JP2019212735A - Magnetic film and manufacturing method therefor - Google Patents

Abstract

To provide a magnetic film having high magnetic permeability.SOLUTION: A magnetic film contains a binder, and ferrite magnetic nanoparticles having an average particle diameter of 100 to 500 nm and ferrite magnetic microparticles having an average particle diameter of 1 to 100 μm dispersed in the binder, and the distribution constant m assuming to follow Rosin-Rammler distribution function in which the particle size distribution (mass basis) of the ferrite magnetic nanoparticles is represented by the formula: F(Dp)=1-exp(-(Dp/De))) (where F represents an integrated mass ratio under the sieve, and Dp represents the particle diameter, De represents the particle size characteristic number, and m represents the distribution constant] is in a range of 1.6 to 2.3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetic film and a method for manufacturing the same, and more particularly to a magnetic film containing ferrite magnetic nanoparticles and ferrite magnetic microparticles and a method for manufacturing the same.

  A magnetic film in which magnetic particles are dispersed in a binder is used for an inductor, a core material of a transformer, an electromagnetic noise absorber, and the like. In such a magnetic film, it is considered that the magnetic permeability is improved by mixing magnetic particles having different average particle diameters and increasing the packing density. The magnetic particles (magnetic nanoparticles) of the nanometer order and the micrometer A magnetic film in which order magnetic particles (magnetic microparticles) are dispersed in a binder is expected as a magnetic film having a particularly high magnetic permeability. Moreover, since magnetic particles adjoin by reducing content of binder resin, it is thought that magnetic permeability further improves.

  A magnetic film in which such magnetic nanoparticles and magnetic microparticles are dispersed in a binder is prepared by applying or printing a coating solution in which the magnetic nanoparticles and magnetic microparticles are dispersed in a solvent and the binder is dissolved. For example, it can be formed by coating by screen printing or the like, and drying the obtained coating film. At this time, by mixing the magnetic nanoparticles and the magnetic microparticles so that the space between the magnetic microparticles is uniformly filled with the magnetic nanoparticles and the packing density of the magnetic nanoparticles is maximized, It is considered that a magnetic film having a high packing density and a high magnetic permeability can be obtained. However, since the magnetic nanoparticles have a distributed particle size, it is necessary to optimize the particle size distribution of the magnetic nanoparticles in order to maximize the packing density of the magnetic nanoparticles.

Takashi Ito et al., Journal of the Japan Institute of Metals, 1986, Vol. 50, No. 8, pp. 740-746 (Non-patent Document 1) shows a particle size distribution (mass basis) represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieving, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
In the particles according to the rosin-Lambler distribution function represented by the formula, it is described that the packing density increases as the distribution constant m decreases. Therefore, the smaller the distribution constant m of the magnetic nanoparticles, the higher the packing density of the magnetic nanoparticles, and the higher the packing density of the entire magnetic particles (magnetic microparticles and magnetic nanoparticles) in the magnetic film. It is expected that the permeability of the film will increase.

  In JP-A-2006-207712 (Patent Document 1), magnetic powder having a ratio D50 / D3 of less than 8 between a particle diameter D50 having a cumulative frequency of 50% and a particle diameter D3 having a cumulative frequency of 3% is pressure-molded. It is described that a high-density molded body can be obtained. However, the magnetic powder described in Patent Document 1 is composed of magnetic microparticles having an average particle diameter of 2 to 5 μm, and magnetic nanoparticles are not used.

JP, 2006-207712, A

Takashi Ito et al., “Relationship between packing density and particle size distribution by random packing model of powder”, Journal of the Japan Institute of Metals, 1986, 50, 8, 740-746.

  However, in order to increase the packing density of the entire magnetic particles in the magnetic film in which the magnetic microparticles are dispersed in the binder, based on the knowledge described in Non-Patent Document 1, the distribution constant m in the rosin-Lambler distribution function The present inventors have found that the magnetic permeability of the magnetic film does not necessarily increase even when magnetic nanoparticles having a small particle size are added.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a magnetic film having a high magnetic permeability.

  As a result of intensive studies to achieve the above object, the present inventors have found that in a magnetic film in which ferrite-based magnetic nanoparticles and ferrite-based magnetic microparticles are dispersed in a binder, the particle size distribution (mass basis) When ferrite-based magnetic nanoparticles with various values of distribution constant m are used, assuming that it follows the Rosin-Lambler distribution function, there is a distribution constant that maximizes the permeability, and the distribution of ferrite-based magnetic nanoparticles It has been found that high permeability can be obtained when the constant m is within a specific range, and the present invention has been completed.

