Magnetic tape, magnetic tape cartridge, and magnetic tape device

Abstract

Provided are: a magnetic tape comprising a non-magnetic support and a magnetic layer containing ferromagnetic powder; a magnetic tape cartridge containing the magnetic tape; and a magnetic tape device. The tape thickness of the magnetic tape is 5.2 μm or less, the magnetic layer has a plurality of servo bands, and σDES, determined by the following (1) to (4), is 30 nm or less. (1) A section of the magnetic tape having a length of 900 m is run once at a speed of 6 m / sec using a reel tester. (2) The servo band spacing at each position along the longitudinal direction is measured during the running. (3) The results of measuring the servo band spacing are subjected to filtering, with a stopband of less than 40 Hz and a passband of 40 Hz or higher, to calculate high-frequency components of the servo band spacing at each position. (4) The standard deviation σ of the calculated high-frequency components is defined as σDES.

Description

Magnetic tape, magnetic tape cartridge, and magnetic tape device

[0001] This invention relates to magnetic tape, magnetic tape cartridges, and magnetic tape devices.

[0002] Magnetic recording media come in tape form and disk form. For data storage applications such as data backup and archiving, tape-shaped magnetic recording media, i.e., magnetic tapes, are primarily used (see, for example, Patent Documents 1 to 3).

[0003] Japanese Patent Publication No. 2016-524774, US2019 / 0164573A1, Japanese Unexamined Patent Publication No. 2023-017433

[0004] Data is typically recorded onto magnetic tape by running the tape through a magnetic tape drive and using a magnetic head to track the data bands of the tape, thereby recording the data on those bands. This creates data tracks on the data bands. During playback of the recorded data, the tape is run through the magnetic tape drive again, and the magnetic head tracks the data bands of the tape to read the data recorded on those bands.

[0005] To improve the accuracy with which the magnetic head follows the data band of the magnetic tape during recording and / or playback as described above, a system that uses servo signals to perform head tracking (hereinafter referred to as the "servo system") has been put into practical use. Furthermore, it has been proposed to use servo signals to acquire dimensional information (contraction, expansion, etc.) in the width direction of the magnetic tape while it is running, and to change the angle at which the axial direction of the magnetic head module is tilted relative to the width direction of the magnetic tape (hereinafter also referred to as the "head tilt angle") according to the acquired dimensional information (see Patent Documents 1 to 3, for example, paragraphs 0059 to 0067 and paragraph 0084 of Patent Document 1). If, during recording or playback, the magnetic head for recording or playing back data is misaligned from the target track position due to deformation in the width direction of the magnetic tape (called "off-track"), phenomena such as overwriting of recorded data and playback failures may occur. The inventors believe that changing the head tilt angle as described above is one means of suppressing off-track by dynamically controlling the track position.

[0006] Incidentally, with the enormous increase in the amount of information in recent years, magnetic tapes are required to have increased capacity per reel (higher capacity) and higher data transmission speeds (called "transfer rates") during recording and / or playback. One way to increase capacity is to reduce the thickness of the magnetic tape (called "thinning the tape" or simply "thinning"). In addition, one way to improve the transfer rate is to increase the speed of magnetic tape travel.

[0007] In view of the above, one aspect of the present invention aims to enable both tape thinning and improved transfer rate of magnetic tape.

[0008] The inventors noticed that as tapes become thinner and travel speeds increase, there is a tendency for off-track events to increase that cannot be suppressed by dynamic track position control alone. In recent years, in order to further increase capacity, it has been considered to narrow the track width of data tracks to increase track density. However, the narrower the track width, the more likely off-track events are to occur. Therefore, suppressing off-track events that cannot be compensated for by dynamic track position control alone is desirable from the viewpoint of tape thinning, travel speeds, and track density improvement. Through further investigation, the inventors came to believe that σDES, which will be detailed below, can serve as an indicator of off-track factors that cannot be suppressed by dynamic track position control alone, and as a result of further diligent investigation, they discovered the following magnetic tape.

[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 tape thickness of the magnetic tape is 5.2 μm or less, the magnetic layer has a plurality of servo bands, and the σDES (Dimensional Error Signal) determined by (1) to (4) below is 30 nm or less; (1) The magnetic tape is run once at a speed of 6 m / s over a 900 m length area using a reel tester; (2) The servo band spacing at each position in the longitudinal direction is measured for the above run; (3) The measurement results of the servo band spacing are filtered with an exclusion band of less than 40 Hz (Hertz) and a transmission band of 40 Hz or more to calculate the high-frequency component of the servo band spacing at each position; (4) The standard deviation σ of the calculated high-frequency component is taken as σDES. [2] The magnetic tape according to [1], wherein the number of wrinkles measured after running a 900 m length of the magnetic tape back and forth 300 times at a speed of 6 m / s in a reel tester is 30 or less. [3] The magnetic tape according to [1] or [2], wherein the number of times an end position shift of 200 μm or more (also called "stack shift") occurs in 0.2 seconds during a run of a 900 m length of the magnetic tape in a reel tester is 40 or less (also called "stack shift frequency"). [4] The magnetic tape according to any one of [1] to [3], further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. [5] The magnetic tape according to any one of [1] to [4], further comprising a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer. [6] The magnetic tape according to any one of [1] to [5], wherein the non-magnetic support is a polyethylene naphthalate support. [7] The magnetic tape according to any one of [1] to [5], wherein the non-magnetic support is a polyethylene terephthalate support. [8] The magnetic tape according to any one of [1] to [5], wherein the non-magnetic support is an aromatic polyamide support. [9] The magnetic tape according to any one of [1] to [8], wherein the vertical aspect ratio of the magnetic tape is 0.60 or more.

[10] The magnetic tape according to [1], wherein the number of wrinkles measured after running the magnetic tape back and forth 300 times at a speed of 6 m / s over a 900 m length area in a reel tester is 30 or less, the number of times the end position fluctuation of 200 μm or more occurs in 0.2 seconds when the magnetic tape is run once at a speed of 6 m / s over a 900 m length area in a reel tester is 40 or less, the non-magnetic layer containing non-magnetic powder is further between the non-magnetic support and the magnetic layer, the back coat layer containing non-magnetic powder is further on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer, the non-magnetic support is a polyethylene naphthalate support, a polyethylene terephthalate support, or an aromatic polyamide support, and the vertical angle ratio of the magnetic tape is 0.60 or more.

[11] A magnetic tape cartridge containing the magnetic tape according to any one of [1] to

[10] .

[12] A magnetic tape device containing the magnetic tape according to any one of [1] to

[10] .

[13] The magnetic tape device according to

[12] , further comprising 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 the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape while the magnetic tape is running within the magnetic tape device.

[0010] According to one aspect of the present invention, it is possible to provide a thin magnetic tape capable of improving the transfer rate, a magnetic tape cartridge including this magnetic tape, and a magnetic tape device.

[0011] This is a schematic diagram showing a part of an example of a magnetic head module. This is an explanatory diagram of the relative positional relationship between the module and the magnetic tape during magnetic tape movement in a magnetic tape drive. This is an explanatory diagram regarding the change in angle θ during magnetic tape movement. This shows an example of the arrangement of data bands and servo bands. This shows an example of the arrangement of servo patterns for LTO Ultrium format tape. This is a schematic diagram for explaining PES. This is a schematic diagram for explaining DES. This is a schematic diagram for explaining the relationship between wrinkles and DES. This is a schematic diagram for explaining the relationship between stack shift and DES. This is an explanatory diagram of the method for measuring the angle θ during magnetic tape movement. This is a schematic diagram showing an example of a magnetic tape drive.

[0012] [Magnetic Tape] One aspect of the present invention relates to a magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder. The tape thickness of the magnetic tape is 5.2 μm or less, the magnetic layer has a plurality of servo bands, and σDES is 30 nm or less. Details regarding σDES will be described later.

[0013] In describing the magnetic tape mentioned above, we will first explain the head tilt angle, servo band, and data band.

[0014] <Head tilt angle>

[0015] For example, each module of a magnetic head conforming to the LTO (Linear Tape-Open) standard, such as an LTO8 head or an LTO9 head (hereinafter also referred to as "LTO head"), includes an element array, i.e., an arrangement of elements, having a total of 32 magnetic head elements between a pair of servo signal reading elements. An "LTO8 head" is a magnetic head conforming to the LTO8 standard, and an "LTO9 head" is a magnetic head conforming to the LTO9 standard. A module having recording elements as magnetic head elements is a recording module for recording data onto magnetic tape. A module having playback elements as magnetic head elements is a playback module for playing back data recorded on magnetic tape. In an LTO head, the three modules are arranged so that the axes of the element arrays of each module are oriented parallel to each other. Such "parallel" does not necessarily mean parallel in the strict sense, but includes a range of error that is normally permissible in the art to which the present invention belongs. The range of error can mean, for example, a range of less than ±10° of strict parallelism.

[0016] In each element array, a pair of servo signal reading elements and a plurality of magnetic head elements (i.e., recording elements or playback elements) are arranged in a straight line and spaced apart. Here, "arranged in a straight line" means that each magnetic head element is arranged on a straight line connecting the center of one servo signal reading element and the center of the other servo signal reading element. Furthermore, in this invention and specification, "axis of the element array" means the straight line connecting the center of one servo signal reading element and the center of the other servo signal reading element.

[0017] Next, the module configuration and other details will be further explained with reference to the drawings. However, the configurations shown in the drawings are illustrative and do not limit the present invention.

[0018] Figure 1 is a schematic diagram showing a part of an example of a magnetic head module. The module shown in Figure 1 has multiple magnetic head elements between a pair of servo signal reading elements (servo signal reading elements 1 and 2). Magnetic head elements are also called "channels". "Ch" in the figure is an abbreviation for Channel. The module shown in Figure 1 has a total of 32 magnetic head elements, Ch0 to Ch31, between a pair (i.e., two) servo signal reading elements.

[0019] In Figure 1, "L" represents the distance between a pair of servo signal reading elements, that is, the distance between one servo signal reading element and the other. In the module shown in Figure 1, "L" represents the distance between servo signal reading element 1 and servo signal reading element 2. More specifically, it is the distance between the center of servo signal reading element 1 and the center of servo signal reading element 2. This distance can be measured, for example, by an optical microscope.

[0020] Figure 2 is an explanatory diagram of the relative positional relationship between the module and the magnetic tape during magnetic tape movement in a magnetic tape device. In Figure 2, dotted line A indicates the width direction of the magnetic tape. Dotted line B indicates the axis of the element array. Angle θ can be said to be the head tilt angle during magnetic tape movement, and is the angle made between dotted line A and dotted line B. When angle θ is 0° during magnetic tape movement, the distance in the magnetic tape width direction between one servo signal reading element and the other servo signal reading element of the element array (hereinafter also referred to as the "effective distance between servo signal reading elements") is "L". In contrast, when angle θ is greater than 0°, the effective distance between servo signal reading elements is "Lcosθ", and Lcosθ is smaller than L. That is, "Lcosθ < L".

[0021] As mentioned earlier, during recording or playback, deformation in the width direction of the magnetic tape can cause the magnetic head responsible for recording or playing back data to shift from the intended track position, resulting in phenomena such as overwriting of recorded data or playback failures. For example, if the width of the magnetic tape shrinks or expands, the magnetic head element that should record or play back at the intended track position may end up recording or playing back at a different track position. Also, if the width of the magnetic tape expands, the effective distance between servo signal reading elements becomes shorter than the distance between two adjacent servo bands separated by a data band (also referred to as "servo band spacing" or "servo band interval"; more specifically, the distance between the two servo bands in the width direction of the magnetic tape), which can result in data not being recorded or played back in areas close to the edge of the magnetic tape. In contrast, if the element array is tilted at an angle θ greater than 0°, as explained earlier, the effective distance between servo signal reading elements becomes "Lcosθ". The larger the value of θ, the smaller the value of Lcosθ, and the smaller the value of θ, the larger the value of Lcosθ. Therefore, by changing the value of θ according to the degree of dimensional change (i.e., contraction or expansion) in the width direction of the magnetic tape, it becomes possible to bring the effective distance between servo signal reading elements closer to or matching the spacing of the servo bands. This prevents or reduces the frequency of phenomena such as overwriting of recorded data or playback failures that occur when the magnetic head for recording or playing back data is misaligned from the target track position due to deformation in the width direction of the magnetic tape during recording or playback.

[0022] Figure 3 is an explanatory diagram regarding the change in angle θ during magnetic tape travel. The angle θ at the start of travel is shown. ｉｎｉｔｉａｌ This can be set to, for example, 0° or greater or greater than 0°. In Figure 3, the center diagram shows the state of the module at the start of operation. In Figure 3, the right diagram shows the angle θ, θ ｉｎｉｔｉａｌ An angle θ is a larger angle. ｃshows the state of the module when set as such. The effective distance between servo signal reading elements Lcosθ ｃ is smaller than Lcosθ at the start of magnetic tape running ｉｎｉｔｉａｌ . When the width of the magnetic tape contracts during the running of the magnetic tape, it is preferable to perform such angle adjustment. On the other hand, in FIG. 3, the left diagram shows the angle θ, which is smaller than θ ｉｎｉｔｉａｌ , that is, angle θ ｅ shows the state of the module when set as such. The effective distance between servo signal reading elements Lcosθ ｅ is larger than Lcosθ at the start of magnetic tape running ｉｎｉｔｉａｌ . When the width of the magnetic tape expands during the running of the magnetic tape, it is preferable to perform such angle adjustment.

[0023] As explained above, changing the head tilt angle during the running of the magnetic tape can contribute to preventing the occurrence of phenomena such as overwriting of recorded data and reproduction failure, which are caused when the magnetic head for recording or reproducing data deviates from the target track position due to deformation occurring in the width direction of the magnetic tape during recording or reproduction, thereby performing data recording or reproduction, or can contribute to reducing the occurrence frequency of such phenomena.

[0024] <Servo Band, Data Band> In the following, the magnetic head that records and / or plays back recorded data will also be called the "recording / playback head." The elements for recording data (recording elements) and the elements for playing back data (playback elements) will be collectively referred to as "magnetic head elements." When recording and / or playing back recorded data, tracking using a servo signal can be performed first. That is, by making the servo signal reading element follow a predetermined servo track, the magnetic head elements can be controlled to pass over the target data track. The movement of the data track is performed by changing the servo track read by the servo signal reading element in the tape width direction. The recording / playback head can also record and / or play back data on other data bands. In that case, the servo signal reading element should be moved to a predetermined servo band using the UDIM (Unique DataBand Identification Method) information described above, and tracking for that servo band should be started.

[0025] The magnetic layer of the above-mentioned magnetic tape has multiple servo bands. Figure 4 shows an example of the arrangement of data bands and servo bands. In Figure 4, five servo bands 1 are arranged on the magnetic layer of the magnetic tape MT, sandwiched between guide bands 3. Multiple regions 2 sandwiched between two servo bands are data bands. A servo pattern is a magnetized region, formed by magnetizing a specific region of the magnetic layer with a servo light head. The region magnetized by the servo light head (the position where the servo pattern is formed) is defined by the standard. For example, in the industry standard LTO Ultrium format tape, multiple servo patterns inclined with respect to the tape width direction are formed on the servo bands during magnetic tape manufacturing, as shown in Figure 5. More specifically, in Figure 5, the servo frame SF on the servo band 1 consists of a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). The servo subframe 1 consists of an A burst (indicated as A in Figure 5) and a B burst (indicated as B in Figure 5). A-burst consists of servo patterns A1 to A5, and B-burst consists of servo patterns B1 to B5. On the other hand, servo subframe 2 consists of C-burst (indicated as C in Figure 5) and D-burst (indicated as D in Figure 5). C-burst consists of servo patterns C1 to C4, and D-burst consists of servo patterns D1 to D4. These 18 servo patterns are arranged in sets of 5 and 4 in subframes arranged in a 5, 5, 4, 4 sequence, and are used to identify the servo frames. Figure 5 shows one servo frame for illustrative purposes. However, in reality, in the magnetic layer of a magnetic tape where timing-based servo head tracking is performed, multiple servo frames are arranged in the direction of travel in each servo band. In Figure 5, the arrows indicate the direction of travel of the magnetic tape. For example, LTO Ultrium format tape typically has more than 5000 servo frames per meter of tape length in each servo band of the magnetic layer.

