Magnetic tape, magnetic tape cartridge, and magnetic tape device

Abstract

To provide a magnetic tape that offers excellent running stability when recording and / or playing back with the head tilted in a high-temperature, high-humidity environment. [Solution] A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder. In an environment of 35°C and 80% relative humidity, the magnetic tape is slid back and forth 1000 times against an LTO8 head at a head tilt angle of 15°. The change rate of the area ratio of protrusions with a height of 5 nm to 10 nm, determined by measuring a 5 μm × 5 μm measurement area on the surface of the magnetic layer using an atomic force microscope, is 10.0% or less. A magnetic tape cartridge and magnetic tape device including the above magnetic tape.

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, that is, magnetic tapes, are mainly used (see, for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Recording data 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.

[0005] In order to improve the accuracy with which the magnetic head follows the data band of the magnetic tape in the above recording and / or reproduction, 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 servo signals to acquire dimensional information (contraction, expansion, etc.) in the width direction of the magnetic tape while it is running, and to change the angle at which the axial direction of the magnetic head module is tilted relative to the width direction of the magnetic tape (hereinafter also referred to as the "head tilt angle") according to the acquired dimensional information (see Patent Documents 1 and 2, for example, paragraphs 0059-0067 and 0084 of Patent Document 1). During recording or playback, if the magnetic head for recording or playing back data is misaligned from the target track position due to width deformation of the magnetic tape, phenomena such as overwriting of recorded data or playback failures may occur. The inventors believe that changing the head tilt angle as described above is one means of suppressing the occurrence of such phenomena.

[0006] For example, if we consider changing the head tilt angle as described above, it is desirable that the magnetic tape has high stability when recording and / or playing back data by tilting the axial direction of the magnetic head module relative to the width direction of the magnetic tape (i.e., tilting the head). This is because high stability in the magnetic tape's movement can, for example, further suppress the occurrence of the above-mentioned phenomenon.

[0007] Incidentally, in recent years, magnetic tape has sometimes been used in data centers where temperature and humidity are controlled. On the other hand, data centers are required to reduce power consumption in order to lower costs. To achieve power consumption, it is desirable to relax the management conditions for the magnetic tape usage environment in data centers, or to eliminate management altogether. However, if the control conditions for the operating environment are relaxed or not controlled at all, magnetic tape may be used in environments such as high temperature and high humidity. Therefore, magnetic tape with excellent running stability when recording and / or playing back data with the head tilted in high temperature and high humidity environments is desirable.

[0008] One aspect of the present invention aims to provide a magnetic tape that exhibits excellent running stability when recording and / or playing back with the head tilted in a high-temperature, high-humidity environment. [Means for solving the problem]

[0009] One aspect of the present invention is as follows: [1] A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, A magnetic tape in which the rate of change of the area ratio of protrusions with a height of 5 nm to 10 nm (hereinafter also referred to as "protrusion area ratio") is 10.0% or less, as determined by measuring a 5 μm × 5 μm measurement area on the surface of the magnetic layer before and after 1000 reciprocating slides against an LTO (Linear Tape-Open) 8 head at a head tilt angle of 15° in an environment of 35°C and 80% relative humidity. [2] The magnetic tape described in [1], wherein the kinetic friction force F (hereinafter also simply referred to as "kinetic friction force F") in the 1000th forward stroke during the above reciprocating sliding is 15 gf or less. [3] The coefficient of variation of the equivalent circle diameter in the bright area (hereinafter also referred to as the "coefficient of variation of the equivalent circle diameter in the bright area") in the binarized image of the secondary electron image obtained by imaging the surface of the magnetic layer before the above reciprocating sliding with a scanning electron microscope at an accelerating voltage of 5kV is 15.0% or less. The lower limit of the threshold for the above binarization process is 100 gradations and the upper limit is 130 gradations, as described in [1] or [2]. [4] The magnetic tape according to any one of [1] to [3], further comprising a non-magnetic powder with a Mohs hardness of 6 or more and 7 or less as the magnetic layer. [5] A magnetic tape according to any one of [1] to [4], further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. [6] The magnetic tape according to any one of [1] to [5], further comprising a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer. [7] A magnetic tape according to any of [1] to [6], wherein the tape thickness of the magnetic tape is 5.0 μm or less. [8] A magnetic tape according to any of [1] to [7], wherein the vertical aspect ratio of the magnetic tape is 0.60 or greater. [9] A magnetic tape according to any of [1] to [8], wherein the vertical aspect ratio of the magnetic tape is 0.65 or greater.

[10] The magnetic tape according to any one of [1] to [9], wherein the non-magnetic support is an aromatic polyamide support.

[11] The kinetic friction force F in the 1000th forward stroke of the above reciprocating sliding is 15gf or less. The coefficient of variation of the equivalent circle diameter of the bright area in the binarized secondary electron image obtained by imaging the surface of the magnetic layer before the above reciprocating sliding using a scanning electron microscope at an acceleration voltage of 5kV is 15.0% or less. The lower limit of the threshold for the above binarization process is 100 gradations, and the upper limit is 130 gradations. The above magnetic layer further contains non-magnetic powder with a Mohs hardness of 6 or more and 7 or less. The non-magnetic support and the magnetic layer further comprise a non-magnetic layer containing non-magnetic powder. The non-magnetic support further has a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer. The tape thickness is 5.0 μm or less, and A magnetic tape as described in any of [1] to

[10] , wherein the vertical aspect ratio of the magnetic tape is 0.60 or greater. A magnetic tape cartridge containing the magnetic tape described in any of

[12] [1] to

[11] . A magnetic tape device containing a magnetic tape as described in any of

[13] [1] to

[11] .

[14] Further including a magnetic head, 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, and The magnetic tape device described in

[13] , wherein the angle θ made between the axis of the element array and the width direction of the magnetic tape while the magnetic tape is running within the magnetic tape device is changed. [Effects of the Invention]

[0010] According to one aspect of the present invention, a magnetic tape with excellent running stability when recording and / or playing back data with the head tilted in a high-temperature, high-humidity environment can be provided. Furthermore, according to one aspect of the present invention, a magnetic tape cartridge and a magnetic tape device including the above-mentioned magnetic tape can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing an example of a magnetic head module. [Figure 2] This is an explanatory diagram illustrating the relative positional relationship between the module and the magnetic tape while the magnetic tape is running in a magnetic tape drive. [Figure 3] This is an explanatory diagram regarding the change in angle θ during magnetic tape travel. [Figure 4] An example of the arrangement of data bands and servo bands is shown. [Figure 5] This shows an example of a servo pattern arrangement for LTO Ultrium format tape. [Figure 6] This is an explanatory diagram of the method for measuring the angle θ while a magnetic tape is running. [Figure 7] This is a schematic diagram showing an example of a magnetic tape drive. [Modes for carrying out the invention]

[0012] [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 rate of change in the area ratio of protrusions with a height of 5 nm to 10 nm (rate of change in protrusion area ratio), which is determined by measuring a 5 μm × 5 μm measurement area on the surface of the magnetic layer before and after 1000 reciprocating slides against an LTO8 head at a head tilt angle of 15° in an environment of 35°C and 80% relative humidity using an atomic force microscope, is 10.0% or less.

[0013] <Head tilt angle> In explaining the head tilt angle described above, we will first describe the LTO8 head. Furthermore, we will explain below why tilting the axial direction of the magnetic head module relative to the width direction of the magnetic tape during magnetic tape transport is thought to suppress the phenomena that occur during recording or playback as described earlier. In the present invention and this specification, "LTO8 head" refers to a magnetic head conforming to the LTO8 standard. The LTO8 head may be a magnetic head removed from an LTO8 drive, or a commercially available magnetic head for LTO drives may be used. Here, an LTO8 drive refers to a drive (magnetic tape device) conforming to the LTO8 standard. An LTO9 drive refers to a drive conforming to the LTO9 standard, and the same applies to other generations of drives. Furthermore, when multiple magnetic tapes to be measured are slid back and forth against an LTO8 head at a head tilt angle of 15°, a new (i.e., unused) LTO8 head shall be used for each magnetic tape measurement. Note that the LTO8 standard was chosen as the head considering its ability to handle recent high-density recording, and the magnetic tapes mentioned are not limited to those used in LTO8 drives. Data may be recorded and / or played back on the above magnetic tape using an LTO8 drive, or using an LTO9 drive or a further next-generation drive, or using an earlier generation drive such as an LTO7 drive.

[0014] The LTO8 head has three modules, each containing an element array with multiple magnetic head elements between a pair of servo signal reading elements. The three modules are arranged in the LTO8 head in a "recording module-playback module-recording module" configuration (total number of modules: 3).

[0015] Each module includes an element array, i.e., an array of elements, having a total of 32 magnetic head elements between a pair of servo signal reading elements. Modules having recording elements as magnetic head elements are recording modules for recording data onto magnetic tape. Modules having playback elements as magnetic head elements are playback modules for reproducing data recorded on magnetic tape. In the LTO8 head, the three modules are arranged so that the axes of the element arrays of each module are oriented parallel to each other. Such "parallel" does not necessarily mean parallel in the strict sense, but includes a range of error that is normally acceptable in the art to which this invention belongs. The range of error can mean, for example, a range of less than ±10° of strict parallelism.

[0016] The head tilt angle during 1000 reciprocating slides shall be the head tilt angle in the regeneration module of the LTO8 head.

[0017] In each element array, a pair of servo signal reading elements and a plurality of magnetic head elements (i.e., recording elements or playback elements) are arranged linearly and spaced apart. Here, "arranged linearly" means that each magnetic head element is arranged on a straight line connecting the center of one servo signal reading element and the center of the other servo signal reading element. Furthermore, in this invention and specification, "axis of the element array" means the straight line connecting the center of one servo signal reading element and the center of the other servo signal reading element.

[0018] Next, the module configuration and other details will be further explained with reference to the drawings. However, the configurations shown in the drawings are illustrative and do not limit the present invention.

[0019] Figure 1 is a schematic diagram showing an example of a magnetic head module. The module shown in Figure 1 has multiple magnetic head elements between a pair of servo signal reading elements (servo signal reading elements 1 and 2). Magnetic head elements are also called "channels". "Ch" in the figure is an abbreviation for Channel. The module shown in Figure 1 has a total of 32 magnetic head elements, from Ch0 to Ch31. The regeneration module for an LTO8 head has a total of 32 regeneration elements, from Ch0 to Ch31.

[0020] In Figure 1, "L" represents the distance between a pair of servo signal reading elements, that is, the distance between one servo signal reading element and the other. In the module shown in Figure 1, "L" represents the distance between servo signal reading element 1 and servo signal reading element 2. More specifically, it is the distance between the center of servo signal reading element 1 and the center of servo signal reading element 2. This distance can be measured, for example, by an optical microscope.

[0021] Figure 2 is an explanatory diagram of the relative positional relationship between the module and the magnetic tape during magnetic tape movement in a magnetic tape device. In Figure 2, dotted line A indicates the width direction of the magnetic tape. Dotted line B indicates the axis of the element array. Angle θ can be said to be the head tilt angle during magnetic tape movement, and is the angle between dotted line A and dotted line B. When angle θ is 0° during magnetic tape movement, the distance in the magnetic tape width direction between one servo signal reading element and the other servo signal reading element of the element array (hereinafter also referred to as the "effective distance between servo signal reading elements") is "L". In contrast, when 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」である。

[0022] As mentioned earlier, during recording or playback, if the magnetic head used to record or play back data is misaligned from the intended track position due to deformation of the magnetic tape's width, phenomena such as overwriting of recorded data or playback failures may occur. For example, if the width of the magnetic tape shrinks or expands, the magnetic head element that should record or play back at the intended track position may end up recording or playing back at a different track position. Also, if the width of the magnetic tape expands, the effective distance between servo signal reading elements may become shorter than the distance between two adjacent servo bands separated by a data band (also referred to as "servo band spacing" or "servo band interval"; more specifically, the distance between the two servo bands in the width direction of the magnetic tape), which may result in data not being recorded or played back in areas close to the edge of the magnetic tape. In contrast, when the element array is tilted at an angle θ greater than 0°, as explained earlier, the effective distance between 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 servo signal reading elements closer to or matching the spacing of the servo bands. This prevents or reduces the frequency of phenomena such as overwriting of recorded data or playback failures that occur when the magnetic head used to record or play back data is misaligned from the target track position due to width deformation of the magnetic tape during recording or playback.

[0023] Figure 3 is an explanatory diagram regarding the change in angle θ during magnetic tape travel. The angle θ at the start of the journey is θ initial This can be set to, for example, 0° or greater than or equal to 0°. In Figure 3, the central diagram shows the state of the module at the start of operation. In Figure 3, the right-hand figure shows the angle θ as θ initial An angle θ is a larger angle. cIt shows the state of the module when [the condition is met]. The effective distance Lcosθ between the servo signal reading elements c is a value smaller than Lcosθ at the start of magnetic tape running. When the width of the magnetic tape contracts during magnetic tape running, it is preferable to perform such angle adjustment. initial On the other hand, in FIG. 3, the left figure shows the state of the module when the angle θ is an angle θ smaller than [a certain value]. The effective distance Lcosθ between the servo signal reading elements initial is a value larger than Lcosθ at the start of magnetic tape running. When the width of the magnetic tape expands during magnetic tape running, it is preferable to perform such angle adjustment. e It shows the state of the module when [the condition is met]. The effective distance Lcosθ between the servo signal reading elements e is a value larger than Lcosθ at the start of magnetic tape running. When the width of the magnetic tape expands during magnetic tape running, it is preferable to perform such angle adjustment. initial 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, which may occur when the magnetic head for recording or playing data deviates from the target track position due to width deformation of the magnetic tape during recording or playback, or can contribute to reducing the occurrence frequency thereof.

[0024] On the other hand, recording data on the magnetic tape and playing back the recorded data are usually performed by running the magnetic tape and sliding the magnetic layer surface and the magnetic head. The inventor considered that when the head is tilted and the magnetic tape is run during such recording and / or playback, the contact state between the magnetic head and the magnetic layer surface becomes unstable, which may be a factor in reducing the running stability. ​Based on the above inferences, the inventors conducted extensive research. As a result, the inventors have newly discovered that magnetic tapes with a protrusion area ratio change rate of 10.0% or less can exhibit excellent running stability when recording and / or playing back data with the head tilted in a high-temperature, high-humidity environment. The temperature and humidity of the measurement environment are adopted as exemplary values ​​for a high-temperature, high-humidity environment. Therefore, the environment in which data is recorded on the magnetic tape and recorded data is played back is not limited to the above temperature and humidity environment. The head tilt angle is also adopted as an exemplary value for an angle that can be used when recording and / or playing back data by changing the head tilt angle during magnetic tape running. Therefore, the head tilt angle when recording and / or playing back data on the magnetic tape is not limited to the above angle. Furthermore, the present invention is not limited by the inventors' inferences described herein. In this specification, the stability of data recording and / or playback when the head is tilted during magnetic tape travel in a high-temperature, high-humidity environment is also simply referred to as "travel stability." A high-temperature, high-humidity environment can be, for example, an environment with a temperature of approximately 30°C to 50°C. The humidity in that environment can be, for example, approximately 70% to 100% as relative humidity. In this invention and this specification, the temperature and humidity described for the environment refer to the ambient temperature and relative humidity of that environment.

