JP2006092672A - Magnetic tape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic tape exhibiting a high-output and good reproducing output noise ratio (C/N) and excellent high recording density characteristics by securing the good reproducing output noise ratio (C/N) in a short wavelength zone corresponding to especially a high capacity of 1 TB or more. <P>SOLUTION: The magnetic tape is provided with a nonmagnetic support and at least one magnetic layer formed in one surface of the support. Magnetic powders contained in the uppermost magnetic layer comprises magnetic particles having particle sizes of 30 nm or less, and a ratio (Hc<SB>M</SB>/Hc<SB>T</SB>) between the coercive force Hc<SB>M</SB>of a longitudinal direction and the coercive force Hc<SB>T</SB>of a width direction is ≥2.2. Especially, the particles sizes of magnetic powders contained in the uppermost magnetic layer are 20 nm or less, and the magnetic tape is made of iron nitride based magnetic powders having an axis ratio (long diameter/short diameter) set to <2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

Magnetic tapes have various uses such as audio tapes, video tapes, computer tapes, etc., but 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. The one with the recording capacity is commercialized. In addition, a large-capacity backup tape exceeding 1 TB has been proposed, and a high recording density of the magnetic tape is indispensable.

When manufacturing coating-type magnetic tapes corresponding to such high recording densities, it is necessary to make magnetic powder fine particles, fill them with high density, smooth the coating, and thin the magnetic layer. Advanced technology is used. In addition, thin film type magnetic tapes in which a metal thin film such as oblique vapor deposition or a sputtered film is provided as a magnetic layer have been commercialized.

In a coating-type magnetic tape, the magnetic powder used is particularly important in order to ensure good electromagnetic conversion characteristics in a short wavelength region corresponding to a high recording density. With regard to the improvement of magnetic powder, mainly in order to cope with short wavelength recording, improvement of magnetic characteristics represented by high coercive force and high saturation magnetization has been achieved year by year with finer particles.

With high recording density magnetic tape, instead of ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, chromium oxide, etc. used for audio and home video tapes, the particle size in the major axis direction is now about 100 nm. The needle-shaped metal magnetic powder is mainly used.

Also, in recent years, rare earth-iron-based magnetism that is essentially granular or elliptical with an average particle size of 5 to 200 nm and a coercive force of about 200 kA / m consisting of a rare earth element and a transition metal element mainly composed of iron or iron. The use of powder has been proposed (see Patent Documents 1 to 3). Specifically, in Patent Documents 1 and 2, a magnetic material having an average particle size of 5 to 200 nm made of a rare earth element and a transition metal element mainly composed of iron or iron (or further boron) on a nonmagnetic support. A magnetic recording medium having a magnetic layer containing a powder and a binder is disclosed.

Patent Document 3 discloses a nonmagnetic support, a lower layer containing nonmagnetic powder formed on one surface of the nonmagnetic support, a magnetic layer containing magnetic powder formed on the lower layer, and a nonmagnetic material. In the magnetic tape having a back coat layer containing nonmagnetic powder formed on the other surface of the support, the magnetic layer has an average particle diameter of 5 to 50 nm made of rare earth element-iron-boron magnetic powder or the like. It is composed of a magnetic layer having a thickness of 0.09 μm or less, including a plate-like, granular or elliptical magnetic powder, and at least one of the lower layer and the backcoat layer is a non-magnetic material having an average particle diameter of 10 to 100 nm. A magnetic tape characterized by containing plate-like particles is disclosed.

Furthermore, it has been proposed to use an iron nitride-based magnetic powder having an average particle diameter of 5 to 50 nm composed of rare earth elements and iron or transition metal elements mainly composed of iron and nitrogen, and its coercive force is 210 kA. / M or more is also disclosed (see Patent Documents 4 and 5).

Specifically, Patent Documents 4 and 5 describe magnetic recording in which a nonmagnetic lower layer and a magnetic layer are formed on one surface of a nonmagnetic support, and a back layer is formed on the other surface of the nonmagnetic support. In the medium, the magnetic powder contained in the uppermost magnetic layer is composed of a rare earth element and a transition metal element mainly composed of iron or iron, in particular, the core portion is composed of Fe ₁₆ N ₂ , and the average particle diameter is 5 to 50 nm. A magnetic recording medium is disclosed which is a substantially granular rare earth-iron-based magnetic powder having an average axial ratio of 1 or more and 2 or less, and the total thickness of the medium is less than 6 μm.

More specifically, Patent Document 4 discloses a magnetic tape cartridge that realizes a high track density by accommodating a magnetic tape on which a servo signal is recorded in a one-reel type cartridge and tracing a data track by the servo signal. Yes. Further, by mounting a magnetoresistive head (MR head) on the reproducing head, even with an upper magnetic layer thickness of 0.09 μm or less, a high reproduction output (high C) and a high reproduction output noise ratio (high C / N) is realized. Patent Document 5 discloses a magnetic tape and a magnetic tape cartridge in which the lower magnetic layer for servo signal recording is formed on the magnetic recording medium of Patent Document 4 described above, the servo signal output is increased, and the servo tracking characteristics are improved. It is disclosed.

In addition, in order to improve electromagnetic conversion characteristics, magnetic recording media in which the orientation structure of the magnetic powder in the magnetic layer is defined have been proposed (see Patent Documents 6 to 8).

For example, in Patent Documents 6 and 7, a plate-like ferromagnetic hexagonal ferrite is used as a magnetic powder for the purpose of obtaining a magnetic recording medium exhibiting high electromagnetic conversion characteristics in a wide recording wavelength region from a short wavelength signal to a long wavelength signal. In a magnetic recording medium having a magnetic layer thickness of 1 μm or less, the coercive force in the longitudinal direction is Hc ₁ , the coercive force in the vertical direction is Hc ₂ , and the coercive force in the width direction is Hc _3. In such a case, a magnetic recording medium having a relationship of Hc ₁ > Hc ₂ > Hc ₃ or a relationship of Hc ₂ > Hc ₁ > Hc ₃ has been proposed.

In Patent Document 8, a granular rare earth-transition metal magnetic powder having an average particle diameter of 5 to 100 nm is used for the purpose of obtaining a magnetic recording medium exhibiting excellent short wavelength characteristics such as high output. In the magnetic recording medium having a thickness of 300 nm or less, the ratio of the coercive force in the longitudinal direction / the coercive force in the width direction is 1.20 or more, preferably 1.25 or more and usually 1.35, and in the longitudinal direction. There has been proposed a magnetic recording medium in which the ratio of the squareness ratio / the squareness ratio in the width direction is 1.9 or more, preferably 2.2 or more and usually 4.0.

JP 2001-181754 A JP 2002-056518 A JP 2004-005896 A WO03 / 079332A1 brochure WO03 / 079333A1 brochure Japanese Patent Laid-Open No. 06-274847 Japanese Patent Laid-Open No. 06-282835 JP 2003-272123 A

The magnetic recording media disclosed in Patent Documents 1 to 8 have a unique effect according to the unique configuration described in each document. It was found that the medium was still not sufficient in terms of improving the electromagnetic conversion characteristics.

For example, when only fine particle magnetic powders such as those disclosed in Patent Documents 1 to 5 are used, the reproduction output (C) is evaluated with an MR head as expected from the coercive force and the average particle size. ) And reproduction output noise ratio (C / N) and other electromagnetic conversion characteristics cannot be greatly improved. Further, even if a magnetic recording medium that defines the orientation structure of the magnetic powder in the magnetic layer as disclosed in Patent Documents 6 to 8, even if characteristics such as high output are obtained, reproduction output noise is as follows. In terms of characteristics such as the ratio (C / N), it was not sufficient.

That is, in Patent Documents 6 and 7, it is preferable that the magnetic powder is a plate-like ferromagnetic hexagonal ferrite having a plate-like ratio of 3 to 7 and an average particle size of about 30 to 100 nm. The magnetic powder is used to regulate the orientation structure of the magnetic powder in the magnetic layer as described above, and in particular, the relationship of coercive force (coercive force) Hc _{1 in the} longitudinal direction> coercive force Hc _{3 in} the width direction. As shown in FIG. 1, a medium in which the ratio between the two is 2.2 or more is shown, but the reproduction output noise ratio (C / N) tends to be low in a short wavelength region as the object of the present invention. I understood it.

In Patent Document 8, as an example, granular rare earth-transition metal magnetic powder having an average particle diameter of 5 to 100 nm is used, and the ratio of the coercive force in the longitudinal direction to the coercive force in the width direction in the magnetic layer is set to 1. Although the magnetic recording medium is set so as to be .26 to 1.33, it has been found that the reproduction output noise ratio (C / N) also tends to be low in this case.

The present invention overcomes the problems of the prior art and provides a magnetic tape exhibiting a high output and a good reproduction output noise ratio (C / N), and can cope with a high capacity of 1 TB or more. It is an object of the present invention to provide a magnetic tape excellent in high recording density characteristics by securing a good reproduction output noise ratio (C / N) in a short wavelength region.

