Magnetic tape, magnetic tape cartridge, and magnetic tape device

Abstract

To provide a magnetic tape device capable of satisfactorily recording and / or reproducing data when recording and / or reproducing the data by changing a tilt angle of a head during a magnetic tape running.SOLUTION: A magnetic tape has a non-magnetic support body and a magnetic layer containing ferromagnetic powder. The number of recesses having an equivalent circle diameter of 0.30 μm or more and 0.60 μm or less on a surface of a magnetic layer is 10 or more and 600 or less per area of 40 μm×40 μm, and the standard deviation σ of the number of recesses is 100 or less. A magnetic tape cartridge and a magnetic tape device include the magnetic tape.SELECTED DRAWING: None

Description

[Technical Field]

[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 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-524774 [Patent Document 2] US2019 / 0164573A1 [Overview of the project] [Problems that the invention aims to solve]

[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 tracks 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 and 2, for example, paragraphs 0059-0067 and 0084 of Patent Document 1). During recording or playback, if the magnetic head for recording or playing back data is misaligned from the target track position due to width deformation of the magnetic tape, phenomena such as overwriting of recorded data or playback failures may occur. The inventors believe that changing the head tilt angle as described above is one means of suppressing the occurrence of such phenomena.

[0006] In view of the above, one aspect of the present invention aims to provide a magnetic tape device that can record and / or reproduce data well when the head tilt angle is changed while the magnetic tape is running. [Means for solving the problem]

[0007] One aspect of the present invention is, A magnetic tape comprising a non-magnetic support and a magnetic layer containing ferromagnetic powder, The number of indentations on the surface of the above magnetic layer with an equivalent circular diameter of 0.30 μm or more and 0.60 μm or less is between 10 and 600 per 40 μm × 40 μm area, and A magnetic tape having a standard deviation σ of the number of indentations in the width direction on the surface of the magnetic layer of 100 or less. Regarding.

[0008] In one configuration, the number of indentations can be between 10 and 100.

[0009] In one configuration, the standard deviation σ of the number of indentations can be 20 or less.

[0010] In one embodiment, the vertical aspect ratio of the magnetic tape can be 0.60 or greater.

[0011] In one embodiment, the magnetic tape may further have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

[0012] In one embodiment, the magnetic tape may further have 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.

[0013] In one embodiment, the tape thickness of the magnetic tape described above can be 5.2 μm or less.

[0014] One aspect of the present invention relates to a magnetic tape cartridge including the magnetic tape described above.

[0015] One aspect of the present invention relates to a magnetic tape device including the magnetic tape described above.

[0016] In one embodiment, the magnetic tape device may further include a magnetic head. The magnetic head may have a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements. The above-described magnetic tape device can change 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. [Effects of the Invention]

[0017] According to one aspect of the present invention, a magnetic tape device can be provided that can record and / or reproduce data well when the head tilt angle is changed while the magnetic tape is running. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic diagram showing an example of a magnetic head module. [Figure 2]This is an explanatory diagram illustrating the relative positional relationship between the module and the magnetic tape while the magnetic tape is running in a magnetic tape drive. [Figure 3] This is an explanatory diagram regarding the change in angle θ during magnetic tape travel. [Figure 4] An example of the manufacturing process for magnetic tape (process schematic diagram) is shown. [Figure 5] An example of the arrangement of data bands and servo bands is shown. [Figure 6] This shows an example of a servo pattern arrangement for an LTO (Linear Tape-Open) Ultrium format tape. [Figure 7] This is an explanatory diagram of the method for measuring the angle θ while a magnetic tape is running. [Figure 8] This is a schematic diagram showing an example of a magnetic tape drive. [Modes for carrying out the invention]

[0019] [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 number of indentations on the surface of the magnetic layer with an equivalent circular diameter of 0.30 μm or more and 0.60 μm or less is 10 to 600 per 40 μm × 40 μm area, and the standard deviation σ of the number of indentations in the width direction of the surface of the magnetic layer is 100 or less.

[0020] <Explanation of head tilt angle> Before describing the magnetic tape mentioned above, the configuration of the magnetic head, the head tilt angle, etc., will be explained below. Furthermore, the reason why the phenomena that occur during recording or playback as described above can be suppressed by tilting the axial direction of the magnetic head module relative to the width direction of the magnetic tape while the magnetic tape is running will also be explained below.

[0021] The magnetic head may have one or more modules, two or more, or three or more, which include an element array having multiple magnetic head elements between a pair of servo signal reading elements. The total number of such modules may be, for example, five or fewer, four or fewer, or three or fewer, or the magnetic head may contain more modules than the total number exemplified herein. Examples of arrangements of multiple modules include "recording module - playback module" (total number of modules: 2), "recording module - playback module - recording module" (total number of modules: 3), etc. However, the arrangement is not limited to the examples shown herein.

[0022] Each module may include an element array, i.e., an array of elements, having multiple magnetic head elements between a pair of servo signal reading elements. 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 a magnetic head, multiple modules are arranged, for example, in a recording / playback head unit, with the axes of the element arrays of each module oriented parallel to each other. Such "parallel" does not necessarily mean parallel in the strict sense, but includes a range of error that is normally acceptable in the art to which this invention belongs. The range of error can mean, for example, a range of less than ±10° of strict parallelism.

[0023] 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 typically 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.

[0024] 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.

[0025] Figure 1 is a schematic diagram showing an example of a magnetic head module. The module shown in Figure 1 has multiple magnetic head elements between a pair of servo signal reading elements (servo signal reading elements 1 and 2). Magnetic head elements are also called "channels." "Ch" in the figure is an abbreviation for Channel. The module shown in Figure 1 has a total of 32 magnetic head elements, from Ch0 to Ch31.

[0026] 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.

[0027] Figure 2 is an explanatory diagram of the relative positional relationship between the module and the magnetic tape during magnetic tape movement in a magnetic tape device. In Figure 2, dotted line A indicates the width direction of the magnetic tape. Dotted line B indicates the axis of the element array. Angle θ can be said to be the head tilt angle during magnetic tape movement, and is the angle between dotted line A and dotted line B. When angle θ is 0° during magnetic tape movement, the distance in the magnetic tape width direction between one servo signal reading element and the other servo signal reading element of the element array (hereinafter also referred to as the "effective distance between servo signal reading elements") is "L". In contrast, when angle θ is greater than 0°, the effective distance between servo signal reading elements is "Lcosθ", and Lcosθ is smaller than L. That is, "Lcosθ <L」である。

[0028] As mentioned earlier, during recording or playback, if the magnetic head used to record or play back data is misaligned from the intended track position due to deformation of the magnetic tape's width, phenomena such as overwriting of recorded data or playback failures may occur. For example, if the width of the magnetic tape shrinks or expands, the magnetic head element that should record or play back at the intended track position may end up recording or playing back at a different track position. Also, if the width of the magnetic tape expands, the effective distance between servo signal reading elements may become shorter than the distance between two adjacent servo bands separated by a data band (also referred to as "servo band spacing" or "servo band interval"; more specifically, the distance between the two servo bands in the width direction of the magnetic tape), which may result in data not being recorded or played back in areas close to the edge of the magnetic tape. In contrast, when the element array is tilted at an angle θ greater than 0°, as explained earlier, the effective distance between servo signal reading elements becomes "Lcosθ". The larger the value of θ, the smaller the value of Lcosθ, and the smaller the value of θ, the larger the value of Lcosθ. Therefore, by changing the value of θ according to the degree of dimensional change (i.e., contraction or expansion) in the width direction of the magnetic tape, it becomes possible to bring the effective distance between servo signal reading elements closer to or matching the spacing of the servo bands. This prevents or reduces the frequency of phenomena such as overwriting of recorded data or playback failures that occur when the magnetic head used to record or play back data is misaligned from the target track position due to width deformation of the magnetic tape during recording or playback.

[0029] Figure 3 is an explanatory diagram regarding the change in angle θ during magnetic tape travel. The angle θ at the start of the journey is θ initial This can be set to, for example, 0° or greater than or equal to 0°. In Figure 3, the central diagram shows the state of the module at the start of operation. In Figure 3, the right-hand figure shows the angle θ as θ initial An angle θ is a larger angle. cshows the state of the module when [condition]. Effective distance Lcosθ between servo signal reading elements c is a value smaller than Lcosθ at the start of magnetic tape running. When the width of the magnetic tape contracts during magnetic tape running, it is preferable to perform such angle adjustment. initial When the width of the magnetic tape contracts during magnetic tape running, it is preferable to perform such angle adjustment. On the other hand, in FIG. 3, the left figure shows the state of the module when the angle θ is set to an angle θ initial smaller than [angle]. Effective distance Lcosθ between servo signal reading elements e shows the state of the module when [condition]. Effective distance Lcosθ between servo signal reading elements e is a value larger than Lcosθ at the start of magnetic tape running. When the width of the magnetic tape expands during magnetic tape running, it is preferable to perform such angle adjustment. initial When the width of the magnetic tape expands during magnetic tape running, it is preferable to perform such angle adjustment.

[0030] As described above, changing the head tilt angle during magnetic tape running can contribute to preventing phenomena such as overwriting of recorded data and playback failure that occur when the magnetic head for recording or playing back data deviates from the target track position due to width deformation of the magnetic tape during recording or playback, or can contribute to reducing the occurrence frequency thereof. On the other hand, recording data onto magnetic tape and playing back recorded data is usually done by bringing the magnetic head into contact with the magnetic layer surface of the magnetic tape and sliding it. When running the magnetic tape for recording and / or playing back data, changing the head tilt angle can result in the head tilt angle being different when recording data to a certain recording bit compared to when reading data from that recording bit (i.e., during playback). The inventors believe that this can cause a change in the contact state between the magnetic head and the magnetic layer surface and a change in running friction between recording and playing back data to a certain recording bit, which can lead to a deterioration in the quality of the played-back signal. As a result of further diligent research, the inventors have newly discovered that, regarding the state of indentations on the surface of the magnetic layer of a magnetic tape, by setting the number of indentations with an equivalent circular diameter of 0.30 μm to 0.60 μm on the surface of the magnetic layer to 10 to 600 per 40 μm × 40 μm area, and setting the standard deviation σ of the number of indentations in the width direction of the surface of the magnetic layer to 100 or less, it becomes possible to record and / or play back data well when changing the head tilt angle while the magnetic tape is running.

