JP4268628B2 - Magnetic recording medium and magnetic recording cartridge - Google Patents

Description

  The present invention relates to a magnetic recording medium excellent in high recording density characteristics, particularly to a coating type magnetic recording tape (hereinafter also simply referred to as “magnetic tape” or “tape”).

  Magnetic tapes have various uses such as audio tapes, video tapes, computer tapes, etc. Especially in the field of data backup tapes, with the increase in capacity of hard disks to be backed up, several 10 to 100 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 density is indispensable.

  In manufacturing magnetic tapes corresponding to such high recording densities, it is necessary to develop advanced magnetic powder particles and high density filling of the coating films, smooth coating films, and thin magnetic layers. Technology is used.

  In addition, in order to increase the recording density, the recording signal has been shortened and the track pitch has been narrowed, and a system that also uses a servo track so that the reproducing head can accurately trace the track has appeared. is doing.

  With regard to the improvement of magnetic powder, the magnetic characteristics have been improved year by year in order to cope with short-wavelength recording. In the past, even for high recording density magnetic tapes, audio and home use have been improved. Magnetic powders such as ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, and chromium oxide used for video tapes were mainly used, but at present, needle-like particles with a major axis direction particle size of about 100 nm are used. Metallic magnetic powder has been proposed. Moreover, in order to prevent output reduction due to demagnetization during short wavelength recording, a high coercive force has been achieved year by year, and a coercive force of about 198.9 kA / m has been realized by alloying iron-cobalt. (For example, JP-A-3-49026, JP-A-5-234064, JP-A-6-25702, JP-A-6-139553, etc.).

  In addition, regarding the improvement of the medium manufacturing technology, the surface of the magnetic layer can be improved by improving the binder technology having various functional groups and the dispersion technology when using the above magnetic powder, and further improving the calendar technology performed after the coating process. The smoothness is remarkably improved and greatly contributes to the improvement of short wavelength output (for example, Japanese Patent Publication No. 64-1297, Japanese Patent Publication No. 7-60504, Japanese Patent Laid-Open No. 4-19815, etc.).

  However, since the recording wavelength has been shortened along with the recent increase in density, if the magnetic layer is thick, the output at the saturation magnetization and coercive force level of the conventional magnetic powder in the shortest recording wavelength region. Can be obtained only about a fraction of the time, and since an extremely short recording wavelength is used, the effects of self-demagnetization loss during recording / reproduction and thickness loss due to the thickness of the magnetic layer, which have not been so much of a problem in the past. There is a problem that the resolution becomes large and sufficient resolution cannot be obtained. It is proposed to reduce the thickness of the magnetic layer because such problems cannot be overcome only by improving the magnetic characteristics by the magnetic powder as described above or by improving the surface properties by the medium manufacturing technique.

  That is, in general, the effective thickness of the magnetic layer is said to be about 1/3 of the shortest recording wavelength used in the system. For example, at the shortest recording wavelength of 0.3 μm, the thickness of the magnetic layer is 0. About 1 μm is required. In addition, along with miniaturization of a cassette (also referred to as a cartridge) for storing a tape, it is necessary to make the entire magnetic recording medium thin in order to improve the recording capacity per volume. It is necessary to make it thinner. Furthermore, in order to increase the recording density, the write magnetic flux generated from the magnetic head must be made into a very small area, and the magnetic head has been miniaturized, so the amount of generated magnetic flux will be reduced. In order to cause complete magnetization reversal by such a small magnetic flux, it is necessary to make the magnetic layer thin.

  However, when the thickness of the magnetic layer is reduced, the surface roughness of the nonmagnetic support affects the surface of the magnetic layer, and the surface smoothness of the magnetic layer is likely to be deteriorated. However, depending on these methods, defects during coating and magnetic powder filling properties may not be improved, and the coating film may be reduced. There is a problem of weakening the strength. For this reason, when the magnetic layer is thinned by improving the medium manufacturing technique, an undercoat layer is provided between the nonmagnetic support and the magnetic layer, and the upper magnetic layer is formed while the undercoat layer is in a wet state. So-called simultaneous multi-layer coating methods have been proposed (JP-A 63-187418, JP-A 63-191315, JP-A-5-73883, JP-A-5-217148, JP-A-5-214148). No. 5-298653).

  When the recording track width is narrowed and the recording density in the tape width direction is increased, the magnetic flux leakage from the magnetic tape is reduced. Therefore, an MR head using a magnetoresistive effect element capable of obtaining a high output even with a minute magnetic flux is used as a reproducing head. Must be used.

  Examples of magnetic recording media compatible with MR heads include those described in JP-A-11-238225, JP-A 2000-40217, JP-A 2000-40218, and the like. In the magnetic recording media described in these publications, the magnetic flux (product of residual magnetic flux density and thickness) is set to a specific value or less to prevent the distortion of the output of the MR head, or the dent on the surface of the magnetic layer is specified. The thermal asperity of the MR head is reduced below the value.

  However, if the recording track width is narrowed, a decrease in reproduction output due to off-track becomes a problem, and thus a track servo is necessary to avoid this. The track servo system includes an optical track servo system (Japanese Patent Laid-Open Nos. 11-213384, 11-339254, 2000-293836) and a magnetic servo system. However, in a magnetic tape cartridge (also referred to as a cassette tape) in which a magnetic tape is stored inside a box-shaped case body, a single reel type (single reel type) having only one magnetic tape winding reel is provided. In addition, it is necessary to perform track servo on the magnetic tape drawn from the cartridge. This is because when the tape running speed is increased (for example, 2.5 m / second or more), the two-reel type having two reels for feeding and taking up the tape cannot stably run. In the 2-reel type, the cartridge size increases and the recording capacity per volume decreases.

  As described above, there are two types of track servo methods: magnetic servo method and optical servo method. The former forms a servo track band, which will be described later, on the magnetic layer by magnetic recording, and reads this magnetically to perform servo tracking. In the latter, a servo track band composed of a concave array is formed on the backcoat layer by laser irradiation or the like, and this is optically read to perform servo tracking. In the magnetic servo system, there is a system (for example, Japanese Patent Application Laid-Open No. 11-126327) in which the back coat layer is also magnetized and a magnetic servo signal is recorded on the back coat layer. There is also a method (for example, Japanese Patent Laid-Open No. 11-126328) in which an optical servo signal is recorded in a layer with a material that absorbs light.

Here, the principle of the track servo will be briefly described by taking the former magnetic servo system as an example.
As shown in FIG. 7, in the magnetic tape 3 employing the magnetic servo system, a servo band 200 for track servo and a data track 300 for data recording are provided on the magnetic layer, respectively, extending along the longitudinal direction of the tape. Among these, the servo band 200 includes a plurality of servo signal recording units 201 that magnetically record each servo track number. A magnetic head array (not shown) for recording / reproducing data on / from a magnetic tape includes a pair of servo track MR heads (for forward traveling and reverse traveling) and, for example, 8 × 2 pairs of recording / reproducing heads ( The recording head is composed of a magnetic induction type head, and the reproducing head is composed of an MR head), and the entire magnetic head array is linked based on the signal from the servo track MR head that reads the servo signal. As a result, the recording / reproducing head moves in the tape width direction and the data track (for example, in the case of a magnetic head array equipped with 8 × 2 pairs of recording / reproducing heads, eight servo tracks correspond to one servo track). Data track exists).

  However, improvement of these magnetic powder and medium manufacturing techniques has almost reached the limit at present. In particular, regarding the improvement of the magnetic powder, as long as the acicular magnetic powder is used, the particle size in the major axis direction is practically limited to about 100 nm. This is because if the particle size is made smaller than that, the specific surface area is remarkably increased, the saturation magnetization is lowered, and it is extremely difficult to disperse the magnetic powder in the binder resin.

  Regarding the coercive force, recording is possible even on a medium having a higher coercive force due to technological innovation of the magnetic head. In particular, in the longitudinal recording method, it is preferable to increase the coercive force as much as possible in order to prevent output reduction due to recording and reproduction demagnetization as long as recording and erasing can be performed with a magnetic head. Therefore, the most effective method for improving the recording density of the magnetic recording medium is to increase the coercive force of the magnetic recording medium.

  Further, in order to reduce the influence of output reduction due to recording and reproduction demagnetization, which is an essential problem of longitudinal recording, it is effective to further reduce the thickness of the magnetic layer. As long as a needle-shaped magnetic powder having a particle size of about 100 nm is used, the thickness of the magnetic layer is also limited. Because, due to the longitudinal orientation, the acicular particles are on average arranged so that the acicular direction is parallel to the in-plane direction of the medium, but since the dispersion of particles is distributed, the acicular direction is on the medium surface. This is because there are also particles that are aligned vertically. The presence of such particles impairs the surface smoothness of the medium and causes an increase in noise. Such a problem becomes more serious as the thickness of the magnetic layer decreases.

  Furthermore, when trying to reduce the thickness of the magnetic layer, it is necessary to dilute the magnetic paint with a large amount of an organic solvent, but the conventional finely divided acicular magnetic powder tends to cause aggregation of the magnetic paint, and also when dried. Due to the evaporation of a large amount of organic solvent, the orientation of the magnetic powder tends to decrease, and the orientation of the tape-like medium that is longitudinal recording is poor. There is a problem that it is difficult to obtain the desired electromagnetic conversion characteristics. Therefore, in the longitudinal recording, although it is known that reducing the thickness of the magnetic layer is effective in improving the recording characteristics, as long as the conventional acicular magnetic powder is used, It is difficult to obtain a coating type magnetic recording medium in which the thickness of the magnetic layer is further reduced.

  Among the magnetic powders proposed so far, barium ferrite magnetic powder is known as a magnetic powder having a particle shape of a plate and a particle size of about 50 nm (for example, Japanese Patent Publication No. 60-50323). No. 6-18062). The shape and particle size of the barium ferrite magnetic powder are suitable for obtaining a thin-layer coating type magnetic recording medium as compared with the needle-shaped magnetic powder. However, since barium ferrite magnetic powder is an oxide, the saturation magnetization is about 7.5 μWb / g at most, and it is theoretically possible to obtain a saturation magnetization of 12.6 μWb / g or more like acicular metal or alloy magnetic powder. Is impossible. For this reason, when barium ferrite magnetic powder is used, a coating type magnetic recording medium with a thin magnetic layer can be obtained, but the output is low due to the low magnetic flux density, which is not suitable for a high density magnetic recording medium. . Further, the barium ferrite magnetic powder has a problem that the plate-like powder is strongly aggregated due to magnetic interaction, and it is difficult to break it into individual plate-like particles in the dispersion step. For this reason, acicular magnetic powder as described above has been the mainstream so far for magnetic powders for high recording density magnetic recording media.

  As described above, in the thinning of the magnetic layer, which is an effective technique for improving the recording density of the magnetic recording medium, the coercive force and saturation magnetization of the magnetic powder are maintained as high as possible, In addition, reducing the particle size is an extremely important issue. To overcome this problem, first focusing on the magnetic properties of conventional magnetic powders, the current acicular magnetic powder has a high coercive force because the origin of the coercive force is based on the shape anisotropy due to the acicular shape. There is a theoretical limit to conversion. That is, in the shape anisotropy, the magnitude of the magnetic anisotropy is represented by 2πIs (where Is is a saturation magnetization) and is proportional to the saturation magnetization. Therefore, in the acicular magnetic powder whose coercive force is based on shape anisotropy, the coercive force increases as the saturation magnetization increases.

  As is well known from the slater poling curve, the saturation magnetization of metals and alloys shows, for example, the maximum value in an Fe—Co alloy having a Fe / Co ratio of around 70/30, and the coercive force is also the above. The maximum value is shown in the composition. Such a needle-like Fe—Co alloy magnetic powder having an Fe / Co ratio of around 70/30 has already been put into practical use, but as described above, as long as the needle-like magnetic powder is used, it is theoretically possible. The current coercive force is about 198.9 kA / m, and it is difficult to obtain a high coercive force. Further, such a needle-like magnetic powder is not suitable for a thin-layer coated magnetic recording medium.

  The magnitude of magnetic anisotropy in the shape anisotropy is expressed by 2πIs as described above. When the acicular ratio (particle length / particle diameter) of the magnetic powder is about 5 or more, the coefficient is approximately Although expressed by 2π, the coefficient decreases rapidly when the acicular ratio is less than 5, and the anisotropy disappears when it becomes spherical. In other words, as long as a magnetic material such as Fe metal or Fe—Co alloy is used as the magnetic powder, the magnetic powder must be theoretically shaped like a needle.

  As described above, in order to improve the short wavelength recording / reproducing characteristics, an undercoat layer having a thickness of about 2.0 μm is provided on the nonmagnetic support, and a thickness of about 0.15 to 0.2 μm is formed thereon. In order to further improve the recording density, the magnetic layer is composed of at least one magnetic layer, and the thickness of the uppermost magnetic layer (hereinafter simply referred to as the upper magnetic layer) is set to 0. It is preferable that the thickness is 09 μm or less.

  However, if the thickness of the upper magnetic layer is reduced, the magnetic servo signal becomes weak in the method of servo tracking using the magnetic servo signal of the magnetic layer. JP-A Nos. 04-248120 (see Examples), JP-A Nos. 2000-315312 and 2002-288817 are known as methods for solving this problem. In this method, the magnetic recording medium has a configuration of “upper magnetic layer / nonmagnetic intermediate layer / lower magnetic layer / nonmagnetic support”, and a magnetic servo signal is recorded on the lower magnetic layer.

  However, in this method, since the acicular magnetic powder having a major axis direction particle size of about 100 nm is used for the upper magnetic layer, as described above, the acicular direction of the acicular magnetic powder of the upper magnetic layer is the medium. Since there are particles arranged so as to be perpendicular to the surface, there is a problem that the surface smoothness of the medium is impaired and noise increases. Such a problem becomes more serious as the thickness of the magnetic layer is reduced.

  Furthermore, when acicular magnetic powder is used, the thickness of the upper magnetic layer becomes thin, especially when the thickness is 0.09 μm or less, the thickness unevenness of the upper magnetic layer becomes large.

  In order to reduce the thickness of the upper magnetic layer to 0.09 μm or less and to reduce the thickness unevenness of the upper magnetic layer, an essentially spherical or elliptical magnetic powder having a particle diameter of 50 nm or less (preferably 30 nm or less) is required. It becomes.

  In addition, the total thickness of the magnetic recording medium can be set to a total thickness of the nonmagnetic intermediate layer and the lower magnetic layer of 1.4 μm or less, a nonmagnetic support thickness of 4.0 μm or less, and a back layer thickness of 0.5 μm or less. It is preferable to reduce to less than 6 μm. The total thickness of the magnetic recording medium is more preferably 5 μm or less, further preferably 4.5 μm or less, and even more preferably 4 μm or less. In practice, it is 2.5 μm or more.

  Further, in order to accurately trace a track corresponding to a track pitch that is becoming narrower, it is necessary that the dimensions between the tape edge and the data track, the servo track and the data track be constant, and the temperature of the tape. Further, a higher level of dimensional stability against humidity is being demanded.

  An object of the present invention is to provide a magnetic recording medium that can solve the above-described problems and is excellent in high recording density characteristics that can cope with a recording capacity of 1 TB or more.

According to the invention, the object is
Nonmagnetic support, at least one nonmagnetic intermediate layer containing nonmagnetic powder and binder resin formed on one surface of the nonmagnetic support, and magnetic powder formed on the nonmagnetic intermediate layer And a magnetic recording medium having at least one magnetic layer containing a binder resin,
The magnetic powder has a core portion and an outer layer portion, the rare earth element is mainly present in the outer layer portion, and the core portion is Fe ₁₆ N ₂ in which iron or a part of iron is substituted with a transition metal element. A magnetic recording medium comprising a phase, wherein the magnetic layer has a thickness of 0.09 μm or less and a coercive force of 200 to 400 kA / m, and a nonmagnetic support, At least one nonmagnetic intermediate layer containing nonmagnetic powder and binder resin formed on one surface of the magnetic support, and magnetic powder and binder resin formed on the nonmagnetic intermediate layer A magnetic recording medium having at least one magnetic layer,
The magnetic powder includes a core portion and an outer layer portion, the rare earth element is mainly present in the outer layer portion, and the core portion is Fe ₁₆ N ₂ phase in which iron or a part of iron is substituted with a transition metal element. And the product (Br · δ) of the residual magnetic flux density (Br) and the thickness (δ) of the uppermost magnetic layer of the magnetic layer is 0.0018 to 0.05 μTm, and the coercive force is 200 to 400 kA. This is achieved by a magnetic recording medium characterized by / m.

