Magnetic tape, magnetic tape cartridge, and magnetic tape device

Abstract

Provided is a magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the peak height Spk as defined in ISO 25178 and measured in a 5 μm × 5 μm measurement region on the surface of the magnetic layer is between 1.0 nm and 2.5 nm inclusive.

Description

Magnetic tape, magnetic tape cartridge and magnetic tape device

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

[0002] Magnetic recording media include tape-type and disk-type recording media, and tape-type magnetic recording media, i.e., magnetic tape, are mainly used for data storage applications such as data backup and archiving (see, for example, Patent Documents 1 to 3).

[0003] Special Publication No. 2016-524774 US2019 / 0164573A1 Patent No. 6590104

[0004] Data is typically recorded on a magnetic tape by running the magnetic tape in a magnetic tape device and recording data on the data band by moving a magnetic head along the data band of the magnetic tape. This forms a data track on the data band. When reproducing the recorded data, the magnetic tape is run in the magnetic tape device and the magnetic head is moved along the data band of the magnetic tape to read the data recorded on the data band.

[0005] To improve the accuracy with which a magnetic head tracks the data band of a magnetic tape during recording and / or playback, systems that use servo signals to perform head tracking (hereinafter referred to as "servo systems") have been put into practical use. Furthermore, it has been proposed to use servo signals to acquire dimensional information (such as contraction or expansion) about the width of a running magnetic tape, and to change the angle at which the axial direction of the magnetic head's module is tilted relative to the width of the magnetic tape (hereinafter also referred to as the "head tilt angle") based on the acquired dimensional information (see Patent Documents 1 and 2, e.g., paragraphs 0059-0067 and 0084 of Patent Document 1). During recording or playback, if the magnetic head used to record or play data deviates from the target track position due to width deformation of the magnetic tape, this can result in problems such as overwriting of recorded data or playback failures. The inventor believes that changing the head tilt angle as described above is one means for suppressing such problems.

[0006] For example, assuming that the head tilt angle is changed as described above, when recording and / or reproducing data by tilting the axial direction of the magnetic head module with respect to the width direction of the magnetic tape (i.e., tilting the head), it is desirable that the magnetic tape have high running stability, since high magnetic tape running stability can be thought of as leading to further suppression of the occurrence of the above-mentioned phenomenon, for example.

[0007] In recent years, magnetic tapes have been used in data centers where temperature and humidity are controlled. At the same time, data centers are seeking to reduce power consumption in order to reduce costs. To achieve this, it is desirable to relax the environmental management conditions for magnetic tape usage in data centers, or to eliminate such management altogether. However, if the environmental management conditions are relaxed or not implemented at all, magnetic tapes may be used in, for example, high-temperature, high-humidity environments. Therefore, a magnetic tape with excellent running stability is desirable when recording and / or reproducing data with a tilted head in a high-temperature, high-humidity environment.

[0008] An object of one aspect of the present invention is to provide a magnetic tape that exhibits excellent running stability when recording and / or reproducing with a tilted head in a high-temperature, high-humidity environment.

[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, wherein the peak height Spk (hereinafter also simply referred to as "Spk") defined in ISO (International Organization for Standardization) 25178, measured in a measurement area of ​​5 μm x 5 μm on the surface of the magnetic layer, is 1.0 nm or more and 2.5 nm or less. [2] The magnetic tape according to [1], wherein the kinetic friction force F (hereinafter also simply referred to as "kinetic friction force F") on the surface of the magnetic layer, measured in an environment of a temperature of 35°C and a relative humidity of 80% with a head tilt angle of 15°, is 15 gf or less. [3] The magnetic tape according to [1] or [2], wherein the Spk is 1.0 nm or more and 2.0 nm or less. [4] The magnetic tape according to any one of [1] to [3], wherein the Spk is 1.0 nm or more and 1.5 nm or less. [5] The magnetic tape according to any one of [1] to [4], further comprising a non-magnetic layer containing a 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 backcoat layer containing a non-magnetic powder on the surface of the non-magnetic support opposite to the surface having the magnetic layer. [7] The magnetic tape according to any one of [1] to [6], wherein the tape thickness is 5.0 μm or less. [8] The magnetic tape according to any one of [1] to [7], wherein the magnetic tape has a squareness ratio in the perpendicular direction of 0.60 or more. [9] The magnetic tape according to any one of [1] to [8], wherein the magnetic tape has a squareness ratio in the perpendicular direction of 0.65 or more.

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

[11] The magnetic tape according to [1], wherein the dynamic friction force F on the surface of the magnetic layer measured at a head tilt angle of 15° in an environment of a temperature of 35°C and a relative humidity of 80% is 15 gf or less, the magnetic tape further comprises a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer, and the non-magnetic support further comprises a backcoat layer containing non-magnetic powder on the surface side opposite to the surface side on which the magnetic layer is formed, the tape thickness is 5.0 μm or less, and the magnetic tape has a squareness ratio in the perpendicular direction of 0.60 or more.

[12] A magnetic tape cartridge including the magnetic tape according to any one of [1] to

[11] .

[13] A magnetic tape device including the magnetic tape according to any one of [1] to

[11] .

[14] The magnetic tape device according to

[13] , further including a magnetic head, wherein the magnetic head has a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, and the magnetic tape device changes an angle θ formed by an axis of the element array with respect to the width direction of the magnetic tape while the magnetic tape is running within the magnetic tape device.

[0010] According to one aspect of the present invention, there is provided a magnetic tape that exhibits excellent running stability when recording and / or reproducing data with a tilted head in a high-temperature, high-humidity environment. Also, according to another aspect of the present invention, there is provided a magnetic tape cartridge and a magnetic tape device that include the magnetic tape.

[0011] 1 is a schematic diagram showing an example of a magnetic head module; FIG. 2 is an explanatory diagram of the relative positional relationship between a module and a magnetic tape while the magnetic tape is running in a magnetic tape device; FIG. 3 is an explanatory diagram regarding changes in angle θ while the magnetic tape is running; FIG. 4 is an explanatory diagram of an example of the arrangement of data bands and servo bands; FIG. 5 is an explanatory diagram of an example of the arrangement of servo patterns on an LTO (Linear Tape-Open) Ultrium format tape; and FIG. 6 is an explanatory diagram of a method for measuring angle θ while the magnetic tape is running. FIG. 7 is a schematic diagram showing an example of a magnetic tape device.

[0012] One aspect of the present invention relates to a magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the peak height Spk, as defined in ISO 25178, measured in a 5 μm × 5 μm measurement area on the surface of the magnetic layer is 1.0 nm or more and 2.5 nm or less.

[0013] <Head Tilt Angle> In the following, before explaining the head tilt angle, we will first explain the "LTO8 head" in relation to the measurement of the dynamic friction force F, which will be described in detail later. Furthermore, we will explain below why it is believed that tilting the axial direction of the magnetic head module relative to the width direction of the magnetic tape while the magnetic tape is running can suppress the phenomenon that occurs during recording or playback described above. In this invention and this specification, an "LTO8 head" refers to a magnetic head that complies with the LTO8 standard. As the LTO8 head, a magnetic head installed in an LTO8 drive may be used, or a commercially available magnetic head for an LTO drive may be used. Here, an LTO8 drive refers to a drive (magnetic tape device) that complies with the LTO8 standard. An LTO9 drive refers to a drive that complies with the LTO9 standard, and the same applies to drives of other generations. 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 is used for each measurement of the magnetic tape. Note that the LTO8 head was adopted in consideration of the LTO8 standard being a standard that can accommodate recent trends toward higher density recording, and the magnetic tapes are not limited to those used in LTO8 drives. Data may be recorded and / or reproduced on the magnetic tape in an LTO8 drive, or in an LTO9 drive or a drive of a later generation, or in a drive of a generation prior to LTO8, such as an LTO7 drive.

[0014] The LTO8 head has three modules, each including an element array with multiple magnetic head elements between a pair of servo signal read elements. The three modules are arranged in the LTO8 head in the following order: recording module - reproduction module - recording module (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 read elements. A module having a write element as a magnetic head element is a recording module for recording data to magnetic tape. A module having a read element as a magnetic head element is a reproducing module for reproducing data recorded on magnetic tape. In the LTO8 head, the three modules are arranged with the axes of the element arrays of each module oriented parallel. This "parallel" does not necessarily mean "parallel" in the strict sense, but also includes the range of error normally accepted in the technical field to which the present invention pertains. The range of error can mean, for example, a range of ±10° or less from strict parallelism.

[0016] The head tilt angle during 100 reciprocal slides for measuring the dynamic friction force F is the head tilt angle in the reproduction module of the LTO8 head.

[0017] In each element array, a pair of servo signal read elements and multiple magnetic head elements (i.e., write elements or read 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 read element to the center of the other servo signal read element. In this specification and the present invention, the "axis of the element array" refers to the straight line connecting the center of one servo signal read element to the center of the other servo signal read element.

[0018] Next, the configuration of the module will be further described with reference to the drawings. However, the embodiments shown in the drawings are merely examples and do not limit the present invention.

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

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

[0021] FIG. 2 is an explanatory diagram of the relative positional relationship between a module and a magnetic tape while the magnetic tape is running in a magnetic tape device. In FIG. 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 while the magnetic tape is running, and is the angle formed by dotted lines A and B. When angle θ is 0° while the magnetic tape is running, the distance in the width direction of the magnetic tape 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 the servo signal reading elements is "L cos θ", and L cos θ is smaller than L. In other words, "L cos θ < L".

[0022] As described above, during recording or playback, if the magnetic head for recording or playing back data deviates from the target track position due to width deformation of the magnetic tape, recording or playback may result in overwriting of recorded data, playback failure, and other problems. For example, if the width of the magnetic tape shrinks or expands, a magnetic head element that should be recording or playing back at the target track position may end up recording or playing back at a different track position. Furthermore, 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 across a data band (also referred to as the "servo band distance" or "servo band distance"; more specifically, the distance between the two servo bands in the width direction of the magnetic tape). This may result in data not being recorded or played back near the edge of the magnetic tape. In contrast, if the element array is tilted at an angle θ greater than 0°, the effective distance between servo signal reading elements becomes "L cos θ," as described above. The larger the value of θ, the smaller the value of L cos θ, and the smaller the value of θ, the larger the value of L cos θ. Therefore, by changing the value of θ according to the degree of dimensional change in the width direction of the magnetic tape (i.e., contraction or expansion), it is possible to make the effective distance between the servo signal read elements closer to or equal to the spacing between the servo bands. This makes it possible to prevent or reduce the frequency of phenomena such as overwriting of recorded data and playback failures caused by the magnetic head for recording or playing back data being shifted from the target track position due to width deformation of the magnetic tape during recording or playback.

[0023] 3 is an explanatory diagram showing the change in the angle θ during magnetic tape running. ｉｎｉｔｉａｌ can be set to, for example, 0° or more or more than 0°. In FIG. 3, the central diagram shows the state of the module at the start of running. In FIG. 3, the right diagram shows the angle θ as ｉｎｉｔｉａｌ The larger angle is angle θ ｃ The effective distance between the servo signal reading elements is L cos θ. ｃis L cos θ when the magnetic tape starts running ｉｎｉｔｉａｌ It is preferable to adjust the angle in this way when the width of the magnetic tape is contracted during the magnetic tape running. On the other hand, in the left diagram of FIG. 3, the angle θ is ｉｎｉｔｉａｌ The smaller angle θ ｅ The effective distance between the servo signal reading elements is L cos θ. ｅ is L cos θ when the magnetic tape starts running ｉｎｉｔｉａｌ It is preferable to perform such angle adjustment when the width of the magnetic tape expands during its running.

[0024] As explained above, changing the head tilt angle during magnetic tape running can contribute to preventing or reducing the frequency of phenomena such as overwriting of recorded data and playback failures, which occur when the magnetic head for recording or playing back data deviates from the target track position due to width deformation of the magnetic tape. Recording and playback of recorded data on a magnetic tape are typically performed by sliding the magnetic head against the magnetic layer surface as the magnetic tape runs. The inventors believed that running the magnetic tape with a tilted head during recording and / or playback can cause unstable contact between the magnetic head and the magnetic layer surface, which can lead to reduced running stability. Based on this conjecture, the inventors conducted extensive research. As a result, they discovered that a magnetic tape with an Spk within the above range, described in detail below, can exhibit excellent running stability when recording and / or playing back data with a tilted head in a high-temperature, high-humidity environment. The temperature and humidity of the environment in which the kinetic friction force F, described in detail below, was measured are illustrative values ​​of the temperature and humidity of a high-temperature, high-humidity environment. Therefore, the environment in which data is recorded on the magnetic tape and the recorded data is reproduced is not limited to the above temperature and humidity environment. The head tilt angle used when measuring the kinetic friction force F, described in detail below, is also used as an example of an angle that can be used when recording and / or reproducing data by changing the head tilt angle while the magnetic tape is running. Therefore, the head tilt angle used when recording and / or reproducing data on the magnetic tape is not limited to the above angle. Furthermore, the present invention is not limited by the inventor's speculations described in this specification. In this specification, running stability when recording and / or reproducing data by tilting the head while the magnetic tape is running in a high-temperature, high-humidity environment is also simply referred to as "running stability." Furthermore, a high-temperature, high-humidity environment can be, for example, an environment with a temperature of approximately 30°C to 50°C. The humidity of this environment can be, for example, approximately 70% to 100% relative humidity.In this invention and herein, the temperatures and humidities referred to in relation to an environment are the ambient temperature and relative humidity of that environment.

[0025] <Spk> In the present invention and this specification, Spk is the protruding peak height Spk defined in ISO 25178. ISO 25178 is an ISO standard related to three-dimensional surface texture parameters, more specifically, ISO 25178-2:2021 (Geometrical product specifications (GPS) - Surface texture: Areal - Part 2: Terms, definitions and surface texture parameters). In order to determine the Spk of the magnetic layer surface, measurements are made on the surface of the magnetic layer of the magnetic tape using an atomic force microscope (AFM) as follows. In this invention and this specification, the term "surface of the magnetic layer" is synonymous with the surface of the magnetic layer of the magnetic tape. The measurement area is a 5 μm square (5 μm × 5 μm) area. Measurements are performed at five randomly selected locations on the magnetic layer surface. Spk, as defined in ISO 25178, is determined for each randomly selected 5 μm square (5 μm × 5 μm) area. Spk can be calculated using known AFM data analysis software. An example of AFM data analysis software is AFM data analysis software (Vision 64) provided by BRUKER. The arithmetic mean of the five measured values ​​thus determined is the Spk of the magnetic layer surface of the magnetic tape being measured. The following measurement conditions can be cited as an example of AFM measurement conditions. An AFM (Nanoscope 5 manufactured by BRUKER) is used in peak force tapping mode to measure a 5 μm × 5 μm area on the surface of the magnetic layer of the magnetic tape. The probe used is a SCANASYST-AIR manufactured by BRUKER, with a resolution of 512 pixels x 512 pixels and a scan speed of measuring one screen (512 pixels x 512 pixels) in 512 seconds.

