JP2009141031A - Iron nitride-based magnetic powder, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide iron nitride-base magnetic powder, usable for backup magnetic tape for high-capacity computers suitable for high recording density. <P>SOLUTION: The method is for manufacturing the iron nitride-based magnetic powder, having an average grain size of 8-20 nm, having a core phase containing a crystal phase, mainly consisting of Fe<SB>16</SB>N<SB>2</SB>, and an outer layer including at least one element selected from among rare earths, Al and Si. It includes a coating process using iron-based oxide or iron-based hydroxide for a start material, for coating an outside layer on the start material. The coating process includes a process of blowing iron-based aqueous solution containing the iron-based oxide or the iron-based hydroxide and solution including a salt of at least one element selected from among the rare earths, Al and Si from separate blow ports for reaction by use of a collision dispersion device 5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an iron nitride-based magnetic powder suitable for use in a magnetic layer of a high recording density medium and a method for producing the same. More specifically, an iron nitride magnetic powder having a uniform thickness on the outer layer of the iron nitride magnetic powder is obtained.

  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. At present, a tape cartridge having a recording capacity of 100 GB or more per roll is 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 in the magnetic layer to cope with short wavelength recording has become more coherent and finer every year, and now the particle major axis length is 0.1 μm or less. Since the needle-shaped ferromagnetic metal powder and the coercive force depend on the crystal anisotropy regardless of the shape anisotropy, it is easy to make fine particles and the coercive force is 200 kA with an average particle diameter of 50 nm or less. An iron nitride-based magnetic powder having an essentially spherical or elliptical Fe ₁₆ N ₂ phase as a main phase is disclosed (Patent Documents 1 to 3).

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 2 and 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, a signal reproduction C / N The volume of the magnetic powder for reducing the noise 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. According} to the calculation by simulation, it is predicted that the particle diameter of 18 nm or less is necessary when the substantially granular iron nitride magnetic powder is used. . 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 is known in the art, a method for producing a substantially granular iron nitride magnetic powder comprises dispersing iron oxide or iron hydroxide as a starting material in an alkaline aqueous solution. A metal salt aqueous solution containing at least one element selected from Al and Si is added to deposit at least one element selected from rare earth and Al and Si on the surface of the iron oxide or iron hydroxide particles. Let 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. In these processes, sintering occurs in the reduction process, and in the deposition process that is the previous process, at least one element selected from rare earth and Al, Si having a sintering preventing function starts uniformly. The point is whether it is attached to the material particles. When the reduction is performed, the particle surface that is the starting material is more uniformly coated, and the smaller the variation in the thickness, the less the sintering occurs in the reduction process.

  If sintering occurs, the coercive force distribution of the iron nitride-based magnetic powder obtained after nitriding becomes wide, and the original excellent magnetic properties represented by the inability to obtain a high coercive force are not sufficiently exhibited. Dispersibility of the magnetic powder is inhibited at the time of particle size distribution and magnetic coating preparation. 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 this purpose, the surface of the particles used as the material of the iron nitride magnetic powder is coated with a uniform thickness. The outer layer referred to here is formed in a form coated with a core phase of iron nitride magnetic powder formed to prevent sintering in the deposition process and to give corrosion resistance to the produced iron nitride magnetic powder. It is an outer layer containing at least one element selected from conventionally known rare earth elements and Al and Si.

In order to solve such problems, various studies have been conducted on production including a reduction step 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 the aqueous solution such as goethite as a raw material in the deposition process and the degree of deposition of the anti-caking agent (uniformity). However, there is no disclosure of a specific technique or apparatus for dispersibility of raw materials and anti-caking agents in the process, and the minimum particle size of the produced iron nitride magnetic powder is not disclosed. It is 19 nm, and it is difficult to say that the target is still fine particle powder.

  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 uniformity of the outer layer having a function to prevent it, and no specific method or apparatus for dispersibility of raw materials or anti-caking agents is disclosed as in Patent Document 4. Moreover, nothing is mentioned about the thickness of the outer layer of the produced iron nitride magnetic powder.

  In Patent Document 7, from the viewpoint of the saturation magnetization amount and storage stability of the iron nitride-based magnetic powder, the average thickness of the outer layer is preferably 1 to 5 nm. However, no mention is made of the variation in the thickness of the outer layer of the iron nitride magnetic powder and its influence.