  The thickness of the uppermost magnetic layer is preferably 0.09 μm or less because high density magnetic recording can be performed. Needless to say, the magnetic powder used in the present invention preferably has an essentially spherical or elliptical particle shape and has a number average particle diameter equal to or smaller than the thickness of the upper magnetic layer. .

  Although the iron-based magnetic powder having the above specific structure is essentially a spherical or elliptical ultrafine magnetic powder, a magnetic recording medium using the same easily obtains a high coercive force and a high magnetic flux density. It is done. As used herein, “essentially spherical or elliptical” (or “essentially spherical or essentially elliptical”) means that the surface has irregularities as shown in the photograph of FIG. Also included are “spherical or elliptical” having some deformation.

  Further, the magnetic recording medium using the iron-based magnetic powder having a spherical shape or an elliptical shape and having a very small particle size as described above has a small magnetic interaction between the magnetic powders. It has also been found that since the magnetization reversal is possible and the magnetization reversal region is narrowed, superior recording characteristics can be obtained as compared with a magnetic recording medium using a conventional needle-shaped magnetic powder.

The magnetic recording medium of the present invention is particularly effective when the thickness of the magnetic layer is as thin as 0.09 μm or less. However, in such a medium with a thin magnetic layer, demagnetization due to a demagnetizing field is achieved. It was found that the recording characteristics were excellent even with a coercive force of 80 kA / m (1,005 Oe).
However, considering erroneous erasure due to an external magnetic field such as a magnet, the coercive force of the magnetic recording medium is preferably 200 kA / m (2,512 Oe) or more even in the present application. Although there is no particular upper limit on the coercive force, it is currently 400 kA / m (5,024 Oe) or less in view of the writing ability of the magnetic head. If the magnetic layer is 0.09 μm or less, excellent overwrite characteristics can be obtained even in a magnetic recording medium having a high coercive force of 200 kA / m to 400 kA / m.

  As a result of diligent investigations on thinning of the nonmagnetic intermediate layer, dimensional stability with respect to temperature and humidity, plate-like particles having a number average particle diameter of 10 nm to 100 nm (hereinafter sometimes referred to as plate-like powder). It was found that a non-magnetic intermediate layer having a uniform thickness, excellent surface smoothness, and excellent dimensional stability against temperature and humidity can be obtained.

  Conventionally used acicular iron-cobalt alloy magnetic powder for high-density coating type magnetic recording media has a coercive force approaching the theoretical limit, and the particle size is smaller than the current one. Then, uniform dispersion is extremely difficult. The biggest problem with iron-cobalt alloy magnetic powder is that it has a uniaxial magnetic anisotropy in which the particle shape is close to a spherical shape with a minimum specific surface area and one direction is the direction of easy magnetization. It is essentially impossible to do. Because the origin of the coercive force is based on the shape magnetic anisotropy due to the needle-like shape, the needle-like ratio can only be reduced to about 5 at the minimum. This is because the properties are reduced and the coercive force is reduced.

  The inventor synthesized various magnetic powders and investigated the magnetic anisotropy in order to improve the magnetic characteristics from a viewpoint different from the magnetic powder based on the conventional shape magnetic anisotropy. As a result, certain iron-based magnetic powders have large magnetocrystalline anisotropy, so there is no need to make them acicular, and even spherical or elliptical magnetic powders have a large coercive force in one direction. It was found that can be expressed. The essentially elliptical magnetic powder referred to in the present invention refers to those having a major axis to minor axis ratio of 2 or less (preferably 1.5 or less), and are used for conventional magnetic recording media. Powder is essentially different in shape.

  Essentially spherical or elliptical magnetic powder includes rare earth-iron-boron magnetic powder (Japanese Patent Laid-Open No. 2001-181754) and rare earth such as rare earth-iron-based magnetic powder (Japanese Patent Laid-Open No. 2002-56518). -There is iron-based magnetic powder. As the rare earth element used in these magnetic powders, at least one element selected from yttrium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium, terbium, and the like is used. Among them, neodymium (Nd) , Samarium (Sm), terbium (Tb), and yttrium (Y) are preferably used because high coercive force is easily obtained when these are used.

Also known is an essentially spherical iron nitride-based magnetic powder (Japanese Patent Laid-Open No. 2000-277311) which does not contain rare earth elements but has a BET specific surface area of 10 m ² / g or more with an Fe ₁₆ N ₂ phase as a main phase. ing. The inventors have improved the magnetic powder to produce the iron nitride magnetic powder of the present invention that is optimal as a high-density magnetic recording medium.

The main improvement is that, as will be described later, the coercive force can be increased by making the outer layer part of the magnetic powder mainly contain rare earth elements having a high effect of preventing sintering, increasing the coercive force, and improving the stability (corrosion resistance). with as high as 200 kA / m or more, is that the BET specific surface area suitable for high density recording is chemically stable fine magnetic powder 40m ² / g~100m ² / g. In addition, the saturation magnetization of the magnetic powder is controlled to 10 to 20 μWb / g by allowing the rare earth element to be mainly present in the outer layer portion of the magnetic powder and performing the oxidation stabilization treatment, and the paint dispersibility and oxidation stability Rare earth-iron nitride magnetic powder with excellent properties. Due to such improvements, a magnetic powder exhibiting optimum characteristics as the magnetic powder for the uppermost layer of the present invention was obtained. The rare earth-iron nitride magnetic powder thus obtained has a coercive force of 200 kA / m or more, is fine, and has high dispersibility and chemical stability during the preparation of the magnetic paint. - iron - boron magnetic powder, a rare earth - iron magnetic powder, as compared with iron nitride-based magnetic powder the Fe ₁₆ N ₂ phase as the main phase not containing a rare earth element, in particular magnetic powder the uppermost magnetic layer of the present invention It is suitable as.

Further, as a result of further investigation, as for the iron-based magnetic powder in which the core portion contains the Fe ₁₆ N ₂ phase as the main phase, aluminum and / or silicon is mainly present in the outer layer portion of the magnetic powder, thereby allowing the rare earth It has been found that an iron nitride magnetic powder having a coercive force of about 200 kA / m is obtained although the coercive force is slightly smaller than that of the element-iron nitride magnetic powder. The content of aluminum and / or silicon is preferably 1 to 20 atomic%, more preferably 2 to 20 atomic%, and still more preferably 4 to 18 atomic% based on Fe. Also in this case, it is more preferable to contain a rare earth element together with aluminum and / or silicon.

  Such an essentially spherical or elliptical iron nitride-based magnetic powder (simply iron-based magnetic powder) is applied to a thin-layer coated magnetic recording medium, particularly a coated magnetic recording medium having a total thickness of less than 6 μm. When applied, high coercivity of the upper magnetic layer, high saturation magnetic flux density, uniform dispersion of magnetic powder by improving paint dispersibility, and improved oxidation stability can be achieved at the same time, realizing high output and high C / N. it can.

As described above, the iron nitride magnetic powder used in the present invention mainly contains an Fe ₁₆ N ₂ phase (hereinafter sometimes simply referred to as “iron nitride phase”) in the core portion. Such iron nitride magnetic powders will be described for each type.

-Rare earth-iron nitride magnetic powder containing an iron nitride phase in the core portion The rare earth-iron nitride magnetic powder containing an iron nitride phase in the core portion is 0.05 to 20 atomic% (preferably 0). When covering the outer layer portion of the magnetic powder in the rare earth element .2～20 atomic%), the coercive force is as high as 200kA / m (2,512Oe) above, BET specific surface area of 40m ² / g~100m ² / g A chemically stable fine magnetic powder can be obtained. Moreover, the saturation magnetization of the magnetic powder is 10 to ²⁰ μWb / g (79.6 to 159.2 Am ² / kg, 79.6 to 159.2 emu / g), and a rare earth-iron nitride magnetic powder excellent in paint dispersibility and oxidation stability can be obtained. The core portion of the magnetic powder mainly consists of Fe ₁₆ N ₂ phase or Fe ₁₆ N ₂ phase and α-Fe phase, and the nitrogen content is 1.0 to 20 atomic% with respect to iron. Further, a part of iron (40 atomic% or less) may be substituted with another transition metal element. However, when a large amount of cobalt is added, a long time is required for the nitriding reaction, so that it is usually 10 atomic% or less. The rare earth-iron nitride magnetic powder containing an iron nitride phase in the core portion is particularly suitable as the magnetic powder of the uppermost magnetic layer of the present invention.

-Aluminum and / or silicon-iron nitride magnetic powder containing an iron nitride phase in the core portion. As described above, regarding the iron magnetic powder in which the core portion contains the Fe ₁₆ N ₂ phase as the main phase, aluminum and By making silicon mainly present in the outer layer portion of the magnetic powder, the coercive force is slightly smaller than that of the rare earth element-iron nitride magnetic powder, but the iron nitride magnetic powder having a coercive force of about 200 kA / m is obtained. can get. The content of aluminum and / or silicon is preferably 1 to 20 atomic%, more preferably 2 to 20 atomic%, and still more preferably 4 to 18 atomic% with respect to Fe. Also in this case, it is more preferable to contain the above-mentioned amount of rare earth elements together with aluminum and / or silicon.

  As a result of studying the particle size of the iron nitride-based magnetic powder, the present inventor has found that when the average particle size is 5 to 50 nm, excellent magnetic properties of the upper magnetic layer can be achieved. In the conventional acicular magnetic powder, in order to maintain a high coercive force, the average particle size in the major axis direction is almost limited to about 100 nm. However, the magnetic powder of the present invention is mainly crystalline anisotropic. Since it has the origin of coercive force, it can be made extremely fine particles having an average particle size of up to 5 nm, and even such fine particles can exhibit excellent magnetic properties. A particularly preferred average particle size is 8 nm or more, more preferably 10 nm or more.

  When the average particle size of the magnetic powder is too large, the filling property of the magnetic powder in the magnetic layer is lowered, and the surface property is lowered when the upper magnetic layer is thinned. Further, a magnetic recording medium is obtained. At the same time, the particle noise due to the size of the particles increases. Therefore, the average particle size needs to be 50 nm or less, preferably 40 nm or less, more preferably 30 nm or less. With this setting, extremely high filling properties can be obtained, and excellent saturation magnetic flux density can be achieved. The average particle size of 50 nm or less, particularly preferably 30 nm or less, is particularly important when the upper magnetic layer thickness is 0.09 μm or less.

  In the present specification, the average particle size of the magnetic powder is measured by measuring the particle size of a photograph taken at a magnification of 250,000 times with a transmission electron microscope (TEM) (the dimension of the maximum portion of each particle), The average particle size of 500 particles or the particle size of a photograph taken at a magnification of 200,000 times was measured in the same manner, and the average of 300 particle sizes was obtained (unless otherwise specified) By the former method).

  In the rare earth-iron nitride-based magnetic powder used in the present invention, when an iron alloy is used as the iron component, transition metals such as Mn, Zn, Ni, Cu, and Co are used as the metal species forming the alloy with iron. . Among these, Co and Ni are preferable, and Co is particularly preferable because it can improve saturation magnetization most. As a quantity of said transition metal element, it is preferable to set it as 5-50 atomic% with respect to iron, and it is more preferable to set it as 10-30 atomic%. However, the Co content is preferably 10 atomic% or less.

  In the case of the rare earth-iron nitride magnetic powder, the amount of rare earth is preferably 0.05 to 20 atomic%, more preferably 0.2 to 20 atomic%, and still more preferably 0.00% with respect to iron in the entire magnetic powder. It is 5 to 15 atomic%, more preferably 1.0 to 10 atomic%.

  Next, the particle shape of the iron nitride magnetic powder will be described from the viewpoint of the dispersibility of the magnetic paint and the characteristics for forming a thin magnetic layer. First, conventional needle-shaped magnetic powders have a smaller particle size to improve recording characteristics such as noise reduction, but as a result, the specific surface area inevitably increases and interacts with the binder resin. It becomes difficult to obtain a uniform dispersion when dispersed in a binder resin, and when diluted with a large amount of an organic solvent for thin layer coating, the magnetic powder tends to agglomerate, and orientation and surface smoothness are likely to occur. Deteriorates. For this reason, there is a limit to the particle size of magnetic powder that can be used as a coating type magnetic recording medium.

  On the other hand, the iron nitride-based magnetic powder used in the present invention has a particle shape that is essentially spherical or elliptical, and can have a shape close to a sphere with a minimum specific surface area. For this reason, compared with conventional magnetic powders, the interaction with the binder resin is small, the fluidity of the magnetic coating is good, and even if the magnetic powders form aggregates, the dispersion becomes easy, and the magnetic layer Magnetic coatings that are particularly suitable for thin layer coating can be prepared. As a result, it is sufficiently practical even if the average particle size is about 5 nm as described above.

  In order to reduce the effect of output reduction due to recording and reproduction demagnetization, which is an essential problem in longitudinal recording, it is effective to reduce the thickness of the upper magnetic layer, but the grain size in the major axis direction is effective. As long as a needle-shaped magnetic powder having a thickness of about 100 nm is used, the upper magnetic layer has a limited thickness. This is because, by magnetic field orientation, the acicular particles are aligned so that the acicular direction is parallel to the in-plane direction of the medium on average, but since the orientation is distributed, the acicular direction is perpendicular to the medium surface. There are also particles distributed as such. When such particles are present, the needle-like magnetic powder protrudes from the surface of the upper magnetic layer, which impairs the surface smoothness of the medium and causes a significant increase in noise. This problem becomes more prominent as the thickness of the upper magnetic layer becomes thinner. Therefore, as long as needle-like magnetic powder is used, a coating film having a smooth surface is produced with the upper magnetic layer thickness being about 0.1 μm or less. It is difficult to do so.

  In addition, when providing a nonmagnetic intermediate layer formed between the upper magnetic layer and the lower magnetic layer in order to reduce the thickness of the upper magnetic layer, acicular magnetic powder is used while the nonmagnetic intermediate layer is wet. In the simultaneous multi-layer coating method in which the contained magnetic paint is applied onto the nonmagnetic intermediate layer, the magnetic powder is dragged to the nonmagnetic intermediate layer, so that the acicular magnetic powder tends to protrude into the nonmagnetic intermediate layer at the interface of the upper magnetic layer. Further, the orientation is more easily disturbed, so that a desired squareness ratio cannot be obtained and the smoothness of the upper magnetic layer surface is lowered. This is also considered to be one of the factors that hinder high density by thin layer coating when using acicular magnetic powder.

  On the other hand, the iron nitride magnetic powder used in the present invention not only has a small particle size, but also has a particle shape that is essentially spherical or elliptical, and can take a shape close to a sphere. The phenomenon that particles protrude from the surface of the upper magnetic layer does not occur unlike acicular magnetic powder, and when providing the nonmagnetic intermediate layer, the magnetic powder protrudes into the nonmagnetic intermediate layer compared to the acicular magnetic powder. And an upper magnetic layer with extremely good surface smoothness can be formed. Further, when the thickness of the upper magnetic layer is reduced, the magnetic flux from the upper magnetic layer is reduced, resulting in a problem that the output is reduced. However, the magnetic powder used in the present invention has essentially a particle shape. Since it can be spherical or elliptical and can have a shape close to a sphere, it is easier to fill the upper magnetic layer with magnetic powder than acicular magnetic powder, and as a result, high magnetic flux density is easily obtained. It also has a great advantage.

  Furthermore, with regard to saturation magnetization, metal or alloy magnetic powder generally has a specific surface area that increases as the particle size decreases, and the proportion of the surface oxide layer that does not contribute to saturation magnetization increases. The part becomes smaller. That is, as the particle size decreases, the saturation magnetization also decreases. This tendency is particularly noticeable in the needle-like magnetic powder, and the saturation magnetization suddenly decreases with the major axis length of around 100 nm as a boundary. Such a decrease in saturation magnetization is one of the factors that determine the limit of usable particle size. On the other hand, the iron nitride magnetic powder used in the present invention is essentially spherical or elliptical in particle shape. Therefore, when compared at the same volume, the specific surface area is minimized and the particles are fine particles. Regardless, it is possible to maintain high saturation magnetization.

  In the present invention, the shape of the iron nitride-based magnetic powder is expressed as “essentially spherical or elliptical”, which includes everything from a substantially spherical shape to an elliptical shape (that is, from a substantially spherical shape). Including an intermediate shape up to an ellipse shape) means that any shape included therein may be used. That is, in order to distinguish from the “needle shape” which is the shape of the conventional magnetic powder, such an expression is used. Among the above shapes, a spherical or elliptical shape having the smallest specific surface area is preferable. This shape can be observed with a scanning electron microscope as in the case of the particle size. As already mentioned, the “essentially spherical or elliptical” as used in the present invention means that the surface has irregularities and a slightly spherical or spherical shape as shown in the photograph of FIG. Including “oval”.