[0026] <σDES> As explained earlier, dynamic track position control by changing the head tilt angle can contribute to suppressing off-tracks caused by different servo band spacings at various positions along the longitudinal direction of the magnetic tape. However, through diligent research, the inventors have newly discovered that the off-tracks that can be suppressed in this way are the low-frequency components of the changes in servo band spacing, and therefore reducing the high-frequency components of the changes in servo band spacing can contribute to further suppressing off-tracks through dynamic track position control. This point will be explained in more detail below with reference to the drawings. However, the embodiments shown in the drawings are illustrative, and the present invention is not limited to the embodiments shown in the drawings. Also, the dimensions, arrangement, number of servo bands, number of servo signal reading elements, number of magnetic head elements, etc. shown in the drawings are merely illustrative for explanation purposes, and the present invention is not limited by these examples.

[0027] Figure 6 is a schematic diagram illustrating PES. "PES" is an abbreviation for "Position Error Signal". In Figure 6, PES is schematically shown with a dashed line. PES is well known in the field of magnetic tape technology as an indicator of the widthwise relative position variation between the magnetic head and the magnetic tape.

[0028] Figure 7 is a schematic diagram for explaining DES. DES is used as an abbreviation for "Dimensional Error Signal". The distance between two adjacent servo bands 1 separated by a data band (servo band interval) can be determined as the difference between Position 1 and Position 2 (Position 1 - Position 2), which will be described later. This is called "dPES". The method for measuring dPES will be described later. Even if the dPES at each position in the longitudinal direction of the magnetic tape was constant before deformation, deformation occurs in the width direction of the magnetic tape due to deformation factors such as temperature changes, humidity changes, and running tension, and the servo band interval changes, so the dPES at each position in the longitudinal direction of the magnetic tape changes. When dPES is frequency-separated as schematically shown in Figure 7, it can be separated into low-frequency components and high-frequency components. The low-frequency component can also be called the low-speed component, and it can be compensated by changing the head tilt angle to control the dynamic track position. In contrast, high-frequency components can also be called high-speed components, and it is considered difficult to compensate for them with such dynamic track position control. The inventors believe that σDES, whose measurement method is described below, can serve as an indicator of these high-frequency components. For thinned magnetic tapes, when the running speed is increased to improve the transfer rate, the effects of high-frequency components become apparent, and therefore, the inventors surmise that it is desirable to reduce high-frequency components. As a result of the inventors' diligent research, it has been newly discovered that magnetic tapes with a small σDES of 30 nm or less can contribute to improved recording and playback performance under high-speed running conditions, that is, they can contribute to improving the transfer rate, even if the tape thickness of the magnetic tape is as thin as 5.2 nm or less. Note that high-speed running conditions refer to conditions in which the running speed of the magnetic tape is 5 m / s or more (for example, 5 to 10 m / s). However, the above range is illustrative, and the running speed of the magnetic tape during data recording on the magnetic tape and playback of recorded data is not limited to the above range.

[0029] The σDES of the above magnetic tape is preferably 30 nm or less, and more preferably 28 nm or less, in the order of 26 nm or less, 24 nm or less, 22 nm or less, and 20 nm or less, from the viewpoint of achieving both tape thinning and improved transfer rate. The σDES can be, for example, 1 nm or more, 5 nm or more, or 10 nm or more. The smaller the σDES, the more preferable it is from the viewpoint of achieving both tape thinning and improved transfer rate.

[0030] (Method for measuring σDES) σDES is determined by the following (1) to (4). (1) The magnetic tape is run once at a speed of 6 m / s over a region of 1,000 to 900 m in length using a reel tester. (2) The servoband spacing is measured at each position in the longitudinal direction during the above run. (3) The measurement results of the servoband spacing are filtered with an exclusion band of less than 40 Hz and a transmission band of 40 Hz or more to calculate the high-frequency component of the servoband spacing at each of the above positions. (4) The standard deviation σ of the calculated high-frequency component is taken as σDES.

[0031] For details, σDES is determined by the following method. In this invention and specification, when "driving" is simply referred to, it means driving one way.

[0032] (A) Sample preparation The magnetic tape to be measured is wound onto a reel with a hub diameter of 44 mm at a tension of 0.60 N (Newtons) and a speed of 20 m / s to prepare a sample.

[0033] (B) Measurement of DES The sample prepared in (A) above is stored in a thermoroom maintained at a temperature of 23°C and a relative humidity of 50% for 24 hours or more. After storage, the sample is attached to a reel tester that has been previously installed in the thermoroom. This reel tester has a magnetic head of an IBM TS1170 tape drive and is adjusted so that the relative inclination between the magnetic head and the magnetic tape is 90° ± 0.02°. A "reel tester" is a device that can feed and rewind magnetic tape from one reel to the other. In the above reel tester, the sample is run once over a 900m length area with a tension of 0.60N and a speed of 6m / sec. The regenerated signals from the two servo signal reading elements are measured using a Teledyne LeCroy MDA810A oscilloscope set to voltage range: ±200mV, sampling rate: 50MHz, sampling rate: 100MS (megasampling), and coupling: 50ΩDC (direct current). The running position of each servo signal reading element in the tape width direction (referred to as Position1 and Position2, respectively) is calculated from the servo signals. The servoband spacing (dPES = Position1 - Position2) is calculated as the difference between these two values, and the high-frequency component DES is measured by applying a high-pass filter using the "FilterFIR" command of WaveMetrix's data analysis software Igor Pro 9.01, with the exclusion band set to less than 40 Hz, the transmission band to 40 Hz or more, and the filter coefficients to 1001 points.

[0034] (C) Calculation of σDES σDES is calculated as the standard deviation (i.e., the positive square root of the variance) of DES obtained at all sampling positions measured with the above number of samples. The σDES calculated in this way is taken as the σDES of the magnetic tape being measured.

[0035] Specific examples of methods for controlling σDES to 30 nm or less will be described later.

[0036] <Magnetic Layer> (Ferromagnetic Powder) The ferromagnetic powder included in the magnetic layer of the magnetic tape can be one 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.

[0037] A preferred specific example of hexagonal ferrite powder ferromagnetic powder is hexagonal ferrite powder. For details on hexagonal ferrite powder, see, for example, paragraphs 0012 to 0030 of Japanese Patent Publication No. 2011-225417, paragraphs 0134 to 0136 of Japanese Patent Publication No. 2011-216149, paragraphs 0013 to 0030 of Japanese Patent Publication No. 2012-204726, and paragraphs 0029 to 0084 of Japanese Patent Publication No. 2015-127985.

[0038] In the present invention and this specification, "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to a hexagonal ferrite crystal structure, it shall be determined that the hexagonal ferrite crystal structure has been detected as the main phase. If only a single structure is detected by X-ray diffraction analysis, this detected structure shall be considered the main phase. The hexagonal ferrite crystal structure includes at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. Divalent metal atoms are metal atoms that can become divalent cations as ions, and examples include strontium atoms, barium atoms, alkaline earth metal atoms such as calcium atoms, and lead atoms. In the present invention and this specification, hexagonal strontium ferrite powder refers to powder in which the main divalent metal atom contained is strontium, and hexagonal barium ferrite powder refers to powder in which the main divalent metal atom contained is barium. The main divalent metal atom refers to the divalent metal atom that accounts for the largest proportion on an atomic percentage basis among the divalent metal atoms contained in the powder. However, rare earth atoms are not included in the above divalent metal atoms. In the present invention and this specification, "rare earth atoms" are selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanide atoms. Lanthanide atoms are selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0039] Below, we will describe hexagonal strontium ferrite powder, a form of hexagonal ferrite powder, in more detail.

[0040] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1600 nm. ３ The activation volume is within the range described above. Finely milled hexagonal strontium ferrite powder exhibiting an activation volume within the above range is suitable for the production of magnetic tapes that exhibit excellent electromagnetic conversion properties. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm. ３ That's all, for example, 850 nm ３ It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of hexagonal strontium ferrite powder is 1500 nm. ３ The following is more preferable: 1400 nm ３ It is even more preferable that the following occur: 1300 nm ３ It is even more preferable that the following conditions be met: 1200 nm ３ It is even more preferable that the following conditions apply: 1100 nm ３ It is even more preferable that the following conditions be met. The same applies to the activation volume of the hexagonal barium ferrite powder.

[0041] "Activation volume" is a unit of magnetization reversal and an indicator of the magnetic size of a particle. The activation volume and the anisotropy constant Ku described herein and below are measured using a vibrating sample type magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes for the coercivity Hc measurement section (measurement temperature: 23°C ± 1°C), and are values ​​obtained from the following relationship between Hc and activation volume V. Regarding the unit of the anisotropy constant Ku, 1 erg / cc = 1.0 × 10⁻⁶ －１ J / m ３ Therefore, 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)]

[0042] As an indicator of reducing thermal fluctuations, or in other words, improving thermal stability, the anisotropy constant Ku can be cited. The hexagonal strontium ferrite powder is preferably 1.8 × 10⁻⁶ ５ J / m ３ It can have a Ku of the above, and more preferably 2.0 × 10 ５ J / m ３ It can have a Ku of the above. Also, the Ku of hexagonal strontium ferrite powder is, for example, 2.5 × 10 ５ J / m ３ The following values ​​are possible. However, since a higher Ku value is preferable as it indicates higher thermal stability, the values ​​are not limited to those exemplified above.

[0043] Hexagonal strontium ferrite powder may or may not contain rare earth atoms. When hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms are present at a concentration of 0.5 to 5.0 atomic percent (bulk concentration) per 100 atomic percent of iron atoms. In one embodiment, hexagonal strontium ferrite powder containing rare earth atoms may have a surface layer segregation of rare earth atoms. In the present invention and this specification, "rare earth atom surface segregation" means that the rare earth atom content relative to 100% of iron atoms in a solution obtained by partially dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom surface content" or simply "surface content" with respect to rare earth atoms) satisfies the ratio of rare earth atom surface content / rare earth atom bulk content > 1.0 with respect to rare earth atoms in a solution obtained by completely dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom bulk content" or simply "bulk content" with respect to rare earth atoms). The rare earth atom content of hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. In contrast, partial dissolution using acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder. Therefore, the rare earth atom content in the solution obtained by partial dissolution is the rare earth atom content in the surface layer of the particles constituting the hexagonal strontium ferrite powder. When the rare earth atom surface layer content satisfies the ratio "rare earth atom surface layer content / rare earth atom bulk content > 1.0", it means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are concentrated in the surface layer (i.e., there are more of them in the surface layer than in the interior). In this invention and specification, the surface layer refers to a part of the region extending from the surface to the interior of the particles constituting the hexagonal strontium ferrite powder.

[0044] When hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atomic percent relative to 100 atomic percent of iron atoms. It is believed that containing rare earth atoms at the bulk content within the above range, and having the rare earth atoms unevenly distributed on the surface of the particles constituting the hexagonal strontium ferrite powder, contributes to suppressing the decrease in regeneration output during repeated regeneration. This is presumed to be because the anisotropy constant Ku can be increased by containing rare earth atoms at the bulk content within the above range, and having the rare earth atoms unevenly distributed on the surface of the particles constituting the hexagonal strontium ferrite powder. The higher the value of the anisotropy constant Ku, the more it is possible to suppress the occurrence of a phenomenon called thermal fluctuation (in other words, to improve thermal stability). By suppressing the occurrence of thermal fluctuation, the decrease in regeneration output during repeated regeneration can be suppressed. It is speculated that the uneven distribution of rare earth atoms on the surface of hexagonal strontium ferrite powder particles contributes to stabilizing the spin of iron (Fe) sites 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 on the surface as the ferromagnetic powder for the magnetic layer contributes to suppressing wear on the magnetic layer surface due to sliding with the magnetic head. In other words, it is speculated that hexagonal strontium ferrite powder with uneven distribution of rare earth atoms on the surface may also contribute to improving the running durability of magnetic tapes. This is because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improved interaction between the particle surface and organic substances (e.g., binders and / or additives) contained in the magnetic layer, resulting in improved strength of the magnetic layer. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration and / or further improving running durability, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic percent, even more preferably in the range of 1.0 to 4.5 atomic percent, and even more preferably in the range of 1.5 to 4.5 atomic percent.

[0045] The bulk content mentioned above is the content obtained by completely dissolving the hexagonal strontium ferrite powder. In this invention and specification, unless otherwise specified, the content of atoms refers to the bulk content obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one type of rare earth atom, or it may contain two or more types of rare earth atoms. When two or more types of rare earth atoms are included, the bulk content mentioned above is determined for the sum of the two or more types of rare earth atoms. This also applies to other components in this invention and specification. That is, unless otherwise specified, a certain component may be used alone, or two or more types may be used. When two or more types are used, the content or content refers to the sum of the two or more types.

[0046] When hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms included may be one or more of any type of rare earth atom. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration, preferred rare earth atoms include neodymium atoms, samarium atoms, yttrium atoms, and dysprosium atoms, with neodymium atoms, samarium atoms, and yttrium atoms being more preferred, and neodymium atoms being even more preferred.

[0047] In hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the rare-earth atoms only need to be segregated in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of segregation is not limited. For example, in hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the ratio of the rare-earth atom surface content obtained by partial dissolution under the dissolution conditions described later to the rare-earth atom bulk content obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," is greater than 1.0 and can be 1.5 or greater. A "surface content / bulk content" greater than 1.0 means that in the particles constituting the hexagonal strontium ferrite powder, the rare-earth atoms are segregated in the surface layer (i.e., there are more of them in the surface layer than in the interior). Furthermore, the ratio of the surface content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in hexagonal strontium ferrite powder having a rare earth atom surface distribution bias, the rare earth atoms only need to be biased towards the surface of the particles constituting the hexagonal strontium ferrite powder, and the above "surface content / bulk content" is not limited to the upper or lower limits exemplified.

[0048] The partial and total dissolution of hexagonal strontium ferrite powder is described below. For hexagonal strontium ferrite powder existing as a powder, the sample powders to be partially and completely dissolved are taken from the same lot of powder. On the other hand, for hexagonal strontium ferrite powder contained in the magnetic layer of a magnetic tape, a portion of the hexagonal strontium ferrite powder extracted from the magnetic layer is subjected to partial dissolution, and another portion is subjected to total dissolution. The extraction of hexagonal strontium ferrite powder from the magnetic layer can be performed, for example, by the method described in paragraph 0032 of Japanese Patent Application Publication No. 2015-91747. Partial dissolution refers to dissolving to the 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 a region of 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder, with the total particles being 100% by mass. On the other hand, total dissolution refers to dissolution to the point where no residue of hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. The measurement of partial dissolution and surface layer content is performed, for example, by the following method. However, the dissolution conditions such as the amount of sample powder below are examples, and any dissolution conditions that enable partial and total dissolution can be arbitrarily adopted. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is held on a hot plate at a set temperature of 70°C for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the resulting filtrate is performed using an inductively coupled plasma (ICP) analyzer. In this way, the surface layer content of rare earth atoms relative to 100 atomic percent of iron atoms can be determined. If multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer content. This also applies to the measurement of bulk content. On the other hand, the measurement of total dissolution and bulk content is performed, for example, by the following method: A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid is held on a hot plate at a set temperature of 80°C for 3 hours.Subsequently, the bulk content relative to 100 atomic percent of iron atoms can be determined by performing the same procedure as described above for partial dissolution and surface layer content measurement.

