JPH06132109A - Compressed powder magnetic core for high frequency - Google Patents

Abstract

PURPOSE:To provide a compressed powder magnetic core for high frequency and a method of manufacturing the same which can improve insulation property and magnetic flux density to lower an iron loss value and extend the available frequency band and moreover can improve mechanical strength to avoid damages which may be given in the manufacturing steps. CONSTITUTION:Soft magnetic powder 1 is covered with a glass structured insulating layer 2 containing Cr and P as the essential elements and the soft magnetic powders 1 are joined with each other via the insulating layer 2. Moreover, a compressed powder core is impregnated, after the annealing process, with water glass and is then dried up.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency powder magnetic core used for a choke coil for a power supply device and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a soft magnetic material for AC, a stack of electromagnetic steel sheets containing silicon has been used for a transformer or the like, and recently, amorphous steel foil has been attracting attention. . Although these materials have excellent direct current magnetic characteristics, when used for alternating current applications, the surface of the plate is insulated,
It is necessary to adopt a structure that prevents current from flowing between the steel sheets (see, for example, Japanese Patent Laid-Open No. 3-39484).

By the way, recently, with the spread of the inverter control system, improvement of magnetic performance in a high frequency region is required. However, the laminated-type magnetic core formed by laminating silicon steel sheets as described above has excellent magnetic permeability at 1 KHz or less, but iron loss due to eddy current increases in the frequency band above 1 KHz, It is not suitable as a magnetic material for high frequencies.

On the other hand, so-called soft ferrite may be used as the high frequency magnetic material. Compared with the above-mentioned silicon steel plate and the like, this soft ferrite is excellent in high frequency characteristics and has a low iron loss value, but has a drawback that the magnetic flux density is low.

In response to the above-mentioned problems, a dust core prepared by mixing an epoxy resin or a fluorine-based resin with a soft magnetic powder and compacting the powder has been proposed in recent years. This is an attempt to improve high-frequency characteristics by coating fine powder such as silicon steel or sendust with an organic insulating binder (see, for example, JP-A-59-50138).

[0006]

However, the soft magnetic powder coated with an organic binder has the drawback that the heat resistance and insulating properties of the magnetic core are governed by the properties of the resin constituting the binder. is there.

Therefore, the use of an inorganic binder such as water glass has been studied as a material capable of further improving the insulating property, and is partially put to practical use.

However, the water glass containing sodium silicate as a main component has a problem that it has a high insulating property but a poor heat resistance. Therefore, the powder cannot be heated to the temperature necessary for releasing the strain generated inside the soft magnetic powder during the powder molding, and it is difficult to reduce the coercive force. Therefore, there is a problem that the iron loss value in the high frequency range becomes large and the frequency band usable as the magnetic core is limited.

The present invention has been made in view of the above conventional problems, and provides a high-frequency powder magnetic core which can improve magnetic flux density, reduce iron loss, and have excellent frequency characteristics, and a method for manufacturing the same. Is intended.

[0010]

According to a first aspect of the present invention, there is provided a high frequency powder magnetic core obtained by compacting, bonding and solidifying soft magnetic powder, wherein the soft magnetic powder contains Cr or P as an essential element. Is characterized in that the soft magnetic powders are bonded to each other via the insulating layer.

According to a second aspect of the present invention, there is provided a method for producing a high-frequency powder magnetic core, which is produced by compacting, bonding and solidifying soft magnetic powder, and the soft magnetic powder and glassy insulation containing Cr or P as an essential element. A first step of mixing the layers and drying the mixture to remove water, a second step of solidifying the dried mixture with a powder molding press, and a third step of annealing the solidified body It is characterized by having a process.

Here, as the soft magnetic powder in the present invention, silicon steel powder, sendust powder, amorphous powder, and permalloy powder can be adopted, but high-purity atomized iron powder is more preferable. Further, in this case, in order to further improve the magnetic properties, it is effective to reduce the demagnetizing factor by subjecting the soft magnetic powder to a flatness of 2 or more with a twin roll or a ball mill.

By the way, when the soft magnetic powders are bonded to each other through the glass insulating layer, pores (voids) are apt to occur in the bonding portion due to their structure, and the strength is lower than that when a resin is used. For example, there is a concern that if some external force is applied during the coil winding work or the component assembly work, the coil may be easily damaged.