That is, the magnetic film of the present invention comprises a binder, ferrite magnetic nanoparticles having an average particle diameter of 100 to 500 nm and ferrite magnetic microparticles having an average particle diameter of 1 to 100 μm dispersed in the binder. A magnetic film containing
The particle size distribution (mass basis) of the ferrite magnetic nanoparticles is represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieving, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
The distribution constant m is assumed to be in the range of 1.6 to 2.3 when it is assumed to follow the rosin-Rammler distribution function represented by
It is characterized by this.

  In the magnetic film of the present invention, the content of the ferrite magnetic nanoparticles is preferably 1 to 50 parts by mass with respect to 100 parts by mass of the total ferrite magnetic particles, and the content of the binder is all ferrite. It is preferable that it is 0.1-10 mass parts with respect to 100 mass parts of magnetic particles. Moreover, as said binder, what consists of at least 1 sort (s) of resin selected from the group which consists of an epoxy resin, an acrylic resin, a phenol resin, a urethane resin, a polyimide resin, a urea resin, a silicone resin, and a pyrrolidone resin is preferable.

In the method for producing a magnetic film of the present invention, a mass of ferrite magnetic nanoparticles is crushed to have an average particle size of 100 to 500 nm, and a particle size distribution (mass basis) is represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieving, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
A step of preparing a ferrite-based magnetic nanoparticle having a distribution constant m in the range of 1.6 to 2.3 assuming that it follows a rosin-Lambler distribution function represented by:
A step of preparing a coating liquid containing the ferrite magnetic nanoparticles prepared in the step, a ferrite magnetic microparticle having an average particle diameter of 1 to 100 μm, a binder, and a solvent;
Applying the coating solution to form a coating film;
The step of heating the coating film while applying pressure to form the magnetic film according to any one of claims 1 to 4,
It is the method characterized by including.

  In the magnetic film of the present invention, the reason why there is a distribution constant that maximizes the magnetic permeability is not necessarily clear, but the present inventors speculate as follows. That is, when the distribution constant m of the ferrite-based magnetic nanoparticles is larger than the distribution constant that maximizes the magnetic permeability, the gaps between the ferrite-based magnetic microparticles are uniformly filled with the ferrite-based magnetic nanoparticles. It is presumed that as the distribution constant m of the system magnetic nanoparticles decreases, the packing density of the entire ferrite system magnetic particles increases and the magnetic permeability of the magnetic film increases. On the other hand, when the distribution constant m of the ferrite-based magnetic nanoparticles is smaller than the distribution constant that maximizes the magnetic permeability, the amount of ferrite-based magnetic nanoparticles having a small particle diameter increases, so that the fan acting between the nanoparticles Aggregates of ferrite-based magnetic nanoparticles are likely to be generated during film formation due to the magnetic force due to the Delwars force or weak residual magnetization. When such an agglomerate is formed, the ferrite magnetic nanoparticles added to uniformly fill the gaps between the ferrite magnetic microparticles are consumed for the formation of the agglomerates. Voids (holes) remain. Since this void (hole) has a lower magnetic permeability than that of the ferrite-based magnetic particles, it is presumed that the magnetic permeability of the magnetic film is lowered. Such a phenomenon becomes more prominent as the distribution constant m of the ferrite-based magnetic nanoparticles decreases, and as the distribution constant m of the ferrite-based magnetic nanoparticles decreases, the amount of ferrite-based magnetic nanoparticles having a smaller particle diameter further increases. Since the aggregates of ferrite-based magnetic nanoparticles are more likely to be generated, voids (holes) between ferrite-based magnetic microparticles are also likely to remain, and as a result, the magnetic permeability of the magnetic film is further reduced. Inferred.

  According to the present invention, it is possible to obtain a magnetic film having a high magnetic permeability.

It is a graph which shows the relationship between the relative magnetic permeability of a magnetic body film, and the distribution constant of a ferrite-type magnetic nanoparticle.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

[Magnetic film]
First, the magnetic film of the present invention will be described. The magnetic film of the present invention contains a binder, ferrite magnetic nanoparticles having an average particle diameter of 100 to 500 nm and ferrite magnetic microparticles having an average particle diameter of 1 to 100 μm dispersed in the binder. It is a magnetic film. In such a magnetic film of the present invention,
The particle size distribution (mass basis) of the ferrite magnetic nanoparticles is represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieve, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
The distribution constant m in the case where it is assumed to follow the rosin-Rammler distribution function expressed by

  The ferrite-based magnetic nanoparticles and ferrite-based magnetic microparticles used in the present invention (hereinafter collectively referred to as “ferrite-based magnetic particles”) are ferrite-based soft magnetic particles having a low coercive force and a high magnetic permeability. If there is no particular limitation, MnZn ferrite particles, MnCu ferrite particles, MnMg ferrite particles, MnZnCu ferrite particles, MnZnMg ferrite particles, MnZnNi ferrite particles, NiZn ferrite particles, NiCu ferrite particles, NiCuZn ferrite particles, NiZnMg ferrite particles, Co ferrites Particles, CuZn ferrite particles, and the like. These ferrite magnetic particles may be used alone or in combination of two or more. Among these ferrite-based magnetic particles, MnZn ferrite particles, NiZn ferrite particles, and NiCuZn ferrite particles are preferable from the viewpoint of high magnetic permeability and relatively low cost of the nanoparticles.

