JP6342127B2 - Method for producing magnetic material for hexagonal ferrite magnetic powder, method for producing molded body of magnetic material for hexagonal ferrite magnetic powder, and method for producing hexagonal ferrite magnetic powder - Google Patents

Description

  The present invention relates to a hexagonal ferrite magnetic powder suitable for high-density magnetic recording media, a production method for obtaining a molded body of a hexagonal ferrite magnetic powder, and a molded body of a hexagonal ferrite magnetic powder.

  In order to further increase the density of the coating type magnetic recording medium, fine magnetic powder is required. Conventionally used metal magnetic powder is a magnetic powder having excellent magnetic properties such as high saturation magnetization and large coercive force. However, as it becomes finer, it has become difficult to maintain both its magnetic properties for a long period of time (weather resistance) and to achieve excellent magnetic properties. In addition, the recent improvement in characteristics of magnetic heads (particularly reproducing heads) has made it possible to sufficiently use magnetic powders that do not have saturation magnetization as high as that of metal magnetic powders.

  Against this background of technology, ferrite-type magnetic powders that have been used only for specific applications due to their low saturation magnetization, but excellent stability of magnetic properties, especially hexagonal ferrite magnetic powders, Attention has been focused on magnetic powder for high density magnetic recording media.

  In addition, in the process of studying hexagonal ferrite magnetic powder suitable for high-density magnetic recording, to obtain hexagonal ferrite magnetic powder that has fine and high magnetic properties and can be suitably used for high-density magnetic recording media. Has been found to be preferred to use the glass crystallization method.

  Here, the glass crystallization method will be briefly described. First, a ferrite component, which is a magnetic material, and a glass forming component (also referred to as “non-magnetic component”) are melted at a high temperature. Other metal elements may be added to the magnetic material as necessary. This is rapidly cooled from the molten state and solidified to obtain a precursor which is an amorphous body (glass body).

  The precursor is subjected to heat treatment, and hexagonal ferrite magnetic powder is precipitated in the precursor. The hexagonal ferrite magnetic powder here becomes the material of the high-density magnetic recording medium. When the glass crystallization method is used, hexagonal ferrite is crystal-grown in a high-temperature glass body, so that crystal growth can be easily controlled. In particular, since it is easy to grow crystals in the C-axis direction, there is an advantage that hexagonal ferrite having excellent magnetic properties can be obtained.

  Furthermore, in order to obtain hexagonal ferrite having excellent magnetic properties, methods for improving the composition and the like are known. For example, Patent Literature 1 discloses at least a hexagonal ferrite forming raw material and a tetravalent element (M4) of 0.004 to 0.045 atoms with respect to one iron (Fe) atom contained in the hexagonal ferrite forming raw material. A method for producing a hexagonal ferrite magnetic powder comprising mixing one material, melting the obtained raw material mixture, rapidly cooling it to an amorphous body, and then heat-treating the amorphous body to precipitate hexagonal ferrite Is disclosed.

  As a method for improving the productivity of the amorphous body, for example, there is a method disclosed in Patent Document 2. When trying to obtain an amorphous body with high productivity by batch processing, it is efficient to process by melting as much raw material as possible. Therefore, Patent Document 2 describes a method in which after the first raw material is melted and the volume is reduced, the heat-resistant container (crucible) is taken out of the furnace, and the raw material is additionally added thereto to increase the melting amount per batch. ing.

  The batch process is a process performed by dividing the production amount into a certain amount of division and making it into a production unit that makes one batch (also referred to as one lot). The advantage of this treatment is that it is easy to obtain a product having a desired composition because the blending of raw materials can be adjusted within one batch.

  However, if the prepared composition ratio deviates from the desired one, the batch of the product cannot be used in the next step, and is discarded or reprocessed.

  In batch processing, when a high-frequency melting furnace is used to melt the raw material, the furnace temperature can be quickly adjusted by adjusting the amount of current flowing through the coil, so the furnace is cooled and added. This is easy, and there is a report used when producing hexagonal ferrite (Patent Document 1).

  In this way, in order to obtain hexagonal ferrite with excellent magnetic properties, finding a new composition and improving productivity, we adopted an increase in throughput and a more efficient heating method in batch processing. It was known to do.

JP 2006-5299 A JP 2012-25598 A

  In the market of high-density magnetic recording media, the demand for high-quality magnetic powder and a stable supply of a certain amount is naturally strong, and for that purpose, the supply of hexagonal ferrite magnetic powder with stable characteristics is urgent. Even if a new composition is found in order to improve the magnetic properties, various tests are required to produce a product that can be stably supplied, and a long time and cost are required.

  On the other hand, the hexagonal ferrite magnetic powder is a high-quality magnetic powder even with an existing composition. However, the magnetic properties of the produced magnetic powder have fluctuations in the magnetic properties even if they have almost the same composition, and it is necessary to supply magnetic powder with more stable quality (magnetic properties) in which the fluctuation is suppressed.

  That is, there has been a demand for the development of a stable quality (magnetic property) magnetic powder and a production method capable of supplying the same even in the existing composition of the high-performance stable hexagonal ferrite magnetic powder.

  The present invention has been conceived in view of the above problems. In the production of hexagonal ferrite magnetic powder, the composition is set in advance, and raw materials of various elements are blended with the composition as a target. As these various elements, iron, barium, and boron are mainly used, and a composition ratio that expresses their composition in terms of molar ratio is set in advance.

