JP5078932B2 - Powder mixture for powder magnetic core and method for producing powder magnetic core using the powder mixture - Google Patents

Description

  The present invention compacts soft magnetic iron-based powders such as pure iron powder and iron-based alloy powders (hereinafter collectively referred to as iron-based powders), and provides a dust core for electromagnetic parts. The present invention relates to a powder used for manufacturing.

  Conventionally, magnetic cores made by laminating electromagnetic steel plates or electric iron plates have been used as core materials for motors, but in recent years, dust cores have been used. A powder magnetic core is a powder formed by compressing powder for a powder magnetic core, and has a higher degree of freedom in forming the shape compared to forming magnetic cores by laminating magnetic steel plates, electric iron plates, etc. Since it can be manufactured easily, it can be made smaller and lighter than conventional motors. The powder magnetic core of such a motor core material is required to have a lower iron loss and a higher magnetic flux density than ever before.

  The dust core exhibits good electromagnetic conversion characteristics in a high frequency band of, for example, 1 kHz or more, but generally under driving conditions in which the motor is operating [for example, the driving frequency is several hundred Hz to 1 kHz and the driving magnetic flux is 1 T (Tesla). Above], the electromagnetic conversion characteristics tend to deteriorate. This deterioration of electromagnetic conversion characteristics [that is, energy loss (iron loss) during magnetic conversion] is the sum of eddy current loss and hysteresis loss if the change in magnetic flux in the material is not accompanied by a relaxation phenomenon (such as magnetic resonance). (For example, refer nonpatent literature 1).

  Eddy current loss is Joule loss of induced current accompanying electromotive force generated by electromagnetic induction with respect to magnetic field change. This eddy current loss is considered to be proportional to the magnetic field change rate, that is, the square of the frequency, and the eddy current loss increases as the electric resistance of the dust core decreases and as the range through which the eddy current flows increases. This eddy current is roughly classified into an intraparticle eddy current flowing in individual iron-based powder particles and an interparticle eddy current flowing between iron-based powder particles. Therefore, if the electrical insulation of the individual iron-based powders is complete, no interparticle eddy currents are generated, so that only intraparticle eddy currents are obtained, and the eddy current loss as a whole can be reduced.

  On the other hand, the hysteresis loss is considered to correspond to the area of a BH (magnetic flux density-magnetic field) curve. Factors that influence the shape of the BH curve and govern the hysteresis loss include the coercivity of the dust core (loop width of the BH curve) and the maximum magnetic flux density. That is, since the hysteresis loss is proportional to the coercive force, the coercive force may be reduced to reduce the hysteresis loss. This coercive force increases as more distortion is introduced when the powder for powder magnetic core is compacted. To reduce the coercive force of the powder magnetic core and reduce hysteresis loss, compaction molding What is necessary is just to release the strain introduced at the time of molding by removing the strain later. Since the introduced strain is more likely to be released at higher temperatures, it is recommended that the strain relief annealing be performed at as high a temperature as possible.

  As described above, in order to reduce the eddy current loss, the surface of the powder magnetic core powder used as a raw material may be covered with an insulating layer, and in order to further reduce the hysteresis loss, this powder magnetic core powder is compressed. What is necessary is just to give heat resistance to the insulating layer coat | covered on the surface of the powder for powder magnetic cores, in order to carry out distortion relief annealing at high temperature after powder shaping | molding.

  As a powder for a powder magnetic core having both insulation and heat resistance, Patent Document 1 proposes a soft magnetic powder whose surface is covered with a glassy insulating layer containing P, Mg, B, and Fe as essential elements. Has been. Patent Document 2 describes that the surface of a powder containing iron as a main component is coated with a film containing a silicone resin and a pigment, and a film containing a phosphorus compound or the like is formed as a lower layer of the film.