[0049] From the perspective of increasing the playback output when reproducing data recorded on magnetic tape, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape to be high. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but lacking surface segregation of rare earth atoms tended to have a significantly lower σs compared to hexagonal strontium ferrite powder that does not contain rare earth atoms. In contrast, hexagonal strontium ferrite powder having surface segregation of rare earth atoms is considered preferable in order to suppress such a large decrease in σs. In one embodiment, the σs of hexagonal strontium ferrite powder is 45 A·m ２ It can be 47 A·m or more per kg. ２ It can also be greater than / kg. On the other hand, σs is 80 A·m from the viewpoint of noise reduction. ２ It is preferable that the value be less than or equal to 60 A·m / kg. ２ It is more preferable that it be less than or equal to / kg. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, the mass magnetization σs is the value measured at a magnetic field strength of 15 kOe. 1 [kOe] = 10 ６ It is 4π [A / m].

[0050] Regarding the constituent atom content (bulk content) of hexagonal strontium ferrite powder, the strontium atom content can be in the range of, for example, 2.0 to 15.0 atomic percent relative to 100 atomic percent of iron atoms. In one embodiment, the hexagonal strontium ferrite powder may contain only strontium atoms as divalent metal atoms. In another embodiment, the hexagonal strontium ferrite powder may contain one or more other divalent metal atoms in addition to strontium atoms. For example, it may contain barium atoms and / or calcium atoms. When other divalent metal atoms besides strontium atoms are included, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder can be in the range of, for example, 0.05 to 5.0 atomic percent relative to 100 atomic percent of iron atoms.

[0051] The known crystal structures of hexagonal ferrites include magnetoplumbite (also called "M-type"), W-type, Y-type, and Z-type. Hexagonal strontium ferrite powder may have any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. Hexagonal strontium ferrite powder may show a single crystal structure or two or more crystal structures by X-ray diffraction analysis. For example, in one embodiment, hexagonal strontium ferrite powder may show only the M-type crystal structure by X-ray diffraction analysis. For example, M-type hexagonal ferrite is AFe １２ O １９It is represented by the following compositional formula: Here, A represents a divalent metal atom, and if the hexagonal strontium ferrite powder is of type M, A is either only a strontium atom (Sr), or if A contains multiple divalent metal atoms, then as described above, strontium atoms (Sr) make up the largest proportion on an atomic percentage basis. The divalent metal atom content of hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite and is not particularly limited. The same applies to the iron atom content and oxygen atom content. Hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms and oxygen atoms, and may also contain rare earth atoms. Furthermore, hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, hexagonal strontium ferrite powder may contain aluminum atoms (Al). The aluminum atom content can be, for example, 0.5 to 10.0 atomic percent relative to 100 atomic percent of iron atoms. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration, 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 percent or less, more preferably in the range of 0 to 5.0 atomic percent, and may even be 0 atomic percent, relative to 100 atomic percent of iron atoms. That is, in one embodiment, the hexagonal strontium ferrite powder does not have to contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The above content expressed in atomic percent is obtained by converting the content of each atom (unit: mass%) obtained by completely dissolving the hexagonal strontium ferrite powder into an atomic percent value using the atomic weight of each atom. Furthermore, in the present invention and this specification, "does not contain" for a certain atom means that the content measured by an ICP analyzer after complete dissolution is 0 mass%. The detection limit of an ICP analyzer is typically 0.01 ppm (parts per million) or less by mass. The term "does not contain" above is used to include the presence of substances in amounts below the detection limit of the ICP analyzer.Hexagonal strontium ferrite powder can, in one form, be bismuth atom-free (Bi).

[0052] A preferred specific example of a metal powder ferromagnetic powder is a ferromagnetic metal powder. For details on ferromagnetic metal powders, see, for example, paragraphs 0137 to 0141 of Japanese Patent Application Publication No. 2011-216149 and paragraphs 0009 to 0023 of Japanese Patent Application Publication No. 2005-251351.

[0053] A preferred specific example of ε-iron oxide powder ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, "ε-iron oxide powder" refers to ferromagnetic powder in which the crystal structure of ε-iron oxide is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystal structure of ε-iron oxide, it shall be determined that the crystal structure of ε-iron oxide was detected as the main phase. Methods for producing ε-iron oxide powder include methods from goethite and the reverse micelle method. All of the above production methods are publicly known. Furthermore, for a method of producing ε-iron oxide powder in which a portion of Fe is substituted with substitution atoms such as Ga, Co, Ti, Al, and Rh, see, for example, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supply, No. S1, pp. See S280-S284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206, etc. However, the method for producing ε-iron oxide powder that can be used as ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the method described herein.

[0054] The activation volume of ε-iron oxide powder is preferably 300 to 1500 nm. ３ The activation volume is within the range described above. Finely milled ε-iron oxide powder exhibiting an activation volume within this range is suitable for producing magnetic tapes that exhibit excellent electromagnetic conversion properties. The activation volume of the ε-iron oxide powder is preferably 300 nm. ３ That's all, for example, 500 nm ３It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of ε-iron oxide powder is 1400 nm. ３ The following is more preferable: 1300 nm ３ It is even more preferable that the following conditions apply: 1200 nm ３ It is even more preferable that the following conditions be met: 1100 nm ３ The following is even more preferable.

[0055] The anisotropy constant Ku can be cited as an indicator of the reduction of thermal fluctuations, or in other words, the improvement of thermal stability. The ε-iron oxide powder is preferably 3.0 × 10 ４ J / m ３ It can have a Ku of the above, and more preferably 8.0 × 10 ４ J / m ３ It is possible to have the above Ku content. Also, the Ku content of ε-iron oxide powder is, for example, 3.0 × 10⁻⁶. ５ J / m ３ The following values ​​are possible. However, a higher Ku value indicates higher thermal stability, which is preferable, so the values ​​are not limited to those exemplified above.

[0056] From the perspective of increasing the playback output when reproducing data recorded on magnetic tape, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape to be high. In this regard, in one embodiment, the σs of ε-iron oxide powder is 8 A·m ２ It can be 12 A·m or more per kg. ２ It can also be more than / kg. On the other hand, the σs of ε-iron oxide powder is 40 A·m from the viewpoint of noise reduction. ２ It is preferable that it be less than or equal to 35 A·m / kg. ２ It is more preferable that the amount is less than or equal to / kg.

[0057] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders shall be the value measured using a transmission electron microscope by the following method. The powder is photographed using a transmission electron microscope at a magnification of 100,000x, and printed onto photographic paper to obtain a photograph of the particles constituting the powder at a total magnification of 500,000x. The target particles are selected from the obtained photographs of the particles, and the contour of the particles is traced with a digitizer to measure the size of the particles (primary particles). Primary particles refer to independent particles that do not aggregate. 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 above-mentioned transmission electron microscope, for example, a Hitachi H-9000 transmission electron microscope can be used. Furthermore, the particle size measurement can be performed using known image analysis software, for example, Carl Zeiss KS-400 image analysis software. The average particle sizes shown in the Examples section below were measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software, unless otherwise specified. In the present invention and this specification, "powder" means an aggregate of multiple particles. For example, ferromagnetic powder means 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, but also includes forms in which binders, additives, etc., described later, are interposed between the particles. The word "particle" is sometimes used to refer to powder.

[0058] For example, the method described in paragraph 0015 of Japanese Patent Publication No. 2011-048878 can be used to collect sample powder from a magnetic tape for particle size measurement.

[0059] In the present invention and this specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is expressed as follows: (1) If the shape of the particles observed in the above particle photograph is needle-shaped, spindle-shaped, columnar (however, the height is greater than the longest major axis of the base), it is expressed as the length of the long axis constituting the particle, i.e., the long axis length; (2) If the shape is plate-shaped or columnar (however, the thickness or height is less than the longest major axis of the plate surface or base), it is expressed as the longest major axis of the plate surface or base; (3) If the shape is spherical, polyhedral, irregular, etc., and the long axis constituting the particle cannot be determined from the shape, it is expressed as the equivalent circle diameter. The equivalent circle diameter refers to the diameter determined by the circular projection method.

[0060] Furthermore, the average needle-shape ratio of the powder refers to the arithmetic mean of the values ​​obtained for the 500 particles by measuring the length of the short axis of each particle in the above measurement, i.e., the short axis length, and determining the (long axis length / short axis length) value for each particle. Here, unless otherwise specified, the short axis length refers to the length of the short axis constituting the particle in the definition of particle size above (1), the thickness or height in the definition of (2), and in the case of (3), since there is no distinction between the long axis and the short axis, (long axis length / short axis length) is considered to be 1 for convenience. And unless otherwise specified, when the shape of the particle is specific, for example, in the definition of particle size above (1), the average particle size is the average long axis length, and in the definition of (2), the average particle size is the average plate diameter. In the definition of (3), the average particle size is the average diameter (also called the average particle size or average particle diameter).

[0061] The content (filling rate) of ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the magnetic layer. A high filling rate of ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving recording density.

[0062] (Binding Agent) The above magnetic tape can be a coated magnetic tape, and the magnetic layer may contain a binding agent. The binding agent is one or more resins. Various resins commonly used as binding agents for coated magnetic tapes can be used as binding agents. For example, as binding agents, a resin selected from polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl alkylal resin such as polyvinyl butyral can be used alone or in mixture of multiple resins. Among these, polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binding agents in the non-magnetic layer and / or back coat layer described later. For more information on the binding agents, refer to paragraphs 0028 to 0031 of Japanese Patent Application Publication No. 2010-24113. The average molecular weight of the resin used as a binder can be, for example, 10,000 to 200,000 as a weight-average molecular weight. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass per 100.0 parts by mass of ferromagnetic powder.

[0063] (Curing agent) A curing agent can also be used together with a resin that can be used as a binder. In one form, the curing agent can be a thermosetting compound, which is a compound that undergoes a curing reaction (crosslinking reaction) by heating, and in another form, it can be a photocurable compound, which undergoes a curing reaction (crosslinking reaction) by light irradiation. As the curing reaction progresses during the magnetic layer formation process, at least a portion of the curing agent may be included in the magnetic layer in a state where it has reacted (crosslinked) with other components such as the binder. This also applies to layers formed using a composition that contains a curing agent when the composition used to form other layers contains a curing agent. Preferred curing agents are thermosetting compounds, and polyisocyanates are preferred. For details on polyisocyanates, refer to paragraphs 0124 to 0125 of Japanese Patent Application Publication No. 2011-216149. The curing agent can be used in the magnetic layer forming composition in an amount of, for example, 0 to 80.0 parts by mass, preferably 50.0 to 80.0 parts by mass, per 100.0 parts by mass of the binder.

[0064] (Additives) The magnetic layer may contain one or more additives as needed. Commercially available additives can be appropriately selected and used according to the desired properties. Alternatively, compounds synthesized by known methods can be used as additives. Additives can be used in any amount. An example of an additive is the curing agent mentioned above. Additives that can be included in the magnetic layer include non-magnetic powders (e.g., inorganic powders, carbon black, etc.), lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, antioxidants, etc. For example, for lubricants, refer to paragraphs 0030 to 0033, 0035 and 0036 of Japanese Patent Application Publication No. 2016-126817. A lubricant may be included in the non-magnetic layer described later. For lubricants that can be included in the non-magnetic layer, refer to paragraphs 0030 to 0031, 0034, 0035 and 0036 of Japanese Patent Application Publication No. 2016-126817. For dispersants, see paragraphs 0061 and 0071 of Japanese Patent Publication No. 2012-133837. Dispersants may be added to the composition for forming a non-magnetic layer. For dispersants that can be added to the composition for forming a non-magnetic layer, see paragraph 0061 of Japanese Patent Publication No. 2012-133837. Non-magnetic powders that can be included in the magnetic layer include non-magnetic powders that can function as abrasives, and non-magnetic powders that can function as protrusion-forming agents that form appropriately protruding protrusions on the surface of the magnetic layer (e.g., non-magnetic colloidal particles). For example, for abrasives, see paragraphs 0030 to 0032 of Japanese Patent Publication No. 2004-273070. Colloidal particles are preferred as protrusion-forming agents, inorganic colloidal particles are preferred from the viewpoint of availability, inorganic oxide colloidal particles are more preferred, and silica colloidal particles (colloidal silica) are even more preferred. The average particle size of the abrasive and the protrusion-forming agent is preferably in the range of 30 to 200 nm, and more preferably in the range of 50 to 100 nm.

[0065] The magnetic layer described above can be provided directly on the surface of a non-magnetic support, or indirectly via a non-magnetic layer.

[0066] <Non-magnetic layer> Next, the non-magnetic layer will be described. The magnetic tape described above may have a magnetic layer directly on the surface of a non-magnetic support, or it may have a magnetic layer on the surface of a non-magnetic support via a non-magnetic layer containing non-magnetic powder. The non-magnetic powder used in the non-magnetic layer may be an inorganic powder or an organic powder. Carbon black can also be used. Examples of inorganic powders include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These non-magnetic powders are commercially available and can also be manufactured by known methods. For details, see paragraphs 0146 to 0150 of Japanese Patent Application Publication No. 2011-216149. For carbon black that can be used in the non-magnetic layer, see paragraphs 0040 and 0041 of Japanese Patent Application Publication No. 2010-24113. The content (filling rate) of non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the non-magnetic layer.

[0067] The non-magnetic layer may contain a binder and may also contain additives. For further details regarding the binder, additives, etc., of the non-magnetic layer, known technology relating to non-magnetic layers can be applied. Furthermore, for example, regarding the type and content of the binder, the type and content of the additives, etc., known technology relating to magnetic layers can also be applied.

[0068] In the present invention and this specification, the non-magnetic layer includes a substantially non-magnetic layer containing a small amount of ferromagnetic powder, for example as an impurity or intentionally, along with the non-magnetic powder. A substantially non-magnetic layer is defined as a layer having a remanent magnetic flux density of 10 mT or less, a coercivity of 7.96 kA / m (100 Oe) or less, or a layer having a remanent magnetic flux density of 10 mT or less and a coercivity of 7.96 kA / m (100 Oe) or less. It is preferable that the non-magnetic layer has no remanent magnetic flux density and coercivity.

[0069] <Non-magnetic support> Examples of non-magnetic support materials (hereinafter also simply referred to as "support") include known materials such as biaxially oriented polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamide-imide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and aromatic polyamide are preferred. In the present invention and this specification, "aromatic polyamide" means a resin containing an aromatic skeleton and multiple amide bonds. The aromatic rings contained in the aromatic skeleton of an aromatic polyamide are not particularly limited. Specific examples of aromatic rings include, for example, benzene rings.

[0070] In one embodiment, the non-magnetic support of the magnetic tape described above may be an aromatic polyester support. In the present invention and this specification, "aromatic polyester" means a resin containing an aromatic skeleton and a plurality of ester bonds, and "aromatic polyester support" means a support containing at least one layer of aromatic polyester film. "Aromatic polyester film" means a film in which the component that constitutes the film by mass is aromatic polyester. In the present invention and this specification, "aromatic polyester support" includes both a support in which all the resin films contained are aromatic polyester films and a support containing aromatic polyester films and other resin films. Specific embodiments of the aromatic polyester support include a single layer of aromatic polyester film, a laminated film of two or more layers of aromatic polyester films with the same constituent components, a laminated film of two or more layers of aromatic polyester films with different constituent components, a laminated film containing one or more layers of aromatic polyester film and one or more layers of resin films other than aromatic polyester, etc. In a laminated film, an adhesive layer or the like may be optionally included between two adjacent layers. Furthermore, the aromatic polyester support may optionally include a metal film and / or a metal oxide film formed by vapor deposition or the like on one or both surfaces. The same applies to the "polyethylene terephthalate support," "polyethylene naphthalate support," and "aromatic polyamide support" as described in the present invention and this specification.

[0071] The aromatic rings contained in the aromatic skeleton of an aromatic polyester are not particularly limited. Specific examples of aromatic rings include, for example, benzene rings and naphthalene rings. For example, polyethylene terephthalate (PET) is a polyester containing a benzene ring and is a resin obtained by polycondensation of ethylene glycol with terephthalic acid and / or dimethyl terephthalate. In the present invention and this specification, "polyethylene terephthalate" also includes structures having one or more other components in addition to the above components (e.g., copolymer components, components introduced into the terminals or side chains, etc.). 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. In the present invention and this specification, "polyethylene naphthalate" also includes structures having one or more other components in addition to the above components (e.g., copolymer components, components introduced into the terminals or side chains, etc.).

