JPH11195520A - Dust core, ferromagnetic powder therefor and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the characteristics by adding titanium oxide sol and/or zirconium oxide sol and phenol resin to ferromagnetic metal powder, thereby allowing high temperature annealing. SOLUTION: To form a uniform insulating film having high flux density and high insulation, using a small quantity of ferromagnetic metal powder by adding microparticles of titanium oxide sol and/or zirconium oxide sol dispersed uniformly into a solvent. When phenol resin is added furthermore, molding strength is enhanced and insulation does not deteriorate even if annealing temperature is raised to 800 deg.C or thereabout. Consequently, strains generated at the time of pulverization or molding are released, hysteresis loss is reduced because coercive force of a dust core is decreased, and core loss is reduced because insulation is sustained and eddy current loss is decreased. Furthermore, heat resistance resin is cured through annealing to increase density of a green compact thus enhancing mechanical strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust core for use in magnetic cores such as transformers and inductors, motor cores, and other electromagnetic components, powder for the dust core, a method for manufacturing the dust core, and About.

[0002]

2. Description of the Related Art Conventionally, as a core of an inductance element for electronic equipment, a laminated silicon steel sheet core obtained by stacking punched silicon steel sheets has been frequently used. However, it is difficult to automate the production of the laminated core, and in particular, the core for a driving device such as a motor has a complicated shape, so that the material yield by punching is extremely low. In order to produce a shaped article, the number of processing steps is increased.

On the other hand, a so-called dust core in which a ferromagnetic metal powder is bound using a binder such as water glass is known. As the ferromagnetic metal powder, iron powder, permalloy powder, sendust powder and the like are known. Is used. The dust core is
Even if it has a complicated shape, it can be integrally formed and the material yield is substantially 100%, so that it is expected to be used as a substitute for a laminated core.

However, ferromagnetic alloy powders such as the above-mentioned permalloy powder and sendust powder have low coercive force but low magnetic flux density, and therefore must be used as a substitute for laminated silicon steel sheet cores conventionally used in drive equipment. Can not.

[0005] On the other hand, iron powders manufactured by various methods such as electrolytic iron powder and water atomized iron powder are commercially available, but all have a coercive force of 2 Oe or more, which is not low enough to compete with silicon steel sheets. Since gas atomized iron powder which can provide a coercive force of about 1 Oe is extremely expensive, it is not suitable for a substitute use of a laminated silicon steel sheet core.

Various proposals have been made for improving the characteristics of the dust core. For example, JP-A-62-72102 discloses that the oxygen content is 0.15 to 0.5% by weight and the average particle size is 40%.
An iron powder for a dust core having an average aspect ratio of 4 to 25 is described. According to the publication, an oxygen coating of iron particles plays a role of insulation between particles and reduces eddy current loss.
Oxygen content is relatively high to cover the high frequency band above MHz. However, in this publication, since a dust core is prepared using an epoxy resin as a binder, high-temperature annealing (annealing) for reducing coercive force cannot be performed, and hysteresis loss increases.

Japanese Patent Application Laid-Open No. Sho 61-824027 discloses, as examples, iron powder having an average particle size of 54 μm and titanium oxide powder having an average particle size of 0.3 μm, or an average particle size of 1 μm.
And the point that an iron core is obtained by adding the above-mentioned titanium oxide powder and press-molding. JP-A-63-260005 describes that a magnetic core is obtained by adding silicon oxide having a particle size of 1 μm or less to -200 mesh iron powder. However, these dust cores have (1) high core loss. (2) Since a large amount of insulating material is required for insulation, a high magnetic flux density cannot be obtained. (3) Since it cannot be annealed at a high temperature, there is a problem that distortion generated at the time of molding cannot be sufficiently alleviated and it is difficult to lower the coercive force.