  Incidentally, the dust core is required to have a high magnetic flux density in addition to low iron loss. The magnetic flux density is defined by the product of magnetic permeability and excitation magnetic field (permeability × excitation magnetic field), and this magnetic flux density corresponds to force (torque). In other words, when the dust core is used as a core material of a motor, for example, if the torque is made constant, the dust core can be made smaller as the dust core has a higher magnetic flux density. On the other hand, when the size of the dust core is the same, a larger torque is obtained with a dust core having a higher magnetic flux density.

  However, as a result of studies by the present inventors, as disclosed in Patent Document 1 and Patent Document 2, the surface of the powder magnetic core powder is coated with a powder coated with a film having both insulating properties and heat resistance. The dust core obtained by powder molding has been found to have a low magnetic flux density and is required to increase the magnetic flux density.

JP-A-6-260319 JP 2003-303711 A

“SEI Technical Review No. 166”, published by Sumitomo Electric Industries, March 2005, p. 1-6

  The present invention has been made in view of such a situation, and an object of the present invention is to produce a dust core for producing a dust core having a small iron loss (eddy current loss and hysteresis loss) and a high magnetic flux density. It is to provide powder for use.

  The present inventors have intensively studied to provide a powder for a dust core that can produce a dust core with a low iron loss and a high magnetic flux density. As a result, if two types of iron-based powders with different types of coatings formed on the surface are mixed, and the compacted powder of this mixed powder is strain-relieved and annealed, the pressure that combines low iron loss and high magnetic flux density The inventors have found that a powder magnetic core can be obtained and completed the present invention.

  That is, the mixed powder for a powder magnetic core according to the present invention that has solved the above-mentioned problems is an iron-based powder A in which an insulating inorganic film a and a heat-resistant resin film b are formed in this order on the surface, It has a gist in that it includes an iron-based powder B having an insulating inorganic coating c formed on the surface.

The mixing ratio of the iron-based powder A and the iron-based powder B preferably satisfies the following formula (1).
0% <[mass of iron-based powder B / (mass of iron-based powder A + mass of iron-based powder B)] × 100 ≦ 60% (1)

  The insulating inorganic film a has an average film thickness of 1 nm or more, the heat-resistant resin film b has an average film thickness of 20 nm or more, the insulating inorganic film c has an average film thickness of 1 nm or more, and the insulating inorganic film a The total of the average film thickness of the heat resistant resin film b and the insulating inorganic film c is preferably 250 nm or less.

  As the insulating inorganic film a and the insulating inorganic film c, a phosphoric acid film is preferably formed, and as the heat-resistant resin film b, a silicone resin film is preferably formed.

  If the mixed powder of the present invention is used, a powder magnetic core can be manufactured by performing strain relief annealing at 400 ° C. or higher after powder molding, and the present invention also includes a powder magnetic core obtained by such a manufacturing method. Is included.

  According to the present invention, the heat resistance occupying the dust core can be obtained by mixing the iron-based powder not formed with the heat-resistant resin film into the iron-based powder formed with the insulating inorganic film and the heat-resistant resin film. The amount of resin used can be reduced. As a result, as will be described later, the magnetic flux density of the dust core can be increased. As described above, the mixed powder of the present invention includes the iron-based powder on which the insulating inorganic film and the heat-resistant resin film are formed, and the iron-based powder on which the insulating inorganic film is formed. Insulation and heat resistance can be ensured, and iron loss of the dust core can be reduced.

FIG. 1 is a view schematically showing a state in which the powder mixture for powder magnetic core of the present invention is in contact. FIG. 2 is a diagram schematically showing how the iron-based powders A are in contact with each other. FIG. 3 is a graph showing the results of measuring the specific resistance. FIG. 4 is a graph showing the relationship between the total film thickness and the magnetic flux density. FIG. 5 is a graph showing the relationship between the mixing ratio of the iron-based powder B and the magnetic flux density. FIG. 6 is a graph showing the relationship between the mixing ratio of iron-based powder B and iron loss.