[0025] In the present invention and this specification, 1000 reciprocating slides of an LTO8 head at a head tilt angle of 15° in an environment of 35°C and 80% relative humidity shall be performed using the magnetic tape to be measured by the following method. Furthermore, the head tilt angle (15°) refers to the angle formed by the axis of the element array of the LTO8 head's regeneration module with respect to the direction perpendicular to the sliding direction during the first forward stroke of the following 1000 reciprocating slides. This angle is the angle θ formed between A and B in Figure 2, where A is read as the direction perpendicular to the sliding direction. The head tilt angle is fixed during the 1000 reciprocating slides. The magnetic tape to be measured is placed on two cylindrical guide rolls, each 1 inch in diameter (1 inch = 2.54 cm), positioned parallel to each other and spaced apart, with the magnetic layer surface in contact with them. Before starting the reciprocating sliding motion, the magnetic tape to be measured is left on the guide rolls as described above for at least 24 hours to allow it to acclimate to the environment (temperature 35°C, relative humidity 80%). In a randomly selected portion of the magnetic tape to be measured, the magnetic layer surface of the magnetic tape is slid against the LTO8 head with a head tilt angle of 15°, and the reciprocating sliding motion is performed 1000 times. For the sliding conditions, the wrap angle θ is 6° and the sliding speed is 30 mm / second. The tension applied to the longitudinal direction of the magnetic tape during sliding is 0.55 N. The sliding distance for both the forward and return strokes is 5 cm. One end of the magnetic tape to be measured in the longitudinal direction is connected to a strain gauge, and a tension of 0.20 N is applied to the other end. When measuring the kinetic friction force F, the resistance force generated during sliding is detected by the strain gauge. Here, the tension applied is T0 (unit: N), and the resistance force detected by the strain gauge is T (unit: N), and the kinetic friction force F is calculated by the following formula. That is, here the kinetic friction force F is calculated as T0 = 0.20. Let "kinetic friction force F" be the kinetic friction force during the 1000th outward journey. Regarding the unit of kinetic friction force F, "gf" represents grams-force, and 1 N (Newton) is approximately 102 gf.

[0026]

number

[0027] <Percentage change in the ratio of protrusion area> In the above magnetic tape, the rate of change in the area ratio of protrusions with a height of 5 nm to 10 nm (rate of change in protrusion area ratio), determined by measuring a 5 μm × 5 μm measurement area on the surface of the magnetic layer before and after 1000 reciprocating slides against an LTO8 head at a head tilt angle of 15° in an environment of 35°C and 80% relative humidity using an atomic force microscope, is 10.0% or less. In this invention and specification, "surface of magnetic layer" is synonymous with the magnetic layer side surface of the magnetic tape. In the present invention and this specification, the rate of change of the protrusion area ratio is determined by measurement using an atomic force microscope (AFM). The measurement area is 5 μm square (5 μm × 5 μm) per location. Measurements are performed at two randomly selected measurement areas on the magnetic layer surface that has undergone the above 1000 reciprocating sliding cycles. Measurements are also performed at two randomly selected measurement areas on the magnetic layer surface that has not undergone the above 1000 reciprocating sliding cycles. From the AFM measurement data of each measurement area (5 μm × 5 μm), the area ratio of protrusions with a height of 5 nm to 10 nm (protrusion area ratio) is calculated. The protrusion area ratio is calculated by adding the area of ​​the protrusions with a height of 5 nm to 10 nm to the total area of ​​the measurement area (i.e., 5 μm × 5 μm = 25 μm). 2 This is the ratio to the area, and is calculated by the following formula. For protrusions with a height of 5 nm or more and 10 nm or less, where only a portion of the protrusion is within the measurement area and the rest is outside the measurement area, the area of ​​the portion within the measurement area is included in the area for calculating the area ratio, and the area of ​​the portion outside the measurement area is not included in the area for calculating the area ratio. Protrusion area ratio (%) = 100 × "Total area of ​​protrusions with a height of 5 nm to 10 nm" / Total area of ​​the measurement region The arithmetic mean of the protrusion area ratios obtained for two measurement areas on the magnetic layer surface where the above 1000 reciprocating sliding cycles were performed is adopted as the protrusion area ratio after reciprocating sliding. The arithmetic mean of the protrusion area ratios obtained for two measurement areas on the magnetic layer surface where the above 1000 reciprocating sliding cycles have not been performed is adopted as the protrusion area ratio before reciprocating sliding. The rate of change in the protrusion area ratio is calculated using the following formula. The percentage change in the protrusion area ratio (%) = 100 × (protrusion area ratio before reciprocating sliding - protrusion area ratio after reciprocating sliding) / protrusion area ratio before reciprocating sliding As for AFM data analysis software, one example is the AFM data analysis software (Nanoscope Analysis) provided by BRUKER. As for the AFM, one example is the BRUKER Nanoscope 5. As for the AFM measurement conditions, the following measurement conditions can be cited. In order to determine the rate of change of the protrusion area ratio described in the Examples section below, a BRUKER Nanoscope 5 was used as the AFM, and the AFM data analysis software (Nanoscope Analysis) provided by BRUKER was used as the AFM data analysis software, and the following measurement conditions were adopted for the measurement. (Measurement conditions) Measurement environment: Temperature 23°C, relative humidity 50% Measurement area: 5μm x 5μm Measurement surface: magnetic layer surface Resolution: 512pixel x 512pixel Scan Rate:3μm / sec Set Point: 100nN AFM probe: SI-AF01 (manufactured by Hitachi High-Tech Corporation) Number of measurements: N=2 before and after reciprocating sliding.

[0028] The magnetic tape having a protrusion area ratio change rate of 10.0% or less exhibits excellent running stability when recording and / or playing back with the head tilted in a high-temperature, high-humidity environment. The inventors surmise that the reason for this excellent running stability is that a magnetic tape with a protrusion area ratio change rate of 10.0% or less can suppress the increase in kinetic friction force F when the head is repeatedly tilted during running. The reason for setting the protrusion area ratio change rate of the magnetic tape to 10.0% or less is that, through diligent research by the inventors, it was confirmed that when the protrusion area ratio change rate exceeds 10.0%, the increase in kinetic friction force F when the head is repeatedly tilted during running becomes significant. From the viewpoint of further suppressing the increase in kinetic friction force F and further improving running stability, the protrusion area ratio change rate is preferably 9.0% or less, and more preferably 8.0% or less, 7.0% or less, 6.0% or less, and 5.0% or less, in that order. The rate of change in the protrusion area ratio can be, for example, 0.0% or more, greater than 0.0%, 0.1% or more, 1.0% or more, or 2.0% or more. The inventors believe that a smaller value for the rate of change in the protrusion area ratio is preferable from the viewpoint of improving driving stability.

[0029] <Dynamic friction force F> The kinetic friction force F during the 1000th forward stroke in the 1000 reciprocating sliding of the magnetic tape described above is preferably 15gf or less, more preferably 12gf or less, and even more preferably 10gf or less, 8gf or less, and 6gf or less, in that order. The kinetic friction force F can be, for example, 4gf or more, and may be lower than the values ​​exemplified herein.

[0030] By controlling the rate of change of the protrusion area ratio to 10.0% or less, the kinetic friction force F can be controlled to 15gf or less. Specific examples of methods for controlling the rate of change of the protrusion area ratio to 10.0% or less will be described later.

[0031] The magnetic tape described above will be explained in more detail below.

[0032] <Magnetic layer> (Ferromagnetic powder) As the ferromagnetic powder contained in the magnetic layer, one or more known ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used in combination. Using a ferromagnetic powder with a small average particle size is preferable from the viewpoint of improving recording density. From this viewpoint, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, even more preferably 35 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and even more preferably 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, even more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more.

[0033] Hexagonal ferrite powder A preferred example of ferromagnetic powder is hexagonal ferrite powder. For details on hexagonal ferrite powder, see, for example, paragraphs 0012 to 0030 of Japanese Patent Publication No. 2011-225417, paragraphs 0134 to 0136 of Japanese Patent Publication No. 2011-216149, paragraphs 0013 to 0030 of Japanese Patent Publication No. 2012-204726, and paragraphs 0029 to 0084 of Japanese Patent Publication No. 2015-127985.

[0034] In the present invention and this specification, "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the hexagonal ferrite crystal structure, it shall be determined that the hexagonal ferrite crystal structure has been detected as the main phase. If only a single structure is detected by X-ray diffraction analysis, this detected structure shall be considered the main phase. The hexagonal ferrite crystal structure contains at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. Divalent metal atoms are metal atoms that can become divalent cations as ions, and examples include strontium atoms, barium atoms, alkaline earth metal atoms such as calcium atoms, and lead atoms. In the present invention and this specification, hexagonal strontium ferrite powder refers to powder in which the main divalent metal atom contained is strontium, and hexagonal barium ferrite powder refers to powder in which the main divalent metal atom contained is barium. The main divalent metal atom refers to the divalent metal atom that accounts for the largest proportion on an atomic percentage basis among the divalent metal atoms contained in the powder. However, rare earth atoms are not included in the above divalent metal atoms. In the present invention and this specification, "rare earth atoms" are selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanide atoms. Lanthanide atoms are selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0035] Below, we will describe hexagonal strontium ferrite powder, a form of hexagonal ferrite powder, in more detail.

[0036] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1600 nm. 3 The activation volume is within the range described above. Finely milled hexagonal strontium ferrite powder exhibiting an activation volume within this range is suitable for the fabrication of magnetic tapes that exhibit excellent electromagnetic conversion properties. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm. 3 That's all, for example, 850nm 3 It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of hexagonal strontium ferrite powder is 1500 nm. 3 The following is more preferable: 1400nm 3 It is even more preferable that the following occur: 1300 nm 3 It is even more preferable that the following conditions be met: 1200 nm 3 It is even more preferable that the following conditions be met: 1100 nm 3 It is even more preferable that the following conditions be met. The same applies to the activation volume of the hexagonal barium ferrite powder.

[0037] "Activation volume" is the unit of magnetization reversal and is an indicator of the magnetic size of a particle. The activation volume and the anisotropy constant Ku described herein and below are values ​​obtained from the following relationship between Hc and activation volume V, measured using a vibrating sample type magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes in the coercivity Hc measurement section (measurement temperature: 23℃±1℃). Regarding the unit of the anisotropy constant Ku, 1erg / cc = 1.0 × 10⁻⁶ -1 J / m 3 That is the case. 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)]

[0038] As an indicator of reducing thermal fluctuations, or in other words, improving thermal stability, the anisotropy constant Ku can be cited. The hexagonal strontium ferrite powder is preferably 1.8 × 10⁻⁶ 5 J / m 3 It can have a Ku of the above, and more preferably 2.0 × 10 5 J / m 3 It can have a Ku content of the above. Also, the Ku content of hexagonal strontium ferrite powder is, for example, 2.5 × 10⁻⁶. 5 J / m 3 The following values ​​are possible. However, since a higher Ku value is preferable as it indicates higher thermal stability, the values ​​are not limited to those exemplified above.

[0039] Hexagonal strontium ferrite powder may or may not contain rare earth atoms. When hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms are present at a concentration of 0.5 to 5.0 atomic percent (bulk concentration) per 100 atomic percent of iron atoms. In one embodiment, hexagonal strontium ferrite powder containing rare earth atoms may exhibit a segregation of rare earth atoms in the surface layer. In the present invention and this specification, "rare earth atom surface layer segregation" means that the rare earth atom content relative to 100% of iron atoms in a solution obtained by partially dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom surface layer content" or simply "surface layer content" with respect to rare earth atoms) is different from the rare earth atom content relative to 100% of iron atoms in a solution obtained by completely dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom bulk content" or simply "bulk content" with respect to rare earth atoms), Rare earth atom surface content / Rare earth atom bulk content > 1.0 This means that the ratio is satisfied. The rare earth atom content of hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. In contrast, partial dissolution using acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder, so the rare earth atom content in the solution obtained by partial dissolution is the rare earth atom content in the surface layer of the particles constituting the hexagonal strontium ferrite powder. When the rare earth atom surface layer content satisfies the ratio "rare earth atom surface layer content / rare earth atom bulk content > 1.0", it means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are concentrated in the surface layer (i.e., there are more of them in the surface layer than in the interior). In this invention and specification, the surface layer means a part of the region extending from the surface to the interior of the particles constituting the hexagonal strontium ferrite powder.

[0040] When 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 percent relative to 100 atomic percent of iron atoms. It is believed that containing rare earth atoms at the bulk content within the above range, and having the rare earth atoms unevenly distributed on the surface of the particles constituting the hexagonal strontium ferrite powder, contributes to suppressing the decrease in regeneration output during repeated regeneration. This is presumed to be because the anisotropy constant Ku can be increased by containing rare earth atoms at the bulk content within the above range, and having the rare earth atoms unevenly distributed on the surface of the particles constituting the hexagonal strontium ferrite powder. The higher the value of the anisotropy constant Ku, the more it is possible to suppress the occurrence of a phenomenon called thermal fluctuation (in other words, to improve thermal stability). By suppressing the occurrence of thermal fluctuation, the decrease in regeneration output during repeated regeneration can be suppressed. It is hypothesized that the uneven distribution of rare earth atoms on the surface of hexagonal strontium ferrite powder particles contributes to stabilizing the spin of iron (Fe) sites within the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. Furthermore, it is presumed that using hexagonal strontium ferrite powder with a rare-earth atom uneven distribution on the surface as the ferromagnetic powder for the magnetic layer contributes to suppressing wear on the magnetic layer surface due to sliding with the magnetic head. In other words, it is presumed that hexagonal strontium ferrite powder with a rare-earth atom uneven distribution on the surface may also contribute to improving the running durability of the magnetic tape. This is presumed to be because the uneven distribution of rare-earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improved interaction between the particle surface and organic substances (e.g., binders and / or additives) contained in the magnetic layer, resulting in improved strength of the magnetic layer. From the viewpoint of suppressing the decrease in regeneration output during repeated regeneration and / or further improving running durability, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic percent, even more preferably in the range of 1.0 to 4.5 atomic percent, and even more preferably in the range of 1.5 to 4.5 atomic percent.

[0041] The bulk content mentioned above is the content obtained by completely dissolving the hexagonal strontium ferrite powder. In this invention and specification, unless otherwise specified, the content of atoms 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 type of rare earth atom, or it may contain two or more types of rare earth atoms. When two or more types of rare earth atoms are included, the bulk content mentioned above is determined for the sum of the two or more types of rare earth atoms. This also applies to other components in this invention and specification. That is, unless otherwise specified, one type of component may be used, or two or more types may be used. When two or more types are used, the content or content refers to the sum of the two or more types.

[0042] When hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms included may be one or more of any type of rare earth atom. From the viewpoint of suppressing a decrease in regeneration output during repeated regeneration, preferred rare earth atoms include neodymium atoms, samarium atoms, yttrium atoms, and dysprosium atoms, with neodymium atoms, samarium atoms, and yttrium atoms being more preferred, and neodymium atoms being even more preferred.

[0043] In hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the rare-earth atoms only need to be segregated in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of segregation is not limited. For example, in hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the ratio of the rare-earth atom surface content obtained by partial dissolution under the dissolution conditions described later to the rare-earth atom bulk content obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," is greater than 1.0 and can be 1.5 or greater. A "surface content / bulk content" greater than 1.0 means that in the particles constituting the hexagonal strontium ferrite powder, rare-earth atoms are segregated in the surface layer (i.e., there are more of them in the surface layer than in the interior). Furthermore, the ratio of the surface content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," 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 hexagonal strontium ferrite powder having a rare earth atom surface distribution bias, the rare earth atoms only need to be biased towards the surface of the particles constituting the hexagonal strontium ferrite powder, and the above "surface content / bulk content" is not limited to the upper or lower limits exemplified.