In recent years, the size of electric and electronic devices has been reduced,
A compact and highly efficient dust core is required. The ferromagnetic metal powder can reduce the size of the core because of its high saturation magnetic flux density, but has the problem that eddy current loss increases because of its low electrical resistance. Therefore, an insulating film is usually formed on the surface of the ferromagnetic metal particles. In the manufacturing process of the dust core, annealing is usually performed in order to reduce distortion (stress) generated at the time of molding and lower the coercive force of the dust core. In order to sufficiently release the stress of the ferromagnetic metal particles, annealing at a high temperature is necessary. However, in the case of water glass or silicone resin conventionally used as an insulating material, the amount of resin reduced at a high temperature is large, so that annealing between ferromagnetic metal particles becomes insufficient when annealing is performed. As a result, the eddy current loss in the high-frequency region is significantly increased, the frequency characteristics of the magnetic permeability are deteriorated, and the core loss is increased, so that sufficient magnetic characteristics cannot be obtained.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a dust core which can be annealed at a high temperature, has a high magnetic flux density, a low coercive force and a low loss, and has a high mechanical strength and a ferromagnetic material therefor. An object of the present invention is to provide a method for producing a powder and a dust core.

[0010]

This and other objects are achieved by the present invention described below. (1) A ferromagnetic powder for a dust core in which a titanium oxide sol and / or a zirconium oxide sol and a phenol resin are added to a ferromagnetic metal powder. (2) The ferromagnetic powder for a dust core according to the above (1), wherein the phenol resin is a resol type phenol resin. (3) The phenol resin has a weight average molecular weight of 300
The ferromagnetic powder for a dust core according to the above (1) or (2), wherein the ferromagnetic powder is from -7000. (4) The ferromagnetic powder for a dust core according to any one of (1) to (3), wherein the phenol resin is added in an amount of 1 to 30 vol% with respect to the ferromagnetic metal powder. (5) The titanium oxide sol and / or zirconium oxide sol is used in an amount of 0.1 to 15 vol.
(1) The ferromagnetic powder for a dust core according to any one of (1) to (4), wherein (6) The ferromagnetic powder for a dust core according to any one of (1) to (5), wherein the titanium oxide sol and / or the zirconium oxide sol have an average particle size of 0.01 to 0.1 μm. (7) A dust core obtained by press-molding the ferromagnetic powder for dust core according to any one of the above (1) to (6). (8) A method for producing a dust core, which is subjected to a heat treatment at 500 to 800 ° C. after pressure molding to obtain the core of (7).

[0011]

The ferromagnetic powder for a dust core according to the present invention is obtained by adding a titanium oxide sol and / or a zirconium oxide sol as an insulating material and a phenol resin to a ferromagnetic metal powder. Even if the dust core of the present invention is annealed at a high temperature of 500 to 800 ° C. in order to improve the magnetic properties, the insulating property is hardly deteriorated. Therefore, distortion (stress) generated during powdering or molding is released more, and the coercive force of the dust core is reduced, so that hysteresis loss is reduced. In addition, eddy current loss is also reduced because insulation is maintained. Since it is small, the total loss (core loss) is small.

As in the present invention, there are the following dust cores using a phenol resin as an insulating material. JP-A-55-130103 discloses the production of a powder magnetic material in which the surface of a metal magnetic powder particle is coated with an inorganic insulating layer, an organic insulating layer is further coated thereon, and then this powder is molded under pressure. A method is disclosed. In the embodiment, pure iron powder is used for the metal magnetic powder, water glass is used for the inorganic insulating layer, and phenol resin is used for the organic insulating layer. However, in this method, since annealing is not performed after molding, molding stress remains, and the coercive force is large.

Japanese Patent Application Laid-Open No. 56-155510 discloses that a metal magnetic powder is added with at least one of water glass and an organic resin insulating agent and 0.2 to 2.0% of zinc stearate and is subjected to pressure molding. A metal dust core obtained by heating is disclosed. In the embodiment, water glass and phenolic resin are added to pure iron powder, zinc stearate is added thereto, and 7 tonnes are added.
/ Cm ² , and then heat-treated at 150 ° C. for 30 minutes to obtain a metal dust core. However, at such a temperature, molding stress remains, and the coercive force remains large.