  The mixed powder for a powder magnetic core of the present invention comprises an iron-based powder A in which an insulating inorganic film a and a heat-resistant resin film b are formed in this order on the surface of the raw iron-based powder, and a surface of the raw iron-based powder. This is a mixture of iron-based powder B on which an insulating inorganic coating c is formed. By mixing the iron-based powder A and the iron-based powder B, the amount of heat-resistant resin contained in the dust core can be reduced. That is, when the iron-based powder A and the iron-based powder B are mixed, when the iron-based powder A and the iron-based powder B are in contact with each other, the adjacent raw material iron is not covered with the heat-resistant resin. The distance of the base powder is shortened. By reducing the distance between the raw iron-base powders, the magnetic gap is reduced, the demagnetizing field generated in the raw iron-base powder is reduced, and as a result, the permeability of the dust core is increased, and the dust core Magnetic flux density can be increased. This will be described with reference to the drawings, but the present invention is not limited to these drawings.

  FIG. 1 is a view schematically showing a state in which the powder mixture for powder magnetic core of the present invention is in contact. In FIG. 1, 1 is a raw material iron-based powder, a is an insulating inorganic film, b is a heat-resistant resin film, and c is an insulating inorganic film. In the iron-based powder A, an insulating inorganic film a and a heat-resistant resin film b are formed in this order on the surface of the raw iron-based powder 1, and the iron-based powder B is formed on the surface of the raw iron-based powder 1. An insulating inorganic film c is formed. X represents the distance between the raw iron-based powder 1 of the iron-based powder A and the iron-based powder B. On the other hand, FIG. 2 is a view schematically showing a state in which the iron-based powders A are in contact with each other, and the same parts as those in FIG. 1 and 2 show sectional views of each iron-based powder for convenience of explanation, and the particle diameter of the raw iron-based powder 1 and the film thickness of the insulating inorganic coating a and the heat-resistant resin coating b are the same. .

  As shown in FIG. 1, the mixed powder for a powder magnetic core of the present invention is obtained by mixing an iron-based powder A on which a heat-resistant resin film b is formed and an iron-based powder B on which a heat-resistant resin film is not formed. Therefore, the distance x of the raw iron-based powder 1 is shortened. On the other hand, when the iron-based powders A are brought into contact with each other, the distance x of the raw iron-based powder 1 becomes longer because the film thickness of the heat-resistant resin film b becomes twice that of FIG. Therefore, when FIG. 1 is compared with FIG. 2, since the distance of the raw material iron-based powder 1 is shorter in FIG. 1, the magnetic gap becomes smaller, and finally the magnetic flux density of the dust core can be increased. In addition, according to the present invention, since the iron-based powder A on which the heat-resistant resin film b is formed and the iron-based powder B on which the heat-resistant resin film is not formed are mixed, the heat resistance that occupies the dust core. Since the amount of resin used can be reduced, the cost can be reduced. Hereinafter, the present invention will be described in detail.

  In the iron-based powder A of the present invention, an insulating inorganic coating a and a heat-resistant resin coating b are formed in this order on the surface of the raw iron-based powder, and the iron-based powder B is formed on the surface of the raw iron-based powder. An insulating inorganic film c is formed. The insulating inorganic coatings a and c are formed to ensure the electrical insulation of the raw iron-based powder, and the heat-resistant resin coating b has the electrical insulating thermal stability of the insulating inorganic coating a. Formed to improve. The heat resistant resin film b also contributes to improving the mechanical properties of the dust core.

  The raw material iron-based powder may be a ferromagnetic metal powder, specifically, pure iron powder, iron-based alloy powder (for example, Fe-Al alloy, Fe-Si alloy, Sendust, Permalloy, etc.) and amorphous A powder etc. are mentioned. Such a soft magnetic powder can be produced by, for example, an atomizing method or a pulverizing method. Moreover, you may reduce | restore the obtained powder as needed. In such a manufacturing method, a soft magnetic powder having an average particle size of about 20 to 250 μm with a cumulative particle size distribution of 50% can be obtained with a particle size distribution evaluated by a sieving method. In the present invention, about 50 to 200 μm is obtained. Are preferably used.