[0026] The magnetic tape having an Spk of 1.0 nm or more and 2.5 nm or less can exhibit excellent running stability when recording and / or reproducing with a tilted head in a high-temperature, high-humidity environment. The inventors speculate that the reason for this excellent running stability is that a magnetic tape having an Spk in the above range can suppress an increase in dynamic friction force F when repeatedly running with a tilted head. The reason for setting the Spk of the magnetic tape to 1.0 nm or more is that, through extensive research, the inventors have confirmed that when the Spk is below 1.0 nm, an increase in dynamic friction force F becomes significant when repeatedly running with a tilted head. On the other hand, from the viewpoint of further improving running stability, Spk is 2.5 nm or less, preferably 2.3 nm or less, more preferably 2.0 nm or less, with 1.9 nm or less, 1.7 nm or less, and 1.5 nm or less being even more preferred in this order.

[0027] <Dynamic Friction Force F> In the present invention and this specification, the kinetic friction force F on the surface of the magnetic layer measured at a head tilt angle of 15° in an environment with a temperature of 35°C and a relative humidity of 80% is determined by the following method. The measurement of Spk described above is performed on a magnetic tape that has not been run 100 times back and forth as described below. The head tilt angle (15°) refers to the angle between the axis of the element array of the playback module of the LTO8 head and the direction perpendicular to the sliding direction during the first outward pass of the 100 back and forth sliding movements described below. This angle is the angle θ formed by A and B in Figure 2, where A is interpreted as the direction perpendicular to the sliding direction. The head tilt angle is fixed during the 100 back and forth sliding movements. The magnetic tape to be measured is placed on two cylindrical guide rolls with a diameter of 1 inch (1 inch = 2.54 cm) arranged parallel to each other and spaced apart, so that the magnetic layer surface is in contact with them. Prior to measurement, the magnetic tape to be measured is placed on the guide roll as described above and left for at least 24 hours to acclimate to the measurement environment (temperature 35°C, relative humidity 80%). At a randomly selected portion of the magnetic tape to be measured, the head tilt angle is set to 15°, and the magnetic layer surface of the magnetic tape is slid against the LTO8 head, and the resistance force generated during sliding is detected with a strain gauge. One hundred back-and-forth sliding cycles are carried out. Regarding the measurement conditions, the wrap angle θ is set to 6°, and the sliding speed is set to 30 mm / sec. The tension applied in the longitudinal direction of the magnetic tape during sliding is set to 0.55 N. The sliding distance for each of the forward and backward passes is set to 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. The tension applied here is T ０ (unit: N) and the resistance force detected by the strain gauge is T (unit: N), the kinetic friction force F is calculated by the following formula. ０ = 0.20. The kinetic friction force on the 100th outward pass is defined as "kinetic friction force F." Regarding the unit of kinetic friction force F, "gf" indicates gram force, and 1 N (Newton) is approximately 102 gf.

[0028]

[0029] The kinetic friction force F of the magnetic tape on the 100th outward movement of the 100 reciprocating movements is preferably 15 gf or less, more preferably 12 gf or less, and further preferably 10 gf or less, 8 gf or less, and 6 gf or less in that order. The kinetic friction force F can be, for example, 4 gf or more, and may be less than the values ​​exemplified here.

[0030] By controlling Spk within the above-mentioned range, the dynamic friction force F can be controlled to 15 gf or less. Specific examples of means for controlling Spk within the above-mentioned range will be described later.

[0031] The magnetic tape will now be described in more detail.

[0032] <Magnetic Layer> (Ferromagnetic Powder) The ferromagnetic powder contained in the magnetic layer can be one or a combination of two or more known ferromagnetic powders used in the magnetic layers of various magnetic recording media. 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 specific example of the ferromagnetic powder is hexagonal ferrite powder. For details of the hexagonal ferrite powder, see, for example, JP 2011-225417 A, paragraphs 0012 to 0030, JP 2011-216149 A, paragraphs 0134 to 0136, JP 2012-204726 A, paragraphs 0013 to 0030, and JP 2015-127985 A, paragraphs 0029 to 0084.

[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 most intense diffraction peak belongs in the X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, if the most intense diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the hexagonal ferrite crystal structure, it is 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 is considered to be 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 of such atoms include alkaline earth metal atoms such as strontium atoms, barium atoms, and calcium atoms, and lead atoms. In the present invention and this specification, the term "hexagonal strontium ferrite powder" refers to a powder in which the main divalent metal atom contained therein is strontium, and the term "hexagonal barium ferrite powder" refers to a powder in which the main divalent metal atom contained therein is barium. The term "main divalent metal atom" refers to the divalent metal atom that is the most prevalent among the divalent metal atoms contained in the powder on an atomic percentage basis. However, the above divalent metal atoms do not include rare earth atoms. In the present invention and this specification, the "rare earth atom" is selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoid atoms. The lanthanoid atom is selected from the group consisting of lanthanum atom (La), cerium atom (Ce), praseodymium atom (Pr), neodymium atom (Nd), promethium atom (Pm), samarium atom (Sm), europium atom (Eu), gadolinium atom (Gd), terbium atom (Tb), dysprosium atom (Dy), holmium atom (Ho), erbium atom (Er), thulium atom (Tm), ytterbium atom (Yb), and lutetium atom (Lu).

[0035] Hereinafter, hexagonal strontium ferrite powder, which is one form of hexagonal ferrite powder, will be described in more detail.

[0036] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1600 nm ３ The microparticulated hexagonal strontium ferrite powder exhibiting an activation volume in the above range is suitable for producing a magnetic tape that exhibits excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm ３ or more, for example, 850 nm ３ From the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the hexagonal strontium ferrite powder can be 1500 nm or more. ３ More preferably, it is 1400 nm or less. ３ More preferably, it is 1300 nm or less. ３ More preferably, it is 1200 nm or less. ３ It is even more preferable that the value is 1100 nm or less. ３ It is even more preferable that the activation volume of the hexagonal barium ferrite powder is equal to or less than 10 ...

[0037] "Activation volume" is a unit of magnetization reversal and is an index showing the magnetic size of a particle. The activation volume described in this invention and this specification and the anisotropy constant Ku described below are values ​​obtained by measuring the coercive force Hc using a vibrating sample magnetometer at magnetic field sweep rates of 3 minutes and 30 minutes (measurement temperature: 23°C ± 1°C) in the coercive force Hc measurement section, and by using the following relational expression between Hc and activation volume V. The unit of the anisotropy constant Ku is 1 erg / cc = 1.0 x 10 －１ J / m ３ Hc = 2Ku / Ms {1 - [(kT / KuV)ln(At / 0.693)] １／２} [In the above formula, Ku: anisotropy constant (unit: J / m ３ ), Ms: saturation magnetization (unit: kA / m), k: Boltzmann constant, T: absolute temperature (unit: K), V: activation volume (unit: cm ３ ), A: spin precession frequency (unit: s －１), t: magnetic field reversal time (unit: s)]

[0038] The anisotropy constant Ku can be used as an index of the reduction in thermal fluctuation, in other words, the improvement in thermal stability. The hexagonal strontium ferrite powder preferably has an anisotropy constant of 1.8×10 ５ J / m ３ and more preferably 2.0 × 10 ５ J / m ３ The Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 ５ J / m ３ However, since a higher Ku value means higher thermal stability and is therefore preferred, the Ku value is not limited to the above-mentioned values.

[0039] The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms be contained at a content (bulk content) of 0.5 to 5.0 atomic % relative to 100 atomic % of iron atoms. In one embodiment, the hexagonal strontium ferrite powder containing rare earth atoms can have rare earth atoms unevenly distributed in the surface layer portion. In the present invention and this specification, "surface layer distribution of rare earth atoms" means that the rare earth atom content relative to 100 atomic % of iron atoms in a solution obtained by partially dissolving a hexagonal strontium ferrite powder in an acid (hereinafter referred to as "surface layer content of rare earth atoms" or simply "surface layer content" for rare earth atoms) satisfies the ratio of the rare earth atom content relative to 100 atomic % of iron atoms in a solution obtained by completely dissolving a hexagonal strontium ferrite powder in an acid (hereinafter referred to as "bulk content of rare earth atoms" or simply "bulk content" for rare earth atoms) > 1.0. The rare earth atom content of the hexagonal strontium ferrite powder described below is synonymous with the bulk content of rare earth atoms. In contrast, partial dissolution using an 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. The rare earth atom surface layer content satisfying the ratio "rare earth atom surface layer content / rare earth atom bulk content > 1.0" means that rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder (i.e., more present in the surface layer than in the interior). In the present invention and this specification, the surface layer refers to a partial region extending from the surface toward the interior of the particles constituting the hexagonal strontium ferrite powder.

[0040] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atomic percent relative to 100 atomic percent of iron atoms. The presence of rare earth atoms at a bulk content within the above range and the uneven distribution of rare earth atoms in the surface layer of the particles constituting the hexagonal strontium ferrite powder is believed to contribute to suppressing a decrease in playback output during repeated playback. This is presumably because the hexagonal strontium ferrite powder contains rare earth atoms at a bulk content within the above range and the uneven distribution of rare earth atoms in the surface layer of the particles constituting the hexagonal strontium ferrite powder can increase the anisotropy constant Ku. The higher the anisotropy constant Ku, the more the occurrence of a phenomenon known as thermal fluctuation can be suppressed (in other words, thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, the decrease in playback output during repeated playback can be suppressed. It is speculated that the uneven distribution of rare earth atoms in the particle surface layer of hexagonal strontium ferrite powder contributes to stabilizing the spin of iron (Fe) sites in the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. Furthermore, it is speculated that using hexagonal strontium ferrite powder with uneven distribution of rare earth atoms in the surface layer as the ferromagnetic powder of the magnetic layer also contributes to suppressing the abrasion of the magnetic layer surface due to sliding with the magnetic head. In other words, it is speculated that hexagonal strontium ferrite powder with uneven distribution of rare earth atoms in the surface layer can also contribute to improving the running durability of magnetic tapes. It is speculated that this is because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improving the interaction between the particle surface and the organic substances (e.g., binders and / or additives) contained in the magnetic layer, resulting in improved strength of the magnetic layer. From the viewpoint of suppressing a decrease in reproduction output during repeated reproduction 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 %, even more preferably in the range of 1.0 to 4.5 atomic %, and even more preferably in the range of 1.5 to 4.5 atomic %.

[0041] The bulk content is the content determined by completely dissolving the hexagonal strontium ferrite powder. In the present invention and this specification, unless otherwise specified, the content of an atom refers to the bulk content determined by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one rare earth atom, or may contain two or more rare earth atoms. When two or more rare earth atoms are contained, the bulk content is determined for the total of the two or more rare earth atoms. This also applies to other components in the present invention and this specification. That is, unless otherwise specified, a certain component may be used alone or in combination with two or more. When two or more components are used, the content or content refers to the total of the two or more components.

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

[0043] In a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, the rare earth atoms need only be unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, for a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, the ratio of the surface content of rare earth atoms determined by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms determined by complete dissolution under the dissolution conditions described below, i.e., "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 rare earth atoms are unevenly distributed in the surface layer (i.e., present in greater amounts than in the interior) in the particles constituting the hexagonal strontium ferrite powder. Furthermore, the ratio of the surface content of rare earth atoms determined by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms determined by complete dissolution under the dissolution conditions described below, i.e., "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 a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, it is sufficient that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the above "surface content / bulk content" is not limited to the exemplified upper or lower limits.

[0044] The partial dissolution and total dissolution of hexagonal strontium ferrite powder are described below. For hexagonal strontium ferrite powder present as a powder, sample powders to be partially and completely dissolved are collected from the same powder lot. 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 removed from the magnetic layer is subjected to partial dissolution, and another portion is subjected to total dissolution. Removal of the hexagonal strontium ferrite powder from the magnetic layer can be performed, for example, by the method described in paragraph 0032 of JP 2015-91747 A. The partial dissolution refers to dissolving the hexagonal strontium ferrite powder to such an extent that residual hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. 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, the term "complete dissolution" refers to dissolution to the point where no residual hexagonal strontium ferrite powder is visually detectable in the solution at the end of dissolution. The 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 merely examples, and any dissolution conditions that allow partial or complete dissolution can be adopted. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is placed on a hot plate set at 70°C for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate obtained in this manner is performed using an inductively coupled plasma (ICP) analyzer. In this way, the surface layer content of rare earth atoms relative to 100 atomic % of iron atoms can be determined. If multiple rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer content. The same applies to the measurement of the bulk content. Meanwhile, the total dissolution and bulk content measurements are carried out, 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 placed on a hot plate set at 80° C. for 3 hours.Thereafter, the same procedures as in the partial dissolution and measurement of the surface layer content are carried out, and the bulk content relative to 100 atomic % of iron atoms can be determined.

[0045] From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but not having uneven distribution of rare earth atoms in the surface layer has been shown to have a tendency to have a significantly lower σs than hexagonal strontium ferrite powder not containing rare earth atoms. In contrast, hexagonal strontium ferrite powder having uneven distribution of rare earth atoms in the surface layer is considered preferable in order to suppress such a large decrease in σs. In one embodiment, the σs of the hexagonal strontium ferrite powder is 45 A m ２ / kg or more, and ２ On the other hand, from the viewpoint of noise reduction, σs is 80 A m ２ / kg or less, and ２ / kg or less is more preferable. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe. 1 [kOe] = 10 ６ / 4π[A / m].

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

[0047] Known crystal structures of hexagonal ferrite include magnetoplumbite type (also called "M type"), W type, Y type, and Z type. The hexagonal strontium ferrite powder may have any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder may be one in which a single crystal structure or two or more types of crystal structures are detected by X-ray diffraction analysis. For example, in one embodiment, the hexagonal strontium ferrite powder may be one in which only the M-type crystal structure is detected by X-ray diffraction analysis. For example, the M-type hexagonal ferrite is AFe １２ O １９The composition is represented by the formula: where A represents a divalent metal atom. When the hexagonal strontium ferrite powder is of M type, A is only strontium atom (Sr). Alternatively, when A contains multiple divalent metal atoms, strontium atom (Sr) accounts for the majority on an atomic % basis as described above. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of crystalline structure of the hexagonal ferrite and is not particularly limited. The same applies to the iron atom content and the oxygen atom content. The hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms, and oxygen atoms, and may further contain rare earth atoms. Furthermore, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain aluminum atoms (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic % relative to 100 atomic % of iron atoms. From the viewpoint of suppressing a decrease in playback output during repeated playback, the hexagonal strontium ferrite powder 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 % or less relative to 100 atomic % of iron atoms, more preferably in the range of 0 to 5.0 atomic %, and may even be 0 atomic %. 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 content expressed in atomic % above is determined by converting the content (unit: mass %) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder into a value expressed in atomic % using the atomic weight of each atom. Furthermore, in the present invention and this specification, "not containing" a certain atom means that the content measured by completely dissolving the hexagonal strontium ferrite powder using an ICP analyzer is 0 mass %. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less by mass. The above term "free from" is used to mean that the amount is below the detection limit of the ICP analyzer.In one form, the hexagonal strontium ferrite powder can be one that does not contain bismuth atoms (Bi).

