JP4057593B2 - Iron nitride magnetic powder, method for producing the same, and magnetic recording medium - Google Patents

Description

The present invention relates to an iron nitride-based magnetic powder and a method for producing the same, and also relates to a magnetic recording medium using the magnetic powder, particularly to a magnetic recording medium requiring high-density recording such as a digital video tape and a computer backup tape. is there.

Coating type magnetic recording media, that is, magnetic recording media having a magnetic layer containing a magnetic powder and a binder on a non-magnetic support, have a higher recording density as the recording / reproducing system shifts from analog to digital. Improvement is demanded. In particular, this demand is increasing year by year for video tapes for high recording density, backup tapes for computers, and the like.

In order to cope with short wavelength recording, which is indispensable for improving the recording density, it is effective to reduce the thickness of the magnetic layer to 300 nm or less, particularly 100 nm or less in order to reduce the thickness loss during recording. As a reproducing magnetic head used in such a high recording density medium, an MR head capable of obtaining a high output is generally used.

Further, in order to reduce noise, the magnetic powder is becoming finer every year, and at present, acicular metal magnetic powder having a particle diameter of about 100 nm is in practical use.

Furthermore, in order to prevent a decrease in output due to demagnetization during short wavelength recording, a high coercive force has been achieved year by year. It is realized (see Patent Documents 1 to 3).

However, in a magnetic recording medium using acicular magnetic particles, since the coercive force depends on the shape, it is difficult to further reduce the particle size from the above particle diameter. That is, when the particle size is further reduced, the specific surface area is remarkably increased and the saturation magnetization is greatly reduced.

Therefore, the merit of high saturation magnetization, which is the greatest feature of metal or alloy magnetic powder, is lost, and the use of metal or alloy itself is meaningless.

Therefore, a magnetic recording medium using a rare earth-transition metal granular magnetic powder, for example, a granular or elliptical rare earth-iron-boron magnetic powder as a magnetic powder completely different from the acicular magnetic powder has been proposed. (See Patent Document 4).

This magnetic recording medium can make ultrafine particles of magnetic powder, can realize high saturation magnetization and high coercive force, and greatly contributes to high recording density.

Further, as an iron-based magnetic powder whose particle shape is not needle-shaped, a magnetic material using an iron nitride-based magnetic powder having an irregular particle shape and a BET specific surface area of about 10 m ² / g with a Fe ₁₆ N ₂ phase as a main phase. A recording medium has also been proposed (see Patent Document 5).

JP-A-3-49026 (Page 4) JP 10-83906 A (page 3) Japanese Patent Laid-Open No. 10-340805 (second page) JP 2001-181754 A (4th page, 22nd page) Japanese Unexamined Patent Publication No. 2000-277311 (page 3, FIG. 4)

However, the rare earth-iron-boron magnetic powder disclosed in Patent Document 4 is a composite material formed on the balance of high magnetic anisotropy due to the rare earth compound and high saturation magnetization due to the iron-based material as the core. Even if an improvement is made, for example, to increase the coercive force, it is difficult to improve the magnetic properties while maintaining the optimum dispersibility and chemical stability for the magnetic recording medium.

In addition, the iron nitride magnetic powder of Patent Document 5 has a BET specific surface area of 10 to 22 m ² / g in the examples. However, the particle size is too large and the object is to reduce noise. Not suitable for high-density magnetic recording.

Further, the iron nitride magnetic powder of Patent Document 5 is characterized by high saturation magnetization, and in the examples, those of 190 to 200 Am ² / kg (190 to 200 emu / g) are shown. . Thus, a magnetic powder with too high saturation magnetization is not suitable for a magnetic recording medium for high-density recording. This is because if the saturation magnetization is too high, the magnetic flux density of the medium becomes too large and recording demagnetization becomes remarkable. Since this tendency becomes more prominent as the recording wavelength becomes shorter, it is not suitable for high-density recording.

In particular, in a high-density recording medium, in order to reduce recording demagnetization, it is essential to appropriately lower the saturation magnetization of the magnetic powder and reduce the thickness of the magnetic layer.

When the magnetic flux density is lowered, the magnetic flux from the medium surface is reduced and the reproduction output is reduced. However, due to remarkable progress in recent magnetic head technologies such as MR heads, even small magnetic fluxes can be reproduced with sufficiently high sensitivity. . Therefore, in order to achieve high density recording, it is necessary to set the saturation magnetization of the magnetic powder to an appropriate value lower than the conventionally required value and to increase the coercive force. .

In high density recording media, storage stability is extremely important. If the storage stability is poor, the rate of decrease in saturation magnetization after a certain period of time increases and the value of saturation magnetization decreases. When this happens, the magnetic flux density becomes lower than in the initial state, the magnetic flux from the medium surface becomes smaller, and the reproduction output becomes smaller, so that reading becomes impossible.

In addition, if the storage stability of the high-density recording medium is poor, the rate of decrease in coercive force after a certain period of time also increases. When the coercive force is lowered, information recorded by the external magnetic field is easily erased, and as a result, the recorded information cannot be stored.

As an index indicating storage stability, in general, the saturation magnetization reduction rate (Δσs ₁ ) and coercivity reduction rate (ΔHc ₁ ) after holding in an atmosphere of 60 ° C. and 90% RH for 7 days, As a reference, a saturation magnetization reduction rate (Δσs ₂ ) and a coercivity reduction rate (ΔHc ₂ ) when 7 days have passed since then are used.

Δσs ₁ and ΔHc ₁ are initial reduction rates. If this value is large, the recorded information cannot be read in a short period of time. Δσs ₂ and ΔHc ₂ are reduction rates when stored over a long period of time. If this value is small, it indicates that reading is possible even after storage for an extremely long time. Ideally, the smaller values of Δσs ₁ , Δσs ₂ , ΔHc ₁ , and ΔHc ₂ are better.

As one of the methods for improving the storage stability, in the production of iron nitride-based magnetic powder containing iron and nitrogen as at least constituent elements, a raw material comprising an iron-based oxide or hydroxide before being subjected to reduction treatment and nitriding treatment It is known to deposit at least one element of rare earth metal elements, aluminum, and silicon on the surface of particles.

However, if a large amount of the above elements is deposited on the surface of the raw material particles by this method, the nitriding reaction does not proceed during the nitriding treatment, and the coercive force does not increase. The reason for this is considered that nitrogen for causing the nitriding reaction cannot pass through the deposition phase on the particle surface. For this reason, in order to facilitate the nitriding reaction, it is necessary to reduce the deposition phase on the particle surface, but in this case, good results cannot be obtained in terms of improving storage stability.

In light of these circumstances, the present invention has a small particle size, an extremely high coercive force, an optimum saturation magnetization for high-density recording, and an iron nitride-based magnetic powder with excellent storage stability. It is another object of the present invention to obtain a magnetic recording medium having excellent magnetic characteristics and good storage stability by using the magnetic powder.

