JP2008071425A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a magnetic recording medium which has an excellent short wave recording characteristic with higher output, by using a magnetic powder which has a small particle size, extremely high coercive force, and coercive force distribution most suitable for high density recording. <P>SOLUTION: The magnetic recording medium comprises a magnetic layer including a magnetic powder and bond on a non magnetic base, and uses the magnetic powder which includes at least iron and nitride as constituent elements, includes at least Fe<SB>16</SB>N<SB>2</SB>phase or Fe<SB>8</SB>N phase and a ferrite phase, and has a diffraction peak corresponding to the ferrite phase (311) within 35.5° to 39° in X-ray diffraction measurement by using Kα1 ray of copper as a radiation source for making the magnetic layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a coating-type magnetic recording medium suitable for high-density magnetic recording, and more specifically to a magnetic tape such as a digital video tape and a computer backup tape.

  In a coating-type magnetic recording medium in which a magnetic layer containing magnetic powder and a binder is coated on a non-magnetic support, as recording / reproducing systems shift from analog to digital, further recording Improvement in density is required. In particular, the demand for video tapes for high recording density and backup tapes for computers is increasing year by year.

  In order to cope with the short wavelength recording indispensable for improving the recording density, it is necessary to reduce the thickness loss at the time of recording. For this purpose, it is effective to reduce the thickness of the magnetic layer. As a reproducing magnetic head for reading data and signals recorded on such a high recording density medium, a magnetoresistive effect type that can obtain a higher output than a conventional magnetic induction type magnetic head (MIG head). A magnetic head (MR head) is generally used.

  In addition, attempts have been made to improve and improve various characteristics of magnetic powders toward higher recording density of magnetic recording media. For example, in order to reduce noise, the magnetic powder is made finer year by year, and at present, acicular metal magnetic powder having a particle diameter of about 100 nm is put into practical use. Furthermore, in order to prevent a decrease in output due to demagnetization at the time of short wavelength recording, the coercive force is increased year by year, and a coercive force of about 238.9 A / m (3000 Oe) is realized by iron-cobalt alloying. (See Patent Documents 1 to 3).

  However, in the magnetic recording medium using the needle-like magnetic particles as described above, since the coercive force depends on the shape of the magnetic particles, it is difficult to further reduce the particle size from the 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-based granular magnetic powder, for example, a granular or elliptical rare earth-iron-boron-based magnetic powder as a magnetic powder completely different from the acicular magnetic powder has been proposed. (See Patent Document 4). This 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).

Further, the average particle size in which the outer layer portion contains at least one element selected from rare earth elements and / or silicon and aluminum, while the inner layer portion containing iron and nitrogen as a constituent element contains the Fe ₁₆ N ₂ phase. There, a magnetic recording medium using a spherical or oval magnetic powder of 5 to 50 nm, a diffraction peak height corresponding to (202) face of the Fe ₁₆ N ₂ phase is a, the Fe ₁₆ N ₂ phase (220) A / B is in the range of 1.0 to 2.0, where B is the height of the diffraction peak generated by overlapping the diffraction peak corresponding to the plane and the diffraction peak corresponding to the (110) plane of α-Fe. And a magnetic recording medium characterized in that C / A is 0.5 or less, where C is the height of the diffraction peak corresponding to the (111) plane of the Fe ₄ N phase. (See Patent Documents 6 and 7).

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) JP 2004-273094 A (page 4) Japanese Patent Laying-Open No. 2005-63525 (page 5)

However, since the rare earth-iron-boron magnetic powder of 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, It is difficult to improve the magnetic characteristics (for example, the holding force) while maintaining the optimum dispersibility and chemical stability for the magnetic recording medium. Further, the iron nitride magnetic powder of Patent Document 5 has a particle size that is too large (in the Examples in the same document, a BET specific surface area of 10 to 22 m ² / g is shown), and the purpose is to reduce noise. It is not suitable for high density magnetic recording.

On the other hand, in the magnetic powder having the Fe ₁₆ N ₂ phase as the main phase described in Patent Document 6, the coexistence of high average coercive force and micronization is achieved, but with micronization. Since the coercive force distribution is wide, it is difficult to obtain a higher output.

Moreover, in the magnetic powder combining the Fe ₁₆ N ₂ phase, α-Fe phase and Fe ₄ N phase described in Patent Document 7, a high coercivity Fe ₁₆ N ₂ phase and a highly saturated magnetization α-Fe phase By combining the two, it is possible to realize a magnetic characteristic that balances the two materials, but since the coercive force distribution and the saturation magnetization distribution are widened, it is difficult to further increase the output.