[0031] <State of existence of depressions on the surface of the magnetic layer> In the present invention and this specification, the number of indentations on the surface of the magnetic layer with an equivalent circular diameter of 0.30 μm or more and 0.60 μm or less is determined by measuring the surface of the magnetic layer of the magnetic tape using an atomic force microscope (AFM) as follows. In the present invention and this specification, "surface of the magnetic layer" is synonymous with the magnetic layer side surface of the magnetic tape. The number of indentations on the surface of the magnetic layer with an equivalent circular diameter of 0.30 μm or more and 0.60 μm or less (per 40 μm × 40 μm area) determined as follows is also simply referred to as "number of indentations". Furthermore, the standard deviation of the number of indentations determined as follows is also referred to as "width direction σ of the number of indentations". The measurement area is a 40 μm square (40 μm × 40 μm) region. Measurements are performed at five locations. The five locations on the magnetic layer surface to be measured are the same in the longitudinal direction but different in the width direction. The longitudinal position is randomly selected on the magnetic layer surface, and at this longitudinal position, the width direction is divided into five sections relative to the magnetic tape width (therefore, if the magnetic tape width is W, the width of each section is "W / 5"), and for a 40 μm square (40 μm × 40 μm) region arbitrarily selected within each section, the number of indentations on the magnetic layer surface with an equivalent circle diameter of 0.30 μm or more and 0.60 μm or less is determined. The arithmetic mean of these five measured values ​​is taken as the number of indentations on the magnetic layer surface of the magnetic tape being measured with an equivalent circle diameter of 0.30 μm or more and 0.60 μm or less (per 40 μm × 40 μm area). Furthermore, the standard deviation σ (i.e., the positive square root of the variance) of the five measured values ​​obtained in this way is taken as the standard deviation σ (widthwise σ of the number of indentations) of the number of indentations in the width direction on the surface of the magnetic layer of the magnetic tape being measured. Regarding the measurement of the number of indentations, in the planar image of the magnetic layer surface obtained using AFM, a reference plane is defined where the volume of the convex component and the concave component within the measurement area are equal. The parts detected as being recessed from this reference plane are identified as "indentations." Among the parts identified as indentations, there may be indentations where part is within the measurement area and the other part is outside the measurement area. When determining the number of indentations, such indentations should also be included in the measurement. In the planar image of the magnetic layer surface obtained using AFM, the area of ​​the parts identified as indentations (hereinafter, "area A") is measured, and the equivalent circle diameter D is calculated using (A / π)^(1 / 2)×2=D. Here, the operator "^" represents exponentiation. The equivalent circle diameter is obtained as a value in units of μm, rounded to three decimal places, and truncated from the fourth decimal place onward, to obtain values ​​in increments of 0.01 μm. An example of AFM measurement conditions is given below. An AFM (BRUKER Nanoscope 5) in peak-force tapping mode will be used to measure a 40 μm × 40 μm area on the surface of the magnetic layer of a magnetic tape. A BRUKER SCANASYST-AIR probe will be used, with a resolution of 512 pixels × 512 pixels and a scan speed of 512 seconds to measure one screen (512 pixels × 512 pixels).

[0032] (Number of indentations) The number of indentations with an equivalent circular diameter of 0.30 μm or more and 0.60 μm or less on the surface of the magnetic layer of the above magnetic tape is between 10 and 600 per 40 μm × 40 μm area. The inventors believe that having 600 or fewer indentations can contribute to suppressing the changes in running friction described above. From this point of view, the number of indentations is preferably 500 or less, more preferably 400 or less, even more preferably 300 or less, even more preferably 200 or less, and even more preferably 100 or less. On the other hand, from the viewpoint of suppressing the degradation of the playback signal caused by foreign matter called debris by reducing the contact area between the magnetic tape and the magnetic head, the number of indentations is 10 or more, preferably 20 or more, more preferably 30 or more, even more preferably 40 or more, and even more preferably 50 or more.

[0033] (The width direction σ of the number of indentations) The standard deviation σ of the number of indentations in the width direction on the surface of the magnetic layer of the magnetic tape (σ in the width direction of the number of indentations) is 100 or less. The inventors believe that this can contribute to suppressing the changes in running friction described above. From this point of view, the σ in the width direction of the number of indentations is preferably 90 or less, and more preferably 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, 30 or less, and 20 or less, in that order. The σ in the width direction of the number of indentations can be, for example, 0 or more, 1 or more, 3 or more, 5 or more, 7 or more, or 10 or more. From the viewpoint of further suppressing the changes in running friction described above, it is presumed that the smaller the value of σ in the width direction of the number of indentations, the more preferable it is.

[0034] The method for controlling the number of indentations and the method for controlling the width σ of the number of indentations will be described later.

[0035] <Magnetic layer> (Ferromagnetic powder) As the ferromagnetic powder contained in the magnetic layer, one or more known ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used in combination. Using a ferromagnetic powder with a small average particle size is preferable from the viewpoint of improving recording density. From this viewpoint, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, even more preferably 35 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and even more preferably 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, even more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more.

[0036] Hexagonal ferrite powder A preferred example of ferromagnetic powder is hexagonal ferrite powder. For details on hexagonal ferrite powder, see, for example, paragraphs 0012 to 0030 of Japanese Patent Publication No. 2011-225417, paragraphs 0134 to 0136 of Japanese Patent Publication No. 2011-216149, paragraphs 0013 to 0030 of Japanese Patent Publication No. 2012-204726, and paragraphs 0029 to 0084 of Japanese Patent Publication No. 2015-127985.

[0037] In the present invention and this specification, "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the hexagonal ferrite crystal structure, it shall be determined that the hexagonal ferrite crystal structure has been detected as the main phase. If only a single structure is detected by X-ray diffraction analysis, this detected structure shall be considered the main phase. The hexagonal ferrite crystal structure contains at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. Divalent metal atoms are metal atoms that can become divalent cations as ions, and examples include strontium atoms, barium atoms, alkaline earth metal atoms such as calcium atoms, and lead atoms. In the present invention and this specification, hexagonal strontium ferrite powder refers to powder in which the main divalent metal atom contained is strontium, and hexagonal barium ferrite powder refers to powder in which the main divalent metal atom contained is barium. The main divalent metal atom refers to the divalent metal atom that accounts for the largest proportion on an atomic percentage basis among the divalent metal atoms contained in the powder. However, rare earth atoms are not included in the above divalent metal atoms. In the present invention and this specification, "rare earth atoms" are selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanide atoms. Lanthanide atoms are selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0038] Below, we will describe hexagonal strontium ferrite powder, a form of hexagonal ferrite powder, in more detail.

[0039] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1600 nm. 3 The activation volume is within the range described above. Finely milled hexagonal strontium ferrite powder exhibiting an activation volume within this range is suitable for the fabrication of magnetic tapes that exhibit excellent electromagnetic conversion properties. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm. 3 That's all, for example, 850nm 3 It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of hexagonal strontium ferrite powder is 1500 nm. 3 The following is more preferable: 1400nm 3 It is even more preferable that the following occur: 1300 nm 3 It is even more preferable that the following conditions be met: 1200 nm 3 It is even more preferable that the following conditions be met: 1100 nm 3 It is even more preferable that the following conditions be met. The same applies to the activation volume of the hexagonal barium ferrite powder.

[0040] "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 values ​​obtained from the following relationship between Hc and activation volume V, measured using a vibrating sample type magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes in the coercivity Hc measurement section (measurement temperature: 23℃±1℃). Note that the unit of the anisotropy constant Ku is 1erg / cc = 1.0 × 10⁻⁶. -1 J / m 3 That is the case. Hc=2Ku / Ms{1-[(kT / KuV)ln(At / 0.693)] 1 / 2} [In the above formula, Ku: anisotropy constant (unit: J / m 3 ), Ms: Saturation magnetization (unit: kA / m), k: Boltzmann constant, T: Absolute temperature (unit: K), V: Activation volume (unit: cm) 3 ), A: Spin precession frequency (unit: s) -1 ), t: magnetic field reversal time (unit: s)]

[0041] 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 × 10⁻⁶. 5 J / m 3 The following values ​​are possible. However, since a higher Ku value is preferable as it indicates higher thermal stability, the values ​​are not limited to those exemplified above.

[0042] Hexagonal strontium ferrite powder may or may not contain rare earth atoms. When hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms are present at a concentration of 0.5 to 5.0 atomic percent (bulk concentration) per 100 atomic percent of iron atoms. In one embodiment, hexagonal strontium ferrite powder containing rare earth atoms may exhibit a segregation of rare earth atoms in the surface layer. In the present invention and this specification, "rare earth atom surface layer segregation" means that the rare earth atom content relative to 100% of iron atoms in a solution obtained by partially dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom surface layer content" or simply "surface layer content" with respect to rare earth atoms) is different from the rare earth atom content relative to 100% of iron atoms in a solution obtained by completely dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom bulk content" or simply "bulk content" with respect to rare earth atoms), Rare earth atom surface content / Rare earth atom bulk content > 1.0 This means that the ratio is satisfied. The rare earth atom content of hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. In contrast, partial dissolution using acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder, so the rare earth atom content in the solution obtained by partial dissolution is the rare earth atom content in the surface layer of the particles constituting the hexagonal strontium ferrite powder. When the rare earth atom surface layer content satisfies the ratio "rare earth atom surface layer content / rare earth atom bulk content > 1.0", it means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are concentrated in the surface layer (i.e., there are more of them in the surface layer than in the interior). In this invention and specification, the surface layer means a part of the region extending from the surface to the interior of the particles constituting the hexagonal strontium ferrite powder.

[0043] 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 within the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. Furthermore, it is presumed that using hexagonal strontium ferrite powder with a rare-earth atom uneven distribution on the surface as the ferromagnetic powder for the magnetic layer contributes to suppressing wear on the magnetic layer surface due to sliding with the magnetic head. In other words, it is presumed that hexagonal strontium ferrite powder with a rare-earth atom uneven distribution on the surface may also contribute to improving the running durability of the magnetic tape. This is presumed to be because the uneven distribution of rare-earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improved interaction between the particle surface and organic substances (e.g., binders and / or additives) contained in the magnetic layer, resulting in improved strength of the magnetic layer. From the viewpoint of 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.

[0044] 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.

[0045] When hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms included may be one or more of the rare earth atoms. 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.

[0046] In hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the rare-earth atoms only need to be segregated in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of segregation is not limited. For example, in hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the ratio of the rare-earth atom surface content obtained by partial dissolution under the dissolution conditions described later to the rare-earth atom bulk content obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," is greater than 1.0 and can be 1.5 or greater. A "surface content / bulk content" greater than 1.0 means that in the particles constituting the hexagonal strontium ferrite powder, rare-earth atoms are segregated in the surface layer (i.e., there are more of them in the surface layer than in the interior). Furthermore, the ratio of the surface content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in hexagonal strontium ferrite powder having a rare earth atom surface distribution bias, the rare earth atoms only need to be biased towards the surface of the particles constituting the hexagonal strontium ferrite powder, and the above "surface content / bulk content" is not limited to the upper or lower limits exemplified.

