CA1252284A - Magnetic powder core with organo-metal compound as coupling agent - Google Patents

Abstract

ABSTRACT
A powder core, used in a reactor or transformer connected to a semiconductor switching element, essentially consists of a powder of a soft magnetic metal or alloy or a mixture of these, an electrically insulating binder polymer for binding the powder, and a coupling agent of an organic metallic compound for coupling the powder and the binder polymer. The powder core has excellent frequency charac-teristics of magnetic permeability, a high magnetic flux density, and a small iron loss at high frequencies.

Description

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The present invention relates to a magnetic powder core in which electric insulation between magnetic powder particles is improved.

It is known to employ in electrical instruments such as electric power converting device, including devices for converting alternabing current to direct current, de-vices for converting alternating current having one fre-quency to alternating current having a different frequency, and devices for converting direct current to alternating current, such as so-called inverters, sem:Lconductor switch-ing elements, typically thyristors and transistors, and reactors for reducing turn-on stress in such semiconductor switching elements, reactors for forced commutation, reac-tors for energy accumulation, and matching transformers for matching these elements.

Iron cores used in such reactors or transformers are conventionally classified as follows:

(a) So called laminated iron cores produced by laminating thin electromagnetic steel plates or permalloy sheets with an insulating interlayer interposed there-between.

(b) So called dust cores obtained produced by ~!3

- 2 -a powder such as a carbonyl iron or permalloy powder with kaolin or a polymeric binder such as a phenol resin.
(c) So called ferrite cores produced by sintering an oxide magnetic material.
Such iron cores used in reactors or transformers which are connected to the semiconductor switching elements must satisfy specific magnetic property requirements. For example, such an iron core must have good frequency characteristics of magnetic permeability, high magnetic f:Lux density, and small iron loss at high frequencies. Especially when a semiconductor switching element is operated, in addi-tion to a current having a period of a switching frequency, a current having a frequency component which is far higher than the switching frequency, e.g., several tens of kilohertz to 500 kHz or higher, may flow in the iron core. In view of these, the iron core must definitely have good characteristics in a 2û high-frequency range.
Of the three types of iron cores, although laminated iron cores exhibit excellent electrical characteristics within a commercial frequency range, they are subject to a large iron loss within a high-frequency range. In particular, in a laminated iron core, the eddy current loss increases in proportion to a square of the frequency. Furthermore 9 with an ~2~

increase in the depth from the surface of the plate or sheet material constituting the iron core, the magnetiz-ing force is less subject to changes due to the skin effect of the iron core material. Therefore, the laminated iron core can only be used at a magnetic flux density which is far lower than a saturated magnetic flux density of the laminated iron core material in a high-frequency range. The laminated iron core also has a very large eddy current loss.
In addition to the above disadvantages, laminated iron cores have a very low e~ective magnetlc permeability at high frequencies as compared to an effective magnetic permeability within a commercial frequency range.
When a laminated iron core having these problems is used for a reactor or transformer connected to a semiconductor switching element through which a high-frequency current flows, the iron core itself must be rendered large so as to compensate for the low effective magnetic permeability and magnetic flux density. When the iron core is thus rendered large, the iron loss of the iron core is increased, and the length of the coil windings wound around the iron core is also increased, thereby increasing copper loss.
Dust cores, as the second type of iron core described above, are also conventionally used as iron 5~

cores. For example, Japanese Patent Registration No.
112,235 registered September 10, 1935 to Minister of Posts and Telecom~unications, discloses the manufacture of a dust core for use as an iron core by compressing and forming a mixture of an iron powder or an iron alloy powder with an organic or inorganic binder and heating the formed mixture.
However, a dust core prepared in this manner generally has a low magnetic flux density and a low magnetic permeability. Even a dust core prepared using a carbonyl iron powder having a relati~ely high magnetic flux density has a magnetic flux dens:Lty at a magnetizing Eorce of 10,000 A/m of slightly higher than O.lT and a magnetic permeability of about 1.25 x 10 H/m. Therefore, in a reactor or transformer using such a dust core as an iron core material, the iron core must be rendered large in order to compensate for a low magnetic flux density and a low magnetic permeabllity. With such an increase in the size of the iron core, the coil windings become longer, also resulting in a large copper loss of the reactor or transformer.
Ferrite cores, as the third type of iron core, are frequently used for small electric equipment and have a high specific resistance and relatively good high-frequency characteristics. However, a ferrite core hasa low magnetic flux density of about 0.4T at a magnetizing force of 10,000 A/m~ In addition to this, the permeability and the magnetic density of the same .. . .
~ ' magne-tizing force change by several tens of percentage points over the temperature range of -~0 to +120C, to which the iron core may be exposed in use. Thus, when a ferrite core is used in a reactor or transformer connected S to a semiconductor switching element, the core must be enlarged to compensate for the low magnetic flux density, resulting in the same problem as with the two other types of iron cores.