[0044] The partial and total dissolution of hexagonal strontium ferrite powder is described below. For hexagonal strontium ferrite powder existing as a powder, the sample powders to be partially and completely dissolved are taken from the same lot of powder. On the other hand, for hexagonal strontium ferrite powder contained in the magnetic layer of a magnetic tape, a portion of the hexagonal strontium ferrite powder extracted from the magnetic layer is subjected to partial dissolution, and another portion is subjected to total dissolution. The extraction of hexagonal strontium ferrite powder from the magnetic layer can be carried out, for example, by the method described in paragraph 0032 of Japanese Patent Application Publication No. 2015-91747. Partial dissolution, as described above, refers to a state where the hexagonal strontium ferrite powder is dissolved to the extent that residual particles can be visually confirmed in the liquid at the end of the dissolution process. For example, partial dissolution can dissolve 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder, with the total particles being 100% by mass. On the other hand, total dissolution, as described above, refers to a state where the hexagonal strontium ferrite powder is dissolved to the extent that no residual particles can be visually confirmed in the liquid at the end of the dissolution process. The above-mentioned partial dissolution and surface layer content measurement are performed, for example, by the following method. However, the dissolution conditions such as the amount of sample powder described below are examples only, and any dissolution conditions that enable partial and total dissolution can be arbitrarily adopted. A container (e.g., a beaker) containing 12 mg of 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 resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the resulting filtrate is performed using an inductively coupled plasma (ICP) analyzer. In this way, the surface content of rare earth atoms relative to 100% iron atoms can be determined. If multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface content. This is also the case when measuring bulk content. On the other hand, the measurement of total dissolution and bulk content is performed, for example, by the following method. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid is held on a hot plate at a set temperature of 80°C for 3 hours. Afterward, the bulk content relative to 100 atomic percent of iron can be determined by performing the same procedure as described above for partial dissolution and surface layer content measurement.

[0045] From the perspective of increasing the playback output when reproducing data recorded on magnetic tape, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape to be high. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but lacking surface segregation of rare earth atoms tended to have a significantly lower σs compared to hexagonal strontium ferrite powder that does not contain rare earth atoms. In contrast, hexagonal strontium ferrite powder with surface segregation of rare earth atoms is considered preferable in order to suppress such a large decrease in σs. In one embodiment, the σs of hexagonal strontium ferrite powder is 45 A·m 2 It can be 47 A·m or more per kg. 2 It can also be more than / kg. On the other hand, σs is 80 A·m from the viewpoint of noise reduction. 2 Preferably less than / kg, at 60A·m 2 It is more preferable that it be less than or equal to / kg. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In this invention and specification, unless otherwise specified, the mass magnetization σs is the value measured at a magnetic field strength of 15 kOe. 1 [kOe] = 10 6 It is / 4π[A / m].

[0046] Regarding the constituent atom content (bulk content) of hexagonal strontium ferrite powder, the strontium atom content can be in the range of, for example, 2.0 to 15.0 atomic percent per 100 atomic percent of iron atoms. In one form, hexagonal strontium ferrite powder may contain only strontium atoms as the divalent metal atom. In another form, hexagonal strontium ferrite powder may contain one or more other divalent metal atoms in addition to strontium atoms. For example, it may contain barium atoms and / or calcium atoms. When other divalent metal atoms besides strontium atoms are included, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder can be in the range of, for example, 0.05 to 5.0 atomic percent per 100 atomic percent of iron atoms.

[0047] The known crystal structures of hexagonal ferrites include magnetoplumbite (also called "M-type"), W-type, Y-type, and Z-type. Hexagonal strontium ferrite powder may have any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. Hexagonal strontium ferrite powder may show a single crystal structure or two or more crystal structures by X-ray diffraction analysis. For example, in one form, hexagonal strontium ferrite powder may show only the M-type crystal structure 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, and if the hexagonal strontium ferrite powder is of type M, A is either only a strontium atom (Sr), or if A contains multiple divalent metal atoms, then as described above, strontium atoms (Sr) make up the largest proportion on an atomic percentage basis. The divalent metal atom content of 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 and oxygen atom content. Hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms and oxygen atoms, and may also contain rare earth atoms. Furthermore, hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, hexagonal strontium ferrite powder may contain aluminum atoms (Al). The aluminum atom content can be, for example, 0.5 to 10.0 atomic percent relative to 100 atomic percent of iron atoms. From the viewpoint of suppressing a decrease in regeneration output during repeated regeneration, the hexagonal strontium ferrite powder preferably contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is preferably 10.0 atomic percent or less, more preferably in the range of 0 to 5.0 atomic percent, and may even be 0 atomic percent, relative to 100 atomic percent of iron atoms. That is, in one embodiment, the hexagonal strontium ferrite powder does not need to contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The above content expressed in atomic percent is obtained by converting the content of each atom (unit: mass%) obtained by completely dissolving the hexagonal strontium ferrite powder into an atomic percent value using the atomic weight of each atom. Furthermore, in the present invention and this specification, "does not contain" for a certain atom means that the content measured by an ICP analyzer after complete dissolution is 0 mass%. The detection limit of an ICP analyzer is typically 0.01 ppm (parts per million) or less by mass. The term "does not contain" above is used to include the presence of substances in amounts below the detection limit of the ICP analyzer.Hexagonal strontium ferrite powder can, in one form, be bismuth-free (Bi).

[0048] metal powder A preferred specific example of ferromagnetic powder is ferromagnetic metal powder. For details on ferromagnetic metal powder, see, for example, paragraphs 0137-0141 of Japanese Patent Publication No. 2011-216149 and paragraphs 0009-0023 of Japanese Patent Publication No. 2005-251351.

[0049] ε-Iron oxide powder A preferred specific example of a ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, "ε-iron oxide powder" refers to a ferromagnetic powder in which the crystalline structure of ε-iron oxide is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystalline structure of ε-iron oxide, it shall be determined that the crystalline structure of ε-iron oxide has been detected as the main phase. Methods for producing ε-iron oxide powder include methods from goethite and the reverse micelle method. All of the above production methods are publicly known. Furthermore, for methods for producing ε-iron oxide powder in which some of the Fe is substituted with substitution atoms such as Ga, Co, Ti, Al, and Rh, see, 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 ferromagnetic powder in the magnetic layer of the magnetic tape described above is not limited to the method described herein.

[0050] The activation volume of ε-iron oxide powder is preferably 300 to 1500 nm. 3 The activation volume is within the range described above. Micronized ε-iron oxide powder exhibiting an activation volume within the above range is suitable for the production of magnetic tapes that exhibit excellent electromagnetic conversion properties. The activation volume of the ε-iron oxide powder is preferably 300 nm. 3 That's all, for example, 500nm3 It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of ε-iron oxide powder is 1400 nm. 3 The following is more preferable: 1300nm 3 It is even more preferable that the following occur: 1200 nm 3 It is even more preferable that the following conditions be met: 1100 nm 3 The following is even more preferable.

[0051] The anisotropy constant Ku can be cited as an indicator of the reduction of thermal fluctuations, or in other words, the improvement of thermal stability. The ε-iron oxide powder is preferably 3.0 × 10⁻⁶ 4 J / m 3 It can have a Ku of the above, and more preferably 8.0 × 10 4 J / m 3 It can have the above amount of Ku. Also, the amount of Ku in ε-iron oxide powder is, for example, 3.0 × 10⁻⁶. 5 J / m 3 The following values ​​are possible. However, a higher Ku value indicates higher thermal stability and is therefore preferable, so the values ​​are not limited to those exemplified above.

[0052] From the perspective of increasing the playback output when reproducing data recorded on magnetic tape, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape to be high. In this regard, in one embodiment, the σs of ε-iron oxide powder is 8 A·m 2 It can be 12 A·m or more / kg. 2 It can also be more than / kg. On the other hand, the σs of ε-iron oxide powder is 40 A·m from the viewpoint of noise reduction. 2 Preferably less than / kg, 35A·m 2 It is more preferable that the amount be less than or equal to / kg.

[0053] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders shall be the value measured using a transmission electron microscope by the following method. The powder is photographed using a transmission electron microscope at a magnification of 100,000x, and the resulting image is printed on photographic paper or displayed on a screen to obtain a total magnification of 500,000x, thereby obtaining a photograph of the particles that make up the powder. From the obtained photographs of the particles, the target particles are selected, and their contours are traced with a digitizer to measure the size of the particles (primary particles). Primary particles are defined as independent particles that do not aggregate. The above measurements are performed on 500 randomly selected particles. The arithmetic mean of the particle sizes of these 500 particles is taken as the average particle size of the powder. As the transmission electron microscope, for example, a Hitachi H-9000 transmission electron microscope can be used. The particle size can be measured using known image analysis software, for example, Carl Zeiss KS-400 image analysis software. Unless otherwise specified, the average particle sizes shown in the examples described later are values ​​measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software. In the present invention and this specification, "powder" means a collection of multiple particles. For example, ferromagnetic powder means a collection of multiple ferromagnetic particles. Furthermore, a collection of multiple particles is not limited to a form in which the particles constituting the collection are in direct contact, but also includes forms in which binders, additives, etc., described later, are interposed between the particles. The word "particle" is sometimes used to refer to powder.

[0054] For example, the method described in paragraph 0015 of Japanese Patent Publication No. 2011-048878 can be used to collect sample powder from a magnetic tape for particle size measurement.

[0055] In the present invention and this specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is determined by the shape of the particles observed in the above particle photograph. (1) In the case of needle-shaped, spindle-shaped, columnar (however, the height is greater than the longest diameter of the base), etc., the length of the long axis constituting the particle is expressed as the long axis length, (2) In the case of a plate or column (provided that the thickness or height is less than the longest diameter of the plate or base), it shall be expressed by the longest diameter of the plate or base. (3) If the shape is spherical, polyhedral, irregular, etc., and the major axis constituting the particle cannot be determined from the shape, it shall be represented by the equivalent diameter of a circle. The equivalent diameter of a circle refers to the diameter obtained by the circular projection method.

[0056] Furthermore, the average needle-shape ratio of the powder refers to the arithmetic mean of the values ​​obtained for the 500 particles by measuring the length of the short axis of each particle, i.e., the short axis length, in the above measurement, and determining the (long axis length / short axis length) value for each particle. Here, unless otherwise specified, the short axis length refers to the length of the short axis constituting the particle in the above definition of particle size (1), the thickness or height in the case of (2), and in the case of (3), since there is no distinction between the long axis and the short axis, (long axis length / short axis length) is considered to be 1 for convenience. Unless otherwise specified, when the particle shape is specific, for example, in the case of definition (1) above, the average particle size is the average major axis length, and in the case of definition (2), the average particle size is the average plate diameter. In the case of definition (3), the average particle size is the average diameter (also called the average particle size or average particle diameter).

[0057] The content (filling rate) of ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the magnetic layer. A high filling rate of ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving recording density.

[0058] (Binder) The above magnetic tape can be a coated magnetic tape, and the magnetic layer may contain a binder. The binder is one or more resins. Various resins commonly used as binders for coated magnetic recording media can be used as the binder. For example, as the binder, a resin selected from 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 alkylal resin such as polyvinyl butyral can be used alone or in mixture of multiple resins. Among these, polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binders in the non-magnetic layer and / or back coat layer described later. For more information on the binders, refer to paragraphs 0028 to 0031 of Japanese Patent Application Publication No. 2010-24113. The binder may also be a radiation-curable resin such as an electron beam-curable resin. For radiation-curable resins, refer to paragraphs 0044 to 0045 of Japanese Patent Publication No. 2011-048878. The average molecular weight of the resin used as a binder can be, for example, 10,000 to 200,000 as a weight-average molecular weight. In this invention and specification, the weight-average molecular weight is the value obtained by converting the value measured under the following measurement conditions by gel permeation chromatography (GPC) to polystyrene equivalent. The weight-average molecular weight of the binders shown in the Examples section below is the value obtained by converting the value measured under the following measurement conditions to polystyrene equivalent. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass per 100.0 parts by mass of ferromagnetic powder. GPC device: HLC-8120 (manufactured by Tosoh Corporation) Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mm ID (Inner Diameter) × 30.0cm) Eluent: Tetrahydrofuran (THF)

[0059] (Hardening agent) A curing agent can also be used together with the binder. In one form, the curing agent can be a thermosetting compound, which undergoes a curing reaction (crosslinking reaction) upon heating, and in another form, it can be a photocurable compound, which undergoes a curing reaction (crosslinking reaction) upon light irradiation. During the manufacturing process of the magnetic tape, the curing reaction of the curing agent can occur, and at least a portion of it may be included in the magnetic layer in a state where it has reacted (crosslinked) with other components such as the binder. A preferred curing agent is a thermosetting compound, and polyisocyanate is preferred. For details on polyisocyanate, refer to paragraphs 0124 to 0125 of Japanese Patent Application Publication No. 2011-216149. The curing agent can be used in the magnetic layer forming composition in an amount of, for example, 0 to 80.0 parts by mass per 100.0 parts by mass of the binder, and preferably 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of each layer such as the magnetic layer.

[0060] (Other ingredients) The magnetic layer may contain one or more additives as needed. Commercially available additives can be appropriately selected and used according to the desired properties. Alternatively, compounds synthesized by known methods can be used as additives. An example of an additive is the curing agent mentioned above. Other possible additives in the magnetic layer include non-magnetic powders, lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, antioxidants, etc. Examples of non-magnetic powders include non-magnetic powders that can function as protrusion-forming agents and non-magnetic powders that can function as abrasives. Furthermore, known additives such as various polymers described in paragraphs 0030 to 0080 of Japanese Patent Application Publication No. 2016-051493 can also be used.

[0061] In one embodiment, the magnetic tape may contain one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides in the portion on the magnetic layer side of the non-magnetic support. In the present invention and this specification, "the portion on the magnetic layer side of the non-magnetic support" refers to the magnetic layer in the case of a magnetic recording medium having a magnetic layer directly on the non-magnetic support, and to the magnetic layer and / or non-magnetic layer in the case of a magnetic recording medium having a non-magnetic layer between the non-magnetic support and the magnetic layer. "The portion on the magnetic layer side of the non-magnetic support" is also simply referred to as "the portion on the magnetic layer side." The presence of a component on the magnetic layer side surface of the magnetic tape is also included in the inclusion of that component in the portion on the magnetic layer side. The fatty acid compounds can function as lubricants. The portion on the magnetic layer side may contain only one fatty acid compound selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides, or it may contain two or more. It may also contain only one or two or more fatty acids. The same applies to fatty acid esters and fatty acid amides. Examples of fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid, with stearic acid, myristic acid, and palmitic acid being preferred, and stearic acid being more preferred. The fatty acids may also be included in the magnetic layer in the form of salts such as metal salts. Examples of fatty acid esters include butyl hexanoate, butyl octanoate, butyl decanoate, butyl laurate, butyl myristate, and butyl palmitate. The inventors surmise that using fatty acid esters with a small number of carbon atoms in the fatty acid portion can contribute to reducing the rate of change in the protrusion area ratio. From this point of view, fatty acid esters with 16 or fewer carbon atoms in the fatty acid portion are preferred. For example, the fatty acid portion of butyl palmitate has 16 carbon atoms. The number of carbon atoms in the fatty acid portion can be, for example, 6 or more and 16 or less. Examples of fatty acid amides include the amides of the various fatty acids listed above. Specific examples include lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide. A magnetic recording medium containing one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides in the magnetic layer portion can, in one embodiment, be manufactured by forming a magnetic layer using a magnetic layer-forming composition containing one or more of the above fatty acid compounds. Alternatively, in one embodiment, a magnetic recording medium containing one or more of the above fatty acid compounds in the magnetic layer portion can be manufactured by forming a non-magnetic layer using a non-magnetic layer-forming composition containing one or more of the above fatty acid compounds. Alternatively, in one embodiment, a magnetic recording medium containing one or more of the above fatty acid compounds in the magnetic layer portion can be manufactured by forming a non-magnetic layer using a non-magnetic layer-forming composition containing one or more of the above fatty acid compounds, and forming a magnetic layer using a magnetic layer-forming composition containing one or more of the above fatty acid compounds. The non-magnetic layer can hold and supply components that can function as lubricants, such as fatty acids, fatty acid esters, and fatty acid amides, to the magnetic layer. The lubricants such as fatty acids, fatty acid esters, and fatty acid amides contained in the non-magnetic layer may migrate to the magnetic layer and be present in the magnetic layer. The fatty acid content in the magnetic layer or magnetic layer forming composition is, for example, 0 to 3.0 parts by mass, preferably 0.5 to 3.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The content of fatty acid ester in the magnetic layer or magnetic layer forming composition is, for example, 0 to 10.0 parts by mass, preferably 0.5 to 7.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The content of fatty acid amide in the magnetic layer or magnetic layer forming composition is, for example, 0 to 1.0 parts by mass, preferably 0.1 to 1.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. Regarding the content of fatty acids, fatty acid esters, and fatty acid amides in the non-magnetic layer or composition for forming a non-magnetic layer, the above description can be applied by replacing the ferromagnetic powder with the non-magnetic powder.