  In the present invention, the insulating inorganic coating a or c is formed on the surface of the raw iron-based powder. The material of the insulating inorganic film may be any material that can insulate the raw iron-based powder. When the specific resistance of the final dust core is measured by the four-terminal method, the specific resistance is about 50 μΩ · m or more. What is necessary.

As the insulating inorganic film, for example, a phosphoric acid film or a chromium film can be used. Among these insulating inorganic films, it is particularly preferable to form a phosphoric acid film. This is because the phosphoric acid-based film is a glassy film formed by a chemical conversion treatment with orthophosphoric acid (H ₃ PO ₄ ) and is excellent in electrical insulation.

  In addition, regarding the iron-based powder A and the iron-based powder B, the types of the insulating inorganic coating a and the insulating inorganic coating c may be the same or different, but are preferably the same. Good. This is because local variations do not occur in the physical properties of the dust core due to the difference in the type of the insulating inorganic film.

  In the iron-based powder A, a heat-resistant resin film b is formed on the surface of the insulating inorganic film a. The material of the heat-resistant resin film b may be any material that improves the thermal stability of the electrical insulation, and any material that does not deteriorate the insulation even if the strain relief annealing is performed at 400 ° C. or higher, for example.

  Examples of the heat resistant resin film include silicone resin, phenol resin, epoxy resin, phenoxy resin, polyamide resin, polyimide resin, polyphenylene sulfide resin, styrene resin, acrylic resin, styrene / acrylic resin, polyester resin, urethane resin, polyethylene. For example, olefin resins such as carbonate resins, ketone resins, fluorine resins such as methacrylate methacrylate and vinylidene fluoride, engineering plastics such as PEEK, or modified products thereof can be used. Among these heat resistant resin films, it is particularly preferable to form a silicone resin film. This is because the silicone resin film has an effect of improving the mechanical stability of the dust core as well as improving the thermal stability of the electrical insulation. That is, at the end of the crosslinking / curing reaction of the silicone resin (when the green compact is molded), a Si—O bond having excellent heat resistance is formed, resulting in an insulating film having excellent thermal stability. Further, since the powders are firmly bonded to each other, the mechanical strength is increased.

As a silicone resin, since the powder is sticky when the curing is slow and the handling property after film formation is poor, the trifunctionality is less than the bifunctional D unit (R ₂ SiX ₂ : X is a hydrolyzable group). T unit: one (RSiX ₃ X is as defined above) with many are preferred. However, if a large amount of tetrafunctional Q units (SiX ₄ : X is the same as above) is contained, the powders are strongly bound during pre-curing, and the subsequent molding process cannot be performed. It is not preferable. Accordingly, a silicone resin having a T unit of 60 mol% or more is preferable, a silicone resin having 80 mol% or more is more preferable, and a silicone resin having all T units is most preferable.

  As the silicone resin, a methylphenyl silicone resin in which R is a methyl group or a phenyl group is generally used, and heat resistance is higher when there are more phenyl groups.

The mixing ratio of the iron-based powder A and the iron-based powder B preferably satisfies the following formula (1).
0% <[mass of iron-based powder B / (mass of iron-based powder A + mass of iron-based powder B)] × 100 ≦ 60% (1)

  When the ratio of the iron-based powder B in the mixed powder of the present invention is high and the ratio of the iron-based powder B exceeds 60%, the amount of heat-resistant resin used is reduced, so that the thermal stability of the insulating inorganic film is reduced. This is because it may not be possible to secure this. Accordingly, the mixing ratio is preferably 60% or less, more preferably 55% or less, and still more preferably 50% or less. The lower limit of the mixing ratio is not particularly limited, and the above-described effect is exhibited even when only a small amount of iron-based powder B is mixed with iron-based powder A. Preferably it is 5% or more, More preferably, it is 10% or more, More preferably, it is 15% or more.

