JP2007305208A - Magnetic recording medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in high density recording characteristics, practical durability and electromagnetic transducing characteristics by solving a problem of reduction of a resistance value of an MR head and to provide its manufacturing method. <P>SOLUTION: In the magnetic recording medium having at least a magnetic layer containing a ferromagnetic powder, a binder, an abrasive and an organic compound containing phosphorus (P) on a non-magnetic support, the ferromagnetic powder is hexagonal ferrite powder or iron nitride-based powder and the magnetic layer contains 1 to 5 pts.mass abrasive to 100 pts.mass ferromagnetic powder. In the manufacturing method of the magnetic recording medium having a liquid preparing step for preparing a magnetic layer liquid and an application step for applying the magnetic layer liquid on the non-magnetic support, dispersion of the ferromagnetic powder in the binder, addition and mixing of the organic compound containing phosphorus (P) and addition and mixing of a fatty acid ester are performed in this order in the liquid preparing step. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium excellent in high-density recording characteristics, practical durability, and electromagnetic conversion characteristics, and a manufacturing method thereof.

  Magnetic recording technology enables other recordings such as the ability to repeatedly use media, the ease of digitizing signals, the construction of a system in combination with peripheral devices, and the simple modification of signals. Since it has excellent features not found in the system, it has been widely used in various fields including video and computer applications.

  In order to meet the demands for downsizing equipment, improving the quality of recording and playback signals, extending the recording time, and increasing the recording capacity, the recording density, reliability, and durability of the recording medium are further increased. There has always been a desire for improvement.

  For example, in order to respond to the practical application of a digital recording system that realizes improvements in sound quality and image quality, and the development of a recording system compatible with high-definition TV, it is possible to record and play back shorter wavelength signals than in conventional systems, and the head and medium Even when the relative speed of the magnetic recording medium increases, a magnetic recording medium excellent in reliability and durability is required. Also, it is desired that a large-capacity digital recording medium be developed in order to store an increasing amount of data for computer use. Even in the field of magnetic disks, the capacity of data to be handled is increasing rapidly, and it is desired to increase the capacity of flexible disks (FD). A high-capacity disk using a ferromagnetic metal fine powder excellent in high-density recording characteristics has been put into practical use with a high-density FD of 100 MB or more, but a system with a larger capacity and a higher transfer speed is required.

    In order to achieve a high recording density of a magnetic recording medium, a shortening of the recording signal wavelength and a narrowing of the track width of the reproducing head have been strongly promoted. When the length of the signal recording area becomes comparable to the size of the magnetic material used, a clear magnetization transition state cannot be created, and recording becomes virtually impossible. For this reason, it is necessary to develop a magnetic material having a sufficiently small particle size with respect to the shortest wavelength to be used, and the finer magnetic material has been directed for many years.

In recent years, means for transmitting terabyte-class information at a high speed have been remarkably developed, and images and data transfer with enormous information have become possible, while advanced techniques for recording, reproducing and storing them have been required. It has come to be. However, with the improvement of the technical level, both the recording / reproducing apparatus and the magnetic recording medium are required to have a higher recording capacity.
Regarding magnetic tape, there are various uses such as audio tape, video tape, computer tape, etc. Especially in the field of data backup tape, with the increase in capacity of the hard disk to be backed up, several 10 to 500 GB per volume. Those with recording capacity have been commercialized.
In the future, a large-capacity backup tape exceeding 1 TB has been proposed, and its high recording capacity is indispensable.

  Further, in order to improve the running durability of the magnetic tape, several techniques for adding a phosphorus (P) -containing organic compound such as a rust preventive have been proposed. For example, Patent Document 1 discloses a magnetic recording medium containing a ferromagnetic powder and a phosphorus (P) -containing organic compound. Patent Document 2 discloses a magnetic recording medium in which a metal element on the surface of a ferromagnetic metal powder in a magnetic layer, its content, crystallite size, and abrasive content are specified and a rust preventive agent is added. ing. Patent Documents 3 to 5 disclose magnetic recording media in which a phosphorus (P) -containing organic compound is added to a lower layer between a nonmagnetic support and a magnetic layer. Patent Documents 6 and 7 disclose magnetic recording media in which the surface of magnetic particles in a magnetic layer is treated with phenylphosphonic acid or the like.

  On the other hand, in recent years, a reproducing head based on an operating principle of magnetoresistance (MR) has been proposed and started to be used in a hard disk or the like, and Patent Document 8 proposes application to a magnetic tape. MR heads can produce a reproduction output several times that of induction type magnetic heads and do not use induction coils, so that equipment noise such as impedance noise is greatly reduced. It has become possible to obtain an S / N ratio.

However, in a high-density recording / reproducing system using an MR head, it has become clear that the electromagnetic conversion characteristics gradually deteriorate as the medium travels. This phenomenon occurs similarly even when the magnetic recording media disclosed in Patent Documents 1 to 7 are used. According to the study by the present inventor, it has been found that the phenomenon in which the electromagnetic conversion characteristics deteriorate with time due to the running of the medium is caused by a decrease in the resistance value of the MR head.
Japanese Patent Laid-Open No. 1-189025 Japanese Patent Laid-Open No. 5-73898 Japanese Patent Laid-Open No. 7-176026 JP-A-8-306032 JP 2001-351224 A JP 2002-146404 A JP 2002-146405 A JP-A-8-227517

  Accordingly, it is an object of the present invention to provide a magnetic recording medium that solves the problem of lowering the resistance value of an MR head and is excellent in high-density recording characteristics, practical durability, and electromagnetic conversion characteristics, and a method for manufacturing the same.

The present invention is as follows.
1) In a magnetic recording medium having at least a magnetic layer containing a ferromagnetic powder, a binder, an abrasive and a phosphorus (P) -containing organic compound on a nonmagnetic support.
The magnetic recording medium is characterized in that the ferromagnetic powder is a hexagonal ferrite powder or an iron nitride-based powder, and the magnetic layer contains 1 to 5 parts by mass of an abrasive with respect to 100 parts by mass of the ferromagnetic powder.
2) The magnetic recording medium as described in 1) above, wherein the ferromagnetic powder has an average plate diameter or average particle diameter of 10 nm to 40 nm.
3) The magnetic recording medium as described in 1) or 2) above, wherein the ferromagnetic powder is a hexagonal ferrite powder and the average plate ratio is 1 to 4.
4) The magnetic recording medium according to any one of 1) to 3) above, wherein the abrasive is diamond particles.
5) The magnetic recording medium as described in any one of 1) to 4) above, wherein the abrasive has an average particle diameter of 20 nm to 150 nm.
6) The phosphorus (P) -containing organic compound is at least one selected from α-naphthyl phosphate, phenyl phosphate, diphenyl phosphate, p-ethylbenzenephosphonic acid, phenylphosphonic acid, phenylphosphinic acid and esters thereof. The magnetic recording medium according to any one of 1) to 5) above, which is a seed.
7) The magnetic layer according to any one of 1) to 6) above, wherein the magnetic layer contains 1 to 15 parts by mass of a phosphorus (P) -containing organic compound with respect to 100 parts by mass of the ferromagnetic powder. recoding media.
8) The magnetic recording medium according to any one of 1) to 7) above, wherein the magnetic layer has a thickness of 20 nm to 100 nm.
9) The magnetic recording according to any one of 1) to 8) above, wherein a nonmagnetic layer containing a nonmagnetic powder and a binder is provided between the nonmagnetic support and the magnetic layer. Medium.
10) A liquid preparation step of preparing a magnetic layer liquid containing at least a ferromagnetic powder, a binder, an abrasive, a phosphorus (P) -containing organic compound and a fatty acid ester; and applying the magnetic layer liquid onto a nonmagnetic support. In a method of manufacturing a magnetic recording medium having at least a coating step of:
The liquid preparation step is performed in the order of dispersion of the ferromagnetic powder in a binder, addition / mixing of the phosphorus (P) -containing organic compound, and addition / mixing of a fatty acid ester. -9) The manufacturing method of the magnetic-recording medium in any one of.

The magnetic recording medium of the present invention specifies a ferromagnetic powder as a hexagonal ferrite magnetic powder or an iron nitride magnetic powder in a magnetic layer containing a ferromagnetic powder, a binder, an abrasive, and a phosphorus (P) -containing organic compound, The amount of abrasive is smaller than in the prior art. In the magnetic recording medium production method of the present invention, in order to achieve this reduction, preferably, in the liquid preparation step of preparing the magnetic layer liquid, the dispersion of the ferromagnetic powder, the phosphorus (P) -containing organic compound The order of addition / mixing and addition / mixing of fatty acid esters is specified. According to these aspects of the present invention, it is surprisingly possible to prevent the MR head from degrading (resistance value drop), and to obtain excellent running durability and high-density recording characteristics by improving the S / N ratio. it can. The reason for this is not clear, but the phosphorous (P) -containing organic compound suppresses the reaction between the magnetic powder and the fatty acid ester decomposition product that gradually progresses during storage, so that the presence distribution of fatty acid esters is more on the surface side. Then, since the floating state of the abrasive in the magnetic layer has changed, it is assumed that a small amount of abrasive protrudes uniformly, and that it is possible to suppress the deterioration of the MR head and to ensure running durability.
Therefore, according to the present invention, it is possible to provide a magnetic recording medium excellent in high density recording characteristics, practical durability, and electromagnetic conversion characteristics, and a method for manufacturing the same, by solving the problem of lowering the resistance value of the MR head. The magnetic recording medium of the present invention is particularly suitable for recording / reproducing using a giant magnetoresistive (GMR) head as a reproducing head.

