethoxy) silane,
p-styryltriethoxysilane,
Naftyltrimethoxysilane,
Anthryltrimethoxysilane,
Benzyltrimethoxysilane,
3-Glysidyloxypropyl (dimethoxy) methylsilane,
Diethoxy (3-glycidyloxypropyl) methylsilane,
3- (2-Aminoethylamino) propyldimethoxymethylsilane,
3- (2-Aminoethylamino) propyltriethoxysilane,
3- (2-Aminoethylamino) propyltrimethoxysilane,
3-Aminopropyldiethoxymethylsilane,
3-Aminopropyltriethoxysilane,
3-Aminopropyltrimethoxysilane,
(3-Mercaptopropyl) Triethoxysilane,
(3-Mercaptopropyl) Trimethoxysilane,
3-Isocyanatepropyltriethoxysilane,
3-Acryloxypropyltrimethoxysilane,
Triethoxy-1H, 1H, 2H, 2H-tridecafluoro-n-octylsilane,
2-Cyanoethyltriethoxysilane,
Thienyltrimethoxysilane,
Pyridyltrimethoxysilane,
Frill triethoxysilane.

In the present invention and the present specification, the silicon-based compound represented by the general formula 2 also includes the salt form of the compound represented by the general formula 2. Examples of the salt form include alkali metal salts such as sodium salt and potassium salt, alkaline earth metal salts such as magnesium salt, and ammonium salts.

Further, in one form, as the silicon-based compound, a silicone-based compound can be mentioned. Examples of the silicone-based compound include polydimethylsiloxane, polyalkylene oxide-modified silicone, hydrogenated polysiloxane such as hydrogen-terminated polydimethylsiloxane, methylhydrosiloxane-dimethylsiloxane copolymer, and polymethylhydrosiloxane. The molecular weight of the silicone compound is not particularly limited. In one form, the molecular weight of the silicone-based compound is preferably about 1 to 300,000 as a weight average molecular weight. In one form, the liquid silicone compound preferably has a viscosity of 100 to 60,000 cSt (centistokes) (measurement temperature: 25 ° C.) from the viewpoint of surface treatment efficiency. In one form, the polyalkylene oxide-modified silicone preferably has an alkylene oxide content in the range of 10 to 90% by mass, more preferably 20 to 80% by mass. In the case of hydrogenated polysiloxane, in one form, the content of the methylhydrosiloxane unit is preferably in the range of 0.1 to 100 mol%, more preferably in the range of 2 to 50 mol%.

The silicon-based compounds described above may be used alone or in combination of two or more at any ratio. By surface-treating the substituted hexagonal ferrite powder by dry-mixing or wet-mixing the silicon-based compound (surface treatment agent) with the substituted hexagonal ferrite powder, at least a part of the particles constituting the powder At least a part of the surface can be coated. As the surface treatment method, a known technique for surface treatment using a surface treatment agent can be adopted. The amount of the surface treatment agent used in the surface treatment is preferably in the range of 0.1 to 100 parts by mass, and 0.5 to 20 parts by mass with respect to 100 parts by mass of the substituted hexagonal ferrite powder. More preferably, it is in the range.

The radio wave absorbing composition and the radio wave absorber include, as magnetic powder, a powder of a substituted hexagonal ferrite surface-treated with the surface treatment agent described above. In the radio wave absorbing composition and the radio wave absorber, the filling rate of the powder of the substituted hexagonal ferrite surface-treated with the surface treatment agent is not particularly limited. For example, the filling rate can be 35% by volume or less as the volume filling rate, and can also be in the range of 15 to 35% by volume. Further, in one form, the volume filling rate can be 35% by volume or more. In this case, the volume filling factor can be, for example, in the range of 35 to 60% by volume, preferably in the range of 35 to 50% by volume. The volume filling rate means the volume-based content of the radio wave absorber with respect to 100% by volume of the total volume of the radio wave absorber. For the radio wave absorbing composition, the volume filling factor means the volume-based content of the solid content (that is, the component excluding the solvent) with respect to 100% by volume of the total volume.

From the viewpoint of radio wave absorption performance, in the radio wave absorbing composition and the radio wave absorber, the powder of the substituted hexagonal ferrite surface-treated with the surface treatment agent is a mixture of this powder and a resin described later. It is preferably contained in an amount of 10% by mass or more, more preferably 30% by mass or more, and further preferably 50% by mass or more based on the total mass (100% by mass). On the other hand, from the viewpoint of chemical resistance, in the radio wave absorbing composition and the radio wave absorber, the powder of the substituted hexagonal ferrite surface-treated with the surface treatment agent is the sum of this powder and the resin described later. It is preferably contained in an amount of 90% by mass or less, more preferably 80% by mass or less, and further preferably 75% by mass or less with respect to the mass (100% by mass).

<Binder>
The radio wave absorbing composition and the radio wave absorber include the magnetic powder and the binder. The binder is a resin, and the radio wave absorbing composition and the radio wave absorber include one or more resins selected from the group consisting of polyester and polycarbonate as the binder. Combining the above resin containing an ester bond with a powder of a substituted hexagonal ferrite surface-treated with a silicon compound contributes to the improvement of the radio wave absorption performance, vibration fatigue resistance and chemical resistance of the radio wave absorber. obtain.

(polyester)
Examples of the polyester include a polyester composed of a dicarboxylic acid component and a diol component, a polyester composed of a hydroxycarboxylic acid component, and the like.

The dicarboxylic acid components include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, and dimer. Examples thereof include acids, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, and cyclohexanedicarboxylic acid.

As the diol component, an aliphatic glycol having 2 to 20 carbon atoms, for example, ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1, Examples thereof include 6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, and dimerdiol. Examples of the diol component include long-chain glycols having a molecular weight of 200 to 100,000, such as polyethylene glycol, poly 1,3-propylene glycol, poly 1,2-propylene glycol, and polytetramethylene glycol. In addition, aromatic dioxy compounds such as 4,4'-dihydroxybiphenyl, hydroquinone, tert-butylhydroquinone, bisphenol A, bisphenol S, bisphenol F and the like can be mentioned. In addition, examples of the diol component include these ester-forming derivatives.

As the hydroxycarboxylic acid components, glycolic acid, lactic acid, hydroxypropioic acid, hydroxybutyric acid, 2-hydroxyisobutyric acid, hydroxyvaleric acid, hydroxycaproic acid, hydroxypivalic acid, hydroxybenzoic acid, p-hydroxybenzoic acid, 6 Examples thereof include -hydroxy-2-naphthoic acid and ester-forming derivatives thereof. Examples of the lactone include caprolactone, valerolactone, propiolactone, undecalactone, 1,5-oxepane-2-one and the like.

