TWI787834B - Powder for powder core - Google Patents

Abstract

An object of the present invention is to provide a powder for a powder magnetic core which contains a lubricant and can increase the flexural strength of the obtained powder magnetic core. A dust core powder according to an aspect of the present invention includes an iron-based powder, a chemical conversion coating formed on the surface of the iron-based powder, and a surface treatment layer formed on the surface of the chemical conversion coating and containing a silane coupling agent. , the resin layer laminated on the surface of the above-mentioned surface treatment layer, and the main component is polysiloxane resin, and the lubricant present on the surface of the above-mentioned resin layer, and the above-mentioned chemical conversion film contains phosphorus, and nickel and cobalt at least one of .

Description

Powder for powder core

The present invention relates to powders for powder magnetic cores.

Powder magnetic cores are used as magnetic cores in inductors such as motors, choke coils, and reactors. The powder magnetic core is required to be excellent in both mechanical properties and magnetic properties.

The powder magnetic core is produced by compressing powder for powder magnetic core containing iron-based powder. The mechanical characteristics of powder magnetic cores require high flexural strength. The flexural strength of the dust core is increased by increasing the density.

The magnetic characteristics of powder cores require small iron loss and high magnetic flux density. In order to reduce the iron loss, it is effective to coat the iron-based powder with an electrically insulating layer. Also, in order to increase the magnetic flux density, it is effective to increase the density of the powder magnetic core.

In this way, in order to improve the mechanical and magnetic properties of the powder magnetic core, it is effective to increase the density of the powder magnetic core while covering the iron-based powder with an electrically insulating layer.

Today, in order to increase the density of the powder magnetic core, it is proposed to apply a lubricant to the inner surface of the mold. However, according to this configuration, the coating operation becomes complicated and the time required for the coating operation becomes longer, so that the production efficiency decreases.

From such a viewpoint, the technique of pre-mixing a lubricant with the powder for powder magnetic cores was examined (refer to Unexamined-Japanese-Patent No. 2013-149659 and International Publication No. 2011/77694). [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2013-149659 [Patent Document 2] International Publication No. 2011/77694

[Problem to be Solved by the Invention]

Patent Document 1 describes a composite powder in which a lubricant is mixed with a composite oxide layer mainly composed of Fe-P, an organic layer containing Si, and a lubricant on the surface of the metal powder in this order.

Patent Document 2 describes a powder for a powder magnetic core in which a lubricating resin is mixed with a granulated product obtained by mixing a soft magnetic powder and an inorganic insulating powder with an adhesive insulating resin. Patent Document 2 describes that at least one of MgO, Al ₂ O ₃ , TiO ₂ , and CaO can be used as the inorganic insulating substance constituting the inorganic insulating powder. In Patent Document 2, it is described that a silane coupling agent can be added in order to improve the adhesion between the soft magnetic powder and the inorganic insulating powder.

However, as described in Patent Document 1 and Patent Document 2, when a lubricant is mixed in advance with the powder for powder magnetic cores, after the lubricant evaporates or is thermally decomposed, the area where the lubricant once existed will become voids, and the obtained powder magnetic There is a risk that the density of the core will decrease. As a result, there is a possibility that the flexural strength of the powder magnetic core cannot be sufficiently increased.

The present invention was made in view of such circumstances, and an object of the present invention is to provide a powder for powder magnetic cores which contains a lubricant and can increase the flexural strength of the resulting powder magnetic core. [Means to solve the problem]

A dust core powder according to an aspect of the present invention includes an iron-based powder, a chemical conversion coating formed on the surface of the iron-based powder, and a surface treatment layer formed on the surface of the chemical conversion coating and containing a silane coupling agent. , the resin layer laminated on the surface of the above-mentioned surface treatment layer, and the main component is polysiloxane resin, and the lubricant present on the surface of the above-mentioned resin layer, and the above-mentioned chemical conversion film contains phosphorus, and nickel and cobalt at least one.

In the dust core powder, the above-mentioned chemical conversion coating, the above-mentioned surface treatment layer, and the above-mentioned resin layer are sequentially provided on the surface side of the above-mentioned iron-based powder, and the above-mentioned lubricant exists on the surface of the above-mentioned resin layer. In the powder for dust cores, wherein the chemical conversion coating contains phosphorus, and at least one of nickel and cobalt, and the resin layer is laminated on the surface of the chemical conversion coating via the surface treatment layer, therefore A powder magnetic core formed using the powder for a powder magnetic core can have a large flexural strength.