~urthermore, since ferrite is a sintered body, the manuEacture of a large core from Eerrite is diEicult.
For -this reason, it is diEficult to use a Eerrite core for harldling high power. Due ko the longer coil ~indings and larger copper loss owing to low magnetic flux density and the great temperature dependencies of magnetic permeability lS and magnetic flux density, a ferrite core used in a reactor or transformer is subject to great variations in character-istics. Compared with electromagnetic steel laminations, it has a higher magnetostriction and generates more noise from the core.

It is an object of the present invention to pro-vide a magnetic powder core suitable for use in a reactor or transformer connected to a semiconductor switching element.

It is another object of the present invention to provide a powder core whose magnetic permeability can exhibit good frequency characteristics, and which can have '~

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high magnetic flux density and small iron loss at high frequencies.

The magnetic powder core of the present invention essentially consists of:
(a) a magnetic powder of a soft magnetic metal or alloy, or a mixture thereof;
(b) an electrically insulating polymer for bind-ing the powder; and (c) an organometallic coupling agent coupling the powder and the polymer.

In the second aspect, the present invention is directed to a powder core manufactured by compressing and forming the above-mentioned constituents and heating the formed constituents to a sufficient temperature to cure the polymer.

When the core further con-tains a powdered inor-ganic compound having an electrical insulating property, the forming or packing density of the powder core can be in-creased, and at the same time the effective electrical resistance against currents induced by AC magnetization of the powder core can be improved.

This invention can be more fully understood from .

the following detailed description when taken in conjunction with the accompanying drawings, in which:
Fig. 1 is a representation showing a state wherein a titanium coupling agent is bonded to the surFaces of the magnetic powder particles:
Fig. 2 is a representation showing a state wherein a silane coupling agent is bonded to the surfaces of the magnetic powder particles: and Figs. 3 to 7 are graphs showing changes in eP~ective magnetic permeabil:Lty within a high-freqùency range o-F an iron core of each Example of the present invention and of an iron core of each Comparative Example.
A magnetic powder used in the composition of the present invention is pure iron or alloys such as an Fe-Si alloy (e.g., Fe-3% Si), an Fe-AQ alloy, an Fe-Si-AQ alloy, an Fe-Ni alloy such as a permalloy, or an Fe-Co alloy. An amorphous magnetic alloy consisting of at least one of Fe, Co, Ni and Nb, and at least one of Si, B and C can also be used.
The magnetic powder has a specific electrical resistance of from 10 ~-cm to several tens of micro-ohm centimeters. In view of this, in order to obtain satisfactory iron core material characteristics with an AC current including high-frequency components which would cause the skin effect, the magnetic powder must be formed into a fine powder to allow contribution to ~52~8 ~

magnetization from the surface right to the inside of each particle.
In an iron core w'nich is excited with a current having frequency components of up to several tens of kilohertz and which must therefore have good magnetic permeability characteristics up to such a frequency range, the magnetic powder preferably has an average particle size of 300 um or less. In an iron core excited with a current having frequency components exceeding 100kHz and which must therefore have good magnetic permeability characteristics up to such a frequency range, the magnetic powder preferably has an average particle size of 100 ~m or less. However, when the average particle size of the magnetic powder becomes as small as 10 ~m or less, it is hard to obtain an iron core from such a fine powder.
Furthermore, even if such a fine powder is compressed, a satisfactory density of the resultant iron core cannot be obtained with a compression pressure below 1,000 MPa.
This imposes a problem of a low magnetic flux density.
In view of this, the magnetic powder preferably has a particle size of 10 ~m or more.
The magnetic powder is preferably contained in the composition in an amount of 55 to 99% by volume. When the amount of the magnetic powder exceeds 99% by volume, the resin content as a binder becomes too small and the binding power of the iron core becomes weak. However, i2~

when the amount of the magnetic powder is below 55% by volume, the magnetic flux density at a magnetizing force of 10,000 A/m is lowered to an equivalent to that obtained with ferrite.
An electrically insulating polymer is used herein as a binder for binding each particle of the magnetic material. At the same time, the polymer serves to cover the surface of each particle of the magnetic powder to electrically insulate one particle from another, thereby providing a satisFactory and effective electrical resistance for an AC magnetization oF the ovcrall lron core. Such a binder may, ~or example, be an epoxy resin, a polyamide resin, a polyimide resin, a polyester resin, or a polycarbonate resin. Such polymers may be used singly or in an admixture of more than one. The polymer is preferably used in the amount of 0.7% by volume or more based on the total volume of the composition. When the amount of the polymer used is less than 0.7% by volume, the binding force of the iron core is deteriorated.
A coupling agent used herein serves to improve wettability and adhesion between the magnetic powder and the binder resin. Due to these effects, the binder resin is introouced well between the magnetic powder particles to improve electrical insulation. Conse-quently, the iron loss of the iron core is reduced and the releasing force of the compressed body from the mold ~22~3~

