JPH05335156A - Ferrite core insulating method - Google Patents

Abstract

PURPOSE:To realize a method of keeping an Mn-Zn ferrite electrically insulated even in a high frequency region. CONSTITUTION:A ferrite core is electrically insulated through such a manner that a crosslinked organic high molecular film is formed on the surface of the ferrite core, where the crosslinked organic high molecular film is formed through such a method that thermoplastic resin where crosslinking assistant is added is subjected to a crosslinking treatment for the formation of the high molecular film concerned. Or, the crosslinked organic high molecular film is formed through such a method that a thermoplastic resin film is irradiated with radiation to turn into a crosslinked resin film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for insulating a Mn-Zn ferrite core for a transformer used mainly in a switching power supply.

[0002]

2. Description of the Related Art The reduction in size and weight of a switching power supply is indispensable for making a computer and OA-related equipment lighter, thinner, and shorter, but the transformer core occupies the largest volume among the basic parts constituting the power supply. Therefore, there is a strong demand for miniaturization and high performance of the transformer core, and the switching frequency is being increased, and the upper limit is reaching 1 MHz. In addition, miniaturization has been achieved from the perspective of the design of the transformer, and a structure in which a terminal section for connecting to an external element is directly provided on the surface of the core is becoming mainstream. As a technical trend up to now, Mn-Zn ferrite materials for transformer cores, which are mainly used for switching power supplies, form a high-resistance grain boundary phase by adding a small amount of SiO ₂ , CaO or other oxides, and mainly eddy currents are formed. It is reducing losses. As a result 2000-4000
Those having an electric resistance as high as Ω · cm have also been obtained.

[0003]

However, when Mn-Zn ferrite is used in the above high frequency region in the transformer having the above structure, the electric resistance of the Mn-Zn ferrite has a negative frequency dependence, so that the DC electric Resistance is 3000Ω ・ c
Even in the case of about m, it drops to several tens of Ω · cm near 1 MHz, and there has been a problem that the function is deteriorated due to electric leakage and other electronic parts are damaged. The detailed cause of this is currently unknown, and it is the current situation that no improvement in material quality can be expected. Therefore, it is conceivable that the core surface is coated with some kind of insulating material to enhance the insulating property of the core. In that case, the insulating film has high dielectric strength and resistivity, and the core surface is The heat resistance of the insulating coating also becomes a big problem because it is necessary to solder at.

By the way, generally, many thermoplastic synthetic resins have a large volume resistivity and a large dielectric strength and a small dielectric loss. Therefore, it can be said that these resins have excellent electrical characteristics as an electric insulating material, and particularly excellent as a high frequency insulating material. However, since these resins are chain polymers, they generally have the drawback of having a low melting point. For this reason, there is a problem in heat resistance, and even if these resins are coated on the surface of the core, they will be melted by the heat during the soldering work.

Therefore, a technical object of the present invention is to provide a method for maintaining the electrical insulation of Mn-Zn ferrite even in a high frequency region.

[0006]

Means for Solving the Problems The inventors of the present invention add a suitable crosslinking aid to the above-mentioned thermoplastic resin or irradiate it with radiation to form a cross-linking bond between chain molecules and The present invention has achieved the present invention by solving the problem of heat resistance by remarkably improving the melting point by making a chain to a three-dimensional network structure.

According to the present invention, in order to solve the above-mentioned problem of reduction in electric resistance, the surface of the Mn-Zn ferrite core is coated with a crosslinked organic polymer film, so that the electric insulation of the core is maintained even in a high frequency region. The cross-linked organic polymer film is added to the thermoplastic resin by adding a cross-linking auxiliary agent such as an organic peroxide, or by irradiating radiation to cause a cross-linking reaction. It is characterized by being formed.

Here, examples of the thermoplastic resin in the present invention include polyethylene, ethylene-vinyl acetate copolymer and the like, but the thermoplastic resin is not limited to these. Further, the crosslinking aid used in the present invention may be any as long as it gives a radical by thermal decomposition, but it is necessary to select the most suitable one depending on the kind of resin and the manufacturing process. In the case of polyethylene, dicumylper Oxide is preferred. Other typical examples include benzoyl peroxide and butyl peroxide, but it goes without saying that the present invention is not limited to these.

[0009]

EXAMPLES The present invention will be described in detail below with reference to examples.

(Example 1) 53.0Fe ₂ O ₃ -35.
After preparing a ferrite core containing 0MnO-12.0ZnO (numerical value is mol%) as a main component by an ordinary powder metallurgy method, polyethylene having a relatively low molecular weight (500 to 2500) is added to toluene and dissolved while heating. Dicumyl peroxide was added to this to adjust the viscosity, and then M
It was applied to an n-Zn ferrite core. Next, 1 in the constant temperature bath
After holding at 00 ° C. for about 3 hours, it was cooled to room temperature to form a film. The film thickness of the film thus obtained was measured and found to be 10 to 20 μm. Further, the core coated with the above insulating film has a frequency of 500 kHz, 1 MH
μi, electric resistance, driving magnetic flux of 500 G, and core loss at a temperature of 60 ° C. were measured at z and 2 MHz, respectively. Table 1 shows the measurement results at a frequency of 500 kHz and 1 MHz.
Table 2 shows the measurement results at 2 MHz, and Table 3 shows the measurement results at 2 MHz. The temperature at which the coating melts was also measured and is shown in Table 4. From the measurement results of Tables 1 to 4, it is understood that no deterioration of the magnetic properties due to the coating of the crosslinked polymer film was observed at any frequency, the electric resistance was remarkably improved, and the heat resistance was also improved.