With respect to 100 parts by mass of the above-mentioned iron-based powder, the content of the above-mentioned silane coupling agent is preferably 0.05 to 0.30 parts by mass, and relative to 100 parts by mass of the above-mentioned iron-based powder, the content of the above-mentioned polysiloxane resin Preferably, it is 0.05 mass part or more and 0.30 mass part or less. Thus, by setting the content of the silane coupling agent and the polysiloxane resin within the above range with respect to 100 parts by mass of the iron-based powder, the flexural strength of the powder magnetic core can be increased.

The amount of the lubricant added is preferably not less than 0.20 parts by mass and not more than 0.40 parts by mass relative to 100 parts by mass of the above-mentioned iron-based powder. In this way, by setting the added amount of the lubricant within the above range with respect to 100 parts by mass of the iron-based powder, the slidability of the molded article obtained by compression-molding the dust core powder to the mold can be improved. Sufficiently improve the flexural strength of the powder magnetic core above.

In addition, in this invention, "main component" means the component whose content is the largest in terms of mass, for example, means the component whose content is 50 mass % or more. [Effect of Invention]

As explained above, the powder for powder magnetic core according to one aspect of the present invention contains a lubricant, and can increase the flexural strength of the obtained powder magnetic core.

Embodiments of the present invention will be described in detail below.

[Powders for powder cores] The dust core powder comprises an iron-based powder, a chemical conversion coating formed on the surface of the iron-based powder, a surface treatment layer formed on the surface of the chemical conversion coating, and a resin laminated on the surface of the surface treatment layer. layer, and a lubricant present on the surface of the resin layer. The above-mentioned chemical conversion film, the above-mentioned surface treatment layer and the above-mentioned resin layer are sequentially arranged on the surface of the above-mentioned iron-based powder. That is, the powder for powder magnetic cores is formed by directly forming the chemical conversion film on the surface of the iron-based powder, forming the above-mentioned surface treatment layer directly on the surface of the above-mentioned chemical conversion film, and directly coating the surface of the above-mentioned surface treatment layer. Combine the above resin layer. The aforementioned lubricant exists on the outermost surface of the powder for powder magnetic core.

(iron-based powder) The above-mentioned iron-based powder is a soft magnetic body. Examples of the iron-based powder include pure iron powder, iron-based alloy powder, and iron-based amorphous powder. The aforementioned iron-based alloy powder includes Fe—Al alloy, Fe—Si alloy, sendust, permalloy, and the like. The above-mentioned iron-based powder is produced, for example, by atomizing molten iron (or molten iron alloy) into fine particles, reducing, and then pulverizing. According to this manufacturing method, the average particle diameter of the above-mentioned iron-based powder can be controlled to about 20 μm or more and 250 μm or less. The lower limit of the average particle diameter is preferably 50 μm. The upper limit of the above average particle size is preferably 150 μm. Furthermore, the "average particle diameter of the iron-based powder" means the particle diameter (median diameter) at which the cumulative particle size distribution becomes 50% of the particle size distribution evaluated by the sieving method.

(chemical conversion coating) The above-mentioned chemical conversion coating is an insulating layer having electrical insulation properties. The above-mentioned chemical conversion coating contains P (phosphorus), and at least one of Ni (nickel) and Co (cobalt).

The above-mentioned chemical conversion coating is a phosphoric acid-based chemical conversion coating produced by a chemical conversion treatment using a treatment solution in which a phosphorus-containing compound (for example, orthophosphoric acid (H ₃ PO ₄ )) is dissolved. The above-mentioned chemical conversion coating may also contain Fe (iron) element derived from the above-mentioned iron-based powder.

By containing Ni in the above-mentioned chemical conversion coating, it is easy to increase the flexural strength of the obtained powder magnetic core. When the chemical conversion coating contains Ni, the lower limit of the Ni content is preferably 0.001 parts by mass, more preferably 0.01 parts by mass relative to 100 parts by mass of the powder having the chemical conversion coating formed on the surface of the iron-based powder. On the other hand, the upper limit of the Ni content is preferably 0.05 parts by mass, more preferably 0.03 parts by mass, with respect to 100 parts by mass of the powder. When the above-mentioned content is within the above-mentioned range, the film thickness of the above-mentioned chemical conversion film can be uniformed (that is, the film thickness of the above-mentioned chemical conversion film can be suppressed at the part where the film thickness is extremely small), and the insulation of the powder for powder magnetic core can be ensured. , and it is easy to increase the density of the molded body (hereinafter also simply referred to as "molded body") obtained by compression molding the powder for the powder magnetic core. In addition, the heat resistance of the powder for a powder magnetic core is improved, the heat treatment of the powder for a powder magnetic core at a high temperature becomes possible, and the iron loss of the obtained powder magnetic core can be easily reduced.

