JP5329069B2 - Composite material for magnetic core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite material for magnetic core capable of forming a magnetic core whose insulating characteristics can be stably maintained over a long period of time. <P>SOLUTION: The composite material for magnetic core in a suitable embodiment contains: ferromagnetic powder; epoxy resin having a thermosetting property; a curing agent of epoxy resin whose molecular weight is 2,000 or more and/or a curing agent of epoxy resin which has at least one kind of structure selected from a group comprising a polyamidimide structure, a polyvinylphenol structure, a bismaleimide structure and a silicone structure. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a composite material for a magnetic core.

Inductors and the like generally have a structure including a magnetic core. This magnetic core is manufactured by molding a magnetic core composite material. As the magnetic core composite material, a material containing ferromagnetic powder and a thermosetting resin is often used. For example, a mixture of a powder binder containing a thermosetting resin that is solid at room temperature, a predetermined solvent, and magnetic powder is known (see Patent Document 1).
Japanese Patent No. 2700713

  However, when the magnetic core is formed using the above conventional composite material for magnetic core, there is a problem that its insulating characteristics are liable to deteriorate if left at high temperature for a long time. When the insulation characteristics of the magnetic core deteriorate, the loss of the inductor increases, and in some cases, a short circuit may occur.

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a composite material for a magnetic core capable of forming a magnetic core capable of stably maintaining an insulating property even at high temperatures. .

In order to achieve the above object, the composite material for magnetic core of the present invention has a ferromagnetic powder, a thermosetting epoxy resin, a molecular weight of 4000-20000, polyvinylphenol, modified polyamideimide resin, and amino-modified silicone. And a curing agent of at least one epoxy resin selected from the group consisting of: and a blending amount of the curing agent is more than 1/2 equivalent of the epoxy resin and less than 2 equivalents.

Such a composite material for magnetic core of the present invention can form a magnetic core by curing. In such curing, curing of the epoxy resin occurs, but the obtained cured product contains a lot of cross-linked structures derived from the curing agent. Here, since the composite material for a magnetic core according to the present invention includes a curing agent having a molecular weight of 4000 to 20000 as a curing agent, the magnetic core obtained by curing this has a cross-linked structure having a large molecular weight. It contains a cured product of an epoxy resin that is difficult to thermally decompose even at high temperatures.

  According to the knowledge of the present inventors, in the magnetic core using the conventional composite material for magnetic core, it is presumed that the thermosetting resin is decomposed at a high temperature, and this causes a decrease in insulation characteristics. . On the other hand, the magnetic core obtained from the composite material for magnetic core according to the present invention contains a cured product of an epoxy resin that is difficult to be thermally decomposed as described above. .

The composite material for a magnetic core of the present invention is at least one selected from the group consisting of a ferromagnetic powder, a thermosetting epoxy resin, an imide structure, a phenol structure, and a silicone structure having a functional group that reacts with the epoxy resin. An epoxy resin curing agent having a structure, the molecular weight of the curing agent is 4000 to 20000 , and the blending amount of the curing agent is more than 1/2 equivalent of the epoxy resin and less than 2 equivalents. It may be a feature.

  According to such a composite material for a magnetic core of the present invention, a magnetic material containing a cured product of an epoxy resin having a crosslinked structure including an imide structure derived from a curing agent, a phenol structure, and a silicone structure having a functional group that reacts with the epoxy resin. A core can be obtained. And since these structures in the crosslinked structure are structures having extremely high heat resistance, the magnetic core obtained from the composite material for magnetic cores of the present invention is also made of a cured epoxy resin that is difficult to thermally decompose even at high temperatures. As a result, the insulating properties can be maintained well even at high temperatures.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the composite material for magnetic cores which can form the magnetic core which can maintain an insulation characteristic stably over a long period of time.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  First, an example of the configuration of an inductor having a magnetic core obtained by using the magnetic core composite material of the present invention will be described. FIG. 1 is a plan view showing the inductor, and FIG. 2 is an end view of the inductor shown in FIG.