JP-A-61-288403 discloses that pure iron powder of 60 mesh or less obtained by atomization is prepared by adding
A powder magnetic core obtained by adding 5% by volume of a phenol resin, performing compression molding and curing treatment is disclosed. In the embodiment, a phenol resin is added to pure iron powder, zinc stearate is added as a lubricant, and the mixture is pressed at 5 ton / cm ² and then cured at 80 ° C. for 2 hours and at 180 ° C. for 2 hours. The powder core is obtained by performing the treatment. However, at such a temperature, molding stress remains, and the coercive force remains large.

Japanese Patent Application Laid-Open No. 1-225303 discloses that a ferromagnetic powder is combined using a binder resin made of a thermosetting resin, and then molded under pressure in a mold to form a molded body. A manufacturing method of forming a dust core by heating and hardening while maintaining a pressurized state in the mold is disclosed. However, in the embodiment, an epoxy resin is used.
In addition, since it is not used in combination with an inorganic substance, low eddy current loss and low core loss as in the present invention cannot be obtained.

[0016]

Embodiments of the present invention will be described below in detail. Ferromagnetic powder for the dust core of the present invention,
A ferromagnetic metal powder to which a titanium oxide sol and / or a zirconium oxide sol and a phenol resin are added. The titanium oxide sol and / or zirconium oxide sol and the phenol resin are used as insulating materials.

In order to improve the magnetic properties of the core, it is preferable to perform heat treatment (annealing) after compacting. However, when the treatment is carried out at a high temperature, the amount of resin reduced is large and insulation between ferromagnetic metal particles is insufficient. become. However, when the titanium oxide sol and / or the zirconium oxide sol and the phenol resin are used as the insulating material, the insulating property is not easily deteriorated even when annealing is performed at a high temperature. Therefore, distortion (stress) generated during powdering or molding is further released, and the coercive force of the dust core is reduced, so that hysteresis loss is reduced. In addition, eddy current loss is reduced because insulation is maintained. Therefore, the total loss (core loss) is reduced.

When the insulating material is only the titanium oxide sol and / or the zirconium oxide sol, the strength of the molded body is low, and it is difficult to handle after molding.

If the insulating material is only phenolic resin, if the annealing temperature is increased to about 600 ° C., the insulating property deteriorates, and the eddy current loss increases, so that the core loss increases.

The ferromagnetic metal powder is not particularly limited. For example, iron, sendust (Fe-Al-
Si), iron silicide, permalloy (Fe-Ni), supermalloy (Fe-Ni-Mo), iron nitride, iron-aluminum alloy, iron-cobalt alloy, phosphorous iron, etc., appropriately selected and used from known magnetic material powders. do it. Above all, in order to replace the core for relatively low frequency range currently manufactured using a laminated silicon steel sheet with a dust core, it is preferable to use iron powder having high saturation magnetization. The method for producing the iron powder may be any of an atomizing method, an electrolytic method, and a method of mechanically pulverizing electrolytic iron.

When an alloy is used for the ferromagnetic metal powder, the particles are harder than when iron is used, so that the stress during molding is large and annealing at a higher temperature is required.
Therefore, the effect of the present invention in which the insulating property is maintained up to a high annealing temperature appears more remarkably.

The average particle size of the ferromagnetic metal powder is preferably in the range of 50 to 200 μm, particularly preferably 75 to 100 μm. If the average particle size is too small, the coercive force will increase. On the other hand, if it is too large, the eddy current loss increases. The ferromagnetic metal powder having a particle diameter in the above range may be obtained by classification using a sieve or the like.

In the present invention, the ferromagnetic metal particles may be flattened as required. For example, in the case of a toroidal core or an E-shaped core in which all the legs have a rectangular parallelepiped shape, it is possible to perform so-called lateral pressing, in which pressing is performed in a direction perpendicular to the magnetic path direction during use. In the horizontal extrusion molding, it is easy to make the main surface of the flat particles substantially parallel to the magnetic path in the dust core, and therefore, by using the flat particles, the magnetic permeability can be easily improved.
The flattening may be performed in any manner, but it is preferable to use a means having a rolling and shearing action such as a ball mill, a rod mill, a vibration mill, and an attrition mill. Although the flattening rate is not particularly limited, it is usually preferable that the average aspect ratio is about 5 to 25. Here, the aspect ratio is a value obtained by dividing the average value of the minor axis and the major axis of the main surface by the thickness.