  If it is an industrial composition, the magnetic powder can be manufactured substantially according to the composition ratio. However, the compositional deviation, which is a comparative difference between the composition of the magnetic powder and the set value, may occur in a very small range. The inventors have found that even this very small compositional deviation causes variations in the overall magnetic properties, and as a result, hinders the provision of stable hexagonal ferrite magnetic powder.

  Furthermore, the inventors have found out that it is important for the magnetic properties of hexagonal ferrite magnetic powder to reduce the composition ratio deviation of the glass raw material (boron) that hardly remains when used as magnetic powder. It was. And it discovered that the composition ratio shift | offset | difference of boron can be decreased by shape | molding a raw material previously spherically (molding process), and throwing into a melting furnace.

  However, it has been found that when the magnetic properties are further stabilized, there is a problem that the amount of boron shifts depending on the conditions even with the molding process. As a result of intensive studies on the cause, it was concluded that it is important that the raw material used has a particle size within a certain range, and the present invention has been achieved.

The method for producing a magnetic material for hexagonal ferrite magnetic powder according to the present invention is as follows:
A step of weighing a plurality of raw material powders containing boric acid powder having a D90 particle size of 1 to 200 μm measured by a laser diffraction method;
It has the process of mixing the said several raw material powder and obtaining a magnetic raw material.

Moreover, in the method for producing the magnetic material,
Before the step of pre-Symbol weighing, the ratio of each of the D90 particle size of the boric acid powder and iron oxide powder included in the plurality of raw material powder (D90 particle diameter of D90 particle size / iron oxide powder boric acid powder) Is characterized by having a step of adjusting the particle size so as to be in the range of 0.5-5.

In addition, the method for producing a molded body of the magnetic material according to the present invention includes:
Aggregating and molding the magnetic material described above,
It has the process of obtaining a molded object, It is characterized by the above-mentioned.

Moreover, in the manufacturing method of said molded object,
The step of obtaining the molded body is a step of adding water to the magnetic material and aggregating the magnetic material.

In addition, the method for producing hexagonal ferrite magnetic powder according to the present invention includes:
A step of melting the molded body after drying to obtain a melt;
A step of making the melt into a fine powder precursor by an atomizing method;
It has the process of heat-processing the said precursor.

  The manufacturing method of the magnetic material for hexagonal ferrite magnetic powder according to the present invention defines the size of the boric acid powder material relative to the iron oxide powder material, so that the size of each material falls within a certain range. Since it was made to do, each raw material powder is not unevenly distributed in mixed powder in the case of mixing.

  For this reason, even with an existing composition of high-characteristic hexagonal ferrite magnetic powder, a stable quality (magnetic characteristic) magnetic powder with suppressed variation in characteristics can be obtained and supplied to the market.

  Hereinafter, the method for producing the hexagonal ferrite magnetic powder of the present invention will be described. However, the following embodiment is an embodiment of the present invention and is not limited to the following embodiment. The following embodiments can be modified without departing from the spirit of the present invention.

  In the present invention, the aggregation means that the surfaces of the particles are joined to form an aggregate of two or more particles, or the surfaces of the particles are simply brought close to each other without contacting each other. It is a state that is an aggregate of particles.

  In the following embodiments, the measurement means used in each example is as follows.

  The particle size was measured by a laser diffraction method using a dry method. Specifically, a laser diffraction particle size distribution analyzer (Heros-Rodos) was used as the laser diffraction method. The lens was 200 mm and the dispersion pressure was measured at 0.5 MPa. The volume particle diameter was measured by this method, and in the volume-based cumulative particle size distribution, the value at 50% was the average particle diameter (D50 particle diameter), and the value at 90% was the D90 particle diameter.

  However, with this 200 mm lens, a size of 350 μm or more cannot be measured, so boric acid before pulverization was photographed at a magnification of 30 times using FE-SEM (S-4700, manufactured by Hitachi, Ltd.). Then, the volume particle diameter of a spherical shape is measured using the longest size of 100 or more particles, and in the volume-based cumulative particle size distribution, the value at 50% is defined as the average particle diameter (D50 particle diameter), and 90% The value at was defined as the D90 particle size.

  In addition, about the particle size of each raw material powder, there may be an error of about 10%, and strict numerical control is not necessary. Since the particle size ratio is adjusted, each raw material powder that has been sieved with a sieve having a certain fine mesh may be used. For example, -200 mesh (75 μm) is available. You may change the magnitude | size (count) of an opening according to the kind of raw material powder.

  The elemental composition in the amorphous body (glass body) was measured by an ICP emission analysis method using ICP (Inductively Coupled Plasma: product name: 720-ES) manufactured by Agilent Technologies.

  The BET specific surface area was determined by the BET method using 4 Sorb US manufactured by Yuasa Ionics Co., Ltd.

  The manufacturing method of the hexagonal ferrite magnetic powder according to the present invention and the manufacturing method of the molded body of the magnetic material for the hexagonal ferrite magnetic powder will be described in the case of barium ferrite.

  First, the particle size of the raw material powder is measured to confirm whether or not the D90 particle size is in the range of 1 to 200 μm. If the particle size is not within this range, pulverization is performed. In particular, since boric acid often has a coarse particle size, it is desirable to perform pulverization so as to fall within the above range.

