Magnetic Tape, Magnetic Tape Cartridge, and Magnetic Tape Device

Abstract

To provide a magnetic tape that can exhibit excellent electromagnetic conversion characteristics, and is excellent in running stability in recording and / or playing back data at different head inclination angles in a high temperature and high humidity environment.SOLUTION: There is provided a magnetic tape in which a vertical direction switching field distribution SFD of the magnetic tape is 1.5 or less, in an environment of a temperature of 32°C and relative humidity of 80%, frictional force F45° on a surface of a magnetic layer with respect to an LTO8 head measured at a head inclination angle of 45° is 4 gf or more and 15 gf or less, and a standard deviation of the frictional force F on the surface of the magnetic layer with respect to the LTO8 head measured at head inclination angles of 0°, 15°, 30°, and 45° is 10 gf or less. Also there are provided a magnetic tape cartridge including the magnetic tape, and a magnetic tape device including the magnetic tape.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a magnetic tape, a magnetic tape cartridge, and a magnetic tape device.

Background Art

[0002] Magnetic recording media include tape-shaped and disk-shaped ones. For data storage applications such as data backup and archiving, tape-shaped magnetic recording media, i.e., magnetic tapes, are mainly used (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is always a demand for further improvement in the electromagnetic conversion characteristics of magnetic recording media. Therefore, a magnetic tape capable of exhibiting excellent electromagnetic conversion characteristics is desirable.

[0005] On the other hand, data recording on a magnetic tape is usually performed by running the magnetic tape in a magnetic tape device and causing a magnetic head to follow the data band of the magnetic tape to record data on the data band. As a result, data tracks are formed on the data band. Also, at the time of reproducing the recorded data, the magnetic tape is run in the magnetic tape device and the magnetic head is caused to follow the data band of the magnetic tape to read the data recorded on the data band.

[0006] In order to improve the accuracy with which the magnetic head follows the data band of the magnetic tape in recording and / or playback as described above, a system that performs head tracking using a servo signal (hereinafter referred to as a "servo system") has been put into practical use. Furthermore, it has been proposed to use a servo signal to obtain dimensional information (such as shrinkage and elongation) in the width direction of a magnetic tape during running, and to change the angle (hereinafter also referred to as the "head tilt angle") at which the axial direction of the magnetic head module is tilted with respect to the width direction of the magnetic tape according to the obtained dimensional information (see Patent Documents 1 and 2, for example, paragraphs 0059 to 0067 and paragraph 0084 of Patent Document 1). When recording or playing back data, if the magnetic head for recording or playing back data is displaced from the target track position due to the width deformation of the magnetic tape and recording or playing back of the data is performed, phenomena such as overwriting of recorded data and playback failure will occur. The present inventor considers that changing the head tilt angle as described above is one of the means for suppressing the occurrence of such phenomena.

[0007] For example, assuming that the head tilt angle is changed as described above, it is desirable that the running stability of the magnetic tape be high when recording and / or playing back data at different head tilt angles. This is because it is considered that high running stability of the magnetic tape can lead to further suppression of the occurrence of the above phenomena.

[0008] By the way, in recent years, magnetic tapes are sometimes used in data centers where temperature and humidity are controlled. On the other hand, in data centers, power saving is required for cost reduction. For power saving, it is desirable that the management conditions of the usage environment of magnetic tapes in data centers can be relaxed from the current level or that management can be made unnecessary. However, if the management conditions of the usage environment are relaxed or not managed, it is also assumed that magnetic tapes will be used in, for example, high-temperature and high-humidity environments. Therefore, a magnetic tape with excellent running stability when recording and / or playing back data at different head tilt angles in a high-temperature and high-humidity environment is desirable.

[0009] One aspect of the present invention aims to provide a magnetic tape that can exhibit excellent electromagnetic conversion characteristics and has excellent running stability when recording and / or reproducing data at different head tilt angles in a high-temperature and high-humidity environment.

Means for Solving the Problems

[0010] One aspect of the present invention is a magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the vertical switching field distribution (SFD) of the magnetic tape is 1.5 or less, in an environment of a temperature of 32°C and a relative humidity of 80%, the frictional force F on the surface of the magnetic layer with respect to the LTO (Linear Tape-Open) 8 heads measured at a head tilt angle of 45° 45° is 4 gf or more and 15 gf or less, and the standard deviation of the frictional force F on the surface of the magnetic layer with respect to the LTO 8 heads measured at head tilt angles of 0°, 15°, 30°, and 45° (hereinafter, simply referred to as "standard deviation of the frictional force F" or "standard deviation of F") is 10 gf or less. The present invention relates to a magnetic tape. Hereinafter, the vertical switching field distribution SFD of the magnetic tape is also referred to as "vertical SFD".

[0011] In one form, the standard deviation of F can be 2 gf or more and 10 gf or less.

[0012] In one form, the vertical SFD can be 0.5 or more and 1.5 or less.

[0013] In one form, the standard deviation of the amount of curvature in the longitudinal direction of the magnetic tape (hereinafter, also simply referred to as "standard deviation of the amount of curvature") can be 5 mm / m or less.

[0014] In one form, the magnetic layer can include inorganic oxide-based particles.

[0015] In one form, the inorganic oxide-based particles can be composite particles of an inorganic oxide and a polymer.

[0016] In one form, the magnetic layer can include carbon black.

[0017] In one form, the magnetic tape can have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

[0018] In one form, the magnetic tape can have a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support.

[0019] In one form, the tape thickness of the magnetic tape can be 5.2 μm or less.

[0020] One aspect of the present invention relates to a magnetic tape cartridge including the magnetic tape.

[0021] One aspect of the present invention relates to a magnetic tape device including the magnetic tape.

[0022] In one form, the magnetic tape device can further include a magnetic head, the magnetic head can have a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, the magnetic tape device can change an angle θ formed by an axis of the element array with respect to the width direction of the magnetic tape during running of the magnetic tape in the magnetic tape device.

Advantages of the Invention

[0023] According to one aspect of the present invention, it is possible to provide a magnetic tape that can exhibit excellent electromagnetic conversion characteristics and has excellent running stability when recording and / or reproducing data at different head tilt angles in a high-temperature and high-humidity environment. Further, according to one aspect of the present invention, it is possible to provide a magnetic tape cartridge and a magnetic tape device including the above magnetic tape.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0025] [Magnetic Tape] One aspect of the present invention relates to a magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder. The perpendicular direction reversal magnetic field distribution SFD (perpendicular SFD) of the above magnetic tape is 1.5 or less. Further, regarding the frictional force on the surface of the magnetic layer with respect to the LTO8 head of the above magnetic tape in an environment of a temperature of 32°C and a relative humidity of 80%, the frictional force F on the surface of the magnetic layer with respect to the LTO8 head measured at a head tilt angle of 45° 45°It is 4 gf or more and 15 gf or less, and the standard deviation of the frictional force F on the surface of the magnetic layer with respect to the LTO8 head measured at head tilt angles of 0°, 15°, 30° and 45° is 10 gf or less. In the present invention and this specification, the "surface of the magnetic layer" is synonymous with the surface of the magnetic layer side of the magnetic tape. Also, regarding units, "gf" indicates gram weight, and 1 N (Newton) is approximately 102 gf.

[0026] <Vertical SFD> In the present invention and this specification, the vertical direction reversal magnetic field distribution SFD (vertical SFD) of the magnetic tape is the reversal magnetic field distribution measured in the vertical direction of the magnetic tape. The "vertical direction" described with respect to the reversal magnetic field distribution is the direction orthogonal to the surface of the magnetic layer, which can also be called the thickness direction. In the present invention and this specification, the vertical direction reversal magnetic field distribution SFD of the magnetic tape is a value obtained by the following method at a measurement temperature of 25°C using a vibrating sample magnetometer. A measurement sample piece is cut out from the magnetic tape to be measured. The size of the sample piece may be any size that can be introduced into the vibrating sample magnetometer used for measurement. For such a sample piece, using a vibrating sample magnetometer, a magnetic field is applied in the vertical direction of the sample piece (the direction perpendicular to the surface of the magnetic layer) at a maximum applied magnetic field of 3979 kA / m, a measurement temperature of 25 °C, and a magnetic field sweep rate of 8.3 kA / m / second, and the magnetization intensity of the sample piece at the maximum applied magnetic field is measured. The measured value shall be obtained as a value obtained by subtracting the magnetization of the sample probe of the vibrating sample magnetometer as background noise. In the magnetic field-magnetization curve (referred to as the "M-H curve") obtained by such measurement, the magnitude H of the magnetic field at which the magnetization intensity M becomes zero shall be defined as the coercive force Hc (unit: Oe). Also, among the peaks seen in the differential curve when the magnetization is differentiated by the magnetic field, the half-width of the peak at a magnetic field higher than 2000 Oe shall be defined as HPW (unit: Oe). "HPW" is an abbreviation for Half Peak Width. SFD is obtained by SFD = HPW ÷ Hc. Regarding the units, 1 Oe (1 oersted) = 79.6 A / m. The measurement temperature is the temperature of the sample piece. By setting the ambient temperature around the sample piece to the measurement temperature (25 °C), the temperature of the sample piece can be set to the measurement temperature (25 °C) due to the establishment of temperature equilibrium.

[0027] The vertical SFD of the above magnetic tape is 1.5 or less from the viewpoint of improving the electromagnetic conversion characteristics, preferably 1.3 or less, and more preferably 1.0 or less. The vertical SFD of the above magnetic tape can be, for example, 0.1 or more, 0.3 or more, or 0.5 or more, or can also be less than the values exemplified herein. A small value of the vertical SFD is preferable from the viewpoint of further improving the electromagnetic conversion characteristics. The vertical SFD of the magnetic tape can be controlled by known methods such as adjusting the vertical alignment treatment conditions.

[0028] <Head tilt angle> Next, in explaining the above head tilt angle, first, the LTO8 head will be described below. Further, the reason why it is considered that the phenomenon occurring during recording or playback described above can be suppressed by tilting the axial direction of the magnetic head module in the width direction of the magnetic tape during magnetic tape travel will also be described below. In the present invention and this specification, the "LTO8 head" is a magnetic head conforming to the LTO8 standard. For measuring the above frictional force, the magnetic head installed in the LTO8 drive may be taken out and used, or a magnetic head commercially available as a magnetic head for LTO drives may be used. Here, the LTO8 drive is a drive (magnetic tape device) conforming to the LTO8 standard. The LTO9 drive is a drive conforming to the LTO9 standard, and the same applies to drives of other generations. Also, when measuring the frictional force F on the surface of the magnetic layer with respect to the LTO8 head at head tilt angles of 0°, 15°, 30°, and 45° respectively, new (i.e., unused) LTO8 heads shall be used for the measurement at each head tilt angle. Considering that the LTO8 standard can cope with recent high-density recording, LTO8 is adopted as the head for measuring the frictional force, and the above magnetic tape is not limited to that used in the LTO8 drive. Data recording and / or playback may be performed on the above magnetic tape in the LTO8 drive, or in the LTO9 drive or a further next-generation drive, or in a drive of a previous generation such as LTO7 before LTO8.

[0029] The LTO8 head has three modules each including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements. The three modules are arranged in the LTO8 head in the arrangement of "recording module - playback module - recording module" (total number of modules: 3).

[0030] Each module includes an element array having a total of 32 magnetic head elements between a pair of servo signal reading elements, that is, an array of elements. A module having a recording element as a magnetic head element is a recording module for recording data on a magnetic tape. A module having a reproducing element as a magnetic head element is a reproducing module for reproducing data recorded on a magnetic tape. In the LTO8 head, the three modules are arranged such that the axes of the element arrays of the respective modules are oriented parallel to each other. Such "parallel" does not necessarily mean only parallel in the strict sense, but includes the range of errors normally allowed in the technical field to which the present invention pertains. The range of errors can mean, for example, a range of within ±10° from strict parallelism.

[0031] The head tilt angle in friction measurement is the head tilt angle in the reproducing module of the LTO8 head.

[0032] In each element array, a pair of servo signal reading elements and a plurality of magnetic head elements (i.e., recording elements or reproducing elements) are arranged linearly spaced apart. Here, "arranged linearly" means that each magnetic head element is arranged on a straight line connecting the central portions of one servo signal reading element and the other servo signal reading element. And the "axis of the element array" in the present invention and in this specification means a straight line connecting the central portions of one servo signal reading element and the other servo signal reading element.

[0033] Next, the configuration of the module and the like will be further described with reference to the drawings. However, the forms shown in the drawings are examples and do not limit the present invention.

[0034] FIG. 1 is a schematic diagram showing an example of a module of a magnetic head. The module shown in FIG. 1 has a plurality of magnetic head elements between a pair of servo signal reading elements (servo signal reading elements 1 and 2). The magnetic head elements are also called "channels". "Ch" in the figure is an abbreviation of "Channel". The module shown in FIG. 1 has a total of 32 magnetic head elements from Ch0 to Ch31. The playback module of the LTO8 head has a total of 32 playback elements from Ch0 to Ch31.

[0035] In FIG. 1, "L" is the distance between a pair of servo signal reading elements, that is, the distance between one servo signal reading element and the other servo signal reading element. In the module shown in FIG. 1, "L" is the distance between servo signal reading element 1 and servo signal reading element 2. Specifically, it is the distance between the central part of servo signal reading element 1 and the central part of servo signal reading element 2. Such a distance can be measured by, for example, an optical microscope or the like.

[0036] FIG. 2 is an explanatory diagram of the relative positional relationship between the module and the magnetic tape during the running of the magnetic tape in the magnetic tape apparatus. In FIG. 2, the dotted line A indicates the width direction of the magnetic tape. The dotted line B indicates the axis of the element array. The angle θ can be called the head tilt angle during the running of the magnetic tape, and it is the angle formed by the dotted line A and the dotted line B. When the angle θ is 0° during the running of the magnetic tape, the distance in the width direction of the magnetic tape (hereinafter, also referred to as the "effective distance between servo signal reading elements") between one servo signal reading element and the other servo signal reading element of the element array is "L". On the other hand, when the angle θ is greater than 0°, the effective distance between servo signal reading elements is "Lcosθ", and Lcosθ is smaller than L. That is, "Lcosθ < L".

[0037] As described above, during recording or playback, if the magnetic head for recording or playing back data is displaced from the target track position due to the width deformation of the magnetic tape and recording or playback of data is performed, phenomena such as overwriting of recorded data and playback failure will occur. For example, when the width of the magnetic tape contracts or expands, a phenomenon may occur in which the magnetic head element that should perform recording or playback at the target track position performs recording or playback at a different track position. Also, when the width of the magnetic tape expands, the effective distance between the servo signal reading elements becomes shorter than the interval between two adjacent servo bands sandwiching the data band (also described as the "servo band interval" or the "interval between servo bands". Specifically, it is the distance between the two servo bands in the width direction of the magnetic tape.), and a phenomenon may occur in which recording or playback of data is not performed at a portion close to the edge of the magnetic tape. On the other hand, when the element array is tilted at an angle θ greater than 0°, as described above, the effective distance between the servo signal reading elements becomes "Lcosθ". The larger the value of θ, the smaller the value of Lcosθ, and the smaller the value of θ, the larger the value of Lcosθ. Therefore, by changing the value of θ according to the degree of dimensional change (i.e., contraction or expansion) in the width direction of the magnetic tape, it becomes possible to bring the effective distance between the servo signal reading elements closer to or equal to the interval between the servo bands. As a result, during recording or playback, it is possible to prevent or reduce the occurrence frequency of phenomena such as overwriting of recorded data and playback failure that occur when the magnetic head for recording or playing back data is displaced from the target track position due to the width deformation of the magnetic tape and recording or playback of data is performed.

[0038] Figure 3 is an explanatory diagram regarding the change in the angle θ during the running of the magnetic tape. θ which is the angle θ at the start of running initial can be set, for example, to 0° or more or greater than 0°. In Figure 3, the central figure shows the state of the module at the start of running. In Figure 3, the right figure shows the angle θ as an angle θ initial greater than θ cshows the state of the module when [condition]. The effective distance Lcosθ between the servo signal reading elements c is a value smaller than Lcosθ at the start of magnetic tape running initial When the width of the magnetic tape contracts during magnetic tape running, it is preferable to perform such angle adjustment. On the other hand, in Fig. 3, the left figure shows the state of the module when the angle θ is set to an angle θ initial smaller than [angle]. e shows the state of the module when [condition]. The effective distance Lcosθ between the servo signal reading elements e is a value larger than Lcosθ at the start of magnetic tape running initial When the width of the magnetic tape expands during magnetic tape running, it is preferable to perform such angle adjustment.