[0062] As a protrusion-forming agent, which is a form of non-magnetic powder, inorganic particles, organic particles, or composite particles of inorganic and organic substances can be used. Examples of inorganic substances include inorganic oxides such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides, with inorganic oxides being preferred. In one embodiment, the protrusion-forming agent can be inorganic oxide-based particles. Here, "based" is used to mean "containing". In one embodiment, non-magnetic colloidal particles can be used as the protrusion-forming agent. In the present invention and this specification, "colloidal particles" means particles that, when added at least 1 g per 100 mL of at least one organic solvent containing methyl ethyl ketone, cyclohexanone, toluene, or ethyl acetate, or a mixed solvent containing two or more of the above solvents in any mixing ratio, do not settle but disperse and produce a colloidal dispersion. As non-magnetic colloidal particles, inorganic colloidal particles are preferred, inorganic oxide colloidal particles are more preferred, and silica colloidal particles (colloidal silica) are particularly preferred from the viewpoint of the availability of monodisperse colloidal particles.

[0063] The average particle size of the protrusion-forming agent can be, for example, 30 to 300 nm, and preferably 40 to 200 nm.

[0064] From the viewpoint of reducing the rate of change of the protrusion area ratio, it is preferable that the magnetic layer contains non-magnetic powder with a Mohs hardness of 6 or more and 7 or less. Such non-magnetic powder can function as a protrusion-forming agent. Mohs hardness is a known physical property, and the maximum value of Mohs hardness is 10 for diamond. The Mohs hardness of various non-magnetic powders can be values ​​known from the literature or can be measured by known methods.

[0065] Another form of nonmagnetic powder, the abrasive, is preferably a nonmagnetic powder with a Mohs hardness greater than 8, and more preferably a nonmagnetic powder with a Mohs hardness of 9 or higher. Specifically, examples of abrasives include powders of 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, and diamond, with alumina powder such as α-alumina and silicon carbide powder being preferred. The average particle size of the abrasive can be in the range of 30 to 300 nm, and is preferably in the range of 50 to 200 nm.

[0066] Furthermore, from the viewpoint of enabling the protrusion-forming agent and abrasive to exhibit their functions more effectively, the content of the protrusion-forming agent in the magnetic layer is preferably 0.1 to 4.0 parts by mass, and more preferably 0.3 to 3.5 parts by mass, per 100.0 parts by mass of ferromagnetic powder. According to the inventors' studies, it was observed that increasing the content of the protrusion-forming agent in the magnetic layer tended to decrease the rate of change in the protrusion area ratio. On the other hand, the content of the abrasive 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 even more preferably 4.0 to 10.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder.

[0067] An example of an additive that can be used in a magnetic layer containing an abrasive is the dispersant described in paragraphs 0012 to 0022 of Japanese Patent Publication No. 2013-131285, which can be used as a dispersant to improve the dispersibility of the abrasive in a magnetic layer forming composition. For more information on dispersants, see paragraphs 0061 and 0071 of Japanese Patent Publication No. 2012-133837. The dispersant may also be included in the non-magnetic layer. For more information on dispersants that can be included in the non-magnetic layer, see paragraph 0061 of Japanese Patent Publication No. 2012-133837.

[0068] (Coefficient of variation of the equivalent circular diameter in the bright area) In one embodiment, it is preferable that the coefficient of variation of the equivalent circle diameter in the bright area (coefficient of variation of the equivalent circle diameter in the bright area) in the binarized secondary electron image obtained by imaging the surface of the magnetic layer before the reciprocating sliding described above, i.e., the magnetic layer not subjected to the reciprocating sliding described above, with a scanning electron microscope at an accelerating voltage of 5kV, is 15.0% or less. Here, the lower limit of the threshold for the binarization process is 100 gradations and the upper limit is 130 gradations.

[0069] The scanning electron microscope (SEM) used in this invention and specification to determine the coefficient of variation of the equivalent circle diameter of the bright area is a field emission scanning electron microscope (FE-SEM). For example, a Hitachi FE-SEM S4800 can be used as the FE-SEM, and this FE-SEM was used in the measurements described in the Examples section below. Before acquiring SEM images to determine the coefficient of variation of the equivalent circle diameter in the bright region, no coating treatment is performed on the magnetic layer surface. Imaging is performed by selecting an unimaged area on the magnetic layer surface. The acquired SEM image is a secondary electron image. The equivalent circle diameter shall be calculated in 1 nm increments, rounded to one decimal place and truncated beyond the second decimal place. When calculating the coefficient of variation of the equivalent circle diameter in the bright area, bright areas that are only partially included in the binarized image and whose remaining portion is outside the binarized image shall be excluded from the measurement. The coefficient of variation of the equivalent circular diameter in the above-mentioned bright area can be determined by the following method. A scanning electron microscope (FE-SEM) is used to capture a secondary electron image of the magnetic layer surface of the magnetic tape to be measured. The measurement site is randomly selected from a single location. Imaging is performed on the magnetic layer surface that is not subjected to the reciprocating sliding described above. The imaging conditions are as follows: acceleration voltage of 5kV, working distance of 8mm, and magnification of 10,000x. During imaging, an unimaged area of ​​the magnetic layer surface is selected, the focus is adjusted under the above imaging conditions, and a secondary electron image is captured. The parts that indicate size, etc. (micron bars, cross marks, etc.) are removed from the captured image, and a secondary electron image with a resolution of 960 pixels × 1280 pixels is obtained. The resulting secondary electron image is imported into image processing software and binarized using the following procedure. For example, the free software ImageJ can be used as image analysis software. Binarization separates the image into bright areas (white parts) and dark areas (black parts). The thresholds for binarizing the secondary electron image obtained above are set to a lower limit of 100 gradations and an upper limit of 130 gradations. Binarization is performed using these two thresholds. After binarization, noise component removal is performed using image analysis software. Noise component removal can be performed, for example, by the following method: In the image analysis software ImageJ, select the Despeckle noise reduction process to remove noise components. The resulting binarized image is then analyzed using image analysis software to determine the area of ​​each of the multiple highlight regions (i.e., white areas) contained within the binarized image. From the areas of these highlight regions, the equivalent diameter of each highlight region is calculated. Specifically, the equivalent diameter L is calculated from the calculated area A using the formula 2 × (A / π)^(1 / 2) = L. Here, the symbol "^" represents exponentiation. For the equivalent diameter L obtained in this way, the coefficient of variation of the equivalent diameter is calculated from the standard deviation σ and the arithmetic mean using the following formula. Coefficient of variation of the equivalent diameter of a circle (%) = 100 × standard deviation / arithmetic mean

[0070] The inventors believe that the coefficient of variation of the equivalent circle diameter in the bright area can serve as an indicator of the presence of the protrusion-forming agent in the magnetic layer when the reciprocating sliding described above is not occurring. The inventors surmise that the presence of the protrusion-forming agent when the coefficient of variation of the equivalent circle diameter in the bright area is 15.0% or less can contribute to reducing the value of the rate of change of the protrusion area ratio. From the viewpoint of further reducing the value of the rate of change of the protrusion area ratio, it is even more preferable that the coefficient of variation of the equivalent circle diameter in the bright area is 14.0% or less, followed by 13.0% or less, and then 12.0% or less. The coefficient of variation of the equivalent circle diameter in the bright area can be, for example, 1.0% or more, 2.0% or more, 3.0% or more, 4.0% or more, 5.0% or more, 6.0% or more, 7.0% or more, or 8.0% or more. It is considered preferable that the value of the coefficient of variation of the equivalent circle diameter in the bright area is smaller in order to further reduce the value of the rate of change of the protrusion area ratio. Therefore, the coefficient of variation of the equivalent circle diameter in the bright area may be lower than the values ​​exemplified here. To reduce the coefficient of variation of the equivalent circle diameter in the bright area, it is preferable to use colloidal particles as a protrusion-forming agent.

[0071] <Nonmagnetic layer> Next, the non-magnetic layer will be described. The magnetic tape described above may have a magnetic layer directly on a non-magnetic support, or it may have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. The non-magnetic powder used in the non-magnetic layer may be an inorganic powder or an organic powder. Carbon black can also be used. Examples of inorganic substances include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These non-magnetic powders are available commercially and can also be manufactured by known methods. For details, see paragraphs 0146 to 0150 of Japanese Patent Publication No. 2011-216149. For carbon black that can be used in the non-magnetic layer, see paragraphs 0040 to 0041 of Japanese Patent Publication No. 2010-24113. The content (filling rate) of non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the non-magnetic layer.

[0072] The non-magnetic layer may contain a binder and may also contain additives. For further details regarding the binder, additives, etc., of the non-magnetic layer, known technology relating to non-magnetic layers can be applied. Furthermore, for example, regarding the type and content of the binder, the type and content of the additives, etc., known technology relating to magnetic layers can also be applied.

[0073] The non-magnetic layer of the magnetic tape described above includes a substantially non-magnetic layer containing a small amount of ferromagnetic powder, for example as an impurity or intentionally, along with non-magnetic powder. Here, a substantially non-magnetic layer means a layer whose remanent magnetic flux density is 10 mT or less, or whose coercivity is 7.96 kA / m(100 Oe) or less, or a layer whose remanent magnetic flux density is 10 mT or less and whose coercivity is 7.96 kA / m(100 Oe) or less. It is preferable that the non-magnetic layer has no remanent magnetic flux density and coercivity.

[0074] <Nonmagnetic support> Next, non-magnetic supports will be described. Examples of non-magnetic supports (hereinafter also simply referred to as "supports") include known materials such as biaxially oriented polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamide-imide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be subjected to pre-treatment such as corona discharge, plasma treatment, easy-adhesion treatment, or heat treatment.

[0075] The non-magnetic support of the magnetic tape described above may, in one embodiment, be an aromatic polyester support. In the present invention and this specification, "aromatic polyester" means a resin containing an aromatic skeleton and multiple ester bonds, and "aromatic polyester support" means a support containing at least one layer of aromatic polyester film. "Aromatic polyester film" means a film in which the most abundant component by mass among the components constituting the film is aromatic polyester. In the present invention and this specification, "aromatic polyester support" includes both a support in which all the resin films contained are aromatic polyester films and a support containing aromatic polyester films and other resin films. Specific forms of aromatic polyester support include a single layer of aromatic polyester film, a laminated film of two or more layers of aromatic polyester films with the same constituent components, a laminated film of two or more layers of aromatic polyester films with different constituent components, a laminated film containing one or more layers of aromatic polyester film and one or more layers of resin films other than aromatic polyester, etc. In a laminated film, an adhesive layer or the like may be optionally included between two adjacent layers. Furthermore, the aromatic polyester support may optionally contain a metal film and / or a metal oxide film formed by vapor deposition or the like on one or both surfaces. The same applies to the "polyethylene terephthalate support" and "polyethylene naphthalate support" in the present invention and this specification.

[0076] The aromatic rings contained in the aromatic skeleton of an aromatic polyester are not particularly limited. Specific examples of aromatic rings include, for example, benzene rings and naphthalene rings. For example, polyethylene terephthalate (PET) is a polyester containing a benzene ring, and is a resin obtained by polycondensation of ethylene glycol with terephthalic acid and / or dimethyl terephthalate. In the present invention and this specification, "polyethylene terephthalate" also includes structures having one or more other components in addition to the above components (e.g., copolymer components, components introduced into terminals or side chains, etc.). Polyethylene naphthalate (PEN) is a polyester containing a naphthalene ring, obtained by esterification of dimethyl 2,6-naphthalenedicarboxylate with ethylene glycol, followed by transesterification and polycondensation reactions. In the present invention and this specification, "polyethylene naphthalate" also includes structures having one or more other components in addition to the above components (e.g., copolymer components, components introduced into terminals or side chains, etc.).

[0077] In one embodiment, the non-magnetic support of the magnetic tape described above may be an aromatic polyamide support. In the present invention and this specification, "aromatic polyamide" means a resin containing an aromatic skeleton and multiple amide bonds. The aromatic rings contained in the aromatic skeleton of the aromatic polyamide are not particularly limited. Specific examples of aromatic rings include, for example, benzene rings. "Aromatic polyamide support" means a support containing at least one layer of aromatic polyamide film. "Aromatic polyamide film" means a film in which the component that constitutes the film by mass is aromatic polyamide. In the present invention and this specification, "aromatic polyamide support" includes both a support in which all the resin films contained are aromatic polyamide films and a support containing aromatic polyamide films and other resin films. Specific forms of aromatic polyamide support include a single layer of aromatic polyamide film, a laminated film of two or more layers of aromatic polyamide films with the same constituent components, a laminated film of two or more layers of aromatic polyamide films with different constituent components, and a laminated film containing one or more layers of aromatic polyamide film and one or more layers of resin films other than aromatic polyamide. In the laminated film, an adhesive layer or the like may be optionally included between two adjacent layers. Furthermore, the aromatic polyamide support may optionally include a metal film and / or a metal oxide film formed by vapor deposition or the like on one or both surfaces.

[0078] Furthermore, as mentioned above, the non-magnetic support can be a biaxially oriented film, and may be a film that has undergone corona discharge, plasma treatment, easy adhesion treatment, heat treatment, etc.

[0079] Examples of indicators of the physical properties of a non-magnetic support include water content. In the present invention and this specification, the water content of a non-magnetic support is a value determined by the following method. A sample piece (for example, a sample piece with a mass of several grams) cut from the non-magnetic support to be measured for moisture content is dried in a vacuum dryer at a temperature of 180°C and a pressure of 100 Pa (Pascals) or less until a constant weight is reached. The mass of the dried sample piece is denoted as W1. W1 is the value measured within 30 seconds after removal from the vacuum dryer in a measurement environment of 23°C and 50% relative humidity. Next, the mass of this sample piece after being placed in an environment of 25°C and 75% relative humidity for 48 hours is denoted as W2. W2 is the value measured within 30 seconds after removal from the above environment in a measurement environment of 23°C and 50% relative humidity. The moisture content is calculated using the following formula. Moisture content (%)=[(W2-W1) / W1]×100 For example, after removing parts other than the non-magnetic support, such as the magnetic layer, from the magnetic tape using a known method (e.g., defilm removal using an organic solvent), the water content of the non-magnetic support can be determined using the method described above.