The polyester may be a polymer consisting of only the above components, a copolymer obtained by copolymerizing other components, and further, trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, pentaerythritol. The trifunctional compound component such as the above may be contained in an arbitrary amount.

It is also preferable that the polyester is a polyester elastomer in one form. The polyester elastomer is a copolymer composed of a high melting point polyester segment (hard segment) and a low melting point polymer segment (soft segment) having a molecular weight of 400 or more, and is preferably a block copolymer. The melting point of the high melting point polyester segment (hard segment) is preferably 200 ° C. or higher (for example, 200 to 300 ° C.), and the melting point of the low melting point polymer segment (soft segment) is 80 ° C. or lower (for example, 40 to 80 ° C.). Is preferable. The melting point of a hard segment is the melting point of a polymer composed only of the components of this segment. This point also applies to the melting point of the soft segment. The molecular weight of the low melting point polymer segment (soft segment) is preferably in the range of 400 to 6000, and more preferably in the range of 400 to 800. Examples of the low melting point polymer segment (soft segment) include polyethers such as polyalkylene oxide and polylactones such as poly-ε-caprolactone. The "molecular weight" in the present invention and the present specification means the weight average molecular weight of the polymer component. The molecular weight of polyester is not particularly limited. In one form, the lower limit of the weight average molecular weight (Mw) is preferably 5,000 or more, and preferably 10,000 or more, from the viewpoint that vibration fatigue and drug resistance tend to be developed. More preferably, it is more preferably 20,000 or more. Further, as the upper limit, in one form, from the same viewpoint as described above, it is preferably 1,000,000 or less, and more preferably 500,000 or less. In the present invention and the present specification, "weight average molecular weight" means the molecular weight relative to the molecular weight of standard polymethyl methacrylate as analyzed by gel permeation chromatography using tetrahydrofuran as a mobile phase.

Specific examples of polyester include polyethylene terephthalate, polypropylene terephthalate (polytrimethylene terephthalate), polybutylene terephthalate, polycyclohexanedimethylene terephthalate, polyhexylene terephthalate, polyethylene naphthalate, polypropylene naphthalate, polybutylene naphthalate, and polybutylene sakushi. Nate, Polyethylene terephthalate / terephthalate, Polyethylene terephthalate / terephthalate, Polybutylene terephthalate / terephthalate, Polyethylene terephthalate / Naphthalate, Polyethylene terephthalate / Naphthalate, Polybutylene terephthalate / Naphthalate, Polybutylene terephthalate / Decandycarboxylate, Polyethylene terephthalate / Cyclohexane Dimethylene terephthalate, polyether ester (polyethylene terephthalate / polyethylene glycol, polypropylene terephthalate / polyethylene glycol, polybutylene terephthalate / polyethylene glycol, polyethylene terephthalate / polytetramethylene glycol, polypropylene terephthalate / polytetramethylene glycol, polybutylene terephthalate / polytetramethylene Glycol, polyethylene terephthalate / isophthalate / polytetramethylene glycol, polypropylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene terephthalate / isophthalate / polytetramethylene glycol, etc.), polyethylene terephthalate / succinate, polypropylene terephthalate / succinate, polybutylene Terephthalate / succinate, polyethylene terephthalate / adipate, polypropylene terephthalate / adipate, polybutylene terephthalate / adipate, polyethylene terephthalate / sebacate, polypropylene terephthalate / sebacate, polybutylene terephthalate / sebacate, polyethylene terephthalate / isophthalate / adipate, polypropylene terephthalate / isophthalate / Adipate, Polyethylene terephthalate / Isophthalate / Succinate, Polybutylene terephthalate / Isophthalate / Adipate, Polybutylene terephthalate / Isophthalate / Sevacate, Bisphenol A / Terephthalic acid, Bispheno Examples thereof include lu A / isophthalic acid, bisphenol A / terephthalic acid / isophthalic acid, polyglycolic acid, polylactic acid, poly (3-hydroxybutanoic acid), poly (3-hydroxyvaleric acid), polybutyrolactone, polycaprolactone and the like. .. The "/" in the notation of specific examples of polyesters is used to represent copolymers.

Specific examples of commercially available polyester elastomers include Hytrel 5557 and Hytrel 7247 manufactured by Toray DuPont, and Perprene S-6001 manufactured by Toyobo Co., Ltd.

Further, as the polyester, polyarylate can be mentioned. The polyarylate is an aromatic polyester composed of a divalent phenolic compound and a dicarboxylic acid component, and may be a polymer composed of only these components or a copolymer in which other components are copolymerized. Examples of the polyarylate include a polyarylate composed of an aromatic divalent phenolic compound and an aromatic dicarboxylic acid component. Examples of the aromatic dicarboxylic acid component include various aromatic dicarboxylic acids exemplified above, such as terephthalic acid and isophthalic acid. For aromatic divalent phenolic compounds, the description below regarding polycarbonate can be referred to. The polyarylate is preferably composed of an equivalent mixture of 2,2-bis (4-hydroxyphenyl) propane and an aromatic dicarboxylic acid selected from the group consisting of terephthalic acid and isophthalic acid.
Specific examples of commercially available polyarylates include U-polymer U-8400H manufactured by Unitika Ltd.

(Polycarbonate)
Polycarbonate is a resin containing a plurality of carbonate groups. Examples of the polycarbonate include aliphatic or aromatic polycarbonate. Examples of the aromatic polycarbonate include aromatic polycarbonates such as aromatic homo or copolycarbonate obtained by reacting an aromatic dihydric phenolic compound with phosgene or a carbonic acid diester. Examples of aromatic dihydric phenolic compounds include 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, and bis (4-hydroxyphenyl) methane. , 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) butane, 2,2-bis (4-hydroxy-3,5-diphenyl) butane, 2,2-bis (4-Hydroxy-3,5-diethylphenyl) propane, 2,2-bis (4-hydroxy-3,5-diethylphenyl) propane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 1-phenyl- 1,1-Bis (4-hydroxyphenyl) ethane and the like can be used alone or as a mixture of two or more. In one form, aromatic polycarbonate having a glass transition temperature in the range of 100 to 155 ° C. as measured by a differential calorimeter is preferred. In one form, the weight average molecular weight of the polycarbonate is preferably in the range previously described for the polyester.
Specific examples of commercially available polycarbonate products include Panlite LV-2225Z manufactured by Teijin Limited.