can be low.
Examples of the coupling agent which may be used herein preferably include a titanium coupling agent, a silane coupling agent, an aluminium coupling agent but may also include an indium coupling agent or a chromium coupling agent. Among these, a Ti, silane or QQ coupl-ing agent having a particularly good adhesion force with the magnetic powder is particularly preferable.
The Ti coupling agent has the following general formula:
Rm -Ti ~Xn wherein R is a group which is easily hydrolyzed, X is a lipophilic group which is not easily hydrolyzed, and m and n are positive integers. Since Ti has a coordination number of 4 or 6, m+n must be 4 to 6 and m must fall within a range of 1 to 4.
The group R which is easily hydrolyzed is a monoalkoxyl group, a hydroxyacetic acid residue, or an ethylene glycol residue. Such a group R readily reacts with water adsorbed in the surface of each magnetlc power particle at room temperature to be hydrolyzed.
Then, as shown in Fig. 1, for example, Ti atoms of the Ti coupling agent are strongly bonded to the surface of a magnetic powder 1 through oxygen atoms 0. The group X
is one or several lipophilic groups including hydrocarbon moiety. The group X does not react with the hydroxyl group on the magnetic powder surface and has ~25~Z~3~

good wettability and adhesion with the binder polymer which is an organic material.
Examples of such a Ti coupling agent are enumerated below:
~ isopropyltriisostearoyl titanate CH3 - CH - O - Ti ~ O - C - C17H35]3 ~ dicumylphenyloxyacetate titanate CH2 o f ~ CH3 2 ~ 4-aminobenzenesulfonyl dodecylbenzenesulfonyl ethylene titanate O - S --~ N H 2 CIH2 - ~ Ti/
CH2 - 0 / \' O - S ~C12H25 ~ isopr~opyl tri(N-aminoethyl-amino-ethyl)tltanate CH CH - O - Ti ~0 - C2H4 - NH C2 4 2 3 tetraoctyl bis(ditridecylphosphite)titanate (C8H17 - O ~ Ti ~ [P - ( ~ Cl3H27)2oH]2 tetra(2,2-diallyloxymethyl-1-butyl)bis~di-tridecylphosphite)titanate ~CH -O-CH -CH=CH ) 1 2 2 2 2 Ti-[P~o-cl3H27)2oH]2 These Ti coupling agents are available from Kenrich Petrochemical Co., U.S.A..
The silane coupling agent has the Following general Formula:

( I H3)3-n (RO)n - Si - X

wherein RO is an alkoxyl group, and X is an organic functional group. Since Si has a coordination number of 4, n is 2 or 3. The alkoxyl group RO may be a methoxyl group or an ethoxyl group. The RO group is hydrolyzed by water adsorbed in the magnetic powder sur~ace or in air to produce a silanol group -SiOH.
Then, as shown in Fig. 2, for example, silicon atoms Si o~ the silane coupling agent are strongly coupled to the sur~ace o~ the magnetic powder 1 through oxygen atoms 0.
The organic functional group X may be an epoxy group, a methacryl group or an amino group and has good wettabllity and adhesion with the binder polymer.
Examples of such a silane coupling agent are _ 13 -enumerated below-~-glycidoxypropyl trimethoxysilane CH2CHCH20(CH2)3 - Si-~OCH3)3 o ~-(3,4-epoxycyclohexyl)ethyltrimethoxysilane ~ CH2CH2 - Si ~OCH3)3 ~ y~aminopropyl triethoxysilane H2NtCH2)3 - Si - tOC2H5)3 ~ N-~taminoethyl)-~-aminopropyl methylcllmethoxy-silane H CH

H2 CH2CH2 (CH2)3 ( 3)2 These silane coupling agents are available from Union Carbide Co., U.S.A..
~ The AR coupling agent has the following general formula:
(RO)n-AQ~X3-n wherein R0 is an alkoxyl group, and X is a lipophilic group including a hydrocarbon moiety. The R0 group may be a methoxy group, an ethoxy group, an isopropoxyl group, or a secondary butoxy group. The R0 group is hydroly7ed by water in the air or water adsorbed in the magnetic powder surface and can therefore be coupled to the surface of the magnetic powder through oxygen atoms 0 of the coupling agent. AQ generally has a coordina-tion number of 3, and so n is 1 or 2. However, an another part of the lipophilic groups X are at times weakly coupled to aluminum atom which then has a pseudo coordination number of 4. In this case, the coupling agent is less subject to decomposition and is preferable.
An example of such an ~ coupling agent is ethylacetoacetate aluminum diisopropylate having the structural Pormula:

ICH3 /--C~

(CH3 - CH - 0) - AQ CH
2 0 = C

According to the present invention, the coupling agent is preferably contained in the amount of 0.3% by volume based on the total volume of the composition.
When the amount of the coupling agent is less than 0.3%
by volume, the polymer cannot completely surround the magnetic powder particles, resulting in poor insulation and an unsatisfactory reduction`in iron loss.
The composition of the present invention may further contain a powder of an inorganic compound. The inorganic compound particles serve to reduce the friction between the magnetic powder particles during formation of the iron core so as to increase the forming density of the iron core. The inorganic compound particles are also present between the conductive magnetic powder particles to increase the effective electrical resistance for the AC magnetization of the overall iron core, thereby reducing iron loss. Such an inorganic compound may be calcium carbonate, magnesium carbonate, magnesia, silica, alumina, mica and various types of glass. A selected inorganic compound may not react with the magnetlc powder or binder polymer described above.
The average particle size of the inorganic compound is preferably smaller than that of the magnetic powder particles in considera-tion of providing good dispersion and iron core material characteristics and is preferably 20 ~m or less.
The inorganic compound is preferably contained in the amount of 0.3 to 30% by volume based on the total volume of the composition. When the amount of the inorganic compound is less than 0.3% by volume, a desired effect cannot be obtained by addition of this compound. ~lowever, when the amount of the inorganic compound exceeds 30% by volume, the resultant iron core has a poor mechanical strength.
A method of manufacturing an iron core from the composition of the present invention will be described i2~
_ 16 -below.
First, a magnetic powder and a coupling agent are mixed together with or without dissolving the coupling agent in a suitable solvent thereof such as isopropanol, toluene, or xylene. Upon this step, the surface of the magnetic powder is covered with the coupling agent.
Next, a binder polymer is added to the mixture and the resultant mixture is well s-tirred.
In the mixing step described above, three compo-nents i.e., the magnetic powder, the binder polymer and-the coupling agent can be well mixed simultaneously.
Also, the magnetic powder can be mixed with a mixture o~`
the binder polymer and the coupling agent.
A mixture containing a powder of an electrically insula-ting inorganic compound can be prepared by various methods including a method of mixing a magnetic powder and a powder of an inorganic compound and then sequentially adding a coupling agent and a binder polymer to the mixture: a method of simultaneously adding all of a magnetic powder, a powder of an inorganic compound, a binder polymer, and a coupling agent; and a method of dispersing a powder of an inorganic compound in a binder polymer before mixing it with other components. Although any such method can be adopted, a better effect is obtained if a powder of an inorganic compound is dispersed in a binder polymer before mixing it with other components.

The resultant mixture is charged in a mold and compressed in accordance with a conventional method to prepare a formed body having a desired shape. The formed body is heat-treated for curing the polymer, as needed, thereby manufacturing an iron core.
_xamples_ Although the present invention will be described by way of examples below, it is to be understood that the present invention is not limited thereto.
Examples Nos. 1 - 25 A rnagnetic powder, a binder polymer, a Ti coupling arJent, and when applicable, a powder o~ an inor~ar~ic compound were well mixed. The resultant mixture was charged into a mold and compressed at a pressure of 600 MPa. After the compressed body was released from the mold, it was heat-treated to prepare an iron core.
In each case, the powder of the inorganic compound was dispersed in the binder polymer before mixing it with other components except for that of Example No. 24. In the iron core of Example No. 24, all the components were mixed simultaneously, The heat-treatment was performed at 160 to 200C ~or 0,5 to 2 hours for the iron cores which used an epoxy resin as a binder polymer and at 160C for 15 minutes for the iron cores which used a polyamide resin as a binder polymer.
The mixing ratios of the respective components used are shown in Tables 1 to 4 below.

Iron cores of Comparative Example Nos. 26 to 40 were prepared following the same procedures as those of Examples except that no coupling agent was contained or only a small amount of a coupling agent was contained in the compositions of these Comparative Examples.
Annular samples of the obtained iron cores were subjected to measurements of magnetic properties such as iron loss within a frequency range of 50 Hz to 200 kHz, magnetic permeability and effective permeability within a D0 voltage frequency of up to lO MHz and magnetic flux density.
0~ the obtained measurement results, Tabl~s l to 4 show only iron loss at 50 kHz and lO0 kHz at a typical magnetic flux density: B = 0.05T.
The releasing force for releasing the formed body from the mold in a step of compressing a columnar iron core having a diameter and a height of 20 mm was also measured.