Japanese Patent No. 3848486 International Publication WO03 / 079332A1 JP 2005-310857 A Japanese Patent Laid-Open No. 2006-41210 JP 2006-303321 A JP 2005-183932 A Japanese Patent Laying-Open No. 2005-093570

The present invention solves the above-mentioned problems, and disperses these fine particle powders well in the process of depositing the anti-coagulant on the iron-based oxide or iron-based hydroxide used as a raw material, and uniformly burns it. A high-capacity computer backup magnetic tape suitable for high recording density (0.5 Gb / in ² or higher), which prevents the sintering of particles in the subsequent reduction step after forming an outer layer mainly composed of an anti-caking agent. The purpose is to obtain an iron nitride magnetic powder used in the above.

  In the production of substantially granular fine particles based on magnetocrystalline anisotropy and high coercivity iron nitride magnetic powder, which is a magnetic powder used for magnetic tape, the present inventors become a raw material in the process of applying an anti-caking agent. As a result of intensive studies on a method for forming an outer layer mainly composed of a sintering inhibitor that uniformly coats the powder, the present invention has been achieved.

That is, the iron nitride magnetic powder having an average particle size of 8 to 20 nm, in which the core phase of the magnetic powder includes a crystal phase mainly composed of Fe ₁₆ N ₂ and the outer layer includes at least one element selected from rare earth and Al, Si. In which the starting material is an iron-based oxide or an iron-based hydroxide, and an outer layer is deposited on the starting material, the depositing step comprising the iron-based oxide or the iron-based hydroxide Iron-based magnetism including a process in which an aqueous iron-based solution containing iron and an aqueous solution containing a salt of at least one element selected from rare earths and Al, Si are ejected from individual jets and reacted using a collision-type disperser A method for producing a powder.

The collision type disperser mentioned here is basically a disperser having the function of dispersion / mixing reaction of the concept disclosed in Japanese Patent Application Laid-Open Nos. 2003-315946 and 2004-296067. The principle is an apparatus that allows different fluids to be ejected from different nozzles at a constant flow rate and allows different substances contained in the respective fluids to be mixed and reacted in a well dispersed state. Japanese Patent Laid-Open No. 2003-315946 discloses a method for producing silver halide emulsifier particles having excellent monodispersibility, and Japanese Patent Laid-Open No. 2004-296067 discloses a method for producing alloy particles capable of forming a CuAu type or Cu ₃ Au type. Since there is no description or suggestion regarding the composite material having a core-shell structure in the present invention and the deposition technique that is the point of formation, the effect and purpose are greatly different.

  The inventors of the present invention have an iron nitride magnetic powder that influences the magnetic characteristics of the magnetic powder and thus has a large influence on the electromagnetic conversion characteristics of the magnetic recording medium. This is the first time that a powerful technique for uniform formation has been obtained.

  By the method of the present invention, an iron nitride-based magnetic powder having a variation rate represented by the formula (1) of the thickness of the outer layer containing at least one element selected from rare earth, Al, and Si is 60% or less is obtained.

According to the present invention, when the iron-based oxide or the iron-based hydroxide is deposited with at least one element selected from rare earths, Al, and Si, a collision type disperser is used, so that the iron-based oxidation is performed. It is possible to disperse the product or iron-based hydroxide in water very well, and to uniformly deposit these elements from an aqueous solution containing at least one element selected from Al and Si. As a result, an iron nitride-based magnetic powder that is prevented from being sintered in the reduction process, which is a subsequent 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.

In the present invention, a magnetic powder containing a crystal phase mainly composed of Fe ₁₆ N ₂ and having an outer layer containing at least one element selected from rare earth and Al, Si and having an average particle diameter of 8 to 20 nm is preferable. The content of nitrogen in the magnetic powder with respect to iron is more preferably 1.0 to 20.0 atomic%. The particle size of the magnetic powder of the present invention was determined from the 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). The average particle diameter of at least 100 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 size is 20 nm or less is that when it exceeds 20 nm, the noise (N) of the magnetic tape increases and the reproduction output noise ratio (C / N) decreases. In addition, when the particle size is 8 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 noise. However, when the particle size is finer than 8 nm, the thickness of the outer layer is reduced. 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 8 nm or more because it is difficult to produce. In our experiments, the limit of about 8 nm is considered.

