JP2009152471A - Method of manufacturing iron nitride-based magnetic powder, and nitride-based magnetic powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an iron nitride-based magnetic powder for use in high capacity backup magnetic tape for a computer which prevents the sintering of particles, has a narrow particle size distribution, and is suitable for high density recording. <P>SOLUTION: The method for manufacturing of the iron nitride-based magnetic powder includes the step of manufacturing metal oxide particles or metal hydroxide particles to which a specific element is adhered by using a media-type dispersion machine for an aqueous dispersion substance containing an aqueous solution of a water soluble compound of the specific element and the metal oxide particles or the metal hydroxide particles. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic powder suitable for use in a magnetic layer of a high recording density medium and a method for producing the same. More specifically, the present invention relates to an iron nitride magnetic powder having a narrow average particle size distribution and a method for producing the same.

  In the field of tape cartridges for data backup of coated magnetic recording media in which magnetic powder is dispersed in a binder, the demand for higher density recording and higher capacity is increasing as the capacity of hard disks to be backed up increases. It's getting warm. In addition, MR (Magneto-Resitie) elements exhibiting a magnetoresistive effect are employed in the reproducing head on the magnetic device (drive) side, so that reproduction of short wavelength recording is facilitated, and now more than 100 GB per volume. Recording capacity tape cartridges are widely commercialized. A large-capacity backup tape cartridge exceeding 1 TB has also been proposed.

In order to improve the recording capacity and recording density, the magnetic powder used for the magnetic layer for short wavelength recording has been made finer every year and the optimum design of the magnetic properties has been made every year. .1μm or less acicular ferromagnetic metal powder and coercive force are based on crystal anisotropy regardless of shape anisotropy, so it is easy to make fine particles and high coercive force. An iron nitride magnetic powder mainly composed of an Fe ₁₆ N ₂ phase having a magnetic force of 200 kA / m or more and having a substantially granular shape (essentially spherical or elliptical) is disclosed (Patent Documents 1 to 3). The average particle size here means the average value of the maximum particle size of particles. For example, in the case of needle shape, the major axis diameter is referred to, in the case of plate shape, the plate diameter is referred to, and in the case of rice grains, the average value of the longer diameter is referred to. When the ratio of the longer diameter to the shorter diameter (axial ratio or plate ratio) is less than 3, more preferably 2 or less, and most preferably 1.5 or less, it becomes close to a spherical particle, and these are collectively referred to. In the present invention, it is substantially granular. In the following description, the term “particle diameter” refers to the average particle diameter unless otherwise specified.

  Patent Document 1 discloses a basic method for producing an iron nitride magnetic powder, but is mainly concerned with nitriding a metal oxide as a starting material. The specific surface area of the particles and the iron nitride magnetic powder produced is as follows. Although it is disclosed, the specific average particle size is not specified, and the particle size distribution is not mentioned at all. Further, although the necessity of adding aluminum or rare earth elements to the metal oxide as a starting material is described, no specific method is disclosed.

  The magnetic powder disclosed in Patent Literature 2 and Patent Literature 3 and the magnetic recording medium using the magnetic powder have a specific effect corresponding to the configuration described in each literature. By using the iron nitride magnetic powder, the tape used as the medium achieves high C / N. However, the iron nitride magnetic powder disclosed and verified in Patent Document 3 has a particle diameter of 20 nm or more, and as a magnetic powder required for a future high-density, large-capacity backup tape, noise of C / N of signal reproduction is expected. The volume of the magnetic powder for making it smaller is still large and has not reached the required level. By the way, to achieve 800GB per cartridge with the standard specifications (current length 700-800m, total thickness 7.0-8.0m) of 1/2 inch wide linear backup tape, which is the mainstream at present. The shortest wavelength is 0.2 μm or less and the surface recording density is about 0.8 Gb / in 2, and the calculation by simulation predicts that the particle diameter needs to be 18 nm or less when using a substantially granular iron nitride magnetic powder. Although it is important to make the particles finer, if the particle size becomes smaller, there arises a problem that sintering is likely to occur in an intermediate manufacturing process. As a result, there is a problem that the C / N required when used for a medium for high-density recording with a wide particle size distribution cannot be ensured. Although Patent Document 2 deals with particles having a particle size of 20 nm or less, the method of adding additive elements is disclosed, but the purpose is limited to improving the storage stability of the produced magnetic powder, and the particle size distribution is uniform. No mention is made of the above, and there is no suggestion of the effect when used as a magnetic powder in a medium.

  As is well known, a method for producing a substantially granular iron nitride magnetic powder is made alkaline by starting with an iron oxide or an iron hydroxide (hereinafter referred to as a metal oxide or the like). Dispersed in an aqueous solution, and an aqueous metal salt solution containing at least one element usually selected from rare earth and Al, Si is added to the particle surface of the metal oxide or the like, and at least selected from rare earth and Al, Si. Deposit one element. The deposited particles are filtered and taken out as a solid content, washed with water and dried. Next, this is reduced at a temperature of 300 ° C. to 600 ° C. to impart magnetism. Thereafter, generally, after nitriding with ammonia gas, stabilization treatment is performed in an atmosphere of N 2 and O 2 to obtain an iron nitride magnetic powder. Among these processes, sintering occurs in the reduction process, and in the deposition process, which is the previous process, how rarely at least one element selected from rare earth and Al, Si having a sintering prevention function is uniformly distributed. The point is whether the particles are deposited on the starting material. In other words, the thickness of the coating layer increases as the metal oxide of the starting material is improved to a degree of dispersion close to the primary particle level and the particle surface is uniformly coated with an element having an anti-sintering function. Sintering is difficult to occur in the reduction process. Therefore, an iron nitride-based magnetic powder close to the original particle size distribution of the iron-based oxide or iron-based hydroxide particles as the starting material can be obtained.

When the sintering occurs, the particle size distribution of the produced magnetic powder becomes wider (the particle size varies), and the coercive force distribution of the iron nitride magnetic powder obtained after nitriding becomes wider, and a high coercive force cannot be obtained. In addition to not fully exhibiting the original excellent magnetic properties, the wide particle size distribution inhibits the uniform dispersion of the magnetic powder when making the magnetic coating. As a result, the electromagnetic conversion characteristics when used for a tape cannot be improved. Therefore, it is a very important issue not to cause sintering in the manufacturing process of the substantially granular iron nitride magnetic powder. For that purpose, an outer layer whose surface is coated with a uniform thickness with an element having an anti-sintering function is formed in a state in which the particles that are the material of the iron nitride magnetic powder are well dispersed as close to the primary particles as possible. is important. The outer layer here is formed in order to prevent sintering in the deposition process and to give the produced iron nitride magnetic powder corrosion resistance, and finally in the iron nitride magnetic powder and is a core phase. It is an outer layer containing at least one element selected from conventionally known rare earth elements and Al and Si, formed in a form covering a crystal phase mainly composed of Fe ₁₆ N ₂ .

In order to solve such a problem, various investigations have been made on a production process including a reduction process of fine iron nitride magnetic powder. (Patent Documents 4 to 6)
In Patent Document 4, a method for producing iron nitride magnetic powder by reducing goethite in which at least one of V, Sc, Ti, Cr, and Mn as a conventionally known element other than Al is dissolved or deposited is reduced. Is disclosed. However, Patent Document 4 is mainly intended to improve the corrosion resistance of the iron nitride magnetic powder, and the dispersibility of an aqueous solution such as goethite as a raw material in the deposition process and the degree of deposition of the sintering inhibitor (uniformity). However, there is no disclosure of a specific method or apparatus for dispersibility of raw materials and sintering inhibitors in the process, and the particle size distribution of the produced iron nitride magnetic powder. Does not touch anything.