[0039] As described above, changing the head tilt angle during magnetic tape running can contribute to preventing phenomena such as overwriting of recorded data and playback failure that may occur when the magnetic head deviates from the target track position due to width deformation of the magnetic tape during recording or playback, or can contribute to reducing the frequency of occurrence of such phenomena. On the other hand, recording data on the magnetic tape and playing back the recorded data are usually performed by bringing the magnetic layer surface of the magnetic tape into contact with the magnetic head and sliding them. The inventor considered that when the head tilt angle changes during such sliding, the contact state between the magnetic head and the magnetic layer surface may change, which can be a factor in reducing running stability. Specifically, if the contact state between the magnetic layer surface of the magnetic tape and the magnetic head (for example, the contact state between the portion near the edge of the module of the magnetic head and the magnetic layer surface) changes significantly due to the difference in the head tilt angle, the running stability will decrease, and the inventor speculated that such a decrease in running stability may become more prominent in a high-temperature and high-humidity environment. Based on the above speculation, the inventor of the present invention has conducted intensive studies. As a result, regarding the friction characteristics of the magnetic tape, in an environment with a temperature of 32°C and a relative humidity of 80%, the frictional force F on the surface of the magnetic layer with respect to the LTO8 head measured at a head tilt angle of 45° 45° and the standard deviation of the frictional force F on the surface of the magnetic layer with respect to the LTO8 head measured at head tilt angles of 0°, 15°, 30°, and 45° respectively are within the ranges described above. As a result, it has been newly found that it is possible to improve the running stability when recording and / or reproducing data at different head tilt angles in a high-temperature and high-humidity environment. The temperature and humidity of the measurement environment are adopted as exemplary values of the temperature and humidity in a high-temperature and high-humidity environment. Therefore, the environment in which data is recorded on the magnetic tape and the recorded data is reproduced is not limited to the above temperature and humidity environment. The head tilt angle when measuring the frictional force is also adopted as an exemplary value of the angle that can be adopted when changing the head tilt angle during the running of the magnetic tape to record and / or reproduce data. Therefore, the head tilt angle when recording data on the magnetic tape and reproducing the recorded data is not limited to the above angle. Also, the present invention is not limited by the speculation of the inventor described in this specification. Hereinafter, the running stability when changing the head tilt angle during the running of the magnetic tape to record and / or reproduce data in a high-temperature and high-humidity environment will also be simply referred to as "running stability". Also, the high-temperature and high-humidity environment can be, for example, an environment with a temperature of about 30 to 50°C. The humidity of that environment can be, for example, about 70 to 100% as the relative humidity. In the present invention and this specification, the temperature and humidity described for the environment are the ambient temperature and relative humidity of that environment.

[0040] In the present invention and this specification, the measurement of the frictional force at head tilt angles of 0°, 15°, 30°, and 45° is assumed to be performed by the following method in an environment with a temperature of 32°C and a relative humidity of 80%. Also, for the head tilt angle regarding the measurement of frictional force, in the first forward stroke of the following 100 reciprocating slides, it refers to the angle formed by the axis of the element array of the playback module of the LTO8 head with respect to the direction orthogonal to the sliding direction. Such an angle is obtained by reinterpreting A in FIG. 2 as the direction orthogonal to the sliding direction, and it is the angle θ formed by this A and B. During the 100 reciprocating slides, the head tilt angle is fixed. Place the magnetic tape to be measured on two cylindrical guide rolls with a diameter of 1 inch (1 inch = 2.54 cm) that are arranged parallel to each other and spaced apart so that the magnetic layer surface is in contact. At a randomly extracted portion of the magnetic tape to be measured, with the head tilt angle set to 0°, 15°, 30°, or 45°, slide the magnetic layer surface of the magnetic tape against the LTO8 head, and detect the resistance force generated during sliding with a strain gauge. Perform 100 reciprocating slides. Regarding the measurement conditions, the wrap angle θ is 6°, and the sliding speed is 30 mm / second. The tension applied in the longitudinal direction of the magnetic tape during sliding is 0.55 N. The sliding distance for each of the forward and return strokes is 5 cm. The dynamic frictional force in the 100th forward stroke is taken as the frictional force at each head tilt angle. During the above measurement, of the two ends in the longitudinal direction of the magnetic tape to be measured, connect one end to the strain gauge and apply a tension of 0.20 N to the other end. Here, the tension applied is designated as T0 (unit: N), and the resistance force detected by the strain gauge is designated as T (unit: N). The frictional force F value is calculated by the following formula. That is, here, the frictional force F is calculated with T0 = 0.20. The measurement of the frictional force F at the above four head tilt angles is carried out in any order at different portions of the magnetic tape to be measured. Also, before each measurement, in order to acclimatize to the measurement environment, leave the magnetic tape to be measured placed on the guide rolls as described above for 24 hours or more. Calculate the standard deviation (i.e., the positive square root of the variance) from the values of the frictional force F at the above four head tilt angles.

[0041]

Number

[0042] <Frictional force F45° , Standard deviation of the frictional force F Regarding the friction characteristics of the magnetic tape, from the viewpoint of improving the running stability when recording and / or reproducing data at different head tilt angles in a high-temperature and high-humidity environment, the frictional force F 45° is 4 gf or more and 15 gf or less. From the viewpoint of further improving the running stability, the frictional force F 45° is preferably 14 gf or less, more preferably 13 gf or less, still more preferably 12 gf or less, and even more preferably 11 gf or less. The frictional force F 45° is 4 gf or more, and from the viewpoint of further improving the running stability, it is preferably 5 gf or more. The standard deviation of the frictional force F on the surface of the magnetic layer with respect to the LTO8 head measured at head tilt angles of 0°, 15°, 30°, and 45° respectively is 10 gf or less from the viewpoint of improving the running stability when recording and / or reproducing at different head tilt angles in a high-temperature and high-humidity environment, preferably 9 gf or less, more preferably 8 gf or less, still more preferably 7 gf or less, even more preferably 6 gf or less, still even more preferably 5 gf or less, and still even more preferably 4 gf or less. The above standard deviation can be, for example, 0 gf or more, more than 0 gf, 1 gf or more, or 2 gf or more. A smaller value of the above standard deviation is preferable from the viewpoint of further improving the running stability. The friction characteristics of the magnetic tape can be adjusted, for example, by the type of components used to form the magnetic layer, etc. Details on this point will be described later.

[0043] <Standard deviation of the amount of curvature> Next, the standard deviation of the amount of curvature will be described. In the present invention and this specification, the amount of curvature in the longitudinal direction of the magnetic tape is a value obtained by the following method in an environment of an ambient temperature of 23°C and a relative humidity of 50%. The magnetic tape is usually housed in a magnetic tape cartridge and distributed. As the magnetic tape to be measured, a magnetic tape taken out from an unused magnetic tape cartridge not attached to a magnetic tape device is used. Figure 4 is an explanatory diagram of the amount of curvature in the longitudinal direction of the magnetic tape. Cut out a tape sample with a length of 100 m in the longitudinal direction from a randomly selected part of the magnetic tape to be measured. Define one end of this tape sample as the 0 m position, and define the position D m (D meters) away in the longitudinal direction from this one end towards the other end as the D m position. Therefore, the position 10 m away in the longitudinal direction is the 10 m position, the position 20 m away is the 20 m position, and in sequence, at 10 m intervals, the 30 m position, 40 m position, 50 m position, 60 m position, 70 m position, 80 m position, 90 m position, and 100 m position are determined. Cut out a tape sample with a length of 1 m from the 0 m position to the 1 m position. Use this tape sample as the tape sample for measuring the amount of curvature at the 0 m position. Cut out a tape sample with a length of 1 m from the 10 m position to the 11 m position. Use this tape sample as the tape sample for measuring the amount of curvature at the 10 m position. Cut out a tape sample with a length of 1 m from the 20 m position to the 21 m position. Use this tape sample as the tape sample for measuring the amount of curvature at the 20 m position. Cut out a tape sample with a length of 1 m from the 30 m position to the 31 m position. Use this tape sample as the tape sample for measuring the amount of curvature at the 30 m position. Cut out a tape sample with a length of 1 m from the 40 m position to the 41 m position. Use this tape sample as the tape sample for measuring the amount of curvature at the 40 m position. Cut out a tape sample with a length of 1 m from the 50 m position to the 51 m position. Use this tape sample as the tape sample for measuring the amount of curvature at the 50 m position. Cut out a tape sample with a length of 1 m from the 60 m position to the 61 m position. Use this tape sample as the tape sample for measuring the amount of curvature at the 60 m position. Cut out a tape sample with a length of 1 m from the position of 70 m to the position of 71 m. This tape sample shall be used as the tape sample for measuring the amount of curvature at the position of 70 m. Cut out a tape sample with a length of 1 m from the position of 80 m to the position of 81 m. This tape sample shall be used as the tape sample for measuring the amount of curvature at the position of 80 m. Cut out a tape sample with a length of 1 m from the position of 90 m to the position of 91 m. This tape sample shall be used as the tape sample for measuring the amount of curvature at the position of 90 m. Cut out a tape sample with a length of 1 m from the position of 99 m to the position of 100 m. This tape sample shall be used as the tape sample for measuring the amount of curvature at the position of 100 m. For each position's tape sample, hold the upper end with a gripping member (such as a clip) with the longitudinal direction vertical, and hang it for 24 hours ± 4 hours in a tension-free state. Then, within 1 hour, perform the following measurements. As shown in Figure 4, place the tape piece on a plane in a tension-free state. The tape piece may be placed on the plane with the surface on the magnetic layer side facing upward, or the other surface facing upward. In Figure 4, S indicates the tape sample, and W indicates the width direction of the tape sample. Using an optical microscope, measure the distance L1 (unit: mm), which is the shortest distance between the virtual line 54 connecting both end portions 52 and 53 of the tape sample S and the maximum curved portion 55 in the longitudinal direction of the tape sample S. Figure 4 shows an example of curving upward on the paper surface. When curving downward, measure the distance L1 (mm) in the same manner. Regardless of which side is curving, the distance L1 shall be displayed as a positive value. When no curvature is confirmed in the longitudinal direction, L1 shall be 0 (zero) mm. In this way, the standard deviation (i.e., the positive square root of the variance) of the measured curvature amounts L1 at a total of 11 positions from the position of 0 m to the position of 100 m shall be taken as the standard deviation (unit: mm / m) of the curvature amount in the longitudinal direction of the magnetic tape to be measured.

[0044] In the above magnetic tape, the standard deviation of the amount of curvature obtained by the above method can be, for example, 7 mm / m or less, 6 mm / m or less. From the viewpoint of further improving the running stability, it is preferably 5 mm / m or less, more preferably 4 mm / m or less, and still more preferably 3 mm / m or less. The standard deviation of the amount of curvature of the above magnetic tape can be, for example, 0 mm / m or more, more than 0 mm / m, 1 mm / m or more, or 2 mm / m or more. A small value of the standard deviation of the amount of curvature is preferable from the viewpoint of further improving the running stability. Also, a small value of the standard deviation of the amount of curvature is preferable from the viewpoint of further improving the electromagnetic conversion characteristics. From such a viewpoint, it is preferable that the standard deviation of the amount of curvature is within the above range. The standard deviation of the amount of curvature can be controlled by adjusting the manufacturing conditions of the manufacturing process of the magnetic tape. Details thereof will be described later.

[0045] Hereinafter, the above magnetic tape will be described in more detail.

[0046] <Magnetic layer> (Ferromagnetic powder) As the ferromagnetic powder contained in the magnetic layer, one or a combination of two or more known ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used. Using a ferromagnetic powder with a small average particle size is preferable from the viewpoint of improving the recording density. From this point, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, still more preferably 40 nm or less, even more preferably 35 nm or less, even more preferably 30 nm or less, still more preferably 25 nm or less, and yet even more preferably 20 nm or less. On the other hand, from the viewpoint of the stability of magnetization, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, still more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more.

[0047] Hexagonal ferrite powder Preferable specific examples of the ferromagnetic powder include hexagonal ferrite powder. For details of the hexagonal ferrite powder, for example, refer to paragraphs 0012 to 0030 of JP-A-2011-225417, paragraphs 0134 to 0136 of JP-A-2011-216149, paragraphs 0013 to 0030 of JP-A-2012-204726, and paragraphs 0029 to 0084 of JP-A-2015-127985.

[0048] In the present invention and in this specification, the "hexagonal ferrite powder" refers to a ferromagnetic powder in which the crystal structure of hexagonal ferrite is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the diffraction peak with the highest intensity in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed. For example, when the diffraction peak with the highest intensity in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystal structure of hexagonal ferrite, it is determined that the crystal structure of hexagonal ferrite has been detected as the main phase. When only a single structure is detected by X-ray diffraction analysis, this detected structure is taken as the main phase. The crystal structure of hexagonal ferrite contains at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. The divalent metal atom is a metal atom that can become a divalent cation as an ion, and examples thereof include alkaline earth metal atoms such as strontium atoms, barium atoms, and calcium atoms, and lead atoms. In the present invention and in this specification, the hexagonal strontium ferrite powder refers to a powder in which the main divalent metal atom contained in this powder is a strontium atom, and the hexagonal barium ferrite powder refers to a powder in which the main divalent metal atom contained in this powder is a barium atom. The main divalent metal atom refers to the divalent metal atom that occupies the most in terms of atomic percentage among the divalent metal atoms contained in this powder. However, rare earth atoms are not included in the above divalent metal atoms. The "rare earth atoms" in the present invention and in this specification are selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanoid atoms. The lanthanoid atoms are selected from the group consisting of lanthanum atoms (La), cerium atoms (Ce), praseodymium atoms (Pr), neodymium atoms (Nd), promethium atoms (Pm), samarium atoms (Sm), europium atoms (Eu), gadolinium atoms (Gd), terbium atoms (Tb), dysprosium atoms (Dy), holmium atoms (Ho), erbium atoms (Er), thulium atoms (Tm), ytterbium atoms (Yb), and lutetium atoms (Lu).

[0049] Hereinafter, the hexagonal strontium ferrite powder, which is a form of the hexagonal ferrite powder, will be described in more detail.

[0050] The activation volume of the hexagonal strontium ferrite powder is preferably in the range of 800 to 1600 nm 3 The particulate hexagonal strontium ferrite powder having an activation volume within the above range is suitable for producing a magnetic tape that exhibits excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm 3 or more, for example, 850 nm 3 or more. Also, from the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the hexagonal strontium ferrite powder is more preferably 1500 nm 3 or less, still more preferably 1400 nm 3 or less, even more preferably 1300 nm 3 or less, still even more preferably 1200 nm 3 or less, yet still even more preferably 1100 nm 3 or less, and even yet still even more preferably. The same applies to the activation volume of the hexagonal barium ferrite powder.

[0051] The "activation volume" is a unit of magnetization reversal and is an index indicating the magnetic size of particles. The activation volume described in the present invention and this specification and the anisotropy constant Ku described later are measured using a vibrating sample magnetometer at magnetic field sweep rates of 3 minutes and 30 minutes in the coercive force Hc measurement section (measurement temperature: 23°C ± 1°C), and are values obtained from the following relational expression between Hc and the activation volume V. Regarding the unit of the anisotropy constant Ku, 1 erg / cc = 1.0×10 -1 J / m 3 . Hc = 2Ku / Ms{1 - [(kT / KuV)ln(At / 0.693)] 1 / 2} [In the above formula, Ku: anisotropy constant (unit: J / m 3 ), Ms: saturation magnetization (unit: kA / m), k: Boltzmann constant, T: absolute temperature (unit: K), V: activation volume (unit: cm 3 ), A: spin precession frequency (unit: s -1 ), t: magnetic field reversal time (unit: s)]

[0052] As an index for reducing thermal fluctuations, in other words, improving thermal stability, the anisotropy constant Ku can be cited. The hexagonal strontium ferrite powder preferably has a Ku of 1.8×10 5 J / m 3 or more, more preferably 2.0×10 5 J / m 3 or more. Also, the Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 5 J / m 3 or less. However, since a higher Ku means higher thermal stability and is preferable, it is not limited to the values exemplified above.

[0053] The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it preferably contains rare earth atoms at a content rate (bulk content rate) of 0.5 to 5.0 atomic% with respect to 100 atomic% of iron atoms. The hexagonal strontium ferrite powder containing rare earth atoms can, in one form, have a rare earth atom surface layer partiality. In the present invention and this specification, the "rare earth atom surface layer partiality" means the rare earth atom content rate (hereinafter, referred to as "rare earth atom surface layer content rate" or simply "surface layer content rate" with respect to rare earth atoms) with respect to 100 atomic% of iron atoms in the dissolution liquid obtained by partially dissolving the hexagonal strontium ferrite powder with an acid, and the rare earth atom content rate (hereinafter, referred to as "rare earth atom bulk content rate" or simply "bulk content rate" with respect to rare earth atoms) with respect to 100 atomic% of iron atoms in the dissolution liquid obtained by completely dissolving the hexagonal strontium ferrite powder with an acid, and Rare earth atom surface layer content rate / Rare earth atom bulk content rate > 1.0 It means satisfying the ratio. The rare earth atom content of the hexagonal strontium ferrite powder described below is synonymous with the rare earth atom bulk content. In contrast, partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder. Therefore, the rare earth atom content in the dissolution solution obtained by partial dissolution is the rare earth atom content in the surface layer of the particles constituting the hexagonal strontium ferrite powder. That the rare earth atom surface layer content satisfies the ratio of "rare earth atom surface layer content / rare earth atom bulk content > 1.0" means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are unevenly distributed in the surface layer (i.e., more exist than in the interior). The surface layer part in the present invention and in this specification means a partial region from the surface to the interior of the particles constituting the hexagonal strontium ferrite powder.