The ferromagnetic powder for a dust core of the present invention contains a titanium oxide sol and / or a zirconium oxide sol.

By adding fine particles, such as titanium oxide sol and zirconium oxide sol, which are uniformly dispersed in a solvent, to a ferromagnetic metal powder, a uniform insulating film can be formed in a small amount, and the While having a magnetic flux density,
It can have high insulation properties.

Titanium oxide sol and zirconium oxide sol are colloidal particles of negatively charged amorphous titanium oxide and zirconium oxide particles dispersed in water or an organic dispersion medium. TiOH
Group, a -ZrOH group is present.

The titanium oxide particles and zirconium oxide particles contained in the sol preferably have an average particle diameter of 0.01 to 0.1 μm, more preferably 0.01 to 0.1 μm.
08 μm, particularly preferably 0.02 to 0.07 μm. The content of these particles in the sol is preferably about 15 to 40% by weight.

A titanium oxide sol for a ferromagnetic metal powder,
The added amount of zirconium oxide sol in terms of solid content, that is, the added amount of titanium oxide and zirconium oxide particles,
0.1 to 15 vol%, further preferably 0.2 to 15 vol%, particularly preferably 0.5 to 5.0 vol%. If the addition amount of titanium oxide and zirconium oxide sol in terms of solid content is too small,
Insulation between the ferromagnetic metal powders in the dust core becomes insufficient. If the addition amount of titanium oxide and zirconium oxide sol in terms of solid content is too large, Ti
Non-magnetic components such as O ₂ and ZrO ₂ increase, resulting in low magnetic permeability and magnetic flux density.

These may be used alone or in combination. In that case, the ratio of the amounts is arbitrary, but the total amount of both must be within the above range.

These sols are usually commercially available [Nissan Chemical Industries, Ltd., NZS-20A, NZS-30A, NZ
S-30B] is preferably adjusted to about pH 7 when the pH value is low. If the pH value is low, the ferromagnetic metal powder is oxidized and non-magnetic oxides increase, and the magnetic permeability and the magnetic flux density may decrease, or the coercive force may deteriorate.

Solvents for these sols include aqueous and non-aqueous solvents. Solvents that are compatible with the phenolic resin and the heat-resistant resin described below are preferred. Particularly, solvents such as ethanol, butanol, toluene, and xylene are preferred. Those using a non-aqueous solvent are preferred. When a commercially available sol is an aqueous solvent, the solvent may be replaced as necessary.

The stabilizer may contain chlorine ions, ammonia and the like.

These sols are usually in the form of a milky white colloid.

The ferromagnetic powder for a dust core of the present invention further contains a phenol resin in addition to the above sol.

By adding a phenolic resin, the strength of the molded body is improved, and even if the annealing temperature is increased to about 800 ° C., the insulating property is hardly deteriorated, and the eddy current loss is reduced, so that the core loss is reduced. .

Examples of the phenol of the phenol resin used in the present invention include phenol, cresols, xylenols, bisphenol A, resorcin and the like. The phenols used may be only one kind or two or more kinds. Aldehydes include formaldehyde,
Examples include paraformaldehyde, acetaldehyde, and benzaldehyde.

The phenolic resin includes resol (Resol)
There is a type resin and a Novolak type resin. The catalyst used when reacting phenol and aldehyde to form a resin is a resol type resin which is a basic substance, and a novolak type resin which is an acidic substance. The resol type resin is cured by heating or an acid catalyst, and becomes insoluble and infusible. The novolak-type resin is a fusible resin that does not thermoset by itself and is cured by heating with a crosslinking agent such as hexamethylenetetramine.

The phenolic resin of the present invention is preferably a resol type resin. When a novolak-type resin is used, the strength of the molded body is weak, and it is difficult to handle in a process after molding. When a novolak resin is used, molding while applying a temperature such as hot pressing is indispensable. The temperature applied varies depending on the resin, but is usually about 150 to 400 ° C.

As the phenol resin, a resol type phenol resin containing N in the form of a tertiary amine has high heat resistance and is particularly preferable.

The novolak type preferably contains hexamine.