When the above-mentioned chemical conversion film contains Ni, when the content of P contained in the above-mentioned chemical conversion film is M _P [mol] and the content of Ni is M _Ni [mol], the ratio of the content of Ni to the content of P ( The lower limit of M _Ni /M _P ) is preferably 0.1, more preferably 0.15. On the other hand, the upper limit of the ratio (M _Ni /M _P ) is preferably 0.5, more preferably 0.4. When the above-mentioned ratio (M _Ni /M _P ) is within the above-mentioned range, it is easy to achieve uniformity of the film thickness of the above-mentioned chemical conversion coating.

When the chemical conversion coating contains Co, the lower limit of the Co content is preferably 0.005 parts by mass relative to 100 parts by mass of the powder having the chemical conversion coating formed on the surface of the iron-based powder. On the other hand, the upper limit of the content of Co is preferably 0.1 parts by mass relative to 100 parts by mass of the powder. When the above-mentioned content is within the above-mentioned range, the film thickness of the above-mentioned chemical conversion film can be uniformed, the insulating property of the powder for powder magnetic core can be ensured, and the high density of the compact can be easily achieved. In addition, the heat resistance of the powder for a powder magnetic core is improved, the heat treatment of the powder for a powder magnetic core at a high temperature becomes possible, and the iron loss of the obtained powder magnetic core is easily reduced.

The above-mentioned chemical conversion coating may contain elements such as Na (sodium), K (potassium), N (nitrogen), S (sulfur), and Cl (chlorine) as other components. These components may be added as necessary because they control the pH of the treatment solution in which the phosphorus-containing compound is dissolved, or because they promote the reaction of the treatment solution.

The above-mentioned chemical conversion coating preferably contains K as the above-mentioned other component. The above-mentioned chemical conversion coating can suppress the combination of O (oxygen) and Fe in the coating to form a semiconductor during heat treatment at high temperature by containing K. Thereby, the decrease of specific resistance and the decrease of flexural strength attributable to heat treatment can be suppressed.

When the above-mentioned chemical conversion coating contains the above-mentioned other components, the content of each of these components is preferably not less than 0.001 parts by mass and not more than 1.0 parts by mass with respect to 100 parts by mass of the above-mentioned iron-based powder. In addition, the above-mentioned chemical conversion coating may contain components other than the above-mentioned other components within the range that does not inhibit the effects of the present invention.

The lower limit of the thickness of the chemical conversion coating is preferably 1 nm, more preferably 10 nm. On the other hand, the upper limit of the film thickness of the chemical conversion coating is preferably 250 nm, more preferably 50 nm. When the said film thickness is less than the said lower limit, there exists a possibility that insulation may become insufficient. Conversely, when the above-mentioned film thickness exceeds the above-mentioned upper limit, it may be difficult to sufficiently increase the density of the molded article obtained.

(surface treatment layer) The above-mentioned surface treatment layer is an insulating layer having electrical insulation properties. The above-mentioned surface treatment layer contains a silane coupling agent. The silane coupling agent has both a functional group that reacts with organic materials such as polysiloxane resin and a functional group that reacts with inorganic materials. The silane coupling agent exists between the above-mentioned chemical conversion film and the above-mentioned resin layer, and improves the adhesion between the above-mentioned chemical conversion film and the above-mentioned resin layer. The silane coupling agent may also be partially arranged in the above-mentioned chemical conversion coating.

There are no special restrictions on the silane coupling agent, and the general formula can be used: X-Si-(OR) _n (except that X is an alkyl group with a polar group at the end, R is an alkyl group with a carbon number of 1 to 3, and n is 1 Integers below 3) above. The polar group in X includes those having an amine group, a urea group, an epoxy group, a thiol group, and a methacryloxy group, among which those having an amine group are particularly preferred.