  Patent Document 5 defines a method for producing iron nitride-based magnetic powder by reducing goethite coated with Zn, and Patent Document 6 defines the amount of addition of Al, Si and rare earth elements as sintering inhibitors during reduction. And specifying the pressure of the reaction system in the nitriding process.

  In Patent Documents 5 and 6, the particle size of the produced iron nitride-based magnetic powder is smaller than 20 nm, but the basis is sintering that occurs in the reduction process (which greatly affects the characteristics of the iron nitride-based magnetic powder as is well known). No mention is made of the homogeneity and particle size distribution of the outer layer having a function of preventing it, and no specific technique or apparatus for dispersibility of raw materials or sintering inhibitors is disclosed as in Patent Document 4.

Japanese Patent No. 3848486 Japanese Patent No. 3886968 JP 2005-310857 A Japanese Patent Laid-Open No. 2006-41210 JP 2006-303321 A JP 2005-183932 A

The present invention solves the above-mentioned problems and prevents sintering agents (rare earth, Al, and Si) from becoming iron-based oxides or iron-based hydroxides (hereinafter referred to as metal oxides) as raw materials. (This is a generic term for a compound containing at least one selected element.) The fine particle powder in the deposition step is dispersed well to uniformly form an outer layer mainly composed of a sintering inhibitor, followed by sintering of the particles in the subsequent reduction step. An object of the present invention is to obtain an iron nitride-based magnetic powder for use in a high-capacity computer backup magnetic tape suitable for high density recording (0.5 Gb / in ² or more), which prevents stagnation and has a narrow particle size distribution.

  In the production of substantially granular fine particles based on crystal magnetic anisotropy and high coercivity iron nitride magnetic powder, which is a magnetic powder used for magnetic tape, the present inventors are well dispersed in the deposition process of the sintering inhibitor. A metal coated with a sintering inhibitor with an extremely narrow particle size distribution (with a uniform particle size) formed by forming an outer layer mainly composed of a sintering inhibitor that uniformly coats the metal oxide or the like used as the raw material. As a result of intensive studies on a method for producing oxides and the like, the present invention has been achieved.

That is, it is an iron nitride-based magnetic powder that can be a manufacturing method including the following configuration.
(1) A step of producing metal oxide particles in which an aqueous dispersion containing an aqueous solution of a water-soluble compound of a specific element to be deposited and particles of a metal oxide or the like is deposited using a media-type disperser. It is the method of including. The water-soluble compound of the specific element is not particularly limited, and examples thereof include hydrochlorides, nitrates, acetates, and silicates.
(2) The particles of metal oxide or the like are substantially granular, the average particle diameter is Φp, and the average media diameter of the media-type disperser is Φm, Φm / Φp is from 1.5k to 35k. A method comprising a step of producing metal oxide particles and the like.
(3) A method comprising a step of producing metal oxide particles by a method in which the specific element is at least one element selected from yttrium (Y), silicon (Si), and aluminum (Al).
(4) A method comprising the step of producing metal oxide particles according to (1) to (3), wherein the average particle diameter of the metal oxide or the like is 5 nm to 20 nm.
(5) An iron nitride-based magnetic powder, the main component of which is produced by the above production method, is composed of an iron nitride phase.

  Basically, the media-type disperser here uses the various kinds of beads that are conventionally well-known and generally used in the production of conventional paints and magnetic paints as media to move the beads and use the shear stress. It is a disperser that disperses the dispersion.

  However, in the case of the present invention, the system used for depositing the specific element to be deposited on the particles such as metal oxide is water-based and generally used in a weakly basic or weakly acidic medium. Is preferably made of a material that is strong against acids and bases and does not rust. Specifically, it is a ceramic bead such as titania or zirconia.

  The inventors of the present invention have an iron nitride magnetic powder that influences its magnetic properties, and thus has an outer layer of the magnetic powder that has a great influence on the electromagnetic conversion characteristics of the magnetic recording medium. This is the first time that an effective method for forming an iron nitride magnetic powder with a very narrow particle size distribution is obtained.

  According to the present invention, when depositing at least one element selected from rare earth and Al, Si on a metal oxide or the like, a particle diameter in which a ratio to the average particle diameter of the metal oxide or the like is in a certain range. By using a media-type disperser using beads of the above, the above metal oxides can be dispersed in water very well and an aqueous solution containing at least one element selected from rare earth and Al, Si can be used. These elements can be deposited uniformly. As a result, an iron nitride-based magnetic powder having a narrow particle size distribution in which sintering is prevented in the subsequent reduction process is obtained. That is, the present invention provides an iron nitride magnetic powder suitable for a coating type magnetic recording medium having a high recording density and excellent electromagnetic conversion characteristics suitable for a large capacity.

The magnetic powder for a magnetic recording medium to be produced by the production method of the present invention contains iron and nitrogen as at least constituent elements, the core phase includes at least an Fe ₁₆ N ₂ phase, and the magnetic powder has a particle size of 5 to 20 nm. The following substantially spherical magnetic powder, wherein the surface of the magnetic powder is composed of a compound layer (outer layer) containing at least one selected from rare earth elements, Si, and Al, and the content of nitrogen in the magnetic powder relative to iron Is more preferably 1.0 to 20.0 atomic%. The core phase may contain Fe ₈ N. The average particle size of the magnetic powder according to the present invention was determined from a photograph of a field of view of 0.7 μm × 0.5 μm taken at a magnification of 200,000 with a transmission electron microscope (TEM) (maximum of spherical shape). The average particle diameter of at least 300 particles. The particle size of the magnetic powder is preferably 20 nm or less, particularly preferably 15 nm or less. The reason why the particle diameter is 20 nm or less is that when the diameter exceeds 20 nm, the noise (N) of the magnetic tape increases and the reproduction output noise ratio (C / N) decreases. Further, when the particle size is 5 nm or more, it is preferable that the dispersion during the preparation of the magnetic coating is facilitated and that the fine particles are used to reduce the noise. Even if 1.5 nm, the volume of the core layer having magnetic properties is reduced, and the coercive force and saturation magnetization required for the magnetic recording medium cannot be obtained. The powder is preferably 5 nm or more because it is difficult to produce. In our experiments, the limit of about 5 nm is considered.

The content of nitrogen relative to iron in the Fe ₁₆ N ₂ phase-containing iron nitride magnetic powder is preferably 1.0 to 20.0 atomic percent, more preferably 5.0 to 18.0 atomic percent, and 8.0 to 8.0. 15.0 atomic% is more preferable. If the amount of nitrogen is too small, the amount of Fe ₁₆ N ₂ phase formed is small, and the effect of increasing the coercive force is small. If the amount is too large, nonmagnetic nitrides are easily formed, and the effect of increasing the coercive force is small. Magnetization decreases excessively.

  Further, the total content of rare earth elements, Si, and Al with respect to iron is preferably 0.10 to 40.0 atomic%, and more preferably 1.0 to 30.0 atomic%. If the total content of these elements is too small, not only the magnetic anisotropy of the magnetic powder is decreased, but also the sintering preventing effect is lowered, and therefore, coarse particles of 50 nm or more are easily formed. Moreover, when there are too many of these elements, an excessive fall of saturation magnetization will occur easily.

Of the rare earth elements and Si and Al, Si and Al have an advantage that nitriding into the Fe ₁₆ N ₂ phase is likely to occur. On the other hand, rare earth elements have the advantage of easily improving the corrosion resistance of the magnetic tape. In addition to rare earth elements and Si, Al, the effect is inferior to rare earth elements and Si, Al, but B, P, Ti, Zr, C, etc. also have an anti-sintering effect. P, Ti, Zr, C, etc. may be used.