[0047] The partial and total dissolution of hexagonal strontium ferrite powder is described below. For hexagonal strontium ferrite powder existing as a powder, the sample powders to be partially and completely dissolved are taken from the same lot of powder. On the other hand, for hexagonal strontium ferrite powder contained in the magnetic layer of a magnetic tape, a portion of the hexagonal strontium ferrite powder extracted from the magnetic layer is subjected to partial dissolution, and another portion is subjected to total dissolution. The extraction of hexagonal strontium ferrite powder from the magnetic layer can be carried out, for example, by the method described in paragraph 0032 of Japanese Patent Application Publication No. 2015-91747. Partial dissolution, as described above, refers to a state where the hexagonal strontium ferrite powder is dissolved to the extent that residual particles can be visually confirmed in the liquid at the end of the dissolution process. For example, partial dissolution can dissolve 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder, with the total particles being 100% by mass. On the other hand, total dissolution, as described above, refers to a state where the hexagonal strontium ferrite powder is dissolved to the extent that no residual particles can be visually confirmed in the liquid at the end of the dissolution process. The above-mentioned partial dissolution and surface layer content measurement are performed, for example, by the following method. However, the dissolution conditions such as the amount of sample powder described below are examples only, and any dissolution conditions that enable partial and total dissolution can be arbitrarily adopted. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is held on a hot plate at a set temperature of 70°C for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the resulting filtrate is performed using an inductively coupled plasma (ICP) analyzer. In this way, the surface content of rare earth atoms relative to 100% iron atoms can be determined. If multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface content. This is also the case when measuring bulk content. On the other hand, the measurement of total dissolution and bulk content is performed, for example, by the following method. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid is held on a hot plate at a set temperature of 80°C for 3 hours. Afterward, the bulk content relative to 100 atomic percent of iron can be determined by performing the same procedure as described above for partial dissolution and surface layer content measurement.

[0048] From the perspective of increasing the playback output when reproducing data recorded on magnetic tape, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic tape to be high. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but lacking surface segregation of rare earth atoms tended to have a significantly lower σs compared to hexagonal strontium ferrite powder that does not contain rare earth atoms. In contrast, hexagonal strontium ferrite powder with surface segregation of rare earth atoms is considered preferable in order to suppress such a large decrease in σs. In one embodiment, the σs of hexagonal strontium ferrite powder is 45 A·m 2 It can be 47 A·m or more per kg. 2 It can also be more than / kg. On the other hand, σs is 80 A·m from the viewpoint of noise reduction. 2 Preferably less than / kg, at 60A·m 2 It is more preferable that it be less than or equal to / kg. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In this invention and specification, unless otherwise specified, the mass magnetization σs is the value measured at a magnetic field strength of 15 kOe. 1 [kOe] = 10 6 It is / 4π[A / m].

[0049] Regarding the constituent atom content (bulk content) of hexagonal strontium ferrite powder, the strontium atom content can be in the range of, for example, 2.0 to 15.0 atomic percent per 100 atomic percent of iron atoms. In one form, hexagonal strontium ferrite powder may contain only strontium atoms as the divalent metal atom. In another form, hexagonal strontium ferrite powder may contain one or more other divalent metal atoms in addition to strontium atoms. For example, it may contain barium atoms and / or calcium atoms. When other divalent metal atoms besides strontium atoms are included, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder can be in the range of, for example, 0.05 to 5.0 atomic percent per 100 atomic percent of iron atoms.

[0050] The known crystal structures of hexagonal ferrites include magnetoplumbite (also called "M-type"), W-type, Y-type, and Z-type. Hexagonal strontium ferrite powder may have any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. Hexagonal strontium ferrite powder may show a single crystal structure or two or more crystal structures by X-ray diffraction analysis. For example, in one form, hexagonal strontium ferrite powder may show only the M-type crystal structure by X-ray diffraction analysis. For example, M-type hexagonal ferrite is AFe 12 O 19It is represented by the following compositional formula: Here, A represents a divalent metal atom, and if the hexagonal strontium ferrite powder is of type M, A is either only a strontium atom (Sr), or if A contains multiple divalent metal atoms, then as described above, strontium atoms (Sr) make up the largest proportion on an atomic percentage basis. The divalent metal atom content of hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite and is not particularly limited. The same applies to the iron atom content and oxygen atom content. Hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms and oxygen atoms, and may also contain rare earth atoms. Furthermore, hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, hexagonal strontium ferrite powder may contain aluminum atoms (Al). The aluminum atom content can be, for example, 0.5 to 10.0 atomic percent relative to 100 atomic percent of iron atoms. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration, the hexagonal strontium ferrite powder preferably contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is preferably 10.0 atomic percent or less, more preferably in the range of 0 to 5.0 atomic percent, and may even be 0 atomic percent, relative to 100 atomic percent of iron atoms. That is, in one embodiment, the hexagonal strontium ferrite powder does not need to contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The above content expressed in atomic percent is obtained by converting the content of each atom (unit: mass%) obtained by completely dissolving the hexagonal strontium ferrite powder into an atomic percent value using the atomic weight of each atom. Furthermore, in the present invention and this specification, "does not contain" for a certain atom means that the content measured by an ICP analyzer after complete dissolution is 0 mass%. The detection limit of an ICP analyzer is typically 0.01 ppm (parts per million) or less by mass. The term "does not contain" above is used to include the presence of substances in amounts below the detection limit of the ICP analyzer.Hexagonal strontium ferrite powder can, in one form, be bismuth-free (Bi).

[0051] metal powder A preferred specific example of ferromagnetic powder is ferromagnetic metal powder. For details on ferromagnetic metal powder, see, for example, paragraphs 0137-0141 of Japanese Patent Publication No. 2011-216149 and paragraphs 0009-0023 of Japanese Patent Publication No. 2005-251351.

[0052] ε-Iron oxide powder A preferred specific example of a ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, "ε-iron oxide powder" refers to a ferromagnetic powder in which the crystalline structure of ε-iron oxide is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystalline structure of ε-iron oxide, it shall be determined that the crystalline structure of ε-iron oxide has been detected as the main phase. Methods for producing ε-iron oxide powder include methods from goethite and the reverse micelle method. All of the above production methods are publicly known. Furthermore, for methods for producing ε-iron oxide powder in which some of the Fe is substituted with substitution atoms such as Ga, Co, Ti, Al, and Rh, see, for example, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206, etc. However, the method for producing ε-iron oxide powder that can be used as ferromagnetic powder in the magnetic layer of the magnetic tape described above is not limited to the method described herein.

[0053] The activation volume of ε-iron oxide powder is preferably 300 to 1500 nm. 3 The activation volume is within the range described above. Micronized ε-iron oxide powder exhibiting an activation volume within the above range is suitable for the production of magnetic tapes that exhibit excellent electromagnetic conversion properties. The activation volume of the ε-iron oxide powder is preferably 300 nm. 3 That's all, for example, 500nm3 It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of ε-iron oxide powder is 1400 nm. 3 The following is more preferable: 1300nm 3 It is even more preferable that the following occur: 1200 nm 3 It is even more preferable that the following conditions be met: 1100 nm 3 The following is even more preferable.

[0054] The anisotropy constant Ku can be cited as an indicator of the reduction of thermal fluctuations, or in other words, the improvement of thermal stability. The ε-iron oxide powder is preferably 3.0 × 10⁻⁶ 4 J / m 3 It can have a Ku of the above, and more preferably 8.0 × 10 4 J / m 3 It can have the above amount of Ku. Also, the amount of Ku in ε-iron oxide powder is, for example, 3.0 × 10⁻⁶. 5 J / m 3 The following values ​​are possible. However, a higher Ku value indicates higher thermal stability, which is preferable, so the values ​​are not limited to those exemplified above.

[0055] 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 12A·m or more / kg. 2 It can also be more than / kg. On the other hand, the σs of ε-iron oxide powder is 40 A·m from the viewpoint of noise reduction. 2 Preferably less than / kg, 35A·m 2 It is more preferable that the amount be less than or equal to / kg.

[0056] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders shall be the value measured using a transmission electron microscope by the following method. The powder is photographed using a transmission electron microscope at a magnification of 100,000x, and the resulting image is printed onto photographic paper at a total magnification of 500,000x to obtain a photograph of the particles that make up the powder. From the obtained photograph of the particles, the target particles are selected, and their outlines are traced with a digitizer to measure the size of the particles (primary particles). Primary particles are independent particles that do not aggregate. The above measurements are performed on 500 randomly selected particles. The arithmetic mean of the particle sizes of these 500 particles is taken as the average particle size of the powder. As the transmission electron microscope, for example, a Hitachi H-9000 transmission electron microscope can be used. The particle size can be measured using known image analysis software, for example, Carl Zeiss KS-400 image analysis software. Unless otherwise specified, the average particle sizes shown in the examples described later are values ​​measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software. In the present invention and this specification, "powder" means a collection of multiple particles. For example, ferromagnetic powder means a collection of multiple ferromagnetic particles. Furthermore, a collection of multiple particles is not limited to a form in which the particles constituting the collection are in direct contact, but also includes forms in which binders, additives, etc., described later, are interposed between the particles. The word "particle" is sometimes used to refer to powder.

[0057] 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.

[0058] In the present invention and this specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is determined by the shape of the particles observed in the above particle photograph. (1) In the case of needle-shaped, spindle-shaped, columnar (however, the height is greater than the longest diameter of the base), etc., the length of the long axis constituting the particle is expressed as the long axis length, (2) In the case of a plate or column (provided that the thickness or height is less than the longest diameter of the plate or base), it shall be expressed by the longest diameter of the plate or base. (3) If the shape is spherical, polyhedral, irregular, etc., and the major axis constituting the particle cannot be determined from the shape, it shall be represented by the equivalent diameter of a circle. The equivalent diameter of a circle refers to the diameter obtained by the circular projection method.

[0059] Furthermore, the average needle-shape ratio of the powder refers to the arithmetic mean of the values ​​obtained for the 500 particles by measuring the length of the short axis of each particle, i.e., the short axis length, in the above measurement, and determining the (long axis length / short axis length) value for each particle. Here, unless otherwise specified, the short axis length refers to the length of the short axis constituting the particle in the above definition of particle size (1), the thickness or height in the case of (2), and in the case of (3), since there is no distinction between the long axis and the short axis, (long axis length / short axis length) is considered to be 1 for convenience. Unless otherwise specified, when the particle shape is specific, for example, in the case of definition (1) above, the average particle size is the average major axis length, and in the case of definition (2), the average particle size is the average plate diameter. In the case of definition (3), the average particle size is the average diameter (also called the average particle size or average particle diameter).

[0060] 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.