Therefore, the invention of claim 3 is characterized in that the solidified molded body annealed in the third step is immersed in water glass and then dried.

[0015]

According to the dust core for high frequency and the method for producing the same according to the present invention, the soft magnetic powder is coated with the glass-like insulating layer, and the soft magnetic powder is formed into a glass-like insulating layer having originally good insulating properties. Since they are bonded via the insulating layer, the insulating property and the magnetic flux density are improved. In the present invention, Cr and P are indispensable as constituent elements of the above glassy insulating layer, so that heat resistance is improved by that much, and annealing can be performed at a temperature necessary to release the strain generated during solidification molding. As a result, the iron loss value can be reduced and the usable frequency band can be expanded.

Further, in the invention of claim 3, since the solidified molded body after the annealing is impregnated with water glass, the water glass penetrates into the pores between the insulating layers to further firmly bond the insulating layers, The mechanical strength such as impact resistance of the dust core itself can be improved accordingly. Therefore, it is possible to avoid the problem of damage when performing the winding work or the assembling work, and it is possible to improve the reliability of quality.

Further, when the soft magnetic powder is made of pure iron powder having an oblateness of 2 or more, the demagnetizing factor can be lowered and the magnetic characteristics such as magnetic flux density can be further improved.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 are views for explaining a high-frequency dust core and a method for manufacturing the same according to an embodiment of the present invention.
FIG. 1 is a schematic diagram of soft magnetic powder subjected to insulation treatment, and FIG. 2 is a schematic diagram showing a manufacturing process.

In FIG. 1, reference numeral 1 is a soft magnetic powder constituting the dust core of this embodiment, and the outer surface of the powder 1 is covered with a glass-like insulating layer 2. The soft magnetic powders 1 are bonded to each other via the insulating layer 2. The soft magnetic powder 1 is obtained by flattening high-purity atomized iron powder with a ball mill or twin rolls to a flatness (major axis / minor axis) of 2 or more. The insulating layer 2 is made of Cr,
It was a glass-like material containing P, and was hardened in the annealing treatment for strain relief described later.

Next, a method of manufacturing a dust core will be described with reference to FIG. First, per liter, magnesium dichromate (120 g), phosphoric acid (75 g), urea (5
g) and an insulating treatment liquid 4 made of a mixed liquid containing glycerin (18 g), and 5 to 100 ml of the treatment liquid 4 is added to and mixed with 60 mesh underpure pure iron powder 3 (100 g). Then, the mixture 5 is heated to 150 ° C to 300
Dry at 5 ° C for about 5 to 25 minutes (Figs. 2 (a), (b),
First step).

The concentration of the insulating layer forming treatment liquid 4 can be changed according to the fluidity of the mixture 5 and the drying treatment method. However, it is necessary to take care not to generate rust, because the characteristics may be deteriorated due to the generation of rust on the powder surface. If necessary, the above coating treatment
It can be repeated more than once, and in this way, there is an effect that the insulating property can be improved, and further improvement in characteristics as a high frequency magnetic material can be expected.

As the soft magnetic powder, in addition to the pure iron powder, silicon steel powder, sendust powder, amorphous powder,
Permalloy powder or the like can be used.

If necessary, a lubricant such as Ca stearate or Zn stearate is added to the mixed powder from which the water content has been removed in an amount of 0.5 to 1.0 wt%, and the mixture containing the lubricant is added. The powder is solidified and molded into a predetermined magnetic core shape by a normal powder molding press 6 (FIG. 2C, second step).

In this solidification molding, the molding pressure of the press 6 is suitably 3 to 6 ton / cm ² . At a pressure of 3 ton / cm ² or less, the molded body becomes brittle and handling becomes difficult.
On the other hand, if it is 6 tons / cm ² or more, the formed insulating coating is destroyed, which causes deterioration of high-frequency characteristics and shortens the die life.

Then, the above-mentioned solidified molded body is heated to 400 ° C. to 6 ° C.
Degreasing and annealing are performed by heating at 00 ° C. for about 1 hour (third step). It is more desirable to perform this annealing treatment in an atmosphere of an inert gas such as Ar or N. As a result, the strain generated in the pure iron powder is released, and at the same time, the insulating layer is hardened to be glass-like, and a dust core having a predetermined shape can be obtained.