[0080] In one embodiment, the non-magnetic support of the magnetic tape preferably has a water content of 2.0% or less, more preferably 1.8% or less, even more preferably 1.6% or less, even more preferably 1.4% or less, even more preferably 1.2% or less, and even more preferably 1.0% or less. Furthermore, the water content of the non-magnetic support of the magnetic tape can be 0%, 0% or more, greater than 0%, or 0.1% or more.

[0081] Young's modulus can also be cited as an indicator of the physical properties of a non-magnetic support. In the present invention and this specification, the Young's modulus of a non-magnetic support is a value measured by the following method in a measurement environment of 23°C and 50% relative humidity. A sample piece cut from the non-magnetic support to be measured is pulled using a universal tensile testing apparatus under the conditions of a chuck distance of 100 mm, a tensile speed of 10 mm / min, and a chart speed of 500 mm / min. As the universal tensile testing apparatus, commercially available universal tensile testing apparatuses such as the Tensilon manufactured by Toyo Baldwin Co., Ltd., or universal tensile testing apparatuses with known configurations can be used. From the tangents of the rising portion of the load-elongation curve thus obtained, the Young's modulus in the longitudinal and width directions of the sample piece is calculated, respectively. Here, the longitudinal and width directions of the sample piece refer to the longitudinal and width directions when the sample piece was contained in a magnetic tape. For example, after removing parts other than the non-magnetic support, such as the magnetic layer, from the magnetic tape using a known method (e.g., defilm removal using an organic solvent), the Young's modulus in the longitudinal and width directions of the non-magnetic support can be determined using the method described above.

[0082] In one embodiment, the non-magnetic support of the magnetic tape preferably has a Young's modulus in the longitudinal direction of 3000 MPa or more, more preferably 4000 MPa or more, even more preferably 5000 MPa or more, and even more preferably 6000 MPa or more. Furthermore, the Young's modulus in the longitudinal direction of the non-magnetic support of the magnetic tape can be 15000 MPa or less, 13000 MPa or less, or 12000 MPa or less. Regarding the width direction, the Young's modulus in the width direction of the non-magnetic support of the magnetic tape preferably has a Young's modulus in the width direction of 2000 MPa or more, more preferably 3000 MPa or more, even more preferably 4000 MPa or more, and even more preferably 5000 MPa or more. Furthermore, the Young's modulus in the width direction of the non-magnetic support of the magnetic tape can be 12000 MPa or less, 11000 MPa or less, or 10000 MPa or less. During the manufacture of the magnetic tape, the non-magnetic support is usually used with the MD direction (Machine direction) of the film as the longitudinal direction and the TD direction (Transverse direction) as the width direction. Furthermore, in one embodiment, it is preferable that the Young's modulus in the longitudinal direction is greater than the Young's modulus in the width direction, and it is more preferable that the difference (Young's modulus in the longitudinal direction - Young's modulus in the width direction) is in the range of 800 to 3000 MPa.

[0083] The water content and Young's modulus of a non-magnetic support can be controlled by the type and mixing ratio of the components constituting the support, the manufacturing conditions of the support, etc. For example, by adjusting the stretching ratio in each direction during biaxial stretching, the Young's modulus in the longitudinal direction and the Young's modulus in the width direction can be controlled, respectively.

[0084] <Backcoat 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. Preferably, the back coat layer contains either or both carbon black and inorganic powder. The back coat layer may contain a binder and may also contain additives. For details regarding the non-magnetic powder, binder, additives, etc. of the back coat layer, known technology relating to back coat layers may be applied, as may known technology relating to magnetic layers and / or non-magnetic layers. For example, paragraphs 0018 to 0020 of Japanese Patent Application Publication No. 2006-331625 and lines 65 to 38 of column 5 of U.S. Patent No. 7,029,774 can be referenced regarding the back coat layer.

[0085] <Various thicknesses> Regarding the thickness (total thickness) of magnetic tape, with the enormous increase in the amount of information in recent years, there is a demand for increased recording capacity (higher capacity) in magnetic tape. Means of increasing capacity include reducing the thickness of the magnetic tape and increasing the length of magnetic tape that can be stored in one magnetic tape cartridge. From this point of view, the thickness (total thickness) of the magnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm or less, more preferably 5.4 μm or less, even more preferably 5.3 μm or less, even more preferably 5.2 μm or less, and even more preferably 5.0 μm or less. Furthermore, 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.

[0086] The thickness (total thickness) of a magnetic tape can be measured by the following method. Ten tape samples (e.g., 5-10 cm in length) are cut from any part of the magnetic tape, and the thickness of these tape samples is measured by stacking them. The measured thickness is divided by 10 to obtain the value obtained (thickness per tape sample), which is defined 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.

[0087] The thickness of the non-magnetic support is preferably 2.0 to 5.0 μm, and more preferably 3.0 to 5.0 μm. The thickness of the magnetic layer can be optimized according to the saturation magnetization of the magnetic head used, the head gap length, the bandwidth of the recording signal, etc., and is generally 0.01 μm to 0.15 μm, preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.1 μm from the viewpoint of high-density recording. At least one magnetic layer is sufficient, and the magnetic layer may be separated into two or more layers having different magnetic properties, and known configurations for multilayer magnetic layers can be applied. When separated into two or more layers, the thickness of the magnetic layer is the total thickness of these layers. The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0.7 μm. The thickness of the backcoat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm. Various thicknesses, such as the thickness of the magnetic layer, can be determined by the following method. After exposing the cross-section of the magnetic tape in the thickness direction using an ion beam, the exposed cross-section is observed using a scanning electron microscope or a transmission electron microscope. Various thicknesses can be determined as the arithmetic mean of the thicknesses obtained at any two locations during the cross-sectional observation. Alternatively, various thicknesses can be determined as design thicknesses calculated from manufacturing conditions, etc.

[0088] <Manufacturing method> (Preparation of compositions for each layer) The process of preparing a composition for forming a magnetic layer, a non-magnetic layer, or a backcoat layer typically includes at least a kneading step, a dispersion step, and mixing steps provided before or after these steps as needed. Each individual step may be divided into two or more stages. The components used in preparing each layer-forming composition may be added at the beginning or in the middle of any of the steps. As the solvent, one or more of the various solvents commonly used in the manufacture of coated magnetic recording media can be used. For solvents, see, for example, paragraph 0153 of Japanese Patent Application Publication No. 2011-216149. Furthermore, individual components may be added in two or more separate steps. For example, a binder may be added in separate steps: a kneading step, a dispersion step, and a mixing step for viscosity adjustment after dispersion.

[0089] To manufacture the above-mentioned magnetic tape, conventional known manufacturing techniques can be used in various processes. In the kneading process, it is preferable to use an open kneader, continuous kneader, pressure kneader, extruder, or other equipment with strong kneading force. For details of these kneading processes, please refer to Japanese Patent Publication No. 1-106338 and Japanese Patent Publication No. 1-79274. Known dispersers can be used. Filtration may be performed by known methods at any stage in preparing each layer-forming composition. Filtration can be performed, for example, by filter filtration. As filters used for filtration, for example, filters with a pore size of 0.01 to 3 μm (e.g., glass fiber filters, polypropylene filters, etc.) can be used.

[0090] Ferromagnetic powder and protrusion-forming agent can also be dispersed simultaneously. More specifically, "simultaneous dispersion" refers to a method of preparing a magnetic layer-forming composition by adding a protrusion-forming agent solution (which substantially does not contain ferromagnetic powder) containing the protrusion-forming agent and solvent to the various components for preparing a magnetic liquid, such as ferromagnetic powder, solvent, and binder, at the mixing stage. "Substantially free of ferromagnetic powder" means that ferromagnetic powder is not added as a component of the protrusion-forming agent solution, and the presence of trace amounts of ferromagnetic powder as unintentionally introduced impurities is acceptable. Alternatively, the ferromagnetic powder and the protrusion-forming agent can be dispersed separately. More specifically, "separate dispersion" refers to a method of preparing a magnetic layer-forming composition by mixing a protrusion-forming agent solution (which substantially does not contain ferromagnetic powder) containing the protrusion-forming agent and solvent with magnetic liquid components such as ferromagnetic powder, solvent, and binder to prepare a magnetic liquid, and then adding the solution to the prepared magnetic liquid. The inventors surmise that by performing simultaneous dispersion, it becomes easier to suppress the aggregation of the protrusion-forming agent in the magnetic layer compared to performing separate dispersion, and as a result, the value of the rate of change in the protrusion area ratio tends to become smaller.

[0091] Furthermore, it is presumed that the longer the dispersion time in the process of preparing the composition for forming the non-magnetic layer, the denser the non-magnetic layer can be formed, thereby suppressing the sinking of the protrusion-forming agent into the magnetic layer due to reciprocating sliding. This is thought to contribute to reducing the value of the rate of change in the protrusion area ratio.

[0092] (coating process) The magnetic layer can be formed by, for example, directly coating a magnetic layer-forming composition onto a non-magnetic support, or by sequentially or simultaneously overcoating it with a non-magnetic layer-forming composition. When orientation processing is performed, the orientation processing is carried out on the coated layer in the orientation zone while the coated layer of the magnetic layer-forming composition is wet. Various known techniques, including those described in paragraph 0052 of Japanese Patent Application Publication No. 2010-24113, can be applied to the orientation processing. For example, vertical orientation processing can be performed by known methods such as using opposite-polarity opposing magnets. In the orientation zone, the drying rate of the coated layer can be controlled by the temperature and airflow of the drying air and / or the transport speed in the orientation zone. Alternatively, the coated layer may be pre-dried before being transported to the orientation zone. The backcoat layer can be formed by applying the backcoat layer forming composition to the side of the non-magnetic support opposite to the side that has (or will have) a magnetic layer. The coating process for forming each layer can be divided into two or more steps. For example, in one embodiment, the magnetic layer-forming composition can be coated in two or more steps. In this case, a drying treatment may or may not be performed between the two coating steps. Also, an orientation treatment may or may not be performed between the two coating steps. For details on the coating process for forming each layer, refer to paragraph 0066 of Japanese Patent Publication No. 2010-231843. Furthermore, known techniques can be applied to the drying process after coating each layer-forming composition.

[0093] (Other processes) After the above coating process, the magnetic tape is usually calendered to improve its surface smoothness. By strengthening the calendering conditions, a denser non-magnetic layer can be formed, which is thought to suppress the sinking of the protrusion-forming agent into the magnetic layer due to reciprocating sliding. This is thought to contribute to reducing the value of the rate of change of the protrusion area ratio. Strengthening the calendering conditions can be done, for example, by increasing the calendering pressure, increasing the calendering temperature, decreasing the calendering speed, or increasing the number of calendering cycles. Regarding the calendering conditions, the calendering pressure is, for example, 200 to 500 kN / m, preferably 250 to 350 kN / m, the calendering temperature is, preferably 90 to 120°C, more preferably 100 to 120°C, and the calendering speed is, for example, 50 to 300 m / min, preferably 80 to 200 m / min. The number of calendering cycles is preferably two or more, for example, it can be two to four times. For other processes for manufacturing magnetic tape, refer to paragraphs 0067 to 0070 of Japanese Patent Publication No. 2010-231843. Through various processes, a long roll of magnetic tape raw material can be obtained. The obtained magnetic tape raw material is then cut (slit) using a known cutting machine to the width of a magnetic tape to be housed in a magnetic tape cartridge, for example. The above width can be determined according to standards and is usually 1 / 2 inch. A servo pattern is typically formed on the magnetic tape obtained by slitting.

[0094] (Formation of servo patterns) "Forming a servo pattern" can also be described as "recording a servo signal." The formation of a servo pattern is explained below.

[0095] Servo patterns are typically formed along the longitudinal direction of the magnetic tape. Examples of control methods that utilize servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0096] As indicated in ECMA (European Computer Manufacturers Association)-319 (June 2001), magnetic tapes conforming to the LTO (Linear Tape-Open) standard (commonly referred to as "LTO tapes") employ a timing-based servo system. In this timing-based servo system, the servo pattern is composed of multiple pairs of non-parallel magnetic stripes (also called "servo stripes") arranged continuously along the longitudinal direction of the magnetic tape. In this invention and specification, "timing-based servo pattern" refers to a servo pattern that enables head tracking in a timing-based servo system. The reason the servo pattern is composed of pairs of non-parallel magnetic stripes, as described above, is to inform the servo signal reading element of its position as it passes over the servo pattern. Specifically, the pair of magnetic stripes are formed such that their spacing continuously changes along the width direction of the magnetic tape, and the servo signal reading element can determine the relative position between the servo pattern and the servo signal reading element by reading this spacing. This relative position information enables tracking of the data track. Therefore, multiple servo tracks are typically set up on the servo pattern, aligned with the width of the magnetic tape.

[0097] A servo band consists of a servo pattern that runs continuously along the longitudinal direction of the magnetic tape. Typically, multiple servo bands are provided on a magnetic tape. For example, in an LTO tape, there are five. The area between two adjacent servo bands is the data band. A data band consists of multiple data tracks, each corresponding to a servo track.

[0098] In one embodiment, as shown in Japanese Patent Publication No. 2004-318983, each servo band has embedded information indicating the servo band number (also called "servo band ID (identification)" or "UDIM (Unique DataBand Identification Method) information"). This servo band ID is recorded by shifting a specific pair of servo stripes within a servo band so that its position is displaced relative to the longitudinal direction of the magnetic tape. Specifically, the method of shifting a specific pair 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 a servo band can be uniquely identified by reading it with a servo signal reading element.

[0099] Furthermore, one method for uniquely identifying a servo band is the staggered method, as described in ECMA-319 (June 2001). In this staggered method, a group of non-parallel magnetic stripes (servo stripes) arranged continuously along the longitudinal direction of the magnetic tape are recorded in a manner that shifts each servo band along the longitudinal direction of the magnetic tape. Since the combination of this shift between adjacent servo bands is unique across the entire magnetic tape, it is possible to uniquely identify a servo band when reading the servo pattern with two servo signal reading elements.

[0100] Furthermore, each servo band typically contains embedded information indicating its position along the longitudinal direction of the magnetic tape (also known as "LPOS (Longitudinal Position) information"), as described in ECMA-319 (June 2001). This LPOS information, like the UDIM information, is recorded by shifting the positions of a pair of servo stripes along the longitudinal direction of the magnetic tape. However, unlike the UDIM information, the same signal is recorded for each servo band in this LPOS information.

[0101] It is also possible to embed information other than the UDIM and LPOS information mentioned above into the servo bands. In this case, the embedded information may be different for each servo band, like the UDIM information, or it may be common to all servo bands, like the LPOS information. Furthermore, methods other than those described above can be used to embed information in the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of servo stripes.

[0102] A servo pattern forming head is called a servo light head. A servo light head typically has a pair of gaps corresponding to the pair of magnetic stripes mentioned above, for each servo band. Typically, a core and a coil are connected to each pair of gaps, and by supplying current pulses to the coils, the magnetic field generated in the core can create a leakage magnetic field in the pair of gaps. When forming a servo pattern, by inputting current pulses while running a magnetic tape over the servo light head, the magnetic patterns corresponding to the pair of gaps are transferred to the magnetic tape, thereby forming the servo pattern. The width of each gap can be appropriately set according to the density of the servo pattern to be formed. For example, the width of each gap can be set to 1 μm or less, 1 to 10 μm, 10 μm or more, etc.