[0048] Metal Powder A preferred specific example of the ferromagnetic powder is ferromagnetic metal powder. For details of the ferromagnetic metal powder, see, for example, paragraphs

[0137] to

[0141] of JP 2011-216149 A and paragraphs

[0009] to

[0023] of JP 2005-251351 A.

[0049] ε-Iron Oxide Powder A preferred example of the ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, the term "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide crystal structure is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in an X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the ε-iron oxide crystal structure, it is determined that the ε-iron oxide crystal structure has been detected as the main phase. Known methods for producing ε-iron oxide powder include a method of producing it from goethite and a reverse micelle method. All of these production methods are publicly known. Furthermore, a method for producing ε-iron oxide powder in which part of the Fe is substituted with a substitution atom such as Ga, Co, Ti, Al, or Rh is described, for example, in J. Jpn. Soc. Powder Metallurgy, Vol. 61, Supplement, No. S1, pp. 111-115. S280-S284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206, etc. However, the method for producing the ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the methods mentioned here.

[0050] The activation volume of the ε-iron oxide powder is preferably 300 to 1500 nm ３ The finely divided ε-iron oxide powder exhibiting an activation volume in the above range is suitable for producing a magnetic tape that exhibits excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably 300 nm ３ or more, for example, 500 nm ３From the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the ε-iron oxide powder can be 1400 nm or more. ３ More preferably, it is 1300 nm or less. ３ More preferably, it is 1200 nm or less. ３ More preferably, it is 1100 nm or less. ３ It is even more preferred that:

[0051] The anisotropy constant Ku can be used as an index for reducing thermal fluctuation, in other words, improving thermal stability. The ε-iron oxide powder preferably has an anisotropy constant of 3.0×10 ４ J / m ３ and more preferably 8.0 × 10 ４ J / m ３ The Ku of the ε-iron oxide powder can be, for example, 3.0×10 ５ J / m ３ However, since a higher Ku value means higher thermal stability and is therefore preferred, it is not limited to the above-mentioned values.

[0052] From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic tape, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape is high. In this regard, in one embodiment, the σs of the ε-iron oxide powder is 8 A m ２ / kg or more, and ２ On the other hand, the σs of the ε-iron oxide powder can be 40 A m ２ / kg or less, and 35 A m ２ / kg or less is more preferable.

[0053] Unless otherwise specified, in this invention and this specification, the average particle size of various powders, such as ferromagnetic powders, is a 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 photograph is printed on photographic paper or displayed on a display so that the total magnification is 500,000x, thereby obtaining a photograph of the particles constituting the powder. From the obtained particle photograph, a target particle is selected, and the particle outline is traced with a digitizer to measure the particle (primary particle) size. Primary particles are independent particles without agglomeration. The above measurement is performed on 500 randomly selected particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is taken as the average particle size of the powder. As the transmission electron microscope, for example, a Hitachi transmission electron microscope model H-9000 can be used. Furthermore, particle size measurement can be performed using known image analysis software, such as Carl Zeiss image analysis software KS-400. Unless otherwise specified, the average particle size shown in the examples below is a value measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software. In this invention and this specification, powder refers to an aggregate of multiple particles. For example, ferromagnetic powder refers to an aggregate of multiple ferromagnetic particles. Furthermore, an aggregate of multiple particles is not limited to a form in which the particles constituting the aggregate are in direct contact with each other, but also includes forms in which a binder, additive, etc., described below, is interposed between the particles. The term "particle" is sometimes used to refer to powder.

[0054] As a method for collecting sample powder from the magnetic tape for particle size measurement, for example, the method described in paragraph 0015 of JP-A-2011-048878 can be used.

[0055] In the present invention and this specification, unless otherwise specified, the size of particles constituting a powder (particle size) is expressed as the length of the major axis constituting the particle, i.e., the major axis length, when the shape of the particle observed in the particle photograph is: (1) needle-like, spindle-like, columnar (however, the height is greater than the maximum major axis of the base), etc. (2) plate-like or columnar (however, the thickness or height is smaller than the maximum major axis of the plate surface or base), it is expressed as the maximum major axis of the plate surface or base, (3) spherical, polyhedral, amorphous, etc., and when the major axis constituting the particle cannot be identified from the shape, it is expressed as the circle-equivalent diameter. The circle-equivalent diameter is determined by the circle projection method.

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

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

[0058] (Binder) The magnetic tape may 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 binders. For example, binders may be selected from polyurethane resins, polyester resins, polyamide resins, vinyl chloride resins, acrylic resins copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resins such as nitrocellulose, epoxy resins, phenoxy resins, polyvinyl acetal, polyvinyl butyral, etc., and may be used alone or in combination. Among these, polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binders in the nonmagnetic layer and / or backcoat layer, as described below. For details on the binders mentioned above, see paragraphs 0028 to 0031 of JP 2010-24113 A. The binder may also be a radiation-curable resin such as an electron beam-curable resin. For details about radiation-curable resins, see paragraphs 0044 to 0045 of JP 2011-048878 A. The average molecular weight of the resin used as the binder may be, for example, 10,000 or more and 200,000 or less in terms of weight average molecular weight. The binder may be used in an amount of, for example, 1.0 to 30.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder.

[0059] (Curing Agent) A curing agent can also be used together with the binder. In one form, the curing agent can be a thermosetting compound, which is a compound that undergoes a curing reaction (crosslinking reaction) upon heating, or in another form, a photocuring compound, which undergoes a curing reaction (crosslinking reaction) upon light irradiation. As the curing reaction progresses during the magnetic tape manufacturing process, at least a portion of the curing agent can be contained in the magnetic layer in a state where it has reacted (crosslinked) with other components such as the binder. Preferred curing agents are thermosetting compounds, and polyisocyanates are suitable. For details on polyisocyanates, see paragraphs 0124 to 0125 of JP 2011-216149 A. The curing agent can be used in the magnetic layer-forming composition in an amount of, for example, 0 to 80.0 parts by weight per 100.0 parts by weight of the binder, preferably 50.0 to 80.0 parts by weight from the perspective of improving the strength of each layer, such as the magnetic layer.

[0060] (Other Components) The magnetic layer may contain one or more additives as needed. Commercially available additives can be selected and used depending on the desired properties. Alternatively, compounds synthesized by known methods can be used as additives. Examples of additives include the curing agents described above. Examples of additives that can be contained in the magnetic layer include non-magnetic fillers, lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, and antioxidants. The term "non-magnetic filler" is synonymous with "non-magnetic particles" or "non-magnetic powder." Examples of non-magnetic fillers include non-magnetic fillers that can function as protrusion-forming agents and non-magnetic fillers that can function as abrasives. Known additives, such as the various polymers described in paragraphs 0030 to 0080 of JP 2016-051493 A, can also be used.

[0061] As a protrusion-forming agent, which is one type of non-magnetic filler, particles of inorganic substances can be used, particles of organic substances can be used, or composite particles of inorganic and organic substances can be used. Carbon black can also be used. Examples of inorganic substances include inorganic oxides such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides, with inorganic oxides being preferred. In one form, the protrusion-forming agent can be inorganic oxide-based particles. Here, the term "based" is used to mean "comprises." One form of inorganic oxide-based particles is particles made of inorganic oxide. Another form of inorganic oxide-based particles is composite particles of inorganic oxide and organic substances, and a specific example is a composite particle of inorganic oxide and polymer. Examples of such particles include inorganic oxide particles with a polymer bonded to the surface.

[0062] The average particle size of the protrusion-forming agent can be, for example, 30 to 300 nm, preferably 40 to 200 nm. Furthermore, with regard to the shape of the protrusion-forming agent, it is believed that the closer the particle shape of the protrusion-forming agent contained in the magnetic layer is to a perfect sphere, the greater the Spk value tends to be. This is thought to be because the closer the particle shape is to a perfect sphere, the smaller the indentation resistance that acts when pressure is applied. In contrast, when the particle shape is far from a perfect sphere, for example, a so-called irregular shape, it is likely that a large indentation resistance acts when pressure is applied, which is thought to lead to suppression of the protrusion-forming agent sinking into the magnetic layer due to contact with the head during running. This is thought to contribute to suppressing an increase in the Spk value. Furthermore, it is thought that particles with an inhomogeneous particle surface and low surface smoothness also tend to experience a large indentation resistance when pressure is applied, which is thought to lead to suppression of the protrusion-forming agent sinking into the magnetic layer due to contact with the head during running. Therefore, the present inventors believe that using a protrusion-forming agent whose particle shape is far from spherical and / or using a protrusion-forming agent whose particle surface is non-uniform and has low surface smoothness can contribute to keeping Spk within the range described above. In one embodiment, a protrusion-forming agent having a so-called irregular shape can also be used.

[0063] The abrasive, which is another form of non-magnetic filler, is preferably a non-magnetic powder having a Mohs hardness of more than 8, and more preferably a non-magnetic powder having a Mohs hardness of 9 or more. In contrast, the Mohs hardness of the protrusion-forming agent can be, for example, 8 or less or 7 or less. The maximum Mohs hardness is 10, which is the maximum value of diamond. Specifically, the abrasive is alumina (e.g., Al ２ O ３ ), silicon carbide, boron carbide (e.g., B ４ C), SiO ２ , TiC, chromium oxide (Cr ２ O ３ ), cerium oxide, zirconium oxide (e.g., ZrO ２Examples of suitable abrasives include powders of α-alumina, iron oxide, and diamond, among which alumina powders such as α-alumina and silicon carbide powder are preferred. The average particle size of the abrasive may be in the range of 30 to 300 nm, and preferably in the range of 50 to 200 nm.

[0064] 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, more preferably 0.3 to 3.5 parts by mass, and even more preferably 0.5 to 2.5 parts by mass, per 100.0 parts by mass of ferromagnetic powder. 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.

[0065] An example of an additive that can be used in the magnetic layer containing an abrasive is the dispersant described in paragraphs 0012 to 0022 of JP 2013-131285 A, which is used as a dispersant for improving the dispersibility of the abrasive in the magnetic layer-forming composition. For more information on dispersants, see paragraphs 0061 and 0071 of JP 2012-133837 A. The dispersant may also be contained in the non-magnetic layer. For more information on dispersants that can be contained in the non-magnetic layer, see paragraph 0061 of JP 2012-133837 A.

[0066] One type of additive that can be contained in the magnetic layer is a compound having an ammonium salt structure of an alkyl ester anion, as represented by the following formula 1:

[0067]

[0068] (In formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms, and Z ＋ represents an ammonium cation.)

[0069] The present inventors believe that the above compound can function as a lubricant. This point will be further explained below. Lubricants can be broadly divided into fluid lubricants and boundary lubricants. The present inventors believe that a compound having an ammonium salt structure of an alkyl ester anion represented by the above formula 1 can function as a fluid lubricant. It is believed that a fluid lubricant can provide lubrication to a magnetic layer by forming a liquid film on the magnetic layer surface. In order to control Spk, it is believed that it is desirable for the fluid lubricant to form a liquid film on the magnetic layer surface. Regarding the liquid film of the fluid lubricant, from the perspective of enabling more stable running, it is believed that it is desirable to use an appropriate amount of fluid lubricant forming a liquid film on the magnetic layer surface. This is because it is believed that if the amount of liquid lubricant forming a liquid film on the magnetic layer surface is excessive, the magnetic layer surface and the head will stick together, making running stability more likely to decrease. Furthermore, it is believed that if the amount of liquid lubricant forming a liquid film on the magnetic layer surface is excessive, protrusions formed on the magnetic layer surface by, for example, non-magnetic fillers will be covered by the liquid film. This is also believed to be a factor that makes running stability more likely to decrease. In this regard, the compound contains an ammonium salt structure of an alkyl ester anion represented by Formula 1. It is believed that a compound containing such a structure can perform an excellent role as a fluid lubricant even in a relatively small amount. Therefore, it is believed that including the compound in the magnetic layer can contribute to controlling Spk.

[0070] The above compounds will be described in more detail below.

[0071] In the present invention and this specification, unless otherwise specified, the groups described may have a substituent or may be unsubstituted. Furthermore, with respect to a group having a substituent, the "number of carbon atoms" means the number of carbon atoms excluding the number of carbon atoms of the substituent, unless otherwise specified. In the present invention and this specification, examples of the substituent include an alkyl group (e.g., an alkyl group having 1 to 6 carbon atoms), a hydroxy group, an alkoxy group (e.g., an alkoxy group having 1 to 6 carbon atoms), a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, etc.), a cyano group, an amino group, a nitro group, an acyl group, a carboxy group, a salt of a carboxy group, a sulfonic acid group, a salt of a sulfonic acid group, etc.

[0072] At least a portion of the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 contained in the magnetic layer can form a liquid film on the surface of the magnetic layer, and a portion can be contained within the magnetic layer and migrate to the surface of the magnetic layer during sliding with the magnetic head, etc., to form a liquid film. Furthermore, a portion can be contained in the non-magnetic layer described below, and can migrate to the magnetic layer and further to the surface of the magnetic layer to form a liquid film. The "alkyl ester anion" can also be called an "alkyl carboxylate anion."

[0073] In formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms. The fluorinated alkyl group has a structure in which some or all of the hydrogen atoms constituting the alkyl group are substituted with fluorine atoms. The alkyl group or fluorinated alkyl group represented by R may have a linear structure, a branched structure, or a cyclic alkyl group or fluorinated alkyl group, and preferably has a linear structure. The alkyl group or fluorinated alkyl group represented by R may have a substituent or may be unsubstituted, and is preferably unsubstituted. The alkyl group represented by R is, for example, C ｎ H ２ｎ＋１ -, where n is an integer of 7 or more. The fluorinated alkyl group represented by R can be, for example, C ｎ H ２ｎ＋１The alkyl group or fluorinated alkyl group represented by R may have a structure in which some or all of the hydrogen atoms constituting the alkyl group represented by - are substituted with fluorine atoms. The number of carbon atoms in the alkyl group or fluorinated alkyl group represented by R is 7 or more, preferably 8 or more, more preferably 9 or more, even more preferably 10 or more, still more preferably 11 or more, even more preferably 12 or more, and still more preferably 13 or more. The number of carbon atoms in the alkyl group or fluorinated alkyl group represented by R is preferably 20 or less, more preferably 19 or less, and even more preferably 18 or less.