  In light of such circumstances, the present invention uses a magnetic powder having a very small particle size, an extremely high coercive force, and an optimum coercive force distribution for high-density recording, thereby further increasing the output. The purpose is to obtain a magnetic recording medium having excellent short wavelength recording characteristics.

As a result of intensive studies to achieve the above object, the inventors of the present invention have at least iron and nitrogen as constituent elements and include an Fe ₁₆ N ₂ phase or an Fe ₈ N phase and a ferrite phase, and the source of copper In the X-ray diffraction measured using the Kα1 line, the magnetic powder having a diffraction peak corresponding to the (311) plane of the ferrite phase at 35.5 ° to 39 ° is an extremely high coercive force and optimum coercivity for high-density recording. It has been found to have a magnetic distribution and a saturation magnetization. By using this magnetic powder as a constituent material of the magnetic layer, it is possible to realize an ultra-thin magnetic layer that does not have a problem of output reduction due to recording demagnetization. As a result, high output can be achieved and excellent. It was found that short wavelength recording characteristics can be obtained.

The present invention has been completed based on such knowledge, and includes a nonmagnetic support and a magnetic layer containing magnetic powder and a binder provided on one surface side of the nonmagnetic support. In a magnetic recording medium having at least iron and nitrogen as constituent elements and including an Fe ₁₆ N ₂ phase or an Fe ₈ N phase and a ferrite phase, ferrite is measured by X-ray diffraction measured using a copper Kα1 line as a radiation source. The magnetic powder having a diffraction peak corresponding to the (311) plane of the phase at 35.5 ° to 39 ° is used as the magnetic powder in the magnetic layer. In this case, it is preferable to use a magnetic powder having an average particle size of 5 to 30 nm for the reason described later. The reason why the copper Kα1 ray was used as the radiation source in the above X-ray diffraction measurement is that it has an appropriate wavelength for the crystal structure analysis of the present magnetic powder, but the radiation source is not particularly limited. However, if a source other than the copper Kα1 line is used, it is necessary to separately correct the analysis peak position. For correction, for example, Bragg's formula (2d × sin θ = nλ, d: lattice spacing, λ: X-ray wavelength, θ: diffraction angle, n: order) can be used.

In addition, the inventors of the present invention have found that the ferrite phase is (311) in the X-ray diffraction measured using the Kα1 line of copper as the radiation source, including at least the Fe ₁₆ N ₂ phase or the Fe ₈ N phase and the Fe ₃ N phase. It has also been found that a magnetic recording medium having a small high coercive force component and suitable for high output can be obtained by using a magnetic powder having a diffraction peak corresponding to the surface of 35.5 ° to 39 °.

Further, in an X-ray diffraction including at least an Fe ₁₆ N ₂ phase or an Fe ₈ N phase and an α-Fe phase and measured using a copper Kα1 line as a radiation source, a diffraction peak corresponding to the (311) plane of the ferrite phase It was also found that a magnetic recording medium having high saturation magnetization and excellent short wavelength recording characteristics can be obtained by using a magnetic powder having an angle of 35.5 ° to 39 °.

Magnetic powder used in the present invention, that is, at least an Fe ₁₆ N ₂ phase or an Fe ₈ N phase and a ferrite phase, and corresponds to the (311) plane of the ferrite phase in X-ray diffraction measured using copper Kα1 ray The details of the mechanism in which the magnetic powder having a diffraction peak of 35.5 ° to 39 ° has high coercive force and excellent coercive force distribution are not clear, but the (112) face of the Fe ₁₆ N ₂ phase and the ferrite phase Since the distance between the (311) planes of (311) is close, by combining such two structures, the crystal structure and magnetic structure are stabilized and the anisotropic magnetic field distribution is sharpened. Are thinking. Further, it is considered that not only the Fe ₁₆ N ₂ phase but also the Fe ₃ N phase and the α-Fe phase are combined to further increase the stability of the crystal structure and the magnetic structure and improve the coercive force distribution. In any case, the present inventors have found for the first time that excellent magnetic characteristics and short wavelength recording characteristics can be obtained in a magnetic recording medium produced using the magnetic powder as described above. .