As described above, the essentially spherical or elliptical iron nitride magnetic powder used in the present invention has a saturation magnetization, a coercive force, a particle size, and a particle shape, all of which provide a thin upper magnetic layer. When this is used and a magnetic recording medium having an upper magnetic layer with an average thickness of 0.09 μm or less is used, particularly excellent recording / reproducing characteristics can be obtained. Among the above magnetic powders, in order to improve characteristics in a high recording density region in a magnetic recording medium having an average thickness of the upper magnetic layer of 0.09 μm or less, the saturation magnetization is 10 to 25 μWb / g (79.6 to 199.0 Am ² / kg) is preferable, and 10 to 20 μWb / g (79.6 to 159.2 Am ² / kg) is more preferable.

  In this specification, the coercive force and saturation magnetization of the magnetic powder are corrected by a reference sample when measured with an applied magnetic field of 1,274 kA / m (16 kOe) at 25 ° C. using a sample vibration magnetometer. Means the value of.

  In order to highly fill and disperse the ultrafine magnetic powder having an average particle size of 50 nm or less in the coating film, it is preferable to carry out coating production in the following steps. As a pre-process of the kneading process, the magnetic powder granules are pulverized using a pulverizer, and then mixed with a phosphoric acid organic acid or a binder resin in a mixer, and then the surface treatment of the magnetic powder and the binder resin are performed. A step of mixing is provided. As the kneading step, kneading is performed by a continuous biaxial kneader at a solid content concentration of 80 to 85% by weight and a ratio of the binder resin to the magnetic powder of 17 to 30% by weight. Subsequent to the kneading step, using a continuous twin-screw kneader or other diluting device, a step of kneading and diluting by adding at least one binder resin solution and / or solvent, rotating a small media such as a sand mill The paint is dispersed by a dispersion process using a mold dispersion device.

  In one aspect of the present invention, the product of the residual magnetic flux density in the tape longitudinal direction and the magnetic layer thickness of the upper magnetic layer (information recording layer) is preferably 0.0018 to 0.05 μTm, and 0.0036 to 0.05 μTm. Is more preferable, and 0.004 to 0.05 μTm is more preferable. If this product is less than 0.0018 μTm, the reproduction output by the MR head is small, and if it exceeds 0.05 μTm, the reproduction output by the MR head tends to be distorted. A magnetic recording medium having such a magnetic layer is preferable because the recording wavelength can be shortened and, in addition, the reproduction output when reproduced by the MR head can be increased, and the distortion of the reproduction output is small and the output-to-noise ratio can be increased. .

  A nonmagnetic intermediate layer is provided between the upper magnetic layer for information recording and the lower magnetic layer for servo signal recording. This non-magnetic intermediate layer prevents the information signal in the upper magnetic layer from being disturbed by the magnetic recording information signal in which the information signal is magnetically recorded in the lower magnetic layer when the information signal is recorded in the upper magnetic layer. Is a layer. As a result of simulation under the condition that the thickness of the upper magnetic layer is 0.09 μm, the coercive force of the upper magnetic layer is 200 kA / m, the coercive force of the lower magnetic layer is 200 kA / m, and the maximum wavelength of the information signal is 0.2 μm. When the thickness of the nonmagnetic intermediate layer is 0.2 μm or more, the information signal is not recorded in the lower magnetic layer, and therefore, the information signal of the upper magnetic layer is not disturbed by the magnetic recording information signal of the lower magnetic layer. . Further, if the nonmagnetic intermediate layer thickness is 0.2 μm or more, the lower magnetic layer has a low coercive force component of about 80 kA / m. Even if an information signal is magnetically recorded, due to spacing loss, It was also found that the noise signal from the lower magnetic layer does not reach the MR head that reproduces the information signal.

  On the other hand, the upper magnetic layer has a thickness of 0.06 μm, the upper magnetic layer has a coercive force of 200 kA / m, the lower magnetic layer has a coercive force of 200 kA / m, the lower magnetic layer has a thickness of 0.5 μm, and has the shortest servo signal. As a result of simulation under the condition that the wavelength is 5 μm, if the non-magnetic intermediate layer thickness is 0.5 μm or less, the servo signal is recorded in saturation in the lower magnetic layer, and the servo signal is recorded only in the upper magnetic layer. As compared with the case where the magnetic head is present, the magnetic flux entering the MR head for reproducing the servo signal is apparently higher by 3.2 dB (1.4 times) or more. Of course, the MR head is controlled so that the same output can be obtained by adjusting the magnetic field applied to the MR head. However, even in this case, the distortion of the MR head signal is caused when a certain amount of magnetic flux enters the MR head. The reading S / N becomes higher as the value decreases.

Similarly, the magnetic flux entering the MR head for reproducing the servo signal when the nonmagnetic intermediate layer thickness is 0.3 μm or less is 6.3 dB (2.1 times) or more.
From the above simulation results, the thickness of the nonmagnetic intermediate layer is preferably 0.2 μm or more and 0.8 μm or less, more preferably 0.6 μm or less, and more preferably 0.5 μm or less.
Note that the simulation was performed using the magnetic field analysis software JMAG (finite element method) manufactured by Japan Research Institute. Moreover, the simulation mentioned later was also performed by the same method.

  Examples of nonmagnetic particles used for the nonmagnetic intermediate layer include titanium oxide, iron oxide, and aluminum oxide. Preferably, iron oxide alone or a mixed system of iron oxide and aluminum oxide is used. Usually, non-magnetic iron oxide having a major axis length of 0.05 to 0.2 μm and a minor axis length of 5 to 200 nm is mainly used, and carbon black having a particle diameter of 0.01 to 0.1 μm as necessary. In many cases, 1 to 0.5 μm of aluminum oxide is supplementarily contained. The non-magnetic particles and carbon black are not particularly sharp in the particle size distribution, and when the thickness of the non-magnetic intermediate layer is 1.0 μm or more, it is not a problem, but the thickness of the non-magnetic intermediate layer is 0. When the thickness is less than .9 μm, the particles in the large particle size portion of the particle size distribution affect the surface roughness of the nonmagnetic intermediate layer.

  Therefore, in the present invention, plate-like aluminum oxide particles having a number average particle diameter of 10 nm to 100 nm are used as aluminum oxide particles suitable for a nonmagnetic intermediate layer having ultrafine particles and a small particle size distribution. The plate-like iron oxide particles alone or a mixed system of the plate-like iron oxide particles and the plate-like aluminum oxide particles may be used. In order to impart conductivity, the same plate-like ITO particles may be mixed with the same plate-like iron oxide particles or the same plate-like aluminum oxide particles, but the same plate-like ITO particles are expensive.

  The plate-like aluminum oxide particles having a particle diameter of 10 nm to 100 nm used in the present invention have two major characteristics. One is a plate-like form of ultrafine particles, so even in a thin layer coating of 0.9 μm or less, the thickness unevenness is small and the smoothness of the surface is not lowered. The second feature is that since the coating film is formed in a state where the plate-like particles are overlapped, the reinforcing effect in the planar direction of the coating film is large, and at the same time, the dimensional stability due to changes in temperature and humidity is also increased.

  A lower magnetic layer is provided for servo signal recording. As shown in FIG. 1, a typical coating composition is “upper magnetic layer (information recording layer) / nonmagnetic intermediate layer / lower magnetic layer / (undercoat layer) / nonmagnetic support”.

  The upper magnetic layer has a thickness of 0.06 μm, the upper magnetic layer has a coercive force of 200 kA / m, the nonmagnetic intermediate layer has a thickness of 0.5 μm, the lower magnetic layer has a coercive force of 200 kA / m, and the servo signal has the shortest wavelength. As a result of simulation under the condition of 5 μm, if the thickness of the lower magnetic layer is 1.0 μm or less, the servo signal is saturated and recorded in the lower magnetic layer. If the thickness of the lower magnetic layer is 0.3 μm or more, the magnetic flux entering the MR head for reproducing the servo signal is 0.5 dB (1... Compared with the case where the servo signal is recorded only in the upper magnetic layer. It became clear that it was higher than (1x). Of course, the MR head is controlled so that the same output can be obtained by adjusting the magnetic field applied to the MR head. However, even in this case, the distortion of the MR head signal is caused when a certain amount of magnetic flux enters the MR head. The reading S / N becomes higher as the value decreases.

  Similarly, the magnetic flux entering the MR head reproducing the servo signal when the lower magnetic layer thickness is 0.6 μm is 4.1 dB (1.6 times), and the lower magnetic layer thickness is 0.8 μm and the servo signal output is 5 0.6 dB (1.9 times) and the thickness of the lower magnetic layer was 1.0 μm, which was 6.7 dB (2.2 times). If the thickness of the lower magnetic layer is 1.0 μm or more, not only the effect is saturated, but also the servo signal is difficult to be saturated.

  From the above simulation, the thickness of the lower magnetic layer is preferably 0.3 μm or more and 1.0 μm or less. In order to reduce the total thickness of the magnetic recording medium, 0.8 μm or less is more preferable, and 0.6 μm or less is preferable. More preferred.

Next, the components of the magnetic recording medium of the present invention will be described in detail.
<Essentially spherical or elliptical iron-based magnetic powder>
-Rare earth-iron nitride magnetic powder containing an iron nitride phase in the core part In the upper magnetic layer, essentially spherical or elliptical iron magnetic powder is used. Here, a magnetic particle comprising a rare earth element and a transition metal element mainly composed of iron or iron, and the rare earth element is mainly present in the outer layer portion of the magnetic powder, and the core portion of the magnetic powder is metallic iron, an iron alloy Alternatively consists of at least one iron compound, essentially spherical or oval rare earth iron compound is part of Fe ₁₆ N ₂ or iron is Fe ₁₆ N ₂ substituted with a transition metal element - iron system magnetic powder The preferred form of will be described in detail.
The rare earth-iron nitride magnetic powder of the present invention is an essentially spherical or elliptical magnetic powder in which rare earth elements are mainly present in the outer layer portion of the magnetic powder, and the average particle size is preferably 5 to 50 nm. 8 nm or more is more preferable, and 10 nm is more preferable. Moreover, 40 nm or less is more preferable and 30 nm or less is further more preferable. The average axial ratio [average value of the ratio of the major axis length (major axis) to the minor axis length (minor axis)] is preferably 2 or less, particularly preferably 1.5 or less. The content of rare earth elements relative to iron is preferably 0.05 to 20 atomic%, and more preferably 0.2 to 20 atomic%. The nitrogen content relative to iron is preferably 1.0 to 20 atomic%. The BET specific surface area is preferably 40 to 100 m ² / g.

  The rare earth-iron nitride magnetic powder of the present invention uses an iron-based oxide or hydroxide as a starting material, and deposits a rare earth element on the iron-based oxide or hydroxide. It is manufactured by performing nitriding at the following temperature.

In the rare earth-iron nitride magnetic powder of the present invention, the rare earth element content relative to iron is preferably 0.05 to 20 atomic%, more preferably 0.2 to 20 atomic%, and 0.5 to 15 atomic%. More preferably, 1.0 to 10 atomic% is even more preferable. The nitrogen content relative to iron is preferably 1.0 to 20 atomic%, more preferably 1.0 to 12.5 atomic%, and still more preferably 3 to 12.5 atomic%. If the amount of rare earth elements is too small, the contribution of magnetic anisotropy based on the rare earth elements becomes small, and coarse particles are likely to be generated by sintering during reduction, resulting in poor particle size distribution. When there are too many rare earth elements, unreacted rare earth elements increase in addition to the rare earth elements contributing to magnetic anisotropy, and an excessive decrease in magnetic properties, particularly saturation magnetization, is likely to occur. If the amount of nitrogen is too small, the amount of Fe ₁₆ N ₂ phase formed is small and the effect of increasing the coercive force is reduced. If the amount is too large, iron nitride having a small coercive force such as Fe ₄ N or Fe ₃ N, and Nonmagnetic nitrides are easily formed, the effect of increasing the coercive force is reduced, and saturation magnetization tends to be excessively lowered.

  The shape of the rare earth-iron nitride magnetic powder of the present invention is essentially spherical or elliptical with an average axial ratio of 2 or less (especially essentially spherical with 1.5 or less), and the average particle size is 5 to 50 nm is preferable. 8 nm or more is more preferable, and 10 nm or more is more preferable. 40 nm or less is more preferable, and 30 nm or less is more preferable. When the particle size is too small, the dispersibility at the time of preparing the magnetic coating material is deteriorated, it becomes thermally unstable, and the coercive force is likely to change with time. If the particle size is too large, it not only causes an increase in noise but also makes it difficult to obtain a smooth magnetic layer surface.

  The average particle size of the rare earth-iron nitride magnetic powder was obtained by actually measuring the particle size of a photograph taken at a magnification of 200,000 times with a transmission electron microscope (TEM) and averaging 300 particle sizes. .

Rare earth present invention - the saturation magnetization of the iron nitride-based magnetic powder, 80~160Am ² /kg(80~160emu/g,10.0~20.1μWb/g) are more preferable, 90~155Am ² / kg (90 ˜155 emu / g, 11.3-19.5 μWb / g) is more preferred, and 100-145 Am ² / kg (100-145 emu / g, 12.6-18.2 μWb / g) is even more preferred. The coercive force is preferably 80 to 400 kA / m (1,005 to 5,024 Oe). 119.4 kA / m (1,500 Oe) or more is more preferable, 159.2 kA / m (2,000 Oe) or more is more preferable, 180 kA / m (2,261 Oe) or more is more preferable, 200 kA / m (2,512 Oe) ) Or more is most preferred. Furthermore, 318.5 kA / m (4,000 Oe) or less is more preferable, and 278.6 kA / m (3,500 Oe) or less is more preferable.

The rare earth-iron nitride magnetic powder of the present invention preferably has a BET specific surface area of 40 to 100 m ² / g. If the BET specific surface area is too small, the particle size becomes large. Therefore, when applied to a magnetic recording medium, the particulate noise tends to increase, and the surface smoothness of the magnetic layer tends to decrease, and the reproduction output tends to decrease. On the other hand, if the BET specific surface area is too large, it is difficult to obtain a uniform dispersion in the magnetic paint due to the aggregation of the magnetic powder, and when applied to a magnetic recording medium, the orientation and the surface smoothness tend to decrease.

  As described above, the rare earth-iron nitride magnetic powder of the present invention has excellent characteristics as a magnetic powder for a magnetic recording medium, but this magnetic powder also has excellent storage stability, itself or When a magnetic recording medium is stored in a high-temperature and high-humidity environment, it is suitable for a magnetic recording medium for high-density recording because there is little deterioration in magnetic characteristics such as saturation magnetization.

In the rare earth-iron nitride magnetic powder of the present invention, it does not exclude the presence of rare earth elements in the magnetic powder, but even in that case, the magnetic powder has a multi-layer structure of an inner layer and an outer layer. The structure mainly exists in the outer layer portion (surface). In this case, the Fe phase of the inner layer (core portion) is the Fe ₁₆ N ₂ phase, but it is not necessary that the inner phase is the entire Fe ₁₆ N ₂ phase, and the Fe ₁₆ N ₂ phase and the α-Fe phase may be mixed. Good. Rather, there is an advantage that the desired coercive force can be easily set by adjusting the ratio of the Fe ₁₆ N ₂ phase and the α-Fe phase.

  Examples of the rare earth element include yttrium, ytterbium, cesium, praseodymium, lanthanum, samarium, europium, neodymium, and terbium. Among these, yttrium, samarium or neodymium has a large effect of improving the coercive force and the effect of maintaining the particle shape at the time of reduction. Therefore, it is desirable to selectively use at least one of these.

  In addition to such rare earth elements, elements such as phosphorus, silicon, aluminum, carbon, calcium, and magnesium may be included. Among these, by using at least one element selected from silicon and aluminum having an anti-sintering effect in combination with a rare earth element, the dispersibility is good and a higher coercive force can be obtained.

  In the production of the rare earth-iron nitride magnetic powder of the present invention, as described above, iron-based oxides or hydroxides such as hematite, magnetite, and goethite are used as starting materials. The average particle size of the raw material is selected in consideration of the volume change during reduction / nitriding, but is usually about 5 to 100 nm.

  A rare earth element is deposited on this starting material. Usually, the starting material is dispersed in an aqueous solution of an alkali or acid, and a salt of the rare earth element is dissolved therein, and a hydroxide or hydrate containing the rare earth element is precipitated in the raw material powder by a neutralization reaction or the like. That's fine.

  The amount of the rare earth element is 0.05 to 20 atomic%, preferably 0.2 to 20 atomic%, more preferably 0.5 to 15 atomic%, and still more preferably 1.0 to 10 with respect to iron in the magnetic powder. The amount will be atomic%.