[0054] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atomic% with respect to 100 atomic% of iron atoms. It is considered that containing rare earth atoms at the bulk content within the above range and the uneven distribution of rare earth atoms in the surface layer of the particles constituting the hexagonal strontium ferrite powder contribute to suppressing the decrease in the reproduction output in repeated reproduction. This is presumably because the hexagonal strontium ferrite powder contains rare earth atoms at the bulk content within the above range and the uneven distribution of rare earth atoms in the surface layer of the particles constituting the hexagonal strontium ferrite powder can increase the anisotropy constant Ku. The higher the value of the anisotropy constant Ku, the more the occurrence of a phenomenon called so-called thermal fluctuation can be suppressed (in other words, the thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, the decrease in the reproduction output in repeated reproduction can be suppressed. It is speculated that the uneven distribution of rare earth atoms in the particle surface layer of the hexagonal strontium ferrite powder contributes to stabilizing the spin of the iron (Fe) sites in the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. In addition, it is presumed that using hexagonal strontium ferrite powder having a rare earth atom surface layer uneven distribution as the ferromagnetic powder of the magnetic layer also contributes to suppressing the wear of the magnetic layer surface due to sliding with the magnetic head. That is, it is presumed that hexagonal strontium ferrite powder having a rare earth atom surface layer uneven distribution can contribute to improving the running durability of the magnetic tape. This is presumably because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improving the interaction between the particle surface and the organic substances (for example, binder and / or additive) contained in the magnetic layer, and as a result, the strength of the magnetic layer is improved. From the viewpoint of suppressing a decrease in the reproduction output during repeated reproduction and / or from the viewpoint of further improving the running durability, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic %, still more preferably in the range of 1.0 to 4.5 atomic %, and even more preferably in the range of 1.5 to 4.5 atomic %.

[0055] The above bulk content is the content obtained by completely dissolving the hexagonal strontium ferrite powder. In the present invention and this specification, unless otherwise specified, the content of an atom refers to the bulk content obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one kind of rare earth atom as the rare earth atom, or may contain two or more kinds of rare earth atoms. The above bulk content in the case of containing two or more kinds of rare earth atoms is obtained for the total of two or more kinds of rare earth atoms. This also applies to other components in the present invention and this specification. That is, unless otherwise specified, one kind of a certain component may be used, or two or more kinds may be used. The content or content rate in the case of using two or more kinds refers to the total of two or more kinds.

[0056] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms contained may be any one or more of the rare earth atoms. From the viewpoint of suppressing the decrease in the reproduction output in repeated reproduction, preferable rare earth atoms include neodymium atoms, samarium atoms, yttrium atoms, and dysprosium atoms, more preferably neodymium atoms, samarium atoms, and yttrium atoms, and even more preferably neodymium atoms.

[0057] In the hexagonal strontium ferrite powder having rare earth atom surface layer partiality, the rare earth atoms only need to be unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, for the hexagonal strontium ferrite powder having rare earth atom surface layer partiality, the ratio of the surface layer content rate of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content rate of rare earth atoms obtained by complete dissolution under the dissolution conditions described later, "surface layer content rate / bulk content rate" is more than 1.0, and can be 1.5 or more. That the "surface layer content rate / bulk content rate" is greater than 1.0 means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are unevenly distributed in the surface layer (that is, there are more than in the interior). Also, the ratio of the surface layer content rate of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content rate of rare earth atoms obtained by complete dissolution under the dissolution conditions described later, "surface layer content rate / bulk content rate" can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in the hexagonal strontium ferrite powder having rare earth atom surface layer partiality, the rare earth atoms only need to be unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the above "surface layer content rate / bulk content rate" is not limited to the exemplified upper or lower limits.

[0058] The partial dissolution and complete dissolution of hexagonal strontium ferrite powder will be described below. For the hexagonal strontium ferrite powder existing as powder, the sample powders for partial dissolution and complete dissolution are taken from the same lot of powder. On the other hand, for the hexagonal strontium ferrite powder contained in the magnetic layer of the magnetic tape, a part of the hexagonal strontium ferrite powder taken out from the magnetic layer is subjected to partial dissolution, and the other part is subjected to complete dissolution. The extraction of the hexagonal strontium ferrite powder from the magnetic layer can be carried out, for example, by the method described in paragraph 0032 of JP-A-2015-91747. The above partial dissolution means dissolution to such an extent that the residue of the hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. For example, by partial dissolution, for the particles constituting the hexagonal strontium ferrite powder, a region of 10 to 20% by mass can be dissolved with the whole particle being 100% by mass. On the other hand, the above complete dissolution means dissolution until the residue of the hexagonal strontium ferrite powder cannot be visually confirmed in the liquid at the end of dissolution. The above partial dissolution and the measurement of the surface layer portion content are carried out, for example, by the following method. However, the dissolution conditions such as the amount of the sample powder below are examples, and any dissolution conditions that enable partial dissolution and complete dissolution can be arbitrarily adopted. A container (for example, a beaker) containing 12 mg of the sample powder and 10 mL of 1 mol / L hydrochloric acid is held on a hot plate at a set temperature of 70°C for 1 hour. The obtained dissolution solution is filtered through a 0.1 μm membrane filter. The elemental analysis of the filtrate thus obtained is carried out by an inductively coupled plasma (ICP) analyzer. Thus, the surface layer portion content of the rare earth atoms with respect to 100 atomic% of iron atoms can be determined. When a plurality of types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer portion content. This is the same in the measurement of the bulk content. On the other hand, the above complete dissolution and the measurement of the bulk content are carried out, for example, by the following method. Place a container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid on a hot plate set at a temperature of 80°C and hold for 3 hours. Thereafter, perform the same operations as in the above partial dissolution and measurement of the surface layer content rate, and the bulk content rate with respect to 100 atomic% of iron atoms can be determined.

[0059] From the viewpoint of increasing the playback output when playing back data recorded on a magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape be high. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but having no uneven distribution of rare earth atoms in the surface layer portion has a tendency that σs decreases significantly compared to hexagonal strontium ferrite powder not containing rare earth atoms. On the other hand, hexagonal strontium ferrite powder having uneven distribution of rare earth atoms in the surface layer portion is considered preferable also for suppressing such a significant decrease in σs. In one form, the σs of the hexagonal strontium ferrite powder can be 45 A·m 2 / kg or more, and can also be 47 A·m 2 / kg or more. On the other hand, from the viewpoint of noise reduction, σs is preferably 80 A·m 2 / kg or less, and more preferably 60 A·m 2 / kg or less. σs can be measured using a known measuring device capable of measuring magnetic properties such as a vibrating sample type magnetometer. In the present invention and this specification, unless otherwise specified, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe.

[0060] Regarding the content ratio (bulk content ratio) of constituent atoms of the hexagonal strontium ferrite powder, the strontium atom content ratio can be in the range of, for example, 2.0 to 15.0 atomic % with respect to 100 atomic % of iron atoms. In one form, the hexagonal strontium ferrite powder can be such that the divalent metal atoms contained in this powder are only strontium atoms. In another form, the hexagonal strontium ferrite powder can also contain one or more other divalent metal atoms in addition to strontium atoms. For example, it can contain barium atoms and / or calcium atoms. When other divalent metal atoms other than strontium atoms are contained, the barium atom content ratio and calcium atom content ratio in the hexagonal strontium ferrite powder can each be in the range of, for example, 0.05 to 5.0 atomic % with respect to 100 atomic % of iron atoms.

[0061] As the crystal structure of hexagonal ferrite, the magnetoplumbite type (also called "M type"), W type, Y type, and Z type are known. The hexagonal strontium ferrite powder can take any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder can be such that a single crystal structure or two or more crystal structures are detected by X-ray diffraction analysis. For example, in one form, the hexagonal strontium ferrite powder can be such that only the M-type crystal structure is detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is AFe 12 O 19It is represented by the following compositional formula. Here, A represents a divalent metal atom. When the hexagonal strontium ferrite powder is of the M type, A is only a strontium atom (Sr), or when A contains a plurality of divalent metal atoms, the strontium atom (Sr) occupies the most in terms of atomic percentage as described above. The content rate of divalent metal atoms in the hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite and is not particularly limited. The same applies to the iron atom content rate and the oxygen atom content rate. The hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms, and oxygen atoms, and may further contain rare earth atoms. Furthermore, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain aluminum atoms (Al). The content rate of aluminum atoms can be, for example, 0.5 to 10.0 atomic percentage with respect to 100 atomic percentage of iron atoms. From the viewpoint of suppressing the reduction in the reproduction output during repeated reproduction, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content rate of atoms other than these atoms is preferably 10.0 atomic percentage or less, more preferably in the range of 0 to 5.0 atomic percentage, and may be 0 atomic percentage with respect to 100 atomic percentage of iron atoms. That is, in one form, the hexagonal strontium ferrite powder may not contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The content rate expressed in the above atomic percentage is obtained by converting the content rate (unit: mass percentage) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder into a value expressed in atomic percentage using the atomic weight of each atom. Also, in the present invention and this specification, "not containing" a certain atom means that the content rate measured by an ICP analyzer after complete dissolution is 0 mass percentage. The detection limit of the ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above "not containing" is used in the sense of including being contained in an amount less than the detection limit of the ICP analyzer.The hexagonal strontium ferrite powder can, in one form, be free of bismuth atoms (Bi).

[0062] Metal powder Preferred specific examples of the ferromagnetic powder can also include ferromagnetic metal powders. For details of the ferromagnetic metal powders, reference can be made to, for example, paragraphs 0137 to 0141 of JP-A-2011-216149 and paragraphs 0009 to 0023 of JP-A-2005-251351.

[0063] ε-Iron oxide powder Preferred specific examples of the ferromagnetic powder can also include ε-iron oxide powder. In the present invention and this specification, the "ε-iron oxide powder" refers to a ferromagnetic powder in which the crystal structure of ε-iron oxide is detected as the main phase by X-ray diffraction analysis. For example, when the diffraction peak with the highest intensity in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystal structure of ε-iron oxide, it is determined that the crystal structure of ε-iron oxide has been detected as the main phase. As methods for producing ε-iron oxide powder, a method of producing from goethite, an inverse micelle method, etc. are known. All of the above production methods are known. Also, for methods of producing ε-iron oxide powder in which a part of Fe is substituted by substitution atoms such as Ga, Co, Ti, Al, Rh, etc., reference can be made to, for example, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mater. Chem. C, 2013, 1, pp.5200-5206, etc. However, the method for producing ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the above magnetic tape is not limited to the methods listed here.

[0064] The activation volume of the ε-iron oxide powder is preferably in the range of 300 to 1500 nm 3 is. The micronized ε-iron oxide powder showing the activation volume in the above range is suitable for producing a magnetic tape that exhibits excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably 300 nm 3 or more, for example 500 nm3 It can also be as described above. Further, from the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the ε-iron oxide powder is 1400 nm 3 It is more preferably below, and 1300 nm 3 It is still more preferably below, and 1200 nm 3 It is even more preferably below, and 1100 nm 3 It is still even more preferably below.

[0065] As an index for reducing thermal fluctuations, in other words, improving thermal stability, the anisotropy constant Ku can be cited. The ε-iron oxide powder preferably has a Ku of 3.0×10 4 J / m 3 or more, and more preferably has a Ku of 8.0×10 4 J / m 3 or more. Also, the Ku of the ε-iron oxide powder can be, for example, 3.0×10 5 J / m 3 or less. However, the higher the Ku, the higher the thermal stability, which is preferable, so it is not limited to the values exemplified above.

[0066] From the viewpoint of increasing the playback output when playing back data recorded on the magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, in one embodiment, the σs of the ε-iron oxide powder can be 8 A·m 2 / kg or more, and can also be 12 A·m 2 / kg or more. On the other hand, from the viewpoint of noise reduction, the σs of the ε-iron oxide powder is preferably 40 A·m 2 / kg or less, and more preferably 35 A·m 2 / kg or less.

[0067] In the present invention and in this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powder is a value measured by the following method using a transmission electron microscope. The powder is photographed at a magnification of 100,000 times using a transmission electron microscope, and printed on photographic paper or displayed on a display so as to have a total magnification of 500,000 times to obtain a photograph of the particles constituting the powder. The target particles are selected from the obtained particle photographs, and the contour of the particles is traced with a digitizer to measure the size of the particles (primary particles). The primary particles refer to independent particles without aggregation. The above measurement is performed on 500 randomly extracted particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is taken as the average particle size of the powder. As the above transmission electron microscope, for example, a Hitachi transmission electron microscope model H-9000 can be used. Also, the measurement of the particle size can be performed using known image analysis software, for example, Carl Zeiss image analysis software KS-400. Unless otherwise specified, the average particle size shown in the examples described later is a value measured using a Hitachi transmission electron microscope model H-9000 as the transmission electron microscope and Carl Zeiss image analysis software KS-400 as the image analysis software. In the present invention and this specification, the powder means an aggregate of a plurality of particles. For example, the ferromagnetic powder means an aggregate of a plurality of ferromagnetic particles. Also, the aggregate of a plurality of particles is not limited to the form in which the particles constituting the aggregate are in direct contact, and forms in which binders, additives, etc. described later are interposed between the particles are also included. The term "particle" may also be used to represent the powder.

[0068] As a method for collecting the sample powder from the magnetic tape for particle size measurement, for example, the method described in paragraph 0015 of JP-A-2011-048878 can be adopted.

[0069] In the present invention and this specification, unless otherwise specified, the size of the particles (particle size) constituting the powder is such that the shape of the particles observed in the above particle photograph is (1) In the case of needle-like, spindle-like, columnar (however, the height is larger than the maximum major axis of the bottom surface), etc., it is represented by the length of the major axis constituting the particle, that is, the major axis length, (2) In the case of a plate shape or column shape (however, the thickness or height is smaller than the maximum major axis length of the plate surface or bottom surface), it is represented by the maximum major axis length of the plate surface or bottom surface, (3) In the case of a spherical shape, polyhedral shape, amorphous shape, etc., and when the major axis constituting the particles cannot be specified from the shape, it is represented by the equivalent circle diameter. The equivalent circle diameter refers to that obtained by the circular projection method.

[0070] Also, the average aspect ratio of the powder refers to measuring the length of the minor axis of the particles, that is, the minor axis length, in the above measurement, obtaining the value of (major axis length / minor axis length) for each particle, and taking the arithmetic mean of the values obtained for the above 500 particles. Here, unless otherwise specified, the minor axis length refers to the length of the minor axis constituting the particles in the case of (1) in the definition of the above particle size, and also refers to the thickness or height in the case of (2), respectively. In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience. And, unless otherwise specified, when the shape of the particles is specified, for example, in the case of the above particle size definition (1), the average particle size is the average major axis length, and in the case of the same definition (2), the average particle size is the average plate diameter. In the case of the same definition (3), the average particle size is the average diameter (also referred to as the average particle diameter, average particle size).

[0071] The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass, based on the total mass of the magnetic layer. A high filling rate of the ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving the recording density.

[0072] (Binder) The magnetic tape can be a coated magnetic tape and can contain a binder in the magnetic layer. The binder is one or more resins. As the binder, various resins commonly used as binders for coated magnetic recording media can be used. For example, as the binder, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl butyral, etc. A resin selected from polyvinyl alkylal resins can be used alone or a plurality of resins can be mixed and used. Among these, preferred are polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin. These resins may be homopolymers or copolymers. These resins can also be used as binders in the non-magnetic layer and / or backcoat layer described later. For the above binders, reference can be made to paragraphs 0028 to 0031 of JP-A-2010-24113. Also, the binder may be a radiation-curable resin such as an electron beam-curable resin. For radiation-curable resins, reference can be made to paragraphs 0044 to 0045 of JP-A-2011-048878. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as the weight average molecular weight. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.

[0073] (Hardening agent) A curing agent can also be used together with the binder. The curing agent can be a thermosetting compound which is a compound in which the curing reaction (crosslinking reaction) proceeds by heating in one form, and can be a photocurable compound in which the curing reaction (crosslinking reaction) proceeds by light irradiation in another form. The curing agent can be contained in the magnetic layer in a state where at least a part thereof has reacted (crosslinked) with other components such as the binder by the progress of the curing reaction during the manufacturing process of the magnetic tape. A preferable curing agent is a thermosetting compound, and polyisocyanate is suitable. For details of the polyisocyanate, reference can be made to paragraphs 0124 to 0125 of JP-A-2011-216149. The curing agent can be used in the composition for forming the magnetic layer in an amount of, for example, 0 to 80.0 parts by mass, preferably 50.0 to 80.0 parts by mass, based on 100.0 parts by mass of the binder, from the viewpoint of improving the strength of each layer such as the magnetic layer.

[0074] (Other components) The magnetic layer may contain one or more additives as required. Commercially available products can be appropriately selected and used as the additives according to the desired properties. Alternatively, a compound synthesized by a known method can also be used as the additive. An example of the additive is the above-mentioned curing agent. In addition, examples of the additives that can be contained in the magnetic layer include non-magnetic fillers, lubricants, dispersants, dispersion aids, fungicides, antistatic agents, antioxidants, and the like. The non-magnetic filler is synonymous with non-magnetic particles or non-magnetic powder. Examples of the non-magnetic filler include a non-magnetic filler that can function as a protrusion-forming agent and a non-magnetic filler that can function as an abrasive. Also, as the additive, known additives such as various polymers described in paragraphs 0030 to 0080 of JP-A-2016-051493 can be used.