[0074] In formula 1, Z ＋ represents an ammonium cation. Specifically, the ammonium cation has the following structure: In the present invention and this specification, an asterisk in a formula representing a part of a compound represents the bonding position between the part of the structure and the adjacent atom.

[0075]

[0076] Nitrogen cation N of ammonium cation ＋ and the oxygen anion O in formula 1 － and form a salt bridging group to form an ammonium salt structure of an alkyl ester anion represented by Formula 1. The presence of a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 in the magnetic layer can be confirmed by analyzing the magnetic tape using X-ray photoelectron spectroscopy (ESCA: Electron Spectroscopy for Chemical Analysis), infrared spectroscopy (IR), or the like.

[0077] In one embodiment, Z ＋The ammonium cation represented by the formula (I) can be obtained, for example, by converting a nitrogen atom of a nitrogen-containing polymer into a cation. A nitrogen-containing polymer refers to a polymer containing nitrogen atoms. In the present invention and this specification, the terms "polymer" and "polymeric polymer" are used to encompass homopolymers and copolymers. In one form, the nitrogen atom can be included as an atom constituting the main chain of the polymer, or in another form, as an atom constituting the side chain of the polymer.

[0078] One example of the nitrogen-containing polymer is polyalkyleneimine, which is a ring-opening polymer of alkyleneimine and has a plurality of repeating units represented by the following formula 2:

[0079]

[0080] The nitrogen atom N constituting the main chain in Formula 2 is a nitrogen cation N ＋ As a result, Z in Equation 1 ＋ This can result in an ammonium cation represented by the formula: and can form an ammonium salt structure with an alkyl ester anion, for example, as follows:

[0081]

[0082] Equation 2 will be explained in more detail below.

[0083] In formula 2, R １ and R ２ each independently represents a hydrogen atom or an alkyl group, and n1 represents an integer of 2 or more.

[0084] R １ or R ２ Examples of the alkyl group represented by R include alkyl groups having 1 to 6 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably a methyl group. １ or R ２ The alkyl group represented by the formula (2) is preferably an unsubstituted alkyl group. １ and R ２The combinations include one in which one is a hydrogen atom and the other is an alkyl group, both in which both are hydrogen atoms, and both in which both are alkyl groups (the same or different alkyl groups), preferably both in which both are hydrogen atoms. As an alkyleneimine that yields a polyalkyleneimine, the structure with the fewest carbon atoms constituting the ring is ethyleneimine, and the alkyleneimine (ethyleneimine) obtained by ring-opening of ethyleneimine has two carbon atoms in the main chain. Therefore, n1 in Formula 2 is 2 or more. n1 in Formula 2 can be, for example, 10 or less, 8 or less, 6 or less, or 4 or less. The polyalkyleneimine may be a homopolymer containing only the same repeating structure represented by Formula 2, or a copolymer containing two or more different repeating structures represented by Formula 2. The number-average molecular weight of a polyalkyleneimine that can be used to form a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 can be, for example, 200 or more, and preferably 300 or more. The number average molecular weight of the polyalkyleneimine can be, for example, 10,000 or less, preferably 5,000 or less, and more preferably 2,000 or less.

[0085] In the present invention and this specification, the average molecular weight (weight average molecular weight and number average molecular weight) refers to a value measured by gel permeation chromatography (GPC) and calculated in terms of standard polystyrene. The average molecular weight shown in the examples described below is a value (polystyrene-equivalent value) calculated in terms of standard polystyrene from a value measured using GPC under the following measurement conditions, unless otherwise specified. GPC apparatus: HLC-8220 (manufactured by Tosoh Corporation) Guard column: TSKguard column Super HZM-H Column: TSKgel Super HZ2000, TSKgel Super HZ 4000, TSKgel Super HZ-M (manufactured by Tosoh Corporation, 4.6 mm (inner diameter) x 15.0 cm, three columns connected in series) Eluent: tetrahydrofuran (THF) containing stabilizer (2,6-di-t-butyl-4-methylphenol) Eluent flow rate: 0.35 mL / min Column temperature: 40°C Inlet temperature: 40°C Refractive index (RI) measurement temperature: 40°C Sample concentration: 0.3% by mass Sample injection volume: 10 μL

[0086] Another example of the nitrogen-containing polymer is polyallylamine, which is a polymer of allylamine and has a plurality of repeating units represented by the following formula 3:

[0087]

[0088] The nitrogen atom N constituting the amino group in the side chain in Formula 3 is a nitrogen cation N ＋ As a result, Z in Equation 1 ＋ This can result in an ammonium cation represented by the formula: and can form an ammonium salt structure with an alkyl ester anion, for example, as follows:

[0089]

[0090] The weight-average molecular weight of the polyallylamine that can be used to form the compound having the ammonium salt structure of an alkyl ester anion represented by Formula 1 can be, for example, 200 or more, preferably 1,000 or more, and more preferably 1,500 or more. The weight-average molecular weight of the polyallylamine can be, for example, 15,000 or less, preferably 10,000 or less, and more preferably 8,000 or less.

[0091] The fact that the compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 includes a compound having a structure derived from polyalkyleneimine or polyallylamine can be confirmed, for example, by analyzing the surface of the magnetic layer using time-of-flight secondary ion mass spectrometry (TOF-SIMS) or the like.

[0092] The compound having the ammonium salt structure of an alkyl ester anion represented by Formula 1 can be a salt of a nitrogen-containing polymer and one or more fatty acids selected from the group consisting of fatty acids having 7 or more carbon atoms and fluorinated fatty acids having 7 or more carbon atoms. The nitrogen-containing polymer that forms the salt can be one or more nitrogen-containing polymers, such as a nitrogen-containing polymer selected from the group consisting of polyalkyleneimines and polyallylamines. The fatty acids that form the salt can be one or more fatty acids selected from the group consisting of fatty acids having 7 or more carbon atoms and fluorinated fatty acids having 7 or more carbon atoms. Fluorinated fatty acids have a structure in which some or all of the hydrogen atoms constituting the alkyl group bonded to the carboxyl group COOH in the fatty acid are substituted with fluorine atoms. For example, the salt-forming reaction can easily proceed by mixing the nitrogen-containing polymer and the fatty acid at room temperature. Room temperature is, for example, about 20 to 25°C. In one embodiment, the salt-forming reaction can proceed by using one or more nitrogen-containing polymers and one or more fatty acids as components of the magnetic layer-forming composition and mixing them during the preparation process of the magnetic layer-forming composition. In one embodiment, prior to preparing the magnetic layer-forming composition, one or more nitrogen-containing polymers and one or more fatty acids are mixed to form a salt, and then this salt is used as a component of the magnetic layer-forming composition to prepare the magnetic layer-forming composition. This also applies to forming a non-magnetic layer containing a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1. For example, for the magnetic layer, 0.1 to 10.0 parts by weight of the nitrogen-containing polymer can be used per 100.0 parts by weight of ferromagnetic powder, with 0.5 to 8.0 parts by weight being preferred. The fatty acids can be used in an amount of, for example, 0.05 to 10.0 parts by weight, with 0.1 to 5.0 parts by weight being preferred, per 100.0 parts by weight of ferromagnetic powder. For the non-magnetic layer, 0.1 to 10.0 parts by weight of the nitrogen-containing polymer can be used per 100.0 parts by weight of non-magnetic powder, with 0.5 to 8.0 parts by weight being preferred.The fatty acids can be used in an amount of, for example, 0.05 to 10.0 parts by mass, and preferably 0.1 to 5.0 parts by mass, per 100.0 parts by mass of the non-magnetic powder. When the nitrogen-containing polymer and the fatty acids are mixed to form the ammonium salt of the alkyl ester anion represented by Formula 1, the nitrogen atoms constituting the nitrogen-containing polymer may also react with the carboxy groups of the fatty acids to form the following structure, and forms including such structures are also encompassed in the above-mentioned compound.

[0093]

[0094] Examples of the fatty acids include fatty acids having an alkyl group as described above for R in Formula 1 and fluorinated fatty acids having a fluorinated alkyl group as described above for R in Formula 1.

[0095] The mixing ratio of the nitrogen-containing polymer and the fatty acids used to form the compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 is preferably 10:90 to 90:10, more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20, in terms of the mass ratio of nitrogen-containing polymer to fatty acids. Furthermore, the compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 is preferably contained in the magnetic layer in an amount of 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100.0 parts by mass of ferromagnetic powder. Here, the content of the compound in the magnetic layer refers to the total amount of the compound forming a liquid film on the surface of the magnetic layer and the amount contained within the magnetic layer. On the other hand, a high content of ferromagnetic powder in the magnetic layer is preferable from the perspective of high-density recording. Therefore, from the perspective of high-density recording, a low content of components other than the ferromagnetic powder is preferable. From this viewpoint, the content of the above compound in the magnetic layer is preferably 15.0 parts by mass or less, more preferably 10.0 parts by mass or less, and even more preferably 8.0 parts by mass or less, per 100.0 parts by mass of the ferromagnetic powder. The same applies to the preferred range of the content of the above compound in the magnetic layer-forming composition used to form the magnetic layer.

[0096] Lubricants that can be used include esters and / or amides of fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid. Specific examples of fatty acid esters include butyl myristate, butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, and butoxyethyl stearate. Specific examples of fatty acid amides include lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide. 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, and 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 part by mass, and preferably 0.1 to 1.0 part by mass, per 100.0 parts by mass of ferromagnetic powder. The above description of the content of fatty acid ester and fatty acid amide in the non-magnetic layer or non-magnetic layer-forming composition can be applied by replacing the ferromagnetic powder with non-magnetic powder.

[0097] For details about dispersants, see paragraphs 0061 and 0071 of JP-A 2012-133837. A dispersant may be added to the non-magnetic layer-forming composition. For details about dispersants that can be added to the non-magnetic layer-forming composition, see paragraph 0061 of JP-A 2012-133837.

[0098] <Nonmagnetic Layer> Next, the nonmagnetic layer will be described. The magnetic tape may have a magnetic layer directly on a nonmagnetic support, or may have a nonmagnetic layer containing nonmagnetic powder between the nonmagnetic support and the magnetic layer. The nonmagnetic powder used in the nonmagnetic layer may be an inorganic powder (inorganic powder) or an organic powder (organic powder). Carbon black, etc., can also be used. Examples of inorganic substances include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These nonmagnetic powders are commercially available or can be produced by known methods. For details, see paragraphs

[0146] to

[0150] of JP 2011-216149 A. For carbon black usable in the nonmagnetic layer, see paragraphs

[0040] to

[0041] of JP 2010-24113 A. The content (filling rate) of the non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the non-magnetic layer.

[0099] The non-magnetic layer may contain a binder and may also contain additives. For other details of the binder, additives, etc. of the non-magnetic layer, known techniques related to non-magnetic layers can be applied. Furthermore, for example, for the type and content of the binder, the type and content of the additive, known techniques related to magnetic layers can also be applied.

[0100] The non-magnetic layer of the magnetic tape also includes a substantially non-magnetic layer that contains a small amount of ferromagnetic powder, either as an impurity or intentionally, along with the non-magnetic powder. Here, a substantially non-magnetic layer refers to a layer having a residual magnetic flux density of 10 mT or less, a coercive force of 7.96 kA / m (100 Oe) or less, or a layer having a residual magnetic flux density of 10 mT or less and a coercive force of 7.96 kA / m (100 Oe) or less. It is preferable that the non-magnetic layer have no residual magnetic flux density or coercive force.

[0101] <Non-magnetic Support> Next, the non-magnetic support will be described. Examples of non-magnetic supports (hereinafter also simply referred to as "support") include known biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, aromatic polyamide, etc. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be previously subjected to corona discharge, plasma treatment, easy-adhesion treatment, heat treatment, etc.

[0102] In one embodiment, the non-magnetic support of the magnetic tape may be an aromatic polyester support. In the present invention and this specification, "aromatic polyester" refers to a resin containing an aromatic backbone and multiple ester bonds, and "aromatic polyester support" refers to a support containing at least one layer of aromatic polyester film. "Aromatic polyester film" refers to a film in which the component that constitutes the film in the largest proportion by mass is an aromatic polyester. In the present invention and this specification, "aromatic polyester support" includes support in which all the resin films contained in the support are aromatic polyester films, and support containing an aromatic polyester film and another resin film. Specific forms of aromatic polyester support include a single-layer aromatic polyester film, a laminate film of two or more aromatic polyester film layers with the same constituent components, a laminate film of two or more aromatic polyester film layers with different constituent components, and a laminate film containing one or more aromatic polyester film layers and one or more resin films other than aromatic polyester. An adhesive layer or the like may optionally be included between two adjacent layers in the laminate film. Furthermore, the aromatic polyester support may optionally include a metal film and / or metal oxide film formed by vapor deposition or the like on one or both surfaces. The same applies to the "polyethylene terephthalate support" and the "polyethylene naphthalate support" in the present invention and this specification.

[0103] The aromatic ring contained in the aromatic skeleton of the aromatic polyester is not particularly limited. Specific examples of aromatic rings include a benzene ring and a naphthalene ring. 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. The term "polyethylene terephthalate" in this invention and this specification also includes structures having one or more other components (e.g., copolymerized components, components introduced into the terminal or side chain) in addition to the above components. Polyethylene naphthalate (PEN) is a polyester containing a naphthalene ring and is a resin obtained by esterification of dimethyl 2,6-naphthalenedicarboxylate with ethylene glycol, followed by transesterification and polycondensation reactions. The term "polyethylene naphthalate" in this invention and this specification also includes structures having one or more other components (e.g., copolymerized components, components introduced into the terminal or side chain) in addition to the above components.