Hereinafter, the present invention will be described in more detail.
First, each component constituting the magnetic recording medium of the present invention will be described.
[Non-magnetic support]
Nonmagnetic supports used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulosic acetate, polycarbonate, polyamide, polyimide, polyamideimide, and polysulfone. , Known films such as polyaramid, aromatic polyamide, and polybenzoxazole can be used. It is preferable to use a high-strength support such as polyethylene naphthalate or polyamide. If necessary, a laminated type support as disclosed in JP-A-3-224127 can be used to change the surface roughness of the magnetic surface and the nonmagnetic support surface. These supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like. It is also possible to apply an aluminum or glass substrate as the support of the present invention.

Of these, a polyester support (hereinafter simply referred to as polyester) is preferred. Such a polyester is a polyester composed of a dicarboxylic acid and a diol, such as polyethylene terephthalate and polyethylene naphthalate.
The main constituent dicarboxylic acid components include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylethanedicarboxylic acid, Examples thereof include cyclohexane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl thioether dicarboxylic acid, diphenyl ketone dicarboxylic acid, and phenylindane dicarboxylic acid.
Examples of the diol component include ethylene glycol, propylene glycol, tetramethylene glycol, cyclohexanedimethanol, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxyethoxyphenyl) propane, bis ( 4-Hydroxyphenyl) sulfone, bisphenol fluorene hydroxyethyl ether, diethylene glycol, neopentyl glycol, hydroquinone, cyclohexanediol and the like.
Among the polyesters having these as main constituents, terephthalic acid and / or 2,6-naphthalenedicarboxylic acid as a dicarboxylic acid component and ethylene glycol as a diol component from the viewpoint of transparency, mechanical strength, dimensional stability, etc. And / or a polyester mainly composed of 1,4-cyclohexanedimethanol is preferred.
Among them, a polyester mainly composed of polyethylene terephthalate or polyethylene-2,6-naphthalate, a copolymer polyester composed of terephthalic acid, 2,6-naphthalenedicarboxylic acid and ethylene glycol, and two or more kinds of these polyesters A polyester having a mixture as a main constituent is preferred. Particularly preferred is a polyester having polyethylene-2,6-naphthalate as a main constituent.
The polyester used in the present invention may be biaxially stretched or a laminate of two or more layers.

The polyester may be further copolymerized with other copolymerization components, or may be mixed with other polyesters. Examples of these include the dicarboxylic acid components and diol components mentioned above, or polyesters composed thereof.
In the polyester used in the present invention, an aromatic dicarboxylic acid having a sulfonate group or an ester-forming derivative thereof, a dicarboxylic acid having a polyoxyalkylene group or an ester-forming derivative thereof, in order to make it difficult for delamination during film formation. A diol having a polyoxyalkylene group may be copolymerized.
Of these, 5-sodium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 4-sodium sulfophthalic acid, 4-sodium sulfo-2,6-naphthalenedicarboxylic acid, and the like in terms of polyester polymerization reactivity and film transparency. Compounds in which sodium is substituted with other metals (for example, potassium, lithium, etc.), ammonium salts, phosphonium salts, etc., or ester-forming derivatives thereof, polyethylene glycol, polytetramethylene glycol, polyethylene glycol-polypropylene glycol copolymers and their A compound obtained by oxidizing the hydroxy groups at both ends to form a carboxyl group is preferred. The proportion of copolymerization for this purpose is preferably 0.1 to 10 mol% based on the dicarboxylic acid constituting the polyester.
For the purpose of improving heat resistance, a bisphenol compound, a compound having a naphthalene ring or a cyclohexane ring can be copolymerized. The copolymerization ratio is preferably 1 to 20 mol% based on the dicarboxylic acid constituting the polyester.

In the present invention, the method for synthesizing the polyester is not particularly limited, and can be produced according to a conventionally known polyester production method. For example, a direct esterification method in which a dicarboxylic acid component is directly esterified with a diol component. First, a dialkyl ester is used as a dicarboxylic acid component, this is transesterified with the diol component, and this is heated under reduced pressure. A transesterification method of polymerizing by removing excess diol component can be used. At this time, if necessary, a transesterification catalyst or a polymerization reaction catalyst can be used, or a heat-resistant stabilizer can be added.
In addition, anti-coloring agents, antioxidants, crystal nucleating agents, slipping agents, stabilizers, anti-blocking agents, UV absorbers, viscosity modifiers, antifoaming and clearing agents, antistatic agents, pH adjustments in each process during synthesis One or more of various additives such as an agent, a dye, a pigment, and a reaction terminator may be added.

Further, a filler may be added to the polyester. Examples of the filler include inorganic powders such as spherical silica, colloidal silica, titanium oxide, and alumina, and organic fillers such as crosslinked polystyrene and silicone resin.
Further, in order to increase the rigidity of the support, these materials can be highly stretched, or a metal, semimetal, or oxide layer thereof can be provided on the surface.

In the present invention, the thickness of the polyester as the nonmagnetic support is preferably 3 to 80 μm, more preferably 3 to 50 μm, and particularly preferably 3 to 10 μm. The center surface average roughness (Ra) of the support surface is 4 nm or less, more preferably 2 nm or less. This Ra was measured with HD2000 manufactured by WYKO.
Further, the Young's modulus in the longitudinal direction and the width direction of the nonmagnetic support is preferably 6.0 GPa or more, and more preferably 7.0 GPa or more.

  The magnetic recording medium of the present invention comprises a magnetic layer containing ferromagnetic powder and a binder on at least one surface of the nonmagnetic support, and is substantially between the nonmagnetic support and the magnetic layer. It is preferable to provide a nonmagnetic layer (lower layer) that is nonmagnetic in nature.

[Magnetic layer]
As the ferromagnetic powder contained in the magnetic layer, preferably has a volume is 1000～20000Nm ^3, further preferably 2000~8000nm ^3. By setting it within this range, it is possible to effectively suppress a decrease in magnetic characteristics due to thermal fluctuations, and to obtain good C / N (S / N) while maintaining low noise. The ferromagnetic powder is hexagonal ferrite powder or iron nitride-based powder.
Of these, hexagonal ferrite powder is preferred.
In the present invention, 50% or more of the total mass of the ferromagnetic powder is preferably hexagonal ferrite powder or iron nitride-based powder, more preferably 80% or more, and most preferably 100%.
In the case of plate-like powder, the volume is determined from the plate diameter and axial length (plate thickness) assuming that the shape is a prism (hexagonal prism in the case of hexagonal ferrite powder).
In the case of iron nitride-based powder, the volume is obtained assuming that the shape is a sphere.
As for the size of the magnetic material, an appropriate amount of the magnetic layer is peeled off. N-Butylamine is added to 30 to 70 mg of the peeled magnetic layer, sealed in a glass tube, set in a thermal decomposition apparatus, and heated at 140 ° C. for about 1 day. After cooling, the contents are taken out from the glass tube and centrifuged to separate the liquid and solids. The separated solid is washed with acetone to obtain a powder sample for TEM. This sample is photographed with a Hitachi transmission electron microscope H-9000, and the particles are photographed at a photographing magnification of 100000 times and printed on a photographic paper to obtain a total magnification of 500,000 times to obtain a particle photograph. The target magnetic material is selected from the particle photograph, the outline of the powder is traced with a digitizer, and the particle size is measured with image analysis software KS-400 made by Carl Zeiss. Measure the size of 500 particles.
In this specification, the size of powder such as a magnetic material (hereinafter referred to as “powder size”) is as follows: (1) The shape of the powder is needle-like, spindle-like, columnar (however, the height is the bottom surface) Is larger than the maximum major axis of the powder) and is represented by the length of the major axis constituting the powder, that is, the major axis length, and (2) the shape of the powder is plate-shaped to column-shaped (however, thickness to height) Is smaller than the maximum major axis of the plate surface or bottom surface), and (3) the shape of the powder is spherical, polyhedral, unspecified, etc. When the major axis constituting the powder cannot be specified, it is represented by the equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.
The average powder size of the powder is an arithmetic average of the above powder sizes, and is obtained by carrying out the measurement as described above for 500 primary particles. Primary particles refer to an independent powder without aggregation.
The average acicular ratio of the powder is determined by measuring the length of the minor axis of the powder in the above measurement, that is, the minor axis length, and calculating the arithmetic average of the values of (major axis length / minor axis length) of each powder. Point to. Here, the minor axis length is defined by the above powder size in the case of (1), the length of the minor axis constituting the powder, and in the case of (2), the thickness or height is defined respectively. In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.
When the shape of the powder is specific, for example, in the case of the definition (1) of the powder size, the average powder size is referred to as an average major axis length, and in the case of the definition (2), the average powder size Is called the average plate diameter, and the arithmetic average of (maximum major axis / thickness to height) is called the average plate ratio. In the case of definition (3), the average powder size is referred to as an average diameter (also referred to as an average particle diameter or an average particle diameter). In powder size measurement, the standard deviation / average value expressed as a percentage is defined as the coefficient of variation.

<Ferromagnetic hexagonal ferrite powder>
Examples of the ferromagnetic hexagonal ferrite powder include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and their substitutes such as Co. More specifically, magnetoplumbite type barium ferrite and strontium ferrite, magnetoplumbite type ferrite whose particle surface is coated with spinel, and magnetoplumbite type barium ferrite and strontium ferrite partially containing a spinel phase, etc. Is mentioned. In addition to predetermined atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg , Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb may be included. In general, elements such as Co—Zn, Co—Ti, Co—Ti—Zr, Co—Ti—Zn, Ni—Ti—Zn, Nb—Zn—Co, Sb—Zn—Co, and Nb—Zn are added. You can use things. Some raw materials and production methods contain specific impurities. Other preferable atoms and the content thereof are the same as those of the ferromagnetic metal powder.