In one form, the resin is selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polytrimethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polylactic acid, polybutylene succinate, polyarylate, polycarbonate and polyester elastomer. It can be one or more kinds of resins.
In one form, the resin is one or more resins selected from the group consisting of polyethylene naphthalate, polytrimethylene terephthalate, polybutylene naphthalate, polylactic acid, polybutylene succinate, polyarylate and polyester elastomer. be able to.

The radio wave absorbing composition and the radio wave absorber may contain only one kind of the resin, or may contain two or more kinds of the resin in an arbitrary ratio. The filling rate of the resin in the radio wave absorbing composition and the radio wave absorber is not particularly limited, and for example, the volume filling rate is preferably 65% by volume or more, preferably 65% by volume or more and 92% by volume or less. It is more preferable that there is 65% by volume or more and 85% by volume or less. When the radio wave absorbing composition and the radio wave absorber contain two or more kinds of the above resins, the filling rate means the total filling rate of the two or more kinds of resins. This point is the same for the filling rate for other components.

<Additives>
The radio wave absorbing composition and the radio wave absorber include a powder of substituted hexagonal ferrite surface-treated with a silicon compound and the resin, and may optionally contain one or more additives. Examples of the additive include a dispersant, a dispersion aid, a fungicide, an antistatic agent, an antioxidant and the like. The additive may have one component having two or more functions. The radio wave absorbing composition and the radio wave absorber may contain a commercially available product or a product manufactured by a known method as an additive at an arbitrary filling rate.

<Manufacturing method of radio wave absorbing composition and radio wave absorber>
The method for producing the radio wave absorbing composition and the radio wave absorber is not particularly limited. The radio wave absorbing composition can be produced by a known method using the magnetic powder, the resin, and if necessary, a solvent, an additive, or the like. For example, the radio wave absorber can be a molded product obtained by molding the radio wave absorbing composition. The radio wave absorbing composition can be prepared as a kneaded product by, for example, kneading a mixture of the magnetic powder, the resin, and, if necessary, a solvent, additives, and the like while heating. The kneaded product can be obtained as pellets, for example. A radio wave absorber (molded product) can be obtained by molding the kneaded product into a desired shape by a known molding method such as extrusion molding, press molding, injection molding, or in-mold molding. The shape of the radio wave absorber is not particularly limited, and may be any shape such as a plate shape or a linear shape. "Plate-shaped" includes sheet-shaped and film-shaped. The plate-shaped radio wave absorber can also be called a radio wave absorbing plate, a radio wave absorbing sheet, a radio wave absorbing film, or the like. The radio wave absorber may be a radio wave absorber having a single composition (for example, a single-layer radio wave absorber), or may be a combination of two or more parts having different compositions (for example, a laminated body). Further, the radio wave absorber may have a planar shape, may have a three-dimensional shape, or may be a combination of a portion having a planar shape and a portion having a three-dimensional shape. Examples of the planar shape include a sheet shape and a film shape. Examples of the three-dimensional shape include a tubular shape (cylindrical shape, square tubular shape, etc.), a horn shape, a box shape (for example, at least one of the surfaces is open) and the like.

For example, the thickness of the radio wave absorber is preferably 20.0 mm or less, more preferably 10.0 mm or less, and further preferably 5.0 mm or less, from the viewpoint of ease of handling. From the viewpoint of mechanical properties, the thickness is preferably 1.0 mm or more, and more preferably 2.0 mm or more. By adjusting the thickness of the radio wave absorber, for example, the transmission attenuation amount described later can be controlled. When the radio wave absorber is a laminated body, the thickness means the total thickness of the radio wave absorbers constituting the laminated body. The thickness of the radio wave absorber is a value measured using a digital length measuring device, and specifically, is an arithmetic mean of the measured values measured at nine randomly selected points.

The radio wave absorbing composition may or may not contain a solvent. When the radio wave absorbing composition contains a solvent, the solvent is not particularly limited, and examples thereof include water, an organic solvent, and a mixed solvent of water and an organic solvent.
Examples of the organic solvent include alcohols such as methanol, ethanol, n-propanol, i-propanol and methoxypropanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, tetrahydrofuran, acetonitrile, ethyl acetate and toluene. Among these, as the solvent, ketones are preferable, and cyclohexanone is more preferable, from the viewpoint of drying speed. When the radio wave absorbing composition contains a solvent, the content of the solvent in the composition is not particularly limited and may be determined according to the method for producing the radio wave absorber.

The radio wave absorbing composition can be prepared by mixing the above components. The mixing method is not particularly limited, and examples thereof include a method of mixing by stirring. As the stirring means, a known stirring device can be used. For example, examples of the stirring device include mixers such as a paddle mixer and an impeller mixer. The stirring time may be set according to the type of stirring device, the composition of the radio wave absorbing composition, and the like.

As one form of the method for producing the radio wave absorber, a method of molding the radio wave absorbing composition into a desired shape by a known molding method as exemplified above can be mentioned.
Further, as another form of the method for manufacturing the radio wave absorber, a method of applying the radio wave absorbing composition to the support and manufacturing the radio wave absorber as the radio wave absorbing layer can be mentioned. The support used here may be removed before the radio wave absorber is incorporated into the article to which the radio wave absorber should be imparted, or may be incorporated into the article together with the radio wave absorber without being removed.

The support is not particularly limited, and a known support can be used. Examples of the support include metal plates (metal plates such as aluminum, zinc, and copper), glass plates, plastic sheets [polyester (polyester terephthalate, polyethylene naphthalate, polybutylene terephthalate, etc.), polyethylene (linear low density). Polyethylene, low density polyethylene, high density polyethylene, etc.), polypropylene, polystyrene, polycarbonate, polyimide, polyamide, polyamideimide, polysulfone, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, polyetherimide, polyethersulfone, polyvinylacetal, acrylic resin Etc.], plastic sheets on which the metal exemplified above for the metal plate is laminated or vapor-deposited, and the like can be mentioned. The plastic sheet is preferably biaxially stretched. The shape, structure, size, etc. of the support can be appropriately selected.
Examples of the shape of the support include a plate shape. The structure of the support may be a single-layer structure or a laminated structure of two 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 usually about 0.01 mm to 10 mm, for example, from the viewpoint of handleability, it is preferably 0.02 mm to 3 mm, and more preferably 0.05 mm to 1 mm.

