JP2005038579A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium wherein an SN ratio of a reading signal of a servo signal and an SN ratio of a data signal are enhanced even though the magnetic recording medium has a thin magnetic layer suitable for high density recording. <P>SOLUTION: The magnetic layer of a magnetic tape MT1 possesses a servo band SB1 in which a servo signal SS1 for controlling tracking of a magnetic head H is written and a data band DB1 in which data are recorded. The servo signal SS1 is magnetized and written on the servo band SB1 having been magnetized in one direction of the track direction thereof in the direction other than the one direction. The thickness of the magnetic layer is specified to be 10 to 180 nm and variation [(standard deviation of Mrt)÷(an average value of Mrt)×100] of the product [Mrt] of the residual magnetization and the thickness of the magnetic layer is specified to be not more than 30% in the track direction of the magnetic layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium.

  In recent years, high-density recording has progressed in magnetic recording media, and there is a recording medium having a storage capacity of about 100 gigabytes for computer backup. For example, in the case of a magnetic tape, several hundred data tracks are formed in the width direction to enable high density recording. Along with this, the width of the data track is very narrow, and the space between adjacent data tracks is also very narrow. Therefore, a servo signal is written in advance on the magnetic tape, and the servo signal is read by the magnetic head and the position of the magnetic head (position in the width direction of the magnetic tape) is servo controlled. Are traced on the data track (see Patent Document 1).

As a system for controlling the position of the magnetic head by this servo signal, an amplitude modulation method for performing position control by the output balance of the read pulse signal, a TBS (Timing Based Servo) method for performing position control by the timing of the read pulse signal, etc. There is.
In a system for recording servo signals on a magnetic tape in the TBS system, for example, as shown in FIG. 3, a servo recording head (not shown) generates a servo signal SP having a non-parallel pattern while transporting the tape in a tape transport system. (FIG. 3). The non-parallel servo signal pattern SP was recorded by applying a recording current so as to be magnetized in one direction to a servo band on a non-magnetized magnetic tape.
That is, as shown in FIG. 3B, in order to avoid the saturation phenomenon of the servo signal reading element (MR element) in the conventional TBS method, the servo band SB which is not magnetized is shown in FIG. The recording pulse current PC composed of a zero current and a plus pulse current as shown in FIG.

  When such a recording pulse current PC is used, the magnetic tape MT is not magnetized in the area other than the servo pattern SP when the recording pulse current PC is zero current, and the servo pattern when the plus pulse current of the recording pulse current PC flows. The SP is magnetized in one direction, and as a result, the servo signal SS is written. Note that the head gap of the magnetic head (not shown) for writing the servo signal SS has a non-parallel C-shape having a predetermined angle with respect to the traveling direction of the magnetic tape MT. The servo pattern SPa shown in FIG. 3B is magnetized with respect to the plus pulse current PPa shown in (a), and further, the servo pattern SPb is magnetized with respect to the plus pulse current PPb.

  On the other hand, in the magnetic tape recording / reproducing apparatus, a change in the magnetic field of the servo signal SS is detected by a change in electric resistance by a servo signal reading element, and is output as a read signal as a differential waveform (voltage value). Therefore, as the change in the electric resistance of the servo signal reading element increases, the peak voltage value of the read signal of the servo signal SS increases, and the SN ratio of the read signal improves. Therefore, when the change in the magnetic field of the servo signal SS itself is large, or when the reading area is large due to the wide width of the servo signal reading element, the peak voltage of the read signal RSL of the servo signal SS as shown in FIG. The value gets bigger.

JP-A-8-309442 (paragraph 0004)

However, in the future, it is predicted that the recording density of magnetic recording media will increase to a recording capacity of several tens of terabytes per cartridge.
Accordingly, in the case of a magnetic tape, the number of data tracks increases, the width of the data track and the space between adjacent data tracks become narrower, and the magnetic tape itself becomes thinner. As a result, the amount of magnetism that can be detected when reading the servo signal is reduced, and the change in the magnetization amount of the servo signal SS that can be detected by the servo signal reading element is also reduced. Therefore, as shown in FIG. 3D, the peak voltage value of the read signal RSS of the servo signal SS becomes small, and the SN ratio of the read signal RSS deteriorates. As a result, in the magnetic tape recording / reproducing apparatus, the servo signal SS cannot be read accurately, and the position control of the magnetic head with high accuracy cannot be performed.

  Accordingly, an object of the present invention is to improve the SN ratio of the read signal of the servo signal (hereinafter referred to as the SN ratio of the servo signal) while having a thin magnetic layer suitable for high-density recording, and the SN ratio of the data signal is good. Is to provide a simple magnetic recording medium.

The problems of the present invention can be solved by the following means.
1) A magnetic recording medium in which a magnetic layer containing magnetic powder is provided on a support,
The magnetic layer has a servo band in which a servo signal for tracking control of the magnetic head is written, and a data band in which data is recorded,
The servo signal is written by being magnetized in a direction opposite to the one direction on the servo band magnetized in any one of the track directions, and
The magnetic layer has a thickness of 10 to 180 nm;
In the track direction of the magnetic layer, the variation rate [(Mrt standard deviation) ÷ (Mrt average value) × 100] of the product (Mrt) of the remanent magnetization and thickness of the magnetic layer is 30% or less. A magnetic recording medium characterized by the above.
2) The magnetic recording medium as described in 1) above, wherein the magnetic powder is a ferromagnetic metal powder having an average major axis length of 30 to 100 nm or a hexagonal ferrite magnetic powder having an average plate diameter of 15 to 50 nm. .
3) The magnetic recording medium according to 1) or 2), wherein the magnetic layer is provided on the support via a nonmagnetic layer containing at least a nonmagnetic powder and a binder.
4) The switching field distribution representing the magnetization reversibility of the magnetic layer in the track direction of the magnetic layer is from 0.10 to 0.70, according to any one of 1) to 3) above Magnetic recording media.
5) The ratio R (φ ₀ / φ ₁ ) between the residual magnetization φ _{0 of the} magnetic layer other than the servo band and the residual magnetization φ ₁ when a 1 T external magnetic field is applied to the portion is 0.01. The magnetic recording medium according to any one of 1) to 4) above, wherein the magnetic recording medium is .about.0.30.
6) The magnetic powder is a ferromagnetic metal powder having a long axis length variation rate [(standard deviation of long axis length) / (average value of long axis length)] of 30% or less, or a plate diameter variation rate [ The magnetic recording medium as described in any one of 1) to 5) above, wherein the magnetic recording medium is a hexagonal ferrite magnetic powder having a (standard deviation of plate diameter) / (average value of plate diameter)] of 30% or less.
7) The magnetic recording medium according to any one of 1) to 6) above, which is recorded and reproduced by a linear serpentine method.

In the magnetic recording medium of the present invention, the servo signal is magnetized in the direction opposite to the one direction on the servo band magnetized in any one of the track directions, so that the servo pattern is switched. Even if the rate of change and amount of change in the magnetic field increase at the portion, the output of the servo signal can be improved even if the magnetic layer is made thinner.
Further, since the thickness of the magnetic layer is 10 to 180 nm, high density recording is possible.
Further, since the rate of change and the amount of change in the magnetic field increase at the switching portion, Mrt (residual magnetization per unit area of the magnetic layer is the product of the residual magnetization (Mr) and the thickness (t) of the magnetic layer. The non-uniformity of the expressed value) is amplified, but by setting the variation rate of Mrt in the track direction of the magnetic layer to 30% or less, the output variation of the servo signal due to the nonuniformity of Mrt can be suppressed. .
The magnetic recording medium of the present invention also has a ratio R (φ ₀ / φ ₁ ) between the remanent magnetization φ ₀ of the part other than the servo band of the magnetic layer and the remanent magnetization φ ₁ when a 1 T external magnetic field is applied to the part. However, since it is 0.01-0.30, when a data signal reading element reads data, a high S / N ratio can be obtained.