The weight average molecular weight of the phenol resin is 300
~ 7000, furthermore 500 ~ 7000, especially 500 ~
6000 is preferred. The smaller the molecular weight, the higher the strength of the molded body, and the smaller the tendency for powder to fall off at the edge of the molded body. However, if the molecular weight is less than 300, annealing at a high temperature causes a large amount of resin to be reduced, so that the insulating properties between the ferromagnetic metal powders in the dust core cannot be maintained, and the eddy current loss increases. May be large.

As the phenol resin, a commercially available phenol resin may be used, and BRS-3801, manufactured by Showa Kogaku KK, may be used.
ELS-572,577,579,580,582,5
83 (above, resol type), BRP-5417 (novolak type) and the like.

The amount of the phenol resin added to the ferromagnetic metal powder is preferably 1 to 30 vol%, particularly preferably 2 to 20 vol%. If the amount of the phenolic resin is too small, the mechanical strength of the core is reduced or insulation failure occurs. If the amount of the phenol resin is too large, the ratio of the non-magnetic component in the dust core increases, and the magnetic permeability and the magnetic flux density of the core decrease.

When the phenolic resin and the ferromagnetic metal powder are mixed, a solid or liquid resin may be made into a solution and mixed, or a liquid resin may be directly mixed. The viscosity of the liquid resin is preferably 10 to 50 at 25 ° C.
00 CPS, more preferably 50 to 2000 CPS. If the viscosity is too low or too high, it becomes difficult to form a uniform coating on the surface of the ferromagnetic metal powder.

In the present invention, a heat-resistant resin may be further added in addition to the phenol resin. By adding the heat-resistant resin, the titanium oxide particles and zirconium oxide particles in the sol are more likely to adhere to the surface of the ferromagnetic metal powder, and assist to adhere so as to cover the surface uniformly. In addition, although it is also effective in improving the strength, if the surface of the ferromagnetic metal powder is uniformly covered too much, the ferromagnetic metal powders will not slip easily, and a predetermined density cannot be obtained even by pressure molding, Conversely, the strength may be lowered, so that a suitable resin may be added as appropriate depending on the sol particles used, the type of ferromagnetic metal powder, the particle size, and the like. The heat-resistant resin is not particularly limited, and examples thereof include a silicone resin, an epoxy resin, a phenoxy resin, a polyamide resin, a polyimide resin, and a polyphenylene sulfide (PPS) resin. The thermal decomposition temperature is preferably 600 ° C. or higher. The addition amount of these heat-resistant resins is preferably in the range of 0.1 to 10 vol%, particularly 0.1 to 1.0 vol%, based on the ferromagnetic metal powder. As the heat-resistant resin, for example, the weight average molecular weight of the silicone resin is usually preferably in the range of about 700 to 3300. If the amount of the heat-resistant resin is too small, the effect of improving the mechanical strength of the core may not be obtained. If the amount of the heat-resistant resin is too large, the ratio of non-magnetic components in the core may increase, and the magnetic permeability and the magnetic flux density of the core may decrease.

Even if one kind of heat-resistant resin is used,
Two or more kinds may be used. When two or more kinds are used, the total addition amount is preferably within the above range.

When the heat-resistant resin and the ferromagnetic metal powder are mixed, a solid or liquid heat-resistant resin may be made into a solution and mixed, or the liquid heat-resistant resin may be directly mixed. The viscosity of the liquid heat-resistant resin is preferably 10 at 25 ° C.
〜１０10000 CP, more preferably 1000０〜9000
CP. If the viscosity is too low or too high, it becomes difficult to form a uniform coating on the surface of the ferromagnetic metal powder.

Next, a method of manufacturing the dust core of the present invention will be described. In the present invention, a ferromagnetic metal powder, a titanium oxide sol and / or a zirconium oxide sol, and a phenol resin are mixed.