[0061] (Binder) The above magnetic tape can be a coated magnetic tape, and the magnetic layer may contain a binder. The binder is one or more resins. Various resins commonly used as binders for coated magnetic tapes can be used as binders. For example, as a binder, a resin selected from polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl alkylal resin such as polyvinyl butyral can be used alone or in mixture of multiple resins. Among these, polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binders in the non-magnetic layer and / or back coat layer described later. For details on the binders mentioned above, please refer to paragraphs 0028 to 0031 of Japanese Patent 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.

[0062] (Hardening 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.

[0063] (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 0030-0033, 0035, and 0036 of Japanese Patent Application Publication No. 2016-126817. A lubricant may also be included in the non-magnetic layer described later. For lubricants that can be included in the non-magnetic layer, refer to paragraphs 0030-0031, 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. As protrusion-forming agents, colloidal particles are preferred, 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.

[0064] The magnetic layer described above can be provided directly on the surface of a non-magnetic support, or indirectly via a non-magnetic layer.

[0065] <Nonmagnetic 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.

[0066] 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.

[0067] 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.

[0068] <Nonmagnetic support> Next, non-magnetic supports will be described. Examples of non-magnetic supports (hereinafter also simply referred to as "supports") include known materials such as biaxially oriented polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamide-imide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be subjected to pre-treatment such as corona discharge, plasma treatment, easy-adhesion treatment, or heat treatment.

[0069] <Backcoat 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 above description regarding the non-magnetic powder of the non-magnetic layer.

[0070] Indentations on the magnetic layer surface can be formed during the manufacturing process of magnetic tape, etc., when the magnetic layer surface and back surface are in contact while the tape is wound into a roll, and the surface shape of the back surface is transferred to the magnetic layer surface (so-called back transfer). The back surface is the surface of the back coat layer if a back coat layer is present, and the surface of the support if there is no back coat layer. One example of a method for controlling the presence of indentations on the magnetic layer surface is to select the type of component to be added to the composition for forming the back coat layer in order to adjust the surface shape of the back surface. From this point of view, it is preferable to use carbon black and a non-magnetic powder other than carbon black in combination as the non-magnetic powder of the back coat layer, or to use carbon black (i.e., the non-magnetic powder of the back coat layer consists of carbon black). Examples of non-magnetic powders other than carbon black include the non-magnetic powders exemplified above that can be contained in the non-magnetic layer. Regarding the non-magnetic powder in the back coat layer, the proportion of carbon black in 100.0 parts by mass of the total non-magnetic powder is preferably in the range of 50.0 to 100.0 parts by mass, more preferably in the range of 70.0 to 100.0 parts by mass, and even more preferably in the range of 90.0 to 100.0 parts by mass. It is also preferable that the entire amount of non-magnetic powder in the back coat layer be carbon black. The content (filling rate) of non-magnetic powder in the back coat 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 back coat layer.

[0071] From the viewpoint of ease of controlling the number of recesses having the above-mentioned circular equivalent diameter present on the surface of the magnetic layer, in one embodiment, it is preferable to use a non-magnetic powder with an average particle size of 50 nm or less as the non-magnetic powder of the back coat layer. Only one type of non-magnetic powder may be used as the non-magnetic powder of the back coat layer, or two or more types may be used. When two or more types (for example, carbon black and a non-magnetic powder other than carbon black) are used, it is preferable that the average particle size of each is 50 nm or less. The average particle size of the non-magnetic powder is more preferably in the range of 10 to 50 nm, and even more preferably in the range of 10 to 30 nm. In one embodiment, it is preferable that the entire amount of non-magnetic powder contained in the back coat layer is carbon black, and its average particle size is 50 nm or less.

[0072] To control the presence of depressions on the surface of the magnetic layer, it is preferable that the backcoat layer forming composition contains a component (dispersant) that can enhance the dispersibility of the non-magnetic powder contained in the composition. More preferably, the backcoat layer forming composition contains a non-magnetic powder with an average particle size of 50 nm or less and a component that can enhance the dispersibility of this non-magnetic powder, and even more preferably, it contains carbon black with an average particle size of 50 nm or less and a component that can enhance the dispersibility of the carbon black.

[0073] As an example of such a dispersant, a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 below can be used. The "alkyl ester anion" can also be called an "alkyl carboxylate anion".

[0074] [ka]

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The following provides a more detailed explanation of Equation 1.

[0079] 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 -, where n is 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 alkyl group or fluorinated alkyl group represented by R has 7 or more carbon atoms, 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 alkyl group or fluorinated alkyl group represented by R has 20 or fewer carbon atoms, more preferably 19 or fewer, and even more preferably 18 or fewer.

[0080] In equation 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 represents the structure of that part and the bond position with an adjacent atom.

[0081] [ka]

[0082] Nitrogen cation of ammonium cation N + and the oxygen anion O in Equation 1 - These can form a salt crosslinking group, creating an ammonium salt structure of an alkyl ester anion represented by formula 1. The presence of a compound having an ammonium salt structure of an alkyl ester anion represented by formula 1 in the backcoat layer can be confirmed by analyzing the magnetic tape using X-ray photoelectron spectroscopy (ESCA: Electron Spectroscopy for Chemical Analysis), infrared spectroscopy (IR: infrared spectroscopy), etc.

[0083] 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.

[0084] 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.

[0085] [ka]

[0086] In Equation 2, the nitrogen atom N that makes up 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.

[0087] [ka]

[0088] The following provides a more detailed explanation of Equation 2.

[0089] 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 greater than or equal to 2.

[0090] R 1 or R 2Examples 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 2 The 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.

[0091] 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 described below are values ​​obtained by converting the values ​​measured using GPC under the following measurement conditions to standard polystyrene equivalent (polystyrene equivalent value). GPC device: HLC-8220 (manufactured by Tosoh Corporation) Guard Column: TSKguardcolumn Super HZM-H Columns: TSKgel Super HZ 2000, TSKgel Super HZ 4000, TSKgel Super HZ-M (manufactured by Tosoh Corporation, 4.6mm (inner diameter) x 15.0cm, three types of columns connected in series) Eluent: Contains tetrahydrofuran (THF) and stabilizer (2,6-di-t-butyl-4-methylphenol). Eluent flow rate: 0.35mL / min Column temperature: 40℃ Inlet temperature: 40℃ Refractive Index (RI) measurement temperature: 40℃ Sample concentration: 0.3% by mass Sample injection volume: 10 μL

[0092] Another form of nitrogen-containing polymer is polyallylamine. Polyallylamine is a polymer of allylamine, having multiple repeating units represented by the following formula 3.

[0093] [ka]

[0094] 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.

[0095] [ka]

[0096] 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 above polyallylamine can be, for example, 15,000 or less, preferably 10,000 or less, and more preferably 8,000 or less.

[0097] 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) or similar methods.

[0098] 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 20-25°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. In another 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 the backcoat layer forming composition. 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 and the carboxyl groups of the above fatty acids may also react to form the following structure, and forms including such a structure are also included in the above compound.

[0099] [ka]

[0100] Examples of the above fatty acids include fatty acids having the alkyl group described earlier as R in Formula 1, and fluorinated fatty acids having the fluorinated alkyl group described earlier as R in Formula 1.

[0101] 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 carbon black. 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 carbon black, and preferably 0.2 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 carbon black, and it is preferable to use 0.1 to 5.5 parts by mass.

[0102] 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 non-magnetic 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.

[0103] <Various thicknesses> Regarding the thickness (total thickness) of magnetic tape, with the enormous increase in the amount of information in recent years, there is a demand for increased recording capacity (higher capacity) in magnetic recording media. For tape-shaped magnetic recording media (i.e., magnetic tape), means of increasing capacity include reducing the thickness of the magnetic tape and increasing the length of magnetic tape that can be accommodated in one reel of magnetic tape cartridge. From this point of view, the thickness (total thickness) of the magnetic tape is preferably 5.6 μm or less, more preferably 5.5 μm or less, even more preferably 5.4 μm or less, even more preferably 5.3 μm or less, and even more preferably 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.

[0104] The thickness (total thickness) of a magnetic tape can be measured by the following method. Ten samples (e.g., 5-10 cm in length) are cut from any section of the magnetic tape, and the thickness of these samples is measured by stacking them. The measured thickness is divided by ten to obtain the value obtained (thickness per sample), which is taken as the total thickness. The above thickness measurement can be performed using a known measuring instrument capable of measuring thickness to the order of 0.1 μm.

[0105] 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. At least one magnetic layer is sufficient, and the magnetic layer may be separated into two or more layers having different magnetic properties, and known configurations for multilayer magnetic layers can be applied. When separated into two or more layers, the thickness of the magnetic layer is the total thickness of these layers. The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, and preferably 0.1 to 1.0 μm. The thickness of the backcoat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm. Various thicknesses, such as the thickness of the magnetic layer, can be determined by the following method. After exposing the cross-section of the magnetic tape in the thickness direction using an ion beam, the exposed cross-section is observed using a scanning electron microscope or a transmission electron microscope. Various thicknesses can be determined as the arithmetic mean of the thicknesses obtained at any two locations during the cross-sectional observation. Alternatively, various thicknesses can be determined as design thicknesses calculated from manufacturing conditions, etc.

[0106] <Manufacturing process> (Preparation of compositions for each layer) A composition for forming a magnetic layer, a non-magnetic layer, or a backcoat layer typically contains a solvent along with the various components described above. As the solvent, one or more of the 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, a non-magnetic layer, or a backcoat layer typically includes at least a kneading step, a dispersion step, and mixing steps provided before or after these steps as needed. Each individual step may be divided into two or more stages. The various components used in the preparation of each layer-forming composition may be added at the beginning or in the middle of any of the steps. Alternatively, individual components may be added in two or more separate steps. For example, a binder may be added in separate steps: a kneading step, a dispersion step, and a mixing step for viscosity adjustment after dispersion. In the manufacturing process of the magnetic tape described above, conventional known manufacturing techniques can be used as some of the steps. In the kneading step, kneaders with strong kneading force, such as open kneaders, continuous kneaders, pressure kneaders, and extruders, can be used. Details of the kneading step 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 step. Filtration can be performed, for example, by filter filtration. As the filter used for filtration, for example, a filter with a pore size of 0.01 to 3 μm (e.g., a glass fiber filter, a polypropylene filter, etc.) can be used.

[0107] (Coating process, cooling process, heat drying process) The magnetic layer can be formed by directly applying the magnetic layer-forming composition onto a non-magnetic support, or by sequentially or simultaneously applying it in layers with the non-magnetic layer-forming composition. For details on the application for each layer formation, refer to paragraph 0066 of Japanese Patent Application Publication No. 2010-231843.