[0103] Before forming a servo pattern on a magnetic tape, it is usually demagnetized (erased). This erasing process can be performed by applying a uniform magnetic field to the magnetic tape using a DC or AC magnet. There are two types of erasing: DC (Direct Current) erasing and AC (Alternating Current) erasing. AC erasing is performed by gradually reducing the strength of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, DC erasing is performed by applying a unidirectional magnetic field to the magnetic tape. There are two further methods of DC erasing. The first method is horizontal DC erasing, which applies a unidirectional magnetic field along the longitudinal direction of the magnetic tape. The second method is vertical DC erasing, which applies a unidirectional magnetic field along the thickness direction of the magnetic tape. The erasing process may be performed on the entire magnetic tape or on each servo band of the magnetic tape.

[0104] The direction of the magnetic field of the formed servo pattern is determined according to the direction of the erase. For example, when a magnetic tape is horizontally DC erased, the servo pattern is formed such that the direction of the magnetic field is opposite to the direction of the erase. This makes it possible to increase the output of the servo signal obtained by reading the servo pattern. As shown in Japanese Patent Application Publication No. 2012-53940, when a magnetic pattern using the above gap is transferred to a vertically DC erased magnetic tape, the servo signal obtained by reading the formed servo pattern is in the shape of a single-pole pulse. On the other hand, when a magnetic pattern using the above gap is transferred to a horizontally DC erased magnetic tape, the servo signal obtained by reading the formed servo pattern is in the shape of a double-pole pulse.

[0105] <Vertical squareness ratio> In one embodiment, the vertical aspect ratio of the magnetic tape can be, for example, 0.55 or more, preferably 0.60 or more, and more preferably 0.65 or more, from the viewpoint of improving electromagnetic conversion characteristics. The upper limit of the aspect ratio is, in principle, 1.00 or less. The vertical aspect ratio of the magnetic tape can be 1.00 or less, and can be 0.95 or less, 0.90 or less, 0.85 or less, or 0.80 or less. A large value for the vertical aspect ratio of the magnetic tape is preferable from the viewpoint of improving electromagnetic conversion characteristics. The vertical aspect ratio of the magnetic tape can be controlled by known methods such as performing a vertical orientation process.

[0106] In the present invention and this specification, "vertical angle ratio" refers to the angle ratio measured in the vertical direction of the magnetic tape. In relation to the angle ratio, "vertical direction" refers to the direction perpendicular to the surface of the magnetic layer, and can also be referred to as the thickness direction. In the present invention and this specification, the vertical angle ratio is determined by the following method. A sample piece of a size suitable for introduction into a vibrating magnetometer is cut from the magnetic tape to be measured. Using a vibrating magnetometer, a magnetic field is applied to this sample piece perpendicular to the sample piece (in the direction perpendicular to the magnetic layer surface) at a maximum applied magnetic field of 3979 kA / m, a measurement temperature of 296 K, and a magnetic field sweep speed of 8.3 kA / m / sec, and the magnetization intensity of the sample piece against the applied magnetic field is measured. The measured magnetization intensity is obtained as a value after demagnetization correction and after subtracting the magnetization of the sample probe of the vibrating magnetometer as background noise. When the magnetization intensity at the maximum applied magnetic field is Ms and the magnetization intensity at zero applied magnetic field is Mr, the squareness ratio SQ is calculated as SQ = Mr / Ms. The measurement temperature refers to the temperature of the sample piece, and the temperature of the sample piece can be set to the measurement temperature by setting the ambient temperature around the sample piece to the measurement temperature, thereby achieving thermal equilibrium.

[0107] [Magnetic tape cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the magnetic tape described above.

[0108] Details of the magnetic tape included in the above magnetic tape cartridge are as described above.

[0109] In a magnetic tape cartridge, the magnetic tape is generally housed inside the cartridge body, wound onto a reel. The reel is rotatably mounted inside the cartridge body. Two types of magnetic tape cartridges are widely used: single-reel cartridges, which have one reel inside the cartridge body, and double-reel cartridges, which have two reels inside the cartridge body. When a single-reel magnetic tape cartridge is mounted in a magnetic tape device for recording and / or playing back data on magnetic tape, the magnetic tape is pulled out of the cartridge and wound onto the reel on the magnetic tape device. A magnetic head is positioned in the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and wound 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 time, the magnetic head and the magnetic layer surface of the magnetic tape come into contact and slide against each other, enabling data recording and / or playback. In contrast, a dual-reel magnetic tape cartridge has both a supply reel and a take-up reel located inside the magnetic tape cartridge.

[0110] The above-described magnetic tape cartridge may, in one embodiment, include a cartridge memory. The cartridge memory may be, for example, a non-volatile memory, and may already contain or contain head tilt angle adjustment information. The head tilt angle adjustment information is information for adjusting the head tilt angle while the magnetic tape is running within the magnetic tape device. For example, the head tilt angle adjustment information may include the values ​​of the servoband interval at each position in the longitudinal direction of the magnetic tape during data recording. For example, when playing back data recorded on the magnetic tape, the value of the servoband interval is measured during playback, and the control device of the magnetic tape device can change the head tilt angle so that the absolute value of the difference between this value and the servoband interval recorded in the cartridge memory at the same longitudinal position during recording approaches 0. The head tilt angle may be, for example, the angle θ described above. When recording and / or playing back data with the head tilted, the angle θ described above may be greater than 0° and may be 45° or less, 40° or less, or 35° or less.

[0111] The magnetic tape and magnetic tape cartridge described above can be suitably used in a magnetic tape device (in other words, a magnetic recording and playback system) that records and / or plays back data by changing the head tilt angle while the magnetic tape is running. In such a usage configuration, since the period during data recording and / or playback includes a period in which the head is tilted, a magnetic tape with high running stability when recording and / or playing back data with the head tilted is preferred. However, the magnetic tape and magnetic tape cartridge described above are not limited to those used in such magnetic tape devices. For example, there may be usage configurations in which the head tilt angle is changed for one recording or playback cycle and for subsequent recording or playback cycles, but the head tilt angle is fixed and does not change during each recording or playback cycle. In such usage configurations, since there is a period during data recording and / or playback in which the head is tilted, magnetic tape with high running stability when recording and / or playing back data with the head tilted is preferred.

[0112] [Magnetic tape drive] One aspect of the present invention relates to a magnetic tape device including the magnetic tape described above. In the magnetic tape device, recording data onto the magnetic tape and / or reproducing data recorded on the magnetic tape can be performed, for example, by bringing the magnetic layer surface of the magnetic tape into contact with a magnetic head and sliding it. The magnetic tape device may detachably include a magnetic tape cartridge according to one aspect of the present invention.

[0113] The above-described magnetic tape cartridge can be mounted in a magnetic tape device equipped with a magnetic head and used for recording and / or reproducing data. In the present invention and herein, “magnetic tape device” means a device capable of recording data onto a magnetic tape and reproducing data recorded on a magnetic tape. Such a device is generally referred to as a drive.

[0114] <Magnetic head> The above magnetic tape device may include a magnetic head. The configuration of the magnetic head and the angle θ, which is the head tilt angle, are as previously explained with reference to Figures 1 to 3. The magnetic head included in the above magnetic tape device may be an LTO8 head in one embodiment, an LTO head of another generation in another embodiment, or a magnetic head other than an LTO head in yet another embodiment. If the magnetic head includes a playback element, a magnetoresistive (MR) element that can read information recorded on the magnetic tape with high sensitivity is preferred as the playback element. Various known MR elements (e.g., GMR (Giant Magnetoresistive) elements, TMR (Tunnel Magnetoresistive) elements, etc.) can be used as the MR element. Hereinafter, the magnetic head that records data and / or plays back recorded data will also be called the "recording / playback head". The elements for recording data (recording elements) and the elements for playing back data (playback elements) will be collectively referred to as "magnetic head elements".

[0115] When recording data and / or playing back recorded data, tracking using servo signals can be performed first. That is, by making the servo signal reading element 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 achieved by changing the servo track read by the servo signal reading element in the tape width direction. Furthermore, the recording / playback head can also record and / or play back data on other data bands. In this case, the servo signal reading element can be moved to a predetermined servo band using the UDIM information described earlier, and tracking for that servo band can be started.

[0116] Figure 4 shows an example of the arrangement of data bands and servo bands. In Figure 4, multiple servo bands 1 are arranged on the magnetic layer of the magnetic tape MT, sandwiched between guide bands 3. Multiple regions 2 sandwiched between two servo bands are the data bands. A servo pattern is a magnetized region, formed by magnetizing a specific region of the magnetic layer with a servo light head. The region magnetized by the servo light head (the position where the servo pattern is formed) is defined by the standard. For example, in the industry standard LTO Ultrium format tape, multiple servo patterns inclined with respect to the tape width direction are formed on the servo bands during magnetic tape manufacturing, as shown in Figure 5. More specifically, in Figure 5, the servo frame SF on the servo band 1 consists of a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). The servo subframe 1 consists of an A-burst (indicated as A in Figure 5) and a B-burst (indicated as B in Figure 5). The A-burst consists of servo patterns A1 to A5, and the B-burst consists of servo patterns B1 to B5. On the other hand, servo subframe 2 consists of C-bursts (indicated as C in Figure 5) and D-bursts (indicated as D in Figure 5). C-bursts consist of servo patterns C1 to C4, and D-bursts consist of servo patterns D1 to D4. These 18 servo patterns are arranged in sets of 5 and 4 on subframes in a 5, 5, 4, 4 sequence, and are used to identify the servo frames. Figure 5 shows one servo frame for illustrative purposes. However, in reality, in the magnetic layer of a magnetic tape where timing-based servo head tracking is performed, multiple servo frames are arranged in the direction of travel for each servo band. In Figure 5, the arrows indicate the direction of travel of the magnetic tape. For example, LTO Ultrium format tape typically has more than 5000 servo frames per meter of tape length in each servo band of the magnetic layer.

[0117] In the above-described magnetic tape device, the head tilt angle can be changed while the magnetic tape is running within the magnetic tape device. The head tilt angle is, for example, the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape. The angle θ is as previously explained. For example, by providing an angle adjustment unit in the recording / playback head unit of the magnetic head to adjust the angle of the magnetic head module, the angle θ can be variably adjusted while the magnetic tape is running. Such an angle adjustment unit may include, for example, a rotation mechanism that rotates the module. Known technologies can be applied to the angle adjustment unit.

[0118] Regarding the head tilt angle during magnetic tape travel, if the magnetic head contains multiple modules, the angle θ can be defined for a randomly selected module, as explained with reference to Figures 1 to 3. The angle θ at the start of magnetic tape travel is θ. initial It can be set to 0° or greater than or equal to 0°. initial The larger the angle θ, the greater the change in the effective distance between servo signal reading elements in response to the change in angle θ. This is preferable from the standpoint of adjustment capability to adjust the effective distance between servo signal reading elements in response to changes in the width direction of the magnetic tape. initial The angle is preferably 1° or more, more preferably 5° or more, and even more preferably 10° or more. On the other hand, regarding the angle between the magnetic layer surface and the contact surface of the magnetic head when the magnetic tape is running and in contact with the magnetic head (generally called the "lap angle"), keeping the deviation in the tape width direction small is effective in improving the uniformity of friction in the tape width direction caused by contact between the magnetic head and the magnetic tape during magnetic tape running. Furthermore, improving the uniformity of the friction in the tape width direction is desirable from the viewpoint of the magnetic head's position tracking ability and running stability. From the viewpoint of reducing the deviation of the lap angle in the tape width direction, θ initial The angle is preferably 45° or less, more preferably 40° or less, and even more preferably 35° or less.

[0119] Regarding the change in angle θ during magnetic tape movement, for recording data onto magnetic tape and / or for playing back data recorded on magnetic tape, the angle θ of the magnetic head remains constant from the initial angle θ while the magnetic tape is moving in the magnetic tape drive. initial When it changes from, the maximum change in angle θ during magnetic tape travel, Δθ, is calculated by the following formula: max and Δθ min Among these, it is the larger value. The maximum value of the angle θ during magnetic tape travel is θ max The minimum value is θ. min That is the case. Note that "max" is an abbreviation for maximum, and "min" is an abbreviation for minimum. Δθ max =θ max -θ initial Δθ min =θ initial -θ min

[0120] In one embodiment, Δθ can be greater than 0.000°, and from the viewpoint of adjustment capability to adjust the effective distance between servo signal reading elements in response to changes in the width direction of the magnetic tape, it is preferably 0.001° or more, and more preferably 0.010° ​​or more. Furthermore, from the viewpoint of ease of ensuring synchronization of recorded data and / or playback data between multiple magnetic head elements during data recording and / or playback, Δθ is preferably 1.000° or less, more preferably 0.900° or less, even more preferably 0.800° or less, even more preferably 0.700° or less, and even more preferably 0.600° or less.

[0121] In the examples shown in Figures 2 and 3, the axis of the element array is tilted toward the direction in which the magnetic tape travels. However, the present invention is not limited to such examples. Embodiments in which the axis of the element array is tilted toward the direction opposite to the direction in which the magnetic tape travels are also included in the present invention.

[0122] θ is the head tilt angle at the start of magnetic tape playback. initialThis can be set by the control device of the magnetic tape drive, etc. Regarding the head tilt angle during magnetic tape travel, Figure 6 is an explanatory diagram of the method for measuring the angle θ during magnetic tape travel. The angle θ during magnetic tape travel can be determined, for example, by the following method. When determining the angle θ during magnetic tape travel by the following method, the angle θ is to be varied within the range of 0 to 90° during magnetic tape travel. That is, if the axis of the element array is tilted toward the direction of magnetic tape travel at the start of magnetic tape travel, the element array will not be tilted during magnetic tape travel so that the axis of the element array is tilted toward the direction of magnetic tape travel at the start of magnetic tape travel, and if the axis of the element array is tilted toward the direction of magnetic tape travel at the start of magnetic tape travel, the element array will not be tilted during magnetic tape travel so that the axis of the element array is tilted toward the direction of magnetic tape travel at the start of magnetic tape travel. The phase difference (i.e., time difference) ΔT of the regenerated signals from a pair of servo signal reading elements 1 and 2 is measured. ΔT can be measured by a measurement unit provided in the magnetic tape device. The configuration of such a measurement unit is well known. The distance L between the center of servo signal reading element 1 and the center of servo signal reading element 2 can be measured using an optical microscope or the like. When the magnetic tape travels at speed v, the distance between the centers of the two servo signal reading elements in the direction of magnetic tape travel is Lsinθ, and the relationship Lsinθ = v × ΔT holds. Therefore, the angle θ during magnetic tape travel can be calculated using the formula "θ = arcsin(vΔT / L)". Note that Figure 6 (right) shows an example where the axis of the element array is tilted toward the direction of magnetic tape travel. In this example, the phase difference (i.e., time difference) ΔT between the phase of the regenerated signal from servo signal reading element 1 and the phase of the regenerated signal from servo signal reading element 2 is measured. If the axis of the element array is tilted in the direction opposite to the direction in which the magnetic tape travels, θ can be determined by the above method, except that ΔT is measured as the phase difference (i.e., time difference) between the phase of the regenerated signal of servo signal reading element 1 and the phase of the regenerated signal of servo signal reading element 2. Furthermore, the measurement pitch for the angle θ, that is, the measurement interval for the angle θ in the longitudinal direction of the tape, can be selected according to the frequency of tape width deformation in the longitudinal direction of the tape. For example, the measurement pitch can be set to, for example, 250 μm.