Next, embodiments of the present invention will be described with reference to the drawings as appropriate.
The shape of the magnetic recording medium of the present invention is not particularly limited, and may be a tape shape, a sheet shape, a disk shape, or the like. Particularly preferred is a sheet-like or tape-like magnetic recording medium in which the magnetic recording / reproducing direction is longer than the direction perpendicular thereto. In this embodiment, a case where the magnetic recording medium of the present invention is applied to a magnetic tape will be described.
The material and shape of the support used in the present invention are not particularly limited, but when applied to a magnetic tape, it is preferably a film. This embodiment demonstrates the case where a base film is used as a support body.
When the magnetic recording medium of the present invention is applied to a magnetic tape, the track direction is preferably the longitudinal direction of the tape. Hereinafter, the case where the track direction is the longitudinal direction of the tape will be described.

[Servo signal]
First, the servo signal will be described. The servo signal used in the present invention is recorded / reproduced by magnetic recording, and any signal form (servo pattern) can be used. These include the above-described amplitude modulation system, TBS (Timing Based Servo) system, and the like. FIG. 2 is an explanatory diagram of a magnetic tape according to an embodiment of the present invention that adopts the TBS method. FIG. 2A is a diagram showing a recording signal used when a servo signal is written and a servo band is provided. ) Is an enlarged plan view for explaining the magnetization state of the magnetic tape, and (c) is a diagram showing a servo signal read from a servo band of the magnetic tape.

As shown in FIG. 2B, the magnetic tape MT1 according to the embodiment of the present invention is provided with a plurality of servo bands SB1 extending in the longitudinal direction of the tape in the width direction, and between the servo bands SB1. A data band DB1 is provided. Each servo band SB1 is magnetized in the forward direction in the longitudinal direction of the magnetic tape MT1. In FIG.2 (b), the direction magnetized by the small arrow is shown. Then, as shown in FIG. 2 (a), a recording pulse current PC1 composed of a zero current (ZC1) and a plus pulse current (PP1) is passed as a recording current, whereby the servo band SB1 is magnetized in the reverse direction and servoed. Signal SS1 is written. The servo signal SS1 has a burst Ba which is a magnetized in two stripes having a positive inclination angle with respect to the traveling direction of the magnetic tape MT1, and a negative inclination angle with respect to the traveling direction following this portion. One servo pattern SP1 is formed by a burst Bb which is a magnetized portion of two stripes, and this servo pattern SP1 is repeatedly formed in the longitudinal direction at a predetermined interval to form a servo signal SS1.
The data band DB1 between the servo bands SB1 is also uniformly magnetized in the forward direction. Of course, the magnetic tape MT1 shown in FIG. 2 (b) is an unrecorded data, and when data is recorded, it is magnetized in the data band DB1 in the reverse direction or the forward direction depending on the data content. The part is formed.
In the present embodiment, the servo pattern SP1 is configured by two positive and negatively inclined stripes. However, for example, the servo pattern SP1 is configured by five positive and negatively inclined stripes or five. Modifications can be made as appropriate, such as alternately forming positive and negative inclined stripes and four positive and negative inclined stripes. In FIG. 2, the servo pattern SP1 is exaggerated with respect to the magnetic tape MT1 for easy understanding.

  FIG. 2B shows the positional relationship of the magnetic head H with respect to the magnetic tape MT1. In the magnetic head H, servo signal reading elements SH for reading the servo signal SS1 are arranged side by side in the width direction of the magnetic tape MT1 (hereinafter simply referred to as “width direction”) at the same intervals as the intervals of the plurality of servo bands SB1. It is installed. The dimension in the width direction of the reading element SH is set to be sufficiently smaller than the width of each servo band SB1. Between the servo signal reading elements SH, a plurality of recording elements WH are arranged in two rows in the width direction in order to record signals in the data band DB1. Further, a plurality of reproducing elements RH are arranged in a line in the width direction between the recording elements WH.

  When data is recorded / reproduced with respect to the magnetic tape MT1 as described above by the magnetic head H of the magnetic tape drive (not shown), the servo signal SS1 is read by the servo signal reading element SH. The servo pattern SP1 of the servo signal SS1 is inclined with respect to the running direction (= longitudinal direction) of the magnetic tape MT1 and is formed by stripes that are not parallel to each other. Therefore, the servo signal reading element SH reads the servo signal SS1. The timing for detecting the pulse differs depending on the relative position of the magnetic tape MT1 and the magnetic head H in the width direction. Therefore, the recording element WH or the reproducing element RH is accurately positioned on a predetermined track of the data band DB1 by controlling the position of the magnetic head H so that the pulse reading timing (phase shift) becomes a predetermined condition. be able to.

At this time, the output (peak voltage value) obtained by reading the servo signal SS1 by the servo signal reading element SH is the rate of change or amount of change in magnetism when switching between a portion where no signal is recorded and a portion where a signal is recorded. Depends on. In this embodiment, the direction of magnetism changes greatly from the forward direction to the reverse direction at the switching portion of the servo pattern SP1 magnetized in the reverse direction from the portion of the ground servo band SB1 magnetized in the forward direction.
Also, the direction of magnetism greatly changes from the reverse direction to the forward direction even when the portion of the servo pattern SP1 magnetized in the reverse direction switches to the portion of the ground servo band SB1 magnetized in the forward direction. Therefore, in response to this large magnetic change, as shown in FIG. 2C, the read signal from the servo band becomes a signal with a large output fluctuation. Therefore, the SN ratio of the servo signal SS1 can be improved.

In addition, the servo signal SS1 is recorded by using at least a first step for magnetizing the servo band SB1 in the forward direction of the longitudinal direction and a recording pulse current PC1 for inducing a single direction magnetic flux for magnetizing in the reverse direction. By applying to the recording head (not shown), it is performed by means having a second step of writing the servo signal SS1 on the servo band SB1 (hereinafter referred to as the servo signal through the first step and the second step). The means for recording is called bidirectional magnetization means).
In order to magnetize the servo band SB1 in the forward direction in the longitudinal direction in the first step, the servo band SB1 may be directly magnetized using a magnetic head (hereinafter referred to as “bidirectional magnetization 1”), or a rare earth magnet. The entire tape may be magnetized in the forward direction of the longitudinal direction using a permanent magnet such as (hereinafter referred to as “bidirectional magnetization 2”). When the latter method is used, as shown in FIG. 2B, portions other than the servo band, such as the data band DB1, are uniformly magnetized in the forward direction. In this embodiment, the ground portion of the servo band SB1 is magnetized in the forward direction and the servo pattern SP1 portion is magnetized in the reverse direction. Conversely, the ground portion of the servo band SB1 is reversed. The servo pattern SP1 may be magnetized in the forward direction by magnetizing in the direction. In this embodiment, as shown in FIG. 2B, the data band DB1 is uniformly magnetized in the forward direction. However, the data band DB1 may be demagnetized by providing a separate AC demagnetization process.

  In the bidirectional magnetization means, it is sufficient that at least the first step and the second step are included in this order, and other steps can be appropriately provided. For example, a tape cutting step may be provided after the first step, and then the second step may be performed.

  In this embodiment, the servo signal SS1 is written by using the servo signal recording head. However, the servo signal SS1 is written on a master carrier (patterned master) in which the pattern of the servo signal SS1 is formed in an uneven shape or embedded structure in advance. A so-called magnetic transfer method may be used in which a servo signal SS1 corresponding to information carried on the master carrier is transferred by applying a transfer magnetic field in a state where the medium to be adhered is in close contact.