In the present invention, as the magnetic powder constituting the magnetic layer, iron and nitrogen are at least constituent elements and at least an Fe ₁₆ N ₂ phase or an Fe ₈ N phase and a ferrite phase are used, and a copper Kα1 wire is used as a radiation source. In the measured X-ray diffraction, a magnetic powder having a diffraction peak corresponding to the (311) plane of the ferrite phase at 35.5 ° to 39 ° was used. This magnetic powder can maintain a sharp coercive force distribution even when it is finely divided. As a result, the output can be further increased as compared with the prior art, and a magnetic recording medium having excellent short wavelength recording characteristics can be realized.

The present inventors have synthesized various magnetic powders and investigated the shape and magnetic anisotropy in order to improve the magnetic characteristics from a viewpoint different from the magnetic powder based on the conventional shape magnetic anisotropy. The diffraction peak corresponding to the (311) plane of the ferrite phase is 35.5 ° to 39 in X-ray diffraction measured using the Kα1 line of copper at least including the Fe ₁₆ N ₂ phase or the Fe ₈ N phase and the ferrite phase. It was found that a magnetic recording medium using magnetic powder existing at a temperature can be the most suitable magnetic recording medium for high-density recording.

In the magnetic powder used in the present invention, the ratio of the ferrite phase to the Fe ₁₆ N ₂ phase or the Fe ₈ N phase is not particularly limited, but is 20 to 75% by weight, preferably 25 to 60% by weight. If it is less than 20% by weight, the lattice matching is poor, and if it exceeds 75% by weight, the saturation magnetization and the coercive force are remarkably lowered.

The ratio of the Fe ₃ N phase to the Fe ₁₆ N ₂ phase or the Fe ₈ N phase is 0.1 to 30% by weight, preferably 0.1 to 25% by weight, and more preferably 0.1 to 20% by weight. If it is less than 0.1% by weight, it is difficult to confirm the Fe ₃ N phase, and if it exceeds 30% by weight, the saturation magnetization and the coercive force are remarkably lowered.

The ratio of the α-Fe phase to the Fe ₁₆ N ₂ phase or the Fe ₈ N phase is 0.1 to 30% by weight, preferably 0.1 to 25% by weight, and more preferably 0.1 to 20% by weight. If the amount is less than 0.1% by weight, it is difficult to confirm the α-Fe phase. If the amount is more than 30% by weight, the coercive force is greatly reduced.

The content of nitrogen with respect to iron is 1.0 to 20.0 atomic%, preferably 5.0 to 18.0 atomic%, more preferably 8.0 to 15.0 atomic%. If the amount of nitrogen is too small, the amount of Fe ₁₆ N ₂ phase formed will be small and the effect of increasing the coercive force will be small. If the amount is too large, nonmagnetic nitride will be easily formed, and the effect of increasing the coercive force will be small. Magnetization decreases excessively.

  Unlike conventional acicular particles, the iron nitride magnetic powder used in the present invention has a granular or elliptical shape. The particle size is optimally in the range of 5 to 50 nm on average for the demand for fine particles. When the average particle size is too small, the dispersibility at the time of preparing the magnetic coating material is deteriorated, and it becomes unstable thermally and the coercive force is likely to change with time. If the particle size is too large, it not only causes an increase in noise but also makes it difficult to obtain a smooth magnetic layer surface. The average particle size referred to here is obtained by measuring the particle size of a photograph taken with a transmission electron microscope (TEM) and calculating the average value of 300 particles.

In the iron nitride magnetic powder used in the present invention, the Fe ₁₆ N ₂ phase may be present inside the magnetic powder, but in order to improve the effect of surface magnetic anisotropy, it is often present in the outer layer portion of the magnetic powder. May be present.

  Next, a method for producing the iron nitride magnetic powder used in the present invention will be described. First, an iron-based oxide or hydroxide is used as a starting material. Examples include hematite, magnetite, and goethite. Although it does not specifically limit as average particle size, Usually, 5-80 nm, Preferably it is 5-50 nm, More preferably, it is 5-30 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.

  Aluminum or silicon, phosphorus, carbon, boron, magnesium, calcium, lithium, etc., or compounds composed of these elements are dissolved at the same time when the above iron-based oxide or hydroxide is produced. Alternatively, it may be produced by incorporating.

  Similarly, titanium, chromium, manganese, barium, strontium, yttrium and rare earth elements may be prepared by simultaneously dissolving and incorporating an iron compound when preparing iron-based oxide or hydroxide particles.