  The illustrated inductor 1 includes an air core coil 4 around which a conducting wire or the like is wound, and a magnetic core 2 formed so as to seal the air core coil 4. Electrode terminals 6 made of a conductive foil or the like for connecting to the outside of the air-core coil 4 are provided at both ends. In other words, the inductor 1 includes a core portion 2a in the magnetic core 2, an air core coil 4 in which a conductive wire is wound around the core portion 2a, and an outer side so as to seal the air core coil 4. And a magnetic core 2 provided on the surface.

  In the inductor 1 having the above-described configuration, the magnetic core 2 (including the core portion 2a) is formed from the composite material for magnetic core according to the preferred embodiment of the present invention. It is formed by curing a composite material. Hereinafter, the suitable composite material for magnetic cores and the magnetic core 2 obtained thereby will be described.

  The composite material for the magnetic core constituting the magnetic core 2 includes ferromagnetic powder, a thermosetting epoxy resin, and a curing agent for this epoxy resin. First, the ferromagnetic powder can be applied without particular limitation as long as it is made of a material having ferromagnetism. For example, Fe-Si-Cr, Fe-Ni, Fe-Si-Al, Fe-Cr, An iron-based powder made of a metal having iron as a basic component, such as Fe-Si, may be mentioned.

  The epoxy resin is a component that is a main component of the thermosetting resin, and examples thereof include an epoxy compound having a plurality of epoxy groups. Examples thereof include bisphenol A type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, brominated bisphenol A type epoxy resins, alicyclic epoxy resins, special epoxy resins, and modified resins thereof. As an epoxy resin, these 1 type (s) or 2 or more types can be used.

  The epoxy resin preferably has a softening point of 60 ° C. or higher, and more preferably 80 ° C. or higher. When the softening point is 60 ° C. or higher, the fluidity of the epoxy resin is sufficiently enhanced, which makes it easier to form a coating structure as will be described later in the composite material for the magnetic core, thereby obtaining even better insulating properties. Be able to.

  A hardening | curing agent is a hardening | curing agent of said epoxy resin, and is specifically a compound which can form the structure (crosslinked structure) which bridge | crosslinks the polymer structure comprised from an epoxy resin in hardening. Examples of such a curing agent include compounds having two or more functional groups capable of reacting with hydroxyl groups and the like contained in a polymerized structure made of an epoxy resin, such as amino groups and hydroxyl groups.

Curing agent in the present embodiment, Ru compound der having a molecular weight of from 4,000 to 20,000. If the molecular weight of the curing agent is less than 2000, the thermal decomposition rate of the cured epoxy resin contained in the magnetic core 2 becomes undesirably large, and it becomes difficult to maintain sufficient insulation properties at high temperatures. On the other hand, when the molecular weight of the curing agent is too larger than the above range, curing of the epoxy resin tends to be insufficient.

Moreover, as a hardening | curing agent, the compound which has at least 1 type of structure chosen from the group which consists of a silicone structure (for example, modified silicone structure) which has an imide structure, a phenol structure, and a functional group which reacts with an epoxy resin is suitable . From the viewpoint of such insulating properties at high temperatures of magnetic core 2 can be more fully maintained, the curing agent, have these structures, and the molecular weight of Ru der those 4000-20000.

  Specific examples of the curing agent as described above include compounds having a polyamideimide structure, a polyvinylphenol structure, a bismaleimide structure, a silicone structure, and a novolac type phenol structure. Among these, a compound having a polyamideimide structure, a polyvinylphenol structure, or a novolac type phenol structure is preferable.

Specific examples of the curing agent having these structures include novolak-type phenol resins represented by the following general formula (1), polyvinylphenols represented by the following general formula (2), and the following general formula (3). An epoxy-modified silicone oil represented by the following general formula (4), an amine-modified silicone oil represented by the following general formula (4), a polybismaleimide represented by the following general formula (5), and an aminotriazine novolak represented by the following general formula (6) Is mentioned. In the following formula, R represents a monovalent organic group, and Ar represents a divalent aromatic group. N and k are each independently a number indicating a repeating unit of a structural unit in parentheses, and a suitable number can be applied to each unit without limitation, but a number such that the molecular weight falls within the above-mentioned preferred range. Is preferable.