The lower limit of the content of the silane coupling agent is preferably 0.05 parts by mass, more preferably 0.10 parts by mass, relative to 100 parts by mass of the above-mentioned iron-based powder. On the other hand, the upper limit of the content is preferably 0.30 parts by mass, more preferably 0.20 parts by mass. When the above content is less than the above lower limit, the surface treatment layer cannot be sufficiently formed on the surface of the chemical conversion coating, and the adhesion between the chemical conversion coating and the resin layer may not be sufficiently improved. Conversely, when the above-mentioned content exceeds the above-mentioned upper limit, there is a possibility that the adhesion between the above-mentioned chemical conversion film and the above-mentioned resin layer cannot be sufficiently improved due to the condensation reaction of unreacted silane coupling agents. Moreover, when the said content exceeds the said upper limit, the said surface treatment layer will become too thick, and there exists a possibility that the density of a molded object may not be made high enough. As a result, magnetic properties such as flexural strength and magnetic flux density of the obtained powder magnetic core may be insufficient.

(resin layer) The above-mentioned resin layer is an insulating layer having electrical insulation properties. Also, at the same time, the above-mentioned resin layer is bonded with other resin layers of the powder for powder magnetic core during compression molding of the powder for powder magnetic core (when the cross-linking/hardening reaction of the silicone resin is completed). the bonding layer.

The above-mentioned resin layer is mainly composed of polysiloxane resin. The polysiloxane resin improves the adhesion between the resin layer and the chemical conversion film by combining with the silane coupling agent constituting the surface treatment layer.

Polysiloxane resin is not particularly limited, and from the viewpoint of suppressing the stickiness of the dust core powder and improving workability, it is preferable to use a D unit (R ₂ SiX ₂ : X is hydrolyzable) compared to a difunctional one. group), those with more trifunctional T units (RSiX ₃ : X is a hydrolyzable group). However, when a large amount of four-functional Q units (SiX ₄ : X is a hydrolyzable group) are contained, the pre-hardening treatment described later must be combined with the polysilicon contained in the resin layer of the powder for powder magnetic cores. Oxygen resin will be firmly bonded. From such a viewpoint, the lower limit of the T unit of the polysiloxane resin is preferably 60 mol%, more preferably 80 mol%. In addition, the above-mentioned T unit is preferably 100 mol%.

R in each of the above units includes, for example, a methyl group and a phenyl group. R contained in the silicone resin preferably has a methyl group of 50 mol % or more, more preferably a methyl group of 70 mol % or more. Furthermore, the above-mentioned polysiloxane resin is preferably a methyl polysiloxane resin in which the above-mentioned R does not have a phenyl group. Furthermore, the ratio of the methyl group to the phenyl group in the polysiloxane resin and the functionality can be analyzed by FT-IR and the like.

The lower limit of the content of the polysiloxane resin in the resin layer is 50% by mass, preferably 70% by mass, more preferably 90% by mass. Moreover, the content of the silicone resin in the above-mentioned resin layer is preferably 100% by mass. When the above-mentioned content is less than the above-mentioned lower limit, it may be difficult to sufficiently increase the density of the molded article obtained.

The lower limit of the content of the polysiloxane resin is preferably 0.05 parts by mass, more preferably 0.10 parts by mass, relative to 100 parts by mass of the above-mentioned iron-based powder. On the other hand, the upper limit of the content is preferably 0.30 parts by mass, more preferably 0.20 parts by mass. When the said content is less than the said lower limit, there exists a possibility that it may become difficult to fully increase the flexural strength of the obtained powder magnetic core. Moreover, when the said content is less than the said minimum, there exists a possibility that the heat resistance of the said resin layer may become insufficient. On the contrary, when the said content exceeds the said upper limit, there exists a possibility that the fall of a magnetic flux density may become large.

(lubricant) The above-mentioned lubricant reduces the frictional resistance between powders for powder magnetic core and between the powder for powder magnetic core and a mold when the powder for powder magnetic core is compression-molded to form a molded body. The aforementioned lubricant is, for example, powdery.

Examples of the aforementioned lubricants include organic lubricants and inorganic lubricants, and these may be used alone or in combination of two or more.

Examples of the organic lubricants include hydrocarbon lubricants, fatty acid lubricants, higher alcohol lubricants, aliphatic amide lubricants, metal soap lubricants, and ester lubricants.