  Aluminum or elements such as silicon, phosphorus, carbon, boron, magnesium, calcium, and lithium, as well as titanium, chromium, manganese, barium, strontium, yttrium, and rare earth elements can be deposited on the above starting materials. . In this case, the starting material may be dispersed in an alkali or acid aqueous solution, and the compound containing the desired element may be precipitated by pH adjustment. These elements may be precipitated together or sequentially.

  Such a raw material is heated and reduced 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 250 to 600 ° C. When the reduction temperature is lower than 250 ° C., the reduction reaction does not proceed sufficiently. When the reduction temperature exceeds 600 ° C., the powder particles are easily sintered, which is not preferable.

  By performing nitriding after such heat reduction treatment, the magnetic powder containing iron and nitrogen as constituent elements of the present invention can be obtained. 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 300 ° 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, excessive nitriding energy is applied, the proportion of Fe ₄ N or Fe ₃ N phase having low crystallinity is increased, the coercive force is rather decreased, and further, the saturation magnetization is likely to be excessively decreased.

After the nitriding treatment, heat treatment is performed in a temperature range of 100 to 200 ° C. The atmosphere for the heat treatment uses an inert gas such as nitrogen gas, helium gas, argon gas or carbon dioxide, but a reducing gas such as hydrogen or carbon monoxide or a mixed gas thereof may be used. The production ratio of Fe ₃ N and α-Fe can be adjusted to an arbitrary ratio in the nitriding process or the heat treatment process.

  Unlike the conventional acicular magnetic powder based only on the shape magnetic anisotropy, the iron nitride-based magnetic powder in the present invention has a large magnetocrystalline anisotropy, and even in a granular shape, it is unidirectional. It is thought that a large coercive force is expressed.

  By making this magnetic material fine particles having an average particle size of 5 to 30 nm as described above, a high coercive force and appropriate saturation magnetization are exhibited within a range in which recording and erasing can be performed with a magnetic head, and a thin layer region (for example, a thickness) As a coating type magnetic recording medium (300 nm or less), excellent electromagnetic conversion characteristics are exhibited. Thus, in the magnetic powder used in the present invention, the saturation magnetization, coercive force, coercive force distribution, particle size, and particle shape are all suitable for obtaining a thin magnetic layer.

  The magnetic recording medium of the present invention is produced by applying a magnetic coating material in which the above iron nitride magnetic powder and a binder are dispersed and mixed in a solvent to a nonmagnetic support and drying to form a magnetic layer. it can. Prior to the formation of the magnetic layer, an undercoat containing 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. A magnetic layer may be formed.

  The magnetic recording medium of the present invention usually comprises a nonmagnetic support, an undercoat layer provided on one surface of the nonmagnetic support, a magnetic layer provided on the undercoat layer, and the other of the nonmagnetic support. And a back coat layer provided on the surface. As the nonmagnetic support, conventionally used nonmagnetic supports for magnetic recording media can be used. For example, the thickness of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide, etc. is 2 to 15 μm, especially 2 to 7 μm. A plastic film is preferably used.

  The thickness of the magnetic layer is preferably a thin layer of 300 nm or less, particularly preferably 10 to 300 nm, more preferably 10 to 250 nm, and more preferably 10 to 200 nm in order to avoid a decrease in output due to demagnetization, which is an essential problem in longitudinal recording. Is most preferred. If it 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 saturation of the MR head. If it is less than 10 nm, it is difficult to obtain a uniform magnetic layer. In a preferred embodiment of the magnetic recording medium of the present invention, since the magnetic powder has an average particle size of 5 to 30 nm and is very fine granular or elliptical, an extremely thin magnetic layer thickness that is almost impossible with conventional acicular magnetic powder is also obtained. Can be realized.

  In the case of a magnetic tape, the coercive force in the longitudinal direction of the magnetic layer is 79.6 to 318.4 kA / m (1,000 to 4,000 Oe), preferably 119.4 to 318.4 kA / m (1,500 to 4,000 Oe). If the recording wavelength is shorter than 79.6 kA / m, the output is likely to decrease due to demagnetization, and if it exceeds 318.4 kA / m, recording with a magnetic head becomes difficult. The squareness ratio (Br / Bm) in the longitudinal direction is usually 0.6 to 0.9, particularly preferably 0.8 to 0.9. The product of the saturation magnetic flux density and the thickness in the longitudinal direction is 0.001 to 0.1 μTm, preferably 0.0015 to 0.05 μTm. If it is less than 0.001 μTm, the reproduction output is small even when an MR head is used, and if it exceeds 0.1 μTm, it tends to be difficult to obtain a high output in the intended short wavelength region. When the MR head is used when the average surface roughness Ra of the magnetic layer is 1.0 to 3.2 nm, the contact with the MR head is improved, and the reproduction output when the MR head is used is preferably high. .