When iron is used for the ferromagnetic metal powder, it is preferable to subject the iron powder to heat treatment for strain relief annealing before mixing. It is preferable to perform a heat treatment at a high temperature to sufficiently reduce the coercive force of the iron powder. The iron powder may be subjected to an oxidation treatment before mixing. By this oxidation treatment,
If a thin oxide film of about several tens of nanometers is formed near the surface of the iron particles, an improvement in insulation can be expected. This oxidation treatment may be performed by heating at 150 to 300 ° C. for about 0.1 to 2 hours in an oxidizing atmosphere such as air. When the oxidation treatment is performed, a dispersant such as ethyl cellulose may be used to improve the wettability of the iron particle surface.

When the ferromagnetic metal powder and the titanium oxide sol and / or the zirconium oxide sol are mixed with the phenol resin, the sol is added as the above sol solution. The mixing is carried out using a pressure kneader, a raikai machine or the like, preferably at about room temperature for 20 to 60 minutes. The obtained mixture is preferably heated at about 100 to 300 ° C. for 20 to 60 hours.
After drying for minutes, a ferromagnetic powder for a dust core is obtained.

After drying and before molding, a lubricant is preferably added to the ferromagnetic powder for the dust core. Lubricants are used to enhance the lubricity between particles during molding and to improve the releasability from a mold. As the lubricant, various kinds of lubricants generally used for a dust core can be selected. For example, a higher fatty acid such as stearic acid, zinc stearate, and aluminum stearate, a salt thereof, an organic lubricant solid at room temperature such as wax, an inorganic lubricant such as molybdenum disulfide may be appropriately selected. The mixing amount of the lubricant varies depending on the kind, but is preferably 0.1 to 1% by weight with respect to the iron powder in the case of an organic lubricant which is solid at room temperature, and is preferably in the case of an inorganic lubricant with respect to the ferromagnetic powder for the dust core. 0.1 ~
0.5 wt%. If the amount of the lubricant is too small, the effect of the addition becomes insufficient. On the other hand, if the amount is too large, the magnetic permeability of the core decreases and the strength of the core decreases.

In the forming step, a desired core shape is formed. The core shape to which the present invention is applied is not particularly limited,
So-called toroidal type, E type, I type, F type, C type, EE
The present invention can be applied to the production of cores of various shapes such as molds, EI molds, ER molds, EPC molds, pot molds, drum molds, pot molds, cup molds and the like. Further, since the core of the present invention is a dust core, a core having a complicated shape can be obtained.

The compacting conditions are not particularly limited, and may be appropriately determined according to the type and shape and size of the ferromagnetic metal particles, the desired core shape and core size, the core density, and the like. The pressure is maintained at about 6 to 20 ton / cm ^{2 at} the maximum pressure for about 0.1 second to 1 minute.

After compacting, preferably heat treatment (annealing)
To improve the magnetic properties of the core. Annealing is to release the strain (stress) generated in the ferromagnetic metal particles during powdering and molding. When the particles are mechanically flattened, the stress caused by the flattening can be released. it can. Also, the annealing hardens the heat-resistant resin, increases the density of the green compact, and improves the mechanical strength.

The annealing conditions may be appropriately determined according to the type of ferromagnetic metal powder, molding conditions, flattening conditions, and the like. Annealing temperature is 500 to 800 ° C., especially 600
~ 750 ° C is preferred. In the present invention, since a phenol resin is added as a heat-resistant resin, it can be processed at a higher temperature than the conventional annealing temperature (about 200 to 500 ° C.).
Therefore, the stress is further released and the coercive force of the dust core is reduced, so that the hysteresis loss is reduced and the core loss is reduced. If the annealing temperature is too low, the restoration of the coercive force becomes insufficient, so that the hysteresis loss does not decrease and the core loss increases. If the annealing temperature is too high, the insulation film is thermally destroyed and insulation becomes insufficient,
Eddy current loss increases and core loss increases. Processing time, i.e., time to pass through the above temperature range, or time to maintain a constant temperature within the above temperature range,
A range from 10 minutes to 2 hours is preferred. If the treatment time is too short, the annealing effect tends to be insufficient, and if the treatment time is too long, dielectric breakdown tends to occur.

Annealing is performed in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen in order to prevent a decrease in magnetic permeability and magnetic flux density due to oxidation of the ferromagnetic metal powder.