As a result of detailed investigations on the electromagnetic conversion characteristics, in particular, the improvement of the reproduction output noise ratio C / N, and the improvement method, the present inventors have obtained an axial ratio (major axis / minor axis) as a magnetic powder. Is a substantially granular magnetic particle having a particle size of less than 2 and a particle size of 30 nm or less, particularly preferably 20 nm or less, particularly a fine particle magnetic powder, particularly an iron nitride magnetic powder, and the orientation of the magnetic layer containing the same. When the structure is an orientation structure in which the ratio of the coercive force Hc _M in the longitudinal direction to the coercive force Hc _{T in the} width direction is greater than a specific value, the output C during short wavelength recording is large and the noise N is small. Knowing that a magnetic tape exhibiting excellent short-wavelength recording / reproducing characteristics with an excellent noise ratio (C / N) can be obtained, the present invention has been completed.

That is, according to the present invention, in a magnetic tape having a nonmagnetic support and at least one magnetic layer formed on one surface of the support, the magnetic powder contained in the uppermost magnetic layer has a particle size of 30 nm. A magnetic tape comprising the following substantially granular magnetic particles, wherein the ratio [Hc _M / Hc _T ] of the coercive force Hc _{M in} the longitudinal direction and the coercive force Hc _{T in the} width direction is 2.2 or more In particular, the magnetic powder contained in the uppermost magnetic layer is composed of substantially granular magnetic particles having a particle size of 20 nm or less, and has an axial ratio (major axis / minor axis) of less than 2. Further, iron nitride The present invention relates to a magnetic tape having the above structure, which is a magnetic powder.

As described above, the inventors of the present invention use specific particulate magnetic powder having a substantially granular shape and increase the coercive force Hc _M in the longitudinal direction as well as the coercive force in the width direction as the orientation structure of the magnetic layer including this. When the magnetic force Hc _T is reduced, the output C at the time of short wavelength recording is increased and the noise N is reduced, and good short wavelength recording / reproducing characteristics can be obtained. Based on this knowledge, the longitudinal coercive force Hc _M and As a result of a detailed study on the relationship between the ratio (Hc _M / Hc _T ) to the coercive force Hc _{T in the} width direction and the reproduction output noise ratio (C / N), the ratio (Hc _M / Hc _T ) is 2.2. It has been found that the C / N is remarkably improved when it is increased as described above.

The ratio of the coercivity in the longitudinal direction to the coercivity in the width direction (Hc _M / Hc _T ) is preferably 2.5 or more, and more preferably 3.0 or more. Ideally, it is preferably infinite, but currently it is 10 or less. The reason is that the particle shape of the magnetic powder is not substantially spherical and is not a perfect sphere, and the rotation of the magnetic particle is constrained by the presence of a filler such as carbon black or alumina, the non-uniform dispersion of the magnetic powder, etc. This is because it is difficult to completely orient the easy magnetization axis of the magnetic powder in the longitudinal direction. In addition, according to a small-scale experiment, in order to set the ratio of the coercive force in the longitudinal direction to the coercive force in the width direction, it is effective if a method of orientation and drying is applied in a magnetic field of 0.7 T or more. It has been confirmed.

The reason why the magnetic tape of the present invention configured as described above can obtain excellent C / N in the short wavelength region is not clear, but is considered as follows.

As shown in FIG. 1, when a signal recorded in the longitudinal direction in the uppermost magnetic layer of the magnetic tape 1 is magnetized in the opposite direction by the magnetic head 3, as shown in FIG. Rotates and reverses magnetization. The rotation direction of the magnetization 2 can be a width direction and a direction perpendicular to the film surface, but if the magnetization is perpendicular to the film surface in the direction perpendicular to the film surface, the demagnetizing field increases in the ultrathin uppermost magnetic layer. Therefore, the width direction (in the magnetic layer plane) is considered to be the magnetization rotation direction.

Therefore, the magnetization reversal can be easily performed even with a magnetic head magnetic field that is weaker in the magnetic layer having a smaller coercive force Hc _T in the width direction. Therefore, magnetization reversal is easily performed even at a portion away from the magnetic head, that is, below the uppermost magnetic layer. As a result, the magnetization can be easily reversed from the surface portion to the lower portion of the uppermost magnetic layer, and the magnetic layer having a smaller coercive force Hc _{T in} the width direction can increase the number of magnetic particles related to magnetic recording. It is considered that the output (C) and the output noise ratio (C / N) when performing short wavelength recording are increased.

In contrast, in a magnetic layer having a large coercive force Hc _T in the width direction, magnetization reversal is not easily caused by a weak magnetic head magnetic field, and magnetization reversal is unlikely to occur in a portion away from the magnetic head, that is, below the uppermost magnetic layer. As a result, the magnetization reversal at the lower portion is reduced compared with the surface portion of the uppermost magnetic layer, and the number of magnetic particles related to magnetic recording is reduced. Therefore, the output (C) and the output noise ratio (C) when performing short wavelength recording. / N) is considered to decrease.

3 and 4 schematically show these relationships.

That is, FIG. 3 is an example in which the coercive force Hc _T in the width direction in the uppermost magnetic layer is reduced and the ratio (Hc _M / Hc _T ) to the coercive force Hc _M in the longitudinal direction is 2.2 or more. In this case, since magnetization can be easily reversed from the surface portion to the lower portion of the uppermost magnetic layer, the output (C) and output noise ratio (C / N) are increased. On the other hand, FIG. 4 is an example in which the coercive force Hc _T in the width direction in the uppermost magnetic layer is increased and the ratio (Hc _M / Hc _T ) to the coercive force Hc _M in the longitudinal direction is less than 2.2. In this case, since the magnetization reversal at the lower portion is reduced as compared with the surface portion of the uppermost magnetic layer, the output (C) and the output noise ratio (C / N) are lowered.

In the above configuration of the present invention, the magnetization transition region (boundary region where the magnetization in the magnetic layer is reversed) 4 shown in FIG. 1 (and FIGS. 3 and 4) also has a large value of Hc _M / Hc _T. Since it becomes narrower, a magnetic tape excellent in short wavelength recording can be obtained.

Since the magnetic powder is a single domain particle, the magnetization transition region does not become smaller than the particle size in the longitudinal direction of the magnetic powder, and when the particle size is 30 nm or less and smaller than the recording wavelength as in the present invention, With the miniaturization, the magnetization transition region becomes 30 nm or less.

The larger the coercive force Hc _M in the longitudinal direction, the smaller the self-demagnetization due to the demagnetizing field. Therefore, the Hc _M in the longitudinal direction is increased and the ratio of this to the width direction Hc _T (Hc _M / Hc _T ) Is increased, that is, the value of Hc _M / Hc _T is set to 2.2 or more, preferably 2.5 or more, more preferably 3.0 or more, so that C / N can be increased. When the value of Hc _M / Hc _T is less than 2.2, the C / N improvement effect is small. When the value of Hc _M / Hc _T exceeds 10, the C / N improvement effect is saturated, and is usually 10 or less. The reason why the C / N improvement effect saturates when the value of Hc _M / Hc _T exceeds 10 is unknown, but it is estimated that the size of the magnetization transition region is comparable to the particle size of the magnetic powder. .

As described above, in the present invention, as a completely new focus, the longitudinal coercive force Hc _M of the magnetic tape is increased, the transverse coercive force Hc _T is decreased, and the longitudinal coercive force Hc _T is reduced. It has been found that the electromagnetic conversion characteristics can be significantly improved by defining the ratio (Hc _M / Hc _T ) to the coercive force to a specific value or more. If the ratio is less than a specific value, the demagnetizing field in the longitudinal direction is large, and the C / N in the short wavelength range cannot be secured. It is difficult to make full use of the technique.

In the present invention, the coercive forces Hc _M and Hc _T are values measured according to a conventional method at 25 ° C. and an external magnetic field of 1273.3 kA / m using a sample vibration magnetometer manufactured by Toei Kogyo. The measurement sample was prepared by attaching 20 magnetic tapes and punching them into a diameter of 8 mm. The measured value is an average value measured ten times in the longitudinal direction and the width direction of the magnetic tape.

Conventionally, the coercive force of a magnetic tape usually refers to the coercive force (Hc _M ) in the longitudinal direction. This is because Hc _M affects the output decrease due to the demagnetizing field at the time of short wavelength recording, and when Hc _M is increased, the output decrease due to the demagnetizing field can be reduced and the short wavelength output can be improved. However, in the present invention, in order to improve C and C / N in a short wavelength region required for a large-capacity high-density recording exceeding 1 TB (approximately exceeding 1.0 GB / in ² ), the width direction of the magnetic tape is used. It is effective to reduce the coercive force (Hc _T ) of the material, and further to adjust the value of (Hc _M / Hc _T ) by controlling the coercive force separately in the longitudinal direction and the width direction. It has been found for the first time that it is extremely effective in improving the above.