  In the present invention, the amount of rare earth elements and Al, Si, contained in the magnetic powder with respect to iron is analyzed in accordance with a conventional method by fluorescent X-ray analysis (analysis field of view: 10 mm in diameter). The analysis was performed according to a conventional method using linear photoelectron spectroscopy (analysis field of view: diameter 5 mm). When analyzing the amount of nitrogen by X-ray photoelectron spectroscopy, after etching with argon gas, the amount of nitrogen relative to iron is analyzed to determine the relationship between the etching time and the amount of nitrogen relative to iron. The amount of nitrogen with respect to iron at a constant etching time can be determined.

The rare earth-Fe ₁₆ N ₂ phase-containing iron nitride magnetic powder has a saturation magnetization of 50 to 150 Am ² / kg (50 to 150 emu / g), preferably 50 to 100 Am ² / kg (50 to 100 emu / g). As for the coercive force and saturation magnetization of the magnetic powder, the product of the coercive force and the residual magnetic flux density (Br) of the magnetic layer of the magnetic tape using the magnetic powder and the thickness δ (Br · δ) is applied to the magnetic tape. The magnetic layer may be selected so as to have preferable characteristics so as to be adapted to hardware such as a system and a drive.

Next, the manufacturing method of the magnetic powder of this invention is demonstrated. As the metal oxide or the like as a starting material, iron-based oxide, iron-based acid hydroxide, or iron-based hydroxide is used. For example, hematite, magnetite, goethite and the like can be mentioned. In the present invention, magnetite is preferred. The particle size is not particularly limited, but in order to produce a final iron nitride magnetic powder of 20 nm or less, there is a step of removing O ₂ in the manufacturing process, so a raw material having a particle size slightly larger than that value is used. Is desirable. If it is too large, the reduction treatment tends to be inhomogeneous, and it becomes difficult to control the particle diameter, particle volume and magnetic properties. In order to produce a magnetic powder having a small coercive force temperature change, a starting material having a small particle size distribution is used. The shape is a particle such as a substantially spherical shape, a substantially granular shape, or a polyhedral shape, and is not particularly limited, but the axial ratio (major axis / minor axis) is preferably less than 2, and more preferably less than 1.5. Substantially spherical and substantially granular means a shape with an axial ratio of 2 or less.

The average particle size and particle size distribution of this starting raw material are measured as follows.
<1> Disperse starting raw material particles in water. The dispersion is placed on a transmission electron microscope (TEM) observation mesh and then naturally dried.
<2> From a photograph taken with a transmission electron microscope (TEM), obtain a particle size of at least 300 particles (a maximum spherical diameter of a substantially spherical shape).
<3> Determine the average value and standard deviation of the particle system.

  A rare earth element and Si, Al, or a compound containing elements such as Ti, Zr, C, P, and B, if necessary, are deposited on the starting metal oxide or the like. A layer formed by depositing a compound is called an outer layer. When depositing a rare earth element, the starting material is dispersed in an aqueous solution, a water-soluble compound of the rare earth element is dissolved therein, and a hydroxide or hydrate containing the rare earth element is applied to the raw material powder by a neutralization reaction or the like. There are methods such as deposition and precipitation. Further, when a compound containing an element such as Si, Al, or P is deposited, these compounds can be dissolved in a solution in which the raw material powder is immersed and deposited by adsorption. Or you may deposit by performing precipitation precipitation. The above elements may be applied simultaneously or alternately to the raw material powder. In order to perform these deposition processes efficiently, additives such as a reducing agent, a pH buffering agent, and a particle size controlling agent may be mixed.

In the present invention, the iron nitride magnetic powder having a narrow (sharp) particle size distribution means that it does not become wider than the particle size distribution of the raw material metal oxide. In other words, the standard deviation of the average particle diameter indicating the wide particle size distribution of the iron nitride magnetic powder as the final product does not exceed the standard deviation of the average particle diameter of the starting raw material. In order to obtain such iron nitride-based magnetic powder, <1> raw material as an aqueous dispersion and <2> water-solubility of a specific element having an anti-sintering effect to be deposited in the deposition process It is important to thoroughly disperse the aqueous solution in which the compound is dissolved to deposit a hydroxide or hydrate containing a rare earth element on the raw material powder.

  As described above, in the conventional literature, although there is a description about the temperature and gas atmosphere in this deposition process, only disclosure of adding <2> to <1> is made. As inferred from the literature, both <1> and <2> are basically elements that contain an aqueous solution <2> in an aqueous dispersion <1> in a container that is dispersed by stirring. Is added quantitatively and over a certain period of time so as to be a predetermined amount of the design. In this case, <1> is deposited on <1>. Is it possible to obtain a uniform outer layer by the dispersibility of <1> and <2> in the same place (the moment of deposition and the physical space)? It depends on how to deposit uniformly so that sintering does not occur in the subsequent reduction step. In the present invention, the dispersion of <1> <2> by stirring is insufficient, and further studies have been made to further improve the dispersibility. As a result, a media type disperser using beads having a predetermined diameter is used for both. Then, it was found that by mixing and carrying out the deposition reaction, it could be dispersed well and deposited uniformly. This makes it possible to obtain an iron nitride magnetic powder having a uniform outer layer and a narrow particle size distribution, which is suitable for dispersing fine particle powder.

  The process of depositing a hydroxide or hydrate containing a rare earth element on the raw material powder includes an aqueous solution of the raw material and a rare earth element, or Si, Al, or elements such as Ti, Zr, C, P, and B as required ( From a step of mixing an aqueous solution of a hydroxide or hydrate containing a rare earth and the like into a media-type disperser and mixing and dispersing them well in the disperser to cause deposition. Become. After the dispersion time corresponding to the volume of the aqueous solution formulated considering the effective volume of the disperser, which is obtained by subtracting the actual volume of the beads used as the media from the internal volume of the disperser, the beads and rare earth as the media are deposited The particles of the metal oxide and the like are sieved with a filter or the like. The sieved particles of metal oxide and the like are sent to the next washing step.

  Beads, which are media used in the disperser, are the point of the present invention. As described above, the material is not rusted or attacked by an aqueous solution of acid or base. Furthermore, as a result of various studies to obtain an iron nitride magnetic powder having a narrow particle size distribution, a relationship between the average particle diameter of beads used as a medium and the average particle diameter of a metal oxide or the like that deposits rare earth or the like is found. Thus, the present invention has been made. In other words, when the average diameter of the beads is Φm, the raw material metal oxide particles and the like are substantially grain-shaped, and the average particle diameter is Φp, and Φm / Φp satisfies 1.5 k to 35 k. Is used as media.

  However, the following must be considered: Since the particle diameter of the iron nitride magnetic powder to be obtained of the present invention is 5 to 20 nm, the average diameter Φm of the beads that can be theoretically used is the lower limit of Φm / Φp when Φp is about 5 nm. From Φm = 7.5 μm when Φm / Φp = 1.5k of Φm = Φμ = 700 μm where Φm / Φp is the upper limit value Φm / Φp = 35 k when Φp is about 20 nm, There is no problem in obtaining the larger diameter bead, but the smaller one is the minimum number of beads that can be used in the present invention which is currently industrially produced (can be used in aqueous solution without being affected by acid-base). The diameter is limited to about 30 μm of zirconia beads.

  Next, heat treatment is performed on a metal oxide powder or the like coated with a sintering inhibitor on the surface in an atmosphere of nitrogen gas or the like while flowing nitrogen gas or the like. The gas used is not particularly limited, and an inert gas such as nitrogen gas, argon gas or helium gas, oxygen, or a mixed gas thereof can be used. The heat treatment temperature is desirably 120 ° C to 700 ° C. 150-500 degreeC is preferable and 200-400 degreeC is more preferable. When the heat treatment temperature exceeds 700 ° C., the particles easily sinter and the particle size distribution becomes large. Further, at a low temperature of less than 120 ° C., reduction tends to be non-uniform during reduction in the next step due to moisture contained in the starting material. Moreover, it is preferable to heat up at a comparatively slow rate of 10-50 degreeC / min.

  After heat treatment, heat reduction is performed in hydrogen gas. The reducing gas is not particularly limited, and a reducing gas such as carbon monoxide gas may be used in addition to hydrogen gas. The reduction temperature is desirably 300 ° C to 600 ° C. When the reduction temperature is lower than 300 ° C., the reduction reaction does not proceed sufficiently, and when it exceeds 600 ° C., the powder particles are easily sintered. In order to produce a magnetic powder with a small change in coercive force temperature, the temperature is raised in an inert gas until the reduction temperature is reached, and after the sample temperature becomes uniform, the reduction gas is switched to a reducing gas. It is preferable to carry out. Moreover, it is preferable to heat up at a comparatively slow rate of 10-50 degreeC / min.

After the heat reduction treatment, nitriding treatment is performed. The nitriding treatment is desirably performed using a gas containing ammonia. In addition to ammonia gas alone, a mixed gas using hydrogen gas, helium gas, nitrogen gas, argon gas or the like as a carrier gas may be used. Nitrogen gas is particularly preferred because it is inexpensive. The nitriding temperature is preferably 90 to 250 ° C. If the nitriding temperature is too low, nitriding does not proceed sufficiently and the effect of increasing the coercive force is small. If it is too high, nitriding will be promoted excessively, the proportion of Fe ₄ N, Fe ₃ N phase, etc. will increase, the coercive force will rather decrease, and it will tend to cause an excessive decrease in saturation magnetization. It is preferable that the temperature is lowered in an inert gas until the nitriding temperature is reached, and the nitriding treatment is performed by switching to the nitriding gas after the sample temperature becomes uniform.

  After such nitriding treatment, by performing oxidation treatment, the particle size distribution is narrow (particle size) having an outer layer (surface compound layer) mainly composed of a uniform sintering inhibitor, comprising iron and nitrogen of the present invention as constituent elements. Of iron nitride based magnetic powder. The oxidation treatment is desirably performed using a mixed gas containing oxygen. For this, nitrogen gas, argon gas, helium gas, or the like can be used.

  The oxidation temperature is preferably 200 ° C. or lower. If the oxidation temperature is too high, the oxidation proceeds excessively, the iron nitride phase is significantly reduced, and the coercive force and saturation magnetization are deteriorated. In order to produce a magnetic powder having a small coercive force temperature change, first, an inert gas containing a low concentration of oxygen (for example, a 200 ppm low concentration oxygen-nitrogen mixed gas) is introduced to form a magnetic powder. After suppressing the temperature rise and forming a surface oxide film at a uniform temperature on the surface of the magnetic powder, an inert gas containing a high concentration of oxygen (for example, an inert gas having an oxygen concentration of 1000 ppm) is introduced to achieve a uniform thickness. It is preferable to form an oxide film. In addition, you may employ | adopt the method of increasing oxygen concentration gradually in the range without the temperature rise of magnetic powder.

  By using the iron nitride magnetic powder according to the present invention to form a multilayer magnetic tape having a thin magnetic layer (for example, a thickness of 150 nm or less) as the uppermost layer, better recording / reproducing characteristics have been obtained. However, the iron nitride-based magnetic powder produced by the production method of the present invention is essentially suitable for obtaining a thin uppermost magnetic layer in terms of saturation magnetization, coercive force, particle shape, and particle size distribution.

  The magnetic tape using the iron nitride magnetic powder according to the present invention comprises a magnetic paint obtained by uniformly dispersing the above iron nitride magnetic powder together with a binder in a solvent using a conventionally known dispersion technique. In addition, it can be produced by applying a magnetic layer on a nonmagnetic support by a conventionally known coating equipment and method and drying it. The magnetic tape production will be briefly described below.

<Configuration of magnetic tape>
The magnetic tape of the present invention has a structure having a nonmagnetic support and at least one magnetic layer on the nonmagnetic support. A magnetic tape having a so-called multilayer structure in which a lower layer is provided between magnetic supports is preferable. Further, it is preferable to provide a back layer on the surface opposite to the magnetic layer forming surface (recording surface). Furthermore, a lower magnetic layer for recording servo signals via a lower layer may be provided under the uppermost magnetic layer.

  The thickness of the magnetic tape (total thickness of the magnetic tape) is preferably less than 8 μm, and more preferably less than 7 μm. This is because when the thickness of the magnetic tape is 8 μm or more, the total length of the magnetic tape that can be wound on the reel is shortened, and the capacity per magnetic tape cartridge is reduced. Moreover, since it is difficult to obtain a thin non-magnetic support and it is expensive even if it is obtained, the thickness of the magnetic tape is usually 5.5 μm or more.

<Preparation of magnetic paint>
In the magnetic layer of the magnetic tape, in order to highly fill and disperse the ultrafine magnetic powder having a particle size of 20 nm or less in the coating film, it is preferable to carry out coating production in the following steps. As a pre-process of the kneading process, the magnetic powder granules are pulverized by a pulverizer, and then mixed with a phosphoric acid organic acid or a binder resin by a mixer, followed by surface treatment of the magnetic powder and mixing with the binder resin. It is preferable to provide the process to perform. A conventionally known kneader can be used for the kneading step.

  Subsequent to the kneading step, using a continuous twin-screw kneader or other diluting device, adding at least one binder resin solution and / or solvent to knead and dilute, minute media rotation such as sand mill It is preferable to disperse the paint by a dispersion process using a mold dispersion device.

  The nonmagnetic powder, which is a constituent material in the magnetic layer, may be dispersed separately from the magnetic powder to form a slurry, and this may be mixed with the magnetic powder dispersion paint to prepare the magnetic layer paint. .

The Young's modulus E _{MD in} the longitudinal direction of the magnetic tape is preferably 5 GPa or more, and more preferably 7 GPa or more. This range is preferable because when the Young's modulus in the longitudinal direction of the magnetic tape is less than 5 GPa, the magnetic tape may be stretched or damaged to deteriorate the electromagnetic conversion characteristics.

<Non-magnetic support>
For the nonmagnetic support, a polyethylene terephthalate film, a naphthalene terephthalate film, an aromatic polyamide film, an aromatic polyimide film, or the like is used.

  Although the thickness of a nonmagnetic support body changes with uses, it is 2-8 micrometers normally, Preferably it is 2-7 micrometers, More preferably, it is 2-5 micrometers, More preferably, it is 2-4.5 micrometers. Nonmagnetic supports with a thickness in this range are used because film formation is difficult if the thickness is less than 2 μm, and the tape strength decreases. If the thickness exceeds 7 μm, the total thickness of the tape increases, and the recording capacity per tape roll This is because becomes smaller.

<Magnetic layer>
The magnetic layer is composed of at least one uppermost magnetic layer provided as a recording layer, and the thickness of the uppermost magnetic layer is preferably 5 to 150 nm or less. 120 nm or less is more preferable, and 90 nm or less is more preferable. Moreover, 10 nm or more is more preferable and 15 nm or more is further more preferable. This range is preferable because when the thickness is less than 5 nm, it is difficult to form a magnetic layer having a uniform thickness, and when it exceeds 150 nm, the reproduction output is likely to decrease due to the thickness demagnetization.

  The product (Br · δ) of the residual magnetic flux density (Br) and the thickness δ of the uppermost magnetic layer of the magnetic tape is preferably 0.001 μTm or more and 0.06 μTm or less. Br · δ is more preferably 0.004 μTm or more and 0.04 μTm or less. When Br · δ is less than 0.001 μTm, even when the MR head is used, the reproduction output (C) becomes small and the reproduction output noise ratio (C / N) becomes small. When Br · δ exceeds 0.06 μTm, This is because the MR head is saturated, the noise (N) increases, and the reproduction output noise ratio (C / N) decreases.

<Lower layer>
In the magnetic tape of the present invention, it is desirable to form a lower layer in order to improve the smoothness and durability of the uppermost magnetic layer. In particular, in the magnetic tape having a magnetic layer thickness of 90 nm or less, the lower layer forming effect is large. Also, the lower layer is usually nonmagnetic in order not to disturb the magnetic recording signal of the uppermost magnetic layer.

  The thickness of the lower layer is preferably 0.10 to 1.5 μm, more preferably 0.10 to 1.0 μm. If it is less than 0.10 μm, the effect of improving the durability of the magnetic tape is small, and if it exceeds 1.5 μm, the effect of improving the durability of the magnetic tape is saturated, and the total thickness of the tape is increased, resulting in a tape length per roll. Becomes shorter and the storage capacity becomes smaller.

  The lower layer can contain nonmagnetic powders such as titanium oxide, iron oxide, and aluminum oxide for the purpose of controlling the viscosity of the paint and the tape rigidity. Nonmagnetic iron oxide is acicular, granular or amorphous. The needle-like one preferably has an average major axis length of 50 to 200 nm, and the granular or amorphous one preferably has an average particle size of 5 to 200 nm. More preferably, it is 5-100 nm. If the particle size is smaller than the above, uniform dispersion is difficult, and if it is larger than the above, irregularities at the interface between the lower layer and the magnetic layer tend to increase.

  The lower layer can contain carbon black such as acetylene black, furnace black, and thermal black for the purpose of improving conductivity.

  These carbon blacks preferably have an average particle size of usually 5 to 200 nm, more preferably 10 to 100 nm. Carbon black has a structure structure, and if the average particle size is too small, it becomes difficult to disperse the carbon black, and if it is too large, the surface smoothness becomes poor. In addition, it is not excluded to include carbon black having a large particle size with an average particle size exceeding the above range as long as the surface smoothness is not impaired. In this case, the amount of carbon black added to the lower layer is preferably 5 to 70 parts by weight, particularly 15 to 50 parts by weight, based on 100 parts by weight of the inorganic powder, by combining both carbon blacks.

<Binder>
The binder used for the lower layer and magnetic layer is vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, vinyl chloride-acetic acid. There is a combination of a polyurethane resin and at least one selected from vinyl chloride resins such as vinyl-maleic anhydride copolymer resin and vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, nitrocellulose, epoxy resin and the like.

  In particular, it is preferable to use a vinyl chloride resin and a polyurethane resin in combination. Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane.

These binders preferably have a functional group in order to improve the dispersibility of magnetic powder or the like and to increase the filling property. Functional groups include COOM, SO ₃ M, OSO ₃ M, P═O (OM) 3, O—P═O (OM) ₂ (M is a hydrogen atom, an alkali metal salt or an amine salt), OH, NR 1 R 2, NR3R4R5 (R1, R2, R3, R4, and R5 are hydrogen or a hydrocarbon group, usually having 1 to 10 carbon atoms), an epoxy group, and the like. When two or more resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

  In addition to these binders, it is desirable to use a thermosetting crosslinking agent that is bonded to a functional group contained in the binder and crosslinked. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferably used.

<Lubricant>
In the magnetic tape, a conventionally known lubricant can be added to the magnetic layer and the lower layer, and the addition amount may be a known amount. For example, it is preferable to contain a higher fatty acid having 10 or more carbon atoms such as myristic acid, stearic acid, and palmitic acid in the lower layer and an ester of higher fatty acid such as butyl stearate because the friction coefficient with the head becomes small. In addition, it is preferable that the magnetic layer contains a fatty acid amide that is an amide such as palmitic acid or stearic acid and an ester of a higher fatty acid because the friction coefficient during running of the tape is reduced.

<Dispersant>
The nonmagnetic powder, carbon black, and magnetic powder contained in the lower layer and the magnetic layer can be surface-treated with an appropriate dispersant in order to improve the dispersibility of the binder (binder resin). Moreover, you may add an appropriate dispersing agent in the coating material for forming the lower layer and magnetic layer containing said each powder. As the dispersant, a phosphoric acid-based dispersant, a carboxylic acid-based dispersant, an amine-based dispersant, a chelating agent, various silane coupling agents and the like are preferably used. These dispersants are preferably blended after the kneading pretreatment step, the kneading step and the initial dispersion step. Examples of the phosphoric acid dispersant include alkyl phosphates such as monomethyl phosphate, dimethyl phosphate, monoethyl phosphate, and diethyl phosphate, and aromatic phosphates such as phenylphosphonic acid and monooctylphenylphosphonic acid. . Moreover, as a carboxylic acid type | system | group dispersing agent, a C12-C18 fatty acid, specifically, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid Linoleic acid, linolenic acid, stearic acid and the like are used. Also, a metal soap composed of an alkali metal or an alkaline earth metal of the fatty acid, an amide of the fatty acid, an ester of the fatty acid or a compound containing fluorine in the fatty acid, a polyalkylene oxide alkyl phosphate ester, lecithin, a trialkyl polyolefinoxy Quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, sulfonate, phosphate, copper phthalocyanine, benzoic acid, phthalic acid, tetracarboxyl naphthalene, dicarboxyl naphthalene And fatty acids having 12 to 22 carbon atoms. Examples of the amine dispersant include aliphatic amines having 8 to 22 carbon atoms, aromatic amines, alkanolamines, and alkoxyalkylamines. Further, examples of chelating agents include 1,10-phenanthroline, EDTA, dimethylglyoxime, acetylacetone, glycine, dithiazone, nitrilotriacetic acid and the like. These may be used alone or in combination.

  In any layer, the dispersant is preferably added in an amount of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder.

<Back layer>
The back layer is not an essential component, but the other surface (the surface opposite to the surface on which the magnetic layer is formed) of the nonmagnetic support constituting the magnetic tape of the present invention has a running property. It is desirable to form a back layer for the purpose of improvement.

  As the back coat layer, a back coat layer made of carbon black and a binder resin is generally used. The thickness of such a back coat layer is preferably 0.2 to 0.8 μm. Moreover, as surface roughness Ra, 3-10 nm is preferable and 4-8 nm is more preferable.

  As the carbon black to be included in the back coat layer, a conventionally known small particle size carbon black such as acetylene black, furnace black and thermal black and a small amount of large particle size carbon black are used. The number average particle size of the small particle size carbon black is 5 to 100 nm, and the number average particle size of the large particle size carbon black is 200 to 400 nm.

  As the binder resin for the backcoat layer, it is preferable to use a cellulose resin and a polyurethane resin. Moreover, in order to harden binder resin, it is preferable to use crosslinking agents, such as a polyisocyanate compound.

  In addition, for the purpose of improving the strength, the backcoat layer may have a number average particle diameter of 50 to 200 nm, rare earth elements such as aluminum oxide and cerium, and oxides of elements such as zirconium, silicon, titanium, manganese, and iron. Alternatively, composite oxide plate-like particles can be added.

<Adjustment of lower layer and back coat paint>
In preparing the lower layer coating material and the back coat coating material, conventionally known coating production apparatuses and methods can be employed, and it is particularly preferable to use a kneading step using a kneader or the like and a primary dispersion step in combination. In the primary dispersion step, it is desirable to use a sand mill because the surface properties can be controlled as well as improving the dispersibility of the filler, carbon black and the like.

  Moreover, when applying a lower layer coating material or a back coating material on a nonmagnetic support, conventionally known coating methods such as gravure coating, roll coating, blade coating, and extrusion coating are used.

  The coating method of the lower layer coating and the magnetic coating is performed by applying the lower layer coating on the non-magnetic support and drying, and then applying the magnetic coating, the sequential multilayer coating method, or simultaneously applying the lower layer coating and the magnetic coating. Any of the simultaneous multilayer coating methods (wet-on-wet) may be employed.

<Organic solvent>
Examples of the organic solvent used in the magnetic coating for coating magnetic tape, the lower layer coating, the back coating layer coating for the thin film type and coating type magnetic tape include, for example, ketone solvents such as methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran, Examples include ether solvents such as dioxane, and acetate solvents such as ethyl acetate and butyl acetate. These organic solvents can be used alone or as a mixture, and can also be used as a mixture with toluene.

  Next, examples of the present invention will be described and described more specifically, but before that, methods for measuring characteristic values obtained in the examples and comparative examples will be described in advance.

[Surface roughness of magnetic tape]
Using a New View 5000 manufactured by ZYGO, using a scanning white light interferometry method with a 50 × objective lens, the zoom setting was set to 100 × (measurement field of view 72 μm × 54 μm), and the center line average roughness Ra was determined. .

[Electromagnetic conversion characteristics of magnetic tape]
A drum tester was used for measuring the electromagnetic conversion characteristics of the tape. The output and noise of the data signal is as follows. The drum tester is equipped with an electromagnetic induction head (track width 25 μm, gap 0.2 μm) and MR head (track width 5.5 μm, shield interval 0.17 μm). Recording and reproduction with an MR head were performed. A rectangular wave was input to a recording current / current generator by a function generator and written, and the output of the MR head was amplified by a preamplifier and then read into a spectrum analyzer manufactured by ShibaSoku. The carrier value of 0.4 μm was set as the medium output C. Further, when a rectangular wave of 0.4 μm was written, an integral value obtained by subtracting the output and system noise from the spectral component corresponding to the recording wavelength of 0.4 μm or more was used as the noise value N. Furthermore, the ratio between the two was taken as C / N, and C / N was determined relative to the value of the tape of Comparative Example 1 as a reference.

  Specific examples will be described below. However, the present invention is not limited only to the following examples. In the following examples and comparative examples, “parts” means “parts by weight”.

  In the present invention, magnetite, which is an iron oxide, and goethite, which is an iron hydroxide, are used as the starting metal oxide of the iron nitride magnetic powder. The amount of Si and Y elements applied to the raw material particles is constant, the iron nitrides A1 to E2 are prepared by changing only the conditions, and then the iron nitride magnetic powder prepared is used. A magnetic sheet was prepared using this. Six kinds of metal oxides having different average particle diameters shown in the column of raw materials were used as raw materials. All six types are substantially granular with an axial ratio of 1.15.

<Example 1>
A) Preparation of iron nitride-based magnetic powder 5 parts of A (magnetite with an average particle diameter of 8 nm) in Table 1 and 3 parts of sodium silicate are added to 100 parts of water as raw materials, and an ultrasonic disperser is used. An aqueous dispersion (hereinafter, a system in which raw materials are dispersed in an aqueous sodium silicate solution is referred to as an aqueous dispersion) (A) was prepared. Separately, 100 parts of 1N nitric acid solution (b) was prepared.

  0.1 liter of water dispersion (I) was put into a mill for a pebble mill disperser having an internal volume of 0.2 liter. Using zirconia beads having an average bead diameter of 100 μm as a medium, the mixture was dispersed for 120 minutes. Thereafter, the content was filtered through a 0.15 mm filter to take out an aqueous dispersion (A) that was dispersed. Next, the aqueous solution (B) was added dropwise to the aqueous dispersion (I) until the pH reached 7.0, and silicon was deposited on the magnetite.

  This aqueous solution was washed with water until the filtrate had a conductivity of 80 μS, filtered, and dried at 90 ° C. to obtain a magnetite powder having silicon deposited on the surface of the magnetite particles.

  The powder having silicon hydroxide deposited on the surface of magnetite particles was heated to 200 ° C. at a rate of 20 ° C./min in a nitrogen stream and heat-treated at 200 ° C. for 1 hour in a nitrogen gas stream. Next, the temperature was raised to 400 ° C. at a rate of 20 ° C./minS in a nitrogen stream, and when the temperature became uniform at 400 ° C., the gas was switched to hydrogen gas, and heat reduction was performed at 400 ° C. for 10 hours in the hydrogen gas stream. An iron nitride magnetic powder was obtained. The completion of the hydrogen reduction was confirmed by the fact that the water vapor concentration in the outlet hydrogen was 100 ppm or less.

  Next, the temperature was lowered to 120 ° C. in about 2 hours with hydrogen gas flowing. In a state where the temperature reached 120 ° C., the gas was switched to ammonia gas, and nitriding was performed for 30 hours while maintaining the temperature at 120 ° C. Thereafter, the ammonia gas was switched to nitrogen gas, and the temperature was lowered from 120 ° C to 100 ° C. After reaching 100 ° C., switch to a mixed gas of oxygen and nitrogen containing 200 ppm of oxygen, and after performing an oxidation treatment for 2 hours, switch to a mixed gas of oxygen and nitrogen containing 1000 ppm of oxygen, and further 4 hours After the oxidation treatment, the iron nitride magnetic powder A1 for magnetic tape coated with yttrium and silicon was obtained by cooling to room temperature. It was transferred to a container as it was and used for magnetic tape production. A sample for measuring magnetic properties and the like was taken out into the air when the oxygen concentration was gradually increased and finally reached 20% while confirming that there was no temperature rise.

The thus obtained iron nitride magnetic powder A1 had a silicon content of 27.0 atomic% with respect to Fe, as measured by fluorescent X-ray analysis and X-ray photoelectron spectroscopy. . Further, from the X-ray diffraction pattern _to obtain a profile indicating a _Fe 16 _{N 2} phase. Further, when the particle shape was observed with a high-resolution analytical transmission electron microscope (TEM), it was a substantially spherical particle, the average particle diameter was 8 nm, the standard deviation σ was 1.8 nm, and the saturation magnetization was 62 Am ² / kg (62 emu). / G), the coercive force was 195.1 kA / m (2,440 oersted).

B) Production of magnetic tape Next, a magnetic tape was produced using the produced iron nitride magnetic powder. First, the paint component and the composition, but the lower layer paint and the back coat paint are exactly the same in the component and composition, in the examples and comparative examples. The magnetic layer paint has the same components and compositions except for the different iron nitride magnetic powders. Each paint component and composition are as follows. These paints were applied to produce a magnetic tape.

<Lower paint component>
(1) Component Nonmagnetic acicular iron oxide powder (average particle diameter: 100 nm, axial ratio: 5) 68 parts Granular alumina powder (average particle diameter: 80 nm) 8 parts Carbon black (average particle diameter: 25 nm) 24 parts Stearic acid 2.0 parts of vinyl chloride - hydroxypropyl acrylate copolymer 8.8 parts (containing _-SO 3 Na group: 1 × ^{10 -4} eq / g)
Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained —SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
Cyclohexanone 25 parts Methyl ethyl ketone 40 parts Toluene 10 parts (2) Component Butyl stearate 1 part Cyclohexanone 70 parts Methyl ethyl ketone 50 parts Toluene 20 parts (3) Component Polyisocyanate 1.4 parts Cyclohexanone 10 parts Methyl ethyl ketone 15 parts Toluene 10 parts

  In the above undercoat component, (1) was kneaded with a batch kneader, (2) was added and stirred, then dispersion treatment was performed with a sand mill with a residence time of 60 minutes, and (3) was added to this and stirred and filtered. Thereafter, an undercoat paint (undercoat paint) was obtained.

<Backcoat layer paint component>
Carbon black (average particle diameter: 25 nm) 80 parts Carbon black (average particle diameter: 350 nm) 10 parts Granular iron oxide powder (average particle diameter: 50 nm) 10 parts Nitrocellulose 45 parts Polyurethane resin (containing SO ₃ Na group) 30 parts Cyclohexanone 260 parts Toluene 260 parts Methyl ethyl ketone 525 parts

<Magnetic paint component>
(1) Components of kneading process Iron nitride magnetic powder (magnetic powder A1) 100 parts Particle size: 8 nm
13 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin 4.5 parts (containing _-SO 3 Na group: 1.0 × ^{10 -4} eq / g)
Methyl acid phosphate 2 parts Tetrahydrofuran 20 parts Methyl ethyl ketone / cyclohexanone (1: 1 by weight) 9 parts (2) Diluting step components Palmitic acid amide 1.5 parts N-butyl stearate 1 part Methyl ethyl ketone / cyclohexanone (1: 1 by weight) 350 parts (3) Separate slurry component Granular alumina powder (average particle size: 80 nm) 10 parts Vinyl chloride-hydroxypropyl acrylate copolymer 1 part Methyl ethyl ketone / cyclohexanone (1: 1 by weight) 15 parts (4) Blending process components Polyisocyanate 1.5 parts Methyl ethyl ketone / cyclohexanone (1: 1 by weight) 29 parts

  Among the magnetic coating components described above, in the kneading step component of (1), the total amount of the magnetic powder and a predetermined amount of resin and solvent are previously stirred and mixed at high speed, and the mixed powder becomes the kneading step component of (1). Kneaded in a continuous biaxial kneader, and further added with the dilution process component (2), diluted in at least two stages with a continuous biaxial kneader, and used as a dispersion medium in a sand mill. Using zirconia beads having a diameter of 0.5 mm, the residence time was dispersed for 45 minutes. To this was added a dispersion slurry component (3) dispersed in a sand mill with a residence time of 40 minutes, and then a blending step component (4) was added, stirred and filtered to obtain a magnetic paint.

  On the nonmagnetic support (base film) composed of a polyethylene naphthalate support (thickness 6.1 μm, MD = 8 GPa, MD / TD = 1.1, trade name: PEN, manufactured by Teijin Limited) Is applied so that the thickness after drying and calendering is 1.0 μm, and the magnetic coating is further coated on the lower layer with the thickness of the magnetic layer after magnetic field orientation treatment, drying and calendering treatment being 80 nm. As described above, the coating was applied wet-on-wet, and after magnetic field orientation treatment, it was dried using a dryer to prepare a magnetic sheet.

  In the magnetic field orientation treatment, an NN counter magnet (5 kG) is installed in front of the dryer, and two NN counter magnets (5 kG) are spaced from each other at a distance of 50 cm from the front side 75 cm of the dry coating position of the coating in the dryer. Installed and went. The coating speed was 100 m / min.

  After dispersing the coating component for the backcoat layer with a sand mill with a residence time of 45 minutes, 15 parts of polyisocyanate was added and filtered to prepare a coating material for the backcoat layer. This paint was applied to the opposite surface of the magnetic layer of the magnetic sheet produced by the above method so that the thickness after drying and calendering was 0.5 μm and dried.

  Thereafter, this magnetic sheet was mirror-finished with a seven-stage calendar made of a metal roll under the conditions of a temperature of 100 ° C. and a linear pressure of 200 kg / cm, and the magnetic sheet was wound around a core and then aged at 70 ° C. for 72 hours. After that, it was cut into 1/2 inch width.

  A magnetic servo signal was recorded on the magnetic tape thus obtained with a servo writer to produce a magnetic tape for computers.

<Example 2>
The same procedure as in Example 1 was performed except that the raw material B in Table 1 having a particle diameter of 15 nm was changed to a starting raw material to obtain an iron nitride magnetic powder.
The obtained iron nitride magnetic powder B1 had an average particle size of 14 nm, a standard deviation σ of 3.6 nm, and silicon was 29.0 atomic% with respect to Fe. The saturation magnetization was 80 Am ² / kg (80 emu / g), and the coercive force was 220.2 kA / m (2,752 Oersted).

<Example 3>
Except that the magnetite with a particle diameter of 15 nm of the raw material B in Table 1 was changed to the starting raw material, and the beads used for the mill disperser for the deposition treatment were changed to titania beads with an average diameter of 100 μm to obtain an iron nitride magnetic powder. Was the same as in Example 1.
The obtained iron nitride magnetic powder B2 had a particle size of 15 nm, a standard deviation of 3.6 nm, and silicon was 28.5 atomic% with respect to Fe. The saturation magnetization was 82 Am ² / kg (82 emu / g), and the coercive force was 218.1 kA / m (2,726 Oersted).

<Example 4>
The same procedure as in Example 2 was performed except that iron hydroxide having a particle diameter of 15 nm of raw material C in Table 1 was changed to a starting raw material to obtain an iron nitride magnetic powder.
The obtained iron nitride magnetic powder C1 had a particle size of 15 nm, a standard deviation of 3.7 nm, and silicon was 27.5 atomic% with respect to Fe. The saturation magnetization was 92 Am ² / kg (92 emu / g), and the coercive force was 220.1 kA / m (2,751 oersted).

<Example 5>
The same procedure as in Example 1 was conducted except that the magnetite having a particle diameter of 20 nm of the raw material D in Table 1 was changed to a starting raw material to obtain an iron nitride magnetic powder. The obtained iron nitride magnetic powder D1 had a particle size of 18 nm, a standard deviation of 4.5 nm, and silicon was 28.4 atomic% with respect to Fe. The saturation magnetization was 91 Am ² / kg (90 emu / g), and the coercive force was 227.1 kA / m (2,838 Oersted).

<Example 6>
Implemented except that the raw material D in Table 1 was magnetite having a particle diameter of 20 nm as a starting raw material, and the beads used in the mill disperser for the deposition treatment were changed to zirconia beads having an average diameter of 30 μm to obtain an iron nitride magnetic powder. Same as Example 1. The obtained iron nitride magnetic powder D2 had a particle size of 19 nm, a standard deviation of 4.7 nm, and silicon was 28.5 atomic% with respect to Fe. The saturation magnetization was 92 Am ² / kg (92 emu / g), and the coercive force was 222.1 kA / m (2,776 oersteds).

<Example 7>
In addition to changing the magnetite of particle size 30 nm of raw material E in Table 1 to the starting raw material and changing the beads used in the mill disperser for the deposition process to zirconia beads having an average diameter of 50 μm to obtain iron nitride magnetic powder Was the same as in Example 1. The obtained iron nitride magnetic powder E1 had a particle size of 28 nm, a standard deviation of 7.1 nm, and silicon was 27.5 atomic% with respect to Fe. The saturation magnetization was 112 Am ² / kg (112 emu / g), and the coercive force was 237.1 kA / m (2,964 oersted).

<Example 8>
The same procedure as in Example 2 was performed except that the beads used in the milling machine for deposition were changed to zirconia beads having an average diameter of 50 μm to obtain an iron nitride magnetic powder. The obtained iron nitride-based magnetic powder B3 had a particle size of 15 nm, a standard deviation of 3.7 nm, and silicon was 27.4 atomic% with respect to Fe. The saturation magnetization was 80 Am ² / kg (80 emu / g), and the coercive force was 220.1 kA / m (2,751 oersted).

<Example 9>
The same procedure as in Example 2 was performed except that the beads used in the milling machine for deposition were changed to zirconia beads having an average diameter of 500 μm to obtain an iron nitride magnetic powder. The obtained iron nitride magnetic powder B4 had a particle size of 14 nm, a standard deviation of 3.4 nm, and silicon was 28.4 atomic% with respect to Fe. The saturation magnetization was 80 Am ² / kg (80 emu / g), and the coercive force was 220.0 kA / m (2,750 oersted).

<Example 10>
The same procedure as in Example 2 was performed except that the beads used in the milling machine for deposition were changed to zirconia beads having an average diameter of 30 μm to obtain an iron nitride magnetic powder. The obtained iron nitride magnetic powder B5 had a particle size of 14 nm, a standard deviation of 3.5 nm, and silicon was 28.3 atomic% with respect to Fe. The saturation magnetization was 81 Am ² / kg (81 emu / g), and the coercive force was 219.5 kA / m (2,744 Oersted).

<Example 11>
The magnetite with a particle size of 15 nm of the raw material B in Table 1 is changed to a starting raw material, 3 parts of sodium silicate is changed to 2 parts of yttrium nitrate, and the aqueous solution (b) is changed to 100 parts of 1 normal sodium hydroxide solution. Then, the same procedure as in Example 1 was performed except that the iron nitride magnetic powder was obtained. The obtained iron nitride magnetic powder B6 had a particle size of 14 nm, a standard deviation of 3.8 nm, and yttrium was 8.0 atomic% with respect to Fe. The saturation magnetization was 83 Am ² / kg (83 emu / g), and the coercive force was 223.4 kA / m (2806 Oersted).

<Example 12>
Example 11 was repeated except that 2 parts of yttrium nitrate was changed to 8.5 parts of aluminum nitrate to obtain an iron nitride magnetic powder. The obtained iron nitride magnetic powder B7 had a particle size of 14 nm, a standard deviation of 3.6 nm, and aluminum was 31.5 atomic% with respect to Fe. The saturation magnetization was 79 Am ² / kg (79 emu / g), and the coercive force was 218.5 kA / m (2744 Oersted).

  In the experiment in which iron nitride magnetic powder was obtained using the raw material F in Table 1 having a particle size of 5 nm as the starting material, as described above, the final yield was extremely poor, and the amount of iron nitride to be used for the measurement. System magnetic powder could not be obtained. Therefore, a magnetic sheet could not be produced.

<Comparative Example 1>
The same procedure as in Example 2 was performed except that the deposition process was performed using a stirrer without using a mill disperser to obtain an iron nitride magnetic powder. The obtained iron nitride magnetic powder B8 had a particle size of 15 nm, a standard deviation of 5.0 nm, and silicon was 26.0 atomic% with respect to Fe. The saturation magnetization was 82 Am ² / kg (82 emu / g), and the coercive force was 207.1 kA / m (2,589 Oersted).

<Comparative example 2>
The same procedure as in Example 1 was performed except that the deposition process was performed using a stirrer without using a mill disperser to obtain an iron nitride magnetic powder. The obtained iron nitride magnetic powder A2 had a particle diameter of 9 nm, a standard deviation of 3.0 nm, and silicon was 27.5 atomic% with respect to Fe. The saturation magnetization was 61 Am ² / kg (61 emu / g), and the coercive force was 190.1 kA / m (2,376 Oersted).

<Comparative Example 3>
The same procedure as in Example 1 was carried out except that the beads used in the deposition mill disperser were changed to zirconia beads having an average diameter of 600 μm (Φm / Φp is smaller than the lower limit) to obtain an iron nitride magnetic powder. The obtained iron nitride magnetic powder A3 had a particle size of 9 nm, a standard deviation of 2.7 nm, and silicon was 27.0 atomic% with respect to Fe. The saturation magnetization was 62 Am ² / kg (62 emu / g), and the coercive force was 191.2 kA / m (2,390 oersted).

<Comparative Example 4>
The same procedure as in Example 2 was performed except that the beads used in the milling machine for deposition were changed to zirconia beads having an average diameter of 1000 μm (Φp / Φm is smaller than the lower limit) to obtain an iron nitride magnetic powder. The obtained iron nitride magnetic powder B9 had a particle size of 15 nm, a standard deviation of 4.7 nm, and silicon was 27.3 atomic% with respect to Fe. The saturation magnetization was 82 Am ² / kg (82 emu / g), and the coercive force was 218.5 kA / m (2,731 oersted).

<Comparative Example 5>
Example 1 except that magnetite having a particle diameter of 30 nm of raw material E in Table 1 is used as a starting raw material, and beads used in a mill disperser for deposition treatment are changed to zirconia beads having an average diameter of 30 μm to obtain an iron nitride magnetic powder. Same as 1. The obtained iron nitride magnetic powder E2 had a particle size of 29 nm, a standard deviation of 11.0 nm, and silicon was 27.3 atomic% with respect to Fe. The saturation magnetization was 112 Am ² / kg (112 emu / g), and the coercive force was 230.0 kA / m (2,875 Oersted).

  Table 2 shows the relationship between the raw material deposition process of the five types of metal oxides A to E having different average particle diameters shown in Table 1 and the created iron nitride, and the iron nitride magnetic powder using them. The average particle diameter of the beads used in the media-type disperser used in the deposition process of the specific element at the time of manufacture and the ratio of the average particle diameter of the raw material particles to the bead diameter are shown. Iron nitrides A1 to E2 were prepared by changing the conditions in the process of depositing the specific elements on these raw material particles.

Table 3 shows the characteristics of the iron nitride-based magnetic powders produced in Examples 1 to 10 and Comparative Examples 1 to 5, and the surface smoothness Ra and the drum, which are indicators of the dispersibility of the magnetic tape produced using the powder. The C / N measured with a tester is shown.

  As is clear from Tables 2 and 3, beads using a media-type disperser in the deposition process shown in the Examples, and the ratio of the average particle diameter of the raw material particles to the bead diameter is within the scope of the present invention. It can be seen that the standard deviation, which is a measure of the uniformity of the particle distribution, of the iron nitride-based magnetic powder produced by using the above-mentioned is close to that of the raw material particles. On the other hand, the iron nitride magnetic powder produced by performing the deposition process with a stirrer as in the prior art as in Comparative Example 1 and Comparative Example 2 has a standard deviation greater than that of the raw material compared to Examples 1 and 2. I understand that. This is presumed that the dispersion of the metal oxide at the time of deposition was not sufficient, and therefore the specific element having a sintering preventing function was not evenly deposited, so that sintering occurred in the reduction process and the particle distribution was widened. .

  Looking at Comparative Examples 3 to 5, although the increase in the standard deviation of the average particle diameter of the iron nitride magnetic powder produced in Comparative Examples 1 and 2 is not large, the average particle diameter of the raw material particles Since the ratio with the bead diameter is out of the scope of the present invention, the increase is large in all cases compared to Examples where the raw materials used are the same.

  In Example 7, since the average particle size of the starting raw material is out of the scope of the present invention, the change in the standard deviation of the average particle size of the manufactured iron nitride magnetic powder from that of the raw material particles is effective. Compared to the example, it is slightly increased. However, it can be seen that the deviation of the average particle diameter of the obtained iron nitride-based magnetic powder is small as compared with Comparative Example 5 using a bead diameter outside the scope of the present invention.

  As is apparent from Table 3, the magnetic tape using the iron nitride magnetic powder produced by the method according to the present invention has a narrow particle size distribution of the iron nitride magnetic powder and is excellent in dispersibility because the particle diameter is uniform. It can be seen that good C / N can be obtained with a small noise level.

Claims (5)

  Metal oxide particles or metal hydroxides in which an aqueous solution containing a water-soluble compound of a specific element and an aqueous dispersion containing metal oxide particles or metal hydroxide particles are deposited using a media-type disperser A method for producing an iron nitride-based magnetic powder comprising a step of producing particles.   The metal oxide particles or metal hydroxide particles are substantially in the form of particles, the average particle diameter is Φp, and the media diameter of the media-type disperser is Φm, Φm / Φp is 1500 to 35000 (from 1.5 k below) The method for producing an iron nitride-based magnetic powder according to claim 1, wherein the method is described as 35 k).   The method for producing an iron nitride magnetic powder according to claim 1 or 2, wherein the specific element is at least one element selected from yttrium (Y), silicon (Si), and aluminum (Al).   4. The method for producing an iron nitride-based magnetic powder according to claim 1, wherein the metal oxide or metal hydroxide particles have an average particle diameter of 5 nm to 20 nm.   An iron nitride-based magnetic powder produced by the production method according to claim 1.