  In the present invention, the average particle diameter of the ferrite-based magnetic nanoparticles is 100 to 500 nm. By using the ferrite magnetic nanoparticles having such an average particle diameter, the gaps between the ferrite magnetic microparticles are sufficiently filled, so that the magnetic permeability of the magnetic film is increased. On the other hand, if the average particle diameter of the ferrite-based magnetic nanoparticles is less than the lower limit, the ferrite-based magnetic nanoparticles are aggregated during film formation due to the van der Waals force acting between the nanoparticles and the magnetic force due to weak residual magnetization. Aggregates are likely to be generated, the gaps between the ferrite-based magnetic microparticles are not sufficiently filled, and the magnetic permeability of the magnetic film is lowered. On the other hand, when the average particle diameter of the ferrite-based magnetic nanoparticles exceeds the upper limit, the gap between the ferrite-based magnetic microparticles is not sufficiently filled, and the magnetic permeability of the magnetic film is lowered. Further, from the viewpoint that aggregates of ferrite-based magnetic nanoparticles are less likely to be formed and the gaps between the ferrite-based magnetic microparticles are sufficiently filled, the average particle diameter of the ferrite-based magnetic nanoparticles is preferably 100 to 400 nm. 200 to 400 nm is more preferable.

  Furthermore, in the present invention, the distribution constant m when the particle size distribution (mass basis) of the ferrite-based magnetic nanoparticles is assumed to follow the rosin-Lambler distribution function represented by the above formula is in the range of 1.6 to 2.3. It is necessary to be in If the distribution constant m of the ferrite-based magnetic nanoparticles is less than the lower limit, the ferrite-based magnetic nanoparticles are likely to aggregate, so that the gaps between the ferrite-based magnetic microparticles are not sufficiently filled, and the magnetic permeability of the magnetic film is reduced. To do. On the other hand, if the distribution constant m of the ferrite-based magnetic nanoparticles exceeds the above upper limit, the packing density of the ferrite-based magnetic nanoparticles decreases, and the packing density of the entire ferrite-based magnetic particles also decreases. descend. In addition, aggregation of ferrite magnetic nanoparticles is suppressed, the gaps between ferrite magnetic microparticles are sufficiently filled, and the packing density of ferrite magnetic nanoparticles is increased, and the packing density of the entire ferrite magnetic particles is also increased. From the viewpoint of increasing the magnetic permeability of the magnetic film as a result, the distribution constant m of the ferrite-based magnetic nanoparticles is preferably 1.7 to 2.2, more preferably 1.8 to 2.1. .

  Moreover, in this invention, the average particle diameter of a ferrite type magnetic microparticle is 1-100 micrometers. If the average particle diameter of the ferrite-based magnetic microparticles exceeds the above upper limit, the printability is remarkably lowered due to clogging at the time of printing or the occurrence of drag marks due to the squeegee. Further, from the viewpoint of ensuring high dispersibility and high packing density of the ferrite magnetic particles, the upper limit of the average particle diameter of the ferrite magnetic microparticles is preferably 20 μm or less. On the other hand, the lower limit of the average particle diameter of the ferrite-based magnetic microparticles is preferably 2 μm or more from the viewpoint of ensuring a particle size difference from the ferrite-based magnetic nanoparticles and achieving high packing.

  In the magnetic film of the present invention, the content of the ferrite-based magnetic nanoparticles is 1 with respect to 100 parts by mass of all ferrite-based magnetic particles (the total of the ferrite-based magnetic nanoparticles and the ferrite-based magnetic microparticles). -50 mass parts is preferable, and 1-30 mass parts is more preferable. When the content of the ferrite-based magnetic nanoparticles is less than the lower limit, the gap between the ferrite-based magnetic microparticles is not sufficiently filled with the ferrite-based magnetic nanoparticles, and particularly in the region where the amount of the binder described below is small, the ferrite While voids (holes) tend to remain between the system magnetic microparticles and the magnetic permeability of the magnetic film tends to decrease, on the other hand, when the upper limit is exceeded, the packing density of the ferrite system magnetic nanoparticles increases, Since the packing density of the ferrite-based magnetic microparticles is remarkably lowered, the packing density of the entire ferrite-based magnetic particles is lowered, and the magnetic permeability of the magnetic film tends to be lowered.