The method of applying the radio wave absorbing composition on the support is not particularly limited, and examples thereof include a method using a die coater, a knife coater, an applicator, and the like. The method for drying the coating film formed by applying the radio wave absorbing composition is not particularly limited, and examples thereof include a method using a known heating device such as an oven. The drying temperature and drying time are not particularly limited. As an example, the drying temperature can be in the range of 70 ° C. to 90 ° C. and the drying time can be in the range of 1 hour to 3 hours.

The radio wave absorber can be incorporated into various articles for which it is desired to impart radio wave absorption. For example, the plate-shaped radio wave absorber can be incorporated into an article in any form as it is or by bending it at an arbitrary portion. Further, it can be adjusted to a desired shape by injection molding or the like and incorporated into an article.

A radio wave absorber having excellent radio wave absorption performance is useful for improving the recognition accuracy of radar. As an example of the index of the radio wave absorption performance, the transmission attenuation amount can be mentioned. For example, the transmission attenuation of the radio wave absorber can be 6.0 dB or more. In order to improve the recognition accuracy of the radar, it is desirable to increase the directivity of the radar. A high transmission attenuation can contribute to improving the directivity of the radar. From the viewpoint of further improving the directivity of the radar, the transmission attenuation of the radio wave absorber is preferably 8.0 dB or more, more preferably 8.5 dB or more, and 9.0 dB or more. More preferably, it is more preferably 10.0 dB or more. The transmission attenuation of the radio wave absorber is, for example, 15.0 dB or less, 14.5 dB or less, 14.0 dB or less, 13.5 dB or less, 13.0 dB or less, 12.5 dB or less, or 12.0 dB or less. be able to. However, from the viewpoint of improving the directivity of the radar, it is preferable that the transmission attenuation of the radio wave absorber is high. Therefore, the transmission attenuation of the radio wave absorber may exceed the value exemplified above.
Further, the amount of reflection attenuation of the radio wave absorber can be, for example, 6.0 dB or more. In order to improve the recognition accuracy of the radar, it is desirable to enhance the selectivity of the radar to selectively receive the radio waves from the object by removing or reducing unnecessary radio wave components by the radio wave absorber. A high amount of reflection attenuation can contribute to removing or reducing unnecessary radio wave components. From this point, the amount of reflection attenuation of the radio wave absorber is preferably 8.0 dB or more, more preferably 8.5 dB or more, further preferably 9.0 dB or more, and 10.0 dB or more. Is more preferable. The amount of reflection attenuation of the radio wave absorber is, for example, 18.0 dB or less, 17.5 dB or less, 17.0 dB or less, 16.5 dB or less, 16.0 dB or less, 15.5 dB or less, or 15.0 dB or less. be able to. However, from the viewpoint of removing or reducing unnecessary radio wave components, it is preferable that the amount of reflection attenuation of the radio wave absorber is high. Therefore, the amount of reflection attenuation of the radio wave absorber may exceed the value exemplified above.

By the way, the in-vehicle radar, which has been attracting attention in recent years, is a radar that uses radio waves in the millimeter wave frequency band. Millimeter waves are electromagnetic waves with a frequency of 30 GHz to 300 GHz. The radio wave absorber preferably exhibits a transmission attenuation amount and a reflection attenuation amount in the above range with respect to the frequency of the radio wave, that is, one or more frequencies in the frequency band of 3 terahertz (THz) or less. The frequency at which the radio wave absorber indicates the transmission attenuation amount and the reflection attenuation amount in the above range is a millimeter wave frequency band, that is, a frequency band of 30 GHz to 300 GHz from the viewpoint of usefulness for improving the recognition accuracy of the in-vehicle radar. It is preferably one or more frequencies in the above, more preferably one or more frequencies in the frequency band of 60 GHz to 90 GHz, and more preferably one or more frequencies in the frequency band of 75 GHz to 85 GHz. More preferred. As an example, the radio wave absorber can be a radio wave absorber having a transmission attenuation amount at a frequency of 76.5 GHz and a reflection attenuation amount at a frequency of 76.5 GHz in the above range. Such a radio wave absorber is suitable as a radio wave absorber to be incorporated in the front side (incoming side of radio waves incident from the outside) of the radio wave transmitting / receiving unit in the in-vehicle radar in order to reduce the side lobe of the in-vehicle millimeter-wave radar. ..

The "permeation attenuation" in the present invention and the present specification is defined as S-parameter S21 by measuring the S-parameters in a measurement environment with an ambient temperature of 15 to 35 ° C. with an incident angle of 0 ° by the free space method. This is the required value. The "reflection attenuation amount" is a value obtained as S11 of the S parameter by the same measurement. The measurement can be performed using a known vector network analyzer and horn antenna. Specific examples of the measurement method include the methods described in Examples described later.

By the way, as for the radio wave absorber, a metal layer may be laminated on a surface (so-called back surface) opposite to the surface on which the radio wave is incident on the radio wave absorber. Such a radio wave absorber is called a matched radio wave absorber. In the matched radio wave absorber, the reflection attenuation characteristic can be enhanced by providing a metal layer and utilizing the phase difference absorption. On the other hand, in one form of the radio wave absorber, the radio wave absorber itself can have excellent reflection attenuation characteristics. Specifically, in one form, the radio wave absorber can exhibit a high amount of reflection attenuation regardless of the metal layer. A radio wave absorber used without laminating a metal layer on the back surface is generally called a transmission type radio wave absorber. In the conventional transmission type radio wave absorber containing the magnetic powder and the binder, in general, the reflection attenuation tends to decrease when the transmission attenuation is increased. On the other hand, in one form, the radio wave absorber can exhibit a high reflection attenuation amount and a high transmission attenuation amount regardless of the metal layer.
As used herein, the term "metal layer" means a layer that contains metal and that substantially reflects radio waves. However, when the radio wave absorber containing the magnetic powder and the binder contains a metal, such a radio wave absorber does not correspond to the metal layer. Here, "substantially reflecting radio waves" means, for example, that 90% or more of the incident radio waves are reflected when the radio waves are incident on the radio wave absorber in a state where a metal layer is laminated on the back surface of the radio wave absorber. Means to do. Examples of the form of the metal layer include a metal plate and a metal foil. For example, a metal layer formed by vapor deposition on the back surface of the radio wave absorber can be mentioned. In one form, the radio wave absorber can be used without providing a metal layer on the back surface. It is preferable that it can be used without a metal layer from the viewpoint of recycling the radio wave absorber and from the viewpoint of cost. Further, the quality of the radio wave absorber used by laminating a metal layer on the back surface may deteriorate due to deterioration of the metal layer, peeling of the metal layer and the radio wave absorber, and the like. It is preferable that it can be used without providing a metal layer on the back surface from the viewpoint that such quality deterioration does not occur.