  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 from 0.1 to 3.0 μm, more preferably from 0.15 to 2.5 μm. If the thickness is less than 0.1 μm, the durability of the magnetic tape may be deteriorated. If the thickness exceeds 3.0 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 per roll. The length becomes shorter and the storage capacity becomes smaller. The undercoat 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. The undercoat layer can contain carbon black such as acetylene black, furnace black, and thermal black for the purpose of improving conductivity.

  Next, the binder and lubricant used for the magnetic layer and the undercoat layer will be described. The binder used in the undercoat layer and the magnetic layer includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride- A combination of at least one selected from vinyl chloride-based resins such as vinyl acetate-maleic anhydride copolymer, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer, nitrocellulose, epoxy resin, and the like, and a polyurethane resin is preferable. used. In particular, it is preferable to use a vinyl chloride resin and a polyurethane resin in combination. Among them, it is most preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer 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 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. Particularly, 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 bonding with a functional group contained in the binder. 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.

  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 these, it is good to use together C10 or more (preferably 12-30) fatty acid and fatty acid ester of melting | fusing point 35 degrees C or less (more preferably 10 degrees C or less).

  The backcoat layer is not an essential component, but in the case of a magnetic tape, it is desirable to form the backcoat layer on the surface opposite to the magnetic layer forming surface of the nonmagnetic support. 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 is less than 0.2 μm, the effect of improving the running performance is insufficient. If the thickness exceeds 0.8 μm, the total thickness of the tape is increased and the storage capacity per roll is reduced. The back coat layer contains carbon black such as acetylene black, furnace black, and thermal black.

  In the preparation of the magnetic paint, the undercoat paint, and the back coat paint, 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.

  In preparing the magnetic paint, undercoat paint, and back coat paint, conventionally known paint production processes can be used, and it is particularly preferable to use a kneading process or a primary dispersion process using a kneader. 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.

  Further, when applying a magnetic paint, an undercoat paint, or a backcoat paint on a nonmagnetic support, conventionally known coating methods such as gravure coating, roll coating, blade coating, and extrusion coating are used. The undercoating paint and magnetic coating application methods include a sequential multi-layer coating method in which a non-magnetic support is coated with a base coating and dried, and then a magnetic coating is applied. A simultaneous multi-layer coating method in which an undercoating paint and a magnetic coating are simultaneously applied ( Either 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 undercoat paint is wet.

[Example]
Examples of the present invention will be described below. In the following, “parts” means parts by weight.

(A) Production of iron nitride magnetic powder:
10 parts of magnetite particles having an average particle size of 16 nm, which is nearly spherical in shape, were dispersed in 500 parts of water for 30 minutes using an ultrasonic disperser. To this dispersion, 1.3 parts of yttrium nitrate and 4.7 parts of aluminum chloride were added and dissolved, and stirred for 30 minutes. Separately, 0.45 parts of sodium hydroxide was dissolved in 100 parts of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, the mixture was further stirred for 1 hour. By this treatment, hydroxides of yttrium and aluminum were deposited on the surface of the magnetite particles. This was washed with water, filtered, and dried at 90 ° C. to obtain a powder deposited on the surface of the magnetite particles.

  The powder deposited on the surface of the magnetite particles in this manner was heated and reduced at 450 ° C. for 2 hours in a hydrogen stream to obtain an yttrium-aluminum-iron-based magnetic powder. Next, the temperature was lowered to 150 ° C. over about 1 hour in a state of flowing hydrogen gas. When the temperature reached 150 ° C., the gas was switched to ammonia gas, and nitriding was performed for 30 hours while maintaining the temperature at 150 ° C. Thereafter, the ammonia gas was switched to argon gas and held for 30 minutes. Thereafter, the temperature was raised from 150 ° C. to 160 ° C., and then heat treatment was performed for 1 hour. Thereafter, the temperature was lowered from 160 ° C. to 80 ° C., and at 80 ° C., the argon gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours. Next, the temperature was lowered from 80 ° C. to 30 ° C. in a state where the mixed gas was flowed, and the mixture was taken out into the air.