  The magnetic film of the present invention is such that such ferrite-based magnetic nanoparticles and ferrite-based magnetic microparticles are dispersed in a binder. The binder is not particularly limited, but a resin binder is preferable. Examples of the resin binder include an epoxy resin, an acrylic resin, a phenol resin, a urethane resin, a polyimide resin, a urea resin, a silicone resin, a pyrrolidone resin, a cellulose resin, Examples include gelatin. These resin binders may be used alone or in combination of two or more. By adding such a binder, it is possible to form a magnetic film having a small number of holes and a high magnetic permeability.

  In the magnetic film of the present invention, the content of the binder is determined by the viscosity of the coating liquid in the applied coating method (for example, screen printing method, mask printing method, bar coating method, flexographic printing method, gravure printing method). It can be set as appropriate according to the coating method, void removal method, etc., so that the rheological properties are optimal and the voids are reduced in the cured film. The amount is preferably 0.1 to 10 parts by mass and more preferably 1 to 8 parts by mass with respect to 100 parts by mass of the particles (the total of the ferrite magnetic nanoparticles and the ferrite magnetic microparticles). When the content of the binder is less than the lower limit, the strength of the magnetic film is reduced, and cracks and peeling are likely to occur. Therefore, voids (holes) increase and the magnetic permeability of the magnetic film tends to decrease. On the other hand, if the upper limit is exceeded, the resin component tends to be excessive, and the magnetic properties of the magnetic film tend to deteriorate.

  In addition, the magnetic film of the present invention may contain various additives such as a surfactant, an antifoaming agent, a leveling agent, a dispersing agent, and a wetting agent as long as the effects of the present invention are not impaired.

[Method of manufacturing magnetic film]
Next, the manufacturing method of the magnetic film of the present invention will be described. In the method for producing a magnetic film of the present invention, a mass of ferrite magnetic nanoparticles is crushed to have a desired average particle diameter, and the particle size distribution (mass basis) is represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieve, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
A step of preparing a ferrite-based magnetic nanoparticle having a distribution constant m within a desired range assuming that it follows a rosin-Lambler distribution function represented by the formula (nanoparticle preparation step);
The ferrite-based magnetic nanoparticles having the desired average particle diameter and the desired distribution constant m, the ferrite-based magnetic microparticles having the desired average particle diameter, the binder, the solvent, prepared in the nanoparticle preparation step A step of preparing a coating liquid containing the coating liquid (coating liquid preparation step);
A step of coating the coating liquid to form a coating film (coating film forming step);
Heating the coating film while applying pressure to form the magnetic film of the present invention (pressure heating step);
It is a method including.

(Nanoparticle preparation process)
In the method for producing a magnetic film of the present invention, first, a mass of ferrite magnetic nanoparticles is crushed to have a desired average particle diameter, and the particle size distribution (mass basis) is represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieving, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
Ferrite-based magnetic nanoparticles having a distribution constant m within a desired range when prepared according to the rosin-Lambler distribution function represented by

  The method for crushing the mass of ferrite magnetic nanoparticles is not particularly limited as long as ferrite magnetic nanoparticles having a desired average particle diameter and a desired distribution constant m can be obtained. For example, a ball mill is used. The method used, the method using a homogenizer, etc. are mentioned. Further, in these methods, for example, in a method using a ball mill, the size and amount of zirconia balls, a homogenizer, and the like are obtained so that ferrite magnetic nanoparticles having a desired average particle diameter and a desired distribution constant m can be obtained. In the method using, conditions such as the rotation speed and time are appropriately adjusted.

  Such a mass of ferrite magnetic nanoparticles is usually crushed in a solvent capable of highly dispersing the ferrite magnetic nanoparticles (hereinafter referred to as “high dispersion solvent”). preferable. Examples of such a high dispersion solvent include isopropanol, ethanol, n-propanol, diethyl ether, ethyl acetate, acetone, and methyl ethyl ketone. The concentration of the ferrite magnetic nanoparticles in the crushing state is such that the ferrite magnetic nanoparticles having a desired average particle diameter and a desired distribution constant m are uniformly dispersed in the high dispersion solvent. It is preferable to adjust appropriately so that it may be obtained.

(Coating liquid preparation process)
Next, the ferrite magnetic nanoparticles having the desired average particle diameter and the desired distribution constant m prepared in this way, the ferrite magnetic microparticles having the desired average particle diameter, the binder, and the solvent The coating liquid containing is prepared. At this time, with respect to 100 parts by mass of all ferrite-based magnetic particles (total of the ferrite-based magnetic nanoparticles and the ferrite-based magnetic microparticles), the content of the ferrite-based magnetic nanoparticles is 1 to 50 parts by mass (more The coating liquid is prepared so that the content of the binder is preferably 0.1 to 10 parts by mass (more preferably 1 to 8 parts by mass). It is preferable. In such a coating solution, the ferrite magnetic nanoparticles and the ferrite magnetic microparticles are dispersed in the solvent, and the binder is dissolved in the solvent.