The particle size of the hexagonal ferrite powder is preferably a size satisfying the above volume, but the average plate diameter is 10 to 40 nm or less, preferably 10 to 30 nm, and more preferably 15 to 25 nm.
The average plate ratio is 1 to 15, more preferably 1 to 7, and particularly preferably 1 to 4. When the average plate ratio is 1 to 15, sufficient orientation can be obtained while maintaining high filling properties in the magnetic layer, and noise increase due to stacking between particles can be suppressed. Further, the specific surface area (S _BET ) by the BET method within the above particle size range is preferably 40 m ² / g or more, more preferably 40 to 200 m ² / g, and 60 to 100 m ² / g. Is most preferred.

  The distribution of the particle plate diameter and plate thickness of the hexagonal ferrite powder is generally preferably as narrow as possible. Quantifying the particle plate diameter and plate thickness can be compared by randomly measuring 500 particles from a particle TEM photograph. In many cases, the distribution of the particle plate diameter and plate thickness is not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0.1 to 1.0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improvement process. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

The coercive force (Hc) of the hexagonal ferrite powder can be in the range of 143.3 to 318.5 kA / m (1800 to 4000 Oe), preferably 159.2 to 238.9 kA / m (2000 to 3000 Oe). ). More preferably, it is 191.0-214.9 kA / m (2200-2800 Oe).
The coercive force (Hc) can be controlled by the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element, the particle generation reaction conditions, and the like.

The saturation magnetization (σs) of the hexagonal ferrite powder is 30 to 80 A · m ² / kg (emu / g). Higher saturation magnetization (σs) is preferable, but tends to be smaller as the particles become finer. In order to improve the saturation magnetization (σs), it is well known to combine spinel ferrite with magnetoplumbite ferrite, and to select the type and amount of contained elements. It is also possible to use W-type hexagonal ferrite. When the magnetic material is dispersed, the surface of the magnetic material particles is also treated with a material suitable for the dispersion medium and the polymer. As the surface treatment agent, inorganic compounds and organic compounds are used. Typical examples of the main compound include oxides or hydroxides such as Si, Al, and P, various silane coupling agents, and various titanium coupling agents. The addition amount is 0.1 to 10% by mass with respect to the mass of the magnetic substance. The pH of the magnetic material is also important for dispersion. Usually, about 4 to 12 has optimum values depending on the dispersion medium and polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects the dispersion. Although there is an optimum value depending on the dispersion medium and the polymer, 0.01 to 2.0% is usually selected.

The hexagonal ferrite powder is manufactured by (1) mixing metal oxides that replace barium oxide, iron oxide, and iron with boron oxide as a glass-forming substance so as to have a desired ferrite composition, and then melting and quenching. A glass crystallization method for obtaining a barium ferrite crystal powder after reheating treatment after being reheated, and (2) neutralizing barium ferrite composition metal salt solution with alkali to produce by-products Hydrothermal reaction method to obtain barium ferrite crystal powder by liquid phase heating at 100 ° C. or higher after removing water, (3) neutralizing barium ferrite composition metal salt solution with alkali, by-product There is a coprecipitation method in which the product is removed and then dried, treated at 1100 ° C. or less, and pulverized to obtain a barium ferrite crystal powder. The hexagonal ferrite powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof as required. The amount thereof is 0.1 to 10% with respect to the ferromagnetic powder, and the surface treatment is preferable because the adsorption of a lubricant such as a fatty acid is 100 mg / m ² or less. The ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they do not particularly affect the characteristics.

[Iron nitride powder]
The average particle diameter of the Fe ₁₆ N ₂ phase in the iron nitride-based powder (iron nitride magnetic particles) is the Fe ₁₆ N ₂ particles not including the layer when a layer is formed on the surface of the Fe ₁₆ N ₂ particles. It means itself.

The magnetic particles of the present invention preferably contain at least the Fe ₁₆ N ₂ phase, but do not contain other iron nitride phases. This is because the crystal magnetic anisotropy of iron nitride (Fe ₄ N or Fe ₃ N phase) is about 1 × 10 ⁵ erg / cc, whereas the Fe ₁₆ N ₂ phase is 2 to 7 × 10 ⁶ erg / cc. This is because it has a high magnetocrystalline anisotropy of cc. Thereby, a high coercive force can be maintained even when the particles are made fine. This high magnetocrystalline anisotropy results from the crystal structure of the Fe ₁₆ N ₂ phase. The crystal structure is a body-centered tetragonal system in which N atoms regularly enter the Fe interstitial positions of Fe, and the strain when N atoms enter the lattice is considered to be the cause of high crystal magnetic anisotropy. . The easy axis of magnetization of the Fe ₁₆ N ₂ phase is the C axis extended by nitriding.

The shape of the particles containing the Fe ₁₆ N ₂ phase is preferably granular or elliptical. More preferably, it is spherical. This is because one of three equivalent directions of cubic α-Fe is selected by nitriding and becomes the c-axis (magnetization easy axis). Therefore, if the particle shape is acicular, the easy magnetization axis is the minor axis. This is because particles in the direction and the major axis direction are mixed, which is not preferable. Therefore, the average value of the axial ratio of major axis length / minor axis length is preferably 2 or less (for example, 1 to 2), more preferably 1.5 or less (for example, 1 to 1.5).

The particle size is determined by the particle size of the iron particles before nitriding, and is preferably monodispersed. This is because, in general, monodispersion reduces the medium noise. The particle size of the iron nitride magnetic powder containing Fe ₁₆ N ₂ as the main phase is determined by the particle size of the iron particles, and the particle size distribution of the iron particles is preferably monodisperse. This is because the degree of nitriding differs between the large and small particles, and the magnetic properties are different. From this point of view, the particle size distribution of the iron nitride magnetic powder is preferably monodispersed.

The particle size of the Fe ₁₆ N ₂ phase, which is a magnetic material, is 9 to 11 nm. This is because as the particle size becomes smaller, the influence of thermal fluctuation becomes larger, and it becomes superparamagnetic and becomes unsuitable for a magnetic recording medium. Also, because of the magnetic viscosity, the coercive force at the time of high-speed recording with a head increases, making it difficult to record. On the other hand, if the particle size is large, the saturation magnetization cannot be reduced, so that the coercive force during recording becomes too high, making it difficult to record. Further, when the particle size is large, the particle noise when the magnetic recording medium is obtained becomes high. The particle size distribution is preferably monodisperse. This is because, in general, monodispersion reduces the medium noise. The variation coefficient of the particle size is 15% or less (preferably 2 to 15%), more preferably 10% or less (preferably 2 to 10%).

The iron nitride magnetic powder containing Fe ₁₆ N ₂ as a main phase preferably has a surface covered with an oxide film. This is because the fine particles Fe ₁₆ N ₂ are easily oxidized and require handling in a nitrogen atmosphere.

  The oxide film preferably contains a rare earth element and / or an element selected from silicon and aluminum. This is because it has the same particle surface as so-called metal particles mainly composed of iron and Co as a main component, and the affinity with the process for handling the metal particles is increased. As the rare earth element, Y, La, Ce, Pr, Nd, Sm, Tb, Dy, and Gd are preferably used, and Y is particularly preferably used from the viewpoint of dispersibility.

  In addition to silicon and aluminum, boron or phosphorus may be included as necessary. Furthermore, carbon, calcium, magnesium, zirconium, barium, strontium, and the like may be included as effective elements. By using these other elements in combination with rare earth elements and / or silicon and aluminum, it is possible to obtain higher shape maintainability and dispersion performance.

  The composition of the surface compound layer is such that the total content of rare earth elements or boron, silicon, aluminum, and phosphorus with respect to iron is preferably 0.1 to 40.0 atomic%, more preferably 1.0 to 30.0 atomic%, More preferably, it is 3.0-25.0 atomic%. If the amount of these elements is too small, it becomes difficult to form the surface compound layer, not only the magnetic anisotropy of the magnetic powder is reduced, but also the oxidation stability is poor. Moreover, when there are too many of these elements, the saturation magnetization will fall excessively easily.

  The thickness of the oxide film is preferably 1 to 5 nm, and more preferably 2 to 3 nm. If the thickness is smaller than this range, the oxidation stability tends to be low, and if the thickness is thick, the particle size may be hardly reduced.

The magnetic properties of iron nitride-based magnetic particles containing Fe ₁₆ N ₂ as the main phase include a coercive force (Hc) of 79.6 to 318.4 kA / m (1,000 to 4,000 Oe). It is more preferable that it is 159.2 to 278.6 kA / m (2000 to 3500 Oe). More preferably, it is 197.5-237 kA / m (2500-3000 Oe). This is because, if Hc is low, for example, in the case of in-plane recording, it is likely to be affected by the adjacent recording bit and may not be suitable for high recording density, and if it is too high, it may be difficult to record. It is.

Saturation magnetization is preferably ^{80~160Am 2 / kg (80~160emu / g} ), 80~120Am 2 / kg (80~120emu / g) is more preferable. This is because if the signal is too low, the signal may be weakened. If the signal is too high, for example, in the case of in-plane recording, the adjacent recording bit is likely to be affected, and the recording density is not suitable. The squareness ratio is preferably 0.6 to 0.9.

The magnetic powder preferably has a BET specific surface area of 40 to 100 m ² / g. This is because when the BET specific surface area is too small, the particle size increases, and when applied to a magnetic recording medium, the particulate noise increases, the surface smoothness of the magnetic layer decreases, and the reproduction output tends to decrease. Further, if the BET specific surface area is too large, particles containing the Fe ₁₆ N ₂ phase are likely to aggregate, and it is difficult to obtain a uniform dispersion and it is difficult to obtain a smooth surface.

  The average particle size of the iron nitride powder is preferably 10 to 40 nm, more preferably 12 to 30 nm, and particularly preferably 15 to 20 nm.

  A known technique can be applied to the method for producing the iron nitride magnetic particles, and for example, the method described in WO2003 / 079332 can be referred to.

[Binder]
The binder, lubricant, dispersant, additive, solvent, dispersion method, and other known techniques for the magnetic layer, nonmagnetic layer, and back layer of the magnetic recording medium of the present invention can be applied to each other as appropriate. In particular, known techniques relating to the amount and type of binder, the additive, and the amount and type of dispersant can be applied.