After annealing, the core may be impregnated with a resin or the like, if necessary. By impregnating the resin, the strength is further improved. Examples of the resin used for the impregnation include a phenol resin, an epoxy resin, a silicone resin, and an acrylic resin. Among them, a phenol resin is preferable. These resins may be used by dissolving them in a solvent such as ethanol, acetone, toluene and pyrrolidone.

As a method for impregnating the core with the resin, the core is placed on a container such as a vat, and a mixed solution of a resin and a solvent (for example, a 10% ethanol solution of a phenol resin) is poured into the container. Be completely hidden.
After holding for about 1 to 30 minutes as it is, take out the core, remove some of the resin solution attached to the surroundings,
A heat treatment is performed. First, the heat treatment is performed by raising the temperature to about 80 to 120 ° C. in an air atmosphere using an oven or the like.
Hold for about 2 hours. Further, the temperature is raised to about 130 to 170 ° C. and maintained for about 1.5 to 3 hours.
The temperature is lowered to about 0 ° C. and maintained for about 0.5 to 2 hours.

After the heat treatment or after the resin impregnation, if necessary, an insulating film is formed to secure insulation with the winding, the winding and the core halves are assembled, and a case is charged.

The particle size distribution of the ferromagnetic powder in the dust core is almost the same as that of the raw material powder.

Such a dust core is suitably used for a magnetic core such as a transformer and an inductor, a motor core, and other electromagnetic components. Also, choke coils for electric vehicles,
It can also be used as an airbag sensor. Use frequency is 1
It is 0 to 500 kHz, preferably 50 to 200 kHz.

[0062]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention. <Example 1> Zirconia sol was manufactured by Nissan Chemical Co., Ltd.
First, pH was adjusted to 7 using rO ₂ sol (NZS-30A) [average particle size: 62 nm], and a dispersion was prepared by replacing a water solvent with an ethanol solvent.

As the phenolic resin, two types of resole type resins and one type of novolak type resin manufactured by Showa Polymer Co., Ltd. shown in Table 1 were used.

The zirconia sol and the phenol resin or only the phenol resin were weighed as shown in Table 1,
Electrolytic iron powder (Furukawa Machinery & Metal Co., Ltd., average particle size 110μ)
m) and mixed for 30 minutes at room temperature using a pressure kneader. Next, it was dried at 200 ° C. for 30 minutes in an air atmosphere to obtain a ferromagnetic powder for dusting.

To this ferromagnetic powder for compacting, 0.2 wt% of zinc stearate manufactured by Nitto Kasei Kogyo Co., Ltd. was added as a lubricant, and mixed for 15 minutes with a V mixer to obtain 12 tons / cm ² .
It was molded into a toroidal shape having an outer diameter of 17.5 mm, an inner diameter of 10.2 mm, and a height of about 6 mm. When using novolak resin,
It is difficult to mold at room temperature.
At 0 ° C., molding was performed at 8 tons / cm ² .

After molding, annealing was performed at 700 ° C. for 60 minutes in an N ₂ atmosphere to obtain each core sample.

As a comparative example, a SiO ₂ sol (trade name NZ, manufactured by Nissan Chemical Industries, Ltd.) was used instead of the zirconia sol.
S-30A) was replaced with a phenolic resin, and a silicone resin (KR153) manufactured by Shin-Etsu Chemical Co., Ltd. [weight average molecular weight: 2600, thermal decomposition temperature around 600 ° C, weight loss of about 30
%] To obtain a core sample.

For each core sample, 100 O
e, the magnetic flux density (B100), the coercive force (Hc), the hysteresis loss (Ph) at 1000 mT, the eddy current loss (Pe), and the core loss (P
c) was determined. The loss and the magnetic permeability (μ) are 1 kH
Measured in z. Magnetic flux density and coercive force are measured by Yokogawa Electric Corporation
DC BH Tracer 3257 type, core loss was measured using Iwasaki Communication Equipment Co., Ltd. BH Analyzer SY-8232.

The outer diameter is 17.5 mm, the inner diameter is 10.2 mm,
A toroidal sample having a height of 6 mm was prepared in the same manner as above, and the strength was determined. The strength was evaluated by performing a radial crushing strength test on the sample using a desktop digital load tester manufactured by Aoki Engineering. Table 1 shows the results.