[0072] Furthermore, the non-magnetic support can be a biaxially oriented film, and may be a film that has been subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, etc.

[0073] One example of an indicator of the physical properties of a non-magnetic support is the widthwise Young's modulus. In the present invention and this specification, the Young's modulus of a non-magnetic support is a value measured by the following method in a measurement environment of 23°C and 50% relative humidity. The widthwise Young's modulus shown in the table below is a value obtained by the following method using a Toyo Baldwin Tensilon as a universal tensile testing apparatus. A sample piece cut from the non-magnetic support to be measured is pulled in a universal tensile testing apparatus under the conditions of a chuck distance of 100 mm, a tensile speed of 10 mm / min, and a chart speed of 500 mm / min. As a universal tensile testing apparatus, for example, a commercially available universal tensile testing apparatus such as a Toyo Baldwin Tensilon or a universal tensile testing apparatus with a known configuration can be used. The widthwise Young's modulus of the sample piece is calculated from the tangent to the rising portion of the load-elongation curve obtained in this way. Here, the widthwise direction of the sample piece refers to the longitudinal direction and widthwise direction when this sample piece was included in a magnetic tape. For example, after removing parts other than the non-magnetic support, such as the magnetic layer, from the magnetic tape using a known method (e.g., defilm removal using an organic solvent), the Young's modulus in the width direction of the non-magnetic support can be determined using the method described above.

[0074] One means of obtaining a magnetic tape with a small σDES is to use a non-magnetic support with a large widthwise Young's modulus. The widthwise Young's modulus of a polyethylene terephthalate support is preferably 7,000 MPa or more, and more preferably 8,000 MPa or more. The widthwise Young's modulus of a polyethylene naphthalate support is preferably 9,000 MPa or more, and more preferably 9,500 MPa or more. The widthwise Young's modulus of an aromatic polyamide support is preferably 10,000 MPa or more, more preferably 12,000 MPa or more, even more preferably 14,000 MPa or more, and even more preferably 16,000 MPa or more. The widthwise Young's modulus of various non-magnetic supports can be, for example, 20,000 MPa or less or 18,000 MPa or less. The widthwise Young's modulus of a non-magnetic support can be controlled by the type and mixing ratio of the components constituting the support, the manufacturing conditions of the support, etc. For example, the widthwise Young's modulus can be controlled by adjusting the stretching ratio in the biaxial stretching process.

[0075] <Back Coat Layer> The above magnetic tape may or may not have a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support. For the non-magnetic powder of the back coat layer, refer to the previous description regarding the non-magnetic powder of the non-magnetic layer.

[0076] Improving the surface smoothness of the backcoat layer can contribute to reducing the σDES value. To improve the surface smoothness of the backcoat layer, it is preferable to use carbon black and other non-magnetic powders in combination as the non-magnetic powder of the backcoat layer, and the lower the proportion of carbon black in the total amount of non-magnetic powder in the backcoat layer, the higher the surface smoothness of the backcoat layer tends to be. The proportion of carbon black in 100.0 parts by mass of the total amount of non-magnetic powder in the backcoat layer is preferably in the range of 10.0 to 70.0 parts by mass, more preferably in the range of 10.0 to 60.0 parts by mass, and even more preferably in the range of 10.0 to 50.0 parts by mass. The content (filling rate) of non-magnetic powder in the backcoat 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 backcoat layer.

[0077] The average particle size of the carbon black in the backcoat layer is preferably 50 nm or less, more preferably in the range of 10 to 50 nm, and even more preferably in the range of 10 to 30 nm. The average particle size of the non-magnetic powder other than carbon black in the backcoat layer is preferably in the range of 0.10 to 0.20 μm. An example of a non-magnetic powder other than carbon black is α-iron oxide powder.

[0078] The backcoat layer forming composition may contain components (dispersants) that can enhance the dispersibility of the nonmagnetic powder contained in the composition. An example of such a dispersant is a compound having an ammonium salt structure of an alkyl ester anion represented by the following formula 1. Note that "alkyl ester anion" can also be called "alkyl carboxylate anion."

[0079]

[0080] 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 ＋ This represents an ammonium cation.

[0081] Furthermore, from the viewpoint of improving the dispersibility of carbon black, in one embodiment, two or more components capable of forming the above-mentioned salt structure compound can be used when preparing the backcoat layer forming composition. As a result, when preparing the backcoat layer forming composition, at least some of these components can form the above-mentioned salt structure compound.

[0082] Unless otherwise specified, the groups described below may or may not have substituents. Furthermore, for groups with substituents, "number of carbon atoms" means the number of carbon atoms excluding the substituent unless otherwise specified. In the present invention and this specification, examples of substituents include alkyl groups (e.g., alkyl groups having 1 to 6 carbon atoms), hydroxyl groups, alkoxy groups (e.g., alkoxy groups having 1 to 6 carbon atoms), halogen atoms (e.g., fluorine atoms, chlorine atoms, bromine atoms, etc.), cyano groups, amino groups, nitro groups, acyl groups, carboxyl groups, salts of carboxyl groups, sulfonic acid groups, salts of sulfonic acid groups, and the like.

[0083] The following provides a more detailed explanation of Equation 1.

[0084] 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. A 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, but a linear structure is preferred. The alkyl group or fluorinated alkyl group represented by R may have substituents or be unsubstituted, but it is preferred to be unsubstituted. The alkyl group represented by R is, for example, C ｎ H ２ｎ＋１ It can be represented by -. Here, n represents an integer greater than or equal to 7. Also, the alkyl fluoride represented by R is, for example, C ｎ H ２ｎ＋１The alkyl group represented by - may have a structure in which some or all of the hydrogen atoms constituting the alkyl group are substituted with fluorine atoms. The number of carbon atoms in the alkyl group or alkyl fluoride represented by R is 7 or more, preferably 8 or more, more preferably 9 or more, even more preferably 10 or more, even more preferably 11 or more, even more preferably 12 or more, and even more preferably 13 or more. Furthermore, the number of carbon atoms in the alkyl group or alkyl fluoride represented by R is preferably 20 or less, more preferably 19 or less, and even more preferably 18 or less.

[0085] In formula 1, Z ＋ * represents an ammonium cation. The ammonium cation has, in detail, the following structure. In this invention and specification, the asterisk (*) in a formula representing a part of a compound indicates the structure of that part and the bond position with an adjacent atom.

[0086]

[0087] Nitrogen cation of ammonium cation N ＋ and the oxygen anion O in Equation 1 － The two can form a salt crosslinking group, creating an ammonium salt structure of the alkyl ester anion represented by formula 1. The presence of a compound having the ammonium salt structure of the alkyl ester anion represented by formula 1 in the backcoat layer can be confirmed by analyzing the magnetic tape using X-ray photoelectron spectroscopy (ESCA), infrared spectroscopy (IR), etc.

[0088] In one form, Z ＋The ammonium cation represented by can be obtained, for example, by the nitrogen atom of a nitrogen-containing polymer becoming a cation. A nitrogen-containing polymer means a polymer that contains nitrogen atoms. In this invention and specification, the terms "polymer" and "polymer" are used to encompass both homopolymers and copolymers. Nitrogen atoms can be included in one form as atoms constituting the main chain of the polymer, and in another form as atoms constituting the side chain of the polymer.

[0089] One form of nitrogen-containing polymer is polyalkyleneimines. Polyalkyleneimines are ring-opening polymers of alkyleneimines, and are polymers having multiple repeating units represented by the following formula 2.

[0090]

[0091] In Equation 2, the nitrogen atom N that constitutes the main chain is a nitrogen cation N ＋ And so Z in equation 1 ＋ An ammonium cation represented by [formula] can be obtained. Then, with an alkyl ester anion, it can form an ammonium salt structure, for example, as shown below.

[0092]

[0093] The following provides a more detailed explanation of Equation 2.

[0094] In formula 2, R １ and R ２ Each of these independently represents a hydrogen atom or an alkyl group, and n1 represents an integer of 2 or more.

[0095] R １ or R ２ Examples of alkyl groups represented by 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 is preferably an unsubstituted alkyl group. １ and R ２The combinations include a form in which one is a hydrogen atom and the other is an alkyl group, a form in which both are hydrogen atoms, and a form in which both are alkyl groups (identical or different alkyl groups), with the form in which both are hydrogen atoms being preferred. As an alkylene imine that yields a polyalkylene imine, the structure with the fewest number of carbon atoms constituting the ring is ethyleneimine, and the number of carbon atoms in the main chain of the alkylene imine (ethyleneimine) obtained by ring-opening of ethyleneimine is 2. Therefore, n1 in formula 2 is 2 or more. n1 in formula 2 can be, for example, 10 or less, 8 or less, 6 or less, or 4 or less. The polyalkylene imine may be a homopolymer containing only the same structure as the repeating structure represented by formula 2, or it may be a copolymer containing two or more different structures as the repeating structure represented by formula 2. The number-average molecular weight of the polyalkylene imine 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, preferably 300 or more, and more preferably 400 or more. Furthermore, 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.

[0096] In the present invention and this specification, average molecular weight (weight-average molecular weight and number-average molecular weight) refers to the value obtained by measuring by gel permeation chromatography (GPC) and converting it to standard polystyrene equivalent. Unless otherwise specified, the average molecular weights shown in the Examples section below are values ​​obtained by converting the values ​​measured using GPC under the following measurement conditions to standard polystyrene equivalent (polystyrene equivalent value). GPC instrument: HLC-8220 (Tosoh Corporation) Guard column: TSKguardcolumn Super HZM-H Columns: TSKgel Super HZ2000, TSKgel Super HZ 4000, TSKgel Super HZ-M (Tosoh Corporation, 4.6 mm (inner diameter) x 15.0 cm, 3 columns connected in series) Eluent: Tetrahydrofuran (THF), 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

[0097] Another form of nitrogen-containing polymer is polyallylamine. Polyallylamine is a polymer of allylamine, having multiple repeating units represented by the following formula 3.

[0098]

[0099] In formula 3, the nitrogen atom N constituting the amino group of the side chain is a nitrogen cation N ＋ And so Z in equation 1 ＋ An ammonium cation represented by [formula] can be obtained. Then, with an alkyl ester anion, it can form an ammonium salt structure, for example, as shown below.

[0100]

[0101] The weight-average molecular weight of the polyallylamine 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, preferably 1,000 or more, and more preferably 1,500 or more. Furthermore, 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.

[0102] The presence of compounds having an ammonium salt structure of an alkyl ester anion represented by Formula 1, specifically compounds with structures derived from polyalkylene imines or polyallylamines, in the backcoat layer can be confirmed by analyzing the backcoat layer surface using time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0103] Compounds having an ammonium salt structure of an alkyl ester anion represented by formula 1 can be salts 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, for example, a nitrogen-containing polymer selected from the group consisting of polyalkylene imines 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 replaced with fluorine atoms. For example, the salt formation reaction can easily proceed by mixing the nitrogen-containing polymer and the above fatty acids at room temperature. Room temperature is, for example, about 20 to 25°C. In one embodiment, one or more nitrogen-containing polymers and one or more of the above fatty acids are used as components of the backcoat layer forming composition, and the salt formation reaction can be carried out by mixing them in the preparation step of the backcoat layer forming composition. Alternatively, in one embodiment, one or more nitrogen-containing polymers and one or more of the above fatty acids can be mixed to form a salt before preparing the backcoat layer forming composition, and this salt can then be used as a component of the backcoat layer forming composition to prepare it. When mixing nitrogen-containing polymers and the above fatty acids to form an ammonium salt of an alkyl ester anion represented by formula 1, the nitrogen atoms constituting the nitrogen-containing polymer may also react with the carboxyl groups of the above fatty acids to form the following structure, and forms including such a structure are also included in the above compound.

[0104]

[0105] Examples of the above fatty acids include fatty acids having the alkyl group previously described as R in Formula 1, and fluorinated fatty acids having the fluorinated alkyl group previously described as R in Formula 1.

[0106] The mixing ratio of the nitrogen-containing polymer used to form the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 to the above fatty acids is preferably 10:90 to 90:10, more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20, as the mass ratio of nitrogen-containing polymer to the above fatty acids. Furthermore, when preparing the composition for forming the back coat layer, the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 can be used in an amount of, for example, 1.0 to 20.0 parts by mass, and preferably 1.0 to 10.0 parts by mass, per 100.0 parts by mass of non-magnetic powder. Also, when preparing the composition for forming the back coat layer, for example, 0.1 to 10.0 parts by mass of nitrogen-containing polymer can be used per 100.0 parts by mass of non-magnetic powder, and preferably 0.5 to 8.0 parts by mass of nitrogen-containing polymer. The above fatty acids can be used in amounts of, for example, 0.05 to 10.0 parts by mass per 100.0 parts by mass of nonmagnetic powder, and it is preferable to use 0.1 to 5.0 parts by mass.

[0107] Regarding the components that may be included in the backcoat layer, the backcoat layer may include a binder and may also include additives. With regard to the binder and additives of the backcoat layer, prior art relating to backcoat layers may be applied, as may prior art relating to the formulation of magnetic and / or nonmagnetic layers. For example, paragraphs 0018 to 0020 of Japanese Patent Application Publication No. 2006-331625 and lines 65 to 38 of column 4 to column 5 of U.S. Patent No. 7,029,774 can be referenced with respect to the backcoat layer.

[0108] (Backcoat layer surface roughness Ra) As an indicator of the surface smoothness of the backcoat layer, the arithmetic mean roughness Ra can be cited. In one embodiment, the arithmetic mean roughness Ra (also called "backcoat layer surface roughness Ra") measured on the surface of the backcoat layer of the magnetic tape is preferably 9.0 nm or less, more preferably 8.0 nm or less, and even more preferably 7.0 nm or less. The backcoat layer surface roughness Ra of the magnetic tape can be, for example, 1.0 nm or more, 1.5 nm or more, or 2.0 nm or more.

[0109] In the present invention and this specification, the backcoat layer surface roughness Ra is defined as the value measured by an atomic force microscope (AFM) over a 40 μm × 40 μm area of ​​the backcoat layer surface. An example of measurement conditions is given below. The backcoat layer surface roughness Ra shown in the Examples section below is the value obtained by measurement under the following measurement conditions. An AFM (Veeco Nanoscope 4) is used in tapping mode to measure a 40 μm × 40 μm area of ​​the backcoat layer surface of the magnetic tape. A BRUKER RTESP-300 probe is used, with a scan speed (probe movement speed) of 40 μm / second and a resolution of 512 pixels × 512 pixels.

[0110] <Various Thicknesses> Regarding the tape thickness (total thickness) of magnetic tape, with the enormous increase in the amount of information in recent years, there is a demand for increased recording capacity (high capacity) in magnetic recording media. As a means of increasing the capacity of tape-shaped magnetic recording media (i.e., magnetic tape), one can reduce the thickness of the magnetic tape and increase the length of magnetic tape that can be stored in one reel of magnetic tape cartridge. From this point of view, the tape thickness (total thickness) of the above-mentioned magnetic tape is 5.2 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.