[0075] As the protrusion-forming agent, which is one form of the non-magnetic filler, particles of inorganic substances can be used, particles of organic substances can be used, and composite particles of inorganic substances and organic substances can be used. Carbon black can also be used. Examples of inorganic substances include inorganic oxides such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like, and inorganic oxides are preferred. In one form, the protrusion-forming agent can be inorganic oxide-based particles. Here, "based" is used to mean "including." One form of inorganic oxide-based particles is particles made of inorganic oxide. Another form of inorganic oxide-based particles is composite particles of inorganic oxide and organic substances, and a specific example is a composite particle of inorganic oxide and polymer. Examples of such particles include, for example, particles in which a polymer is bonded to the surface of inorganic oxide particles.

[0076] The average particle size of the protrusion-forming agent can be, for example, 30 to 300 nm, and is preferably 40 to 200 nm. In addition, with regard to the shape of the protrusion-forming agent, it is considered that the closer the shape of the particles of the protrusion-forming agent contained in the magnetic layer is to a perfect sphere, the more likely the friction characteristics tend to change due to differences in head tilt angle. This is for the following reasons. If the head tilt angle is different, the contact state between the LTO8 head and the magnetic layer surface of the magnetic tape when measuring the friction force may change, so the pressure applied to the magnetic layer surface by contact with the LTO8 head may also change. It is considered that the closer the shape of the particles is to a perfect sphere, the smaller the indentation resistance that acts when pressure is applied, and therefore the more likely it is to be affected by changes in pressure. In contrast, if the shape of the particles is far from a perfect sphere, for example, a shape that is so-called an irregular shape, it is likely that a large indentation resistance acts when pressure is applied, and therefore the particles tend to be less susceptible to changes in pressure. In addition, it is considered that particles with an inhomogeneous particle surface and low surface smoothness also tend to be less susceptible to changes in pressure, because a large indentation resistance acts when pressure is applied. Therefore, using a protrusion-forming agent whose particle shape is far from a perfect sphere and / or using a protrusion-forming agent whose particle surface is non-uniform and has low surface smoothness increases the friction force F 45°The inventors consider that it may contribute to setting the standard deviation of the frictional force F within the ranges described above. Further, in one embodiment, a so-called amorphous-shaped material can also be used as the protrusion-forming agent.

[0077] Another form of the non-magnetic filler, the abrasive, is preferably a non-magnetic powder with a Mohs hardness greater than 8, more preferably a non-magnetic powder with a Mohs hardness of 9 or more. In contrast, the Mohs hardness of the protrusion-forming agent can be, for example, 8 or less or 7 or less. The maximum value of the Mohs hardness is 10 for diamond. Specifically, examples of the abrasive include powders such as alumina (e.g., Al2O3), silicon carbide, boron carbide (e.g., B4C), SiO2, TiC, chromium oxide (Cr2O3), cerium oxide, zirconium oxide (e.g., ZrO2), iron oxide, diamond, etc. Among them, alumina powders such as α-alumina and silicon carbide powders are preferred. Also, the average particle size of the abrasive can be, for example, in the range of 30 to 300 nm, preferably in the range of 50 to 200 nm.

[0078] Also, from the viewpoint that the protrusion-forming agent and the abrasive can better exhibit their functions, the content of the protrusion-forming agent in the magnetic layer is preferably 0.1 to 4.0 parts by mass, more preferably 0.3 to 3.5 parts by mass, and still more preferably 0.5 to 2.5 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. On the other hand, for the abrasive, the content in the magnetic layer is preferably 1.0 to 20.0 parts by mass, more preferably 3.0 to 15.0 parts by mass, and still more preferably 4.0 to 10.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.

[0079] As an example of an additive that can be used in a magnetic layer containing an abrasive, a dispersant described in paragraphs 0012 to 0022 of JP-A-2013-131285 can be cited as a dispersant for improving the dispersibility of the abrasive in the magnetic layer-forming composition. For the dispersant, reference can be made to paragraphs 0061 and 0071 of JP-A-2012-133837. The dispersant may be contained in the non-magnetic layer. For the dispersant that can be contained in the non-magnetic layer, reference can be made to paragraph 0061 of JP-A-2012-133837.

[0080] Further, as one form of the additive that can be contained in the magnetic layer, a compound having an ammonium salt structure of an alkyl ester anion represented by the following formula 1 can be cited.

[0081]

Chemical formula

[0082] (In formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms, and Z + represents an ammonium cation.)

[0083] The present inventor believes that the above compound can function as a lubricant. This point will be further described below. Lubricants can be broadly classified into fluid lubricants and boundary lubricants. The present inventor believes that the compound having an ammonium salt structure of an alkyl ester anion represented by the above formula 1 can function as a fluid lubricant. It is considered that a fluid lubricant can play a role of imparting lubricity to the magnetic layer by forming a liquid film on the surface of the magnetic layer itself. In order to control the frictional force F 45° and the standard deviation of the frictional force F, it is presumed that it is desirable for a fluid lubricant to form a liquid film on the surface of the magnetic layer. Further, the more stably the magnetic layer surface and the LTO8 head can slide during the frictional force measurement, the frictional force F 45°And the value of the standard deviation of the frictional force F can be made smaller. Regarding the liquid film of the fluid lubricant, from the viewpoint of enabling more stable sliding, it is considered desirable to have an appropriate amount of the fluid lubricant forming the liquid film on the surface of the magnetic layer. This is because if the amount of the liquid lubricant forming the liquid film on the surface of the magnetic layer is excessive, it is presumed that the surface of the magnetic layer and the LTO8 head will stick together, and the sliding stability will tend to decrease. Also, if the amount of the liquid lubricant forming the liquid film on the surface of the magnetic layer is excessive, it is presumed that, for example, the protrusions formed on the surface of the magnetic layer by the non-magnetic filler will be covered by the liquid film. This is also considered to be a factor that can cause the sliding stability to tend to decrease. Regarding the above points, the above compound contains an ammonium salt structure of an alkyl ester anion represented by Formula 1. A compound containing such a structure is considered to be able to play an excellent role as a fluid lubricant even in a relatively small amount. Therefore, incorporating the above compound into the magnetic layer leads to an improvement in the sliding stability between the surface of the magnetic layer of the magnetic tape and the LTO8 head, and the frictional force F 45° and is considered to contribute to controlling the standard deviation of the frictional force F.

[0084] Hereinafter, the above compound will be described in more detail.

[0085] In the present invention and this specification, unless otherwise specified, the groups described may have substituents or may be unsubstituted. Also, for a group having a substituent, "number of carbon atoms" means the number of carbon atoms excluding the carbon atoms of the substituent, unless otherwise specified. In the present invention and this specification, examples of the substituent include an alkyl group (e.g., an alkyl group having 1 to 6 carbon atoms), a hydroxy group, an alkoxy group (e.g., an alkoxy group having 1 to 6 carbon atoms), a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, etc.), a cyano group, an amino group, a nitro group, an acyl group, a carboxy group, a salt of a carboxy group, a sulfonic acid group, a salt of a sulfonic acid group, and the like.

[0086] A compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 can form a liquid film on the surface of the magnetic layer at least in part, and part of it can be contained inside the magnetic layer and move to the surface of the magnetic layer during sliding with the magnetic head to form a liquid film. Further, part of it can be contained in the non-magnetic layer described later, move to the magnetic layer, and further move to the surface of the magnetic layer to form a liquid film. Note that "alkyl ester anion" can also be referred to as "alkyl carboxylate anion".

[0087] In Formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms. The fluorinated alkyl group has a structure in which part or all of the hydrogen atoms constituting the alkyl group are substituted by fluorine atoms. The alkyl group or fluorinated alkyl group represented by R may have a linear structure, a branched structure, or a cyclic alkyl group or fluorinated alkyl group, and preferably has a linear structure. The alkyl group or fluorinated alkyl group represented by R may have a substituent or may be unsubstituted, and is preferably unsubstituted. The alkyl group represented by R can be represented by, for example, C n H 2n+1 -. Here, n represents an integer of 7 or more. Further, the fluorinated alkyl group represented by R can have a structure in which part or all of the hydrogen atoms constituting the alkyl group represented by, for example, C n H 2n+1 - are substituted by fluorine atoms. The number of carbon atoms of the alkyl group or fluorinated alkyl group represented by R is 7 or more, preferably 8 or more, more preferably 9 or more, still more preferably 10 or more, even more preferably 11 or more, still even more preferably 12 or more, and still even more preferably 13 or more. Further, the number of carbon atoms of the alkyl group or fluorinated alkyl group represented by R is preferably 20 or less, more preferably 19 or less, and still more preferably 18 or less.

[0088] In Formula 1, Z +represents an ammonium cation. The ammonium cation has, in detail, the following structure. In the present invention and this specification, "*" in the formula representing a part of a compound represents the bonding position of that part of the structure to an adjacent atom.

[0089]

Chemical formula

[0090] The nitrogen cation N of the ammonium cation + and the oxygen anion O in Formula 1 - can form a salt crosslinking group to form an ammonium salt structure of the alkyl ester anion represented by Formula 1. That a compound having an ammonium salt structure of the alkyl ester anion represented by Formula 1 is contained in the magnetic layer can be confirmed by analyzing the magnetic tape by X-ray photoelectron spectroscopy (ESCA: Electron Spectroscopy for Chemical Analysis), infrared spectroscopy (IR: infrared spectroscopy), etc.

[0091] In one form, Z + The ammonium cation represented by can be brought about, for example, by the nitrogen atom of a nitrogen-containing polymer becoming a cation. A nitrogen-containing polymer means a polymer containing a nitrogen atom. In the present invention and this specification, the terms "polymer" and "polymer" are used in a meaning that includes homopolymers and copolymers. The nitrogen atom can be included as an atom constituting the main chain of the polymer in one form, and can also be included as an atom constituting the side chain of the polymer in one form.

[0092] As one form of the nitrogen-containing polymer, polyalkyleneimine can be mentioned. Polyalkyleneimine is a ring-opening polymer of alkyleneimine and is a polymer having a plurality of repeating units represented by the following Formula 2.

[0093]

Chemical formula

[0094] The nitrogen atom N constituting the main chain in Formula 2 becomes a nitrogen cation N + so that the ammonium cation represented by Z in Formula 1 + can be obtained. And it can form an ammonium salt structure with an alkyl ester anion, for example, as follows.

[0095] [Chemical formula]

[0096] Hereinafter, Formula 2 will be described in more detail.

[0097] In Formula 2, R 1 and R 2 each independently represent a hydrogen atom or an alkyl group, and n1 represents an integer of 2 or more.

[0098] Examples of the alkyl group represented by R 1 or R 2 include, for example, an alkyl group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and still more preferably a methyl group. The alkyl group represented by R 1 or R 2 is preferably an unsubstituted alkyl group. R 1 and R 2Examples of the combination include a form in which one is a hydrogen atom and the other is an alkyl group, a form in which both are hydrogen atoms, and a form in which both are alkyl groups (the same or different alkyl groups). Preferably, both are hydrogen atoms. As the alkyleneimine that provides the polyalkyleneimine, the structure with the fewest carbon atoms forming the ring is ethyleneimine, and the number of carbon atoms in the main chain of the alkyleneimine (ethyleneimine) obtained by ring-opening of ethyleneimine is 2. Therefore, n1 in Formula 2 is 2 or more. n1 in Formula 2 can be, for example, 10 or less, 8 or less, 6 or less, or 4 or less. The polyalkyleneimine may be a homopolymer containing only the same structure as the repeating structure represented by Formula 2, or may be a copolymer containing two or more different structures as the repeating structure represented by Formula 2. The number average molecular weight of the polyalkyleneimine that can be used to form the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 can be, for example, 200 or more, preferably 300 or more, and more preferably 400 or more. Also, the number average molecular weight of the above polyalkyleneimine can be, for example, 10,000 or less, preferably 5,000 or less, and more preferably 2,000 or less.

[0099] In the present invention and this specification, the average molecular weight (weight average molecular weight and number average molecular weight) refers to a value measured by gel permeation chromatography (GPC) and determined by standard polystyrene conversion. The average molecular weight shown in the examples described later is, unless otherwise specified, a value obtained by converting the value measured under the following measurement conditions using GPC to standard polystyrene conversion (polystyrene conversion value). GPC apparatus: HLC-8220 (manufactured by Tosoh Corporation) Guard column: TSKguardcolumn Super HZM-H Column: TSKgel Super HZ 2000, TSKgel Super HZ 4000, TSKgel Super HZ-M (manufactured by Tosoh Corporation, 4.6 mm (inner diameter) × 15.0 cm, three columns connected in series) Eluent: containing tetrahydrofuran (THF) and a stabilizer (2,6-di-t-butyl-4-methylphenol) Eluent flow rate: 0.35 mL / min Column temperature: 40 °C Inlet temperature: 40 °C Refractive index (RI) measurement temperature: 40 °C Sample concentration: 0.3 mass% Sample injection volume: 10 μL

[0100] As another form of the nitrogen-containing polymer, polyallylamine can be mentioned. Polyallylamine is a polymer of allylamine and is a polymer having a plurality of repeating units represented by the following formula 3.

[0101]

Chemical formula

[0102] The nitrogen atom N constituting the amino group in the side chain in formula 3 becomes a nitrogen cation N + and can result in an ammonium cation represented by Z in formula 1 + And it can form an ammonium salt structure with an alkyl ester anion, for example, as follows.

[0103]

Chemical formula

[0104] The weight average molecular weight of polyallylamine that can be used to form a compound having an ammonium salt structure of the alkyl ester anion represented by formula 1 can be, for example, 200 or more, preferably 1,000 or more, and more preferably 1,500 or more. Also, the weight average molecular weight of the above polyallylamine can be, for example, 15,000 or less, preferably 10,000 or less, and more preferably 8,000 or less.

[0105] As a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1, a compound having a structure derived from a polyalkyleneimine or polyallylamine is included, which can be confirmed by analyzing the surface of the magnetic layer by time-of-flight secondary ion mass spectrometry (TOF-SIMS) or the like.

[0106] The compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 can be a salt with one or more fatty acids selected from the group consisting of a nitrogen-containing polymer and fatty acids having 7 or more carbon atoms and fluorinated fatty acids having 7 or more carbon atoms. The nitrogen-containing polymer forming the salt can be one or more nitrogen-containing polymers, and can be, for example, a nitrogen-containing polymer selected from the group consisting of polyalkyleneimine and polyallylamine. The fatty acids forming the salt can be one or more fatty acids selected from the group consisting of fatty acids having 7 or more carbon atoms and fluorinated fatty acids having 7 or more carbon atoms. The fluorinated fatty acid has a structure in which some or all of the hydrogen atoms constituting the alkyl group bonded to the carboxy group COOH in the fatty acid are substituted with fluorine atoms. For example, by mixing the nitrogen-containing polymer and the above fatty acids at room temperature, the salt formation reaction can proceed easily. Room temperature is, for example, about 20 to 25°C. In one form, one or more nitrogen-containing polymers and one or more fatty acids are used as components of the composition for forming the magnetic layer, and the salt formation reaction can be made to proceed by mixing them in the process of preparing the composition for forming the magnetic layer. Also, in one form, before preparing the composition for forming the magnetic layer, one or more nitrogen-containing polymers and one or more fatty acids are mixed to form a salt, and then this salt is used as a component of the composition for forming the magnetic layer to prepare the composition for forming the magnetic layer. This also applies to the case of forming a non-magnetic layer containing a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1. For example, regarding the magnetic layer, 0.1 to 10.0 parts by mass of a nitrogen-containing polymer can be used per 100.0 parts by mass of the ferromagnetic powder, and it is preferable to use 0.5 to 8.0 parts by mass of the nitrogen-containing polymer. The above fatty acids can be used, for example, in an amount of 0.05 to 10.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder, and it is preferable to use 0.1 to 5.0 parts by mass. Also, regarding the non-magnetic layer, 0.1 to 10.0 parts by mass of a nitrogen-containing polymer can be used per 100.0 parts by mass of the non-magnetic powder, and it is preferable to use 0.5 to 8.0 parts by mass of the nitrogen-containing polymer.The above fatty acids can be used, for example, in an amount of 0.05 to 10.0 parts by mass, preferably 0.1 to 5.0 parts by mass, per 100.0 parts by mass of the non-magnetic powder. When the nitrogen-containing polymer and the above fatty acids are mixed to form an ammonium salt of the alkyl ester anion represented by Formula 1, the nitrogen atom constituting the nitrogen-containing polymer may react with the carboxy group of the above fatty acids to form the following structure, and a form containing such a structure is also included in the above compound.

[0107]

Chemical formula

[0108] Examples of the above fatty acids include fatty acids having an alkyl group described as R in Formula 1 above and fluorinated fatty acids having a fluorinated alkyl group described as R in Formula 1 above.