[Recording and playback method]
In the magnetic recording medium of the present invention, the linear recording density is 100 kfci or more, and the difference between the recording track width (the width of the track recorded by the recording element WH) and the reproducing track width (the width read by the reproducing element RH) is 0 to 16 μm. It is preferably used in a magnetic recording / reproducing apparatus. That is, in the case of a system in which the difference between the recording track width and the reproduction track width exceeds 16 μm, the SN ratio of the read signal RS of the servo signal SS1 is small, so that the position of the magnetic head H cannot be controlled with high accuracy and is about several μm. Even if it fluctuates, since the recording track width is sufficiently wider than the reproducing track width, the reproducing element RH of the magnetic head H can run on the recording track without any problem. However, in a magnetic recording / reproducing apparatus having a high linear recording density in which the difference between the recording track width and the reproducing track width must be 16 μm or less, the width of the servo signal reading element SH becomes smaller in accordance with the recording track pitch. Therefore, the change in the magnetization amount of the servo signal SS1 that can be detected is also reduced, and the SN ratio of the read signal RS is degraded. As a result, in the magnetic recording / reproducing apparatus, the servo signal SS1 cannot be read accurately, and it becomes difficult to control the position of the magnetic head H with high accuracy. Therefore, the effect of the magnetic recording medium of the present invention becomes remarkable when a magnetic recording / reproducing apparatus having a high linear recording density is used.

  The linear recording density is preferably 100 kfci or more, more preferably 120 kfci or more, and still more preferably 140 kfci or more.

The recording track width is preferably 25 μm or less, and more preferably 15 μm or less.
The reproduction track width is preferably 15 μm or less, and more preferably 10 μm or less.
The difference between the recording track width and the reproduction track width is preferably 0 to 16 μm, more preferably 0 to 12 μm, and still more preferably 0 to 8 μm.
The effect of the magnetic recording medium of the present invention is remarkably exhibited in a linear serpentine system that performs bidirectional recording / reproduction in the longitudinal direction.

[Layer structure]
Next, a preferred example of the layer structure of the magnetic recording medium of the present invention will be described. In the present invention, it is preferable that the base film has a nonmagnetic layer containing at least a nonmagnetic powder and a binder, and further has a magnetic layer thereon. In such a magnetic recording medium, a nonmagnetic layer containing at least a nonmagnetic powder and a binder is provided below the magnetic layer, so that the surface roughness of the magnetic layer becomes an appropriate value and a servo error occurs. The frequency can be reduced.
In order to improve the running durability of the magnetic recording medium, a back coat layer may be provided on the base film on the side opposite to the side on which the magnetic layer is provided. The thickness of the base film is 1 to 100 μm, preferably 4 to 80 μm, and the combined thickness of the magnetic layer and the nonmagnetic layer is 1/100 to 2 times the thickness of the base film. It is preferably 1/100 to 1 time, more preferably 1/100 to 30/100. When the backcoat layer is provided, the thickness of the backcoat layer is 0.1 to 2 μm, preferably 0.3 to 1.0 μm, and more preferably 0.3 to 0.6 μm. Further, an undercoat layer may be provided between the base film and the nonmagnetic layer for improving adhesion. The thickness of the undercoat layer is 0.01 to 2 μm, preferably 0.02 to 0.5 μm. In addition, a well-known thing is used for this undercoat. Further, the magnetic recording medium of the present invention may contain a layer other than the nonmagnetic layer, the magnetic layer, and the backcoat layer. For example, you may have a 2nd magnetic layer, a cushion layer, an overcoat layer, an adhesive layer, and a protective layer. These layers can be provided at appropriate positions so that their functions can be effectively exhibited.

[Magnetic layer]
The magnetic layer used in the present invention is obtained by applying a coating solution obtained by dispersing magnetic powder in a binder onto a base film. The coating method includes a method of directly coating the magnetic layer coating liquid on the base film, a method of coating the magnetic layer coating liquid after providing the nonmagnetic layer on the base film, and a nonmagnetic layer on the base film. For example, there is a method of simultaneously applying the coating liquid for magnetic layer and the coating liquid for magnetic layer. The thickness of the magnetic layer is 10 to 180 nm, preferably 30 to 180 nm, more preferably 40 to 160 nm. By setting the thickness of the magnetic layer to 10 nm or more, a satisfactory servo signal output can be ensured. Further, by setting the thickness to 180 nm or less, the resolution of the written servo signal is improved, and a high SN ratio of the servo signal can be obtained.
The coercive force Hc of the magnetic layer is 127 to 356 kA / m, preferably 142 to 316 kA / m, and more preferably 158 to 177 kA / m. By setting Hc to 127 kA / m or more, a high output can be obtained, and the influence of the demagnetizing field can be reduced even when the recording wavelength is reduced. When Hc exceeds 356 kA / m, recording with a magnetic head becomes difficult, so Hc is preferably 356 kA / m or less.
The product (Mrt) of remanent magnetization and thickness of the magnetic layer is 5 × 10 ^{−10 to} 7.5 × 10 ⁻⁸ T · m, preferably 5 × 10 ^{−10 to} 5 × 10 ⁻⁸ T · m, more preferably Is 5 × 10 ^{−10 to} 3 × 10 ⁻⁸ T · m. By setting Mrt to 5 × 10 ^{−10 to} 7.5 × 10 ⁻⁸ T · m, saturation of the MR element can be prevented and noise can be reduced.

The variation rate of Mrt in the longitudinal direction of the magnetic layer is 30% or less, preferably 25% or less, more preferably 20% or less. By setting the variation rate of Mrt to 30% or less, a good SN ratio of the servo signal and the data signal can be obtained.
There are various methods for setting the variation rate of Mrt within an appropriate range. For example, the following method can be used.
1) In the method of directly applying the magnetic layer coating liquid onto the base film, the thickness variation rate in the longitudinal direction of the base film is set to 30% or less, and the pulsation of the pump for feeding the magnetic layer coating liquid is reduced.
2) In the method using a nonmagnetic layer, the thickness variation rate in the longitudinal direction of the base film is set to 30% or less as in 1), and the pulsation of the pump for feeding the coating liquid for the magnetic layer and the nonmagnetic layer is reduced. . If a thixotropic coating solution is used as the coating solution for the nonmagnetic layer, the variation rate of Mrt can be further suppressed. Further, if the so-called wet on dry method is used in which the magnetic layer coating liquid is applied after the nonmagnetic layer is dried, the variation rate of Mrt can be further suppressed. After drying the nonmagnetic layer, a calendar process may be provided before applying the magnetic layer coating solution.

Switching field distribution in the longitudinal direction of the magnetic layer (a value representing the magnetization reversibility of the magnetic layer, hereinafter referred to as “SFD”) is 0.10 to 0.70, preferably 0.15 to 0.65, Preferably it is 0.15-0.60. As shown in FIG. 1, the SFD is calculated from a differential curve (FIG. 1 (b)) of a magnetization curve (FIG. 1 (a)) representing the relationship between the applied magnetic field (H) and the magnetization (M) of the recording medium. The Here, when the peak half width of the dM / dH-H curve shown in FIG. 1B is ΔH and the coercive force of the recording medium is Hc, it is defined as SFD = ΔH / Hc. The smaller the SFD, the steeper the rise of magnetization. For this reason, the width of the magnetization inversion region of the recording signal is narrowed, and good magnetization reversibility is exhibited.
By setting the SFD to 0.70 or less, the width of the magnetization switching region can be narrowed, and an excellent SN ratio of the servo signal can be obtained.
Further, the SFD becomes smaller as the particle size distribution of the magnetic powder particles becomes sharper. In order to sharpen this particle size distribution, the magnetic powder production reaction system should be made as uniform as possible, and the produced magnetic powder may be subjected to a known distribution improving process. In addition, even if it performs the said process, since it is difficult to adjust a particle size distribution so that SFD may become smaller than 0.10, the lower limit of SFD was set to 0.10.
Moreover, the center plane average surface roughness SRa of the magnetic layer measured with HD-2000 manufactured by WYKO is preferably 1 to 5 nm, and more preferably 1.5 to 4.5 nm. By setting SRa within the above range, the error rate can be suppressed.