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(1) In Example Nos. 1 7 and Comparative Example Nos. 26 to 29, the iron loss was measured while the composition, the average diameter and the mixing ratio of the magnetic powder were kept the same but the mixing ratios of the binder polymer, the Ti coupling agent, and the powder of an inorganic compound (CaC03) were varied.
As a result of these measurements, there was no great difference in the iron loss at 50 Hz in a commercial frequency range. However, regarding the iron loss at 50 k~lz and 100 kHz within a high-frequency range, as can be seen From Table 1 above, the lron cores of Example Nos. 1 to 7 in which the Ti coupling agent was added in the amounts of 0.3% or more had smaller iron losses than those of Comparative Example Nos. 26 to 29. At 200 kHz, the iron core of Example No. 3 had an iron loss of 1,170 W/kg, while that of Comparative Example No. 28 had an iron loss of 4,060 W/kg, revealing a greate~ difference. Note that the Example wherein a portion of the binder polymer was replaced with CaC0}
had a still smaller iron loss.
The difference in the iron loss within a high-frequency range including 50 kHz and 100 kHz in the Example and Comparative Example is an eddy current loss difference and is attributable to the electrical insulation state between the magnetic powder particles.
This reveals the fact that the iron cores of the present invention have an excellent electrical insulating property Fig. 3 shows the results obtained with the measurement of an effective permeab;lity at respective frequencies (40 kHz to l~000 kHz). Curve a in Fig. 3 corresponds to Example No. 3, while curve b corresponds to Comparative Example No. 28. The effective permeability of the iron core of Example No. 3 remained substantially the same over a wide frequency range of 40 kHz to l,00~ kHz. In contrast to this, in the iron core of Comparative Example No. 28 which did not contain a Ti coupllrlg agent, the e~fective permeabillty is significantly lowered in a high-~requency range.
A similar tendency is seen between the iron core of Example No. 5 which contained CaC03 and the iron core of Comparative Example No. 29 which did not. Such a low eddy current means a low effective permeability within a high-frequency range.
Using the samples of the iron cores of Example No. 3 and Comparative Example No. 28, the releasing force from a mold for forming a formed body of the same shape and size was measured. The releasing force was 500 kg or less in Example No. 3 and was as high as 1,500 to 2,000 kg in Comparative Example No. 28. This fact revealed the facts that the addition of a Ti coupling agent can reduce the releasing force of a formed body from a mold to allow easy formation, and prevent damage to the formed body being released from the mold, thereby i ~L~25:~2~3~

improving the manufacturing yield.
The iron core samples of Example Nos. 1 to 7 all had magnetic flux densities of û.6T or higher at a magnitizing Force of 10 000 A/m.
(2) The iron loss was measured for the iron cores of Example Nos. 8 to 14 wherein the mixing ratio of the magnetic powder was varied within the range of 55.0 to 98.4% and a Ti coupling agent was added and for those of Comparakive Example Nos. 30 to 35 wherein the mixing lû ratio of the magnetic powder was also varied within a range of 6~.0 ~o 98 ~% and a Ti coupling agent was flOt used. The obtained results are shown in Table 2 above.
As can be seen from Table 2, when a comparison is made between the samples cbntaining the same amount of magnetic powder, the iron cores of the Examples have a smaller iron loss, and a difference in iron loss between the Examples and Comparative Examples is enhanced at a frequency of 100 kHz. A particularly large difference in iron loss was seen between Example No. 10 and Comparative Example No. 32 in both of which a CaC03 powder was added as a powder of an inorganic compound and between Example No. 12 and Comparative Example No. 34 in both of which an SiO2 powder was added as a powder of an inorganic compound.
The iron cores of these Examples exhibit magnetic flux densities of O.5T or higher at a magnetizing force of lO OOû A/rn. However, in Example No. 14 in which -the ~252~

mixing ratio of the magnetic powder was less than 60%~
although the iron loss was small, the magnetic flux density at a magnetizing force of 1~,000 A/m was 0.4T or less.
(3) The iron loss was measured for the iron cores of Examples 15 to 18 wherein the composition of the magnetic powder was varied and a Ti coupling agent was added, and for those of Comparative Examples 36 to 39 wherein the composition of the magnetic powder was simi-larly varied but a Ti coupling agent was not added. The obtained results are shown in Table 3. The iron cores o~ the Examples have smaller lron loss than the iron cores of the Comparatlve Examples at 50 kHz and 100 kHz At 200 kHz, the iron core of Example No. 16 had an iron loss of 869 W/kg, that o~ Comparative Example No. 37 had an iron loss of 4,840 W/kg, that of Example No. 18 had an iron loss of 690 W/kg, and that of Comparative Example No. 39 had an iron loss larger than 1,400 W/kg.
Fig. 4 is a graph showing changes in effective permeability in a frequency range of 40 kHz to 1,000 kHz.
Curve c in Fig. 4 corresponds to Example No. 1~, and curve d corresponds to Comparative Example No. 37.
Although the iron core of the Example experiences substantially no decrease in effective permeability in a high-frequency range, the iron core of the Comparative Example experiences a substantial decrease in effective permeability within a frequency higher than 100 kHz.
!