[0070]

[Table 1]

When a novolak-type phenol resin was used, when molded at room temperature, the strength of the molded article was low, and subsequent handling was not possible.

It can be seen that the dust core of the present invention has the same magnetic flux density, hysteresis loss, and magnetic permeability, and has significantly reduced eddy current loss and core loss.

In particular, when a phenol resin having a weight average molecular weight of 5500 and a novolak phenol resin having a weight average molecular weight of 3000 are used in combination with a zirconia sol, eddy current loss and core loss are significantly reduced. I understand.

When the phenol resin is used alone or in combination with the silica sol and the silicone resin,
It can be seen that when annealed at a high temperature, insulation between particles cannot be maintained and eddy current loss increases.

Example 2 As shown in Table 2, core samples were obtained and evaluated in the same manner as in Example 1 using resole-type phenol resins having different weight average molecular weights. Table 2 shows the results.

[0076]

[Table 2]

It can be seen that the phenolic resin having a weight average molecular weight of 300 or more has very small eddy current loss and core loss as compared with those having a molecular weight of less than 300.

Example 3 In Example 1, the electrolytic iron powder was changed to Supermalloy (Mo Permalloy, average particle size 60 μm) manufactured by Höganäs, and the annealing temperature was as shown in Table 3. A core sample was obtained in the same manner as in Example 1. The core sample was evaluated in the same manner as in Example 1 except that the loss was measured at 50 kHz and 100 mT, and the magnetic permeability was measured at 50 kHz. Table 3 shows the results.

[0079]

[Table 3]

It can be seen that the powder core of the present invention has significantly reduced eddy current loss and core loss even when the ferromagnetic metal powder is replaced with an alloy. Further, the effect of the present invention is more conspicuous as the annealing temperature is higher.

Example 4 A core sample was obtained and evaluated in the same manner as in Example 1 except that zirconia sol was replaced with titania sol. In titania sol,
Using TiO ₂ sol (TA-15) manufactured by Nissan Chemical Co., Ltd. (average particle size: 5 to 50 nm), the pH was first adjusted to 7 to prepare a dispersion in which the aqueous solvent was replaced with an ethanol solvent.

The powder core of the present invention using the titania sol also had a significantly reduced core loss, similarly to the case using the zirconia sol.

[0083]

As described above, according to the present invention, a dust core which can be annealed at a high temperature, has a high magnetic flux density, a low coercive force, and a low loss, and has a high mechanical strength, and a A method for producing a magnetic powder and a dust core can be provided.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiaki Yamada 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (72) Inventor Noriyuki Yamaguchi 1-13-1 Nihonbashi, Chuo-ku, Tokyo T (72) Inventor Hideki Kitajima 3-20-20 Kandanishikicho, Chiyoda-ku, Tokyo Showa Polymer Co., Ltd.

Claims (8)

[Claims] 1. A ferromagnetic powder for a dust core in which a ferromagnetic metal powder is added with a titanium oxide sol and / or a zirconium oxide sol and a phenol resin. 2. The ferromagnetic powder for a dust core according to claim 1, wherein the phenol resin is a resol type phenol resin. 3. The ferromagnetic powder for a dust core according to claim 1, wherein the phenol resin has a weight average molecular weight of 300 to 7000. 4. The ferromagnetic powder for a dust core according to claim 1, wherein the phenol resin is added in an amount of 1 to 30 vol% based on the ferromagnetic metal powder. 5. The method according to claim 1, wherein the titanium oxide sol and / or the zirconium oxide sol is 0.1 to 1 with respect to the ferromagnetic metal powder.
The ferromagnetic powder for a dust core according to any one of claims 1 to 4, which is added at 5 vol%. 6. The ferromagnetic powder for a dust core according to claim 1, wherein the titanium oxide sol and / or the zirconium oxide sol have an average particle size of 0.01 to 0.1 μm. 7. A dust core obtained by press-molding the ferromagnetic powder for dust core according to claim 1. 8. A method for producing a dust core, wherein the core of claim 7 is obtained by subjecting to heat treatment at 500 to 800 ° C. after pressure molding.