  In the present invention, the average film thickness of the insulating inorganic film a and the insulating inorganic film c is preferably 1 nm or more. When the average film thickness is less than 1 nm, since the film thickness is too thin, it is difficult to form an insulating inorganic film uniformly on the surface of the raw iron-based powder, and the raw iron-based powder may be exposed. As a result, the insulation properties may be reduced and eddy current loss may increase. Therefore, the average film thickness of the insulating inorganic film a and the insulating inorganic film c is preferably 1 nm or more, more preferably 5 nm or more, and further preferably 10 nm or more. The film thickness of the insulating inorganic film is preferably as large as possible in order to improve the insulation, but as the film thickness increases, the distance between the raw iron-based powders increases, and a magnetic gap is generated. Therefore, the magnetic flux density of the dust core is reduced. Accordingly, the film thickness is preferably 230 nm or less, more preferably 150 nm or less, and still more preferably 100 nm or less.

  The average film thickness of the insulating inorganic film a and the insulating inorganic film c may be the same or different. Preferably they are the same. This is because local variations in the physical properties of the dust core are not caused by the difference in film thickness of the insulating inorganic coating.

  On the other hand, the average film thickness of the heat resistant resin film b is preferably 20 nm or more. If the average film thickness is less than 20 nm, since the film thickness is too thin, it is difficult to form a heat-resistant resin film uniformly on the surface of the raw iron-based powder, and it becomes difficult to improve the thermal stability of the electrical insulation. is there. For this reason, strain relief annealing cannot be performed at a high temperature, and it is difficult to reduce hysteresis loss. Accordingly, the average film thickness of the heat-resistant resin film b is preferably 20 nm or more, more preferably 25 nm or more, and further preferably 30 nm or more. The film thickness of the heat-resistant resin film b is preferably as large as possible in order to increase the thermal stability of the electrical insulation. However, as the film thickness increases, the distance between the raw iron-based powders increases, and the magnetic gap Produce. Therefore, the magnetic flux density of the dust core is reduced. Accordingly, the film thickness is preferably 230 nm or less, more preferably 150 nm or less, and still more preferably 100 nm or less. In order to reduce the iron loss (eddy current loss and hysteresis loss), it is desirable to form the insulating inorganic film a thicker than the heat-resistant resin film b.

  In this invention, it is preferable that the sum total of the average film thickness of the said insulating inorganic membrane | film | coat a, the said heat resistant resin membrane | film | coat b, and the said insulating inorganic membrane | film | coat c is 250 nm or less. When the total of the average film thicknesses of these films a to c exceeds 250 nm, the distance x between the raw iron-based powders shown in FIG. 1 is increased, so that a magnetic gap is generated and the magnetic flux density of the dust core is reduced. Because. Therefore, the total may be 250 nm or less, more preferably 200 nm or less, and still more preferably 150 nm or less. In addition, the film thickness of the said insulating inorganic membrane | film | coat or heat resistant resin membrane | film | coat can be measured by the method described in the Example mentioned later.

  The mixed powder for a dust core of the present invention may further contain a lubricant. The action of this lubricant can reduce the frictional resistance between powders when compacting iron-based powders, or between iron-based powders and the inner wall of the mold, and prevent mold galling and heat generation during molding. Can do.

  In order to effectively exhibit such an effect, it is preferable that the lubricant is contained in an amount of 0.2% by mass or more in the total amount of the powder. However, if the amount of lubricant increases, it is against the densification of the green compact, so it is preferable to keep it at 0.8% by mass or less. In the case of compacting, if the lubricant is applied to the inner wall surface of the mold and then molded (mold lubrication molding), the amount of lubricant may be less than 0.2% by mass.