~æ~22~

- 31 ~

This also applies to Example No. 15 and Comparative Example No. 36, Example No. 17 and Comparative Example No. 38, and Example No. 18 and Comparative Example No. 39.
The iron cores of Example Nos. 15 to 18 all had magnetic flux densities of 0.6T or higher at a magnetizing force of 10,000 A/m.

(4) The iron loss was measured for -the iron core of Example Nos. 19 to 22 wherein the average diameter of the magnetic powder was varied, those o~ Example Nos. 23 and 24 where.~n ~Q23 was used and was added in d.~f~erent orders, and for those of Example No. 25 and Comparative Example No. 40 wherein a polyamide resin was used as a binder polymer. The obtained results are shown in Table 4.
It is seen from the results obtained that the iron loss in a high-frequency range decreases with a decrease in an average diameter of the magnetic powder. However, the change in iron loss with changes in particle size was very small near a commercial frequency range. The iron loss of Example No. 23 wherein AQ203 was dispersed in an epoxy resin before mixing it with other components had smaller iron loss and better characteristics than those of the iron core of Example No. 24 wherein AQ203, a magnetic powder, a Ti coupling agent, and an epoxy resin were mixed simultaneously.
When a polyamide resin was used as a binder polymer, the iron core of Example No. 25 in which a Ti coupling agent was added had a smaller iron loss than that of the iron core of Comparative Example No. 40 wherein no such Ti coupling agent was added.
The iron cores of these Examples had magnetic flux densities of 0.6T or higher at a magnetizing force of 10,000 ~/m.
Exa_ple_Nos._41 - 6~
Iron cores were prepared ~ollowing -the same procedures as ~hose in Example Nos. 1 to 25 using the compos.ltions shown :In Tables 5 to ~ below.
Except for Example No. 59, the powder o~ an inorganic compound used was dispersed in a binder polymer before mixing it with other components. In Example No. 59, all the components were mixed simultaneously.
The heat-treatment conditions, and measurement conditions for the magnetic properties such as iron loss, effective permeability, or magnetic flux density and releasing force from a mold were performed under the same conditions as those in Example Nos. 1 to 40 described above.

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(1) The iron loss was measured for the iron cores of Example Nos. 41 to 45 and Comparative Example Nos. 61 to 64 wherein the composition, average particle size~
and mixing ratio of the magnetic powder were kept the same, while the mixing ratios of the binder polymer, the silane coupling agent, and the powder of the inorganic compound (CaC03) were varied. The obtained results are shown in Table 5.
Each sample had substantially the same iron loss at 50 Hz in a commercial frequency range. However, at 50 k~lz and 100 kHz in a high-frequency range, the Iron loss of Example Nos. 41 to 45 in which the silane coupl-ing agent was added in the amounts of 0.3% or more was smaller than that of Comparative Example Nos. 61 to 64 wherein the silane coupling agent was added in amounts less than 0.3%. Particularly at 200 kHz, the iron core of Example No. 43 had an iron loss of 1,290 W/kg while that of Comparative Example No. 63 had an iron loss o~
4 7 060 W/kg. Thus, the higher the frequency, the greater the difference in the iron loss of iron cores of the Example and Comparative Example. An iron core wherein a portion of the binder polymer is replaced with CaC03 had a still smaller iron loss.
Fig. 5 is a graph showing changes in effective permeability within a frequency range of 40 kHz to 1,000 kHz. Curve e in Fig. 5 corresponds to Example No 43, while curve f corresponds to Comparative Example No. 63. As can be seen from this graph, the iron core of Example No. 43 experiences substantially no change in effective permeability within a wide frequency range.
However, in the iron core of Comparative Example No. 63 wherein no silane coupling agent is used, the effective permeability significantly decreased within the high-frequency range. The effective permeability was measured up -to a high-frequency range for the iron cores of Example No. 45 and Comparative Example No. 64 in both of which CaC03 was added. Q similar tendency as that shown :in Fig, 5 ~as also observed, The releaslng force of a formed body from the mold was measured for Example No. 43 and Comparative Example No. 63. The iron core of Example No. 43 required a ; 15 releasing force of 700 kg or less, and that of Comparative Example No. 63 required a releasing force of 1,50û to 2,000 kg.
The iron cores of Example Nos. 41 to 45 had magnetic flux densities of 0.6T or higher at a magnetizing force of 10,000 Q/m.
(2) The iron loss was measured for the iron cores of Example Nos. 46 to 51 wherein the mixing ratio of the magnetic powder was varied within a range of 55.0 to 98.4% and a silane coupling agent was added, and for the iron cores of Comparative Example Nos. 65 to 69 wherein the mixing ratio of the magnetic powder was varied within a range of 64.0 to 98.4% and no silane coupling I