In the present invention, the means for setting the value of (Hc _M / Hc _T ) to 2.2 or more is not particularly limited, but the following methods (a) to (d) are preferable.

A magnetic tape having a predetermined value (Hc _M / Hc _T ) can be produced by using the following methods (a) to (d) alone, and preferably using some of them together. . Of course, the method of controlling the value of (Hc _M / Hc _T ) is not limited to the following methods (a) to (d), and other known methods may be used in combination as appropriate.

(A) To reduce the coercive force in the width direction and increase the value of (Hc _M / Hc _T ) even with the same longitudinal coercive force, the shape of the magnetic powder is selected.

The shape of the magnetic powder is substantially granular. The substantially granular magnetic powder is a spherical, substantially spherical, ellipsoidal or substantially ellipsoidal shape having an axial ratio (major axis / minor axis) of less than 2, preferably 1.5 or less, more preferably less than 1.5. , Polyhedral, substantially polyhedral, plate-like, and substantially plate-like particles.

In addition, the major axis is the maximum diameter in the case of substantially spherical shape, ellipsoidal shape, substantially elliptical shape, polyhedral shape, and substantially polyhedral shape, and the plate diameter in the case of plate-like and substantially plate-like particles. In addition, the minor axis is the maximum diameter in the direction perpendicular to the diameter of the sphere, ellipsoid, substantially ellipsoid, polyhedron, or polyhedron. For particles, it is the plate thickness.

In order to make Hc _T relatively smaller than Hc _M , the particle size of the substantially granular fine magnetic powder is preferably 30 nm or less, more preferably 20 nm or less, further preferably 15 nm or less, and most preferably less than 15 nm. Moreover, 3 nm or more is preferable, 5 nm or more is more preferable, and 8 nm or more is further more preferable. The particle size in this range is preferable because if the particle size is less than 3 nm, it is difficult to disperse the magnetic powder in the magnetic coating material, so that the Hc _T is relatively high. Moreover, when it exceeds 30 nm, the noise of a magnetic tape will become high. In addition, although mixing of the particle | grains with a particle size exceeding 30 nm is not excluded, even when the particle | grains exceeding 30 nm are mixed, the number average particle size is preferably 30 nm or less.

(B) It is preferable to use a magnetic powder with little sintering.

As the substantially granular magnetic powder contained in the uppermost magnetic layer used in the magnetic tape of the present invention, its oxides, such as rare earth elements, aluminum, silicon, zirconium and titanium, are not reduced by hydrogen reduction at 600 ° C. or lower. It is preferable that at least one of elements (particularly, rare earth element, aluminum, silicon) is mainly present in the outer layer part, and a transition metal element mainly composed of iron or iron and nitrogen are mainly present in the core part.

By configuring the outer layer portion of the magnetic powder in such a configuration, sintering of the magnetic powders during the production of the magnetic powder can be prevented, and Hc _T can be made relatively smaller than Hc _M. Furthermore, an iron nitride-based magnetic powder whose core portion contains an Fe ₁₆ N ₂ phase is more preferable. Moreover, it is preferable that composition distribution, such as nitrogen for every particle | grains of magnetic powder, is small.

(C) It is preferable to control the square in the longitudinal direction of the medium.

In order to increase the coercive force Hc _M in the recording direction, that is, the longitudinal direction and not to deteriorate the electromagnetic conversion characteristics, the longitudinal square is preferably 0.75 or more. The larger the square, the better. The theoretical ideal value is 1, but in reality, about 0.95 is the limit. The medium preferably has a smaller SFD (anisotropic magnetic field distribution). SFD is preferably 1.0 or less, and more preferably 0.7 or less. When magnetic powder having a uniform particle size, that is, a narrow particle size distribution is used, the SFD is improved. A smaller SFD of the medium has an effect of reducing the coercive force Hc _T in the width direction even if the same longitudinal square is shown. If the particle diameter is uniform, the dispersion can be performed uniformly and the same effect is produced.

As a method for embodying these, a strong (for example, 0.5 T or more) orientation magnetic field is applied after the uppermost magnetic layer is applied, and then the uniform magnetic field (for example, 0.1 T or more) is applied to the uppermost magnetic layer. What is necessary is just to apply continuously until it dries. As a method for applying a uniform magnetic field, there are a method in which a large number of repulsive magnets are arranged, a method in which a solenoid is used, and a method in which both are used, and either method may be adopted. The method of arranging a large number of repulsive magnets has the advantage that the running cost is low, but the magnetic field between the repulsive magnets and the repulsive magnets stands perpendicular to the magnetic medium film surface direction, or there is no magnetic field or inversion. Therefore, it is necessary to adjust the drying position of the magnetic coating film to the portion where the magnetic field is generated in the longitudinal direction. On the other hand, the method using a solenoid has a high running cost such as electric power, but since the orientation magnetic field is accurately oriented in the longitudinal direction of the magnetic recording medium, the orientation of the magnetic powder in the longitudinal direction of the easy axis of magnetization is improved. The ratio (Hc _M / Hc _T ) between the coercive force and the coercive force in the width direction is very large.

(D) It is effective to improve the dispersibility of the magnetic powder in the magnetic coating material in order to make Hc _T relatively smaller than Hc _M.

As a technique for this purpose, a known technique conventionally used for increasing the dispersibility of the fine particle magnetic powder is possible, and these may be carried out by appropriately combining them. In preparing the magnetic coating material, it is preferable to stir and mix with a dispersant and a resin in advance at high speed before kneading the magnetic powder so that the magnetic powder can be unraveled well.

For kneading, it is preferable to use a pressure-type kneader or a continuous biaxial kneader that applies a large shearing force so as to be well blended with the resin. If it is a normal kneader, the batch amount of the magnetic powder is appropriately set. It is preferable to devise. The dispersion may be a normal sand mill type disperser. As the dispersion medium, a conventional general material can be used, but it is preferable to use beads having a particle diameter of less than 1 mm and mainly composed of titania and zirconia. This is because the smaller the particle size and the larger the specific gravity, the larger the dispersion ability, the more easily the magnetic powder is loosened and oriented, and the coercive force in the tape width direction tends to be small. Moreover, you may process with a well-known surface treating agent so that the surface of magnetic powder may be disperse | distributed easily. Furthermore, as the resin used as the binder, it is preferable to use a conventionally known resin having a functional group that improves dispersibility.

Preferred embodiments of the present invention are as follows.

(1) In a magnetic tape having a nonmagnetic support and at least one magnetic layer including a magnetic powder and a binder resin formed on one surface of the support, the magnetic content contained in the uppermost magnetic layer The powder is a substantially granular magnetic particle having a particle size of 30 nm or less, and the ratio of the coercive force in the longitudinal direction to the coercive force in the width direction in the recording surface (coercive force in the longitudinal direction / coercive force in the width direction) is 2. Magnetic tape that is 2 or more. In particular, the particle size of the magnetic powder contained in the uppermost magnetic layer is more preferably 20 nm or less.

(2) A magnetic tape in which the coercive force in the longitudinal direction of the uppermost magnetic layer is 160 to 400 kA / m, more preferably 200 to 400 kA / m.

(3) A magnetic tape in which the coercive force in the width direction of the uppermost magnetic layer is 16 to 180 kA / m, more preferably 20 to 120 kA / m.

(4) A magnetic tape having a value of [(coercivity in the longitudinal direction) − (coercivity in the width direction)] in the uppermost magnetic layer is 155 to 360 kA / m.

(5) A magnetic tape in which the uppermost magnetic layer has a thickness of 0.09 μm or less.

(6) The magnetic tape in which the product (Br · δ) of the residual magnetic flux density (Br) and the thickness (δ) of the uppermost magnetic layer is 0.0018 μTm or more and 0.05 μTm or less.

(7) A magnetic tape having at least one lower layer containing nonmagnetic powder and a binder resin between the nonmagnetic support and the uppermost magnetic layer.

(8) A magnetic tape having a back layer formed on the other surface of the nonmagnetic support.

(9) A magnetic tape in which the back layer is a back coat layer containing carbon black powder and a binder.

(10) Magnetic tape whose total thickness is less than 6 μm.

(11) A magnetic tape in which the substantially granular magnetic powder contained in the uppermost magnetic layer is a magnetic powder comprising an outer layer portion and a core portion.

(12) A magnetic tape in which the magnetic powder contained in the uppermost magnetic layer is substantially granular particles having a particle size of 20 nm or less and an axial ratio is less than 1.5.

(13) A magnetic tape in which the particle size of the substantially granular magnetic powder contained in the uppermost magnetic layer is less than 15 nm and the axial ratio is less than 1.5.

(14) The magnetic powder contained in the uppermost magnetic layer is an element in which the oxide is not reduced at a hydrogen reduction temperature of 600 ° C. or less, such as rare earth elements, aluminum, silicon, titanium, zirconium (especially rare earth elements, aluminum, A magnetic tape in which at least one of silicon is a magnetic powder mainly existing in an outer layer portion of the magnetic powder.