  In addition to rare earth elements, compounds composed of elements having an anti-sintering effect such as silicon and aluminum are dissolved, and the raw material powder is immersed in the raw material powder together with the rare earth elements. Elements may be deposited simultaneously or sequentially. In order to perform these deposition processes efficiently, additives such as a reducing agent, a pH buffering agent, and a particle size controlling agent may be mixed. As these deposition treatments, these elements may be deposited after the rare earth elements are deposited.

  Next, the raw material on which the rare earth element or the rare earth element and, if necessary, other elements are deposited is heated and reduced in a hydrogen stream. The reducing gas is not particularly limited, and a reducing gas such as carbon monoxide gas may be used in addition to the normally used hydrogen gas.

  The reduction temperature is preferably 300 to 600 ° C. When the reduction temperature is lower than 300 ° C., the reduction reaction does not proceed sufficiently, and when it exceeds 600 ° C., the powder particles are easily sintered.

  By performing nitriding after the heat reduction treatment, the rare earth-iron nitride magnetic powder, rare earth-aluminum-iron nitride magnetic powder, rare earth-silicon-iron nitride magnetic powder, rare earth-aluminum-silicon-nitriding of the present invention. An iron-based magnetic powder is obtained. The nitriding treatment is desirably performed using a gas containing ammonia. In addition to ammonia gas alone, a mixed gas using hydrogen gas, helium gas, nitrogen gas, argon gas or the like as a carrier gas may be used. Nitrogen gas is particularly preferred because it is inexpensive.

The nitriding temperature is preferably 100 to 300 ° C. If the nitriding temperature is too low, nitriding does not proceed sufficiently and the effect of increasing the coercive force is small. If it is too high, nitriding will be promoted excessively, the proportion of Fe ₄ N, Fe ₃ N phase, etc. will increase, the coercive force will rather decrease, and it will tend to cause an excessive decrease in saturation magnetization.

  The conditions for such nitriding are as follows: rare earth-iron nitride magnetic powder, rare earth-aluminum-iron nitride magnetic powder, rare earth-silicon-iron nitride magnetic powder, rare earth-aluminum-silicon-iron nitride magnetic powder Is selected so that the amount of nitrogen relative to iron is 1.0 to 20 atom%, more preferably 1.0 to 12.5 atom%, and still more preferably 3 to 12.5 atom%.

-Aluminum and / or silicon-based iron nitride magnetic powder containing an iron nitride phase in the core part. With respect to the iron-based magnetic powder in which the core part contains the Fe ₁₆ N ₂ phase as the main phase, aluminum and / or silicon is used as the magnetic powder. It has been found that the iron nitride magnetic powder having a coercive force of about 200 kA / m can be obtained by being mainly present in the outer layer portion, although the coercive force is slightly smaller than that of the rare earth element-iron nitride magnetic powder. The content of aluminum and / or silicon is preferably 1 to 20 atomic%, more preferably 2 to 20 atomic%, and still more preferably 4 to 18 atomic% based on Fe. At present, the coercive force in the case of aluminum and / or silicon and containing no rare earth is about 200 kA / m. However, there is a possibility that a higher coercive force can be obtained by further study. Other preferred forms are the same as those of the rare earth-iron nitride magnetic powder. Also in this case, it is more preferable to contain a rare earth element together with aluminum and / or silicon.

The rare earth-iron-boron magnetic powder mainly containing metallic iron or iron alloy in the core portion can be produced by, for example, the following method.
First, an aqueous solution containing iron ions or, if necessary, transition metal ions such as Mn, Zn, Ni, Cu, and Co, and an alkaline aqueous solution are mixed to produce a coprecipitate of iron or this and the above transition metal. To do. Also in this case, iron sulfate or iron nitrate is used as a raw material for iron ions or transition metal ions. Next, a rare earth salt such as neodymium or samarium and a boron compound are added to the coprecipitate, and this is heat-treated at 60 to 400 ° C. to form a boron-containing rare earth and iron (or this and the above transition metal). An oxide is formed. Then, excess boron is removed, and when heated and reduced in hydrogen gas as described above, a rare earth-iron-boron magnetic powder is obtained. This method is suitable for obtaining a rare earth-iron-boron magnetic powder having a structure in which the core part is mainly metallic iron or an iron alloy with the above transition metal and the outer layer part is mainly a rare earth-iron-boron compound. Yes. Even in this method, the magnetic powder can contain other elements for improving the corrosion resistance, etc., but even in this case, the amount of rare earth and boron in the entire magnetic powder is different from that of iron. It is desirable to be 0.2 to 20 atomic% and 0.5 to 30 atomic%.

-Rare earth-iron-based magnetic powder mainly containing metallic iron or iron alloy in the core portion The method for producing the rare earth-iron-based magnetic powder mainly containing metallic iron or iron alloy in the core portion is as follows. That is, spherical or elliptical particles such as magnetite or cobalt ferrite particles are dispersed in an aqueous solution containing at least rare earth ions, and an alkaline aqueous solution having the number of moles necessary for converting the rare earth ions into hydroxides is added. It was found that the target magnetic powder can be obtained by forming a rare earth hydroxide on the surface layer of magnetite or cobalt ferrite particles, followed by filtration, drying, and heat reduction. The spherical or elliptical particles such as magnetite or cobalt ferrite particles are not particularly limited. For example, in the case of magnetite particles, an alkali is added to an aqueous solution in which divalent iron ions are dissolved to add a divalent particle. Particles of any size can be obtained by making an iron hydroxide and subjecting this hydroxide to a heat reaction at an appropriate temperature and pH. In the case of cobalt ferrite particles, an alkali is added to an aqueous solution of divalent cobalt ions and trivalent iron ions to produce a hydroxide composed of divalent cobalt and trivalent iron. Cobalt ferrite particles of an arbitrary size can be obtained by heating and reacting at a temperature and pH. Further, it is formed as a rare earth hydroxide on the surface layer of magnetite or cobalt ferrite particles, and then filtered and dried, and is usually heated and reduced at 400 to 800 ° C. However, this heating and reduction is not particularly limited. The target magnetic powder can be obtained by overheating reduction at an appropriate temperature in a neutral atmosphere. Further, by performing a stabilization treatment after the overheat reduction, the magnetic powder becomes more reliable when used as a medium. In the rare earth-iron-based magnetic powder obtained by this method and containing mainly metallic iron or iron alloy in the core portion, rare earth elements are mainly present in the outer layer portion of the magnetic powder.

<Non-magnetic plate-like fine particles>
The nonmagnetic plate-like fine particles and the production method thereof will be described in detail using plate-like alumina as an example.
Despite the demand for finely divided aluminum oxide having a particle size of 100 nm or less with good crystallinity and a sharp particle size distribution, no aluminum oxide particles have been developed so far.

  The inventor has newly developed particles (fine particles) such as plate-like aluminum oxide particles that satisfy the above-mentioned requirements. If such plate-like particles are used in the undercoat layer of a magnetic tape, the present inventors have developed a thin film. We thought that it would be possible to reduce thickness unevenness in layer coating, improve surface smoothness, improve strength in the coating plane direction, and improve dimensional stability against temperature change and humidity change.

  Here, the newly developed method for producing plate-like particles will be described by taking aluminum oxide particles as an example. In obtaining an aluminum oxide suitable for a nonmagnetic intermediate layer or an undercoat layer, first, as a first step, an aqueous solution of an aluminum salt is added to an alkaline aqueous solution, and the resulting aluminum hydroxide or hydrate is added to water. In the presence of, the target shape and particle diameter are adjusted by a hydrothermal reaction treatment in which the heat treatment is performed at a temperature range of 110 to 300 ° C.

  The problem at this time is the unique property of aluminum hydroxide or hydrate, which dissolves in both alkaline and acidic solutions and forms a precipitate only at a neutral pH. However, in order to obtain an aluminum hydroxide or hydrate having a desired shape and particle size by hydrothermal reaction, it is necessary to use an alkaline solution. As a result of intensive investigations to overcome this trade-off property, the present inventors have found that a target reaction proceeds only at a specific pH.

  Next, as a second step, the aluminum hydroxide or hydrate is heat-treated in air. By passing through these steps, aluminum oxide particles having a uniform particle size distribution, extremely little sintering and aggregation, and good crystallinity can be obtained.

  Thus, in the production of aluminum oxide particles, the process is divided into a process for the purpose of adjusting the shape and particle diameter and a process for the purpose of maximizing the physical properties inherent in the material. Based on the idea, the present inventors have succeeded in developing aluminum oxide particles having a plate shape and an average particle diameter in the range of 10 nm to 100 nm, which was impossible with the conventional production methods. Here, the plate shape means a plate ratio (maximum diameter / thickness) exceeding 1, and the plate ratio exceeds 2 and is preferably 100 or less. Furthermore, 3 or more and 50 or less are more preferable, and 5 or more and 30 or less are even more preferable. When the plate ratio is 2 or less, for example, when used in a non-magnetic intermediate layer, particles may rise from the coated surface, and the surface smoothness of the upper magnetic layer may be deteriorated. Particles may be destroyed.

  In addition, the manufacturing method that separates into a process aimed at adjusting the shape and particle diameter and a process aimed at maximizing the physical properties inherent in the material is not limited to aluminum oxide, The present invention can also be applied to various oxides or composite oxides of rare earth elements such as cerium, elements such as zirconium, silicon, titanium, manganese, and iron, and mixed crystals of these elements having an average particle diameter of 5 to 100 nm.

<Non-magnetic support>
Although the thickness of a magnetic support body changes with uses, a 2-5 micrometers thing is used normally. Preferably it is 2-4.5 micrometers, More preferably, it is 2-4 micrometers. When the thickness of the non-magnetic support is less than 2 μm, film formation becomes difficult, and the tape strength decreases. When the thickness exceeds 4.5 μm, the total thickness of the tape increases to 6 μm or more, and the recording capacity per tape roll decreases. .

The Young's modulus in the longitudinal direction of the nonmagnetic support is preferably 9.8 GPa (1000 kg / mm ² ) or more, and more preferably 10.8 GPa (1100 kg / mm ² ) or more. When the Young's modulus in the longitudinal direction of the nonmagnetic support is less than 9.8 GPa (1000 kg / mm ² ), the tape running becomes unstable. In the helical scan type, the Young's modulus (MD) in the longitudinal direction / Young's modulus (TD) in the width direction is preferably in a specific range of 0.60 to 0.80. The Young's modulus in the longitudinal direction / Young's modulus in the width direction is more preferably in the range of 0.65 to 0.75. When the Young's modulus in the longitudinal direction / Young's modulus in the width direction is less than 0.60 or exceeds 0.80, the mechanism is unknown at present, but the output variation between the entrance side and the exit side of the track of the magnetic head ( (Flatness) increases. This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.70. In the linear recording type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.70 to 1.30, although the reason is not clear. Nonmagnetic supports that satisfy these characteristics include biaxially stretched aromatic polyamide base films and aromatic polyimide films.

<Nonmagnetic intermediate layer>
The thickness of the nonmagnetic intermediate layer is preferably 0.2 to 0.8 μm. 0.2-0.6 micrometer is more preferable. If the thickness of the nonmagnetic intermediate layer is less than 0.2 μm, the information signal may be recorded also in the lower magnetic layer, and the C / N of the information signal may deteriorate. If the thickness of the nonmagnetic intermediate layer exceeds 0.8 μm, the servo signal will not be recorded in saturation in the lower magnetic layer, or the signal recorded in the lower magnetic layer will not generate magnetic flux outside due to spacing loss. In other words, the total thickness of the magnetic recording medium becomes too thick, and the recording capacity per tape roll is reduced.

  To the nonmagnetic intermediate layer, nonmagnetic plate-like particles having a particle diameter of 10 nm to 100 nm as described above are added in order to ensure film thickness uniformity, surface smoothness, and control of rigidity and dimensional stability. It is preferable to do. The component of the nonmagnetic plate-like particles is not limited to aluminum oxide, and rare earth elements such as cerium, oxides or complex oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used. For the purpose of improving conductivity, plate-like ITO (indium, tin composite oxide) particles may be added. If necessary, plate-like ITO particles may be added to the nonmagnetic intermediate layer at 15 to 95% by weight based on the weight of the total inorganic powder in the nonmagnetic intermediate layer. If necessary, carbon black may be added for the purpose of improving conductivity. Carbon black preferably has a particle size of 10 nm to 100 nm. Further, conventionally known oxide particles such as iron oxide and aluminum oxide may be added. In that case, it is preferable to use fine particles as much as possible. The binder resin used for the nonmagnetic intermediate layer is the same as that used for the magnetic layer.

  In order to increase the surface smoothness of the upper magnetic layer, plate-like particles having a particle diameter of 10 nm to 100 nm are mainly added to the nonmagnetic powder of the nonmagnetic intermediate layer, and the lower magnetic layer, the nonmagnetic support, In the meantime, a conductive undercoat layer made of conventionally known carbon black or granular nonmagnetic powder and a binder resin may be formed. In that case, since ITO is expensive, the nonmagnetic powder of the nonmagnetic intermediate layer is preferably a rare earth element such as aluminum or cerium, or an oxide or composite oxide of an element such as zirconium, silicon, titanium, manganese, or iron. used.

<Lower magnetic layer>
A conventionally known magnetic layer is provided in the lower magnetic layer for recording a long-wavelength magnetic recording signal such as a servo signal. The thickness of the lower magnetic layer is preferably 0.2 μm or more and 1.0 μm or less. In order to reduce the total thickness of the magnetic recording medium, 0.8 μm or less is more preferable, and 0.6 μm or less is more preferable. Practically, it is 0.3 μm or more. When the thickness of the lower magnetic layer is 0.2 μm or more, the servo signal recorded in the upper magnetic layer is strengthened by the servo signal recorded in the lower magnetic layer. On the other hand, if the thickness of the lower magnetic layer is 1.0 μm or less, the servo signal is likely to be saturated and recorded in the lower magnetic layer.

  The coercive force of the lower magnetic layer is preferably 120 to 400 kA / m, and more preferably 140 to 320 kA / m. If the coercive force of the lower magnetic layer is less than 120 kA / m, information recording may also be recorded on the lower magnetic layer, and the C / N of the information signal may deteriorate, and if it exceeds 400 kA / m, recording by the magnetic head becomes difficult. There is a case. The coercivity of the lower magnetic layer is a value measured with an external magnetic field of 1.274 MA / m (16 kOe) using a sample vibration magnetometer.

  Conventionally known magnetic powders can be used as the magnetic powder added to the lower magnetic layer, but ferromagnetic iron metal powders are preferably used because of their high saturation magnetization. The coating material for the lower magnetic layer is used by diverting a coating material used for other magnetic recording media.

The average major axis length of the ferromagnetic iron-based metal powder is preferably 0.1 to 0.2 μm. The particle size in this range is preferably used because it is used by diverting a paint used for other magnetic recording media. The non-surface area of the ferromagnetic iron-based metal powder is usually 40 m ² / g or more from the viewpoint of diverting a coating used for other magnetic recording media.

<Undercoat layer>
An undercoat layer may be provided between the nonmagnetic support and the lower magnetic layer. The thickness of the undercoat layer is usually 0.3 to 1.0 μm. When the thickness of the undercoat layer is 0.3 μm or more, the effect of improving the conductivity is large and the undercoat layer is easy to apply. However, when the thickness is 1.0 μm or more, the total thickness of the tape is increased.

  Carbon black (hereinafter also referred to as CB) and nonmagnetic particles can be added to the undercoat layer for the purpose of controlling the viscosity of the paint and the tape rigidity. The carbon black (CB) and nonmagnetic particles used for the undercoat layer are the same as those used for the nonmagnetic intermediate layer described above.

As carbon black (CB) added to the undercoat layer, acetylene black, furnace black, thermal black, and the like can be used. Usually, those having a particle size of 5 nm to 200 nm are used, but those having a particle size of 10 to 100 nm are preferred. The amount of CB added is usually 15 to 35% by weight although it varies depending on the particle size of CB. It is more preferable to use 15 to 35% by weight of CB having a particle size of 15 nm to 80 nm, and it is preferable to use 20 to 30% by weight of CB having a particle size of 20 to 50 nm. The electrical resistance is reduced by adding carbon black having such a particle diameter and amount.
The binder resin used for the undercoat layer is the same as that used for the magnetic layer.