In the present invention, the core phase in the iron nitride-based magnetic powder is mainly Fe ₁₆ N ₂ , but the core phase may contain Fe ₈ N.

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%. When the total content of these elements is too small, not only the magnetic anisotropy of the magnetic powder is reduced, but also the sintering preventing effect is lowered, so that coarse particles of 30 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, 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, Si, and AL, the effect is inferior to rare earth elements, Si, and Al, but B, P, Ti, Zr, and C also have a sintering preventing effect. Ti, Zr, and C may be used.

  In the present invention, the amount of rare earth elements, Al, and Si contained in the magnetic powder with respect to iron is analyzed according to a conventional method using fluorescent X-ray analysis (analysis field of view: diameter 10 mm), and the amount of nitrogen with respect to iron is determined with X-rays. The photoelectron spectroscopic analysis was performed according to a conventional method (analysis field: 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 relative to iron at a constant etching time was 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 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. What is necessary is just to select so that it may become the preferable characteristic of the above-mentioned magnetic layer so that it may adapt to hardware, such as a system and a drive. Br · δ will be described later.

  Next, the method for producing the magnetic powder of the present invention will be described.

As starting materials, iron-based oxides, acid hydroxides or hydroxides are 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 less than 2.

  A magnetite, which is a starting material, is coated with a rare earth element, Si, Al, or a compound containing elements such as Ti, Zr, C, P, and B as required. A layer formed by depositing a compound is called an outer layer. When depositing a rare earth element, a starting material is usually dispersed in an alkali or acid aqueous solution, a salt of the rare earth element is dissolved therein, and a hydroxide containing a rare earth element in the raw material powder by a neutralization reaction or the like. A hydrate may be deposited and precipitated. 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, in order to obtain an iron nitride-based magnetic powder having a uniform thickness of the outer layer and a variation rate of the thickness of 60% or less, (1) an aqueous solution of raw materials (2) deposition It is important to disperse together the aqueous solution in which the salt of the anti-caking agent to be dissolved is well dispersed so that a neutralization reaction is sufficiently caused to deposit the hydroxide or hydrate containing rare earth elements on the raw material powder. .

As described in the prior art, in the conventional literature, there is only a disclosure of adding (2) to (1) although there is a description of the temperature and gas atmosphere in this deposition process. As inferred from the literature, both (1) and (2) are basically carried out by stirring for dispersion of the aqueous solution, and the element containing the aqueous solution of (2) is added to the aqueous solution of (1) in the container being dispersed by stirring. It is presumed that the addition is made quantitatively and over a certain period of time so as to be a predetermined amount for the design. Is the uniform outer layer obtained by the dispersibility of (1) and (2) in the same place (the moment of reaction in which the deposition occurs and the physical space) where (2) is deposited on (1) at this time? How it depends.
In the present invention, dispersion by stirring is insufficient, and investigations have been made to further improve dispersibility. As a result, the steps of mixing and dispersing the aqueous solutions (1) and (2) with a stirrer, which is a conventional general method, are performed. After that, both aqueous solutions are sufficiently dispersed and neutralized by colliding the aqueous solutions (1) and (2) at a predetermined speed from separate nozzles facing each other at a predetermined interval. Found to do. Suitable for dispersion of fine particle powders, and it is possible to obtain an iron nitride magnetic powder having a uniform outer layer by adopting a collision type disperser in which impurities are not mixed in the aqueous solution of (1) and (2) It is.

  FIG. 1 is a schematic view conceptually showing a production line in which only a step of depositing a hydroxide or hydrate containing a rare earth element on a raw material powder in a production process of an iron nitride magnetic powder in the present invention is taken. FIG.

  The step of depositing a hydroxide or hydrate containing a rare earth element on the raw material powder is performed in the first mixing vessel 1 equipped with a stirrer with the aqueous solution 6 of the raw material adjusted to weak alkalinity and the second equipped with the stirrer. A step of separately sending the aqueous solution 7 of the hydroxide or hydrate containing rare earth elements in the mixing vessel 2 to the collision type disperser 5 by the first pump 3 and the second pump 4 capable of pressurization, and the collision type It consists of a step of causing both to collide in the disperser 5 to cause a neutralization reaction and deposition. The solution 8 containing the powder after the deposition treatment is sent to the next water washing step.