The ratio R (φ ₀ / φ ₁ ) between the residual magnetization φ _{0 of the} magnetic layer other than the servo band and the residual magnetization φ ₁ when a 1 T external magnetic field is applied to the portion is 0.01 to 0.30. , Preferably 0.04 to 0,25, more preferably 0.04 to 0.20. By setting R to 0.01 to 0.30, a high S / N ratio can be obtained when data is read by the data signal reading element.
There are various methods for setting the ratio R (φ ₀ / φ ₁ ) of the remanent magnetization φ ₁ to an appropriate range. For example, the following method can be used.
(1) When the entire tape is magnetized in the forward direction of the traveling direction of the head with a permanent magnet in the bidirectional magnetization 1, the magnitude of magnetization to be applied is adjusted.
(2) The data band DB1 is uniformly magnetized, and a demagnetizing step is separately provided to adjust the magnitude of the erasing magnetic field when the data band DB1 is demagnetized.

The magnetic powder used in the magnetic layer of the present invention is preferably a ferromagnetic metal powder or a hexagonal ferrite magnetic powder in order to enable high density recording. In the case of a ferromagnetic metal powder, for example, an acicular powder mainly composed of Fe and an alloy powder containing Co, Mn, Ni, Sm, Nb, or the like is used.
Further, compounds such as Al and Y can be used as sintering inhibitors. The average major axis length of the ferromagnetic metal powder is preferably 30 to 100 nm, more preferably 35 to 90 nm, and still more preferably 40 to 80 nm. By setting the average major axis length to 100 nm or less, noise can be reduced, and a good SN ratio of servo signals and data signals can be obtained. Moreover, favorable holding power Hc can be ensured by setting the average major axis length to 30 nm or more.
The average needle ratio of the ferromagnetic metal powder is preferably 3 to 10, more preferably 3 to 8, and still more preferably 4 to 8.
The variation rate of the long axis length of the ferromagnetic metal powder [(standard deviation of long axis length) / (average value of long axis length)] is preferably 30% or less, more preferably 25% or less, More preferably, it is 20% or less. By setting the variation rate of the major axis length to 30% or less, it is possible to reduce noise due to the mixing of magnetic particles having different major axis lengths and improve the SN ratio of the servo signal and the data signal.
Preferably saturation magnetization σs of the ferromagnetic metal powder is 70~150A · m ² / kg, more preferably 80~140A · m ² / kg, it is 90~125A · m ² / kg Is more preferable. The coercive force Hc is preferably 127 to 356 kA / m, more preferably 142 to 316 kA / m, and still more preferably 158 to 177 kA / m.
The specific surface area by BET method of the ferromagnetic metal powder (S _BET) is preferably 40 to 80 m ² / g, more preferably 45~70m ² / g. If the specific surface area (S _BET ) by the BET method is 40 m ² / g or more, noise is reduced, and if it is 80 m ² / g or less, good surface properties can be obtained.

In the case of hexagonal ferrite magnetic powder, Ba ferrite is suitable. Further, Ti or the like may be included as a substitution element. The average plate diameter of the hexagonal ferrite magnetic powder is preferably 15 to 50 nm, more preferably 20 to 45 nm, and still more preferably 20 to 40 nm. As in the case of using the ferromagnetic metal powder, by setting the average plate diameter to 50 nm or less, noise can be reduced and a good SN ratio of servo signals and data signals can be obtained. Moreover, the favorable holding force Hc is securable by making an average board diameter into 15 nm or more.
The average plate ratio of the hexagonal ferrite magnetic powder is preferably 2 to 7, and more preferably 3 to 5.
The plate diameter variation rate [(standard deviation of plate diameter) / (average value of plate diameter)] of the hexagonal ferrite magnetic powder is preferably 30% or less, more preferably 25% or less, and 20%. More preferably, it is as follows. By setting the variation rate of the plate diameter to 30%, it is possible to reduce noise caused by the mixing of magnetic particles having different plate diameters and improve the SN ratio of the servo signal and the data signal.
Saturation magnetization σs of the hexagonal ferrite magnetic powder is preferably 40~80A · m ² / kg, more preferably 45~75A · m ² / kg, in 45~65A · m ² / kg More preferably it is. The coercive force Hc is preferably 127 to 356 kA / m, more preferably 142 to 316 kA / m, and still more preferably 158 to 177 kA / m.
The specific surface area according to the BET method within the above particle size range is 10 to ²⁰⁰ m ² / g. This specific surface area approximately agrees with the calculated value from the particle plate diameter and plate thickness.

Known binders can be used for the binder used in the magnetic layer of the present invention. For example, a vinyl chloride copolymer, a polyurethane resin, an acrylic resin, etc., or a mixture thereof can be used. The number average molecular weight of these resins is 2 to 100,000, preferably 3 to 80,000. In order to improve the dispersibility of the magnetic powder, polar groups are preferably introduced into these resins. Examples of the polar group _{-COOM, -SO 3 M, -P =} O (OM) 2 (M is a hydrogen atom or an alkali metal) is known.
Furthermore, the magnetic layer can contain an abrasive, carbon black, a lubricant and the like as required. When an abrasive is contained, those having an average particle size of 10 to 300 nm and not more than twice the thickness of the magnetic layer are preferred.

[Nonmagnetic layer]
The nonmagnetic layer used in the present invention preferably contains at least a nonmagnetic powder and a binder. The nonmagnetic powder can be used known ones, TiO _{2 These, Fe 2 O 3, Al 2} O 3, CeO 2, ZrO 2, BaSO 4, ZnO, carbon black, graphite and the like. Among these, TiO ₂ and α-Fe ₂ O ₃ are preferable, and it is more preferable to use these in combination with carbon black. Further, when a resin into which a polar group has been introduced is used as a binder, a metal oxide is excellent in terms of dispersibility. These nonmagnetic powders have an average particle size (average major axis length in the case of needles) of 10 to 300 nm, preferably 30 to 200 nm, and the shape may be granular, needle-like, or dice-like. A plurality of types of nonmagnetic powders are used as necessary. For example, a nonmagnetic oxide, carbon black or the like can be mixed to impart conductivity. As the binder used for the nonmagnetic layer, a known binder is used as in the magnetic layer. Furthermore, the nonmagnetic layer can contain an antistatic agent, a lubricant, and the like, if necessary.

[Base film]
Examples of the base film used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide (particularly preferably aromatic polyamide), polyimide, polyamideimide, polysulfone, and aramid. Can be used. These base films may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment and the like. In order to achieve the object of the present invention, the base film has a center line average roughness Ra (cutoff value: 0.25 mm) of 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01 μm or less. Need to use. In addition, these base films preferably have not only a small center line average roughness Ra but also no coarse protrusions of 1 μm or more. Moreover, the roughness shape of the surface can be freely controlled by the size and amount of the filler added to the base film, if necessary.
The F-5 value in the longitudinal direction of the base film used in the present invention is preferably 5 to 50 kg / mm ² , and the F-5 value in the width direction is preferably 3 to 30 kg / mm ^2. The -5 value is generally higher than the F-5 value in the width direction, but this is not necessarily the case when it is necessary to increase the strength in the width direction. The heat shrinkage rate at 100 ° C. for 30 minutes in the longitudinal direction and the width direction of the base film is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage rate at 80 ° C. for 30 minutes is Preferably it is 1% or less, More preferably, it is 0.5% or less. Further, the breaking strength in both the longitudinal direction and the cross direction, preferably 5 to 100 kg / mm ^2, the modulus of elasticity in both the longitudinal direction and the cross direction, preferably 100 to 2,000 kg / mm ^2.

[Back coat layer]
The backcoat layer used in the present invention may be a known one, but preferably contains a binder and carbon black. The back coat layer may be composed of carbon black having fine particles and excellent electrical conductivity as a main filler, and may contain two types of carbon blacks having different average particle sizes, or may contain an inorganic powder as required. For example, an inorganic powder having a Mohs hardness of 5 to 9 can be contained. The compounding amount of the inorganic powder in the back coat layer is usually 0.5 to 150 parts by mass, preferably 0.5 to 100 parts by mass with respect to 100 parts by mass of carbon black.