  As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C., a number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and a polymerization degree of about 50 to 1,000. .

  Examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetate. There are polymers or copolymers containing polyurethane, vinyl ether, etc. as structural units, polyurethane resins, and various rubber resins. Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamides. Resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like. These resins are described in detail in “Plastic Handbook” published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. These examples and their production methods are described in detail in JP-A No. 62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer, A combination of at least one selected from the group consisting of a polyurethane resin and a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane and polycaprolactone polyurethane can be used. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and _{durability, -COOM, -SO 3 M, -OSO} 3 M, -P = O (OM) 2, - O—P═O (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), —OH, —NR ₂ , —N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, —SH, It is preferable to use one in which at least one polar group selected from —CN, etc. is introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.

  Specific examples of these binders used in the present invention include VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYES, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC, PKFE, manufactured by Dow Chemical Co., Ltd. Nissin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, MPR-TAO, Denki Kagaku 1000W, DX80, DX81, DX82 , DX83, 100FD, Nippon Zeon's MR-104, MR-105, MR110, MR100, MR555, 400X-110A, Nippon Polyurethane Nipporan N2301, N2302, N2304, Dainippon Ink, Pandex T-5105, T -R3080, T-520 Barnock D-400, D-210-80, Crisbon 6109, 7209, Byron UR8200, UR8300, UR-8700, RV530, RV280, manufactured by Toyobo Co., Ltd. 9020, 9022, 7020, Mitsubishi Chemical Co., Ltd., MX5004, Sanyo Chemical Co., Ltd. sampler SP-150, Asahi Kasei Co., Ltd. Saran F310, F210, etc. are mentioned.

The binder used in the nonmagnetic layer and magnetic layer of the present invention is used in the range of 5 to 50% by mass, preferably 10 to 30% by mass, based on the nonmagnetic powder or magnetic powder. When using a vinyl chloride resin, it is preferable to use 5-30% by weight, when using a polyurethane resin, 2-20% by weight, and polyisocyanate in a range of 2-20% by weight. When head corrosion occurs due to a small amount of dechlorination, it is possible to use only polyurethane or only polyurethane and isocyanate. In the present invention, when polyurethane is used, the glass transition temperature is −50 to 150 ° C., preferably 0 ° C. to 100 ° C., the breaking elongation is 100 to 2000%, and the breaking stress is 0.05 to 10 kg / mm ² (0.49). ˜98 MPa) and the yield point is preferably 0.05 to 10 kg / mm ² (0.49 to 98 MPa).

  Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5- Isocyanates such as diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and products of these isocyanates and polyalcohols In addition, polyisocyanate produced by condensation of isocyanates can be used. Commercially available product names of these isocyanates are: Nippon Polyurethane, Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Made, Takenet D-102, Takenet D-110N, Takenet D-200, Takenet D-202, manufactured by Sumitomo Bayer, Death Module L, Death Module IL, Death Module N, There is a desmodule HL, etc., and these can be used for each layer alone or in combination of two or more by utilizing the difference in curing reactivity.

The magnetic layer in the present invention contains a phosphorus (P) -containing organic compound. As the phosphorus (P) -containing organic compound, conventionally known compounds can be used as rust inhibitors or antioxidants, but those that can be adsorbed or reacted with a magnetic substance are preferred.
That is, the present invention intends to relatively reduce the ratio or probability of the adsorption state between the magnetic substance and the fatty acid during storage and running by containing a phosphorus (P) -containing organic compound in the magnetic layer. It is. As a result, the floating state of the abrasive in the magnetic layer changes, and the effect of the present invention is considered to be manifested.
In the present invention, a preferable phosphorus (P) -containing organic compound has the following structural formula, specifically, α-naphthyl phosphate, phenyl phosphate, diphenyl phosphate, p-ethylbenzenephosphonic acid. , Phenylphosphonic acid, phenylphosphinic acid and their esters. In the present invention, it is preferable to use at least one selected from these. Moreover, those compounding ratios can be used arbitrarily.
(1) (R—O) _n PO (OM) _3-n
(2) (R—O) _n P (OM) _3-n
(3) (R) _n P (OM) _3-n
(4) RPO (OM) ₂
In each formula, R represents a substituted or unsubstituted alkyl group having 6 to 40 carbon atoms, an aralkyl group, an alkylphenyl group, an alkylphenylalkylene oxide group, an alkenyl group, or an aryl group, and M represents a hydrogen atom, an alkali metal, or —N (R ¹ ) ₄ is represented, R ¹ represents an alkyl group having 1 to 20 carbon atoms, and n represents 1 or 2.
The phosphorus (P) -containing organic compound is added in an amount of 1 to 15 parts by weight, preferably 2 to 10 parts by weight, and more preferably 3 to 7 parts by weight with respect to 100 parts by weight of the ferromagnetic powder.
The following additives can be added to the magnetic layer in the present invention, if necessary, including the above-described phosphorus (P) -containing organic compound. Examples of the additive include an abrasive, a lubricant, a dispersant / dispersion aid, an antifungal agent, an antistatic agent, an antioxidant, a solvent, and carbon black. Examples of these additives include molybdenum disulfide, tungsten disulfide, graphite, boron nitride, fluorinated graphite, silicone oil, silicone having a polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, Polyolefin, polyglycol, fluorine-containing alkyl sulfates and alkali metal salts thereof, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, erucic acid, etc. A monobasic fatty acid which may contain or be branched, and a metal salt thereof, or butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate , Monobasic fatty acids which may contain or be branched, such as butyl laurate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan tristearate, etc. 1 to 6-valent alcohols that may contain or be branched from 2 to 22 unsaturated bonds, monohydric alcohols or alkylene oxide polymers that may contain or be branched from 12 to 22 carbon atoms A mono-fatty acid ester, di-fatty acid ester or polyhydric fatty acid ester composed of any one of alkyl ethers, fatty acid amides having 2 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like can be used. In addition to the above hydrocarbon groups, nitro groups and alkyl groups, aryl groups, and aralkyl groups in which groups other than hydrocarbon groups such as halogen-containing hydrocarbons such as F, Cl, Br, CF ₃ , CCl ₃ , and CBr ₃ are substituted. You may have something.

  In addition, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocyclics, phosphonium or sulfoniums, etc. Amphoteric interfaces such as cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, and sulfate ester groups, amino acids, aminosulfonic acids, sulfuric or phosphate esters of aminoalcohols, and alkylbetaines An activator or the like can also be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.).

  The lubricants, antistatic agents, and the like are not necessarily pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, and oxides in addition to the main components. These impurities are preferably 30% by mass or less, more preferably 10% by mass or less.

  Specific examples of these additives include, for example, NAF-102, castor oil hardened fatty acid, NAA-42, cation SA, Naimine L-201, Nonion E-208, Anon BF, Anon LG, Takemoto, manufactured by NOF Corporation. Oil and fat: FAL-205, FAL-123, Shin Nippon Chemical Co., Ltd .: NJ Lube OL, Shin-Etsu Chemical Co., Ltd .: TA-3, Lion Corporation: Armido P, Lion Corporation: Duomin TDO, Nisshin Oilio Co., Ltd .: BA-41G, Sanyo Kasei Co., Ltd .: Profan 2012E, New Pole PE61, Ionette MS-400, etc. are mentioned.

  In the magnetic layer of the present invention, the addition amount of the fatty acid ester as a lubricant is preferably 0.01 to 30 parts by mass, more preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of the ferromagnetic powder. Especially preferably, it is 1 to 5 parts by mass.

In addition, carbon black can be added to the magnetic layer in the present invention as necessary. Examples of carbon black that can be used in the magnetic layer include rubber furnace, rubber thermal, color black, and acetylene black. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle diameter is 5 to 300 nm, pH is 2 to 10, water content is 0.1 to 10%, tap density is 0.1 to 1 g / ml is preferred.

  Specific examples of carbon black used in the present invention include Cabot's BLACKPEARLS 2000, 1300, 1000, 900, 905, 800, 700, VULCAN XC-72, Asahi Carbon Co., Ltd. # 80, # 60, # 55. # 50, # 35, Mitsubishi Chemical Corporation # 2400B, # 2300, # 900, # 1000, # 30, # 40, # 10B, Columbian Carbon Corporation CONDUCTEX SC, RAVEN150, 50, 40, 15, RAVEN- MT-P, Ketjen Black International Ketjen Black EC, etc. are mentioned. Carbon black may be surface-treated with a dispersant, or may be used after being grafted with a resin, or may be obtained by graphitizing a part of the surface. Carbon black may be dispersed with a binder in advance before being added to the magnetic coating. These carbon blacks can be used alone or in combination. When using carbon black, it is preferable to use 0.1-30 mass% with respect to the mass of a magnetic body. Carbon black functions to prevent the magnetic layer from being charged, reduce the friction coefficient, impart light-shielding properties, and improve the film strength. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the magnetic layer and the nonmagnetic layer, and are based on the above-mentioned characteristics such as particle size, oil absorption, conductivity, pH, etc. Of course, it is possible to use them properly according to the purpose, but rather they should be optimized in each layer. For the carbon black that can be used in the magnetic layer of the present invention, for example, “Carbon Black Handbook” edited by Carbon Black Association can be referred to.