[0108] As described above, in one embodiment, the magnetic tape may have a non-magnetic layer between a non-magnetic support and a magnetic layer. Such a magnetic tape can preferably be manufactured by sequential layer coating. The manufacturing process for sequential layer coating can preferably be carried out as follows: The non-magnetic layer is formed by a coating step of forming a coated layer by applying a non-magnetic layer-forming composition onto a non-magnetic support, and a heat drying step of drying the formed coated layer by heat treatment. Then, the magnetic layer is formed by a coating step of forming a coated layer by applying a magnetic layer-forming composition onto the formed non-magnetic layer, and a heat drying step of drying the formed coated layer by heat treatment.

[0109] In the non-magnetic layer formation step of such a manufacturing method that involves sequential multi-layer coating, the inventors believe that it is preferable to perform a coating step using a non-magnetic layer forming composition to form a coated layer, and to perform a cooling step to cool the coated layer between the coating step and the heating and drying step, in order to control the number of indentations in the width direction σ to 100 or less.

[0110] The following describes an example of the manufacturing process for the magnetic tape described above, based on Figure 4. However, the present invention is not limited to the example below.

[0111] Figure 4 is a schematic diagram showing an example of a process for manufacturing a magnetic tape having a non-magnetic layer and a magnetic layer in that order on one side of a non-magnetic support, and a back coat layer on the other side. In the example shown in Figure 4, the non-magnetic support (long film) is continuously wound from the feed-out section to the feed-back section, and various processes such as coating, drying, and orientation are performed in each section or zone shown in Figure 4. This allows for the sequential layering of the non-magnetic and magnetic layers on one side of the moving non-magnetic support, and the formation of a back coat layer on the other side. The example shown in Figure 4 can be carried out in the same way as the manufacturing process normally performed for the manufacture of coated magnetic recording media, except that it includes a cooling zone.

[0112] On the non-magnetic support fed from the dispensing unit, a non-magnetic layer-forming composition is applied in the first coating unit (coating step of non-magnetic layer-forming composition).

[0113] After the above coating step, the coated layer of the non-magnetic layer-forming composition formed in the coating step is cooled in a cooling zone (cooling step). For example, the cooling step can be performed by passing the non-magnetic support on which the above-mentioned coated layer is formed through a cooling atmosphere. The ambient temperature of the cooling atmosphere can preferably be in the range of -10°C to 0°C, and more preferably in the range of -5°C to 0°C. The time for performing the cooling step (for example, the time from when any part of the coated layer is brought into the cooling zone until it is brought out (hereinafter also referred to as "residence time")) is not particularly limited. The longer the residence time, the smaller the value of the width direction σ of the number of indentations tends to be. In the cooling step, cooled gas may be blown onto the surface of the coated layer.

[0114] After the cooling zone, in the first heat treatment zone, the coated layer is dried by heating it after the cooling process (heat drying process). The heat drying process can be carried out by passing the nonmagnetic support having the coated layer after the cooling process through a heated atmosphere. The ambient temperature of the heated atmosphere here, as well as the ambient temperature of the heated atmosphere in the heat drying process in the second heat treatment zone and the heat drying process in the third heat treatment zone described later, are also called the "drying temperature". Increasing the drying temperature in each heat treatment zone can contribute to reducing the value of the width direction σ of the number of indentations. From this point of view, the drying temperature in each heat treatment zone is preferably 95°C or higher, and more preferably 100°C or higher. In addition, the drying temperature in each heat treatment zone can be, for example, 140°C or lower or 130°C or lower, and can be higher than the temperatures listed here. Optionally, heated gas may be blown onto the surface of the coated layer.

[0115] Next, in the second coating section, a magnetic layer-forming composition is applied to the non-magnetic layer formed by the heat drying process in the first heat treatment zone (application process of magnetic layer-forming composition).

[0116] Subsequently, in the configuration in which orientation processing is performed, the orientation processing of the ferromagnetic powder in the coated layer of the magnetic layer-forming composition is carried out in the orientation zone while the coated layer is still wet. Various known techniques, including those described in paragraph 0067 of Japanese Patent Application Publication No. 2010-231843, can be applied to the orientation processing. For example, vertical orientation processing can be performed by known methods such as using opposite-polarity opposing magnets. In the orientation zone, the drying rate of the coated layer can be controlled by the temperature and airflow of the drying air and / or the transport speed of the magnetic tape in the orientation zone. Alternatively, the coated layer may be pre-dried before being transported to the orientation zone.

[0117] The coated layer, after orientation treatment, is subjected to a heat drying process in a second heat treatment zone.

[0118] Next, in the third coating section, the back coat layer forming composition is applied to the surface of the non-magnetic support opposite to the surface on which the non-magnetic and magnetic layers are formed, thereby forming a coating layer (coating step of back coat layer forming composition). After that, the coating layer is heat-treated and dried in the third heat treatment zone.

[0119] Through the above process, a magnetic tape can be obtained having a non-magnetic layer and a magnetic layer in that order on one side of a non-magnetic support, and a back coat layer on the other side.

[0120] (Other processes) In the manufacturing process of magnetic tape, calendering is usually performed to improve the surface smoothness of the magnetic tape. Strengthening the calendering conditions can contribute to reducing the value of the widthwise σ of the number of indentations. Specific examples of strengthening the calendering conditions include increasing the calendering pressure, increasing the calendering temperature, and decreasing the calendering speed. Regarding the calendering conditions, the calendering pressure (linear pressure) is preferably 300 to 500 kN / m, more preferably 310 to 350 kN / m, the calendering temperature (surface temperature of the calendering roll) is preferably 95 to 120°C, more preferably 100 to 120°C, and the calendering speed is preferably 50 to 75 m / min. For other processes for manufacturing magnetic tape, refer to paragraphs 0067 to 0070 of Japanese Patent Publication No. 2010-231843. Through various processes, a long roll of magnetic tape raw material can be obtained. The obtained magnetic tape raw material is then cut (slit) using a known cutting machine to the width of a magnetic tape to be housed in a magnetic tape cartridge, for example. The above width can be determined according to standards and is usually 1 / 2 inch. 1 inch = 2.54 cm. A servo pattern is typically formed on the magnetic tape obtained by slitting.

[0121] (Formation of servo patterns) "Forming a servo pattern" can also be described as "recording a servo signal." The formation of a servo pattern is explained below.

[0122] 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.

[0123] As indicated in ECMA (European Computer Manufacturers Association) - 319 (June 2001), magnetic tapes conforming to the LTO (Linear Tape-Open) standard (commonly referred to as "LTO tapes") employ a timing-based servo system. In this timing-based servo system, the servo pattern is composed of multiple pairs of non-parallel magnetic stripes (also called "servo stripes") arranged continuously along the longitudinal direction of the magnetic tape. In this invention and specification, "timing-based servo pattern" refers to a servo pattern that enables head tracking in a timing-based servo system. The reason the servo pattern is composed of pairs of non-parallel magnetic stripes, as described above, is to inform the servo signal reading element of its position as it passes over the servo pattern. Specifically, the pair of magnetic stripes described above are formed such that their spacing changes continuously along the width direction of the magnetic tape, and the servo signal reading element can determine the relative position between the servo pattern and the servo signal reading element by reading this spacing. This relative position information enables tracking of the data track. Therefore, multiple servo tracks are typically set up on the servo pattern, aligned with the width of the magnetic tape.

[0124] 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.

[0125] 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.

[0126] 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 way that they are shifted along the longitudinal direction of the magnetic tape for each servo band. Since the combination of this shift between adjacent servo bands is unique across the entire magnetic tape, it is possible to uniquely identify a servo band when reading the servo pattern with two servo signal reading elements.

[0127] Furthermore, each servo band typically contains embedded information indicating its position along the longitudinal direction of the magnetic tape (also known as "LPOS (Longitudinal Position) information"), as described in ECMA-319 (June 2001). This LPOS information, like the UDIM information, is recorded by shifting the positions of a pair of servo stripes along the longitudinal direction of the magnetic tape. However, unlike the UDIM information, the same signal is recorded for each servo band in this LPOS information.

[0128] It is also possible to embed information other than the UDIM and LPOS information mentioned above into the servo bands. In this case, the embedded information may be different for each servo band, like the UDIM information, or it may be common to all servo bands, like the LPOS information. Furthermore, methods other than those described above can be used to embed information in the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of servo stripes.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] <Vertical squareness ratio> In one embodiment, the vertical aspect ratio of the magnetic tape can be, for example, 0.55 or more, and preferably 0.60 or more. A vertical aspect ratio of 0.60 or more is preferable from the viewpoint of improving electromagnetic conversion characteristics. In principle, the upper limit of the aspect ratio is 1.00 or less. The vertical aspect ratio of the magnetic tape can be 1.00 or less, and can be 0.95 or less, 0.90 or less, 0.85 or less, or 0.80 or less. A large value for the vertical aspect ratio of the magnetic tape is preferable from the viewpoint of improving electromagnetic conversion characteristics. The vertical aspect ratio of the magnetic tape can be controlled by known methods such as performing a vertical orientation process.

[0133] In the present invention and this specification, "vertical angle ratio" refers to the angle ratio measured in the vertical direction of the magnetic tape. In relation to the angle ratio, "vertical direction" refers to the direction perpendicular to the surface of the magnetic layer, and can also be referred to as the thickness direction. In the present invention and this specification, the vertical angle ratio is determined by the following method. A sample piece of a size suitable for introduction into a vibrating magnetometer is cut from the magnetic tape to be measured. Using a vibrating magnetometer, a magnetic field is applied to this sample piece perpendicular to the sample piece (in the direction perpendicular to the magnetic layer surface) at a maximum applied magnetic field of 3979 kA / m, a measurement temperature of 296 K, and a magnetic field sweep speed of 8.3 kA / m / sec, and the magnetization intensity of the sample piece against the applied magnetic field is measured. The measured magnetization intensity is obtained as a value after demagnetization correction and after subtracting the magnetization of the sample probe of the vibrating magnetometer as background noise. When the magnetization intensity at the maximum applied magnetic field is Ms and the magnetization intensity at zero applied magnetic field is Mr, the squareness ratio SQ is calculated as SQ = Mr / Ms. The measurement temperature refers to the temperature of the sample piece, and the temperature of the sample piece can be set to the measurement temperature by setting the ambient temperature around the sample piece to the measurement temperature, thereby achieving thermal equilibrium.

[0134] [Magnetic tape cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the magnetic tape described above.

[0135] Details of the magnetic tape included in the above-mentioned magnetic tape cartridge are as previously described. The above-mentioned magnetic tape cartridge can be mounted in a magnetic tape device equipped with a magnetic head and used for recording and / or playing back data.

[0136] 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 onto 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). For example, during this process, 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 cartridge.