(15) A magnetic tape in which a core portion of a substantially granular magnetic powder contained in the uppermost magnetic layer is an iron nitride-based magnetic powder composed of iron nitride phase in which iron or a part of iron is substituted with a transition metal element.

(16) A magnetic tape containing an Fe ₁₆ N ₂ phase in which the iron nitride phase of the core portion of the substantially granular iron nitride magnetic powder contained in the uppermost magnetic layer is iron or a part of the iron is replaced with a transition metal element . In the Fe ₁₆ N ₂ phase, a part of iron (Fe) is replaced with an element other than iron, a part of nitrogen (N) is replaced with an element other than nitrogen, and the stoichiometric amount of iron and nitrogen is 16 : Includes deviations from 2.

(17) A magnetic tape in which the content of rare earth elements in the substantially granular iron nitride magnetic powder contained in the uppermost magnetic layer is 0.05 to 20 atomic% with respect to iron.

(18) A magnetic tape in which the content of rare earth elements in the substantially granular magnetic powder contained in the uppermost magnetic layer is 0.5 to 15 atomic% with respect to iron.

(19) A magnetic tape in which the content of aluminum in the substantially granular magnetic powder contained in the uppermost magnetic layer is 0.5 to 15 atomic% with respect to iron.

(20) A magnetic tape in which the content of silicon in the substantially granular magnetic powder contained in the uppermost magnetic layer is 0.5 to 15 atomic% with respect to iron.

(21) A magnetic tape in which the content of nitrogen in the substantially granular iron nitride magnetic powder contained in the uppermost magnetic layer is 1.0 to 20 atomic% with respect to iron.

(22) A magnetic tape in which the content of nitrogen in the substantially granular iron nitride magnetic powder contained in the uppermost magnetic layer is 2.0 to 12.5 atomic% with respect to iron.

(23) The magnetic tape in which the rare earth element in the substantially granular rare earth-iron nitride magnetic powder contained in the uppermost magnetic layer is at least one element selected from samarium, neodymium, and yttrium.

(24) It has a box-shaped case body and a reel on which a magnetic tape disposed inside the case body is wound, and a magnetic recording signal recorded on the magnetic tape is a magnetoresistive effect type magnetic head ( MR recording head).

As described above, according to the present invention, a magnetic tape having excellent electromagnetic conversion characteristics, in particular, a reproduction output, is obtained by using a fine-particle magnetic powder having a specific shape and regulating the orientation structure of the magnetic layer containing the powder. A magnetic tape having a high noise ratio (C / N) can be provided.

The components of the magnetic tape of the present invention are as follows: magnetic powder, nonmagnetic support, magnetic layer, magnetic coating preparation, magnetic field orientation treatment, lower layer, lubricant, back layer, and organic solvent. I will explain in detail.

<Magnetic powder>
The substantially granular fine particle magnetic powder includes rare earth-iron-boron magnetic powder having an average particle size of 5 to 200 nm and a coercive force of 80 to 400 kA / m (Japanese Patent Laid-Open No. 2001-181754), rare earth-iron magnetic powder. (Japanese Patent Laid-Open No. 2002-56518).

Moreover, there is an iron nitride-based magnetic powder (Japanese Patent Laid-Open No. 2000-277311) that 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. The coercive force obtained is as small as less than 200 kA / m, and the particle size is unknown.

Furthermore, by making at least one element selected from rare earth elements, aluminum, and silicon, which have a high anti-sintering effect, a high coercive force effect, and a stability (corrosion resistance) improving effect, mainly present in the outer layer portion of the magnetic powder, (Rare earth, aluminum, silicon) -iron nitride magnetic powder (WO03 / 079322A1, WO03 /) having a coercive force as high as 210 kA / m or more, excellent in paint dispersibility and oxidation stability, and having an average particle size of 5 to 50 nm 079333A1).

Among these magnetic powders, a substantially granular iron nitride fine particle magnetic powder having a particle size of 30 nm or less and an axial ratio (major axis length / minor axis length) of less than 2 is the uppermost magnetic layer of the present invention. Particularly preferred as a fine magnetic powder.

Further, at least one element such as rare earth, aluminum, silicon, zirconium, titanium, etc. whose oxide is not reduced at a hydrogen reduction temperature of 600 ° C. or less (particularly rare earth element, aluminum, silicon) is mainly used in the outer layer portion. It is more preferable to use iron nitride-based fine particle magnetic powder mainly containing iron or a transition metal nitride mainly composed of iron in the core portion.

Furthermore, an iron nitride-based fine particle magnetic powder containing at least one element of rare earth element, aluminum, or silicon in the outer layer portion and Fe ₁₆ N ₂ in the core portion is more preferable. The iron nitride-based fine particle magnetic powder containing Fe ₁₆ N ₂ in the core portion mentioned here has an Fe ₁₆ N ₂ phase, an iron (Fe) part of which is an element other than iron, and a part of nitrogen (N). Includes those substituted with elements other than nitrogen, and those in which the stoichiometric amounts of iron and nitrogen deviate from 16: 2.

The reason why the outer layer portion mainly contains an element whose oxide is not reduced at a hydrogen reduction temperature of 600 ° C. or less, such as rare earth, aluminum, silicon, zirconium, titanium, etc. is one of the manufacturing processes of magnetic powder. This is to prevent sintering between particles in the hydrogen reduction step and to easily obtain an iron nitride fine particle magnetic powder having a small particle size. The reason why the core portion mainly contains nitride (particularly, Fe ₁₆ N ₂ phase) is to make it easy to obtain iron nitride-based fine particle magnetic powder having high coercive force and saturation magnetization.

Further, if necessary, an element or compound effective for improving dispersibility such as aluminum, silicon, phosphorus, and zirconium may be further contained or adsorbed on the surface of the magnetic powder. If necessary, carbon, calcium, manganese, magnesium, barium, strontium, or a compound thereof may be contained or adsorbed on the surface of the magnetic powder.

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

The particle size is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably less than 15 nm. When the particle size is 3 nm or more, dispersion during preparation of the magnetic paint is easy. 5 nm or more is more preferable, and 8 nm or more is more preferable.

Although it does not exclude the inclusion of magnetic particles having a particle size of more than 30 nm or less than 3 nm, even in that case, the average particle size is preferably 30 nm or less and 3 nm or more. Further, the axial ratio (major axis / minor axis) is preferably less than 2, since the filling property of the magnetic powder becomes high, preferably 1.5 or less, more preferably less than 1.5. Although mixing of magnetic particles with an axial ratio exceeding 2 is not excluded, even in that case, the average axial ratio is preferably less than 2.

The particle size is the maximum diameter (major axis diameter) obtained from a photograph taken at a magnification of 200,000 with a transmission electron microscope (TEM).

The average particle size was obtained by calculating the particle size (maximum diameter and major axis diameter) from the photograph and arithmetically averaging 50 particle sizes.

Also, the axial ratio is the ratio of the maximum diameter (long axis diameter) obtained from the photo to the maximum diameter (short axis diameter) in the direction perpendicular to the maximum diameter direction. Sashimi diameter) / (maximum squeezing diameter in the direction perpendicular to the squeezing diameter direction)].

The average axial ratio was obtained by calculating the axial ratio of individual particles and arithmetically averaging the 50 axial ratios. The magnetic powder particle size in the tape-shaped medium was determined by taking a scanning electron microscope (SEM) photograph of the longitudinal section (cut in the longitudinal direction) of the medium at a magnification of 200,000 times.

The total content of iron such as rare earth elements, aluminum, silicon, zirconium, titanium, and the like mainly present in the outer layer portion of the magnetic powder is preferably 0.2 to 20 atomic%, and more preferably 2 to 10 atomic%. If the total content of rare earth elements, aluminum, silicon, zirconium, titanium, etc. is too small, coarse particles are likely to be generated by sintering during reduction, particle size distribution is deteriorated, and the coercive force (Hc _T ) in the width direction is reduced. It tends to be large and is not preferable. Further, if the total content of rare earth elements, aluminum, silicon, zirconium, titanium, etc. is too large, the saturation magnetization tends to be excessively lowered, which is not preferable.

In the total content, the content of rare earth elements is preferably 0.2 to 15 atomic%, and more preferably 2 to 10 atomic%. If there are too many rare earth elements, not only will the cost increase, but the saturation magnetization will tend to decrease excessively. When there are too few rare earth elements, the contribution of the magnetic anisotropy based on rare earth elements may become small.

The content of nitrogen with respect to iron is preferably 1.0 to 20 atomic%, and more preferably 3 to 13 atomic%. 8-13 atomic% is more preferable.

If the content of nitrogen relative to iron is too small, the amount of Fe ₁₆ N ₂ phase formed will be small, the contribution of magnetic anisotropy will be small, and the effect of increasing coercivity and increasing saturation magnetization (especially the effect of increasing coercivity) will be small. Become. In addition, if the content of nitrogen relative to iron is too large, iron nitride with a small coercive force and saturation magnetization such as Fe ₄ N and Fe ₃ N and nonmagnetic nitride are likely to be formed, and increase in coercive force and increase in saturation magnetization will occur. The effect is reduced, and particularly the saturation magnetization is excessively lowered.