In this way, the soft magnetic powder 1 is separated by the glass-like insulating layer 2 in the texture state of the high-frequency powder magnetic core obtained in this example, so that the insulating property and magnetic flux are The density can be improved.

C is used as a constituent element of the insulating layer 2.
Since r and P are indispensable, the heat resistance of the insulating layer 2 can be improved as compared with the case of conventional water glass, and therefore, up to the temperature necessary for releasing the strain generated inside the soft magnetic powder during powder molding. You can now heat. As a result, it is possible to solve the problem that it is difficult to reduce the coercive force as in the case of using an inorganic binder such as water glass, the iron loss value in the high frequency range becomes small, and the usable frequency band is reduced. Can be expanded.

Further, since the above powder is not coated with the organic insulating binder, it is possible to solve the problem that the heat resistance and insulating characteristics of the material are governed by the characteristics of the constituting resin.

Further, the high-frequency current tends to concentrate on the surface of the metal conductor, but in this embodiment, the soft magnetic powder is finely pulverized to 60 mesh under, so that not only the iron loss value but also the frequency characteristic can be improved. Furthermore, in this embodiment, since the soft magnetic powder is flattened with a twin roll or a ball mill to have an oblateness of 2 or more, there is an effect of lowering the demagnetizing factor and the magnetic flux density can be further improved.

FIG. 3 is a diagram showing the frequency dependence of the AC initial magnetic permeability in various samples for explaining the experimental results of the present invention.

In the figure, the characteristic curve (1) shows the characteristics of the sample of the first example which was powder-molded at 4.5 ton / cm ² after the coating treatment in the above-mentioned example and then annealed and solidified at 500 ° C. The characteristic curve (2) is 400 ° C. of the powder obtained by adding and mixing 1% by weight of the imide resin after the film treatment in the above example.
The characteristic curve (3) of the second embodiment sample annealed and solidified in Example 3 is that the powder obtained by adding 1% of the epoxy resin powder after the coating treatment in the above embodiment and mixing is annealed and solidified at 200 ° C. The characteristics of each sample are shown below.

The characteristic curve (4) is the characteristic curve of the first comparative sample in which only the imide resin was added to the same iron powder as that used in the above-mentioned example without the insulating coating treatment.
Shows the characteristics of the second comparative example sample in which only the epoxy resin was added to the same iron powder without the insulating film treatment.

In the figure, the first and second comparative samples (4) and (5) not subjected to the coating treatment have excellent magnetic permeability in the frequency band around 1 KHz. It can be seen that it is unsuitable as a high frequency material due to the increase in iron loss.

On the other hand, in the samples (1) and (2) of the first and second embodiments, which have been subjected to the insulating film treatment according to the present embodiment,
It can be seen that stable magnetic permeability is exhibited even when the frequency becomes high, and excellent characteristics are maintained as a high frequency magnetic material.

Further, in the third embodiment sample (3), since the epoxy resin is added for binding and solidifying the powder, the frequency characteristics are inferior to those of the above (1) and (2), but at a lower temperature. There is an advantage that it can be solidified.

Next, a method of manufacturing a high frequency powder magnetic core according to an embodiment of the present invention will be described. In the method of this example, a dust core is manufactured by a method substantially similar to the above-described first to third steps. Then, the powder magnetic core obtained in the third step is immersed in a glass aqueous solution, and then dried in the atmosphere at a temperature of 300 ° C. or lower. As a result, the water glass permeates into the pores formed between the insulating layers of the dust core, and the insulating layers are further firmly joined together.

Here, it is desirable that the glass aqueous solution has a ratio of water glass: water = 1: 1 to 8. This is because if the amount of water is too large, the joint strength cannot be improved so much. To improve the impregnation effect of the glass aqueous solution,
For example, it is preferable to add a surfactant such as commercially available Ebara cordierite # 62. Furthermore, the immersion time differs depending on the size, shape, etc. of the dust core, but is not particularly limited. For example, 5t × 36φ × 24φ (molding density 8
(0% or more), when the immersion time was changed in the range of 1 minute to 60 minutes using a dust core, the radial crushing strength did not change in any case, but in order to be more certain, the water glass solution was vacuum degassed. Good to do.