[0137] 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 in one embodiment, head tilt angle adjustment information may already be recorded or will be recorded. The head tilt angle adjustment information is information for adjusting the head tilt angle while the magnetic tape is running within the magnetic tape device. For example, the head tilt angle adjustment information may include the values ​​of the servoband interval at each position in the longitudinal direction of the magnetic tape during data recording. For example, when playing back data recorded on the magnetic tape, the value of the servoband interval is measured during playback, and the control device of the magnetic tape device can change the head tilt angle so that the absolute value of the difference between this value and the servoband interval recorded in the cartridge memory at the same longitudinal position during recording approaches 0. The head tilt angle may be, for example, the angle θ described above.

[0138] 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 at different head tilt angles. In one embodiment, such a magnetic tape device can record and / or play back data by changing the head tilt angle while the magnetic tape is running. For example, the head tilt angle can be changed according to the widthwise dimensional information of the magnetic tape acquired while the magnetic tape is running. Alternatively, for example, the head tilt angle for one recording and / or playback cycle may be changed from the head tilt angle for subsequent recordings and / or playback cycles, and the head tilt angle may be fixed without changing it during the magnetic tape running for each recording and / or playback cycle.

[0139] [Magnetic tape drive] One aspect of the present invention relates to a magnetic tape device including the magnetic tape described above. In the magnetic tape device, recording data onto the magnetic tape and / or reproducing data recorded on the magnetic tape can be performed, for example, by bringing the magnetic layer surface of the magnetic tape into contact with and sliding a magnetic head.

[0140] In one configuration, the magnetic tape is treated as a removable medium (a so-called interchangeable medium), and a magnetic tape cartridge containing the magnetic tape is inserted into and removed from a magnetic tape device. In another configuration, the magnetic tape is not treated as an interchangeable medium, and the magnetic tape is wound onto a reel of a magnetic tape device equipped with a magnetic head, and the magnetic tape is housed within the magnetic tape device.

[0141] In the present invention and this specification, “magnetic tape device” means a device capable of recording data onto a magnetic tape and playing back data recorded on a magnetic tape. Such a device is generally called a drive.

[0142] <Magnetic head> The above magnetic tape device may include a magnetic head. The configuration of the magnetic head and the angle θ, which is the head tilt angle, are as previously explained with reference to Figures 1 to 3. If the magnetic head includes a playback element, a magnetoresistive (MR) element that can read information recorded on the magnetic tape with high sensitivity is preferred as the playback element. Various known MR elements (e.g., GMR (Giant Magnetoresistive) elements, TMR (Tunnel Magnetoresistive) elements, etc.) can be used as the MR element. Hereinafter, the magnetic head that records data and / or plays back recorded data will also be called the "recording / playback head". The elements for recording data (recording elements) and the elements for playing back data (playback elements) will be collectively referred to as "magnetic head elements".

[0143] By using a regeneration element with a narrow width as the regeneration element, high-density recorded data 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, "regenerative element width" refers to the physical dimension of the regenerative element width. Such physical dimensions can be measured using an optical microscope, a scanning electron microscope, or the like.

[0144] When recording data and / or playing back recorded data, tracking using servo signals can be performed first. That is, by making the servo signal reading element follow a predetermined servo track, the magnetic head element can be controlled to pass over the target data track. The movement of the data track is achieved by changing the servo track read by the servo signal reading element in the tape width direction. Furthermore, the recording / playback head can also record and / or play back data for other data bands. In this case, the servo signal reading element can be moved to a predetermined servo band using the UDIM information described earlier, and tracking for that servo band can be started.

[0145] Figure 5 shows an example of the arrangement of data bands and servo bands. In Figure 5, multiple servo bands 1 are arranged on the magnetic layer of the magnetic tape MT, sandwiched between guide bands 3. Multiple regions 2 sandwiched between two servo bands are the data bands. A servo pattern is a magnetized region, formed by magnetizing a specific region of the magnetic layer with a servo light head. The region magnetized by the servo light head (the position where the servo pattern is formed) is defined by the standard. For example, in the industry standard LTO Ultrium format tape, multiple servo patterns inclined with respect to the tape width direction are formed on the servo bands during magnetic tape manufacturing, as shown in Figure 6. More specifically, in Figure 6, 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 6) and a B-burst (indicated as B in Figure 6). The A-burst consists of servo patterns A1 to A5, and the B-burst consists of servo patterns B1 to B5. On the other hand, servo subframe 2 consists of C-bursts (indicated as C in Figure 6) and D-bursts (indicated as D in Figure 6). The C-bursts consist of servo patterns C1 to C4, and the D-bursts consist of servo patterns D1 to D4. These 18 servo patterns are arranged in sets of 5 and 4 on subframes in a 5, 5, 4, 4 sequence, and are used to identify the servo frames. Figure 6 shows one servo frame for illustrative purposes. However, in reality, in the magnetic layer of a magnetic tape where timing-based servo head tracking is performed, multiple servo frames are arranged in the direction of travel for each servo band. In Figure 6, 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.

[0146] 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.

[0147] 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 formed between the magnetic layer surface and the contact surface of the magnetic head when the magnetic tape is running and contacts 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.

[0148] Regarding the change in the angle θ during the running of the magnetic tape, for recording data on the magnetic tape and / or for reproducing the data recorded on the magnetic tape, while the magnetic tape is running in the magnetic tape device, the angle θ of the magnetic head changes from θ at the start of running initial If it changes, the maximum change amount Δθ of the angle θ during the running of the magnetic tape is the Δθ calculated by the following formula max and Δθ min Among them, it is the larger value. The maximum value of the angle θ during the running of the magnetic tape is θ max and the minimum value is θ min Note that "max" is an abbreviation of maximum and "min" is an abbreviation of minimum. Δθ max = θ max - θ initial Δθ min = θ initial - θ min

[0149] In one form, Δθ can be more than 0.000°, and from the viewpoint of the adjustment ability to adjust the effective distance between the servo signal reading elements corresponding to the dimensional change in the width direction of the magnetic tape, it is preferably 0.001° or more, and more preferably 0.010° or more. Also, from the viewpoint of the ease of ensuring the synchronization of the recorded data and / or the reproduced data between the plurality of magnetic head elements during data recording and / or reproduction, Δθ is preferably 1.000° or less, more preferably 0.900° or less, still more preferably 0.800° or less, even more preferably 0.700° or less, and even more preferably 0.600° or less.

[0150] In the examples shown in FIGS. 2 and 3, the axis of the element array is inclined toward the running direction of the magnetic tape. However, the present invention is not limited to such examples. In the above magnetic tape device, an embodiment in which the axis of the element array is inclined in the direction opposite to the running direction of the magnetic tape is also included in the present invention.

[0151] θ which is the head tilt angle at the start of running of the magnetic tape initialThis can be set by the control device of the magnetic tape drive, etc. Regarding the head tilt angle during magnetic tape travel, Figure 7 is an explanatory diagram of the method for measuring the angle θ during magnetic tape travel. The angle θ during magnetic tape travel can be determined, for example, by the following method. When determining the angle θ during magnetic tape travel by the following method, the angle θ is to be varied within the range of 0 to 90° during magnetic tape travel. That is, if the axis of the element array is tilted toward the direction of magnetic tape travel at the start of magnetic tape travel, the element array will not be tilted during magnetic tape travel so that the axis of the element array is tilted toward the direction of magnetic tape travel at the start of magnetic tape travel, and if the axis of the element array is tilted toward the direction of magnetic tape travel at the start of magnetic tape travel, the element array will not be tilted during magnetic tape travel so that the axis of the element array is tilted toward the direction of magnetic tape travel at the start of magnetic tape travel. The phase difference (i.e., time difference) ΔT of the regenerated signals from a pair of servo signal reading elements 1 and 2 is measured. ΔT can be measured by a measurement unit provided in the magnetic tape device. The configuration of such a measurement unit is well known. The distance L between the center of servo signal reading element 1 and the center of servo signal reading element 2 can be measured using an optical microscope or the like. When the magnetic tape travels at speed v, the distance between the centers of the two servo signal reading elements in the direction of magnetic tape travel is Lsinθ, and the relationship Lsinθ = v × ΔT holds. Therefore, the angle θ during magnetic tape travel can be calculated using the formula "θ = arcsin(vΔT / L)". Note that Figure 7 (right) shows an example where the axis of the element array is tilted toward the direction of magnetic tape travel. In this example, the phase difference (i.e., time difference) ΔT between the phase of the regenerated signal from servo signal reading element 1 and the phase of the regenerated signal from servo signal reading element 2 is measured. If the axis of the element array is tilted in the direction opposite to the direction in which the magnetic tape travels, θ can be determined by the above method, except that ΔT is measured as the phase difference (i.e., time difference) between the phase of the regenerated signal of servo signal reading element 1 and the phase of the regenerated signal of servo signal reading element 2. Furthermore, the measurement pitch for the angle θ, that is, the measurement interval for the angle θ in the longitudinal direction of the tape, can be selected according to the frequency of tape width deformation in the longitudinal direction of the tape. For example, the measurement pitch can be set to 250 μm.

[0152] <Configuration of a magnetic tape drive> The magnetic tape device 10 shown in Figure 8 controls the recording and playback head unit 12 based on commands from the control device 11, and performs data recording and playback on the magnetic tape MT. The magnetic tape device 10 has a configuration that allows for the detection and adjustment of tension applied in the longitudinal direction of the magnetic tape from spindle motors 17A, 17B and their drive units 18A, 18B that control the rotation of the magnetic tape cartridge reel and the take-up reel. The magnetic tape device 10 has a configuration that allows a magnetic tape cartridge 13 to be loaded. The magnetic tape device 10 has a cartridge memory read / write device 14 that can read from and write to the cartridge memory 131 in the magnetic tape cartridge 13. From the magnetic tape cartridge 13 mounted in the magnetic tape device 10, the end of the magnetic tape MT or the leader pin is pulled out by an automatic loading mechanism or manually, and the magnetic layer surface of the magnetic tape MT passes over the recording / playback head of the recording / playback head unit 12 through guide rollers 15A and 15B with the magnetic layer surface of the magnetic tape MT in contact with the surface of the recording / playback head, and the magnetic tape MT is wound onto the take-up reel 16. The rotation and torque of spindle motors 17A and 17B are controlled by signals from the control device 11, so that the magnetic tape MT runs at a desired speed and tension. A servo pattern pre-formed on the magnetic tape can be used to control the tape speed and head tilt angle. A tension detection mechanism may be provided between the magnetic tape cartridge 13 and the take-up reel 16 for tension detection. In addition to control by spindle motors 17A and 17B, tension may also be controlled using guide rollers 15A and 15B. The cartridge memory read / write device 14 is configured to read and write information to the cartridge memory 131 in response to commands from the control device 11. For example, the ISO (International Organization for Standardization) 14443 standard can be used as the communication method between the cartridge memory read / write device 14 and the cartridge memory 131.