The present inventors have found that in order to overcome the above problems, a result of intensive studies, in the production of iron nitride-based magnetic powder, with respect to particles after subjected to reduction treatment and nitriding treatment, the rare earth metal element, at least one of aluminum By subjecting an inorganic compound containing one element, an organic carboxylic acid, an organic sulfonic acid, an organic phosphoric acid, an organic compound comprising an esterified product or an amidated product of these acids to the particle surface, In addition, by applying a specific heat treatment in an inert gas atmosphere after this deposition treatment, the particle size is small, the coercive force is extremely high, and the saturation magnetization is optimal for high-density recording, and further storage. It is possible to obtain an iron nitride magnetic powder with excellent stability, and by using this iron nitride magnetic powder, it has excellent magnetic properties and is preserved. Found that good magnetic recording medium of the qualitative is obtained in which the present invention has been completed.

That is, the present invention comprises iron and nitrogen as at least constituent elements, contains at least one element of a rare earth metal element and aluminum , contains at least an Fe ₁₆ N ₂ phase, and has a nitrogen content of 1. In the production of an iron nitride magnetic powder having an average particle size of 0 to 20.0 atomic% and an average particle size in the range of 5 to 20 nm, the rare earth metal element and aluminum are formed after the formation of the Fe ₁₆ N ₂ phase. An inorganic compound containing at least one element of the above or / and an organic carboxylic acid, organic sulfonic acid, organic phosphoric acid, or an organic compound comprising an esterified product or an amidated product of these acids applied to the particle surface. The present invention relates to a method for producing an iron nitride magnetic powder.

Further, in the present invention, after performing an adhesion treatment for depositing an inorganic compound and / or an organic compound on the particle surface, in an inert gas or a mixed gas of an oxygen gas and an inert gas, a temperature of 30 to 150 ° C. This relates to a method for producing an iron nitride-based magnetic powder having the above-described configuration in which heat treatment is performed.

Furthermore, the present invention is obtained by the production method of the above-described configuration, the iron and nitrogen and at least an element, rare earth element contains at least one element selected from aluminum, and comprises at least a Fe ₁₆ N ₂ phase It is possible to provide an iron nitride magnetic powder having a granular or elliptical shape in which the content of nitrogen relative to iron is 1.0 to 20.0 atomic% and the average particle size is in the range of 5 to 20 nm.

In particular, the saturation magnetization is 80 to 120 Am ² / kg (80 to 120 emu / g), the coercive force is 160 to 280 kA / m (2,000 to 3,500 Oe), and it is 7 in an atmosphere of 60 ° C. and 90% RH. The saturation magnetization reduction rate (Δσs ₁ ) after holding for 0.1 days is 0.1 to 11%, the coercive force reduction rate (ΔHc ₁ ) is 0.1 to 10%, and 7 days have passed since the seventh day. In this case, the iron nitride magnetic powder having the above-described structure, in which the saturation magnetization reduction rate (Δσs ₂ ) is 0.1 to 10% and the coercive force reduction rate (ΔHc ₂ ) is 0.1 to 9%, can be provided. .

The present invention also provides a magnetic recording medium using the iron nitride-based magnetic powder having the above-described configuration, particularly a coercive force of 180 to 300 kA / m (2,300 to 3,800 Oe), 60 ° C. and 90% RH. The saturation magnetization decrease rate (Δσs ₁ ) after being held in the atmosphere for 7 days is 0.01 to 10%, the coercive force decrease rate (ΔHc ₁ ) is 0.01 to 5%, based on the 7th day, and further What can provide a magnetic recording medium having the above-described structure in which the saturation magnetization reduction rate (Δσs ₂ ) after 7 days is 0.01 to 8% and the coercive force reduction rate (ΔHc ₂ ) is 0.01 to 4%. It is.

Thus, in the present invention, after the raw material particles made of iron-based oxides or hydroxides are subjected to reduction treatment and nitriding treatment, the deposition treatment for depositing a specific inorganic compound and / or organic compound on the particle surface is performed. By applying it, and then applying a specific heat treatment, the particle size is small, the coercive force is extremely high, and the saturation magnetization is optimal for high-density recording. An iron nitride magnetic powder having excellent storage stability can be obtained. Further, by using this iron nitride magnetic powder, a magnetic recording medium having excellent magnetic properties and good storage stability can be obtained.

In the method for producing an iron nitride magnetic powder of the present invention, an iron oxide or hydroxide is used as a starting material. For example, hematite, magnetite, goethite and the like can be mentioned. The average particle size is not particularly limited, but is usually 5 to 20 nm. If the particle size is too small, inter-particle sintering is likely to occur during the reduction treatment, and if it is too large, the reduction treatment tends to be heterogeneous, making it difficult to control the particle size and magnetic properties.

In the present invention, a rare earth metal element can be deposited on the above starting material. In this case, the starting material powder is usually dispersed in an aqueous solution of alkali or acid, a salt of the rare earth metal element is dissolved in the starting material powder, and the starting material powder contains hydroxide or hydration containing the rare earth metal element. What is necessary is just to make it precipitate. Alternatively, the starting material may be immersed in a solution in which a compound composed of elements such as silicon and aluminum is dissolved, and silicon and aluminum may be deposited on the starting material powder.

As the solvent used during such surface treatment, water is preferable, but other solvents can naturally be used. 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. As these deposition treatments, rare earth elements, silicon, and aluminum may be deposited simultaneously or alternately.

In the present invention, such raw material particles are first subjected to heat reduction in a hydrogen stream. 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 preferably 300 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 likely to be sintered, which is not preferable.

Next, the Fe ₁₆ N ₂ phase is generated by nitriding after the above heat reduction treatment. 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 100 to 200 ° C. If the nitriding temperature is too low, nitriding does not proceed sufficiently and the effect of increasing the coercive force is small. On the other hand, if the nitriding temperature is too high, nitriding is excessively promoted, the proportion of Fe ₄ N, Fe ₃ N phase, etc. increases, the coercive force is rather lowered, and the saturation magnetization is liable to be excessively lowered.

Usually, after the Fe ₁₆ N ₂ phase is generated by the above nitriding treatment, it is desirable to perform a stabilizing treatment using a mixed gas of oxygen gas and nitrogen gas. The present invention is characterized in that after the Fe ₁₆ N ₂ phase is generated and stabilized as described above, a deposition treatment for depositing an inorganic compound and / or an organic compound on the particle surface is further performed. .

In this deposition treatment, the magnetic particles after the stabilization treatment are redispersed in a solution in which an inorganic compound or / and an organic compound is dissolved in a solvent, so that the inorganic compound or / and An organic compound is deposited. In order to perform the deposition process efficiently, additives such as a reducing agent, a pH buffering agent, and a particle size controlling agent may be mixed.

The above inorganic compound is an inorganic compound containing a rare earth metal element, at least one element of aluminum.