  As the lubricant, conventionally known ones may be used. Specifically, metal stearate powder such as zinc stearate, lithium stearate, calcium stearate, and paraffin, wax, natural or synthetic resin derivatives. Etc.

  The mixed powder of the present invention obtained by mixing the iron-based powder A and the iron-based powder B (a lubricant if necessary) is used when producing a dust core, and from the mixed powder of the present invention. The obtained dust core is also included in the present invention.

  In producing the dust core, the mixed powder may be formed and then subjected to strain relief annealing. The compacting method is not particularly limited, and a known method can be adopted. The suitable conditions for compacting are 490 to 1960 MPa (more preferably 390 to 1000 MPa) in terms of surface pressure. The molding temperature can be either room temperature molding or warm molding (for example, 100 to 250 ° C.). It is preferable to perform warm molding by mold lubrication molding because a high-strength powder magnetic core can be obtained.

  After molding, strain relief annealing is performed to reduce the hysteresis loss of the dust core. The conditions for strain relief annealing are not particularly limited, and known conditions can be applied. However, if the mixed powder of the present invention is used, the temperature for strain relief annealing can be increased. That is, since the mixed powder of the present invention is coated with a combination of an insulating inorganic film and a heat-resistant resin film, the thermal stability of the insulating inorganic film is maintained even when the temperature of strain relief annealing is 400 ° C. or higher. Does not deteriorate. Therefore, the distortion introduced at the time of compacting can be released at a high temperature, and the hysteresis loss of the dust core can be further reduced.

  The atmosphere for performing strain relief annealing is not particularly limited as long as it does not contain oxygen, but is preferably an inert gas atmosphere such as nitrogen. The time for performing strain relief annealing is not particularly limited, but is preferably 20 minutes or longer, more preferably 30 minutes or longer, and even more preferably 1 hour or longer.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention. Unless otherwise specified, “part” means “part by mass” and “%” means “% by mass”.

[Experimental Example 1]
Pure iron powder ("Atomel 300NH" manufactured by Kobe Steel; average particle size 80 μm, average crystal particle size 30 μm) was used as the soft magnetic iron-based powder. ~ C was obtained. The iron-based powder A is an iron-based powder in which an insulating inorganic film and a heat-resistant resin film are formed in this order on the surface of the pure iron powder, and the iron-based powder B is insulated on the surface of the pure iron powder. The iron-based powder and iron-based powder C on which a heat-resistant inorganic film is formed are iron-based powders in which a heat-resistant resin film is formed on the surface of the pure iron powder.

As the insulating inorganic film, a phosphoric acid film was formed by the following procedure. 1000 parts of water, 193 parts of H ₃ PO ₄ , 31 parts of MgO and 30 parts of H ₃ BO ₃ were mixed, and 50 parts of the treatment solution diluted 10 times was passed through a sieve having an opening of 300 μm and the pure iron powder 1000 After mixing for 5 minutes using a V-type mixer, it was dried in the atmosphere at 200 ° C. for 30 minutes and passed through a sieve having an opening of 300 μm.

  As the heat resistant resin film, a silicone resin film was formed by the following procedure. A silicone resin (“KR220L” manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in toluene to prepare a resin solution having a solid content concentration of 5 mass%. After adding and mixing so that resin solid content might be 0.1% with respect to iron powder, it heat-dried at 75 degreeC in air | atmosphere for 20 minutes, Then, it passed through the sieve with the opening of 500 micrometers.