[0153] The control device 11 includes, for example, a control unit, a storage unit, a communication unit, and the like.

[0154] 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.

[0155] 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.

[0156] The control device 11 has a mechanism to determine the running position of the magnetic tape MT from the servo signals read from the servo bands when the magnetic tape MT is running, and to control the servo tracking actuator so that the recording element and / or playback element are positioned at the target running position (track position). This track position control is performed, for example, by feedback control. The control device 11 has a mechanism to determine the servo band spacing from the servo signals read from two adjacent servo bands when the magnetic tape MT is running. The control device 11 can store the determined servo band spacing information in its internal storage unit, cartridge memory 131, or external connected equipment. Furthermore, the control device 11 can change the head tilt angle according to the dimensional information in the width direction of the running magnetic tape. This makes it possible to bring the effective distance between servo signal reading elements close to or match the servo band spacing. The above dimensional information can be obtained using a servo pattern pre-formed on the magnetic tape. For example, while the magnetic tape is running within the magnetic tape device, the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape can be changed according to the width direction dimensional information of the magnetic tape acquired during the running process. The head tilt angle can be adjusted, for example, by feedback control. Alternatively, the head tilt angle can also be adjusted, for example, by the method described in Japanese Patent Application Publication No. 2016-524774 (Patent Document 1) or US2019 / 0164573A1 (Patent Document 2). [Examples]

[0157] The present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. In the following, "parts" and "%" refer to "parts by mass" and "mass%", respectively. Furthermore, unless otherwise specified, the processes and evaluations described below were carried out in an environment of 23°C ± 1°C. In the following, "eq" refers to equivalent and is a unit that cannot be converted to SI units.

[0158] [Ferromagnetic powder] In Table 1, "BaFe" refers to hexagonal barium ferrite powder (coercivity Hc: 196 kA / m, average particle size (average plate diameter) 24 nm).

[0159] In Table 1, "SrFe1" is hexagonal strontium ferrite powder prepared by the following method. 1707g of SrCO3, 687g of H3BO3, 1120g of Fe2O3, 45g of Al(OH)3, 24g of BaCO3, 13g of CaCO3, and 235g of Nd2O3 were weighed out and mixed in a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390°C. While stirring the molten material, the outlet at the bottom of the platinum crucible was heated, and the molten material was dispensed in a rod shape at approximately 6 g / second. The dispensed material was rolled and rapidly cooled using water-cooled twin rollers to produce an amorphous body. 280g of the prepared amorphous material was placed in an electric furnace and heated to 635°C (crystallization temperature) at a heating rate of 3.5°C / min. The temperature was maintained at this temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystalline material obtained above, containing hexagonal strontium ferrite particles, was coarsely ground in a mortar. 1000g of 1mm particle size zirconia beads and 800ml of 1% aqueous acetic acid solution were added to a glass bottle and 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 precipitated in a centrifuge and washed by repeated decantation. Finally, it was dried in a heating furnace at a temperature of 110°C for 6 hours to obtain hexagonal strontium ferrite powder. The average particle size of the hexagonal strontium ferrite powder obtained above was 18 nm, and the activation volume was 902 nm. 3 The anisotropy constant Ku is 2.2 × 10⁻⁶. 5 J / m 3 , mass magnetization σs is 49A m 2 It was / kg. A sample powder of 12 mg was taken from the hexagonal strontium ferrite powder obtained above, and the elemental analysis of the filtrate obtained by partially dissolving this sample powder under the dissolution conditions exemplified earlier was performed using an ICP analyzer to determine the surface layer content of neodymium atoms. Separately, 12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and the elemental analysis of the filtrate obtained by completely dissolving this sample powder under the dissolution conditions exemplified earlier was performed using an ICP analyzer to determine the bulk content of neodymium atoms. The neodymium atom content (bulk content) relative to 100 atomic percent of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic percent. Furthermore, the neodymium atom content in the surface layer was 8.0 atomic percent. The ratio of surface layer content to bulk content, "surface layer content / bulk content," was 2.8, confirming that neodymium atoms were concentrated in the surface layer of the particles. The hexagonal ferrite crystal structure of the powder obtained above was confirmed by scanning with CuKα rays at a voltage of 45kV and intensity of 40mA, and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above showed a magnetoplanbite-type (M-type) hexagonal ferrite crystal structure. Furthermore, the crystalline phase detected by X-ray diffraction analysis was a single phase of the magnetoplanbite type. PANalytical X'Pert Pro diffractometer, PIXcel detector Soller slit for incident and diffracted beams: 0.017 radians Fixed angle of dispersion slit: 1 / 4 degree Mask: 10mm Scatter prevention slit: 1 / 4 degree Measurement mode: Continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degrees per second Measurement step: 0.05 degrees

[0160] In Table 1, "SrFe2" is hexagonal strontium ferrite powder prepared by the following method. Weighed 1725 g of SrCO3, 666 g of H3BO3, 1332 g of Fe2O3, 52 g of Al(OH)3, 34 g of CaCO3, and 141 g of BaCO3, and mixed them in a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1380 °C. While stirring the melt, the pouring outlet provided at the bottom of the platinum crucible was heated, and the melt was poured out in a rod shape at about 6 g / second. The poured liquid was rolled and rapidly cooled by a water-cooled double roller to produce an amorphous body. Charged 280 g of the obtained amorphous body into an electric furnace, heated it to 645 °C (crystallization temperature), and held it at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was coarsely pulverized in a mortar. 1000 g of zirconia beads with a particle size of 1 mm and 800 ml of an acetic acid aqueous solution with a concentration of 1% were added to a glass bottle, and dispersion treatment was carried out for 3 hours with a paint shaker. Then, the obtained dispersion liquid was separated from the beads and put into a stainless steel beaker. After the dispersion liquid was allowed to stand at a liquid temperature of 100 °C for 3 hours for dissolution treatment of the glass component, it was precipitated with a centrifuge and decantation was repeated for washing, and dried in a heating furnace with an internal temperature of 110 °C for 6 hours to obtain hexagonal strontium ferrite powder. The average particle size of the obtained hexagonal strontium ferrite powder was 19 nm, and the activation volume was 1102 nm 3 The anisotropy constant Ku was 2.0×10 5 J / m 3 The mass magnetization σs was 50 A·m 2 / kg.

[0161] In Table 1, "ε-iron oxide" is ε-iron oxide powder prepared by the following method. In 90 g of pure water, 8.3 g of iron(III) nitrate nonahydrate, 1.3 g of gallium(III) nitrate octahydrate, 190 mg of cobalt(II) nitrate hexahydrate, 150 mg of titanium(IV) sulfate, and 1.5 g of polyvinylpyrrolidone (PVP) were dissolved. While stirring with a magnetic stirrer in an air atmosphere at an ambient temperature of 25°C, 4.0 g of a 25% aqueous ammonia solution was added, and the mixture was stirred for 2 hours at the same ambient temperature of 25°C. To the resulting solution, a citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added, and the mixture was stirred for 1 hour. After stirring, the precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating furnace at an ambient temperature of 80°C. 800g of pure water was added to the dried powder, and the powder was dispersed in the water again to obtain a dispersion. The obtained dispersion was heated to 50°C, and 40g of a 25% aqueous ammonia solution was added dropwise while stirring. After stirring for 1 hour while maintaining the temperature at 50°C, 14mL of tetraethoxysilane (TEOS) was added dropwise, and the mixture was stirred for 24 hours. 50g of ammonium sulfate was added to the resulting reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating furnace at a temperature of 80°C for 24 hours to obtain a precursor of ferromagnetic powder. The obtained ferromagnetic powder precursor was loaded into a heating furnace at a temperature of 1000°C under an atmospheric environment and subjected to a heat treatment for 4 hours. A heat-treated ferromagnetic powder precursor was added to a 4 mol / L sodium hydroxide (NaOH) aqueous solution, and the solution was stirred for 24 hours while maintaining the temperature at 70°C to remove silicate compounds, which are impurities, from the heat-treated ferromagnetic powder precursor. Subsequently, the ferromagnetic powder, from which the silicate compounds were removed by centrifugation, was collected and washed with pure water to obtain ferromagnetic powder. The composition of the obtained ferromagnetic powder was confirmed by inductively coupled plasma emission spectroscopy (ICP-OES), revealing that it was a Ga, Co, and Ti-substituted ε-iron oxide (ε-Ga 0.28 Co 0.05 Ti 0.05 Fe 1.62It was O3). Furthermore, X-ray diffraction analysis was performed under the same conditions as described earlier for SrFe1, and from the peaks of the X-ray diffraction pattern, it was confirmed that the obtained ferromagnetic powder had a single-phase crystalline structure of the ε phase (crystalline structure of ε-iron oxide), which did not contain the crystalline structures of the α phase and γ phase. The average particle size of the obtained ε-iron oxide powder was 12 nm, and the activation volume was 746 nm. 3 The anisotropy constant Ku is 1.2 × 10⁻⁶. 5 J / m 3 , mass magnetization σs is 16A m 2 It was / kg.

[0162] The activation volume and anisotropy constant Ku of the hexagonal strontium ferrite powder and ε-iron oxide powder described above were obtained for each ferromagnetic powder using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) and the method described above. Furthermore, the mass magnetization σs was measured using a vibrating sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.) at a magnetic field strength of 15 kOe.