[Abrasive]
The abrasive used in the present invention is α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide titanium carbide having an α conversion rate of 90% or more. A known material having a Mohs hardness of 6 or more, such as a bite, titanium oxide, silicon dioxide, boron nitride, etc. is used alone or in combination. Moreover, you may use the composite_body | complex (what surface-treated the abrasive | polishing agent with the other abrasive | polishing agent) of these abrasive | polishing agents. These abrasives may contain compounds or elements other than the main component, but the effect is not affected if the main component is 90% or more. The average particle size of these abrasives is preferably 20 to 150 nm, more preferably 30 to 100 nm, and particularly preferably 50 to 80 nm. In particular, in order to enhance electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as necessary, or to obtain the same effect by widening the particle size distribution even with a single abrasive. The tap density is preferably 0.3 to ² g / cc, the water content is 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, a dice shape, and a plate shape, but those having a corner in a part of the shape are preferable because of high polishing properties. Specifically, AKP-12, AKP-15, AKP-20, AKP-30, AKP-50, HIT-20, HIT-30, HIT-55, HIT-60, HIT-70, HIT- manufactured by Sumitomo Chemical Co., Ltd. 80, HIT-100, Reynolds, ERC-DBM, HP-DBM, HPS-DBM, Fujimi Abrasives, WA10000, Uemura Kogyo, UB20, Nippon Kagaku Kogyo, G-5, Chromex U2, Chromex U1, Toda Kogyo, TF100, TF140, Ibiden, Beta Random Ultra Fine, Showa Mining, B-3, and the like. These abrasives can be added to the nonmagnetic layer as required. By adding to the nonmagnetic layer, the surface shape can be controlled, and the protruding state of the abrasive can be controlled. The particle size and amount of the abrasive added to these magnetic and nonmagnetic layers should of course be set to optimum values. In the present invention, diamond particles are particularly preferred as the abrasive for the magnetic layer. The average particle diameter of the diamond particles is preferably 20 nm to 150 nm, more preferably 30 to 100 nm, and particularly preferably 50 to 80 nm.

  The addition amount of the abrasive is 1 to 5 parts by mass, preferably 2 to 4 parts by mass with respect to 100 parts by mass of the ferromagnetic powder.

  Known organic solvents can be used in the present invention. The organic solvent used in the present invention is an arbitrary ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methyl Alcohols such as cyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene, Aromatic hydrocarbons such as cresol and chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethyl Nkuroruhidorin, chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane.

  These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The organic solvent used in the present invention is preferably the same in the magnetic layer and the nonmagnetic layer. The amount added may be changed. Use a solvent with high surface tension (such as cyclohexanone or dioxane) in the nonmagnetic layer to increase the coating stability. Specifically, the arithmetic average value of the upper layer solvent composition may not fall below the arithmetic average value of the nonmagnetic layer solvent composition. It is essential. In order to improve dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that 50% or more of a solvent having a dielectric constant of 15 or more is included in the solvent composition. Moreover, it is preferable that a solubility parameter is 8-11.

  These dispersants, lubricants, and surfactants used in the present invention can be properly used in the magnetic layer and further in the nonmagnetic layer described later as needed. For example, of course, the dispersant is not limited to the example shown here, but the dispersant has a property of adsorbing or binding with a polar group, and in the magnetic layer, mainly on the surface of the ferromagnetic metal powder and nonmagnetic. In the layer, it is presumed that the organic phosphorus compound adsorbed or bonded mainly to the surface of the non-magnetic powder with the above-mentioned polar group, for example, is difficult to desorb from the surface of metal or metal compound. Accordingly, since the surface of the ferromagnetic metal powder or the nonmagnetic powder of the present invention is in a state of being coated with an alkyl group, an aromatic group, etc., the affinity for the binder component of the ferromagnetic metal powder or the nonmagnetic powder. In addition, the dispersion stability of the ferromagnetic metal powder or nonmagnetic powder is also improved. In addition, since the lubricant exists in a free state, fatty acids with different melting points are used in the nonmagnetic layer and magnetic layer to control the bleeding to the surface, and leaching to the surface using esters with different boiling points and polarities. It is conceivable to improve the coating stability by controlling the amount of the surfactant, to improve the lubrication effect by increasing the additive amount of the lubricant in the nonmagnetic layer. All or part of the additives used in the present invention may be added in any step during the production of the coating solution for the magnetic layer or nonmagnetic layer. For example, when mixing with a ferromagnetic powder before the kneading step, when adding at a kneading step with a ferromagnetic powder, a binder and a solvent, when adding at a dispersing step, when adding after dispersing, when adding just before coating, etc. There is.

[Nonmagnetic layer]
Next, detailed contents regarding the nonmagnetic layer will be described. The magnetic recording medium of the present invention can have a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support. The nonmagnetic powder that can be used in the nonmagnetic layer may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides.

Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α-alumina, β-alumina having an α conversion of 90 to 100%, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide , Titanium carbide, ITO, etc. are used alone or in combination of two or more. Further, the shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. Preferable are α-iron oxide and titanium oxide.

  The shape of the nonmagnetic powder may be any of acicular, spherical, polyhedral and plate shapes. The crystallite size of the nonmagnetic powder is preferably 4 nm to 500 nm, more preferably 40 to 100 nm. If the crystallite size is in the range of 4 nm to 500 nm, it is preferable because dispersion does not become difficult and it has a suitable surface roughness. The average particle size of these non-magnetic powders is preferably 5 nm to 500 nm. However, if necessary, non-magnetic powders having different average particle sizes may be combined, or a single non-magnetic powder may have a wide particle size distribution. It can also have an effect. The average particle size of the particularly preferred nonmagnetic powder is 10 to 200 nm. The range of 5 nm to 500 nm is preferable because the dispersion is good and the surface roughness is suitable.

The specific surface area of the nonmagnetic powder is 1 to 150 m ² / g, preferably 20 to 120 m ² / g, and more preferably 50 to 100 m ² / g. A specific surface area in the range of 1 to 150 m ² / g is preferred because it has a suitable surface roughness and can be dispersed with a desired amount of binder. The oil absorption using dibutyl phthalate (DBP) is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. When the tap density is in the range of 0.05 to 2 g / ml, there are few particles to be scattered, the operation is easy, and there is a tendency that it is difficult to adhere to the apparatus. The pH of the nonmagnetic powder is preferably 2 to 11, but the pH is particularly preferably between 6 and 9. When the pH is in the range of 2 to 11, the friction coefficient does not increase due to high temperature, high humidity, or liberation of fatty acids. The moisture content of the nonmagnetic powder is 0.1 to 5% by mass, preferably 0.2 to 3% by mass, and more preferably 0.3 to 1.5% by mass. A water content in the range of 0.1 to 5% by mass is preferable because the dispersion is good and the viscosity of the paint after dispersion is stable. The ignition loss is preferably 20% by mass or less, and the ignition loss is preferably small.

When the nonmagnetic powder is an inorganic powder, the Mohs hardness is preferably 4-10. If the Mohs hardness is in the range of 4 to 10, durability can be ensured. The nonmagnetic powder has a stearic acid adsorption amount of 1 to 20 μmol / m ² , more preferably ² to 15 μmol / m ² . The heat of wetting of the nonmagnetic powder into water at 25 ° C. is preferably in the range of 200 to 600 erg / cm ² (200 to 600 mJ / m ² ). Moreover, the solvent which exists in the range of this heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C. is suitably 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 9. It is preferable that Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , and ZnO are present on the surface of these nonmagnetic powders by surface treatment. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ , and ZrO ₂ , but more preferred are Al ₂ O ₃ , SiO ₂ , and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface-treated layer co-precipitated according to the purpose may be used, or a method of treating the surface layer with silica after first treating with alumina, or vice versa may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

  Specific examples of the non-magnetic powder used in the non-magnetic layer of the present invention include, for example, Showa Denko Nanotite, Sumitomo Chemical HIT-100, ZA-G1, Toda Kogyo DPN-250, DPN-250BX, DPN-245, DPN-270BX, DPB-550BX, DPN-550RX, Ishihara Sangyo Titanium oxide TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-55S, TTO-55D, SN-100, MJ -7, α-iron oxide E270, E271, E300, STT-4D, STT-30D, STT-30, STT-65C manufactured by Titanium Industry, MT-100S, MT-100T, MT-150W, MT-500B manufactured by Teika T-600B, T-100F, T-500HD, etc. are mentioned. FINEX-25, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 500A, Titanium Industry Y-LOP manufactured and what baked it are mentioned. Particularly preferred nonmagnetic powders are titanium dioxide and α-iron oxide.

Carbon black can be mixed in the nonmagnetic layer together with nonmagnetic powder to lower the surface electrical resistance, reduce the light transmittance, and obtain a desired micro Vickers hardness. The micro-Vickers hardness of the nonmagnetic layer is generally 25~60kg ^/ mm 2 (245~588MPa), preferably in order to adjust the head ^contact, a 30~50kg / mm 2 (294~490MPa), thin film hardness meter ( Using a HMA-400 manufactured by NEC, measurement can be performed using a diamond triangular pyramid needle having a ridge angle of 80 degrees and a tip radius of 0.1 μm at the tip of the indenter. For details, refer to Realize Co., Ltd. It is standardized that the light transmittance is generally 3% or less for absorption of infrared rays having a wavelength of about 900 nm, for example, 0.8% or less for a VHS magnetic tape. For this purpose, rubber furnace, rubber thermal, color black, acetylene black and the like can be used.

Non specific surface area of the carbon black used in the magnetic layer is 100 to 500 m ² / g, preferably 150~400m ² / g, DBP oil absorption of the present invention are 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g . The particle size of carbon black is 5 to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. Carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

  Specific examples of carbon black that can be used in the non-magnetic layer of the present invention include BLACKPEARLS 2000, 1300, 1000, 900, 800, 880, 700, VULCAN XC-72, manufactured by Cabot Corporation, # 3050B, manufactured by Cabot Corporation. # 3150B, # 3250B, # 3750B, # 3950B, # 950B, # 650B, # 970B, # 850B, MA-600, CONDUCTEX SC, Raven8800, 8000, 7000, 5750, 5250, 3500, 2100, Columbia Carbon Co., Ltd. 2000, 1800, 1500, 1255, 1250, and Ketjen Black EC manufactured by Ketjen Black International.