Although the drying time can be shortened as the drying temperature is raised, problems such as bending and swelling of the dust core are likely to occur if the drying is performed rapidly. Further, if the drying temperature exceeds 300 ° C., oxidation is likely to occur, and as a result, the magnetic properties deteriorate, so it is desirable to set the temperature below this.

[0039]

[Table 1]

[Table 2]

Table 1 shows the crush strength and the AC initial permeability of each of the samples No. 1 to No. 17 for explaining the experimental results of this example.

In the table, Sample No. 1 is not impregnated with water glass, and Samples No. 2, No. 12 and No. 13 are when the drying temperature is changed to 80 ° C., 250 ° C. and 300 ° C., respectively. , Sample Nos. 3 to 7 have annealing temperatures of 400 ° C to 600 ° C.
When the temperature was changed to ° C, Samples No. 8 and No. 9 show the cases where the water glass concentration was changed to 1: 4 and 1: 8. Also sample
No. 10 and No. 11 are dipping times of 15 minutes and 60 minutes, Sample No. 14 is 3% silicon steel powder and Sendust powder as magnetic powder, and Sample No. 17 is lubricant. The case where Zn stearate is used is shown.

In Table 1, in the case of Sample No. 1 which is not impregnated with water glass, the crushing strength is 0.8 kg / cm ² . On the other hand, each sample No. 2 to N impregnated with water glass
In the case of o.17, the crushing strength is 1.3 to 6.0 Kg / cm.
You can see that it has improved to ² . By the way, each sample No.
In Nos. 2 to 17, when the annealing temperature is 400 ° C., the crush strength is relatively low at 1.3 kg / cm ^2, and the strength increases as the temperature increases. However, when the temperature is set to 600 ° C., a decrease in magnetic permeability is recognized, so the annealing temperature is 425 to 5
The range of 00 ° C is preferred. Moreover, the crushing strength becomes lower as the concentration of water glass becomes thinner, and the drying temperature is set to 3
When it is set to 00 ° C, the magnetic permeability is slightly lowered. On the other hand, even if the immersion time, magnetic powder, activator, etc. are changed, there is almost no effect on the crush strength.

Thus, by impregnating the powder magnetic core after the annealing treatment with water glass and drying it, the mechanical strength can be greatly improved, the winding and the damage during handling can be avoided, and the reliability of the quality can be improved. Can be improved.

[0044]

As described above, according to the high-frequency dust core and the method for producing the same according to the present invention, the soft magnetic powder is coated with the glass-like insulating layer containing Cr or P as an essential element, and the soft magnetic powder is coated. Since they are bonded to each other via the glass-like insulating layer, the insulating property and the magnetic flux density can be improved, the iron loss can be reduced, and the usable frequency band can be expanded. Further, according to the invention of claim 3, since the annealed powder magnetic core is impregnated with water glass, the bonding strength between the glass insulating layers can be improved without deteriorating the magnetic properties, and the damage during handling can be avoided. There is.

[Brief description of drawings]

FIG. 1 is a schematic view of an insulating-treated soft magnetic powder according to an embodiment of the invention of claim 1.

FIG. 2 is a schematic view of a method of manufacturing a dust core according to an embodiment of the invention of claim 2.

FIG. 3 is an AC initial permeability-frequency characteristic diagram showing experimental results for explaining the effect of the present invention.

[Explanation of symbols]

 1 soft magnetic powder 2 glassy insulating layer

Claims (3)

[Claims] 1. A high frequency powder magnetic core obtained by compacting, bonding and solidifying soft magnetic powder, wherein the soft magnetic powder is covered with a glass-like insulating layer containing Cr or P as an essential element.
Further, the soft magnetic powders are bonded to each other via the insulating layer, so that a high-frequency powder magnetic core. 2. A method for producing a high-frequency powder magnetic core, which is obtained by compacting, bonding, and solidifying soft magnetic powder, wherein the soft magnetic powder is mixed with a glass-like insulating layer containing Cr or P as an essential element. In addition, a first step of drying the mixture to remove water, a second step of solidifying and molding the dried mixture with a powder molding press, and a third step of annealing the solidified body A method of manufacturing a high-frequency dust core, comprising: 3. The method for producing a high-frequency powder magnetic core according to claim 2, wherein the solidified compact that has been annealed in the third step is immersed in water glass and then dried.