<Lubricant>
For the nonmagnetic intermediate layer and / or the undercoat layer, the magnetic layer (the magnetic layer comprising the upper magnetic layer and the lower magnetic layer), and the total powder (solid content) contained in the nonmagnetic intermediate layer and the undercoat layer It is preferable to contain 0.5 to 5.0% by weight of higher fatty acid and 0.2 to 3.0% by weight of higher fatty acid ester because the coefficient of friction with the head becomes small. If the amount of the higher fatty acid added is less than 0.5% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 5.0% by weight, the nonmagnetic intermediate layer and the undercoat layer may be plasticized and the toughness may be lost. is there. If the amount of the higher fatty acid ester added is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3.0% by weight, the amount transferred to the magnetic layer is too large. It may cause side effects such as sticking. As the fatty acid, it is preferable to use a fatty acid having 10 or more carbon atoms. The fatty acid having 10 or more carbon atoms may be any of isomers such as linear, branched and cis / trans, but is preferably a linear type having excellent lubricating performance. Examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid, and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable. The amount of fatty acid added to the magnetic layer is not particularly limited since the fatty acid is transferred between the nonmagnetic intermediate layer, the undercoat layer and the magnetic layer, and the magnetic layer, the nonmagnetic intermediate layer and the undercoat layer are not limited. What is necessary is just to let the addition amount of the combined fatty acid be said amount. If fatty acids are added to the nonmagnetic intermediate layer and the undercoat layer, it is not always necessary to add fatty acids to the magnetic layer.

  When the magnetic layer, particularly the upper magnetic layer, contains 0.5 to 3.0% by weight of fatty acid amide and 0.2 to 3.0% by weight of higher fatty acid ester with respect to the magnetic powder, This is preferable because the coefficient of friction during running becomes small. If the amount of fatty acid amide added is less than 0.5% by weight, direct contact at the head / magnetic layer interface is likely to occur, and the effect of preventing seizure is small. Defects may occur. As the fatty acid amide, amides such as palmitic acid and stearic acid can be used. Further, if the amount of the higher fatty acid ester added is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3.0% by weight, side effects such as sticking to the head may occur. Note that the mutual movement of the lubricant in the magnetic layer and the lubricant in the nonmagnetic intermediate layer and the undercoat layer is not excluded.

<Upper magnetic layer>
As described above, an essentially spherical or elliptical iron-based magnetic powder is used for the upper magnetic layer. The thickness of the upper magnetic layer is preferably 0.09 μm or less, and more preferably 0.06 μm. Practically, it is 0.01 μm or more. The coercive force is preferably 160 kA / m or more, more preferably 180 kA / m or more, and even more preferably 200 kA / m or more. Although there is no upper limit on the coercive force, 400 kA / m is a practical upper limit at present due to the writing ability of the magnetic head.

  As a binder resin (hereinafter simply referred to as a binder) used for the upper magnetic layer (the same applies to the lower magnetic layer, nonmagnetic intermediate layer, and undercoat layer), a vinyl chloride resin, a vinyl chloride-vinyl acetate copolymer resin ( Hereinafter, simply referred to as a copolymer), vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, vinyl chloride-hydroxyl group-containing alkyl A combination of at least one selected from cellulose-based resins such as acrylate copolymers and nitrocellulose and a polyurethane resin may be used. Among these, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer and a polyurethane resin in combination. Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane.

-COOH as a functional _{group, -SO 3 -M, OSO 3 M} , -P = O (OM) 3, -O-P = O (OM) 2 [ in these formulas, M represents a hydrogen atom, an alkali metal base or an amine Represents a salt], —OH, —NR ¹ R ² , —N ⁺ R ³ R ⁴ R ⁵ [wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ are the same or different and represent hydrogen Alternatively, a binder such as a urethane resin made of a polymer having an epoxy group is used. The reason for using such a binder is to improve the dispersibility of magnetic powder and the like as described above. When two or more kinds of resins are used in combination, the polarities of the functional groups are preferably matched, and a combination of —SO ₃ M groups is particularly preferable.

These binders are used in the range of 7 to 50 parts by weight, preferably 10 to 35 parts by weight with respect to 100 parts by weight of the magnetic powder. In particular, it is most preferable to use a composite of 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin as a binder.
It is desirable to use together with these binders a thermosetting cross-linking agent that cross-links by bonding with functional groups contained in the binder. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are usually used in a proportion of 1 to 30 parts by weight with respect to 100 parts by weight of the binder. More preferably, it is 5 to 20 parts by weight. However, when the magnetic layer is applied wet-on-wet on the nonmagnetic intermediate layer and the undercoat layer, a certain amount of polyisocyanate is diffusely supplied from the nonmagnetic intermediate layer paint and the undercoat layer paint. Therefore, the magnetic layer is crosslinked to some extent without using polyisocyanate.

  In addition, nonmagnetic plate-like particles having a particle diameter of 10 nm to 100 nm as described above may be added to the magnetic layer. In addition, conventionally known abrasives can be added as necessary. Examples of these abrasives include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, and corundum. Those having a Mohs hardness of 6 or more, such as artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. As the particle size of the abrasive, it is preferable that the average particle size is usually 10 nm to 150 nm in a thin magnetic layer of 0.01 to 0.09 μm. The addition amount is preferably 5 to 20% by weight with respect to the magnetic powder. More preferably, it is 8 to 18% by weight.

  Further, in order to improve conductivity, the plate-like ITO particles prepared by the above-described manufacturing method and conventionally known carbon black (CB) are added to the magnetic layer of the present invention for the purpose of improving conductivity and surface lubricity. However, as these carbon blacks, acetylene black, furnace black, thermal black and the like can be used. A particle diameter of 10 nm to 100 nm is preferred. When the particle size of the carbon black is 5 nm or less, it is difficult to disperse the carbon black. When the particle size is 100 nm or more, it is necessary to add a large amount of carbon black. In any case, the surface becomes rough, which causes a decrease in output. The addition amount is preferably 0.2 to 5% by weight with respect to the magnetic powder. More preferably, it is 0.5 to 4% by weight.

<Back coat layer>
A back coat layer as an example of the back layer will be described.
A back coat layer is provided on the other surface (the surface opposite to the surface on which the magnetic layer is formed) of the non-magnetic support constituting the magnetic recording medium of the present invention for the purpose of improving running performance. Can do. The thickness of the back coat layer is preferably 0.2 to 0.8 μm. 0.5 μm or less is more preferable. If the thickness of the backcoat layer is less than 0.2 μm, the effect of improving running performance is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape becomes thick and the recording capacity per roll becomes small. As carbon black (CB), acetylene black, furnace black, thermal black, etc. can be used. Usually, small particle size carbon black and large particle size carbon black are used. As the small particle size carbon black, those having a particle size of 5 nm to 200 nm are used, and those having a particle size of 10 nm to 100 nm are more preferable. When the particle size of the small particle size carbon black is 5 nm or less, it is difficult to disperse the carbon black, and when the particle size exceeds 200 nm, it is necessary to add a large amount of carbon black, and in any case, the surface becomes rough, This is because it causes a back-off (embossing) to the magnetic layer. When the large particle size carbon black is used in an amount of 5 to 15% by weight of the small particle size carbon black and a particle size of 300 to 400 nm, the surface is not roughened, and the effect of improving running performance is increased. The total addition amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 98% by weight, more preferably 70 to 95% by weight based on the weight of the inorganic powder. The surface roughness Ra is preferably 3 to 8 nm, and more preferably 4 to 7 nm.

  In addition, for the purpose of improving the strength, nonmagnetic plate-like particles having a particle diameter of 10 nm to 100 nm as described above can be added to the backcoat layer. The component of the nonmagnetic plate-like particles is not limited to aluminum oxide, and rare earth elements such as cerium, oxides or complex oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used. For the purpose of improving conductivity, plate-like ITO (indium and tin composite oxide) particles prepared by the above-described manufacturing method may be added. It is preferable to add the plate-like ITO particles and carbon black to the back coat layer so that the total amount thereof is 60 to 98% by weight based on the weight of the total inorganic powder in the back coat layer. Carbon black preferably has a particle size of 10 nm to 100 nm. Moreover, you may add the iron oxide whose particle diameter is 0.1 micrometer-0.6 micrometer as needed. The addition amount is preferably 2 to 40% by weight, more preferably 5 to 30% by weight, based on the weight of the total inorganic powder in the backcoat layer.

  For the back coat layer, the same resin as that used for the magnetic layer and undercoat layer described above can be used as the binder resin. Among these, in order to reduce the coefficient of friction and improve the runnability, the cellulose resin and the polyurethane resin are used. It is preferable to combine and use resin. The content of the binder resin is usually 40 to 150 parts by weight, preferably 50 to 120 parts by weight, more preferably 60 to 110 parts by weight with respect to 100 parts by weight of the total amount of the carbon black and the inorganic nonmagnetic powder. More preferably, it is 70 to 110 parts by weight. If the binder resin content is less than 50 parts by weight, the strength of the backcoat layer is insufficient, and if it exceeds 120 parts by weight, the friction coefficient tends to increase. It is preferable to use 30 to 70 parts by weight of cellulose resin and 20 to 50 parts by weight of polyurethane resin. Further, in order to further cure the binder resin, it is preferable to use a crosslinking agent such as a polyisocyanate compound.

  For the back coat layer, the same cross-linking agent as that used for the magnetic layer and the undercoat layer described above is used. The amount of the crosslinking agent is usually 10 to 50 parts by weight, preferably 10 to 35 parts by weight, and more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the binder resin. If the amount of the crosslinking agent is less than 10 parts by weight, the coating strength of the backcoat layer tends to be weak, and if it exceeds 35 parts by weight, the dynamic friction coefficient against SUS increases.

<Organic solvent>
Examples of organic solvents used in magnetic paints, undercoat paints, and backcoat paints include ketone solvents such as methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, and acetates such as ethyl acetate and butyl acetate. System solvents and the like. These solvents are used alone or in combination, and further mixed with toluene or the like.

<Magnetic tape>
A magnetic tape according to the present invention will be described.
FIG. 1 (a) shows a cross-sectional view of one typical example of the magnetic tape 3 of the present invention. In the magnetic tape 3 of the present invention, a lower magnetic layer (servo signal layer) 42, a nonmagnetic intermediate layer 43, and an upper magnetic layer (information recording layer) 44 are arranged in this order on one surface of a nonmagnetic support 40. Is formed. A back layer 45 is formed on the other surface of the nonmagnetic support 40.
FIG. 1 (b) shows a cross-sectional view of another typical example of the magnetic tape 3 of the present invention in which the conductive undercoat layer 41 is provided in FIG. 1 (a). In the magnetic tape 3 of the present invention, a conductive undercoat layer 41, a lower magnetic layer (servo signal layer) 42, a nonmagnetic intermediate layer 43, an upper magnetic layer (information recording layer) are formed on one surface of a nonmagnetic support 40. ) 44 are formed in this order. A back layer 45 is formed on the other surface of the nonmagnetic support 40.

<Magnetic (recording) tape cartridge>
A magnetic tape cartridge using a magnetic tape according to the present invention will be described.
FIG. 2 shows a general structure of the magnetic tape cartridge of the present invention, and FIG. 3 shows its internal structure. In FIG. 2, the magnetic tape cartridge has a rectangular box-shaped case body 1 formed by joining upper and lower cases 1 a and 1 b, and the magnetic tape 3 is wound around one reel 2 arranged inside the case body 1. is doing. A tape outlet 4 is opened at one end of the front wall 6 of the case body 1. The tape outlet 4 can be opened and closed by a door 5 that can be opened and closed. In order to pull out the magnetic tape 3 wound around the reel 2 out of the case, a tape drawing tool 7 is connected to the feeding end of the magnetic tape 3. Reference numeral 20 in FIG. 2 indicates a door spring for closing and energizing the door 5 without permission.

  EXAMPLES The present invention will be described in detail below by examples, but the present invention is not limited to these. In addition, the part of an Example and a comparative example shows a weight part.

Example 1:
<Synthesis of ultrafine magnetic powder>
A rare earth-iron nitride magnetic powder was synthesized. As a synthesis example, an example in which yttrium is used as a rare earth will be described below.
0.419 mol of iron (II) sulfate heptahydrate and 0.974 mol of iron (III) nitrate nonahydrate were dissolved in 1500 g of water. Next, 3.76 moles of sodium hydroxide were dissolved in 1500 g of water. Next, 3.76 moles of sodium hydroxide were dissolved in 1500 g of water. An aqueous solution of sodium hydroxide was added to the aqueous solution of these two types of iron salts and stirred for 20 minutes to generate magnetite particles.

  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 elliptical with a particle size of 25 nm.

  10 g of the magnetite particles were dispersed in 500 cc of water for 30 minutes using an ultrasonic disperser. To this dispersion, 2.5 g of yttrium nitrate was added and dissolved, and stirred for 30 minutes. Separately, 0.8 g of sodium hydroxide was dissolved in 100 cc of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, the mixture was further stirred for 1 hour. By this treatment, yttrium hydroxide was deposited on the surface of the magnetite particles. This was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which yttrium hydroxide was deposited on the surface of magnetite particles.

Thus, the powder in which the hydroxide of yttrium was deposited on the surface of the magnetite particles was heated and reduced at 450 ° C. for 2 hours in a hydrogen stream to obtain an yttrium-iron magnetic powder. Next, the temperature was lowered to 150 ° C. over about 1 hour in a state of flowing hydrogen gas. When the temperature reached 150 ° C., the gas was switched to ammonia gas, and nitriding was performed for 30 hours while maintaining the temperature at 150 ° C. Thereafter, the temperature was lowered from 150 ° C. to 90 ° C. with ammonia gas flowing, and at 90 ° C., the ammonia gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours.
Next, with the mixed gas flowing, the temperature was lowered from 90 ° C. to 40 ° C., held at 40 ° C. for about 10 hours, and then taken out into the air.

The thus obtained yttrium-iron nitride magnetic powder had a content of yttrium and nitrogen measured by fluorescent X-ray of 5.3 atomic% and 10.8 atomic%, respectively. Further, from the X-ray diffraction pattern to obtain a profile indicating a Fe ₁₆ N ₂ phase. FIG. 4 shows an X-ray diffraction pattern of this yttrium-iron nitride based magnetic powder. A diffraction peak based on Fe ₁₆ N ₂ and a diffraction peak based on α-Fe are observed, and this yttrium-iron nitride is observed. It was found that the system magnetic powder was composed of a mixed phase of Fe ₁₆ N ₂ phase and α-Fe phase.

Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 20 nm. FIG. 5 shows a transmission electron micrograph (magnification: 200,000 times) of this magnetic powder. The specific surface area determined by the BET method was 53.2 m ² / g.

Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1274 kA / m (16 kOe) is 135.2 Am ² / kg (135.2 emu / g), and the coercive force is 226.9 kA / m (2,850 Oe). )Met. Further, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above. As a result, it was 118.2 Am ^{2 /} kg (118.2 emu / g), which was saturated before storage. The magnetization maintenance ratio was 87.4%.

  Using the rare earth-iron nitride magnetic powder prepared as described above, the following magnetic coating was prepared. In preparing the magnetic coating material, the rare earth-iron nitride magnetic powder used was prepared by scaling up the manufacturing method of this example 100 times.

<Synthesis of plate-like alumina particles>
0.075 mol of sodium hydroxide was dissolved in 90 ml of water to prepare an aqueous alkali solution. Apart from this alkaline aqueous solution, 0.0074 mol of aluminum (III) chloride heptahydrate was dissolved in 40 ml of water to prepare an aqueous aluminum chloride solution. The latter aqueous aluminum chloride solution was added dropwise to the former alkaline aqueous solution to produce a precipitate containing aluminum hydroxide, and then hydrochloric acid was added dropwise to adjust the pH to 10.2. This precipitate was aged in a suspension state for 20 hours, and then washed with about 1000 times water.

  Next, after removing the supernatant, the suspension of this precipitate was readjusted to pH 10.0 using an aqueous sodium hydroxide solution, charged into an autoclave, and hydrothermally treated at 200 ° C. for 2 hours.

  The obtained hydrothermal treatment product was filtered, dried in the air at 90 ° C., and then lightly crushed in a mortar, followed by heat treatment in the air at 600 ° C. for 1 hour to obtain aluminum oxide particles. After the heat treatment, in order to remove unreacted substances and residues, they were further washed with an ultrasonic disperser and filtered and dried.

  When the X-ray diffraction spectrum of the obtained aluminum oxide (that is, alumina) particles was measured, a spectrum corresponding to γ-alumina was observed. Furthermore, when shape observation was performed with the transmission electron microscope, it turned out that it is a square-plate-shaped particle | grain (plate-shaped ratio: 5-10) whose particle diameter is 30-50 nm.

  The obtained aluminum oxide particles were further heat-treated in air at 1250 ° C. for 1 hour. When the X-ray diffraction spectrum of the obtained aluminum oxide particles was measured, a spectrum corresponding to α-alumina was observed. Furthermore, when the shape was observed with a transmission electron microscope, it was a square plate-like particle having a particle diameter of 40 to 60 nm.