[0104] In one embodiment, the non-magnetic support of the magnetic tape can be an aromatic polyamide support. In the present invention and this specification, "aromatic polyamide" refers to a resin containing an aromatic backbone and multiple amide bonds. The aromatic ring contained in the aromatic backbone of the aromatic polyamide is not particularly limited. Specific examples of aromatic rings include a benzene ring. An "aromatic polyamide support" refers to a support containing at least one layer of aromatic polyamide film. An "aromatic polyamide film" refers to a film in which aromatic polyamide is the predominant component by mass among the components constituting the film. In the present invention and this specification, "aromatic polyamide support" includes support in which all resin films contained in the support are aromatic polyamide films, and support containing an aromatic polyamide film and another resin film. Specific forms of aromatic polyamide support include a single-layer aromatic polyamide film, a laminate film of two or more layers of aromatic polyamide films with the same constituent components, a laminate film of two or more layers of aromatic polyamide films with different constituent components, and a laminate film containing one or more layers of aromatic polyamide film and one or more layers of resin film other than aromatic polyamide. The laminated film may optionally contain an adhesive layer or the like between two adjacent layers. The aromatic polyamide support may also optionally contain a metal film and / or a metal oxide film formed by vapor deposition or the like on one or both surfaces.

[0105] As described above, the non-magnetic support may be a biaxially stretched film, and may be a film that has been subjected to corona discharge, plasma treatment, easy-adhesion treatment, heat treatment, or the like.

[0106] An example of an index of the physical properties of a non-magnetic support is moisture content. In the present invention and this specification, the moisture content of a non-magnetic support is a value determined by the following method. A sample piece (e.g., a sample piece having a mass of several grams) cut out from the non-magnetic support to be measured for moisture content is dried to a constant mass in a vacuum dryer at a temperature of 180°C and a pressure of 100 Pa (Pascal) or less. The mass of the dried sample piece is designated as W1. W1 is a value measured in a measurement environment at a temperature of 23°C and a relative humidity of 50% within 30 seconds after removal from the vacuum dryer. Next, W2 is the mass of the sample piece after placing it in an environment at a temperature of 25°C and a relative humidity of 75% for 48 hours. W2 is a value measured in a measurement environment at a temperature of 23°C and a relative humidity of 50% within 30 seconds after removal from the environment. The moisture content is calculated using the following formula: Water content (%) = [(W2 - W1) / W1] × 100 For example, after removing the magnetic layer and other portions of the magnetic tape other than the non-magnetic support by a known method (for example, film removal using an organic solvent), the water content of the non-magnetic support can be determined by the above method.

[0107] In one embodiment, the moisture content of the non-magnetic support of the magnetic tape is preferably 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. The moisture content of the non-magnetic support of the magnetic tape can be 0%, 0% or more, more than 0%, or 0.1% or more.

[0108] Young's modulus can also be used as an indicator of the physical properties of a non-magnetic support. In this 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 at a temperature of 23°C and a relative humidity of 50%. A sample piece cut out from the non-magnetic support to be measured is pulled using a universal tensile tester under conditions of a chuck distance of 100 mm, a pulling speed of 10 mm / min, and a chart speed of 500 mm / min. As the universal tensile tester, for example, a commercially available universal tensile tester such as the Tensilon manufactured by Toyo Baldwin Co., Ltd., or a universal tensile tester with a known configuration can be used. The Young's modulus in the longitudinal and width directions of the sample piece is calculated from the tangent to the rising portion of the load-elongation curve thus obtained. Here, the longitudinal and width directions of the sample piece refer to the longitudinal and width directions when the sample piece is included in a magnetic tape. For example, after removing the magnetic layer and other portions of the non-magnetic support from the magnetic tape by a known method (e.g., removal using an organic solvent), the Young's modulus in the longitudinal and transverse directions of the non-magnetic support can be determined by the above-mentioned method.

[0109] In one embodiment, the Young's modulus of the non-magnetic support of the magnetic tape in the longitudinal direction is preferably 3,000 MPa or more, more preferably 4,000 MPa or more, even more preferably 5,000 MPa or more, and even more preferably 6,000 MPa or more. The Young's modulus of the non-magnetic support of the magnetic tape in the longitudinal direction may be 15,000 MPa or less, 13,000 MPa or less, or 12,000 MPa or less. In the width direction, the Young's modulus of the non-magnetic support of the magnetic tape in the width direction is preferably 2,000 MPa or more, more preferably 3,000 MPa or more, even more preferably 4,000 MPa or more, and even more preferably 5,000 MPa or more. The Young's modulus of the non-magnetic support of the magnetic tape in the width direction may be 12,000 MPa or less, 11,000 MPa or less, or 10,000 MPa or less. In the manufacture of magnetic tapes, non-magnetic supports are typically used with the MD (machine direction) of the film as the longitudinal direction and the TD (transverse direction) as the width direction. In one embodiment, the Young's modulus in the longitudinal direction is preferably greater than the Young's modulus in the width direction, and the difference (Young's modulus in the longitudinal direction - Young's modulus in the width direction) is more preferably in the range of 800 to 3000 MPa.

[0110] The water content and Young's modulus of the non-magnetic support can be controlled by the types and mixing ratios of the components constituting the support, the manufacturing conditions of the support, etc. For example, by adjusting the stretching ratio in each direction in a biaxial stretching process, the Young's modulus in the longitudinal direction and the Young's modulus in the width direction can be controlled.

[0111] <Backcoat Layer> The tape may or may not have a backcoat layer containing nonmagnetic powder on the surface of the nonmagnetic support opposite the surface having the magnetic layer. The backcoat layer preferably contains one or both of carbon black and inorganic powder. The backcoat layer may also contain a binder and additives. For details on the nonmagnetic powder, binder, additives, etc. of the backcoat layer, known techniques related to backcoat layers can be applied, as can known techniques related to magnetic layers and / or nonmagnetic layers. For example, see paragraphs

[0018] to

[0020] of Japanese Patent Laid-Open No. 2006-331625 and U.S. Patent No. 7,029,774, column 4, line 65 to column 5, line 38, for information on backcoat layers.

[0112] <Various Thicknesses> With regard to the thickness (total thickness) of magnetic tape, with the enormous increase in the amount of information in recent years, there is a demand for magnetic tape with an increased recording capacity (higher capacity). One way to achieve higher capacity is to reduce the thickness of the magnetic tape and increase the length of magnetic tape accommodated in one magnetic tape cartridge. From this perspective, 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.

[0113] The thickness (total thickness) of the magnetic tape can be measured by the following method. Ten tape samples (e.g., 5 to 10 cm long) are cut from any part of the magnetic tape, and these tape samples are stacked and the thickness is measured. The measured thickness is divided by 10, and the resulting value (thickness per tape sample) is taken as the tape thickness. The thickness measurement can be performed using a known measuring device capable of measuring thickness to the order of 0.1 μm.

[0114] The thickness of the non-magnetic support is preferably 2.0 to 5.0 μm, more preferably 3.0 to 5.0 μm. The thickness of the magnetic layer can be optimized depending on 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. From the viewpoint of high-density recording, it is preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.1 μm. The magnetic layer must be at least one layer, and may be separated into two or more layers with different magnetic properties, and known multilayer magnetic layer configurations can be applied. When the magnetic layer is separated into two or more layers, the thickness refers to 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. A cross section of the magnetic tape in the thickness direction is exposed to an ion beam, and then 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 thicknesses determined at any two points in the cross section observation. Alternatively, various thicknesses can be determined as design thicknesses calculated from manufacturing conditions, etc.

[0115] <Manufacturing Method> (Preparation of Layer-Forming Compositions) The compositions for forming the magnetic layer, non-magnetic layer, or backcoat layer typically contain a solvent in addition to the various components described above. Various organic solvents commonly used in the production of particulate magnetic recording media can be used as the solvent. In particular, from the perspective of the solubility of binders commonly used in particulate magnetic recording media, it is preferable that each layer-forming composition contain one or more ketone solvents, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran. The amount of solvent in each layer-forming composition is not particularly limited and can be the same as that used in typical layer-forming compositions for particulate magnetic recording media. Furthermore, the process for preparing each layer-forming composition typically includes at least a kneading step, a dispersing step, and mixing steps, optionally performed before or after these steps. Each individual step may be divided into two or more stages. The components used in the preparation of each layer-forming composition may be added at the beginning or during any of the steps. Individual components may also be added in separate steps over two or more steps. For example, the binder may be added in portions during the kneading process, the dispersion process, and the mixing process for adjusting the viscosity after dispersion. As described above, one or more nitrogen-containing polymers and one or more fatty acids may be used as components of the magnetic layer-forming composition, and the salt-forming reaction may be promoted by mixing these components in the magnetic layer-forming composition preparation process. In one embodiment, prior to the preparation of the magnetic layer-forming composition, one or more nitrogen-containing polymers and one or more fatty acids may be mixed to form a salt, and then this salt may be used as a component of the magnetic layer-forming composition to prepare the magnetic layer-forming composition. This also applies to the preparation process of the non-magnetic layer-forming composition. In one embodiment, in the process of preparing the magnetic layer-forming composition, a dispersion containing a protrusion-forming agent (hereinafter referred to as a "protrusion-forming agent liquid") may be prepared, and then this protrusion-forming agent liquid may be mixed with one or more other components of the magnetic layer-forming composition. For example, the protrusion-forming agent liquid may be prepared by a known dispersion process such as ultrasonication. The ultrasonic treatment is carried out using, for example, 200 cc (1 cc = 1 cm ３The dispersion treatment can be carried out for 1 to 300 minutes at an ultrasonic output of about 10 to 2000 watts per dispersion. Filtration may also be carried out after the dispersion treatment. For details on the filters used for filtration, please refer to the following description.

[0116] In the manufacturing process of the magnetic tape, conventional, well-known manufacturing techniques can be used in some or all of the steps. In the kneading process, it is preferable to use a kneader with strong kneading power, such as an open kneader, continuous kneader, pressure kneader, or extruder. Details of these kneading processes are described in Japanese Patent Application Laid-Open Nos. 1-106338 and 1-79274. Glass beads and / or other beads can also be used to disperse the compositions for forming each layer. High-specific-gravity dispersing beads such as zirconia beads, titania beads, and steel beads are suitable. It is preferable to optimize the particle size (bead diameter) and packing rate of these dispersing beads. Known dispersing machines can be used. According to the inventor's research, the longer the dispersion time of the nonmagnetic layer-forming composition, the smaller the Spk value tends to be. It is believed that extending the dispersion time of the nonmagnetic layer-forming composition can form a denser nonmagnetic layer, thereby preventing the protrusion-forming agent from sinking into the magnetic layer due to contact with the head during running. This is thought to contribute to suppressing an increase in the Spk value. Each layer-forming composition may be filtered by a known method before being subjected to the coating step. Filtration can be carried out, for example, by filter filtration. The filter used for filtration may be, for example, a filter with a pore size of 0.01 to 3 μm (e.g., a glass fiber filter, a polypropylene filter, etc.).

[0117] (Coating Process) The magnetic layer can be formed, for example, by directly applying the magnetic layer-forming composition onto the non-magnetic support, or by sequentially or simultaneously applying a multilayer coating with the non-magnetic layer-forming composition. When performing an orientation treatment, the magnetic layer-forming composition is oriented in an orientation zone while the coating layer is still wet. Various known techniques can be applied to the orientation treatment, including those described in paragraph 52 of JP 2010-24113 A. For example, vertical orientation can be performed by known methods, such as using magnets with opposite poles facing each other. In the orientation zone, the drying rate of the coating layer can be controlled by the temperature and volume of the drying air and / or the transport speed in the orientation zone. The coating layer may also 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 the side containing the magnetic layer (or the side on which the magnetic layer will be subsequently formed). For details on the coating process for each layer, see paragraph 66 of JP 2010-231843 A.

[0118] (Other Steps) After the above coating step, the magnetic tape is typically subjected to a calendering treatment to improve its surface smoothness. Strengthening the calendering conditions can form a denser non-magnetic layer, which is thought to prevent the protrusion-forming agent from sinking into the magnetic layer due to contact with the head during running. This is thought to contribute to preventing the Spk value from increasing. Strengthening the calendering conditions includes, for example, increasing the calendering pressure, increasing the calendering temperature, slowing the calendering speed, and increasing the number of calendering passes. 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 passes is preferably two or more, and can be, for example, two to four times. For other various processes for manufacturing magnetic tape, see paragraphs 0067 to 0070 of Japanese Patent Laid-Open Publication No. 2010-231843. A long magnetic tape raw web can be obtained through various processes. The obtained magnetic tape raw web is cut (slit) using a known cutting machine to the width of the magnetic tape to be housed in a magnetic tape cartridge, for example. The width can be determined according to a standard and is usually 1 / 2 inch. A servo pattern is usually formed on the magnetic tape obtained by slitting.

[0119] (Formation of Servo Pattern) “Formation of servo pattern” can also be called “recording of servo signal.” Formation of servo pattern will be explained below.

[0120] The servo patterns are usually formed along the longitudinal direction of the magnetic tape. Control methods using servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0121] As set forth 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, a servo pattern is formed by a pair of non-parallel magnetic stripes (also referred to as "servo stripes") arranged continuously in the longitudinal direction of the magnetic tape. In this invention and this specification, the term "timing-based servo pattern" refers to a servo pattern that enables head tracking in a servo system employing the timing-based servo system. As described above, the reason that the servo pattern is formed by a pair of non-parallel magnetic stripes is to inform a servo signal reading element passing over the servo pattern of its passing position. Specifically, the pair of magnetic stripes is formed so that the spacing between them changes continuously across the width 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 the spacing. This relative position information enables tracking of the data track. For this purpose, multiple servo tracks are usually set on the servo pattern across the width of the magnetic tape.

[0122] A servo band is made up of a continuous servo pattern in the longitudinal direction of the magnetic tape. A magnetic tape usually has multiple servo bands. For example, in an LTO tape, there are five such bands. The area sandwiched between two adjacent servo bands is the data band. A data band is made up of multiple data tracks, and each data track corresponds to one of the servo tracks.

[0123] Also, in one embodiment, as disclosed in Japanese Patent Laid-Open Publication No. 2004-318983, information indicating the servo band number (also referred to as "servo band ID (identification)" or "UDIM (Unique Data Band Identification Method) information") is embedded in each servo band. This servo band ID is recorded by shifting a specific one of a plurality of pairs of servo stripes in the servo band so that its position is displaced relative to the longitudinal direction of the magnetic tape. Specifically, the way in which a specific one of a plurality of pairs of servo stripes is shifted is changed for each servo band. As a result, the recorded servo band ID is unique for each servo band, and therefore, simply by reading one servo band with a servo signal reading element, that servo band can be uniquely identified.

[0124] One method for uniquely identifying servo bands is the staggered method described in ECMA-319 (June 2001). In this staggered method, a group of pairs of non-parallel magnetic stripes (servo stripes) arranged continuously along the longitudinal direction of the magnetic tape are recorded so that each servo band is shifted 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 using two servo signal reading elements.

[0125] Furthermore, as specified in ECMA-319 (June 2001), information indicating the longitudinal position of the magnetic tape (also called "LPOS (Longitudinal Position) information") is usually embedded in each servo band. Like UDIM information, this LPOS information is also recorded by shifting the positions of a pair of servo stripes in the longitudinal direction of the magnetic tape. However, unlike UDIM information, the same signal is recorded in each servo band for this LPOS information.