[0109] The mixing ratio of the nitrogen-containing polymer and the above fatty acids used to form a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 is preferably in the range of 10:90 to 90:10, more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20, in terms of the mass ratio of the nitrogen-containing polymer to the above fatty acids. Further, the compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 is preferably contained in an amount of 0.01 part by mass or more, more preferably 0.1 part by mass or more, and even more preferably 0.5 part by mass or more, based on 100.0 parts by mass of the ferromagnetic powder in the magnetic layer. Here, the content of the above compound in the magnetic layer refers to the total amount of the amount forming a liquid film on the surface of the magnetic layer and the amount contained inside the magnetic layer. On the other hand, a large content of the ferromagnetic powder in the magnetic layer is preferable from the viewpoint of high-density recording. Therefore, from the viewpoint of high-density recording, it is preferable that the content of components other than the ferromagnetic powder is small. From this viewpoint, the content of the above compound in the magnetic layer is preferably 15.0 parts by mass or less, more preferably 10.0 parts by mass or less, and even more preferably 8.0 parts by mass or less, based on 100.0 parts by mass of the ferromagnetic powder. Further, the preferable range of the content of the above compound in the composition for forming a magnetic layer used to form the magnetic layer is the same.

[0110] As the lubricant, for example, a fatty acid amide that can function as a boundary lubricant can be used. A boundary lubricant is considered to be a lubricant that can reduce contact friction by adsorbing on the surface of the powder (for example, ferromagnetic powder) and forming a strong lubricating film. Examples of the fatty acid amide include amides of various fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid. Specifically, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, etc. can be mentioned. The fatty acid amide content in the magnetic layer is, for example, 0 to 3.0 parts by mass, preferably 0 to 2.0 parts by mass, and more preferably 0 to 1.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder. Also, the non-magnetic layer may contain a fatty acid amide. The fatty acid amide content in the non-magnetic layer is, for example, 0 to 3.0 parts by mass, preferably 0 to 1.0 parts by mass per 100.0 parts by mass of the non-magnetic powder. Regarding the dispersant, reference can be made to paragraphs 0061 and 0071 of JP-A-2012-133837. The dispersant may be added to the composition for forming the non-magnetic layer. Regarding the dispersant that can be added to the composition for forming the non-magnetic layer, reference can be made to paragraph 0061 of JP-A-2012-133837.

[0111] <Non-magnetic layer> Next, the non-magnetic layer will be described. The magnetic tape may have a magnetic layer directly on a non-magnetic support, or may have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. The non-magnetic powder used for the non-magnetic layer may be a powder of an inorganic substance (inorganic powder) or a powder of an organic substance (organic powder). Also, carbon black or the like can be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. These non-magnetic powders are available as commercial products and can also be manufactured by known methods. For details, reference can be made to paragraphs 0146 to 0150 of JP-A-2011-216149. Regarding the carbon black that can be used for the non-magnetic layer, reference can also be made to paragraphs 0040 to 0041 of JP-A-2010-24113. The content (filling rate) of the non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass, based on the total mass of the non-magnetic layer.

[0112] The non-magnetic layer can contain a binder and can also contain additives. Regarding other details such as the binder and additives of the non-magnetic layer, known techniques related to the non-magnetic layer can be applied. Also, for example, regarding the type and content of the binder, the type and content of the additives, etc., known techniques related to the magnetic layer can also be applied.

[0113] The non-magnetic layer of the magnetic tape is also intended to include a substantially non-magnetic layer containing a small amount of ferromagnetic powder, for example, as an impurity or intentionally, together with the non-magnetic powder. Here, the substantially non-magnetic layer means a layer having a residual magnetic flux density of 10 mT or less, a coercive force of 7.96 kA / m (100 Oe) or less, or a layer having a residual magnetic flux density of 10 mT or less and a coercive force of 7.96 kA / m (100 Oe) or less. The non-magnetic layer preferably has no residual magnetic flux density and coercive force.

[0114] <Non-magnetic support> Next, the non-magnetic support will be described. Examples of the non-magnetic support (hereinafter also simply referred to as "support") include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, etc. in advance.

[0115] <Back coat layer> The above tape may or may not have a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support. It is preferable that the back coat layer contains one or both of carbon black and inorganic powder. The back coat layer can contain a binder and can also contain additives. Regarding the details of the non-magnetic powder, binder, additives, etc. of the back coat layer, known techniques related to the back coat layer can be applied, and known techniques related to the magnetic layer and / or non-magnetic layer can also be applied. For example, the descriptions in paragraphs 0018 to 0020 of JP-A-2006-331625 and lines 65 to 38 of column 5 of US Patent No. 7,029,774 can be referred to for the back coat layer.

[0116] <Various thicknesses> Regarding the tape thickness (total thickness) of the magnetic tape, with the huge increase in the amount of information in recent years, there is a demand for increasing the recording capacity (high-capacity) of the magnetic tape. As a means for high-capacity, reducing the tape thickness of the magnetic tape and increasing the length of the magnetic tape accommodated per magnetic tape cartridge can be mentioned. From this point, the tape thickness of the above magnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm or less, still more preferably 5.4 μm or less, further more preferably 5.3 μm or less, and even more preferably 5.2 μm or less. Also, from the viewpoint of ease of handling, the thickness of the magnetic tape is preferably 3.0 μm or more, and more preferably 3.5 μm or more.

[0117] The tape thickness of the magnetic tape can be measured by the following method. Cut out 10 tape samples (for example, 5 to 10 cm in length) from an arbitrary part of the magnetic tape, stack these tape samples, and measure the thickness. The value obtained by dividing the measured thickness by 10 (the thickness per tape sample) is taken as the tape thickness. The above thickness measurement can be performed using a known measuring instrument capable of measuring thickness on the order of 0.1 μm.

[0118] The thickness of the non-magnetic support is preferably 3.0 to 5.0 μm. The thickness of the magnetic layer can be optimized according to the saturation magnetization amount of the magnetic head used, the head gap length, the band of the recording signal, etc. Generally, it is 0.01 μm to 0.15 μm. From the viewpoint of high-density recording, it is preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.1 μm. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic properties, and a configuration regarding a known multi-layer magnetic layer can be applied. The thickness of the magnetic layer in the case of separating into two or more layers is the total thickness of these layers. The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, and preferably 0.1 to 1.0 μm. The thickness of the backcoat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm. The various thicknesses such as the thickness of the magnetic layer can be obtained by the following method. After exposing the cross-section in the thickness direction of the magnetic tape by an ion beam, perform cross-section observation on the exposed cross-section using a scanning electron microscope or a transmission electron microscope. The various thicknesses can be obtained as the arithmetic mean of the thicknesses obtained at any two locations in the cross-section observation. Alternatively, the various thicknesses can also be obtained as the designed thickness calculated from the manufacturing conditions, etc.

[0119] <Manufacturing method> (Preparation of the composition for forming each layer) Compositions for forming a magnetic layer, a non-magnetic layer, or a backcoat layer generally contain a solvent together with the various components described above. As the solvent, various organic solvents commonly used for manufacturing a coated magnetic recording medium can be used. Among them, from the viewpoint of the solubility of the binder usually used for the coated magnetic recording medium, the composition for forming each layer preferably contains one or more ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran. The amount of the solvent in the composition for forming each layer is not particularly limited and can be the same as that of the composition for forming each layer of a normal coated magnetic recording medium. Further, the process of preparing the composition for forming each layer can usually include at least a kneading process, a dispersion process, and a mixing process provided as necessary before and after these processes. Each individual process may be divided into two or more stages. The components used in the preparation of the composition for forming each layer may be added at the beginning or during any of the processes. The individual components may be added in divided portions in two or more processes. For example, the binder may be added in divided portions in the kneading process, the dispersion process, and the mixing process for adjusting the viscosity after dispersion. Also, as described above, by using one or more nitrogen-containing polymers and one or more of the above fatty acids as components of the composition for forming the magnetic layer and mixing them in the preparation process of the composition for forming the magnetic layer, the salt formation reaction can be advanced. Further, in one embodiment, before preparing the composition for forming the magnetic layer, one or more nitrogen-containing polymers and one or more fatty acids are mixed to form a salt, and then this salt is used as a component of the composition for forming the magnetic layer to prepare the composition for forming the magnetic layer. This also applies to the preparation process of the composition for forming the non-magnetic layer. In one embodiment, in the process of preparing the composition for forming the magnetic layer, after preparing a dispersion containing a projection-forming agent (hereinafter referred to as "projection-forming agent liquid"), this projection-forming agent liquid can be mixed with one or more of the other components of the composition for forming the magnetic layer. For example, the preparation of the projection-forming agent liquid can be carried out by a known dispersion treatment such as ultrasonic treatment. The ultrasonic treatment can be, for example, 200 cc (1 cc = 1 cm 3)It can be carried out for about 1 to 300 minutes with an ultrasonic output of about 10 to 2000 watts per unit area. Further, filtration may be performed after the dispersion treatment. Refer to the following description for the filter used for filtration.

[0120] In the manufacturing process of the above magnetic tape, conventional known manufacturing techniques can be used in part or all of the processes. In the kneading process, it is preferable to use a kneader having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, an extruder, etc. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, in order to disperse the composition for forming each layer, glass beads and / or other beads can be used. As such dispersion beads, zirconia beads, titania beads, and steel beads which are high specific gravity dispersion beads are suitable. It is preferable to use these dispersion beads by optimizing the particle size (bead diameter) and the filling rate. A known disperser can be used. The composition for forming each layer may be filtered by a known method before being subjected to the coating process. Filtration can be performed, for example, by filter filtration. As the filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, etc.) can be used.

[0121] (Coating process) The magnetic layer can be formed by directly applying a composition for forming a magnetic layer, for example, onto a non-magnetic support, or by applying it in a multilayer sequentially or simultaneously with a composition for forming a non-magnetic layer. When performing an alignment treatment, the alignment treatment is performed on the coating layer in the alignment zone while the coating layer of the composition for forming a magnetic layer is in a wet state. Regarding the alignment treatment, various known techniques can be applied, including the description in paragraph 0052 of JP-A-2010-24113. For example, the vertical alignment treatment can be performed by a known method such as a method using a magnet with opposite poles facing each other. The magnetic field strength in the vertical alignment treatment can be, for example, 0.40 T (tesla) or more and 1.20 T or less. As the magnetic field strength increases, the value of the vertical SFD tends to decrease. In the alignment zone, the drying rate of the coating layer can be controlled by the temperature, air volume of the drying air, and / or the conveyance speed in the alignment zone. Also, the coating layer may be pre-dried before being conveyed to the alignment zone. The backcoat layer can be formed by applying a composition for forming a backcoat layer to the side of the non-magnetic support opposite to the side having (or to be provided with) the magnetic layer. For details of the coating for forming each layer, reference can be made to paragraph 0066 of JP-A-2010-231843.

[0122] (Other processes) After performing the above coating process, usually, a calendering process is performed to improve the surface smoothness of the magnetic tape. Regarding the calendering conditions, the calendering pressure is, for example, 200 to 500 kN / m, preferably 250 to 350 kN / m, the calendering temperature (the surface temperature of the calendering roll) is, for example, 70 to 120 °C, preferably 80 to 100 °C, and the calendering speed is, for example, 50 to 300 m / min, preferably 80 to 200 m / min. Also, the more a roll with a hard surface is used as the calendering roll and the more the number of stages is increased, the more the surface of the magnetic layer tends to be smoothed. For various other processes for manufacturing a magnetic tape, reference can be made to paragraphs 0067 to 0070 of JP-A-2010-231843. By going through various processes, a long magnetic tape reel can be obtained. The obtained magnetic tape reel is cut (slit) by a known cutting machine to the width of the magnetic tape to be accommodated in, for example, a magnetic tape cartridge. The above width can be determined according to the standard and is usually 1 / 2 inch. A servo pattern is usually formed on the magnetic tape obtained by slitting.

[0123] (Heat treatment) In one form, the magnetic tape can be a magnetic tape manufactured through the following heat treatment. Also, in another form, it can be a magnetic tape manufactured without going through the following heat treatment.

[0124] The heat treatment can be performed with the magnetic tape cut to the width determined according to the standard by slitting wound around a core member.

[0125] In one form, the above heat treatment is performed with the magnetic tape wound around a core member for heat treatment (hereinafter referred to as "heat treatment core"). After the heat treatment, the magnetic tape is wound onto the cartridge reel of the magnetic tape cartridge, and a magnetic tape cartridge with the magnetic tape wound on the cartridge reel can be produced. The core for heat treatment can be made of metal, resin, paper, etc. From the viewpoint of suppressing the occurrence of winding failures such as spoke winding, the material of the core for heat treatment is preferably a material with high rigidity. From this point, the core for heat treatment is preferably made of metal or resin. Further, as an index of rigidity, the flexural modulus of the material of the core for heat treatment is preferably 0.2 GPa (gigapascal) or more, and more preferably 0.3 GPa or more. On the other hand, since high-rigidity materials are generally expensive, using a core for heat treatment made of a material having a rigidity exceeding the rigidity that can suppress the occurrence of winding failures leads to an increase in cost. Considering the above points, the flexural modulus of the material of the core for heat treatment is preferably 250 GPa or less. The flexural modulus is a value measured in accordance with ISO (International Organization for Standardization) 178, and the flexural moduli of various materials are known. Further, the core for heat treatment can be a solid or hollow core member. In the case of a hollow shape, from the viewpoint of maintaining rigidity, the wall thickness is preferably 2 mm or more. Further, the core for heat treatment may or may not have a flange. Prepare a magnetic tape that is longer than the length to be finally accommodated in the magnetic tape cartridge as the magnetic tape wound around the core for heat treatment (hereinafter referred to as the "final product length"), and it is preferable to perform heat treatment by placing this magnetic tape wound around the core for heat treatment in a heat treatment environment. The length of the magnetic tape wound around the core for heat treatment is equal to or greater than the final product length, and from the viewpoint of ease of winding around the core for heat treatment and the like, it is preferably set to "final product length + α". This α is preferably 5 m or more from the viewpoint of the above-mentioned ease of winding. The tension during winding around the core for heat treatment is preferably 0.1 N (Newton) or more. Also, from the viewpoint of suppressing excessive deformation during manufacturing, the tension during winding around the core for heat treatment is preferably 1.5 N or less, and more preferably 1.0 N or less. The outer diameter of the core for heat treatment is preferably 20 mm or more, and more preferably 40 mm or more, from the viewpoints of ease of winding and suppression of coiling (curl in the longitudinal direction). Also, the outer diameter of the core for heat treatment is preferably 100 mm or less, and more preferably 90 mm or less. The width of the core for heat treatment may be equal to or greater than the width of the magnetic tape wound around this core. Further, when removing the magnetic tape from the core for heat treatment after heat treatment, in order to suppress the occurrence of unintended tape deformation during the removal operation, it is preferable to remove the magnetic tape from the core for heat treatment after the magnetic tape and the core for heat treatment are sufficiently cooled. The removed magnetic tape is preferably wound around another core (referred to as the "temporary winding core") once, and then the magnetic tape is wound from the temporary winding core onto the cartridge reel of the magnetic tape cartridge (the outer diameter is generally about 40 to 50 mm). Thereby, the relationship between the inner side and the outer side of the magnetic tape with respect to the core for heat treatment during heat treatment can be maintained, and the magnetic tape can be wound onto the cartridge reel of the magnetic tape cartridge. For details of the temporary winding core and the tension when winding the magnetic tape around this core, reference can be made to the previous description regarding the core for heat treatment. In the form of performing the above heat treatment on a magnetic tape having a length of "final product length + α", the length of "+α" can be cut off at an arbitrary stage. For example, in one form, the magnetic tape of the final product length can be wound from the temporary winding core onto the reel of the magnetic tape cartridge, and the remaining length of "+α" can be cut off.From the viewpoint of reducing the portion to be cut off and discarded, it is preferable that the above α is 20 m or less.

[0126] The specific form of the heat treatment performed in the state of being wound around the core member as described above will be described below. The ambient temperature at which the heat treatment is performed (hereinafter referred to as "heat treatment temperature") is preferably 40°C or higher, more preferably 50°C or higher. On the other hand, from the viewpoint of suppressing excessive deformation, the heat treatment temperature is preferably 75°C or lower, more preferably 70°C or lower. The absolute humidity by weight of the atmosphere in which the heat treatment is performed is preferably 0.1 g / kg Dry air or more, more preferably 1 g / kg Dry air or more. An atmosphere with an absolute humidity by weight in the above range is preferable because it can be prepared without using a special device for reducing moisture. On the other hand, from the viewpoint of suppressing the occurrence of dew condensation and reducing workability, the absolute humidity by weight is preferably 70 g / kg Dry air or less, more preferably 66 g / kg Dry air or less. The heat treatment time is preferably 0.3 hours or more, more preferably 0.5 hours or more. Also, from the viewpoint of production efficiency, the heat treatment time is preferably 48 hours or less.

[0127] Regarding the control of the standard deviation of the bending amount described above, the heat treatment temperature, heat treatment time, bending elastic modulus of the heat treatment core, and tension during winding around the heat treatment core all tend to make the value of the standard deviation of the bending amount smaller as the values are larger.

[0128] (Formation of servo pattern) "Formation of servo pattern" can also be said to be "recording of servo signal". The formation of the servo pattern will be described below.

[0129] The servo pattern is usually formed along the longitudinal direction of the magnetic tape. Examples of the method of control (servo control) using the servo signal include timing-based servo (TBS), amplitude servo, frequency servo, and the like.