The coercive force in the longitudinal direction of the uppermost magnetic layer is preferably 160 to 400 kA / m, more preferably 200 to 400 kA / m, still more preferably 220 kA / m or more, and even more preferably 250 kA / m or more. If it is less than 160 kA / m, it is difficult to make the recording wavelength sufficiently small, and if it exceeds 400 kA / m, recording by the magnetic head may be insufficient. 380 kA / m or less is preferable, and 350 kA / m or less is more preferable.

BET specific surface area of the magnetic powder is preferably 40 to 200 m ² / g, more preferably at least 50 m ² / g, more 60 m ² / g is more preferred. If it is less than 40 m ² / g, the coercive force is not likely to be sufficiently high, and if it exceeds 200 m ² / g, the dispersibility of the paint may be lowered or chemically unstable. 100 m ² / g or less is more preferable.

The saturation magnetization of the magnetic powder is preferably 70 to 160 Am ² / kg (70 to 160 emu / g). This range is preferable, 70 Am ² / is less than kg likely lower reproduction output, 160Am ² / kg increased more than the cohesive force of the magnetic powder, and in some cases the dispersion time at the paint preparation is too long Because. 80 Am ² / kg or more is more preferable, and 90 Am ² / kg or more is more preferable. In addition, 140 Am ² / kg or less is easy to disperse at the time of preparing the coating material, and there is little deterioration of the saturation magnetization with time.

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. At the same time, the magnetic powder is excellent in 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 present invention, in order to achieve a high C / N ratio using an MR head, a substantially granular iron nitride-based fine particle magnetic powder including the rare earth-iron nitride-based magnetic powder is particularly preferable. Below, the manufacturing method of this especially preferable iron nitride type magnetic powder is demonstrated.

The (rare earth element, aluminum, silicon) -based iron nitride magnetic powder of the present invention is prepared by using iron-based oxides such as hematite, magnetite, goethite, or water as described in WO03 / 079332A1 and WO03 / 079333A1. An oxide is used, and at least an element selected from rare earth elements, aluminum, and silicon is deposited thereon, and then heat reduction treatment is performed at a temperature of 300 to 600 ° C. in a reducing gas such as hydrogen gas. It manufactures by performing a nitriding process at the temperature of 100-300 degreeC in the gas to contain.

Here, the particle size distribution of the iron-based oxide or hydroxide as the starting material is preferably smaller because the coercive force (Hc _T ) in the width direction tends to be smaller. In order to suppress the nitrogen composition distribution for each particle, it is preferable to perform nitriding for a long time at a low temperature.

The (rare earth element, aluminum, silicon) -based iron nitride magnetic powder thus produced may be further adsorbed or contained with aluminum, silicon, phosphorus, zirconium, carbon, calcium, magnesium, zirconium, barium, strontium, or the like. Good. Examples of the treatment method include a method in which magnetite particles coated with a rare earth element and the like produced by the method described in WO03 / 079333A1 are immersed in an aqueous solution such as an aluminum salt to adsorb aluminum on the surface of the magnetite particles. .

Hexagonal Ba-ferrite magnetic powder can also be used as the magnetic powder. In this case, the saturation magnetization of the hexagonal Ba-ferrite magnetic powder is 40 to 70 A · m ² / kg (40 to 70 emu / g). It is preferable that it exists in the range. In the case of this hexagonal Ba-ferrite magnetic powder, the coercive force in the longitudinal direction of the uppermost magnetic layer is preferably 160 to 400 kA / m, more preferably 200 to 400 kA / m, and 220 kA for the same reason as described above. / M or more is more preferable, and 250 kA / m or more is more preferable. Further, the BET specific surface area of the hexagonal Ba-ferrite magnetic powder is preferably in the range of 1 to 100 m ² / g.

The particle size (maximum size in the plate surface direction) (hereinafter also referred to as plate diameter) is preferably 3 to 30 nm, more preferably 5 to 20 nm. If it is less than 3 nm, the surface energy of the particles increases, so that dispersion in the paint becomes difficult. If it exceeds 30 nm, particle noise based on the size of the particles increases.

Furthermore, the axial ratio (plate diameter / plate thickness) (hereinafter also referred to as plate-like ratio) is preferably less than 2, more preferably 1.5 or less, and even more preferably less than 1.5. When the plate ratio is 2 or more, even if a magnetic field is applied in the longitudinal direction and the plate surface of the plate-like magnetic powder is oriented in the longitudinal direction of the uppermost magnetic layer, the plate surface of the plate-like magnetic powder is the most in the calendar process. Tilt in the vertical direction of the upper magnetic layer, (Hc _M / Hc _T ) becomes smaller, or plate-like magnetic powder bites into the lower layer in the calendar process, disturbing the interface between the uppermost magnetic layer and the lower layer and increasing noise There is a fear.

As described above, the inclusion of magnetic particles with a plate diameter exceeding 30 nm or less than 3 nm is not excluded, but even in that case, the average plate diameter is preferably 30 nm or less and 3 nm or more. Moreover, although it does not exclude mixing of magnetic particles having a plate ratio of 2 or more, it is preferable that the average plate ratio is less than 2 even in that case.

The plate diameter is the maximum diameter (plate diameter) obtained from a photograph taken at a magnification of 200,000 with a transmission electron microscope (TEM). The average plate diameter was obtained by calculating the plate diameter from the photograph and arithmetically averaging the 50 plate diameters.

The plate ratio is the ratio of plate diameter to plate thickness (plate diameter / plate thickness) determined from the photograph. The average plate ratio was obtained by calculating the plate ratio of individual particles and arithmetically averaging the 50 plate ratios. The method of obtaining the average plate diameter in the case of a tape is the same as in the case of iron nitride magnetic powder.

<Non-magnetic support>
For the nonmagnetic support, a polyethylene terephthalate film, a naphthalene terephthalate film, an aromatic polyamide film, an aromatic polyimide film, or the like is used.

Although the thickness of a nonmagnetic support body changes with uses, it is 2-5 micrometers normally, Preferably it is 2-4.5 micrometers, More preferably, it is 2-4 micrometers. Nonmagnetic supports with a thickness in this range are used because film formation is difficult if the thickness is less than 2 μm, and the tape strength is reduced. If the thickness exceeds 5 μm, the total thickness of the tape is increased, and the recording capacity per tape roll This is because becomes smaller.

<Magnetic layer>
The magnetic layer is composed of at least an uppermost magnetic layer provided as a recording layer, and the thickness of the uppermost magnetic layer is preferably 5 to 90 nm. This range is preferable because it is difficult to form a magnetic layer having a uniform thickness below 5 nm, and the reproduction output tends to decrease due to thickness demagnetization above 90 nm. When the uppermost magnetic layer is as thin as 90 nm or less, a lower magnetic layer for servo signal recording may be provided below the uppermost magnetic layer via a nonmagnetic lower layer.

For the magnetic layer, a binder resin (hereinafter simply referred to as a binder) and an amount described in WO03 / 079332A1 and WO03 / 079333A1 can be applied. When two or more kinds of resins are used in combination as the binder, the polarities of the functional groups are preferably matched, and a combination of —SO ₃ M groups is particularly preferable. A vinyl chloride resin having a functional group such as -SO ₃ M group, or a composite of a polyurethane resin having a functional group such as -SO ₃ M group, combining a plurality of polyurethane resins having a functional group of the same type More preferably, it is used.

It is desirable to use a thermosetting cross-linking agent such as a polyisocyanate compound in combination with these binders in order to bond and crosslink with functional groups contained in the binder. However, when a magnetic layer is applied on the lower layer by wet-on-wet, a certain amount of the polyisocyanate compound is diffused and supplied from the lower layer coating, so that the magnetic layer can be used to some extent even without using a polyisocyanate compound. Cross-linked.

A conventionally known abrasive having a Mohs hardness of 6 or more, such as α-alumina and α-iron oxide, can be added alone or in combination. Usually, the number average particle size of these abrasives is 10 to 150 nm. Moreover, you may add the plate-shaped particle | grain with a number average particle diameter of 10-100 nm as needed.

Furthermore, carbon black having a conventionally known number average particle size of 10 to 100 nm can be added to the magnetic layer in order to improve conductivity and surface lubricity. In order to improve conductivity, plate-like ITO particles having a number average particle diameter of 10 to 100 nm may be added.

A nonmagnetic powder such as an abrasive or carbon black contained in the magnetic layer is preferably as the particle size distribution is smaller because the coercive force (Hc _T ) in the width direction tends to be smaller.

<Preparation of magnetic paint>
In order to highly fill and disperse the ultrafine magnetic powder having a particle size of 30 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. It is preferable to provide a step of mixing.

In the kneading step, it is preferable to perform kneading with 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.