The above organic compounds are organic carboxylic acids (for example, lactic acid, palmitic acid, stearic acid, salicylic acid, glutaric acid, p-hydroxybenzoic acid, etc.), organic sulfonic acids in which the carboxylic acid moiety is substituted with sulfonic acid, phosphorus An organic compound composed of an organic phosphoric acid substituted with an acid, an esterified product of these acids (for example, a fatty acid ester) or an amidated product (for example, an amide of a higher fatty acid such as palmitic acid or stearic acid).

Only one of these inorganic compounds and organic compounds may be deposited, or both may be deposited. When both are deposited, the inorganic compound and the organic compound may be mixed and deposited together, or may be deposited alternately.

Further, in the present invention, after the above-described deposition treatment, further improvement in storage stability and the like is achieved by performing heat treatment in an inert gas or a mixed gas of oxygen gas and inert gas. Can do. The heat treatment temperature is preferably in the range of 30 to 150 ° C. If the heat treatment temperature is too high, the produced iron nitride may be decomposed and the coercive force may be reduced. Note that this heat treatment is not necessarily required, and may be omitted depending on circumstances.

Iron nitride-based magnetic powder of the present invention obtained in this way, the iron and nitrogen and at least an element, rare earth element contains at least one element selected from aluminum, and comprises at least a Fe ₁₆ N ₂ phase The content of nitrogen relative to iron is 1.0 to 20.0 atomic%, preferably 3.0 to 16.0 atomic%, and the average particle size is granular or elliptical in the range of 5 to 20 nm. It is characterized by.

The above-mentioned “granular or elliptical” means that the magnetic powder has an axial ratio (major axis ratio / minor axis ratio) of 1 to 2, particularly preferably 1 to 1.5. In addition, the above “average particle size” means a value obtained by measuring the particle size of a photograph taken with a transmission electron microscope (TEM) and calculating an average value of 300 particles.

The iron nitride magnetic powder has a saturation magnetization of 80 to 120 Am ² / kg (80 to 120 emu / g), a coercive force of 160 to 280 kA / m (2,000 to 3,500 Oe), 60 ° C., After holding for 7 days in an atmosphere of 90% RH, the saturation magnetization reduction rate (Δσs ₁ ) is 0.1 to 11%, the coercive force reduction rate (ΔHc ₁ ) is 0.1 to 10%, and the seventh day It is characterized by a saturation magnetization reduction rate (Δσs ₂ ) of 0.1 to 10% and a coercivity reduction rate (ΔHc ₂ ) of 0.1 to 9% when 7 days have passed since that time.

In the present invention, a magnetic recording medium using the iron nitride magnetic powder having the above-described configuration can be provided. In particular, by using the iron nitride-based magnetic powder having the above configuration, the coercive force was 180 to 300 kA / m (2,300 to 3,800 Oe), and the film was held for 7 days in an atmosphere of 60 ° C. and 90% RH. The saturation magnetization reduction rate (Δσs ₁ ) is 0.01 to 10%, the coercive force reduction rate (ΔHc ₁ ) is 0.01 to 5%, and the saturation magnetization when 7 days have passed since the 7th day as a reference. A magnetic recording medium having a reduction rate (Δσs ₂ ) of 0.01 to 8% and a coercive force reduction rate (ΔHc ₂ ) of 0.01 to 4% can be provided.

Hereinafter, the magnetic recording medium having the above configuration will be described in more detail.

The magnetic recording medium of the present invention is a magnetic coating material prepared by dispersing and mixing an iron nitride-based magnetic powder and a binder having the above structure in a solvent, coating this on a nonmagnetic support, and drying to form a magnetic layer. It can produce by doing. Prior to the formation of the magnetic layer, an undercoat paint containing a nonmagnetic powder such as iron oxide, titanium oxide or aluminum oxide and a binder is applied onto the nonmagnetic support and dried to form an undercoat layer thereon. A magnetic layer may be formed.

As the nonmagnetic support, any conventionally used nonmagnetic support for magnetic recording media can be used. For example, the thickness composed of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide, etc. is usually 2 to 15 μm, especially 2 to 7 μm. The plastic film is used. If the thickness is less than 2 μm, it is difficult to form a film, and the tape strength is reduced. If it exceeds 7 μm, the total thickness of the tape is increased, and the storage capacity per tape roll is reduced.

The thickness of the magnetic layer is 300 nm or less, particularly preferably 10 to 300 nm, more preferably 10 to 250 nm, and most preferably 10 to 200 nm. When the thickness of the magnetic layer exceeds 300 nm, the reproduction output becomes small due to the thickness loss, or the product of the residual magnetic flux density and the thickness becomes too large, and the reproduction output is distorted due to the saturation of the MR head. Moreover, if the thickness of the magnetic layer is less than 10 nm, it is difficult to obtain a uniform magnetic layer.

In the present invention, the iron nitride magnetic powder to be used is an extremely fine particle or ellipse having an average particle size of 5 to 20 nm, so that an extremely thin magnetic layer thickness almost impossible with conventional acicular magnetic powder is realized. It can be done.

The average surface roughness Ra of the magnetic layer is preferably 1.0 to 3.2 nm. When the central value of the unevenness of the magnetic layer is P0, the maximum convex amount is P1, (P1-P0) is 10 to 30 nm, and the twentieth convex amount is P20, (P1 -P20) When the MR head is used, the contact with the MR head is improved when the MR head is used, and the reproduction output when the MR head is used is preferable. For the purpose of improving electrical conductivity and surface lubricity, the magnetic layer preferably contains conventionally known carbon black.

The undercoat layer is not an essential component, but is provided between the nonmagnetic support and the magnetic layer for the purpose of improving durability. The thickness of the undercoat layer is preferably 0.1 to 3.0 μm, more preferably 0.15 to 2.5 μm. If the thickness of the undercoat layer is less than 0.1 μm, the durability of the magnetic tape may deteriorate. If the thickness of the undercoat layer exceeds 3.0 μm, the effect of improving the durability of the magnetic tape is saturated, the total thickness of the tape is increased, the tape length per roll is shortened, and the storage capacity is reduced. Become.

As binders used for the undercoat layer and the magnetic layer, 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- There is a combination of a polyurethane resin and at least one selected from vinyl chloride-based resins such as vinyl acetate-maleic anhydride copolymer resin, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, nitrocellulose, epoxy resin, etc. . In particular, it is preferable to use a vinyl chloride resin and a polyurethane resin in combination. Among these, it is most preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination.

These binders are used in an amount of 7 to 50 parts by weight, preferably 10 to 35 parts by weight, based on 100 parts by weight of solid powder such as magnetic powder and nonmagnetic powder. In particular, it is preferable to use a composite of 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin as a binder. In addition to these binders, it is desirable to use in combination with a thermosetting crosslinking agent that crosslinks by binding to a functional group or the like contained in the binder.