[0130] As shown in ECMA (European Computer Manufacturers Association)-319 (June 2001), in a magnetic tape compliant with the LTO (Linear Tape-Open) standard (commonly referred to as an "LTO tape"), a timing-based servo system is adopted. In this timing-based servo system, the servo pattern is constituted by arranging a plurality of pairs of magnetic stripes (also called "servo stripes") that are non-parallel to each other continuously in the longitudinal direction of the magnetic tape. In the present invention and this specification, the "timing-based servo pattern" refers to a servo pattern that enables head tracking in the servo system of the timing-based servo method. As described above, the reason why the servo pattern is constituted by a pair of magnetic stripes that are non-parallel to each other is to inform the servo signal reading element passing over the servo pattern of its passing position. Specifically, the above-mentioned pair of magnetic stripes are formed such that their interval changes continuously along the width direction of the magnetic tape. By the servo signal reading element reading this interval, the relative position between the servo pattern and the servo signal reading element can be known. This relative position information enables tracking of the data track. For this purpose, usually, a plurality of servo tracks are set along the width direction of the magnetic tape on the servo pattern.

[0131] The servo band is constituted by a servo pattern that is continuous in the longitudinal direction of the magnetic tape. Usually, a plurality of such servo bands are provided on the magnetic tape. For example, in an LTO tape, the number is five. The region sandwiched between two adjacent servo bands is the data band. The data band is constituted by a plurality of data tracks, and each data track corresponds to each servo track.

[0132] Also, in one form, as disclosed in Japanese Patent Application Laid-Open No. 2004-318983, information indicating the number of each servo band (also referred to as "servo band ID (identification)" or "UDIM (Unique DataBand Identification Method) information") is embedded in each servo band. This servo band ID is recorded by shifting a specific one of a plurality of pairs of servo stripes in the servo band so that its position is relatively displaced in the longitudinal direction of the magnetic tape. Specifically, the shifting method of a specific one of the plurality of pairs of servo stripes is changed for each servo band. As a result, the recorded servo band ID is unique for each servo band, so that by simply reading one servo band with a servo signal reading element, the servo band can be uniquely identified.

[0133] Note that there is also a method of uniquely identifying a servo band that uses a staggered method as disclosed in ECMA-319 (June 2001). In this staggered method, a group of a pair of magnetic stripes (servo stripes) that are arranged continuously in the longitudinal direction of the magnetic tape and are not parallel to each other is recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. Since the combination of this shifting method between adjacent servo bands is unique throughout the magnetic tape, it is also possible to uniquely identify a servo band when reading a servo pattern with two servo signal reading elements.

[0134] Also, as disclosed in ECMA-319 (June 2001), information indicating the position in the longitudinal direction of the magnetic tape (also referred to as "LPOS (Longitudinal Position) information") is usually embedded in each servo band. This LPOS information is also recorded by shifting the positions of a pair of servo stripes in the longitudinal direction of the magnetic tape. However, unlike the UDIM information, the same signal is recorded in each servo band in this LPOS information.

[0135] It is also possible to embed other information different from the above UDIM information and LPOS information in the servo band. In this case, the information to be embedded may be different for each servo band like the UDIM information, or may be common to all servo bands like the LPOS information. Also, as a method of embedding information in the servo band, it is possible to adopt a method other than the above. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of a pair of servo stripes.

[0136] The servo pattern forming head is called a servo write head. The servo write head usually has a pair of gaps corresponding to the above pair of magnetic stripes, the number of which is the same as the number of servo bands. Usually, a core and a coil are connected to each pair of gaps, and by supplying a current pulse to the coil, a magnetic field generated in the core can cause a leakage magnetic field in the pair of gaps. When forming the servo pattern, by inputting a current pulse while running a magnetic tape on the servo write head, a magnetic pattern corresponding to the pair of gaps can be transferred to the magnetic tape to form a servo pattern. The width of each gap can be appropriately set according to the density of the servo pattern to be formed. The width of each gap can be set, for example, to 1 μm or less, 1 to 10 μm, 10 μm or more, etc.

[0137] Before forming a servo pattern on a magnetic tape, the magnetic tape is usually subjected to a demagnetization (erase) process. This erase process can be performed by applying a uniform magnetic field to the magnetic tape using a DC magnet or an AC magnet. There are two types of erase processes: DC (Direct Current) erase and AC (Alternating Current) erase. The AC erase is performed by gradually decreasing the intensity of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, the DC erase is performed by applying a magnetic field in one direction to the magnetic tape. There are further two methods for DC erase. The first method is a horizontal DC erase in which a magnetic field in one direction is applied along the longitudinal direction of the magnetic tape. The second method is a vertical DC erase in which a magnetic field in one direction is applied along the thickness direction of the magnetic tape. The erase process may be performed on the entire magnetic tape or for each servo band of the magnetic tape.

[0138] The direction of the magnetic field of the servo pattern to be formed is determined according to the direction of the erase. For example, when a horizontal DC erase is performed on the magnetic tape, the servo pattern is formed such that the direction of the magnetic field is opposite to the direction of the erase. Thereby, the output of the servo signal obtained by reading the servo pattern can be increased. As shown in Japanese Patent Laid-Open No. 2012-53940, when a magnetic pattern is transferred using the above gap to a vertically DC-erased magnetic tape, the servo signal obtained by reading the formed servo pattern has a monopolar pulse shape. On the other hand, when a magnetic pattern is transferred using the above gap to a horizontally DC-erased magnetic tape, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[0139] [Magnetic Tape Cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the above magnetic tape.

[0140] Details of the magnetic tape included in the above magnetic tape cartridge are as described above.

[0141] In a magnetic tape cartridge, generally, a magnetic tape is accommodated in a state of being wound around a reel inside a cartridge body. The reel is rotatably provided inside the cartridge body. As the magnetic tape cartridge, a single-reel type magnetic tape cartridge having one reel inside the cartridge body and a double-reel type magnetic tape cartridge having two reels inside the cartridge body are widely used. When the single-reel type magnetic tape cartridge is mounted on a magnetic tape device for recording and / or reproducing data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and wound around the reel on the magnetic tape device side. A magnetic head is disposed in the magnetic tape conveyance path from the magnetic tape cartridge to the take-up reel. The feeding and take-up of the magnetic tape are performed between the reel on the magnetic tape cartridge side (supply reel) and the reel on the magnetic tape device side (take-up reel). During this period, data recording and / or reproduction are performed by the contact and sliding between the magnetic head and the surface of the magnetic layer of the magnetic tape. On the other hand, in the double-reel type magnetic tape cartridge, both the supply reel and the take-up reel are provided inside the magnetic tape cartridge.

[0142] In one form, the magnetic tape cartridge can include a cartridge memory. The cartridge memory can be, for example, a non-volatile memory, in which head tilt angle adjustment information is already recorded or to which head tilt angle adjustment information is recorded. The head tilt angle adjustment information is information for adjusting the head tilt angle during magnetic tape travel in a magnetic tape device. For example, as the head tilt angle adjustment information, values of servo band intervals at each position in the longitudinal direction of the magnetic tape at the time of data recording can be recorded. For example, when reproducing data recorded on the magnetic tape, the value of the servo band interval is measured during reproduction, and the head tilt angle is changed by a control device of the magnetic tape device so that the absolute value of the difference from the servo band interval at the time of recording at the same longitudinal position recorded in the cartridge memory approaches zero. The head tilt angle can be, for example, the angle θ described above.

[0143] The above magnetic tape and magnetic tape cartridge can be suitably used in a magnetic tape device (in other words, a magnetic recording and reproducing system) that records and / or reproduces data at different head tilt angles. In such a magnetic tape device, in one form, the head tilt angle can be changed during magnetic tape travel to record and / or reproduce data. For example, the head tilt angle can be changed according to the dimension information in the width direction of the magnetic tape obtained during magnetic tape travel. Also, for example, there can be a usage form in which the head tilt angle in a certain recording and / or reproduction is changed from the head tilt angle in the recording and / or reproduction after the next time, and the head tilt angle is fixed without being changed during magnetic tape travel for each recording and / or reproduction. In any usage form, a magnetic tape with high running stability when recording and / or reproducing data at different head tilt angles is preferable.

[0144] [Magnetic Tape Device] One aspect of the present invention relates to a magnetic tape device including the above magnetic tape. In the magnetic tape device, recording of data on the magnetic tape and / or reproduction of data recorded on the magnetic tape can be performed, for example, by bringing the surface of the magnetic layer of the magnetic tape into contact with and sliding it against the magnetic head. The magnetic tape device can detachably include a magnetic tape cartridge according to one aspect of the present invention.

[0145] The above magnetic tape cartridge can be attached to a magnetic tape device equipped with a magnetic head and used for recording and / or reproducing data. In the present invention and this specification, the "magnetic tape device" shall mean a device capable of performing at least one of recording data on a magnetic tape and reproducing data recorded on the magnetic tape. Such a device is generally called a drive.

[0146] <Magnetic head> The above magnetic tape device can include a magnetic head. The configuration of the magnetic head and the angle θ which is the head tilt angle are as described above with reference to FIGS. 1 to 3. The magnetic head included in the magnetic tape device can be an LTO8 head in one form, can be an LTO head of another generation in another form, and can be a magnetic head other than an LTO head in yet another form. When the magnetic head includes a reproducing element, as the reproducing element, a magnetoresistive (MR) element capable of reading the information recorded on the magnetic tape with high sensitivity is preferable. As the MR element, various known MR elements (for example, Giant Magnetoresistive (GMR) elements, Tunnel Magnetoresistive (TMR) elements, etc.) can be used. Hereinafter, a magnetic head that performs recording of data and / or reproduction of the recorded data is also referred to as a "recording and reproducing head". An element for data recording (recording element) and an element for data reproduction (reproducing element) are collectively referred to as a "magnetic head element".

[0147] By performing data reproduction using a reproducing element with a narrow reproducing element width as the reproducing element, it is possible to reproduce highly densely recorded data with high sensitivity. From this perspective, the reproducing element width of the reproducing element is preferably 0.8 μm or less. The reproducing element width of the reproducing element can be, for example, 0.3 μm or more. However, from the above perspective, it is also preferable to be below this value. Here, the "reproducing element width" refers to the physical dimension of the reproducing element width. Such a physical dimension can be measured by an optical microscope, a scanning electron microscope, or the like.

[0148] When recording data and / or reproducing the recorded data, first, tracking using a servo signal can be performed. That is, by causing the servo signal reading element to follow a predetermined servo track, the magnetic head element can be controlled to pass over the target data track. The movement of the data track is performed by changing the servo track read by the servo signal reading element in the tape width direction. In addition, the recording and reproducing head can also perform recording and / or reproduction with respect to other data bands. In that case, the servo signal reading element can be moved to a predetermined servo band using the UDIM information described above, and tracking with respect to that servo band can be started.

[0149] Fig. 5 shows an example of the arrangement of data bands and servo bands. In Fig. 5, on the magnetic layer of the magnetic tape MT, a plurality of servo bands 1 are arranged sandwiched between guide bands 3. A plurality of regions 2 sandwiched between two servo bands are data bands. The servo pattern is a magnetized region and is formed by magnetizing a specific region of the magnetic layer with a servo write head. The region magnetized by the servo write head (the position where the servo pattern is formed) is defined by a standard. For example, in the LTO Ultrium format tape, which is an industry standard, a plurality of servo patterns inclined with respect to the tape width direction as shown in Fig. 6 are formed on the servo bands during the manufacture of the magnetic tape. Specifically, in Fig. 6, the servo frame SF on the servo band 1 is composed of a servo sub-frame 1 (SSF1) and a servo sub-frame 2 (SSF2). The servo sub-frame 1 is composed of an A burst (reference sign A in Fig. 6) and a B burst (reference sign B in Fig. 6). The A burst is composed of servo patterns A1 to A5, and the B burst is composed of servo patterns B1 to B5. On the other hand, the servo sub-frame 2 is composed of a C burst (reference sign C in Fig. 6) and a D burst (reference sign D in Fig. 6). The C burst is composed of servo patterns C1 to C4, and the D burst is composed of servo patterns D1 to D4. Such 18 servo patterns are arranged in sets of 5 and 4, in an arrangement of 5, 5, 4, 4, in the sub-frames and are used to identify the servo frame. Fig. 6 shows one servo frame for the purpose of explanation. However, actually, on the magnetic layer of the magnetic tape where head tracking of the timing-based servo method is performed, a plurality of servo frames are arranged in the running direction on each servo band. In Fig. 6, the arrow indicates the running direction of the magnetic tape. For example, an LTO Ultrium format tape usually has 5000 or more servo frames per meter of tape length on each servo band of the magnetic layer.

[0150] In the above magnetic tape device, the tilt angle of the head can be changed while the magnetic tape is running inside the magnetic tape device. The head tilt angle is, for example, the angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape. The angle θ is as described above. For example, by providing an angle adjustment unit for adjusting the angle of the module of the magnetic head in the recording and reproducing head unit of the magnetic head, the angle θ can be variably adjusted while the magnetic tape is running. Such an angle adjustment unit can include, for example, a rotation mechanism for rotating the module. Known techniques can be applied to the angle adjustment unit.

[0151] Regarding the head tilt angle during magnetic tape running, when the magnetic head includes a plurality of modules, for a randomly selected module, the angle θ described with reference to FIGS. 1 to 3 can be defined. θ which is the angle θ at the start of magnetic tape running initial can be set to 0° or more or more than 0°. θ initial The larger θ is, the larger the change amount of the effective distance between the servo signal reading elements with respect to the change amount of the angle θ becomes. Therefore, it is preferable from the viewpoint of the adjustment ability to adjust the effective distance between the servo signal reading elements in response to the dimensional change in the width direction of the magnetic tape. From this point, θ initial is preferably 1° or more, more preferably 5° or more, and even more preferably 10° or more. On the other hand, regarding the angle formed by the contact surface between the magnetic layer surface and the magnetic head when the magnetic tape runs and contacts the magnetic head (generally referred to as the "wrap angle"), keeping the deviation in the tape width direction small is effective for enhancing the uniformity in the tape width direction of the friction generated when the magnetic head and the magnetic tape contact during magnetic tape running. Also, enhancing the uniformity in the tape width direction of the above friction is desirable from the viewpoints of the position tracking performance and running stability of the magnetic head. From the viewpoint of reducing the deviation in the tape width direction of the above wrap angle, θ initial is preferably 45° or less, more preferably 40° or less, and even more preferably 35° or less.

[0152] Regarding the change in the angle θ during the running of the magnetic tape, for recording data on the magnetic tape and / or for reproducing the data recorded on the magnetic tape, while the magnetic tape is running in the magnetic tape device, the angle θ of the magnetic head changes from θ at the start of running initial When it changes, the maximum change amount Δθ of the angle θ during the running of the magnetic tape is the Δθ calculated by the following formula max and Δθ min Among them, it is the larger value. The maximum value of the angle θ during the running of the magnetic tape is θ max and the minimum value is θ min Here, "max" is an abbreviation of maximum, and "min" is an abbreviation of minimum. Δθ max = θ max - θ initial Δθ min = θ initial - θ min

[0153] In one form, Δθ can be more than 0.000°, and from the viewpoint of the adjustment ability to adjust the effective distance between the servo signal reading elements corresponding to the dimensional change in the width direction of the magnetic tape, it is preferably 0.001° or more, and more preferably 0.010° or more. Also, from the viewpoint of the ease of ensuring synchronization of the recorded data and / or the reproduced data among a plurality of magnetic head elements during data recording and / or reproduction, Δθ is preferably 1.000° or less, more preferably 0.900° or less, still more preferably 0.800° or less, even more preferably 0.700° or less, and even more preferably 0.600° or less.

[0154] In the examples shown in FIGS. 2 and 3, the axis of the element array is inclined toward the running direction of the magnetic tape. However, the present invention is not limited to such examples. In the above magnetic tape device, an embodiment in which the axis of the element array is inclined in the direction opposite to the running direction of the magnetic tape is also included in the present invention.

[0155] θ which is the head tilt angle at the start of running of the magnetic tape initialIt can be set by a control device of a magnetic tape device or the like. Regarding the head tilt angle during magnetic tape running, FIG. 7 is an explanatory diagram of a method for measuring the angle θ during magnetic tape running. The angle θ during magnetic tape running can be obtained, for example, by the following method. When obtaining the angle θ during magnetic tape running by the following method, during magnetic tape running, the angle θ is changed in the range of 0 to 90°. That is, if the axis of the element array is inclined toward the magnetic tape running direction at the start of magnetic tape running, the element array is not inclined so that the axis of the element array is inclined in the direction opposite to the magnetic tape running direction at the start of magnetic tape running during magnetic tape running. If the axis of the element array is inclined in the direction opposite to the magnetic tape running direction at the start of magnetic tape running, it is assumed that the element array is not inclined so that the axis of the element array is inclined toward the magnetic tape running direction at the start of magnetic tape running during magnetic tape running. Measure the phase difference (i.e., time difference) ΔT of the reproduction signals of the pair of servo signal reading elements 1 and 2. The measurement of ΔT can be performed by a measurement unit provided in the magnetic tape device. The configuration of such a measurement unit is known. The distance L between the central part of the servo signal reading element 1 and the central part of the servo signal reading element 2 can be measured by an optical microscope or the like. When the running speed of the magnetic tape is v, the distance in the magnetic tape running direction between the central parts of the two servo signal reading elements is Lsinθ, and the relationship Lsinθ = v×ΔT holds. Therefore, the angle θ during magnetic tape running can be calculated by the formula "θ = arcsin(vΔT / L)". In the right figure of FIG. 7, an example in which the axis of the element array is inclined toward the magnetic tape running direction is shown. In this example, the phase difference (i.e., time difference) ΔT of the reproduction signal of the servo signal reading element 2 with respect to the reproduction signal of the servo signal reading element 1 is measured. When the axis of the element array is inclined in the direction opposite to the magnetic tape running direction, θ can be obtained by the above method except that ΔT is measured as the phase difference (i.e., time difference) of the reproduction signal of the servo signal reading element 1 with respect to the reproduction signal of the servo signal reading element 2. Note that the measurement pitch of the angle θ, that is, the measurement interval of the angle θ in the longitudinal direction of the tape, can be selected to be a pitch suitable according to the frequency of the tape width deformation in the longitudinal direction of the tape. As an example, the measurement pitch can be, for example, 250 μm.