[0126] It is also possible to embed information other than the above-mentioned UDIM information and LPOS information in the servo bands. In this case, the embedded information may be different for each servo band, such as UDIM information, or may be common to all servo bands, such as LPOS information. Furthermore, methods other than those described above can also 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 pairs of servo stripes.

[0127] The head for forming a servo pattern is called a servo write head. A servo write head typically has a pair of gaps corresponding to the pair of magnetic stripes, the number of which is equal to the number of servo bands. Typically, a core and a coil are connected to each pair of gaps, and by supplying a current pulse to the coil, the magnetic field generated in the core can generate a leakage magnetic field in the pair of gaps. When forming a servo pattern, a current pulse is input while running a magnetic tape over the servo write head, thereby transferring the magnetic pattern corresponding to the pair of gaps to the magnetic tape, thereby forming the servo pattern. The width of each gap can be appropriately set depending on the density of the servo pattern to be formed. The width of each gap can be set, for example, to 1 μm or less, 1 to 10 μm, or 10 μm or more.

[0128] Before forming a servo pattern on a magnetic tape, the magnetic tape is usually subjected to a demagnetization (erase) process. This erase process can be performed by applying a uniform magnetic field to the magnetic tape using a direct current magnet or an alternating current magnet. Erase processes include DC (direct current) erase and AC (alternating current) erase. AC erase 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 erase is performed by applying a unidirectional magnetic field to the magnetic tape. There are two other DC erase methods. The first method is horizontal DC erase, in which a unidirectional magnetic field is applied along the longitudinal direction of the magnetic tape. The second method is vertical DC erase, in which a unidirectional magnetic field is applied along the thickness direction of the magnetic tape. The erase process can be performed on the entire magnetic tape or on each servo band of the magnetic tape.

[0129] The direction of the magnetic field of the formed servo pattern is determined according to the direction of erasure. For example, when horizontal DC erasure is performed on a magnetic tape, the servo pattern is formed so that the direction of the magnetic field is opposite to the direction of erasure. This makes it possible to increase the output of the servo signal obtained by reading the servo pattern. As shown in Japanese Patent Application Laid-Open No. 2012-53940, when a magnetic pattern is transferred using the above-mentioned gap to a magnetic tape that has been vertically DC erased, the servo signal obtained by reading the formed servo pattern has a unipolar pulse shape. On the other hand, when a magnetic pattern is transferred using the above-mentioned gap to a magnetic tape that has been horizontally DC erased, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[0130] <Perpendicular Squareness> In one embodiment, the perpendicular squareness of the magnetic tape can be, for example, 0.55 or more, and from the viewpoint of improving electromagnetic conversion characteristics, it is preferably 0.60 or more, and more preferably 0.65 or more. In principle, the upper limit of the squareness is 1.00 or less. The perpendicular squareness 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 perpendicular squareness of the magnetic tape is preferable from the viewpoint of improving electromagnetic conversion characteristics. The perpendicular squareness of the magnetic tape can be controlled by a known method such as performing a perpendicular orientation treatment.

[0131] In the present invention and this specification, "perpendicular squareness" refers to the squareness measured in the perpendicular direction of the magnetic tape. The "perpendicular direction" in relation to squareness refers to the direction perpendicular to the magnetic layer surface, which can also be referred to as the thickness direction. In the present invention and this specification, the perpendicular squareness is determined by the following method: A sample piece of a size that can be introduced into a vibrating sample magnetometer is cut from the magnetic tape to be measured. A magnetic field is applied to this sample piece in the perpendicular direction (perpendicular to the magnetic layer surface) using a vibrating sample magnetometer at a maximum applied magnetic field of 3979 kA / m, a measurement temperature of 296 K, and a magnetic field sweep rate of 8.3 kA / m / sec, and the magnetization intensity of the sample piece relative to the applied magnetic field is measured. The measured value of the magnetization intensity is obtained as a value after demagnetization field correction and after subtracting the magnetization of the sample probe of the vibrating sample magnetometer as background noise. When the magnetization strength at the maximum applied magnetic field is Ms and the magnetization strength at zero applied magnetic field is Mr, the squareness ratio SQ is a value calculated as SQ = Mr / Ms. The measurement temperature refers to the temperature of the sample piece, and by setting the ambient temperature around the sample piece to the measurement temperature, temperature equilibrium is established and the temperature of the sample piece can be set to the measurement temperature.

[0132] [Magnetic Tape Cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the above-described magnetic tape.

[0133] The details of the magnetic tape contained in the magnetic tape cartridge are as described above.

[0134] A magnetic tape cartridge generally contains a magnetic tape wound on a reel within the cartridge body. The reel is rotatably mounted within the cartridge body. Widely used magnetic tape cartridges include single-reel magnetic tape cartridges with one reel within the cartridge body and dual-reel magnetic tape cartridges with two reels within the cartridge body. When a single-reel magnetic tape cartridge is loaded into a magnetic tape device for recording and / or reproducing data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and rewound onto a reel on the magnetic tape device. A magnetic head is disposed along the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and rewound between the reel (supply reel) on the magnetic tape cartridge and the reel (take-up reel) on the magnetic tape device. During this process, the magnetic head comes into contact with and slides against the magnetic layer surface of the magnetic tape, thereby recording and / or reproducing data. In contrast, a dual-reel magnetic tape cartridge is provided with both a supply reel and a take-up reel inside the magnetic tape cartridge.

[0135] In one embodiment, the magnetic tape cartridge may include a cartridge memory. The cartridge memory may be, for example, a non-volatile memory, and may already have head tilt angle adjustment information recorded therein, or may be recorded with 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 in the magnetic tape device. For example, the head tilt angle adjustment information may record the value of the servo band spacing at each position in the longitudinal direction of the magnetic tape when data is recorded. For example, when reproducing data recorded on the magnetic tape, the value of the servo band spacing during reproduction may be measured, and the head tilt angle may be changed by a control device of the magnetic tape device so that the absolute value of the difference between the servo band spacing during recording at the same longitudinal position recorded in the cartridge memory approaches zero. The head tilt angle may be, for example, the angle θ described above. When recording and / or reproducing data by tilting the head, the angle θ described above may be greater than 0°, and may be 45° or less, 40° or less, or 35° or less.

[0136] 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 scenario, a period in which the head is tilted during data recording and / or playback is included, and therefore a magnetic tape with high running stability when recording and / or playing back data with a tilted head is preferred. However, the magnetic tape and magnetic tape cartridge described above are not limited to those used in such a magnetic tape device. For example, there may be a usage scenario in which the head tilt angle during one recording or playback is changed from that during the next recording or playback to that during subsequent recordings or playbacks, and then the head tilt angle is fixed without changing during each recording or playback. Even in such a usage scenario, a period in which the head is tilted during data recording and / or playback is included, and therefore a magnetic tape with high running stability when recording and / or playing back data with a tilted head is preferred.

[0137] [Magnetic Tape Device] One aspect of the present invention relates to a magnetic tape device including the magnetic tape. In the magnetic tape device, data can be recorded on the magnetic tape and / or data recorded on the magnetic tape can be recorded on the magnetic tape by, for example, contacting and sliding a magnetic head against the magnetic layer surface of the magnetic tape. The magnetic tape device can detachably include a magnetic tape cartridge according to one aspect of the present invention.

[0138] The magnetic tape cartridge can be mounted in a magnetic tape device equipped with a magnetic head and used to record and / or reproduce data. In this invention and this specification, the term "magnetic tape device" refers to a device that can record data on a magnetic tape and / or reproduce data recorded on a magnetic tape. Such devices are generally called drives.

[0139] <Magnetic Head> The magnetic tape device can include a magnetic head. The configuration of the magnetic head and the angle θ, which is the head tilt angle, are as described above with reference to FIGS. 1 to 3. The magnetic head included in the magnetic tape device can be an LTO8 head in one embodiment, an LTO head of another generation in another embodiment, or a magnetic head other than an LTO head in another embodiment. When the magnetic head includes a reproducing element, the reproducing element is preferably a magnetoresistive (MR) element that can read information recorded on a magnetic tape with high sensitivity. As the MR element, various known MR elements (e.g., a GMR (Giant Magnetoresistive) element, a TMR (Tunnel Magnetoresistive) element, etc.) can be used. Hereinafter, a magnetic head that records data and / or reproduces recorded data is also referred to as a "recording / reproducing head." The element for recording data (recording element) and the element for reproducing data (reproducing element) are collectively called the "magnetic head element."

[0140] When recording data and / or reproducing recorded data, tracking can first be performed using a servo signal. That is, by making the servo signal reading element follow a predetermined servo track, the magnetic head element can be controlled so that it passes over the target data track. The data track is moved by changing the servo track read by the servo signal reading element in the tape width direction. The recording / reproducing head can also record and / or reproduce data on other data bands. In this case, the servo signal reading element is moved to a predetermined servo band using the UDIM information described above, and tracking on that servo band can be started.

[0141] FIG. 4 shows an example of the arrangement of data bands and servo bands. In FIG. 4, multiple servo bands 1 are sandwiched between guide bands 3 on the magnetic layer of the magnetic tape MT. Multiple regions 2 sandwiched between two servo bands form data bands. Servo patterns are magnetized regions formed by magnetizing specific regions of the magnetic layer with a servo write head. The regions magnetized by the servo write head (the positions where servo patterns are formed) are determined by standards. 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 FIG. 5. More specifically, in FIG. 5, a servo frame SF on servo band 1 is composed of a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). Servo subframe 1 is composed of an A burst (labeled A in FIG. 5) and a B burst (labeled B in FIG. 5). The A burst is composed of servo patterns A1 to A5, and the B burst is composed of servo patterns B1 to B5. Meanwhile, servo subframe 2 is composed of a C burst (labeled C in FIG. 5 ) and a D burst (labeled D in FIG. 5 ). The C burst is composed of servo patterns C1 to C4, and the D burst is composed of servo patterns D1 to D4. These 18 servo patterns are arranged in subframes, arranged in a 5, 5, 4, 4, 5 ...

[0142] In the magnetic tape device, the head tilt angle can be changed while the magnetic tape is running inside the magnetic tape device. The head tilt angle is, for example, the angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape. The angle θ is as described above. For example, by providing an angle adjustment unit that adjusts the angle of the magnetic head module in the recording / reproducing head unit of the magnetic head, the angle θ can be variably adjusted while the magnetic tape is running. Such an angle adjustment unit can include, for example, a rotation mechanism that rotates the module. Publicly known technology can be applied to the angle adjustment unit.

[0143] Regarding the head tilt angle during magnetic tape running, if the magnetic head includes multiple modules, the angle θ described with reference to Figures 1 to 3 can be defined for randomly selected modules. ｉｎｉｔｉａｌ can be set to be equal to or greater than 0°. ｉｎｉｔｉａｌ The larger the angle θ, the larger the change in the effective distance between the servo signal read elements relative to the change in angle θ, which is preferable in terms of the ability to adjust the effective distance between the servo signal read elements in response to changes in the width direction of the magnetic tape. ｉｎｉｔｉａｌ is preferably 1° or more, more preferably 5° or more, and even more preferably 10° or more. On the other hand, with regard to the angle formed by the magnetic layer surface and the contact surface of the magnetic head when the magnetic tape runs and comes into contact with the magnetic head (generally called the "wrap angle"), keeping the deviation in the tape width direction small is effective in increasing the uniformity in the tape width direction of the friction generated by contact between the magnetic head and the magnetic tape while the magnetic tape is running. Furthermore, increasing the uniformity of the friction in the tape width direction is desirable from the viewpoint of the position tracking ability and running stability of the magnetic head. From the viewpoint of reducing the deviation in the tape width direction of the wrap angle, θ ｉｎｉｔｉａｌ is preferably 45° or less, more preferably 40° or less, and even more preferably 35° or less.

[0144] Regarding the change in angle θ during magnetic tape running, while the magnetic tape is running in the magnetic tape device for recording data on the magnetic tape and / or for reproducing data recorded on the magnetic tape, the angle θ of the magnetic head is changed from θ at the start of running. ｉｎｉｔｉａｌ When the angle θ changes from ｍａｘ and Δθ ｍｉｎ The maximum value of the angle θ during magnetic tape running is θ ｍａｘ and the minimum value is θ ｍｉｎ 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

[0145] In one embodiment, Δθ can be greater than 0.000°, and from the viewpoint of the ability to adjust the effective distance between the servo signal reading elements in response to dimensional changes in the width direction of the magnetic tape, Δθ is preferably 0.001° or greater, and more preferably 0.010° ​​or greater. Furthermore, from the viewpoint of ease of ensuring synchronization of recording data and / or reproduction data between multiple magnetic head elements during data recording and / or reproduction, 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.

[0146] 2 and 3, the axis of the element array is inclined toward the magnetic tape running direction. However, the present invention is not limited to such an example. The present invention also includes an embodiment in which the axis of the element array in the above-mentioned magnetic tape device is inclined toward the direction opposite to the magnetic tape running direction.

[0147] θ is the head tilt angle when the magnetic tape starts running ｉｎｉｔｉａｌcan be set by a control device of the magnetic tape device, etc. Regarding the head tilt angle during magnetic tape running, FIG. 6 is an explanatory diagram of a method for measuring the angle θ during magnetic tape running. The angle θ during magnetic tape running can be determined, for example, by the following method. When determining the angle θ during magnetic tape running by the following method, the angle θ is changed within the range of 0 to 90° during magnetic tape running. That is, if the axis of the element array is tilted toward the magnetic tape running direction at the start of magnetic tape running, the element array is not tilted during magnetic tape running so that the axis of the element array is tilted toward the direction opposite to the magnetic tape running direction at the start of magnetic tape running. If the axis of the element array is tilted toward the direction opposite to the magnetic tape running direction at the start of magnetic tape running, the element array is not tilted during magnetic tape running so that the axis of the element array is tilted toward the magnetic tape running direction at the start of magnetic tape running. The phase difference (i.e., time difference) ΔT of the reproduced signals of the 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 known. The distance L between the center of servo signal read element 1 and the center of servo signal read element 2 can be measured using an optical microscope or the like. When the magnetic tape running speed is v, the distance in the magnetic tape running direction between the centers of the two servo signal read elements is L sin θ, and the relationship L sin θ = v × ΔT holds. Therefore, the angle θ during magnetic tape running can be calculated using the formula "θ = arcsin(vΔT / L)." Note that the right diagram in Figure 6 shows an example in which the axis of the element array is tilted toward the magnetic tape running direction. In this example, the phase difference (i.e., time difference) ΔT between the phase of the playback signal of servo signal read element 1 and the phase of the playback signal of servo signal read element 2 is measured. When the axis of the element array is tilted toward the opposite direction to the magnetic tape running direction, θ can be obtained by the above method, except that ΔT is measured as the phase difference (i.e., time difference) between the phase of the playback signal of servo signal read element 1 and the phase of the playback signal of servo signal read element 2.The measurement pitch of the angle θ, i.e., the measurement interval of the angle θ relative to the tape longitudinal direction, can be selected to be appropriate depending on the frequency of the tape width deformation relative to the tape longitudinal direction. As an example, the measurement pitch can be set to 250 μm.