Conventionally known fatty acids, fatty acid esters, fatty acid amides and the like are used for the lubricant contained in the undercoat layer and the magnetic layer. Among them, it is particularly preferable to use a fatty acid having 10 or more carbon atoms, preferably 12 to 30 carbon atoms, and a fatty acid ester having a melting point of 35 ° C. or lower, preferably 10 ° C. or lower. In the case of a magnetic tape provided with an undercoat layer, it is desirable to contain lubricants having different roles in the coating layer composed of the undercoat layer and the magnetic layer.

The magnetic layer contains 0.2 to 3% by weight of fatty acid amide (for example, amides of higher fatty acids such as palmitic acid and stearic acid) with respect to the magnetic powder, and 0.2 to 3% by weight of higher fatty acid. The inclusion of an ester is preferable because the friction coefficient between the magnetic tape and the guide of the traveling system, the slider of the MR head, and the like becomes small.

When the magnetic recording medium of the present invention is a magnetic tape, it is desirable to form a backcoat layer on the surface opposite to the magnetic layer forming surface of the nonmagnetic support. However, this back coat layer is not an essential component. The thickness of the back coat layer is preferably 0.2 to 0.8 μm, more preferably 0.3 to 0.8 μm, and still more preferably 0.3 to 0.6 μm. If the thickness of the backcoat layer is less than 0.2 μm, the effect of improving the running property is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape is increased and the storage capacity per roll is reduced.

Further, the center line surface roughness Ra of the backcoat layer is preferably 3 to 15 nm, and more preferably 4 to 10 nm.

In the preparation of magnetic paints, undercoat paints, and back coat paints, all conventionally used organic solvents can be used as the solvent. For example, aromatic solvents such as benzene, toluene and xylene, ketone solvents such as acetone, cyclohexanone, methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, carbonate esters such as dimethyl carbonate and diethyl carbonate Solvents and alcohol solvents such as ethanol and isopropanol can be used. In addition, various organic solvents such as hexane, tetrahydrofuran and dimethylformamide are used.

Moreover, conventionally well-known paint manufacturing processes can be used for the preparation of magnetic paints, undercoat paints, and backcoat paints. In particular, a kneading step using a kneader or the like and a primary dispersion step are preferably used in combination. In the primary dispersion step, it is desirable to use a sand mill because the surface properties can be controlled while improving the dispersibility of the magnetic powder and the like.

Furthermore, when applying a magnetic paint, an undercoat paint, or a backcoat paint on the nonmagnetic support, conventionally known coating methods such as gravure coating, roll coating, blade coating, and extrusion coating are used.

The undercoat paint and magnetic paint can be applied by applying the undercoat paint on the non-magnetic support and drying, then applying the magnetic paint, or by applying the successive overlay coating method or by applying the undercoat paint and the magnetic paint simultaneously. Any of the application methods (wet on wet) can be adopted. Considering the leveling of the thin magnetic layer at the time of coating, it is preferable to adopt a simultaneous multilayer coating method in which the magnetic coating is applied while the undercoat coating is wet.

Examples of the present invention will be described below in more detail. In the following, “parts” means parts by weight.

(A) Manufacture of iron nitride-based magnetic powder 100 g of magnetite particles having an average particle size of approximately 15 nm and a substantially spherical shape were dispersed in 1,500 cc of water for 30 minutes using an ultrasonic disperser. Further, 5 g of yttrium nitrate was dissolved in 200 cc of water, and this was dropped into the above dispersion and stirred for 30 minutes. Separately, 1.6 g of sodium hydroxide was dissolved in 500 cc of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over 30 minutes, and the mixture was further stirred for 1 hour. By this treatment, yttrium hydroxide was deposited on the surface of the magnetite particles.

Moreover, 20 g of aluminum nitrate was dissolved in 200 cc of water. This aluminum nitrate solution was dropped into the dispersion after the yttrium deposition treatment over about 30 minutes, and after completion of the dropping, the solution was further stirred for 1 hour. Thereafter, 2.5 g of sodium hydroxide was dissolved in 500 cc water, and this solution was added dropwise over about 30 minutes, followed by further stirring for 1 hour. By this treatment, sodium aluminate was deposited on the surface of the magnetite particles.

This was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which yttrium hydroxide and aluminum were deposited on the surface of the magnetite particles.

Thus, the powder which adhered and formed the hydroxide of the yttrium and the aluminum on the surface of the magnetite particle | grain was heat-reduced for 2 hours at 450 degreeC in hydrogen stream, and the yttrium-aluminum-iron type magnetic powder was obtained. Next, the temperature was lowered to 140 ° C. over about 1 hour in a state where hydrogen gas was allowed to flow. When the temperature reached 140 ° C., the gas was switched to ammonia gas, and nitriding was performed for 20 hours while maintaining the temperature at 140 ° C.

Thereafter, while maintaining the temperature, the ammonia gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours. Next, with the mixed gas flowing, the temperature was lowered from 140 ° C. to 40 ° C., held at 40 ° C. for about 10 hours, and then taken out into the air.

100 g of this magnetic powder was dispersed again in water. A solution prepared by dissolving 5 g of yttrium nitrate in 200 cc of water was added dropwise to the dispersion and stirred for 30 minutes. Separately, 1.6 g of sodium hydroxide was dissolved in 500 cc of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over 30 minutes, and the mixture was further stirred for 1 hour. By this treatment, yttrium hydroxide was re-deposited on the surface of the magnetic powder particles.

The magnetic powder subjected to the re-deposition treatment was heated to 100 ° C. in an argon gas stream, held for 1 hour, cooled to room temperature while flowing argon gas, and taken out into the air.

The iron nitride-based magnetic powder thus obtained was measured for its yttrium, aluminum and nitrogen contents by fluorescent X-ray, and found to be 4.1 atomic%, 5.1 atomic% and Fe respectively. It was 10.8 atomic%. Further, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 16 nm. Furthermore, the specific surface area determined by the BET method was 64.2 m ² / g.

The iron nitride magnetic powder had a saturation magnetization of 90.2 Am ² / kg (90.2 emu / g) measured by applying a magnetic field of 1,270 kA / m (16 kOe), and the coercive force was It was 230.9 kA / m (2,900 Oe), and the squareness ratio (Br / Bm) was 0.53.

Moreover, as a result of storing this iron nitride magnetic powder at 60 ° C. and 90% RH for 7 days, the saturation magnetization reduction rate (Δσs ₁ ) was 9%, the coercive force reduction rate (ΔHc ₁ ) was 6%, The saturation magnetization reduction rate (Δσs ₂ ) was 8% and the coercivity reduction rate (ΔHc ₂ ) was 5% when 7 days had passed since the 7th day as a reference.

(B) Production of magnetic tape The following undercoat paint components were kneaded with a kneader, then subjected to a dispersion treatment with a residence time of 60 minutes with a sand mill, and 6 parts of polyisocyanate was added thereto and stirred. Thereafter, it was filtered to prepare an undercoat paint.

Separately, the following magnetic coating component (1) is kneaded with a kneader, and then dispersed in a sand mill with a residence time of 45 minutes. The following magnetic coating component (2) is added to this and mixed. did. After that, stirring was performed in a container in which a cylindrical permanent magnet magnetized in the radial direction was inserted to prepare a magnetic paint.