[0111] The tape thickness (total thickness) of the magnetic tape in this invention and specification shall be measured by the following method. Before measurement, the magnetic tape or the magnetic tape cartridge containing the magnetic tape shall be left in an environment with a temperature of 20 to 25°C and a relative humidity of 40 to 60% for at least 5 days to allow it to acclimate to the environment. Subsequently, in the same environment, one tape sample (5 cm in length) shall be cut from three or more locations (randomly selected) that differ in the longitudinal position of the magnetic tape. Thus, three or more tape samples shall be cut. At a randomly selected position of each tape sample, one of the two ends of the tape sample in the width direction shall be designated as the reference position (0 mm), and the tape thickness shall be measured at measurement points every 1 mm toward the other end in the width direction. For example, in the case of a tape sample cut from a 1 / 2-inch (12.7 mm) magnetic tape, the tape thickness is measured at a total of 12 measurement points: 1 mm from the reference position, 2 mm from the reference position, 3 mm from the reference position, 4 mm from the reference position, 5 mm from the reference position, 6 mm from the reference position, 7 mm from the reference position, 8 mm from the reference position, 9 mm from the reference position, 10 mm from the reference position, 11 mm from the reference position, and 12 mm from the reference position. The arithmetic mean of the measurements obtained by performing the above operation for all the tape samples cut above is taken as the tape thickness of the magnetic tape being measured. A known measuring instrument capable of measuring thickness on the order of 5 nm can be used to measure the tape thickness.

[0112] The thickness of the non-magnetic support is preferably 3.0 to 5.0 μm. The thickness of the magnetic layer can be optimized according to the saturation magnetization of the magnetic head used, the head gap length, the bandwidth of the recording signal, etc., and is generally 0.01 μm to 0.15 μm, preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.1 μm, from the viewpoint of high-density recording. There only needs to be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic properties, and known configurations for multilayer magnetic layers can be applied. When separated into two or more layers, the thickness of the magnetic layer is the total thickness of these layers. The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, and preferably 0.1 to 1.0 μm. The thickness of the back coat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm. Various thicknesses such as the thickness of the magnetic layer can be determined by the following method. After exposing the cross-section of the magnetic tape in the thickness direction using an ion beam, the exposed cross-section is observed using a scanning electron microscope or a transmission electron microscope. Various thicknesses can be determined as the arithmetic mean of the thicknesses obtained at any two points during the cross-sectional observation. Alternatively, various thicknesses can be determined as design thicknesses calculated from manufacturing conditions, etc.

[0113] <Manufacturing Process> (Preparation of Layer-Forming Compositions) Compositions for forming magnetic layers, non-magnetic layers, or backcoat layers usually contain a solvent along with the various components described above. As the solvent, one or more of the various solvents commonly used in the manufacture of coated magnetic recording media can be used. The solvent content of each layer-forming composition is not particularly limited. For solvents, refer to paragraph 0153 of Japanese Patent Application Publication No. 2011-216149. The solid content concentration and solvent composition of each layer-forming composition may be appropriately adjusted in accordance with the handling suitability of the composition, the coating conditions, and the thickness of each layer to be formed. The process of preparing a composition for forming a magnetic layer, non-magnetic layer, or backcoat layer usually includes at least a kneading step, a dispersion step, and mixing steps provided before or after these steps as needed. Each individual step may be divided into two or more stages. The various components used in the preparation of each layer-forming composition may be added at the beginning or in the middle of any step. Alternatively, individual components may be added in two or more separate steps. For example, the binder may be added in separate steps during the kneading process, the dispersion process, and the mixing process for adjusting the viscosity after dispersion. In the above magnetic tape manufacturing process, conventional known manufacturing techniques can be used as some of the steps. In the kneading process, kneaders with strong kneading force, such as open kneaders, continuous kneaders, pressure kneaders, and extruders, can be used. Details of the kneading process are described in Japanese Patent Publication No. 1-106338 and Japanese Patent Publication No. 1-79274. As the disperser, various known dispersers that utilize shear force, such as bead mills, ball mills, sand mills, or homomixers, can be used. Dispersion beads can preferably be used for dispersion. Examples of dispersion beads include ceramic beads and glass beads, with zirconia beads being preferred. Two or more types of beads may be used in combination. The bead diameter (particle size) and bead packing rate of the dispersion beads are not particularly limited and should be set according to the powder to be dispersed. Each layer-forming composition may be filtered by a known method before being subjected to the coating process. Filtration can be performed, for example, by filter filtration.For filtration, filters with pore sizes of 0.01 to 3 μm (e.g., glass fiber filters, polypropylene filters, etc.) can be used.

[0114] (Coating process) The magnetic layer can be formed by directly coating the magnetic layer-forming composition onto the surface of the non-magnetic support, or by sequentially or simultaneously coating it with the non-magnetic layer-forming composition. The back coat layer can be formed by coating the back coat-forming composition onto the surface of the non-magnetic support opposite to the surface having the non-magnetic layer and / or magnetic layer (or where the non-magnetic layer and / or magnetic layer are subsequently provided). For details of the coating process for each layer formation, refer to paragraph 0066 of Japanese Patent Application Publication No. 2010-231843.

[0115] (Other Processes) For other processes for manufacturing magnetic tape, known technologies can be applied. For various processes, see, for example, paragraphs 0067 to 0070 of Japanese Patent Application Publication No. 2010-231843. For example, the coated layer of the magnetic layer forming composition can be subjected to orientation treatment in the orientation zone while the coated layer is wet. For orientation treatment, various known technologies, including the description in paragraph 0052 of Japanese Patent Application Publication No. 2010-24113, can be applied. For example, vertical orientation treatment can be performed by known methods such as using opposite-polarity opposing magnets. In the orientation zone, the drying rate of the coated layer can be controlled by the temperature and airflow of the drying air and / or the transport speed in the orientation zone. Alternatively, the coated layer may be pre-dried before being transported to the orientation zone. As an example, the magnetic field strength in the vertical orientation treatment can be 0.1 to 1.5 T.

[0116] A long roll of magnetic tape can be obtained by going through various processes. The obtained roll of magnetic tape is cut (slit) to the width of the magnetic tape to be wound onto a magnetic tape cartridge using a known cutting machine. The above width is determined according to standards, for example, 1 / 2 inch. A servo pattern is usually formed on the magnetic tape obtained by slitting. Details on the formation of the servo pattern will be described later.

[0117] (Heat Treatment) In one embodiment, the magnetic tape may be a magnetic tape manufactured through the following heat treatment. In another embodiment, the magnetic tape may be a magnetic tape manufactured without the following heat treatment.

[0118] For heat treatment, the magnetic tape, which has been slit and cut to a width determined according to the standard, can be wrapped around a core-shaped member, and the heat treatment can be performed while the tape is still wrapped around the member.

[0119] In one embodiment, the above heat treatment is performed with a magnetic tape wound around a core-shaped member for heat treatment (hereinafter referred to as the "heat treatment core"), and the heat-treated magnetic tape is wound onto a cartridge reel of a magnetic tape cartridge to produce a magnetic tape cartridge with the magnetic tape wound on the cartridge reel. The heat treatment core can be made of metal, resin, paper, etc. From the viewpoint of suppressing the occurrence of winding failures such as spocking, it is preferable that the material of the heat treatment core is a material with high rigidity. From this point of view, it is preferable that the heat treatment core is made of metal or resin. Furthermore, as an indicator of rigidity, the flexural modulus of the material of the heat treatment core is preferably 0.2 GPa or higher, and more preferably 0.3 GPa or higher. On the other hand, since high-rigidity materials are generally expensive, using a heat treatment core made of a material with rigidity exceeding the rigidity that can suppress the occurrence of winding failures will lead to increased costs. Considering the above points, it is preferable that the flexural modulus of the material of the heat treatment core is 250 GPa or lower. The method for measuring the flexural modulus will be described later. Furthermore, the core for heat treatment can be a solid or hollow core-shaped member. In the case of a hollow core, from the viewpoint of maintaining rigidity, the wall thickness is preferably 2 mm or more. The core for heat treatment may or may not have a flange. It is preferable to prepare a magnetic tape of a length equal to or greater than the length to be finally housed in a magnetic tape cartridge (hereinafter referred to as the "final product length") as the magnetic tape to be wound around the core for heat treatment, and to perform heat treatment by winding this magnetic tape around the core for heat treatment and placing it in a heat treatment environment. The length of the magnetic tape wound around the core for heat treatment is equal to or greater than the final product length, and from the viewpoint of ease of winding onto the core for heat treatment, it is preferable to set it to "final product length + α". From the viewpoint of ease of winding, this α is preferably 5 m or more. The tension when winding onto the core for heat treatment is preferably 0.1 N (Newtons) or more. Furthermore, from the viewpoint of suppressing excessive deformation during manufacturing, the tension when winding onto the core for heat treatment is preferably 1.5 N or less, and more preferably 1.0 N or less. The outer diameter of the core for heat treatment is preferably 20 mm or more, and more preferably 40 mm or more, from the viewpoint of ease of winding and suppression of coiling (longitudinal curling).Furthermore, the outer diameter of the heat-treated core is preferably 100 mm or less, and more preferably 90 mm or less. The width of the heat-treated core should be greater than or equal to the width of the magnetic tape wound around it. Also, when removing the magnetic tape from the heat-treated core after heat treatment, it is preferable to remove the magnetic tape from the heat-treated core only after both the magnetic tape and the heat-treated core have cooled sufficiently, in order to prevent unintended tape deformation during the removal process. It is preferable to first wind the removed magnetic tape onto another core (referred to as a "temporary winding core"), and then wind the magnetic tape from the temporary winding core onto the cartridge reel of the magnetic tape cartridge (generally with an outer diameter of about 40 to 50 mm). This allows the relationship between the inside and outside of the magnetic tape relative to the heat-treated core during heat treatment to be maintained while winding the magnetic tape onto the cartridge reel of the magnetic tape cartridge. For details of the temporary winding core and the tension when winding the magnetic tape onto this core, please refer to the previous description regarding the heat-treated core. In the configuration in which the above heat treatment is applied to a magnetic tape of a length of "final product length + α", the "+ α" length can be cut off at any stage. For example, in one configuration, the magnetic tape of the final product length can be wound from the temporary winding core onto the reel of the magnetic tape cartridge, and the remaining "+ α" length can be cut off. From the viewpoint of minimizing the portion that is cut off and discarded, it is preferable that α is 20m or less.

[0120] The specific form of the heat treatment performed with the material wrapped around the core member as described above is explained below. The ambient temperature for heat treatment (hereinafter referred to as "heat treatment temperature") is preferably 40°C or higher, and more preferably 50°C or higher. On the other hand, from the viewpoint of suppressing excessive deformation, the heat treatment temperature is preferably 75°C or lower, more preferably 70°C or lower, and even more preferably 65°C or lower. The absolute humidity by weight of the atmosphere for heat treatment is preferably 0.1 g / kg Dry air or higher, and more preferably 1 g / kg Dry air or higher. An atmosphere with an absolute humidity by weight within the above range is preferable because it can be prepared without using special equipment to reduce moisture. On the other hand, from the viewpoint of suppressing condensation and a decrease in workability, the absolute humidity by weight is preferably 70 g / kg Dry air or lower, and more preferably 66 g / kg Dry air or lower. The heat treatment time is preferably 0.3 hours or more, and more preferably 0.5 hours or more. Furthermore, from the viewpoint of production efficiency, the heat treatment time is preferably 48 hours or less.

[0121] (Formation of servo patterns) The formation of servo patterns on the magnetic layer of magnetic tape can be carried out by known methods. The servo patterns enable tracking control of the magnetic head in a magnetic tape device, control of the magnetic tape's running speed, and so on. "Formation of servo patterns" can also be referred to as "recording of servo signals."

[0122] The formation of the servo pattern will be explained below.

[0123] Servo patterns are typically formed along the longitudinal direction of the magnetic tape. Examples of control methods that utilize servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0124] As stated in ECMA (European Computer Manufacturers Association)-319 (June 2001), magnetic tapes conforming to the LTO (Linear Tape-Open) standard (commonly called "LTO tapes") employ a timing-based servo system. In this timing-based servo system, the servo pattern is composed of multiple pairs of non-parallel magnetic stripes (also called "servo stripes") arranged continuously in the longitudinal direction of the magnetic tape. A servo system is a system that performs head tracking using a servo signal. In the present invention and this specification, "timing-based servo pattern" refers to a servo pattern that enables head tracking in a timing-based servo system. As described above, the reason why the servo pattern is composed of pairs of non-parallel magnetic stripes is to inform the servo signal reading element passing over the servo pattern of its position. Specifically, the pair of magnetic stripes described above are formed such that their spacing changes continuously along the width of the magnetic tape, and the servo signal reading element reads this spacing to determine the relative position between the servo pattern and the servo signal reading element. This relative position information enables the tracking of data tracks. For this purpose, multiple servo tracks are typically set up on the servo pattern along the width of the magnetic tape.

[0125] A servo band consists of a servo pattern that runs continuously along the longitudinal direction of the magnetic tape. Typically, multiple servo bands are provided on a magnetic tape. For example, in an LTO tape, there are five. The area between two adjacent servo bands is the data band. A data band consists of multiple data tracks, each corresponding to a servo track.

[0126] In one embodiment, as shown in Japanese Patent Publication No. 2004-318983, each servo band has embedded information indicating the servo band number (also called "servo band ID (identification)" or "UDIM (Unique DataBand Identification Method) information"). This servo band ID is recorded by shifting a specific pair of servo stripes within a servo band so that its position is displaced relative to the longitudinal direction of the magnetic tape. Specifically, the method of shifting a specific pair of servo stripes is changed for each servo band. As a result, the recorded servo band ID is unique for each servo band, so that a servo band can be uniquely identified by reading it with a servo signal reading element.

[0127] Furthermore, one method for uniquely identifying a servo band is the staggered method, as described in ECMA-319 (June 2001). In this staggered method, a group of non-parallel magnetic stripes (servo stripes) arranged continuously along the longitudinal direction of the magnetic tape are recorded in a manner that shifts each servo band along the longitudinal direction of the magnetic tape. Since the combination of this shift between adjacent servo bands is unique across the entire magnetic tape, it is possible to uniquely identify a servo band when reading the servo pattern using two servo signal reading elements.

[0128] Furthermore, each servo band typically has embedded information indicating its position along the longitudinal direction of the magnetic tape (also known as "LPOS (Longitudinal Position) information"), as shown in ECMA-319 (June 2001). This LPOS information, like the UDIM information, is recorded by shifting the positions of a pair of servo stripes along the longitudinal direction of the magnetic tape. However, unlike the UDIM information, the same signal is recorded for each servo band in this LPOS information.

[0129] It is also possible to embed information other than the UDIM and LPOS information described above into the servo bands. In this case, the embedded information may be different for each servo band, like the UDIM information, or it may be common to all servo bands, like the LPOS information. Furthermore, methods other than those described above can be used to embed information into the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of servo stripes.

[0130] A servo pattern forming head is called a servo light head. A servo light head typically has a pair of gaps corresponding to the pair of magnetic stripes mentioned above, for each servo band. Typically, a core and a coil are connected to each pair of gaps, and by supplying current pulses to the coils, the magnetic field generated in the core can create a leakage magnetic field in the pair of gaps. When forming a servo pattern, by inputting current pulses while running a magnetic tape over the servo light head, the magnetic patterns corresponding to the pair of gaps are transferred to the magnetic tape, thereby forming the servo pattern. The width of each gap can be appropriately set according to the density of the servo pattern to be formed. For example, the width of each gap can be set to 1 μm or less, 1 to 10 μm, 10 μm or more, etc.

[0131] Before forming a servo pattern on a magnetic tape, it is usually demagnetized (erased). This erasing process can be performed by applying a uniform magnetic field to the magnetic tape using a DC or AC magnet. There are two types of erasing: DC (Direct Current) erasing and AC (Alternating Current) erasing. AC erasing is performed by gradually reducing the strength of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, DC erasing is performed by applying a unidirectional magnetic field to the magnetic tape. There are two further methods of DC erasing. The first method is horizontal DC erasing, which applies a unidirectional magnetic field along the longitudinal direction of the magnetic tape. The second method is vertical DC erasing, which applies a unidirectional magnetic field along the thickness direction of the magnetic tape. The erasing process may be performed on the entire magnetic tape or on each servo band of the magnetic tape.