The present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. Unless otherwise specified, the steps and evaluations described below were performed in an environment with an ambient temperature of 23 ° C. ± 1 ° C.

[Preparation of magnetic powder]
<Preparation of magnetic powder A-1 (powder of substituted hexagonal strontium ferrite)>
Stirred distilled water 400.0g was kept in liquid temperature 35 ° C., the water in the stirring, the iron (III) chloride hexahydrate [FeCl ₃ · 6H ₂ O] 57.0 g, strontium chloride hexahydrate [ a raw solution of SrCl _₂ · 6H ₂ O] 27.8g and aluminum hexahydrate [AlCl ₃ · 6H ₂ O] 10.7g chloride was prepared by dissolving in water 216.0 g, hydroxide concentration 5 mol / L A total amount of a solution prepared by adding 113.0 g of water to 181.3 g of an aqueous sodium solution was added at a flow rate of 10 mL / min at the same timing of addition to obtain a first solution.
Next, after changing the liquid temperature of the first liquid to 25 ° C., 24.7 g of a sodium hydroxide aqueous solution having a concentration of 1 mol / L was added while maintaining this liquid temperature to obtain a second liquid. The pH of the obtained second liquid was 9.0. The pH of the second liquid was measured using a desktop pH meter (F-71 manufactured by HORIBA, Ltd.).
Next, the second liquid was stirred for 15 minutes to obtain a liquid (precursor-containing liquid) containing a reaction product serving as a precursor of magnetoplumbite-type hexagonal ferrite.
Next, the precursor-containing liquid was subjected to a centrifugation treatment [rotation speed: 3000 rpm, rotation time: 10 minutes] three times, and the obtained precipitate was recovered.
Then, the recovered precipitate was dried in an oven having an internal ambient temperature of 80 ° C. for 12 hours to obtain a precursor powder.
Next, the powder of the precursor was placed in a muffle furnace, the temperature in the furnace was set to 1100 ° C. in an air atmosphere, and the mixture was fired for 4 hours to obtain a fired product.
Next, the obtained fired body was used as a crusher using a cutter mill crusher (Wonder Crusher WC-3 manufactured by Osaka Chemical Co., Ltd.), and the variable speed dial of this crusher was set to "5" (rotation speed: about 10,000 to 15,000 rpm). ) And crushed for 90 seconds.
From the above, magnetic powder A-1 was obtained.

<Preparation of magnetic powders A-2 to A-7 (powder of substituted hexagonal strontium ferrite)>
The same operation as in the production of the magnetic powder A1 was carried out except that the pH of the second liquid was adjusted to the pH shown in Table 1 described later, to obtain magnetic powders A-2 to A-7.

<Preparation of magnetic powder A-8 (unsubstituted hexagonal strontium ferrite powder)>
15.02 g of strontium carbonate [SrCO ₃ ] and 90.24 g of iron oxide [Fe ₂ O ₃ ] were mixed and pulverized in a Menou mortar to obtain a powder of a precursor of a magnetoplumbite-type hexagonal ferrite.
Next, the precursor powder was placed in a muffle furnace, the temperature inside the furnace was set to 1200 ° C. in an air atmosphere, and the mixture was fired for 4 hours to obtain a fired product.
Next, the obtained fired body was used as a crusher using a cutter mill crusher (Wonder Crusher WC-3 manufactured by Osaka Chemical Co., Ltd.), and the variable speed dial of this crusher was set to "5" (rotation speed: about 10,000 to 15,000 rpm). ) And crushed for 90 seconds.
From the above, powder A-8 was obtained.

<Confirmation of crystal structure>
The crystal structure of the magnetic material constituting each of the above magnetic powders was confirmed by X-ray diffraction analysis. As the measuring device, X'Pert Pro manufactured by PANalytical Co., Ltd., which is a powder X-ray diffractometer, was used. The measurement conditions are shown below.
-Measurement condition-
X-ray source: CuKα ray [wavelength: 1.54 Å (0.154 nm), output: 40 mA, 45 kV]
Scan range: 20 ° <2θ <70 °
Scan interval: 0.05 °
Scan speed: 0.75 ° / min

As a result of the above X-ray diffraction analysis, the magnetic powders A-1 to A-8 have a magnetoplumbite-type crystal structure and do not contain a crystal structure other than the magnetoplumbite-type single-phase magnetoplumbite. It was confirmed that it was a powder of type hexagonal ferrite.

<Confirmation of composition>
The composition of the magnetic material constituting each of the above magnetic powders was confirmed by high-frequency inductively coupled plasma emission spectroscopy. Specifically, it was confirmed by the following method.
A container beaker containing 12 mg of magnetic powder and 10 mL of a hydrochloric acid aqueous solution having a concentration of 4 mol / L was held on a hot plate at a set temperature of 120 ° C. for 3 hours to obtain a solution. After adding 30 mL of pure water to the obtained solution, the mixture was filtered using a membrane filter having a filter pore size of 0.1 μm. Elemental analysis of the filtrate thus obtained was performed using a high-frequency inductively coupled plasma emission spectroscopic analyzer [ICPS-8100 manufactured by Shimadzu Corporation]. Based on the results of the obtained elemental analysis, the content of each atom with respect to 100 atomic% of iron atoms was determined. Then, the composition of the magnetic material was confirmed based on the obtained content. As a result, it was confirmed that the compositions of the magnetic powders A-1 to A-7 were such that A in the general formula 1 was Sr and x was the value shown in Table 1. Further, it was confirmed that the magnetic powder A-8 had the composition of SrFe ₁₂ O ₁₉ (that is, it was an unsubstituted strontium ferrite).