The cross sections of the obtained iron-based powders A to C were observed with an Auger electron spectrometer at 500 times, and the film thickness of the phosphoric acid film or the silicone resin film formed on the surface of the pure iron powder was measured by depth analysis. The film thickness was measured by quantitatively analyzing P and Si in the depth direction and measuring the depth until the P or Si concentration became constant. The number of measurement points was five, and the average film thickness was calculated by averaging the measurement results. The film thicknesses of the iron-based powders A to C were as follows.
Iron-based powder A: The film thickness of the phosphoric acid film is 40 nm, and the film thickness of the silicone resin film is 40 nm.
Iron-based powder B: Phosphate film thickness is 40 nm
Iron-based powder C: The film thickness of the silicone resin film is 40 nm

Next, the obtained iron-based powders A to C were respectively compacted to obtain molded bodies. In compaction molding, zinc stearate is dispersed in alcohol and applied to the surface of the mold, and then iron powder is placed. The surface pressure is 784 to 1176 MPa, room temperature (25 ° C), and the density of the compact is 7.5 g / cm. ³ was formed. The dimensions of the molded body are 31.75 mm × 12.7 mm and the height is about 5 mm. Then, heated to 400 ° C, 450 ° C, 500 ° C, 550 ° C, or 600 ° C at a temperature increase rate of about 50 ° C / min in a nitrogen atmosphere, held at this temperature for 1 hour, cooled in the furnace, and strained. Taken and annealed.

  The surface of the molded body obtained by strain relief annealing was polished with No. 400, and the specific resistance was measured by a 4-terminal method using a digital multimeter “VOAC-7510” manufactured by Iwasaki Tsushinki. The measurement results are shown in Table 1 below (heat treatment temperature of 400 to 600 ° C. in Table 1). In addition, in the following Table 1, the result of measuring the specific resistance of a molded body (without strain relief annealing) obtained by compacting the iron-based powders A to C is also shown (heat treatment temperature of 25 ° C. in Table 1). . Moreover, the result of Table 1 is shown in FIG. In FIG. 3, ● represents the result of the iron-based powder A, ■ represents the result of the iron-based powder B, and ▲ represents the result of the iron-based powder C.

  As is clear from Table 1 and FIG. 3, even if the strain relief annealing temperature is increased by forming a phosphoric acid film and a silicone resin film (● in FIG. 3) on the surface of pure iron powder, phosphoric acid It can be seen that the thermal stability of the film can be secured and the specific resistance can be maintained high.

[Experiment 2]
Iron-based powders A-1 to A- based on the iron-based powder A and the iron-based powder B prepared in Experimental Example 1 and having the phosphoric acid film and the silicone resin film changed in thickness as shown in Table 2 below. 3 and iron-based powders B-1 to B-3 were prepared. The iron-based powders A-1 to A-3 are based on the iron-based powder A obtained in the experimental example 1, and the iron-based powders B-1 to B-3 are iron-based powders obtained in the experimental example 1. Based on B. The film thickness of the phosphoric acid film was controlled by adjusting the dilution ratio of the phosphoric acid treatment solution and changing the phosphoric acid concentration. The film thickness of the silicone resin film was controlled by adjusting the silicone resin concentration of the silicone resin solution.

The obtained iron-base powder A-1 and iron-base powder B-1, iron-base powder A-2 and iron-base powder B-2, iron-base powder A-3 and iron-base powder B-3 were each in a mass ratio of 1 : Using the mixed powder (No. 1 to 3 in Table 3 below) or only the iron-based powder A-1 to A-3 (No. 4 to 6 in Table 3 below), A molded body was obtained. Compacting the zinc stearate was dispersed in an alcohol put iron powder was applied to a mold surface, at 0.99 ° C. at a surface pressure 980～1176MPa, as the density of the molded body is 7.65 g / cm ³ Went to. The dimensions of the molded body are 31.75 mm × 12.7 mm and the height is about 5 mm. Thereafter, the sample was heated to 600 ° C. at a rate of temperature increase of about 50 ° C./min in a nitrogen atmosphere, held at this temperature for 1 hour, then cooled in a furnace and subjected to strain relief annealing.