  As described above, the backcoat layer can contain two types of carbon black having different average particle sizes. For example, fine particulate carbon black having an average particle size of 15 to 50 nm and coarse particulate carbon black having an average particle size of 80 to 300 nm can be used. Thus, by using two types of carbon black, a magnetic recording medium with little show-through to the magnetic layer can be obtained even when the backcoat layer is roughened.

  In general, by adding fine particulate carbon black as described above, the surface electrical resistance of the backcoat layer can be set low, and the light transmittance can also be set low. Depending on the magnetic recording apparatus, there are many which use the light transmittance of the tape and are used for the operation signal. In such a case, the addition of fine carbon black is particularly effective. In addition, the particulate carbon black is generally excellent in the retention of the lubricant and contributes to the reduction of the friction coefficient when used in combination with the lubricant.

  On the other hand, the coarse particulate carbon black having an average particle size of 80 to 300 nm has a function as a solid lubricant, forms fine protrusions on the surface of the backcoat layer, reduces the contact area, and has a friction coefficient. Contributes to the reduction of

Specific products of the particulate carbon black that can be used in the present invention include the following. The average particle size is shown in parentheses. REGAL 99R (38 nm), RAVEN2000B (18 nm), RAVEN1500B (17 nm) (manufactured by Columbia Carbon Co., Ltd.), BP800 (17 nm) (manufactured by Cabot Corporation), PRINTERX90 (14 nm), PRINTEX95 (15 nm), PRINTEX85 (16 nm), PRINTEX75 (17 nm) (above, manufactured by Degussa), # 3950 (16 nm) (manufactured by Mitsubishi Chemical Corporation).
As examples of specific products of coarse particle carbon black, Asahi # 51 (91 nm) (manufactured by Asahi Carbon Co., Ltd.), thermal black (270 nm) (manufactured by Khan Calbu Co., Ltd.), RAVENMTP (275 nm) (manufactured by Columbia Carbon Co., Ltd.) Can be mentioned. Coarse particulate carbon black having an average particle size of 80 to 300 nm can be selected from carbon black for rubber and carbon black for color.

  In the present invention, the content ratio (mass ratio) of the fine particle carbon black and the coarse particle carbon black in the back coat layer is preferably in the range of the former: the latter = 98: 2 to 75:25, more preferably, 95: 5 to 85:15. In addition, the content of carbon black in the back coat layer (when using two types of carbon black, the total amount of fine carbon black and coarse carbon black) is usually 30 with respect to 100 parts by mass of the binder. It can be made into the range of -80 mass parts, Preferably, it is the range of 45-65 mass parts.

  Examples of the inorganic powder that can be added to the backcoat layer include inorganic powders having an average powder size of 80 to 250 nm and a Mohs hardness of 5 to 9. As the inorganic powder, those similar to the nonmagnetic powder and abrasive used in the above-described nonmagnetic layer can be used, and among these, α-iron oxide, α-alumina and the like are preferably used. The amount of the inorganic powder added to the backcoat layer is preferably in the range of 0.5 to 40 parts by mass, more preferably in the range of 1 to 30 parts by mass with respect to 100 parts by mass of the binder.

  As the binder used for the back coat layer, conventionally known thermoplastic resins, thermosetting resins, reactive resins and the like can be used. Preferred binders are vinyl chloride resins, vinyl chloride-vinyl acetate resins, fibrous resins such as nitrocellulose, phenoxy resins, and polyurethane resins. Among these, it is more preferable to use vinyl chloride resin, vinyl chloride-vinyl acetate resin, and polyurethane resin.

  In addition to the aforementioned components, a dispersant and a lubricant can be added to the back coat layer as other optional components. Examples of the dispersant include 12 to 18 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, reelic acid, linolenic acid, stearic acid, and the like. A fatty acid (RCOOH; R is an alkyl group having 11 to 17 carbon atoms, or an alkenyl group), a metal soap composed of an alkali metal or an alkaline earth metal of the fatty acid, a compound containing fluorine of the fatty acid ester, Fatty acid amide, polyalkylene oxide alkyl phosphate ester, lecithin, trialkyl polyolefinoxy quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate ester, copper phthalocyanine, precipitation Barium sulfate or the like can be used. A dispersing agent can be added in 0.5-20 mass parts with respect to 100 mass parts of binder resin.

  The back coat layer is provided on the side opposite to the side on which the magnetic layer of the nonmagnetic support is provided according to a usual method. That is, a back coating layer is provided on a nonmagnetic support by preparing a coating solution in which each of the above components is dissolved and dispersed in a suitable organic solvent, and coating and drying the coating solution according to a conventional coating method. be able to. In the present invention, the back coat layer preferably has an average surface roughness Ra of 20 to 30 nm, more preferably 22 to 28 nm. The surface roughness of the backcoat layer affects the reproduction output or the coefficient of friction against the guide pole by transferring the surface of the backcoat layer to the surface of the magnetic layer while the tape is wound. Therefore, it is preferable to adjust to the above range. The surface roughness Ra can be adjusted by adjusting the material of the calender roll to be used, its surface property, pressure, and the like in the surface treatment process using the calender after the back coat layer is applied and formed. In the present invention, the back coat layer has a thickness of 0.1 to 2 μm, preferably 0.3 to 1.0 μm, and more preferably 0.3 to 0.6 μm.

[Production method]
A preferred example of the method for producing a magnetic recording medium of the present invention will be described. The production process includes at least a step of preparing a coating solution for a magnetic layer, a step of applying a coating solution for a magnetic layer on a base film, and a rare earth magnet. A method having an orientation step for orienting the magnetic material, a drying step, a calendar step for increasing the surface smoothness with a roller, a slit step, and a servo signal recording step is preferred. Moreover, when providing a nonmagnetic layer, the preparation process and application | coating process of the coating liquid for nonmagnetic layers are added separately. Hereinafter, a method for producing the magnetic recording medium of the present invention provided with a nonmagnetic layer will be described. In addition, the manufacturing method of the magnetic recording medium of this invention is not limited to the method shown below, For example, you may add the process of providing a backcoat layer etc. as needed.

  The preparation process of the coating solution for the magnetic layer and the nonmagnetic layer has at least a kneading process and a dispersion process. Moreover, you may provide a mixing process before and behind these processes as needed, and each process may be divided into two or more steps, respectively. All raw materials such as ferromagnetic metal powder, hexagonal ferrite magnetic powder, nonmagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, solvent, etc. used in the present invention are added at the beginning or middle of any process. It doesn't matter. Moreover, you may divide | segment and add each raw material at two or more processes. For example, the polyurethane resin may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

  In order to obtain a magnetic layer having a high residual magnetization used in the present invention, it is preferable to use a magnetic layer coating liquid having a strong kneading force such as a continuous kneader or a pressure kneader. In the case of using a kneader, the magnetic powder and 15 to 500 parts by mass of a binder with respect to 100 parts by mass of the magnetic powder are kneaded. In order to disperse the coating solution for the nonmagnetic layer, it is preferable to use a dispersion medium having a high specific gravity. As such a dispersion medium, zirconia beads, titania beads, steel beads and the like are suitable.

A well-known method can be used for the application | coating process of the said coating liquid on a base film, For example, the method shown below is mentioned.
1) First, a non-magnetic layer coating solution is applied by a gravure coating, roll coating, blade coating, extrusion coating apparatus, etc., and the non-magnetic layer is in a wet state. A method of applying a coating solution for a magnetic layer by a base film pressure type extrusion coating apparatus disclosed in Japanese Patent No. -238179 and Japanese Patent Laid-Open No. 2-265672.
2) One coating head incorporating two coating liquid passage slits as disclosed in JP-A-63-88080, JP-A-2-17971, and JP-A-2-265672 is used to provide magnetic properties. A method of applying the coating liquid for the layer and the nonmagnetic layer almost simultaneously.
3) A method of applying the coating liquid for the magnetic layer and the non-magnetic layer almost simultaneously using an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.
Note that, as described above, if the method using a thixotropic coating solution as the coating solution for the nonmagnetic layer or the method using the wet-on-dry method is used, the variation rate of Mrt can be further suppressed.