~ 41 -agent was added. The obtained resu:Lts are shown in Table 6.
As can be seen from Table 6, when a comparison is made between iron cores having the same mixing ratio of the magnetic powder, iron cores of the Examples have a smaller iron loss than those of the Comparative Examples. The difference in iron loss is particularly enhanced at 100 kHz. With iron cores of the Examples containing an SiO2 or CaC03 powder as a powder o-f an lnorgan:ic compound, they have conslderably smaller iron loss than those oF the Comparative Example having the same magnetic powder mixing ratio.
The iron cores of these Examples have magnetic flux densities of 0.5T or higher at a magnetizing force of 10,000 A/m. However, in Example No. 51 wherein the mixing ratio of the magnetic powder is less than 60%, although the iron loss is small, the magnetic flux density at a magnetizing force of 10,000 A/m was 0.4T or less.
(3) The iron loss was measured for the iron cores of Example Nos. 52 to 54 wherein the magnetic powder composition was varied a~d a silane coupling agent was added, and for those of Comparative Example Nos. 70 to 72 wherein the composition of the magnetic powder was similarly changed but no silane coupling agent was ; added. The obtained results are shown in Table 7. As can be seen from this table, the iron cores of the present invention had smaller iron loss at 50 kHz and 100 kHz. In particular, the iron core of Example No. 53 had an iron loss of 1,010 W/kg at 200 kHz. However, at the same frequency, the iron core of Comparative Example No. 71 had an iron loss of 49840 ~/kg, providing a big difference from tha-t of the Example.
Fig. 6 is a graph showing changes in effective permeability within a frequency range of 40 kHz to l,ûO0 kHz. Curve g in Fig. 6 corresponds to Example No. 53, and curve h corresponds to Cornparative Example No. 71. The iron core o~ the present invention experienced substantlally no decrease in effective permeability even within a high-frequency range.
However, the iron core of the Comparative Example 71 underwent a significant decrease in effective permeability at frequencies above 100 kHz. This substantially applied to Example No. 52 and Comparative Example No. 70, and Example No. 54 and Comparative Example No. 72.
The iron cores of Example Nos. 52 to 54 had magnetic flux densities of 0.6T or higher at a magnetizing force of 10,000 A/m.
(4) The iron loss was measured for the iron cores of Example Nos. 55 to 57 wherein the average diameter of the magnetic powder was varied, the iron cores of Example Nos. 58 and 59 wherein the addition timing of AQ203 was varied, and the iron cores of Example No. 60 .

and Comparative Example No. 73 wherein a polyamide resin was used as a binder polymer. The obtained results are shown in Table 8.
It is seen from the obtained results that a change in iron loss due to changes in particle diameter is small near a commercial frequency range, but the smaller the average diameter of the magnetic powder the smaller the iron loss in a high-frequency range.
As ~or the time to add a powder o-f an inorganic compound, the iron core o~ Example No. 58 wherein AQ203 was dispersed ln the epoxy resin had a smaller .iron loss than that of the iron core of Example No. 59 wherein AQ203, the magnetic powder, the silane coupling agent, and the epoxy resin were mixed together simultaneously.
When a polyamide resin is used as a binder polymer, the iron core of Example No. 60 in which a silane coupling agent was added had a smaller iron loss than that of Comparative Example No. 73 wherein no silane coupling agent was added.
2û The iron core of these Examples had excellent magnetic flux densities of 0.6T or higher at a magnetizing force of 10,000 A/m.
Example Nos 61 62 ___ _ .
Iron cores were prepared following the same procedures as those in Example Nos. 1 to 25 and using the components shown in Table 9. The powder of an inorganic compound was dispersed in a binder polymer.

~L%5~

The heat treatment conditions, and rneasurement conditions for magnetic properties such as iron loss, effective permeability, and magnetic flux density, and a releasing force from a mold were the same as those in Example Nos. 1 to 25. The obtained results are shown in Table 9.