[0156] <Configuration of Magnetic Tape Device> The magnetic tape device 10 shown in FIG. 8 controls the recording and reproducing head unit 12 according to a command from the control device 11, and records and reproduces data on the magnetic tape MT. The magnetic tape device 10 has a configuration capable of detecting and adjusting the tension applied in the longitudinal direction of the magnetic tape from the spindle motors 17A and 17B that rotationally control the magnetic tape cartridge reel and the take-up reel, and their driving devices 18A and 18B. The magnetic tape device 10 has a configuration capable of loading the magnetic tape cartridge 13. The magnetic tape device 10 has a cartridge memory read / write device 14 capable of reading and writing the cartridge memory 131 in the magnetic tape cartridge 13. From the magnetic tape cartridge 13 attached to the magnetic tape device 10, the end of the magnetic tape MT or the leader pin is automatically pulled out by the loading mechanism or manually, and the magnetic tape MT passes over the recording and reproducing head through the guide rollers 15A and 15B in a direction in which the magnetic layer surface of the magnetic tape MT contacts the recording and reproducing head surface of the recording and reproducing head unit 12, and the magnetic tape MT is wound around the take-up reel 16. The rotation and torque of the spindle motor 17A and the spindle motor 17B are controlled by a signal from the control device 11, and the magnetic tape MT runs at an arbitrary speed and tension. For the control of the tape speed and the control of the head tilt angle, a servo pattern pre-formed on the magnetic tape can be used. For the detection of the tension, a tension detection mechanism may be provided between the magnetic tape cartridge 13 and the take-up reel 16. The control of the tension may be performed using the guide rollers 15A and 15B in addition to the control by the spindle motors 17A and 17B. The cartridge memory read / write device 14 is configured to be able to read and write information of the cartridge memory 131 according to an instruction from the control device 11. As a communication method between the cartridge memory read / write device 14 and the cartridge memory 131, for example, the ISO (International Organization for Standardization) 14443 method can be adopted.

[0157] The control device 11 includes, for example, a control unit, a storage unit, a communication unit, etc.

[0158] The recording / reproducing head unit 12 is composed of, for example, a recording / reproducing head, a servo tracking actuator for adjusting the position of the recording / reproducing head in the track width direction, a recording / reproducing amplifier 19, a connector cable for connecting to the control device 11, etc. The recording / reproducing head is composed of, for example, a recording element for recording data on a magnetic tape, a reproducing element for reproducing data on the magnetic tape, and a servo signal reading element for reading a servo signal recorded on the magnetic tape. In one magnetic head, one or more recording elements, reproducing elements, and servo signal reading elements are mounted, respectively. Or, each element may be separately provided in a plurality of magnetic heads according to the running direction of the magnetic tape.

[0159] The recording / reproducing head unit 12 is configured to be able to record data on the magnetic tape MT according to an instruction from the control device 11. Also, it is configured to be able to reproduce the data recorded on the magnetic tape MT according to an instruction from the control device 11.

[0160] The control device 11 has a mechanism for obtaining the running position of the magnetic tape from the servo signal read from the servo band during the running of the magnetic tape MT, and controlling the servo tracking actuator so that the recording element and / or the reproducing element is located at the target running position (track position). The control of this track position is performed, for example, by feedback control. The control device 11 has a mechanism for obtaining the servo band interval from the servo signals read from two adjacent servo bands during the running of the magnetic tape MT. The control device 11 can store the obtained servo band interval information in the storage unit inside the control device 11, the cartridge memory 131, an external connected device, etc. Further, the control device 11 can change the head tilt angle according to the dimension information in the width direction of the magnetic tape during running. Thereby, the effective distance between the servo signal reading elements can be made close to or equal to the interval of the servo bands. The above dimension information can be obtained by using a servo pattern formed in advance on the magnetic tape. For example, in this way, during the running of the magnetic tape in the magnetic tape device, the angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape can be changed according to the dimension information in the width direction of the magnetic tape obtained during running. The adjustment of the head tilt angle can be performed, for example, by feedback control. Further, for example, the adjustment of the head tilt angle can also be performed by the method described in Japanese Patent Application Laid-Open No. 2016-524774 (Patent Document 1) or US2019 / 0164573A1 (Patent Document 2).

Example

[0161] Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments shown in the examples. "Part" described below indicates "part by mass". Further, the processes and evaluations described below were performed in an environment at a temperature of 23°C ± 1°C unless otherwise specified. "eq" described below is equivalent, which is a unit that cannot be converted into SI units.

[0162] [Protrusion forming agent] The nucleating agents used for preparing the magnetic layer-forming composition for producing the magnetic tapes of the examples or comparative examples are as follows. Nucleating agent A and nucleating agent D are particles with low surface smoothness on the particle surface. The particle shape of nucleating agent B is so-called amorphous. The particle shape of nucleating agent C is a cocoon-like shape. The particle shape of nucleating agent E is a shape close to a perfect sphere. Nucleating agent A: ATLAS manufactured by Cabot Corporation (composite particles of silica and polymer), average particle size 100 nm Nucleating agent B: Asahi #52 manufactured by Asahi Carbon Co., Ltd. (carbon black), average particle size 60 nm Nucleating agent C: TGC6020N manufactured by Cabot Corporation (silica particles), average particle size 140 nm Nucleating agent D: Cataloid manufactured by JGC Catalysts & Chemicals Ltd. (aqueous dispersion sol of silica particles; as a nucleating agent for preparing the magnetic layer-forming composition, the dried product obtained by heating the above aqueous dispersion sol to remove the solvent is used), average particle size 120 nm Nucleating agent E: Quotron PL-10L manufactured by Fuso Chemical Industry Co., Ltd. (aqueous dispersion sol of silica particles; as a nucleating agent for preparing the magnetic layer-forming composition, the dried product obtained by heating the above aqueous dispersion sol to remove the solvent is used), average particle size 130 nm

[0163] [Ferromagnetic powder] In Table 1, "BaFe" is hexagonal barium ferrite powder (coercive force Hc: 196 kA / m, average particle size (average plate diameter) 24 nm).

[0164] In Table 1, "SrFe1" is hexagonal strontium ferrite powder prepared by the following method. 1707 g of SrCO3, 687 g of H3BO3, 1120 g of Fe2O3, 45 g of Al(OH)3, 24 g of BaCO3, 13 g of CaCO3, and 235 g of Nd2O3 were weighed and mixed in a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390 °C. While stirring the melt, the outlet provided at the bottom of the platinum crucible was heated, and the melt was discharged in a rod shape at about 6 g / second. The discharged liquid was rolled and rapidly cooled by a water-cooled double roller to produce an amorphous body. 280 g of the produced amorphous body was charged into an electric furnace and heated to 635 °C (crystallization temperature) at a heating rate of 3.5 °C / min, and held at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was roughly pulverized in a mortar, 1000 g of zirconia beads with a particle size of 1 mm and 800 ml of an acetic acid aqueous solution with a concentration of 1% were added to a glass bottle, and dispersion treatment was performed with a paint shaker for 3 hours. Then, the obtained dispersion was separated from the beads and put into a stainless steel beaker. The dispersion was allowed to stand at a liquid temperature of 100 °C for 3 hours for dissolution treatment of the glass component, then precipitated with a centrifuge and decantation was repeated for washing, and dried in a heating furnace at a furnace temperature of 110 °C for 6 hours to obtain hexagonal strontium ferrite powder. The average particle size of the hexagonal strontium ferrite powder obtained above was 18 nm, and the activation volume was 902 nm 3 , and the anisotropy constant Ku was 2.2×10 5 J / m 3 , and the mass magnetization σs was 49 A·m 2 / kg. 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above, and elemental analysis of the filtrate obtained by partially dissolving this sample powder under the dissolution conditions exemplified above was performed using an ICP analyzer to determine the surface layer content rate of neodymium atoms. Separately, 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above, and elemental analysis of the filtrate obtained by completely dissolving this sample powder under the dissolution conditions exemplified above was performed using an ICP analyzer to determine the bulk content rate of neodymium atoms. The content rate (bulk content rate) of neodymium atoms with respect to 100 atomic % of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic %. Also, the surface layer content rate of neodymium atoms was 8.0 atomic %. The ratio of the surface layer content rate to the bulk content rate, "surface layer content rate / bulk content rate", was 2.8, and it was confirmed that neodymium atoms were unevenly distributed on the surface of the particles. That the powder obtained above exhibits the crystal structure of hexagonal ferrite was confirmed by scanning with CuKα rays under the conditions of a voltage of 45 kV and an intensity of 40 mA and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above exhibited the crystal structure of a magnetoplumbite-type (M-type) hexagonal ferrite. Also, the crystal phase detected by X-ray diffraction analysis was a single phase of the magnetoplumbite type. PANalytical X’Pert Pro diffractometer, PIXcel detector Soller slits for the incident beam and the diffracted beam: 0.017 radians Fixed angle of the dispersion slit: 1 / 4 degree Mask: 10 mm Anti-scattering slit: 1 / 4 degree Measurement mode: continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degrees per second Measurement step: 0.05 degrees

[0165] In Table 1, "SrFe2" is hexagonal strontium ferrite powder produced by the following method. Weighed 1725 g of SrCO3, 666 g of H3BO3, 1332 g of Fe2O3, 52 g of Al(OH)3, 34 g of CaCO3, and 141 g of BaCO3, and mixed them with a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1380 °C, and while stirring the melt, the outlet provided at the bottom of the platinum crucible was heated, and the melt was discharged in a rod shape at about 6 g / second. The discharged liquid was rolled and rapidly cooled with a water-cooled double roll to produce an amorphous body. 280 g of the obtained amorphous material was charged into an electric furnace, heated to 645 °C (crystallization temperature), and held at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was roughly pulverized in a mortar, 1000 g of zirconia beads with a particle size of 1 mm and 800 ml of an acetic acid aqueous solution with a concentration of 1% were added to a glass bottle, and dispersion treatment was carried out with a paint shaker for 3 hours. Then, the obtained dispersion was separated from the beads and put into a stainless steel beaker. The dispersion was allowed to stand at a liquid temperature of 100 °C for 3 hours to dissolve the glass component, and then precipitated with a centrifuge and washed by repeating decantation, and dried in a heating furnace with a furnace temperature of 110 °C for 6 hours to obtain hexagonal strontium ferrite powder. The average particle size of the obtained hexagonal strontium ferrite powder was 19 nm, and the activation volume was 1102 nm 3 The anisotropy constant Ku was 2.0×10 5 J / m 3 The mass magnetization σs was 50 A·m 2 / kg.

[0166] In Table 1, "ε-iron oxide" is ε-iron oxide powder prepared by the following method. 8.3 g of iron(III) nitrate nonahydrate, 1.3 g of gallium(III) nitrate octahydrate, 190 mg of cobalt(II) nitrate hexahydrate, 150 mg of titanium(IV) sulfate, and 1.5 g of polyvinylpyrrolidone (PVP) were dissolved in 90 g of pure water. While stirring using a magnetic stirrer, 4.0 g of an aqueous ammonia solution with a concentration of 25% was added under the conditions of an air atmosphere and an ambient temperature of 25 °C, and stirring was carried out for 2 hours while maintaining the temperature condition of an ambient temperature of 25 °C. To the obtained solution, a citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added, and stirring was carried out for 1 hour. The powder precipitated after stirring was collected by centrifugation, washed with pure water, and dried in a heating furnace with a furnace temperature of 80 °C. 800 g of pure water was added to the dried powder, and the powder was dispersed in water again to obtain a dispersion. The obtained dispersion was heated to a liquid temperature of 50 °C, and 40 g of a 25% aqueous ammonia solution was added dropwise while stirring. After stirring for 1 hour while maintaining the temperature at 50 °C, 14 mL of tetraethoxysilane (TEOS) was added dropwise, and the mixture was stirred for 24 hours. 50 g of ammonium sulfate was added to the obtained reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating furnace at a furnace temperature of 80 °C for 24 hours to obtain a precursor of the ferromagnetic powder. The obtained precursor of the ferromagnetic powder was loaded into a heating furnace with a furnace temperature of 1000 °C under an air atmosphere and subjected to a heat treatment for 4 hours. The heat-treated precursor of the ferromagnetic powder was put into a 4 mol / L aqueous sodium hydroxide (NaOH) solution, and the liquid temperature was maintained at 70 °C and stirred for 24 hours to remove the silicate compound, which is an impurity, from the heat-treated precursor of the ferromagnetic powder. Thereafter, the ferromagnetic powder from which the silicate compound had been removed was collected by centrifugation and washed with pure water to obtain the ferromagnetic powder. When the composition of the obtained ferromagnetic powder was confirmed by high-frequency inductively coupled plasma optical emission spectrometry (ICP-OES: Inductively Coupled Plasma-Optical Emission Spectrometry), it was found to be Ga, Co, and Ti-substituted ε-iron oxide (ε-Ga 0.28 Co 0.05 Ti 0.05 Fe 1.62 O3). Also, X-ray diffraction analysis was performed under the same conditions as those described above for SrFe1, and from the peaks of the X-ray diffraction pattern, it was confirmed that the obtained ferromagnetic powder had a single-phase crystal structure of the ε-phase (crystal structure of ε-iron oxide) that did not contain the crystal structures of the α-phase and γ-phase. The average particle size of the obtained ε-iron oxide powder was 12 nm, the activation volume was 746 nm 3 , the anisotropy constant Ku was 1.2×10 5 J / m 3 , and the mass magnetization σs was 16 A·m 2 / kg.

[0167] The activation volume and anisotropy constant Ku of the above hexagonal strontium ferrite powder and ε-iron oxide powder are values obtained by the method described above using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) for each ferromagnetic powder. The mass magnetization σs is a value measured at a magnetic field strength of 15 kOe using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.).

[0168] [Example 1] [Composition for forming magnetic layer]

[0169] (Magnetic liquid) Ferromagnetic powder (see Table 1): 100.0 parts Oleic acid: 2.0 parts Vinyl chloride copolymer (MR-104 manufactured by Kaneka Corporation): 10.0 parts SO3Na group-containing polyurethane resin: 4.0 parts (Weight average molecular weight 70000, SO3Na group: 0.07 meq / g) Additive A: 10.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts (Abrasive liquid) α-Alumina (average particle size: 110 nm): 6.0 parts Vinyl chloride copolymer (MR110 manufactured by Kaneka Corporation): 0.7 part Cyclohexanone: 20.0 parts (Projection forming agent liquid) Projection forming agent (see Table 1): See Table 1 Methyl ethyl ketone: 9.0 parts Cyclohexanone: 6.0 parts (Other components) Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 300): 2.0 parts Stearic acid: 0.5 part Stearamide: 0.3 part Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Coronate (registered trademark) L manufactured by Tosoh Corporation): 3.0 parts

[0170] The above-mentioned additive A is a polymer synthesized by the method described in paragraphs 0115 to 0123 of JP-A-2016-051493.