(Example 2) Mn having the same composition as in Example 1
After preparing a -Zn ferrite core, ethylene-vinyl acetate copolymer was added to toluene and dissolved with heating, dicumyl peroxide was added to this, the viscosity was adjusted, and then the above Mn-Zn ferrite was coated. did. Next, after holding at 100 ° C. in a constant temperature bath for about 3 hours, it was cooled to room temperature to form a film. The film thickness of the film thus obtained was measured and found to be 15 to 30 μm. Further, with respect to the core coated with the insulating coating, μi and electric resistance at frequencies of 500 kHz, 1 MHz and 2 MHz respectively, driving magnetic flux of 500 G and core loss at a temperature of 60 ° C. were measured in the same manner as in Example 1. The measurement results at a frequency of 500 kHz are shown in Table 1, the measurement results at 1 MHz are shown in Table 2,
Table 3 shows the measurement results at 2 MHz. The temperature at which the coating melts was also measured and is shown in Table 4. From the measurement results of Tables 1 to 4, it is understood that no deterioration of the magnetic properties due to the crosslinked polymer film coating was observed at any frequency, the electric resistance was remarkably improved, and the heat resistance was also improved.

(Example 3) Mn having the same composition as in Example 1
After making the -Zn ferrite core, add a relatively low molecular weight polyethylene (500-2500) to toluene,
Melt while heating and adjust the viscosity.
It was applied to an n-Zn ferrite core. After drying in a constant temperature bath at 70 ° C. for about 5 hours, this was irradiated with an electron beam to carry out a crosslinking treatment. The film thickness of the coating film thus obtained was measured and found to be 15 to 25 μm. Further, with respect to the core coated with the above insulating film, the measurement frequency is 500 kHz, 1
Μi and electric resistance at MHz and 2 MHz,
The core loss was measured at a driving magnetic flux of 500 G and a temperature of 60 ° C. Table 1 shows the measurement results at a frequency of 500 kHz.
Table 2 shows the measurement results at MHz, and Table 3 shows the measurement results at 2 MHz. The temperature at which the coating melts was also measured and is shown in Table 4. From the measurement results of Tables 1 to 4, it is understood that no deterioration of the magnetic properties due to the crosslinked polymer film coating was observed at any frequency, the electric resistance was remarkably improved, and the heat resistance was also improved.

(Example 4) Mn having the same composition as in Example 1
After the -Zn ferrite core was prepared, the ethylene-vinyl acetate copolymer was added to toluene and dissolved while heating to adjust the viscosity, and this was then applied to the Mn-Zn ferrite core. After drying in a constant temperature bath at 80 ° C. for about 5 hours, this was irradiated with an electron beam for cross-linking treatment. When the film thickness of the coating film thus obtained was measured, it was 17 to 28.
was μm. Further, regarding the core coated with the above-mentioned insulating film, μi and electric resistance at measurement frequencies of 500 kHz, 1 MHz and 2 MHz, driving magnetic flux 500 G, temperature 60
The core loss at ° C was measured. Table 1 shows the measurement results at a frequency of 500 kHz and Table 2 shows the measurement results at 1 MHz.
Table 3 shows the measurement results at 2 MHz. The temperature at which the coating melts was also measured and is shown in Table 4. From the measurement results of Tables 1 to 4, it is understood that no deterioration of the magnetic properties due to the crosslinked polymer film coating was observed at any frequency, the electric resistance was remarkably improved, and the heat resistance was also improved.

(Comparative Example) 53.0Fe ₂ O ₃ -35.0
A ferrite core containing MnO-12.0ZnO (numerical value: mol%) as a main component was prepared by a normal powder metallurgy method, and no insulation treatment was performed as a comparative material. The frequency of this comparative material is 500kHz, 1MHz, 2MHz
, Magnetic flux of 500 G, core loss at a temperature of 60 ° C., and electric resistance were measured. Table 1 shows the measurement results at a frequency of 500 kHz, Table 2 shows the measurement results at 1 MHz, and Table 3 shows the measurement results at 2 MHz.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

[0019]

As described above, according to the insulating method of the present invention, the Mn-Zn ferrite coated with the insulating coating obtained by the crosslinking reaction of the thermoplastic resin does not cause the deterioration of the magnetic characteristics and is extremely excellent. It can be seen that it has high insulating properties. Therefore, the ferrite core according to the insulation method of the present invention can be used as a transformer core for a switching power supply without fear of leakage even in a high frequency region.

Since the ferrite core manufactured by the insulating method of the present invention has improved heat resistance, it does not melt during the soldering work. The fact that this contributes to the expansion of new applications for transformer cores for high-frequency power supplies is extremely large, and is extremely important in industry.

Claims (3)

[Claims] 1. A method for insulating a ferrite core, which comprises coating the surface of the ferrite core with a crosslinked organic polymer film. 2. The method of insulating a ferrite core according to claim 1, wherein the organic polymer film is a thermoplastic resin to which a cross-linking aid is added and cross-linking is performed. Insulation method. 3. The method of insulating a ferrite core according to claim 1, wherein the organic polymer film is a thermoplastic resin film irradiated with radiation to be crosslinked. Insulation method.