<Undercoat paint component>
Iron oxide powder (average particle size: 55 nm) 70 parts

Aluminum oxide powder (average particle size: 80 nm) 10 parts

Carbon black (average particle size: 25 nm) 20 parts

10 parts of vinyl chloride-hydroxypropyl methacrylate copolymer resin (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)

Polyester polyurethane resin 5 parts (containing -SO ₃ Na group: 1.0 × 10 ^-4 equivalent / g)

Methyl ethyl ketone 130 parts

80 parts of toluene

Myristic acid 1 part

Butyl stearate 1.5 parts

65 parts of cyclohexanone

<Magnetic paint component (1)>
100 parts of iron nitride magnetic powder produced in (A) above

8 parts of vinyl chloride-hydroxypropyl acrylate copolymer resin (containing-SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g)

Polyester polyurethane resin 4 parts (containing -SO ₃ Na group: 1.0 × 10 ^-4 equivalent / g)

α-alumina (average particle size: 80 nm) 10 parts

Carbon black (average particle size: 25 nm) 1.5 parts

1.5 parts of myristic acid

133 parts of methyl ethyl ketone

100 parts of toluene

<Magnetic paint component (2)>
Stearic acid 1.5 parts

4 parts of polyisocyanate ("Coronate L" manufactured by Nippon Polyurethane Industry Co., Ltd.)

133 parts of cyclohexanone

33 parts of toluene

The above-mentioned undercoat paint is a non-magnetic support and a polyethylene naphthalate film having a thickness of 6 μm (105 ° C., 30 minutes heat shrinkage ratio of 0.8% in the vertical direction and 0.6% in the horizontal direction) The undercoat layer after drying and calendering is applied so that the thickness of the undercoat layer is 2 μm, and the magnetic coating is further coated thereon with a magnetic layer thickness of 120 nm after magnetic field orientation, drying and calendering. And then dried.

Next, the back coat paint was applied to the surface opposite to the surface on which the non-magnetic support undercoat layer and magnetic layer were formed so that the thickness of the back coat layer after drying and calendering was 700 nm and dried. .

The back coat paint used here is the following back coat paint component, subjected to a dispersion treatment with a sand mill with a residence time of 45 minutes, added with 8.5 parts of polyisocyanate, stirred, and then filtered. And prepared.

<Back coat paint component>
Carbon black (average particle size: 25 nm) 40.5 parts

Carbon black (average particle size: 370 nm) 0.5 part

4.05 parts barium sulfate

Nitrocellulose 28 parts

20 parts of polyurethane resin (containing SO ₃ Na group)

100 parts of cyclohexanone

100 parts of toluene

100 parts of methyl ethyl ketone

The magnetic sheet thus obtained was mirror-finished with a five-stage calendar (temperature: 70 ° C., linear pressure: 150 kg / cm), and this was wound on a sheet core at 60 ° C. under 40% RH for 48 hours. Aged. Thereafter, the magnetic layer surface is polished with a ceramic wheel (rotation speed + 150%, winding angle 30 °) while being cut at a width of 1/2 inch and running at 100 m / min, and a magnetic tape having a length of 609 m. Was made.

Next, a tape for a computer was produced by incorporating this magnetic tape into a cartridge by a conventional method.

The magnetic tape had a longitudinal coercive force of 286.6 kA / m (3,600 Oe) and a longitudinal squareness ratio (Br / Bm) of 0.89. Furthermore, the SFD was 0.50.

Further, the magnetic tape was stored at 60 ° C. and 90% RH for 7 days. As a result, the saturation magnetization reduction rate (Δσs ₁ ) was 4%, the coercive force reduction rate (ΔHc ₁ ) was 3%, and 7 days. The saturation magnetization reduction rate (Δσs ₂ ) was 3% and the coercivity reduction rate (ΔHc ₂ ) was 2% when 7 days had passed since then.

During the re-deposition treatment, a solution obtained by dissolving 5 g of lactic acid in 45 g of water was added dropwise to a dispersion obtained by re-dispersing 100 g of magnetic powder in water, followed by stirring for 1 hour. By this deposition treatment, lactic acid was deposited on the particle surface of the magnetic powder.

In this manner, iron nitride magnetic powder was produced in the same manner as in Example 1 except that lactic acid, which is an organic carboxylic acid, was used instead of yttrium during the re-deposition treatment. Further, using this iron nitride magnetic powder, a magnetic tape and a computer tape were produced in the same manner as in Example 1.

The iron nitride-based magnetic powder thus obtained was measured for its yttrium, aluminum, and nitrogen content by fluorescent X-ray, and found to be 2.2 atomic%, 4.8 atomic%, and Fe, respectively. It was 11.3 atomic%. Further, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 16 nm. Furthermore, the specific surface area determined by the BET method was 63.8 m ² / g.

Further, with respect to this iron nitride magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 91.3 Am ² / kg (91.3 emu / g), and the coercive force is It was 228.5 kA / m (2,870 Oe), and the squareness ratio (Br / Bm) was 0.53.

Moreover, as a result of storing this iron nitride magnetic powder at 60 ° C. and 90% RH for 7 days, the saturation magnetization reduction rate (Δσs ₁ ) is 10%, the coercive force reduction rate (ΔHc ₁ ) is 6%, The saturation magnetization reduction rate (Δσs ₂ ) was 9% and the coercivity reduction rate (ΔHc ₂ ) was 5% when 7 days had passed since the 7th day as a reference.

Further, the magnetic tape had a longitudinal coercivity of 283.4 kA / m (3,560 Oe) and a longitudinal squareness ratio (Br / Bm) of 0.88. Furthermore, the SFD was 0.52.

The magnetic tape was stored at 60 ° C. and 90% RH for 7 days. As a result, the saturation magnetization reduction rate (Δσs ₁ ) was 4%, the coercive force reduction rate (ΔHc ₁ ) was 4%, and the seventh day. The saturation magnetization reduction rate (Δσs ₂ ) was 3% and the coercive force reduction rate (ΔHc ₂ ) was 3% after 7 days had passed.

During the re-deposition treatment, a solution prepared by dissolving 5 g of yttrium nitrate in 200 cc of water was added dropwise to a dispersion in which 100 g of magnetic powder was dispersed again in water, followed by stirring for 30 minutes. Separately, 1.6 g of sodium hydroxide was dissolved in 500 cc of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over 30 minutes, and the mixture was further stirred for 1 hour. By this treatment, yttrium hydroxide was re-deposited on the surface of the magnetic powder particles. Thereafter, a solution obtained by dissolving 5 g of lactic acid in 45 g of water was further added dropwise to the dispersion of the magnetic powder, and the mixture was stirred for 1 hour. By this treatment, lactic acid was deposited on the surface of the magnetic powder particles.