[0171] <Composition for forming non-magnetic layer> Non-magnetic inorganic powder (α-iron oxide): 80.0 parts (Average particle size: 0.15 μm, average aspect ratio: 7, BET (Brunauer-Emmett-Teller) specific surface area: 52 m 2 / g) Carbon black (average particle size: 20 nm): 20.0 parts Electron beam curable vinyl chloride copolymer: 13.0 parts Electron beam curable polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Butyl stearate: 2.0 parts Stearic acid: 1.0 part

[0172] <Composition for forming backcoat layer> Non-magnetic inorganic powder (α-iron oxide): 80.0 parts (Average particle size: 0.15 μm, average aspect ratio: 7, BET specific surface area: 52 m 2 / g) Carbon black (average particle size: 20 nm): 20.0 parts Carbon black (average particle size: 100 nm): 3.0 parts Vinyl chloride copolymer: 13.0 parts Sulfonic acid group-containing polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Stearic acid: 3.0 parts Polyisocyanate (Coronate (registered trademark) L manufactured by Tosoh Corporation): 5.0 parts Methyl ethyl ketone: 400.0 parts

[0173] <Preparation of the composition for forming each layer> The composition for forming the magnetic layer was prepared by the following method. After kneading and diluting the components of the above magnetic liquid with an open kneader, using zirconia (ZrO2) beads with a particle size of 0.5 mm (hereinafter referred to as "Zr beads") in a horizontal bead mill disperser, with a bead filling rate of 80% by volume and a rotor tip peripheral speed of 10 m / sec, the residence time per pass was set to 2 minutes, and a dispersion treatment of 12 passes was performed. For the abrasive liquid, after mixing the components of the above abrasive liquid, it was put into a vertical sand mill disperser together with Zr beads with a particle size of 1 mm, adjusted so that the bead volume / (abrasive liquid volume + bead volume) was 60%, and subjected to a sand mill dispersion treatment for 180 minutes. After the treatment, the liquid was taken out and subjected to ultrasonic dispersion filtration treatment using a flow-type ultrasonic dispersion filtration device. The protrusion-forming agent liquid was prepared by mixing the components of the above protrusion-forming agent liquid and then subjecting it to ultrasonic treatment (dispersion treatment) for 60 minutes with an ultrasonic output of 500 watts per 200 cc using a horn-type ultrasonic disperser, and filtering the resulting dispersion liquid through a filter with a pore size of 0.5 μm. The magnetic liquid, abrasive liquid, protrusion-forming agent liquid, and the other above components were introduced into a dissolver stirrer, stirred at a peripheral speed of 10 m / sec for 30 minutes, then subjected to a 3-pass treatment at a flow rate of 7.5 kg / min using a flow-type ultrasonic disperser, and then filtered through a filter with a pore size of 1 μm to prepare the composition for forming the magnetic layer.

[0174] The composition for forming the non-magnetic layer was prepared by the following method. The above components excluding the lubricants (butyl stearate and stearic acid) were kneaded and diluted with an open kneader, and then subjected to a dispersion treatment using a horizontal bead mill disperser. Thereafter, the lubricants (butyl stearate and stearic acid) were added and stirred using a dissolver stirrer to perform a mixing treatment to prepare the composition for forming the non-magnetic layer.

[0175] The composition for forming the backcoat layer was prepared by the following method. The above components except for the lubricant (stearic acid), polyisocyanate and methyl ethyl ketone (400.0 parts) were kneaded and diluted by an open kneader, and then dispersed by a horizontal bead mill disperser. Thereafter, the lubricant (stearic acid), polyisocyanate and methyl ethyl ketone (400.0 parts) were added and stirred by a dissolver stirrer for mixing treatment to prepare a composition for forming a back coat layer.

[0176] <Manufacture of Magnetic Tape and Magnetic Tape Cartridge> On a biaxially stretched polyethylene naphthalate support with a thickness of 4.1 μm, a composition for forming a non-magnetic layer was applied so that the thickness after drying would be 0.7 μm, and after drying, an electron beam was irradiated at an accelerating voltage of 125 kV to have an energy of 40 kGy. A composition for forming a magnetic layer was applied thereon so that the thickness after drying would be 0.1 μm to form a coating layer. While this coating layer was in a wet state, in the alignment zone, a magnetic field with the magnetic field strength shown in Table 1 was applied in a direction perpendicular to the surface of the coating layer for vertical alignment treatment, and then the coating layer was dried to form a magnetic layer. Thereafter, a composition for forming a back coat layer was applied to the surface of the support opposite to the surface on which the non-magnetic layer and the magnetic layer were formed so that the thickness after drying would be 0.3 μm, and dried to form a back coat layer. Thereafter, calendering was performed at a calendering speed of 80 m / min, a linear pressure of 294 kN / m, and a calendering temperature (the surface temperature of the calender roll) of 80 °C using a seven-stage calender roll composed only of metal rolls. Thereafter, heat treatment was performed for 36 hours in an environment with an ambient temperature of 70 °C. After the heat treatment, it was slit to a width of 1 / 2 inch, and the surface of the magnetic layer was cleaned with a tape cleaning device attached to a device having a feeding and winding device for the slit product so that a non-woven fabric and a razor blade would press against the surface of the magnetic layer to obtain a magnetic tape. A servo signal was recorded on the magnetic layer of the obtained magnetic tape by a commercially available servo writer, thereby obtaining a magnetic tape having a data band, a servo band, and a guide band in an arrangement conforming to the LTO (Linear Tape-Open) Ultrium format, and having a servo pattern (timing-based servo pattern) in an arrangement and shape conforming to the LTO Ultrium format on the servo band. The servo pattern thus formed is a servo pattern conforming to the descriptions of JIS (Japanese Industrial Standards) X6175:2006 and Standard ECMA-319 (June 2001). The total number of servo bands is 5, and the total number of data bands is 4. The magnetic tape (length 960 m) on which the servo signal was thus recorded was wound around the reel of a magnetic tape cartridge (LTO Ultrium8 data cartridge), and at its end, a leader tape conforming to item 9 of Section 3 of Standard ECMA (European Computer Manufacturers Association)-319 (June 2001) was joined by a commercially available splicing tape. Thus, a magnetic tape cartridge with the magnetic tape wound around the reel was produced.

[0177] That the magnetic layer of the magnetic tape contains a compound containing an ammonium salt structure of an alkyl ester anion represented by Formula 1 formed by polyethyleneimine and stearic acid can be confirmed by the following method. A sample is cut out from the magnetic tape, and X-ray photoelectron spectroscopy is performed on the surface of the magnetic layer (measurement area: 300 μm × 700 μm) using an ESCA apparatus. Specifically, wide scan measurement is performed by the ESCA apparatus under the following measurement conditions. In the measurement results, peaks are confirmed at the positions of the binding energy of the ester anion and the binding energy of the ammonium cation. Apparatus: AXIS-ULTRA manufactured by Shimadzu Corporation Excitation X-ray source: Monochromatic Al-Kα ray Scan range: 0 to 1200 eV Pass energy: 160 eV Energy resolution: 1 eV / step Capture time: 100 ms / step Number of integrations: 5 In addition, a 3-cm long sample piece was cut out from the magnetic tape, and ATR-FT-IR (Attenuated total reflection - fourier transform - infrared spectrometer) measurement (reflection method) was performed on the surface of the magnetic layer. In the measurement results, the wave numbers corresponding to the absorption of COO - (1540 cm -1 or 1430 cm -1 ), and the wave number corresponding to the absorption of ammonium cation (2400 cm -1 ) showed absorption.

[0178] [Examples 2 to 27, Comparative Examples 1 to 34] Magnetic tapes and magnetic tape cartridges were obtained by the method described for Example 1, except that the items shown in Table 1 were changed as shown in Table 1. In Comparative Examples 1 to 11, since no vertical alignment treatment was performed, "none" was described in the column of "vertical alignment treatment conditions" in Table 1. For Examples 23 to 27 and Comparative Examples 30 to 34, the steps after servo signal recording were changed as follows. That is, heat treatment was performed after servo signal recording. On the other hand, for Examples 1 to 22 and Comparative Examples 1 to 29, since such heat treatment was not performed, "none" was described in the column of "heat treatment conditions" in Table 1. For Examples 23 to 27 and Comparative Examples 30 to 34, the magnetic tape (length 970 m) after recording the servo signal as described for Example 1 was wound around a heat treatment core, and heat treatment was performed in the state of being wound around this core. As the heat treatment core, a solid resin core member (outer diameter: 50 mm) with a flexural modulus of the value shown in Table 1 was used, and the tension during winding was set to the value shown in Table 1. The heat treatment temperature and heat treatment time in the heat treatment were set to the values shown in Table 1. The absolute humidity by weight of the atmosphere in which the heat treatment was performed was 10 g / kg Dry air. After the above heat treatment, after the magnetic tape and the heat treatment core are sufficiently cooled, the magnetic tape is removed from the heat treatment core, wound around a temporary winding core, and then, from the temporary winding core, a magnetic tape of the final product length (960 m) is wound around a reel of a magnetic tape cartridge (LTO Ultrium8 data cartridge), and the remaining 10 m is cut off. At the end on the cut-off side, a leader tape conforming to item 9 of Standard ECMA (European Computer Manufacturers Association)-319 (June 2001) Section 3 is joined by a commercially available splicing tape. As the temporary winding core, a solid core member made of the same material as the heat treatment core and having the same outer diameter was used, and the tension during winding was set to 0.6 N. Thus, a magnetic tape cartridge in which the magnetic tape is wound around a reel was produced.

[0179] Regarding the above Examples and Comparative Examples, six magnetic tape cartridges were produced respectively. One was used for the following evaluation of running stability, another was used for the following evaluation of electromagnetic conversion characteristics, and the other four were used for the following evaluations (1) to (4) of the magnetic tape respectively.

[0180] [Evaluation of Running Stability] In an environment of temperature 32°C and relative humidity 80%, the running stability was evaluated by the following method. Using each magnetic tape cartridge of the Examples and Comparative Examples, data recording and reproduction were performed using a magnetic tape apparatus having the configuration shown in FIG. 8. The arrangement order of the modules included in the recording / reproducing head in the recording / reproducing head unit is "recording module - reproducing module - recording module" (total number of modules: 3). The number of magnetic head elements in each module is 32 (Ch0 to Ch31), and these magnetic head elements are sandwiched between a pair of servo signal reading elements to form an element array. The reproducing element width of the reproducing elements included in the reproducing module is 0.8 μm. By the following method, data recording and playback were performed, and the running stability during playback was evaluated. This was carried out a total of 4 times by sequentially changing the head tilt angle in the order of 0°, 15°, 30°, and 45°. The above head tilt angle is the angle θ formed by the axis of the element array of the playback module with respect to the width direction of the magnetic tape at the start of each run. The angle θ was set by the control device of the magnetic tape apparatus at the start of each magnetic tape run, and the head tilt angle was fixed during each magnetic tape run. Set a magnetic tape cartridge in the magnetic tape apparatus and load the magnetic tape. Next, while performing servo tracking, the recording and playback head unit records pseudo-random data having a specific data pattern on the magnetic tape. The tension in the longitudinal direction of the tape at that time shall be a constant value. Simultaneously with the recording of the data, the value of the servo band interval over the entire length of the tape is measured every 1 m in the longitudinal position and recorded in the cartridge memory. Next, while performing servo tracking, the recording and playback head unit plays back the data recorded on the magnetic tape. The tension in the longitudinal direction of the tape at that time shall be a constant value. Based on the servo signal obtained by the servo signal reading element during the above playback, the running stability was evaluated using the standard deviation of the reading position PES (Position Error Signal) in the width direction (hereinafter referred to as "σPES"). PES is obtained by the following method. To obtain PES, the dimensions of the servo pattern are required. The standards for the dimensions of the servo pattern vary depending on the generation of LTO. Therefore, first, using a magnetic force microscope or the like, the average distance AC between the corresponding 4 stripes of the A burst and the C burst, and the azimuth angle α of the servo pattern are measured. Define the average time a between five stripes corresponding to A bursts and B bursts over the length of one LPOS word. Define the average time b between four stripes corresponding to A bursts and C bursts over the length of one LPOS word. At this time, the value defined by AC×(1 / 2 - a / b) / (2×tan(α)) is the read position PES (Position Error Signal) in the width direction based on the servo signal obtained by the servo signal reading element over the length of one LPOS word. For the magnetic tape, the end on the side wound around the reel of the magnetic tape cartridge is called the inner end, and the end on the opposite side is called the outer end. With the outer end set to 0 m, the standard deviation (σPES) of PES obtained by the above method was calculated for the region in the longitudinal direction of the tape with a length ranging from 30 m to 200 m. The arithmetic mean of σPES obtained for a total of four recordings and reproductions is shown in the column of "σPES" in Table 1. If σPES is less than 70 nm, it can be determined that the running stability is excellent.

[0181] [Evaluation of Electromagnetic Conversion Characteristics (SNR: Signal - to - Noise Ratio)] The magnetic tapes taken out from each of the magnetic tape cartridges of the examples and comparative examples were respectively attached to a 1 / 2 - inch reel tester, and the electromagnetic conversion characteristics (SNR: Signal - to - Noise Ratio) were evaluated by the following method. In the following evaluation, the head tilt angle was set to 0°. In an environment with a temperature of 23°C and a relative humidity of 50%, recording and playback were performed 10 passes in the longitudinal direction of the magnetic tape with a tension of 0.70 N. The relative speed between the magnetic tape and the magnetic head was 6 m / s. For recording, a MIG (Metal-in-gap) head (gap length 0.15 μm, track width 1.0 μm) was used as the recording head, and the recording current was set to the optimum recording current for each magnetic tape. For playback, a GMR (Giant-magnetoresistive) head (element thickness 15 nm, shield interval 0.1 μm, playback element width 0.8 μm) was used as the playback head. A signal with a linear recording density of 350 kfci was recorded, and the playback signal was measured with a spectrum analyzer manufactured by Shibasoku Corporation, and the SNR was obtained from the measurement results. In Table 1, the SNR is shown as a relative value with respect to Comparative Example 12. The unit kfci is a unit of linear recording density (not convertible to the SI unit system). As the signal, a portion where the signal was sufficiently stable after the start of magnetic tape running was used.

[0182] [Evaluation of Magnetic Tape] (1) Perpendicular SFD Sample pieces with a size of 3.6 cm × 3.2 cm (area: 11.5 cm 2 ) were cut out from each magnetic tape of the examples and comparative examples. For this sample piece, using a TM-VSM6050-SM type manufactured by Tamagawa Seiki Co., Ltd. as a vibrating sample magnetometer, the perpendicular SFD (measurement temperature 25°C) was determined by the method described above.

[0183] (2) Frictional Force The magnetic tape was taken out from each magnetic tape cartridge of the examples and comparative examples, and in an environment with a temperature of 32°C and a relative humidity of 80%, the frictional force F 45° and the standard deviation of the frictional force F were determined by the method described above. As the LTO8 head, a commercially available LTO8 head (manufactured by IBM) was used.

[0184] (3) Standard Deviation of the Amount of Curvature in the Longitudinal Direction of the Magnetic Tape The magnetic tape was taken out from the magnetic tape cartridge, and the standard deviation of the amount of curvature in the longitudinal direction of the magnetic tape was determined by the method described above.

[0185] (4) Tape thickness Ten tape samples (5 cm in length) were cut out from arbitrary portions of the magnetic tapes taken from each of the magnetic tape cartridges of the examples and comparative examples, and these tape samples were stacked and the thickness was measured. The thickness was measured using a digital thickness gauge of a Millimar 1240 compact amplifier and a Millimar 1301 induction probe manufactured by MARH. The value obtained by dividing the measured thickness by 10 (thickness per tape sample) was taken as the tape thickness. For each magnetic tape, the tape thickness was 5.2 μm in all cases.

[0186] The above results are shown in Table 1 (Tables 1-1 to 1-2).

[0187]

Table 1-1

[0188]

Table 1-2

[0189] From the results shown in Table 1, it can be confirmed that the magnetic tapes of the examples, in which the frictional force F 45° measured in an environment of a temperature of 32 ° C and a relative humidity of 80% and the standard deviation of the frictional force F are both within the ranges described above, showed excellent running stability when the magnetic tape was run at different head tilt angles in a high-temperature and high-humidity environment. Furthermore, from the results shown in Table 1, it can also be confirmed that the magnetic tapes of the examples in which the vertical SFD is 1.5 or less exhibited excellent electromagnetic conversion characteristics.

Industrial Applicability

[0190] One aspect of the present invention is useful in the technical field of various data storage.

Claims

1. A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the perpendicular direction reversal magnetic field distribution SFD of the magnetic tape is 1.5 or less, in an environment of a temperature of 32 °C and a relative humidity of 80%, The frictional force F on the surface of the magnetic layer with respect to the LTO8 head measured at a head tilt angle of 45° ４５° is 4 gf or more and 15 gf or less, and a magnetic tape, wherein the standard deviation of the frictional force F on the surface of the magnetic layer with respect to an LTO8 head measured at head tilt angles of 0°, 15°, 30° and 45° respectively is 10 gf or less.

2. The magnetic tape according to claim 1, wherein the standard deviation of the F is 2 gf or more and 10 gf or less.

3. The magnetic tape according to claim 1 or 2, wherein the perpendicular direction reversal magnetic field distribution SFD of the magnetic tape is 0.5 or more and 1.5 or less.

4. The magnetic tape according to any one of claims 1 to 3, wherein the standard deviation of the amount of curvature in the longitudinal direction of the magnetic tape is 5 mm / m or less.

5. The magnetic tape according to any one of claims 1 to 4, wherein the magnetic layer contains inorganic oxide-based particles.

6. The magnetic tape according to claim 5, wherein the inorganic oxide-based particles are composite particles of an inorganic oxide and a polymer.

7. The magnetic tape according to any one of claims 1 to 4, wherein the magnetic layer contains carbon black.

8. The magnetic tape according to any one of claims 1 to 7, having a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

9. The magnetic tape according to any one of claims 1 to 8, having a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support.

10. The magnetic tape according to any one of claims 1 to 9, wherein the tape thickness is 5.2 μm or less.

11. A magnetic tape cartridge containing the magnetic tape according to any one of claims 1 to 10.

12. A magnetic tape device containing the magnetic tape according to any one of claims 1 to 10.

13. Further including a magnetic head, wherein the magnetic head has a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, The magnetic tape device according to claim 12, wherein the magnetic tape device changes an angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape during running of the magnetic tape in the magnetic tape device.

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