The iron nitride magnetic powder thus obtained was measured for its yttrium and aluminum contents with a high frequency inductively coupled plasma (ICP) emission spectrometer, and found to be 2.5 atomic% and 10. It was 8 atomic%. Further, a profile showing a mixed phase of Fe ₁₆ N ₂ phase (or Fe ₈ N phase), Fe ₃ N phase and oxide phase was obtained from the X-ray diffraction pattern. A diffraction peak corresponding to the (311) plane of the oxide phase (ferrite phase) was observed around 37 °.

Furthermore, 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 15 nm. Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1270 kA / m (16 kOe) was 85.2 Am ² / kg (85.2 emu / g), and the coercive force was 226.9 kA / m (2,850). Oersted).

(B) Production of magnetic tape:
The following undercoat paint components were kneaded with a kneader and then dispersed in a sand mill with a residence time of 60 minutes. To this, 6 parts of polyisocyanate was added, followed by stirring and filtration to prepare an undercoat paint. Separately, the following magnetic coating component (1) was kneaded with a kneader, dispersed in a sand mill with a residence time of 45 minutes, and the following magnetic coating component (2) was added thereto and mixed.

<Undercoat paint component>
Iron oxide powder (average particle size: 55 nm) 70 parts Aluminum oxide powder (average particle diameter: 80 nm) 10 parts Carbon black (average particle diameter: 25 nm) 20 parts Vinyl chloride-hydroxypropyl methacrylate copolymer resin 10 parts (Contained -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin 5 parts (containing -SO ₃ Na group: 1.0 × 10 ^-4 eq / g)
・ Methyl ethyl ketone 130 parts ・ Toluene 80 parts ・ Myristic acid 1 part ・ Butyl stearate 1.5 parts ・ Cyclohexanone 65 parts

<Magnetic paint component (1)>
- the yttrium prepared in (A) - vinyl iron nitride-based magnetic powder 100 parts chloride - hydroxypropyl acrylate copolymer resin 8 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 eq / g)
Polyester polyurethane resin 4 parts (contained -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 ・ Myristic acid 1.5 parts ・ Methyl ethyl ketone 133 parts ・ Toluene 100 parts

<Magnetic paint component (2)>
-Stearic acid 1.5 parts-Polyisocyanate 4 parts ("Coronate L" manufactured by Nippon Polyurethane Industry Co., Ltd.)
・ Cyclohexanone 133 parts ・ Toluene 33 parts

  Dry the above-mentioned undercoat paint onto a 6-μm thick polyethylene naphthalate film (105 ° C., 30 minutes thermal shrinkage ratio of 0.8% in the vertical direction and 0.6% in the horizontal direction) as a nonmagnetic support. The undercoat layer after the calendering is applied so that the thickness of the undercoat layer is 2 μm, and the magnetic coating is further applied thereon so that the thickness of the magnetic layer after the magnetic field orientation treatment, drying and calendering is 90 nm. It was applied to.

  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 is prepared by dispersing the following back coat paint components in a sand mill with a residence time of 45 minutes, adding 8.5 parts of polyisocyanate, and stirring and filtering.

<Back coat paint component>
-Carbon black (average particle size: 25 nm) 40.5 parts-Carbon black (average particle size: 370 nm) 0.5 parts-Barium sulfate 4.05 parts-Nitrocellulose 28 parts-Polyurethane resin (containing -SO ₃ Na group) ) 20 parts ・ Cyclohexanone 100 parts ・ Toluene 100 parts ・ Methyl ethyl ketone 100 parts

  The magnetic sheet thus obtained was mirror-finished with a 5-stage calendar (temperature: 70 ° C., linear pressure: 150 kg / cm), and this was wound on a sheet core at 60 ° C. and 40% RH for 48 hours. Aged. Then, the magnetic layer surface was polished with a ceramic wheel (rotation measure + 150%, winding angle 30 °) while cutting at 1/2 inch width and running at 100 m / min, and a magnetic tape having a length of 609 m. Was made. This magnetic tape was incorporated into a cartridge to obtain a computer tape.

  A magnetic powder and a magnetic tape were produced in the same manner as in Example 1 except that the heat treatment temperature after nitriding was changed from 160 ° C. to 170 ° C. in the manufacture of the iron nitride magnetic powder, and this was incorporated into a cartridge to be used as a computer tape. It was.