[0132] The direction of the magnetic field of the formed servo pattern is determined according to the direction of the erase. For example, when a magnetic tape is horizontally DC erased, the servo pattern is formed such that the direction of the magnetic field is opposite to the direction of the erase. This makes it possible to increase the output of the servo signal obtained by reading the servo pattern. As shown in Japanese Patent Application Publication No. 2012-53940, when a magnetic pattern using the above gap is transferred to a vertically DC erased magnetic tape, the servo signal obtained by reading the formed servo pattern is in the shape of a single-pole pulse. On the other hand, when a magnetic pattern using the above gap is transferred to a horizontally DC erased magnetic tape, the servo signal obtained by reading the formed servo pattern is in the shape of a double-pole pulse.

[0133] <Number of wrinkles> In one embodiment, the number of wrinkles measured after running the magnetic tape over a length of 900 m in a reel tester back and forth 300 times at a speed of 6 m / s can be 30 or less. Having a small number of wrinkles, 30 or less, can contribute to reducing the value of σDES. This point will be explained with reference to Figure 8.

[0134] Figure 8 is a schematic diagram illustrating the relationship between wrinkles and DES. During the 300 back-and-forth runs described above, strong localized stress is applied to the magnetic tape while it is wound on the reel, causing deformation in the width direction. If this deformation is not restored, wrinkles will form. In DES measurement, when the magnetic head passes over the location where wrinkles have formed, a momentary fluctuation in dPES occurs (see the right diagram in Figure 8), and it is presumed that this results in a larger value of σDES.

[0135] From the viewpoint of reducing the value of σDES, the number of wrinkles is preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less, 15 or less, and 10 or less, in that order. The number of wrinkles can be, for example, 0 or more or 1 or more. The fewer the number of wrinkles, the more preferable it is from the viewpoint of reducing the value of σDES. The number of wrinkles can be controlled by the Young's modulus in the width direction of the nonmagnetic support, which is one of the means previously exemplified as a means of controlling σDES.

[0136] The number of wrinkles mentioned above can be determined in detail by the following method.

[0137] (A) Sample preparation The magnetic tape to be measured is wound onto a reel with a hub diameter of 44 mm at a tension of 0.60 N (Newtons) and a speed of 20 m / s to prepare a sample.

[0138] (B) Reciprocating run The sample prepared in (A) above is stored in a thermoroom maintained at a temperature of 23°C and a relative humidity of 50% for at least 24 hours. After storage, the sample is attached to a reel tester that has been previously installed in the thermoroom. This reel tester has a magnetic head of an IBM TS1170 tape drive and is adjusted so that the relative inclination between the magnetic head and the magnetic tape is 90° ± 0.02°. In the reel tester, the sample is run back and forth 300 times over a 900m length area at a tension of 1.4N and a speed of 6m / sec.

[0139] (C) Measurement of wrinkle count After (B) above, the reel tester is run over the 900m length area with a tension of 0.4N and a speed of 1m / sec, and at the same time, the brightness profile in the tape width direction is measured using a Keyence XG-HL04M line scan camera set to a scan rate of 5kHz or higher. Edge detection processing described below is applied to the brightness profile measured at each time point. In the edge detection processing, first, the brightness profile is smoothed using a Gaussian filter to remove noise. Next, the brightness profile after smoothing is differentiated, and the positions of positive and negative peaks are identified from it. These positions are the edges. The average value (arithmetic mean) of the brightness in the interval between the upper and lower edge positions of the magnetic tape (i.e., between the position of the positive peak and the position of the negative peak) determined by this edge detection process is calculated. In the data array obtained by arranging the average brightness in this way in a time series, a wrinkle is considered to have occurred each time the average brightness at a given time crosses a 90% threshold with respect to the mode of the average brightness calculated for the entire data array, and the total number of wrinkled locations is taken as the number of wrinkles in the magnetic tape being measured.

[0140] <Stack Shift Frequency> In one embodiment, when the magnetic tape is run once through a 900 m length region in a reel tester at a speed of 6 m / s, the number of times an end position shift of 200 μm or more (stack shift) occurs in 0.2 seconds during this run (stack shift frequency) can be 40 times or less. A low stack shift frequency of 40 times or less can contribute to reducing the value of σDES. This point will be explained with reference to Figure 9.

[0141] Figure 9 is a schematic diagram illustrating the relationship between stack shift and DES. The above-mentioned end position fluctuation (stack shift) can be described as a phenomenon in which the winding position of the magnetic tape wound on the reel is reversed. When a magnetic tape experiencing this phenomenon is sequentially pulled out from the outside, the relative angle between the magnetic tape and the magnetic head (more specifically the module) changes instantaneously during the winding position shift (see the center and right diagrams in Figure 9), and it is presumed that as a result the value of σDES increases.

[0142] From the viewpoint of reducing the value of σDES, the stack shift frequency is preferably 40 times or less, and more preferably 35 times or less. The stack shift frequency can be, for example, 0 or more, 1 or more, 5 or more, 10 or more, 15 or more, 20 or more, or 25 or more. A lower stack shift frequency is preferable from the viewpoint of reducing the value of σDES. The stack shift frequency can be controlled by means of the surface smoothness of the backcoat layer and the rigidity of the hub of the reel of the magnetic tape cartridge, which are exemplified herein as means of controlling σDES.

[0143] The stack shift frequency can be determined in detail by the following method.

[0144] (A) Sample preparation The magnetic tape to be measured is wound onto a reel with a hub diameter of 44 mm at a tension of 0.60 N (Newtons) and a speed of 20 m / s to prepare a sample.

[0145] (B) Measurement of stack shift frequency The sample prepared in (A) above is stored in a thermoroom maintained at a temperature of 23°C and a relative humidity of 50% for 24 hours or more. After storage, the sample is attached to a reel tester that has been previously installed in the thermoroom. This reel tester has a magnetic head of an IBM TS1170 tape drive and is adjusted so that the relative inclination between the magnetic head and the magnetic tape is 90° ± 0.02°. In the reel tester, the sample is run once over a 900m length area with a tension of 0.60N and a speed of 6m / sec. During this run, the height of the upper end of the ejected magnetic tape is measured at a scan rate of 5kHz or higher using a Keyence XG-HL04M line scan camera installed in the tape ejection section of the reel tester's feed reel. If a height change of 200μm or more occurs in 0.2 seconds, it is considered a stack shift, and the number of stack shifts is counted. The number of stack shifts determined in this way is defined as the stack shift frequency of the magnetic tape being measured.

[0146] Different samples shall be used for measuring σDES, wrinkle count, and stack shift frequency.

[0147] <Vertical Angle Ratio> In one embodiment, the vertical angle ratio of the magnetic tape can be, for example, 0.55 or more, and from the viewpoint of improving electromagnetic conversion characteristics, it is preferable to be 0.60 or more, and more preferable to be 0.65 or more. The upper limit of the angle ratio is, in principle, 1.00 or less. The vertical angle ratio of the magnetic tape can be 1.00 or less, and can be 0.95 or less, 0.90 or less, 0.85 or less, or 0.80 or less. A large value for the vertical angle ratio of the magnetic tape is preferable from the viewpoint of improving electromagnetic conversion characteristics. The vertical angle ratio of the magnetic tape can be controlled by known methods such as performing a vertical orientation process.

[0148] In the present invention and this specification, "vertical angular ratio" refers to the angular ratio measured in the vertical direction of the magnetic tape. "Vertical direction" as used in relation to the angular ratio refers to the direction perpendicular to the magnetic layer surface, and can also be referred to as the thickness direction. In the present invention and this specification, the vertical angular ratio is determined by the following method: A sample piece of a size suitable for introduction into a vibrating sample magnetometer is cut from the magnetic tape to be measured. Using a vibrating sample magnetometer, a magnetic field is applied to this sample piece in the direction perpendicular to the sample piece (perpendicular to the magnetic layer surface) at a maximum applied magnetic field of 3979 kA / m, a measurement temperature of 296 K, and a magnetic field sweep speed of 8.3 kA / m / sec, and the magnetization intensity of the sample piece with respect to the applied magnetic field is measured. The measured magnetization intensity is obtained as a value after demagnetization correction and after subtracting the magnetization of the sample probe of the vibrating sample magnetometer as background noise. When the magnetization intensity at the maximum applied magnetic field is Ms and the magnetization intensity at zero applied magnetic field is Mr, the squareness ratio SQ (Squareness Ratio) is 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 achieved, thereby setting the sample piece temperature to the measurement temperature.

[0149] [Magnetic Tape Cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the magnetic tape described above.

[0150] Details of the magnetic tape included in the above magnetic tape cartridge are as described above.

[0151] In a magnetic tape cartridge, the magnetic tape is generally housed inside the cartridge body, wound onto a reel. The reel is rotatably mounted inside the cartridge body. Two types of magnetic tape cartridges are widely used: single-reel cartridges, which have one reel inside the cartridge body, and double-reel cartridges, which have two reels inside the cartridge body. When a single-reel magnetic tape cartridge is mounted in a magnetic tape device for recording and / or playing back data on magnetic tape, the magnetic tape is pulled out of the cartridge and wound onto the reel on the magnetic tape device. A magnetic head is positioned in the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and wound between the reel on the magnetic tape cartridge side (supply reel) and the reel on the magnetic tape device side (take-up reel). During this time, the magnetic head and the magnetic layer surface of the magnetic tape come into contact and slide against each other, enabling data recording and / or playback. In contrast, a dual-reel magnetic tape cartridge has both a supply reel and a take-up reel located inside the magnetic tape cartridge.

[0152] In a magnetic tape cartridge, the reel around which the magnetic tape is wound consists of at least a hub, and typically flanges are provided at both ends of the hub.

[0153] The hub of a reel is a cylindrical member that constitutes the central axis around which the magnetic tape is wound. The hub of the reel can be a single-layer cylindrical member, or it can be a multi-layer cylindrical member with two or more layers. From the viewpoint of manufacturing cost and ease of manufacture, it is preferable that the hub of the reel be a single-layer cylindrical member.

[0154] In a magnetic tape cartridge, high rigidity of the hub of the reel around which the magnetic tape is wound can contribute to reducing the value of σDES. From this perspective, in one embodiment, the flexural modulus of the material constituting at least the outer surface layer of the hub is preferably 50 GPa (gigapascals) or more, and more preferably 60 GPa or more. The above flexural modulus can be, for example, 100 GPa or less or 90 GPa or less. A high flexural modulus is considered desirable in reducing σDES.

[0155] The above flexural modulus is the flexural modulus of the material constituting the cylindrical member when the hub of the reel is a single-layer cylindrical member. On the other hand, when the hub is a multilayer cylindrical member with two or more layers, the above flexural modulus is the flexural modulus of the material constituting at least the outer surface layer of the hub. In the present invention and this specification, "flexural modulus" is a value obtained in accordance with JIS (Japanese Industrial Standards) K 7171:2016. JIS K 7171:2016 is a Japanese Industrial Standard created without changing the technical content, based on ISO (International Organization for Standardization) 178 and Amendment 1:2013, which were published as the 5th edition in 2010. The test specimens used to measure the flexural modulus shall be prepared in accordance with item 6, "Test Specimens," of JIS K 7171:2016.

[0156] Materials that make up the hub of a magnetic tape cartridge reel include resin and metal. Examples of metals include aluminum. Examples of resins include fiber-reinforced resin. Examples of fiber-reinforced resins include glass fiber reinforced resin and carbon fiber reinforced resin.

[0157] The thickness of the hub described above is preferably in the range of 2.0 to 3.0 mm, from the viewpoint of achieving both hub strength and dimensional accuracy during molding. The thickness of the hub refers to the total thickness of the multilayer structure in the case of a hub with two or more layers. The outer diameter of the hub is usually determined by the specifications of the magnetic tape device and can be in the range of, for example, 20 to 60 mm.

[0158] The above-described magnetic tape cartridge may, in one embodiment, include a cartridge memory. The cartridge memory may be, for example, a non-volatile memory, and preferably, head tilt angle adjustment information is already recorded in it or will be recorded in it. 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 include the values ​​of the servoband interval at each position in the longitudinal direction of the magnetic tape during data recording. For example, when playing back data recorded on the magnetic tape, the value of the servoband interval is measured during playback, and the control device of the magnetic tape device can change the head tilt angle so that the absolute value of the difference between this value and the servoband interval recorded in the cartridge memory at the same longitudinal position during recording approaches zero. The head tilt angle may be, for example, the angle θ described above. When recording and / or playing back data with the head tilted, the angle θ described above may be greater than 0° and may be 45° or less, 40° or less, or 35° or less.

[0159] The magnetic tape and magnetic tape cartridge described above can be suitably used in a magnetic tape device (in other words, a magnetic recording and playback system) that records and / or plays back data by changing the head tilt angle while the magnetic tape is running. In such a usage configuration, since the period during data recording and / or playback includes a period in which the head is tilted, a magnetic tape with high running stability when recording and / or playing back data with the head tilted is preferred. However, the magnetic tape and magnetic tape cartridge described above are not limited to those used in such a magnetic tape device. For example, there may be a usage configuration in which the head tilt angle during one recording or playback is changed from the head tilt angle during subsequent recordings or playbacks, but the head tilt angle is fixed and not changed during each recording or playback. In such a usage configuration as well, since the period during data recording and / or playback includes a period in which the head is tilted, a magnetic tape with high running stability when recording and / or playing back data with the head tilted is preferred.

[0160] [Magnetic Tape Device] One aspect of the present invention relates to a magnetic tape device including the magnetic tape described above. In the magnetic tape device, recording data onto the magnetic tape and / or reproducing data recorded on the magnetic tape can be performed, for example, by bringing the magnetic layer surface of the magnetic tape into contact with a magnetic head and sliding it. The magnetic tape device may detachably include a magnetic tape cartridge according to one aspect of the present invention.

[0161] The above-described magnetic tape cartridge can be mounted in a magnetic tape device equipped with a magnetic head and used for recording and / or reproducing data. In the present invention and this specification, “magnetic tape device” means a device capable of recording data onto a magnetic tape and reproducing data recorded on a magnetic tape. Such a device is generally called a drive.

[0162] <Magnetic Head> The above magnetic tape device may include a magnetic head. The configuration of the magnetic head and the angle θ, which is the head tilt angle, are as previously described with reference to Figures 1 to 3. In one embodiment, the magnetic head included in the above magnetic tape device may be an LTO8 head or an LTO9 head; in another embodiment, it may be an LTO head of another generation; and in yet another embodiment, it may be a magnetic head other than an LTO head. If the magnetic head includes a regeneration element, a magnetoresistive (MR) element that can read information recorded on the magnetic tape with high sensitivity is preferred as the regeneration element. Various known MR elements (for example, GMR (Giant Magnetoresistive) elements, TMR (Tunnel Magnetoresistive) elements, etc.) can be used as the MR element.

[0163] By using a regeneration element with a narrow width as the regeneration element, data recorded at high density can be regenerated with high sensitivity. From this viewpoint, the regeneration element width is preferably 0.8 μm or less. The regeneration element width can be, for example, 0.3 μm or more. However, a value lower than this is also preferable from the above viewpoint. Here, "regeneration element width" refers to the physical dimension of the regeneration element width. Such physical dimensions can be measured using an optical microscope, scanning electron microscope, etc.

[0164] In the above-described magnetic tape device, the head tilt angle can be changed while the magnetic tape is running within the magnetic tape device. The head tilt angle is, for example, the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape. The angle θ is as previously explained. For example, by providing an angle adjustment unit in the recording / playback head unit of the magnetic head to adjust the angle of the magnetic head module, the angle θ can be variably adjusted while the magnetic tape is running. Such an angle adjustment unit may include, for example, a rotation mechanism that rotates the module. Known technologies can be applied to the angle adjustment unit.