[0148] <Configuration of Magnetic Tape Device> The magnetic tape device 10 shown in Figure 7 controls a recording / reproducing head unit 12 in response to commands from a control device 11, and records and reproduces data on a magnetic tape MT. The magnetic tape device 10 is configured to detect and adjust the tension applied to the magnetic tape in the longitudinal direction from spindle motors 17A, 17B that control the rotation of the magnetic tape cartridge reel and take-up reel, and their drive devices 18A, 18B. The magnetic tape device 10 is configured to allow a magnetic tape cartridge 13 to be loaded. The magnetic tape device 10 has a cartridge memory read / write device 14 that can read and write data from a cartridge memory 131 in the magnetic tape cartridge 13. The end or leader pin of the magnetic tape MT is pulled out of the magnetic tape cartridge 13 loaded into the magnetic tape device 10 by an automatic loading mechanism or manually. The magnetic tape MT passes over the recording / reproducing head via guide rollers 15A and 15B with the magnetic layer surface in contact with the recording / reproducing head surface of the recording / reproducing head unit 12, and is then wound onto the take-up reel 16. The rotation and torque of the spindle motors 17A and 17B are controlled by signals from the control device 11, allowing the magnetic tape MT to run at a desired speed and tension. Servo patterns 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 to detect tension. In addition to control by the spindle motors 17A and 17B, tension control may also be performed using the guide rollers 15A and 15B. The cartridge memory read / write device 14 is configured to be able to read and write information from and to the cartridge memory 131 in response to commands from the control device 11. As a communication method between the cartridge memory read / write device 14 and the cartridge memory 131, for example, the ISO (International Organization for Standardization) 14443 method can be adopted.

[0149] The control device 11 includes, for example, a control unit, a storage unit, a communication unit, and the like.

[0150] The recording / playback head unit 12 is composed of, for example, a recording / playback head, a servo tracking actuator that adjusts the position of the recording / playback head in the track width direction, a recording / playback amplifier 19, a connector cable for connecting to the control device 11, etc. The recording / playback head is composed of, for example, a recording element that records data on the magnetic tape, a reproducing element that reproduces the data from the magnetic tape, and a servo signal reading element that reads the servo signals recorded on the magnetic tape. One magnetic head may have, for example, one or more recording elements, one or more reproducing elements, and one or more servo signal reading elements. Alternatively, each element may be provided separately in multiple magnetic heads corresponding to the running direction of the magnetic tape.

[0151] The recording / reproducing head unit 12 is configured to be able to record data onto the magnetic tape MT in response to a command from the control device 11. It is also configured to be able to reproduce data recorded onto the magnetic tape MT in response to a command from the control device 11.

[0152] The control device 11 has a mechanism for determining the running position of the magnetic tape MT from servo signals read from the servo bands and controlling the servo tracking actuator so that the recording element and / or reproducing element is 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 for determining the servo band spacing from servo signals read from two adjacent servo bands as the magnetic tape MT runs. The control device 11 can store the determined servo band spacing information in its internal memory, the cartridge memory 131, an external connected device, etc. The control device 11 can also change the head tilt angle according to dimensional information in the width direction of the running magnetic tape. This allows the effective distance between the servo signal reading elements to approach or match the spacing between the servo bands. The dimensional information can be obtained using servo patterns pre-formed on the magnetic tape. For example, while the magnetic tape is running in the magnetic tape device, the angle θ formed by the axis of the element array with respect to the width direction of the magnetic tape can be changed in accordance with the dimensional information of the magnetic tape in the width direction acquired during running. The head tilt angle can be adjusted, for example, by feedback control. Furthermore, the head tilt angle can also be adjusted, for example, by the method described in JP-A-2016-524774 (Patent Document 1) or US 2019 / 0164573 A1 (Patent Document 2).

[0153] The present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. "Parts" described below refer to "parts by mass." Furthermore, the steps and evaluations described below were carried out in an environment at a temperature of 23°C ± 1°C unless otherwise specified. "eq" described below is equivalent, and is a unit that cannot be converted to SI units.

[0154] [Protrusion-Forming Agents] The protrusion-forming agents used in preparing the magnetic layer-forming compositions for producing the magnetic tapes of the Examples and Comparative Examples are as follows. Protrusion-Forming Agent B is a particle with low surface smoothness. Protrusion-Forming Agent A and Protrusion-Forming Agent C have what is known as an amorphous particle shape. Protrusion-Forming Agent A: Asahi #50 (carbon black) manufactured by Asahi Carbon Co., Ltd., average particle size 60 nm Protrusion-Forming Agent B: ATLAS (composite particles of silica and polymer) manufactured by Cabot Corporation, average particle size 100 nm Protrusion-Forming Agent C: #45L (carbon black) manufactured by Mitsubishi Carbon Co., Ltd., average particle size 60 nm

[0155] [Ferromagnetic Powder] In Table 1, "BaFe" is a hexagonal barium ferrite powder (coercive force Hc: 196 kA / m, average particle size (average plate diameter) 24 nm). In Table 1, "SrFe1" is a hexagonal strontium ferrite powder prepared by the following method. SrCO ３ 1707g, H ３ BO ３ 687g, Fe ２ O ３ 1120 g of Al(OH) ３ 45g, BaCO ３ 24 g, CaCO ３ 13 g, and Nd ２ O ３235 g of the above was weighed and mixed in a mixer to obtain a raw material mixture. The resulting raw material mixture was melted in a platinum crucible at a melting temperature of 1,390 ° C. The melt was stirred while heating the tapping port at the bottom of the platinum crucible, and the melt was tapped into a rod-like shape at approximately 6 g / sec. The tapped liquid was rolled and quenched with a water-cooled twin roller to produce an amorphous material. 280 g of the produced amorphous material was placed in an electric furnace, heated to 635 ° C (crystallization temperature) at a heating rate of 3.5 ° C / min, and held at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystallized material obtained above containing hexagonal strontium ferrite particles was coarsely crushed in a mortar, and 1,000 g of zirconia beads with a particle size of 1 mm and 800 ml of a 1% aqueous acetic acid solution were added to the glass bottle containing the material, and the mixture was dispersed for 3 hours using a paint shaker. The resulting dispersion was then separated from the beads and placed in a stainless steel beaker. The dispersion was left to stand at a liquid temperature of 100°C for 3 hours to dissolve the glass component, and then the mixture was precipitated in a centrifuge and washed by repeated decantation, and dried in a heating furnace at a furnace temperature of 110°C for 6 hours to obtain a hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder obtained above had an average particle size of 18 nm and an activation volume of 902 nm. ３ , the anisotropy constant Ku is 2.2 × 10 ５ J / m ３ , mass magnetization σs is 49A・m ２ / kg. 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above, and this sample powder was partially dissolved under the dissolution conditions exemplified above. The obtained filtrate was subjected to elemental analysis using an ICP analyzer to determine the surface content of neodymium atoms. Separately, 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above. This sample powder was completely dissolved under the dissolution conditions exemplified above. The obtained filtrate was subjected to elemental analysis using an ICP analyzer to determine the bulk content of neodymium atoms. The content of neodymium atoms (bulk content) relative to 100 atomic % of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic %. The surface content of neodymium atoms was 8.0 atomic %. The ratio of the surface content to the bulk content, "surface content / bulk content," was 2.8, confirming that neodymium atoms were unevenly distributed in the surface layers of the particles. The powder obtained above was confirmed to have a hexagonal ferrite crystal structure by scanning with CuKα radiation at a voltage of 45 kV and an intensity of 40 mA and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above exhibited a magnetoplumbite-type (M-type) hexagonal ferrite crystal structure. The crystalline phase detected by X-ray diffraction analysis was a single magnetoplumbite-type phase. PANalytical X'Pert Pro diffractometer, PIXcel detector. Soller slits for incident beam and diffracted beam: 0.017 radians. Fixed angle of dispersion slit: 1 / 4 degree. Mask: 10 mm. Anti-scatter 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.

[0156] In Table 1, "SrFe2" is a hexagonal strontium ferrite powder prepared by the following method: SrCO ３ 1725g, H ３ BO ３ 666g, Fe ２ O ３ 1332 g of Al(OH) ３ 52 g, CaCO ３ 34 g, BaCO ３141 g of the above was weighed and mixed in a mixer to obtain a raw material mixture. The resulting raw material mixture was melted in a platinum crucible at a melting temperature of 1380 °C. The melt was stirred while heating the tapping port at the bottom of the platinum crucible, and the melt was tapped into a rod-like shape at approximately 6 g / sec. The tapped liquid was rolled and quenched with a water-cooled twin roller to produce an amorphous material. 280 g of the resulting 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 crystallized material obtained above containing hexagonal strontium ferrite particles was coarsely crushed in a mortar, and 1000 g of zirconia beads with a particle size of 1 mm and 800 ml of a 1% acetic acid aqueous solution were added to the glass bottle containing the material, and the mixture was dispersed for 3 hours using a paint shaker. The resulting dispersion was then separated from the beads and placed in a stainless steel beaker. The dispersion was left to stand at a liquid temperature of 100°C for 3 hours to dissolve the glass component, and then the mixture was precipitated in a centrifuge and washed by repeated decantation, and dried in a heating furnace at a furnace temperature of 110°C for 6 hours to obtain a hexagonal strontium ferrite powder. The obtained hexagonal strontium ferrite powder had an average particle size of 19 nm and an activation volume of 1102 nm. ３ , the anisotropy constant Ku is 2.0 × 10 ５ J / m ３ , mass magnetization σs is 50A・m ２ / kg.

[0157] In Table 1, "ε-iron oxide" refers to ε-iron oxide powder prepared by the following method. 8.3 g of iron(III) nitrate nonahydrate, 1.3 g of gallium(III) nitrate octahydrate, 190 mg of cobalt(II) nitrate hexahydrate, 150 mg of titanium(IV) sulfate, and 1.5 g of polyvinylpyrrolidone (PVP) were dissolved in 90 g of pure water. While stirring using a magnetic stirrer, 4.0 g of a 25% aqueous ammonia solution was added in the air at an ambient temperature of 25°C, and the mixture was stirred for 2 hours at an ambient temperature of 25°C. A citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added to the resulting solution, and the mixture was stirred for 1 hour. The precipitated powder after stirring was collected by centrifugation, washed with pure water, and dried in a heating furnace at an internal temperature of 80°C. 800 g of pure water was added to the dried powder, and the powder was dispersed in water again to obtain a dispersion. The resulting dispersion was heated to 50°C, and 40 g of a 25% aqueous ammonia solution was added dropwise while stirring. After stirring for 1 hour while maintaining the temperature at 50°C, 14 mL of tetraethoxysilane (TEOS) was added dropwise and stirred for 24 hours. 50 g of ammonium sulfate was added to the resulting reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried for 24 hours in a heating furnace at an internal temperature of 80°C to obtain a ferromagnetic powder precursor. The resulting ferromagnetic powder precursor was loaded into a heating furnace at an internal temperature of 1000°C under atmospheric conditions and subjected to heat treatment for 4 hours. The heat-treated ferromagnetic powder precursor was then added to a 4 mol / L aqueous sodium hydroxide (NaOH) solution, and the liquid temperature was maintained at 70°C while stirring for 24 hours to remove impurities, such as silicate compounds, from the heat-treated ferromagnetic powder precursor. The ferromagnetic powder from which the silicate compounds had been removed was then collected by centrifugation and washed with pure water to obtain a ferromagnetic powder. The composition of the obtained ferromagnetic powder was confirmed by inductively coupled plasma-optical emission spectrometry (ICP-OES), and it was found to be Ga, Co, and Ti substituted ε-iron oxide (ε-Ga ０．２８ Co ０．０５ Ti ０．０５ Fe １．６２ O ３) In addition, X-ray diffraction analysis was performed under the same conditions as those described above for SrFe1, and it was confirmed from the peaks in the X-ray diffraction pattern that the obtained ferromagnetic powder had a single-phase ε-phase crystal structure (ε-iron oxide crystal structure) that did not contain α-phase or γ-phase crystal structures. 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 ５ J / m ３ , mass magnetization σs is 16A・m ２ / kg.

[0158] The activation volume and anisotropy constant Ku of the hexagonal strontium ferrite powder and ε-iron oxide powder were determined for each ferromagnetic powder by the method described above using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) The mass magnetization σs was measured at a magnetic field strength of 15 kOe using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.).

[0159] [Non-magnetic Support] In Table 1, "PEN" indicates a polyethylene naphthalate support, and "PA" indicates an aromatic polyamide support.

[0160] Example 1 Magnetic Layer Forming Composition

[0161] (Magnetic liquid) Ferromagnetic powder (see Table 1): 100.0 parts Oleic acid: 2.0 parts Vinyl chloride copolymer (MR-104 manufactured by Kaneka Corporation): 10.0 parts SO ３ Na group-containing polyurethane resin: 4.0 parts (weight average molecular weight 70,000, SO ３Na group: 0.07 meq / g) Additive A: 10.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts (Abrasive liquid) α-alumina (average particle size: 110 nm): 6.0 parts Vinyl chloride copolymer (MR110 manufactured by Kaneka Corporation): 0.7 parts Cyclohexanone: 20.0 parts (Protrusion-forming agent liquid) Protrusion-forming agent (see Table 1): see Table 1 Methyl ethyl ketone: 9.0 parts Cyclohexanone: 6.0 parts (Other components) Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 300): see Table 1 Stearic acid: see Table 1 Stearamide: 0.3 parts Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Coronate (registered trademark) L manufactured by Tosoh Corporation): 3.0 parts

[0162] The additive A is a polymer synthesized by the method described in paragraphs 0115 to 0123 of JP-A-2016-051493.