[0123] <Configuration of a magnetic tape drive> The magnetic tape device 10 shown in Figure 7 controls the recording and playback head unit 12 based on commands from the control device 11, and performs data recording and playback on the magnetic tape MT. The magnetic tape device 10 has a configuration that allows for the detection and adjustment of tension applied in the longitudinal direction of the magnetic tape from spindle motors 17A, 17B and their drive units 18A, 18B that control the rotation of the magnetic tape cartridge reel and the take-up reel. The magnetic tape device 10 has a configuration that allows a magnetic tape cartridge 13 to be loaded. The magnetic tape device 10 has a cartridge memory read / write device 14 that can read from and write to the cartridge memory 131 in the magnetic tape cartridge 13. From the magnetic tape cartridge 13 mounted in the magnetic tape device 10, the end of the magnetic tape MT or the leader pin is pulled out by an automatic loading mechanism or manually, and the magnetic layer surface of the magnetic tape MT passes over the recording / playback head of the recording / playback head unit 12 through guide rollers 15A and 15B with the magnetic layer surface of the magnetic tape MT in contact with the surface of the recording / playback head, and the magnetic tape MT is wound onto the take-up reel 16. The rotation and torque of spindle motors 17A and 17B are controlled by signals from the control device 11, so that the magnetic tape MT runs at a desired speed and tension. A servo pattern pre-formed on the magnetic tape can be used to control the tape speed and head tilt angle. A tension detection mechanism may be provided between the magnetic tape cartridge 13 and the take-up reel 16 for tension detection. In addition to control by spindle motors 17A and 17B, tension may also be controlled using guide rollers 15A and 15B. The cartridge memory read / write device 14 is configured to read and write information to the cartridge memory 131 in response to commands from the control device 11. For example, the ISO (International Organization for Standardization) 14443 standard can be used as the communication method between the cartridge memory read / write device 14 and the cartridge memory 131.

[0124] The control device 11 includes, for example, a control unit, a storage unit, a communication unit, and the like.

[0125] The recording / playback head unit 12 consists of, for example, a recording / playback head, a servo tracking actuator for adjusting the position of the recording / playback head in the track width direction, a recording / playback amplifier 19, and a connector cable for connecting to the control device 11. The recording / playback head consists of, for example, a recording element for recording data on magnetic tape, a playback element for reproducing data on magnetic tape, and a servo signal reading element for reading servo signals recorded on magnetic tape. Within a single magnetic head, for example, one or more recording elements, playback elements, and servo signal reading elements are mounted. Alternatively, each element may be separately contained in multiple magnetic heads corresponding to the direction in which the magnetic tape travels.

[0126] The recording / playback head unit 12 is configured to record data onto the magnetic tape MT in response to commands from the control device 11. It is also configured to play back data recorded on the magnetic tape MT in response to commands from the control device 11.

[0127] The control device 11 has a mechanism to determine the running position of the magnetic tape MT from the servo signals read from the servo bands when the magnetic tape MT is running, and to control the servo tracking actuator so that the recording element and / or playback element are positioned at the target running position (track position). This track position control is performed, for example, by feedback control. The control device 11 has a mechanism to determine the servo band spacing from the servo signals read from two adjacent servo bands when the magnetic tape MT is running. The control device 11 can store the determined servo band spacing information in its internal storage unit, cartridge memory 131, or external connected equipment. Furthermore, the control device 11 can change the head tilt angle according to the dimensional information in the width direction of the running magnetic tape. This makes it possible to bring the effective distance between servo signal reading elements close to or match the servo band spacing. The above dimensional information can be obtained using a servo pattern pre-formed on the magnetic tape. For example, while the magnetic tape is running within the magnetic tape device, the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape can be changed according to the width direction dimensional information of the magnetic tape acquired during the running process. The head tilt angle can be adjusted, for example, by feedback control. Alternatively, the head tilt angle can also be adjusted, for example, by the method described in Japanese Patent Publication No. 2016-524774 (Patent Document 1) or US2019 / 0164573A1 (Patent Document 2). [Examples]

[0128] The present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. In the following, "parts" refers to "parts by mass". Furthermore, unless otherwise specified, the processes and evaluations described below were carried out in an environment of 23°C ± 1°C. In the following, "eq" refers to equivalent, and is a unit that cannot be converted to SI units.

[0129] [Protrusion-forming agent] The protrusion-forming agents used in the preparation of the magnetic layer-forming compositions for the production of the magnetic tapes in the examples or comparative examples are as follows: Protrusion-forming agent A: Asahi Carbon Co., Ltd. Asahi #50 (carbon black), average particle size 60 nm, Mohs hardness is shown in Table 1. Protrusion-forming agent B: Colloidal silica manufactured by Fuso Chemical Co., Ltd., average particle size 90 nm, Mohs hardness is shown in Table 1. Protrusion-forming agent C: Colloidal silica TPX-5200 manufactured by Cabot, average particle size 60 nm, Mohs hardness is shown in Table 1.

[0130] [Fatty acid esters] The fatty acid esters used in the preparation of the magnetic layer-forming composition and the non-magnetic layer-forming composition for the production of the magnetic tapes in the examples or comparative examples are as follows: Fatty acid ester a: sec(secondary) butyl stearate Fatty acid ester b: Butyl palmitate

[0131] [Ferromagnetic powder] In Table 1, "BaFe" refers to hexagonal barium ferrite powder (coercivity Hc: 196 kA / m, average particle size (average plate diameter) 24 nm). In Table 1, "SrFe1" is hexagonal strontium ferrite powder prepared by the following method. 1707g of SrCO3, 687g of H3BO3, 1120g of Fe2O3, 45g of Al(OH)3, 24g of BaCO3, 13g of CaCO3, and 235g of Nd2O3 were weighed out 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 molten material, the outlet at the bottom of the platinum crucible was heated, and the molten material was dispensed in a rod shape at approximately 6 g / second. The dispensed material was rolled and rapidly cooled using water-cooled twin rollers to produce an amorphous body. 280g of the prepared amorphous material was placed in an electric furnace and heated to 635°C (crystallization temperature) at a heating rate of 3.5°C / min. The temperature was maintained at this temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystalline material obtained above, containing hexagonal strontium ferrite particles, was coarsely ground in a mortar. 1000g of 1mm particle size zirconia beads and 800ml of 1% aqueous acetic acid solution were added to this mixture in a glass bottle, and the mixture was dispersed in a paint shaker for 3 hours. After that, the resulting dispersion was separated from the beads and placed in a stainless steel beaker. The dispersion was allowed to stand at a temperature of 100°C for 3 hours to dissolve the glass components, then precipitated using a centrifuge, and washed by repeated decantation. Finally, it was dried in a heating furnace at a 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 The anisotropy constant Ku is 2.2 × 10⁻⁶. 5 J / m 3 , mass magnetization σs is 49A m 2 It was / kg. A sample powder of 12 mg was taken from the hexagonal strontium ferrite powder obtained above, and the elemental analysis of the filtrate obtained by partially dissolving this sample powder under the dissolution conditions exemplified earlier was performed using an ICP analyzer to determine the surface layer content of neodymium atoms. Separately, 12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and the elemental analysis of the filtrate obtained by completely dissolving this sample powder under the dissolution conditions exemplified earlier was performed using an ICP analyzer to determine the bulk content of neodymium atoms. The neodymium atom content (bulk content) relative to 100 atomic percent of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic percent. Furthermore, the neodymium atom content in the surface layer was 8.0 atomic percent. The ratio of surface layer content to bulk content, "surface layer content / bulk content," was 2.8, confirming that neodymium atoms were concentrated in the surface layer of the particles. The hexagonal ferrite crystal structure of the powder obtained above was confirmed by scanning with CuKα rays at a voltage of 45kV and intensity of 40mA, and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above showed a magnetoplanbite-type (M-type) hexagonal ferrite crystal structure. Furthermore, the crystalline phase detected by X-ray diffraction analysis was a single phase of the magnetoplanbite type. PANalytical X'Pert Pro diffractometer, PIXcel detector Soller slit for incident and diffracted beams: 0.017 radians Fixed angle of dispersion slit: 1 / 4 degree Mask: 10mm Scatter prevention 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

[0132] In Table 1, "SrFe2" is hexagonal strontium ferrite powder prepared by the following method. 1725g of SrCO3, 666g of H3BO3, 1332g of Fe2O3, 52g of Al(OH)3, 34g of CaCO3, and 141g of BaCO3 were weighed out 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 1380°C. While stirring the molten material, the outlet at the bottom of the platinum crucible was heated, and the molten material was dispensed in a rod shape at a rate of approximately 6 g / second. The dispensed material was rolled and rapidly cooled using water-cooled twin rollers to produce an amorphous body. 280g of the obtained amorphous material was placed in 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 crystalline material obtained above, containing hexagonal strontium ferrite particles, was coarsely ground in a mortar. 1000g of 1mm particle size zirconia beads and 800ml of 1% aqueous acetic acid solution were added to this mixture in a glass bottle, and the mixture was dispersed in a paint shaker for 3 hours. After that, the resulting dispersion was separated from the beads and placed in a stainless steel beaker. The dispersion was allowed to stand at a temperature of 100°C for 3 hours to dissolve the glass components, then precipitated using a centrifuge, and washed by repeated decantation. Finally, it was dried in a heating furnace at a 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 is 2.0 × 10⁻⁶. 5 J / m 3 , mass magnetization σs is 50A m 2 It was / kg.

[0133] In Table 1, "ε-iron oxide" refers to ε-iron oxide powder prepared by the following method. In 90 g of pure water, 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. While stirring with a magnetic stirrer in an air atmosphere at an ambient temperature of 25°C, 4.0 g of a 25% aqueous ammonia solution was added, and the mixture was stirred for 2 hours at the same ambient temperature of 25°C. To the resulting solution, a citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added, and the mixture was stirred for 1 hour. After stirring, the precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating furnace at an ambient temperature of 80°C. 800g of pure water was added to the dried powder, and the powder was dispersed in the water again to obtain a dispersion. The obtained dispersion was heated to 50°C, and 40g of a 25% aqueous ammonia solution was added dropwise while stirring. After stirring for 1 hour while maintaining the temperature at 50°C, 14mL of tetraethoxysilane (TEOS) was added dropwise, and the mixture was stirred for 24 hours. 50g of ammonium sulfate was added to the resulting reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating furnace at a temperature of 80°C for 24 hours to obtain a precursor of ferromagnetic powder. The obtained ferromagnetic powder precursor was loaded into a heating furnace at a temperature of 1000°C under an atmospheric environment and subjected to a heat treatment for 4 hours. A heat-treated ferromagnetic powder precursor was added to a 4 mol / L sodium hydroxide (NaOH) aqueous solution, and the solution was stirred for 24 hours while maintaining the temperature at 70°C to remove silicate compounds, which are impurities, from the heat-treated ferromagnetic powder precursor. Subsequently, the ferromagnetic powder, from which the silicate compounds were removed by centrifugation, was collected and washed with pure water to obtain ferromagnetic powder. The composition of the obtained ferromagnetic powder was confirmed by inductively coupled plasma emission spectroscopy (ICP-OES), revealing that it was a Ga, Co, and Ti-substituted ε-iron oxide (ε-Ga 0.28 Co 0.05 Ti 0.05 Fe 1.62 It was O3). Furthermore, X-ray diffraction analysis was performed under the same conditions as described earlier for SrFe1, and from the peaks of the X-ray diffraction pattern, it was confirmed that the obtained ferromagnetic powder had a single-phase crystalline structure of the ε phase (crystalline structure of ε-iron oxide), which did not contain the crystalline structures of the α phase and γ phase. The average particle size of the obtained ε-iron oxide powder was 12 nm, and the activation volume was 746 nm. 3 The anisotropy constant Ku is 1.2 × 10⁻⁶. 5 J / m 3 , mass magnetization σs is 16A m 2 It was / kg.

[0134] The activation volume and anisotropy constant Ku of the hexagonal strontium ferrite powder and ε-iron oxide powder described above were obtained for each ferromagnetic powder using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) and the method described above. Furthermore, the mass magnetization σs was measured using a vibrating sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.) at a magnetic field strength of 15 kOe.

[0135] [Nonmagnetic support] In Table 1, "PEN" indicates a polyethylene naphthalate support, and "PA" indicates an aromatic polyamide support.

[0136] [Example 1] <Composition for forming magnetic layer> (Magnetic liquid) Ferromagnetic powder (see Table 1): 100.0 parts Oleic acid: 2.0 parts Vinyl chloride copolymer (Kaneka Corporation MR-104): 10.0 parts SO3Na group-containing polyurethane resin: 4.0 parts (Weight average molecular weight 70000, SO3Na group: 0.07meq / g) Additive A: 10.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts (Abrasive solution) α-Alumina (average particle size: 110 nm): 6.0 parts Vinyl chloride copolymer (Kaneka Corporation MR110): 0.7 parts Cyclohexanone: 20.0 parts (Protrusion-forming agent liquid) Protrusion-forming agent (see Table 1): See Table 1 Methyl ethyl ketone: 6.0 parts Cyclohexanone: 4.0 parts (Other ingredients) 1.0 part stearic acid Stearic acid amide: 0.3 parts Fatty acid esters (see Table 1): See Table 1 Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Tosoh Corporation's Coronate® L): 3.0 parts

[0137] The additive A described above is a polymer synthesized by the method described in paragraphs 0115 to 0123 of Japanese Patent Publication No. 2016-051493.

[0138] <Composition for forming non-magnetic layer> Non-magnetic inorganic powder (α-iron oxide): 80.0 parts (Average particle size: 0.15 μm, average acicular ratio: 7, BET (Brunauer-Emmett-Teller) specific surface area: 52 m 2 / g) Carbon black (average particle size: 20nm): 20.0 parts Electron beam curable vinyl chloride copolymer: 13.0 parts Electron beam curable polyurethane resin: 6.0 parts Phenylephosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Fatty acid esters of the same type as those added to the magnetic layer forming composition: 2.0 parts Stearic acid: 1.0 part

[0139] <Composition for forming a backcoat layer> Non-magnetic inorganic powder (α-iron oxide): 80.0 parts (Average particle size: 0.15 μm, average needle-like ratio: 7, BET specific surface area: 52 m²) 2 / g) Carbon black (average particle size: 20nm): 20.0 parts Carbon black (average particle size: 100nm): 3.0 parts Vinyl chloride copolymer: 13.0 parts Sulfonic acid group-containing polyurethane resin: 6.0 parts Phenylephosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Stearic acid: 3.0 parts Polyisocyanate (Tosoh Corporation's Coronate® L): 5.0 parts Methyl ethyl ketone: 400.0 parts

[0140] <Preparation of compositions for forming each layer> The magnetic layer formation composition was prepared by the following method. After mixing and diluting the components of the magnetic liquid and the protrusion-forming agent liquid using an open kneader, a dispersion was obtained by performing a dispersion process (simultaneous dispersion) in 12 passes using a horizontal bead mill disperser with zirconia (ZrO2) beads with a particle size of 0.5 mm (hereinafter referred to as "Zr beads"), at a bead filling rate of 80 volume%, a rotor tip peripheral speed of 10 m / sec, and a residence time of 2 minutes per pass. After mixing the components of the abrasive solution, it was placed in a vertical sand mill disperser along with 1 mm particle size Zr beads. The mixture was adjusted so that 100 × bead volume / (abrasive liquid volume + bead volume) was 60%, and the sand mill dispersion treatment was performed for 180 minutes. The treated liquid was then removed and subjected to ultrasonic dispersion filtration using a flow-type ultrasonic dispersion filtration device. The dispersion prepared by the above simultaneous dispersion method, the abrasive solution, and the other components were introduced into a dissolver stirrer and stirred at a peripheral speed of 10 m / sec for 30 minutes. After that, the mixture was subjected to three passes using a flow-type ultrasonic disperser at a flow rate of 7.5 kg / min, and then filtered through a filter with a pore size of 1 μm to prepare a composition for forming a magnetic layer.