The iron nitride magnetic powder thus obtained was measured for its yttrium and aluminum contents with a high frequency inductively coupled plasma (ICP) emission spectrometer, and found to be 2.6 atomic% and 10. It was 8 atomic%. Further, a profile showing a mixed phase of Fe ₁₆ N ₂ phase (or Fe ₈ N phase), Fe ₃ N phase and oxide phase was obtained from the X-ray diffraction pattern. A diffraction peak corresponding to the (311) plane of the oxide phase (ferrite phase) was observed around 38 °.

Furthermore, 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 15 nm. Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) was 80.7 Am ² / kg (80.7 emu / g), and the coercive force was 215.8 kA / m (2710). Oersted).

  In the production of iron nitride magnetic powder, magnetic powder and magnetic tape were produced in the same manner as in Example 1 except that the reduction temperature was changed from 450 ° C. to 550 ° C. in the production of the magnetic tape, and this was incorporated into the cartridge. A computer tape was obtained.

The iron nitride magnetic powder thus obtained was measured for its yttrium and aluminum contents with a high frequency inductively coupled plasma (ICP) emission spectrometer, and found to be 2.5 atomic% and 10. It was 7 atomic%. Also, obtained from X-ray diffraction pattern, Fe ₁₆ N ₂ phase (or Fe ₈ N phase) and alpha-Fe phase, a profile indicating the mixed phase of the oxide phase. A diffraction peak corresponding to the (311) plane of the oxide phase (ferrite phase) was observed around 36 °.

Furthermore, 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. Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1270 kA / m (16 kOe) is 92.5 Am ² / kg (92.5 emu / g), and the coercive force is 217.4 kA / m (2,730). Oersted).

  10 parts of magnetite particles having an average particle diameter of 16 nm were dispersed in 500 parts of water for 30 minutes using an ultrasonic disperser. To this dispersion, 1.3 parts of yttrium nitrate was added and dissolved, and stirred for 30 minutes. Separately, 0.4 part of sodium hydroxide was dissolved in 100 cc of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, the mixture was further stirred for 1 hour. 2.1 parts of sodium silicate was dissolved in the dispersion of magnetite particles coated with the yttrium hydroxide and stirred for 30 minutes. Separately, 200 parts of a 0.1N nitric acid aqueous solution was prepared. This aqueous nitric acid solution was added dropwise over about 1 hour so that the pH of the dispersion was 7.0, and after completion of the addition, the mixture was further stirred for 3 hours. By this treatment, a compound of yttrium hydroxide and silicon was deposited on the magnetite surface. This was washed with water, filtered, and dried at 90 ° C. to obtain a powder deposited on the surface of the magnetite particles.

  This powder was subjected to hydrogen reduction, nitriding in ammonia and heat treatment in the same manner as in Example 1 to obtain an yttrium-silicon based iron nitride magnetic powder.

The iron nitride magnetic powder thus obtained was 2.4 atomic% and 11.0 atomic%, respectively, based on Fe, when the yttrium and silicon contents were measured by fluorescent X-rays. Further, a profile showing a mixed phase of Fe ₁₆ N ₂ phase (or Fe ₈ N phase), Fe ₃ N phase and oxide phase was obtained from the X-ray diffraction pattern. A diffraction peak corresponding to the (311) plane of the oxide phase (ferrite phase) was observed around 37 °.

Furthermore, 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 15 nm. With respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1270 kA / m (16 kOe) was 85.7 Am ² / kg (85.7 emu / g), and the coercive force was 230.9 kA / m (2900 Oersted). It was.

  A magnetic tape was produced in the same manner as in Example 1 except that the above iron nitride magnetic powder was used in producing the magnetic tape, and this was incorporated into a cartridge to obtain a computer tape.

[Comparative Example 1]
In the production of iron nitride-based magnetic powder, the temperature is lowered from 150 ° C. to 80 ° C. after nitriding without performing the heat treatment after nitriding, and at 80 ° C., the argon gas is switched to a mixed gas of oxygen and nitrogen for 2 hours. An iron nitride magnetic powder was obtained in the same manner as in Example 1 except that the treatment was performed.

The iron nitride magnetic powder thus obtained was measured for its yttrium and aluminum contents with a high frequency inductively coupled plasma (ICP) emission spectrometer, and found to be 2.4 atomic% and 10.9%, respectively, with respect to Fe. Atomic%. Further, a profile showing a mixed phase of Fe ₁₆ N ₂ phase (or Fe ₈ N phase), Fe ₃ N phase and oxide phase was obtained from the X-ray diffraction pattern. A diffraction peak corresponding to the (311) plane of the oxide phase (ferrite phase) was observed around 35 °.