[0165] Regarding the head tilt angle during magnetic tape travel, if the magnetic head contains multiple modules, the angle θ can be defined for a randomly selected module, as explained with reference to Figures 1 to 3. The angle θ at the start of magnetic tape travel is θ. ｉｎｉｔｉａｌ It can be set to 0° or greater than or equal to 0°. ｉｎｉｔｉａｌ The larger the angle θ, the greater the change in the effective distance between servo signal reading elements in response to the change in angle θ. This is preferable from the standpoint of adjustment capability to adjust the effective distance between servo signal reading elements in response to changes in the width direction of the magnetic tape. ｉｎｉｔｉａｌ The angle is preferably 1° or more, more preferably 5° or more, and even more preferably 10° or more. On the other hand, regarding the angle between the magnetic layer surface and the contact surface of the magnetic head when the magnetic tape is running and contacting the magnetic head (generally called the "lap angle"), keeping the deviation in the tape width direction small is effective in improving the uniformity of friction in the tape width direction caused by contact between the magnetic head and the magnetic tape during magnetic tape running. Furthermore, improving the uniformity of the friction in the tape width direction is desirable from the viewpoint of the magnetic head's position tracking ability and running stability. From the viewpoint of reducing the deviation of the lap angle in the tape width direction, θ ｉｎｉｔｉａｌ The angle is preferably 45° or less, more preferably 40° or less, and even more preferably 35° or less.

[0166] Regarding the change in angle θ during magnetic tape movement, for recording data onto magnetic tape and / or for playing back data recorded on magnetic tape, the angle θ of the magnetic head remains constant from the initial angle θ while the magnetic tape is moving in the magnetic tape drive. ｉｎｉｔｉａｌ When it changes from, the maximum change in angle θ during magnetic tape travel, Δθ, is calculated by the following formula: ｍａｘ and Δθ ｍｉｎ Among these, it is the larger value. The maximum value of the angle θ during magnetic tape travel is θ ｍａｘ The minimum value is θ. ｍｉｎ Therefore, "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

[0167] In one embodiment, Δθ can be more than 0.000°, and from the viewpoint of the adjustment capability of adjusting the effective distance between servo signal reading elements in response to dimensional change in the width direction of the magnetic tape, Δθ is preferably 0.001° or more, more preferably 0.010° or more. In addition, from the viewpoint of facilitating synchronization of recorded data and / or reproduced data among a plurality of magnetic head elements during data recording and / or reproduction, Δθ is preferably 1.000° or less, more preferably 0.900° or less, still more preferably 0.800° or less, even more preferably 0.700° or less, and still even more preferably 0.600° or less.

[0168] In the examples shown in FIG. 2 and FIG. 3, the axis of the element array is inclined toward the running direction of the magnetic tape. However, the present invention is not limited to such examples. The present invention also encompasses embodiments in which, in the magnetic tape device described above, the axis of the element array is inclined toward a direction opposite to the running direction of the magnetic tape.

[0169] θ, which is the head tilt angle at the start of magnetic tape running ｉｎｉｔｉａｌThis can be set by the control device of the magnetic tape device, etc. Regarding the head tilt angle during magnetic tape travel, Figure 10 is an explanatory diagram of the method for measuring the angle θ during magnetic tape travel. The angle θ during magnetic tape travel can be determined, for example, by the following method. When determining the angle θ during magnetic tape travel by the following method, the angle θ shall be varied within the range of 0 to 90° during magnetic tape travel. That is, if the axis of the element array is tilted toward the magnetic tape travel direction at the start of magnetic tape travel, the element array shall not be tilted during magnetic tape travel so that the axis of the element array is tilted toward the direction opposite to the magnetic tape travel direction at the start of magnetic tape travel, and if the axis of the element array is tilted toward the direction opposite to the magnetic tape travel direction at the start of magnetic tape travel, the element array shall not be tilted during magnetic tape travel so that the axis of the element array is tilted toward the magnetic tape travel direction at the start of magnetic tape travel. Measure the phase difference (i.e., time difference) ΔT of the playback signals of a pair of servo signal reading elements 1 and 2. ΔT can be measured by a measurement unit provided in the magnetic tape device. The configuration of such a measurement unit is well known. The distance L between the center of servo signal reading element 1 and the center of servo signal reading element 2 can be measured by an optical microscope or the like. When the magnetic tape is traveling at speed v, the distance between the centers of the two servo signal reading elements in the direction of magnetic tape travel is Lsinθ, and the relationship Lsinθ = v × ΔT holds. Therefore, the angle θ during magnetic tape travel can be calculated by the formula "θ = arcsin(vΔT / L)". Note that the right-hand figure of Figure 10 shows an example where the axis of the element array is tilted toward the direction of magnetic tape travel. In this example, the phase difference (i.e., time difference) ΔT between the phase of the playback signal of servo signal reading element 2 and the phase of the playback signal of servo signal reading element 1 is measured. If the axis of the element array is tilted in the direction opposite to the direction in which the magnetic tape travels, θ can be determined by the above method, except that ΔT is measured as the phase difference (i.e., time difference) between the phase of the regenerated signal of servo signal reading element 1 and the phase of the regenerated signal of servo signal reading element 2.Furthermore, the measurement pitch of the angle θ, that is, the measurement interval of the angle θ in the longitudinal direction of the tape, can be selected to be appropriate according to the frequency of deformation in the tape width direction in the longitudinal direction of the tape. For example, the measurement pitch can be set to, for example, 250 μm.

[0170] <Configuration of the Magnetic Tape Device> The magnetic tape device 10 shown in Figure 11 controls the recording and playback head unit 12 by command from the control device 11 to record and play back data on the magnetic tape MT. The magnetic tape device 10 has a configuration that allows detection and adjustment of tension applied in the longitudinal direction of the magnetic tape from the spindle motors 17A, 17B and their drive devices 18A, 18B that control the rotation of the magnetic tape cartridge reel and the take-up reel. The magnetic tape device 10 has a configuration that allows loading of a magnetic tape cartridge 13. The magnetic tape device 10 has a cartridge memory read / write device 14 that can read from and write to the cartridge memory 131 in the magnetic tape cartridge 13. From the magnetic tape cartridge 13 mounted in the magnetic tape device 10, the end of the magnetic tape MT or the leader pin is pulled out by an automatic loading mechanism or manually, and the magnetic layer surface of the magnetic tape MT passes over the recording / playback head of the recording / playback head unit 12 through guide rollers 15A and 15B so that it is in contact with the surface of the recording / playback head, and the magnetic tape MT is wound onto the take-up reel 16. The rotation and torque of the spindle motors 17A and 17B are controlled by signals from the control device 11, and the magnetic tape MT runs at an arbitrary speed and tension. A servo pattern pre-formed on the magnetic tape can be used to control the tape speed and the head tilt angle. A tension detection mechanism may be provided between the magnetic tape cartridge 13 and the take-up reel 16 for tension detection. In addition to control by 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 read and write information 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.

[0171] The control device 11 includes, for example, a control unit, a storage unit, a communication unit, and the like.

[0172] The recording / playback head unit 12 consists of, for example, a recording / playback head, a servo tracking actuator for adjusting the position of the recording / playback head in the track width direction, a recording / playback amplifier 19, and a connector cable for connecting to the control device 11. The recording / playback head consists of, for example, a recording element for recording data on magnetic tape, a playback element for reproducing data on magnetic tape, and a servo signal reading element for reading servo signals recorded on magnetic tape. Within a single magnetic head, for example, one or more recording elements, playback elements, and servo signal reading elements are mounted. Alternatively, each element may be separately contained in multiple magnetic heads corresponding to the direction in which the magnetic tape travels.

[0173] The recording / playback head unit 12 is configured to record data onto the magnetic tape MT in response to commands from the control device 11. It is also configured to play back data recorded on the magnetic tape MT in response to commands from the control device 11.

[0174] The control device 11 has a mechanism to determine the running position of the magnetic tape MT from the servo signals read from the servo bands when the magnetic tape MT is running, and to control the servo tracking actuator so that the recording element and / or playback element are positioned at the target running position (track position). This track position control is performed, for example, by feedback control. The control device 11 has a mechanism to determine the servo band spacing from the servo signals read from two adjacent servo bands when the magnetic tape MT is running. The control device 11 can store the determined servo band spacing information in its internal storage unit, cartridge memory 131, or external connected equipment. Furthermore, the control device 11 can change the head tilt angle according to the dimensional information in the width direction of the running magnetic tape. This makes it possible to make the effective distance between servo signal reading elements close to or match the servo band spacing. The above dimensional information can be obtained using a servo pattern pre-formed on the magnetic tape. For example, in this way, while the magnetic tape is running within the magnetic tape device, the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape can be changed according to the width direction dimensional information of the magnetic tape acquired during the running process. The head tilt angle can be adjusted, for example, by feedback control. Alternatively, the head tilt angle can also be adjusted, for example, by the method described in Japanese Patent Publication No. 2016-524774 (Patent Document 1) or US2019 / 0164573A1 (Patent Document 2).

[0175] The present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. Unless otherwise specified, the terms "parts" and "%" below refer to "parts by mass" and "% by mass," respectively. The processes and evaluations described below were carried out in an environment with an ambient temperature of 23°C ± 1°C unless otherwise specified. Furthermore, "eq" below refers to the equivalent, a unit that cannot be converted to the SI unit system.

[0176] [Non-magnetic Support] In the table shown below, "PET" in the column for the type of non-magnetic support indicates a polyethylene terephthalate support, "PEN" indicates a polyethylene naphthalate support, and "PA" indicates an aromatic polyamide support. In the table shown below, the Young's modulus in the width direction of the non-magnetic support is a value obtained by the method described above.

[0177] [Ferromagnetic Powder] In the table shown below, "BaFe" in the column for ferromagnetic powder indicates hexagonal barium ferrite powder having an average particle size (average plate diameter) of 21 nm.

[0178] In the table shown below, "SrFe1" in the column for ferromagnetic powder indicates hexagonal strontium ferrite powder produced as follows.

[0179] SrCO ３ 1707 g of ３ BO ３ 687 g of, Fe ２ O ３ 1120 g of, Al(OH) ３ 45 g of, BaCO ３ 24 g of, CaCO ３ 13 g of, and Nd ２ O ３235 g was weighed and mixed in a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390°C. While stirring the molten material, the outlet at the bottom of the platinum crucible was heated, and the molten material was dispensed in a rod shape at a rate of approximately 6 g / second. The dispensed material was rolled and rapidly cooled with water-cooled twin rollers to produce an amorphous material. 280 g of the prepared amorphous material was placed in an electric furnace and heated to 635°C (crystallization temperature) at a heating rate of 3.5°C / min. It was held at this temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystalline material obtained above, containing the hexagonal strontium ferrite particles, was coarsely ground in a mortar. 1000 g of zirconia beads with a particle size of 1 mm and 800 ml of a 1% aqueous acetic acid solution were added to a glass bottle containing this material, and the mixture was dispersed in a paint shaker for 3 hours. After that, the resulting dispersion was separated from the beads and placed in a stainless steel beaker. The dispersion was allowed to stand at a liquid temperature of 100°C for 3 hours to dissolve the glass components. Then, the material was precipitated using a centrifuge, washed by repeated decantation, and dried in a heating furnace at a temperature of 110°C for 6 hours to obtain hexagonal strontium ferrite powder. The average particle size of the hexagonal strontium ferrite powder obtained was 18 nm, and the activation volume was 902 nm. ３ The anisotropy constant Ku is 2.2 × 10⁻⁶. ５ J / m ３ , mass magnetization σs is 49A・m ２The result was / kg. 12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and elemental analysis of the filtrate obtained by partially dissolving this sample powder under the previously exemplified dissolution conditions was performed using an ICP analyzer to determine the surface layer content of neodymium atoms. Separately, 12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and elemental analysis of the filtrate obtained by completely dissolving this sample powder under the previously exemplified dissolution conditions was performed using an ICP analyzer to determine the bulk content of neodymium atoms. The neodymium atom content (bulk content) relative to 100 atomic percent of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic percent. The surface layer content of neodymium atoms was 8.0 atomic percent. The ratio of surface layer content to bulk content, "surface layer content / bulk content", was 2.8, confirming that neodymium atoms are unevenly distributed on the surface of the particles. The hexagonal ferrite crystal structure of the powder obtained above was confirmed by scanning CuKα rays 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 showed a magnetoplanbite-type (M-type) hexagonal ferrite crystal structure. Furthermore, the crystal phase detected by X-ray diffraction analysis was a single phase of the magnetoplanbite type. PANical X'Pert Pro diffractometer, PIXcel detector. Soller slits for incident and diffracted beams: 0.017 radians. Fixed angle of dispersion slit: 1 / 4 degree (°). Mask: 10 mm. Anti-scattering slit: 1 / 4 degree. Measurement mode: Continuous. Measurement time per step: 3 seconds. Measurement speed: 0.017 degrees per second. Measurement step: 0.05 degrees.

[0180] The activation volume and anisotropy constant Ku of the hexagonal strontium ferrite powder described above were obtained using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) by the method described above. The mass magnetization σs was measured using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) at a magnetic field strength of 15 kOe.

[0181] [Comparative Example 1] (1) Formulation of composition for forming a magnetic layer (magnetic liquid) Ferromagnetic powder (see table below): 100.0 parts SO ３Na group-containing polyurethane resin: 14.0 parts; weight-average molecular weight: 70,000, SO ３ Na group: 0.4 meq / g Cyclohexanone: 150 parts Methyl ethyl ketone: 150 parts (Abrasive solution A) Alumina abrasive (average particle size: 100 nm): 3.0 parts Sulfonic acid group-containing polyurethane resin: 0.3 parts Weight-average molecular weight: 70,000, SO ３ Na group: 0.3 meq / g Cyclohexanone: 26.7 parts (Abrasive solution B) Diamond abrasive (average particle size: 100 nm): 1.0 part Sulfonic acid group-containing polyurethane resin: 0.1 part Weight-average molecular weight: 70,000, SO ３ Na group: 0.3 meq / g Cyclohexanone: 26.7 parts (Silica sol) Colloidal silica (average particle size: 100 nm): 0.2 parts Methyl ethyl ketone: 1.4 parts (Other components) Stearic acid: 2.0 parts Butyl stearate: 10.0 parts Polyisocyanate (Coronate, manufactured by Nippon Polyurethane Co., Ltd.): 2.5 parts Cyclohexanone: 200.0 parts Methyl ethyl ketone: 200.0 parts

[0182] (2) Formulation of composition for forming a non-magnetic layer Non-magnetic inorganic powder (α-iron oxide): 100.0 parts Average particle size (average long axis length): 10 nm Average needle-like ratio: 1.9 BET (Brunauer-Emmett-Teller) specific surface area: 75 m² ２ Carbon black: 25.0 parts / g Average particle size: 20 nm SO ３ Na group-containing polyurethane resin: 18.0 parts; weight-average molecular weight: 70,000, SO ３ Na group: 0.2 meq / g Stearic acid: 1.0 part Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

[0183] (3) Formulation of composition for backcoat layer formation Carbon black: 100.0 parts Cabot BP-800, average particle size: 17 nm SO ３ Na group-containing polyurethane resin (SO ３ Na group: 70eq / ton): 20.0 parts OSO ３ K-group-containing polyvinyl chloride resin (OSO ３K group: 70 eq / ton): 30.0 parts Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 600): 2.7 parts Stearic acid: 5.3 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Butyl stearate: 2.0 parts Stearamide: 0.1 parts