  Carbon black may be surface-treated with a dispersant, or may be grafted with a resin, or may be obtained by graphitizing a part of the surface. Moreover, before adding carbon black to a coating material, you may disperse | distribute with a binder beforehand. These carbon blacks can be used in a range not exceeding 50% by mass with respect to the inorganic powder and in a range not exceeding 40% of the total mass of the nonmagnetic layer. These carbon blacks can be used alone or in combination. The carbon black that can be used in the nonmagnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

  Further, an organic powder can be added to the nonmagnetic layer according to the purpose. Examples of such organic powder include acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin, and the like. Resin powder and polyfluorinated ethylene resin can also be used. As the production method, those described in JP-A Nos. 62-18564 and 60-255827 can be used.

  As the binder, lubricant, dispersant, additive, solvent, dispersion method and the like of the nonmagnetic layer, those of the magnetic layer can be applied. In particular, known techniques relating to the magnetic layer can be applied to the amount of binder, type, additive, and amount of dispersant added, and type.

  The magnetic recording medium of the present invention may be provided with an undercoat layer. By providing the undercoat layer, the adhesive force between the support and the magnetic layer or the nonmagnetic layer can be improved. As the undercoat layer, a solvent-soluble polyester resin is used.

[Layer structure]
As for the thickness structure of the magnetic recording medium used in the present invention, the thickness of the non-magnetic support is 3 to 80 μm, more preferably 3 to 50 μm, and particularly preferably 3 to 10 μm as described above. When an undercoat layer is provided between the nonmagnetic support and the nonmagnetic layer or magnetic layer, the thickness of the undercoat layer is 0.01 to 0.8 μm, preferably 0.02 to 0.6 μm.

  The thickness of the magnetic layer is optimized by the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used, but is preferably 20 to 100 nm, and more preferably 60 to 80 nm. Further, the thickness variation rate of the magnetic layer is preferably within ± 50%, more preferably within ± 30%. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.

  The thickness of the nonmagnetic layer of the present invention is 0.1 to 3.0 μm, preferably 0.3 to 2.0 μm, and more preferably 0.5 to 1.5 μm. The non-magnetic layer of the magnetic recording medium of the present invention exhibits its effect if it is substantially non-magnetic. For example, even if it contains a small amount of magnetic material as an impurity or intentionally, This shows the effect of the invention and can be regarded as substantially the same configuration as the magnetic recording medium of the invention. Note that “substantially the same” means that the residual magnetic flux density of the nonmagnetic layer is 10 mT or less or the coercive force is 7.96 kA / m (100 Oe) or less, and preferably has no residual magnetic flux density and coercive force. Means.

[Back layer]
In the magnetic recording medium of the present invention, a back layer is preferably provided on the other surface of the nonmagnetic support. The back layer preferably contains carbon black and inorganic powder. For the binder and various additives, the formulation of the magnetic layer and the nonmagnetic layer is applied. The thickness of the back layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm.

[Production method]
The liquid preparation step for producing the magnetic layer coating material, nonmagnetic layer coating material or back layer coating material used in the present invention includes at least a kneading step, a dispersion step, and a mixing step provided before and after these steps as necessary. Consists of. Each process may be divided into two or more stages. Ferromagnetic powder, non-magnetic powder, binder, carbon black, abrasive, phosphorus (P) -containing organic compound, antistatic agent, lubricant, solvent, etc. used in the present invention are all raw materials at the beginning or middle of any process. It may be added. In addition, individual raw materials may be added in two or more steps. For example, polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

  However, in the present invention, in order to make the amount of the abrasive smaller than that of the magnetic recording medium of the prior art, in the liquid preparation step of preparing the magnetic layer liquid, the ferromagnetic powder is dispersed in the binder, followed by It is preferable to add and mix the phosphorus (P) -containing organic compound and then add and mix the fatty acid ester as the lubricant. The abrasive is preferably mixed after the addition of the phosphorus (P) -containing organic compound. Carbon black is preferably mixed after the addition of the phosphorus (P) -containing organic compound. Furthermore, it is preferable that the mixing of the phosphorus (P) -containing organic compound is performed while applying ultrasonic waves.

  In order to achieve the object of the present invention, a conventional known manufacturing technique can be used as a part of the steps. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, glass beads can be used to disperse the magnetic layer coating material, the nonmagnetic layer coating material, or the back layer coating material. Such glass beads are preferably zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media. The particle diameter and filling rate of these dispersion media are optimized. A well-known thing can be used for a disperser.

  In the method for producing a magnetic recording medium of the present invention, for example, a magnetic layer is applied to the surface of a nonmagnetic support under running so that the magnetic layer has a predetermined thickness. Here, a plurality of magnetic layer coating materials may be applied sequentially or simultaneously, and a nonmagnetic layer coating material and a magnetic layer coating material may be applied sequentially or simultaneously. Examples of the coating machine for applying the magnetic layer coating material or the nonmagnetic layer coating material include air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, and gravure coating. A coat, a kiss coat, a cast coat, a spray coat, a spin coat, etc. can be used. As for these, for example, “Latest Coating Technology” (May 31, 1983) issued by General Technology Center Co., Ltd. can be referred to.

  In the case of a magnetic tape, the magnetic layer coating layer may be subjected to magnetic field orientation treatment using a cobalt magnet or a solenoid on the ferromagnetic powder contained in the magnetic layer coating layer. In the case of a disk, a sufficiently isotropic orientation may be obtained even without non-orientation without using an orientation device, but known random methods such as alternately arranging cobalt magnets obliquely and applying an alternating magnetic field with a solenoid. It is preferable to use an alignment device. In the case of a ferromagnetic metal powder, the isotropic orientation is generally preferably in-plane two-dimensional random, but can also be three-dimensional random with a vertical component. Further, isotropic magnetic characteristics can be imparted in the circumferential direction by using a well-known method such as a counter-polarized magnet and making it vertically oriented. In particular, when performing high density recording, vertical alignment is preferable. Moreover, circumferential orientation can also be achieved using spin coating.

  It is preferable that the drying position of the coating film can be controlled by controlling the temperature, air volume, and coating speed of the drying air, the coating speed is preferably 20 m / min to 1000 m / min, and the temperature of the drying air is preferably 60 ° C. or higher. Also, moderate pre-drying can be performed before entering the magnet zone.

The coating raw material thus obtained is once taken up by a take-up roll, and then unwound from the take-up roll and subjected to a calendar process.
For the calendar process, for example, a super calendar roll or the like is used. The calendering improves the surface smoothness and eliminates the voids generated by the removal of the solvent during drying and improves the filling rate of the ferromagnetic powder in the magnetic layer. Obtainable. The step of calendering is preferably performed while changing the calendering conditions according to the smoothness of the surface of the coating raw material.

In general, the gloss value of the coating raw material decreases from the core side of the winding roll toward the outside, and the quality may vary in the longitudinal direction. It is known that the gloss value has a correlation (proportional relationship) with the surface roughness Ra. Therefore, in the calendar processing step, if the calendar processing conditions, for example, the calendar roll pressure is kept constant without being changed, no measures are taken for the difference in smoothness in the longitudinal direction caused by the winding of the coating raw material. As a result, the final product also varies in quality in the longitudinal direction.
Therefore, it is preferable to change the calendering conditions, for example, the calender roll pressure, in the calendering process to offset the difference in smoothness in the longitudinal direction caused by the winding of the coating raw material. Specifically, it is preferable to reduce the pressure of the calendar roll from the core side of the coating raw material unwound from the winding roll toward the outside. According to the study by the present inventors, it has been found that when the pressure of the calender roll is lowered, the gloss value is lowered (smoothness is lowered). As a result, the difference in smoothness in the longitudinal direction caused by the winding of the coating raw material is offset, and a final product having no variation in quality in the longitudinal direction is obtained.

  In addition, although the example which changes the pressure of a calendar roll was demonstrated above, it can carry out by controlling a calendar roll temperature, a calendar roll speed, and a calendar roll tension besides this. In consideration of the properties of the coating type medium, it is preferable to control the calender roll pressure and the calender roll temperature. By decreasing the calender roll pressure or lowering the calender roll temperature, the surface smoothness of the final product is lowered. Conversely, increasing the calender roll pressure or the calender roll temperature increases the surface smoothness of the final product.

  Apart from this, the magnetic recording medium obtained after the calendering process can be thermo-processed to allow thermosetting to proceed. Such a thermo treatment may be appropriately determined depending on the formulation of the magnetic layer coating material, and is, for example, 35 to 100 ° C, and preferably 50 to 80 ° C. The thermo treatment time is 12 to 72 hours, preferably 24 to 48 hours.

  As the calender roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyamideimide or the like is used. Moreover, it can also process with a metal roll.

  The magnetic recording medium of the present invention preferably has an extremely smooth surface as described above. As the calendering conditions employed for this purpose, the temperature of the calender roll is in the range of 60 to 100 ° C., preferably in the range of 70 to 100 ° C., particularly preferably in the range of 80 to 100 ° C., and the pressure is 100 to 500 kg / cm (98 to 490 kN / m), preferably 200 to 450 kg / cm (196 to 441 kN / m), particularly preferably 300 to 400 kg / cm (294 to 392 kN / m). Conditions are preferred.

  The obtained magnetic recording medium can be cut into a desired size using a cutting machine or the like. The cutting machine is not particularly limited, but is preferably provided with a plurality of pairs of rotating upper blades (male blades) and lower blades (female blades). The slitting speed, the engagement depth, and the upper blade (male blade) are appropriately selected. The peripheral speed ratio (upper blade peripheral speed / lower blade peripheral speed) between the blade and the lower blade (female blade), the continuous use time of the slit blade, and the like are selected.