Examples of the above-mentioned hydrocarbon-based lubricants include liquid paraffin, paraffin wax, synthetic polyethylene wax, and the like. Examples of the fatty acid-based lubricant include stearic acid. Examples of the above-mentioned higher alcohol-based lubricants include stearyl alcohol. The aforementioned aliphatic amide-based lubricants include, for example, fatty acid amides such as stearic acid amide, oleic acid amide, and erucic acid amide, or methylenebisstearylamide, ethylidenebisstearylamide, etc. Alkyl fatty acid amides such as acid amides, etc. Examples of the metal soap-based lubricants include zinc stearate, calcium stearate, and lithium stearate. Examples of the ester-based lubricants include monoglyceryl stearate.

As the above-mentioned inorganic lubricant, for example, an inorganic compound having a density of 4.0 g/cm ³ or higher can be used. Examples of the above-mentioned inorganic compounds include molybdenum disulfide (MoS ₂ ), zinc oxide (ZnO), and the like.

The lower limit of the amount of the lubricant added is preferably 0.20 parts by mass, more preferably 0.25 parts by mass, relative to 100 parts by mass of the above-mentioned iron-based powder. On the other hand, the upper limit of the content is preferably 0.40 parts by mass, more preferably 0.35 parts by mass. When the said content is less than the said lower limit, there exists a possibility that the slidability of this powder for powder magnetic cores to a mold etc. cannot fully be improved. Conversely, when the above-mentioned content exceeds the above-mentioned upper limit, in a powder magnetic core manufactured using the powder for a powder magnetic core, there is a high concern that voids originating from the above-mentioned lubricant will be formed. As a result, it may be difficult to sufficiently increase the density of the powder magnetic core.

＜Manufacturing method of powder for powder magnetic core＞ The method for producing a powder for a dust core comprises: a step of forming a chemical conversion coating on the surface of the iron-based powder (chemical conversion coating forming step), and a step of forming a surface treatment layer on the surface of the chemical conversion coating (surface treatment layer forming step), a step of laminating a resin layer on the surface of the surface treatment layer (resin layer lamination step), and a step of mixing the powder after the above resin layer lamination step with a lubricant (lubricant mixing step).

(Chemical conversion film formation step) In the step of forming the chemical conversion film, for example, a solution (treatment solution) obtained by dissolving a compound containing P and a compound containing Ni or Co in an aqueous solvent is mixed with the iron-based powder and dried.

The compound containing P includes orthophosphoric acid (H ₃ PO ₄ ), (NH ₂ OH) ₂ ·H ₂ PO ₄ , and the like. Ni-containing compounds include nickel nitrate (Ni(NO ₃ ) ₂ ), nickel sulfate, nickel chloride, nickel carbonate, and the like. Co-containing compounds include Co ₃ (PO ₄ ) ₂ , Co ₃ (PO ₄ ) ₂ ·8H ₂ O, and the like. Moreover, nickel _{pyrophosphate} ( _Ni2P2O7 ) etc. can also be used as a _compound containing P and Ni together.

Additives such as alkali salts such as Na or K, ammonia and ammonium salts, sulfates, nitrates, and phosphates may also be contained in the above-mentioned treatment liquids for pH control or reaction acceleration. Examples of the above-mentioned sulfates include (NH ₂ OH) ₂ ·H ₂ SO ₄ and the like. Examples of the above-mentioned phosphates include KH ₂ PO ₄ , NaH ₂ PO ₄ , (NH ₂ OH) ₂ ·H ₂ PO ₄ , and the like. Among them, KH ₂ PO ₄ and NaH ₂ PO ₄ are helpful for the pH control of the treatment solution, and (NH ₂ OH) ₂ ･H ₂ SO ₄ and (NH ₂ OH) ₂ ･H ₂ PO ₄ are helpful for the treatment The liquid reaction is promoted. When the above-mentioned treatment solution contains the above-mentioned additives, elements such as Na, K, and S are contained in the obtained chemical conversion film. When the chemical conversion coating contains K, the powder for a powder magnetic core can easily suppress a decrease in specific resistance and a decrease in flexural strength due to heat treatment.

As the above-mentioned aqueous solvent, water, or hydrophilic organic solvents such as alcohols and ketones, and mixtures thereof can be used. A known surfactant may also be added to the above-mentioned aqueous solvent.