  FIG. 2 is an example of a schematic configuration diagram of the impingement type disperser 5 used in the method for producing the iron nitride magnetic powder of the present invention. The collision type disperser 5 of this example includes a first supply nozzle 51 that introduces a solution 7, a second supply nozzle 52 that introduces a solution 6, a mixing chamber 54 that mixes and processes two liquids, and two liquids that are mixed and processed It is comprised from the discharge nozzle 53 which discharges.

  A first orifice 61 having a diameter smaller than the nozzle diameter of the first supply nozzle 51 and a second orifice 62 having a diameter smaller than the noise diameter of the second supply nozzle 52 are provided at the outlets of the first supply nozzles 51 and 52 on the mixing chamber 4 side. Each is arranged to eject the solution from a small gap.

  The discharge nozzle 53 may be provided with a third orifice 63 having a diameter smaller than the diameter of the discharge nozzle 53 at the entrance from the mixing chamber 54, or may not have a third orifice. From this discharge nozzle 53, a mixed solution of treated solutions (in this application, a solution containing particles that have been subjected to the deposition process) can be discharged.

  The main body structure and usage conditions such as the diameter and flow velocity of the nozzle and orifice of the collision type disperser 5 and the pressure applied to the fluid were determined in consideration of the conventionally known analysis methods and experimental results disclosed in Document 7.

  The raw material slurry after the deposition treatment is sent to a container (not shown) for the next step, filtered by a conventional method, washed with water and dried.

  Next, heat treatment is performed on the magnetite powder coated with the anti-caking agent 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, an oxidation treatment is performed to obtain an iron nitride magnetic powder having an outer layer (surface compound layer) mainly composed of a uniform sintering inhibitor and comprising iron and nitrogen as constituent elements of the present invention. It is done. 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 magnetic powder of the present invention is essentially suitable for obtaining a thin top magnetic layer in terms of saturation magnetization, coercive force, and particle shape.

  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, and the magnetic layer contributing to high-density recording is the same as the upper magnetic layer, which is the uppermost magnetic layer. 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.

  As a subsequent step of the kneading step, using a continuous twin-screw kneader or other diluting device, the step of kneading and diluting by adding a binder resin solution and / or a solvent at least once, a fine media rotating type such as a sand mill It is preferable to disperse the paint by a dispersion process using a 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.

  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 , NR ₃ R ₄ R ₅ (R ₁ , R ₂ , R ₃ , R ₄ , R ₅ 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. Considering the leveling of the thin magnetic layer at the time of application, it is preferable to adopt a simultaneous multi-layer application method in which the magnetic paint is applied while the lower layer paint is wet.

<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, an embodiment of the present invention will be described and described in more detail. Before that, a method of measuring characteristic values obtained in each of the embodiments not described above will be described in advance.

[Magnetic properties of magnetic powder and magnetic tape]
The coercive force Hc, the saturation magnetization σs, and the squareness ratio Br / Bm were measured with a sample vibration type magnetometer (VSM manufactured by Toei Industry Co., Ltd.) with an external magnetic field of 790 KA / m (16 kOe).

[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. For the output of data signals and noise, 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 was performed with a head, and reproduction was performed with an MR head. 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 both C and C / N were determined relative to the value of the tape of Comparative Example 1 as a reference.

[Thickness fluctuation rate of outer layer of iron nitride magnetic powder]
The outer layer is a compound different from the composition and crystal structure inside the particles present on the surface of the particles, and the thickness of the outer layer is a transmission electron micrograph taken at a magnification (1 million times or more) at which these boundaries can be discriminated at least. Calculated from particles. It is preferable to select a particle corresponding to the average particle size as the measurement particle, and the boundary between the outer layer and the inside of the particle is determined by a contrast or lattice image of an electron microscope, a microscopic analysis using a field emission transmission electron microscope (FE-TEM), or the like. It is desirable to discriminate. The average outer layer thickness includes the maximum outer layer thickness and the minimum outer layer thickness. The outer layer thickness is obtained by averaging approximately 10 measurement points, and the difference between the maximum and minimum outer layer thicknesses is divided by the average outer layer thickness. Was determined using the formula 1 as the thickness variation rate. The variation rate is desirably obtained as an average value of three or more particles corresponding to the average particle size.