Thus, an iron nitride magnetic powder was produced in the same manner as in Example 1 except that lactic acid, which is an organic carboxylic acid, was used together with yttrium during the re-deposition treatment. Further, using this iron nitride magnetic powder, a magnetic tape and a computer tape were produced in the same manner as in Example 1.

The iron nitride-based magnetic powder thus obtained was measured for its yttrium, aluminum, and nitrogen contents by fluorescent X-ray, and found to be 4.5 atomic%, 4.7 atomic%, and Fe, respectively. It was 10.6 atomic%. Further, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 16 nm. Furthermore, the specific surface area determined by the BET method was 65.1 m ² / g.

Further, with respect to this iron nitride magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 88.3 Am ² / kg (88.3 emu / g), and the coercive force is It was 226.9 kA / m (2,850 Oe), and the squareness ratio (Br / Bm) was 0.52.

Moreover, as a result of storing this iron nitride magnetic powder at 60 ° C. and 90% RH for 7 days, the saturation magnetization reduction rate (Δσs ₁ ) is 10%, the coercive force reduction rate (ΔHc ₁ ) is 6%, The saturation magnetization reduction rate (Δσs ₂ ) was 8% and the coercivity reduction rate (ΔHc ₂ ) was 5% when 7 days had passed since the 7th day as a reference.

Furthermore, the magnetic tape had a longitudinal coercive force of 282.5 kA / m (3,550 Oe) and a longitudinal squareness ratio (Br / Bm) of 0.88. Furthermore, the SFD was 0.52.

The magnetic tape was stored at 60 ° C. and 90% RH for 7 days. As a result, the saturation magnetization reduction rate (Δσs ₁ ) was 4%, the coercive force reduction rate (ΔHc ₁ ) was 4%, and the seventh day. The saturation magnetization reduction rate (Δσs ₂ ) was 3% and the coercive force reduction rate (ΔHc ₂ ) was 3% after 7 days had passed.

An iron nitride-based magnetic powder was produced in the same manner as in Example 1 except that no heat treatment (held at 100 ° C. in an argon gas stream for 1 hour) was performed after the re-deposition treatment. Further, using this iron nitride magnetic powder, a magnetic tape and a computer tape were produced in the same manner as in Example 1.

The iron nitride-based magnetic powder thus obtained was measured for its yttrium, aluminum and nitrogen contents by fluorescent X-ray, and found to be 4.3 atomic%, 4.9 atomic% and Fe, respectively. 11.1 atomic%. Further, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 16 nm. Furthermore, the specific surface area determined by the BET method was 64.4 m ² / g.

The iron nitride magnetic powder has a saturation magnetization of 98.3 Am ² / kg (98.3 emu / g) measured by applying a magnetic field of 1,270 kA / m (16 kOe), and the coercive force is It was 222.9 kA / m (2,800 Oe), and the squareness ratio (Br / Bm) was 0.52.

Further, when this iron nitride magnetic powder was stored at 60 ° C. and 90% RH for 7 days, the saturation magnetization reduction rate (Δσs ₁ ) was 11% and the coercive force reduction rate (ΔHc ₁ ) was 10%. The saturation magnetization reduction rate (Δσs ₂ ) was 10% and the coercive force reduction rate (ΔHc ₂ ) was 9% when 7 days had passed since then.

Further, the magnetic tape had a longitudinal coercive force of 280.2 kA / m (3,520 Oe) and a longitudinal squareness ratio (Br / Bm) of 0.86. Furthermore, the SFD was 0.52.

Further, the magnetic tape was stored at 60 ° C. and 90% RH for 7 days. As a result, the saturation magnetization reduction rate (Δσs ₁ ) was 8%, the coercive force reduction rate (ΔHc ₁ ) was 5%, and the seventh day. The saturation magnetization reduction rate (Δσs ₂ ) was 6% and the coercive force reduction rate (ΔHc ₂ ) was 4% after 7 days had passed.

Comparative Example 1
An iron nitride magnetic powder was produced in the same manner as in Example 1 except that the re-deposition treatment was not performed. Further, using this iron nitride magnetic powder, a magnetic tape and a computer tape were produced in the same manner as in Example 1.

The iron nitride magnetic powder thus obtained was measured for its yttrium, aluminum, and nitrogen contents by fluorescent X-ray, and found to be 2.0 atomic%, 5.1 atomic%, and Fe, respectively. It was 10.6 atomic%. Further, when the particle shape was observed with a transmission electron microscope, it was found that the particles were substantially spherical and the average particle size was 16 nm. Furthermore, the specific surface area determined by the BET method was 63.1 m ² / g.

Further, with respect to this iron nitride magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 112.3 Am ² / kg (112.3 emu / g), and the coercive force is It was 226.9 kA / m (2,850 Oe), and the squareness ratio (Br / Bm) was 0.53.

Further, as a result of storing this magnetic powder at 60 ° C. and 90% RH for 7 days, the saturation magnetization reduction rate (Δσs ₁ ) was 13%, the coercive force reduction rate (ΔHc ₁ ) was 12%, and the seventh day The saturation magnetization reduction rate (Δσs ₂ ) was 11% and the coercive force reduction rate (ΔHc ₂ ) was 10% after 7 days had passed.

Furthermore, the magnetic tape had a longitudinal coercivity of 250.8 kA / m (3,150 Oe) and a longitudinal squareness ratio (Br / Bm) of 0.86. Furthermore, the SFD was 0.54.

The magnetic tape was stored at 60 ° C. and 90% RH for 7 days. As a result, the saturation magnetization reduction rate (Δσs ₁ ) was 8%, the coercive force reduction rate (ΔHc ₁ ) was 8%, and the seventh day. The saturation magnetization reduction rate (Δσs ₂ ) was 7% and the coercive force reduction rate (ΔHc ₂ ) was 7% after 7 days had passed.

Comparative Example 2
After the nitriding treatment, the yttrium hydroxide was not re-deposited, and the same treatment was performed before the heat reduction, that is, the yttrium hydroxide was deposited twice before the heat reduction. Except for the above, iron nitride magnetic powder was produced in the same manner as in Example 1. Further, using this iron nitride magnetic powder, a magnetic tape and a computer tape were produced in the same manner as in Example 1.

The iron nitride-based magnetic powder thus obtained was measured for its yttrium, aluminum and nitrogen contents by fluorescent X-ray, and found to be 4.5 atomic%, 4.9 atomic% and Fe, respectively. It was 0.3 atomic%. Further, when the particle shape was observed with a transmission electron microscope, it was a substantially spherical particle and the average particle size was 16 nm. Furthermore, the specific surface area determined by the BET method was 65.6 m ² / g.

Further, with respect to the iron nitride magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 132.5 Am ² / kg (132.5 emu / g), and the coercive force is It was 44.6 kA / m (560 Oe), and the squareness ratio (Br / Bm) was 0.38.