In the step of forming the above-mentioned chemical conversion film, for example, the above-mentioned treatment solution is added to the above-mentioned iron-based powder, and after mixing with a known mixer, ball mill, kneader, V-type mixer, granulator, etc. Dry at 150°C or higher and 250°C or lower under vacuum. Thereby, the above-mentioned chemical conversion film is formed on the surface of the above-mentioned iron-based powder. In the step of forming the chemical conversion film, the particle size of the powder can also be controlled by passing the dried powder through a sieve with a pore size of about 200 μm to 600 μm.

(Surface treatment layer forming step) In the step of forming the surface treatment layer, a solution obtained by dissolving a silane coupling agent in a solvent is added to the surface of the chemical conversion film formed in the step of forming the chemical conversion film, followed by drying.

The solvent for dissolving the silane coupling agent is not particularly limited, for example, water, or hydrophilic organic solvents such as alcohols and ketones, and mixtures thereof can be used.

(resin layer lamination step) In the step of laminating the resin layer, a solution obtained by dissolving a silicone resin in a solvent is added to the surface of the surface treatment layer formed in the step of forming the surface treatment layer, followed by drying.

As a solvent for dissolving the silicone resin, for example, alcohol, or petroleum-based organic solvents such as toluene and xylene can be used.

In the resin layer laminating step, it is preferable to heat at a temperature at which the solvent that dissolves the polysiloxane resin volatilizes, and at a temperature lower than the hardening temperature of the polysiloxane resin, so that the solvent is fully volatilized. Although the drying temperature in the resin layer lamination step also varies depending on the type of the solvent, for example, it is preferably not less than 60°C and not more than 80°C. In the resin layer lamination step, it is preferable to pass the dried powder through a sieve with a pore size of 300 μm or more and 600 μm or less in order to remove aggregates.

In the above step of laminating the resin layer, it is preferable to heat the powder on which the above resin layer is laminated after the above drying to complete the softening process of the polysiloxane resin in a powder state (hereinafter, the polysiloxane resin will be made into a powder). The process in which the softening process of the resin ends in the powder state is also called "preparatory hardening process"). The method of performing the preliminary hardening treatment mentioned above includes a method of heating the above-mentioned dried powder near the hardening temperature of silicone resin for a short time. The heating temperature in the preliminary hardening treatment mentioned above is, for example, 100°C or higher and 200°C or lower. The heating time in the preliminary hardening treatment mentioned above is, for example, not less than 5 minutes and not more than 100 minutes. In addition, as a method of performing the above-mentioned preliminary hardening treatment, a method using a hardening agent may also be adopted.

The powders after the above-mentioned pre-hardening treatment are not completely bonded to each other and solidified, so they can be easily cracked. After the silicone resin is preliminarily hardened, it can be cracked to obtain a powder with excellent fluidity. This powder can be put into a mold like sand when performing compression molding in warm molding at about 100°C to 250°C, for example. Thereby, the powder for powder magnetic cores can be easily and reliably injected into the mold. In addition, by performing this preliminary hardening treatment, the adhesion between powders for powder magnetic cores can be improved during molding, and the densification of the obtained molded body can be promoted. Furthermore, the powder after the preliminary hardening treatment is preferably passed through a sieve with a hole diameter of 300 μm or more and 600 μm or less to make the particle diameter uniform.

＜Manufacturing method of dust core＞ The powder for a powder magnetic core is formed into a powder magnetic core by performing heat treatment after compression molding. That is, the method for producing a powder magnetic core includes a step of compression molding the powder for a powder magnetic core (compression molding step), and a step of heat-treating the compression-molded compact (heat treatment step).

(compression molding step) The above-mentioned compression molding step can be performed, for example, by a known method using a mold. The surface pressure in the compression molding step is preferably from 490 MPa to 1960 MPa, more preferably from 790 MPa to 1180 MPa. In particular, in the above-mentioned compression molding step, by performing compression molding with a surface pressure of 980 MPa or more, it is easy to manufacture a high-density powder magnetic core. The above-mentioned compression molding step can be performed by both room temperature molding and warm molding, but warm molding is preferred because a high-strength powder magnetic core can be obtained.

(heat treatment step) In the above-mentioned heat treatment step, the molded body obtained in the above-mentioned compression molding step is annealed. In this heat treatment step, the above-mentioned lubricant contained in the above-mentioned compact is evaporated or thermally decomposed. Since the powder for powder magnetic cores has the above-mentioned chemical conversion coating, the above-mentioned surface treatment layer, and the above-mentioned resin layer sequentially on the surface of the above-mentioned iron-based powder, even if the above-mentioned lubricant evaporates or thermally decomposes, the obtained powder magnetic The flexural strength of the core is sufficiently increased.