2~

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. __ 1 A comparison was made between Example Nos. 61 and 62 and Comparative Example Nos. 63 and 64 shown in Table 5 above. As a result of such a comparison, the iron loss at 50 Hz was seen to be substantially the same for all these iron cores. However, at 50 kHz and 100 kHz in a high-frequency range, the iron core of Example No. 61 had a smaller iron loss than that of Comparative Example No. 63. The difference in iron loss between these iron cores is particularly notable at 100 kHz. The iron core of Example No. 62 wherein a powder oF an inorganic compound was adcled had a still smaller iron loss.
Fig. 7 shows changes in e~fective permeability within a frequency range of 40 to 1,000 kHz. Curve i in Fig. 7 corresponds to Example No. 61, and curve f corresponds to Comparative Example No. 63 and is the same as the curve in Fig. 5. The iron core of Example No. 61 experiences substantially no change in effective permeability over a wide frequency range. The iron core of Example No. 62 in which CaC03 was added and that of Comparative Example No. 64 had the same tendencies as that in Fig. 7.
The releasing force of a formed body from a mold after formation was measured for the iron cores of Example No. 61 and Comparative Example No. 63. The iron core of Example No. 61 required a releasing force of only 700 kg or less, which was less than half that of Comparative Example No. 63.

2 ~

The iron cores of Example Nos. 61 and 62 both had magnetic flux densities of 1.0T or higher at a magnetizing force of 10,000 A/m.
In addition to the iron cores described above, another iron core was prepared using as a magnetic powder a powder of an Fe-Si-AQ alloy called cendust having an average diameter of 73 ~m, a polycarbonate resin as a binder polymer, a~d a Ti coupling agent.
This iron core had an iron loss at 100 kHz of about 1/3 of an lron core prepared similarly but without addition of the Ti coupling agent.
Still another iron core was prepared in accordance with a conventional method using powders of an Fe-Co alloy and an Fe-Si-B amorphous alloy and mixing them with a binder polymer and a coupling agent. The resultant iron core had a very small iron loss within a high-frequency ranye of 50 kHz or higher, a small efFective permeability within the high-frequency range, and a very low releasing force from a mold after compression and formation therein.
As can be seen from the above description, when a powder core is manufactured from a magnetic powder composition of the present invention, the surface of each magnetic powder particle is covered with the coupling agent. Owing to the lipophilic function of the coupling agent, the binder polymer has a good wettability, dispersibility and bindability with respect . , ~2~a~
- ~18 -to the magnetic powder. Of iron loss, an eddy current loss component increases in proportion to a square of the frequency, and most of the iron loss in a high-frequency range is attributed to the eddy current loss.
However, since the iron core of the present invention has an excellent electric insulating property due to the presence of the binder polymer between the adjacent magnetic powder particles, the iron loss due to an eddy current 105s component can be reduced. Furthermore, since the iron core of the present invention has a small iron loss in a high-~requency ranye, heat generation is suppressed, a decrease in e~fective permeability is not experienced, and a high magnetic flux density can be maintained. In addition to these advantages, the releasing force from the mold after compression can be small, and the workability is improved.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A magnetic powder core comprising 55% to 99 by volume of a powder of a soft magnetic metal or alloy, or a mixture of these, the powder having an average particle size of 10µm to 300µm; an electrically insulating binder polymer for binding the powder; and at least 0.3%
by volume of an organo-metallic coupling agent for coupling the powder and the binder polymer, and selected from the group consisting of a titanium coupling agent, a silane coupling agent, an aluminum coupling agent, an indium coupling agent and a chromium coupling agent.

2. A core according to Claim 1, hwerein the coupling agent comprises a titanium coupling agent having a general formula:

Rm-Ti-Xn wherein R is a group which is readily hydrolized, X is a lipophilic group which is not readily hydrolized, and m and n are positive integers satisfying 4 < m+n < 6 and 1 <
m < 4.

3. A core according to Claim 1, wherein the coupling agent is a silane coupling agent having a general formula:

wherein RO is an alkoxyl group, X is an organic functional group, and n is 2 or 3.

4. A core according to Claim 1, wherein the couplin agent is an aluminum coupling agent having a general formula:

(RO)n-A?-X3-n wherein RO is an alkoxyl group, X is a lipophilic group, and n is 1 or 2.

5. A core according to Claim 1, wherein the binder polymer is present in an amount of at least 0.7% by volume.

6. A core according to Claim 1, further comprising a powder of an electrically insulating inorganic compound.

7. A core according to Claim 6, wherein the powder of the inorganic powder is present in an amount of 0.3 to 30% by volume.

8. A powder core obtained by compressing and forming a magnetic powder composition into a predetermined shape and heat-treating the compressed composition at a sufficient temperature to cure the binder polymer, said magnetic powder composition comprising: 55% to 99% by volume of a powder of a soft magnetic metal or alloy, or a mixture of these, the powder having an average particle size of 10µm to 300µm; an electrically insulating binder polymer for binding the powder; and at least 0.3% by volume of an organo-metallic coupling agent for coupling the powder and the binder polymer, and selected from the group consisting of a titanium coupling agent, a silane coupling agent, an aluminum coupling agent, an indium coupling agent and a chromium coupling agent.