  For example, the composite material for a magnetic core containing the above components preferably has a structure as shown below. FIG. 3 is a view showing the structure of the composite material for magnetic core according to a preferred embodiment.

  As shown in the drawing, the composite material for a magnetic core according to the present embodiment is preferably composed of an aggregate of a plurality of particles 20. Here, each particle 20 includes a ferromagnetic particle 20a and a coating film 20b that covers the ferromagnetic particle 20a. In this particle 20, the above-described ferromagnetic particle 20 a is formed of the above-described ferromagnetic powder constituent material, while the coating film 20 b contains an epoxy resin and its curing agent.

  Since the composite material for magnetic core has such a structure, the insulating property between the ferromagnetic particles 20a is kept high. As a result, the magnetic core 2 obtained from the composite material for magnetic core has high insulating properties. be able to.

  The composite material for a magnetic core preferably contains the above components in the following proportions. That is, first, the epoxy resin is preferably contained in an amount of 0.5 to 5 parts by mass and more preferably 1 to 4 parts by mass with respect to 100 parts by mass of the ferromagnetic powder. If the content of the epoxy resin is too smaller than the above range, the insulating properties and strength of the magnetic core 2 may be insufficient. On the other hand, if the amount is too large, sufficient magnetic properties may not be obtained.

  Moreover, it is preferable that the hardening | curing agent is mix | blended equivalent of an epoxy resin. The blending amount of the curing agent may be slightly increased or decreased from the equivalent of the epoxy resin, but if the amount is significantly less than this equivalent (for example, ½ equivalent or less), the epoxy resin cured product has a sufficient crosslinked structure. It is not introduced, and the cured product is likely to be thermally decomposed, and as a result, the magnetic core may not be able to maintain good insulation characteristics at high temperatures. On the other hand, if the amount of the curing agent is too large (for example, 2 equivalents or more), the number of cross-linked portions of the cured product is reduced, which may result in insufficient strength, insulating properties, and the like.

  The composite material for the magnetic core may further contain a molding aid, a coupling agent, a flame retardant, and the like as necessary in addition to the above-described components as long as the effects of the present invention are not hindered. . Examples of the molding aid include metal soaps such as Al stearate, Zn stearate, Sr stearate Ba, stearic acid Ba and Ca stearate, higher fatty acids such as stearamide and behenic acid, melamine cyanurate, boron nitride, Examples include molybdenum sulfide.

  The magnetic core 2 in the inductor 1 is formed by a cured product of the above-described composite material for magnetic core. For example, when the magnetic core 2 is formed of a composite material for a magnetic core as shown in FIG. 3, the magnetic core 2 has a structure in which a large number of particles 20 are aggregated. What has the structure in which the coating film 20b which covers the particle | grains 20a is formed from the hardened | cured material of an epoxy resin is suitable. The cured product of the epoxy resin contains many cross-linked structures derived from a curing agent, has excellent heat resistance, and hardly causes thermal decomposition.

  The above-described composite material for magnetic core and magnetic core 2 can be manufactured, for example, by the following manufacturing method.

  First, in the manufacture of the composite material for the magnetic core, a ferromagnetic powder, an epoxy resin and a curing agent are prepared and mixed. Mixing is preferably performed using a resin dissolved in a solvent from the viewpoint of improving workability and uniformity. In order to coat the ferromagnetic powder uniformly with the resin, it is preferable to coat the ferromagnetic powder with a solution in which the resin is dissolved.

  Further, depending on the type of the curing agent, after the epoxy resin and the curing agent are melt mixed, the ferromagnetic powder can be further mixed therewith. In that case, the melting temperature is preferably lower than the melting point of the curing agent. Thereby, hardening of the epoxy resin in the mixing stage can be sufficiently suppressed, and the above-described covering structure can be easily formed.

  Then, the composite material for magnetic cores containing a ferromagnetic powder and a resin component (an epoxy resin and a hardening | curing agent) is obtained by said mixing and coating. Such a composite material for a magnetic core can be crushed and sized as necessary.