[0163] [Example 1] (1) Formulation of a composition for forming a magnetic layer (Magnetic liquid) Ferromagnetic powder (see Table 1): 100.0 parts SO3Na group-containing polyurethane resin: 14.0 parts Weight average molecular weight: 70,000, SO3Na group: 0.4meq / g Cyclohexanone: 150 copies 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, SO3Na group: 0.3meq / g Cyclohexanone: 26.7 parts (Abrasive solution B) Diamond abrasive (average particle size: 100nm): 1.0 part Sulfonic acid group-containing polyurethane resin: 0.1 part Weight average molecular weight: 70,000, SO3Na group: 0.3meq / g Cyclohexanone: 26.7 parts (Silica sol) Colloidal silica (average particle size: 100 nm): 0.2 parts Methyl ethyl ketone: 1.4 parts (Other ingredients) 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

[0164] (2) Formulation of composition for forming a non-magnetic layer Non-magnetic inorganic powder (α-iron oxide): 100.0 parts Average particle size (average major axis length): 10nm Average acicular ratio: 1.9 BET (Brunauer-Emmett-Teller) specific surface area: 75m 2 / g Carbon Black: 25.0 parts Average particle size: 20nm SO3Na group-containing polyurethane resin: 18 parts Weight average molecular weight: 70,000, SO3Na group: 0.2meq / g Stearic acid: 1.0 part Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

[0165] (3) Formulation of composition for forming backcoat layer Carbon Black: 100.0 parts Cabot BP-800, average particle size: 17nm SO3Na group-containing polyurethane resin (SO3Na group: 70 eq / ton): 20.0 parts OSO3K group-containing polyvinyl chloride resin (OSO3K group: 70 eq / ton): 30.0 parts Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 600): See Table 1. Stearic acid: See Table 1 Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Butyl stearate: 2.0 parts Stearic acid amide: 0.1 part

[0166] (4) Preparation of each layer-forming composition For the magnetic layer forming composition, the above components of the magnetic liquid were dispersed for 24 hours using a batch-type vertical sand mill to prepare the magnetic liquid. Zirconia beads with a diameter of 0.5 mm were used as the dispersion beads. For the abrasive solutions, the above components of abrasive solution A and abrasive solution B were dispersed for 24 hours using a batch-type ultrasonic device (20kHz, 300W) to obtain abrasive solution A and abrasive solution B. The magnetic liquid, abrasive liquid A, and abrasive liquid B were mixed with the silica sol and other components mentioned above, and then dispersed using a batch-type ultrasonic device (20 kHz, 300 W) for 30 minutes. The mixture was then filtered using a filter with a pore size of 0.5 μm to prepare a composition for forming a magnetic layer. For the composition for forming a non-magnetic layer, the above components were dispersed for 24 hours using a batch-type vertical sand mill. Zirconia beads with a diameter of 0.1 mm were used as the dispersion beads. The obtained dispersion was filtered using a filter with a pore size of 0.5 μm to prepare the composition for forming a non-magnetic layer. For the backcoat layer forming composition, 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 resulting dispersion, and the mixture was filtered using a filter with a pore size of 1 μm to prepare the backcoat layer forming composition.

[0167] (5) Manufacturing of magnetic tape and magnetic tape cartridges Magnetic tape was manufactured according to the manufacturing process shown in Figure 4. Details are as follows: A polyethylene naphthalate support with a thickness of 4.1 μm was fed from a feeding section, and a non-magnetic layer-forming composition was applied to one surface in the first coating section so that the thickness after drying was 0.7 μm to form a coating layer. While the formed coating layer was still wet, it was passed through a cooling zone adjusted to an ambient temperature of 0°C for the stay time shown in Table 1 to perform a cooling process, and then passed through a first heat treatment zone at the drying temperature (ambient temperature, the same applies hereafter) shown in Table 1 to perform a heat drying process and form a non-magnetic layer. Subsequently, in the second coating area, the magnetic layer-forming composition prepared above was applied onto the non-magnetic layer to form a coating layer, such that the thickness after drying was 0.1 μm. While this coating layer was still wet, a magnetic field of strength 0.3 T was applied perpendicularly to the surface of the coating layer of the magnetic layer-forming composition in the orientation zone to perform a vertical orientation treatment, and then it was dried in the second heat treatment zone at the drying temperature shown in Table 1. Subsequently, in the third coating section, the backcoat layer-forming composition prepared above was applied to the surface of the polyethylene naphthalate support opposite to the surface on which the non-magnetic and magnetic layers were formed, so that the thickness after drying would be 0.3 μm, thereby forming a coating layer. The formed coating layer was then dried in the third heat treatment zone at the drying temperature shown in Table 1. Subsequently, calendering (surface smoothing treatment) was performed using a calendering roll consisting solely of metal rolls, under the calendering conditions shown in Table 1. Subsequently, the material was heat-treated for 36 hours in an environment with an ambient temperature of 70°C. After heat treatment, the material was slit into 1 / 2-inch width strips to produce magnetic tape. With the magnetic layer of the fabricated magnetic tape demagnetized, servo signals were recorded on the magnetic layer using a commercially available servo writer. This resulted in a magnetic tape having data bands, servo bands, and guide bands arranged in accordance with the LTO (Linear Tape-Open) Ultrium format, and having a servo pattern (timing-based servo pattern) on the servo bands arranged and shaped in accordance with the LTO Ultrium format. The servo pattern thus formed conforms to the servo pattern described in JIS (Japanese Industrial Standards) X6175:2006 and Standard ECMA-319 (June 2001). The total number of servo bands is 5, and the total number of data bands is 4. The magnetic tape (length 960m) on which the servo signals were recorded was wound onto a reel of a magnetic tape cartridge (LTO Ultrium8 data cartridge), 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 end of the reel using commercially available splicing tape. In this way, a magnetic tape cartridge was created in which magnetic tape was wound onto a reel.

[0168] 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 the 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 measurements are performed using the 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 Corporation AXIS-ULTRA Excitation X-ray source: Monochromatic Al-Kα rays Scan range: 0~1200eV Pass energy: 160 eV Energy resolution 1 eV / step Data acquisition time: 100ms / step Total number of times: 5 Furthermore, a 3cm long sample piece was cut from the magnetic tape, and ATR-FT-IR (Attenuated total reflection-fourier transform-infrared spectrometer) measurement (reflection method) was performed on the surface of the backcoat layer. In the measurement results, COO - Wavefrequency 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 ).

[0169] [Examples 2-17, Comparative Examples 1-9] A magnetic tape and magnetic tape cartridge were obtained using the method described for Example 1, except that the items shown in Table 1 were changed as shown in Table 1. In the comparative examples where "none" is written in the column for cooling zone residence time in Table 1, the magnetic tape was manufactured using a manufacturing process that did not include a cooling zone in the non-magnetic layer formation step.

[0170] For each example and comparative example, two magnetic tape cartridges were prepared; one was used to evaluate recording and playback performance, and the other was used for other evaluations.

[0171] [Evaluation Method] <Number of indentations, width σ of the number of indentations> The following conditions were adopted as the measurement conditions for AFM, and the number of indentations with an equivalent circle diameter of 0.30 μm or more and 0.60 μm or less (per 40 μm × 40 μm area) and the width σ of the number of indentations were determined on the magnetic layer surface of the magnetic tape using the method described above. Using an AFM (Nanoscope 5 manufactured by Bruker) in peak force tapping mode, a region with an area of 40 μm × 40 μm on the surface of the magnetic layer of the magnetic tape is measured. As the probe, SCANASYST-AIR manufactured by Bruker is used, the resolution is set to 512 pixel × 512 pixel, and the scan speed is the speed at which one screen (512 pixel × 512 pixel) is measured in 512 seconds.

[0172] <Total thickness of the magnetic tape (tape thickness)> Ten tape samples (length: 5 cm) were cut out from arbitrary parts of each magnetic tape in the examples and comparative examples, and these tape samples were stacked to measure the thickness. The thickness measurement was performed using a digital thickness gauge of Millimar 1240 compact amplifier and Millimar 1301 induction probe manufactured by MARH. The value obtained by dividing the measured thickness by 10 (thickness per tape sample) was taken as the tape thickness. For any of the magnetic tapes, the tape thickness was 5.2 μm.

[0173] <Recording and playback performance> Using each magnetic tape cartridge in the examples and comparative examples, data recording and playback were performed using a magnetic tape device with the configuration shown in FIG. 8. The arrangement order of the modules included in the recording / playback head unit is "recording module - playback module - recording module" (total number of modules: 3). The number of magnetic head elements in each module is 32 (Ch0 to Ch31), and these magnetic head elements are sandwiched between a pair of servo signal reading elements to form an element array. The playback element width of the playback elements included in the playback module is 0.8 μm. The head tilt angle during recording was set to 0°, and the head tilt angle during playback was set to 5°. The above head tilt angle is the angle θ formed by the axis of the element array of the playback module with respect to the width direction of the magnetic tape during recording and playback. The angle θ was set by the control device of the magnetic tape device at the start of recording and the start of playback, respectively, and the head tilt angle was fixed during the running of the magnetic tape during recording and during the running of the magnetic tape during playback. In this evaluation, since the head tilt angles during recording and playback are different, for each recording bit, the head tilt angle at the time of data recording is different from the head tilt angle at the time of data reading (i.e., during playback). The number of reproducing elements (number of channels) in the above reproduction is 32 channels. During playback, when all data of the 32 channels are correctly read, the recording and playback performance is evaluated as "3", when data of 31 - 28 channels are correctly read, the recording and playback performance is evaluated as "2", and in other cases, the recording and playback performance is evaluated as "1".

[0174] The above results are shown in Table 1 (Table 1 - 1 to Table 1 - 3).

[0175]

Table 1 - 1

[0176]

Table 1 - 2

[0177]

Table 1 - 3

[0178] A magnetic tape cartridge was produced by the method described for Example 1, except that no vertical alignment treatment was performed during the production of the magnetic tape. A sample piece was cut from the magnetic tape removed from the magnetic tape cartridge mentioned above. Using a Tamagawa Seisakusho TM-TRVSM5050-SMSL vibrating sample magnetometer, the vertical angular ratio of this sample piece was determined using the method described above, and it was found to be 0.55. A magnetic tape was also removed from the magnetic tape cartridge of Example 1, and the vertical aspect ratio was similarly determined for a sample piece cut from this magnetic tape, which was found to be 0.60.

[0179] 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 2 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 (Newtons) 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. For recording, a MIG (Metal-in-gap) head (gap length 0.15 μm, track width 1.0 μm) was used as the recording head, and the recording current was set to the optimal recording current for each magnetic tape. For playback, a GMR (Giant-magnetoresistive) head (element thickness 15 nm, shielding gap 0.1 μm, playback element width 0.8 μm) was used as the playback head. The head tilt angle was set to 0°. 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 system). As the signal, the portion where the signal was sufficiently stable after the start of magnetic tape movement was used. [Industrial applicability]

[0180] One aspect of the present invention is useful in the technical field of various data storage technologies.

Claims

1. A magnetic tape comprising a non-magnetic support and a magnetic layer containing ferromagnetic powder, The number of indentations on the surface of the magnetic layer with an equivalent circular diameter of 0.30 μm or more and 0.60 μm or less is 10 to 100 per 40 μm × 40 μm area, and A magnetic tape in which the standard deviation σ of the number of indentations in the width direction on the surface of the magnetic layer is 20 or less.

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

3. The magnetic tape according to claim 1 or 2, further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

4. The magnetic tape according to any one of claims 1 to 3, 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.

5. A magnetic tape according to any one of claims 1 to 4, wherein the tape thickness is 5.2 μm or less.

6. A magnetic tape cartridge comprising the magnetic tape described in any one of claims 1 to 5.

7. A magnetic tape device including the magnetic tape according to any one of claims 1 to 5.

8. Further including a magnetic head, The magnetic head has a module including an element array having a plurality of magnetic head elements between a pair of servo signal reading elements, and The magnetic tape device according to claim 7, wherein the magnetic tape device changes the angle θ that the axis of the element array makes with respect to the width direction of the magnetic tape while the magnetic tape is running within the magnetic tape device.

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