  The solvent (solvent for the coating solution) is not particularly limited as long as the ferrite magnetic nanoparticles and the ferrite magnetic microparticles are uniformly dispersed and the binder is sufficiently dissolved. From the viewpoint of good wettability with the magnetic magnetic nanoparticles and the ferrite magnetic microparticles, the aggregation of the ferrite magnetic nanoparticles and the ferrite magnetic microparticles is suppressed, and the cost is low. Ethanol, 2-ethoxyethanol, 2- (2-methoxyethoxy) ethanol, 2- (2-ethoxyethoxy) ethanol, 2- [2- (2-methoxyethoxy) ethoxy] ethanol, 2- [2- (2- Ethoxyethoxy) ethoxy] ethanol is preferred. Such a solvent may be used individually by 1 type, or may use 2 or more types together.

  Moreover, in the said coating liquid, although there is no restriction | limiting in particular as content of the said solvent (solvent for coating liquid), 1-35 mass% is preferable with respect to the coating liquid whole quantity, and 4-30 mass% is. More preferred. When the content of the solvent is less than the lower limit, the viscosity of the coating liquid tends to be high and coating tends to be difficult. On the other hand, when the upper limit is exceeded, the solvent for the coating liquid is removed after film formation. In order to form a magnetic film having a desired thickness, it is necessary to repeat coating and drying many times, and the manufacturing cost tends to increase.

  The method for preparing the coating liquid is not particularly limited as long as the ferrite magnetic nanoparticles and the ferrite magnetic microparticles are uniformly dispersed in the solvent for the coating liquid and the binder is sufficiently dissolved. However, for example, first, a slurry in which the ferrite magnetic nanoparticles are dispersed in the solvent for the coating solution is prepared, and then the binder is added to the slurry and dissolved, and then the binder is added. A method of adding and dispersing the ferrite-based magnetic microparticles in the slurry to be contained is preferable.

  The method for preparing the slurry is not particularly limited as long as the ferrite magnetic nanoparticles are uniformly dispersed in the coating solution solvent. For example, the ferrite magnetic nanoparticles are used in the coating solution solvent. In order to obtain a slurry in which the ferrite-based magnetic nanoparticles are highly dispersed because the ferrite-based magnetic nanoparticles are likely to be aggregated. For example, in the dispersion after the crushing treatment in the nanoparticle preparation step, that is, in the dispersion in which the ferrite magnetic nanoparticles are uniformly dispersed in the high dispersion solvent, the high dispersion A method of replacing the solvent for use with the solvent for the coating solution is preferred.

  The method for replacing the solvent for high dispersion with the solvent for coating liquid is not particularly limited. For example, the coating liquid is added to a dispersion liquid in which the ferrite-based magnetic nanoparticles are dispersed in the solvent for high dispersion. A method of distilling off the high-dispersion solvent using a rotary evaporator after adding the solvent for use can be mentioned. At this time, operating conditions (temperature, pressure, etc.) are set so that the solvent for the coating solution remains and the solvent for high dispersion is removed.

  Next, the binder is added and dissolved in the slurry thus prepared. At this time, the content of the binder is 0.1 to 10 parts by mass (more preferably 1 to 8 parts by mass) with respect to 100 parts by mass of the total ferrite-based magnetic particles in the obtained coating liquid. It is preferable to add a binder. Thereby, the effect that the aggregation of the ferrite magnetic nanoparticles and the ferrite magnetic microparticles is suppressed by using the solvent for the coating solution is exhibited. Also, if the binder content is less than the lower limit, the strength of the magnetic film is reduced and cracks and peeling are likely to occur, so the voids (voids) increase and the magnetic permeability of the magnetic film decreases. On the other hand, if the upper limit is exceeded, the resin component tends to increase so that the magnetic properties of the magnetic film tend to deteriorate.

  Next, the ferrite-based magnetic microparticles are added and dispersed in the slurry containing the binder thus prepared. At this time, the content of the ferrite magnetic nanoparticles with respect to 100 parts by mass of all ferrite magnetic particles in the obtained coating liquid is 1 to 50 parts by mass (more preferably 1 to 30 parts by mass). It is preferable to add ferrite-based magnetic microparticles. As a result, the gaps between the ferrite-based magnetic microparticles are filled with the ferrite-based magnetic nanoparticles at a high density, and the magnetic permeability of the magnetic film is increased.

(Coating film formation process)
Next, the coating liquid prepared in this way is applied onto, for example, a substrate and dried to form a coating film. There is no restriction | limiting in particular as a coating method, For example, well-known methods, such as application | coating, screen printing, mask printing, bar coating, flexographic printing, gravure printing, are employable. Such coating and drying may be repeated until a coating film having a desired thickness is formed.