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

If the non-magnetic powder contained in the magnetic layer is larger than the magnetic powder, the non-magnetic powder blocks the shearing stress due to the dispersion media that becomes the dispersion force when dispersing the magnetic paint, thereby inhibiting the dispersion of the magnetic powder. There is. Such a non-magnetic powder is dispersed separately from the magnetic powder to form a slurry, and this is mixed with a paint in which the magnetic powder is dispersed to prepare a magnetic layer paint. (Hc _T ) is preferred because it tends to be small.

<Magnetic field orientation treatment>
The magnetic field alignment treatment of the uppermost magnetic layer can be performed by a conventionally known magnetic field alignment method as described above. After application, a strong (for example, 0.5 T or more) orientation magnetic field is applied with a repulsion magnet, and then a uniform orientation magnetic field (for example, 0.1 T or more) is continuously applied with a solenoid electromagnet until the uppermost magnetic layer is substantially dried. Preferably it is done. In order to reduce the running cost, a method of arranging a large number of repulsive magnets may be employed. However, since the reversal of the magnetic field is repeated, it is preferable that the uniform magnetic field generating unit be dried.

<Lower layer>
In the magnetic tape of the present invention, it is desirable to form a lower layer in order to improve the smoothness of the uppermost magnetic layer, reduce the thickness unevenness, and improve the durability. Usually, the lower layer is non-magnetic so as not to disturb the magnetic recording signal of the uppermost magnetic layer.

The thickness of the lower layer is preferably 0.3 to 0.9 μm. When the thickness is less than 0.3 μm, the effect of reducing the thickness unevenness of the magnetic layer and the effect of improving the durability are reduced. If it exceeds 0.9 μm, the total thickness of the magnetic tape becomes too thick, and the recording capacity per tape roll becomes small.

The binder resin used for the lower layer is the same as the magnetic layer. For the lower layer, conventionally known nonmagnetic particles such as titanium oxide, iron oxide, aluminum oxide, silicon oxide, zirconium oxide and the like and carbon black are used.

Usually, nonmagnetic iron oxide having a number average major axis length of 0.05 to 0.2 μm, a number average minor axis length of 5 to 100 nm, and carbon black having a number average particle diameter of 0.01 to 0.1 μm, If necessary, aluminum oxide particles having a number average particle diameter of 10 to 500 nm, particularly aluminum oxide particles having a number average particle diameter of 10 to 100 nm are used.

Further, as described in WO03 / 079332A1 and WO03 / 079333A1, plate-like aluminum oxide particles or iron oxide having a number average plate diameter of 10 to 100 nm can be used for a thin lower layer of 0.9 μm or less. .

When such an ultrafine plate-like non-magnetic powder is used, even when a thin layer of 0.9 μm or less is applied, the thickness unevenness is small and the smoothness of the surface is not lowered. Further, 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 increased.

The nonmagnetic plate-like particles are not limited to aluminum oxide, and rare earth elements such as cerium, and oxides or composite 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. As a method for producing the nonmagnetic plate-like fine particles, methods described in WO030 / 079332A1 and WO03 / 079333A1 are used.

<Lubricant>
A conventionally known lubricant described in WO03 / 079332A1 and WO03 / 079333A1 can be added to the magnetic layer and the lower layer, and the addition amount thereof may be the above known amount.

For example, it is preferable to contain a higher fatty acid having 10 or more carbon atoms such as myristic acid, stearic acid, and palmitic acid in the lower layer and an ester of higher fatty acid such as butyl stearate because the friction coefficient with the head becomes small. In addition, it is preferable that the magnetic layer contains a fatty acid amide that is an amide such as palmitic acid or stearic acid, and an ester of a higher fatty acid because the friction coefficient during running of the tape is reduced. The mutual movement of the lubricant in the magnetic layer and the lubricant in the lower layer is not excluded.

<Back layer>
A back layer can be formed on the other surface (the surface opposite to the surface on which the magnetic layer is formed) of the nonmagnetic support constituting the magnetic tape of the present invention for the purpose of improving running performance.

The back layer can be formed by vapor deposition, sputtering, CVD, or coating, but a back coat layer made of carbon black and a binder resin is generally used. The thickness of such a back coat layer is preferably 0.2 to 0.8 μm. Moreover, as surface roughness Ra, 3-8 nm is preferable and 4-7 nm is more preferable.

As the carbon black to be included in the back coat layer, a conventionally known small particle size carbon black such as acetylene black, furnace black and thermal black and a small amount of large particle size carbon black are used. The number average particle size of the small particle size carbon black is 5 to 200 nm, and the number average particle size of the large particle size carbon black is 300 to 400 nm.

As the binder resin for the backcoat layer, it is preferable to use a cellulose resin and a polyurethane resin. Moreover, in order to harden binder resin, it is preferable to use crosslinking agents, such as a polyisocyanate compound.

In addition, for the purpose of improving the strength, the back coat layer may have a number average particle diameter of 10 to 100 nm, rare earth elements such as aluminum oxide and cerium, and oxides of elements such as zirconium, silicon, titanium, manganese, and iron. Alternatively, composite ITO plate-like particles and plate-like ITO can be added for the purpose of improving conductivity.

<Organic solvent>
Examples of organic solvents used in magnetic paints, lower layer paints, and back coat layer paints include ketone solvents such as methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, and acetic acid such as ethyl acetate and butyl acetate. Examples include ester solvents. These organic solvents can be used alone or as a mixture, and can also be used as a mixture with toluene.

Next, examples of the present invention will be described and described in more detail. However, the present invention is not limited only to the following examples. In the following examples and comparative examples, “parts” means “parts by weight”.

<Lower paint component>
(1) Component Acicular iron oxide powder (average particle size: 100 nm, axial ratio: 5) 68 parts

8 parts of granular alumina powder (average particle size: 80 nm)

Carbon black (average particle size: 25 nm) 24 parts

Stearic acid 2.0 parts

8.8 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing-SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)

Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained—SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)

25 parts of cyclohexanone

40 parts of methyl ethyl ketone

Toluene 10 parts


(2) Component 1 part butyl stearate

70 parts of cyclohexanone

50 parts of methyl ethyl ketone

20 parts of toluene


(3) Component Polyisocyanate 1.4 parts

10 parts of cyclohexanone

15 parts of methyl ethyl ketone

Toluene 10 parts

<Magnetic paint component>
(1) Components of kneading process Granular magnetic powder (YN-Fe) [hereinafter referred to as (A) powder] 100 parts (Mainly containing Y and Al in the outer layer part and Fe ₁₆ N ₂ phase in the core part) Contained, Y / Fe: 5.5 atomic%, Al / Fe: 8.2 atomic%,
N / Fe: 11.9 atomic%, Fe ₁₆ N ₂ phase: main phase,
Saturation magnetization: 101.5 Am ^{2 /} kg (101.5 emu / g),
Hc: 211.0 kA / m (2,650 Oe),
(Average particle size: 17 nm, average axial ratio: 1.2)

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

Polyester polyurethane resin 4.5 parts (contained -SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalent / g)

2 parts of methyl acid phosphate

Tetrahydrofuran 20 parts

Methyl ethyl ketone / cyclohexanone 9 parts


(2) Dilution process components Palmitic acid amide 1.5 parts

1 part of n-butyl stearate

Methyl ethyl ketone / cyclohexanone 350 parts


(3) Another dispersed slurry component Granular alumina powder (average particle size: 80 nm) 10 parts

1 part of vinyl chloride-hydroxypropyl acrylate copolymer

Methyl ethyl ketone / cyclohexanone 15 parts


(4) Compounding process component Polyisocyanate 1.5 parts

Methyl ethyl ketone / cyclohexanone 29 parts

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

Apart from this, among the magnetic coating components described above, in the kneading step component of (1), the total amount of the magnetic powder and a predetermined amount of resin and solvent are preliminarily stirred and mixed, and the mixed powder is kneaded in (1). After adjusting to be a process component, knead in a continuous biaxial kneader, further add the dilution process component (2), perform dilution in at least two stages or more in a continuous biaxial kneader, Using a zirconia bead having a diameter of 0.5 mm as a dispersion medium in a sand mill, the residence time was dispersed for 45 minutes. To this was added a dispersion slurry component (3) dispersed in a sand mill with a residence time of 40 minutes, and then a blending step component (4) was added, stirred and filtered to obtain a magnetic paint.

On the nonmagnetic support (base film) 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.) Is applied so that the thickness after drying and calendering is 0.6 μm, and the magnetic coating is further coated on the lower layer with a magnetic layer thickness of 0.1 μm after magnetic field orientation treatment, drying and calendering treatment. The coating was applied wet-on-wet so that the thickness was 09 μm, and after magnetic field orientation treatment, drying was performed using a dryer and far infrared rays to prepare a magnetic sheet.