<Synthesis of plate-like ITO particles>
0.75 mol of sodium hydroxide was dissolved in 180 ml of water to prepare an aqueous alkaline solution. Separately, 0.067 mol of indium (III) chloride tetrahydrate and 0.007 mol of tin (IV) chloride pentahydrate are dissolved in 400 ml of water to obtain an aqueous solution of tin chloride and indium chloride. Adjusted. The latter aqueous solution of tin chloride and indium chloride was dropped into the former alkaline aqueous solution to prepare a precipitate of hydroxide or hydrate consisting of tin and indium. The pH at this time was 10.2. The precipitate was aged in a suspension at room temperature for 20 hours, and then washed with water until the pH reached 7.6.

Next, an aqueous solution of sodium hydroxide was added to the precipitate suspension to readjust the pH to 10.8, and the mixture was charged into an autoclave and subjected to hydrothermal treatment at 200 ° C. for 2 hours.
The obtained hydrothermal treatment product was washed with water until the pH became 7.8, filtered, dried in air at 90 ° C., lightly crushed in a mortar, and heat-treated at 600 ° C. in air for 1 hour. To obtain tin-containing indium oxide particles. After the heat treatment, in order to remove unreacted substances and residues, they were further washed with an ultrasonic disperser and filtered and dried.

  When the shape of the obtained tin-containing indium oxide particles was observed with a transmission electron microscope, it was found that the particles were disk-shaped or square-shaped particles having a particle diameter of 30 to 50 nm (plate ratio: 5 to 10). It was.

  When the X-ray diffraction spectrum of the tin-containing indium oxide particles was measured, the X-ray diffraction spectrum showed that the tin-containing indium oxide particles were composed of a single-structure substance. I found out that

<Synthesis of plate-like iron oxide particles>
0.75 mol of sodium hydroxide was dissolved in 180 ml of water to prepare an alkaline aqueous solution. Separately from this alkaline aqueous solution, 0.074 mol of ferric chloride (III) hexahydrate was dissolved in 400 ml of water to prepare a ferric chloride aqueous solution. The ferric chloride aqueous solution was dropped into the alkaline aqueous solution to prepare a precipitate containing ferric hydroxide. The pH at this time was 11.3. This precipitate was aged in a suspension state for 20 hours, and then washed with water until the pH reached 7.5.

Next, after removing the supernatant, the precipitate suspension was charged into an autoclave and hydrothermally treated at 150 ° C. for 2 hours.
The hydrothermal treatment product was filtered, dried in air at 90 ° C., and then lightly crushed in a mortar, and heat-treated at 600 ° C. in air for 1 hour to obtain alpha-iron oxide particles. After the heat treatment, in order to remove unreacted substances and residues, they were further washed with an ultrasonic disperser and filtered and dried.

  When the X-ray diffraction spectrum of the obtained alpha-iron oxide particles was measured, the spectrum of the alpha-hematite structure was clearly observed. Furthermore, when shape observation was performed with the transmission electron microscope, it turned out that it is a hexagonal plate-shaped particle | grain (plate-shaped ratio: 5-10) whose particle diameter is 40-60 nm.

<Making magnetic tape>
<Undercoat paint component A>
(1)
・ Plate-like alumina powder (average particle size: 50 nm) 10 parts ・ Plate-like ITO powder (average particle size: 40 nm) 90 parts ・ Stearic acid 2.0 parts ・ Vinyl chloride-hydroxypropyl acrylate copolymer 8.8 parts ( Contained -SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g)
Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained -SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Cyclohexanone 25 parts ・ Methyl ethyl ketone 40 parts ・ Toluene 10 parts (2)
・ Butyl stearate 1 part ・ Cyclohexanone 70 parts ・ Methyl ethyl ketone 50 parts ・ Toluene 20 parts (3)
・ Polyisocyanate 1.4 parts ・ Cyclohexanone 10 parts ・ Methyl ethyl ketone 15 parts ・ Toluene 10 parts

<Undercoat paint component B>
(1)
-Acicular iron oxide powder (average particle size: 100 nm) 68 parts-Granular alumina powder (average particle size: 80 nm) 8 parts-Carbon black (average particle size: 25 nm) 24 parts-Stearic acid 2.0 parts-Vinyl chloride -Hydroxypropyl acrylate copolymer 8.8 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained -SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Cyclohexanone 25 parts ・ Methyl ethyl ketone 40 parts ・ Toluene 10 parts (2)
・ Butyl stearate 1 part ・ Cyclohexanone 70 parts ・ Methyl ethyl ketone 50 parts ・ Toluene 20 parts (3)
・ Polyisocyanate 1.4 parts ・ Cyclohexanone 10 parts ・ Methyl ethyl ketone 15 parts ・ Toluene 10 parts

<Coating component for lower magnetic layer>
(1) Components of kneading process / acicular ferromagnetic iron-based metal powder 100 parts (Co / Fe: 30 atomic%,
Y / (Fe + Co): 3 atomic%,
Al / (Fe + Co): 5 wt%,
σs: 145 A · m ² / kg (145 emu / g),
Hc: 187 kA / m (2350 Oe),
(Average axis length: 100 nm)
Vinyl chloride - hydroxypropyl acrylate copolymer 14 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 eq / g)
Polyester polyurethane resin (PU) 5 parts (containing -SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalent / g)
-Particulate alumina (average particle size: 80 nm) 10 parts-Carbon black (average particle size: 75 nm) 5 parts-Methyl acid phosphate (MAP) 2 parts-Tetrahydrofuran (THF) 20 parts-Methyl ethyl ketone / cyclohexanone (MEK / A) 9 Part (2) Dilution process component: Palmitic acid amide (PA) 1.5 part ・ N-butyl stearate (SB) 1 part ・ Methyl ethyl ketone / cyclohexanone (MEK / A) 350 parts (3) Compounding process component: Polyisocyanate 1 .5 parts Methyl ethyl ketone / cyclohexanone (MEK / A) 29 parts

<Non-magnetic interlayer coating composition>
(1)
・ Plate-like alumina powder (average particle size: 50 nm) 10 parts ・ Plate-like ITO powder (average particle size: 40 nm) 90 parts ・ Stearic acid 2.0 parts ・ Vinyl chloride-hydroxypropyl acrylate copolymer 8.8 parts ( Contained -SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g)
Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained -SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Cyclohexanone 25 parts ・ Methyl ethyl ketone 40 parts ・ Toluene 10 parts (2)
・ Butyl stearate 1 part ・ Cyclohexanone 70 parts ・ Methyl ethyl ketone 50 parts ・ Toluene 20 parts (3)
・ Polyisocyanate 1.4 parts ・ Cyclohexanone 10 parts ・ Methyl ethyl ketone 15 parts ・ Toluene 10 parts

<Coating component for upper magnetic layer>
(1) Kneading process component / Ultrafine particulate magnetic powder (YN-Fe) 100 parts [Y / Fe: 5.3 atomic%
N / Fe: 10.8 atomic%
σs: μWb / g (135.2 Am ² /kg=13.5 emu / g),
Hc: 226.9 kA / m (2,850 Oe),
Average axial length: 20 nm, average axial ratio: 1.2]
Vinyl chloride - hydroxypropyl acrylate copolymer 14 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 eq / g)
Polyester polyurethane resin (PU) 5 parts (containing -SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalent / g)
・ Plate-like alumina powder (average particle size: 50 nm) 10 parts ・ Plate-like ITO powder (average particle size: 40 nm) 5 parts ・ Methyl acid phosphate (MAP) 2 parts ・ Tetrahydrofuran (THF) 20 parts ・ Methyl ethyl ketone / cyclohexanone (MEK) / A) 9 parts (2) Diluting process components: 1.5 parts palmitic acid amide (PA) 1 part n-butyl stearate (SB) 350 parts methyl ethyl ketone / cyclohexanone (MEK / A) (3) Blending process components・ Polyisocyanate 1.5 parts ・ Methyl ethyl ketone / cyclohexanone (MEK / A) 29 parts

First, the component (1) of the above-mentioned <undercoat paint component A> is first kneaded with a batch kneader, the component (2) is added, and after stirring, a dispersion treatment is performed using a sand mill with a residence time of 60 minutes. 3) was added, and the mixture was stirred and filtered to obtain an undercoat paint <undercoat layer paint A>.
Apart from this, the kneading step component (1) of the above <coating for lower magnetic layer> is previously mixed at high speed, the mixed powder is kneaded with a continuous biaxial kneader, and further the dilution step component (2) In a continuous twin-screw kneader, dilute in at least two stages and disperse with a sand mill with a residence time of 45 minutes. Add the compounding process component (3) to this, and after stirring and filtering, lower magnetic coating <Coating for lower magnetic layer> was obtained.

  The above-described <undercoat layer coating material A> is made of an aromatic polyamide film (thickness 3.3 μm, MD = 11 GPa, MD / TD = 0.70, trade name: Mikutron, manufactured by Toray Industries, Inc.). (Base film) is dried and applied so that the thickness after calendering is 0.5 μm, and the magnetic coating <lower magnetic layer coating A> is further subjected to magnetic field orientation treatment on the undercoat layer. The lower magnetic layer after drying and calendering was applied by wet-on-wet so that the thickness of the lower magnetic layer was 0.5 μm, and after magnetic field orientation treatment, it was dried using a dryer and far infrared rays to obtain a magnetic sheet. In the magnetic field orientation treatment, an NN counter magnet (5 kG) is installed in front of the dryer, and two NN counter magnets (5 kG) are spaced from each other at a distance of 50 cm from the front side 75 cm of the position of dry coating of the coating in the dryer. It was installed at. The coating speed was 100 m / min.

  Next, after the component (1) of the above <Non-magnetic intermediate layer coating material> is kneaded with a batch kneader, the component (2) is added, and after stirring, a dispersion treatment is performed using a sand mill with a residence time of 60 minutes. After adding component (3) to the mixture and stirring and filtering, <Nonmagnetic interlayer coating material> was obtained.

  Separately, the kneading step component (1) of the above <coating for upper magnetic layer> is previously mixed at high speed, the mixed powder is kneaded with a continuous biaxial kneader, and further the dilution step component (2). In a continuous twin-screw kneader, dilute in at least two stages and disperse in a sand mill with a residence time of 45 minutes. Add the compounding process component (3), stir and filter, and then <upper layer magnetism Layer coating> was obtained.

  Apply the above <Non-magnetic intermediate layer coating material> onto an aromatic polyamide film magnetic tape on which an undercoat layer and a lower magnetic layer have already been formed, so that the thickness after drying and calendering is 0.3 μm. On the non-magnetic intermediate layer, the above-mentioned <upper magnetic layer coating material> is wet-on-wet so that the thickness of the upper magnetic layer after the magnetic field orientation treatment, drying, and calendering treatment is 0.06 μm. After coating and magnetic field orientation treatment, drying was performed using a dryer and far infrared rays to obtain a magnetic sheet. In the magnetic field orientation treatment, an NN counter magnet (5 kG) is installed in front of the dryer, and two NN counter magnets (5 kG) are spaced from each other at a distance of 50 cm from the front side 75 cm of the position of dry coating of the coating in the dryer. It was installed at. The coating speed was 100 m / min.

<Backcoat layer paint component>
Plate ITO powder (average particle diameter: 40 nm) 80 parts Carbon black (average particle diameter: 25 nm) 10 parts of plate-like iron oxide powder (average particle diameter: 50 nm) 10 parts Nitrocellulose 45 parts Polyurethane resin (-SO ₃ Na group 30 parts) cyclohexanone 260 parts toluene 260 parts methyl ethyl ketone 525 parts

  After the coating component for the backcoat layer is dispersed in a sand mill with a residence time of 45 minutes, 15 parts of polyisocyanate is added to adjust the coating for the backcoat layer, and after filtration, on the opposite side of the magnetic layer of the magnetic sheet prepared above , Dried and coated so that the thickness after calendering was 0.5 μm and dried.

  The magnetic sheet thus obtained was mirror-finished at a temperature of 100 ° C. and a linear pressure of 196 kN / m with a seven-stage calendar made of a metal roll, and the magnetic sheet was wound on a core at 70 ° C. for 72 hours. After aging, the film was cut into ½ inch widths, and the magnetic layer surface was subjected to post-processing such as lapping tape polishing, blade polishing, and surface wiping while running at 200 m / min to produce a magnetic tape. At this time, K10000 was used for the wrapping tape, a carbide blade was used for the blade, and Toraysee (trade name) manufactured by Toray was used for wiping the surface. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape. The product Br · δ of coercive force, residual magnetic flux density and magnetic layer thickness measured in the orientation direction of this magnetic tape was 299.5 kA / m and 0.020 μTm, respectively. This magnetic measurement value is measured separately for a magnetic tape obtained by coating, orienting, drying, and calendaring a nonmagnetic intermediate layer and an upper magnetic layer on a nonmagnetic support under the same conditions as described above. Indicates the value. The same applies hereinafter. The results are summarized in Table 1.

Example 2
In Example 1, a magnetic tape was produced in the same manner as in Example 1 except that the undercoat layer paint was changed from <undercoat layer paint A> to <undercoat layer paint B>.

Example 3
In Example 1, the coating material for the nonmagnetic intermediate layer was changed from 10 parts of the plate-like aluminum oxide powder and 90 parts of the plate-like ITO powder to 100 parts of the plate-like aluminum oxide, and the coating for the undercoat layer was <undercoat A magnetic tape was produced in the same manner as in Example 1 except that the layer coating material B> was changed.

Example 4
In Example 1, the coating material for the nonmagnetic intermediate layer was changed from 10 parts of the plate-like aluminum oxide powder and 90 parts of the plate-like ITO powder to 100 parts of the plate-like iron oxide, and the coating for the undercoat layer was <undercoat A magnetic tape was produced in the same manner as in Example 1 except that the layer coating material B> was changed.

Example 5
In Example 1, a magnetic tape was produced in the same manner as in Example 1 except that the thickness of the nonmagnetic intermediate layer was changed from 0.3 μm to 0.5 μm.

Example 6
A magnetic tape was produced in the same manner as in Example 1 except that the thickness of the nonmagnetic intermediate layer was changed from 0.3 μm to 0.2 μm in Example 1.

Example 7
In Example 1, a magnetic tape was produced in the same manner as in Example 1 except that the thickness of the lower magnetic layer was changed from 0.5 μm to 0.3 μm.

Example 8
In Example 1, a magnetic tape was produced in the same manner as in Example 1 except that the thickness of the lower magnetic layer was changed from 0.5 μm to 1.0 μm.

Example 9
In Example 8, a magnetic tape was produced in the same manner as in Example 8 except that the undercoat layer was not provided.

Comparative Example 1:
Except that the composition in (1) Kneading step component, <Nonmagnetic intermediate layer coating component>, <Backcoat layer coating component> in <Upper layer magnetic coating component> of Example 1 was changed as follows. A computer tape of Comparative Example 1 was produced in the same manner as Example 1. However, since the magnetic powder was changed to needle-like powder having a particle diameter (average axial length) of 100 nm, the thickness of the magnetic layer could not be controlled to 0.06 μm and became 0.11 μm.

<Upper magnetic coating component> (1) Kneading step component / Acoustic ferromagnetic iron-based metal powder 100 parts (Co / Fe: 30 atomic%,
Y / (Fe + Co): 3 atomic%,
Al / (Fe + Co): 5 wt%,
σs: 145 A · m ² / kg (145 emu / g),
Hc: 187 kA / m (2,350 Oe),
(Average axis length: 100 nm)
Vinyl chloride - hydroxypropyl acrylate copolymer 14 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 eq / g)
Polyester polyurethane resin (PU) 5 parts (containing -SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalent / g)
-Particulate alumina (average particle size: 80 nm) 10 parts-Carbon black (average particle size: 75 nm) 5 parts-Methyl acid phosphate (MAP) 2 parts-Tetrahydrofuran (THF) 20 parts-Methyl ethyl ketone / cyclohexanone (MEK / A) 9 Part

<Non-magnetic interlayer coating composition>
(1)
-Acicular iron oxide powder (average particle size: 100 nm) 68 parts-Granular alumina powder (average particle size: 80 nm) 8 parts-Carbon black (average particle size: 25 nm) 24 parts-Stearic acid 2.0 parts-Vinyl chloride -Hydroxypropyl acrylate copolymer 8.8 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained -SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Cyclohexanone 25 parts ・ Methyl ethyl ketone 40 parts ・ Toluene 10 parts (2)
・ Butyl stearate 1 part ・ Cyclohexanone 70 parts ・ Methyl ethyl ketone 50 parts ・ Toluene 20 parts (3)
・ Polyisocyanate 1.4 parts ・ Cyclohexanone 10 parts ・ Methyl ethyl ketone 15 parts ・ Toluene 10 parts

<Backcoat layer paint component>
Carbon black (average particle size: 25 nm) 80 parts Carbon black (average particle size: 0.35 μm) 10 parts Granular iron oxide (average particle size: 0.4 μm) 10 parts Nitrocellulose 45 parts Polyurethane resin (containing SO ₃ Na group) ) 30 parts cyclohexanone 260 parts toluene 260 parts methyl ethyl ketone 525 parts

Comparative Example 2
In Example 1, a magnetic tape of Comparative Example 2 was produced in the same manner as in Example 1 except that the lower magnetic layer was not provided and the same nonmagnetic interlayer coating material as in Comparative Example 1 was used.