(Pressurized heating process)
Next, the obtained coating film is heated while being pressurized to cure or increase the viscosity of the binder (preferably cured), and then release the pressure to obtain the magnetic film of the present invention. . There is no restriction | limiting in particular as a method of applying a pressure to a coating film, For example, a uniaxial pressure, a hydrostatic pressure, etc. can be applied.

  Although there is no restriction | limiting in particular as a pressure applied to a coating film, 5-90 Mpa is preferable and 20-70 Mpa is more preferable. When the applied pressure is less than the lower limit, the ferrite magnetic nanoparticles do not flow easily, so the gap between the ferrite magnetic microparticles is not sufficiently filled with the ferrite magnetic nanoparticles, and the magnetic film has voids (holes). Therefore, when the applied pressure exceeds the above upper limit, the substrate may be destroyed.

  Moreover, there is no restriction | limiting in particular as heating temperature, However, 100-400 degreeC is preferable and 100-300 degreeC is more preferable. When the heating temperature is lower than the lower limit, the binder is not sufficiently cured or increased in viscosity, and when the pressure is released in this state, voids (holes) that have shrunk due to pressurization are re-expanded. On the other hand, when the heating temperature exceeds the upper limit, the binder is decomposed and the binding force between the ferrite-based magnetic particles is reduced, the strength of the magnetic film is reduced, and The magnetostatic interaction is weakened and the magnetic permeability of the magnetic film tends to decrease. In addition, also when performing heat processing after releasing a pressure, it is preferable to heat at the temperature within the said range.

  Furthermore, in the method for producing a magnetic film of the present invention, it is preferable to perform the pressurizing / heating treatment under the condition that the viscosity of the coating film is 1000 Pa · s or less. When the viscosity of the coating film is within the above range, the ferrite magnetic particles flow due to the pressurization and heat treatment, so that voids (holes) remaining in the magnetic film can be reduced. Magnetic permeability increases.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example. In addition, the particle size distribution (mass basis) of the iron oxide ferrite nanoparticles and the relative permeability of the magnetic film were obtained by the following methods.

<Size distribution of ferrite-based magnetic nanoparticles>
Ferrite-based magnetic nanoparticles were embedded in a clear cup using a two-component mixed epoxy resin, polished until the cross-section of the ferrite-based magnetic nanoparticles was exposed, and then processed by ion milling as necessary. The cross section of the ferrite-based magnetic nanoparticles may be exposed by cutting using a focused ion beam or a microtome. Next, the cross section of the exposed ferrite magnetic nanoparticles was observed using a scanning electron microscope. The observation magnification was set so that 200 or more nanoparticles were present in the field of view. Such electron microscope observation is carried out at 10 locations (10 visual fields) or more, and image processing is performed as follows for a total of 2000 or more ferrite-based magnetic nanoparticles, and the particle size distribution (mass basis) of the ferrite-based magnetic nanoparticles )

  That is, using a commercially available image analysis software (for example, “A Image-kun” manufactured by Asahi Kasei Engineering Co., Ltd.), the obtained SEM image is converted to gray scale, and then image processing is performed to extract ferrite-based magnetic nanoparticles. Then, the particle diameter (equivalent circle diameter) of the extracted ferrite magnetic nanoparticles was determined. Assuming that the shape of the ferrite-based magnetic nanoparticles is spherical, the volume of the ferrite-based magnetic nanoparticles is obtained using the particle diameter of the ferrite-based magnetic nanoparticles, and the mass of the ferrite-based magnetic nanoparticles is multiplied by the material density. Was calculated. Based on the particle diameter and mass of each ferrite-based magnetic nanoparticle, the particle size distribution (mass basis) of the ferrite-based magnetic nanoparticle was determined.

<Relative permeability of magnetic film>
First, the thickness of the magnetic film formed on the silicon substrate was measured using a stylus type step meter. Next, a 1 cm square test specimen was cut from the silicon substrate on which the magnetic film was formed. A 1 cm square silicon substrate on which no magnetic film was formed was prepared. Using a magnetic permeability measuring device (“PMF-001” manufactured by Ryowa Denshi Co., Ltd.), the relative magnetic permeability of the test specimen for measurement and the silicon substrate was measured under a condition of a frequency of 1 MHz under a room temperature (23 ° C.) environment. The relative permeability of the magnetic film was determined from the difference in relative permeability between the test specimen for measurement and the silicon substrate and the film thickness of the magnetic film.