  The sizing is preferably performed so that the average particle diameter of the composite material for magnetic core is 50 to 180 μm, and more preferably 70 to 120 μm. When the average particle size of the composite material for magnetic core is within the above range, there is an advantage that the fluidity of the composite material for magnetic core is higher than when the average particle size is out of the above range. In addition, although sizing may be performed once, you may perform it twice or more as needed. Moreover, as a crushing means, a cutter mill, a feather mill, a flake crusher, a goose grinder, etc. can be used, for example.

  And the composite material for magnetic cores obtained in this way can form the magnetic core 2 by making it harden | cure, for example after shape | molding in a desired shape. Molding can be performed by a known method. In addition, it is not always necessary to perform the molding to the final shape of the magnetic core 2 at a time. For example, when the magnetic core 2 of the inductor 1 as shown in FIG. 1 is formed, first, the core portion 2a of the magnetic core 2 is formed, and the air core coil 4 is wound around the core 2a. The magnetic core 2 may be completed by sealing with a material. Moreover, the composite material for magnetic cores can be cured by heating to a temperature at which the epoxy resin contained therein is cured.

  Since the magnetic core 2 in the inductor 1 as described above is formed of the above-described composite material for magnetic core of the present invention, it has the following characteristics. That is, the magnetic core 2 includes a cured product of epoxy resin, and preferably has a configuration in which ferromagnetic particles are covered with a cured product of epoxy resin. And the hardened | cured material of this epoxy resin has many crosslinked structures derived from the hardening | curing agent containing the structure which has high molecular weight or is excellent in heat resistance, and does not produce thermal decomposition easily also at high temperature. Therefore, the magnetic core 2 having such a configuration hardly deteriorates in insulation characteristics due to thermal decomposition of the cured epoxy resin, and has good insulation characteristics even when exposed to high temperatures for a long time. Can be maintained.

  Here, from the viewpoint of molecular weight, it is conceivable to increase the molecular weight of the epoxy resin itself rather than the curing agent. However, in this case, in the cured product of the epoxy resin, the polymerized structure made of the epoxy resin becomes longer, so the proportion of the crosslinked structure derived from the curing agent is rather reduced. As a result, the cured product is likely to have low solvent resistance in addition to Tg, and it is considered that sufficient insulating properties cannot be imparted to the magnetic core at high temperatures. On the other hand, in the present invention, as in the above-described embodiment, since a cross-linked structure made of a curing agent having low thermal decomposability can be introduced, the insulating properties can be maintained better than increasing the molecular weight of the epoxy resin. The magnetic core 2 can be obtained.

  The composite material for magnetic core and magnetic core of the present invention and the production method thereof are not necessarily limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention. For example, the magnetic core is not limited to the shape of the magnetic core 2 in the inductor 1 of the above embodiment, and may be a cylindrical shape, a toroidal shape, or other various shapes.

  Further, the composite material for magnetic core does not necessarily have the above-described coating structure, and may have a structure in which ferromagnetic powder is dispersed in, for example, an epoxy resin and a curing agent. . Furthermore, in the manufacture of the composite material for the magnetic core, the ferromagnetic powder, the epoxy resin, and the curing agent may be mixed in order without being mixed at once.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.
[Production of composite material for magnetic core]

(Examples 1-6 , Reference Example 7, Comparative Examples 1-6)
First, while preparing a Fe-Ni-Si-Co-based soft magnetic powder, the main agent and its curing agent were added to acetone, ethanol, or toluene as a solvent. Next, after the soft magnetic powder and the resin solution were mixed and stirred, the solvent was removed, and the resulting mixture was pulverized to obtain a granular composite material for a magnetic core. At this time, the total content of the main agent and the curing agent was set to 2% by weight, and the equivalent of the main agent was added to the curing agent.

［特性評価］ In Examples 1 to 6, Reference Example 7 and Comparative Examples 1 to 6, the combination of the main agent (epoxy resin or silicone resin) and the curing agent was changed as shown in Table 1 below.

[Characteristic evaluation]

While evaluating the magnetic properties, voltage resistance and solvent resistance using the magnetic cores prepared from the composite materials for magnetic cores of Examples 1 to 6, Reference Example 7 and Comparative Examples 1 to 6 prepared above, these The crushing strength was measured. Moreover, the powder fluidity of these composite materials for magnetic cores was also measured. The results obtained are summarized in Table 2.