Further, as a result of storing this iron nitride magnetic powder at 60 ° C. and 90% RH for 7 days, the saturation magnetization reduction rate (Δσs ₁ ) is 10%, the coercive force reduction rate (ΔHc ₁ ) is 2%, The saturation magnetization reduction rate (Δσs ₂ ) was 9% and the coercivity reduction rate (ΔHc ₂ ) was 1% when 7 days had passed since the 7th day as a reference.

Furthermore, this magnetic tape had a coercive force in the longitudinal direction of 51.7 kA / m (650 Oe) and a squareness ratio (Br / Bm) in the longitudinal direction of 0.51. Furthermore, the SFD was 0.81.

Further, the magnetic tape was stored at 60 ° C. and 90% RH for 7 days. As a result, the saturation magnetization reduction rate (Δσs ₁ ) was 6%, the coercive force reduction rate (ΔHc ₁ ) was 1%. And the saturation magnetization reduction rate (Δσs ₂ ) after 7 days had passed, and the coercive force reduction rate (ΔHc ₂ ) was 0.5%.

Reference example 1
An iron nitride magnetic powder was produced in the same manner as in Example 1 except that the heat treatment temperature after the re-deposition treatment was changed to 200 ° C. Further, using this iron nitride magnetic powder, a magnetic tape and a computer tape were produced in the same manner as in Example 1.

The iron nitride magnetic powder thus obtained was measured for its yttrium, aluminum and nitrogen contents by fluorescent X-ray, and found to be 4.1 atomic%, 5.4 atomic% and Fe, respectively. It was 10.4 atomic%. Further, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 16 nm. Furthermore, the specific surface area determined by the BET method was 62.3 m ² / g.

The iron nitride magnetic powder has a saturation magnetization of 55.0 Am ² / kg (55.0 emu / g) measured by applying a magnetic field of 1,270 kA / m (16 kOe), and the coercive force is It was 96.2 kA / m (1,230 Oe), and the squareness ratio (Br / Bm) was 0.38.

Moreover, as a result of storing this iron nitride magnetic powder at 60 ° C. and 90% RH for 7 days, the saturation magnetization reduction rate (Δσs ₁ ) was 5%, the coercive force reduction rate (ΔHc ₁ ) was 7%, The saturation magnetization reduction rate (Δσs ₂ ) was 4% and the coercivity reduction rate (ΔHc ₂ ) was 5% when 7 days had passed since the 7th day as a reference.

Further, this magnetic tape had a coercive force in the longitudinal direction of 129.1 kA / m (1,650 Oe) and a squareness ratio in the longitudinal direction (Br / Bm) of 0.48. Furthermore, the SFD was 0.53.

The magnetic tape was stored at 60 ° C. and 90% RH for 7 days. As a result, the saturation magnetization reduction rate (Δσs ₁ ) was 3%, the coercive force reduction rate (ΔHc ₁ ) was 4%, and the seventh day. The saturation magnetization reduction rate (Δσs ₂ ) was 2% and the coercive force reduction rate (ΔHc ₂ ) was 4% after 7 days had passed.

About each iron nitride type magnetic powder obtained by said Examples 1-4, Comparative Examples 1-2, and Reference Example 1, the characteristic value (Average particle size, BET specific surface area, saturation magnetization, coercive force, squareness ratio, The saturation magnetization reduction rate and the coercive force reduction rate are collectively shown in Table 1 (Examples 1 to 4) and Table 2 (Comparative Examples 1 to 2 and Reference Example 1).

Table 1

┌───────────┬─────┬─────┬┬─────┬─────┐
│ │ Example 1 | Example 2 | Example 3 | Example 4 |
├───────────┼─────┼─────┼┼─────┼─────┤
│ │ │ │ │ │
│Average particle size (nm) │ 16 │ 16 │ 16 │ 16 │
│ │ │ │ │ │
│BET specific surface area │ 64.2│ 63.8│ 65.1│ 64.4│
│ (m ² / g) │ │ │ │ │
│ │ │ │ │ │
├───────────┼─────┼─────┼┼─────┼─────┤
│ │ │ │ │ │
│saturation magnetization σs │ 90.2│ 91.3│ 88.3│ 98.3│
│ (Am ² / kg) │ │ │ │ │
│ │ │ │ │ │
│Coercive force Hc (kA / m) │230.9│228.5│226.9│222.9│
│ │ │ │ │ │
│Square ratio [Br / Bm] │ 0.53│ 0.53│ 0.52│ 0.52│
│ │ │ │ │ │
├───────────┼─────┼─────┼┼─────┼─────┤
│ │ │ │ │ │
│ Saturation decrease rate │ │ │ │ │
│ Δσs ₁ (%) │ 9 │ 10 │ 10 │ 11 │
│ │ │ │ │ │
│ Δσs ₂ (%) │ 8 │ 9 │ 8 │ 10 │
│ │ │ │ │ │
├───────────┼─────┼─────┼┼─────┼─────┤
│ │ │ │ │ │
│ Coercivity reduction rate │ │ │ │ │
│ ΔHc ₁ (%) │ 6 │ 6 │ 6 │ 10 │
│ │ │ │ │ │
│ ΔHc ₂ (%) │ 5 │ 5 │ 5 │ 9 │
│ │ │ │ │ │
└───────────┴─────┴─────┴┴─────┴─────┘

Table 2

┌───────────┬─────┬─────┬─────┐
│ │ Comparative Example 1 | Comparative Example 2 | Reference Example 1 |
├───────────┼─────┼─────┼─────┤
│ │ │ │ │
│Average particle size (nm) │ 16 │ 16 │ 16 │
│ │ │ │ │
│BET specific surface area │ 63.1│ 65.6│ 62.3│
│ (m ² / g) │ │ │ │
│ │ │ │ │
├───────────┼─────┼─────┼─────┤
│ │ │ │ │
│saturation magnetization σs │112.3│132.5│ 55.0│
│ (Am ² / kg) │ │ │ │
│ │ │ │ │
│Coercivity Hc (kA / m) │226.9│ 44.6│ 96.2│
│ │ │ │ │
│Square ratio [Br / Bm] │ 0.53│ 0.38│ 0.38│
│ │ │ │ │
├───────────┼─────┼─────┼─────┤
│ │ │ │ │
│ Saturation reduction rate │ │ │ │
│ Δσs ₁ (%) │ 13 │ 10 │ 5 │
│ │ │ │ │
│ Δσs ₂ (%) │ 11 │ 9 │ 4 │
│ │ │ │ │
├───────────┼─────┼─────┼─────┤
│ │ │ │ │
│ Coercivity reduction rate │ │ │ │
│ ΔHc ₁ (%) │ 12 │ 2 │ 7 │
│ │ │ │ │
│ ΔHc ₂ (%) │ 10 │ 1 │ 5 │
│ │ │ │ │
└───────────┴─────┴─────┴─────┘

From the results shown in Table 1, it can be seen that each of the iron nitride magnetic powders of Examples 1 to 4 has excellent magnetic properties and excellent storage stability (corrosion resistance).