Example 1
After adding 30 g of powder (average particle diameter: 300 nm) containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles to 170 g of isopropanol, and further adding 500 g of zirconia balls having a diameter of 3 mm, ball mill (Yamato Science) Crushing using “UB32” manufactured by Co., Ltd. to obtain a dispersion of ferrite-based magnetic nanoparticles. After collecting a small amount of this dispersion and removing the solvent by drying, the particle size distribution (mass basis) of the obtained ferrite-based magnetic nanoparticles is determined according to the above method, and the obtained particle size distribution (mass basis) is represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieve, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
When the distribution constant m was calculated on the assumption that it follows the rosin-Rammler distribution function expressed as follows, the distribution constant m was 1.9.

To the dispersion containing the ferrite-based magnetic nanoparticles, 40 g of 2- (2-ethoxyethoxy) ethanol is added, and isopropanol is distilled off under the conditions of 40 ° C. and 50 mTorr (6.7 Pa) using a rotary evaporator. A slurry in which the ferrite magnetic nanoparticles were dispersed in (2-ethoxyethoxy) ethanol was obtained. To this slurry, a phenol resin (“thermosetting phenol resin 110” manufactured by Cemedine Co., Ltd.) was added as a binder so that the resin component would be 4.8 g. And the phenolic resin was completely dissolved, and then 90 g of powder containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic microparticles (average particle size: 7 μm) was added, The mixture was stirred using the autorotation / revolution mixer to obtain a coating solution.

  This coating solution was applied on a silicon substrate by a screen printing method, left in the atmosphere at 50 ° C. for 30 minutes, and this operation was repeated to form a coating film having a thickness of 50 μm. This coating film was heated at 150 ° C. for 30 minutes while being pressurized to 60 MPa using a heating and pressing apparatus (“TBH-100H” manufactured by Sansho Industry Co., Ltd.). Thereafter, the pressure was released and the sample was taken out and heat-treated at 200 ° C. for 1 hour in a nitrogen atmosphere to obtain a magnetic film. The relative magnetic permeability μ ′ of the obtained magnetic film was determined to be 83.

(Example 2)
Powder containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles in the same manner as in Example 1 except that 500 g of zirconia balls having a diameter of 1 mm was used instead of zirconia balls having a diameter of 3 mm (average particle diameter: 300 nm) ) Was crushed to obtain a dispersion of the ferrite-based magnetic nanoparticles. The distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1 and was 1.6. Further, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite-based magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 62.

(Example 3)
Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles were prepared in the same manner as in Example 1 except that 250 g of zirconia balls having a diameter of 1 mm and 250 g of zirconia balls having a diameter of 3 mm were used instead of 500 g of zirconia balls having a diameter of 3 mm. The contained powder (average particle size: 300 nm) was pulverized to obtain a dispersion of the ferrite-based magnetic nanoparticles. When the distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1, it was 1.75. In addition, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 72.

(Example 4)
Powder containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles in the same manner as in Example 1 except that 500 g of zirconia balls having a diameter of 5 mm was used instead of zirconia balls having a diameter of 3 mm (average particle diameter: 300 nm ) Was crushed to obtain a dispersion of the ferrite-based magnetic nanoparticles. When the distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1, it was 2.1. Further, a magnetic film was prepared in the same manner as in Example 1 except that this dispersion containing ferrite-based magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 79.

(Example 5)
Powder (average particle diameter) containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles at 10000 rpm for 5 minutes using a homogenizer (manufactured by IKA, homogenizer T25 digital + shaft generator S25KV-25F) instead of the ball mill : 300 nm) in the same manner as in Example 1 except for crushing to obtain a dispersion of the ferrite-based magnetic nanoparticles. The distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1 and was 2.3. Further, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 60.

(Comparative Example 1)
Other than crushing powder (average particle diameter: 300 nm) containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles using a jet mill (“MJT-LAB” manufactured by Hosokawa Micron Corporation) instead of a ball mill Was the same as in Example 1 to obtain a dispersion of the ferrite-based magnetic nanoparticles. When the distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1, it was 1.4. Further, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 42.

(Comparative Example 2)
30 g of powder (average particle size: 300 nm) containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles was added to 170 g of isopropanol to obtain a dispersion of the ferrite-based magnetic nanoparticles. The distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1 and was 2.5. Further, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite-based magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 43.

(Comparative Example 3)
Powder containing ferrite-based magnetic nanoparticles obtained after heat treatment at 900 ° C. for 120 minutes to 30 g of powder containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles (average particle size: 300 nm) Was added to 170 g of isopropanol to obtain a dispersion of the ferrite-based magnetic nanoparticles. The distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1 and was 2.7. Further, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 25.