The lower limit of the heat treatment temperature in the above heat treatment step is preferably 500°C, more preferably 550°C. On the other hand, the upper limit of the heat treatment temperature in the above heat treatment step is preferably 700°C, more preferably 650°C. When the above-mentioned heat treatment temperature is less than the above-mentioned lower limit, there is a possibility that the hysteresis loss of the obtained powder magnetic core cannot be sufficiently reduced. Conversely, when the heat treatment temperature exceeds the upper limit, the insulating layer covering the surface of the iron-based powder (the chemical conversion coating, the surface treatment layer, and the resin layer) may deteriorate.

The environment during the heat treatment in the above heat treatment step is not particularly limited, but an inert gas environment such as nitrogen is preferred. The heat treatment time in the above heat treatment step can be set within a range in which the specific resistance of the obtained powder magnetic core does not decrease. The lower limit of the heat treatment time is, for example, preferably 20 minutes, more preferably 30 minutes, and still more preferably 60 minutes.

＜Powder core＞ The above-mentioned powder magnetic core can be obtained by cooling to normal temperature after the above-mentioned heat treatment step. The lower limit of the flexural strength of the powder magnetic core is preferably 46 MPa, more preferably 50 MPa, and still more preferably 60 MPa. The powder for the powder magnetic core can increase the flexural strength of the obtained powder magnetic core to the above lower limit by sequentially disposing the above-mentioned chemical conversion coating, the above-mentioned surface treatment layer, and the above-mentioned resin layer on the surface of the above-mentioned iron-based powder. above. In addition, the upper limit of the above-mentioned flexural strength is not particularly limited because the higher the better, for example, it may be 100 MPa. In addition, "flexural strength" means the value based on JIS-Z2511:2006.

＜Advantages＞ In the dust core powder, the chemical conversion coating contains phosphorus, and at least one of nickel and cobalt, and the resin layer is laminated on the surface of the chemical conversion coating through the surface treatment layer, so that it can be used A powder magnetic core formed using the powder for a powder magnetic core has a high flexural strength.

[Other Embodiments] The above-mentioned embodiments do not limit the configuration of the present invention. Therefore, in the above-mentioned embodiment, omission, substitution or addition of constituent elements of each part of the above-mentioned embodiment can be performed based on the description of this specification and common technical knowledge, and these should be construed as fully falling within the scope of the present invention. [Example]

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limitedly interpreted based on the description of the examples.

[Example] [No.1~No.7] (Preparation of Powder for Dust Core) The iron-based powder is pure iron powder obtained by water atomization method, and contains C≦0.01% by mass as an unavoidable impurity , Si≦0.03% by mass, P≦0.02% by mass, S≦0.01% by mass, and the particle size distribution is 16% by mass for less than 150 μm, 41% by mass for more than 150 μm and less than 180 μm, and 42 for more than 180 μm and less than 250 μm % by mass, 1% by mass of iron-based powder with a diameter of 250 μm or more, on the surface of the iron-based powder, a chemical conversion film containing P and Ni, a surface treatment layer containing a silane coupling agent, and a silicone resin-based After the resin layer of the components, the resin layer laminated powder is mixed with the lubricant. Specifically, for a phosphoric acid solution mixed with water: 50 parts by mass, KH ₂ PO ₄ : 35 parts by mass, H ₃ PO ₄ : 10 parts by mass, (NH ₂ OH) ₂ ·H ₂ PO ₄ : 10 parts by mass For 100mL of the base agent, a total of 10 parts by mass of nickel pyrophosphate and nickel nitrate was mixed, and further diluted so that the difference between the phosphorus content after film formation and the phosphorus content before film formation became 0.04%. After mixing 50 parts by mass of the solution with 1000 parts by mass of the iron-based powder, it was dried in the air at 200° C. for 30 minutes, and passed through a sieve with a pore size of 600 μm (chemical conversion film lamination step).