Furthermore, 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 15 nm. For this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1270 kA / m (16 kOe) was 87.3 Am ² / kg (87.3 emu / g) and the coercive force was 261.1 kA / m (2800 Oersted). It was.

  A magnetic tape was produced in the same manner as in Example 1 except that the above iron nitride magnetic powder was used in producing the magnetic tape, and this was incorporated into a cartridge to obtain a computer tape.

[Comparative Example 2]
In the production of iron nitride-based magnetic powder, the temperature is lowered from 150 ° C. to 80 ° C. after nitriding without performing the heat treatment after nitriding, and at 80 ° C., the argon gas is switched to a mixed gas of oxygen and nitrogen for 2 hours. An iron nitride magnetic powder was obtained in the same manner as in Example 4 except that the treatment was performed.

The thus obtained iron nitride magnetic powder was measured for its yttrium and silicon contents by fluorescent X-ray, and was 2.5 atomic% and 10.8 atomic%, respectively, with respect to Fe. Further, a profile showing a mixed phase of Fe ₁₆ N ₂ phase (or Fe ₈ N phase), Fe ₃ N phase and oxide phase was obtained from the X-ray diffraction pattern. A diffraction peak corresponding to the (311) plane of the oxide phase (ferrite phase) was observed around 35 °.

Furthermore, 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 15 nm. With respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1270 kA / m (16 kOe) was 88.0 Am ² / kg (88.0 emu / g), and the coercive force was 229.3 kA / m (2880 Oersted). It was.

  A magnetic tape was produced in the same manner as in Example 1 except that the above iron nitride magnetic powder was used in producing the magnetic tape, and this was incorporated into a cartridge to obtain a computer tape.

<Evaluation of magnetic properties>
About each magnetic tape of said Examples 1-4 and Comparative Examples 1-2, as a magnetic characteristic, the product of longitudinal coercive force and coercive force distribution, squareness ratio, saturation magnetic flux density, and magnetic layer thickness is measured, Further, the electromagnetic conversion characteristics were measured in the following manner. These results are shown in Table 1. In the table, for reference, the saturation magnetization and the coercive force of the magnetic powder used for the production of each magnetic tape are also shown. Moreover, the diffraction peak in the table means a diffraction peak corresponding to the (311) plane of the oxide phase (ferrite phase).

<Measurement of electromagnetic conversion characteristics>
As an electromagnetic conversion characteristic, an LTO drive manufactured by Hewlett-Packard Company was used, and after running 5 times under the conditions of 40 ° C. and 5% RH, a random data signal with the shortest recording wavelength of 0.33 μm was recorded, and the output from the reproducing head was The relative value (dB) was determined by reading and using the value of Comparative Example 1 as the reference (0).

As is clear from the results in Table 1, each of the magnetic powders according to Examples 1 to 4 shows a sharp coercive force distribution and high C / N characteristics as compared with the magnetic powders according to Comparative Examples 1 and 2. Have. The details of the mechanism in which the magnetic powder having a diffraction peak corresponding to the (311) plane of the ferrite phase at 35.5 ° to 39 ° has a sharp coercive force distribution and excellent electromagnetic conversion characteristics are not clear. Since the spacing between the (112) face of the Fe ₁₆ N ₂ phase and the (311) face of the ferrite phase is close, combining these two structures stabilizes the crystal structure and magnetic structure, and makes anisotropy It is estimated that the magnetic field distribution has become sharper. In addition, combining the Fe ₃ N phase and the Fe phase is considered to increase the stability of the crystal structure and the magnetic structure and further improve the coercive force distribution. It has been found for the first time by the present inventors that satisfactory short wavelength recording characteristics can be obtained by satisfying the constituent requirements of such magnetic powder and magnetic recording medium.

Claims (3)

A non-magnetic support;
A magnetic recording medium having a magnetic layer containing a magnetic powder and a binder provided on one surface side of the nonmagnetic support,
The magnetic powder includes at least iron and nitrogen as constituent elements and includes an Fe ₁₆ N ₂ phase or an Fe ₈ N phase and a ferrite phase, and a ferrite phase in X-ray diffraction measured using a copper Kα1 line as a radiation source. A magnetic recording medium comprising a magnetic powder having a diffraction peak corresponding to the (311) plane of 35.5 ° to 39 °. The magnetic recording medium according to claim 1, wherein the magnetic powder contains an Fe ₃ N phase.   The magnetic recording medium according to claim 1, wherein the magnetic powder contains an α-Fe phase.