  Further, in order to prevent a decrease in electromagnetic conversion characteristics and the like of the magnetic recording medium due to agglomeration of the magnetic powder particles, the coating is performed by a method as disclosed in Japanese Patent Application Laid-Open Nos. 62-95174 and 1-2236968. It is preferable to apply shear to the coating solution inside the head. Furthermore, if the viscosity of the coating solution satisfies the numerical range disclosed in Japanese Patent Laid-Open No. 3-8471, the aggregation of the magnetic powder particles can be further prevented.

  For the orientation step of orienting the magnetic material, for example, a known method such as a method of randomly arranging rare earth magnets obliquely and a method of performing random orientation by applying an alternating magnetic field with a solenoid is used. it can. However, in order to obtain the magnetic recording medium of the present invention, it is necessary to perform strong orientation. Therefore, an orientation method using a rare earth magnet of 0.2T or more and an orientation method using a solenoid of 0.1T or more are used in combination. Is preferred. Furthermore, in order to improve the orientation, it is preferable to provide an appropriate drying step in advance before the orientation.

The calendering process for increasing the surface smoothness by the roller is preferably performed between the plastic roll and the metal roll or between the metal rolls. Examples of the plastic roll used in the calendar process include those having heat resistance such as epoxy, polyimide, polyamide, and polyamideimide.
The calendering temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure of the roll is preferably 200 kg / cm or more, more preferably 300 kg / cm or more.

[Physical properties]
In the magnetic recording medium of the present invention, the surface resistivity of the magnetic layer is preferably 1 × 10 ⁴ to 1 × 10 ¹² ohm / sq, and the elastic modulus at 0.5% elongation is preferably in both the running direction and the width direction. 100 to 2,000 kg / mm ^2, the breaking strength is preferably 1 to 30 kg / cm ^2, the (maximum point of loss elastic modulus measured at 110 Hz) the glass transition temperature is preferably 50 to 120 ° C., which is preferably non-magnetic layer Is 0-100 ° C. The loss elastic modulus of the magnetic layer is preferably in the range of 1 × 10 ⁷ to 8 × 10 ⁸ Pa, and the loss tangent is preferably 0.2 or less. By setting the loss tangent to 0.2 or less, it is possible to prevent adhesion failure during running of the magnetic recording medium.
The elastic modulus of the magnetic recording medium of the present invention is preferably 100-1500 kg / mm ^{2 in} both the running direction and the width direction, the residual elongation is preferably 0.5% or less, and the heat shrinkage rate at any temperature of 100 ° C. or less. Is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.
The friction coefficient of the magnetic layer surface of the magnetic recording medium and the opposite surface (base film or back coat layer) to the stainless steel plate (SUS420J) is preferably 0.5 or less, more preferably 0.3 or less.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less. The porosity is preferably 30% by volume or less, and more preferably 20% by volume or less for both the nonmagnetic layer and the magnetic layer. The void ratio is preferably small in order to achieve high output, but it may be better to ensure a predetermined value depending on the purpose. For example, in a magnetic recording medium in which repetitive usage is important, running durability is often preferable when the porosity is large.

  In the magnetic recording medium of the present invention, the nonmagnetic layer and the magnetic layer may have different physical characteristics depending on the purpose. For example, if the elastic modulus of the magnetic layer is increased to improve running durability and at the same time the elastic modulus of the nonmagnetic layer is lower than that of the magnetic layer, the per-head of the magnetic recording medium (the degree of close contact between the magnetic recording medium and the head) ) Can be improved. When two or more magnetic layers are used, the physical characteristics may be different depending on the purpose. For example, as described in JP-A-58-56228, the reproduction output characteristics can be improved by making the Hc of the upper magnetic layer higher than the Hc of the lower magnetic layer.

  In the present specification, various powder sizes (hereinafter referred to as “powder size”) such as ferromagnetic metal powder and carbon black are obtained from a high-resolution transmission electron micrograph and an image analysis apparatus. The powder size of the high-resolution transmission electron micrograph can be traced with an image analyzer to determine the size of the powder. That is, the powder size is (1) the length of the long axis constituting the powder when the shape of the powder is needle-like, spindle-like, or columnar (however, the height is larger than the maximum major axis of the bottom). (2) When the shape of the powder is a plate or columnar shape (however, the thickness or height is smaller than the maximum major axis of the plate surface or the bottom surface) like hexagonal ferrite magnetic powder Is represented by the maximum major axis of the plate surface or bottom surface, that is, the plate diameter, and (3) the powder has a spherical shape, a polyhedral shape, an unspecified shape, etc., and the major axis constituting the powder from the shape. When it cannot be specified, it is represented by the equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.

Further, the average powder size of the powder is an arithmetic average of the powder size, and is obtained by performing the measurement as described above on about 500 primary particles. Primary particles refer to an independent powder without aggregation.
And when the shape of the powder is specific, for example, in the case of the definition (1) of the above powder size, the average powder size is called the average major axis length, and the value of (major axis length / minor axis length) is The arithmetic average is called the average needle ratio.
The short axis length is the maximum axis that is perpendicular to the long axis. In the case of the definition (2), the average powder size is referred to as an average plate diameter, and the arithmetic average of (plate diameter / plate thickness) is referred to as an average plate ratio. Here, the plate thickness is a thickness or a height. In the case of definition (3), the average powder size is referred to as the average particle size.
The variation coefficient of each data is (standard deviation / average value) × 100 (%).

  Hereinafter, the present invention will be described more specifically with reference to examples. It should be noted that the components, ratios, operations, order, and the like shown here can be changed without departing from the spirit of the present invention, and the present invention should not be limited to the following examples. Moreover, "part" in an Example shows a mass part.

[Preparation of magnetic recording medium]
The coating liquid components for the magnetic layer used in the examples and comparative examples and the preparation methods thereof are as follows. The average size of the magnetic powder was set to the values shown in Tables 1 and 2, and the particle size distribution of the magnetic powder particles was adjusted so that the SFD in the longitudinal direction of the magnetic layer was the value shown in Tables 1 and 2. .
1) Examples 1-4, 9-10, 11-18, 23-27 and Comparative Examples 1-15
Ferromagnetic metal powder 100 parts Composition ratio (Fe / Co)
Example 1, Comparative Example 1 and Comparative Example 3: 90/10
Examples 2 to 4, Comparative Example 2 and Comparative Example 4: 75/25
Coercive force Hc: 175 kA / m
Specific surface area by BET method: 64 m ² / g
Crystallite size: 11 nm
Needle ratio: 4.1
Saturation magnetization σs: 110 A · m ² / kg
Sintering inhibitor: Al, Y
Vinyl chloride copolymer 12 parts -SO ₃ Na content: 1 × 10 ^-4 mol / g
Degree of polymerization: 300
Polyester polyurethane resin 3 parts Neopentyl glycol / Caprolactone polyol /
Diphenylmethane diisocyanate = 0.9 / 2.6 / 1
—SO ₃ Na content: 1 × 10 ⁻⁴ mol / g
α-alumina (particle size 0.17 μm) 2 parts Carbon black (particle size 0.09 μm) 0.5 part Butyl stearate 1 part Stearic acid 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts 2) Examples 5-8 19-22
Hexagonal ferrite (Ba ferrite) magnetic powder 100 parts to Ba molar ratio composition: Fe 9.10, Co 0.20,
Zn 0.77
Coercive force Hc: 183 kA / m
Specific surface area by BET method: 55 m ² / g
Saturation magnetization σs: 58 A · m ² / kg
Plate thickness: 8nm
Vinyl chloride copolymer 10 parts -SO ₃ Na content: 1 × 10 ^-4 mol / g
Degree of polymerization: 300
Polyester polyurethane resin 4 parts Neopentyl glycol / Caprolactone polyol /
Diphenylmethane diisocyanate = 0.9 / 2.6 / 1
—SO ₃ Na content: 1 × 10 ⁻⁴ mol / g
α-alumina (particle size 0.17 μm) 8 parts Carbon black (particle size 0.09 μm) 1 part Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 Part The above components were kneaded with a continuous kneader and then dispersed using a sand mill. To each of the obtained dispersions, 3 parts of polyisocyanate was added, and 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone was added, followed by filtration using a filter having an average pore diameter of 1 μm, and a coating solution for magnetic layer Was prepared.