  Next, the raw material powder used as the magnetic material is weighed. The raw material powder includes a ferrite raw material to be magnetic powder, a glass raw material necessary for forming an amorphous body, and an additive material added to the magnetic powder. Note that the additive substances include substances that are not included in the final magnetic powder, but are added to influence the precipitation of ferrite particles in the precursor. Each of the ferrite raw material, the glass raw material, and the additive substance may be referred to as raw material powder.

Specifically, as a ferrite raw material, elements that constitute ferrite such as Fe ₂ O ₃ (iron oxide, HRT made by Tetgen), BaCO ₃ (barium carbonate, made by Nippon Solvay / industrial use) and the like are preferably used. The ferrite raw material is preferably a powdery ferrite raw material.

As the glass raw material, boric acid (H ₃ BO ₃ ) (manufactured by US Borax / ordinary product) and barium carbonate are preferably used. The glass raw material is used for crystallizing and precipitating ferrite melted in the melting step described later in glass. The glass raw material is preferably a glass raw material each in powder form.

Additives include Bi ₂ O ₃ (bismuth oxide, manufactured by Sakai Shogyo / Industrial), Nb ₂ O ₅ (Niobium oxide, manufactured by Mitsui Mining & Mining / Industrial), CoO (Cobalt oxide, manufactured by Wako Pure Chemicals / Reagent) ZnO (Zinc oxide, manufactured by Hakusuitec / Industrial), Nd ₂ O ₃ (Neodymium oxide, manufactured by Shin-Etsu Chemical / Industrial), and the like. The additive substances are preferably powdered additive substances. These additive substances are contained in a molar ratio of a magnetic material for hexagonal ferrite magnetic powder in a few percent or less.

  Each raw material has already been processed to have a D90 particle size of 1 to 200 μm. However, it is further preferred that the D90 particle size is in the range of 3-100 μm, respectively. More preferably, the D90 particle size is 3 to 80 μm.

  The iron oxide powder of the ferrite raw material preferably has a D50 particle size in the range of 1 to 10 μm and a D90 particle size in the range of 30 to 100 μm.

  The barium carbonate powder has a D50 particle size of 1 to 10 μm and a D90 particle size of about 1 to 50 μm.

  The boric acid powder preferably has a D50 particle size of 5 to 20 μm, a D90 particle size of 500 μm or less, and a D90 particle size of about 20 to 500 μm. More preferably, the D90 particle size is preferably about 20 to 80 μm. This is because the particle size of the boric acid powder depends on the size of the other raw material powder, but when it is 500 μm or more, it is difficult to uniformly mix with the other raw material.

  Here, the D90 particle size ratio between the D90 particle size value of boric acid powder and the D90 particle size value of iron oxide powder is considered. The ratio of D90 particle size of boric acid powder / D90 particle size of iron oxide powder is preferably 5 or less. Furthermore, the range of 0.5-5 is preferable. From the viewpoint of productivity, 0.5 to 3.5 can be stably produced.

  These particle size ratios (D90 particle size ratio) are determined when the boric acid powder and the iron oxide powder are mixed, the composition ratios of the respective raw materials are equal even in any part of the mixture. This is to ensure that they are distributed. In particular, by setting the D90 particle size ratio as described above, it is possible to realize a state in which the vitreous material (boric acid) surrounds the ferrite raw material in the precursor produced in the subsequent melting step. Further, the vitreous material and the ferrite raw material can be present in the precursor with good dispersion.

  In general, the D50 particle size of boric acid powder is often larger than that of other raw material powders. This is because other raw material powders are commercially available depending on a certain particle size. Therefore, it is preferable to adjust the particle size (particle size) of the boric acid powder with a dry pulverizer (also referred to as a mill).

  As the dry pulverizer, an impact mill and an ixed mill are preferable, and a ball mill and a Henschel mixer are also possible. In the wet pulverization method, since the boric acid is dissolved in the liquid, the dry pulverization method is preferable.

  The glass raw material becomes unnecessary and is removed after the ferrite particles are precipitated in the crystallization step in the subsequent step. However, it was found in the examples described later that the ratio of boric acid (especially boron) in the glass raw material greatly affects the magnetic properties of the ferrite to be precipitated. The particle size is also an important factor in the glass raw material, and by setting the particle size or particle size ratio of each raw material powder, an excellent magnetic material with little variation in magnetic properties can be obtained as a result.

  Next, the subsequent steps will be described using this raw material. In order to avoid a chemical reaction between the raw materials during mixing, the mixing is desirably performed in the atmosphere, at room temperature, or in a dry state. A commercially available blender, Henschel mixer, and various mixers may be used as the mixer. In the next molding step, when the raw material powders are mixed at the same time, the mixing operation is unnecessary here. This is because, in the molded body, each raw material powder (element) may be in a desired composition ratio state.

  In order to stabilize the composition ratio of the precursor, it is necessary to reduce the moisture in the raw material powder and the carbonic acid in the barium carbonate, and to keep the composition ratio of the raw material powder to be fed into the melting furnace constant during the charging. It was considered important. In order to keep the composition ratio of the raw material powder charged into the melting furnace constant during the charging, a well-mixed raw material powder (referred to as “mixed raw material powder”) is formed into a pellet shape, etc. It is preferable that the compact is put into a melting furnace.

  If the mixed raw material powder is in a mixed state, it is in a powder state and cannot maintain a certain shape. Therefore, the mixed raw material powder is formed into a coagulated state. It can be said that the molded body is obtained by subdividing the magnetic material powder. The amount here can be freely set according to the size and density of the molded body. That is, it is possible to set an optimum condition that minimizes the composition deviation in accordance with the material components and the specifications of the apparatus.

  For agglomeration of the mixed raw material powder, a binder as a bonding agent or water may be added to form a molded body having a predetermined size. Further, the mixed raw material powder may be compacted and solidified with pressure to form a molded body. It is desirable to perform agglomeration molding so that the mixed raw material powder is joined using a liquid (water). This is because the molding cost is low and the size and shape can be easily set. As a device for forming a molded body, there are a pelletizer, a press molding machine, and the like.

  Specifically, a granulation method for forming with a pan pelletizer is exemplified. Pane pelletizer is an apparatus that can put mixed raw material powder into a container that is tilted and rotated, agglomerate the mixed raw material powder by spraying and spraying the liquid, and granulate it into a spherical molded body It is. This is a granulation method in which no pressure is applied when forming a molded body.

  Molding is performed by putting the mixed raw material powder in a pan pelletizer and rolling the pan while adding the liquid by spraying or the like. By adding the mixed raw material powder and liquid in an appropriate amount, the mixed raw material powder is formed into granules and granulated. Conditions such as angle are adjusted so that the mixed raw material powder overflows from the pan pelletizer when it reaches a desired diameter. The liquid here has a function of joining the raw material powders.

In the present invention, the liquid used may be water (H ₂ O). This is because water is used to promote aggregation and granulate to form. The purpose of using water is to dissolve a part of boric acid in water and blend it with other raw material powders. As described above, when water is used, there is an effect that boric acid water reacts with barium carbonate to generate carbon dioxide gas.

  Since the water used as the “tether (adhesive)” is not crystal water, it can be evaporated by drying at 100 ° C. or higher. Further, since the pan pelletizer is not press-worked, the molded body has many voids and can be well dried to the inside. Water may be room temperature (10 to 40 ° C.), pure water is desirable, and chemicals that promote bonding may be further mixed. Further, the molding temperature is set to be equal to or lower than the melting point of each raw material so as not to be fused. This is because the composition ratio is unevenly distributed in the molded body.

  The granulated molded body is spherical and preferably has an outer diameter of φ1 mm or more and φ50 mm or less. The size is set according to the apparatus and the amount of melting in the next melting step. In the case of a size of φ1 mm or less, it approaches the powder state of each raw material, and the effect of granulation is hardly exhibited. On the other hand, when the formed body is larger than φ50 mm, the effect of suppressing the deviation of the composition ratio is reduced because it approaches the state of the mixed raw material powder. In addition, when it is not spherical, the maximum length should just be 1 mm or more and 50 mm or less in the outer dimension of a molded object.

  The molded body having a predetermined size is dried with a dryer at 200 ° C. or higher (drying step). By drying, not only the added water but also the decomposition and dehydration of boric acid itself can be promoted, and the generation of steam during melting can be suppressed. The moisture contained in the dried molded body (referred to as “dried molded body”) is preferably 2% by mass or less.

  When the moisture content in the dried molded body is 2% by mass or more, steam may be generated when it is put into a melting furnace in the next melting step. In the melting step, when steam is generated, powdery raw material powder that has not been melted is blown off. In particular, boric acid powder having a low specific gravity is often blown away. This causes a composition shift. The drying conditions are not particularly limited as long as the water content is 2% by mass or less, but is preferably 200 ° C. or more and 14 hours or more.

  After processing into a molded body while adding water to the mixed raw material powder, the water (including crystal water) in the dried molded body is put into a melting furnace through a drying step of drying at a temperature of 200 ° C. or higher. Can be removed before. Furthermore, boric acid powder as a glass raw material is partially dissolved in water, and the boric acid water and barium carbonate cause a neutralization reaction, and carbon dioxide gas is generated during the drying process. Therefore, carbon dioxide gas can also be partially removed before melting.

  If moisture or carbon dioxide gas is removed before melting, generation of bubbles due to water vapor or carbon dioxide gas is suppressed when it is put into the melting furnace, and volatilization of elements (particularly boron) in the raw material powder is suppressed. As a result, the content of the element (especially boron) in the raw material powder is stable, and even when the hexagonal ferrite magnetic powder having the same composition is manufactured, the deviation in composition and characteristics due to so-called lot differences can be suppressed.

  The dry molded body thus obtained is melted in a melting furnace (melting step). The melting furnace can use any method such as a resistance heating method or a high frequency induction heating method. There is a crucible made of platinum in the furnace, and it is heated and maintained at a temperature of 1000 ° C. to 1400 ° C. The granulated dried molded body is put into this heated furnace. Addition may be performed at once, or may be performed in divided portions in accordance with the melting state.

  It is desirable to use a charging pipe installed at the top of the furnace. Since the mixed raw material powder (magnetic powder raw material) is formed, it can be charged easily without worrying about the mixed raw material powder dancing. Also, since the magnetic powder raw material is put into a high-temperature furnace, the temperature of the magnetic powder raw material rises rapidly, but since it is processed into a dry molded body, foaming due to evaporation, volatilization, decomposition, etc. is melted very little. . After the dry molded body is put into the furnace, it is melted and reduced in volume when held for a certain period of time. Therefore, the dry molded body is additionally added again according to the molten metal level.

  The raw magnetic powder material that has been melted is rapidly cooled. Although the method used in the case of rapid cooling is not specifically limited, It is preferable to select the atomizing method. Normally, the water atomization method and the gas atomization method are selected as the atomization method, but a method such as a centrifugal force atomization method can also be selected depending on circumstances.

  In the atomizing method, molten metal is sprayed into the air while chipping with an atomizing nozzle, and fine particles with a particle diameter of about several to several tens of microns (mostly about 1 to 500 μm) are 1 mm or less. It becomes cooled by becoming. In this way, it is formed by cooling to obtain a precursor (amorphous body).

  By heat-treating the precursor thus obtained, a ferrite-containing precursor in which ferrite is precipitated in the precursor is obtained. In the heat treatment at this time, the precursor may be allowed to stand or may be heat-treated while being rolled.

  The temperature of the heat treatment only needs to be such that ferrite can be formed in the precursor. Specifically, it is 450 ° C. or higher and 750 ° C. or lower, preferably 500 ° C. or higher and 750 ° C. or lower, more preferably 550 ° C. or higher and 700 ° C. or lower. It is. The heat treatment may be performed at a single temperature, that is, heating in a single stage, or may be a so-called multi-stage process performed in several stages at different processing temperatures. The heat treatment time is 30 minutes or longer, preferably 1 hour or longer.

  Next, the glass component is removed from the obtained ferrite-containing precursor to obtain ferrite particles. At this time, dilute acetic acid diluted to about 10% by mass is preferably used, and the treatment temperature is preferably 50 ° C. or higher. Acetic acid may optionally be boiled or stirred for uniform removal. At this time, the pH of the treatment liquid is preferably 4.0 or less acidic.

  Thereafter, the ferrite particles are recovered from the slurry in which the glass component is dissolved and the ferrite particles are dispersed using a solid-liquid separator.

  From the ferrite particles obtained by solid-liquid separation, acetic acid and the like adhering to the surface is removed by washing. The adhering component may be removed by washing with pure water or boiling pure water. In some cases, it is also preferable to wash while neutralizing acetic acid adhering during washing with aqueous ammonia, aqueous sodium hydroxide, aqueous potassium hydroxide, or the like.

  If it is sodium hydroxide aqueous solution, it is good to set it as 0.01-1.5 mol / L, Preferably it is 0.05-1.2 mol / L, More preferably, it is 0.1-1.0 mol / L. If the concentration is low, there is no cleaning effect, and if the concentration is high, the cleaning effect is saturated and the risk of contamination is increased.

  Thereafter, the cleaning liquid is pure water, and the filtrate is sufficiently washed until the filtrate has a conductivity of 1 mS / m or less, preferably 0.8 mS / m or less.

  The obtained ferrite particles after the washing treatment can be obtained as dry powder by subjecting them to moisture removal treatment under conditions of 100 ° C. or higher in the atmosphere. Then, in order to improve the dispersibility with respect to a binder, you may make a water | moisture content adhere to the dry magnetic powder surface about 0.5-5.0 mass% in the wet environment of about 80% RH.

  Through the above steps, a high-characteristic hexagonal ferrite magnetic powder with little compositional deviation can be obtained.

  In addition, the fluctuation of the magnetic characteristics could be made extremely small. As a result, high-quality magnetic materials can be stably supplied with high quality.

  The hexagonal ferrite magnetic powder produced according to the present invention can be widely used for industrial products such as various recording media.

  Examples using the production method of the present invention will be described below.

<Example 1>
Magnetic material for hexagonal ferrite magnetic powder is 35.5 kg of iron oxide powder (HRT manufactured by Tetsugen), 59.7 kg of barium carbonate powder (Nihon Solvay / industrial use), boric acid powder (manufactured by US Borax / pulverized product) 32.5 kg, as additive elements, bismuth oxide powder (manufactured by Sakai Shogyo / industrial), niobium oxide powder (manufactured by Mitsui Kinzoku Mining / industrial), cobalt oxide powder (manufactured by Wako Pure Chemicals / reagent), zinc oxide powder ( Hakusui Tech / Industrial).

  Here, the D90 particle diameter of the iron oxide powder was 63 μm, the barium carbonate powder was 14 μm, the boric acid powder was 953 μm (SEM measurement), and the D90 particle diameters of the other additive elements were 50 μm or less, respectively. The particle size of the boric acid powder was judged to be too large, and the boric acid powder was pulverized by a dry method.

  For the pulverization, an impact mill (AVIS-150) manufactured by Mill System was used. As for the particle size of the boric acid powder after pulverization, the D90 particle size was 56 μm (measured with a laser diffraction particle size distribution analyzer). The ratio of each D90 particle size (D90 particle size of boric acid powder / D90 particle size of iron oxide powder) with boric acid powder to iron oxide powder was 0.9. As a result, the D90 particle size of the boric acid powder could be adjusted sufficiently.

  These raw material powders were weighed and mixed with an Mitsui Miike FM mixer to obtain mixed raw material powders. The mixed raw material powder was put into a pan pelletizer and agglomerated so as to be granulated into a spherical shape while spraying water to form a plurality of mixed raw material powder compacts. One size of the molded body at this time was a mixture of diameters (maximum diameter) in the range of 4 to 30 mm. No boric acid powder remained on the bottom of the pan pelletizer. Next, this compact was dried at 270 ° C. for 14 hours. At this time, the moisture content of the dried molded body was 2% by mass or less.

  Sampling was performed 5 times from this dried molded body. Composition analysis was performed on each of five samples obtained by sampling. In the composition analysis, 1 g was randomly extracted from the molded body 5 times, and each was pulverized. Then, 0.1 g of 1 g was dissolved and diluted with hydrochloric acid, and then composition analysis was performed by ICP (Inductively Coupled Plasma) analysis. This is for grasping the composition variation of the entire dried molded body produced.

  The results are shown below. Table 1 shows the average mass% of iron, boron, and barium, the average B / Fe molar ratio, the standard deviation of each average, and the coefficient of variation of the five dried molded body samples. The B / Fe molar ratio is a value determined by boron content (mol) / iron content (mol). The variation coefficient is a value obtained by CV (%) = (σ / average) × 100.

  According to the ICP analysis method, the composition of the sample of each dry molded body was as follows. With iron, 19.8% by mass, 19.8% by mass, 20.0% by mass, 20.0% by mass, 19.7% by mass, the average of samples of five molded bodies was 19.86% by mass, σ Was 0.13 and the coefficient of variation (σ / average) was 0.65%.

  Similarly, boron is 4.70% by mass, 4.69% by mass, 4.66% by mass, 4.71% by mass, 4.64% by mass, the average is 4.68% by mass, σ is 0.03, The coefficient of variation (σ / average) was 0.64%.

  Barium is 33.4% by mass, 33.6% by mass, 33.5% by mass, 33.8% by mass, 33.2% by mass, the average is 33.50% by mass, σ is 0.22, and the coefficient of variation (Σ / average) was 0.66%.

  B / Fe molar ratio is 1.23, 1.22, 1.20, 1.22, 1.22, average 1.22, σ is 0.01, coefficient of variation (σ / average) 0.82% Met.

  Next, this dry molded body was melted. The dried molded body was put into a melting furnace at 1200 ° C. using a feeding pipe. Part of the dried molded body was not blown away by the rising airflow from the furnace, and there was little foaming when the dried molded body melted.

  The dry molded body was put in a platinum crucible, and when the melt was reduced, the operation of adding additional dry molded body was repeated to melt 70 kg of the dry molded body. Thereafter, the temperature of the platinum crucible is raised to 1400 ° C., and the dried molded body (magnetic material raw material) is completely melted and held with stirring for 60 minutes to completely dissolve the magnetic material raw material. State.

  The obtained molten metal was discharged from the nozzle and rapidly cooled by a gas atomization method to form an amorphous glass body (precursor). Thereafter, the precursor was heat-treated at 627 ° C. for 1 hour to obtain a ferrite-containing precursor. The ferrite-containing precursor was immersed in 10% by mass acetic acid heated to 60 ° C. and held for 60 minutes to remove the glass component. Thereafter, acetic acid adhering to the surface was removed using pure water to obtain hexagonal ferrite particles.

  The operation until the hexagonal ferrite particles were obtained from the raw material weighing was repeated four times. The precursor was subjected to composition analysis to evaluate the composition difference between batches. The obtained hexagonal ferrite was evaluated for shape and magnetic properties.

  For the composition analysis of the precursor, 0.1 g of the precursor was dissolved in hydrochloric acid, diluted, and then analyzed by ICP analysis. The results are shown below. The average, standard deviation, and coefficient of variation are shown in Table 2.

  The composition of the precursor was as follows. First, iron is 23.0% by mass, 22.9% by mass, 22.8% by mass, 23.0% by mass, the average is 22.93% by mass, σ is 0.10, and the coefficient of variation (σ / average) is It was 0.44%.

  Similarly, boron is 5.44% by mass, 5.46% by mass, 5.42% by mass, 5.36% by mass, the average is 5.42% by mass, σ is 0.04, and the coefficient of variation (σ / average ) 0.74%.

  Barium is 38.4% by mass, 38.8% by mass, 38.2% by mass, 38.9% by mass, the average is 38.58% by mass, σ is 0.33, and the coefficient of variation (σ / average) is 0. .86%.

  The B / Fe molar ratios were 1.22, 1.23, 1.23, and 1.20, the average was 1.22, σ was 0.01, and the coefficient of variation (σ / average) was 0.82%.

<Powder magnetic property evaluation>
The magnetic powder is packed in a plastic container having a diameter of 6 mm, and a coercive force Hc (Oe, Oe, with an external magnetic field of 795.8 kA / m (10 kOe) using a VSM device (VSM-P7-15) manufactured by Toei Industry Co., Ltd. kA / m), saturation magnetization σs (Am ² / kg), powder SQ (square ratio), powder BSFD (bulk state SFD value). The SFD value is a value (no unit) obtained by normalizing the half-value width of the differential curve of the hysteresis curve obtained by the VSM device with the coercive force. Each measurement result is shown below. Table 3 shows the average, standard deviation, and coefficient of variation of each characteristic.

  The coercive force Hc (kA / m) is 193, 197, 197, 194, the average value (ave) is 195.16, the standard deviation (σ) is 1.98, and the coefficient of variation (σ / average) is 1.01%. there were.

Saturation magnetization σs (A · m ² / kg) is 47.2, 48.0, 47.5, 47.0, average value (ave) 47.43, standard deviation (σ) 0.43, fluctuation The coefficient (σ / average) was 0.91%.

  The SQ (square ratio) of the powder is 0.51, 0.52, 0.51, 0.51, the average value (ave) 0.51, the standard deviation (σ) 0.00, the coefficient of variation (σ / Average) 0.00%.

  The BSFD (SFD value in the bulk state) of the powder is 0.67, 0.61, 0.63, 0.65, the average value (ave) 0.64, the standard deviation (σ) 0.03, and the coefficient of variation It was 4.69% (σ / average).

<Example 2>
In Example 2, the grinding machine was an Exceed Mill (Makino Sangyo, EM-2-5.5). The particle size of the boric acid powder after pulverization was 48 μm in D90 particle size (measured with a laser diffraction particle size distribution analyzer). The ratio of D90 particle size of boric acid powder to iron oxide powder (D90 particle size of boric acid powder / D90 particle size of iron oxide powder) was 0.8. The D90 particle size of the boric acid powder could be adjusted sufficiently. The other conditions are the same as in the first embodiment.

  In the same manner as in Example 1, the above-described raw material adjustment to magnetic property evaluation were repeated four times. That is, 4 batches were performed. Table 1 shows the composition of the dried molded body, Table 2 shows the composition of the precursor, and Table 3 shows the magnetic properties of the magnetic powder.

  The composition of the dried molded body was as follows. First, with iron, 20.4 mass%, 20.2 mass%, 20.5 mass%, 20.6 mass%, 20.6 mass%, the average is 20.46 mass%, σ is 0.17, The coefficient of variation (σ / average) was 0.83%.

  Similarly, boron is 4.81% by mass, 4.76% by mass, 4.84% by mass, 4.78% by mass, 4.72% by mass, the average is 4.78% by mass, σ is 0.05, The coefficient of variation (σ / average) was 1.05%.

  Barium is 34.0 mass%, 33.8 mass%, 34.2 mass%, 34.4 mass%, 34.2 mass%, the average is 34.12 mass%, σ is 0.23, coefficient of variation (Σ / average) was 0.67%.

  The B / Fe molar ratio is 1.22, 1.22, 1.22, 1.20, 1.18, the average is 1.21, σ is 0.02, and the coefficient of variation (σ / average) is 1.65. %Met.

  The composition of the precursor was as follows. First, with iron, 23.2% by mass, 23.1% by mass, 23.1% by mass, 23.1% by mass, the average is 23.13% by mass, σ is 0.05, and the coefficient of variation (σ / average) is 0. .22%.

  Similarly, boron is 5.30% by mass, 5.32% by mass, 5.25% by mass, 5.28% by mass, the average is 5.29% by mass, σ is 0.03, and the coefficient of variation (σ / average ) 0.57%.

  Barium is 38.9 mass%, 39.0 mass%, 38.9 mass%, 38.3 mass%, the average is 38.78 mass%, σ is 0.32, and the coefficient of variation (σ / average) is 0. 0.83%.

  The B / Fe molar ratios were 1.18, 1.23, 1.23, and 1.20, the average was 1.21, σ was 0.02, and the coefficient of variation (σ / average) was 1.65%.

  The magnetic properties of the magnetic powder were as follows. First, coercive force Hc (kA / m) is 195, 195, 196, 193, average value (ave) 194.87, standard deviation (σ) 1.48, coefficient of variation (σ / average) 0.76. %Met.

Saturation magnetization σs (A · m ² / kg) is 48.0, 48.0, 48.0, 48.0, average value (ave) 48.00, standard deviation (σ) 0.00, fluctuation The coefficient (σ / average) was 0.00%.

  The SQ (square ratio) of the powder is 0.51, 0.51, 0.51, 0.51, the average value (ave) 0.51, the standard deviation (σ) 0.00, the coefficient of variation (σ / Average) 0.00%.

  The BSFD (SFD value in the bulk state) of the powder is 0.61, 0.60, 0.61, 0.65, the average value (ave) 0.62, the standard deviation (σ) 0.02, the coefficient of variation It was 3.23% (σ / average).

<Comparative Example 1>
In Example 1, boric acid powder which is a glass raw material was not crushed. Other conditions were the same. The particle size of boric acid not pulverized was D90 particle size 953 μm (SEM measurement). The ratio of each D90 particle diameter with boric acid powder to iron oxide powder (D90 particle diameter of boric acid powder / D90 particle diameter of iron oxide powder) was 15.1. Table 1 shows the composition of the dried molded body, Table 2 shows the composition of the precursor, and Table 3 shows the magnetic properties of the magnetic powder.

  The composition of the dried moldings was as follows. First, iron is 19.6 mass%, 19.9 mass%, 19.4 mass%, 19.8 mass%, 19.9 mass%, the average is 19.72 mass%, σ is 0.22, The coefficient of variation (σ / average) was 1.12%.

  Similarly, boron is 4.47 mass%, 4.36 mass%, 4.76 mass%, 4.20 mass%, 4.43 mass%, the average is 4.44 mass%, σ is 0.20, The coefficient of variation (σ / average) was 4.50%.

  Barium is 33.0% by mass, 33.4% by mass, 32.5% by mass, 33.1% by mass, 33.3% by mass, average is 33.06% by mass, σ is 0.35, coefficient of variation (Σ / average) was 1.06%.

  The B / Fe molar ratio was 1.18, 1.13, 1.27, 1.10, 1.15 and an average of 1.16, σ was 0.06, and the coefficient of variation (σ / average) was 5.17%. there were.

  The composition of the precursor was as follows. First, with iron, 22.9 mass%, 23.1 mass%, 23.2 mass%, 23.1 mass%, the average is 23.08 mass%, σ is 0.13, and the coefficient of variation (σ / average) is 0. 56%.

  Similarly, boron is 5.43% by mass, 5.21% by mass, 5.49% by mass, 5.22% by mass, the average is 5.34% by mass, σ is 0.14, and the coefficient of variation (σ / average ) 2.62%.

  Barium is 39.2 mass%, 39.1 mass%, 39.1 mass%, 39.0 mass%, the average is 39.10 mass%, σ is 0.08, and the coefficient of variation (σ / average) is 0. 20%.

  The B / Fe molar ratios were 1.23, 1.17, 1.17, and 1.17, the average was 1.18, σ was 0.03, and the coefficient of variation (σ / average) was 2.54%. .

  The magnetic properties of the magnetic powder were as follows. First, coercive force Hc (kA / m) is 199, 180, 203, 186, average value (ave) 192.06, standard deviation (σ) 10.72, coefficient of variation (σ / average) 5.58. %Met.

Saturation magnetization σs (A · m ² / kg) is 47.7, 45.1, 48.2, 45.8, average value (ave) 46.70, standard deviation (σ) 1.49, fluctuation The coefficient (σ / average) was 3.19%.

  The SQ (square ratio) of the powder is 0.51, 0.49, 0.51, 0.50, average value (ave) 0.50, standard deviation (σ) 0.01, coefficient of variation (σ / Average) 2.00%.

  The BSFD (SFD value in the bulk state) of the powder is 0.64, 0.81, 0.62, 0.76, average value (ave) 0.71, standard deviation (σ) 0.09, coefficient of variation It was 12.68% (σ / average).

  From Table 1, it can be seen that Example Sample 1 and Example Sample 2 have smaller standard deviations (σ) and less variation for Fe, B, and Ba than the comparative sample. In particular, the standard deviation and variation coefficient of boron (B) are extremely small. That is, as in Example Samples 1 and 2, by adjusting the particle size of the raw material powder (D90 particle size), the composition ratio deviation of the magnetic material mixed with a plurality of raw material powders was suppressed, and was stable and excellent. Magnetic properties Hexagonal ferrite magnetic material can be supplied. In particular, boron (B) often has a large particle size of the raw material powder itself, and it can be said that the effect of suppressing the composition deviation by adjusting the particle size is high.

  Table 2 shows the composition of each element of the precursor. As a result of melting the dried molded body, the standard deviations of iron and boron in Example Samples 1 and 2 are narrower, and the spread from the average value is further reduced.

  Table 3 shows the magnetic properties of the magnetic powder. In Example Samples 1 and 2, the coercive force and the standard deviation (σ) of σs were very small, and hexagonal ferrite magnetic powder having almost no variation between batches could be obtained. Referring to Table 2, although the variation in the composition of Fe and B in Example Samples 1 and 2 is small, the compositional deviation of barium (Ba) is rather larger than that in the Comparative Example sample. Considering this, in the case of hexagonal ferrite magnetic powder, when it becomes magnetic powder, it is very effective in suppressing variation in magnetic properties by suppressing the compositional deviation of the remaining boron (B). I understand that.

  The method for producing ferrite magnetic powder of the present invention can be widely used for producing fine powder using a glass crystallization method.

Claims (5)

A step of weighing a plurality of raw material powders containing boric acid powder having a D90 particle size of 1 to 200 μm measured by a laser diffraction method;
A method for producing a magnetic material for hexagonal ferrite magnetic powder, comprising the step of mixing the plurality of raw material powders to obtain a magnetic material. Before the step of pre-Symbol weighing, the ratio of each of the D90 particle size of the boric acid powder and iron oxide powder included in the plurality of raw material powder (D90 particle diameter of D90 particle size / iron oxide powder boric acid powder) 2. The method for producing a magnetic material for hexagonal ferrite magnetic powder according to claim 1, further comprising a step of adjusting the particle size such that the particle size is in a range of 0.5 to 5. 5. Aggregating and molding the magnetic material according to any one of claims 1 to 2,
It has the process of obtaining a molded object,
A method for producing a molded body of a magnetic material for hexagonal ferrite magnetic powder. The step of obtaining the molded body includes
The method for producing a molded body of a magnetic material for hexagonal ferrite magnetic powder according to claim 3, wherein the magnetic material is agglomerated by adding water to the magnetic material. A step of drying and then melting the molded body according to any one of claims 3 or 4 to obtain a melt;
A step of making the melt into a fine powder precursor by an atomizing method;
A method for producing hexagonal ferrite magnetic powder, comprising a step of heat-treating the precursor.