Comparative Example 3
A magnetic tape of Comparative Example 3 was produced in the same manner as in Example 1 except that the lower magnetic layer was not provided in Example 1.
The characteristics of the magnetic tapes obtained in the above examples and comparative examples were evaluated as follows. It was measured.

<Surface roughness of magnetic layer>
Measurement was performed at a scanning length of 5 μm by scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer NewView 5000 manufactured by ZYGO. The measurement visual field is 350 μm × 260 μm. The center line average surface roughness of the magnetic layer was determined as Ra.

<Magnetic properties>
The magnetic characteristics are values measured at 25 ° C. and an external magnetic field of 1,274 kA / m using a sample vibrating magnetometer, as in the case of magnetic powder. It is a correction value when a sample punched out to 8 mm is measured.

  The anisotropic magnetic field distribution is a value obtained by measuring a differential curve in the second quadrant (demagnetization curve) of the tape hysteresis curve and dividing the magnetic field corresponding to the half-value width of the differential curve by the coercive force value of the tape. It showed in. In other words, the narrower the coercive force distribution of the magnetic powder and the better the dispersion / orientation of the magnetic powder in the tape, the smaller the Ha. When compared with the same coercive force, the smaller the Ha, the shorter the recording. Good characteristics.

<Output and output vs. noise>
A drum tester was used for measuring the electromagnetic conversion characteristics of the tape. The drum tester was equipped with an electromagnetic induction head (track width 25 μm, gap 0.1 μm) and MR head (8 μm), and recording was performed with the induction head and reproduction was performed with the MR head. Both heads are installed at different locations with respect to the rotating drum, and tracking can be adjusted by operating both heads in the vertical direction. An appropriate amount of the magnetic tape was drawn out from the state of being wound in the cartridge and discarded, and further 60 cm was cut, further processed into a width of 4 mm, and wound around the outer periphery of the rotating drum.

  For output and noise, a rectangular wave with a wavelength of 0.2 μm was written by a function generator, and the output of the MR head was read into a spectrum analyzer. The carrier value of 0.2 μm was set as the medium output C. Further, when a rectangular wave of 0.2 μm was written, an integrated value obtained by subtracting the output and system noise from the spectral component corresponding to the recording wavelength of 0.2 μm or more was used as the noise value N. Further, the ratio between the two was taken as C / N, and the relative value of the C and C / N with the value of Comparative Example 1 tape used as a reference was determined.

<Servo signal output>
Immediately after writing the magnetic servo signal with the servo writer, servo verification was performed and simultaneously the output (C) of the servo signal was measured to obtain a relative value to the value of the magnetic tape of Comparative Example 2. Normally, when the leakage magnetic field from the magnetic tape is small, a bias magnetic field is applied to the MR head to obtain a constant output (C). However, when the leakage magnetic field is too small, C / N causes a decrease.

<Tape temperature and humidity expansion coefficient>
A sample having a width of 12.65 mm and a length of 150 mm is prepared from the width direction of the produced magnetic tape raw material. Asked. The humidity expansion coefficient was determined from the difference in sample length between 20 ° C., 30% RH and 20 ° C., 70% RH.

<Amount of off-track>
The off-track amount was recorded using a modified LTO drive at a temperature of 20 ° C. and a humidity of 45% RH (recording wavelength 0.55 μm), at a temperature of 20 ° C., a humidity of 45% RH, a temperature of 35 ° C., and a humidity of 70% RH. It was determined from the ratio of the playback output when played back. A recording head and a reproducing head (MR head) having a track width of 20 μm and 12 μm were used, respectively.

  Table 1 summarizes the magnetic tape characteristics of Examples 1 to 9 and Comparative Examples 1 to 3 and the conditions employed in the examples and comparative examples.

  As can be seen from Table 1, computer magnetic tapes having a total thickness of less than 6 μm, using essentially spherical or elliptical iron-based magnetic powders of Examples 1 to 9 of the present invention as the uppermost magnetic layer. The recording medium) is superior in electromagnetic conversion characteristics (C, C / N) to the computer tape of Comparative Example 1 using the needle-like metal magnetic powder as the uppermost magnetic layer. In addition, a computer magnetic tape using an essentially spherical or elliptical iron-based magnetic powder as the uppermost magnetic layer, which contains a plate-like nonmagnetic powder in the undercoat layer, has excellent C / N characteristics.

  In addition, a linear recording type using an essentially spherical or elliptical rare earth-iron magnetic powder containing a plate-like nonmagnetic powder for the undercoat layer and / or the backcoat layer as the uppermost magnetic layer. Since the computer magnetic tape has good temperature / humidity stability, the amount of off-track is small even when the temperature and humidity change.

  Further, as is apparent from Examples 1 to 9 of the present invention and Comparative Example 2, by forming the lower magnetic layer, the servo output is increased, and improvement in servo characteristics can be expected.

  Due to the equipment, the undercoat layer and the lower magnetic layer were applied and dried by wet-on-wet, and the nonmagnetic intermediate layer and the upper magnetic layer were formed thereon by wet-on-wet. More preferably, the coating layer, the lower magnetic layer, the nonmagnetic intermediate layer, and the upper magnetic layer are formed by wet-on-wet.

Example 10
An yttrium-iron nitride magnetic powder was produced in the same manner as in Example 1 except that the magnetite particles having an average particle size of 25 nm as the starting material were changed to magnetite particles having an average particle size of 20 nm. The magnetite particles were produced by changing the hydrothermal treatment conditions from 200 ° C. for 4 hours to 180 ° C. for 4 hours in the production of the magnetite particles in Example 8, and the other conditions being the same.

The yttrium-iron nitride magnetic powder had a yttrium and nitrogen content of 5.5 atomic% and 11.9 atomic%, respectively, as measured by fluorescent X-ray. In addition, a profile indicating the presence of the Fe ₁₆ N ₂ phase was obtained from the X-ray diffraction pattern.

Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was a spherical or elliptical particle having an average particle size of 17 nm. The specific surface area determined by the BET method was 60.1 m ² / g.

The saturation magnetization measured by applying a magnetic field of 1,274 kA / m (16 kOe) was 130.5 Am ² / kg (130.5 emu / g), and the coercive force was 211.0 kA / m (2,650 Oe). It was. Further, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above. As a result, it was 106.9 Am ^{2 /} kg (106.9 emu / g), which was saturated before storage. The maintenance ratio of magnetization was 81.9%.

  Using the rare earth-iron nitride magnetic powder produced as described above, an upper magnetic coating material was produced in the same manner as in Example 1. In preparing the magnetic coating material, the rare earth-iron nitride magnetic powder used was prepared by scaling up the manufacturing method of this example 100 times. Further, in the same manner as in Example 1, a lower magnetic coating material, an undercoat coating material, a nonmagnetic intermediate layer coating material, and a backcoat layer coating material were also produced. In addition, the same plate-like oxide particles as those explained in Example 1 such as plate-like alumina and plate-like ITO were used for these paints. Using the magnetic coating material, the undercoat coating material, the non-magnetic intermediate layer coating material, and the back coating layer coating material thus prepared, each coating material was applied in the same manner as in Example 1, and the magnetic tape was applied under the same conditions as in Example 1. Was made. Next, the magnetic sheet that has been mirror-finished and aged as in Example 1 is cut into ½ inch, and lapping tape polishing, blade polishing, and surface wiping as in Example 1 are followed by magnetic treatment. A tape was prepared. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape. The product Br · δ of the coercive force, residual magnetic flux density and magnetic layer thickness measured in the magnetic tape orientation direction was 278.5 kA / m and 0.019 μTm, respectively.

Example 11
An yttrium-iron nitride magnetic powder was produced in the same manner as in Example 1 except that the magnetite particles having an average particle size of 25 nm as the starting material were changed to magnetite particles having an average particle size of 30 nm. The magnetite particles were produced by changing the hydrothermal treatment conditions from 200 ° C. for 4 hours to 220 ° C. for 4 hours in the production of the magnetite particles in Example 1, with the other conditions being the same.

The yttrium-iron nitride magnetic powder had a yttrium and nitrogen content of 4.8 atomic% and 10.1 atomic%, respectively, as measured by fluorescent X-ray. In addition, a profile indicating the presence of the Fe ₁₆ N ₂ phase was obtained from the X-ray diffraction pattern.

Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was spherical or elliptical particles having an average particle size of 27 nm. FIG. 6 shows a transmission electron micrograph (magnification: 200,000 times) of this magnetic powder. The specific surface area determined by the BET method was 42.0 m ² / g.

The saturation magnetization measured by applying a magnetic field of 1,274 kA / m (16 kOe) was 155.1 Am ² / kg (155.1 emu / g), and the coercive force was 235.4 kA / m (2,957 Oe). It was. Further, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above. As a result, it was 140.1 Am ^{2 /} kg (140.1 emu / g), which was saturated before storage. The maintenance ratio of magnetization was 90.3%.

  Using the rare earth-iron nitride magnetic powder produced as described above, an upper magnetic coating material was produced in the same manner as in Example 1. In preparing the magnetic coating material, the rare earth-iron nitride magnetic powder used was prepared by scaling up the manufacturing method of this example 100 times. Further, in the same manner as in Example 1, a lower magnetic coating material, an undercoat coating material, a nonmagnetic intermediate layer coating material, and a backcoat layer coating material were also produced. In addition, the same plate-like oxide particles as those explained in Example 1 such as plate-like alumina and plate-like ITO were used for these paints. Using the magnetic coating material, the undercoat coating material, the non-magnetic intermediate layer coating material, and the back coating layer coating material thus prepared, each coating material was applied in the same manner as in Example 1, and the magnetic tape was applied under the same conditions as in Example 1. Was made. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape. The product Br · δ of the coercive force, residual magnetic flux density and magnetic layer thickness measured in the magnetic tape orientation direction was 294.3 kA / m and 0.023 μTm, respectively.

Example 12
The yttrium-iron nitride system was the same as in Example 1 except that the addition amount of yttrium nitrate was changed from 2.5 g to 7.4 g and the addition amount of sodium hydroxide was changed from 0.8 g to 2.3 g. Magnetic powder was produced.

The yttrium-iron nitride magnetic powder had a yttrium and nitrogen content of 14.6 atomic% and 9.5 atomic%, respectively, as measured by fluorescent X-ray. In addition, a profile indicating the presence of the Fe ₁₆ N ₂ phase was obtained from the X-ray diffraction pattern.

Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was a spherical or elliptical particle having an average particle size of 21 nm. The specific surface area determined by the BET method was 64.3 m ² / g.

The saturation magnetization measured by applying a magnetic field of 1,274 kA / m (16 kOe) was 105.8 Am ² / kg (105.8 emu / g), and the coercive force was 232.5 kA / m (2,920). It was. Further, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above. As a result, it became 95.8 Am ^{2 /} kg (95.8 emu / g), and saturation before storage The maintenance ratio of magnetization was 90.5%.

  Using the rare earth-iron nitride magnetic powder produced as described above, an upper magnetic coating material was produced in the same manner as in Example 1. In preparing the magnetic coating material, the rare earth-iron nitride magnetic powder used was prepared by scaling up the manufacturing method of this example 100 times. Further, in the same manner as in Example 1, a lower magnetic coating material, an undercoat coating material, a nonmagnetic intermediate coating material, and a backcoat layer coating material were also produced. In addition, the same plate-like oxide particles as those explained in Example 1 such as plate-like alumina and plate-like ITO were used for these paints. Using the magnetic coating material, the undercoat coating material, the non-magnetic intermediate layer coating material, and the back coating layer coating material thus prepared, each coating material was applied in the same manner as in Example 1, and the magnetic tape was applied under the same conditions as in Example 1. Was made. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape. The product Br · δ of the coercive force, residual magnetic flux density and magnetic layer thickness measured in the magnetic tape orientation direction was 297.6 kA / m and 0.017 μTm, respectively.

Example 13
As the magnetic powder, an aluminum-iron nitride magnetic powder was used. This magnetic powder uses the same magnetite particles as in Example 1 and is subjected to aluminum treatment instead of yttrium. That is, in Example 1, 5.1 g of aluminum chloride was used instead of 2.5 g of yttrium nitrate. The other conditions were the same as in Example 1 to obtain a powder in which aluminum hydroxide was deposited on the surface of the magnetite particles, and reduction and nitriding were performed in the same manner as in Example 1 to obtain aluminum-iron nitride. A system magnetic powder was obtained.
The contents of aluminum and nitrogen in the aluminum-iron nitride magnetic powder thus obtained were measured by fluorescent X-ray and found to be 8.1 atomic% and 8.9 atomic%, respectively. Further, from the X-ray diffraction pattern, a diffraction peak based on Fe ₁₆ N ₂ and a diffraction peak based on the α-Fe phase are observed, and this aluminum-iron nitride magnetic powder is composed of Fe ₁₆ N ₂ phase and α-Fe phase. It was found that it consisted of a mixed phase.

Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 25 nm. Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,274 kA / m (16 kOe) was 136.7 Am ² / kg (136.7 emu / g), and the coercive force was 171.9 kA / m (2, 160 Oe). Further, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above. As a result, it was 115.3 Am ^{2 /} g (115.3 emu / g), which was saturated before storage. The maintenance ratio of magnetization was 84.3%.

  Using the aluminum-iron nitride magnetic powder produced by enlarging the above method to a 100-fold scale, an upper magnetic coating material was produced in the same manner as in Example 1. For the other layers, a magnetic tape was produced in the same manner as in Example 1. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape. The product Br · δ of coercive force, residual magnetic flux density and magnetic layer thickness measured in the orientation direction of this magnetic tape was 198.6 kA / m and 0.023 μTm, respectively.

Example 14
An yttrium-iron nitride magnetic powder was produced in the same manner as in Example 1 except that the nitriding temperature was changed from 150 ° C to 170 ° C.
The yttrium-iron nitride magnetic powder had a content of yttrium and nitrogen of 5.1 atomic% and 15.1 atomic%, respectively, as measured by fluorescent X-ray. In addition, a profile indicating the presence of the Fe ₁₆ N ₂ phase was obtained from the X-ray diffraction pattern.
Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was a spherical or elliptical particle having an average particle size of 21 nm. The specific surface area determined by the BET method was 54.6 m ² / g.

The saturation magnetization measured by applying a magnetic field of 1,274 kA / m (16 kOe) was 123.3 Am ² / kg (123.3 emu / g), and the coercive force was 226.1 kA / m (2,840 Oe). It was. Further, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above. As a result, the magnetic powder was 105.2 Am ^{2 /} kg (105.2 emu / g), which was saturated before storage. The magnetization maintenance factor was 85.3%.

  Using the rare earth-iron nitride magnetic powder produced as described above, an upper magnetic coating material was produced in the same manner as in Example 1. In preparing the magnetic coating material, the rare earth-iron nitride magnetic powder used was prepared by scaling up the manufacturing method of this example 100 times. Further, in the same manner as in Example 1, a lower magnetic coating material, an undercoat coating material, a nonmagnetic intermediate layer coating material, and a backcoat layer coating material were also produced. In addition, the same plate-like oxide particles as those explained in Example 1 such as plate-like alumina and plate-like ITO were used for these paints. Using the magnetic coating material, the undercoat coating material, the non-magnetic intermediate layer coating material, and the back coating layer coating material thus prepared, each coating material was applied in the same manner as in Example 1, and the magnetic tape was applied under the same conditions as in Example 1. Was made. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape. The product Br · δ of coercive force, residual magnetic flux density and magnetic layer thickness measured in the magnetic tape orientation direction was 293.6 kA / m and 0.019 μTm, respectively.