  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, was used as a starting raw material for the iron nitride magnetic powder. Five kinds of magnetites A to E shown in the column of raw materials in Table 1 were used as raw materials. All five types are substantially granular magnetites having an axial ratio of 1.5 or less.

(A) Preparation of iron nitride magnetic powder 10 parts of raw material A shown in Table 1 was dispersed in 300 parts of water for 30 minutes using an ultrasonic disperser and 5 parts of sodium hydroxide was added to 100 parts of water. An aqueous solution (I) in which an aqueous sodium solution dissolved in the mixture was mixed was prepared.

Separately, 1 part of yttrium nitrate [Y (NO ₃ ) ₃ · 6H ₂ O] and 14.6 parts of aluminum nitrate [Al (NO ₃ ) ₃ · 9H ₂ O] are added to 100 parts of water to dissolve, An aqueous solution (b) dispersed for 30 minutes using a sonic disperser was prepared.
12 liters of the aqueous solution (a) is put into the mixing container 1 shown in FIG. 1 and stirred with a stirrer. 3 liters of the aqueous solution (b) is placed in the mixing vessel 2 and stirred with a stirrer.

  Next, the aqueous solution (b) well stirred and mixed in the mixing vessel 1 is sent to the collision disperser 5 by the flanger pump 3 and the aqueous solution (b) in the mixing vessel 2 is sent to the collision disperser 5 by pressure. At this time, the stirrer is operated.

  The collision disperser 5 and liquid feeding conditions at this time are as follows. In FIG. 2, the diameter R1 of the first orifice 61 was 0.3 mm, and the diameter R2 of the second orifice 62 was 0.6 mm. In addition, the ejection flow rate of the solution 6 was about 230 m / second, the ejection pressure was about 30 Mpa, the ejection flow rate of the solution 7 was 25 m / second, and the ejection pressure was about 0.3 Mpa. An aqueous solution of magnetite particles treated in the collision disperser 5 and having yttrium or aluminum hydroxide deposited on the surface thereof is sent as a solution 8 to the next process vessel. This was washed with water until the conductivity of the filtrate reached 80 μS, filtered, and dried at 90 ° C. to obtain a powder in which hydroxide of yttrium or aluminum was deposited on the surface of magnetite particles.

  The powder obtained by depositing yttrium or aluminum hydroxide on the surface of the magnetite particles was obtained in a nitrogen stream at 20 ° C./min. The temperature was raised to 200 ° C. at a rate of, and heat treatment was performed at 200 ° C. for 1 hour in a nitrogen gas stream. Then, 20 ° C./min. The temperature was raised to 400 ° C. at a rate of 400 ° C., and when the temperature became uniform at 400 ° C., the gas was switched to hydrogen gas and heated and reduced at 400 ° C. for 10 hours in a hydrogen gas stream to obtain an iron nitride magnetic powder . 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 stabilizing for 2 hours, switch to a mixed gas of oxygen and nitrogen containing 1000 ppm of oxygen. After performing the time stabilization treatment, the iron nitride magnetic powder A1 for magnetic tape coated with yttrium and aluminum 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 iron nitride magnetic powder A1 thus obtained was measured for its yttrium and aluminum content by fluorescent X-ray analysis and X-ray photoelectron spectroscopy. And 27.0 atomic%. Further, from the X-ray diffraction pattern _to obtain a profile indicating a _Fe 16 _{N 2} phase. Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope (TEM), the particle shape was almost spherical, the particle diameter was 8 nm, the saturation magnetization was 62 Am ² / kg (62 emu / g), and the coercive force was 195.1 kA. / M (2,450 oersteds).

(B) Production of magnetic tape Next, the magnetic tape of the present invention was produced. 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

<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 process 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

  After kneading the component (1) in the above-mentioned lower layer coating component with a batch kneader, the component (2) is added, and after stirring, dispersion treatment is carried out with a sand mill for 60 minutes, and (3) The ingredients were added, stirred and filtered, and then used as the lower layer coating (lower layer coating).