  The magnetic flux density of the molded product obtained by strain relief annealing was measured using an automatic magnetic test apparatus “Y-1807” manufactured by Yokogawa Electric Corporation at a frequency of 200 Hz and an excitation magnetic field of 10,000 A / m. The results are shown in Table 3 below. FIG. 4 shows the relationship between the total thickness of the iron-based powder (the distance x between the raw iron-based powders shown in FIG. 1 or 2) and the magnetic flux density. In FIG. 4, ■ indicates No. in Table 3 below. As a result of Nos. 1 to 3, ● indicates No. in Table 3 below. The results of 4-6 are shown.

  As is apparent from Table 3 and FIG. 4, it can be seen that the magnetic flux density can be increased by mixing the iron-based powder A and the iron-based powder B.

[Experiment 3]
Using a mixed powder obtained by mixing the iron-based powder A and the iron-based powder B obtained in Experimental Example 1 in the proportions shown in Table 4 below, a compact was obtained by compacting. Compacting the zinc stearate was dispersed in an alcohol put iron powder was applied to a mold surface, at 0.99 ° C. at a surface pressure 980～1176MPa, as the density of the molded body is 7.65 g / cm ³ Molded into. The dimensions of the molded body are 31.75 mm × 12.7 mm and the height is about 5 mm. Thereafter, the sample was heated to 500 ° C. at a temperature increase rate of about 50 ° C./min in a nitrogen atmosphere, held at this temperature for 1 hour, and then furnace-cooled and strain-relieved annealed.

  The specific resistance, magnetic flux density, and iron loss of the molded product obtained by strain relief annealing were measured. The specific resistance of the molded body was measured under the same conditions as in Experimental Example 1. The measurement results are shown in Table 4 below. The magnetic flux density of the compact was measured under the same conditions as in Experimental Example 2. The measurement results are shown in Table 4 below. FIG. 5 shows the relationship between the mixing ratio of the iron-based powder B and the magnetic flux density. The iron loss of the molded body was measured using an automatic magnetic test apparatus “Y-1807” manufactured by Yokogawa Electric Corporation at a frequency of 200 Hz and an excitation magnetic flux density of 1.5T. The results are shown in Table 4 below. Moreover, the relationship between the mixing ratio of the iron-based powder B and the iron loss is shown in FIG.

  As apparent from Table 4 and FIG. 5, the magnetic flux density can be increased by increasing the mixing ratio of the iron-based powder B. On the other hand, as is apparent from Table 4 and FIG. 6, when the mixing ratio of the iron-based powder B is up to 60%, the iron loss can be kept low. Therefore, if the mixing ratio of the iron-based powder B is 60% or less, the magnetic flux density can be increased without increasing the iron loss of the dust core.

1 Raw material iron-based powder a Insulating inorganic coating b Heat-resistant resin coating c Insulating inorganic coating A and B Iron-based powder x Distance between raw iron-based powder 1

Claims (5)

  It includes an iron-based powder A in which an insulating inorganic film a and a heat-resistant resin film b are formed in this order on the surface, and an iron-based powder B in which an insulating inorganic film c is formed on the surface. Mixed powder for dust cores. The mixed powder according to claim 1, wherein a mixing ratio of the iron-based powder A and the iron-based powder B satisfies the following formula (1).
0% <[mass of iron-based powder B / (mass of iron-based powder A + mass of iron-based powder B)] × 100 ≦ 60% (1) The average film thickness of the insulating inorganic coating a is 1 nm or more,
The heat-resistant resin film b has an average film thickness of 20 nm or more,
The average film thickness of the insulating inorganic film c is 1 nm or more, and the total of the average film thicknesses of the insulating inorganic film a, the heat-resistant resin film b, and the insulating inorganic film c is 250 nm or less. Or the mixed powder of 2.   The mixing according to any one of claims 1 to 3, wherein a phosphoric acid film is formed as the insulating inorganic film a and the insulating inorganic film c, and a silicone resin film is formed as the heat resistant resin film b. Powder.   A powder magnetic core manufacturing method, wherein after the powder mixture according to any one of claims 1 to 4 is compacted, strain relief annealing is performed at 400 ° C or higher.

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