Next, the coating liquid components for the nonmagnetic layer used in Examples 1 to 7, 9 to 20, 22 to 27, and Comparative Examples 1 to 15 and the preparation methods thereof are as follows.
Nonmagnetic powder (α-Fe ₂ O ₃ ) 85 parts Average long axis length: 0.15 μm
Specific surface area by BET method: 52 m ² / g
pH: 7.6
Carbon black 15 parts Average primary particle size: 16 nm
DBP oil absorption: 80ml / 100g
pH: 8.0
Specific surface area by BET method: 250 m ² / g
Volatile content: 1.5%
Vinyl chloride copolymer 12 parts -SO ₃ Na content: 5 × 10 ^-6 mol / g
Degree of polymerization: 280
Polyester polyurethane resin 5 parts Neopentyl glycol / Caprolactone polyol /
Diphenylmethane diisocyanate = 0.9 / 2.6 / 1
—SO ₃ Na content: 1 × 10 ⁻⁴ mol / g
Butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts The above components were kneaded with a continuous kneader and then dispersed using a sand mill. 1 part of polyisocyanate is added to the resulting dispersion, and 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone is added, followed by filtration using a filter having an average pore size of 1 μm to prepare a coating solution for a nonmagnetic layer. did.

Next, the coating liquid components for backcoat layer and the preparation methods used in Examples 1 to 27 and Comparative Examples 1 to 15 are as follows.
1) Mixture A
Carbon black 100 parts BP-800 (Cabot)
Nitrocellulose 100 parts RS1 / 2
Polyurethane 30 parts N2301 (manufactured by Nippon Polyurethanes)
Copper oleate (dispersant) 5 parts Copper phthalocyanine (dispersant) 5 parts Precipitated barium sulfate (dispersant) 5 parts Methyl ethyl ketone 500 parts Toluene 500 parts 2) Mixture B
Carbon black 100 parts SSA: 8.5 m ² / g
Average particle size: 270 nm
DBP oil absorption: 36ml / 100g
pH: 10
Nitrocellulose 100 parts Polyurethane 30 parts N2301 (manufactured by Nippon Polyurethanes)
Methyl ethyl ketone 300 parts Toluene 300 parts After the mixture A was pre-kneaded with a roll mill, the mixture A and the mixture B were dispersed with a sand grinder, and the following components were added to 100 parts of the obtained dispersion.
Polyester resin 5 parts Byron 300 (Toyobo Co., Ltd.)
Polyisocyanate 5 parts Coronate L (Nippon Polyurethane)

Subsequently, the coating amount of the coating solution for the magnetic layer and the nonmagnetic layer is set so that the thickness of the nonmagnetic layer after drying is 1.5 μm, and the thickness of the magnetic layer provided thereon is as follows. It adjusted so that it might become the value shown in 1, and applied simultaneous multilayer coating on the base film. As the base film, polyethylene terephthalate having a thickness of 6.5 μm and a center line average roughness Ra (cut-off value 0.25 mm) of 0.01 μm was used. In Example 8, the magnetic layer coating solution was applied directly on the base film without providing the nonmagnetic layer. Further, the variation rate of the thickness in the longitudinal direction of the base film was controlled so that the variation rate of Mrt in the longitudinal direction of the magnetic layer became the value shown in Table 1.
Then, while the magnetic layer and the nonmagnetic layer were still wet, they were oriented by a 0.3T rare earth magnet and a 0.15T solenoid and dried.
And the coating liquid for backcoat layers was apply | coated on the base film on the opposite side to the side in which the magnetic layer was provided so that the thickness after drying might be 0.3 micrometer, and it dried.
Further, the treatment was performed at a temperature of 90 ° C. with a seven-stage calendar composed only of metal rolls, and slit to a 1/2 inch width.

(Servo signal writing method)
1) Examples 1 to 10, 24, Comparative Examples 3 to 6, 12
After the servo band SB1 is uniformly magnetized in the forward direction of the head traveling direction by the magnetic head, a recording pulse current PC1 for inducing a single direction magnetic flux for magnetizing in the reverse direction is applied to the magnetic head. Thus, a servo signal in the LTO Ultrium 2 format was written on the servo band SB1 (bidirectional magnetization 1).
2) Comparative Examples 1 and 2, 7-9, 15
A servo signal was written on a non-magnetized servo band (unidirectional magnetization).
3) Examples 11-23, 25-27, Comparative Examples 10, 11, 13, 14
The entire ½ inch tape is magnetized uniformly in the forward direction of the head running direction so that a predetermined residual magnetization is generated using a permanent magnet, and then a unidirectional magnetic flux for magnetizing in the reverse direction is used. By applying a recording pulse current PC1 to be induced to the magnetic head, a servo signal of the LTO Ultrium2 format was written on the servo band SB1 (bidirectional magnetization 2).

[Evaluation methods]
The obtained magnetic tape was evaluated by the evaluation method described below, and the results are shown in Table 1.
1) Servo signal output When the servo signal is written by the servo writer, the servo signal is read from the magnetic tape by the read head provided in the running system after the write head, and the output of the read servo signal is measured using an oscilloscope. . At this time, when the output of the servo signal is −2 dB or more, it is determined as “◯” because the output characteristic is excellent, and when it is smaller than −2 dB, it is determined as “x” because the output characteristic is inferior.
2) Data error rate When the S / N ratio of the servo signal deteriorates, servo errors frequently occur and the data error rate deteriorates. Therefore, the superiority or inferiority of the SN ratio of the servo signal was evaluated by the data error rate. The data error rate was measured using an LTO-2 drive after modulating a signal having a linear recording density of 80 kfci by 8-10 conversion, recording it on a magnetic tape by the PRI equalization method. At this time, when the data error rate is 2.5 × 10 ⁻⁵ or less, the frequency of occurrence of servo errors is low and the signal-to-noise ratio of the servo signal is excellent, “◯”, exceeding 2.5 × 10 ⁻⁵ Furthermore, it was determined as “x” because there were many servo errors and the SN ratio of the servo signal was inferior.
3) Thickness of magnetic layer A small piece of magnetic tape was embedded in an epoxy resin, and cut out in the thickness direction using a diamond cutter to obtain a measurement piece having a thickness of about 0.8 μm. This measurement piece was cross-sectional observed with a TEM (transmission electron microscope) to obtain thickness data.
4) Fluctuation rate of Mrt The magnetic tape was sampled 1 m, and further cut out every 1 cm in the longitudinal direction to obtain a measurement piece. Mrt was measured by applying a maximum magnetic field of 796 kA / m (10 kOe) to each measurement piece by a VSM (sample vibration magnetometer). From the obtained Mrt, the variation rate of Mrt in the longitudinal direction of the magnetic layer was calculated by the above formula.
5) SFD
A magnetic field of 796 kA / m (10 kOe) at maximum was applied to a small piece of the magnetic tape using the VSM, and the magnetization curve was measured. A differential curve was drawn from the obtained magnetization curve, and SFD was calculated by the above formula.
6) SN ratio of data signal The signal-to-noise ratio of the data signal was measured by modifying an LTO Ultrium 2 data drive manufactured by IBM. The recording current was set to the optimum recording current for each tape. A signal with a recording wavelength of 0.3 μm is recorded, and the reproduction signal is frequency-analyzed with a spectrum analyzer manufactured by Shiba-Soku, and the ratio of the output of the carrier signal (wavelength of 0.3 μm) to the integrated noise in the entire spectrum is defined as the SN ratio. .
When the S / N ratio of the data signal was 23 dB or more, it was determined that the output characteristics were excellent, “◯”, and when it was smaller than 23 dB, the output characteristics were determined to be “x”.