The resonance frequencies of the magnetic powders A-1 to A-7 were measured by the following methods. The measurement results are shown in Table 1.
(Measurement method of resonance frequency)
Using each magnetic powder, a sheet sample for resonance frequency measurement was prepared by the following method.
9.0 g of magnetic powder, 1.05 g of acrylonitrile butadiene rubber (NBR) [JSR N215SL manufactured by JSR], and 6.1 g of cyclohexanone (solvent) were used with a stirrer [Awatori Rentaro ARE-310 manufactured by Shinky]. , Stirred at a rotation speed of 2000 rpm for 5 minutes and mixed to prepare a composition for preparing a sheet sample.
Next, the prepared composition was applied onto a glass plate (support) using an applicator to form a coating film of the above composition.
Next, the formed coating film was dried in an oven having an internal atmospheric temperature of 80 ° C. for 2 hours, and then the sheet sample (thickness: 0.3 mm) was peeled off from the glass plate.
Using the sheet sample obtained as described above, a vector network analyzer (product name: N5225B) manufactured by Keysight and a horn antenna (product name: RH12S23) manufactured by Keycom Co., Ltd. were used, and the incident angle was set to 0 ° by the free space method. The S parameter was measured with the sweep frequency set to 60 GHz to 90 GHz. The peak frequency of the magnetic permeability μ ″ of the imaginary part was calculated from this S parameter using the Nicholson loss model method, and this peak frequency was used as the resonance frequency. The results are shown in Table 1.

From the results shown in Table 1, it can be confirmed that the value of x (that is, the Al content) in the general formula 1 can be controlled by adjusting the pH of the second liquid. Furthermore, it can be confirmed that the resonance frequency of the magnetic powder can be controlled by controlling the Al content. It can be said that the higher the resonance frequency of the magnetic powder, the better the radio wave absorption performance in the high frequency band.

<Preparation of magnetic powder R-1 surface-treated with a surface treatment agent>
20 g of the magnetic powder A-1 obtained above and 0.2 g of the surface treatment agent SP-3 (allyltrimethoxysilane) were used in a cutter mill crusher (Wonder Crusher WC-3 manufactured by Osaka Chemical Co., Ltd.). Using, the variable speed dial of this crusher was set to "3" and mixed for 60 seconds.
Next, the mixed powder was placed in an oven at a set temperature of 90 ° C. and dried by heating for 3 hours to obtain a magnetic powder R-1 surface-treated with a surface treatment agent.

<Preparation of magnetic powders R-2 to R-29 surface-treated with a surface treatment agent>
Except for the fact that the magnetic powder shown in Table 2 was used and the surface treatment agent shown in Table 2 was used in the amount used shown in Table 2, the same operation as in the production of the magnetic powder R-1 was performed, and the surface treatment agent was used. Surface-treated magnetic powders R-2 to R-29 were obtained.

Details of the magnetic powders R-1 to R-29 are shown in Table 2 (Tables 2-1 to 2-3). The amount of the surface treatment agent used in the table below is the amount with respect to 100 parts by mass of the magnetic powder to be surface-treated.

The surface treatment agents in Table 2 are the following surface treatment agents.

[Surface treatment agent]
SK-1: Allyltrimethoxysilane (SIA0540.0 manufactured by Gelest)
SK-2: Phenethyl alcoholimethoxysilane (SIP6722.6 manufactured by Gelest)
SK-3: [2- (3-Cyclohexenyl) ethyl] trimethoxysilane (SIC2460.0 manufactured by Gelest)
SV-1: Vinyl trimethoxysilane (KBM-1003 manufactured by Shin-Etsu Chemical Co., Ltd.)
SV-2: 7-octenyltrimethoxysilane (KBM-1083 manufactured by Shin-Etsu Chemical Co., Ltd.)
SV-3: (3-methacryloxypropyl) trimethoxysilane (SIM687.4 manufactured by Gelest)
SV-4: 8-methacryloxyoctyltrimethoxysilane (KBM-5803 manufactured by Shin-Etsu Chemical Co., Ltd.)
SV-5: 3-acrylamide propyltrimethoxysilane (SIA0146.0 manufactured by Gelest)
SP-1: 3-glycidylpropyltrimethoxysilane (SIG840.0 manufactured by Gelest)
SP-2: 5,6-epoxyhexyltriethoxysilane (SIE4675.0 manufactured by Gelest)
SP-3: 8-glycidoxyoctyltrimethoxysilane (KBM-4803 manufactured by Shin-Etsu Chemical Co., Ltd.)
SP-4: 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane (SIE4670.0 manufactured by Gelest)
SI-1: Polydimethylsiloxane (DMS-T21 manufactured by Gelest, weight average molecular weight 5,970)
SI-2: Polyalkylene oxide-modified silicone (DBE-621 manufactured by Gelest, ethylene oxide content 50%, weight average molecular weight 2,500)
SI-3: Hydrogen-terminated polydimethylsiloxane (DMS-H21 manufactured by Gelest, weight average molecular weight 6,000)
ST-1: Tristearoyl isopropyl titanate (manufactured by AIM)

[Making a radio wave absorber]
<Example 1>
3.0 g of magnetic powder R-1, 2.0 g of polyester B-1 (polyester elastomer), and 0.05 g of hindered phenol compound (Irganox 1330 manufactured by BASF) as an antioxidant, set temperature to 220 ° C. The mixture was introduced into a kneader (Laboplast Mill Micro manufactured by Toyo Seiki Co., Ltd.) and mixed, and kneaded at a rotor speed of 100 rpm for 5 minutes to obtain a massive kneaded product.
The obtained massive kneaded product was press-molded using a heating press machine (heating temperature: 190 ° C., press time: 1 minute, pressure: 20 MPa), length 10.0 cm x width 10.0 cm x thickness 2.0 mm. A radio wave absorber (radio wave absorption sheet) was prepared.

<Examples 2-36>
The magnetic powder shown in Table 3 was used as the magnetic powder surface-treated with the surface treatment agent, and the same operation as in Example 1 was performed except that the polyester or polycarbonate shown in Table 3 was used. Radio wave absorption sheet) was prepared.

<Examples 37-40>
The contents of the magnetic powder and the polyester in the mixture for preparing the kneaded product of Example 1 were 60% by mass of the magnetic powder and 40% by mass of the polyester with respect to the total mass of the magnetic powder and the polyester. is there. In Examples 37 to 40, the same operation as in Example 1 was performed except that the contents of the magnetic powder and the polyester were changed as shown in Table 3, to prepare a radio wave absorber (radio wave absorber sheet).

<Comparative example 1>
A polyester sheet was produced by performing the same operation as in Example 1 except that the magnetic powder R-1 was not used.

<Comparative Examples 2 and 3>
A radio wave absorber (radio wave absorbing sheet) was produced by performing the same operation as in Example 1 except that the magnetic powder shown in Table 3 (without surface treatment) was used as the magnetic powder.

<Comparative example 4>
The same operation as in Example 1 was performed except that the magnetic powder shown in Table 3 (unsubstituted hexagonal ferrite powder surface-treated with a surface treatment agent) was used as the magnetic powder. Radio wave absorption sheet) was prepared.

<Comparative example 5>
A radio wave absorber (radio wave absorbing sheet) was produced by performing the same operation as in Example 1 except that the magnetic powder R-29 surface-treated with the titanium compound ST-1 was used.

In the above Examples and Comparative Examples, a plurality of sheets were prepared, and each sheet was used for the following evaluation.

[Evaluation methods]
<Radio wave absorption performance>
The transmission attenuation (unit: dB) and reflection attenuation (unit: dB) of each sheet of Examples and Comparative Examples were measured by the following methods.
Using a keysight vector network analyzer (product name: N5225B) and a keycom horn antenna (product name: RH12S23) as measuring devices, the incident angle is set to 0 ° and the sweep frequency is set to 60 GHz to 90 GHz by the free space method. , One plane of each of the above sheets is directed to the incident side, the S parameter is measured, S21 of the S parameter at the frequency of 76.5 GHz is used as the transmission attenuation amount, and S11 of the S parameter at the frequency of 76.5 GHz is used. The amount of reflection attenuation was used.
From the measured values, the radio wave absorption performance was evaluated according to the following criteria.
(Evaluation criteria)
A: Transmission attenuation and reflection attenuation are both 10.0 dB or more B: Transmission attenuation and reflection attenuation are both 8.0 dB or more and less than 10.0 dB C: Transmission attenuation and reflection attenuation are both 6. 0 dB or more and less than 8.0 dB D: Both the transmission attenuation and the reflection attenuation are less than 6.0 dB.

<Vibration fatigue resistance>
A specimen having a length of 9.0 cm, a width of 2.6 cm, and a thickness of 2.0 mm was cut out from each sheet of Examples and Comparative Examples, and was subjected to JIS K7119-1972 using a repeated vibration fatigue tester (manufactured by Toyo Seiki Co., Ltd.). In accordance with the described double-sided bending test method, a double-sided bending test is performed at a test temperature of 20 ° C., a relative humidity of 50%, a load of 10 kN, a repetition rate of 1,800 cpm (cycle per minute), and a maximum amplitude of ± 8 mm. The number of times until the piece broke was determined, and the vibration fatigue resistance was evaluated according to the following criteria.
(Evaluation criteria)
A: Repeated vibration frequency until break is 1 million or more B: Repeated vibration frequency until break is 200,000 or more and less than 1 million C: Repeated vibration frequency until break is 10,000 or more and less than 200,000 times D: Break The number of repeated vibrations up to is less than 10,000

<Chemical resistance>
A specimen of 10.0 cm in length × 1.0 cm in width × 2.0 mm in thickness was cut out from each sheet of Examples and Comparative Examples, attached to a quarter elliptical jig, and four kinds of chemicals (kerosene, diethylene glycol, ethyl cellosolve). , Brake oil (type: DOT-3)), left in an atmosphere with a temperature of 23 ° C for 17 hours, read the crack generation length L, and use the smallest L value of the four chemicals below. The critical strain ε was calculated by the formula of. From the calculated values, drug resistance was evaluated according to the following criteria.
epsilon (%) = ^{^{[0.03 × (1-0.0364 × L 2)}} -3/2 ] t
[Ε: Critical strain (%), t: Sample thickness (mm), L: Crack generation length (mm)
(Evaluation criteria)
A: Critical strain is 0.7% or more or no cracks occur B: Critical strain is 0.5% or more and less than 0.7% C: Critical strain is 0.2% or more and less than 0.5% D : Critical distortion is less than 0.2%

The above results are shown in Table 3 (Tables 3-1 to 3-6).

The binder in Table 3 is the following polyester or polycarbonate.

[binder]
B-1: Polyester Elastic Polyester Elastomer (TPEE) (Toyobo Perprene P-90B)
B-2: Polyethylene naphthalate (PEN) (Teijin's Theonex TN8050SC)
B-3: Polytrimethylene terephthalate (PTT) (DuPont Solona 3301 NC010)
B-4: Polybutylene naphthalate (PBN) (PBN TQB-OT manufactured by Teijin Limited)
B-5: Polylactic acid (PLA) (Unitika's Terramac TE-7003)
B-6: Polybutylene succinate (PBS) (FZ71PD manufactured by Mitsubishi Chemical Corporation)
B-7: Polyarylate (PAR) (Unitika U Polymer U-8400H)
B-8: Polybutylene terephthalate (PBT) (Wintech Polymer Ltd. Juranex 2002)
B-9: Polyethylene terephthalate (PET) (Toyobo Biropet EMC307)
B-10: Polycarbonate (PC) (Teijin Panlite LV-2225Z)

The radio wave absorbers of Examples 1 to 40 contain a substituted hexagonal ferrite powder surface-treated with a silicon compound as a magnetic powder, and contain polyester or polycarbonate as a binder.
On the other hand, the radio wave absorber of Comparative Example 2 was a substitution type hexagonal ferrite powder and polyester without surface treatment, and the radio wave absorber of Comparative Example 3 was an unsubstituted hexagonal ferrite powder without surface treatment. The radio wave absorber of Polyester and Comparative Example 4 contains an unsubstituted hexagonal ferrite powder surface-treated with a silicon-based compound and polyester. The radio wave absorber of Comparative Example 5 contains a powder of substituted hexagonal ferrite surface-treated with a titanium-based compound and polyester.
From the comparison between Examples 1 to 40 and Comparative Examples 2 to 5 in Table 3, a group consisting of a substituted hexagonal ferrite powder surface-treated with a silicon-based compound as a magnetic powder and a binder, and polyester and polycarbonate. It can be confirmed that a radio wave absorber having excellent radio wave absorption performance, vibration fatigue resistance and chemical resistance can be obtained by combining with a binder selected from the above.

One aspect of the present invention is useful in the technical field of performing various automatic driving controls such as automatic driving control of automobiles.

Claims

A radio wave absorbing composition containing a magnetic powder and a binder.
The magnetic powder is a substituted hexagonal ferrite powder surface-treated with a surface treatment agent.
A radio wave absorbing composition in which the surface treatment agent is a silicon-based compound, and the binder is one or more resins selected from the group consisting of polyester and polycarbonate.
The radio wave absorbing composition according to claim 1, wherein the substituted hexagonal ferrite has a composition represented by the following general formula 1.
General formula 1: AFe (12-x) Al x O 19
In the general formula 1, A represents one or more kinds of atoms selected from the group consisting of Sr, Ba, Ca and Pb, and x satisfies 1.50 or more ≦ x ≦ 8.00.
The radio wave absorbing composition according to claim 1 or 2, wherein the substituted hexagonal ferrite is a substituted hexagonal strontium ferrite.
The radio wave absorbing composition according to any one of claims 1 to 3, wherein the surface treatment agent is a silicon-based compound represented by the following general formula 2.
General formula 2: (XL) m- Si-Z 4-m
In general formula 2,
X is a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, an alicyclic group, a heterocyclic group, a hydroxy group, an acrylamide group, a sulfanyl group, an isocyanate group, a thiocyanate group, a ureido group, a cyano group, an acid anhydride group and an azide. Represents a group, carboxy group, acyl group, thiocarbamoyl group, phosphate group, phosphanyl group, sulfonic acid group or sulfamoyl group.
L is selected from the group consisting of a single bond, an alkylene group, an alkenylene group, an alkynylene group, an arylene group, -O-, -S-, -NR a- , an ester bond, a thioester bond, an amide bond, a thioamide bond and a sulfonyl group. Represents one type of divalent group or bond, or a combination of two or more of these divalent groups or bonds.
Ra represents a hydrogen atom or a substituent and represents
Z represents a hydroxy group, an alkoxy group or an alkyl group.
m is an integer in the range of 1 to 3.
In general formula 2,
m is 1 and X represents an alkenyl group or a heterocyclic group, or m is 2 or 3 and a plurality of Xs contained in the general formula 2 independently form an alkenyl group or a heterocyclic group. The radio wave absorbing composition according to claim 4.
In general formula 2,
m is 1 and X represents an acyl group, an acrylamide group or a heterocyclic group, or m is 2 or 3 and a plurality of Xs contained in the general formula 2 are independently acyl groups and acrylamides, respectively. Represents a group or heterocyclic group
The acyl group is a (meth) acryloyl group and
The radio wave absorbing composition according to claim 4, wherein the heterocyclic group is an epoxy group.
The radio wave absorbing composition according to claim 4, wherein X represents a heterocyclic group in the general formula 2, and the heterocyclic group is an epoxy group.
The radio wave absorbing composition according to claim 7, wherein L in the general formula 2 contains an alkylene group having 4 to 12 carbon atoms.
One or more of the resins selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polytrimethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polylactic acid, polybutylene succinate, polyallylate, polycarbonate and polyester elastomer. The radio wave absorbing composition according to any one of claims 1 to 8, which is the resin of the above.
Claims 1 to 9 wherein the resin is one or more resins selected from the group consisting of polyethylene naphthalate, polytrimethylene terephthalate, polybutylene naphthalate, polylactic acid, polybutylene succinate, polyarylate and polyester elastomer. The radio wave absorbing composition according to any one of the above items.
A radio wave absorber containing magnetic powder and a binder,
The magnetic powder is a substituted hexagonal ferrite powder surface-treated with a surface treatment agent.
The surface treatment agent is a silicon-based compound, and the binder is a radio wave absorber which is one or more resins selected from the group consisting of polyester and polycarbonate.
The radio wave absorber according to claim 11, wherein the substituted hexagonal ferrite has a composition represented by the following general formula 1.
General formula 1: AFe (12-x) Al x O 19
In the general formula 1, A represents one or more kinds of atoms selected from the group consisting of Sr, Ba, Ca and Pb, and x satisfies 1.50 or more ≦ x ≦ 8.00.
The radio wave absorber according to claim 11 or 12, wherein the substituted hexagonal ferrite is a substituted hexagonal strontium ferrite.
The radio wave absorber according to any one of claims 11 to 13, wherein the surface treatment agent is a silicon-based compound represented by the following general formula 2.
General formula 2: (XL) m- Si-Z 4-m
In general formula 2,
X is a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, an alicyclic group, a heterocyclic group, a hydroxy group, an acrylamide group, a sulfanyl group, an isocyanate group, a thiocyanate group, a ureido group, a cyano group, an acid anhydride group and an azide. Represents a group, carboxy group, acyl group, thiocarbamoyl group, phosphate group, phosphanyl group, sulfonic acid group or sulfamoyl group.
L is selected from the group consisting of a single bond, an alkylene group, an alkenylene group, an alkynylene group, an arylene group, -O-, -S-, -NR a- , an ester bond, a thioester bond, an amide bond, a thioamide bond and a sulfonyl group. Represents one type of divalent group or bond, or a combination of two or more of these divalent groups or bonds.
Ra represents a hydrogen atom or a substituent and represents
Z represents a hydroxy group, an alkoxy group or an alkyl group.
m is an integer in the range of 1 to 3.
In general formula 2,
m is 1 and X represents an alkenyl group or a heterocyclic group, or m is 2 or 3 and a plurality of Xs contained in the general formula 2 independently form an alkenyl group or a heterocyclic group. The radio wave absorber according to claim 14.
In general formula 2,
m is 1 and X represents an acyl group, an acrylamide group or a heterocyclic group, or m is 2 or 3 and a plurality of Xs contained in the general formula 2 are independently acyl groups and acrylamides, respectively. Represents a group or heterocyclic group
The acyl group is a (meth) acryloyl group and
The radio wave absorber according to claim 14, wherein the heterocyclic group is an epoxy group.
The radio wave absorber according to claim 14, wherein in the general formula 2, X represents a heterocyclic group, and the heterocyclic group is an epoxy group.
The radio wave absorber according to claim 17, wherein L in the general formula 2 contains an alkylene group having 4 to 12 carbon atoms.
One or more of the resins selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polytrimethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polylactic acid, polybutylene succinate, polyallylate, polycarbonate and polyester elastomer. The radio wave absorber according to any one of claims 11 to 18, which is the resin of the above.
Claims 11 to 19 wherein the resin is one or more resins selected from the group consisting of polyethylene naphthalate, polytrimethylene terephthalate, polybutylene naphthalate, polylactic acid, polybutylene succinate, polyarylate and polyester elastomer. The radio wave absorber according to any one of the above items.