In the magnetic field orientation treatment, one 50 cm long NN counter magnet (0.5T) is installed in front of the dryer, and five 50 cm long solenoid electromagnets (0.1T) are installed in the dryer at intervals of 20 cm. And went. The distance between the NN counter magnet and the solenoid electromagnet is 20 cm, and the pole of the solenoid electromagnet close to the counter magnet is the S pole. The finger-drying position of the coating film (the position where the particles do not move at all) was between the fourth and fifth solenoid electromagnets. The coating speed was 100 m / min. Hereinafter, this method of applying a magnetic field is referred to as an orientation method (A).

<Backcoat layer paint component>
80 parts of carbon black (average particle size: 25 nm)

Carbon black (average particle size: 0.35 μm) 10 parts

Granular iron oxide powder (average particle size: 50 nm) 10 parts

45 parts of nitrocellulose

Polyurethane resin (containing SO ₃ Na group) 30 parts

260 parts of cyclohexanone

260 parts of toluene

525 parts of methyl ethyl ketone

After dispersing the coating component for the backcoat layer with a sand mill with a residence time of 45 minutes, 15 parts of polyisocyanate was added and filtered to prepare a coating material for the backcoat layer. This paint was applied to the opposite surface of the magnetic layer of the magnetic sheet produced by the above method so that the thickness after drying and calendering was 0.5 μm and dried.

Thereafter, this magnetic sheet was mirror-finished with a seven-stage calendar made of a metal roll under the conditions of a temperature of 100 ° C. and a linear pressure of 200 kg / cm, and the magnetic sheet was wound around a core and then aged at 70 ° C. for 72 hours. After that, it was cut into 1/2 inch width. While running this at 200 m / min, the surface of the magnetic layer was subjected to post-processing such as lapping tape polishing, blade polishing, and surface wiping to produce a magnetic tape.

The wrapping tape was K10000, the blade was a carbide blade, and the surface was wiped off using a trade name “Toraysee” manufactured by Toray Industries, Ltd., and was treated with a running tension of 0.294N.

A magnetic servo signal was recorded on the magnetic tape thus obtained with a servo writer to produce a magnetic tape for computers. The product Br · δ of the residual magnetic flux density and the magnetic layer thickness of this magnetic tape was 0.030 μTm. Further, this magnetic tape was incorporated into a cartridge to produce a magnetic tape cartridge for a computer.

A magnetic tape was produced in the same manner as in Example 1 except that the average particle size of the magnetic powder (YN-Fe) in the magnetic coating component was changed to 13 nm (average axis ratio was 1.2). . Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

A magnetic tape was produced in the same manner as in Example 1 except that the average particle size of the magnetic powder (YN-Fe) was changed to 28 nm (average axial ratio was 1.2) in the magnetic coating component. . Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

A magnetic tape was produced in the same manner as in Example 1 except that the strength of the solenoid electromagnet was changed to 0.3 T in the magnetic field orientation treatment. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

A magnetic tape was produced in the same manner as in Example 1 except that the magnetic field orientation treatment was changed as follows. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

A 50cm long NN counter magnet (0.5T) is installed in front of the dryer, and a 50cm long SS counter magnet (0.5T) from the front side 75cm of the finger-drying position of the coating in the dryer. And NN counter magnets (0.5T), one set each at 50 cm intervals. The coating speed was 100 m / min. Hereinafter, this method of applying a magnetic field is referred to as an orientation method (B).

A magnetic tape was produced in the same manner as in Example 1 except that the addition of the separate dispersion slurry component (3) in the magnetic paint component was omitted. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

Comparative Example 1
In the magnetic coating component, as magnetic powder, σs: 110 A · m ² / kg (110 emu / g), Hc: 159.2 kA / m (2,000 Oe), average particle size: 35 nm, average axial ratio: 3.5 A magnetic tape was produced in the same manner as in Example 1 except that the alloy magnetic powder (Al—Y—Co—Fe) was used. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

Comparative Example 2
In the magnetic field orientation treatment, only one 50 cm long NN counter magnet (0.5T) was installed before the dryer. This method of applying a magnetic field is referred to as an orientation method (C). Otherwise, a magnetic tape was produced in the same manner as in Example 1. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

Comparative Example 3
A magnetic tape was produced in the same manner as in Example 1 except that the average particle diameter of the granular alumina in the magnetic coating component was changed to 160 nm, and the dispersion media of the sand mill was changed to titania beads having a diameter of 1.5 mm. did. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

Comparative Example 4
In the magnetic coating component, as magnetic powder, Y / Fe: 0.4 atomic%, Al / Fe: 1.5 atomic%, N / Fe: 12.2 atomic%, Fe ₁₆ N ₂ phase: main phase, saturation magnetization Amount: 105.5 Am ^{2 /} kg (105.5 emu / g), Hc: 202.9 kA / m (2,550 Oe), average particle size: 17 nm, average axial ratio: 1.2) granular magnetic powder (Y− A magnetic tape was produced in the same manner as in Example 1 except that N-Fe) [hereinafter referred to as (B) powder] was used. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

Comparative Example 5
A magnetic tape was produced in the same manner as in Example 5 except that the average particle diameter of the granular alumina in the magnetic coating component was changed to 160 nm, and the dispersion media of the sand mill was changed to titania beads having a diameter of 1.0 mm. did. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

Comparative Example 6
In the magnetic coating component, as magnetic powder, σs: 120 A · m ² / kg (120 emu / g), Hc: 171.1 kA / m (2,150 Oe), average particle size: 100 nm, average axial ratio: 6.0 A magnetic tape was produced in the same manner as in Example 1 except that the alloy magnetic powder (Al—Y—Co—Fe) was used. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

Comparative Example 7
In the magnetic coating component, as magnetic powder, Y / Fe: 5.5 atomic%, Al / Fe: 8.2 atomic%, N / Fe: 12.2 atomic%, Fe ₁₆ N ₂ phase: main phase, saturation magnetization Amount: 105.5 Am ^{2 /} kg (105.5 emu / g), Hc: 211.0 kA / m (2,650 Oe), average particle size: 35 nm, average axial ratio: 1.2 granular magnetic powder (Y-N A magnetic tape was produced in the same manner as in Example 1 except that -Fe) [hereinafter referred to as (C) powder] was used. Moreover, the magnetic tape for computers and the magnetic tape cartridge for computers were produced using this.

For each of the magnetic tapes of Examples 1 to 6 and Comparative Examples 1 to 7, the structure of the magnetic powder used for forming the magnetic layer (the uppermost magnetic layer), the orientation method, and the structure of the disperser beads are shown in Table 1. Shown together. Note that the particle size of the magnetic powder in the magnetic layer was measured by the following method, and it was confirmed that the magnetic powder had the same average particle size and average axial ratio as the raw magnetic powder. In Table 1, “SC” means a solenoid electromagnet.

<Particle size of magnetic powder>
The magnetic tape is filled with resin, and the cross-section in the thickness direction is cut out with a focused ion beam processing device, and the cross-section is photographed with a scanning electron microscope (SEM) at 200,000 times the required number of magnetic layer cross-sections. The outer shape of the magnetic powder in the magnetic layer is trimmed. Measure the maximum outside diameter as the particle size. Fifty magnetic powders were measured, and the average value was taken as the average particle size.

In addition, the thickness of the magnetic layer and the lower layer of each magnetic tape is measured by the following method.
<Thickness of magnetic layer and lower layer>
The magnetic tape is filled with resin, and a cross section in the thickness direction is cut out with a focused ion beam processing apparatus, and the cross section is photographed with 10 fields of view at a magnification of 20,000 with a scanning electron microscope (SEM). (1) Border the surface of the magnetic layer, (2) the interface between the magnetic layer and the lower layer, and (3) the interface between the lower layer and the nonmagnetic support. Next, arbitrary five locations where non-magnetic powder is not applied to the interface per field of view of the photograph are selected, and the distance between the bordered lines of (1)-(2) is set to the thickness of the magnetic layer, (2)-( The distance between the bordered lines in 3) was measured as the thickness of the lower layer. The thicknesses of the magnetic layer and the lower layer were averaged over 10 fields to obtain the thickness of each layer.

Next, for each of the magnetic tapes of Examples 1 to 6 and Comparative Examples 1 to 7, the output (C) and the output-to-noise ratio (C / N) are obtained as the electromagnetic characteristics along with the magnetic characteristics by the following method. Was measured. Table 2 shows the results of magnetic characteristics, and Table 3 shows the results of electromagnetic conversion characteristics.

Of the electromagnetic conversion characteristics of each magnetic tape, the C / N and the longitudinal Hc (longitudinal direction Hc _M ) / width Hc (width direction Hc _T ) are the results of the output-to-noise ratio (C / N). 5 is plotted in FIG.

<Output and output to noise ratio>
A drum tester was used to measure the electromagnetic conversion characteristics of the magnetic tape. The drum tester was equipped with an electromagnetic induction type magnetic head (track width 25 μm, gap 0.1 μm) and an MR magnetic head (track width 8 μm), and recording was performed with the induction type 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 around the cartridge and discarded, and further 60 cm was cut out, further processed into a width of 4 mm, and wound around the outer periphery of the rotating drum.