(Production of magnetic core)
St-Zn was added to the obtained composite material for the magnetic core, mixed, and then molded at 7 ton / cm ² , and the resulting molded body was heated and cured at 180 ° C. for 1 hour. It was. As a result, a magnetic core having a toroidal shape was obtained.

(Magnetic properties)
First, the permeability (μi (initial)) of the magnetic core after preparation was measured with an LCR meter. Thereafter, after the magnetic core was left to stand at 125 ° C. for 1000 hours, the magnetic permeability (μi (1000 hr)) of the magnetic core after the treatment was measured again. This indicates that the smaller the change in permeability before and after the treatment, the better the magnetic properties can be maintained even at high temperatures.

(Withstand voltage)
A voltage was applied to the magnetic core after preparation, and this voltage was gradually increased to measure the voltage (withstand voltage) until dielectric breakdown of the magnetic core occurred. Further, the separately produced magnetic core was subjected to the treatment of leaving at 125 ° C. for 1000 hours, and then the withstand voltage was measured in the same manner for the magnetic core after the treatment. The smaller the difference between the withstand voltage (initial) of the magnetic core that has not been subjected to the above treatment and the withstand voltage (1000 hr) of the magnetic core that has undergone the above treatment, the better the characteristics of maintaining the insulation characteristics at higher temperatures. Is shown.

(Solvent resistance)
The solvent resistance was evaluated by observing the appearance after the magnetic core was immersed in acetone and toluene and treated with an ultrasonic cleaner for 10 minutes. In this evaluation, it was judged that the magnetic core had no change in appearance and had no powder fall off.

(Crushing strength)
The crushing strength was measured according to JIS-Z-2507.

(Powder fluidity)
The powder fluidity was measured according to JIS-Z-2504 using a composite material for magnetic core.

The solvent resistance was good when the composite materials for magnetic cores of Examples 1 to 6, Reference Example 7 and Comparative Examples 1 to 3 and 5 to 6 were used, but for the magnetic core of Comparative Example 4 The use of composite materials was insufficient.

As can be seen from the above results, according to Examples 1 to 6 and Reference Example 7 corresponding to the composite material for magnetic core of the present invention, a magnetic core capable of sufficiently maintaining magnetic properties and insulating properties even under high temperature conditions can be obtained. It has been found. Good results were also obtained in terms of solvent resistance, powder flowability and crushing strength. On the other hand, when the composite materials for magnetic cores of Comparative Examples 1 to 6 are used, the insulation characteristics are remarkably lowered at a high temperature or the solvent resistance is insufficient, and the magnetic characteristics, powder flowability and crushing strength Was found to be insufficient.

It is a top view which shows an inductor. FIG. 2 is an end view of the inductor shown in FIG. 1. It is a figure which shows the structure of the composite material for magnetic cores of suitable embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Inductor, 2 ... Magnetic core, 2a ... Core part, 4 ... Air core coil, 6 ... Electrode terminal, 20 ... Particle | grains, 20a ... Ferromagnetic particle | grains, 20b ... Coating film.

Claims (2)

Ferromagnetic powder,
An epoxy resin having thermosetting properties;
A molecular weight of 4000 to 20000, and at least one curing agent for the epoxy resin selected from the group consisting of polyvinylphenol, modified polyamideimide resin and amino-modified silicone;
Containing
The composite material for magnetic cores, wherein the compounding amount of the curing agent is more than 1/2 equivalent of the epoxy resin and less than 2 equivalents. Ferromagnetic powder,
An epoxy resin having thermosetting properties;
A curing agent for the epoxy resin having at least one structure selected from the group consisting of an imide structure, a phenol structure, and a silicone structure having a functional group that reacts with the epoxy resin;
Containing
A magnetic core composite material, wherein the molecular weight of the curing agent is 4000 to 20000, and the blending amount of the curing agent is more than 1/2 equivalent of the epoxy resin and less than 2 equivalents.

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