[0184] (4) Preparation of magnetic tape and magnetic tape cartridge The above components of the magnetic solution were dispersed for 24 hours using a batch-type vertical sand mill to prepare the magnetic solution. Zirconia beads with a bead diameter of 0.5 mm were used as dispersion beads. For the polishing solution, the above components of polishing solution A and polishing solution B were dispersed for 24 hours using a batch-type ultrasonic device (20 kHz, 300 W) to obtain polishing solution A and polishing solution B. The magnetic solution, polishing solution A and polishing solution B were mixed with the above silica sol and other components, and then dispersed for 30 minutes using a batch-type ultrasonic device (20 kHz, 300 W). After that, the mixture was filtered using a filter with a pore size of 0.5 μm to prepare the composition for forming the magnetic layer. For the composition for forming the non-magnetic layer, the above components were dispersed for 24 hours using a batch-type vertical sand mill. Zirconia beads with a bead diameter of 0.1 mm were used as dispersion beads. The obtained dispersion was filtered using a filter with a pore size of 0.5 μm to prepare a composition for forming a non-magnetic layer. For the composition for forming a back coat layer, the above components were kneaded in a continuous kneader and then dispersed using a sand mill. 40.0 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) and 1000.0 parts of methyl ethyl ketone were added to the obtained dispersion, and then filtered using a filter with a pore size of 1 μm to prepare a composition for forming a back coat layer. A non-magnetic layer was formed on the surface of a non-magnetic support with a thickness of 4.1 μm (see the table below for type and widthwise Young's modulus) by coating and drying the non-magnetic layer composition prepared above so that the thickness after drying was 0.7 μm. Next, a magnetic layer was formed on the non-magnetic layer by coating it with the magnetic layer composition prepared above so that the thickness after drying was 0.1 μm. Subsequently, while the coated layer of the magnetic layer-forming composition was still wet, a magnetic field of 0.5 T was applied perpendicularly to the surface of the coated layer to perform a vertical orientation treatment, after which it was dried to form a magnetic layer. Then, the back coat layer was formed by applying and drying the back coat layer-forming composition prepared above to the non-magnetic layer of the support and the surface opposite to the surface where the magnetic layer was formed, so that the thickness after drying was 0.3 μm.Subsequently, a surface smoothing treatment (calendering treatment) was performed using a calendering roll composed solely of metal rolls at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a calendering temperature of 90°C (surface temperature of the calendering roll). In this way, a long magnetic tape raw material was obtained. After heat treatment for 36 hours in an ambient temperature of 70°C, the long magnetic tape raw material was slit into 1 / 2-inch widths to obtain magnetic tape. By recording servo signals on the magnetic layer of the obtained magnetic tape using a commercially available servo writer, a magnetic tape having a servo pattern (timing-based servo pattern) arranged according to the LTO (Linear Tape-Open) Ultrium format was obtained. By recording servo signals on the magnetic layer of the obtained magnetic tape using a commercially available servo writer, a magnetic tape was obtained having data bands, servo bands, and guide bands arranged in accordance with the LTO (Linear Tape-Open) Ultrium format, and having a servo pattern (timing-based servo pattern) on the servo band in an arrangement and shape in accordance with the LTO Ultrium format. The servo pattern thus formed is a servo pattern that conforms to the descriptions in JIS (Japanese Industrial Standards) X6175:2006 and Standard ECMA-319 (June 2001). The magnetic tape (length 960 m) after recording the servo signals was wound onto a heat treatment core, and heat treatment was performed while the tape was wound on this core. For the heat treatment core, a solid resin core member (outer diameter: 50 mm) with a flexural modulus of 0.8 GPa was used, and the tension during winding was 0.8 N. The heat treatment temperature was 70°C, and the heat treatment time was 10 hours. The absolute humidity by weight of the atmosphere during heat treatment was 10 g / kg Dry air.After the heat treatment described above, once the magnetic tape and the heat treatment core had cooled sufficiently, the magnetic tape was removed from the heat treatment core and wound onto a temporary winding core. Then, the final product length (950 m) of magnetic tape was wound from the temporary winding core onto a magnetic tape cartridge reel. The remaining 10 m was cut off, and a leader tape conforming to item 9 of Section 3 of Standard ECMA (European Computer Manufacturers Association)-319 (June 2001) was joined to the cut end using commercially available splicing tape. A solid core member made of the same material and having the same outer diameter as the heat treatment core was used as the temporary winding core, and the tension during winding was set to 0.6 N. A single-reel type magnetic tape cartridge was used as the magnetic tape cartridge to house the magnetic tape described above. The reel hub of this magnetic tape cartridge is a single-layer reel hub (thickness: 2.5 mm, outer diameter: 44 mm) injection-molded from glass fiber reinforced polycarbonate. The glass fiber content of this glass fiber reinforced polycarbonate (referred to as "fiber-reinforced polycarbonate" in the table below) is 30% by mass. A portion of the glass fiber reinforced polycarbonate for injection molding was taken, and according to item 6.3.1 (Preparation from molding material) of JIS K 7171:2016, the recommended test specimens described in item 6.1.2 of the same JIS were prepared, and the flexural modulus (arithmetic mean of five test specimens) was determined according to the same JIS. In the examples and comparative examples described below, the flexural modulus of the reel hub material was also determined by the above method. The flexural modulus of the winding core for heat treatment described above was also determined in the same way. The magnetic tape was wound onto the reel hub of the magnetic tape cartridge while applying a tension of 1.0 N or less in the longitudinal direction of the tape, and the magnetic tape was then housed in the magnetic tape cartridge. In this way, a single-reel type magnetic tape cartridge of Comparative Example 1, with a magnetic tape length of 950 m wound on a reel, was produced.

[0185] 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 backcoat layer of magnetic tape can be confirmed by the following method: A sample is cut from the magnetic tape, and X-ray photoelectron spectroscopy analysis is performed on the backcoat layer surface (measurement area: 300 μm × 700 μm) using an ESCA instrument. For details, wide-scan measurement is performed using an ESCA instrument under the measurement conditions described below. In the measurement results, peaks are observed at the bond energy positions of the ester anion and the ammonium cation. Equipment: Shimadzu AXIS-ULTRA Excitation X-ray source: Monochromatic Al-Kα rays Scan range: 0-1200 eV Pass energy: 160 eV Energy resolution: 1 eV / step Acquisition time: 100 ms / step Number of integrations: 5 In addition, a 3 cm long sample piece was cut from the magnetic tape, and ATR-FT-IR (Attenuated total reflection-fourier transform-infrared spectrum) measurement (reflection method) was performed on the surface of the backcoat layer, and in the measurement results, COO － The wavenumber corresponding to absorption (1540 cm) －１ or 1430cm －１ ), and the wavenumber corresponding to the absorption of ammonium cations (2400 cm²). －１ Absorption is confirmed in ).

[0186] [Examples 1-8, Comparative Examples 2-12] Magnetic tape cartridges were manufactured using the method described for Comparative Example 1, except that the items shown in the table below were changed as shown in the table. For the examples and comparative examples where "aluminum" is listed in the column for the type of reel hub material in the table below, a single-layer aluminum reel hub (thickness: 2.5 mm, outer diameter: 44 mm) was used. For the examples and comparative examples where something other than "0 / 100" is listed in the column for "mixing ratio of non-magnetic powder (α-iron oxide / carbon black)" of the back coat layer forming composition in the table below, a portion of the carbon black in the back coat layer forming composition in Comparative Example 1 was replaced with α-iron oxide powder (average particle size: 0.15 μm, average needle-like ratio: 7, BET specific surface area: 52 m²) so that the mixing ratio becomes the value shown in the table. 2 Changed to / g).

[0187] For each of Examples 1 to 8 and Comparative Examples 1 to 12, five magnetic tape cartridges were prepared using the method described above. Two samples were cut from one of these magnetic tape cartridges and used for evaluations (4) and (5) below, while the remaining four magnetic tape cartridges were used for evaluations (1) to (3) and (6) below.

[0188] [Evaluation Method] (1) σDES σDES was calculated using the method described above.

[0189] (2) Number of wrinkles The number of wrinkles was determined using the method described above.

[0190] (3) Stack shift frequency The stack shift frequency was determined using the method described above.

[0191] (4) Backcoat layer surface roughness Ra The surface roughness Ra of the backcoat layer was determined by measuring a 40 μm × 40 μm area on the surface of the backcoat layer of the magnetic tape using an AFM (Veeco Nanoscope 4) in tapping mode. A BRUKER RTESP-300 probe was used, with a scan speed (probe movement speed) of 40 μm / second and a resolution of 512 pixels × 512 pixels.

[0192] (5) Tape Thickness The magnetic tape cartridge was left in an environment with a temperature of 20-25°C and a relative humidity of 40-60% for more than 5 days to allow it to acclimate to the environment. Subsequently, under the same environment, one tape sample (5 cm in length) was cut from three different locations (randomly selected) along the longitudinal direction of the magnetic tape removed from the magnetic tape cartridge. Thus, three tape samples were cut. At a randomly selected position on each tape sample, one randomly selected end of the tape sample in the width direction was set as the reference position (0 mm), and the tape thickness was measured at measurement points every 1 mm toward the other end in the width direction. Therefore, the tape thickness was measured at a total of 12 measurement points: 1 mm from the reference position, 2 mm from the reference position, 3 mm from the reference position, 4 mm from the reference position, 5 mm from the reference position, 6 mm from the reference position, 7 mm from the reference position, 8 mm from the reference position, 9 mm from the reference position, 10 mm from the reference position, 11 mm from the reference position, and 12 mm from the reference position. The arithmetic mean of the measurements obtained by performing the above procedure for all three tape samples cut out above was taken as the tape thickness of the magnetic tape being measured. The tape thickness was measured using a digital thickness meter consisting of a MARP Millimar 1240 compact amplifier and a Millimar 1301 inductive probe. The tape thickness of each magnetic tape was 5.2 μm.

[0193] (6) Degradation of signal quality due to high-speed operation The recording and playback performance (degradation of signal quality) during high-speed operation was evaluated by the following method. As a reel tester, a reel tester equipped with the magnetic head of an IBM TS1170 tape drive was used, and the relative tilt between the magnetic head and the magnetic tape was adjusted to 90° ± 0.02°. Recording and playback were performed using the reel tester under the following first and second running conditions. Under the first running condition, the magnetic tape was first run with a tension of 0.60 N and a speed of 6 m / s while servo tracking over a 900 m area, and at the same time, AC erasure was performed at a single frequency equivalent to 2000 kbpi or higher using the channel closest to the servo signal reading element. Next, the position of the magnetic head was shifted 400 nm downwards in the tape width direction, and recording was performed at a single frequency equivalent to 600 kbpi under the same conditions as above. Finally, the position of the head was shifted another 400 nm downwards in the tape width direction, and AC erasure was performed under the same conditions as above. In this way, a data track was formed on the magnetic tape. The head was adjusted so that the regeneration element of the same channel as above was positioned in the center of this data track, and the regenerated signal waveform was measured under the same running conditions as above. The regenerated signal waveform was measured using a Teledyne LeCroy MDA810A oscilloscope set to voltage range: ±200mV, sampling rate: 250MHz, sampling rate: 100MS, and coupling: 50ΩDC. Next, the spectrum of the measured waveform was calculated using the "DSPPeriodogram" command of WaveMetrix data analysis software Igor 9.0.1, and the integrated output of the carrier signal band and the integrated noise of the entire spectrum were obtained from the obtained spectrum. The signal quality SNR (unit: dB) was set to 10 * log １０The result was obtained by ([integrated output] ÷ [integrated noise]). The average value (arithmetic mean) of the SNR calculated over the entire length of the tape was determined in this way. The SNR thus obtained was defined as the "average SNR under the first running condition". Under the second running condition, the magnetic tape was run at a speed of 7 m / s, and the other conditions were set to the above conditions, and the average value (arithmetic mean) of the SNR was determined. The SNR thus obtained was defined as the "average SNR under the second running condition". The difference between the average SNR values ​​measured under the first and second running conditions (average SNR under the second running condition - average SNR value under the first running condition) was calculated. If the decrease in the average SNR value under the second running condition compared to the average SNR value under the first running condition is -0.4 dB or more, it can be determined that the magnetic tape exhibits good recording and playback performance at high track density and high transfer rates because there is little signal quality degradation due to high-speed running. "SNR" is an abbreviation for "Signal-to-Noise Ratio". The unit "kbps" is a unit of linear recording density (cannot be converted to the SI unit system).

[0194]

[0195]

[0196]

[0197]

[0198]

[0199]

[0200]

[0201]

[0202]

[0203]

[0204] From the results shown in the table above, it was confirmed that the magnetic tapes of Examples 1 to 8 are thinned magnetic tapes with a tape thickness of 5.2 μm or less, and contribute to achieving good recording and playback performance at high transfer rates and high track densities.

[0205] Except for the fact that vertical orientation processing was not performed during the manufacturing of the magnetic tape, a magnetic tape cartridge was manufactured in the same manner as described above for Example 1. A sample piece was cut from the magnetic tape removed from the above magnetic tape cartridge. The vertical angular ratio of this sample piece was determined using a Tamagawa Seisakusho TM-TRVSM5050-SMSL type vibrating sample magnetometer in the same manner as described above, and was found to be 0.55. A magnetic tape was also removed from the magnetic tape cartridge of Example 1, and the vertical angular ratio of a sample piece cut from this magnetic tape was similarly determined, and was found to be 0.65.

[0206] The magnetic tapes extracted from the two magnetic tape cartridges described above were each mounted on a 1 / 2-inch reel tester, and their electromagnetic conversion characteristics (SNR: Signal-to-Noise Ratio) were evaluated using the following method. As a result, the magnetic tape extracted from the magnetic tape cartridge of Example 1 showed an SNR value 4 dB higher than that of the magnetic tape manufactured without vertical orientation treatment. Recording and playback were performed in 10 passes under a tension of 0.7 N in the longitudinal direction of the magnetic tape in an environment of 23°C and 50% relative humidity. The relative speed between the magnetic tape and the magnetic head was set to 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 optimal recording current for each magnetic tape. Playback was performed using a GMR (Giant-magnetoresistive) head (element thickness 15 nm, shielding gap 0.1 μm, playback element width 0.8 μm) as the playback head. A signal with a linear recording density of 300 kfci was recorded, and the playback signal was measured using a spectrum analyzer manufactured by Shibasoku. The unit kfci is the unit of linear recording density (cannot be converted to the SI unit system). The signal used was a portion of the signal that had stabilized sufficiently after the magnetic tape started running.

[0207] One aspect of the present invention is useful in the technical field of various data storage, such as backup and archiving.

Claims

1. A magnetic tape having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the tape thickness of the magnetic tape is 5.2 μm or less, the magnetic layer has a plurality of servo bands, and the σDES determined by (1) to (4) below is 30 nm or less; (1) The magnetic tape is run once at a speed of 6 m / s over a 900 m length area using a reel tester; (2) The servo band spacing at each position in the longitudinal direction is measured for the run; (3) The measurement results of the servo band spacing are filtered with an exclusion band of less than 40 Hz and a transmission band of 40 Hz or more to calculate the high-frequency component of the servo band spacing at each position; (4) The standard deviation σ of the calculated high-frequency component is defined as σDES.

2. The magnetic tape according to claim 1, wherein the number of wrinkles measured after running the magnetic tape back and forth 300 times over a 900 m length area at a speed of 6 m / s in a reel tester is 30 or less.

3. The magnetic tape according to claim 1, wherein, in a reel tester, the magnetic tape is run once through a 900 m length region at a speed of 6 m / s, and the number of times an end position variation of 200 μm or more occurs in 0.2 seconds during the run is 40 times or less.

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

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

6. The magnetic tape according to claim 1, wherein the non-magnetic support is a polyethylene naphthalate support.

7. The magnetic tape according to claim 1, wherein the non-magnetic support is a polyethylene terephthalate support.

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

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

10. The magnetic tape according to claim 1, wherein the number of wrinkles measured after running the magnetic tape back and forth 300 times at a speed of 6 m / s over a 900 m length area in a reel tester is 30 or less, the number of times the end position fluctuation of 200 μm or more occurs in 0.2 seconds during a run of the magnetic tape over a 900 m length area in a reel tester at a speed of 6 m / s is 40 or less, the magnetic tape further comprises a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer, the non-magnetic support further comprises a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer, the non-magnetic support is a polyethylene naphthalate support, a polyethylene terephthalate support, or an aromatic polyamide support, and the vertical angular ratio of the magnetic tape is 0.60 or more.

11. A magnetic tape cartridge comprising the magnetic tape described in any one of claims 1 to 10.

12. A magnetic tape device comprising a magnetic tape according to any one of claims 1 to 10.

13. The magnetic tape device according to claim 12, 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 that the axis of the element array makes with respect to the width direction of the magnetic tape while the magnetic tape is running within the magnetic tape device.

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