As shown in Table 1, in Examples 1 to 10, all conditions were within the range regulated by claim 1 of the present invention. As a result, the servo signal output and the data error rate showed good values.
In Examples 1 to 7 in which the nonmagnetic layer is provided between the support and the magnetic layer, and the average size and SFD of the magnetic particle powder are in the preferable ranges, the servo signal output and the data error rate are particularly good. It was.

On the other hand, none of Comparative Examples 1 to 9 satisfies the conditions regulated in claim 1 of the present invention. Among them, in Comparative Example 1, the servo signal is written by unidirectional magnetization, and the thickness of the magnetic layer and the variation rate of Mrt exceed the upper limit values of the conditions regulated in claim 1. The error rate is inferior to the embodiment.
In Comparative Example 2, since the servo signal is written by unidirectional magnetization, an excellent SN ratio of the servo signal cannot be obtained, and the SFD value exceeds the upper limit value of the condition regulated in claim 4 Therefore, the data error rate deteriorated (“×”).
In Comparative Example 3, since the variation rate of Mrt and the average size of the magnetic powder particles exceed the upper limit values of the conditions regulated in claims 1 and 2 of the present invention, respectively, the data error rate and the servo signal SN The ratio has deteriorated.
In Comparative Example 4, the data error rate deteriorated because the thickness of the magnetic layer exceeded the upper limit value of the condition regulated in claim 1 of the present invention.
In Comparative Example 5, the data error rate was deteriorated because the variation rate of Mrt exceeded the upper limit value of the condition regulated in claim 1 of the present invention.
In Comparative Example 6, since the magnetic layer thickness exceeded the upper limit value of the condition regulated in claim 1 of the present invention, the data error rate was deteriorated.
In Comparative Example 7, since the servo signal was written by unidirectional magnetization, an excellent SN ratio of the servo signal could not be obtained, and the data error rate was deteriorated.

  In addition, although the sizes of the magnetic powder particles of Example 1 and Example 4 are both within the range regulated in Claim 2, since Example 4 is larger, the servo signal output characteristics are excellent. In addition, since the nonmagnetic layer was not provided in Example 8, the data error rate was inferior to that in Example 6, but it was not a problem level.

As shown in Table 2, in Examples 11 to 27, all the conditions are within the range regulated by claim 1 of the present invention. As a result, the output of the servo signal and the data error rate, and the SN ratio of the data signal are good. The value is shown.
In Examples 11 to 20 and 22, which have a nonmagnetic layer between the support and the magnetic layer, and the average size of the magnetic particle powder and its variation rate, SFD, and residual magnetization ratio R are in the preferred range Especially, servo signal output and data error rate were good.
In Example 21, since the nonmagnetic layer was not provided, the data error rate was inferior, but it was not a problem level. The output of the servo signal and the SN ratio of the data signal showed good values.
On the other hand, none of Comparative Examples 8 to 15 satisfies the conditions regulated by claim 1 of the present invention. Among them, the comparative example 8 is good because the servo signal is written by unidirectional magnetization, and further, the thickness of the magnetic layer and the variation rate of Mrt exceed the upper limit values of the conditions regulated in claim 1. Servo signal output cannot be obtained, and the data error rate and the S / N ratio of the data signal are inferior to the embodiment.
In Comparative Example 9, the servo signal is written by unidirectional magnetization, and the SFD and the magnetic material size variation rate exceed the upper limit values of the conditions regulated in claims 4 and 6, so that the servo signal is good. No signal output is obtained, and the data error rate and the S / N ratio of the data signal are inferior to those of the embodiment.
In Comparative Example 10, since the variation rate of Mrt and the average size of the magnetic powder particles exceed the upper limits of the conditions regulated in claims 1 and 2 of the present invention, respectively, the data error rate and the SN of the servo signal The ratio has deteriorated.
In Comparative Example 11, since the thickness of the magnetic layer exceeded the upper limit value of the condition regulated in claim 1 of the present invention, the data error rate and the SN ratio of the data signal were deteriorated.
In Comparative Example 12, since the magnetic layer thickness and the magnetic material size fluctuation rate exceeded the upper limit values of the conditions regulated in claims 1 and 6 of the present invention, the data error rate and the SN ratio of the data signal were deteriorated. .
In Comparative Example 13, the data error rate and the SN ratio of the data signal were deteriorated because the variation rate of Mrt exceeded the upper limit value of the condition regulated in claim 1 of the present invention.
In Comparative Example 14, the magnetic layer thickness exceeded the upper limit value of the condition regulated in claim 1 of the present invention, so that the data error rate and the SN ratio of the data signal were deteriorated.
In Comparative Example 15, since the servo signal was written by unidirectional magnetization, an excellent SN ratio of the servo signal could not be obtained, and the data error rate was deteriorated. The S / N ratio of the data signal was good.

  The sizes of the magnetic powder particles of Example 11 and Example 14 are both within the range defined in claim 2. However, since Example 14 is larger, the output characteristics of the servo signal are excellent.

  The magnetic recording medium of the present invention can be suitably used as a magnetic recording medium for high density digital recording.

(A) is a graph showing the relationship between the applied magnetic field (H) and the magnetization (M) of the recording medium, and (b) is a graph showing the differential curve of (a). BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the magnetic tape (magnetic recording medium) which concerns on embodiment of this invention, (a) is a figure which shows the recording signal used when writing a servo signal and providing a servo band, (b) is a magnetic tape FIG. 4C is an enlarged plan view for explaining the magnetization state of FIG. 2, and FIG. 5C is a diagram showing a servo signal read from a servo band of the magnetic tape. It is a figure explaining the magnetic tape which has the conventional servo signal, (a) is a figure which shows the recording signal used when writing a servo signal and providing a servo band, (b) is a top view of a magnetic tape, (C) is a diagram showing a read signal of a servo signal when the peak voltage value is large, and (d) is a diagram showing a read signal of the servo signal when the peak voltage value is small.

Explanation of symbols

DB1 Data band H Magnetic head MT1 Magnetic tape PC1 Recording pulse current SB1 Servo band SS1 Servo signal

Claims (6)

A magnetic recording medium provided with a magnetic layer containing magnetic powder on a support,
The magnetic layer includes a servo band in which a servo signal is written, and
A data band in which data is recorded,
The servo signal is written by being magnetized in a direction opposite to the one direction on the servo band magnetized in any one of the track directions, and
The magnetic layer has a thickness of 10 to 180 nm;
In the track direction of the magnetic layer, the variation rate [(Mrt standard deviation) ÷ (Mrt average value) × 100] of the product (Mrt) of the remanent magnetization and thickness of the magnetic layer is 30% or less. A magnetic recording medium characterized by the above.   2. The magnetic recording medium according to claim 1, wherein the magnetic powder is a ferromagnetic metal powder having an average major axis length of 30 to 100 nm or a hexagonal ferrite magnetic powder having an average plate diameter of 15 to 50 nm.   The magnetic recording medium according to claim 1, wherein the magnetic layer is provided on the support through a nonmagnetic layer containing at least a nonmagnetic powder and a binder.   4. The switching field distribution representing the magnetization reversibility of the magnetic layer in the track direction of the magnetic layer is 0.10 to 0.70. 5. The magnetic recording medium described. The ratio R (φ ₀ / φ ₁ ) between the residual magnetization φ _{0 of the} magnetic layer other than the servo band and the residual magnetization φ ₁ when a 1 T external magnetic field is applied to the portion is 0.01-0. . The magnetic recording medium according to claim 1, wherein the magnetic recording medium is.   The magnetic powder is a ferromagnetic metal powder having a long axis length variation rate [(standard deviation of long axis length) / (average value of long axis length)] of 30% or less, or a plate diameter variation rate [(plate 6. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a hexagonal ferrite magnetic powder having a standard deviation of diameter / (average value of plate diameter)] of 30% or less.

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