[0141] The non-magnetic layer forming composition was prepared by the following method. The above components, excluding the lubricants (fatty acid ester and stearic acid), were kneaded and diluted using an open kneader, and then dispersed using a horizontal bead mill disperser for the dispersion time shown in Table 1. Subsequently, the lubricants (fatty acid ester and stearic acid) were added and mixed using a dissolver stirrer to prepare a composition for forming a non-magnetic layer.

[0142] The backcoat layer forming composition was prepared by the following method. The above components, excluding the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts), were kneaded and diluted using an open kneader, and then dispersed using a horizontal bead mill disperser. Subsequently, the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts) were added and mixed using a dissolver stirrer to prepare a composition for forming the back coat layer.

[0143] <Manufacturing of magnetic tapes and magnetic tape cartridges> A non-magnetic layer-forming composition was applied to a biaxially oriented non-magnetic support (type: see Table 1) of the thickness shown in Table 1, so that the thickness after drying was 0.6 μm. After drying, it was irradiated with an electron beam at an accelerating voltage of 125 kV to an energy of 40 kGy. A magnetic layer-forming composition was then applied on top of this to form a coated layer with a thickness after drying of 0.1 μm. While this coated layer was still wet, a magnetic field of strength 0.5 T was applied perpendicularly to the surface of the coated layer of the magnetic layer-forming composition in the orientation zone to perform a vertical orientation treatment, and then the coated layer was dried. Furthermore, a back coat layer-forming composition was applied to the surface of the support opposite to the surface where the non-magnetic layer and magnetic layer were formed, so that the thickness after drying was 0.3 μm, and it was dried. Subsequently, a seven-stage calender roll consisting solely of metal rolls was used to perform calendering at a calendering speed of 80 m / min, a linear pressure of 294 kN / m, and the calendering temperature (surface temperature of the calender roll) listed in Table 1, for the number of times listed in Table 1. After that, a heat treatment was performed for 36 hours in an ambient temperature of 70°C. After the heat treatment, the material was slit into 1 / 2-inch width strips, and the surface of the magnetic layer was cleaned using a tape cleaning device equipped with a feed and winding mechanism for the slit strips, in which the nonwoven fabric and razor blade were mounted so as to press against the magnetic layer surface, thereby obtaining a magnetic tape. By recording servo signals on the magnetic layer of the obtained magnetic tape using a commercially available servo writer, a magnetic tape was obtained having data bands, servo bands, and guide bands arranged in accordance with the LTO (Linear Tape-Open) Ultrium format, and having a servo pattern (timing-based servo pattern) on the servo bands arranged and shaped in accordance with the LTO Ultrium format. The servo pattern thus formed is a servo pattern that conforms to the descriptions in 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 (960m in length) on which the servo signals were recorded was then wound onto a reel of a magnetic tape cartridge (LTO Ultrium8 data cartridge). In this way, a magnetic tape cartridge was created in which magnetic tape was wound onto a reel.

[0144] [Examples 2-17, Comparative Examples 1-5] A magnetic tape and magnetic tape cartridge were obtained using the method described for Example 1, except that the items shown in Table 1 were changed as shown in Table 1. In Table 1, for the examples where "simultaneous dispersion" is indicated in the column for the mixing method of the protrusion-forming agent, simultaneous dispersion was performed as described in Example 1. For the comparative examples in Table 1 where "separate dispersion" is indicated in the column for the mixing format of the protrusion-forming agent, the magnetic layer-forming compositions were prepared as follows. After mixing and diluting the components of the magnetic liquid using an open kneader, the magnetic liquid was obtained by dispersing them in a horizontal bead mill using zirconia (ZrO2) beads (Zr beads) with a particle size of 0.5 mm, at a bead filling rate of 80 volume%, a rotor tip peripheral speed of 10 m / sec, and a residence time of 2 minutes per pass, for a total of 12 passes. After mixing the components of the abrasive solution, it was placed in a vertical sand mill disperser along with 1 mm particle size Zr beads. The ratio of bead volume to (abrasive liquid volume + bead volume) was adjusted to 60%, and the sand mill dispersion treatment was performed for 180 minutes. The treated liquid was then removed and subjected to ultrasonic dispersion filtration using a flow-type ultrasonic dispersion filtration device. The protrusion-forming agent solution was prepared by mixing its components and then ultrasonically treating (dispersing) it with a horn-type ultrasonic disperser at an ultrasonic output of 500 watts per 200 cc for 60 minutes. The resulting dispersion was then filtered through a filter with a pore size of 0.5 μm. The magnetic liquid, abrasive liquid, protrusion-forming agent liquid, and the other components mentioned above were introduced into a dissolver stirrer and stirred at a peripheral speed of 10 m / s for 30 minutes. After that, the mixture was subjected to three passes 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 a composition for forming a magnetic layer.

[0145] For each of the above examples and comparative examples, four magnetic tape cartridges were prepared. One was used for the evaluation of running stability described below, and the other three were used for the evaluations of the magnetic tape described below (1) to (3).

[0146] [Evaluation of driving stability] The driving stability was evaluated using the following method in an environment with a temperature of 35°C and a relative humidity of 80%. Data recording and playback were performed using the magnetic tape cartridges of the examples and comparative examples, with a magnetic tape device configured as shown in Figure 7. The arrangement of modules included in the recording / playback head mounted on the recording / playback head unit is "recording module - playback module - recording module" (total number of modules: 3). Each module has 32 magnetic head elements (Ch0 to Ch31), and these magnetic head elements are sandwiched between a pair of servo signal reading elements to form an element array. The following method was used to record and play back data and evaluate playback stability during playback, with the head tilt angle set to 15°. The head tilt angle is the angle θ that the axis of the element array of the playback module makes with respect to the width direction of the magnetic tape at the start of playback. The angle θ was set by the control device of the magnetic tape device at the start of magnetic tape playback, and the head tilt angle was fixed during magnetic tape playback. A magnetic tape cartridge is set in the magnetic tape drive, and the magnetic tape is loaded. Next, while performing servo tracking, the recording / playback head unit records pseudo-random data with a specific data pattern onto the magnetic tape. The tension applied along the length of the tape is kept constant. Simultaneously with data recording, the servo band spacing along the entire length of the tape is measured every 1 meter along the length and recorded in the cartridge memory. Next, the recording / playback head unit plays back the data recorded on the magnetic tape while performing servo tracking. The tension applied in the longitudinal direction of the tape during this process is kept constant. During the playback described above, the standard deviation of the reading position PES (Position Error Signal) in the width direction, based on the servo signal obtained by the servo signal reading element (hereinafter referred to as "σPES"), was used as an indicator to evaluate driving stability. PES is calculated using the following method. To determine the PES, the dimensions of the servo pattern are necessary. The standard for servo pattern dimensions varies depending on the generation of the LTO. Therefore, first, the average distance AC between the four corresponding stripes of the A-burst and C-burst, and the azimuth angle α of the servo pattern are measured using a magnetic force microscope or similar device. The average time between the 5 stripes corresponding to A-bursts and B-bursts over the length of 1 LPOS word is defined as 'a'. The average time between the 4 corresponding stripes of A-bursts and C-bursts over the length of 1 LPOS word is defined as 'b'. In this case, the value defined as AC × (1 / 2 - a / b) / (2 × tan(α)) is the widthwise reading position PES (Position Error Signal) based on the servo signal obtained by the servo signal reading element over the length of 1 LPOS word. For magnetic tape, the end on the side wound onto the reel of the magnetic tape cartridge is called the inner end, and the opposite end is called the outer end. With the outer end set to 0m, the standard deviation (σPES) of the PES obtained using the above method was calculated for the longitudinal region of the tape from 30m to 200m. If the σPES obtained in this way is 50nm or less, it can be judged that the running stability is excellent.

[0147] [Evaluation of magnetic tape] (1) Rate of change of the ratio of the protrusion area, kinetic friction force F Magnetic tapes were removed from each magnetic tape cartridge in the examples and comparative examples, and subjected to 1000 reciprocating slides in an environment of 35°C and 80% relative humidity using the method described above. The ratio of the protrusion area after the reciprocating slides was determined using the method described above. The ratio of the protrusion area was also determined for the portion of the magnetic tape that had not undergone 1000 reciprocating slides using the method described above. From the ratio of the protrusion area before and after the reciprocating slides, the rate of change in the protrusion area ratio was calculated using the formula described above. Furthermore, the kinetic friction force F during the 1000th forward stroke in 1000 reciprocating sliding cycles was determined using the method described above. For the LTO8 head, a commercially available LTO8 head (manufactured by IBM) was used.

[0148] (2) Coefficient of variation of the equivalent circular diameter in the bright area Using a Hitachi FE-SEM S4800 as the scanning electron microscope (FE-SEM), the coefficient of variation of the equivalent circle diameter in the bright area region of each magnetic tape was determined by the following method. A scanning electron microscope (FE-SEM) was used to capture a secondary electron image of the magnetic layer surface of the magnetic tape being measured. The measurement location was randomly selected from a single location. Imaging was performed on the magnetic layer surface where the aforementioned reciprocating sliding had not occurred. The imaging conditions were: acceleration voltage of 5kV, working distance of 8mm, and magnification of 10,000x. During imaging, an unimaged area of ​​the magnetic layer surface was selected, and the focus was adjusted under the above imaging conditions to capture a secondary electron image. From the captured image, the parts indicating size (micron bars, cross marks, etc.) were removed, and a secondary electron image with a resolution of 960 pixels × 1280 pixels was obtained. The resulting secondary electron images were imported into image processing software and binarized using the following procedure. ImageJ, a free software, was used for image analysis. The thresholds used to binarize the secondary electron image obtained above were set to a lower limit of 100 gradations and an upper limit of 130 gradations. Binarization was performed using these two thresholds. After binarization, noise component removal was performed using image analysis software. Specifically, the noise reduction process, Despeckle, was selected in the image analysis software ImageJ to remove noise components. The resulting binarized image was then analyzed using image analysis software to determine the area of ​​each of the multiple highlight regions (i.e., white areas) contained within the binarized image. From the areas of these highlight regions, the equivalent circular diameter of each highlight region was calculated. Specifically, the equivalent circular diameter L was calculated from the calculated area A using the formula 2 × (A / π)^(1 / 2) = L. For the equivalent diameter L obtained in this way, the coefficient of variation of the equivalent diameter was calculated from the standard deviation σ and the arithmetic mean using the formula described earlier.

[0149] (3) Tape thickness Ten tape samples (5 cm in length) were cut out from an arbitrary part of the magnetic tape 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 consisting 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 (the thickness per tape sample) was taken as the tape thickness. For each of the magnetic tapes of Examples 1 to 14 and Comparative Examples 1 to 5, the tape thickness was 5.0 μm in all cases. The tape thicknesses of the magnetic tapes of Examples 15 to 17 were as follows. Example 15: 4.6 μm, Example 16: 4.0 μm, Example 17: 3.4 μm.

[0150] The above results are shown in Table 1 (Tables 1-1 to 1-5).

[0151]

Table 1-1

[0152]

Table 1-2

[0153]

Table 1-3

[0154]

Table 1-4

[0155]

Table 1-5

[0156] From the results shown in Table 1, it can be confirmed that the magnetic tape of the embodiment with a change rate of the protrusion area ratio of 10.0% or less exhibited excellent running stability when the magnetic tape was run with the head tilted in a high-temperature and high-humidity environment.

[0157] A magnetic tape was produced by the method described for Example 1, except that no vertical orientation treatment was performed during the production of the magnetic tape. A sample piece was cut out from the above magnetic tape. For this sample piece, using a TM-TRVSM5050-SMSL type manufactured by Tamagawa Seiki Co., Ltd. as a vibrating sample magnetometer, the vertical direction angular ratio was determined by the method described above, and it was 0.55. When the vertical direction angular ratio was similarly determined for the sample piece cut out from the magnetic tape of Example 1, it was 0.65.

[0158] The above two magnetic tapes were each attached to a 1 / 2-inch reel tester, and the electromagnetic conversion characteristics (SNR: Signal-to-Noise Ratio) were evaluated by the following method. As a result, for the magnetic tape of Example 1, a SNR value 4 dB higher was obtained compared to the above magnetic tape produced without vertical orientation treatment. In an environment of a temperature of 23°C and a relative humidity of 50%, a tension of 0.7 N (Newton) was applied in the longitudinal direction of the magnetic tape, and recording and playback were performed for 10 passes. 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. The head tilt angle was 0°. A signal with a linear recording density of 300 kfci was recorded, and the playback signal was measured with a spectrum analyzer manufactured by Shibasoku Co., Ltd. The unit kfci is a unit of linear recording density (inconvertible 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.

Industrial Applicability

[0159] One aspect of the present invention is useful in the technical field of various data storage technologies.

Claims

1. A magnetic tape comprising a non-magnetic support and a magnetic layer containing ferromagnetic powder, A magnetic tape in which the rate of change in the area ratio of protrusions with a height of 5 nm to 10 nm is 10.0% or less, determined by measuring a 5 μm × 5 μm measurement area on the surface of the magnetic layer before and after 1000 reciprocating sliding cycles against an LTO8 head at a head tilt angle of 15° in an environment of 35°C and 80% relative humidity.

2. The magnetic tape according to claim 1, wherein the kinetic friction force F during the 1000th forward stroke in the aforementioned reciprocating sliding is 15 gf or less.

3. The coefficient of variation of the equivalent circle diameter of the bright area in the binarized secondary electron image obtained by imaging the surface of the magnetic layer before the aforementioned reciprocating sliding with a scanning electron microscope at an acceleration voltage of 5 kV is 15.0% or less. The magnetic tape according to claim 1, wherein the lower limit of the threshold for the binarization process is 100 gradations and the upper limit is 130 gradations.

4. The magnetic tape according to claim 3, wherein the magnetic layer further comprises a non-magnetic powder with a Mohs hardness of 6 or more and 7 or less.

5. The magnetic tape according to claim 1, further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

6. The magnetic tape according to claim 1, further comprising a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.

7. The magnetic tape according to claim 1, wherein the tape thickness of the magnetic tape is 5.0 μm or less.

8. The magnetic tape according to claim 1, wherein the vertical aspect ratio of the magnetic tape is 0.60 or greater.

9. The magnetic tape according to claim 1, wherein the vertical aspect ratio of the magnetic tape is 0.65 or more.

10. The magnetic tape according to claim 1, wherein the non-magnetic support is an aromatic polyamide support.

11. The kinetic friction force F during the 1000th forward stroke in the aforementioned reciprocating sliding motion is 15 gf or less. The coefficient of variation of the equivalent circle diameter of the bright area in the binarized secondary electron image obtained by imaging the surface of the magnetic layer before the aforementioned reciprocating sliding with a scanning electron microscope at an acceleration voltage of 5 kV is 15.0% or less. The lower limit of the threshold for the binarization process is 100 gradations, and the upper limit is 130 gradations. The magnetic layer further comprises a non-magnetic powder with a Mohs hardness of 6 or more and 7 or less. The non-magnetic support and the magnetic layer further comprise a non-magnetic layer containing non-magnetic powder. The non-magnetic support further has a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer, The tape thickness is 5.0 μm or less, and The magnetic tape according to claim 1, wherein the vertical aspect ratio of the magnetic tape is 0.60 or greater.

12. A magnetic tape cartridge comprising the magnetic tape described in any one of claims 1 to 11.

13. A magnetic tape device including the magnetic tape according to any one of claims 1 to 11.

14. Further including a magnetic head, 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, and The magnetic tape device according to claim 13, wherein the magnetic tape device changes the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape while the magnetic tape is running within the magnetic tape device.

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