[Physical properties]
The saturation magnetic flux density of the magnetic layer of the magnetic recording medium used in the present invention is preferably 100 to 400 mT. The coercive force (Hc) of the magnetic layer is preferably 143.2 to 318.3 kA / m (1800 to 4000 Oe), more preferably 159.2 to 278.5 kA / m (2000 to 3500 Oe). The coercive force distribution is preferably narrow, and SFD and SFDr are 0.6 or less, more preferably 0.3 or less.

The friction coefficient with respect to the head of the magnetic recording medium used in the present invention is 0.50 or less, preferably 0.3 or less in the range of temperature -10 to 40 ° C. and humidity 0 to 95%. The surface resistivity is preferably 10 ⁴ to 10 ⁸ Ω / sq of the magnetic surface, and the charging position is preferably within −500 V to +500 V. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 0.98 to 19.6 GPa (100 to 2000 kg / mm ² ) in each in-plane direction, and the breaking strength is preferably 98 to 686 MPa (10 to 70 kg). / Mm ² ), the elastic modulus of the magnetic recording medium is preferably 0.98 to 14.7 GPa (100 to 1500 kg / mm ² ) in each in-plane direction, and the residual spread is preferably 0.5% or less, 100 ° C. The thermal shrinkage at any of the following temperatures is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.

The glass transition temperature of the magnetic layer (the maximum point of the loss tangent of the dynamic viscoelasticity measurement measured at 110 Hz with a dynamic viscoelasticity measuring device, Leo Vibron, etc.) is preferably 50 to 180 ° C., and that of the nonmagnetic layer is 0 to 180. ° C is preferred. The loss elastic modulus is preferably in the range of 1 × 10 ⁷ to 8 × 10 ⁸ Pa (1 × 10 ⁸ to 8 × 10 ⁹ dyne / cm ² ), and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. These thermal characteristics and mechanical characteristics are preferably almost equal within 10% in each in-plane direction of the medium.

The residual solvent contained in the magnetic layer is preferably 20 mg / m ² or less, more preferably 50 mg / m ² or less. The porosity of the coating layer is preferably 30% by volume or less, more preferably 10% by volume or less for both the nonmagnetic layer and the magnetic layer. The porosity is preferably small in order to achieve high output, but it may be better to ensure a certain value depending on the purpose. For example, in the case of a disk medium in which repeated use is important, a larger void ratio is often preferable for running durability.

  The surface average roughness Ra of the magnetic layer is preferably 3 nm or less, and the ten-point average roughness Rz is preferably 30 nm or less. This can be easily controlled by controlling the surface properties with the filler of the support or the surface of the calendered roll. The curl is preferably within ± 3 mm.

  In the magnetic recording medium of the present invention, these physical characteristics can be changed between the nonmagnetic layer and the magnetic layer according to the purpose. For example, the elastic modulus of the magnetic layer can be increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer can be made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

As a reproducing method in the magnetic recording medium of the present invention, it is preferable that a signal magnetically recorded at a maximum linear recording density of 200 KFC I or more is reproduced by an AMR head or a GMR head. Particularly preferred is a reproducing method using a GMR head.
The distance between the shields is, for example, 0.08 μm to 0.2 μm, and the reproduction track width is, for example, 0.5 μm to 3.5 μm.

  When the magnetic recording medium of the present invention is a tape-like magnetic recording medium, an AMR head or a GMR head is used as a reproducing head, so that even a signal recorded in a high frequency region can be reproduced at a higher S / N ratio than before. It is. Therefore, the magnetic recording medium of the present invention is most suitable as a magnetic tape for computer data recording for higher density recording and a disk-shaped magnetic recording medium.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples. In the examples, “part” means part by mass unless otherwise specified.

Example with magnetic tape (1)
Example 1
<Preparation of paint>
"Coating for magnetic layer"
Ingredient (U1)
100 parts of barium ferrite magnetic powder Surface treatment: 6% by mass of Al ₂ O ₃ is present with respect to the entire particle Coercive force Hc: 199 kA / m (2500 Oe)
Average plate diameter: 25nm
Average plate ratio: 2.5
Saturation magnetization σs: 50 A · m ² / kg (50 emu / g)
BET specific surface area: 60 m ² / g
Polyurethane resin 15 parts Branched side chain-containing polyester polyol / diphenylmethane diisocyanate-SO ₃ Na = 150 eq / ton
Ingredient (U2)
Abrasive 3 parts Diamond [Average particle diameter: 80 nm (coefficient of variation: 20%)]
Ingredient (U3)
Carbon black [average particle size: 80 nm] 5 parts Component (U4)
Isobutyl stearate 4 parts Isohexadecyl stearate 4 parts Stearic acid 2 parts Solvent Methyl ethyl ketone 125 parts Cyclohexanone 125 parts

"Non-magnetic layer paint"
Ingredient (L1)
Nonmagnetic inorganic powder: 75 parts of acicular α-Fe ₂ O ₃ Average major axis length: 80 nm, Average acicular ratio: 5
Carbon black 20 parts Conductex SC-U (manufactured by Colombian Carbon)
Polyurethane (Glass transition point (Tg): 70 ° C.) 12 parts Phenylphosphonic acid 4 parts Component (L2)
Butyl stearate 3 parts Hexadecyl stearate 3 parts Stearic acid 3 parts Solvent Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts

<Preparation of magnetic tape>
After the above magnetic layer coating component (U1) was kneaded with a kneader, a solvent was added and dispersed using a zirconia bead having a diameter of 0.3 mm for 16 hours using a sand mill. To the obtained dispersion, 5 parts of phenylphosphonic acid was added and stirred for 30 minutes, and then components (U2) and (U3) separately ultrasonically dispersed were added, followed by further ultrasonic mixing for 2 hours and stirring and mixing for 30 minutes. . Further, 3 parts of component (U4) and polyisocyanate and 40 parts of cyclohexanone were added and filtered using a filter having an average pore diameter of 1 μm to prepare a coating solution for the magnetic layer. On the other hand, after the nonmagnetic layer coating component (L1) was kneaded with a kneader, a solvent was added and dispersed using a zirconia bead having a diameter of 0.5 mm for 12 hours using a sand mill. To the resulting dispersion, 2.5 parts of component (L2) and polyisocyanate were added and filtered using a filter having an average pore size of 1 μm to prepare a coating solution for the nonmagnetic layer. This non-magnetic coating solution is applied to a thickness of 0.6 μm, dried at 100 ° C., and the magnetic layer thickness is 0.08 μm thereon, and the average thickness of the center plane is 6 μm. Wet-on-dry coating was performed on polyethylene naphthalate having a surface roughness of 2 nm and a thickness variation of 2%. A seven-stage calendar composed of only metal rolls is processed at a temperature of 90 ° C. and a linear pressure of 300 kg / cm at a speed of 100 m / min, and then heat-cured at 70 ° C. for 24 hours for a 1/2 inch width. The magnetic tape was made by slitting.

(Example 2)
In the addition of phenylphosphonic acid at the time of preparing the magnetic layer coating material of Example 1, the addition of 5 parts of phenylphosphonic acid after the dispersion of component (U1) was changed only by adding the same amount during kneading of component (U1). Made a magnetic tape.

(Example 3)
In the addition of phenylphosphonic acid when preparing the magnetic layer coating material of Example 1, 5 parts of phenylphosphonic acid was added after the dispersion of component (U1), and the same amount was added after 30 minutes of stirring by adding component (U4) The only thing that changed was to make a magnetic tape.

(Comparative Example 1)
In the magnetic layer coating preparation of Example 1, magnetic tapes different only in that no phenylphosphonic acid was added were prepared.

(Comparative Example 2)
In the preparation of the magnetic layer coating material of Example 1, 5 parts of α-Al ₂ O ₃ (average particle size: 0.15 μm) and 5 parts of plate-like alumina powder (average plate diameter: 50 nm) were added to the component (U1). Only changed that and made a magnetic tape.

(Evaluation)
1) SNR measurement In Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2, electrical characteristic measurement was performed using a drum tester (relative speed 5 m / sec).
A signal having a linear recording density of 200 kFCI was recorded using a write head having a Bs = 1.6 T Gap length of 0.2 μm and reproduced by an AMR head (Tw width 3 μm, sh-sh = 0.18 μm). The ratio of 200 kFCI output to 0-400 kFCI integrated noise was measured.

2) MR head deterioration evaluation Each magnetic tape (1 roll 680 m) of Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2 was prepared. Each magnetic tape was set on a reel-to-reel plate tester equipped with an MR head of an IBM drive (model LTO Ultrium 3) and run for 150 hours. A tester was clamped from the MR head to the circuit entrance, and the current value was read to measure the current value change before and after running, that is, the magnitude of the output decrease, and the following criteria were applied.
○: Output decrease is less than 20% Δ: Output decrease is 20% or more and less than 70% ×: Output decrease is 70% or more In addition, 5 plate testers are prepared for each example or each comparative example, and the average of output decrease Evaluated by value. After the evaluation, it was confirmed that a decrease in output occurred due to a decrease in the resistance value of the MR head.
The results are shown in Table 1.

Example with magnetic tape (2)
Example 4
Synthesis of YN-Fe magnetic powder:
While mixing and stirring 840 ml of 0.5 mol / liter iron (II) sulfate heptahydrate aqueous solution and 1000 ml of 1 mol / liter iron nitrate (III) nonahydrate aqueous solution, 2.5 mol / liter hydroxylation 1500 ml of an aqueous sodium solution was added to generate magnetite particles. (Stir for 30 minutes)

  The magnetite particles were placed in an autoclave and heated at 200 ° C. for 4 hours. Washed with water after hydrothermal treatment. The magnetite particles were spherical or spindle-shaped and the average particle diameter was 25 nm from the photograph taken by TEM by the above-described method.

  To 20 g of the magnetite particles, 1000 ml of water was added and treated for 30 minutes using an ultrasonic disperser. To this treatment solution, 2.5 g of yttrium nitrate was added and dissolved. After stirring for 30 minutes, 200 ml of a 0.1 mol / liter sodium hydroxide aqueous solution was added dropwise over 1 hour. After completion of the addition, the mixture was further stirred for 2 hours. Next, this was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which yttrium hydroxide was deposited on the surface of the magnetite particles.