For the 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 magnetic head was read into a spectrum analyzer. The carrier value of 0.2 μm was set as the medium reproduction output C. Further, when a rectangular wave of 0.2 μm was written, the integrated value of the value obtained by subtracting the reproduction 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. Furthermore, the ratio of both was taken as C / N. Both C and C / N were determined as values relative to the value of the magnetic tape of Example 5.

Table 1

┌────┬────────────────┬ ─────┬─────────┐
│ │ Top layer magnetic powder │ Orientation │ Disperser beads │
│ ├───┬────┬───┬───┤ Method ├─────┬───┤
│ │Type │Average particle │Average │Composition│ │ Material │Grain size│
│ │ │Size │ Axis ratio │ │ │ │ (mm) │
│ │ │ (nm) │ │ │ │ │ │
├────┼───┼────┼───┼───┼─────┼─────┼───┤
│ │ │ │ │ │ │ │ │
│Example 1│Iron nitride│ 17 │1.2│ (A) │A (SC) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
│Example 2│Iron nitride│ 13 │1.2│ (A) │A (SC) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
│Example 3│Iron nitride│ 28 │1.2│ (A) │A (SC) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
│Example 4│Iron nitride│ 17 │1.2│ (A) │A (SC) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
│Example 5│Iron nitride│ 17 │1.2│ (A) │B (Magnet) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
│Example 6│Iron nitride│ 17 │1.2│ (A) │A (SC) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
├────┼───┼────┼───┼───┼─────┼─────┼───┤
│ │ │ │ │ │ │ │ │
│Comparative Example 1 │Iron alloy │ 35 │3.5│ − │A (SC) │Zirconia │0.5│
│ │ │ │ │ │ │ │ │
│Comparative example 2│Iron nitride│ 17 │1.2│ (A) │C (magnet) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
│Comparative example 3│Iron nitride│ 17 │1.2│ (A) │A (SC) │ Titania│1.5│
│ │ │ │ │ │ │ │ │
│Comparative example 4│Iron nitride│ 17 │1.2│ (B) │A (SC) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
│Comparative Example 5│Iron nitride│ 17 │1.2│ (A) │B (Magnet) │ Titania│1.0│
│ │ │ │ │ │ │ │ │
│Comparative Example 6│Iron alloy│100 │6.0│ − │A (SC) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
│Comparative example 7│Iron nitride│ 35 │1.2│ (C) │A (SC) │Zirconia│0.5│
│ │ │ │ │ │ │ │ │
└────┴───┴────┴───┴───┴─────┴─────┴───┘

Table 2

┌────┬────────────────────────────────┐
│ │ Magnetic properties │
│ ├────┬────┬─────┬─────┬────┬─────┤
│ │ Square │SFD │Longitudinal │ Width │Hc _M │ Hc _M │
│ │ │ │Hc _M │ Hc _T │ / Hc _T │ -Hc _T │
│ │ │ │ (kA / m) │ (kA / m) │ │ (kA / m) │
├────┼────┼────┼─────┼┼─────┼────┼─────┤
│ │ │ │ │ │ │ │
│Example 1│0.82│0.61│250.2│ 89.0│2.81│161.2│
│ │ │ │ │ │ │ │
│Example 2│0.80│0.64│245.3│ 90.1│2.72│155.2│
│ │ │ │ │ │ │ │
│Example 3│0.83│0.63│257.7│101.9│2.53│155.8│
│ │ │ │ │ │ │ │
Example 4 | 0.83 | 0.59 | 268.5 | 81.1 | 3.31 | 187.4 |
│ │ │ │ │ │ │ │
│Example 5│0.77│0.65│235.2│106.4│2.21│128.8│
│ │ │ │ │ │ │ │
│Example 6│0.82│0.60│251.5│ 90.8│2.77│160.7│
│ │ │ │ │ │ │ │
├────┼────┼────┼─────┼┼─────┼────┼─────┤
│ │ │ │ │ │ │ │
│Comparative Example 1│0.86│0.65│190.5│121.4│1.57│ 69.1│
│ │ │ │ │ │ │ │
│Comparative Example 2│0.70│0.70│220.7│131.5│1.68│ 89.2│
│ │ │ │ │ │ │ │
│Comparative Example 3│0.77│0.67│226.4│132.0│1.72│ 94.4│
│ │ │ │ │ │ │ │
│Comparative Example 4│0.82│0.66│249.4│135.5│1.84│113.9│
│ │ │ │ │ │ │ │
│Comparative Example 5│0.70│0.67│220.2│133.4│1.65│ 86.8│
│ │ │ │ │ │ │ │
│Comparative Example 6│0.87│0.49│202.5│132.7│1.53│ 69.8│
│ │ │ │ │ │ │ │
│Comparative Example 7│0.84│0.60│250.0│113.0│2.21│137.0│
│ │ │ │ │ │ │ │
└────┴────┴────┴─────┴┴─────┴────┴─────┘

Table 3

┌──────┬─────────────┐
│ │ Electromagnetic conversion characteristics │
│ ├──────┬──────┤
│ │ C │ C / N │
│ │ (dB) │ (dB) │
├──────┼──────┼──────┤
│ │ │ │
│ Example 1 │ 2.4 │ 3.1 │
│ │ │ │
│ Example 2 │ 1.6 │ 2.8 │
│ │ │ │
│ Example 3 │ 2.5 │ 1.5 │
│ │ │ │
│ Example 4 │ 2.7 │ 3.4 │
│ │ │ │
│ Example 5 │ 0.0 │ 0.0 │
│ │ │ │
│ Example 6 │ 2.3 │ 3.1 │
│ │ │ │
├──────┼──────┼──────┤
│ │ │ │
│ Comparative Example 1 │ 0.5 │ -3.1 │
│ │ │ │
│ Comparative Example 2 │ −1.5 │ −2.1 │
│ │ │ │
│ Comparative Example 3 │ −1.4 │ −1.8 │
│ │ │ │
│ Comparative Example 4 │ -1.0 │ -0.8 │
│ │ │ │
│ Comparative Example 5 │ −2.1 │ −2.0 │
│ │ │ │
│ Comparative Example 6 │ −1.2 │ −7.5 │
│ │ │ │
│ Comparative Example 7 │ 3.0 │ -3.7 │
│ │ │ │
└──────┴──────┴──────┘

From the results of Tables 1 to 3, the magnetic powder contained in the uppermost magnetic layer is substantially granular particles having an average particle size of 30 nm or less, and the ratio of the coercive force in the longitudinal direction to the coercive force in the width direction (Hc _M / For each of the magnetic tapes of Examples 1 to 6 with Hc _T ) of 2.2 or more, a magnetic powder having an average particle size larger than 30 nm or other than granular is used as the magnetic powder, or the ratio (Hc _M / Hc). _It can be seen that the reproduction output (C) and reproduction output noise ratio (C / N) are higher than those of the magnetic tapes of Comparative Examples 1 to 7 in which _T ) is less than 2.2. Furthermore, it can be seen from the results of FIG. 5 that C / N increases as the ratio (Hc _M / Hc _T ) increases.

It is a figure which shows typically the mode of magnetization of the magnetic layer by which the magnetic recording was carried out in the magnetic tape. It is a model figure which shows the mode of the reversal of the magnetization of the magnetic layer at the time of the magnetic recording in a magnetic tape. The state of magnetization of the magnetic layer in the case of magnetic recording on the magnetic tape of the present invention (Hc _M / Hc _T is 2.2 or higher) is a view schematically showing. The present invention is a diagram schematically showing a state of magnetization of the magnetic layer in the case of magnetic recording on different magnetic tapes (less than Hc _M / Hc _T 2.2). It is a characteristic view showing the relationship between the ratio of the longitudinal Hc (longitudinal direction Hc _M ) / width Hc (width direction Hc _T ) and C / N of the magnetic tape.

Explanation of symbols

1 Magnetic tape (magnetic layer)
2 Magnetization 3 Magnetic head 4 Magnetization transition region T Time lapse

Claims (4)

In a magnetic tape having a nonmagnetic support and at least one magnetic layer formed on one side of the support, the magnetic powder contained in the uppermost magnetic layer is a substantially granular magnetic particle having a particle size of 30 nm or less. A magnetic tape comprising particles and having a ratio [Hc _M / Hc _T ] of a coercive force Hc _M in the longitudinal direction and a coercive force Hc _{T in the} width direction of 2.2 or more.

The magnetic tape according to claim 1, wherein the magnetic powder contained in the uppermost magnetic layer is formed of substantially granular magnetic particles having a particle size of 20 nm or less.

The magnetic tape according to claim 1, wherein the substantially granular magnetic particles contained in the uppermost magnetic layer have an axial ratio (major axis / minor axis) of less than 2. 4.

4. The magnetic tape according to claim 1, wherein the substantially granular magnetic particles contained in the uppermost magnetic layer are iron nitride magnetic powder.

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