[0163] <Nonmagnetic layer forming composition> Nonmagnetic 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: 20 nm): 20.0 parts Electron beam curable vinyl chloride copolymer: 13.0 parts Electron beam curable polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Butyl stearate: 2.0 parts Stearic acid: 1.0 part

[0164] <Composition for forming backcoat layer> Non-magnetic inorganic powder (α-iron oxide): 80.0 parts (average particle size: 0.15 μm, average acicular ratio: 7, BET specific surface area: 52 m 2 / g) Carbon black (average particle size: 20 nm): 20.0 parts Carbon black (average particle size: 100 nm): 3.0 parts Vinyl chloride copolymer: 13.0 parts Sulfonic acid group-containing polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Stearic acid: 3.0 parts Polyisocyanate (Tosoh Corporation, Coronate (registered trademark) L): 5.0 parts Methyl ethyl ketone: 400.0 parts

[0165] <Preparation of Compositions for Forming Each Layer> The magnetic layer-forming composition was prepared by the following method. The components of the magnetic liquid were kneaded and diluted using an open kneader, and then dispersed in a horizontal bead mill disperser using zirconia (ZrO2) beads (hereinafter referred to as "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 / s, and a residence time of 2 minutes per pass for 12 passes. The components of the abrasive liquid were mixed and then placed in a vertical sand mill disperser together with Zr beads with a particle size of 1 mm. The ratio of bead volume to (abrasive liquid volume + bead volume) was adjusted to 60%, and the sand mill dispersion process was performed for 180 minutes. The processed liquid was then removed and subjected to ultrasonic dispersion filtration using a flow-type ultrasonic dispersion filtration device. The protrusion-forming agent liquid was prepared by mixing the components of the protrusion-forming agent liquid, then subjecting the mixture to ultrasonic treatment (dispersion treatment) for 60 minutes using a horn-type ultrasonic disperser at an ultrasonic output of 500 watts per 200 cc, and filtering the resulting dispersion through a filter with a pore size of 0.5 μm. The magnetic liquid, abrasive liquid, protrusion-forming agent liquid, and the other components described above were introduced into a dissolver stirrer and stirred for 30 minutes at a peripheral speed of 10 m / sec, then 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 magnetic layer-forming composition.

[0166] The nonmagnetic layer-forming composition was prepared by the following method: The above components, excluding the lubricants (butyl stearate 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. The lubricants (butyl stearate and stearic acid) were then added, and the mixture was stirred and mixed using a dissolver stirrer to prepare the nonmagnetic layer-forming composition.

[0167] The backcoat layer-forming composition was prepared by the following method. The above components, except for the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts), were kneaded and diluted using an open kneader, and then dispersed using a horizontal bead mill disperser. The lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts) were then added, and the mixture was stirred and mixed using a dissolver stirrer to prepare the backcoat layer-forming composition.

[0168] <Preparation of Magnetic Tape and Magnetic Tape Cartridge> A non-magnetic layer-forming composition was applied to a biaxially oriented non-magnetic support (type: see Table 1) having the thickness shown in Table 1 to a dry thickness of 0.6 μm, dried, and then irradiated with an electron beam at an acceleration voltage of 125 kV and an energy of 40 kGy. A magnetic layer-forming composition was applied thereon to a dry thickness of 0.1 μm to form a coating layer. While this coating layer was still wet, a magnetic field with a strength of 0.5 T was applied perpendicularly to the surface of the magnetic layer-forming composition coating in the orientation zone to perform a vertical orientation treatment, and then the coating layer was dried. Furthermore, a backcoat layer-forming composition was applied to the surface of the support opposite the surface on which the non-magnetic layer and magnetic layer were formed, to a dry thickness of 0.3 μm, and then dried. Subsequently, calendering was performed using a seven-stage calender roll consisting only of metal rolls at a calender speed of 80 m / min, a linear pressure of 294 kN / m, and the calender temperature (calender roll surface temperature) shown in Table 1 for the number of times shown in Table 1. The tape was then heat-treated for 36 hours in an ambient temperature of 70°C. After the heat treatment, it was slit into 1 / 2-inch widths, and the surface of the magnetic layer was cleaned using a tape cleaning device equipped with a device for feeding and winding the slit product, with a nonwoven fabric and a razor blade pressed against the surface of the magnetic layer, to obtain a magnetic tape. Servo signals were recorded on the magnetic layer of the obtained magnetic tape using a commercially available servo writer, to obtain a magnetic tape having data bands, servo bands, and guide bands arranged in accordance with the LTO (Linear Tape-Open) Ultrium format, and having servo patterns (timing-based servo patterns) on the servo bands arranged and shaped in accordance with the LTO Ultrium format. The servo pattern thus formed conforms to the specifications of JIS (Japanese Industrial Standards) X6175:2006 and Standard ECMA-319 (June 2001). There are five servo bands in total, and four data bands in total.The magnetic tape (length: 960 m) on which the servo signals were recorded was wound onto a reel of a magnetic tape cartridge (LTO Ultrium 8 data cartridge). In this way, a magnetic tape cartridge with the magnetic tape wound onto a reel was produced.

[0169] The presence of a compound containing an ammonium salt structure of an alkyl ester anion represented by Formula 1, formed from polyethyleneimine and stearic acid, in the magnetic layer of a magnetic tape can be confirmed by the following method. A sample is cut out from the magnetic tape, and X-ray photoelectron spectroscopy is performed on the surface of the magnetic layer (measurement area: 300 μm × 700 μm) using an ESCA device. Specifically, wide scan measurement is performed using the ESCA device under the following measurement conditions. The measurement results show peaks at the position of the binding energy of the ester anion and the position of the binding energy of the ammonium cation. Apparatus: AXIS-ULTRA manufactured by Shimadzu Corporation Excitation X-ray source: Monochromated Al-Kα ray Scan range: 0 to 1200 eV Pass energy: 160 eV Energy resolution: 1 eV / step Acquisition time: 100 ms / step Number of accumulations: 5 Furthermore, a sample piece having a length of 3 cm was cut out from the magnetic tape, and ATR-FT-IR (Attenuated total reflection-Fourier transform-infrared spectrometer) measurement (reflection method) was performed on the surface of the magnetic layer. － The wave number corresponding to the absorption of －１ or 1430 cm －１ ), and the wavenumber corresponding to the absorption of the ammonium cation (2400 cm －１ ) absorption is confirmed.

[0170] Examples 2 to 14, Comparative Examples 1 to 5 Magnetic tapes and magnetic tape cartridges were obtained by the method described for Example 1, except that the items shown in Table 1 were changed as shown in Table 1.

[0171] For each of the above examples and comparative examples, four magnetic tape cartridges were produced, one of which was used to evaluate the running stability described below, and the other three were used to evaluate the magnetic tapes (1) to (3) described below.

[0172] [Evaluation of Running Stability] Running stability was evaluated using the following method in an environment with a temperature of 35°C and a relative humidity of 80%. Using each of the magnetic tape cartridges of the example and comparative examples, data was recorded and reproduced using a magnetic tape device configured as shown in FIG. 7. The order of the modules included in the recording and reproduction head mounted in the recording and reproduction head unit was "recording module - reproduction module - recording module" (total number of modules: 3). Each module had 32 magnetic head elements (Ch0 to Ch31), and these magnetic head elements were sandwiched between a pair of servo signal reading elements to form an element array. Data was recorded and reproduced using the following method, and running stability during playback was evaluated with a head tilt angle of 15°. The head tilt angle was the angle θ formed by the axis of the element array of the reproduction module relative to the width direction of the magnetic tape at the start of running. The angle θ was set by the control device of the magnetic tape device when the magnetic tape started running, and the head tilt angle was fixed during magnetic tape running. The magnetic tape cartridge was set in the magnetic tape device, and the magnetic tape was loaded. Next, while performing servo tracking, the recording / playback head unit records pseudo-random data having a specific data pattern onto the magnetic tape. A constant tension is applied to the tape in the longitudinal direction. Simultaneously with the data recording, the servo band spacing across the entire length of the tape is measured every 1 meter along the tape length and recorded in the cartridge memory. Next, while performing servo tracking, the recording / playback head unit reproduces the data recorded on the magnetic tape. A constant tension is applied to the tape in the longitudinal direction. Running stability was evaluated using the standard deviation (hereinafter referred to as "σPES") of the widthwise read position PES (Position Error Signal) based on the servo signal obtained by the servo signal reading element during the reproduction. The PES can be calculated using the following method. The servo pattern dimensions are required to calculate the PES. The servo pattern dimension specifications vary depending on the LTO generation. Therefore, first, the average distance AC between the four corresponding stripes of the A burst and the C burst, and the azimuth angle α of the servo pattern, are measured using a magnetic force microscope or similar.The average time between five stripes corresponding to the A burst and the B burst over the length of one LPOS word is defined as a. The average time between four stripes corresponding to the A burst and the C burst over the length of one LPOS word is defined as b. In this case, the value defined as AC × (1 / 2 − a / b) / (2 × tan(α)) is the widthwise read position PES (Position Error Signal) based on the servo signal obtained by the servo signal read element over the length of one LPOS word. For magnetic tape, the end wound on the reel of the magnetic tape cartridge is called the inner end, and the end opposite is called the outer end. The outer end is defined as 0 m, and the standard deviation (σPES) of the PES determined using the above method was calculated for a region in the tape longitudinal direction over a length of 30 m to 200 m. If the σPES determined in this way is 50 nm or less, it can be determined that the tape has excellent running stability.

[0173] [Evaluation of Magnetic Tape] (1) Spk The magnetic tapes removed from the magnetic tape cartridges of the Examples and Comparative Examples were measured using the following conditions for AFM measurement, and the Spk of the magnetic layer surface of the magnetic tape was determined by the method described above. The AFM data analysis software used was Vision 64, provided by BRUKER. An AFM (Nanoscope 5 manufactured by BRUKER) was used in peak force tapping mode to measure a 5 μm x 5 μm area on the surface of the magnetic layer of the magnetic tape. A SCANASYST-AIR manufactured by BRUKER was used as the probe, with a resolution of 512 pixels x 512 pixels and a scan speed of 512 seconds per screen (512 pixels x 512 pixels).

[0174] (2) Dynamic Friction Force F The magnetic tape was removed from each magnetic tape cartridge of the Examples and Comparative Examples, and subjected to 100 reciprocating movements in an environment of a temperature of 35°C and a relative humidity of 80% by the method described above, and the dynamic friction force F on the 100th forward movement was determined. A commercially available LTO8 head (manufactured by IBM) was used as the LTO8 head.

[0175] (3) Tape Thickness Ten tape samples (5 cm long) were cut from any portion of the magnetic tape removed from each magnetic tape cartridge of the Examples and Comparative Examples, and the thickness of these tape samples was measured by stacking them. The thickness was measured using a digital thickness meter equipped with a Millimar 1240 compact amplifier and a Millimar 1301 inductive probe manufactured by MARH. The measured thickness was divided by 10 to obtain the value (thickness per tape sample) as the tape thickness. The tape thickness of each of the magnetic tapes of Examples 1 to 11 and Comparative Examples 1 to 5 was 5.0 μm. The tape thickness of each of the magnetic tapes of Examples 12 to 14 was as follows: Example 12: 4.6 μm, Example 13: 4.0 μm, Example 14: 3.4 μm.

[0176] The above results are shown in Table 1 (Table 1-1 to Table 1-4).

[0177]

[0178]

[0179]

[0180]

[0181] From the results shown in Table 1, it can be confirmed that the magnetic tapes of the examples, whose Spk was within the range described above, exhibited excellent running stability when the magnetic tape was run with the head tilted in a high-temperature, high-humidity environment.

[0182] A magnetic tape was produced in the same manner as in 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 magnetic tape. The vertical squareness of this sample piece was determined by the method described above using a Tamagawa Seisakusho TM-TRVSM5050-SMSL vibration sample magnetometer, and was found to be 0.55. The vertical squareness of the sample piece cut out from the magnetic tape of Example 1 was also determined to be 0.65.

[0183] The two magnetic tapes were each mounted on a 1 / 2-inch reel tester, and the electromagnetic conversion characteristics (SNR: Signal-to-Noise Ratio) were evaluated using the following method. As a result, the magnetic tape of Example 1 achieved an SNR value 4 dB higher than that of the magnetic tape produced without vertical orientation treatment. In an environment with a temperature of 23°C and a relative humidity of 50%, 10 passes of recording and reproduction were performed with a tension of 0.7 N (Newton) applied in the longitudinal direction of the magnetic tape. The relative speed between the magnetic tape and the magnetic head was 6 m / s, and recording was performed using a MIG (Metal-in-gap) head (gap length 0.15 μm, track width 1.0 μm) as the recording head, with the recording current set to the optimum recording current for each magnetic tape. Reproduction was performed using a GMR (Giant-magnetoresistive) head (element thickness 15 nm, shield spacing 0.1 μm, reproduction element width 0.8 μm) as the reproduction head. The head tilt angle was set to 0°. A signal with a linear recording density of 300 kfci was recorded, and the reproduction signal was measured with a spectrum analyzer manufactured by Shibasoku Corporation. The unit kfci is a unit of linear recording density (cannot be converted to SI units). The signal was taken from a portion where the signal had sufficiently stabilized after the magnetic tape started running.

[0184] One aspect of the present invention is useful in various data storage technical fields.

Claims

1. A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the peak height Spk as defined in ISO 25178, measured in a 5 μm x 5 μm measurement area on the surface of the magnetic layer, is 1.0 nm or more and 2.5 nm or less.

2. The magnetic tape according to claim 1, wherein the dynamic friction force F on the surface of the magnetic layer measured at a head tilt angle of 15° in an environment of a temperature of 35° C. and a relative humidity of 80% is 15 gf or less.

3. The magnetic tape according to claim 1, wherein the Spk is 1.0 nm or more and 2.0 nm or less.

4. The magnetic tape according to claim 1, wherein the Spk is 1.0 nm or more and 1.5 nm or less.

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

6. The magnetic tape according to claim 1, further comprising a backcoat layer containing nonmagnetic powder on the surface of said nonmagnetic support opposite to the surface having said magnetic layer.

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

8. The magnetic tape according to claim 1, wherein the squareness ratio in the perpendicular direction of said magnetic tape is 0.60 or more.

9. The magnetic tape according to claim 1, wherein the squareness ratio in the perpendicular direction of said magnetic tape is 0.65 or more.

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

11. The magnetic tape according to claim 1, wherein the kinetic friction force F on the surface of the magnetic layer measured at a head tilt angle of 15° in an environment of a temperature of 35°C and a relative humidity of 80% is 15 gf or less, further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer, further comprising a backcoat layer containing non-magnetic powder on the surface of the non-magnetic support opposite to the surface having the magnetic layer, the tape thickness is 5.0 μm or less, and the perpendicular squareness ratio of the magnetic tape is 0.60 or more.

12. A magnetic tape cartridge containing the magnetic tape according to 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. A magnetic tape device according to claim 13, further comprising a magnetic head, the magnetic head having 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 changes the angle θ formed by the axis of the element array 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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