  This powder was reduced by heating in a hydrogen stream at 450 ° C. for 2 hours to obtain an yttrium-iron magnetic powder.

  Next, the temperature was gradually lowered to 150 ° C. with hydrogen gas flowing. When the temperature reached 150 ° C., hydrogen gas was switched to ammonia gas, and nitriding was performed for 30 hours while maintaining the temperature at 150 ° C. Thereafter, with the ammonia gas flowing, the temperature was lowered to 90 ° C., the ammonia gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours.

Further, with the mixed gas flowing, the temperature was lowered to 40 ° C., held for 12 hours, and then taken out into the air. The yttrium-iron nitride magnetic powder thus obtained was 4 atomic% and 12 atomic%, respectively, when the contents of yttrium and nitrogen were measured by fluorescent X-ray. Further, from the X-ray diffraction pattern _to obtain a profile indicating a _Fe 16 _{N 2} phase. A diffraction peak based on Fe ₁₆ N ₂ and a diffraction peak based on α-Fe are observed, and this yttrium-iron nitride magnetic powder is composed of a mixed phase of Fe ₁₆ N ₂ phase and α-Fe phase. all right.

Furthermore, as described above, the particle shape was observed and measured with a TEM, and as a result, it was found that the average axial ratio was 1.2, and the average particle size was 20 nm. The specific surface area determined by the BET method was 57 m ² / g.

Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,194 kA / m (15 kOe) was 140 Am ² / kg (140 emu / g), and the coercive force was 215 kA / m (2,700 Oe). .

  In the preparation of the magnetic layer coating material of Example 1, a magnetic tape was produced which was different only in that the barium ferrite magnetic powder was changed to the yttrium-iron nitride magnetic powder prepared above.

(Example 5)
In the preparation of the magnetic layer coating material of Example 2, a magnetic tape was produced which was different only in that the barium ferrite magnetic powder was changed to the yttrium-iron nitride magnetic powder prepared above.

(Example 6)
In the preparation of the magnetic layer coating material of Example 3, a magnetic tape that differs only in that the barium ferrite magnetic powder was changed to the yttrium-iron nitride magnetic powder prepared above was prepared.

(Comparative Example 3)
In the preparation of the magnetic layer coating material of Comparative Example 1, a magnetic tape differing only in that the barium ferrite magnetic powder was changed to the yttrium-iron nitride magnetic powder prepared above.

(Comparative Example 4)
In the preparation of the magnetic layer coating material of Comparative Example 2, a magnetic tape differing only in that the barium ferrite magnetic powder was changed to the yttrium-iron nitride magnetic powder prepared above.

(Evaluation)
Evaluations similar to those performed in Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2 were performed in Example 4, Example 5, Example 6, Comparative Example 3, and Comparative Example 4. Went about. Table 2 shows the results.

Example with magnetic disk (Example 7)
The nonmagnetic layer coating material prepared in Example 1 was applied to a thickness of 1.5 μm, dried at 100 ° C., and then the magnetic layer coating material prepared in Example 1 was coated on the magnetic layer. Wet-on-dry coating was performed on polyethylene naphthalate having a thickness of 52 μm, a center surface average surface roughness of 4 nm, and a thickness variation of 2% so as to be 0.08 μm. A seven-stage calendar composed of only metal rolls is processed at a temperature of 90 ° C and a linear pressure of 300 kg / cm at a speed of 50 m / min, then punched into a disk shape with a diameter of 1.8 inches, and an alumina polishing tape Was subjected to surface treatment to obtain a magnetic disk.

(Example 8)
The nonmagnetic layer coating material prepared in Example 2 was applied to a thickness of 1.5 μm, dried at 100 ° C., and then the magnetic layer coating material prepared in Example 2 was coated on the magnetic layer. Wet-on-dry coating was performed on polyethylene naphthalate having a thickness of 52 μm, which was the same as that used in Example 7, so as to be 0.08 μm. A seven-stage calendar composed of only metal rolls is processed at a temperature of 90 ° C and a linear pressure of 300 kg / cm at a speed of 50 m / min, then punched into a disk shape with a diameter of 1.8 inches, and an alumina polishing tape Was subjected to surface treatment to obtain a magnetic disk.

Example 9
The nonmagnetic layer coating material prepared in Example 3 was applied to a thickness of 1.5 μm, dried at 100 ° C., and then the magnetic layer coating material prepared in Example 3 was coated on the magnetic layer. Wet-on-dry coating was performed on polyethylene naphthalate having a thickness of 52 μm, which was the same as that used in Example 7, so as to be 0.08 μm. A seven-stage calendar composed of only metal rolls is processed at a temperature of 90 ° C and a linear pressure of 300 kg / cm at a speed of 50 m / min, then punched into a disk shape with a diameter of 1.8 inches, and an alumina polishing tape Was subjected to surface treatment to obtain a magnetic disk.

(Comparative Example 5)
The nonmagnetic layer coating material prepared in Comparative Example 1 was applied to a thickness of 1.5 μm, dried at 100 ° C., and then the magnetic layer coating material prepared in Comparative Example 1 was coated on the magnetic layer. Wet-on-dry coating was performed on polyethylene naphthalate having a thickness of 52 μm, which was the same as that used in Example 7, so as to be 0.08 μm. A seven-stage calendar composed of only metal rolls is processed at a temperature of 90 ° C and a linear pressure of 300 kg / cm at a speed of 50 m / min, then punched into a disk shape with a diameter of 1.8 inches, and an alumina polishing tape Was subjected to surface treatment to obtain a magnetic disk.

(Comparative Example 6)
The nonmagnetic layer coating material prepared in Comparative Example 2 was applied to a thickness of 1.5 μm, dried at 100 ° C., and then the magnetic layer coating material prepared in Comparative Example 2 was coated on the magnetic layer. Wet-on-dry coating was performed on polyethylene naphthalate having a thickness of 52 μm, which was the same as that used in Example 7, so as to be 0.08 μm. A seven-stage calendar composed of only metal rolls is processed at a temperature of 90 ° C and a linear pressure of 300 kg / cm at a speed of 50 m / min, then punched into a disk shape with a diameter of 1.8 inches, and an alumina polishing tape Was subjected to surface treatment to obtain a magnetic disk.

(Evaluation)
1) Signal-to-noise ratio (SNR) measurement Read / write analyzer RWA1632, manufactured by Guzik, USA, spin stand LS-90 manufactured by Kyodo Electronics System Co., Ltd. The signal was recorded on and reproduced from the magnetic disk by changing the recording frequency so that the linear recording density was 350 kfci at a predetermined rotational speed at a predetermined disk position (outer and inner periphery). The waveform of the reproduced signal was taken into a spectrum analyzer, the output was obtained, and the noise was obtained by integrating the region up to twice the recording frequency. The ratio between this output and noise was taken as the SN ratio. The measurement was carried out five times for each of Example 7, Example 8, Example 9, Comparative Example 5 and Comparative Example 6, and averaged.

2) MR head deterioration evaluation In the above SNR measurement, the entire recording area of each magnetic disk was randomly sought, and the output reduction after 120 hours was evaluated as follows.
○: Output decrease is less than 20% △: Output decrease is 20% or more and less than 70% ×: Output decrease is 70% or more In addition, 5 drives are prepared for each example or each comparative example, and the average value of output decrease It was evaluated with. After the measurement, it was confirmed that a decrease in output occurred due to a decrease in the resistance value of the MR head.

  The medium of the present invention has a high SNR and can maintain a high SNR even after traveling, that is, the deterioration of the MR head can be reduced.

Claims (10)

In a magnetic recording medium having at least a magnetic layer containing a ferromagnetic powder, a binder, an abrasive and a phosphorus (P) -containing organic compound on a nonmagnetic support.
The magnetic recording medium is characterized in that the ferromagnetic powder is a hexagonal ferrite powder or an iron nitride-based powder, and the magnetic layer contains 1 to 5 parts by mass of an abrasive with respect to 100 parts by mass of the ferromagnetic powder.   The magnetic recording medium according to claim 1, wherein the ferromagnetic powder has an average plate diameter or average particle diameter of 10 nm to 40 nm.   The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is a hexagonal ferrite powder, and an average plate ratio thereof is 1 to 4. 4.   The magnetic recording medium according to claim 1, wherein the abrasive is diamond particles.   The magnetic recording medium according to claim 1, wherein the abrasive has an average particle diameter of 20 nm to 150 nm.   The phosphorus (P) -containing organic compound is at least one selected from α-naphthyl phosphate, phenyl phosphate, diphenyl phosphate, p-ethylbenzenephosphonic acid, phenylphosphonic acid, phenylphosphinic acid and esters thereof. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is provided.   The magnetic recording medium according to claim 1, wherein the magnetic layer contains 1 to 15 parts by mass of a phosphorus (P) -containing organic compound with respect to 100 parts by mass of the ferromagnetic powder.   The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of 20 nm to 100 nm.   The magnetic recording medium according to claim 1, wherein a nonmagnetic layer containing a nonmagnetic powder and a binder is provided between the nonmagnetic support and the magnetic layer. A liquid preparation step for preparing a magnetic layer liquid containing at least a ferromagnetic powder, a binder, an abrasive, a phosphorus (P) -containing organic compound and a fatty acid ester, and an application for applying the magnetic layer liquid on a nonmagnetic support. In a method of manufacturing a magnetic recording medium having at least a process,
2. The liquid preparation step is performed in the order of dispersion of the ferromagnetic powder in a binder, addition / mixing of the phosphorus (P) -containing organic compound, and addition / mixing of a fatty acid ester. The manufacturing method of the magnetic-recording medium in any one of -9.