Next, the solution obtained by dissolving the silane coupling agent "Z-6011" manufactured by Dow Corning Toray Co., Ltd. in water was mixed so that the ratio of the silane coupling agent to 100 parts by mass of the iron-based powder was as shown in Table 1. After chemically converting the powder after the film lamination step, it was dried at 125° C. for 30 minutes (surface treatment layer forming step). Next, a solution obtained by dissolving silicone resin "SR2400" manufactured by Dow Corning Toray Co., Ltd. in toluene was prepared so that the content of the silicone resin relative to 100 parts by mass of the iron-based powder was as shown in Table 1. After mixing the powder after the surface treatment layer formation step, it was dried at 75° C. for 30 minutes (resin layer lamination step). Further, a lubricant is mixed in the powder after the resin layer lamination step. As a lubricant, stearic acid amide and zinc oxide were used, and stearic acid amide and zinc oxide were added in the ratio of Table 1 with respect to 100 mass parts of iron-based powders (lubricant mixing process).

(Preparation of dust core sample) The powder after the lubricant mixing step (powder for dust core) was compression-molded into a molded body. Specifically, powder for powder magnetic cores at room temperature is placed into a mold heated to 80°C, and pressed to a surface pressure of 800MPa (8.16ton/cm ² ), forming a rectangular shape of 18mm×32mm×12.5mm Formed body (compression forming step). Thereafter, the molded body was subjected to stress relief annealing (heat treatment step) under a nitrogen atmosphere at a heating rate of 10° C./min, a reaching temperature of 600° C., and a holding time of 30 minutes. The molded body after the heat treatment step was furnace-cooled to room temperature to obtain samples No.1-No.7.

[No.8] (Production of powder for powder magnetic core) As the iron-based powder, the same powder as No.1~No.7 is used. On the surface of the iron-based powder, a chemical conversion film containing P and Ni and a resin layer mainly composed of polysiloxane resin are sequentially provided. , Mix the powder after the resin layer is laminated with the lubricant. In No.8, it is the same as No.1~ No. 7 produced powder for powder magnetic cores in the same manner.

(Preparation of dust core samples) The powder after the lubricant mixing step (powder for powder magnetic core) was compression-molded into a compact in the same manner as No. 1 to No. 7 (compression molding step). Thereafter, stress relief annealing (heat treatment step) was performed on the formed body under the same conditions as No. 1 to No. 7. The molded body after the heat treatment step was furnace-cooled to room temperature to obtain a sample No. 8.

<Density> The density [g/cm ³ ] of the samples No.1 to No.8 was obtained. Density is calculated by measuring the mass and size of each sample. The calculation results are shown in Table 1.

＜Flexural strength＞ According to JIS Z-2511:2006, the flexural strength [MPa] of the samples No. 1 to No. 8 was determined. The measurement results are shown in Table 1.

＜Assessment Results＞ As shown in Table 1, a chemical conversion coating containing P and Ni, a surface treatment layer containing a silane coupling agent, and a resin layer mainly composed of polysiloxane resin are sequentially arranged on the surface of the iron-based powder, and the resin layer The flexural strength of No.1 to No.7 with a lubricant on the surface was higher than that of No.8 without a surface treatment layer containing a silane coupling agent. In particular, No. 2 to No. 7, in which the content of the silane coupling agent is 0.10 parts by mass or more with respect to 100 parts by mass of the iron-based powder, had the highest flexural strength compared to No. 8. [Industrial availability]

As explained above, the powder for powder magnetic core according to one aspect of the present invention is suitable for increasing the flexural strength of the powder magnetic core.

Claims (3)

A powder for a powder magnetic core, comprising an iron-based powder, a chemical conversion film formed on the surface of the iron-based powder, a surface treatment layer formed on the surface of the chemical conversion film and containing a silane coupling agent, laminated on the above-mentioned The surface of the surface treatment layer, and the resin layer mainly composed of polysiloxane resin, and the lubricant existing on the surface of the above resin layer, and the above-mentioned chemical conversion film and the above-mentioned surface treatment are sequentially provided on the surface of the above-mentioned iron-based powder layer, the resin layer, and the chemical conversion coating contain phosphorus, and at least one of nickel and cobalt. The powder for powder magnetic core according to Claim 1, wherein the content of the above-mentioned silane coupling agent is not less than 0.05 parts by mass and not more than 0.30 parts by mass relative to 100 parts by mass of the above-mentioned iron-based powder, and relative to 100 parts by mass of the above-mentioned iron-based powder In terms of parts, the content of the above silicone resin is not less than 0.05 parts by mass and not more than 0.30 parts by mass. The dust core powder according to claim 1 or claim 2, wherein the amount of the lubricant added is 0.20 to 0.40 parts by mass relative to 100 parts by mass of the iron-based powder.