Example 15
As the magnetic powder, yttrium-silicon-iron nitride magnetic powder was used. This magnetic powder uses the same magnetite particles as in Example 1 and is subjected to yttrium-silicon treatment. That is, in Example 1, after depositing and forming yttrium hydroxide, 0.5 g of sodium silicate was further dissolved, and neutralized with dilute nitric acid to form silicon oxide. This powder was reduced and nitrided in the same manner as in Example 1 to obtain an yttrium-silicon-iron nitride magnetic powder.

The contents of yttrium, silicon and nitrogen in the thus obtained yttrium-silicon-iron nitride magnetic powder were measured by fluorescent X-ray, and found to be 5.1 atomic%, 1.8 atomic% and 9 atomic%, respectively. It was 2 atomic%. Further, from the X-ray diffraction pattern, a diffraction peak based on Fe ₁₆ N ₂ and a diffraction peak based on the α-Fe phase are observed, and this yttrium-silicon-iron nitride magnetic powder has a Fe ₁₆ N ₂ phase and an α- It was found to be composed of a mixed phase of Fe phase.

Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 20 nm. Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,274 kA / m (16 kOe) was 131.0 Am ² / kg (131.0 emu / g), and the coercive force was 231.6 kA / m (2, 910 Oe). Furthermore, after storing this magnetic powder at 60 ° C. and 90% RH for 1 week, the saturation magnetization was measured in the same manner as described above. As a result, it was 118.3 Am ^{2 /} g (118.3 emu / g), which was saturated before storage. The maintenance ratio of magnetization was 90.3%.

  Using the yttrium-silicon-iron nitride magnetic powder produced by enlarging the above method to a 100-fold scale, an upper magnetic coating material was produced in the same manner as in Example 1. For the other layers, a magnetic tape was produced in the same manner as in Example 1. The product Br · δ of coercive force and residual magnetic flux density and magnetic layer thickness measured in the direction of orientation of the magnetic tape was 298.8 kA / m and 0.021 μTm, respectively.

Comparative Example 4
In the synthesis of the ultrafine particle magnetic powder of Example 1, spherical or elliptical magnetite particles having a particle size of 25 nm were heated and reduced at 400 ° C. for 2 hours in a hydrogen stream without performing yttrium deposition treatment. Got. Next, the temperature is lowered to 90 ° C. with hydrogen gas flowing, switched to a mixed gas of oxygen and nitrogen, stabilized for 2 hours, and further cooled to 90 ° C. to 40 ° C. with the mixed gas flowing. After being kept at 40 ° C. for about 10 hours, it was taken out into the air. When the shape of the magnetic powder thus obtained was observed with a high resolution analytical transmission electron microscope, it was spherical or elliptical particles having an average particle size of 70 nm. The specific surface area determined by the BET method was 15.6 m ² / g. Further, this magnetic powder had a saturation magnetization measured by applying a magnetic field of 1,274 kA / m (16 kOe) of 195.2 Am ² / kg (195.2 emu / g), and a coercive force of 49.4 kA / m (620 Oe). )Met.

The magnetic powder produced as described above was further scaled up 100 times, and an upper magnetic coating material was produced in the same manner as in Example 1. Using this upper magnetic coating material, an attempt was made to produce a magnetic tape having an upper magnetic layer with a thickness of 0.06 μm in the same manner as in Example 10. However, the thickness variation of the upper magnetic layer thickness was large and uniform. It was not possible to produce a magnetic tape with a sufficient magnetic layer thickness.
For this magnetic tape, the coercive force measured in the orientation direction and the product Br · δ of the residual magnetic flux density and the magnetic layer thickness were measured and found to be 66.7 kA / m and 0.066 μTm, respectively.

Comparative Example 5
In Example 1, magnetite having an average particle size of 25 nm was heat-reduced at 400 ° C. for 2 hours in a hydrogen stream without performing yttrium deposition treatment, and then subjected to nitriding treatment at 150 ° C. for 30 hours in an ammonia stream. A powder was prepared.
The nitrogen content of the magnetic powder was measured by fluorescent X-ray and found to be 8.9 atomic%. When observed with a high-resolution analytical transmission electron microscope, the particles were spherical or elliptical with a particle size of 75 nm. The specific surface area determined by the BET method was 14.9 m ² / g. A profile showing the Fe ₁₆ N ₂ phase was obtained from the X-ray diffraction pattern. The saturation magnetization measured by applying a magnetic field of 1,274 A / m (16 kOe) was 186.4 Am ² / kg (186.4 emu / g), and the coercive force was 183.1 kA / m (2,300 Oe).

The magnetic powder produced as described above was further scaled up 100 times, and an upper magnetic coating material was produced in the same manner as in Example 1. Using this upper magnetic coating material, an attempt was made to produce a magnetic tape having an upper magnetic layer with a thickness of 0.06 μm in the same manner as in Example 1. However, since the particle size was large, the thickness of the upper magnetic layer was A magnetic tape having a large variation and a uniform magnetic layer thickness could not be produced.
For this magnetic tape, the coercive force measured in the orientation direction and the product Br · δ of the residual magnetic flux density and the magnetic layer thickness were measured and found to be 217.9 kA / m and 0.068 μTm, respectively.

The production conditions for the magnetic powders of Example 1, Examples 10 to 15 and Comparative Examples 4 to 5 are summarized in Table 2. In addition, the elemental composition (rare earth element and nitrogen atom%), the presence or absence of the Fe ₁₆ N ₂ phase, the average particle size, and the BET specific surface area of each of the magnetic powders of Examples 1 to 8 and Comparative Examples 4 to 5 are listed. 3 is shown collectively. Further, Table 4 summarizes the saturation magnetization, coercive force, and storage stability (saturation magnetization and retention rate after storage) of each of the magnetic powders of Example 1, Examples 10-15, and Comparative Examples 4-5. Indicated.

Example 16
In Example 1, the yttrium-iron nitride magnetic powder shown in Example 1 as magnetic powder (coercive force: 226.9 kA / m, saturation magnetization: 135.2 Am ² / kg, particle size: 20 nm, particle shape: spherical Or an elliptical shape) was used to produce an upper magnetic coating material in the same manner as in Example 1, and this upper magnetic coating material was subjected to magnetic field orientation treatment, drying and calendering treatment. The thickness of the upper magnetic layer after the calendar treatment was set to be 0.06 μm to 0.08 μm in Example 1. The same plate-like oxide particles as those explained in Example 1 such as plate-like alumina and plate-like ITO were used. Using the thus-prepared magnetic paint, undercoat paint, and backcoat layer paint, each paint was applied in the same manner as in Example 10, and a magnetic tape was produced under the same conditions as in Example 1. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape. The product Br · δ of coercive force, residual magnetic flux density and magnetic layer thickness measured in the magnetic tape orientation direction was 283.6 kA / m and 0.027 μTm, respectively.

Example 17
In Example 1, as the magnetic powder, the yttrium-iron nitride magnetic powder shown in Example 10 (coercivity: 211.0 kA / m, saturation magnetization: 130.5 Am ² / kg, particle size: 17 nm, particle shape: spherical Or an elliptical shape) was used to produce an upper magnetic coating material in the same manner as in Example 1, and this upper magnetic coating material was subjected to magnetic field orientation treatment, drying and calendering treatment. The thickness of the upper magnetic layer after the calendar treatment was set to be 0.06 μm to 0.08 μm in Example 1. The same plate-like oxide particles as those explained in Example 1 such as plate-like alumina and plate-like ITO were used. Using the thus-prepared magnetic paint, undercoat paint, and backcoat layer paint, each paint was applied in the same manner as in Example 1, and a magnetic tape was produced under the same conditions as in Example 10. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape. The product Br · δ of the coercive force, residual magnetic flux density and magnetic layer thickness measured in the magnetic tape orientation direction was 280.6 kA / m and 0.024 μTm, respectively.

Comparative Example 6
As magnetic powder in the magnetic coating component, needle-like Fe—Co alloy magnetic powder (Co / Fe: 22.1 wt%, coercive force: 195.0 kA / m, saturation magnetization: 108.7 Am ² / kg, average major axis) An upper magnetic coating material was produced in the same manner as in Example 1 using a diameter of 60 nm and an axial ratio of 5), and a magnetic tape was produced under the same conditions as in Example 10. The thickness of the upper magnetic layer could not be controlled to 0.06 μm and became 0.09 μm. A magnetic servo signal was recorded on the magnetic tape obtained as described above with a servo writer, and then incorporated into the cartridge shown in FIG. 2 to produce a computer tape.

The product Br · δ of coercive force, residual magnetic flux density and magnetic layer thickness measured in the magnetic tape orientation direction was 200.8 kA / m and 0.017 μTm, respectively.
About each magnetic tape of said Examples 10-17 and Comparative Examples 4-6, as a magnetic characteristic, coercive force (Hc), saturation magnetic flux density (Bm), squareness ratio (Br / Bm), and anisotropic magnetic field distribution ( Ha) was measured. The results are shown in Table 5.

  For the anisotropic magnetic field distribution, the differential curve in the second quadrant (demagnetization curve) of the tape hysteresis curve is measured, and the magnetic field corresponding to the half width of this differential curve is divided by the coercive force value of the tape. The value is shown. In other words, the narrower the coercive force distribution of the magnetic powder and the better the dispersion / orientation of the magnetic powder in the tape, the smaller the Ha. When compared with the same coercive force, the smaller the Ha, the more C, C / N characteristics. Will improve.

  From Table 3 and Table 4 above, the iron nitride magnetic powder containing rare earth, Al and Si of the present invention shown in Example 1 and Examples 10 to 15 has a thin magnetic layer thickness of 0.09 μm or less. It can be seen that the particles have an essentially spherical or elliptical particle shape that is optimal for magnetic recording media and have a particle size of 5 to 50 nm. Despite being spherical or elliptical, it has a high coercive force and an appropriate saturation magnetization that is optimal for high-density recording, and at the same time has excellent storage stability of saturation magnetization. .

  As shown in Examples 10 to 17 in Table 5, the iron nitride-based magnetic powder of the present invention has a high magnetic property despite being essentially spherical or elliptical when used as a magnetic recording medium. Due to the directivity, it exhibits excellent magnetic field orientation. Furthermore, the magnetic recording medium of the present invention exhibits an excellent anisotropic magnetic field distribution, which reflects the sharp coercive force distribution of the magnetic powder of the present invention. Such a magnetic tape having a small anisotropic magnetic field distribution exhibits excellent electromagnetic conversion characteristics (C, C / N).

Further, the excellent characteristics of the magnetic recording medium of the present invention as such a high-density recording medium is that a rare earth-nitrided magnetic powder containing iron nitride having a composition represented by Fe ₁₆ N ₂ is used as the magnetic powder. Appears more prominently.

  On the other hand, although the magnetic powders shown in Comparative Examples 4 to 5 have a shape close to a sphere, the particle size is as large as 50 nm or more, so that the magnetic recording essentially has a thin magnetic layer thickness of 0.09 μm or less. Cannot be used for media. Further, since the magnetic powder of Comparative Example 4 does not contain a rare earth element, the coercive force is significantly smaller than that of the magnetic powder of the present invention. Further, the magnetic powder of Comparative Example 5 is made of iron nitride, so that a relatively high coercive force can be obtained. However, since the magnetic powder does not contain rare earth elements, Al, or Si, it is 5 to 50 nm suitable for high-density magnetic recording media. It will not be the size.

  In the magnetic tape using the needle-shaped magnetic powder of Comparative Example 6, high coercive force and high orientation can be obtained, but the anisotropic magnetic field is larger than that of the magnetic tape of the present invention. C, C / N) also decreases. This is because the shape of the magnetic powder of the present invention is essentially spherical or elliptical, whereas the acicular particles have a wider particle size distribution, resulting in a wider coercive force distribution of the magnetic powder. It is done. Further, when such a needle-shaped magnetic powder is essentially a magnetic recording medium having a thin magnetic layer, the ratio of the needle-shaped magnetic powder protruding from the surface of the magnetic layer is increased, and recording is performed when a signal is recorded. Tends to be non-uniform and causes noise during playback. This is considered to be the reason why the electromagnetic conversion characteristics (C, C / N) of Comparative Example 6 are lower than those of the magnetic powder of the present invention. Further, from comparison between Examples 10 to 17 and Comparative Example 2 in Table 1, in Examples 10 to 17, the servo output is increased by forming the lower magnetic layer, and improvement in servo characteristics can be expected.

As described above, the iron-based magnetic powder used in the examples according to the present invention exhibits a high coercive force based on uniaxial crystal magnetic anisotropy while having a spherical or elliptical shape, and extremely fine particles. In spite of this, it has saturation magnetization that is optimal for high-density recording. In particular, a magnetic tape using an iron nitride magnetic powder containing rare earth elements containing iron nitride having a composition represented by Fe ₁₆ N ₂ , Al, Si as an upper magnetic layer as an iron magnetic powder is higher. It exhibits coercive force and exhibits excellent electromagnetic conversion characteristics (C, C / N).

  Further, by forming the lower magnetic layer, the servo signal output (C) is increased, and improvement in servo characteristics can be expected.

  As described above, according to the present invention, a linear recording type computer magnetic tape has excellent electromagnetic conversion characteristics (C, C / N), and a magnetic recording medium excellent in temperature and humidity stability can be obtained. Thereby, for example, a magnetic recording medium and a magnetic recording cartridge for a computer or the like that can cope with a recording capacity of 1 TB or more can be realized. Further, by forming the lower magnetic layer, the servo signal output (C) is increased, and improvement in servo characteristics can be expected.

1A and 1B are cross-sectional views of two typical examples of the magnetic tape of the present invention. It is a perspective view which shows the general structure of the magnetic tape cartridge of this invention. It is sectional drawing of the magnetic tape cartridge of FIG. 2 is an X-ray diffraction pattern of the yttrium-iron nitride magnetic powder produced in Example 1. FIG. 2 is a transmission electron micrograph (magnification: 200,000 times) of the yttrium-iron nitride magnetic powder produced in Example 1. FIG. 4 is a transmission electron micrograph (magnification: 200,000 times) of the yttrium-iron nitride magnetic powder produced in Example 11. FIG. It is a figure for demonstrating the magnetic servo system which is an example of the track servo system used for a magnetic tape, and is the model which shows the state which provided the data track and the servo band alternately on the magnetic recording surface (magnetic layer) of a magnetic tape FIG.

Explanation of symbols

1: Case body 1a, 1b: Case 2: Reel 3: Magnetic tape 4: Tape outlet 5: Door 6: Front wall 7: Tape drawer 20: Door spring 12: Brake button 17: Spring 21: Upper collar 22 : Lower collar part 23: Core part 23c: Bottom wall 23d: Bottom hole 40: Nonmagnetic support 41: Conductive undercoat layer 42: Lower magnetic layer 43: Nonmagnetic intermediate layer 44: Upper magnetic layer 45 Back layer

Claims (5)

Nonmagnetic support, at least one nonmagnetic intermediate layer containing nonmagnetic powder and binder resin formed on one surface of the nonmagnetic support, and magnetic powder formed on the nonmagnetic intermediate layer And a magnetic recording medium having at least one magnetic layer containing a binder resin,
The magnetic powder has a core portion and an outer layer portion, the rare earth element is mainly present in the outer layer portion, and the core portion is Fe ₁₆ N ₂ in which iron or a part of iron is substituted with a transition metal element. A magnetic recording medium comprising a phase, wherein the uppermost magnetic layer of the magnetic layer has a thickness of 0.09 μm or less and a coercive force of 200 to 400 kA / m. Nonmagnetic support, at least one nonmagnetic intermediate layer containing nonmagnetic powder and binder resin formed on one surface of the nonmagnetic support, and magnetic powder formed on the nonmagnetic intermediate layer And a magnetic recording medium having at least one magnetic layer containing a binder resin,
The magnetic powder includes a core portion and an outer layer portion, the rare earth element is mainly present in the outer layer portion, and the core portion is Fe ₁₆ N ₂ phase in which iron or a part of iron is substituted with a transition metal element. And the product (Br · δ) of the residual magnetic flux density (Br) and the thickness (δ) of the uppermost magnetic layer of the magnetic layer is 0.0018 to 0.05 μTm, and the coercive force is 200 to 400 kA. A magnetic recording medium characterized by being / m.   The magnetic recording medium according to claim 1, wherein the magnetic powder further contains at least one element selected from the group consisting of aluminum and silicon.   A box-shaped case body, comprising a reel on which the magnetic recording medium according to any one of claims 1 to 3 is disposed, and a magnetic field recorded on the magnetic recording medium. A magnetic recording cartridge in which a recording signal is reproduced by a magnetoresistive effect type magnetic head (MR head).   A box-shaped case main body, and a single reel on which the magnetic recording medium according to any one of claims 1 to 3 is disposed, and recorded on the magnetic recording medium. Magnetic recording cartridge that is tracked by the recorded servo signal.

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