  Apart from this, 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 preliminarily stirred and mixed, and the mixed powder is kneaded in (1). After adjusting to be a process component, knead in a continuous biaxial kneader, further add the dilution process component (2), perform dilution in at least two stages or more in a continuous biaxial kneader, Using a zirconia bead having a diameter of 0.5 mm as a dispersion medium in a sand mill, 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 the 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 winding core at 70 ° C. for 72 hours. After aging, 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>
In the production of the iron nitride magnetic powder, the same procedure as in Example 1 was performed except that the magnetite having a particle diameter of 17 nm was changed to a raw material to obtain the iron nitride magnetic powder B1.

The particle size of the iron nitride magnetic powder B was 15 nm, and yttrium and aluminum were 1.9 atomic% and 29.0 atomic%, respectively, with respect to Fe. The saturation magnetization was 80 Am ² / kg (80 emu / g), and the coercive force was 220.2 kA / m (2,750 oersted).

<Example 3>
In the production of the iron nitride magnetic powder, the same procedure as in Example 1 was performed except that the magnetite having a particle diameter of 20 nm was changed to a raw material to obtain an iron nitride magnetic powder C1.

The particle size of the iron nitride magnetic powder C was 18 nm, and yttrium and aluminum were 1.8 atom% and 25.0 atom%, respectively, with respect to Fe. The saturation magnetization was 90 Am ² / kg (90 emu / g), and the coercive force was 238.1 kA / m (2,976 Oersted).

<Comparative Example 1>
In the production of the iron nitride magnetic powder, the same procedure as in Example 1 was conducted except that the magnetite having a particle diameter of 25 nm was changed to a raw material to obtain an iron nitride magnetic powder D1. The particle diameter of the iron nitride magnetic powder D was 23 nm, and yttrium and aluminum were 1.8 atom% and 23.0 atom%, respectively, with respect to Fe. The saturation magnetization was 104 Am ² / kg (1040 emu / g), and the coercive force was 246.8 kA / m (3100 Oersted).

<Comparative example 2>
In the production of the iron nitride magnetic powder, the same procedure as in Example 1 was performed except that the magnetite having a particle diameter of 8 nm was changed to a raw material to obtain the iron nitride magnetic powder E. However, since the yield of the finally obtained iron nitride magnetic powder E1 was as low as 5% or less and the magnetic properties were inferior, no magnetic tape was produced. The particle diameter of the iron nitride magnetic powder E was 7 nm, and yttrium and aluminum were 2.1 atomic percent and 30.0 atomic percent, respectively, with respect to Fe. The saturation magnetization was 10 Am ² / kg (10 emu / g), and the coercive force was 51.0 kA / m (637 Oersted).

<Comparative Example 3>
In Example 1, in the process of depositing yttrium and aluminum on the raw material magnetite during the manufacturing process of the iron nitride magnetic powder, except that the use of the collision disperser was changed and the following method was adopted. Same as Example 1.

While stirring 12 liters of the aqueous solution (a) in a vessel equipped with a stirrer, 3 liters of the aqueous solution (b) was added over 30 minutes, followed by further stirring for 1 hour. The particle size of the iron nitride magnetic powder A2 thus obtained was 10 nm, and yttrium and aluminum were 1.7 atomic percent and 25.0 atomic percent, respectively, with respect to Fe. The saturation magnetization was 59 Am ² / kg (59 emu / g), and the coercive force was 143.3 kA / m (1800 Oersted).

<Comparative example 4>
In Example 1, in the process of depositing yttrium and aluminum on the raw material magnetite during the manufacturing process of the iron nitride magnetic powder, except that the use of the collision disperser was changed and the following method was adopted. Same as Example 1.

12 liters of the aqueous solution (I) and 3 liters of the aqueous solution (B) were fed into a beadless shear stress type disperser (manufactured by XX Co.) and dispersed so that the residence time was 30 minutes.
The particle size of the iron nitride magnetic powder A3 thus obtained was 9 nm, and yttrium and aluminum were 1.8 atom% and 26.0 atom%, respectively, with respect to Fe. The saturation magnetization was 55 Am ² / kg (55 emu / g), and the coercive force was 155.3 kA / m (1950 Oersted).
<Comparative Example 5>
In Example 1, in the process of depositing yttrium and aluminum on the raw material magnetite during the manufacturing process of the iron nitride magnetic powder, except that the use of the collision disperser was changed and the following method was adopted. Same as Example 1.