  FIG. 1 shows the result of plotting the relative permeability μ ′ of the magnetic films obtained in Examples 1 to 5 and Comparative Examples 1 to 3 against the distribution constant m of the ferrite-based magnetic nanoparticles. As is apparent from the results, the magnetic films (Examples 1 to 5) containing the ferrite-based magnetic nanoparticles having the distribution constant m within a predetermined range have a relative permeability μ ′ of 60 or more and distribution. Compared with a magnetic film containing ferrite-based magnetic nanoparticles having a constant m of 1.4 (Comparative Example 1), 2.5 (Comparative Example 2) or 2.7 (Comparative Example 3), the relative permeability is high. It was confirmed that

(Example 6)
30 g of powder (average particle size: 300 nm) containing Mn _0.5 Zn _0.5 Fe ₂ O ₄ magnetic nanoparticles was crushed instead of powder containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles A dispersion of the ferrite-based magnetic nanoparticles was obtained in the same manner as in Example 1 except that. When the distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1, it was 1.8. Further, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite-based magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 65.

(Comparative Example 4)
30 g of powder (average particle size: 50 nm) containing Mn _0.5 Zn _0.5 Fe ₂ O ₄ magnetic nanoparticles was crushed instead of powder containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles A dispersion of the ferrite-based magnetic nanoparticles was obtained in the same manner as in Example 1 except that. The distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1 and was 1.7. In addition, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite-based magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 27.

(Comparative Example 5)
500 g of zirconia balls having a diameter of 5 mm are used instead of zirconia balls having a diameter of 3 mm, and Mn _0.5 Zn _0.5 Fe ₂ O ₄ is used instead of the powder containing Ni _0.4 Zn _0.6 Fe ₂ O ₄ magnetic nanoparticles. A dispersion of the ferrite-based magnetic nanoparticles was obtained in the same manner as in Example 1 except that 30 g of powder containing magnetic nanoparticles (average particle size: 50 nm) was pulverized. The distribution constant m of the ferrite-based magnetic nanoparticles was determined in the same manner as in Example 1 and was 1.9. Further, a magnetic film was prepared in the same manner as in Example 1 except that the dispersion containing the ferrite magnetic nanoparticles was used, and the relative permeability μ ′ was determined to be 19.

  As is apparent from the results obtained in Example 6 and Comparative Examples 4 to 5, when ferrite-based magnetic nanoparticles having an average particle diameter and a distribution constant m within a predetermined range are used (Example 6). When the average particle diameter is small (Comparative Examples 4 to 5) even when the magnetic constant of the magnetic film is high, the ferrite-based magnetic nanoparticles having a distribution constant m within a predetermined range are used. It was found that the relative permeability of the magnetic film was lowered. This is presumably because ferrite-based magnetic nanoparticles having a small average particle diameter aggregated during film formation.

  As described above, according to the present invention, it is possible to obtain a magnetic film having a high magnetic permeability. Therefore, the magnetic film of the present invention is useful as a magnetic material used for inductors, transformers, electromagnetic noise absorbers, magnetic sensors and the like.

Claims (5)

A magnetic film containing a binder, ferrite magnetic nanoparticles having an average particle diameter of 100 to 500 nm and ferrite magnetic microparticles having an average particle diameter of 1 to 100 μm dispersed in the binder,
The particle size distribution (mass basis) of the ferrite magnetic nanoparticles is represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieving, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
The distribution constant m is within the range of 1.6 to 2.3 when it is assumed to follow the rosin-Rammler distribution function represented by
A magnetic film characterized by the above.   2. The magnetic film according to claim 1, wherein the content of the ferrite-based magnetic nanoparticles is 1 to 50 parts by mass with respect to 100 parts by mass of all ferrite-based magnetic particles.   The magnetic film according to claim 1 or 2, wherein the content of the binder is 0.1 to 10 parts by mass with respect to 100 parts by mass of all ferrite magnetic particles.   The binder is made of at least one resin selected from the group consisting of epoxy resin, acrylic resin, phenol resin, urethane resin, polyimide resin, urea resin, silicone resin, and pyrrolidone resin. The magnetic film as described in any one of Claims 1-3. The mass of ferrite magnetic nanoparticles is crushed to have an average particle size of 100 to 500 nm, and the particle size distribution (mass basis) is represented by the following formula:
F (Dp) = 1−exp (− (Dp / De) ^m )
[In the formula, F represents the total mass fraction under sieve, Dp represents the particle size, De represents the particle size characteristic number, and m represents the distribution constant.]
A step of preparing a ferrite-based magnetic nanoparticle having a distribution constant m in the range of 1.6 to 2.3 assuming that it follows a rosin-Lambler distribution function represented by:
A step of preparing a coating liquid containing the ferrite magnetic nanoparticles prepared in the step, a ferrite magnetic microparticle having an average particle diameter of 1 to 100 μm, a binder, and a solvent;
Forming a coating film by applying the coating liquid;
The step of heating the coating film while applying pressure to form the magnetic film according to any one of claims 1 to 4,
A method for producing a magnetic film, comprising: