KR100653425B1 - Ferrite-polymer nanocomposite - Google Patents

Abstract

Provided is a ferrite-polymer nanocomposite, which has high permeability and low loss characteristics at the high-frequency zone and is applicable to electronic equipment such as high-frequency layered chip inductors, wire-wound inductors, transformers, converters, etc. The ferrite-polymer nanocomposite is obtained by dispersing conglomerate of soft magnetic ferrite nanopowder in polymer matrix. The soft magnetic ferrite is any one selected from Mn-Zn, Ni-Zn, Ni-Cu-Zn, Ni-Cu-Co-Zn, Ni-Co, Mg-Zn, Mg-Mn-Zn, Cu-Zn-based spinel ferrites, cobalt-substituted Y type and Z type hexagonal ferrites, and a mixture of two or more thereof. The polymer is any one selected from a thermoplastic resin, a thermosetting resin, and a mixture of two or more thereof. The thermoplastic resin is polyphenylene sulfide, polyamide, polyethylene, polyimide, polysulfone, polyetherether ketone, polystyrene, etc. The thermosetting resin is epoxy resin, phenolic resin, polyimide, diarylphthalate resin, etc.

Description

Ferrite-Polymer Nanocomposites {FERRITE-POLYMER NANOCOMPOSITE}

1 is an electron micrograph showing the microstructure of the ferrite-polymer resin nanocomposites prepared according to the present invention.

2 is a frequency characteristic of a complex magnetic permeability real part μ ′ of a nanocomposite made of nanopowder agglomerates prepared with a ferrite powder content of 30% by volume according to the present invention and a composite made of an average particle diameter of 0.7 μm powder and 60 nm nanopowders. Is a graph.

Figure 3 is a frequency characteristic of the complex complex permeability imaginary μ˝ of nanocomposites made of nanopowder aggregates prepared with a ferrite powder content of 30% by volume according to the present invention and a composite made of a nanoparticle powder with an average particle diameter of 0.7 μm and 60 nm nanopowders. Is a graph.

Figure 4 is a graph showing the frequency characteristics of the complex real magnetic permeability μ 'of the composite made of nanoparticle aggregates prepared with a ferrite powder content of 45% by volume in accordance with the present invention and an average particle diameter of 0.7 ㎛ powder.

Figure 5 is a graph showing the frequency characteristics of the complex complex permeability imaginary μμ 의 of the nanocomposite made of nanopowder agglomerates prepared with a ferrite powder content of 45% by volume according to the present invention and a composite made of powder having an average particle diameter of 0.7 μm.

The present invention relates to a ferrite-polymer nanocomposite, and more particularly, to a new ferrite-polymer nanocomposite having improved microstructure to have improved high permeability and low loss characteristics up to the GHz band.

Ferrites with soft magnetic properties have long been used in electromagnetic components such as inductors, transformers, converters, and radio absorbers. However, the frequency of use of typical Mn-Zn ferrites or Ni-Zn ferrites is limited to several MHz or tens of MHz, respectively.

Recently, as the frequency band used in electronic circuits of communication equipment and portable equipment becomes high frequency, high frequency characteristics of component materials corresponding thereto are required.

Since it is known that the permeability of ferrite-polymer composites has higher frequency characteristics than that of ferrite sintered bodies in the high frequency region, many researchers have studied the ferrite-polymer composites. In the ferrite-polymer composite in which the ferrite powder and the polymer are mixed, the ferrite powder is not magnetically connected because the ferrite powder is dispersed and separated at the polymer base. Accordingly, it is well known that a demagnetizing field is generated on the surface of the ferrite powder so that the permeability of the ferrite-polymer composite is much lower than that of the experimental mixing law. For this reason, the permeability of ferrite-polymer composites has not been influenced by ferrite type or powder size.

A representative electromagnetic component using high frequency characteristics of ferrite-polymer composite is a radio wave absorber. That is, the ferrite-polymer complex has been used as a radio absorber in the GHz band for a long time by using a characteristic of high magnetic loss in the GHz band. However, the use of ferrite-polymer composites has been extremely limited in inductor materials requiring high permeability and low loss characteristics, but recently, they have started to be used as wirewound chip inductors and PCB embedded inductors.

Japanese Patent for Murata Composite Magnetic Material (Korean Patent No. 0349081- Japanese Patent No. 3551863, and Korean Patent No. 0385122- Japanese Patent No. 3449322) have a composite of ferrite powder and resin with winding chip inductor. Although it shows that it can be used up to GHz band, there is a problem that the permeability real part value is only 2.

Accordingly, an object of the present invention is to provide a magnetic material having a high permeability and a low loss characteristic up to the GHz band, and another object of the present invention is to use an electromagnetic device such as an inductor that can be used at high frequency and has excellent inductance characteristics using a composite magnetic material. To provide.

In order to achieve the above object, the present inventors have studied in various angles, when the composite is prepared by artificially agglomerated ferrite nanopowders to disperse magnetically connected aggregates in a polymer matrix, high frequency characteristics and high permeability characteristics appear simultaneously I found out. That is, by artificially contacting the ferrite powders magnetically when manufacturing the ferrite-polymer composite, it was possible to suppress the effect of reducing the magnetic permeability due to the anti-magnetic field generated on the surface of the powder.

In order to prepare such ferrite agglomerates, a conventional powder having a size of about 1 μm may be used to make the agglomerates, and not only high temperature is required but also the agglomerates themselves become too large to obtain the reduction effect. Found. As a result of intensive research by the present inventors, it was confirmed that a more enhanced effect can be obtained from the aggregates made of ferrite nanopowders. In addition, when the ferrite-polymer composite is manufactured from agglomerates made of nanopowders, the high resonant frequency, which is a characteristic of the ferrite-polymer composite, is further increased by adding a high frequency characteristic, which is inherent in the nanostructure. This is because when the ferrite particles become nano-sized, they become a single magnetic domain and do not cause magnetic domain wall motion, but only spin rotation, thereby increasing the resonance frequency. to be. The present inventors confirmed that the ferrite nanopowder size for exhibiting such properties is effective at 200 nm or less, preferably 100 nm or less, and the size of the nanopowder aggregate is 1-50 μm, preferably 1-30 μm. It was.

The ferrite-polymer composite of the present invention is preferably a resin composition containing 10 to 90% by volume of ferrite powder and 90 to 10% by volume of polymer. If the volume of ferrite powder is less than 10%, the permeability of the composite is too low, and if more than 90%, there is a problem in the manufacturing process of the composite. In view of high permeability and high frequency characteristics, 20 to 80% by volume of ferrite powder and 80 to 20% by volume of polymer are preferred. As the ferrite powder content increases, the permeability increases but the high frequency characteristics decrease. As the ferrite powder content decreases, the permeability decreases but the high frequency characteristics improve, so the ferrite content may be selected according to a desired purpose.

As the soft magnetic ferrite of the ferrite-polymer nanocomposite according to the present invention, Mn-Zn-based, Ni-Zn-based, Ni-Cu-Zn-based, Ni-Cu-Co-Zn-based, Ni-Co-based, Mg-Zn-based, Various spinel type ferrites such as Mg-Mn-Zn type and Cu-Zn type, cobalt substituted Y type and Z type hexagonal type ferrites, and two or more kinds of mixed ferrites thereof were applicable. In addition, polymer resins usable in the present invention include polyphenylene sulfides, polyamides, polyethylenes, polyimides, polysulfones, polyetheretherkitones, polystyrenes, and the like, and thermosetting resins include epoxy resins, phenol resins, and polyimides. And diallyl phthalate resins.

The ferrite-polymer nanocomposite according to the present invention can be widely applied to electromagnetic devices such as stacked chip inductors, wound chip inductors, PCB embedded inductors, transformers, converters, and radio absorbers.

Next, the ferrite-polymer nanocomposite according to the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example  One

Ferrite-polymer nanocomposites were prepared by selecting Mn-Zn ferrite, a typical spinel-based ferrite, and epoxy resin, a representative thermosetting resin. Of Mn-Zn ferrite composition was selected as _{Mn 0 .53 Zn 0 .42 Fe 2} .05 O 4 represents the high permeability characteristics. Fe ₂ O ₃ , Mn ₃ O ₄ , ZnO powders are weighed in accordance with the above composition and mixed by ball milling. After drying, it is calcined at 1200 ° C. and milled again by ball milling. The average size of the ferrite powder ground for 24 hours was 0.7 μm. The powder was again milled for 54 hours to prepare nanopowders by mechanical grinding, and the average particle size was 60 nm. Thus prepared nano-powder was put in a mold and compacted to a mortar by heat treatment in 600 ℃-nitrogen atmosphere, to prepare an artificial nano-powder aggregates.

Three kinds of ferrite powders of average particle diameter 0.7㎛ powder, 60nm size nanopowder and nanopowder agglomerate are mixed well with polymer mixed with epoxy and curing agent, injected into toroid mold and cured. A polymer composite toroidal specimen was prepared. At this time, the volume ratio of the ferrite powder and the epoxy resin was 30:70. The toroid specimens were 7 mm in diameter and 3 mm in diameter, and the complex permeability was measured at a frequency of 0.1 to 10 GHz using the S-parameter method using a network analyzer.

Figure 1 is an electron micrograph showing the microstructure of the resin composite made of ferrite nanopowder aggregates. Here, it can be seen that ferrite aggregates of several tens to several micrometers are well dispersed in the epoxy resin. An enlarged photo of the inside of the white agglomerate (bottom left) shows that the ferrite nanopowders are in contact with each other and epoxy has penetrated the remaining gaps. An enlarged photo of the outside of the gray aggregate (bottom right) shows that not only the epoxy resin but also the nanopowders that were broken during mixing were mixed together.

Figures 2 and 3 show the frequency characteristics of the complex composite magnetic permeability μ 'and imaginary part μ 의 of the nanocomposite made of the nanopowder agglomerates prepared by the above method and the composite made of the nanoparticles with an average particle diameter of 0.7 μm and 60 nm as an example. The graph shown.

As the ferrite powder particle size becomes smaller from 0.7 µm to 60 nm, µ 'falls further. This is because the smaller the particle size is, the larger the surface area is, thereby increasing the permeability reduction effect due to the anti-magnetic field generated on the surface of the ferrite particles. However, the composite prepared from the nanopowder aggregates of the present invention was larger in size than the composite using a simple nanopowder (60 nm size), and it was shown to have a high frequency characteristic than the average particle diameter 0.7 ㎛ powder composite. This is due to the effects of the magnetic coupling and nanostructures between the powder particles described above, and is a key effect of the present invention.

As shown in the results of the permeability imaginary part of Figure 3 μμ of the composite prepared with nanopowder is the smallest, μ 에서는 of the composite prepared with the nanopowder agglomerates of the present invention above 1 GHz average particle diameter 0.7 ㎛ powder Greater than μ˝ of the complex, reversed below 1 GHz. This property means that composites made of nanopowder aggregates can be used as thinner wave absorbers above GHz. In addition, the μ 의 of the composite made of nanopowder aggregates appears to be close to zero up to about 500 MHz, which means that the loss is less, and therefore, it has lower loss characteristics than the powder composite having an average particle diameter of 0.7 μm.

Example  2

In Example 2, Mn-Zn ferrite powder was prepared in the same manner as in Example 1 to prepare an epoxy resin composite, but the ferrite powder content was increased to 45 vol%. When the ferrite powder content was increased, the viscosity was sharply increased when preparing the resin composite with the nanopowder, and thus the specimen was not manufactured and thus excluded from the comparison.

4 and 5 are graphs showing the frequency characteristics of the complex magnetic permeability real part μ 'and the imaginary part μ 의 of the nanocomposite made of the nanopowder agglomerates prepared by the above method and the composite made of the powder having an average particle diameter of 0.7 μm as a comparative example. In FIG. 4, as the ferrite powder content was increased, μ ′ of the composite was increased to 3 or more. In Fig. 5, as the ferrite powder content was increased, the μ 의 of the composite was also increased, but the characteristic difference between the nanocomposite made of the nanopowder aggregates and the composite made of the powder having an average particle diameter of 0.7 μm was clearly seen. That is, as the ferrite powder content increases, the μ 'of the composite made of powder with an average particle diameter of 0.7 μm increases, but the μ˝ of several hundred MHz also increases, so that the frequency of use decreases, but the μ˝ of the nanocomposite made of nanopowder aggregates decreases. It has been shown to have near zero loss characteristics up to 500 MHz. If sintered Mn-Zn ferrite sintered body is used to produce a resin composite with tens of micrometers of powder, the real permeability μ 'becomes larger, resulting in higher permeability characteristics. The use frequency of the furnace drops sharply.

As a result, it can be seen that the composite prepared from the Mn-Zn ferrite nanopowder aggregate prepared by the present invention exhibits high permeability and low loss characteristics up to about 1 GHz, which is a very innovative result. If you want more high frequency characteristics, you can use Ni-Zn ferrite or Mg-Zn ferrite. If you want more high frequency characteristics, use hexagonal ferrite. Those skilled in the art can obtain the desired physical properties by controlling the type of ferrite, powder content, powder particle size and the like according to the principles of the present invention. In addition, in the present invention, a mechanical grinding method was selected as a method for preparing ferrite nanopowder, which is made in consideration of manufacturing cost, and any nanopowder preparation method may be selected including chemical methods such as sol-gel, coprecipitation method, and hydrothermal synthesis method. There is no limit to this. Therefore, when manufacturing a finer ferrite nanopowder by a chemical method to produce a resin composite by the method according to the present invention, the high frequency, high permeability, low loss characteristics are further improved.

According to the present invention, a soft magnetic material having high permeability and low loss characteristics can be manufactured in the high frequency band up to the GHz band, and using this, a high frequency band stacked chip inductor, a wound chip inductor, a PCB built-in inductor, a transformer, a converter and a radio wave absorber It can be applied to an electromagnetic device such as.

Claims (6)

A ferrite-polymer nanocomposite in which agglomerates of soft magnetic ferrite nanopowders are dispersed in a polymer matrix. The method of claim 1, wherein the soft magnetic ferrite is Mn-Zn-based, Ni-Zn-based, Ni-Cu-Zn-based, Ni-Cu-Co-Zn-based, Ni-Co-based, Mg-Zn-based, Mg-Mn A ferrite-polymer nanocomposite, which is any one selected from -Zn-based and Cu-Zn-based spinel-based ferrites and cobalt substituted Y-type and Z-type hexagonal ferrites and two or more mixed ferrites thereof. The method of claim 1, wherein the polymer is a thermoplastic resin such as polyphenylene sulfide, polyamide, polyethylene, polyimide, polysulfone, polyether ether ketone, polystyrene, and the like, and epoxy resin, phenol resin, polyimide and di A ferrite-polymer nanocomposite which is any one selected from allyl phthalate resin and the like and two or more kinds of mixed polymers thereof. The ferrite-polymer nanocomposite of claim 1, wherein the ferrite nanopowder has a size of 200 nm or less, and the aggregate of the aggregated nanopowder has a size of 1 to 50 μm. The ferrite-polymer nanocomposite of claim 1, wherein the ferrite nanopowder content is 10-90 vol% and the polymer content is 90-10 vol%. Electromagnetic device using the ferrite-polymer nanocomposite according to any one of claims 1 to 5.

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