12 liters of aqueous solution (I) and 3 liters of aqueous solution (B) were fed into a sand grind disperser (made by XX Co.) using zirconia beads having a bead diameter of 1 mm as a medium so that the residence time was 30 minutes. Distributed. The particle size of the iron nitride magnetic powder A4 thus obtained was 9 nm, and yttrium and aluminum were 1.8 atom% and 26.0 atom%, respectively, with respect to Fe. The saturation magnetization was 55 Am ² / kg (55 emu / g), and the coercive force was 147.2 kA / m (1840 Oersted).

Table 1 shows the particle size of the magnetite used as the raw material of the iron nitride-based magnetic powder prepared above, the apparatus used in the step of depositing Al and Y elements on the magnetite, and the particles of the iron nitride-based magnetic powder prepared. The diameter, the content of Al and Y (atomic% vs. Fe), and the thickness variation rate of the outer layer mainly composed of Al and Y are shown.

  As is apparent from Table 1, the iron nitride magnetic powder produced using the collision type disperser of the present invention in the deposition process is subjected to deposition of Al and Y elements with the raw material powder well dispersed. Therefore, the thickness variation rate of the outer layer is small. Further, when the iron nitride magnetic powder A1 of Example 1 and the iron nitride magnetic powders A2, A3, and A4 of Comparative Examples 3 to 5 are compared, the magnetic powder A1 is uniformly and sufficiently dispersed in the deposition process. From the subsequent reduction process and nitriding process, it can be seen that the coercive force (Hc) and the saturation magnetization (σs) are superior to the iron nitride magnetic powders A2, A3, A4, and the like. Further, since the iron nitride magnetic powder E1 of Comparative Example 2 has a magnetite particle diameter of 10 nm as a starting raw material, the particle diameter is obtained as a result of being produced through a reduction process (a little smaller when the O element in the powder is removed). However, Hc and σs are inferior because the volume of the core phase having ultrafine particles of 8 nm and magnetic properties is too small. In addition, the yield was extremely poor, and it was very difficult to obtain an iron nitride magnetic powder.

  Table 2 summarizes C and C / N of the magnetic layer surface smoothness (Ra), squareness ratio, and electromagnetic conversion characteristics of the magnetic tape produced using the iron nitride magnetic powder shown in Table 1. It was.

  As is apparent from the results in Table 2, the magnetic tape using the iron nitride magnetic powder according to the present invention in the step of depositing the element as the anti-caking agent on the raw material powder with the particle diameter according to the present invention is as follows. It can be seen that dispersion is good, Ra and squareness ratio are good, and electromagnetic conversion characteristics (C, C / N) are also excellent. As described above, the iron nitride magnetic powder of the present invention is excellent as a magnetic powder for magnetic tapes for high recording density.

It is the schematic diagram which showed notionally the process which adheres the hydroxide and hydrate which contain rare earth elements to raw material powder in the manufacturing process of an iron nitride type magnetic powder. It is the cross-sectional schematic which showed an example of the collision type disperser used in the manufacturing process of the iron nitride type magnetic powder of this application.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st mixing container with a stirrer 2 2nd mixing container with a stirrer 3 1st pump 4 2nd pump 5 Collision type | mold disperser 51 1st supply nozzle 52 2nd supply nozzle 54 Mixing chamber 61 1st orifice 62 2nd orifice

Claims (2)

Manufacture of iron nitride-based magnetic powder having an average particle diameter of 8 to 20 nm, in which the core phase of the magnetic powder includes a crystal phase mainly composed of Fe ₁₆ N ₂ and the outer layer includes at least one element selected from rare earth and Al, Si In the way to
The starting material is iron-based oxide or iron-based hydroxide,
Including a deposition step of depositing an outer layer on the starting material;
In the deposition process, the iron-based aqueous solution containing the iron-based oxide or the iron-based hydroxide and the aqueous solution containing a salt of at least one element selected from rare earths and Al and Si are ejected from individual nozzles to collide with each other. A method of producing an iron nitride magnetic powder including a process of reaction using a mold disperser.
The iron nitride-based magnetic powder produced by the production method according to claim 1, wherein the variation rate of the thickness of the outer layer containing at least one element selected from rare earth, Al, and Si is 60% or less.

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