On the other hand, from the results of Table 2 above, unless the re-deposition treatment is performed after the formation of the Fe ₁₆ N ₂ phase as in Comparative Example 1, the storage stability is particularly deteriorated. Further, it can be seen that when the re-deposition treatment after the nitriding treatment is performed before the nitriding treatment as in Comparative Example 2, the nitriding does not proceed and the nitrogen content is lowered, resulting in a lower coercive force. Furthermore, it can be seen that if the heat treatment temperature after re-deposition treatment is too high as in Reference Example 1, the initial magnetic properties are particularly inferior.

Next, about each magnetic tape obtained in said Examples 1-4, Comparative Examples 1-2, and Reference Example 1, the characteristic value (Coercive force, squareness ratio, SFD, saturation magnetization reduction rate, and coercivity reduction rate) ) Are summarized in Table 3 (Examples 1 to 4) and Table 4 (Comparative Examples 1 and 2 and Reference Example 1).

Table 3

┌───────────┬─────┬─────┬┬─────┬─────┐
│ │ Example 1 | Example 2 | Example 3 | Example 4 |
├───────────┼─────┼─────┼┼─────┼─────┤
│ │ │ │ │ │
│Coercivity Hc (kA / m) │286.6│283.4│282.5│280.2│
│ │ │ │ │ │
│Square ratio [Br / Bm] │ 0.89│ 0.88│ 0.88│ 0.86│
│ │ │ │ │ │
│SFD │ 0.50│ 0.52│ 0.52│ 0.52│
│ │ │ │ │ │
├───────────┼─────┼─────┼┼─────┼─────┤
│ │ │ │ │ │
│ Saturation decrease rate │ │ │ │ │
│ Δσs ₁ (%) │ 4 │ 4 │ 4 │ 8 │
│ │ │ │ │ │
│ Δσs ₂ (%) │ 3 │ 3 │ 3 │ 6 │
│ │ │ │ │ │
├───────────┼─────┼─────┼┼─────┼─────┤
│ │ │ │ │ │
│ Coercivity reduction rate │ │ │ │ │
│ ΔHc ₁ (%) │ 3 │ 4 │ 4 │ 5 │
│ │ │ │ │ │
│ ΔHc ₂ (%) │ 2 │ 2 │ 3 │ 4 │
│ │ │ │ │ │
└───────────┴─────┴─────┴┴─────┴─────┘

Table 4

┌───────────┬─────┬─────┬─────┐
│ │ Comparative Example 1 | Comparative Example 2 | Reference Example 1 |
├───────────┼─────┼─────┼─────┤
│ │ │ │ │
│Coercive force Hc (kA / m) │250.8│51.7│129.1│
│ │ │ │ │
│Square ratio [Br / Bm] │ 0.86│ 0.51│ 0.48│
│ │ │ │ │
│SFD │ 0.54│ 0.81│ 0.53│
│ │ │ │ │
├───────────┼─────┼─────┼─────┤
│ │ │ │ │
│ Saturation reduction rate │ │ │ │
│ Δσs ₁ (%) │ 8 │ 6 │ 3 │
│ │ │ │ │
│ Δσs ₂ (%) │ 7 │ 4 │ 2 │
│ │ │ │ │
├───────────┼─────┼─────┼─────┤
│ │ │ │ │
│ Coercivity reduction rate │ │ │ │
│ ΔHc ₁ (%) │ 8 │ 1 │ 4 │
│ │ │ │ │
│ ΔHc ₂ (%) │ 7 │ 0.5 │ 4 │
│ │ │ │ │
└───────────┴─────┴─────┴─────┘

From the results in Table 3 above, it can be seen that each of the magnetic tapes of Examples 1 to 4 has excellent magnetic properties and excellent storage stability (corrosion resistance).

On the other hand, from the results of Table 4 above, unless the re-deposition treatment is performed after the formation of the Fe ₁₆ N ₂ phase as in Comparative Example 1, the storage stability is particularly deteriorated. Moreover, when the re-deposition process after the nitriding process is performed before the nitriding process as in Comparative Example 2, the initial magnetic characteristics are inferior. Furthermore, it can be seen that when the heat treatment temperature after the re-deposition treatment becomes too high as in Reference Example 1, the initial magnetic properties are particularly inferior.

Claims (6)

Iron and nitrogen at least as constituent elements, containing at least one element of rare earth metal elements and aluminum , and at least an Fe ₁₆ N ₂ phase, the nitrogen content with respect to iron being 1.0 to 20.0 atoms % and is, in the production of granular or iron nitride-based magnetic powder as the elliptical range of the average size of the particles is 5 to 20 nm, after the generation of the Fe ₁₆ N ₂ phase, rare earth metal element, of aluminum of at least one An inorganic compound containing an element or / and an organic carboxylic acid, an organic sulfonic acid, an organic phosphoric acid, or an organic compound comprising an esterified product or an amidated product of these acids is applied to the particle surface. Manufacturing method of iron nitride magnetic powder.

The heat treatment is performed at 30 to 150 ° C in an inert gas or a mixed gas of an oxygen gas and an inert gas after performing an adhesion treatment for depositing an inorganic compound and / or an organic compound on the particle surface. 2. A method for producing an iron nitride magnetic powder according to 1.

Claim 1 or 2 obtained by the method according to the iron and nitrogen and at least an element, rare earth element contains at least one element selected from aluminum, and comprises at least a Fe ₁₆ N ₂ phase, An iron nitride magnetic powder having a granular or elliptical shape in which the content of nitrogen with respect to iron is 1.0 to 20.0 atomic% and the average particle size is in the range of 5 to 20 nm.

The saturation magnetization is 80 to 120 Am ² / kg (80 to 120 emu / g), the coercive force is 160 to 280 kA / m (2,000 to 3,500 Oe), and it is kept for 7 days in an atmosphere of 60 ° C. and 90% RH. After that, the saturation magnetization reduction rate (Δσs ₁ ) is 0.1 to 11%, the coercive force reduction rate (ΔHc ₁ ) is 0.1 to 10%, and when 7 days have passed since the seventh day as a reference. The iron nitride magnetic powder according to claim 3, wherein the saturation magnetization reduction rate (Δσs ₂ ) is 0.1 to 10% and the coercive force reduction rate (ΔHc ₂ ) is 0.1 to 9%.

A magnetic recording medium using the iron nitride magnetic powder according to claim 3.

The coercive force is 180 to 300 kA / m (2,300 to 3,800 Oe), and the saturation magnetization reduction rate (Δσs ₁ ) after being held in an atmosphere of 60 ° C. and 90% RH for 7 days is 0.01 to 10%. The coercive force reduction rate (ΔHc ₁ ) is 0.01 to 5%, and the saturation magnetization reduction rate (Δσs ₂ ) is 0.01 to 8% when 7 days have passed since the seventh day as a reference. The magnetic recording medium according to claim 5, wherein the magnetic force reduction rate (ΔHc ₂ ) is 0.01 to 4%.